NASASpaceFlight.com Forum

SpaceX Vehicles and Missions => SpaceX Reusability => Topic started by: meekGee on 03/31/2017 12:55 AM

Title: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 12:55 AM
Biggest news of the day, other than that bit about the flight-proven stage being reproven, is that "Next thing is Second Stage reusability".

This should have its own thread
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 12:59 AM
To me, the main argument against second stage reusability was that most launches are commercial GTO launches, and this makes recovering the second stage very difficult.

But as the BFC became real, and now the vBFC tripled the number of LEO/vLEO satellites that need to be launched (12,000), we're looking at LEO launch rates of several per week.

It is inconceivable that they'll throw away second stages at that rate.

It is also such a repeating problem that I can't imagine it won't get its own custom engineering solution.

So my prediction is either an integrated S2/deployer, or a reusable S2 with an expendable deployer/cover combo that does not require a full-scope fairing.

EDIT:

I should add, I think landing vertically is not the right approach for S2.

Since it can orbit multiple times, it takes negligible dV to make sure the deorbit pass is near the launch site.  Then deorbit, re-entry (possibly ballistic, since there's nobody on board), parachute deployment, and helicopter capture.

All the factors that make helicopter capture difficult for the fairing (range, duration, etc) are non-issues with S2.
Title: Re: F9 Second Stage Reusability
Post by: Bubbinski on 03/31/2017 01:23 AM
That is big news indeed, that they will try for 2nd stage recovery.

I recall the video shown a few years back where the first stage landed, the 2nd stage deployed a Dragon, then deorbited with heat shielding material covering part of the stage, then the 2nd stage landing on a land landing pad. Would SpaceX still plan it this way, or have they come up with something else in the intervening years? If they do land the 2nd stage would they need extra barges, or try to land at a landing pad somewhere away from populated areas (like say at Vandenberg AFB)?

Edited to add: how much would second stage recovery eat into the payload mass? Would SX have to use Falcon Heavy as its "go to" launcher for most payloads because of this?
Title: Re: F9 Second Stage Reusability
Post by: Lar on 03/31/2017 01:30 AM
That is big news indeed, that they will try for 2nd stage recovery.

I recall the video shown a few years back where the first stage landed, the 2nd stage deployed a Dragon, then deorbited with heat shielding material covering part of the stage, then the 2nd stage landing on a land landing pad. Would SpaceX still plan it this way, or have they come up with something else in the intervening years? If they do land the 2nd stage would they need extra barges, or try to land at a landing pad somewhere away from populated areas (like say at Vandenberg AFB)?

Edited to add: how much would second stage recovery eat into the payload mass? Would SX have to use Falcon Heavy as its "go to" launcher for most payloads because of this?

I seem to recall that
10 Kg of recovery gear on S1 costs 1 Kg of payload,
N (>1, <10) Kg of recovery gear on the fairing costs 1 Kg of payload
1Kg of recovery gear on S2 costs 1 Kg of payload

(gear is anything other than fuel, fuel is a slightly different calculation)

but I can't remember where I saw this or who did the analysis or if 10 is the right number or what N is....  And that these were rough/typical, that the numbers differ for LEO and GEO...
Title: Re: F9 Second Stage Reusability
Post by: Nomadd on 03/31/2017 01:46 AM
That is big news indeed, that they will try for 2nd stage recovery.

I recall the video shown a few years back where the first stage landed, the 2nd stage deployed a Dragon, then deorbited with heat shielding material covering part of the stage, then the 2nd stage landing on a land landing pad. Would SpaceX still plan it this way, or have they come up with something else in the intervening years? If they do land the 2nd stage would they need extra barges, or try to land at a landing pad somewhere away from populated areas (like say at Vandenberg AFB)?

Edited to add: how much would second stage recovery eat into the payload mass? Would SX have to use Falcon Heavy as its "go to" launcher for most payloads because of this?

I seem to recall that
10 Kg of recovery gear on S1 costs 1 Kg of payload,
N (>1, <10) Kg of recovery gear on the fairing costs 1 Kg of payload
1Kg of recovery gear on S2 costs 1 Kg of payload

(gear is anything other than fuel, fuel is a slightly different calculation)

but I can't remember where I saw this or who did the analysis or if 10 is the right number or what N is....  And that these were rough/typical, that the numbers differ for LEO and GEO...
The fairing number should be close to the S1 number since it's jettisoned soon after staging.
Title: Re: F9 Second Stage Reusability
Post by: ClayJar on 03/31/2017 02:49 AM
Since this is a new topic on second stage reusability, I'm copying my reply from the other thread so people can easily find the a copy of the presser and the particular part at issue, which is right after he talks about the fairing (after a guy walks in and shows him the photo):

https://www.youtube.com/watch?v=jC3LQFpuzqs

Quote from: Elon Musk from the presser at 14:23
But then the only thing left is the upper stage, which we didn't originally intend for Falcon 9 to have a reusable upper stage, but it might be fun to try like a hail mary, and you know.  What's the worst thing that can happen?  It blows up.  You know, it blows up anyway. [Martin Halliway chimes in humorously. "We need to discuss this."]


Edit/Lar: see also http://forum.nasaspaceflight.com/index.php?topic=42365.msg1661789 "Testing upper stage reusability" which is similar but different in focus.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 03:09 AM
Since this is a new topic on second stage reusability, I'm copying my reply from the other thread so people can easily find the a copy of the presser and the particular part at issue, which is right after he talks about the fairing (after a guy walks in and shows him the photo):

https://www.youtube.com/watch?v=jC3LQFpuzqs

Quote from: Elon Musk from the presser at 14:23
But then the only thing left is the upper stage, which we didn't originally intend for Falcon 9 to have a reusable upper stage, but it might be fun to try like a hail mary, and you know.  What's the worst thing that can happen?  It blows up.  You know, it blows up anyway. [Martin Halliway chimes in humorously. "We need to discuss this."]

Yeah, that doesn't sound like "second stage reuse is next".

Still though.

That "hail Mary" would still require (at a minimum) a heat shield, and some ways of keeping the stage stable.

But if it can be done, even with a significant penalty, then now the door is open to getting S2 back on missions that do not max-out the F9.  And that's a lot of missions.

It might even make sense to go from RTLS to Barge landing, if the extra mass means you get S2 back.

Heh - you'll get S2 back before you get S1 back...
Title: Re: F9 Second Stage Reusability
Post by: Req on 03/31/2017 03:26 AM
I should add, I think landing vertically is not the right approach for S2.

Since it can orbit multiple times, it takes negligible dV to make sure the deorbit pass is near the launch site.  Then deorbit, re-entry (possibly ballistic, since there's nobody on board), parachute deployment, and helicopter capture.

All the factors that make helicopter capture difficult for the fairing (range, duration, etc) are non-issues with S2.

I had this thought as well after the "hail mary" comment.  "Hail mary" doesn't sound like the type of commitment it would take to add legs, deal with the nozzle ratio somehow, perform a flip maneuver, and perform a propulsive landing as in the old video, and definitely rules out a raptor S2.  A natural extension of the fairing recovery system("bouncy castle" seems more likely than helicopter to me though) does seem to fit the bill in my mind.  But I remember a discussion here which concluded that the first stage is nowhere near terminal velocity by the time it performs it's landing burn, something like mach 2-3 IIRC.  I wonder what that figure would be for a second stage that only uses TPS to re-enter, and whether that would preclude parachute landings.  I know drogues can help with this, but does it work out?  As it is there is surprisingly little time between S1's entry burn and it's landing burn on these GTO missions, if that window gets even shorter for a faster S2 then I for one would be pretty impressed if they could get chutes deployed and bleed it all off.

Edit:  Having thought about this a bit more, I realized that the second stage could come in at a much more shallow angle, so perhaps there's no need to speculate about this.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 05:13 AM
I should add, I think landing vertically is not the right approach for S2.

Since it can orbit multiple times, it takes negligible dV to make sure the deorbit pass is near the launch site.  Then deorbit, re-entry (possibly ballistic, since there's nobody on board), parachute deployment, and helicopter capture.

All the factors that make helicopter capture difficult for the fairing (range, duration, etc) are non-issues with S2.

I had this thought as well after the "hail mary" comment.  "Hail mary" doesn't sound like the type of commitment it would take to add legs, deal with the nozzle ratio somehow, perform a flip maneuver, and perform a propulsive landing as in the old video, and definitely rules out a raptor S2.  A natural extension of the fairing recovery system("bouncy castle" seems more likely than helicopter to me though) does seem to fit the bill in my mind.  But I remember a discussion here which concluded that the first stage is nowhere near terminal velocity by the time it performs it's landing burn, something like mach 2-3 IIRC.  I wonder what that figure would be for a second stage that only uses TPS to re-enter, and whether that would preclude parachute landings.  I know drogues can help with this, but does it work out?  As it is there is surprisingly little time between S1's entry burn and it's landing burn on these GTO missions, if that window gets even shorter for a faster S2 then I for one would be pretty impressed if they could get chutes deployed and bleed it all off.

Edit:  Having thought about this a bit more, I realized that the second stage could come in at a much more shallow angle, so perhaps there's no need to speculate about this.

S2, if you're standing far enough away, is a lot closer to Dragon than it is to S1.

(Mass, aspect ratio, etc).

The c.g. is off, but adding a Dragon-quality heat shield, and a parachute pack, will help move it forward somewhat.

S2 already has some maneuvering capacity which might help it with reentry stabilization.

This to me sounds like a "minimum effort".

---

Also "bouncy castle" sound like a classic code word.  :)
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 03/31/2017 05:23 AM
For me, the biggest issue with second stage reuse isn't so much the hardware to get it through the atmosphere and land it, it's the fuel mass to de-orbit it, especially from GTO.

From Bob Zubrin, a rough rule of thumb for a heat shield mass is 15% of the dry mass of an object (though I think PicaX does better) and from some quick googling, the US military uses guided para-foils to land air dropped 5t payloads that weigh about 500 kg themselves with accuracies of 50m or better. Therefore, one could potentially have the hardware to get a second stage through the atmosphere and descending slowly by parachute for 1-2 tonnes. Then just grab in midair or land on a bouncy castle.

However, to deorbit a stage on a GTO with the M1D+ Vac, you would need approximately 2 tonnes of fuel based on some very basic calcs I've done. Essentially doubling the mass you need to recover it. So there goes at least 4t in total from your GTO mass....how much was SES-10? 5.5t?

Unless the ISP of the Upper Stage can be boosted magically, successful GTO reuse is, I think, off the table. LEO would work MUCH better or, in the case of their SatNet, MEO.

Does anyone have accurate numbers on what it would take to deorbit the Upper Stage from a GTO? I think that's a starting point. Then we can worry about heat shields and mid-air bouncy castles, etc.

Title: Re: F9 Second Stage Reusability
Post by: ppb on 03/31/2017 06:07 AM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 03/31/2017 06:19 AM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.

Oh I don't think it's that much different, I'm just wondering:

A) how much DeltaV it takes to lower the perigee of the GTO so that it's low enough to rapidly de orbit
B) How accurately you can do it?

570m/s delta V equates to roughly an extra 1t of fuel, which is 1t less of GTO payload at least, assuming the upper stage weighs about 4.5t (that's the number I'm using but I don't know how accurate that is) and your reentry/landing hardware is only 1t extra on top of that. GTO payload starts disappearing rapidly when you add mass to the second stage. Also it needs to be accurate to several hundred square kilometres at least. If you can't bring it down in a reliably accurate way, it's useless.

Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 03/31/2017 06:32 AM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.

Sorry to be a pedant but you mean aerobraking. Aerocapture refers to an object travelling higher than escape velocity, and is something that has never been done to date, strictly speaking.
Title: Re: F9 Second Stage Reusability
Post by: ppb on 03/31/2017 06:42 AM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.

Sorry to be a pedant but you mean aerobraking. Aerocapture refers to an object travelling higher than escape velocity, and is something that has never been done to date, strictly speaking.

Correction noted.  I'm not saying aerobraking would be easy, but I think the crack group of engineers at SpaceX has proven they're up to the task.
Title: Re: F9 Second Stage Reusability
Post by: ppb on 03/31/2017 07:08 AM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.

Oh I don't think it's that much different, I'm just wondering:

A) how much DeltaV it takes to lower the perigee of the GTO so that it's low enough to rapidly de orbit
B) How accurately you can do it?

570m/s delta V equates to roughly an extra 1t of fuel, which is 1t less of GTO payload at least, assuming the upper stage weighs about 4.5t (that's the number I'm using but I don't know how accurate that is) and your reentry/landing hardware is only 1t extra on top of that. GTO payload starts disappearing rapidly when you add mass to the second stage. Also it needs to be accurate to several hundred square kilometres at least. If you can't bring it down in a reliably accurate way, it's useless.



From my back of the envelope calculations, for a 150 x 35622 km GTO, I get an apogee speed of 1598 m/s.  Lowering perigee to 75 km requires an apogee speed of 1590 m/s, a deltaV of only 8 m/s.  That of course is a Hohmann transfer and current S2 design may make surviving that long difficult. Did you assume your delta V happens soon after satellite deploy when both it and S2 are going fast ?  That will definitely cost much more fuel there.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 03/31/2017 07:19 AM
Brillant!

That was my main question and I've never seen it answered as to how much it would take to deorbit. Every one always seemed to go straight to the 'how' and not think about 'how much payload is left?'

How much would it take to do a direct entry? And what mass ratio would that need? If that's small enough, second stage recovery using something similar to ULA's SMART could do the trick.
Title: Re: F9 Second Stage Reusability
Post by: biosehnsucht on 03/31/2017 07:36 AM
How slow would it already have to move under parachutes for a helicopter to grab it?

Assuming you can get it that slow... how much slower can you get it?

Why not a jumbo bouncy castle?

And, of course... how much does all this equipment weigh vs a couple of SuperDracos and their fuel?

For TPS perhaps you can eject the remains of the payload adapter and have Pica-X underneath it, like Dragon jettisons the trunk? Trying to go nose first with the payload adapter still there seems rather difficult, it would probably melt/mangle and damage the TPS on the way in, leading to loss of vehicle.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 03/31/2017 07:59 AM
How slow would it already have to move under parachutes for a helicopter to grab it?

Assuming you can get it that slow... how much slower can you get it?

Why not a jumbo bouncy castle?

And, of course... how much does all this equipment weigh vs a couple of SuperDracos and their fuel?

For TPS perhaps you can eject the remains of the payload adapter and have Pica-X underneath it, like Dragon jettisons the trunk? Trying to go nose first with the payload adapter still there seems rather difficult, it would probably melt/mangle and damage the TPS on the way in, leading to loss of vehicle.

I think it would depend on how slow you could get it with just aero-drag, but given that the Dragon comes in fine, I think it could be slow enough. Only reason to do the aerocapture is to avoid landing gear mass and/or salt water from a sea landing.

As ULA has said, aero-capture of orbital returning, parachuted payloads has been done loads, just not necessarily for as heavy a payload... would be easy to test though.... are there any test Merlin1D vacs hanging around to make a dummy test stage?
Title: Re: F9 Second Stage Reusability
Post by: douglas100 on 03/31/2017 01:56 PM
Agree that air capture is a very promising way to go.

In addition to a heat shield and other recovery aids, the stage also needs more endurance. It needs to become more "spacecraft like." If you wished for something close to RTLS, for some inclinations and launch azimuths you might have to wait up to 24 hours to recover from LEO. That restriction can be relaxed if you are prepared to recover at sea away from the launch site. It all depends on the urgency for refurbishment.

This is particularly true for recovery from GTO. The delta V to bring the perigee into the atmosphere is quite small, as already noted, but the perigee is always close to the equator. That means it will be difficult to recover the stage anywhere near the launch site. With a properly positioned ship and on board helicopter that is perfectly doable. But it will result in some delay in getting the stage back.

However, all that's a bit down the line. One step at a time...
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 03/31/2017 03:03 PM
Assuming the launch vehicle does no inclination change, is the perigee still at the equator? They could use supersynchronous insertion orbits to reduce the satellites work for inclination change.
Title: Re: F9 Second Stage Reusability
Post by: RoboGoofers on 03/31/2017 03:25 PM
If they go to a methane upper stage on F9, as some have promoted, it would be even larger and more unwieldy for a parachute grab.
Title: Re: F9 Second Stage Reusability
Post by: Okie_Steve on 03/31/2017 03:45 PM
I've been pondering the fuel/heat trade off between S2 recovery from circular LEO and elliptical GTO.  In some ways, LEO would be much like Dragon return from ISS so they have lots of data to work with on those conditions. GTO would be more like Apollo 13 Lunar return or Mars capture and I suspect there is much much less known about those condition. Obviously it can be done though. However, judicious timing of burns on GTO changes maximized the benefit for minimum fuel expended. Now consider doing it in reverse. Where is the sweet spot trading fuel to slow down with TPS to allow hotter entry? After all PICAX is supposed to be good for Mars return as I recall, and that's really trucking.

Also, if they only want to get one back for engineering study and not reflight (yet) is just needs to be  in more-or-less one piece :-)
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 04:29 PM
I honestly wouldn't bother with GTO recovery.  Too few flights.

The Impetus is the very high launch rates of LEO sats.  Make a dedicated stage for that, and just expend GTO stages.  Seems to me like a better trade off.
Title: Re: F9 Second Stage Reusability
Post by: Semmel on 03/31/2017 06:58 PM
I honestly wouldn't bother with GTO recovery.  Too few flights.

The Impetus is the very high launch rates of LEO sats.  Make a dedicated stage for that, and just expend GTO stages.  Seems to me like a better trade off.

Thats quite a good argument here. For the massive constellation, a dedicated second stage design would make sense. However, it doesnt solve the problem of near 0 payload when adding all the required bits to the current second stage. Dedicated design or not, there is just not enough margin. Maybe with a raptor, larger diameter, carbon fibre tank and a lot of luck. But that would take away development talent from ITS. Might be better to concentrate on an ITS version that can deploy stats. Should be easier than a design of a F9 reusable second stage.
Title: Re: F9 Second Stage Reusability
Post by: NX-0 on 03/31/2017 07:03 PM

@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

https://twitter.com/elonmusk/status/847882289581359104
Title: Re: F9 Second Stage Reusability
Post by: dglow on 03/31/2017 07:03 PM
Maybe with a raptor, larger diameter, carbon fibre tank and a lot of luck. But that would take away development talent from ITS.

Wouldn't a Raptor + carbon fiber tanked F9 S2 be a perfect milestone toward ITS development? Real world experience with the engine and tank tech behind your Mars vehicle.

I can anticipate one objection: there's no room in Musk's ITS timeline. That's probably true. But without efficiently launching CommX there's no funding for Musk's ITS timeline, either.
Title: Re: F9 Second Stage Reusability
Post by: mme on 03/31/2017 07:07 PM

@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

https://twitter.com/elonmusk/status/847882289581359104
I thought his comments about a "Hail Mary" during the presser were just the adrenaline talking and I'll be super surprised if SX attempts this on the first FH demo.

But it wouldn't be the first time SX surprised me.  Never a dull moment.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 03/31/2017 07:12 PM
I thought his comments about a "Hail Mary" during the presser were just the adrenaline talking and I'll be super surprised if SX attempts this on the first FH demo.

But it wouldn't be the first time SX surprised me.  Never a dull moment.

Agreed. I found the way he spoke about it slightly suspicious, as if he was holding something back. Sure enough... and what better mission to test it on?

Damn, SpaceX is just running balls-out. Bravo to them.
Title: Re: F9 Second Stage Reusability
Post by: shooter6947 on 03/31/2017 07:29 PM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...
Title: Re: F9 Second Stage Reusability
Post by: whitelancer64 on 03/31/2017 07:42 PM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...

For a first test, that's pretty easy, I'd do something that requires minimal modifications to the 2nd stage, like put a heat shield on the nose and attempt a controlled re-entry. If it survives reentry, you win, if it doesn't, you really haven't lost much of anything, and if the FH demo payload is a wheel of cheese or something similarly silly, then cutting into the payload margin doesn't matter much. The question really is - how long have they been preparing to attempt 2nd stage reuse? As with everything that SpaceX has done that surprises us, they may be much further along than any of us can guess.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 07:42 PM
I honestly wouldn't bother with GTO recovery.  Too few flights.

The Impetus is the very high launch rates of LEO sats.  Make a dedicated stage for that, and just expend GTO stages.  Seems to me like a better trade off.

Thats quite a good argument here. For the massive constellation, a dedicated second stage design would make sense. However, it doesnt solve the problem of near 0 payload when adding all the required bits to the current second stage. Dedicated design or not, there is just not enough margin. Maybe with a raptor, larger diameter, carbon fibre tank and a lot of luck. But that would take away development talent from ITS. Might be better to concentrate on an ITS version that can deploy stats. Should be easier than a design of a F9 reusable second stage.

Does it?

The mass penalty is 1:1, and current payload to LEO is 20 tons.

How much is a heat shield, a parachute?  A ton?

Second stage, dry, is under 5 tons I believe.  Suppose structural reinforcement is 20%.  Another ton?

Another ton lurking in the details?

It's a long way to 20 tons.

Title: Re: F9 Second Stage Reusability
Post by: JasonAW3 on 03/31/2017 07:47 PM
<SNIP>

But without efficiently launching CommX there's no funding for Musk's ITS timeline, either.

What get's me is that the CommX deployment by SpaceX gives them good practice for doing the same thing around Mars.

      I wouldn't be entirely suprised to see SpaceX putting multiple colonies at different locations to avoid any catastrophic situations that would wipe out all of the colonists.

      People will die on Mars, that much is unavoidable.  But putting everyone in one colony, with one TYPE of colony habitat, is way too much like putting all of your eggs in one basket.  You're just asking for trouble.

      Admittedly, spreading out the people to multiple colonies will cost more, but the chances to establish a foothold there increase dramatically by spreading them out and diversifying the approaches to how the colony is outfitted.

      Yeah; nothing of what I just said has anything to do with second stage reusability, but if you think about it, the hypersonic reentry that the second stage would have to do, especially in the upper atmosphere, is not all together that different than the conditions that the ITS will have to go through to land on Mars.

      Returning a second stage to Earth successfully would be good practice for landing the ITS itself.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 03/31/2017 07:55 PM
 see also http://forum.nasaspaceflight.com/index.php?topic=42365 "Testing upper stage reusability" which is similar but different in focus.
Title: Re: F9 Second Stage Reusability
Post by: shooter6947 on 03/31/2017 08:06 PM
For a first test, that's pretty easy, I'd do something that requires minimal modifications to the 2nd stage, like put a heat shield on the nose and attempt a controlled re-entry.
This probably wouldn't work, though, without a lot of ballast.  The engine is the heaviest part of the 2nd stage -- it needs to have the center of mass forward otherwise it would flip around on re-entry.
Title: Re: F9 Second Stage Reusability
Post by: Helodriver on 03/31/2017 08:14 PM
If they are thinking of doing a second stage return test, its seems likely clue then that the mission profile of FH Demo will not be a rehearsal of a Dragon 2 lunar free return trajectory mission. 

Returning a second stage after a TLI burn would be nothing short of miraculous.
Title: Re: F9 Second Stage Reusability
Post by: Lars-J on 03/31/2017 08:23 PM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...

I don't think they would be able to do much modification for shielding... My assumption is that they would use mostly propulsive braking. A quick de-orbit burn, and then a 2nd longer burn as a pre-atmospheric braking burn (to kill virtually all velocity), and then hope that it stays intact until a parachute deploys.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/31/2017 09:16 PM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...

I don't think they would be able to do much modification for shielding... My assumption is that they would use mostly propulsive braking. A quick de-orbit burn, and then a 2nd longer burn as a pre-atmospheric braking burn (to kill virtually all velocity), and then hope that it stays intact until a parachute deploys.

That's a huge amount of fuel of course. You're talking about the same delta-V, give or take, as S2 gave the payload on the way up (though with only 5 ton empty weight)

I don't know the exact numbers, but if it was 6 km/sec for the S2 contribution, and ISP =3000 sec, the mass ratio is 7:1...

So the starting mass in orbit is 35 tons... 

So while maybe FH as a stunt can do it, it's not leading to a viable solution.

But adding 3 tons or so of re-entry hardware, or even 5, is still perfectly viable, since if the payload maximizes S2 performance, then you can choose to expend S2.
Title: Re: F9 Second Stage Reusability
Post by: Lemurion on 03/31/2017 09:31 PM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...

I don't think they would be able to do much modification for shielding... My assumption is that they would use mostly propulsive braking. A quick de-orbit burn, and then a 2nd longer burn as a pre-atmospheric braking burn (to kill virtually all velocity), and then hope that it stays intact until a parachute deploys.

The thing is that the rocket equation really hurts you when reserving propellant for upper stage return, while the first stage is more forgiving.

With an upper stage propulsive return, the more performance you need the more propellant you need to reserve for return. If your return relies primarily on adding a heat shield for aerobraking you don't need to reserve even more mass for high performance missions. That's why ITS is planning for propulsive landing on the first stage and using aerobraking on the upper stage.

Use the right tool for the job.
Title: Re: F9 Second Stage Reusability
Post by: Arb on 04/01/2017 01:11 AM
My maths and physics is very rusty but...

According to Wikipedia[1], the Merlin 1D can throttle to 360 kN (81,000 lbf).
According to Space Launch Report[2], the F9 second stage dry mass is ~4.5t

We know F=m.a[3] where F=force in N, m=mass in Kg and a=acceleration in m/s/s
We also know g=acceleration-due-to-gravity=9.8m/s/s

so at 1g F=4500.9.8/1000=44kN
and 360/44=8.16
so it seems that a Merlin 1Dvac could land a second stage with an ~8g hoover slam.

Two question for the experts on NSF:
1) Is this calculation correct?
2) Could the stage survive 8g?

[1] https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D_Vacuum (https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D_Vacuum)
[2] http://www.spacelaunchreport.com/falcon9ft.html (http://www.spacelaunchreport.com/falcon9ft.html)
[3] https://en.wikipedia.org/wiki/Newton_(unit)#Definition (https://en.wikipedia.org/wiki/Newton_(unit)#Definition)
Title: Re: F9 Second Stage Reusability
Post by: Arb on 04/01/2017 01:28 AM
I'm not totally clear how they would do it at all without fitting some kind of kit to give it legs and a second engine etc. (as we've discussed in many many threads) unless he means just seeing if they can splash it down gently (or land ON the bell which then gets squished)
Given that Musk has said it's as much about retiring ITS risk as F9 economics, how about a version of the roomba that's a prototype of the landing platform[1]... Obviates the need for legs.

And if the 1D can land the stage (see my post just above) that gets rid of the second engine leaving just TPS and, perhaps, grid fins as extra mass (plus the extra fuel).

We'll see in due course.

[1] To my eye those arms soooo look like they want to grab something hovering just above...
Title: Re: F9 Second Stage Reusability
Post by: watermod on 04/01/2017 02:50 AM
Why does it need to quickly de-orbit and land.  That requires lots of fuel mass.
What about doing something the new sats are doing?
Like putting on some small lightweight ion engines and a ring of solar cells somewhere on the stage?
Would there be a problem taking months to get into a de-orbit situation?

Title: Re: F9 Second Stage Reusability
Post by: su27k on 04/01/2017 03:24 AM

@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

https://twitter.com/elonmusk/status/847882289581359104

LOL, I was so sure he was joking during the presser...

This reminds me, on one of the old threads (probably 10 years ago, couldn't find it now), Jon Goff mentioned an early concept of 2nd stage reuse from SpaceX, I think it involves flying with MVac engine bell forward and run cooling around it (again I don't quite remember the details), not sure if the idea went anywhere but just to throw it out there...
Title: Re: F9 Second Stage Reusability
Post by: Ludus on 04/01/2017 05:15 AM
There's a good case for a dedicated BFC deployer second stage that's fully reusable. It's optimized to do only that one thing, but it brings back everything ready for rapid turn around. No separate capture of farings, no lost deployment hardware.

If the BFC is 12000 very similar satellites, once they get serious about launching it will be the majority of global orbital launches just for that for years.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/01/2017 05:40 AM

@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

https://twitter.com/elonmusk/status/847882289581359104
We're too close to April 1st to be certain.

That said, he's debated this one for a while. My guess is that the fairly rapid success of fairing recovery leaves the US as a glaring omission with a very nice benefit. The man is nothing if not obsessive.

But here's what holds back. US's are finicky beasts, thoroughbreds of a particular breed.

You can't just waste performance like on the booster, because of the tyranny of the rocket equation.   

And ... everything they've done to eek out more from F9US, fights you on reuse. So you can end up working against yourself. To win here takes finesse, like with the fairing reuse, only 1000x more ... difficult.

Centaur is an excellent US because of all of the subtleties employed in every detail of its design - its in many ways an engineering work of art, touchy too. These kinds of designs thrive on esoterica to do more with less, so its working a puzzle to get N things all done by M mechanisms , where N >> M.

Which again makes it attractive to an obsessive personality. As well as a definite red flag to anyone booking more to the manifest.

Oh, and you don't want to have many changes/variants to them either. They are impossible to thoroughly test, only if you do missions, and definitely you don't want to test them then.

You could make passive changes to allow you to incrementally take the US ever lower into the atmosphere with remaining props by increasing drag, after all you need to dispose of all those US following missions, finding ways to creatively dissipate energy.

A higher performance engine gives you more margin to play with, however, the 2x+ cost of multiple US's would be extremely painful, close to that of what BFR/BFS likely would consume at this stage, so not a good distraction.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/01/2017 05:45 AM
You can waste performance on the Falcon Heavy demo mission.
Title: Re: F9 Second Stage Reusability
Post by: Clueless Idiot on 04/01/2017 05:55 AM
Hi all,

Now I just cant imagine a tube flying aerodynamically through the atmosphere without grid fins, theres no way S2 wont have grid fins will it? Can grid fins survive reentry without burning up, imagine grid fins covered in pica-x.
Title: Re: F9 Second Stage Reusability
Post by: dorkmo on 04/01/2017 06:07 AM
Hi all,

Now I just cant imagine a tube flying aerodynamically through the atmosphere without grid fins, theres no way S2 wont have grid fins will it? Can grid fins survive reentry without burning up, imagine grid fins covered in pica-x.

maybe instead of grid they could do simple flat fins like blue origin
Title: Re: F9 Second Stage Reusability
Post by: MKremer on 04/01/2017 06:14 AM
Hi all,

Now I just cant imagine a tube flying aerodynamically through the atmosphere without grid fins, theres no way S2 wont have grid fins will it? Can grid fins survive reentry without burning up, imagine grid fins covered in pica-x.
We don't know, and I'd bet SpX isn't really sure, so it might be worthwhile to "experiment" with a LEO 2nd stage.

The fact that it's a short tube with a long engine nozzle (and that it's COG is probably around the tank/thrust structure interface level) has probably presented an interesting challenge to finding the 'best' re-entry-to-subsonic orientation and control mechanism (plus heat shielding designs).
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 06:31 AM
Why does it need to quickly de-orbit and land.  That requires lots of fuel mass.
What about doing something the new sats are doing?
Like putting on some small lightweight ion engines and a ring of solar cells somewhere on the stage?
Would there be a problem taking months to get into a de-orbit situation?



SEP works well on the way up, but on the way down I'm certain that it's better in many ways to use atmospheric braking. You need a small nudge to dip the perigee of your GTO into the upper atmosphere, and you trade off time against heating and aero loads to decide how many passes you make before setting up for entry. I doubt SEP would shave any time off this and the extra mass for the required systems would be more than the propellant needed for the perigee change.
Title: Re: F9 Second Stage Reusability
Post by: MP99 on 04/01/2017 08:39 AM


My maths and physics is very rusty but...

According to Wikipedia[1], the Merlin 1D can throttle to 360 kN (81,000 lbf).
According to Space Launch Report[2], the F9 second stage dry mass is ~4.5t

We know F=m.a[3] where F=force in N, m=mass in Kg and a=acceleration in m/s/s
We also know g=acceleration-due-to-gravity=9.8m/s/s

so at 1g F=4500.9.8/1000=44kN
and 360/44=8.16
so it seems that a Merlin 1Dvac could land a second stage with an ~8g hoover slam.

Two question for the experts on NSF:
1) Is this calculation correct?
2) Could the stage survive 8g?

The nozzle wouldn't survive a burn in atmosphere.

OTOH, discard the nozzle and the thrust would be lower (and the Isp a lot lower, too).

Cheers, Martin
Title: Re: F9 Second Stage Reusability
Post by: MP99 on 04/01/2017 08:42 AM
@elonmusk
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Any ideas how they might go about achieving this?  Parachute landing, or propulsive landing?  Deployable heat shield, or ablative-covered tanks?  Probably going to need some serious heat protection as Stage 2 will need to re-enter at much faster than LEO speeds if it's sent a sat to GTO.  Will need bigger batteries and maybe other consumables, too, to be able to still have power 4.5 hours or so after launch when it will be re-entering from a GTO mission...

Elon needs to chat with Jon Goff and friends about testing out Magnetoshell Aero Capture.

Edit: see http://forum.nasaspaceflight.com/index.php?topic=29912.0

Cheers, Martin
Title: Re: F9 Second Stage Reusability
Post by: Alastor on 04/01/2017 12:52 PM
Quote
Elon Musk‏Compte certifié @elonmusk 13 hil y a 13 heures
En réponse à @BadAstronomer

We can def bring it back like Dragon. Just a question of how much weight we need to add.

It seems the main question is about the weight of TPS, and breaking/parachute systems. Not so much about how to capture.
Which would be a logical step to take for SpaceX. Solve 1 problem at a time! :-)
Title: Re: F9 Second Stage Reusability
Post by: robert_d on 04/01/2017 02:06 PM
Because of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage.
It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage.
How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge.
 
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 02:13 PM
Because of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage.
It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage.
How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge.
 

If i'm visualising this correctly, it puts too much surface area ahead of the centre of gravity, and the stage would be extemely unstable and want to fly backwards.
Title: Re: F9 Second Stage Reusability
Post by: nacnud on 04/01/2017 02:17 PM
Given that aerobraking seems to be a given for any reasonable payload fraction, the big problem to me seems to be COG, the stage will want to enter engin first.

So why not let it do that. Use an inflatable heat shield mounted on the side of the stage so the stage comes in horizontal. If the COG and COP are offset you can use rotation to allow it to stear.

Now the problem is how to decelerate the last few m/s and land.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/01/2017 02:18 PM
If i'm visualising this correctly, it puts too much surface area ahead of the centre of gravity, and the stage would be extemely unstable and want to fly backwards.

For sure if they come in engine first it can not survive reentry. It would need to be sideways somewhat like ITS and IXV reentry, with flaps doing the steering and protecting the engine. It needs a heatshield on the side of the stage.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 02:23 PM
Or an aft mounted toroidal inflatable skirt using similar technology to HIAD, and a forward mounted Pica-X heatshield.
Title: Re: F9 Second Stage Reusability
Post by: nacnud on 04/01/2017 02:27 PM
Entering nose first, shuttlecock style?
Title: Re: F9 Second Stage Reusability
Post by: alang on 04/01/2017 03:01 PM
Perhaps this is more about getting a sample second stage back for engineering purposes (after all, they've lost a couple of them) rather than a plan to do it on a regular basis.
I like the inflatable heat shield idea. Hope someone answers the ion thruster/photovoltaic panel deorbit idea that someone upthread suggested.
Title: Re: F9 Second Stage Reusability
Post by: saliva_sweet on 04/01/2017 04:00 PM
Would the base of dragon 2 fit under the fairing?

edit: On second thought they would probably go for ocean splashdown on first attempt anyway. I think they'll take a used dragon1 heatshield and parachutes and stick them in the fairing, apply spam to the tankage, maybe some ballast to tip the cg forward and read the hail marys. The tank will act as a flotation device.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 04/01/2017 04:12 PM
Or an aft mounted toroidal inflatable skirt using similar technology to HIAD, and a forward mounted Pica-X heatshield.

Entering nose first, shuttlecock style?

Isn't that what they showed in their 2011 reusability video? TPS covering the top of the stage and partially down one of the sides.

That video also showed an extending/retracting engine bell to create clearance for the legs, IIRC.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 04:22 PM
. Hope someone answers the ion thruster/photovoltaic panel deorbit idea that someone upthread suggested.

Erm, I did...
Title: Re: F9 Second Stage Reusability
Post by: douglas100 on 04/01/2017 04:29 PM

Isn't that what they showed in their 2011 reusability video? TPS covering the top of the stage and partially down one of the sides...

Yes, but minus the toroidal aft skirt. In previous discussion folks have questioned the stability of entering nose first when most of the mass is in the rear. The skirt would enhance stability, shuttlecock style as already mentioned. An alternative might be deployable flaps covered in TPS.

Quote
That video also showed an extending/retracting engine bell to create clearance for the legs, IIRC.

I like the idea of air capture as mentioned by meekgee and others. It avoids flipping the stage, making any modifications to the engine and eliminates the weight of the legs. It also adds operational flexibility and safety. The stage can be recovered offshore and be brought directly back to the launch point. The recovery equipment on the stage would then only be a heatshield and a steerable parachute. The capture helicopter would do the rest.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 04:31 PM
Or an aft mounted toroidal inflatable skirt using similar technology to HIAD, and a forward mounted Pica-X heatshield.

Entering nose first, shuttlecock style?

Isn't that what they showed in their 2011 reusability video? TPS covering the top of the stage and partially down one of the sides.

That video also showed an extending/retracting engine bell to create clearance for the legs, IIRC.

The 2011 video didn't show an inflatable skirt, it was more of a sideways entry. For all we know that is still exactly what they plan to do. The stage might already be strong enough in that axis, unlike the much finer first stage.
Title: Re: F9 Second Stage Reusability
Post by: GORDAP on 04/01/2017 04:57 PM
I think SpaceX has a fine line to skate here:  They don't want to modify the US so much that it invalidates this first flight as a test flight of the FH in any way.

On the other hand, they probably have some ideas or plans on a future design of a reusable US and this flight is a good opportunity to use as a test bed for those ideas.  That is, they don't in any way plan to evolve the present Merlin US stage to be reusable - Musk has pretty much indicated the ISP is too low for this - but they can use this US as a space based 'grasshopper'. 

So what would be some minimal changes that could answer some basic questions?  I'm thinking maybe they could just add TPS to the top and TPS covered titanium grid fins to the 'base'.  Then have the stage descend top forward, with the fins used to add a bit of drag and precision steering.  Would grid fins back near the engine help with the CG being on the wrong end for stable flight? 

Anyway, forget soft landing; just aim for a spot in the ocean and see how close you get.  Maybe have a drone ship nearby to record video, etc.  This would at least answer if they can survive reentry with this mode and if they can come close to the intended spot.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/01/2017 04:59 PM
Two words: bouncy castle! :-)
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/01/2017 05:03 PM
They couod just keep a heap of residual propellant in the stage and enter nose first- this would significantly affect the CG and increase stability.
Or, thinking this through, add ballast (shudder) to the top of the stage...
Title: Re: F9 Second Stage Reusability
Post by: saliva_sweet on 04/01/2017 05:13 PM
They couod just keep a heap of residual propellant in the stage and enter nose first- this would significantly affect the CG and increase stability.
Or, thinking this through, add ballast (shudder) to the top of the stage...

They have plenty of payload capacity to add as much ballast as they could ever need. What does a single merlin weigh anyway? ~1t I'd wager.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 04/01/2017 05:17 PM
Hi all,

Now I just cant imagine a tube flying aerodynamically through the atmosphere without grid fins, theres no way S2 wont have grid fins will it? Can grid fins survive reentry without burning up, imagine grid fins covered in pica-x.

maybe instead of grid they could do simple flat fins like blue origin

I think that's a bad idea. Grid fins are far more efficient in terms of control authority/lift per unit mass. That's why people use them.  Blue may reconsider their thinking on flat fins, we'll see..  Flat fins may heat less though... except at the leading edge. Grid fins are ALL leading edge :)
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/01/2017 05:19 PM
Hi all,

Now I just cant imagine a tube flying aerodynamically through the atmosphere without grid fins, theres no way S2 wont have grid fins will it? Can grid fins survive reentry without burning up, imagine grid fins covered in pica-x.

maybe instead of grid they could do simple flat fins like blue origin

I think that's a bad idea. Grid fins are far more efficient in terms of control authority/lift per unit mass. That's why people use them.  Blue may reconsider their thinking on flat fins, we'll see..  Flat fins may heat less though... except at the leading edge. Grid fins are ALL leading edge :)

Also, grid fins are much better for high mach numbers.  Blue Origin hasn't dealt with those kinds of speeds yet.  When they do, I expect them to go with grid fins.  That's what grid fins were invented for.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/01/2017 05:53 PM
You can waste performance on the Falcon Heavy demo mission.
True. And he's hinted at something ... surprising.

Here's how you might use that (but for a lot of reasons its unlikely).

You could either loft an entire, fueled stage in the fairing ... or tanks to refill the second stage, including excess for boil-off.

In effect you'd want to end up on orbit with a fully loaded US that has a Dragon heat shield on top.

The autonomous program would check out the refuel, and orient/phase the stage for a grazing entry precisely.

The US RCS would control buffeting as EI occured, getting the stage as low as possible given CG, with perhaps a cooled/vented heat shield. Then, before aerodynamic pressure built up too high, the stage would flip and RCS would maintain orientation. You'd go as low as you could heating the engine bell, then ignite and burn for an extended entry burn, likely wiggling the gimbal to increase drag, and likely burning to exhaustion. Hopefully making it to transonic.

Passive CG would keep you from tumbling. Assuming you survive to free fall velocities, you pop the chutes around 5K feet, and perhaps there's something floating on the surface for a little while to be admired.

You
Title: Re: F9 Second Stage Reusability
Post by: mr. mark on 04/01/2017 06:11 PM
What no one seems to be talking about is that the FH launch is 5 months out. Clearly SpaceX already has a second stage prototype ready to go. You just don't slap things on to an existing stage. This brings up an important point. Is SpaceX conducting super secret testing such as a black ops program for future designs away from the public eye.
Title: Re: F9 Second Stage Reusability
Post by: alang on 04/01/2017 06:15 PM
You can waste performance on the Falcon Heavy demo mission.
True. And he's hinted at something ... surprising.

Here's how you might use that (but for a lot of reasons its unlikely).

You could either loft an entire, fueled stage in the fairing ... or tanks to refill the second stage, including excess for boil-off.

In effect you'd want to end up on orbit with a fully loaded US that has a Dragon heat shield on top.

The autonomous program would check out the refuel, and orient/phase the stage for a grazing entry precisely.

The US RCS would control buffeting as EI occured, getting the stage as low as possible given CG, with perhaps a cooled/vented heat shield. Then, before aerodynamic pressure built up too high, the stage would flip and RCS would maintain orientation. You'd go as low as you could heating the engine bell, then ignite and burn for an extended entry burn, likely wiggling the gimbal to increase drag, and likely burning to exhaustion. Hopefully making it to transonic.

Passive CG would keep you from tumbling. Assuming you survive to free fall velocities, you pop the chutes around 5K feet, and perhaps there's something floating on the surface for a little while to be admired.

You

This is getting into party thread territory, so maybe it would need another thread: I wonder what the aerodynamics of a dragon mounted upside down on the payload adapter would be...:-)
Title: Re: F9 Second Stage Reusability
Post by: cppetrie on 04/01/2017 06:18 PM
Is SpaceX conducting super secret testing such as a black ops program for future designs away from the public eye.
I can't imagine the answer to this question is anything other than absolutely yes. As a bleeding edge aerospace company how could they not have numerous R&D projects that aren't public. There is some stuff that shows up in L2 that isn't "public" but there is probably plenty more than isn't at all known outside of the small group working on it.
Title: Re: F9 Second Stage Reusability
Post by: saliva_sweet on 04/01/2017 06:28 PM
Clearly SpaceX already has a second stage prototype ready to go. You just don't slap things on to an existing stage. This brings up an important point. Is SpaceX conducting super secret testing such as a black ops program for future designs away from the public eye.

I seriously doubt that. He wouldn't have called it "hail mary" then. Spacex doesn't have the time or resources to seriously devote to a one off hail mary attempt right now. I think it's more likely Elon is considering giving a couple of interns access to a used dragon and a healthy budget of zero, telling them to make something happen. Thinking it might be worth to fly that in lieu of a couple of extra tons of cheese (cheese is expensive you know).
Title: Re: F9 Second Stage Reusability
Post by: mr. mark on 04/01/2017 07:09 PM
Highly doubtful of that. New designs take years to develop. You just don't tell interns to throw something together. I wouldn't doubt they have the prototype sitting somewhere in Hawthorne ready and waiting.
Title: Re: F9 Second Stage Reusability
Post by: saliva_sweet on 04/01/2017 07:33 PM
New designs take years to develop.

Spacex doesn't have years to develop a hail mary reusable second stage as a cheese replacement for the falcon heavy demo :'(
Title: Re: F9 Second Stage Reusability
Post by: Kosmos2001 on 04/01/2017 07:46 PM
My maths and physics is very rusty but...

According to Wikipedia[1], the Merlin 1D can throttle to 360 kN (81,000 lbf).
According to Space Launch Report[2], the F9 second stage dry mass is ~4.5t

We know F=m.a[3] where F=force in N, m=mass in Kg and a=acceleration in m/s/s
We also know g=acceleration-due-to-gravity=9.8m/s/s

so at 1g F=4500.9.8/1000=44kN
and 360/44=8.16
so it seems that a Merlin 1Dvac could land a second stage with an ~8g hoover slam.

Two question for the experts on NSF:
1) Is this calculation correct?
2) Could the stage survive 8g?

[1] https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D_Vacuum (https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D_Vacuum)
[2] http://www.spacelaunchreport.com/falcon9ft.html (http://www.spacelaunchreport.com/falcon9ft.html)
[3] https://en.wikipedia.org/wiki/Newton_(unit)#Definition (https://en.wikipedia.org/wiki/Newton_(unit)#Definition)

IDK, but probably using the MDVac close to SL would generate problems associated with flow separation.
Title: Re: F9 Second Stage Reusability
Post by: northenarc on 04/01/2017 07:49 PM
 A couple years ago there was a thread around here speculating about landing the second stage as a lifting body, with some kind of stub wings and landing skids. I thought it sounded like an interesting idea, but never heard any more in that direction, or any talk of scouting for landing sites.   
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/01/2017 08:18 PM
Because of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage.
It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage.
How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge.
 
That gives me an idea (sorry if it's been suggested.) Behold, my first NFS Rube Goldberg device.  It must be contagious:

Rocket LEGO Landing Element.  A landing module that connects to the PAF and is used as a PAF for the "real" payload.  It includes integrated SDs and landing legs and it's mass shifts the COM forward so it reenters "head first." No idea how to add a heat shield or control the trajectory w/o some sort of fins.

Similar idea could use a controllable parafoil instead of propulsive landing (or maybe with propulsive assist.)

Basically I like the idea of the PAF as a PAF so that there is only one S2 and you plug on the "reuse option."  Some assembly and lots of hand waving required.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/01/2017 08:31 PM
If i'm visualising this correctly, it puts too much surface area ahead of the centre of gravity, and the stage would be extemely unstable and want to fly backwards.

For sure if they come in engine first it can not survive reentry. It would need to be sideways somewhat like ITS and IXV reentry, with flaps doing the steering and protecting the engine. It needs a heatshield on the side of the stage.
The problem is that this is a stage, not a vehicle. It's very strong in exactly one axis. In the same way you can stack 10 loaded soda cans vertically. Now stack nine of those vertically so the base of the stack is pressing on the side of the bottom can, making sure to catch the spray when it ruptures.

Making something return intact from orbital velocity  and reusable (or at least refurbishable) is a solved problem if you start from a clean slate.

It's the fact that you start from something so far away from a clean slate that makes it hard.  :(

The question is what has changed from 2014 for Musk to consider upper stage recovery might be viable?

He's said the engines on the FH demo will have about 10% more thrust but he's also said that it's Isp that's the problem.

Now a bigger nozzle could increase Isp a few seconds, but is that a big enough change to consider giving this a go? the ongoing talk about a Methane upper stage would increase that by a fair bit more but is that enough?

A possibly relevant side item from the presser was that SX will be switching to forged Titanium alloy grid fins in future, from TPS coated Aluminum.

It's possible this would increase the maximum usage temperature enough to make putting a set of them on the US worthwhile.

Which leaves the landing legs to be installed.

Another obvious question is how close to a complete, stage landing on ship, first attempt they would be looking for?  Would ditching within a Km of the ship (with no provision for actual landing) be viewed as a good start, or a full actual landing?



Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/01/2017 09:32 PM
This a a modification of a Flyback Falcon I made up 6 years back using an X-37 like mold line for S2 before F9R. The current S2 would slide in the external airframe, once around and land back on a runway... (not to scale)
https://forum.nasaspaceflight.com/index.php?topic=27477.20
Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/01/2017 10:05 PM
Or an aft mounted toroidal inflatable skirt using similar technology to HIAD, and a forward mounted Pica-X heatshield.

Could they go even simpler where they just unfurl a consumable tail  "streamer" out the aft to provide stability?  Same flexible heat resistant materials as HIAD.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/01/2017 10:11 PM
This a a modification of a Flyback Falcon I made up 6 years back using an X-37 like mold line for S2 before F9R. The current S2 would slide in the external airframe and land on a runway
https://forum.nasaspaceflight.com/index.php?topic=27477.20
The joker in any winged design is the shift in Cg and Cp as the design operates Mach 23.

Think of it as a vertically launched HOTOL.   :(

Logically the strongest area of the stage after the engine area would be the common bulkhead.

Again it's how much mass you'll have to add to give the strength to resist side loads.
Title: Re: F9 Second Stage Reusability
Post by: Lars-J on 04/01/2017 10:24 PM
Long term we already know what SpaceX's design will be for a reusable upper stage. We have already seen it - the ITS spacecraft. Sideways reentry using body fins and movable tail flaps (much like ESA's IXV), and then vertical landing.

I would not rule out them flying some subscale version of this as an FH upper stage if they decide they need to try it at a smaller scale. But I don't consider it likely.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/01/2017 11:40 PM
I haven't given up yet on propulsive landing as SpaceX has relatively all the components in house for such or capability to produce them. The trades are mass of prop vs the small wings on a lifting entry such as the proven X-37 plan form. It would also remove the pitch-up maneuver needed for a tail first landing. Other trades would be landing legs vs landing gear so it may be a wash there... The KISS rule is always how I view things... I have always known in my gut that Elon had not given up on an S2 reusabilty, it was just a matter of priorities... He could still go with the initial blunt body with TPS that he has showed in his videos in some variant, perhaps with Super Dracos on the sides....
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/01/2017 11:41 PM
Clearly SpaceX already has a second stage prototype ready to go. You just don't slap things on to an existing stage. This brings up an important point. Is SpaceX conducting super secret testing such as a black ops program for future designs away from the public eye.

I seriously doubt that. He wouldn't have called it "hail mary" then. Spacex doesn't have the time or resources to seriously devote to a one off hail mary attempt right now. I think it's more likely Elon is considering giving a couple of interns access to a used dragon and a healthy budget of zero, telling them to make something happen. Thinking it might be worth to fly that in lieu of a couple of extra tons of cheese (cheese is expensive you know).

Ironically, "maybe a few interns working on it" is how some folks characterized the Raptor project a couple of years ago.
Title: Re: F9 Second Stage Reusability
Post by: MichaelBlackbourn on 04/02/2017 04:23 AM
Can an entire S2 with a stub nozzle, experimental TPS over the nose+side, nearly empty tanks, and Grid fins fit inside the fairing as the payload?

That way you get a nominal testing standard S2, and you get an experimental S2 with modifications up there at the same time. Best of both worlds.

Title: Re: F9 Second Stage Reusability
Post by: MichaelBlackbourn on 04/02/2017 04:39 AM
Hell, you can probably mate the 'nose' of the experimental S2 to interface used to mount the payload. So it would ride uphill backwards.

This really seems like the best 'weight simulator' they could do, and fill with as much propellant in it as they need to get the weight up for a proper test.
Title: Re: F9 Second Stage Reusability
Post by: Long EZ on 04/02/2017 04:55 AM
My idea for getting the second stage through re-entry is as follows. Fly the payload fairing to orbit. Open the fairing to a 90 degree angle but do not release them. Release the payload. Rotate each fairing 180 degrees about the radial axis. Then close them encapsulating the second stage within. This would put the second stage engine and nozzle inside the fairing pointing at its tip. Then re-enter the atmosphere fairing tip first. This obviously would require heat shield material on the front of the payload fairing. Not sure if the second stage would fit, or if the cg and the geometry of the pointy end of the fairing would result in a stable re-entry.

Super sonic flight is solved by two ways, first is the blunt body with the shock wave standing off of the vehicle. The second is with pointy noses like all super sonic aircraft. So this idea is essentially inverting the payload fairing around the second stage then re-enter pointy end first. Hope this sparks some interesting discussion.

This seems to follow the idea described in the previous few posts.


Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/02/2017 06:17 AM
That has been propsed many times. Couple problems:
-the fairing is actually quite heavy, would mean a big hit to payload
-they have invested time and money to recover fairings as is
Title: Re: F9 Second Stage Reusability
Post by: gin455res on 04/02/2017 06:56 AM
How hard would it be to re-engineer stage 2 to have an oxygen drop tank?


Would the remaining heat-shield, fuel tank, engine, nozzle have shifted the centre of gravity far enough backwards to be passively stable on re-entry?


It would definitely look more like a shuttlecock.


Could the nozzle act like grid fins?
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/02/2017 07:58 AM
How hard would it be to re-engineer stage 2 to have an oxygen drop tank?


Would the remaining heat-shield, fuel tank, engine, nozzle have shifted the centre of gravity far enough backwards to be passively stable on re-entry?


It would definitely look more like a shuttlecock.


Could the nozzle act like grid fins?

Pretty hard given it is a common bulkhead.
Title: Re: F9 Second Stage Reusability
Post by: gin455res on 04/02/2017 09:46 AM
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/02/2017 01:00 PM
Anything that changes the basic design of the stage, such as adding heat shields, let alone adding thrusters or dropping the tanks, just takes too long. There are lots of things to do, specification, basic and detailed design, simulation, manufacture, testing, installation, changes to software and procedures. It would amaze me if these could be done in less than a couple of years, let alone the 6 months before the FH first flight.

For the FH demo flight the second stage must be fairly close to what will be flown on subsequent flights, so no major changes will be allowed. Even minor changes will be discouraged if they could possibly affect the success of the demonstration.

The only way that I can think of, which does not involve major changes to S2 (not going to happen for FH demo flight) and which will take under 2 years from decision to start to flight, is to use a ballute.

Potentially, deploying a ballute in LEO, then using it to bleed off much of the velocity high in the atmosphere, then capturing the descending stage by helicopter could work.

Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/02/2017 02:20 PM
When people are thinking about this they might like to consider how SX approached their first PLF recovery attempt.

No attachment to the PAF, no keeping the two halves together. Let each run operationally exactly as normal but add some hardware to them to. That works in this context.

At this late stage in the preparations for the FH test your options will be quite limited. It's way too late to design, model, mfg and install any complex hardware that's not already sitting on the shelf, but perhaps not deployed for whatever reason.

Musk mentioned that the heating energy involved rises as the cube of the velocity you have to bleed off. That suggests every m/s you can avoid adding to the US is better.

The obvious tactic in that case is to have the US burn to near orbital velocity, then separate the payload.
This means the payload has to add some delta V of its own. While not directly applicable I'll note that REL looked at this wrt to Skylon and found it could double payload to orbit, if the payload could supply the last 100m/s. Payload separation while still (nominally) in the atmosphere is in principal easier for a VTO rocket. 

The stage then essentially falls back to Earth by falling around the Earth in a not quite complete full orbit.

This cuts on orbit time from a day to come back over the landing area (plane changes eat a lot of propellant) to less than 90 mins. It also allows time for any kind of decellerator to work and bleed off more of that speed through the very high atmosphere. Perhaps early deployment of the grid fins spread wide in drag brake mode?

The fact the stage is not in orbit means it needs no retro burn to bring it out of orbit, which should be quite a substantial saving. Every m/s shaved in it's near 90min orbital coast can be directly calculated as a thinner TPS layer on the relevant parts, since that delta V does not have to be bled off passing through the much denser lower atmosphere.

The higher thrust engines should also mean they can thrust for a shorter time to kill the residual velocity in the hoverslam landing. It's not clear if that would put them closer to the stages -ve g limit or if they are already there now.

And yet none of this seems quite enough of an improvement.

OK the engine thrust's going to be quite a bit higher than it was in 2014 (Musk said 10% above what it is now, which is quite a lot higher than its 2014 level), when Musk said US reuse was "uneconomic" but that just does not seem enough to put reuse back on the agenda. Wasn't most of this predictable in 2014?
 
Eliminating the retro burn (since technically the stage is not in orbit) eliminates an engine restart and potentially a large chunk of propellant, which didn't have to be carried up the hill in the first place.

Having seen how many attempts it took SX to land their first first stage intact on the barge bringing the US to within 1Km of the barge would be a significant achievement from orbit.  The ultimate of course would be to land the US on the barge without hitting the already secured first stage, which is still attached to the deck.  Ironic to think you could get the US back from NEO only to be destroyed by hitting the successfully landed first stage.

The downside of this plan is that any payload that wants to use it will have to do some of the heavy lifting of getting to LEO in the first place. This would also apply if the payload was to GTO to allow the US to fall back to Earth.
 
I'm excited that Musk has not given up on reuse for the F9 US, even if it will take an FH stack to make it happen.
Title: Re: F9 Second Stage Reusability
Post by: robert_d on 04/02/2017 03:00 PM
This is why I think my idea of developing a Falcon Medium (a two core Falcon that has the two cores stay together and land as a unit) has merit. It gives enough margin for a substantially heavier 2nd stage, while eliminating all expendable 1st stage launches. Reusable 2nd stage could have an elliptical cross section with extra fuel tanks for both a wider TPS surface and larger deceleration burn. 

The 1st stages can likely be equivalent to the Falcon heavy booster stages (and not the upgraded heavy core) because they would not be concentrating all of the compression force onto either booster and there would never be a single core pushing the much heavier payload (and heavier 2nd stage?) by itself. 
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/02/2017 05:15 PM
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)
So essentially apply the ULA Vulcan plan to the US.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/02/2017 06:45 PM
@JohnSmith19
The difference between now and 2014 isn't simply that the MVac thrust has changed. IMHO it's much simpler than that. They were unsure whether the first FH was going to have a payload until quite recently and having determined that it's not going to have one, Musk says they might have a go at bringing back the US. Basically it's a free opportunity to do something interesting.

I think everyone is reading way too much into this and assuming it implies some sort of future US recovery program, of which this will be a demo.
Title: Re: F9 Second Stage Reusability
Post by: gin455res on 04/02/2017 07:09 PM
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)
So essentially apply the ULA Vulcan plan to the US.


yes.
The Vulcan video says 25% the weight, but 65% the cost. I don't know if it would be similar for the Falcon-9 S2.  If it were, the loading of the heat shield would become much lower than for full recovery.


It might be great in a world of 12,000-satellite constellations, if the tanks could become payload. Perhaps, cannibalized for structural components; or sent to an 'exterrestrial scrap yard' for use sometime in the future.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/02/2017 07:29 PM
Long term we already know what SpaceX's design will be for a reusable upper stage. We have already seen it - the ITS spacecraft. Sideways reentry using body fins and movable tail flaps (much like ESA's IXV), and then vertical landing.

I would not rule out them flying some subscale version of this as an FH upper stage if they decide they need to try it at a smaller scale. But I don't consider it likely.

The ITS second stage ist not only a second stage, it is a spacecraft. Which means it has LOTS of mass forward of the tanks which means it has a very different CoG. The F9 second stage has its center of gravity very far back and will NOT reenter sideways.

To make the F9 second stage into some subscale version of the ITS craft you'd need to add quite a bit of mass in front of the tanks. Even then big thin-walled vacuum nozzle at the bottom wouldn't survive reentry and you can't land on it anyway, it has much too much thrust for that (and has the wrong expansion ratio for sea level use).

If mass isn't that important (as with a second stage for the FH which can loft much bigger payloads) you could add a heat shield, four SuperDracos, propellant tanks and legs on top of the stage. This would move the CoG far forward and you could make it reenter and land on its head. Basically make it like a stretched Dragon 2 that has the second stage propellant tanks instead of the pressure vessel and the vacuum Merlin on the top, mounted on the first stage on its head. This would probably add 2-4 tons of mass to the stage and reduce the payload by the same amount, but with FH you have quite a bit of leg room here.

Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/02/2017 09:02 PM
Interstage heat shield

Some discussions addressed aerobraking the Falcon S2 using a heatshield one side of the vehicle. Even if we can employ RCS thrusters to maintain orientation during re-entry, we would still need to protect the MD-1D engine from heat and pressure coming from the side. The most mass efficient way I could conceive for SpaceX to accomplish this is to employ the interstage ring as a heatshield. Rather than being discarded, the ring would stay with the second stage and would represent the principal mass penalty for stage reuse.  If the second stage sports a PICA-x shield on one side, then the ring would also have PICA-x on the same side. To provide protection to the engine, it would be closed off on the end like a tin can.

To employ the ring-shield, the stage would first do the re-entry burn while in space. To allow this, the ring-shield mist be hinged, like a 2-part reusable fairing (see sketch). It must open wide enough to allow the gimballed engine freedom of motion. After the burn, the "split can" would re-close during atmospheric re-entry and serve as an extended side shield as well as an end protector. Once stage velocity had dropped sufficiently to allow a second engine ignition inside the atmosphere, the split can would open again. This time it would be torn off, hopefully in a controlled manner, with no damage to the stage. Ultimately, it would be disposable, but only after serving a second purpose.
Title: Re: F9 Second Stage Reusability
Post by: RotoSequence on 04/02/2017 09:07 PM
Interstage heat shield

Some discussions addressed aerobraking the Falcon S2 using a heatshield one side of the vehicle. Even if we can employ RCS thrusters to maintain orientation during re-entry, we would still need to protect the MD-1D engine from heat and pressure coming from the side. The most mass efficient way I could conceive for SpaceX to accomplish this is to employ the interstage ring as a heatshield. Rather than being discarded, the ring would stay with the second stage and would represent the principal mass penalty for stage reuse.  If the second stage sports a PICA-x shield on one side, then the ring would also have PICA-x on the same side. To provide protection to the engine, it would be closed off on the end like a tin can.

To employ the ring-shield, the stage would first do the re-entry burn while in space. To allow this, the ring-shield mist be hinged, like a 2-part reusable fairing (see sketch). It must open wide enough to allow the gimballed engine freedom of motion. After the burn, the "split can" would re-close during atmospheric re-entry and serve as an extended side shield as well as an end protector. Once stage velocity had dropped sufficiently to allow a second engine ignition inside the atmosphere, the split can would open again. This time it would be torn off, hopefully in a controlled manner, with no damage to the stage. Ultimately, it would be disposable, but only after serving a second purpose.

Might be doable... this seems like the kind of design where you want the fairing failing to close to be the primary failure mode. If that fairing doesn't open after staging, you have instant Loss of Mission unless that fairing easily breaks off by activation of the second stage engine. The whole setup is a bit risky, but it looks at least plausibly interesting.

The design would probably need to be nested within the dimensions of the existing interstage and a new pusher design would be needed. Don't mind me, I'm just "thinking out loud." Overall? I think I kind of like it.
Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/02/2017 09:17 PM
Interstage heat shield

Some discussions addressed aerobraking the Falcon S2 using a heatshield one side of the vehicle. Even if we can employ RCS thrusters to maintain orientation during re-entry, we would still need to protect the MD-1D engine from heat and pressure coming from the side. The most mass efficient way I could conceive for SpaceX to accomplish this is to employ the interstage ring as a heatshield. Rather than being discarded, the ring would stay with the second stage and would represent the principal mass penalty for stage reuse.  If the second stage sports a PICA-x shield on one side, then the ring would also have PICA-x on the same side. To provide protection to the engine, it would be closed off on the end like a tin can.

To employ the ring-shield, the stage would first do the re-entry burn while in space. To allow this, the ring-shield mist be hinged, like a 2-part reusable fairing (see sketch). It must open wide enough to allow the gimballed engine freedom of motion. After the burn, the "split can" would re-close during atmospheric re-entry and serve as an extended side shield as well as an end protector. Once stage velocity had dropped sufficiently to allow a second engine ignition inside the atmosphere, the split can would open again. This time it would be torn off, hopefully in a controlled manner, with no damage to the stage. Ultimately, it would be disposable, but only after serving a second purpose.

Might be doable... this seems like the kind of design where you want the fairing failing to close to be the primary failure mode. If that fairing doesn't open after staging, you have instant Loss of Mission unless that fairing easily breaks off by activation of the second stage engine. The whole setup is a bit risky, but it looks at least plausibly interesting.

The design would probably need to be nested within the dimensions of the existing interstage and a new pusher design would be needed. Don't mind me, I'm just "thinking out loud." Overall? I think I kind of like it.
Yeah. Now I'm wondering if starting the engine could blast it away safely.
Edit: Trying to think of a way to have a sloped surface inside the ring-shield so that the blast force would be unbalanced against the inside, causing it to move out and sideways.
Edit 2: Of course your breakaway hinges are needed.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/02/2017 09:33 PM
Interstage heat shield

Some discussions addressed aerobraking the Falcon S2 using a heatshield one side of the vehicle. Even if we can employ RCS thrusters to maintain orientation during re-entry, we would still need to protect the MD-1D engine from heat and pressure coming from the side. The most mass efficient way I could conceive for SpaceX to accomplish this is to employ the interstage ring as a heatshield. Rather than being discarded, the ring would stay with the second stage and would represent the principal mass penalty for stage reuse.  If the second stage sports a PICA-x shield on one side, then the ring would also have PICA-x on the same side. To provide protection to the engine, it would be closed off on the end like a tin can.

To employ the ring-shield, the stage would first do the re-entry burn while in space. To allow this, the ring-shield mist be hinged, like a 2-part reusable fairing (see sketch). It must open wide enough to allow the gimballed engine freedom of motion. After the burn, the "split can" would re-close during atmospheric re-entry and serve as an extended side shield as well as an end protector. Once stage velocity had dropped sufficiently to allow a second engine ignition inside the atmosphere, the split can would open again. This time it would be torn off, hopefully in a controlled manner, with no damage to the stage. Ultimately, it would be disposable, but only after serving a second purpose.

But you can't employ RCS thrusters to maintain orientation during re-entry. You'd basically need to balance the mass difference between the heavy and the light end (bottom and top) by thrust. Do you want to run some 1000 lbf thrusters all the time during reentry?

And even then you would end up with a vacuum Merlin for landing, which has both much too much thrust and the wrong nozzle. And the nozzle is big which forces long (and with that wide) legs.

What you need anyway is a heat shield, propellants for landing and legs. Now put all of this on top of the stage and it will reenter head first. Now the Merlin is nicely tucked away in the plasma shadow and the only price you have to pay for that is four SuperDracos to land the thing on the head. Which is just as fine because you couldn't land it with the Merlin anyway.


Also the interstage is left with the first stage, and with good reasons. The nozzle is radiation cooled and needs to look at cold space, not at the inside of an interstage.
Title: Re: F9 Second Stage Reusability
Post by: RotoSequence on 04/02/2017 09:50 PM
But you can't employ RCS thrusters to maintain orientation during re-entry. You'd basically need to balance the mass difference between the heavy and the light end (bottom and top) by thrust. Do you want to run some 1000 lbf thrusters all the time during reentry?

And even then you would end up with a vacuum Merlin for landing, which has both much too much thrust and the wrong nozzle. And the nozzle is big which forces long (and with that wide) legs.

What you need anyway is a heat shield, propellants for landing and legs. Now put all of this on top of the stage and it will reenter head first. Now the Merlin is nicely tucked away in the plasma shadow and the only price you have to pay for that is four SuperDracos to land the thing on the head. Which is just as fine because you couldn't land it with the Merlin anyway.


Also the interstage is left with the first stage, and with good reasons. The nozzle is radiation cooled and needs to look at cold space, not at the inside of an interstage.

I suspect that engine-first re-entry would remain the dynamically stable approach, since most of the stage mass is and would remain in the engine. You are right about the rest, though; the clamshell heat shield would need to open very wide for radiative cooling, and super-dracos are the only viable engine for propulsive landing in SpaceX's inventory.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/02/2017 10:15 PM
As an evolution SpaceX's concept from their video: This is my reusable S2 using a sliding rearward skirt with petals that open to a "shuttlecock" configuration for drag stability, controlability, lift (biasing) and to protect the engine bell from heat (think afterburner "turkey feathers" in video). 8 Super Dracos with hypergolic prop tanks in the nose for CoG on 4 telescopic landing legs. TPS is in tan... WIP... (Note: I'm also thinking along the lines of utilizing the stage 1-2 inter-stage adapter to create the "shuttlecock petals") since it is now discarded...
https://www.youtube.com/watch?v=y_YVYj6vuas
https://history.nasa.gov/SP-4220/ch7.htm
http://www.dtic.mil/dtic/tr/fulltext/u2/a231552.pdf
We have experience with "blunt body" re-entry vehicle from our experience with the Atlas warhead.
https://forum.nasaspaceflight.com/index.php?topic=39314.260
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/02/2017 10:23 PM
But you can't employ RCS thrusters to maintain orientation during re-entry. You'd basically need to balance the mass difference between the heavy and the light end (bottom and top) by thrust. Do you want to run some 1000 lbf thrusters all the time during reentry?

And even then you would end up with a vacuum Merlin for landing, which has both much too much thrust and the wrong nozzle. And the nozzle is big which forces long (and with that wide) legs.

What you need anyway is a heat shield, propellants for landing and legs. Now put all of this on top of the stage and it will reenter head first. Now the Merlin is nicely tucked away in the plasma shadow and the only price you have to pay for that is four SuperDracos to land the thing on the head. Which is just as fine because you couldn't land it with the Merlin anyway.


Also the interstage is left with the first stage, and with good reasons. The nozzle is radiation cooled and needs to look at cold space, not at the inside of an interstage.

I suspect that engine-first re-entry would remain the dynamically stable approach, since most of the stage mass is and would remain in the engine. You are right about the rest, though; the clamshell heat shield would need to open very wide for radiative cooling, and super-dracos are the only viable engine for propulsive landing in SpaceX's inventory.

Well, I think a Merlin is about 500kg, add the nozzle and whatever, the thrust structure etc... Maybe 1500kg or 2000kg.

At the top you will add about 200kg for the heat shield, again 200kg for the SuperDracos and mounting, 1000kg propellants, then tanks for those and for helium, then the legs, more batteries for a day in orbit (deploying and retracting solar panels would be a bit over the top), some structure... I think with empty main tanks it will end up top-heavy then. I would guess you'd end up with at least 2000kg or 3000kg additional hardware on the top, maybe more. You'd basically bolt an inverted Dragon 2 minus the pressure vessel on top of the second stage. If it's still bottom-heavy, add ballast or more propellant.

The FH can spare a few tons of payload. If cutting even 4 tons into the payload gives you the second stage back and means flying for basically just the propellant costs (Ok, ideally) it would be worth it.


Of course this would only make sense for LEO launches... You're not getting your second stage back when you're throwing a Dragon to Mars.
Title: Re: F9 Second Stage Reusability
Post by: RotoSequence on 04/02/2017 10:43 PM
Well, I think a Merlin is about 500kg, add the nozzle and whatever, the thrust structure etc... Maybe 1500kg or 2000kg.

At the top you will add about 200kg for the heat shield, again 200kg for the SuperDracos and mounting, 1000kg propellants, then tanks for those and for helium, then the legs, more batteries for a day in orbit (deploying and retracting solar panels would be a bit over the top), some structure... I think with empty main tanks it will end up top-heavy then. I would guess you'd end up with at least 2000kg or 3000kg additional hardware on the top, maybe more. You'd basically bolt an inverted Dragon 2 minus the pressure vessel on top of the second stage. If it's still bottom-heavy, add ballast or more propellant.

The FH can spare a few tons of payload. If cutting even 4 tons into the payload gives you the second stage back and means flying for basically just the propellant costs (Ok, ideally) it would be worth it.


Of course this would only make sense for LEO launches... You're not getting your second stage back when you're throwing a Dragon to Mars.

Another 3000 kilos of hardware that comes right out of your payload capacity to every orbit, and two utterly distinct versions of S2? That's not the kind of thing that's going to make reuse pay off.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/02/2017 10:55 PM
@JohnSmith19
The difference between now and 2014 isn't simply that the MVac thrust has changed. IMHO it's much simpler than that. They were unsure whether the first FH was going to have a payload until quite recently and having determined that it's not going to have one, Musk says they might have a go at bringing back the US. Basically it's a free opportunity to do something interesting.

I think everyone is reading way too much into this and assuming it implies some sort of future US recovery program, of which this will be a demo.
SX know that hard data is better than any amount of simulations, especially in an area like this, where there's still plenty of doubt over models for airflow and heat transfer.

Now that they know no payload is going to get damaged this allows them to do a detailed test and anchor their models. Even if US recovery is a complete failure I expect it to be returning data through the whole launch.  Maybe it will prove that US recovery is completely impossible. Maybe it will refine the uncertainties to a point where a more serious attempt can be made.

Time will tell.
yes.
The Vulcan video says 25% the weight, but 65% the cost. I don't know if it would be similar for the Falcon-9 S2.  If it were, the loading of the heat shield would become much lower than for full recovery.


It might be great in a world of 12,000-satellite constellations, if the tanks could become payload. Perhaps, cannibalized for structural components; or sent to an 'exterrestrial scrap yard' for use sometime in the future.
I thought ULA were talking about doing that for the booster stage only. IOW it's only good for the first stage. The Centaur US remains completely expendable. So it won't give SX what they already have.

The idea of reusing the tank material dates back to proposals to reuse the Shuttle ET, given it was only about 150 m/s below achieving full orbital velocity. Of course that would have meant moving away for a hand built, bespoke space station, which is what NASA wanted. 

The down side is that package becomes much denser, meaning it drops through the atmosphere fast. That means  rather than lose speed gradually in thin air it slams into thick air, giving a massive frictional heating rate.

With SX starting to work out PLF recovery and reuse US recovery and reuse is the last remaining big item that is still expendable.  I'm optimistic the FH maiden flight will teach them quite a lot, but I'm less so about wheather it will result in a full recovery.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/02/2017 11:01 PM
Well, I think a Merlin is about 500kg, add the nozzle and whatever, the thrust structure etc... Maybe 1500kg or 2000kg.

At the top you will add about 200kg for the heat shield, again 200kg for the SuperDracos and mounting, 1000kg propellants, then tanks for those and for helium, then the legs, more batteries for a day in orbit (deploying and retracting solar panels would be a bit over the top), some structure... I think with empty main tanks it will end up top-heavy then. I would guess you'd end up with at least 2000kg or 3000kg additional hardware on the top, maybe more. You'd basically bolt an inverted Dragon 2 minus the pressure vessel on top of the second stage. If it's still bottom-heavy, add ballast or more propellant.

The FH can spare a few tons of payload. If cutting even 4 tons into the payload gives you the second stage back and means flying for basically just the propellant costs (Ok, ideally) it would be worth it.


Of course this would only make sense for LEO launches... You're not getting your second stage back when you're throwing a Dragon to Mars.

Another 3000 kilos of hardware that comes right out of your payload capacity to every orbit, and two utterly distinct versions of S2? That's not the kind of thing that's going to make reuse pay off.

Yes, honestly I think that the F9 is just too small to make full reusability worthwhile. You can try to do it with the FH, but if you really want to have a common reusable design for everything you need a bigger launcher along the lines of the ITS, with the second stage being an actual spacecraft (and a payload bay for satellite launches, with a kicker stage for GTO). It doesn't need to be as big as the ITS, but the F9 is just hitting the limits of growth.

(I'm still wondering how they want to exploit the 50t of LEO payload of the FH. Isn't the F9 already fairly volume limited? As long as you don't want to launch a payload of lead, you need to go massively hammerhead or make the thing even longer as it is.)
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/03/2017 12:34 AM
What about Magnetoshell Aerobraking/Aerocapture?
Did you make that trip to SpaceX, Jon?

Quote
... short answer is that using MAC for returning an upper stage may be feasible. I did some calculations a few months ago, and while I haven't had MSNW vet them, they at least suggest something like this could work. There are details--normal copper probably won't cut it, but there are at least three other ways of solving it. I haven't had the chance to pitch the idea to SpaceX, but it's definitely one I've been thinking about a lot lately.
http://forum.nasaspaceflight.com/index.php?topic=36285.msg1300481#msg1300481
Title: Re: F9 Second Stage Reusability
Post by: su27k on 04/03/2017 03:16 AM
Well, I think a Merlin is about 500kg, add the nozzle and whatever, the thrust structure etc... Maybe 1500kg or 2000kg.

At the top you will add about 200kg for the heat shield, again 200kg for the SuperDracos and mounting, 1000kg propellants, then tanks for those and for helium, then the legs, more batteries for a day in orbit (deploying and retracting solar panels would be a bit over the top), some structure... I think with empty main tanks it will end up top-heavy then. I would guess you'd end up with at least 2000kg or 3000kg additional hardware on the top, maybe more. You'd basically bolt an inverted Dragon 2 minus the pressure vessel on top of the second stage. If it's still bottom-heavy, add ballast or more propellant.

The FH can spare a few tons of payload. If cutting even 4 tons into the payload gives you the second stage back and means flying for basically just the propellant costs (Ok, ideally) it would be worth it.


Of course this would only make sense for LEO launches... You're not getting your second stage back when you're throwing a Dragon to Mars.

Another 3000 kilos of hardware that comes right out of your payload capacity to every orbit, and two utterly distinct versions of S2? That's not the kind of thing that's going to make reuse pay off.

It would need to be an addon kit, you could design it to be like a payload, and stack the real payload on top of it, either directly like Boeing 702SP, or using a dual launch adapter like Ariane 5
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 04/03/2017 06:04 AM
So a thought about Elon's 'Hail Mary' comment and some of the numbers being batted around here.

Based on how light weight PicaX is (~600kg/m3 is a number a found recently though I’m not sure how accurate that is), you could have conceivably have a heat shield on the front of the second stage 3.7m in diameter and .078m (78mm) thick for 500kg. Alternatively, it could be thinner and partially wrap around the sides.

This would help to balance the stage, but wouldn’t do the full job, so to further stabilise it, several (4?) ‘paddles’ of reinforced picaX could extend from rear next to the engine, similar to the grid fins on the first stage, in order to act as control surfaces providing aerodynamic control and to shift the Centre of Pressure backwards behind the Centre of Gravity, shuttlecocking the stage. Potentially 125 kg each, totalling another 500 kg. 

Finally, a 250kg parachute system could also be installed near the engine. I don’t think this is an unreasonable number as systems approximately 190kg are used to air drop GPS guided payloads up to 4,500kg with parafoils that have and accuracy of less than 50 meters. This is roughly the current Stage 2 mass.

Add in roughly 250kg of propellant for 145 m/s of deltaV to deorbit from GTO via direct entry once the orbit lines itself up (assuming it does or at least comes close enough for an ASDS with a helicopter to go out and meet it…. sea water sucks…) and the total additional hardware to bring down a second stage COULD be as low as 1,500kg including fuel.

Now this is all purely hypothetical and my numbers probably miss something crucial (specifically how much deltaV/fuel it would takes to deorbit), but if it could save something worth ~$15,000,000, it could be worth it, as the Falcon 9 would still be able to deliver some worthwhile payload to GTO (maybe 4-5000kg with a first stage ASDS landing), with the Falcon Heavy filling in the gap.

Now to the point. This is why I think Elon referred to it as a ‘Hail Mary’. The big question is, is that enough hardware to bring the second stage back from GTO? If it isn’t, then there is almost no additional payload to be spent before the Falcon 9 becomes essentially useless for the GTO market. Maybe another 250-500kg, but after that, how many birds going to GTO weigh less than 3,500kg? How many weigh less than 4,000kg for that matter?
So that may be the direction they go in, if they get a chance. Slap the bare minimum that can fit within a 1,500kg mass budget, and if that doesn’t work, give up completely now on second stage reuse until ITS or some hypothetical dense methalox second stage using a mini-Raptor. And the perfect flight TO slap the bare minimum on would be Falcon Heavy Demo, assuming it can be done without holding it up further. And on top of all this, Spacex literally has all the parts now thanks to Dragon…

TL;DR – If they can return a Second Stage from GTO for less than 1,500kg of extra hardware and fuel, now you’re talking, other than that, not worth it…
Title: Re: F9 Second Stage Reusability
Post by: Ludus on 04/03/2017 06:34 AM
So a thought about Elon's 'Hail Mary' comment and some of the numbers being batted around here.

Based on how light weight PicaX is (~600kg/m3 is a number a found recently though I’m not sure how accurate that is), you could have conceivably have a heat shield on the front of the second stage 3.7m in diameter and .078m (78mm) thick for 500kg. Alternatively, it could be thinner and partially wrap around the sides.

This would help to balance the stage, but wouldn’t do the full job, so to further stabilise it, several (4?) ‘paddles’ of reinforced picaX could extend from rear next to the engine, similar to the grid fins on the first stage, in order to act as control surfaces providing aerodynamic control and to shift the Centre of Pressure backwards behind the Centre of Gravity, shuttlecocking the stage. Potentially 125 kg each, totalling another 500 kg. 

Finally, a 250kg parachute system could also be installed near the engine. I don’t think this is an unreasonable number as systems approximately 190kg are used to air drop GPS guided payloads up to 4,500kg with parafoils that have and accuracy of less than 50 meters. This is roughly the current Stage 2 mass.

Add in roughly 250kg of propellant for 145 m/s of deltaV to deorbit from GTO via direct entry once the orbit lines itself up (assuming it does or at least comes close enough for an ASDS with a helicopter to go out and meet it…. sea water sucks…) and the total additional hardware to bring down a second stage COULD be as low as 1,500kg including fuel.

Now this is all purely hypothetical and my numbers probably miss something crucial (specifically how much deltaV/fuel it would takes to deorbit), but if it could save something worth ~$15,000,000, it could be worth it, as the Falcon 9 would still be able to deliver some worthwhile payload to GTO (maybe 4-5000kg with a first stage ASDS landing), with the Falcon Heavy filling in the gap.

Now to the point. This is why I think Elon referred to it as a ‘Hail Mary’. The big question is, is that enough hardware to bring the second stage back from GTO? If it isn’t, then there is almost no additional payload to be spent before the Falcon 9 becomes essentially useless for the GTO market. Maybe another 250-500kg, but after that, how many birds going to GTO weigh less than 3,500kg? How many weigh less than 4,000kg for that matter?
So that may be the direction they go in, if they get a chance. Slap the bare minimum that can fit within a 1,500kg mass budget, and if that doesn’t work, give up completely now on second stage reuse until ITS or some hypothetical dense methalox second stage using a mini-Raptor. And the perfect flight TO slap the bare minimum on would be Falcon Heavy Demo, assuming it can be done without holding it up further. And on top of all this, Spacex literally has all the parts now thanks to Dragon…

TL;DR – If they can return a Second Stage from GTO for less than 1,500kg of extra hardware and fuel, now you’re talking, other than that, not worth it…

If it's just the sort of additional mass you describe, it might be very useful even if it only allowed recovery of S2 with a class of FH flights not single core. If they're looking ahead to deploying the Constellation, that alone might be dozens of FH flights per year with precisely controllable inhouse payloads. It wouldn't matter if other S2s still had to be expendable.

With PicaX on one side and grid fins it might make it to deploying a parafoil, then it could be snagged midair by a heavy helicopter like a Skycrane.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/03/2017 06:52 AM
For second stage reusability it all comes down to propellant and heat.

The stage is naturally bottom heavy. So the question is can the rear end and the nozzle survive the heating. If it can you don't need propellant (main or RCS) to keep the front end to bear the brunt of the heating through TPS.

2nd worst is if you have to run the engine to generate a "nose bubble" An interesting question would be could you run the engine quite fuel rich, as that's lighter. Keeping in mind that at these altitudes we're talking a few 10s of psi is 100x of (ambient) atmospheric pressure.

If that doesn't work then you have to keep the nose end on to the airstream, which suggests continuous movement of some kind of dynamic control surfaces, probably a set of grid of fins. SX are familiar with them and they operate over a wide range of Mach numbers, which will be even more important for US than booster stage recovery.

TBH doing SECO just below orbital velocity still seems like the best way to save a lot of propellant on the de-orbit burn. Just have the payload provide the last 10s of m/s delta V.  But as always the question is will it be enough?
Can side stepping needing a de-orbit burn at all, coupled with the the decelleration from control surfaces during a once around flight, coupled with thinner TPS due to the lower starting velocity lower the mass penalty for recovery enough?

This is an area where approximations don't really cut it and you're looking at fairly detailed simulation to see if something is at all possible. Slight mishaps don't add, they multiply.
Title: Re: F9 Second Stage Reusability
Post by: Semmel on 04/03/2017 07:38 AM
Maybe I am being a party pooper here, but I dont think the second stage will see any substantial design changes for the (if any) recovery attempt. And I think of things like heat shields, wings,  fold-up legs etc. that sit on the outside of the stage.
It would probably invalidate the use of the FH launch for the DOD certification process. Therefore, I suspect the recovery attempt will be something like a parachute mounted in the payload fairing adapter and have it reenter without burning up by spending fuel. How, I have no idea. But I think the most important thing is to get the DOD certification. Anything that would violate it is not going to happen.
Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/03/2017 10:56 AM
Interstage shield 2

   In Reply #101 above I suggested employing a modified interstage ring as a heat shield that would allow stage 2 to enter the atmosphere. In the following discussion the idea was found to be interesting, but the underlying assumption that RCS thrusters could hold its orientation during the maneuver wouldn't work because the CG was just too low on the rocket stage.

Now consider instead that stage 2 will enter the atmosphere tail first, allowing the heavy engine to assist in holding the correct orientation of the stage. In this case, the interstage shield would become essential for a successful return to Earth. The end cap of the interstage shield, when closed, should be constructed as a blunt capsule ablative shield in its own right. It could withstand the heat of re-entry as a capsule with a long body, but it would not have sufficient surface area to decelerate stage 2 to low velocity.  Therefore, Spx would employ the side of the rocket as the primary resistance body, as it now does with stage 1. The interstage heat shield would only serve to protect the M1D engine components during the hypersonic phase of re-entry.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/03/2017 02:37 PM
Maybe I am being a party pooper here, but I dont think the second stage will see any substantial design changes for the (if any) recovery attempt. And I think of things like heat shields, wings,  fold-up legs etc. that sit on the outside of the stage.
It would probably invalidate the use of the FH launch for the DOD certification process. Therefore, I suspect the recovery attempt will be something like a parachute mounted in the payload fairing adapter and have it reenter without burning up by spending fuel. How, I have no idea. But I think the most important thing is to get the DOD certification. Anything that would violate it is not going to happen.

Agree, as well as invalidating the FH certification, there does not seem to be enough time to do anything major.
Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/03/2017 02:38 PM
To make the interstage heat shield concept actually work, there are engineering questions for which I have no good answers:
1. What materials and thicknesses should comprise the different surfaces?
2. What kind of hinge system would work best in space?
3. What sequence of opening and closing of the "tin can" and engine firing would work best?
4. What would be the final disposition of the interstage shield and how to do it? 
Edit: 5. How would the heat shield, now a component of S2, attach and detach from S1?
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 04/03/2017 02:54 PM
Maybe I am being a party pooper here, but I dont think the second stage will see any substantial design changes for the (if any) recovery attempt. And I think of things like heat shields, wings,  fold-up legs etc. that sit on the outside of the stage.
It would probably invalidate the use of the FH launch for the DOD certification process. Therefore, I suspect the recovery attempt will be something like a parachute mounted in the payload fairing adapter and have it reenter without burning up by spending fuel. How, I have no idea. But I think the most important thing is to get the DOD certification. Anything that would violate it is not going to happen.

Pretty much agree with this - it all sounds like Musk is going to give something that is right on the edge of possible a quick go to see what happens. It may not even be part of a longer term 'get the 2nd stage back` plan, but something they can try because they have a lot of spare payload mass (ie all of it) they can use.

If they do have more plans great, but I'm not holding my breath! It's not like he can get Scotty to change the laws of Physics and whack the warp core up to 11.
Title: Re: F9 Second Stage Reusability
Post by: Okie_Steve on 04/03/2017 03:25 PM
Getting back the first S1 led to statement that they found something to make future flights more reliable.No reason that getting back a S2 would not be equally valuable even if it is a one time event because of FH demo extra fuel for S2/no payload.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/03/2017 04:41 PM
For second stage reusability it all comes down to propellant and heat.

The stage is naturally bottom heavy. So the question is can the rear end and the nozzle survive the heating. If it can you don't need propellant (main or RCS) to keep the front end to bear the brunt of the heating through TPS.

2nd worst is if you have to run the engine to generate a "nose bubble" An interesting question would be could you run the engine quite fuel rich, as that's lighter. Keeping in mind that at these altitudes we're talking a few 10s of psi is 100x of (ambient) atmospheric pressure.

If that doesn't work then you have to keep the nose end on to the airstream, which suggests continuous movement of some kind of dynamic control surfaces, probably a set of grid of fins. SX are familiar with them and they operate over a wide range of Mach numbers, which will be even more important for US than booster stage recovery.

TBH doing SECO just below orbital velocity still seems like the best way to save a lot of propellant on the de-orbit burn. Just have the payload provide the last 10s of m/s delta V.  But as always the question is will it be enough?
Can side stepping needing a de-orbit burn at all, coupled with the the decelleration from control surfaces during a once around flight, coupled with thinner TPS due to the lower starting velocity lower the mass penalty for recovery enough?

This is an area where approximations don't really cut it and you're looking at fairly detailed simulation to see if something is at all possible. Slight mishaps don't add, they multiply.
Just a note John, the "shock-wave" interactions within the grid-fins "may" cause extreme temps even using titanium and even with an ablator...

Edit:typo
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/03/2017 08:34 PM
Just a note John, the "shock-wave" interactions within the grid-fins "may" cause extreme temps even using titanium and even with an abaltor...
I'd not considered Edney III and IV heating but I'm sure the SX engineers will have. This suggests the US grid fin sizing and grid spacing and layout would be different to that of the first stage.
Title: Re: F9 Second Stage Reusability
Post by: hrissan on 04/03/2017 10:04 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 04/03/2017 11:28 PM
FYI – didn't see this Twitter exchange of Elon's noted here:

Quote from: Phil Plait‏Verified account @BadAstronomer
This is a very hard problem. It’s moving at orbital velocity, will need leftover fuel, & some way to protect it from heat of re-entry.

Quote from: Elon Musk‏Verified account @elonmusk
Replying to @BadAstronomer
We can def bring it back like Dragon. Just a question of how much weight we need to add.

https://twitter.com/elonmusk/status/847958571895619584
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/04/2017 01:14 PM
There seem likely to be a large number of ex-stage-1 merlins, for the foreseeable future, sitting in warehouses.
How much is the performance hit of making a stage based on a reused engine, not vac optimised?
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 04/04/2017 02:38 PM
I've often wondered why SpaceX didn't go with a plug nozzle type engine for the second stage.  It would do double duty as the heat shield.  It was considered for the second stage of Saturn IB and Saturn V before they were cancelled.  It was based on the J2 engine at that time.  The Octoweb is almost like a plug nozzle using he engines as heat shield for the first stage.  I know it might be more expensive to develop, but in the long run to get 2nd stage reusable, it may be the best overall to do.  No need for heat resistant nose or sides, parachutes, etc.  Just landing legs like the first stage. 
Title: Re: F9 Second Stage Reusability
Post by: Jim on 04/04/2017 03:15 PM
I've often wondered why SpaceX didn't go with a plug nozzle type engine for the second stage.  It would do double duty as the heat shield.  It was considered for the second stage of Saturn IB and Saturn V before they were cancelled.  It was based on the J2 engine at that time.  The Octoweb is almost like a plug nozzle using he engines as heat shield for the first stage.  I know it might be more expensive to develop, but in the long run to get 2nd stage reusable, it may be the best overall to do.  No need for heat resistant nose or sides, parachutes, etc.  Just landing legs like the first stage. 

Because it would not be a merlin then.
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 04/04/2017 03:59 PM
Couldn't the Merlin turbopump machinery be used to supply the plug nozzle? 
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/04/2017 05:16 PM
Couldn't the Merlin turbopump machinery be used to supply the plug nozzle? 
The turbopump would have be redesigned to fuel a series of individual chambers all opening onto the plug nozzle, driving up mass considerably. Multiple smaller chambers mean square-cube losses. The plug nozzle itself would be much heavier than the current nozzle and would have nowhere near the specific impulse. And the combustion chambers would not be sufficiently shielded from re-entry plasma, so there's not really much of an advantage there.

Not to say it couldn't be done; there are plenty of ways to make it work. But you're definitely no longer dealing with a Merlin in any form or fashion.

The Octoweb is almost like a plug nozzle using he engines as heat shield for the first stage.
I'm afraid the Octaweb is nothing like a plug nozzle at all.

There seem likely to be a large number of ex-stage-1 merlins, for the foreseeable future, sitting in warehouses.
How much is the performance hit of making a stage based on a reused engine, not vac optimised?
Not vacuum-optimizing is a complete nonstarter. The performance hit is immense. With a notional payload of 10 tonnes, the second stage has about 7.4 km/s of dV; if it was using a SL Merlin, that drops to 6.6 km/s.

However, it may be possible to retrofit a used SL Merlin. The two differences I know of are larger engine bell and the injection of the gas generator exhaust back into the bell.
Title: Re: F9 Second Stage Reusability
Post by: saliva_sweet on 04/04/2017 05:33 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.

I think even that is too ambitious for this flight. Superdracos are tricky. I'm thinking just a dragon1 heat shield as a payload along with enough ballast to make it top heavy. Everything is payload and zero changes to the second stage proper. What burns burns. They may include parachutes if they have the time and resources, but they could also let it crash to the ocean and optionally fish it out later from the bottom.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/04/2017 05:40 PM
They are designing pressure fed methalox RCS-thrusters for ITS. I wonder if it is possible to modify the design for kerolox and use those. It is experimental, does not need to be super efficient.
Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/04/2017 05:55 PM
I think even that is too ambitious for this flight. Superdracos are tricky. I'm thinking just a dragon1 heat shield as a payload along with enough ballast to make it top heavy. Everything is payload and zero changes to the second stage proper. What burns burns. They may include parachutes if they have the time and resources, but they could also let it crash to the ocean and optionally fish it out later from the bottom.

The dragon heatshield/trunk interface could be repurposed at least so they can place loads above the head shield without dealing with numerous perforations for structure.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/04/2017 08:49 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.
Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/04/2017 09:23 PM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/04/2017 09:28 PM
They are designing pressure fed methalox RCS-thrusters for ITS. I wonder if it is possible to modify the design for kerolox and use those. It is experimental, does not need to be super efficient.
RP-1 boils at 147 C, so...maybe?
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/04/2017 09:28 PM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.
Like grid fins.
Title: Re: F9 Second Stage Reusability
Post by: Barrie on 04/04/2017 09:34 PM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.

Like a really big nozzle extension?
Title: Re: F9 Second Stage Reusability
Post by: cambrianera on 04/04/2017 09:35 PM
A couple years ago there was a thread around here speculating about landing the second stage as a lifting body, with some kind of stub wings and landing skids. I thought it sounded like an interesting idea, but never heard any more in that direction, or any talk of scouting for landing sites.

This?
Happy you found it interesting.
Old Lobo idea, I did some rendering and dimensioning.
Reentering at high angle of attack (like Max Faget's shuttle) heatshield could be thin (and light).
But protection of nozzle is an issue, and SpaceX seems not found of Carbon-Carbon nozzles.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/04/2017 09:41 PM
Keep in mind what is claimed for fairing recovery - thruster packs that stabilize entry.

Fairings and US's are alike in being "fluffy".

They now have experience and flight data in hypersonic entry stabilization.

So you can apply that to a computer model of the US. That gives you a props usage expectation for the stage.

You then adjust the US/RV model with thruster positions/authority and rerun sims, doing trade-offs.

The benefit of a FH Demo flight to do this on is that you class the additions as part of the payload weight - so what if your mass simulator is 53-2t instead of 53t.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/04/2017 09:52 PM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.
That's what my petals do create drag...
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/04/2017 10:02 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.

Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.
Title: Re: F9 Second Stage Reusability
Post by: Wolfram66 on 04/04/2017 10:07 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.

Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.

better to have a PICA-X nose on the S2 with a Ballute collar like the LDSD. that will work with initial atmospheric interface as well as post max-heating while falling tail first. shuttlecock would probably fold up like an umbrella in the wind. IMHO
Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/04/2017 10:08 PM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.

Like a really big nozzle extension?

Would this in itself be enough to shift CP behind COG though?   
Spaceflight 101 estimates approx 4000kg for total stage, 490kg of which is Mvac.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/04/2017 10:21 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.

Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.

better to have a PICA-X nose on the S2 with a Ballute collar like the LDSD. that will work with initial atmospheric interface as well as post max-heating while falling tail first. shuttlecock would probably fold up like an umbrella in the wind. IMHO
They would be controlled by actuators, just like the Shuttle's body flap...
https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/bodyflap.html
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/04/2017 10:23 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.

Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.

I agree, this is the most likely configuration.  The PICA shield, landing legs and landing Draco's could come  Dragon V2. 

Using the Merlin for landing doesn't work for a few reasons, but the show stopper to me seems to be the heating or lose of cryogenic fuel.  Maybe it can do the retro burn or orbit reduction, as long as it's not too long after the mission is completed.

The cross range on the US and where it might bre able to land is an issue too.  With Draco's perhaps they could target a landing location at a time when orbital mechanics work out.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/04/2017 10:24 PM
My bet is what user NovaSilisko suggested year ago.

https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695

His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.

P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme.

The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.

Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.

better to have a PICA-X nose on the S2 with a Ballute collar like the LDSD. that will work with initial atmospheric interface as well as post max-heating while falling tail first. shuttlecock would probably fold up like an umbrella in the wind. IMHO
They would be controlled by actuators, just like the Shuttle's body flap...

Or like an air brake
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/04/2017 10:29 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/04/2017 10:40 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.
An inflatable toroid could conceivably be packed around the base of the MVac. There's plenty of space. If the toroid had TPS on it, that would also protect the rather fragile engine bell.
Title: Re: F9 Second Stage Reusability
Post by: Wolfram66 on 04/04/2017 10:47 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.

what happens when S2 flips to perform hypersonic retro-burn? are the pedals extended or retracted and what is the weight penalty for the pedal and actuator systems?   

just playing Satan's Barrister aka: Devil's Advocate  :o ;D
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/04/2017 10:52 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.

what happens when S2 flips to perform hypersonic retro-burn? are the pedals extended or retracted and what is the weight penalty for the pedal and actuator systems?   

just playing Satan's Barrister aka: Devil's Advocate  :o ;D

No flip or retroburn needed in the atmosphere; after the deorbit burn (in vacuum), the MVac does not relight. RCS reorients the stage for entry, and it maintains that orientation all the way to the ground. Landing either on dedicated thrusters or an airbag.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/04/2017 11:00 PM
I've often wondered why SpaceX didn't go with a plug nozzle type engine for the second stage.  It would do double duty as the heat shield.  It was considered for the second stage of Saturn IB and Saturn V before they were cancelled.  It was based on the J2 engine at that time.  The Octoweb is almost like a plug nozzle using he engines as heat shield for the first stage.  I know it might be more expensive to develop, but in the long run to get 2nd stage reusable, it may be the best overall to do.  No need for heat resistant nose or sides, parachutes, etc.  Just landing legs like the first stage.

Plug nozzles are heavy. They are basically a nozzle turned inside out, which means that the nozzle is surrounded by hot gas on all sides, so you have to actively cool it (or use ablative cooling, which is bad for reusability). Radiative cooling as with the current nozzle isn't possible then.

It would be an entirely different engine. You also still would need to have dedicated landing engines, since the main engine would be much too powerful for landing. Other than a bell nozzle it could adapt to sea level pressures though.

I mean, it's not a totally crazy idea. You could have the nozzle act as (part of a) heat shield and if you could throttle it deep enough you even might be able to land on it. You still would need very long and with that wide legs. And lots of development effort.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/04/2017 11:05 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.
I made them long in order to protect the nozzle from entry heat, just like the Shuttle's body flap protected them. If you read my original post a couple of pages back I wrote in that they would move rearward, then expand in deployment in a controlled fashion, similar how an afterburner "turkey feathers" moves only outward more...#106
https://forum.nasaspaceflight.com/index.php?topic=42637.100
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 04/04/2017 11:19 PM
Here is some information on plug nozzle engines:

http://www.bing.com/images/search?view=detailV2&ccid=SoR555Fu&id=9C3B12E727ADA4CAD160E6E6B72DA3345FCE9E66&q=plug+nozzle+rocket+engine&simid=608008924879391049&selectedIndex=0

My idea was the simple inside out one round, not the linear one.  It was originally going to replace the J2 on the Saturn IB 2nd stage which was the same as the 3rd stage on Saturn V.  It was to return the 3rd stage to land using the engine as a heat shield.  They even built a J2 circular plug nozzle and tested it.  I just don't believe it would be that much heavier than adding a bunch of heat shield material to the sides of an upper stage or on top, and a shield to protect the engine. 

With the plug nozzle the engine becomes the heat shield on the way down.  Not much extra work other than legs, and being able to throttle down low enough to land the stage.  Look at the various pictures.  I'll try to find some more on the Saturn version.  The third stage was also suggested, that with the plug nozzle engine, it could become a small SSTO vehicle. 
Title: Re: F9 Second Stage Reusability
Post by: Jcc on 04/04/2017 11:49 PM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.

what happens when S2 flips to perform hypersonic retro-burn? are the pedals extended or retracted and what is the weight penalty for the pedal and actuator systems?   

just playing Satan's Barrister aka: Devil's Advocate  :o ;D

No flip or retroburn needed in the atmosphere; after the deorbit burn (in vacuum), the MVac does not relight. RCS reorients the stage for entry, and it maintains that orientation all the way to the ground. Landing either on dedicated thrusters or an airbag.

The benefit of having TPS is that it can take the heating and bleed off most of the velocity from orbit. S1 has no TPS so has to do a reentry burn, S2 should not have to. It will need to do most of a full orbit to land back in the US, so most of the remaining fuel would probably be needed to achieve an orbital track that can get it to a convenient landing place, probably in California. Then, I figure dracos (not super dracos) would be enough to bring it out of orbit, then land with parachutes and airbags.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/05/2017 01:02 AM
That's what my petals do create drag...

That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.

A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.
I made them long in order to protect the nozzle from entry heat, just like the Shuttle's body flap protected them. If you read my original post a couple of pages back I wrote in that they would move rearward, then expand in deployment in a controlled fashion, similar how an afterburner "turkey feathers" moves only outward more...#106
https://forum.nasaspaceflight.com/index.php?topic=42637.100

Found this image searching Google for Falcon 9 second stage.  Small graphic image on the far right is interesting.
 http://blogs.esa.int/rocketscience/2014/04/22/dragon-lofts-cargo-to-the-iss/dragonlaunch_20140418_setp1/

Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/05/2017 02:04 AM
And of course we have this from a few years back.  Be interesting to know the full history of the image.
https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198
Title: Re: F9 Second Stage Reusability
Post by: ZachS09 on 04/05/2017 04:31 AM
This is obviously not a finished design of the reusable second stage because there's no landing legs.

At least the aerosurfaces and heat shield are on this second stage.
Title: Re: F9 Second Stage Reusability
Post by: Gliderflyer on 04/05/2017 05:03 AM
This is obviously not a finished design of the reusable second stage because there's no landing legs.
That image appears to be from this 2008 paper (http://selenianboondocks.com/wp-content/uploads/2008/11/s12-11.pdf), which puts it back in the parachute recovery era (no legs). Jon Goff had some posts on Selenian Boondocks about it back in the day:
http://selenianboondocks.com/2008/11/fun-spacex-paper-and-presentation/
http://selenianboondocks.com/2008/12/falcon-ix-upper-stage-recovery-kremlinology/

I don't know how applicable that image is to the current Falcon 9 upper stage, but it may be one of the simpler recovery options.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/05/2017 05:56 AM
This is obviously not a finished design of the reusable second stage because there's no landing legs.
That image appears to be from this 2008 paper (http://selenianboondocks.com/wp-content/uploads/2008/11/s12-11.pdf), which puts it back in the parachute recovery era (no legs). Jon Goff had some posts on Selenian Boondocks about it back in the day:
http://selenianboondocks.com/2008/11/fun-spacex-paper-and-presentation/
http://selenianboondocks.com/2008/12/falcon-ix-upper-stage-recovery-kremlinology/

I don't know how applicable that image is to the current Falcon 9 upper stage, but it may be one of the simpler recovery options.

wow, time flies....   2008....

From the paper: "Consistent with SpaceX’s corporate philosophy of rapid and continuous improvement..." 

Easy words to say, but looking back..  From Falcon 1, Kestrel and Merlin 1A (ablative) - boy they ain't kidding.

"Cum continua emendationem et corporatum rebus philosophia est celeri consistent"
Title: Re: F9 Second Stage Reusability
Post by: MP99 on 04/05/2017 06:38 AM


The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.

Reminder that the concepts we've seen for Magnetoshell AeroCapture have this trailing behind on a tether. The analogy with a parachute is very strong, and could provide a very stable way to keep the stage orientated nose first.

Because this generates drag magnetically, at altitudes where the stage experiences negligible drag, and therefore no heating, all heat is produced behind the stage and dissipated harmlessly.

The two big questions are whether this can provide enough drag to slow the stage so that the stage experiences low heating (like S1 entry burn), and how low into the atmosphere it can continue operating.

Another advantage is that the level of braking is adjustable, which allows to target a particular landing distance downrange in the face of differing atmospheric conditions.

Cheers, Martin

PS I also wonder if the same tether might provide a good mounting point for a parasail to land the stage on an airbag, like the fairings. This could compensate for lack of steerability by MAC.

Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/05/2017 09:48 AM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.
That's what my petals do create drag...
Part of why a Shuttlecock is stable is because of its mass distribution. Let's see how this works for your idea.

Merlin is reported to be about 470Kg. The counter balance would presumably be a layer of PICAX on the nose. PICAX is much lighter than AVCOAT c0.27 g/cm^3  IE 2.7Kg/sq. m.
F9 is 5.2m in diameter so that's about 21 sq. metres, needing a mass of more than 22Kg/sq. m of PICAX to keep it nose heavy. That means a layer 8cm thick would be needed to be nose heavy.

If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks.

And you have put your "petals" on the back end, making it back end heavier still.
Does this still sound like a viable idea to you?

Keep in  mind the angles being talked about are no more than about 5deg below the local horizontal.

The trade offs in system design are tricky. It's not between drag/control surface weight and propellant. It's between drag/control surface weight and propellant and TPS mass. The "exchange rates" between the three are a PITA to calculate without detailed mass and thermophysical properties.

The easy one is every m/s you can shave off in the upper atmosphere means so many Kg of TPS you don't have to apply to resist such a high level of heating in the lower, denser atmosphere (provided your drag device can survive the heating). But control surfaces are measured in Kgs of mass, not m/s

But every Kg you add means another Kg of dead weight that builds up terminal velocity the Merlin will have to cancel.

So to be a net win your drag/control surface (and its control system) has to trade better than 1:1 in terms of mass in order to lower the propellant needed to cancel the terminal velocity of the stage at landing. Anything less and you might as well just leave the TPS layer in place (if that is adequate to do the job).
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/05/2017 09:58 AM
F9 is 3.6m diameter, not 5.2m (your number probaboy refers to the PLF, not the stage itself).
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/05/2017 10:15 AM
F9 is 3.6m diameter, not 5.2m (your number probaboy refers to the PLF, not the stage itself).
Oops. Yes I pulled the fairing number by mistake.

That gives about 10.75 sq. m. of nose, which means the PICAX has to cover it at about 43Kg/Sq. m. IE about 17cm thick to balance the 470Kg of a Merlin in the back.

One point I should have mentioned is that from previous work the maximum heating is normally on the lip of the cylinder rather than its face (and that ignores the details around the Payload Attach Fitting as well). This is quite a tricky location to mount TPS. 


Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 11:27 AM
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.

"Drag" something behind it.
That's what my petals do create drag...
Part of why a Shuttlecock is stable is because of its mass distribution. Let's see how this works for your idea.

Merlin is reported to be about 470Kg. The counter balance would presumably be a layer of PICAX on the nose. PICAX is much lighter than AVCOAT c0.27 g/cm^3  IE 2.7Kg/sq. m.
F9 is 5.2m in diameter so that's about 21 sq. metres, needing a mass of more than 22Kg/sq. m of PICAX to keep it nose heavy. That means a layer 8cm thick would be needed to be nose heavy.

If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks.

And you have put your "petals" on the back end, making it back end heavier still.
Does this still sound like a viable idea to you?

Keep in  mind the angles being talked about are no more than about 5deg below the local horizontal.

The trade offs in system design are tricky. It's not between drag/control surface weight and propellant. It's between drag/control surface weight and propellant and TPS mass. The "exchange rates" between the three are a PITA to calculate without detailed mass and thermophysical properties.

The easy one is every m/s you can shave off in the upper atmosphere means so many Kg of TPS you don't have to apply to resist such a high level of heating in the lower, denser atmosphere (provided your drag device can survive the heating). But control surfaces are measured in Kgs of mass, not m/s

But every Kg you add means another Kg of dead weight that builds up terminal velocity the Merlin will have to cancel.

So to be a net win your drag/control surface (and its control system) has to trade better than 1:1 in terms of mass in order to lower the propellant needed to cancel the terminal velocity of the stage at landing. Anything less and you might as well just leave the TPS layer in place (if that is adequate to do the job).
John, you keep "conveniently ignoring" that I stated that the hypergolic tanks, legs and their tanks and actuators are all in the nose... So you have "no definitive"  CoG to speak of... My grid-fin idea  on S1 worked out pretty good, wouldn't you say? Lets hear your great concept...
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 11:45 AM
And of course we have this from a few years back.  Be interesting to know the full history of the image.
https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198
Thanks for posting. These short-small petals may work for controllabilty, but "may not" protect the engine from entry plasma and "may need" to be made longer and around the entire stage with gap seals just like my shuttlecock concept...
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/05/2017 12:38 PM
If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks.
Au contraire. The stage is under deceleration, so the propellant (if any remains) will be urged to the forward bulkheads of the two tanks.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/05/2017 12:46 PM
And of course we have this from a few years back.  Be interesting to know the full history of the image.
https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198
Thanks for posting. These short-small petals may work for controllabilty, but "may not" protect the engine from entry plasma and "may need" to be made longer and around the entire stage with gap seals just like my shuttlecock concept...

That depends on the angle of attack, and the angle of plasma departure. Shuttle flew a very high AOA for high lift and drag. F9 US could generate some lift at a very low AOA (or just dive straight into the atmosphere on a ballistic return) and the engine would just sit in the wake. Sure, it gets pretty hot back there, but not hot enough to bother niobium. The other engine parts would need some TPS.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/05/2017 12:48 PM
...
If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks.
...

Uhh.... do you get pinned back into your seat when you brake your car? That's not how inertia defies deceleration, at all.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 01:00 PM
And of course we have this from a few years back.  Be interesting to know the full history of the image.
https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198
Thanks for posting. These short-small petals may work for controllabilty, but "may not" protect the engine from entry plasma and "may need" to be made longer and around the entire stage with gap seals just like my shuttlecock concept...

That depends on the angle of attack, and the angle of plasma departure. Shuttle flew a very high AOA for high lift and drag. F9 US could generate some lift at a very low AOA (or just dive straight into the atmosphere on a ballistic return) and the engine would just sit in the wake. Sure, it gets pretty hot back there, but not hot enough to bother niobium. The other engine parts would need some TPS.
As I stated my petals are "controllable independently" so that the shape of the shuttlecock can be actively "morph" into any shape for lift, side to side, roll etc... during flight... The stage "will change into a lifting body during entry" then into a ballistic terminal flight to land nose down...... "The petals are "not" passive"...
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/05/2017 05:43 PM
John, you keep "conveniently ignoring" that I stated that the hypergolic tanks, legs and their tanks and actuators are all in the nose... So you have "no definitive"  CoG to speak of... My grid-fin idea  on S1 worked out pretty good, wouldn't you say?

Actually I just looked at the picture of the petals you posted and wondered how exactly were they going to support the whole loaded weight of a stage sitting on them?

But you're right putting a bunch of hypergolic tanks and landing legs in the nose will shift the Cg.

That will put the nozzles of the super dracos pointing into the airstream but I presume you have a plan to protect them till they get nearer the ground.

Quote from: Rocket Science
Lets hear your great concept...
Funny you should say that as I posted it a few days ago.

TL:DR Sub orbital velocity, near single orbit eliminates retro burn. Large nose grid fins and TPS. If the grid fins size and mass trades for reduced TPS but propellant for hoverslam also has to be factored in to ensure a net win.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 06:40 PM
John, you keep "conveniently ignoring" that I stated that the hypergolic tanks, legs and their tanks and actuators are all in the nose... So you have "no definitive"  CoG to speak of... My grid-fin idea  on S1 worked out pretty good, wouldn't you say?

Actually I just looked at the picture of the petals you posted and wondered how exactly were they going to support the whole loaded weight of a stage sitting on them?

But you're right putting a bunch of hypergolic tanks and landing legs in the nose will shift the Cg.

That will put the nozzles of the super dracos pointing into the airstream but I presume you have a plan to protect them till they get nearer the ground.

Quote from: Rocket Science
Lets hear your great concept...
Funny you should say that as I posted it a few days ago.

TL:DR Sub orbital velocity, near single orbit eliminates retro burn. Large nose grid fins and TPS. If the grid fins size and mass trades for reduced TPS but propellant for hoverslam also has to be factored in to ensure a net win.
They don't support the stage, they all slide back in unison as "a ring of control surfaces" prior to entry...
Sub orbital means your payload now needs an assist-motor and now you take a hit for that. So you plan on using MVac to land, how? Give us a sketch...
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/05/2017 08:34 PM
I posted this at ars technica, but thought I might also subject it to the flames here.   :D

Apologies if it's been done to death already.

-----

An expedient way to add reusability to the US would be to make a bolt-on "module" containing the complete recovery package--heat shield, reentry RCS, guidance, retracted landing legs, SuperDracos, and prop tanks. The module would mount on the stage exactly as the payload adapter or Dragon, so no major redesign of the stage would be necessary. It would place all of the recovery mass at the front of the stage. Reentry would be nose-first, with no "swoop of death" because the stage would land upside down. The module could be omitted if max performance was required, just as the boosters are still occasionally expended for big payloads.

The design would share one issue with other nose-first reentry designs: mounting the payload above (or through) the heat shield. The Shuttle had hatches in its heat shield for connections to the external tank, and a similar arrangement might work for Falcon.
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/05/2017 08:42 PM
I posted this at ars technica, but thought I might also subject it to the flames here.   :D

Apologies if it's been done to death already.

-----

An expedient way to add reusability to the US would be to make a bolt-on "module" containing the complete recovery package--heat shield, reentry RCS, guidance, retracted landing legs, SuperDracos, and prop tanks. The module would mount on the stage exactly as the payload adapter or Dragon, so no major redesign of the stage would be necessary. It would place all of the recovery mass at the front of the stage. Reentry would be nose-first, with no "swoop of death" because the stage would land upside down. The module could be omitted if max performance was required, just as the boosters are still occasionally expended for big payloads.

The design would share one issue with other nose-first reentry designs: mounting the payload above (or through) the heat shield. The Shuttle had hatches in its heat shield for connections to the external tank, and a similar arrangement might work for Falcon.
That's what I was thinking here:
Because of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage.
It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage.
How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge.
 
That gives me an idea (sorry if it's been suggested.) Behold, my first NFS Rube Goldberg device.  It must be contagious:

Rocket LEGO Landing Element.  A landing module that connects to the PAF and is used as a PAF for the "real" payload.  It includes integrated SDs and landing legs and it's mass shifts the COM forward so it reenters "head first." No idea how to add a heat shield or control the trajectory w/o some sort of fins.

Similar idea could use a controllable parafoil instead of propulsive landing (or maybe with propulsive assist.)

Basically I like the idea of the PAF as a PAF so that there is only one S2 and you plug on the "reuse option."  Some assembly and lots of hand waving required.
But you said it better. :)
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/05/2017 08:57 PM
I posted this at ars technica, but thought I might also subject it to the flames here.   :D

Apologies if it's been done to death already.

-----

An expedient way to add reusability to the US would be to make a bolt-on "module" containing the complete recovery package--heat shield, reentry RCS, guidance, retracted landing legs, SuperDracos, and prop tanks. The module would mount on the stage exactly as the payload adapter or Dragon, so no major redesign of the stage would be necessary. It would place all of the recovery mass at the front of the stage. Reentry would be nose-first, with no "swoop of death" because the stage would land upside down. The module could be omitted if max performance was required, just as the boosters are still occasionally expended for big payloads.

The design would share one issue with other nose-first reentry designs: mounting the payload above (or through) the heat shield. The Shuttle had hatches in its heat shield for connections to the external tank, and a similar arrangement might work for Falcon.

A good solution. As you say mounting the payload through the heat shield is likely to be difficult. It shares that problem with other nose first designs, the payload adapter might have to be thrown away.

I'm not sure it is worth making the module bolt-on. Only reusable upper stages will be reused (by definition) so the module is only needed on reusable upper stages. It would be slightly more efficient to design the module integrated into the upper stage and the existing stage would need no changes, it could just go on being flown on expendable missions. Making it a bolt-on module would require minor mods to the upper stage, for attachment points, power and signalling, it would be better in my opinion not to have to make them for stages that are not going to be reused.

Although a good long term solution, I don't see how they could do all the engineering, manufacturing and testing of this "module" within 6 months.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/05/2017 09:04 PM
You are assuming starting now; they didn't have that constraint.
That's how.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 09:11 PM
I posted this at ars technica, but thought I might also subject it to the flames here.   :D

Apologies if it's been done to death already.

-----

An expedient way to add reusability to the US would be to make a bolt-on "module" containing the complete recovery package--heat shield, reentry RCS, guidance, retracted landing legs, SuperDracos, and prop tanks. The module would mount on the stage exactly as the payload adapter or Dragon, so no major redesign of the stage would be necessary. It would place all of the recovery mass at the front of the stage. Reentry would be nose-first, with no "swoop of death" because the stage would land upside down. The module could be omitted if max performance was required, just as the boosters are still occasionally expended for big payloads.

The design would share one issue with other nose-first reentry designs: mounting the payload above (or through) the heat shield. The Shuttle had hatches in its heat shield for connections to the external tank, and a similar arrangement might work for Falcon.
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?
Title: Re: F9 Second Stage Reusability
Post by: smfarmer11 on 04/05/2017 09:16 PM
A kind of crazy idea would be to elongate the fairing and coat one shell in TPS, then instead of jettisoning it move it to cover the second stage after payload deployment. Re- enter using that as an ablator testing biconic re-entry and saving the half the fairing.
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/05/2017 09:27 PM
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/05/2017 09:31 PM
They don't support the stage, they all slide back in unison as "a ring of control surfaces" prior to entry...
Let me see if I have this straight. You are talking about a ring of petals on the side of the upper stage that after stage separation will move backwards to act as control surfaces and protect the engine during re-entry?
Meanwhile there is a package of super dracos, landing gear, prop tanks and TPS mounted around, under or inside the payload attach fitting for the main payload. Is that right?
Quote from: Rocket Science
Sub orbital means your payload now needs an assist-motor and now you take a hit for that.
Yes. I pointed that out when I originally posted the idea.
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/05/2017 09:36 PM
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
What I like about this is that:

1. Same S2 for expendable and recoverable missions (just connect the recovery module to the PAF).
2. GTO, mass and volume limited missions expend the S2.
3. First test does not need functioning legs, SDs, etc.  Just the heat shield and enough mass to shift the CG forward.  Being in one piece and hitting the water at terminal velocity is a good first step.

No idea how the (module's) PA through the heat shield works but it seems solvable.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/05/2017 09:53 PM
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/05/2017 10:03 PM
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?

I was thinking propulsive landing just like (eventually) Dragon, using the SDs. The MVac does the deorbit burn, the SDs do the landing. But I must leave the dV calculations showing that to be impossible, to you guys.   ;)

Perhaps a drogue would save some propellant, I don't know.

In answer to the PA question... maybe little T.Rex arms that retract into the shell after payload sep?
Title: Re: F9 Second Stage Reusability
Post by: Lars-J on 04/05/2017 10:55 PM
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?

I was thinking propulsive landing just like (eventually) Dragon, using the SDs. The MVac does the deorbit burn, the SDs do the landing. But I must leave the dV calculations showing that to be impossible, to you guys.   ;)

Perhaps a drogue would save some propellant, I don't know.

In answer to the PA question... maybe little T.Rex arms that retract into the shell after payload sep?

Load bearing can be done through the heat shield... Dragon already does it. (See picture below - there are 6 connecting points through the heat shield) This type of attachment has been in use since Apollo. (probably even Mercury and Gemini as well)

But that is a simple mechanical interface. For fluids and power you'll likely need a similar "claw arm" (like Dragon to its trunk) to the disposable payload adapter.
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/05/2017 11:07 PM
Like this one on the Apollo CSM? But yes, it would somehow have to retract behind the heat shield on the "mme-punder-you-land" module.   ;D
Title: Re: F9 Second Stage Reusability
Post by: shooter6947 on 04/05/2017 11:13 PM
Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!

Still need a way to make sure that the center of drag is behind the center of mass so that the entry is stable.  Maybe an inflatable module at the engine end, or extendable ablative airbrakes back there?
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/05/2017 11:22 PM
Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!

Still need a way to make sure that the center of drag is behind the center of mass so that the entry is stable.  Maybe an inflatable module at the engine end, or extendable ablative airbrakes back there?

The module has to be pretty massive, what with the TPS, legs, a number of SuperDracos, and prop tanks--but I don't know how it stacks up against the engine on the other end. There are also the COPVs inside... someone else would have to do the math.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/05/2017 11:54 PM
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/06/2017 02:03 AM
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/06/2017 02:26 AM
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.
Does the whole engine compartment need to be open, or just the nozzle? If just the nozzle, then can the nozzle be reinforced to survive tail-first reentry loads?
(Not the engine gimbal surviving, just the nozzle- there might need to be some kind of mechanical brace that secures the nozzle from gimballing during a nozzle-first reentry)
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/06/2017 10:29 AM
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.
Does the whole engine compartment need to be open, or just the nozzle? If just the nozzle, then can the nozzle be reinforced to survive tail-first reentry loads?
(Not the engine gimbal surviving, just the nozzle- there might need to be some kind of mechanical brace that secures the nozzle from gimballing during a nozzle-first reentry)


I think having something like the sharp circumference of the thin open nozzle  (as opposed to a flat or rounded heatshield) sticking into the supersonic stream is the worst you can do to something that you want to survive reentry.


Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/06/2017 11:03 AM
Elon has stated his intention to develop a reusable second stage. We are scrambling to figure out how the second stage with the M1D engine could be modified with add-ons. We might add on landing legs, a nose-end heatshield, and my own modified interstage heat shield.

Elon has a Air Force contract for a Raptor engine intended for a second stage F9 or FH.

But SpaceX especially wants to develop an ITS spaceship using multiple Raptors. Some people suggest that a small version of a Raptor-equipped vehicle would be a desirable testbed for the full-size version, which is also a second stage spacecraft to be recovered and reused. But Elon wouldn't roll three objectives into one project. That would mean we should start with the ITS spaceship design and work backward with legs and heatshields to see how a FH reusable second stage with legs and shields could be derived from the ITS design.

But Elon wouldn't roll three objectives into one project, would he?  :)
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 04/06/2017 11:24 AM
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/06/2017 02:07 PM
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
Title: Re: F9 Second Stage Reusability
Post by: rpapo on 04/06/2017 02:16 PM
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
Yes, but these are the same people who step by step worked out many of the issues with recovering boosters by getting data from boosters they expected to lose anyway.  So it is perfectly possible they will simply be trying to get data from an attempt they don't seriously expect will succeed.  Remember the early GTO launches where the first stage was reorienting itself after MECO, even though they weren't attempting even a sea landing?

They've discarded 30+ second stages already (some are still orbiting).  What we don't know is whether they gathered any information from the ones that reentered on their way down.
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/06/2017 02:23 PM
Maybe I'm  fooling myself, but the nose-mounted recovery module just seems like a very doable, relatively inexpensive way to make the US reusable. Basically, it just replaces the Dragon 2 pressure vessel with an upside-down 2nd stage!

Would be nice if someone could run the numbers. I seem to remember the US dry weight is a lot less than that of the spacecraft.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/06/2017 03:06 PM
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
Yes, but these are the same people who step by step worked out many of the issues with recovering boosters by getting data from boosters they expected to lose anyway.  So it is perfectly possible they will simply be trying to get data from an attempt they don't seriously expect will succeed.  Remember the early GTO launches where the first stage was reorienting itself after MECO, even though they weren't attempting even a sea landing?

They've discarded 30+ second stages already (some are still orbiting).  What we don't know is whether they gathered any information from the ones that reentered on their way down.
I'm not interpreting it as they plan to succeed on the next flight, only that the will continue trying...YMMV
Title: Re: F9 Second Stage Reusability
Post by: Ionmars on 04/06/2017 03:57 PM
Maybe I'm  fooling myself, but the nose-mounted recovery module just seems like a very doable, relatively inexpensive way to make the US reusable. Basically, it just replaces the Dragon 2 pressure vessel with an upside-down 2nd stage!

Would be nice if someone could run the numbers. I seem to remember the US dry weight is a lot less than that of the spacecraft.
IMHO the question is whether a heat shield on one end alone will provide the area required to protect the stage and also to reduce speed sufficiently. Usually it is a short capsule rather than a stage that employs a blunt ablative heat shield. Someone has a model to run that analysis. If it lacks area, you just need to take a tip from ITS and place PICA-x on one side of the stage. Then rerun the model. Even if the shield on one side is the primary shield for re-entry, you will still need your shield on the end.

Edit: If you still lack the needed area, you will have to broaden the side with heat shield until you have enough area to protect the stage. At some point you will approach the shape of the Space Shuttle. There are reasons for that shape that go beyond aesthetics.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/06/2017 05:13 PM
Putting some numbers to this, a Soyuz descent module has a heatshield area of 3.8m2, and a mass of 2850kg, for a loading of 750kg/m2.
F9 US would have a frontal heatshield area of 10.5m2, but we don't know the mass. If we assume the same loading as Soyuz the mass could be up to 7875kg.

Estimates for the dry mass of the US are around 4500kg- so that gives a margin of 3375kg to add the recovery systems. Seems pretty healthy to me.

Another factor to consider is that Soyuz is manned; an unmanned re-entry vehicle could possibly endure higher deceleration, which is what would happen if the spacecraft was 'denser' and hit the lower atmosphere before slowing down as much. Further, Soyuz was designed for return from lunar velocities, not just LEO. So it is possible that the F9 US could be even heavier and still not need a larger frontal heatshield area.

However, a separate issue is sidewall heating. All re-entry capsule have some degree of taper from the widest point at the base, towards a narrower top. This keeps the sidewalls out of the worst of the plasma, but they still need some degree of TPS. The greater the sidewall protection (by angle and/or TPS), the higher an angle of attack can be flown, opening up the option of using a lifting entry. So it's not as simple as slapping a heatshield on the front of a cylindrical stage- there will need to be some sort of TPS on the sides as well.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/06/2017 06:36 PM
Putting some numbers to this, a Soyuz descent module has a heatshield area of 3.8m2, and a mass of 2850kg, for a loading of 750kg/m2.
F9 US would have a frontal heatshield area of 10.5m2, but we don't know the mass. If we assume the same loading as Soyuz the mass could be up to 7875kg.

Why don't you compare it with Dragon? Same diameter, same heat shield technology.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/06/2017 06:52 PM
Putting some numbers to this, a Soyuz descent module has a heatshield area of 3.8m2, and a mass of 2850kg, for a loading of 750kg/m2.
F9 US would have a frontal heatshield area of 10.5m2, but we don't know the mass. If we assume the same loading as Soyuz the mass could be up to 7875kg.

Why don't you compare it with Dragon? Same diameter, same heat shield technology.


Is there a definitive number available for a returning Dragon? SpaceX appear to only publish cargo mass, not the mass of the spacecraft itself.
Title: Re: F9 Second Stage Reusability
Post by: Elmar Moelzer on 04/07/2017 05:00 AM
From what I have seen the dry mass of the Dragon 1 is 4,200 kg. The Dry mass of Dragon 2 is 6,400 kg.
Of course that includes lots of things a second stage wont need.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/07/2017 07:14 AM
From what I have seen the dry mass of the Dragon 1 is 4,200 kg. The Dry mass of Dragon 2 is 6,400 kg.
Of course that includes lots of things a second stage wont need.


That would put a returning Dragon at 9,400kg (SpaceX state a return payload of up to 3t). With a heatshield area of 10.7m2 that gives us 878kg/m2, which is somewhat denser than Soyuz, and allows our putative returning US to have a margin of up to 4719kg for recovery equipment.

What is the source of that Dragon dry mass figure? If true, it does make the Dragon much denser than other entry vehicles like the Apollo CM, which worked out at about 485kg/m2.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 04/07/2017 12:48 PM
From what I have seen the dry mass of the Dragon 1 is 4,200 kg. The Dry mass of Dragon 2 is 6,400 kg.
Of course that includes lots of things a second stage wont need.


That would put a returning Dragon at 9,400kg (SpaceX state a return payload of up to 3t). With a heatshield area of 10.7m2 that gives us 878kg/m2, which is somewhat denser than Soyuz, and allows our putative returning US to have a margin of up to 4719kg for recovery equipment.

What is the source of that Dragon dry mass figure? If true, it does make the Dragon much denser than other entry vehicles like the Apollo CM, which worked out at about 485kg/m2.

Does that "dry" mass include the LAS/landing propellants? If not, add another 500-1000kg or so.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/07/2017 01:33 PM
From what I have seen the dry mass of the Dragon 1 is 4,200 kg. The Dry mass of Dragon 2 is 6,400 kg.
Of course that includes lots of things a second stage wont need.


That would put a returning Dragon at 9,400kg (SpaceX state a return payload of up to 3t). With a heatshield area of 10.7m2 that gives us 878kg/m2, which is somewhat denser than Soyuz, and allows our putative returning US to have a margin of up to 4719kg for recovery equipment.

What is the source of that Dragon dry mass figure? If true, it does make the Dragon much denser than other entry vehicles like the Apollo CM, which worked out at about 485kg/m2.

Does that "dry" mass include the LAS/landing propellants? If not, add another 500-1000kg or so.

The source is probably the DragonFly test article FAA application, which listed the vehicle as 14000 lbm dry (6350 kg) and the propellants as 400 gallons (1800 kg).

That doesn't include the trunk (the DragonFly vehicle didn't fly with a trunk) however, it might include ballast to represent payload. IMO testing at flight weight (including payload) would be much more representative than flying an empty Dragon - something that would never happen in a real flight.

So IMO the entry mass of Dragon 2 would be nominally 8150 kg. A reuseable second stage should be a bit lighter.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/07/2017 02:47 PM
They don't support the stage, they all slide back in unison as "a ring of control surfaces" prior to entry...
Let me see if I have this straight. You are talking about a ring of petals on the side of the upper stage that after stage separation will move backwards to act as control surfaces and protect the engine during re-entry?
Meanwhile there is a package of super dracos, landing gear, prop tanks and TPS mounted around, under or inside the payload attach fitting for the main payload. Is that right?
Quote from: Rocket Science
Sub orbital means your payload now needs an assist-motor and now you take a hit for that.
Yes. I pointed that out when I originally posted the idea.
Are you trolling me John? Now I had to go back to find your post#95 and slog through to extract your point. (It would a courtesy if you would provide the post reference # when you do so, if you couldn't remember it why should have I?) Speaking of... could you please refrain from writing a "professorial-sounding short story" with each of you posts that generally have to refer to Skylon) BTW we are still waiting for a sketch of "your  concept"...
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/07/2017 05:42 PM
If they can reenter from LEO they can do it without much more weight penalty from GTO.  How?  Aerocapture.  We've been doing it already on many missions at Mars with flimsy satellites.  S2 with a nice sturdy heatshield wouldn't take many passes at perigee before the reentry would be the same as LEO. But, but, but this is much different you say than the Mars application.  I say the SpaceX engineers will find a way to make it work.

Oh I don't think it's that much different, I'm just wondering:

A) how much DeltaV it takes to lower the perigee of the GTO so that it's low enough to rapidly de orbit
B) How accurately you can do it?

570m/s delta V equates to roughly an extra 1t of fuel, which is 1t less of GTO payload at least, assuming the upper stage weighs about 4.5t (that's the number I'm using but I don't know how accurate that is) and your reentry/landing hardware is only 1t extra on top of that. GTO payload starts disappearing rapidly when you add mass to the second stage. Also it needs to be accurate to several hundred square kilometres at least. If you can't bring it down in a reliably accurate way, it's useless.



From my back of the envelope calculations, for a 150 x 35622 km GTO, I get an apogee speed of 1598 m/s.  Lowering perigee to 75 km requires an apogee speed of 1590 m/s, a deltaV of only 8 m/s.  That of course is a Hohmann transfer and current S2 design may make surviving that long difficult. Did you assume your delta V happens soon after satellite deploy when both it and S2 are going fast ?  That will definitely cost much more fuel there.

I may be wrong but I think it takes less fuel to reenter from GTO than LEO. Simply put the deltaV at apogee is much more effective for the GTO orbit because of the lower velocity.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 04/07/2017 08:22 PM
Play the ball, not the man. Some people should dial back their pot shots at each other a bit. Thanks.
Title: Re: F9 Second Stage Reusability
Post by: launchwatcher on 04/07/2017 09:07 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/07/2017 09:28 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.
We've gone from "Hail Mary" to "fairly confident" in one week. Never a dull moment.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/07/2017 09:42 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.
We've gone from "Hail Mary" to "fairly confident" in one week. Never a dull moment.

So much for those who think this is a spur of the moment idea that EM threw out last week.  Second stage reuse has been studied for 8-10 years I'd bet.  Too many other priorities to allow it to rise up the queue.

Might also seal the deal for a reusable ConnX sat dispenser. (plus tankers, whatever)
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/07/2017 09:53 PM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/07/2017 10:01 PM
I think they were further along on s2 reusable design(maybe hardware) when Elon canned it.
Title: Re: F9 Second Stage Reusability
Post by: RonM on 04/07/2017 10:02 PM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.

Another positive view is that FH second stage reuse testing directly applies to ITS. Perhaps a mini-ITS design like has been discussed in many threads.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/07/2017 10:03 PM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
I think it's more likely that more work was already done on S2 than elon was aware of last week.

"Alright team, we've got Stage 1 ironed out, and it looks like fairings are well on their way with just some debugging. That leaves stage 2. We didnt design stage 2 for recovery, but lets hear some proposals."

"Sir, here's a detailed proposal I worked up in my free time, and a 1 page summary why my approach is better than the others."
Title: Re: F9 Second Stage Reusability
Post by: philw1776 on 04/07/2017 10:28 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
2) What are the implications for NASA and the AF who want one design "Block 5" certified and flown again and again?
3) What is the implication for ITS schedule if finite # of SpaceX engineers are working on fairing and S2 re-usability and not ITS through "late next year" at least?
4) Obviously unknown but the S2 mechanisms for recovery and payload penalty will be "interesting".
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/07/2017 10:53 PM
My guess is it will be s2 variant only for f9heavy and therefore won't impact manned missions. Now what f9heavy missions would allow a experimental s2 variant with reduced performance? I don't know.
Title: Re: F9 Second Stage Reusability
Post by: punder on 04/07/2017 10:56 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
2) What are the implications for NASA and the AF who want one design "Block 5" certified and flown again and again?
3) What is the implication for ITS schedule if finite # of SpaceX engineers are working on fairing and S2 re-usability and not ITS through "late next year" at least?
4) Obviously unknown but the S2 mechanisms for recovery and payload penalty will be "interesting".

They could fly B5 exclusively for gov customers while testing upgrades on commercial flights. Or fly reusable S2 on FH only.
Title: Re: F9 Second Stage Reusability
Post by: Helodriver on 04/07/2017 11:13 PM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
I think it's more likely that more work was already done on S2 than elon was aware of last week.

"Alright team, we've got Stage 1 ironed out, and it looks like fairings are well on their way with just some debugging. That leaves stage 2. We didnt design stage 2 for recovery, but lets hear some proposals."

"Sir, here's a detailed proposal I worked up in my free time, and a 1 page summary why my approach is better than the others."

I would think assuming Elon was somehow "unaware" of the state of stage 2 recovery work is a very bad assumption. Just because he hasn't talked about it publicly does not mean it was 1. abandoned or 2. he is not apprised of what his company is spending money and manpower on. It appears they always have many irons in the fire simultaneously and only choose to use them when the time is right.
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/07/2017 11:57 PM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
2) What are the implications for NASA and the AF who want one design "Block 5" certified and flown again and again?
3) What is the implication for ITS schedule if finite # of SpaceX engineers are working on fairing and S2 re-usability and not ITS through "late next year" at least?
4) Obviously unknown but the S2 mechanisms for recovery and payload penalty will be "interesting".
I'm still a fan of the "reusability option" (if it could be made to work).  Bolts on top of a standard-ish S2 for head first reentry.

No idea if it can be made to work.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/07/2017 11:58 PM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
I think it's more likely that more work was already done on S2 than elon was aware of last week.

"Alright team, we've got Stage 1 ironed out, and it looks like fairings are well on their way with just some debugging. That leaves stage 2. We didnt design stage 2 for recovery, but lets hear some proposals."

"Sir, here's a detailed proposal I worked up in my free time, and a 1 page summary why my approach is better than the others."

I would think assuming Elon was somehow "unaware" of the state of stage 2 recovery work is a very bad assumption. Just because he hasn't talked about it publicly does not mean it was 1. abandoned or 2. he is not apprised of what his company is spending money and manpower on. It appears they always have many irons in the fire simultaneously and only choose to use them when the time is right.

The most viable approach to second stage reuse should include the following elements:
1. Don't bother on GTO launches with F9 (you are already making a bundle on these flights)
2. Don't bother on USG 'certified' flights (ditto)
3. Be very worried about the cost of lofting a 12,000 sat constellation (this is an out-of-pocket Capex)
4. Think globally about 'second stage' which traditionally was booster + fairing + adaptor/dispenser, and find solution that gets the job done and returns everything in rapid reusable mode
5. Use whatever propulsion and configuration needed to get the job done (don't be constrained by 6 year old animations)
6. Don't tell anyone what you are up to because it is for a heavily contested market
7. Don't dare touch the Block 5 core (Hands-off... this means you, Elon! --GS)
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/08/2017 12:18 AM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
I think it's more likely that more work was already done on S2 than elon was aware of last week.

"Alright team, we've got Stage 1 ironed out, and it looks like fairings are well on their way with just some debugging. That leaves stage 2. We didnt design stage 2 for recovery, but lets hear some proposals."

"Sir, here's a detailed proposal I worked up in my free time, and a 1 page summary why my approach is better than the others."

I would think assuming Elon was somehow "unaware" of the state of stage 2 recovery work is a very bad assumption. Just because he hasn't talked about it publicly does not mean it was 1. abandoned or 2. he is not apprised of what his company is spending money and manpower on. It appears they always have many irons in the fire simultaneously and only choose to use them when the time is right.
Exactly.

There was simply never any way that a company that is contemplating several LEO launches per week won't reuse S2.

It was true with the LEO constellation, and twice as true now with the vLEO one.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 12:29 AM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.

How is flying an orbital vehicle (not an inherently stable capsule) through the atmosphere and landing not still working on ITS?  This is probably the second toughest technical challenge.  (making sufficient fuel on Mars is the toughest by far)
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/08/2017 01:51 AM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.

... and, there isn't a single person in the world who wasn't floored by ITS's schedule.

But the road to Mars appears go to through the constellation, and the constellation is much more viable with a reusable second stage, so I think it's ok.

And I'm also sure that work on ITS is nowhere near stopped.  Just maybe slowed down a bit since some people will also be engaged on S2 recovery.

Meanwhile S2 recovery is not holding up day-to-day launches, so it's not a "critical" item that stops all other work.

In other words, it's all good.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/08/2017 01:55 AM
Am I the only one who thinks this may be bad news? Seems they scale down work on ITS and have more time to work on reusable S2. They may have to do that and scale up ITS again when money comes in from the satellite constellation.

Edit: Or the positive view. They have come to the conclusion that reuse is so easy and cheap that they can fly FH a lot and so can afford the payload loss through second stage reuse.
I think it's more likely that more work was already done on S2 than elon was aware of last week.

"Alright team, we've got Stage 1 ironed out, and it looks like fairings are well on their way with just some debugging. That leaves stage 2. We didnt design stage 2 for recovery, but lets hear some proposals."

"Sir, here's a detailed proposal I worked up in my free time, and a 1 page summary why my approach is better than the others."

I would think assuming Elon was somehow "unaware" of the state of stage 2 recovery work is a very bad assumption. Just because he hasn't talked about it publicly does not mean it was 1. abandoned or 2. he is not apprised of what his company is spending money and manpower on. It appears they always have many irons in the fire simultaneously and only choose to use them when the time is right.
You assume company money/official manpower were used for the development.
I'm talking about bored engineers doodling off the clock.
Title: Re: F9 Second Stage Reusability
Post by: CyclerPilot on 04/08/2017 01:58 AM
Wow.  Crazy news.  What a difference a week makes.
I will throw in my guess for S2 reuse.  Re-entry and descent will be handled by picaX on top, down one, a flap to protect the nozzle, and some grid fins for control.  "Landing" will be handled by a chopper catching the chute and returning it to land near the launch site.  I think legs, thrusters, tankage, and propellant will add too much dry mass.
Payload adaptors will sit on top of the dome heat shield, and will probably have to be jettisoned, but the CommX deployer might be able to be designed to fold back to the side opposite the PicaX to stay out of the re-entry plasma stream.
I think a non-reusable version will be available as well and will be such that it can be easily be converted to reusable and vise versa.
I think the changes can be light enough where it can work for both heavy and F9, LEO and GTO.
Raptor will eventually be used to up the payload capacity, but probably won't be ready for the first reused S2.
Title: Re: F9 Second Stage Reusability
Post by: su27k on 04/08/2017 04:05 AM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

Just to be pedantic, he is saying they have this ability, not that they will actually do it...
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/08/2017 05:00 AM
I'll put in a vote for an Stage 2 EDL kit that can optionally be added on top of the stage. This has a great deal in common with a Crew Dragon, minus the crew module.

The interstage can stay with the S1 (as usual) for expendable missions, or now optionally stay with S2 if the stage is to be returned. After the re-entry burn by the MVac, the EDL kit detaches and flies to the bottom of S2 and attaches there.

Assumptions made: 1] re-using Dragon propulsion, heat shield, RCS, and navigation is a good idea. 2] relocating the kit is not a big deal in 2017 using flight-proven hardware and software, 3] the mass of the MVac means engine first entry is favored/required, 4] loads from the payload can be passed through or by the EDL kit.
Title: Re: F9 Second Stage Reusability
Post by: shooter6947 on 04/08/2017 05:39 AM

The interstage can stay with the S1 (as usual) for expendable missions, or now optionally stay with S2 if the stage is to be returned.



Isn't the MVac bell radiatively cooled?  It would overheat with the interstate surrounding it.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/08/2017 06:43 AM
The nozzle extension is indeed radiatively cooled, but I'm not sure if the entire engine needs to be exposed. I'd always assumed interstages were left behind mainly to shed mass, but you could be right and what I show would cause overheating.

This needn't be fatal to the idea, however; you could shorten the interstage by x feet to expose the nozzle extension, and then bring x feet of additional enclosure with the EDL-kit.
Title: Re: F9 Second Stage Reusability
Post by: WBY1984 on 04/08/2017 07:20 AM
What about a cone shaped ballute that deploys from the base of the second stage? Kind if shuttlecock shaped, so that the Centre of Pressure is moved closer to that massive MVac?

An even wackier idea I had was to have the thing land on lengthy inflatable tubular 'legs' which are angled slightly outwards, so they splay outwards on landing. A series of elastic connecting straps between the legs would dampen the splaying movement, the first if which would be very elastic, and the last being the least elastic.

Probably unfeasible and I should go back to playing KSP...
Title: Re: F9 Second Stage Reusability
Post by: FutureSpaceTourist on 04/08/2017 07:27 AM
So Elon has a new bone to play with :D

I was thinking that this must surely only be for FH, where there's more likely to be plenty of margin to cope with S2 additions for re-use. But then I wondered - doesn't F9 S1 use a lot of fuel on a boost back burn for RTLS? So what if you took an F9 RTLS flight (e.g. CRS) and instead of doing S1 RTLS did a ballistic trajectory ASDS landing (like SES-10).

Would that give much more S2 mass budget? (obviously allowing for the much greater proportionate impact on payload mass that S2 additions have vs S1 additions)
Title: Re: F9 Second Stage Reusability
Post by: FutureSpaceTourist on 04/08/2017 07:34 AM
As it's been mentioned a few times, here's the 2011 SpaceX re-use animation showing the original S2 re-use concept (with S1 RTLS as well ...)

https://www.youtube.com/watch?v=sSF81yjVbJE (https://www.youtube.com/watch?v=sSF81yjVbJE)
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/08/2017 09:07 AM
So Elon has a new bone to play with :D

I was thinking that this must surely only be for FH, where there's more likely to be plenty of margin to cope with S2 additions for re-use. But then I wondered - doesn't F9 S1 use a lot of fuel on a boost back burn for RTLS? So what if you took an F9 RTLS flight (e.g. CRS) and instead of doing S1 RTLS did a ballistic trajectory ASDS landing (like SES-10).

Would that give much more S2 mass budget? (obviously allowing for the much greater proportionate impact on payload mass that S2 additions have vs S1 additions)

Block 5 payload expendable is about 22 tonnes to LEO, 18.5 tonnes ASDS landing (15% reduction) and 15.5 RTLS (30% reduction).

So assuming reusability kit is 2 tonnes, F9 is probably still capable of cargo & crew Dragon missions and  half plane (25 satellite) with a RTLS landing. With ASDS landing it might just be possible to launch a whole plane (50 satellite) but I doubt it, given the figures we know.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 10:48 AM
...
You assume company money/official manpower were used for the development.
I'm talking about bored engineers doodling off the clock.

Bored engineers at SpaceX?
Yes, that's it.  ::)
Title: Re: F9 Second Stage Reusability
Post by: FutureSpaceTourist on 04/08/2017 11:07 AM
...
You assume company money/official manpower were used for the development.
I'm talking about bored engineers doodling off the clock.

Bored engineers at SpaceX?
Yes, that's it.  ::)

Yes, bored engineers about as likely as SpaceX engineers with free time ...
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 11:12 AM
For this reusability to have max financial impact on the Constellation capital expense, the dispenser will also need to be retrieved.  EM said 100%...

As discussed by many, an integral second stage with dispenser and cargo bay doors that returns as a unit would be a good investment in ConnX and a pathfinder for ITS EDL.  The rough outline of the BFS could serve as the outer mold line.  At 5-6m wide and approximately as long as current fairing plus second stage, it would be a one third scale model of BFS.

The animation shows a retractable Merlin Vac... a possibility.  ITS animation shows a section of interstage retained for an tail heat shield, which must also be workable in their hydro simulations.  With all BFS modeling done to date, they probably have a good handle on the viable parameter space for reentry configurations.

Note: Refueling is another approach to increasing the capability of second stage. Also needed for ITS operations.  And carbon composite construction.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 11:15 AM
...
You assume company money/official manpower were used for the development.
I'm talking about bored engineers doodling off the clock.

Bored engineers at SpaceX?
Yes, that's it.  ::)

Yes, bored engineers about as likely as SpaceX engineers with free time ...

Agree. 
This will 'divert' some talent for sure, but not a sidetrack from Mars. 
Similar to booster RTLS 'practice' they've been doing... or Red Dragon.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/08/2017 11:26 AM
Reusable upper stage work is essentially subscale ITS spaceship testing.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 12:00 PM
Wow.  Crazy news.  What a difference a week makes.
I will throw in my guess for S2 reuse.  Re-entry and descent will be handled by picaX on top, down one, a flap to protect the nozzle, and some grid fins for control.  "Landing" will be handled by a chopper catching the chute and returning it to land near the launch site.  I think legs, thrusters, tankage, and propellant will add too much dry mass.
Payload adaptors will sit on top of the dome heat shield, and will probably have to be jettisoned, but the CommX deployer might be able to be designed to fold back to the side opposite the PicaX to stay out of the re-entry plasma stream.
I think a non-reusable version will be available as well and will be such that it can be easily be converted to reusable and vise versa.
I think the changes can be light enough where it can work for both heavy and F9, LEO and GTO.
Raptor will eventually be used to up the payload capacity, but probably won't be ready for the first reused S2.

Not sure this is true.

SpaceX proposed to Air Force to build a Raptor prototype for F9/FH second stage... by end of 2018.  Despite protestations to the contrary* on this forum, maybe they intend to use the Raptor for exactly that. 
Stranger things have happened.

* Many based on the statement by EM that they won't build a reusable second stage...   ;) ;) ;)
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/08/2017 12:27 PM
The Merlin main engine can not use all of the propellant. There is always an unusable residue left. How about SpaceX develops a small pressure fed kerolox engine for course adjustment and landing, maybe 2 or 3 are needed. They are not afraid of engine development. During the coasting phase they collect remaining propellant in 2 pressure tanks, separating any He bubbles and use that. Fully powered landing without any extra propellant, especially not hypergols.

I was taking a nap. During that time I had this idea. Tell me if it is completely off. I just don't believe in helicopter air recovery.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/08/2017 12:36 PM
The Merlin main engine can not use all of the propellant. There is always an unusable residue left. How about SpaceX develops a small pressure fed kerolox engine for course adjustment and landing, maybe 2 or 3 are needed. They are not afraid of engine development. During the coasting phase they collect remaining propellant in 2 pressure tanks, separating any He bubbles and use that. Fully powered landing without any extra propellant, especially not hypergols.

I was taking a nap. During that time I had this idea. Tell me if it is completely off. I just don't believe in helicopter air recovery.

SpaceX already has a small pressure fed kerolox engine with flight history... Kestrel. Without the vac nozzle it would have about 5 kN of thrust, perfect size for 2 or 3 of them to land the upper stage. And they weigh under 50 kg without the big nozzle
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/08/2017 12:42 PM
The Merlin main engine can not use all of the propellant. There is always an unusable residue left.
The unusable residue claimed is startlingly small for F9 first stage reuse.
A couple of hundred kilos from memory, or ~1s of thrust time on merlin.

It seems unlikely that the second stage has substantially more dead volume.

I question if you can get meaningful pressure fed engines, a pump, tank to hold the propellant in the meantime, and ... in a weight at all comparable to the remaining fuel.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/08/2017 01:26 PM
The Merlin main engine can not use all of the propellant. There is always an unusable residue left.
The unusable residue claimed is startlingly small for F9 first stage reuse.
A couple of hundred kilos from memory, or ~1s of thrust time on merlin.

It seems unlikely that the second stage has substantially more dead volume.

I question if you can get meaningful pressure fed engines, a pump, tank to hold the propellant in the meantime, and ... in a weight at all comparable to the remaining fuel.

From all the discussion I was under the impression that it would amount to maybe 1t for the upper stage. That would be enough to brake the slow terminal velocity. If it is really that low it would not be worth the effort.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/08/2017 02:05 PM
The Merlin main engine can not use all of the propellant. There is always an unusable residue left. How about SpaceX develops a small pressure fed kerolox engine for course adjustment and landing, maybe 2 or 3 are needed. They are not afraid of engine development. During the coasting phase they collect remaining propellant in 2 pressure tanks, separating any He bubbles and use that. Fully powered landing without any extra propellant, especially not hypergols.

I was taking a nap. During that time I had this idea. Tell me if it is completely off. I just don't believe in helicopter air recovery.

This is what I think they will do for the ITS ship, but that has autogenous presurant, so scavenging that + left over liquid propellant is more important, then it can be stored in smaller tanks that are easier to insulate and cool.

My feeling is that scavenging propellant for the F9 second stage is only marginally worth it at best and is probably a net loss when considering the extra complexity involved.
Title: Re: F9 Second Stage Reusability
Post by: GORDAP on 04/08/2017 03:26 PM
Wow.  Crazy news.  What a difference a week makes.
I will throw in my guess for S2 reuse.  Re-entry and descent will be handled by picaX on top, down one, a flap to protect the nozzle, and some grid fins for control.  "Landing" will be handled by a chopper catching the chute and returning it to land near the launch site.  I think legs, thrusters, tankage, and propellant will add too much dry mass.
Payload adaptors will sit on top of the dome heat shield, and will probably have to be jettisoned, but the CommX deployer might be able to be designed to fold back to the side opposite the PicaX to stay out of the re-entry plasma stream.
I think a non-reusable version will be available as well and will be such that it can be easily be converted to reusable and vise versa.
I think the changes can be light enough where it can work for both heavy and F9, LEO and GTO.
Raptor will eventually be used to up the payload capacity, but probably won't be ready for the first reused S2.

Not sure this is true.

SpaceX proposed to Air Force to build a Raptor prototype for F9/FH second stage... by end of 2018.  Despite protestations to the contrary* on this forum, maybe they intend to use the Raptor for exactly that. 
Stranger things have happened.

* Many based on the statement by EM that they won't build a reusable second stage...   ;) ;) ;)


I suspect you may be right. 

Back when EM threw cold water on a reusable 2nd stage, he said (a) it would take time away from designing the ITS and (b) a higher ISP stage was needed to make up for the added 'reuse' mass.

It may be that he's changed his mind on (a) (perhaps realizing that he needs higher profits from CommX to get to ITS) but the math probably didn't change on (b).  If so, that means a Raptor reusable US sooner rather than later.

I'm wondering then if SpaceX will use the FH on the demo flight, plus a few others, to test out some technologies as 'bolt ons' to the existing US.  Things like TPS, grid fins and a parachute.  Then snag it with a helicopter and/or lay it on a bouncy castle.  All with no intention to actually incorporate these features onto the Merlin US (or indeed to ever reuse that stage), but rather to gather data for the design of the Raptor US.

Then the Raptor US will forgo the parachute, helicopter and bouncy castle in favor of propulsive landing and legs, in line with SpaceX's original vision.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/08/2017 03:50 PM
Elon Musk saying reusable upper stage too heavy without Raptor or whatever was referring to the 2-stage Falcon 9 and to GTO. Same logic doesn't apply to Falcon Heavy or to LEO, and definitely not both together.
Title: Re: F9 Second Stage Reusability
Post by: GORDAP on 04/08/2017 04:59 PM
Elon Musk saying reusable upper stage too heavy without Raptor or whatever was referring to the 2-stage Falcon 9 and to GTO. Same logic doesn't apply to Falcon Heavy or to LEO, and definitely not both together.

Robo, I don't think that's right.  At Elon's talk at MIT in '14, he said "I don't expect the Falcon line (emphasis mine) to have a reusable upper stage, just because the...with a kerosene based system the specific impulse isn't really high enough to do that."  And he says the later system will be fully reusable.  But he clarifies what he means by specifying that the 'later' system is Methane based.  So he's clearly talking about ITS/Raptor.  So by 'Falcon line' he's clearly talking about both F9 and FH.

Do you have a source where he indicates or hints that re-usability might be possible with a Merlin base US for the FH?
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/08/2017 05:09 PM
I am sure at one point he said FH has enough lift to make the second stage reusable but they want instead to concentrate on the Mars vehicle.

With the present increased capabilities F9 to LEO is also quite feasible with a reusable upper stage and they will have plenty of launches through the satellite constellation.

There is no indication that they are planning the reusable upper stage to be methane/raptor.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/08/2017 05:35 PM
What makes this so fascinating is Musk saying they may try to bring the FH demo S2 back this summer! No-one expected that. Presumably that rules out anything but the simplest modifications. And definitely not a Raptor.

My guess is this is simply data gathering, and not a prototype reusable stage. Similar to trying to return the Falcon 1 on parachutes, or 'landing' F9 S1 at sea; why not give it a go? Perhaps simply a propulsive entry and inevitable destruction: the capacity of FH lobs an S2 into LEO leaving it with an unprecedented quantity of propellant. Absent a heat shield, once it nears the atmosphere, it lights the MVac and keep it pointed into the airstream until it runs out of fuel. See how low you get. Then splash.

The only thing this really achieves is more supersonic retropulsion time. But Earth's atmosphere at ~130,000 ft is about as dense as Mars so maybe that's sufficiently interesting?

But for S2 reusability it seems less helpful. As others have pointed out firing rockets in the direction of travel is probably not the best idea for Earth entry as it actually makes the craft more streamlined. Blunt heat shields are likely more efficient at braking pound-for-pound. Plus the MVac plumbing is not protected from the heat of entry so who knows how long that would last. It's all quite mysterious.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/08/2017 07:32 PM
Elon Musk saying reusable upper stage too heavy without Raptor or whatever was referring to the 2-stage Falcon 9 and to GTO. Same logic doesn't apply to Falcon Heavy or to LEO, and definitely not both together.

Robo, I don't think that's right.  At Elon's talk at MIT in '14, he said "I don't expect the Falcon line (emphasis mine) to have a reusable upper stage, just because the...with a kerosene based system the specific impulse isn't really high enough to do that."  And he says the later system will be fully reusable.  But he clarifies what he means by specifying that the 'later' system is Methane based.  So he's clearly talking about ITS/Raptor.  So by 'Falcon line' he's clearly talking about both F9 and FH.

Do you have a source where he indicates or hints that re-usability might be possible with a Merlin base US for the FH?

It's not just the interpretation of what "line" means.

It's the basic numbers.

The second stage weighs 5 tons, empty.  Payload is 22 tons expendable, let's call it 15 tons reusable RTLS. (though straight through down-range barge recovery has less penalty, so somewhere in between)

There is little doubt that you can return the second stage with a "huge" penalty of, say, 100%.  (Highly conservative, I'd say the correct number is 50%)

So now the second stage weighs up  to 10 tons, empty, and payload is reduced to ~10 tons worst case.

Except that this was the payload 2 iterations ago, and everyone thought it's fine...

The only question is - is this good enough?

I think if you achieve rapid turn-around and >10 flights per core, it becomes a no-brainer, even if you go from 2 launches per orbital plane to 3.

(I don't think the constellation will use FH, since barge turn-around times are too long)
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 09:01 PM
What makes this so fascinating is Musk saying they may try to bring the FH demo S2 back this summer! No-one expected that. Presumably that rules out anything but the simplest modifications. And definitely not a Raptor.

...

This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/08/2017 10:00 PM
I'd be happy to be proven wrong. I think most of us took Elon at his word when he said plans to re-use Falcon S2 were on hold. And the experts believed him because it's very, very hard to pull off.

SpaceX typically hint at progress on projects years before flight, so if a reusable S2 is ready to test soon this will have involved uncharacteristic secrecy. Hopefully more will be revealed soon.
Title: Re: F9 Second Stage Reusability
Post by: The Amazing Catstronaut on 04/08/2017 10:35 PM
Reusable upper stage work is essentially subscale ITS spaceship testing.

Do you mean 'essentially the role a subscale ITS would have', or 'testing for a subscale ITS'?

Because I would love to knock this conjecture-darling subscale ITS concept on its head since it seems to be coming out the woodwork without any proof other than that the idea is popular. People bring it up all the time like it's anything more than some concept we dreamed up on Nasaspaceflight without any bearing on any info that has come out of SpaceX. It's a fiction rocket. It's like falcon 5 to me - irrelevant; a stop-gap which doesn't fulfil the endgoal and only has a reason for creation because of worries the endgoal might be too challenging.

Reusable stage 2 on F9 -massively reduces- the need for subscale ITS from my perception.

That's not how SpaceX approaches problem resolution. They don't half-arse it because they think they need a tech demo, they go big, then iterate.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/08/2017 11:03 PM
The point of the FH Demo mission is for the AF to see a "stock" FH in action. No configuration changes allowed for three flights.

They will not have any major changes.

And perhaps you don't need any major things to make this work. That it has been overthought too much.

Perhaps the answer is in subtlety. Where both this board and aerospace in general often fail miserably.

BTW, many of the aspects of Centaur that I enjoyed understanding for decades ... are subtle ones ... FWIW.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/08/2017 11:26 PM
Reusable upper stage work is essentially subscale ITS spaceship testing.

Do you mean 'essentially the role a subscale ITS would have', or 'testing for a subscale ITS'?

Because I would love to knock this conjecture-darling subscale ITS concept on its head since it seems to be coming out the woodwork without any proof other than that the idea is popular. People bring it up all the time like it's anything more than some concept we dreamed up on Nasaspaceflight without any bearing on any info that has come out of SpaceX. It's a fiction rocket. It's like falcon 5 to me - irrelevant; a stop-gap which doesn't fulfil the endgoal and only has a reason for creation because of worries the endgoal might be too challenging.

Reusable stage 2 on F9 -massively reduces- the need for subscale ITS from my perception.

That's not how SpaceX approaches problem resolution. They don't half-arse it because they think they need a tech demo, they go big, then iterate.

The track record proves otherwise...

When proving all the pieces of the booster reuse strategy, they totally used tech demos (e.g., Grasshopper, F9 v1.1, ..., soft landing on the ocean, ...).  Going big then iterating would have been to launch the first F9 booster toward a fully kitted out (like they are today) ASDS, then iterate (after repairs). (Kinda like what people think JB will do with NG. He won't.)  Dragon 2 had Dragon 1, launch abort using a tech demo Dragon 1, tether testing SuperDraco hovering, and tech demos still in progress...  They'll land a few cargo Dragon 2s on land before crewed land landings.

When EM discussed the 'updated strategy' making 'a lot more sense' -- at the same presser that he used to reveal the second stage 'Hail Mary' -- it was game-on for speculating what the more sensible strategy involved.

Quote
Robin... Robinson Manuel, with the New York Observer, Could you give us an update on the development of the Interplanetary Transport System, and what's next in terms of - what's the next component to be tested following the carbon fuel tank and the Raptor engine, what's next?

E: So, I think we'll provide an update on the design of the Interplanetary Transport System - Interplanetary Transport System also includes the propellant depot on Mars - that's why it's sort of - I actually usually don't like the word 'system', but we can't call it a rocket if it includes a propellant depot. So the Mars planetary transporter or Mars Transporter, or Interplanetary Transporter - We've come up with a number of design refinements, and I think we'll probably be ready to put that on the Website within a month or so.

RM: Just one follow-up, The time frame has kind of shifted since Guadalajara, I was wondering if if you guys had any updated time frame of when you think that first mission will be launched - If I'm correct, the first one is uncrewed, correct?

E: Yeah the first ones will be uncrewed. I don't want to steal thunder from that announcement. I'm pretty excited about the updated strategy since Guadalajara, it makes a lot more sense, it's - we have to not just get it done technically, but figure out how to get this done without going bankrupt.
https://www.reddit.com/r/spacex/comments/62i6m1/recap_of_the_elon_musk_and_martin_halliwell_press/dfmw95b/

Good news: We'll know more 'within a month or so'
Bad News: EM time
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/08/2017 11:31 PM
I'd be happy to be proven wrong. I think most of us took Elon at his word when he said plans to re-use Falcon S2 were on hold. And the experts believed him because it's very, very hard to pull off.

SpaceX typically hint at progress on projects years before flight, so if a reusable S2 is ready to test soon this will have involved uncharacteristic secrecy. Hopefully more will be revealed soon.

I think that's a common misconception.

S1 reuse is much harder.

S2 reuse is not hard - it is similar to Dragon re-entry and reuse.  It's just that it imposes a certain penalty that was considered prohibitive.

So it's a matter of economics, and with higher S1 performance, it has become non-prohibitive.

Consider what S1 reuse entails:  Re-entry with a very awkward and fragile vehicle, with no real heat shield, doing everything propulsively, and coming to a soft landing on a tiny target.

S2 on the other hand can use a real heat-shield, Dragon style.  No need for propulsive landing since the empty mass is small, and the stage can come down right off-shore, where it's a lot easier to operate a helicopter.  Or, for what it's worth - bouncy castles and all that.  Once past re-entry, it's easier than catching a fairing.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/09/2017 01:00 AM
Returning S2 will be 'similar to Dragon' in that it comes in from orbital velocity and will involve the use of Pica-X heat-shield material, but there are also many differences. The shape and mass characteristics are totally different.

Are you thinking S2 comes down nose first ~vertically? The stock S2 is tail (engine) heavy but I suppose a big parafoil stored in the nose will weigh something, perhaps enough to make it fly nose first. Would it be a lifting-entry a la Dragon for steering?

Or... the ITS fans would be happy if it had TPS on the side and it came in ITS/shuttle-style! But then you'd need a flap or something to protect the MVac - as recent posts have suggested.

Looks like guesstimate of S2 dry mass is <5mT before re-use hardware is added. At what mass does helicopter capture become too hairy, I wonder.

Edit to add:

A couple of years ago I threw out the possibility of landing something S2-like (ESA's IXV) at very high speed on a runway. FWIW: http://forum.nasaspaceflight.com/index.php?topic=36856.msg1335557#msg1335557
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/09/2017 01:23 AM
Reusable upper stage work is essentially subscale ITS spaceship testing.

Do you mean 'essentially the role a subscale ITS would have', or 'testing for a subscale ITS'?

Because I would love to knock this conjecture-darling subscale ITS concept on its head since it seems to be coming out the woodwork without any proof other than that the idea is popular. People bring it up all the time like it's anything more than some concept we dreamed up on Nasaspaceflight without any bearing on any info that has come out of SpaceX. It's a fiction rocket. It's like falcon 5 to me - irrelevant; a stop-gap which doesn't fulfil the endgoal and only has a reason for creation because of worries the endgoal might be too challenging.

Reusable stage 2 on F9 -massively reduces- the need for subscale ITS from my perception.

That's not how SpaceX approaches problem resolution. They don't half-arse it because they think they need a tech demo, they go big, then iterate.

The track record proves otherwise...

When proving all the pieces of the booster reuse strategy, they totally used tech demos (e.g., Grasshopper, F9 v1.1, ..., soft landing on the ocean, ...).  Going big then iterating would have been to launch the first F9 booster toward a fully kitted out (like they are today) ASDS, then iterate (after repairs). (Kinda like what people think JB will do with NG. He won't.)  Dragon 2 had Dragon 1, launch abort using a tech demo Dragon 1, tether testing SuperDraco hovering, and tech demos still in progress...  They'll land a few cargo Dragon 2s on land before crewed land landings.

When EM discussed the 'updated strategy' making 'a lot more sense' -- at the same presser that he used to reveal the second stage 'Hail Mary' -- it was game-on for speculating what the more sensible strategy involved.

Quote
Robin... Robinson Manuel, with the New York Observer, Could you give us an update on the development of the Interplanetary Transport System, and what's next in terms of - what's the next component to be tested following the carbon fuel tank and the Raptor engine, what's next?

E: So, I think we'll provide an update on the design of the Interplanetary Transport System - Interplanetary Transport System also includes the propellant depot on Mars - that's why it's sort of - I actually usually don't like the word 'system', but we can't call it a rocket if it includes a propellant depot. So the Mars planetary transporter or Mars Transporter, or Interplanetary Transporter - We've come up with a number of design refinements, and I think we'll probably be ready to put that on the Website within a month or so.

RM: Just one follow-up, The time frame has kind of shifted since Guadalajara, I was wondering if if you guys had any updated time frame of when you think that first mission will be launched - If I'm correct, the first one is uncrewed, correct?

E: Yeah the first ones will be uncrewed. I don't want to steal thunder from that announcement. I'm pretty excited about the updated strategy since Guadalajara, it makes a lot more sense, it's - we have to not just get it done technically, but figure out how to get this done without going bankrupt.
https://www.reddit.com/r/spacex/comments/62i6m1/recap_of_the_elon_musk_and_martin_halliwell_press/dfmw95b/

Good news: We'll know more 'within a month or so'
Bad News: EM time
Hmmm....

Very interesting quotes. Makes me think there's going to be less "steal underpants then ???" and more of a straightforward development plan.

Possible plan:
1) Reusable upper stage demo on FH. Could just test ITS-like side reentry with body flaps, followed by parachute and splashdown (ala Dragon) or it could mean a full simulation of ITS using propulsive landing with Superdracos (ala the old reuse video) plus the previously mentioned body flaps. Or it could even mean a Raptor-based upper stage* as an even closer analogue to ITS, but I doubt that. In any case, they get experience with the rest of the hard parts of ITS before fabricating it and needing a big launch site.

2) They could even use this upper stage reuse concept operationally on flights they have a lot of margin on.

3) F9 testing of the launch cradle idea on paid flights.

4) Develop a smaller version of ITS (could still be Saturn V level of thrust!) that's still at least big enough to put Falcon Heavy out of a job. This can take over constellation work with full and rapid reuse. It could also be designed with room to barrel-stretch and upgrade to the full envisioned ITS over time. Once this works, they can retire Falcon Heavy and move any customers that signed up for Falcon Heavy over to this new, cheaper-to-operate rocket (just like they moved people who signed up for F1, F5 and the early F9 to the new F9 v1.1 and full thrust). By being lower thrust, it's much easier to convince folks to let them launch it from LC-39A and/or Brownsville. It also would be significantly cheaper up-front, partly because they could operate with fewer Raptors (9 to 20?) and also because Raptor could be lower thrust as well, which reduces its development risk a LOT.

At every step, they can reduce risk and pay for development using their existing business or the constellation's business, not requiring a big $10B bolus of money. It also directly enhances their competitiveness at every step, making it harder for upstart competitors (like New Glenn) to steal away marketshare. It also may be faster if they don't need a totally new launch site (as might be required if they pushed for full-thrust ITS right away). And by developing upper stage reuse earlier, they can get relevant reentry experience faster as well, which might help them avoid some really expensive mistakes once they bite the bullet on the (possibly smallish) initial ITS. They can also do so primarily by being funded by paying payloads, just like they did for first stage reuse.

And I don't think they'd lose anything by first pursuing a smaller ITS. Every SpaceX rocket has significantly improved its performance over time. F9 v1.0 block I (which we have only little information on, since their first User's Guide was for F9 v1.0 block II, which never flew) got about 8-10 tons of payload to LEO. F9 full thrust block 5 is 22.8t, about 2.5x as much payload plus twice as much thrust even with the same number of engines.


*Optionally, they could develop a Raptor-based upper stage for F9 and Falcon Heavy as an intermediate step before the smallish ITS version, though I don't know if that's required. If they do develop it, they can test refueling and perhaps even Mars landing and early crewed missions this way. But I doubt this is the plan.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/09/2017 01:35 AM
Returning S2 will be 'similar to Dragon' in that it comes in from orbital velocity and will involve the use of Pica-X heat-shield material, but there are also many differences. The shape and mass characteristics are totally different.

Are you thinking S2 comes down nose first ~vertically? The stock S2 is tail (engine) heavy but I suppose a big parafoil stored in the nose will weigh something, perhaps enough to make it fly nose first. Would it be a lifting-entry a la Dragon for steering?

Or... the ITS fans would be happy if it had TPS on the side and it came in ITS/shuttle-style! But then you'd need a flap or something to protect the MVac - as recent posts have suggested.

Looks like guesstimate of S2 dry mass is <5mT before re-use hardware is added. At what mass does helicopter capture become too hairy, I wonder.

Edit to add:

A couple of years ago I threw out the possibility of landing something S2-like (ESA's IXV) at very high speed on a runway. FWIW: http://forum.nasaspaceflight.com/index.php?topic=36856.msg1335557#msg1335557

Well, if you were to put Dragon, S2, and S1 next to each other, which one is the odd man out in terms of proportion?  Of Mass?

S2 has a c.g problem, but it's not that acute, since it's only one engine in the back (~500kg?), and all the reusability hardware will go in the front. (Heat shield, parachute).

Perhaps a small drag device can help shift the center of drag backwards, and also allow for active steering so that parachute deployment occurs at a precise location.  (Or alternatively, the whole 9 yards, SuperDraco and legs, as some have proposed)
Title: Re: F9 Second Stage Reusability
Post by: deruch on 04/09/2017 01:53 AM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
Surprise!  Hey....wait....why is no one surprised?
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/09/2017 01:54 AM
Elon's latest  (https://twitter.com/elonmusk/status/850453029987917824) on twitter:
Quote
Fairing is ~$5M, but that should be reusable this year. Am fairly confident we can reuse upper stage too by late next year to get to 100%.

I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
Surprise!  Hey....wait....why is no one surprised?
Maybe it's part of Block 5, now.
Title: Re: F9 Second Stage Reusability
Post by: deruch on 04/09/2017 02:15 AM
I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
Surprise!  Hey....wait....why is no one surprised?
Maybe it's part of Block 5, now.
If so, I would have much larger concerns about SpaceX meeting their schedule goals for Commercial Crew certification.  I could sort of see it as part of a Block 5.5 update that included planned changes/updates to the upper stage to address some DoD needs related to direct GEO insertion that they will eventually fold in after a while.  But, I can't see them including the mods I expect will be needed in time to achieve their stated flight rate goals for CC prior to their deadlines.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/09/2017 02:25 AM
Here's what you can do:
 * add autonomous cold gas thruster packs
 * add autonomous drag devices
 * means to link/coordinate them
 * payloads that attaches to the payload adapter. Possibly a TPS?
 * stuff that only becomes active following primary mission
 * surface application TPS of marginal weight/drag to primary mission

What you can't touch:
 * F9US systems including propulsion/RCS
 * Flight guidance/abort
 * Payload adapter
 * Separation
 * Autonomous operation (other than location/means/attitude/orientation of US disposal)
 * Any other use of propellants/systems/structural

To play this game, the means would be to "ride down" through EI while retaining stability/guidance, avoiding hot spots ("rotisserie?"), and maximizing drag as high as possible, to avoid the sudden "fist" of dynamic pressure waiting at lower altitudes.

The passive stability will be engine first, with high stagnation pressure on the MVac nozzle. If you keep it axially stable, all the thrust will ride through the same load paths that the engine fires through, and the niobium nozzle extension will heat and radiate like with engine operation. The shock wave will buffet well ahead of the nozzle, and the real questions are: a) can you keep it stable through to transonic, and b) can the nozzle survive the impulse of hitting the pressure transient to the sensible atmosphere.

After that point, various drag devices could slow the stage to ocean impact of the resultant "test article".

That's one way to keep to a realistic AF demo mission and a permittable attempt at US recovery.

This is the kind of thing that would be most likely to be attempted.

SX knows a lot about engines as they hit the sensible atmosphere nozzle first. And the loads/heating. And the props required to stabilize (perhaps from fairing recovery?). They could and probably have simulated this.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/09/2017 03:41 AM
I'm floored.
1) Does this mean that the Block 5 design freeze slated for this year is NOT a design freeze?
Surprise!  Hey....wait....why is no one surprised?
Maybe it's part of Block 5, now.
If so, I would have much larger concerns about SpaceX meeting their schedule goals for Commercial Crew certification.  I could sort of see it as part of a Block 5.5 update that included planned changes/updates to the upper stage to address some DoD needs related to direct GEO insertion that they will eventually fold in after a while.  But, I can't see them including the mods I expect will be needed in time to achieve their stated flight rate goals for CC prior to their deadlines.

Almost everything in the "reusability kit" doesn't affect the up-mission.

The only thing that can be an issue is the heat shield, but who said they won't have that option in block 5?  (as an optional component).

If it's in the design when block 5 is "frozen", then it's good.

Then everything else is a per-mission add-on.  They can refrain from adding it on manned flights until it's proven itself enough times with unmanned flights.
Title: Re: F9 Second Stage Reusability
Post by: ArbitraryConstant on 04/09/2017 05:03 AM
Here's what you can do:
 * add autonomous cold gas thruster packs
 * add autonomous drag devices
 * means to link/coordinate them
 * payloads that attaches to the payload adapter. Possibly a TPS?
 * stuff that only becomes active following primary mission
 * surface application TPS of marginal weight/drag to primary mission
How about using the real upper stage to carry a reentry demonstrator upper stage on top of the payload adapter and inside the fairing? Doesn't need a real Merlin or anything like that, just a needs to reproduce the weight distribution. Add TPS and hypergolic propulsion and so forth to the demonstrator. There's no way a Falcon Heavy couldn't handle launching that.
Title: Re: F9 Second Stage Reusability
Post by: codevalley on 04/09/2017 06:46 AM
Can I point out that a) the S2 CG problem, b) engine heat-shielding problem, c) in-atmosphere vacuum engine thrust problem, d) super draco weight penalty, and/or a mother of all hover-slam problems, are all alleviated by 3D printing an annular aerospike nozzle in place of the Merlin 1D vac bell nozzle.

S2's CG stays aft with S2 reentering engine-first, as a truncated aerospike provides natural heatshielding for the vehicle. Also, the vacuum/sea-level problem is now solved as aerospikes have good performance from vacuum all the way to sea-level, making for an efficient braking and landing burns. Super Dracos are thus not needed, as the aerospike replaces one large combustion chamber with essentially a dozen smaller chambers on its annulus, meaning we can throttle deeper by simply not lighting the full annulus. Deeper throttling removes the need for a 30g hover-slam. Finally, the CG need only move a little to provide some lift, permitting steering in the atmosphere not dissimilar to how ITS will do it, so no grid fins either.

S2 and aerospikes are a match made in engineering heaven.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/09/2017 07:16 AM
How about using the real upper stage to carry a reentry demonstrator upper stage on top of the payload adapter and inside the fairing? Doesn't need a real Merlin or anything like that, just a needs to reproduce the weight distribution. Add TPS and hypergolic propulsion and so forth to the demonstrator. There's no way a Falcon Heavy couldn't handle launching that.

I was going to suggest the same. They probably have several non-functional Merlin sitting around. Fuel in the reentry demonstrator would be used to add mass, so as to demonstrate FH full payload - which could be vented before reentry.

Title: Re: F9 Second Stage Reusability
Post by: Lars-J on 04/09/2017 07:29 AM
S2 and aerospikes are a match made in engineering heaven.

A good match perhaps, but not a heavenly one, because an aerospike nozzle will cause an isp/efficiency loss for the 2nd stage during ascent (where it is most needed).

Aerospike nozzles are never going to be as efficient in vacuum as vacuum optimized bell nozzles.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/09/2017 03:18 PM
Wacky idea but... Could Stratalaunch perform air-recovery of a large parachuting payload like S2?
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/09/2017 09:09 PM
Here's what you can do:
 * add autonomous cold gas thruster packs
 * add autonomous drag devices
 * means to link/coordinate them
 * payloads that attaches to the payload adapter. Possibly a TPS?
 * stuff that only becomes active following primary mission
 * surface application TPS of marginal weight/drag to primary mission

How about using the real upper stage to carry a reentry demonstrator upper stage on top of the payload adapter and inside the fairing?

Yes - this would have three benefits,  a) no mods at all to the FH/F9US just to the unfueled (kerolox) payload, b) as many mods to payload "stage" as you wish, and c) a significant scale payload in weight/bulk to demo.

Quote
Doesn't need a real Merlin or anything like that, just a needs to reproduce the weight distribution. Add TPS and hypergolic propulsion and so forth to the demonstrator.
If necessary.

The point you are making would be to treat it as an depleted stage would arrive on orbit, but at launch as an ordinary payload for launch. BTW - likely inside the fairing upside down.

Quote
There's no way a Falcon Heavy couldn't handle launching that.

Absolutely. And easy to build from stores on hand. Also, easy to validate as a payload because you already have all of the particulars modelled, just not as a payload. And it wouldn't be impossible as a payload to be processed, because you are not expecting to use it as a stage at all, just a payload.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/09/2017 10:04 PM
Wacky idea but... Could Stratalaunch perform air-recovery of a large parachuting payload like S2?

No need to think that wacky when it comes the Falcon second stage: the Erickson S-64 Skycrane has an advertised max payload of 9mT. I doubt you'd want to catch 9 tonnes in mid-air, but it a Falcon second stage might be doable. (For arguments sake, call it ~5 mT.)

I recently learned that mid-air capture is simplified by fitting the target with a parafoil that's designed to leave it with a fairly high horizontal speed. Or course that's not helpful if you want to land, but for mid-air capture it means smaller gusts have relatively less effect on it's path due to its momentum. The same is true for the helicopter that's matching it's speed. Plus the helicopter downwash trails the target rather than interfering. Smoother, more predictable motion makes for easier capture.
Title: Re: F9 Second Stage Reusability
Post by: DAZ on 04/10/2017 12:27 AM
SpaceX is not known with starting with a Rube Goldberg solution. They may ultimately end up with a Rube Goldberg solution but that’s generally not where they start. Most of the solutions suggested here somewhat resemble a Rube Goldberg solution.

SpaceX usually starts with the minimum conceivable starting point and builds on a minimum solution for each failure point. So Elon Musk has indicated that they may try some kind of a Hail Mary recovery test. So the question really is what is the absolute minimum you would need to do this test?

1st off you need a reaction control system for pointing the retro burn and reentry. The US already has this as part of its existing functions. Next, it needs to be able to restart the engine for the deorbit burn. This would require a small amount of reserve fuel but otherwise, the US can already do this also. So the minimum experiment would be perform the deorbit burn and keep the engine bell into the wind, as it were.

The above would assume that SpaceX knows next to nothing about reentry for their 1st try. Most likely they know a little bit more than that and would decide to add a few other items to the US. For example, they might need some heat shielding around the engine and possibly some SPAM near the base of the US. They may also choose to add some additional reaction mass to the cold gas thruster system.

This is obviously not the final recovery solution but a starting point for experimentation. The question, in this case, would be what is a successful test? A successful test would seem to be that the stage survives intact until at least the high supersonic altitude. The next parameter may be that it is approximately where they predicted it to be, for example within 10 miles of their aim point. The most important parameter is can they gather telemetry to determine what the failure was if it isn’t intact.

After the 1st test, they can then evaluate and make changes as need be. For example, do they need more heat shielding, was there enough cold gas for control or do they need to add more, was the control and the deceleration adequate or do they need to add something like a HIAD. If they need to add a HIAD they could possibly add this around the payload adapter in the space reserved for SpaceX that the payload is not to encroach upon. When they get an intact stage that survives predictably into the high supersonic they can then add a drag shoots and a Parafoil for eventual recovery. No use wasting any of the above if they can’t get the stage down to high supersonic velocities. After that, they can decide how to ultimately recover the stage whether by aircraft snatching it out of the sky (with either a fixed wing cargo aircraft or a heavy lift helicopter) or possibly landing on some kind of a “bouncy castle”.

This is essentially the same way they approached S1 recovery. It requires the minimum of modifications with the minimum of additional costs. As with the S1, they are experimenting with something that is going to be thrown away anyway. This could ultimately lead to a very inexpensive way (not only monies but potential payload mass to orbit) to recover the US. Even if they can only recover 50% of the upper stages that they launch the savings for the upcoming CommX project could be enormous.
Title: Re: F9 Second Stage Reusability
Post by: Ludus on 04/10/2017 01:42 AM
Wacky idea but... Could Stratalaunch perform air-recovery of a large parachuting payload like S2?

No need to think that wacky when it comes the Falcon second stage: the Erickson S-64 Skycrane has an advertised max payload of 9mT. I doubt you'd want to catch 9 tonnes in mid-air, but it a Falcon second stage might be doable. (For arguments sake, call it ~5 mT.)

I recently learned that mid-air capture is simplified by fitting the target with a parafoil that's designed to leave it with a fairly high horizontal speed. Or course that's not helpful if you want to land, but for mid-air capture it means smaller gusts have relatively less effect on it's path due to its momentum. The same is true for the helicopter that's matching it's speed. Plus the helicopter downwash trails the target rather than interfering. Smoother, more predictable motion makes for easier capture.

That makes sense. Also, S2 is returning from orbit so there's more choice about returning it offshore from the launch site but not very far, so a helicopter like a S-64 has the range to go out, snag it mid air and carry it back to the launch site reprocessing building.

This is pretty similar to what ULA has in mind to develop for Vulcan engines by the mid 2020s. So Elon's take is they should be able to do that in a year or so. ;)
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/10/2017 01:56 AM
Back to the heat shield for a moment... How about just having the heat shield come up to the end of the thrust chamber and jettisoning the nozzle extension. 2nd stage would return engine first.

CG  (I assume) would much closer to the heat shield than it would be if it were on the nose of the 2nd stage.  Aerodynamic center of pressure (I assume) would be way behind the CG. Jettisoning the huge bell would hopefully reduce the likelihood of it's area causing the 2nd stage to swap ends at hypersonic speeds.

Curious what you guys think.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/10/2017 02:45 AM
Let's all review the only real info we've had on 2nd stage reuse:
https://www.youtube.com/watch?v=OX2-qEC7P_I
Compare with:
https://www.youtube.com/watch?v=0qo78R_yYFA
(and the slides here: http://www.spacex.com/sites/spacex/files/mars_presentation.pdf )

...so what's the simplest way to reconcile these two? ITS EDL and 2nd Stage reentry/landing are both fairly similar to each other. PICA shielding (or related). legs from the bottom on the side where the engine bell is.
Differences:

1) The F9 2nd stage isn't shown changing its orientation from a nose-first to tail-first configuration.ITS is shown to transition from side-first to tail-first, and in the presentation and later info, Musk makes clear it uses tail flaps like Shuttle (except two of them so you can use them to steer).

2) 2nd Stage nose is blunt, since nominally it is streamlined behind a Dragon (or fairing, I suppose) whereas ITS is more rounded/pointy.

3) ITS isn't shown with a retractable nozzle like F9 2nd stage is.

4) 2nd Stage uses auxillary thrusters, maybe like Superdracos, to land, whereas ITS uses Raptors.

5) The legs are different.

I expect that IF SpaceX pursues VTVL for the upper stage (which you would think they would, since just about everything suggests that direction), they would use ITS' version for 1), 3), and 5) while using F9's version for 4) and possibly 2).

Otherwise, they skip VTVL and instead just do body flaps and PICA-X with a parachute for splashdown recovery.
Title: Re: F9 Second Stage Reusability
Post by: docmordrid on 04/10/2017 05:56 AM
Or a bouncy castle bounce-down.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/10/2017 06:57 AM
How about using the real upper stage to carry a reentry demonstrator upper stage on top of the payload adapter and inside the fairing? Doesn't need a real Merlin or anything like that, just a needs to reproduce the weight distribution. Add TPS and hypergolic propulsion and so forth to the demonstrator. There's no way a Falcon Heavy couldn't handle launching that.
That's very attractive, and fits into the time frame given the they probably have at least one on hand.

One constraint no one has mentioned is the stress levels during flight.

All stages have a maximum survivable g level in both +ve and -ve values.  I  think S1 was rated at -5g but I've no idea what S2 is.

In principle the ideal deceleration is full engine thrust for the minimal period but the stage is so light that's impossible (I think that period could be less than 1 second). So it's all down to how deep you can throttle.

One other idea that's not been suggested would be pulsing the main engine with multiple re-starts.
I don't think pulsing the main engine on a stage has ever been tried anywhere, but I may be wrong.

The key issue is the stage is designed to certain g levels and. It's not that exceeding them will probably wreck the stage for reuse (it probably will) but SX have a lot of data and done a lot of analysis on the present structure. Exceeding those current limits will mean a detailed re-analysis of the stage to confirm it would survive. It probably wouldn't so then they'd be into a re-design to figure out what parts need strengthening.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/10/2017 10:58 AM
What makes this so fascinating is Musk saying they may try to bring the FH demo S2 back this summer! No-one expected that. Presumably that rules out anything but the simplest modifications. And definitely not a Raptor.

...

This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.

I agree with all that.

It's not like Musk was telling us each week "This week we continued to do no work on upper stage recovery" until last week.

All we had was one data point that said that at a particular time some time ago their current thinking was that they were de-emphasizing upper-stage reusability.  We really don't know whether that meant nobody working on it or a significant team working on it but considering it risky so not the most likely plan.  And we don't know if a week after they spoke they changed their minds and decided to go full speed ahead on upper stage reusability again.

They also might have purposely been sandbagging to avoid bad publicity.  Imaging they never really stopped working on upper stage reusability at all, but they wanted the press off their back, and no stories about how they had promised upper stage reusability but failed to deliver.  They might just say they weren't planning for it, which is technically correct because they have a plan to succeed even without upper stage reusability, but, really, it was mainly just to lower expectations.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/10/2017 12:15 PM
This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.

I agree with all that.

It's not like Musk was telling us each week "This week we continued to do no work on upper stage recovery" until last week.

All we had was one data point that said that at a particular time some time ago their current thinking was that they were de-emphasizing upper-stage reusability. 
"de-emphasizing upper-stage reusability " is PR speak.

Musk was quite clear when he said (MIT 25th of September 2014) that
a) Upper stage use was "uneconomic" and
b) Full reusability will only come with the next generation after F9 or F9 derived (IE FH) hardware.

That suggests SX found something in their data that was not in their models and not in the textbooks that ruled out US reuse. 

The technical term for such a change in the knowledgebase is "science."

Quote from: ChrisWilson68 
We really don't know whether that meant nobody working on it or a significant team working on it but considering it risky so not the most likely plan.  And we don't know if a week after they spoke they changed their minds and decided to go full speed ahead on upper stage reusability again.
That's the thing about science. New discoveries invalidate old theories. Looking over those old proposals for stage recovery aerospace companies pitched to the USG in the 60's and 70's none of them show control surfaces on the top end of the stage. In fact SX didn't show them either in their 2011 video.

Yet that's what it takes to have adequate authority to get the job done.

It took actual flight tests of a high aspect ratio structure to find that out. It's quite conceivable that it was not the only new science that SX have discovered.

The trouble is science (except in funding proposals) does not operate on a timetable.

Quote from: ChrisWilson68 
They also might have purposely been sandbagging to avoid bad publicity.  Imaging they never really stopped working on upper stage reusability at all, but they wanted the press off their back, and no stories about how they had promised upper stage reusability but failed to deliver. 
Just to be clear there was a very clear implication that this was what they were going to do so such stories would be correct.

So far.
Quote from: ChrisWilson68 
They might just say they weren't planning for it, which is technically correct because they have a plan to succeed even without upper stage reusability, but, really, it was mainly just to lower expectations.
What would typically happen in a publicly quoted company which had created then not delivered on such an expectation would be the stock price would have fallen and the senior executives started spinning PR while the engineers responsible for non-delivery would be suitably punished for such termidity.

But SX is not subject (yet) to the whims of stock market expectations. It looks liked they did the smart thing and kept taking more data.

Somewhere between there (Sept 2014) and here something has shown up in their analyses that their previous assessment was harsh and it might yet be viable using LOX/RP1. IOW the science has changed again, as it tends to do.

However from S1 reuse I think it's clear this is a process and not an event. Even getting it back to close proximity to its planned landing area (IE not disintegrating in the upper atmosphere) will be a huge achievement. By then there will have also presumably have been several more PLF recovery attempts, perhaps to a state that some of them are reusable.

2017 will be quite an exciting year for space. and SpaceX.
Title: Re: F9 Second Stage Reusability
Post by: Jim on 04/10/2017 01:36 PM

That's the thing about science. New discoveries invalidate old theories. Looking over those old proposals for stage recovery aerospace companies pitched to the USG in the 60's and 70's none of them show control surfaces on the top end of the stage. In fact SX didn't show them either in their 2011 video.

Yet that's what it takes to have adequate authority to get the job done.

It took actual flight tests of a high aspect ratio structure to find that out. It's quite conceivable that it was not the only new science that SX have discovered.

The trouble is science (except in funding proposals) does not operate on a timetable.


Wrong takeaway and summary.  It isn't science, it is an engineering.  It was just a standard engineering trade within established ground rules.  Nothing new was discovered.  The control surfaces were required because Spacex uses low impulse GN2 thrusters (a ground rule).  Using higher performance thrusters (hyper or RP-1/GOX) would negate the need for control surfaces.   It was a complexity trade.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/10/2017 01:44 PM
SpaceX has done their fair share of innovation, but not much of what you might call science.

There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/10/2017 01:50 PM
Seems like we have several 2nd stage reusability threads that are becoming redundant now. I suggested an inflatable heat shield a couple of years back...Post#42
https://forum.nasaspaceflight.com/index.php?topic=37069.40
Title: Re: F9 Second Stage Reusability
Post by: Okie_Steve on 04/10/2017 04:16 PM
It isn't science, it is engineering.
Maybe a bit of both. SpaceX may well know more about high velocity retro-propulsion than anybody, which is why NASA was so interested in data from the early reentry attempts - remember the aircraft they scheduled to observe them? So, if somebody analyzing the engineering telemetry data said "That's funny*" some science may have crept in too.

* http://quoteinvestigator.com/2015/03/02/eureka-funny/
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/10/2017 04:52 PM
Would SpaceX's pad failure count as science? They (presumably) created novel states of matter outside a lab, after all.
Title: Re: F9 Second Stage Reusability
Post by: Jim on 04/10/2017 04:52 PM
It isn't science, it is engineering.
Maybe a bit of both.

No, engineering.  The discussion was about control and not entry
Title: Re: F9 Second Stage Reusability
Post by: CraigLieb on 04/10/2017 04:58 PM
One reason for this announcement may be to tighten the screws on the competition. 
     SpaceX 100% planned reuse
              vs.
     Getting most of the propulsion sub-system back in pieces.

Companies that make buggy whips no longer have the same level of business they used to have...
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/10/2017 06:03 PM
Suggest that what's on the table is F9US recovery like fairing recovery was. Actual reuse may depend on the what one finds afterward.

Don't get the cart too far ahead of the horse.

And ... as to motivations ... suggest for F9/FH it is simply aggressive ROI to justify launch provider costs, over life of vehicle operations.
Title: Re: F9 Second Stage Reusability
Post by: orulz on 04/10/2017 09:17 PM
If spacex is seriously considering their satellite constellation, which it certainly seems they are, it will involve a rather large number of launches to LEO. Throwing away an US for every launch probably is not desirable. If they could only carry half as many satellites per launch, but recover and reuse the upper stage every time, then the economics of the constellation start to look pretty good. Whatever customizations to the US are needed can be included in the budget for the satellite constellation, along with things like a dedicated payload adapter and satellite dispenser.

For a lack of a better way of saying it, when customers are paying them to launch something, they can just bundle an expendable US up into the cost of the launch. Nobody can really touch them on price anyway. But when they are launching their own satellites, the full cost of every launch comes straight out of their bottom line, so there is more incentive to get the savings that US reuse would provide.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/10/2017 09:32 PM
Back to the heat shield for a moment... How about just having the heat shield come up to the end of the thrust chamber and jettisoning the nozzle extension. 2nd stage would return engine first.

CG  (I assume) would much closer to the heat shield than it would be if it were on the nose of the 2nd stage.  Aerodynamic center of pressure (I assume) would be way behind the CG. Jettisoning the huge bell would hopefully reduce the likelihood of it's area causing the 2nd stage to swap ends at hypersonic speeds.

Curious what you guys think.

You'd better be damn sure that nozzle separates on the way down, not the way up :)
There may also be issues with radiative heat if the engine is enclosed behind a heatshield- although the s1 engines face a similar environment.
And then there is the hole left in the heatshield... little GNC door style hatch, maybe?
Title: Re: F9 Second Stage Reusability
Post by: orulz on 04/10/2017 10:07 PM
Could a new nozzle extension be attached to the engine after recovery or are the nozzles manufactured as a unit? If you can't put on a new extension, then recovering the US without the nozzle extension would be pretty pointless.
Title: Re: F9 Second Stage Reusability
Post by: DatUser14 on 04/10/2017 10:15 PM
MVac's are static tested w/o the nozzle, so maybe. Probably not, rockets aren't LEGO elements.


Edit/Lar: fixed pet peeve.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/10/2017 10:29 PM
And then there is the hole left in the heatshield... little GNC door style hatch, maybe?

Yup, something like that should do the trick!

Question for the experts:  If the CG is maybe 10 feet behind the heatshield, does the heatshield still need to wrap around under the second stage as it does in the SpaceX video?   
Seems like having a farther aft CG almost requires that the second stage act like a lifting body.

Edit: Typo
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/10/2017 10:50 PM
This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.

I agree with all that.

It's not like Musk was telling us each week "This week we continued to do no work on upper stage recovery" until last week.

All we had was one data point that said that at a particular time some time ago their current thinking was that they were de-emphasizing upper-stage reusability. 
"de-emphasizing upper-stage reusability " is PR speak.


Seems like it might not have been.

Sounds more like they wanted to just hush it down, a bit like GS was downplaying commX, prompting some folks to declare it all-but-dead.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/11/2017 05:47 AM
SpaceX has done their fair share of innovation, but not much of what you might call science.
That would be a fair statement if it was started "AFAIK"
Quote from: Robotbeat
There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
No company want to do science unless that's it's core function. It is not SpaceX's.

Science is unpredictable and difficult to cost. It might work, it might not work or it might work too late to matter.


Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/11/2017 10:26 AM
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 04/11/2017 11:04 AM
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.

Cooper vs Walowitz....
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/11/2017 12:09 PM
SpaceX has done their fair share of innovation, but not much of what you might call science.
That would be a fair statement if it was started "AFAIK"
Quote from: Robotbeat
There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
No company want to do science unless that's it's core function. It is not SpaceX's.

Science is unpredictable and difficult to cost. It might work, it might not work or it might work too late to matter.
My post was not supposed to be critical of SpaceX. They're not in business to do science.
Title: Re: F9 Second Stage Reusability
Post by: Radical_Ignorant on 04/11/2017 06:00 PM
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.
Title: Re: F9 Second Stage Reusability
Post by: macpacheco on 04/11/2017 06:12 PM
People make too much of the 4400 satellite number of CommX.
SpaceX can generate a large % of CommX revenue with less than 10% of the constellation in operation.
The goal of so many satellites is to provide services even for customers that have quite a restricted view of the sky (urban canyons), and ultra high bandwidth on the full system.
If they start without catering to such customers, they can make due with a few hundred satellites and generate billions USD/yr in revenue.
The balance of satellites can wait until ITS/mini ITS/Raptor F9 is operating.

The best customers for CommX are those that must choose between unreliable internet, slow internet or ultra high latency internet. CommX delivers reliable/fast/mobile/low latency, but can charge a substantial premium in return. Competing in urban canyon scenarios are the low profitability situation where you must go against the big fiber telcos.

GEO dedicated satellite links cost over 20x as much as land line links with huge latency. SpaceX can win over that entire market with moderately lower costs.

CommX has a lot more market potential outside mainland USA and Europe, several times more market. In places where there's no fiber or there's a single fiber cable that's fails nearly every month.

It makes zero sense to launch the entire constellation with Gen I satellites. It makes far more sense to operate a reduced Gen I constellation, roll out a fuller constellation with Gen IIs and only roll out the full thing with Gen III satellites. By the time Gen IIIs are ready to roll, ITS or mini ITS is flying.
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 04/11/2017 06:56 PM
People make too much of the 4400 satellite number of CommX.
SpaceX can generate a large % of CommX revenue with less than 10% of the constellation in operation.
The goal of so many satellites is to provide services even for customers that have quite a restricted view of the sky (urban canyons), and ultra high bandwidth on the full system.
If they start without catering to such customers, they can make due with a few hundred satellites and generate billions USD/yr in revenue.
The balance of satellites can wait until ITS/mini ITS/Raptor F9 is operating.

The best customers for CommX are those that must choose between unreliable internet, slow internet or ultra high latency internet. CommX delivers reliable/fast/mobile/low latency, but can charge a substantial premium in return. Competing in urban canyon scenarios are the low profitability situation where you must go against the big fiber telcos.

GEO dedicated satellite links cost over 20x as much as land line links with huge latency. SpaceX can win over that entire market with moderately lower costs.

CommX has a lot more market potential outside mainland USA and Europe, several times more market. In places where there's no fiber or there's a single fiber cable that's fails nearly every month.

It makes zero sense to launch the entire constellation with Gen I satellites. It makes far more sense to operate a reduced Gen I constellation, roll out a fuller constellation with Gen IIs and only roll out the full thing with Gen III satellites. By the time Gen IIIs are ready to roll, ITS or mini ITS is flying.

Space X themselves have said 800 to start the constellation up, that's 20% of the final number, not 10%. These satellite are travelling fast in LEO. That means you need more as they go out of line of sight more quickly.

I have no problems with the concept of the system, I think its a fantastic idea and will make Musk very very rich, but can only work with very cheap launches, and lots of them. Which is their plan! So rock on!
Title: Re: F9 Second Stage Reusability
Post by: RedLineTrain on 04/11/2017 09:57 PM
Space X themselves have said 800 to start the constellation up, that's 20% of the final number, not 10%.

More like 7%.

http://spacenews.com/fcc-gets-five-new-applications-for-non-geostationary-satellite-constellations/
Title: Re: F9 Second Stage Reusability
Post by: sanman on 04/11/2017 10:26 PM
And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

If landing on dry land is required, then can that be done with chutes, or would it require powered thrust?
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/11/2017 10:51 PM
It seems mid-air helicopter capture is an option for something the size of an empty Falcon second stage (but not much heavier).

This method won't earn SpaceX the style-points they usually get for powered vertical landings, but it adds up in terms of practicality, low-mass, and gentle loads on structure.
Title: Re: F9 Second Stage Reusability
Post by: ZachS09 on 04/11/2017 11:15 PM
Musk wants to make Falcon rockets fully reusable

https://spaceflightnow.com/2017/04/11/musk-wants-to-make-falcon-9-rocket-fully-reusable/

Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/12/2017 12:31 AM
Musk wants to make Falcon rockets fully reusable

https://spaceflightnow.com/2017/04/11/musk-wants-to-make-falcon-9-rocket-fully-reusable/
Thanks for posting the link Zach. Like I kept saying, I don't know why folks were thinking otherwise...
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/12/2017 02:37 AM
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

I like the KISS approach for 2nd stage reusability.  Seems possible that a nose mounted heat shield and some nose weight could be ready to go for this flight.  Don't even really need a parachute.  Just good telemetry showing how things worked out.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 08:46 AM
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
If you build something directly from the equations in a design handbook or ASME standards and delivers adequate, predicted performance it's engineering.

If the design equations in the open literature don't give you the performance you need.
If you're simulations don't match the recorded flight data or do so with so much uncertainty they are practically useless.
If you can't put a model in a wind tunnel because no wind tunnel exists that comes anywhere close to matching the conditions you need to model.
If you have to do curve fitting, dimensional analysis on the equations and restructure your CFD to get a model that matches the real world.


That's science.

I have great respect and admiration for what SX have accomplished. I'm quite sure they have raised the bar for any future competitor. 

The joker in the pack is of course the question of how much more science will they have to do before they get to full reuse and that answer is impossible to know.

This is "Unknown unknowns" territory.  :(
Title: Re: F9 Second Stage Reusability
Post by: Radical_Ignorant on 04/12/2017 08:49 AM
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

I like the KISS approach for 2nd stage reusability.  Seems possible that a nose mounted heat shield and some nose weight could be ready to go for this flight.  Don't even really need a parachute.  Just good telemetry showing how things worked out.

They could do that. It would fit their approach how they made booster reusable by experimenting with hardware as it is. But then they have parachutes for fairing - making bigger parachute doesn't seem complicated *if* nothing critical is relying on it. So why not?

And my guess is that their investigation which caused them to say "no reusability for F9 second stage" stands correct and there is nothing which invalidates it (given their initial powered landing idea). But after test of fairing recovery thing they came up with different idea "hi, this works so well, maybe we can even bring whole 2nd stage" and then run the numbers and they are convinced it can work.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 08:50 AM
Musk wants to make Falcon rockets fully reusable

https://spaceflightnow.com/2017/04/11/musk-wants-to-make-falcon-9-rocket-fully-reusable/
So for the first stage refurb was about 50% of new build and they expect future refurbs to be 5% of new build cost.

That's very useful information. Thank you.
Title: Re: F9 Second Stage Reusability
Post by: Rei on 04/12/2017 09:14 AM
So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

Almost certainly on a landing pad (whether on an ASDS or on land). They'll never achieve economic reuse viability if they let their turbopumps flood with seawater.  I think SpaceX has made their feelings about splashdown landings pretty clear.

I actually posted a thread the other day thinking over the issues of some of the economic issues of returning a second stage back to the US for relaunch, because it would end so far downrange that the amortization and operations costs on the ASDS would start to become significant. Not problematic at first, but if they ever wanted to achieve the case where propellant becomes the majority of their launch costs, it would be problematic then. However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Title: Re: F9 Second Stage Reusability
Post by: Radical_Ignorant on 04/12/2017 09:44 AM
And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

If landing on dry land is required, then can that be done with chutes, or would it require powered thrust?

As stated by Rei that's very impractical solution. But it doesn't mean first try (demo FH flight) won't target bringing S2 into water. And they stated that fairing won't end up in water as well, so the same technique maybe can be applied.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/12/2017 10:18 AM
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
If you build something directly from the equations in a design handbook or ASME standards and delivers adequate, predicted performance it's engineering.

If the design equations in the open literature don't give you the performance you need.
If you're simulations don't match the recorded flight data or do so with so much uncertainty they are practically useless.
If you can't put a model in a wind tunnel because no wind tunnel exists that comes anywhere close to matching the conditions you need to model.
If you have to do curve fitting, dimensional analysis on the equations and restructure your CFD to get a model that matches the real world.

That's science.

Nope.  That's R&D.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/12/2017 10:24 AM
I firmly believe it will be powered landing on land or ASDS. I have some doubt that deorbit with the main engine can provide the needed precision with startup and wind down instabilities. So they need smaller engines. The next step, making the engines strong enough for landing and providing the fuel, won't make it that much more complex. The harder part is getting it through reentry without breaking up, heatshield and aerosurfaces, protection for the engine, if not the engine bell extension.

The first attempt with the FH maiden flight may not have the landing engines and propellant. It may just be a water landing with the lowest speed attainable with the main engine. It would demonstrate the harder part, the reentry and with some luck (plus maybe a floating device) ability to recover the wreckage.

I see the second stage closer to the first stage than to the fairing.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/12/2017 12:19 PM
I firmly believe it will be powered landing on land or ASDS. I have some doubt that deorbit with the main engine can provide the needed precision with startup and wind down instabilities. So they need smaller engines. The next step, making the engines strong enough for landing and providing the fuel, won't make it that much more complex. The harder part is getting it through reentry without breaking up, heatshield and aerosurfaces, protection for the engine, if not the engine bell extension.

The first attempt with the FH maiden flight may not have the landing engines and propellant. It may just be a water landing with the lowest speed attainable with the main engine. It would demonstrate the harder part, the reentry and with some luck (plus maybe a floating device) ability to recover the wreckage.

I see the second stage closer to the first stage than to the fairing.

A single Merlin is controllable enough to bring a vehicle to zero velocity at zero altitude- that's pretty impressive. Yes the US is a quarter of the mass so it is a tougher task, but it doesn't seem unreasonable to me that they have a good enough handle on the startup/shutdown transients that the MVac is up to the job. And if a small additional correction is needed, there are N2 thrusters and prop venting available too.


The big question (time for a poll??) is whether the US is going to enter engine first or not- and also whether the Hail Mary attempt on the FH demo will be representative of any future operational plans in this regard.
Title: Re: F9 Second Stage Reusability
Post by: FutureSpaceTourist on 04/12/2017 01:31 PM
Recovering first and second stages, plus fairings too, make the logistics of recovery rather more interesting:

Quote
All at sea about reusability

SpaceX is talking about not only increasing their flight rates, but attempting to recover the Falcon 9 payload fairing and second stage as well. Dick Eagleson examines how efforts to prove out second stage and payload fairing recovery might proceed and looks at related logistic challenges for SpaceX as it moves to greatly increase its launch cadence.
Monday, April 10, 2017

http://www.thespacereview.com/article/3212/1 (http://www.thespacereview.com/article/3212/1)
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 01:36 PM
Would SpaceX's pad failure count as science? They (presumably) created novel states of matter outside a lab, after all.
Definitely given no other rockets blown up like that during a GHe load.

If it wasn't that would imply SX were pretty sure it would go bang on the pad or simply did not care one way or the other.

I don't think anyone believes SX are reckless.


Wrong takeaway and summary.  It isn't science, it is an engineering.  It was just a standard engineering trade within established ground rules.  Nothing new was discovered.  The control surfaces were required because Spacex uses low impulse GN2 thrusters (a ground rule).  Using higher performance thrusters (hyper or RP-1/GOX) would negate the need for control surfaces.   It was a complexity trade.
Plausible.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 01:43 PM
MVac's are static tested w/o the nozzle, so maybe. Probably not, rockets aren't LEGO elements.


Edit/Lar: fixed pet peeve.
Which implies you could jettison the Niobium extension and run the Merlin on its basic nozzle during landing. I'm assuming it's bolted on. Of course that puts explosive bolts into your refurb and testing costs. That brings a load of baggage.

That said Niobium is also quite expensive. It's about $40 000/tonne and is a "Strategic Metal" in the US. I think SX would prefer to keep the nozzle on the Merlin if at all reasonably possible. [EDIT I think they'd burn a lot of sim time to avoid it before they accepted there was no alternative. And assuming it worked they'd still keep working to eliminate it on general principles of added operational risk, materials cost and refurb time  ]
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 01:48 PM
However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Or you can got the other way and have the US deliver slightly sub orbital so it comes down without a de-orbit burn on the "other" US coast.
Title: Re: F9 Second Stage Reusability
Post by: smfarmer11 on 04/12/2017 02:32 PM
They could jettison the extension if they went with an extendable nozzle, like on the RL-10 of the D-IV. As that one slides into position, it would just need a mechanism to detach it from the movement mechanism from the stage.
Title: Re: F9 Second Stage Reusability
Post by: whitelancer64 on 04/12/2017 02:37 PM
However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Or you can got the other way and have the US deliver slightly sub orbital so it comes down without a de-orbit burn on the "other" US coast.
The issue there is that if the 2nd stage is sub-orbital, then so is the payload...
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/12/2017 02:56 PM
And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

If landing on dry land is required, then can that be done with chutes, or would it require powered thrust?
SpaceX is becoming masters of propulsive landing.  And the ethos is full and rapid reuse ability.  Therefore I see long term it will be nose down propulsive landing near a launch site.

However to start, I can imagine them trying to do a landing on off with the west coast with JRTI ASDS.  Not much licensing needed for that attempt.   If they prove that out then why not at LZ1 at CCAFS?

All that said, avoiding propulsive landing fuel and landing gear would be very nice if a helicopter could in fact do the job. 
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/12/2017 03:14 PM
They could jettison the extension if they went with an extendable nozzle, like on the RL-10 of the D-IV. As that one slides into position, it would just need a mechanism to detach it from the movement mechanism from the stage.

I haven't seen how the nozzle extension is deployed on the delta but it seems if it slides into position then it could just as easily slide up before decent. After a little redesign of course. It also solves the Mvac at sea level problem for landing.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/12/2017 04:40 PM
They could jettison the extension if they went with an extendable nozzle, like on the RL-10 of the D-IV. As that one slides into position, it would just need a mechanism to detach it from the movement mechanism from the stage.

I haven't seen how the nozzle extension is deployed on the delta but it seems if it slides into position then it could just as easily slide up before decent. After a little redesign of course. It also solves the Mvac at sea level problem for landing.
Agreed, like I said last year for raptor, just retract the lower half....#299
https://forum.nasaspaceflight.com/index.php?topic=39314.280

Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/12/2017 08:10 PM
They could jettison the extension if they went with an extendable nozzle, like on the RL-10 of the D-IV. As that one slides into position, it would just need a mechanism to detach it from the movement mechanism from the stage.

I haven't seen how the nozzle extension is deployed on the delta but it seems if it slides into position then it could just as easily slide up before decent. After a little redesign of course. It also solves the Mvac at sea level problem for landing.
True. The fact the engine is not operating while this happens and the process should have a fair bit of time in which to operate suggests the modifications could be fairly light. The key thing would be the joint has to be strong. 
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/12/2017 08:36 PM
However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Or you can got the other way and have the US deliver slightly sub orbital so it comes down without a de-orbit burn on the "other" US coast.
The issue there is that if the 2nd stage is sub-orbital, then so is the payload...
Too true, a significant 3rd stage would be required for GTO, while only a small 3rd stage would be needed for vLEO commX satellites. So would SpaceX be throwing this fairly costly 3rd stage away (it would need avionics, etc.), which would hardly save any money, but add risk due to extra staging events, and added complexity.

Another issue is that to land on the "other" US coast, the launch needs to fly over land (if launching from the West Coast), or have a very lofted trajectory if launching from Texas, or have a lot of cross range for a once round landing if launching from the East Coast. Launching to different inclinations leads to very different S2 landing sites for suborbital.
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 04/12/2017 09:13 PM
However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Or you can got the other way and have the US deliver slightly sub orbital so it comes down without a de-orbit burn on the "other" US coast.
The issue there is that if the 2nd stage is sub-orbital, then so is the payload...
Too true, a significant 3rd stage would be required for GTO, while only a small 3rd stage would be needed for vLEO commX satellites. So would SpaceX be throwing this fairly costly 3rd stage away (it would need avionics, etc.), which would hardly save any money, but add risk due to extra staging events, and added complexity.

no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.

The problem is more about the reliability and orbit flexibility side than delta-v side. It might be beneficial to stay on the GTO for multiple orbits, not circulizing the orbit to GEO on the first orbit, to get to correct position on the GEO. On a trajectory that has pegiree of under 100km this is not possible. And if there is some technical proplem delaying the circularization burn, re-entering after one orbit is also quite a bad thing.
Title: Re: F9 Second Stage Reusability
Post by: sojourner on 04/13/2017 02:45 AM
OK, this idea may have come up, but I haven't had time to read the entire thread.  I know at one point there was talk of how would SpaceX be able to keep the upper stage in a nose down orientation during re-entry. The most common answer I see to this is the wasteful idea of adding dead weight in the nose to change the center of gravity.

Now, feel free to ignore me if this has been suggested and discounted, but why not put heat resistant grid fins at the base of the stage that would open up in a "shuttle cock" configuration? Could that achieve enough stability for re-entry? We already know that F9 Block 5 is getting titanium grid fins that are more heat tolerant. Maybe they are thinking of 2nd stage recovery as well with that change?  Heck, with some smart engineering they could even integrate the landing leg system into the gird fin/shuttlecock system.  If you're going to add weight make it work for you too..
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/13/2017 02:59 AM
While that will probably be nessisary, the latest discussion is focused on a "landing module" between the second stage and the Dragon/Payload adapter.

This optional module has the heat shield, landing legs, Superdracos and fuel. The mass of this module tips the stage into nose first entry, and the whole LM/second stage lands like Dragon II.
Title: Re: F9 Second Stage Reusability
Post by: sojourner on 04/13/2017 04:10 AM
.

This optional module has the heat shield, landing legs, Superdracos and fuel. The mass of this module tips the stage into nose first entry, and the whole LM/second stage lands like Dragon II.

I guess that would be a good way to go if they can't manage to make the Merlin vac do double duty as the landing engine.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/13/2017 04:32 AM
I was curious about the actual location of the 2nd stage CG location so I put together a very basic CAD model in Solidworks to get a rough idea.

Model assumes a 5 ton empty weight with a 1,400 pound Mvac and bell as part of that.  I may have these weights wrong.  Input welcome!
Model is 12 feet in diameter and 30 feet long with engine placement based on images on the SpaceX website.  Obviously there is a lot of stuff left out.  I'm going with the theory that all the left out stuff is distributed more or less evenly.

CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!


Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/13/2017 08:00 AM
CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!

To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/13/2017 08:10 AM
OK, this idea may have come up, but I haven't had time to read the entire thread.  I know at one point there was talk of how would SpaceX be able to keep the upper stage in a nose down orientation during re-entry. The most common answer I see to this is the wasteful idea of adding dead weight in the nose to change the center of gravity.

Now, feel free to ignore me if this has been suggested and discounted, but why not put heat resistant grid fins at the base of the stage that would open up in a "shuttle cock" configuration? Could that achieve enough stability for re-entry? We already know that F9 Block 5 is getting titanium grid fins that are more heat tolerant. Maybe they are thinking of 2nd stage recovery as well with that change?  Heck, with some smart engineering they could even integrate the landing leg system into the gird fin/shuttlecock system.  If you're going to add weight make it work for you too..

Yes it has come up multiple times and in multiple formats. From memory:
- aft mounted grid fins
- aft mounted HIAD type torus
- retained interstage 'flowerpetal' device (would resemble turkey feathers on a jet afterburner)

Speculation is fun. Learning what SpaceX actually plan to do will be moreso :)
Title: Re: F9 Second Stage Reusability
Post by: Rei on 04/13/2017 10:36 AM
How hard do you think would it be to lower the minimum throttle level for the mvac?  Even if it took a whole extra "mini turbopump" I'd think that would be a lot lower mass than adding tons of ablative nosecone.  It'd both support the engine-forward "hypersonic retropropulsion heatshield" concept (reducing propellant consumption to rates that could be sustained throughout the whole peak heating period) as well as simplifying powered landing.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/13/2017 11:24 AM
How hard do you think would it be to lower the minimum throttle level for the mvac?  Even if it took a whole extra "mini turbopump" I'd think that would be a lot lower mass than adding tons of ablative nosecone.  It'd both support the engine-forward "hypersonic retropropulsion heatshield" concept (reducing propellant consumption to rates that could be sustained throughout the whole peak heating period) as well as simplifying powered landing.

In both these cases there is significant backpressure from the super/hypersonic flow and atmospheric pressure. This will limit throttling with a large nozzle expansion. Thrust much below 30% will be be hard.

A way around this would be an extending nozzle, which you might want to do anyway for an engine first reentry.

I'm inclined to think that the major changes to the vacuum engine, still considerable fuel use and general difficulty of engine first reentry make this concept not viable.
Title: Re: F9 Second Stage Reusability
Post by: wes_wilson on 04/13/2017 12:06 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast. 

While dissimilar in fuel and scale; mixing different size engines for vacuum and landing is a concept they're planning for ITS.



Title: Re: F9 Second Stage Reusability
Post by: Steve G on 04/13/2017 12:55 PM
While that will probably be nessisary, the latest discussion is focused on a "landing module" between the second stage and the Dragon/Payload adapter.

This optional module has the heat shield, landing legs, Superdracos and fuel. The mass of this module tips the stage into nose first entry, and the whole LM/second stage lands like Dragon II.

I think this would be the direction to pursue. The vacuum Merlin would likely not be used for landing. Since you need to add a heavy heat shield, ya, just put a Dragon-like landing system into the heat shield assembly. The weight penalty would obviously determine which missions you can recover a 2nd stage and which you cannot. So I'd expect a field-kit type approach that could be added to a standard 2nd stage should the performance requirements permit it.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/13/2017 01:05 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX. 

The production line of Kelstrel no longer exists. If they use kerolox pressure fed, which I think is not unlikely, they will design a new engine with emphasis on easy manufacturing. It would profit from their experience with Kestrel and with SuperDraco as well as early development of methane RCS thrusters. My guess it would be with electric spark ignition. I still believe they may be able to use fuel from the main tank that Merlin vac could not burn, reducing the need for extra landing fuel.

Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/13/2017 01:11 PM
Nah, use Superdracos. That way you can share tech with Dragon and don't need a new engine type. Also, you can still get the benefit of using landing propellant in case of first stage underperformance to put the payload into the right orbit.
Title: Re: F9 Second Stage Reusability
Post by: Lemurion on 04/13/2017 03:55 PM
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/13/2017 04:02 PM
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
Sure... You wouldn't need them to burn for long...
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/13/2017 04:02 PM
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
If in vacuum or close to it, then use Merlin Vac. Otherwise, use Superdracos.
Title: Re: F9 Second Stage Reusability
Post by: ArbitraryConstant on 04/13/2017 05:38 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/13/2017 06:28 PM
no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.
My point exactly. The payoff with this is no propellant needed for the de-orbit burn.

Quote from: hkultala
The problem is more about the reliability and orbit flexibility side than delta-v side. It might be beneficial to stay on the GTO for multiple orbits, not circulizing the orbit to GEO on the first orbit, to get to correct position on the GEO.
I think this is generically called a "phasing burn."
Quote from: hkultala
On a trajectory that has pegiree of under 100km this is not possible. And if there is some technical proplem delaying the circularization burn, re-entering after one orbit is also quite a bad thing.
I suggested it more for completeness than anything else, on the basis that Musk was suggesting something just now. Flying the US sub orbital simplified the de orbit problem, as not doing a full burn to orbit is not an add on, just a change in the mission flight program.

In fact it's likely they've been working on this since they discovered whatever it is that potentially puts US recovery back on the table.

It's true that the odds against whatever they've got planned leading to a successful US recovery of a stage in good enough condition are a "Hail Mary" but I doubt the hardware preparations will be anywhere near so spur of the moment.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/13/2017 06:46 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
That miniature Raptor/methane/BFS idea is looking better all the time...
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 04/13/2017 07:40 PM
Please fix your quotes. I did not say things that look like my quotes in your original post.

no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.
My point exactly. The payoff with this is no propellant needed for the de-orbit burn.
No propellant needed is not a big win compared to something like "100 kg of propellant needed". Deorbiting from some 300 km-pegiree GTO requires only VERY small deorbit burn at apogee.

suborbital seconds stage is a solution to non-existing problem, introducing much worse problems.

Whatever engines they are using for landing burn, they can very cheaply use same engines for deorbit burn.
Title: Re: F9 Second Stage Reusability
Post by: JasonAW3 on 04/13/2017 07:55 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
That miniature Raptor/methane/BFS idea is looking better all the time...

The question I have is; how well can that setup be scaled?

       Obviously some design compromises would creep into the equation, but depending on whether or not the designed in a significant amount of additional tolerances, it might work.

        I suspect the square-cube law might be an issue here.  Would have to have someone with more time than myself to run the numbers to see if such a subscale idea is even possible.  (Yes, I DID suggest building a subscale version of the BFR/ITS, but that was strictly for testing, not achieving orbit).
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/13/2017 08:07 PM
I think I like the modular approach.
One module which closely resembles the bottom half of dragon.
Heat shield, draco's, CH6N2 and N2O4 tanks, parachute optional.
Maybe grid fins near the S2 merlin engine.
One module to either include or not.
Grid fins to include or not.

Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?
Title: Re: F9 Second Stage Reusability
Post by: stcks on 04/13/2017 08:09 PM
Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?

The S2 attaches to the trunk, which attaches to the dragon with the attachment points on the bottom: http://i.imgur.com/s7yORbX.jpg
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/13/2017 08:36 PM
Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?

The S2 attaches to the trunk, which attaches to the dragon with the attachment points on the bottom: http://i.imgur.com/s7yORbX.jpg

I was wondering how the trunk attaches with the heat shield in the way. Your picture shows circular (maybe 6") things around the outside. Maybe 6 of them. So would the Payload Adapter attach to these points in the modular approach? Are these circular things heat resistant?
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/13/2017 11:49 PM
CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!

To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/14/2017 12:02 AM

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

Would the almost existing titanium grid fins be good enough for reentry velocity. The front picax should break the front and reduce the heat on the back? For peak heating keeping the stage straight into the blast would be best. After peak heating grid fins should be able to steer it a lot. Elon said on the S1 a L/D of 1.
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/14/2017 12:09 AM
1 kg and the size of a dinner plate...

https://linuxacademy.com/blog/space/comparing-heat-shields-mars-science-lab-vs-spacex-dragon/

Quote
One improvement that PICA-X represents is greater ease of manufacturing. Like many things at SpaceX, PICA-X is made in-house and at a fraction of the cost of NASA’s PICA. Produced in large pieces and then cut into tiles about the size of a cafeteria tray they are placed, in a similar fashion to the MLS shield, on to a carbon-composite mold. The tiles are about 3 in (8 cm) thick, and weigh about 2 lbs (1 kg).
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/14/2017 06:38 AM
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.
Title: Re: F9 Second Stage Reusability
Post by: docmordrid on 04/14/2017 07:03 AM
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.

I've seen 0.35 and 0.38g/cm³, but that was PICA-X 1.0 and Dragon 2 is 3.0. If it's as black as portrayed how should we interpret that, more carbon / less phenolic? What does that do to density?
Title: Re: F9 Second Stage Reusability
Post by: Elmar Moelzer on 04/14/2017 07:19 AM
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.
This and other sources I have seen claim 0.27g/cm3
https://solarsystem.nasa.gov/docs/13_Stackpoole-Poster.pdf
Title: Re: F9 Second Stage Reusability
Post by: Lar on 04/14/2017 11:40 AM
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.
This and other sources I have seen claim 0.27g/cm3
https://solarsystem.nasa.gov/docs/13_Stackpoole-Poster.pdf
How does that compare to shuttle tiles? Not AS good I think?

Quote
The HRSI tile was composed of high purity silica fibers. Ninety percent of the volume of the tile was empty space, giving it a very low density (9 lb/cu ft or 140 kg/m3) making it light enough for spaceflight.
[1] .... which is .14g/cm3 if I got my math right[2]

From the same article here are the other densities. To convert to g/cm3 shift the decimal point 3 places leftward

Quote
While RCC had the best heat protection characteristics, it was also much heavier than the silica tiles and FIB blankets, so it was limited to relatively small areas. In general the goal was to use the lightest weight insulation consistent with the required thermal protection. Weight per unit volume of each TPS type:
RCC: 1986 kg/m³ (124 lb/ft³)
LI-2200 tiles: 352 kg/m³ (22 lb/ft³)
FRCI tiles: 192 kg/m³ (12 lb/ft³)
LI-900 (black or white) tiles: 144 kg/m³ (9 lb/ft³)
FIB blankets: 144 kg/m³ (9 lb/ft³)

1 - from https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
2 - well, if Google did...   https://www.google.com/search?q=convert+140+kg%2Fm3+to+g%2Fcm3
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/14/2017 01:05 PM
Found this:

Here's what I have....

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36039.0;attach=621091;sess=43050

Quote
PICA-X heat shield material boasts a density of only 0.27 g/ cm3, near the density of solid cork (0.24 g/cm3) [22]. The material needs only be a few centimeters thick (typically around 6 cm)


Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/14/2017 01:17 PM
CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!

To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.
Charlie, your drag flap components and actuators are going to impact your CoG much more significantly than any TPS estimates due to their relatively low densities...
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/14/2017 03:55 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast. 

While dissimilar in fuel and scale; mixing different size engines for vacuum and landing is a concept they're planning for ITS.
Before looking for trouble it's better to look at the simplest possible solution.

The simplest solution is to land like the booster stage with the Merlin engine firing through its full vacuum nozzle.

So the questions are
1) Can the nozzle end be made survive the air flow, given that with the stage slightly nose down part of it will be in the air stream (for example could slowly spinning the stage on the long axis be enough to spread the heat)?

2)Can the Vac nozzle be run without destructive flow separation at Sea Level pressure. Note it's asymmetrical flow sep that's the problem. A smooth peeling off the wall all the way around is survivable. The Rocketdyne team that worked on the original J-2X programme were able to substantially increase the nozzle size at which flow sep started by relatively simple nozzle reshaping.

3)Can the Merlin throttle down enough to land IE below landing mass? The improved maximum thrust actually makes this problem worse as you need a smaller fraction of a larger number to equal the landing stage weight. However even the SSME was tested and capable of throttling down to about 17% of full power. Note the Pintle injector SX use is capable of "deep" throttling (which IIRC is below 15% of full thrust). Splitting the propellant between 2 sets of injectors (say 0-10% thrust and the other cutting in to give 11-100%) is another option.

If the answer to all these question is yes then the Merlin main engine is all you need, but I think it's going to take serious data collection and simulation to prove it (and if not why not) and only SX know for sure (or rather with a high degree of probability).
Title: Re: F9 Second Stage Reusability
Post by: babakm on 04/14/2017 04:57 PM
Wondering:  Considering the remaining LOX visible after SECO in the webcast and noted by many in the Echostar discussion thread, did they do a dry run of recovery (or at least the reentry burn)?

https://forum.nasaspaceflight.com/index.php?topic=40374.msg1654865#msg1654865 (https://forum.nasaspaceflight.com/index.php?topic=40374.msg1654865#msg1654865)
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/14/2017 06:03 PM
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast. 

While dissimilar in fuel and scale; mixing different size engines for vacuum and landing is a concept they're planning for ITS.
Before looking for trouble it's better to look at the simplest possible solution.

The simplest solution is to land like the booster stage with the Merlin engine firing through its full vacuum nozzle.

So the questions are
1) Can the nozzle end be made survive the air flow, given that with the stage slightly nose down part of it will be in the air stream (for example could slowly spinning the stage on the long axis be enough to spread the heat)?

2)Can the Vac nozzle be run without destructive flow separation at Sea Level pressure. Note it's asymmetrical flow sep that's the problem. A smooth peeling off the wall all the way around is survivable. The Rocketdyne team that worked on the original J-2X programme were able to substantially increase the nozzle size at which flow sep started by relatively simple nozzle reshaping.

3)Can the Merlin throttle down enough to land IE below landing mass? The improved maximum thrust actually makes this problem worse as you need a smaller fraction of a larger number to equal the landing stage weight. However even the SSME was tested and capable of throttling down to about 17% of full power. Note the Pintle injector SX use is capable of "deep" throttling (which IIRC is below 15% of full thrust). Splitting the propellant between 2 sets of injectors (say 0-10% thrust and the other cutting in to give 11-100%) is another option.

If the answer to all these question is yes then the Merlin main engine is all you need, but I think it's going to take serious data collection and simulation to prove it (and if not why not) and only SX know for sure (or rather with a high degree of probability).
While that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.

I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.
Title: Re: F9 Second Stage Reusability
Post by: philw1776 on 04/14/2017 06:40 PM
Found this:

Here's what I have....

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36039.0;attach=621091;sess=43050

Quote
PICA-X heat shield material boasts a density of only 0.27 g/ cm3, near the density of solid cork (0.24 g/cm3) [22]. The material needs only be a few centimeters thick (typically around 6 cm)


So roughly, a 5m wide 6cm thick PICA-X heat shield masses under 350Kg.  A good start.  Say 500Kg total to cover other hot spots.
If the recovery system masses 1.5 to 2 tons the 2 ton payload loss may be acceptable for a number of launches.
But it does look like S2 recovery will not be anywhere close to all missions because of any substantive payload mass subtraction.  More S1s recovered % wise.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/14/2017 06:55 PM
But it does look like S2 recovery will not be anywhere close to all missions because of any substantive payload mass subtraction.  More S1s recovered % wise.

They could shift those missions to FH 3 core RTLS. It depends on how much cores will cost per flight with reuse.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/15/2017 12:55 AM
Thanks every one for finding the PicaX density.  I went with .27g/cm^3.

New drawings show the drag flaps and the start of a modular nose structure and heat shield.  Nose heat shield with 3 inch thick PicaX comes in at 637 lbs. Guesstimated aluminum structure is 1,248 lbs

Drag flaps are modeled with 2 inch aluminum honeycomb topped with .093 inch thick carbon skins.  2 inches of PicaX cover one surface and three edges. Total weight for each flap is 61.6 lb.  Flaps are 4 x 4 feet. 

Drag flap size is based on the old SpaceX drawing.  They look small to me given the CG and stretched 2nd stage.  Might make sense to move them farther aft and increase their area. And  as RocketScience mentions, there is a lot of wight that will have to go in to the rear end to get the flaps moving.
Title: Re: F9 Second Stage Reusability
Post by: DAZ on 04/15/2017 01:05 AM
A question, if you don't mind.  What do you get for center of gravity when you reverse this situation?  If you put the control flaps at the top and the heat shielding around the base and the engine but not the engine bell.  Allow the engine bell to keep most of the heat for heat from everything.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/15/2017 01:26 AM
A question, if you don't mind.  What do you get for center of gravity when you reverse this situation?  If you put the control flaps at the top and the heat shielding around the base and the engine but not the engine bell.  Allow the engine bell to keep most of the heat for heat from everything.

That is a very interesting question.  Something I have been thinking about too.  Don't have time tonight, but in the next day or two I'll rearrange the model with the flaps at the nose and heat shield at the rear along with a retracting engine bell.   
Title: Re: F9 Second Stage Reusability
Post by: DAZ on 04/15/2017 01:33 AM
No retracting engine bell, let it set up a shockwave as far from the stage as possible. The material is so thin and so susceptible to damage at the end that most likely no matter what you do you will not be able to reuse it. Once on the ground, it could be easily unbolted and a replacement bolted in place. The material from the old engine bell would, of course, be recycled. Most likely entering engine bell 1st the thinner material would just be folded over but still would set up a shockwave that would help protect the rest of the stage.
Title: Re: F9 Second Stage Reusability
Post by: pmonta on 04/15/2017 04:49 AM
To go way out on a limb with a probably ridiculous idea:  ideally the heat shield would be in front of the second-stage engine during reentry.  That's kind of hard to manage during ascent for obvious reasons.  So carry the heat shield uphill at the top of the second stage (opposite the engine), then, once in orbit, detach the shield, maneuver it, and reattach at the engine end.

There's plenty of time---the stage is in orbit---and humans can help with teleoperation of the robotics if needed.  Perhaps there would be a small kit of struts and fasteners along with the shield, and anchor points around the S2 engine base.

Is it reasonable to deorbit with RCS?
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/15/2017 08:33 AM
Thanks every one for finding the PicaX density.  I went with .27g/cm^3.

New drawings show the drag flaps and the start of a modular nose structure and heat shield.  Nose heat shield with 3 inch thick PicaX comes in at 637 lbs. Guesstimated aluminum structure is 1,248 lbs

Drag flaps are modeled with 2 inch aluminum honeycomb topped with .093 inch thick carbon skins.  2 inches of PicaX cover one surface and three edges. Total weight for each flap is 61.6 lb.  Flaps are 4 x 4 feet. 

Drag flap size is based on the old SpaceX drawing.  They look small to me given the CG and stretched 2nd stage.  Might make sense to move them farther aft and increase their area. And  as RocketScience mentions, there is a lot of wight that will have to go in to the rear end to get the flaps moving.
Nice work Charlie, keep at it! :)
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/15/2017 09:31 AM
While that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.

I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.
Watch the video again from 1:18 to 1:59

It shows the US flipping, then a de-orbit burn. It does not show it flipping again to do a nose first entry (although that's what it does show). Nor does it show how the US does the 90deg shift from nose front to nose top (or the 180 deg flip post re-entry). Both of which occur when the stage is deep in the atmosphere and GN2 or even Dracos would probably not have the authority to overcome the drag forces without ripping the stage apart.

But it does show it landing tail down with no other obvious engines firing apart from the main one.

That suggests either it's the main engine doing the work or any separate landing engines are inside the tail skirt.

Mechanically and structurally the simplest answer is to use what has to be on the stage anyway IE the main engine, provided it can survive the environment and throttle down enough.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/15/2017 09:34 AM
No retracting engine bell, let it set up a shockwave as far from the stage as possible. The material is so thin and so susceptible to damage at the end that most likely no matter what you do you will not be able to reuse it. Once on the ground, it could be easily unbolted and a replacement bolted in place. The material from the old engine bell would, of course, be recycled. Most likely entering engine bell 1st the thinner material would just be folded over but still would set up a shockwave that would help protect the rest of the stage.

Surely the nozzle extension would deform in a somewhat random way- sounds a bit tricky to model- would the stage have sufficient control authority to deal with this? Worst case might be the nozzle folds over to one side, producing an asymmetric aero load.
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/15/2017 04:11 PM
While that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.

I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.
Watch the video again from 1:18 to 1:59

It shows the US flipping, then a de-orbit burn. It does not show it flipping again to do a nose first entry (although that's what it does show). Nor does it show how the US does the 90deg shift from nose front to nose top (or the 180 deg flip post re-entry). Both of which occur when the stage is deep in the atmosphere and GN2 or even Dracos would probably not have the authority to overcome the drag forces without ripping the stage apart.

But it does show it landing tail down with no other obvious engines firing apart from the main one.

That suggests either it's the main engine doing the work or any separate landing engines are inside the tail skirt.

Mechanically and structurally the simplest answer is to use what has to be on the stage anyway IE the main engine, provided it can survive the environment and throttle down enough.
Watch it again. First during the flip, see where the thrusters next to the engine bell are that fire during the flip. Then the landing, where you can see 4 of those thrusters firing, not the main bell.
Title: Re: F9 Second Stage Reusability
Post by: GWH on 04/15/2017 04:34 PM
You guys are arguing about a really old video that I am pretty sure Musk himself had said was done with a lot of artistic license. I wouldn't get hung up on anything.
Title: Re: F9 Second Stage Reusability
Post by: DAZ on 04/15/2017 05:31 PM
No retracting engine bell, let it set up a shockwave as far from the stage as possible. The material is so thin and so susceptible to damage at the end that most likely no matter what you do you will not be able to reuse it. Once on the ground, it could be easily unbolted and a replacement bolted in place. The material from the old engine bell would, of course, be recycled. Most likely entering engine bell 1st the thinner material would just be folded over but still would set up a shockwave that would help protect the rest of the stage.

Surely the nozzle extension would deform in a somewhat random way- sounds a bit tricky to model- would the stage have sufficient control authority to deal with this? Worst case might be the nozzle folds over to one side, producing an asymmetric aero load.

Yes probably, but so are some arrowheads, that’s what feathers are for.  Besides, it could possibly be an advantage.

When you are trying to get something to do a thing with a minimum of effort is usually best to figure out what it wants to do on its own and see if you can work with that.  If the center of gravity is more toward the engine because of the engine's weight and this means that it wants to reenter engine 1st why not see if you can work with that.  If you have to add some TPS why not add it to make the stage do more of what is going to do anyway.  If you’re adding TPS to protect the most valuable component on the stage, the engine, this would just move the center of gravity more toward the engine making it more stable.  As long as it’s not too unstable the only additional control authority needed is to set up a role that will cancel out the random direction.  You could even use this, to some extent, to help aim the stage downrange.

If this is not enough stability you could add, as others have suggested, flaps at the opposite end.  If this is still not enough stability you could add a HIAD like device.  Adding a HIAD has the added advantage of producing more drag sooner/higher and will thus reduce the heat load later on.  Although it is still probably possible to steer with a HIAD it may be better to use movable flaps for this instead.

For a 1st attempt just trying to get the stage to survive reentry and get telemetry from it would probably be more than adequate.  After you get past this step you can add the additional bells and whistles (flaps etc.) eventually with the stage coming down under a large parachute.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/15/2017 06:47 PM
Here is a comparison showing the rough CG location for nose first and engine first re-entry.
I added a painfully guesstimated carbon structure (interstage like) to the engine first model to connect the heat shield aluminum structure to the tank.  It weighs in at 153 Kg for the bell jettisoning model and 360 kg for the retracting bell model.

Adding Superdracos, prop tanks and plumbing will help the CG situation for both nose first (assuming Dracos in the nose) and engine first methods.  Any residual prop in the main tanks, assuming both RP1 and LOX, will also help the CG for both methods.

Title: Re: F9 Second Stage Reusability
Post by: macpacheco on 04/15/2017 11:59 PM
how about a small wing, optimized for hypersonic and Mach 2+ flight ?
Optimally it would provide a lot of lift above 50Km altitude, which could be used both to give the stage a lot of cross range to facilitate getting to the LZ/ASDS, substantially reducing re-entry speeds, perhaps even fixing CG problems (place the wings at CG).
But landing would still be done straight up.
The shuttle orbiter massed 100 tons. A 2nd stage with re-entry gear perhaps would mass 5-6 tons.
Shuttle wings provided enough lift for a ~200 knot landing. These wings would be of little use at terminal speed below 5km altitude.
Possibly the wings could even help on the way up, as long as L:D > 3.

The re-entry scenario would be to put the stage on an elliptical orbit such that the perigee skims the upper atmosphere just enough to produce a little lift (and a little drag) at perigee. At first the stage would want to go up both by its initial orbit and the lift it produces, but drag quickly slows the stage enough such that its orbit no longer pushes it up. Then it becomes a descent at lowest drag levels = lowest heating.

I'm thinking something like the X15 wing with a lot of TPS on the bottom/leading edge.

The dream scenario is to give the stage 1000Km of cross range, including a short minimum thrust engine burn after drag heating is low enough (but the air is still very thin). Enough to lift the stage by as much as 10 Km and increase speed quite a bit.

Probably a stupid idea. Shoot it down already  ;D
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/16/2017 01:24 AM
how about a small wing, optimized for hypersonic and Mach 2+ flight ?
Optimally it would provide a lot of lift above 50Km altitude, which could be used both to give the stage a lot of cross range to facilitate getting to the LZ/ASDS, substantially reducing re-entry speeds, perhaps even fixing CG problems (place the wings at CG).
But landing would still be done straight up.
The shuttle orbiter massed 100 tons. A 2nd stage with re-entry gear perhaps would mass 5-6 tons.
Shuttle wings provided enough lift for a ~200 knot landing. These wings would be of little use at terminal speed below 5km altitude.
Possibly the wings could even help on the way up, as long as L:D > 3.

The re-entry scenario would be to put the stage on an elliptical orbit such that the perigee skims the upper atmosphere just enough to produce a little lift (and a little drag) at perigee. At first the stage would want to go up both by its initial orbit and the lift it produces, but drag quickly slows the stage enough such that its orbit no longer pushes it up. Then it becomes a descent at lowest drag levels = lowest heating.

I'm thinking something like the X15 wing with a lot of TPS on the bottom/leading edge.

The dream scenario is to give the stage 1000Km of cross range, including a short minimum thrust engine burn after drag heating is low enough (but the air is still very thin). Enough to lift the stage by as much as 10 Km and increase speed quite a bit.

Probably a stupid idea. Shoot it down already  ;D
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
Title: Re: F9 Second Stage Reusability
Post by: macpacheco on 04/16/2017 01:52 AM
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
But is SpaceX interested in such an idea ?
Title: Re: F9 Second Stage Reusability
Post by: darkenfast on 04/16/2017 03:31 AM
Thanks every one for finding the PicaX density.  I went with .27g/cm^3.

New drawings show the drag flaps and the start of a modular nose structure and heat shield.  Nose heat shield with 3 inch thick PicaX comes in at 637 lbs. Guesstimated aluminum structure is 1,248 lbs

Drag flaps are modeled with 2 inch aluminum honeycomb topped with .093 inch thick carbon skins.  2 inches of PicaX cover one surface and three edges. Total weight for each flap is 61.6 lb.  Flaps are 4 x 4 feet. 

Drag flap size is based on the old SpaceX drawing.  They look small to me given the CG and stretched 2nd stage.  Might make sense to move them farther aft and increase their area. And  as RocketScience mentions, there is a lot of wight that will have to go in to the rear end to get the flaps moving.

May I add something from the safety of my uneddicated armchair?  Change to three flaps, to save weight, maybe even two (with roll control by other means).  Add a small extension (2'?), to the front of the second stage cylinder, capped by the heat shield.  Into that goes a Draco-derived (NOT Super Draco) set of tanks and thrusters to keep control during re-entry and a similar-to-the-fairing (but larger) steerable parachute to recover on the same bag that the fairings will (hopefully!) land on, perhaps the next day.  Cable risers would run down the side to orient the stage for landing.  I agree with others that the nozzle extension will not survive and will be jettisoned.   This adds more useful weight to the front end and keeps overall weight increase to about the minimum that I can see.

Which, of course, means that it's probably all wrong!
Title: Re: F9 Second Stage Reusability
Post by: RDMM2081 on 04/16/2017 05:07 AM
Here is a comparison showing the rough CG location for nose first and engine first re-entry.
I added a painfully guesstimated carbon structure (interstage like) to the engine first model to connect the heat shield aluminum structure to the tank.  It weighs in at 153 Kg for the bell jettisoning model and 360 kg for the retracting bell model.

Adding Superdracos, prop tanks and plumbing will help the CG situation for both nose first (assuming Dracos in the nose) and engine first methods.  Any residual prop in the main tanks, assuming both RP1 and LOX, will also help the CG for both methods.

Please, forgive the late-night speculation.   But I have followed this thread and read all the (ideas) to date, none have struck me yet as a "spaceX" solution.  Suddenly this seems close! (If you flip it back around!) Add some amount of PicaX as necessary to the side wall, jettison the vac-nozzle(can only the extended vac-nozzle be jettisoned, leaving a SL nozzle intact?), extend a (grid-fin-ish) flap (with heavy heat xfer properties) TOWARDS the nozzle/CG, ride that in, and THEN, hmm, I dunno, pick a landing method? Mvac seems unlikely (imho, throttling issues), and so does the addition of superdracos (crazy mass penalties!) which leaves "float-testing" (salt-water bath, minus 100 style points) or some type of mid-air recovery (also not perfect, but the mass penalties otherwise are, um, "silly" (imho))

I dunno, probably shouldn't bother typing up stuff like this after the amount of tequila which was actually involved.....
Title: Re: F9 Second Stage Reusability
Post by: RDMM2081 on 04/16/2017 05:32 AM
Here is a comparison showing the rough CG location for nose first and engine first re-entry.
I added a painfully guesstimated carbon structure (interstage like) to the engine first model to connect the heat shield aluminum structure to the tank.  It weighs in at 153 Kg for the bell jettisoning model and 360 kg for the retracting bell model.

Adding Superdracos, prop tanks and plumbing will help the CG situation for both nose first (assuming Dracos in the nose) and engine first methods.  Any residual prop in the main tanks, assuming both RP1 and LOX, will also help the CG for both methods.

I feel like I need to type more words, sorry mods if you need to delete or combine. But take the top picture, except imagine nozzle first re-entry, extend the flap(entry-wise?) and reinforce the pica type properties, now you shield the sensitive engine nozzle (whether you think it's usable for entry/landing at all) (at least you protect it somewhat for re-use) and I think you spread the heating loads across the stage somewhat. 

Seems like this flap mod could add less mass(maintain current CG anyway), add a "lifting-body" aspect, (IANARS), and obviously won't solve every problem and create world peace, but at least now the "last mile" recovery bit is hopefully on the table (think back to "soft water landing" on Cassiopeia, did not solve the problem, but it cut the solution-set by ~80% (or whatever, pick a number))
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/16/2017 06:44 AM
Landing prop tanks at the top make sense to me, that's most of the weight. But legs and engines at the top don't add up. You need an aerodynamic side for reentry, not more equipment that needs protection. Any remaining stability issues need to be adressed with flaps. the early animation does it that way, ITS does it that way, so will a reusable upper stage IMO.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/16/2017 04:08 PM
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
But is SpaceX interested in such an idea ?
That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHO
Title: Re: F9 Second Stage Reusability
Post by: Lar on 04/16/2017 04:52 PM
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
But is SpaceX interested in such an idea ?
That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHO

He has in the past disdained wings as not worth the mass. But grid fins are a kind of wing (if you stretch the definition) and if someone put together a proposal that showed that wings of a certain size were the least mass penalty (integrating across the increased drag on the way up, the probability of success, and all the other variables in the trade space) way to recover S2, I think he'd give it very serious and detailed consideration.

So yeah. what Rocket Science said.
Title: Re: F9 Second Stage Reusability
Post by: CharlieWildman on 04/16/2017 06:02 PM
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
But is SpaceX interested in such an idea ?
That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHO

He has in the past disdained wings as not worth the mass. But grid fins are a kind of wing (if you stretch the definition) and if someone put together a proposal that showed that wings of a certain size were the least mass penalty (integrating across the increased drag on the way up, the probability of success, and all the other variables in the trade space) way to recover S2, I think he'd give it very serious and detailed consideration.

So yeah. what Rocket Science said.

Sigh. If I only had an engineering team and a wind tunnel...
I was actually playing with the idea of CADing up a 2nd stage with X-37 ish wings and tail and doing some DIY aerodynamic testing.  There would be so much structural guess work though...  I think any findings would be useless for determining the mass hit.  So shelving that idea for now. 
Title: Re: F9 Second Stage Reusability
Post by: Lemurion on 04/16/2017 07:21 PM
No matter what I see, I keep coming back to a tail-first entry. I can't call myself an expert, but the one thing I'm sure SpaceX won't do is add mass primarily to move the CG. If gravity is pulling the upper stage into a tail-first orientation, I think SpaceX will work with it rather than against it.
Title: Re: F9 Second Stage Reusability
Post by: mme on 04/16/2017 07:54 PM
No matter what I see, I keep coming back to a tail-first entry. I can't call myself an expert, but the one thing I'm sure SpaceX won't do is add mass primarily to move the CG. If gravity is pulling the upper stage into a tail-first orientation, I think SpaceX will work with it rather than against it.
Ah, but there is a difference between adding mass "just to move the CG" and the potential situation where the mass of a heatshield, SDs, fuel, landing legs etc. is enough to move CG.  In other words, recovery will require more mass.  You might as well put it to use.

In the end I think it will come down to a trade off between engineering complexity (and therefore probable reliability), total mass penalty and what is physically possible starting with the current S2 design.

I have no confidence in what approach they will take.
Title: Re: F9 Second Stage Reusability
Post by: macpacheco on 04/17/2017 03:09 AM
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81
https://forum.nasaspaceflight.com/index.php?topic=42637.80
But is SpaceX interested in such an idea ?
That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHO

He has in the past disdained wings as not worth the mass. But grid fins are a kind of wing (if you stretch the definition) and if someone put together a proposal that showed that wings of a certain size were the least mass penalty (integrating across the increased drag on the way up, the probability of success, and all the other variables in the trade space) way to recover S2, I think he'd give it very serious and detailed consideration.

So yeah. what Rocket Science said.

I wouldn't interpret Musk's statements as disdain, but rather the bigger thinking that wings are 100% useless on the moon and of little use on the thin Martian atmosphere. He wanted a generic solution. I have a lot of respect for that.
But F9/FH upper stages aren't intended to ever land on the Moon or Mars. There's already very long runways at the cape and at vandy.
So I wouldn't be surprised if EM decides to go that route. I'm sure what we're thinking has already been discussed internally.
It wouldn't be the first time he changed his mind.
But I sense he already has a better solution and a more generic one.
What I want is they find any solution that works well and advance the goal post several miles. Whatever the solution is.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/17/2017 05:18 AM
Re disdain for wings: We do at least know that making use of aerodynamic lift is in favor at SpaceX: They experimented with it on the last Falcon launch. And the ITS designs are clearly 'lifting bodies' with entry attitudes closer to the shuttle orbiter than the tail-first boosters.

If SpaceX were designing the Falcon stage 2 now I'd easily believe it would look and behave like a massively scaled down ITS, and part of the justification for that design would be proving/maturing plans for ITS.

But what's actually coming in the near term S2 recovery attempts? I've no idea.
Title: Re: F9 Second Stage Reusability
Post by: Oersted on 04/17/2017 12:00 PM
Another idea would be a Rogallo wing, like that employed on the Gemini TT-1 test vehicle:

https://www.youtube.com/watch?v=jub8y6WSI8M

- I am more of the belief that they'll try with a simple parachute and grab it with a helicopter. Seems to me that it would be the lightest and most practical solution.
Title: Re: F9 Second Stage Reusability
Post by: robert_d on 04/17/2017 01:48 PM
I wonder if while they were looking at options for recovering the payload fairing, they discovered that the strength and flexibility of new materials made a parasail/parafoil option viable instead of the legs. And, if they had calculated the cost for a "bouncy castle" recovery ship as too high, spreading it over many fairings/several 2nd stages might just possibly be economic. Fairing recovered on East coast and 2nd stage on West, and possibly visa versa for west coast launches. Could also be that PICA-X has worked well enough on dragon that weight estimates for 2nd stage have come down.

The 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads, Maybe they can also support super-dracos at least on the F9. Maybe these tanks could also change the outer mold line to increase lift.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/17/2017 03:12 PM
Re disdain for wings: We do at least know that making use of aerodynamic lift is in favor at SpaceX: They experimented with it on the last Falcon launch. And the ITS designs are clearly 'lifting bodies' with entry attitudes closer to the shuttle orbiter than the tail-first boosters.

If SpaceX were designing the Falcon stage 2 now I'd easily believe it would look and behave like a massively scaled down ITS, and part of the justification for that design would be proving/maturing plans for ITS.

But what's actually coming in the near term S2 recovery attempts? I've no idea.
Agreed, who knows? Keeps things interesting IMHO! :) Just a note about a lifting body plan-form, you need those stubby wings on the hybrid-like X-37 to  give it more cross-range and keep the landing speeds reasonable...
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/17/2017 03:42 PM
Sigh. If I only had an engineering team and a wind tunnel...
I was actually playing with the idea of CADing up a 2nd stage with X-37 ish wings and tail and doing some DIY aerodynamic testing.  There would be so much structural guess work though...  I think any findings would be useless for determining the mass hit.  So shelving that idea for now.
In CAD, anything is possible.  :(

But your engineering instincts are right to be weary of wings.

The key problem is not making them light enough to carry the load, or how to extend them if they are retractable.

It's that those loads are now pressing on the side of a structure that's been designed (from day one) to be very strong lengthwise. It's the old soda can analogy. You can stack 10 full loaded soda cans on one empty provided it's longwise. Put the empty on its side and it's crushed.

It's true most large aircraft are cylinders-with-wings-stuck-on-them but those cylinders don't have to sit on their tails prior to launch.

I don't think there have been more than 10  "tail sitter" aircraft designs in the whole history of flight (including Shuttle, Buran and the X37b). AFAIK outside Shuttle and Buran all were all 1 (or no) person vehicles for military test programmes and their performance was substantially below that of HTOL aircraft of similar size.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/17/2017 03:54 PM
The 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads,
That's sort of right, but reminds me of something else.

Shotwell said there are 2 F9 designs.  One is a regular F9 and can serve as the booster for an FH. The other is the design that serves as an FH core. Presumably it can also serve as a regular F9. But now you mention it both core stages would have to be stronger than the base F9 stages to carry the maximum 64 tonnes, unless F9 is built with a lot of structural margin, which I don't think is the case.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/17/2017 04:09 PM
While that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.

I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.
Watch the video again from 1:18 to 1:59

It shows the US flipping, then a de-orbit burn. It does not show it flipping again to do a nose first entry (although that's what it does show). Nor does it show how the US does the 90deg shift from nose front to nose top (or the 180 deg flip post re-entry). Both of which occur when the stage is deep in the atmosphere and GN2 or even Dracos would probably not have the authority to overcome the drag forces without ripping the stage apart.

But it does show it landing tail down with no other obvious engines firing apart from the main one.

That suggests either it's the main engine doing the work or any separate landing engines are inside the tail skirt.

Mechanically and structurally the simplest answer is to use what has to be on the stage anyway IE the main engine, provided it can survive the environment and throttle down enough.
Watch it again. First during the flip, see where the thrusters next to the engine bell are that fire during the flip. Then the landing, where you can see 4 of those thrusters firing, not the main bell.
I have and you're right there does appear to be some non main engine firing from inside the main skirt. However what's still missing is how the US goes from being engine first to being nose first (and how it's kept nose first) during reentry and how it goes from nose first to tail sitting to fire whatever engines are being used for landing.
You guys are arguing about a really old video that I am pretty sure Musk himself had said was done with a lot of artistic license.
Except it's the only official description of how SX thought they were going to solve the problem before Musk stated that upper stage reuse was completely off the table for F9 based hardware.
Quote from: GWH
I wouldn't get hung up on anything.
Good to know.
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 04/17/2017 04:41 PM
The 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads,
That's sort of right, but reminds me of something else.

Shotwell said there are 2 F9 designs.  One is a regular F9 and can serve as the booster for an FH. The other is the design that serves as an FH core. Presumably it can also serve as a regular F9. But now you mention it both core stages would have to be stronger than the base F9 stages to carry the maximum 64 tonnes, unless F9 is built with a lot of structural margin, which I don't think is the case.

What does the different S1 structural versions(F9 S1 vs FH S1) have to do with the S2?
If the S2 can take 64 tons on the top on the ground then it doesn't make any difference in flight.
A heavier payload does not increase the load during flight. The load is just the thrust in flight.
What am I missing?
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/17/2017 04:53 PM
The 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads,
That's sort of right, but reminds me of something else.

Shotwell said there are 2 F9 designs.  One is a regular F9 and can serve as the booster for an FH. The other is the design that serves as an FH core. Presumably it can also serve as a regular F9. But now you mention it both core stages would have to be stronger than the base F9 stages to carry the maximum 64 tonnes, unless F9 is built with a lot of structural margin, which I don't think is the case.

What does the different S1 structural versions(F9 S1 vs FH S1) have to do with the S2?
If the S2 can take 64 tons on the top on the ground then it doesn't make any difference in flight.
A heavier payload does not increase the load during flight. The load is just the thrust in flight.
What am I missing?
FH has 3x as much thrust but not nearly 3x as much mass to accelerate, so it can hit much higher g loads, especially near burnout. Heavier payload and higher acceleration mean much higher loads on the second stage: F=m*a

More acceleration also means higher speeds in the dense part of the atmosphere, so aero loads are higher as well.
Title: Re: F9 Second Stage Reusability
Post by: garidan on 04/17/2017 05:05 PM
I think SpaceX is not willing to spend a lot on developing S2 reusability, it makes no sense on the medium term and the value to recover is a lot less than S1.
You have to consider as well that this "attempts" will happen during paid missions (apart the demo flight of falcon heavy, not by chance the first to try a S2 recovery) and as it was for S1, they cannot increase risk to the main mission, that is deliver payloads.
So I guess they will capitalize on S1 experience and try to recover ithe same way as S1,  tail first, with pica reenforcement on the tail and, if and when they get one S2 intact in the sea, they will add legs, far lighter then the S1 ones being the weight so much less.
So the first attempt, at a minimum, requires (a lot more) thermal protection on the tail and a way to trim down the engine nozzle, too big and too "thin" for reentry, and certainly not a big loss in reuse terms.
If the engine with nozzle trimmed short is too much powerfull for an overslam landing (I'm not so sure), they can add 2 or 3 superdracos just for the last burn, I don't know how much weight it adds.

But for the first attempt I guess there will be only a trimmed nozzle, just to test if it together with additional thermal protection allows for an intact S2 to reach above the sea.

For the first attempt the nozzle could be shortened just from the start, if S2 performance is not part of the certification. If flyback and reentry proves itself good, than a way to trim the bell after payload delivery will be studied: I think a hot bell that thin is not hard to cut short, and it's easier to cut it than jettison that part without putting at risk the reliability of S2 engine.
Title: Re: F9 Second Stage Reusability
Post by: ArbitraryConstant on 04/17/2017 05:19 PM
But it does show it landing tail down with no other obvious engines firing apart from the main one.
Disagree, video shows a number of thruster plumes around the edge of the stage quite clearly.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/17/2017 10:24 PM
But it does show it landing tail down with no other obvious engines firing apart from the main one.
Disagree, video shows a number of thruster plumes around the edge of the stage quite clearly.
You're behind the curve. As I already noted.
I have and you're right there does appear to be some non main engine firing from inside the main skirt.

However what's still missing is how the US goes from being engine first to being nose first (and how it's kept nose first) during reentry and how it goes from nose first to tail sitting to fire whatever engines are being used for landing.
My instinct is SX will use what they know and what works.  Grid fins, being mostly drag devices should keep the nose down during most of the deceleration following a main engine burn. If they can respond fast enough that would suggest they could bring about a controlled "pendulum swing" of the stage to the vertical in time to be ready for landing.

The alternative would be a full 180deg flip and then let the tail end "fall" to vertical.

The joker in the pack is this major shift in attitude has to occur deep in the atmosphere where the aerodynamic loads are on the side of the stage.
Title: Re: F9 Second Stage Reusability
Post by: ArbitraryConstant on 04/18/2017 01:58 AM
My instinct is SX will use what they know and what works.  Grid fins, being mostly drag devices should keep the nose down during most of the deceleration following a main engine burn.
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps. Also seems like a lifting entry is more desirable, so center of gravity would be somewhat off center. In this scenario, the transition to vertical flight can be accomplished by increasing angle of attack until stall.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/18/2017 04:41 AM
My instinct is SX will use what they know and what works.  Grid fins, being mostly drag devices should keep the nose down during most of the deceleration following a main engine burn.
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps. Also seems like a lifting entry is more desirable, so center of gravity would be somewhat off center. In this scenario, the transition to vertical flight can be accomplished by increasing angle of attack until stall.

Agreed - what they know works in a different regime.  Grid fins may still be used, but not to provide guidance/stabilization during reentry.

The cleanest way to achieve active guidance during reentry is c.g. shifting.  But AFAIK, it's used to tweak the angle of naturally stable bodies, not to actively keep them from flipping around and tumbling.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 04/18/2017 08:29 AM
The cleanest way to achieve active guidance during reentry is c.g. shifting. 

Yes, but when this is not feasible shifting center of drag is good as well. IMO PicaX covered drag and steering flaps at the bottom will do that nicely. Similar to the 2 flaps on ITS. They may need more than two lacking the wing like extensions on ITS.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/18/2017 01:17 PM
The cleanest way to achieve active guidance during reentry is c.g. shifting. 

Yes, but when this is not feasible shifting center of drag is good as well. IMO PicaX covered drag and steering flaps at the bottom will do that nicely. Similar to the 2 flaps on ITS. They may need more than two lacking the wing like extensions on ITS.
True, but the flaps are more effective in belly first flight, since they see non separated  flow.  If coming in head first, flaps in the back may be less effective.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/18/2017 01:45 PM
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps. Also seems like a lifting entry is more desirable, so center of gravity would be somewhat off center. In this scenario, the transition to vertical flight can be accomplished by increasing angle of attack until stall.
You have to understand that all capsule entries since Mercury have been lifting body entries. Once you have offset Cg then you can vary the relevant vectors and get lift. I think the Russians opted for unconditional stability, that's why they stayed spherical.

Musk has said the new grid fins they are planning to use will increase stage L/D ratio to 1. Apollo was about 0.5 at hypersonic speed. What I'm not clear on is how got a cross range this will the stage and wheather it's good enough to do a RTLS after the first orbit or if it will remain the case that the simplest move is to wait about a day til the launch site comes back under its ground track.
Title: Re: F9 Second Stage Reusability
Post by: RedLineTrain on 04/18/2017 07:59 PM
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps.

Titanium is fairly durable with heating.  For example, see X-33 as an example of a titanium SSTO vehicle.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/18/2017 08:02 PM
Is there a way of placing some sort of ITS-wing-like extensions on a redesigned upper stage to allow for a biconic lifting-body re-entry, without compromising aerodynamic stability during launch?

Not for S2 reuse on Falcon Heavy, but something further down the road.

The hardware difference between an expendable first stage and a reusable first stage isn't much: bolt on the legs and tap the helium pressurant system, bolt on the grid fins and add their control system, add some TPS and you're good to go. Could we see something similar for a reusable second stage? Like, bolt on the wing extensions, wrap TPS around one side of the stage, and install SuperDracos in the wing extensions?
Title: Re: F9 Second Stage Reusability
Post by: Gliderflyer on 04/19/2017 01:12 AM
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps.

Titanium is fairly durable with heating.  For example, see X-33 as an example of a titanium SSTO vehicle.
I thought that the X-33 was inconel, but in any case, that isn't the problem. Aerodynamic heating is much higher on sharp edges than it is on blunt ones, and grid fins consist entirely of sharp edges. The X-33 was flat and "fluffy" so it could get away with using a relatively normal material for the TPS. There might be some magic material that would allow a grid fin to survive orbital reentry heating, but it would be MUCH easier to use flat plates/body flaps.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/19/2017 01:20 AM
Both wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.
Title: Re: F9 Second Stage Reusability
Post by: HMXHMX on 04/19/2017 01:28 AM
Both wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.

I think Gliderflyer might be referring to the Inco "tiles" that covered the carbon fiber frame on the windward side.

http://www.styleofspeed.com/images/space/x-33/tps_c.jpg
Title: Re: F9 Second Stage Reusability
Post by: Gliderflyer on 04/19/2017 02:35 AM
Both wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.

I think Gliderflyer might be referring to the Inco "tiles" that covered the carbon fiber frame on the windward side.

http://www.styleofspeed.com/images/space/x-33/tps_c.jpg
Yep, I was referring to the tiles. I forgot that the X-33 was only the mach 13 version (I have a bad habit of using X-33/Venture Star interchangeably), but I assume that Venture Star would have used the same TPS.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/19/2017 07:58 AM
Yeah the grid fins have sharp edges, but they're going to be behind the main shockwave.  The blunt main heat shield will take the bulk of the heating.  Actually, more accurately, the atmosphere compressed by the blunt main heat shield will take the bulk of the heating.  The blunt main heat shield will take less of it, but still a lot more than any grid fins back on the body will.

Look at how the main shock wave is far to the side as you go back for a re-entry capsule.  For S2 the sides are straight, not angled back, but they are still far from the shock wave.  The grid fins wouldn't reach out far enough to get the kind of heating the main heat shield will get.

http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/blunt-body-shockwave.jpg?itok=dDTHT4aH
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/19/2017 08:23 AM
Another idea would be a Rogallo wing, like that employed on the Gemini TT-1 test vehicle:

https://www.youtube.com/watch?v=jub8y6WSI8M

- I am more of the belief that they'll try with a simple parachute and grab it with a helicopter. Seems to me that it would be the lightest and most practical solution.

I have to agree that a parachute in air recovery would be the lightest weight option. 

It's a reasonable starting point.  Get some S2's back, learn, iterate.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 01:30 PM
I have to agree that a parachute in air recovery would be the lightest weight option. 

It's a reasonable starting point.  Get some S2's back, learn, iterate.
Where would they put the TPS, how would they prevent ballistic re-entry, and where would they put the chute?
Title: Re: F9 Second Stage Reusability
Post by: RedLineTrain on 04/19/2017 01:57 PM
Both wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.

I stand corrected.  At least early on, Venturestar's skin was planned to be titanium.  I guess that must have changed.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/19/2017 02:12 PM
Yeah the grid fins have sharp edges, but they're going to be behind the main shockwave.  The blunt main heat shield will take the bulk of the heating.  Actually, more accurately, the atmosphere compressed by the blunt main heat shield will take the bulk of the heating.  The blunt main heat shield will take less of it, but still a lot more than any grid fins back on the body will.

Look at how the main shock wave is far to the side as you go back for a re-entry capsule.  For S2 the sides are straight, not angled back, but they are still far from the shock wave.  The grid fins wouldn't reach out far enough to get the kind of heating the main heat shield will get.

http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/blunt-body-shockwave.jpg?itok=dDTHT4aH

If the grid-fins are deep in the wake they won't help solve the pitch/yaw control problems S2 appears to have; you need to keep it upright with the heat shield facing into the airstream. So... spin stabilize S2 for entry, and only use the grid fins for terminal guidance a la S1.

In fact spinning up the S2 for entry might be something you could do with a stock stage. I guess it depends where the thrusters are and if it naturally spins in the desired axis.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/19/2017 02:19 PM
Don't get all myopic by strictly focusing on CoG... It is the relationship between it and the CoP for lifting entry. The CoP will shift while traveling from hypersonic, supersonic and subsonic flight regimes. Not discussing CoP and strictly focusing on CoG is not adequately addressing the challenge of lifting entry...
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 02:20 PM
Yeah the grid fins have sharp edges, but they're going to be behind the main shockwave.  The blunt main heat shield will take the bulk of the heating.  Actually, more accurately, the atmosphere compressed by the blunt main heat shield will take the bulk of the heating.  The blunt main heat shield will take less of it, but still a lot more than any grid fins back on the body will.

Look at how the main shock wave is far to the side as you go back for a re-entry capsule.  For S2 the sides are straight, not angled back, but they are still far from the shock wave.  The grid fins wouldn't reach out far enough to get the kind of heating the main heat shield will get.

http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/blunt-body-shockwave.jpg?itok=dDTHT4aH

If the grid-fins are deep in the wake they won't help solve the pitch/yaw control problems S2 appears to have; you need to keep it upright with the heat shield facing into the airstream. So... spin stabilize S2 for entry, and only use the grid fins for terminal guidance a la S1.

In fact spinning up the S2 for entry might be something you could do with a stock stage. I guess it depends where the thrusters are and if it naturally spins in the desired axis.
Oh, I didn't think of spin-stabilization. That's a fantastic idea.

Per the Falcon 9 user's guide: "In addition, the second stage contains a cold nitrogen gas (GN2) attitude control system (ACS) for pointing and roll control." The included table notes that while the first stage uses engine gimbals for pitch, yaw, and roll control, the second stage uses the cold gas thrusters for all three, with pitch and yaw also aided by engine gimbal during burns.

I also noted that in the attached SpaceX CGI rendering, there are a series of flaps around the engine that aren't present in the current flown model...TPS guidance flaps?
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 03:01 PM
As a very basic first step toward second-stage reuse, SpaceX could simply equip one of the two standard payload adapters with spray-on or stick-on TPS, spin-stabilize the stage for re-entry, and let it come down in a ballistic trajectory. It would still impact the ocean at terminal velocity, but it would be a demonstration of re-entry.

Chutes could be added for a survivable splashdown...they would only run around 50 kg...but I don't know that there's any space for them to fit. Maybe around the engine, if there's room? There's not much room there.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/19/2017 03:24 PM
As a very basic first step toward second-stage reuse, SpaceX could simply equip one of the two standard payload adapters with spray-on or stick-on TPS, spin-stabilize the stage for re-entry, and let it come down in a ballistic trajectory. It would still impact the ocean at terminal velocity, but it would be a demonstration of re-entry.

Chutes could be added for a survivable splashdown...they would only run around 50 kg...but I don't know that there's any space for them to fit. Maybe around the engine, if there's room? There's not much room there.
If you are going with this approach, why not allow the heat shield to drop down on retaining straps (similar to Mercury) allowing landing bags to inflate and deploy for a soft landing on land, rather than a splash down and salt water incursion...
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 03:37 PM
As a very basic first step toward second-stage reuse, SpaceX could simply equip one of the two standard payload adapters with spray-on or stick-on TPS, spin-stabilize the stage for re-entry, and let it come down in a ballistic trajectory. It would still impact the ocean at terminal velocity, but it would be a demonstration of re-entry.

Chutes could be added for a survivable splashdown...they would only run around 50 kg...but I don't know that there's any space for them to fit. Maybe around the engine, if there's room? There's not much room there.
If you are going with this approach, why not allow the heat shield to drop down on retaining straps (similar to Mercury) allowing landing bags to inflate and deploy for a soft landing on land, rather than a splash down and salt water incursion...
Wind is a problem there. The second stage can come down on chutes, splash down, and tip over without being damaged because it is far shorter than the first stage, but if it came down on land it would likely cartwheel due to residual horizontal velocity and rip itself apart. Plus, there's the issue of the landing site; bringing down a spent stage on land requires a very large exclusion zone because there's really no way to control exactly where it comes down.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/19/2017 03:39 PM
Parafoil + mid-air helicopter recovery still seems appealing to me - if the total reusable-S2 weight can be kept down. Set it down on a 'bouncy castle' or the far superior - and fun - ball pit in order to deal with any swinging or rotation that's induced as the speed lowers. (I'm only 90% joking.)
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/19/2017 03:57 PM
As a very basic first step toward second-stage reuse, SpaceX could simply equip one of the two standard payload adapters with spray-on or stick-on TPS, spin-stabilize the stage for re-entry, and let it come down in a ballistic trajectory. It would still impact the ocean at terminal velocity, but it would be a demonstration of re-entry.

Chutes could be added for a survivable splashdown...they would only run around 50 kg...but I don't know that there's any space for them to fit. Maybe around the engine, if there's room? There's not much room there.
If you are going with this approach, why not allow the heat shield to drop down on retaining straps (similar to Mercury) allowing landing bags to inflate and deploy for a soft landing on land, rather than a splash down and salt water incursion...
Wind is a problem there. The second stage can come down on chutes, splash down, and tip over without being damaged because it is far shorter than the first stage, but if it came down on land it would likely cartwheel due to residual horizontal velocity and rip itself apart. Plus, there's the issue of the landing site; bringing down a spent stage on land requires a very large exclusion zone because there's really no way to control exactly where it comes down.
A deploy-able tripod gear may stop a tip-over if you release the the chutes or parafoil and a landing can be made at one of the many dry lakes sites out west... (quick sketch below)
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 05:14 PM
A deploy-able tripod gear may stop a tip-over if you release the the chutes and a landing can be made at one of the many dry lakes sites out west... (quick sketch below)
If you have large enough landing legs and you cut the chutes at precisely the right moment, then you might be able to land it without tipover. If wind speed is low enough.

The dry lakes out west have pretty high winds, usually, and you still need a large exclusion zone in case re-entry ends up lower than expected.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 04/19/2017 05:23 PM
A deploy-able tripod gear may stop a tip-over if you release the the chutes and a landing can be made at one of the many dry lakes sites out west... (quick sketch below)
If you have large enough landing legs and you cut the chutes at precisely the right moment, then you might be able to land it without tipover. If wind speed is low enough.

The dry lakes out west have pretty high winds, usually, and you still need a large exclusion zone in case re-entry ends up lower than expected.
Agreed, that's when you choose to de-orbit when landing conditions are within limits. NASA landed "Stardust" out in Utah and was considering Orion to land at KSC with a parafoil...
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/19/2017 05:28 PM
The stock S2 can spin up to 5 rpm. Not sure if that's enough, or if it can maintain that all the way through re-entry though:
http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf Section 3.7

Here's some modest steps you could follow to investigate S2 return across four test missions:

+ On a Dragon/FH test mission*, add Pica-X to the nose of S2, spin it up and see how close to Earth it gets.
+ If it gets low enough, add grid fins to the next flight, confirm they can null the spin and fly to the pickup co-ordinates.
+ If that works, add a parafoil and see how it flies.
+ If all is well, attempt to capture the next one with a helicopter.
_______
* I say Dragon mission because the payload mount for a satellite needs to be dealt with. I guess you could build up the Pica-X shield and add a hinged trap door that closes over the payload mount. But that's beginning to sound too complicated if we're just proving the concept.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/19/2017 05:34 PM
The stock S2 can spin up to 5 rpm. Not sure if that's enough, or if it can maintain that all the way through re-entry though:
I'm sure it could spin faster if it wanted to; that limit is for customers. The cold gas thrusters could spin up the stage well beyond its structural capacity if that was desired.

Quote
Here's some modest and steps you could follow to investigate S2 return across four test missions:

+ On a Dragon mission*, add Pica-X to the nose of S2, spin it up and see how close to Earth it gets.
+ If it gets low enough, add grid fins to the next flight, confirm they can null the spin and fly to the pickup co-ordinates.
+ If that works, add a parafoil and see how it flies.
+ If all is well, attempt to capture the next one with a helicopter.
_______
* I say Dragon mission because the payload mount for a satellite needs to be dealt with. I guess you could build up the Pica-X shield and add a hinged trap door that closes over the payload mount. But that's beginning to sound too complicated if we're just proving the concept.
Elon said he'd like to test it out on the Falcon Heavy inaugural launch, which will definitely feature a payload fairing and adapter rather than the Dragon. But the payload fairing is pretty tough; if you attached Pica-X panels to the surface and painted the adapter attachment points with ablative paint, it might be enough. Recall that peak heating is on the edge of a heat shield; the center gets less heat than any other point.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 03:41 PM
If they wanted to go full-propulsive-landing on the F9 second stage, the only way to do it without significant modifications to the outside of the stage would be something like this:

(https://s18.postimg.org/byipaicq1/more_modding.png)

Basically they would be designing a replacement payload adapter with all the recovery hardware on it, including expendable payload attachment adapter, heat shield, landing legs, bipropellant tanks, pressurant tanks, and SuperDracos. Note the high cosine losses on the SuperDracos.

Might be simpler to jettison the heat shield completely, though that goes against rapid reuse.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/20/2017 03:51 PM
The stock S2 can spin up to 5 rpm. Not sure if that's enough, or if it can maintain that all the way through re-entry though:
I'm sure it could spin faster if it wanted to; that limit is for customers. The cold gas thrusters could spin up the stage well beyond its structural capacity if that was desired.

Quote
Here's some modest and steps you could follow to investigate S2 return across four test missions:

+ On a Dragon mission*, add Pica-X to the nose of S2, spin it up and see how close to Earth it gets.
+ If it gets low enough, add grid fins to the next flight, confirm they can null the spin and fly to the pickup co-ordinates.
+ If that works, add a parafoil and see how it flies.
+ If all is well, attempt to capture the next one with a helicopter.
_______
* I say Dragon mission because the payload mount for a satellite needs to be dealt with. I guess you could build up the Pica-X shield and add a hinged trap door that closes over the payload mount. But that's beginning to sound too complicated if we're just proving the concept.
Elon said he'd like to test it out on the Falcon Heavy inaugural launch, which will definitely feature a payload fairing and adapter rather than the Dragon. But the payload fairing is pretty tough; if you attached Pica-X panels to the surface and painted the adapter attachment points with ablative paint, it might be enough. Recall that peak heating is on the edge of a heat shield; the center gets less heat than any other point.
If the changes to S2 are just Pica-X around the payload mount hardware and spinning up for entry, I guess there's no harm in trying. My guess is it would eventually conduct too much heat to internal structure, but even if it failed it could be useful to know how long it survived.

If spin stabilization is indeed the answer to S2's CG/CP challenges, then we can imagine grid fins maintaining that spin (windmilling) once in the sensible atmosphere. They'd be deep in the wake, so wouldn't get too hot.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/20/2017 03:58 PM
If they wanted to go full-propulsive-landing on the F9 second stage, the only way to do it without significant modifications to the outside of the stage would be something like this:

(https://s18.postimg.org/byipaicq1/more_modding.png)

Basically they would be designing a replacement payload adapter with all the recovery hardware on it, including expendable payload attachment adapter, heat shield, landing legs, bipropellant tanks, pressurant tanks, and SuperDracos. Note the high cosine losses on the SuperDracos.

Might be simpler to jettison the heat shield completely, though that goes against rapid reuse.

The space-cadet in me would prefer to see this approach, but it's hard to see how in practical terms it's better than mid-air capture...
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/20/2017 03:59 PM
If they wanted to go full-propulsive-landing on the F9 second stage, the only way to do it without significant modifications to the outside of the stage would be something like this:

(https://s18.postimg.org/byipaicq1/more_modding.png)

Basically they would be designing a replacement payload adapter with all the recovery hardware on it, including expendable payload attachment adapter, heat shield, landing legs, bipropellant tanks, pressurant tanks, and SuperDracos. Note the high cosine losses on the SuperDracos.

Might be simpler to jettison the heat shield completely, though that goes against rapid reuse.

Legs can go straight through the heatshield, see Dragon 2. So can the landing thrusters, they just need to blow off a tile when they start up.

Shouldn't need to add more than 1/2 a stage diameter to the height of the stage to fit everything in.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 04:40 PM
If the changes to S2 are just Pica-X around the payload mount hardware and spinning up for entry, I guess there's no harm in trying. My guess is it would eventually conduct too much heat to internal structure, but even if it failed it could be useful to know how long it survived.
Seems like this would satisfy Elon's "we want to try second stage recovery" claim without incurring substantial development cost and without endangering FH launch qualification. The initial tests of first-stage return were never intended to be actually recoverable; they were intended to test supersonic retropropulsion and in-atmo retrograde engine restarts, primarily.

Quote
If spin stabilization is indeed the answer to S2's CG/CP challenges, then we can imagine grid fins maintaining that spin (windmilling) once in the sensible atmosphere. They'd be deep in the wake, so wouldn't get too hot.
Ooooh, now here's an idea: what about autorotation? With the larger grid fins planned for Block 5, supposedly capable of getting an L/D ratio of 1:1 on the first stage, autorotating the second stage could really dramatically reduce its terminal velocity...perhaps even to the point of being able to land on a "bouncy castle" without RUD. The grid fins would be able to guide it down to a pinpoint trajectory and then allow autorotation to reduce the terminal velocity to something survivable.

EDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...

...I'm estimating an impact velocity with autorotation on the order of 20 m/s. If it comes down on the heat shield/payload adapter, that's not half bad. I wish we knew how much cushioning the bouncy castle would provide. Does anyone know if the cold gas thrusters can provide any meaningful prograde thrust?
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 05:00 PM
Legs can go straight through the heatshield, see Dragon 2. So can the landing thrusters, they just need to blow off a tile when they start up.

Shouldn't need to add more than 1/2 a stage diameter to the height of the stage to fit everything in.
The existing S2 is more than three times the height of the Dragon 2, so those stubby little legs wouldn't provide nearly enough stability to avoid tip-over. And blowing a hole in the heat shield doesn't fit with reuse plans.
Title: Re: F9 Second Stage Reusability
Post by: Digitalchromakey on 04/20/2017 05:17 PM
If they wanted to go full-propulsive-landing on the F9 second stage, the only way to do it without significant modifications to the outside of the stage would be something like this:

(https://s18.postimg.org/byipaicq1/more_modding.png)

Basically they would be designing a replacement payload adapter with all the recovery hardware on it, including expendable payload attachment adapter, heat shield, landing legs, bipropellant tanks, pressurant tanks, and SuperDracos. Note the high cosine losses on the SuperDracos.

Might be simpler to jettison the heat shield completely, though that goes against rapid reuse.
Have been thinking about an approach similar to this, however perhaps everything necessary for a S2 landing could be contained within one self contained 'standalone' module (minus the PICA heat shield) fixed between a standard S2 and the payload adaptor, also with grid fins fitted to this same module, first using the Merlin 1D/grid fins  for a stable re-entry similar to S1, then only once the stage has significantly slowed (perhaps after another short Merlin 1D burn) inverting the S2 for a RTLS Super Draco powered landing.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/20/2017 05:34 PM
EDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...

Erm, that's not how it works. You're working off mass and drag. But you need lift and drag.

An object with a L/D of 4:1 is essentially a crude glider. Think Shuttle orbiter, or jump chute. It doesn't matter how many grid fins you stick on the back of a rocket, it's not going to turn into a glider.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 05:42 PM
EDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...

Erm, that's not how it works. You're working off mass and drag. But you need lift and drag.

An object with a L/D of 4:1 is essentially a crude glider. Think Shuttle orbiter, or jump chute. It doesn't matter how many grid fins you stick on the back of a rocket, it's not going to turn into a glider.
Autorotation works a little differently. I don't know whether the AOA of the grid fins can be adjusted in real-time as readily as the collective and pitch on a chopper, but it's worth investigation.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 05:58 PM
Another thought: the S2 is coming in from orbit, so there's no penalty for RTLS. If fitting landing legs behind the plasma shield is a problem, the S2 could simply come in and land upside-down on SuperDracos in a fixed cradle with a blast trench underneath. It would reduce plume impingement/wash dramatically and really simplify the recovery hardware needed for the S2.

Have been thinking about an approach similar to this, however perhaps everything necessary for a S2 landing could be contained within one self contained 'standalone' module (minus the PICA heat shield) fixed between a standard S2 and the payload adaptor, also with grid fins fitted to this same module, first using the Merlin 1D/grid fins  for a stable re-entry similar to S1, then only once the stage has significantly slowed (perhaps after another short Merlin 1D burn) inverting the S2 for a RTLS Super Draco powered landing.
Heat shield is a non-negotiable. Hypersonic retroprop won't work at orbital speeds.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/20/2017 06:10 PM
... Block 5, supposedly capable of getting an L/D ratio of 1:1 on the first stage ...

Here's Musks's comment:
Quote
the new grid fins should be capable of taking a scorching and being fine. And they'll also have significantly more control authority, so, that should improve reusability of the rocket. It will improve the payload to orbit by being able to fly at a higher angle of attack and use the aerodynamic element of the rocket to effectively glide like a big cylinder. It does have an L/D of roughly 1 if flown at the right angle of attack, but you need control authority, particularly pitch control authority, that's higher than we currently have to achieve that.
It's hard to tease this apart, but I think he's talking about increasing payload to orbit by by 'flying' the first stage which has a L/D of 1 at certain (high) speeds. Not clear if the gain comes from going uphill (engine gimbaling), or RTLS landing (less prop needed for boostback because cross range 'flying' with grid fins is increased). TL;DR I don't think this helps S2 landing scenarios.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/20/2017 06:20 PM
Another thought: the S2 is coming in from orbit, so there's no penalty for RTLS. If fitting landing legs behind the plasma shield is a problem, the S2 could simply come in and land upside-down on SuperDracos in a fixed cradle with a blast trench underneath. It would reduce plume impingement/wash dramatically and really simplify the recovery hardware needed for the S2.

Have been thinking about an approach similar to this, however perhaps everything necessary for a S2 landing could be contained within one self contained 'standalone' module (minus the PICA heat shield) fixed between a standard S2 and the payload adaptor, also with grid fins fitted to this same module, first using the Merlin 1D/grid fins  for a stable re-entry similar to S1, then only once the stage has significantly slowed (perhaps after another short Merlin 1D burn) inverting the S2 for a RTLS Super Draco powered landing.
Heat shield is a non-negotiable. Hypersonic retroprop won't work at orbital speeds.

Sure, but is developing that a better plan than having an Erickson Skycrane on standby and a couple of pilots available to pick one up in mid-air? They don't come cheap, but think of the mass you save on S2 as well as the reduced complexity (risk), and also the cost of developing the SuperDraco landing hardware - and the cradle.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/20/2017 07:12 PM
Legs can go straight through the heatshield, see Dragon 2. So can the landing thrusters, they just need to blow off a tile when they start up.

Shouldn't need to add more than 1/2 a stage diameter to the height of the stage to fit everything in.
The existing S2 is more than three times the height of the Dragon 2, so those stubby little legs wouldn't provide nearly enough stability to avoid tip-over. And blowing a hole in the heat shield doesn't fit with reuse plans.

The legs can extend through the heat shield a bit sideways to make the footprint wider. If the CG is far enough forward for a forward entry, it's far enough forward for a stable nose-down landing. Especially with 6 legs.

Make it an easily replaceable tile, should be simple enough. The tiles under Dragon 2's legs will probably have to be replaced each flight.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 07:42 PM
... Block 5, supposedly capable of getting an L/D ratio of 1:1 on the first stage ...

Here's Musks's comment:
Quote
the new grid fins should be capable of taking a scorching and being fine. And they'll also have significantly more control authority, so, that should improve reusability of the rocket. It will improve the payload to orbit by being able to fly at a higher angle of attack and use the aerodynamic element of the rocket to effectively glide like a big cylinder. It does have an L/D of roughly 1 if flown at the right angle of attack, but you need control authority, particularly pitch control authority, that's higher than we currently have to achieve that.
It's hard to tease this apart, but I think he's talking about increasing payload to orbit by by 'flying' the first stage which has a L/D of 1 at certain (high) speeds. Not clear if the gain comes from going uphill (engine gimbaling), or RTLS landing (less prop needed for boostback because cross range 'flying' with grid fins is increased). TL;DR I don't think this helps S2 landing scenarios.
Ah, hmm. May not. I'm fairly sure the gain doesn't come from going uphill -- engine gimbaling is by far the most dV-efficient approach -- but the "flying it back to land" thing makes sense.

That being said, autorotation on the second stage could still be viable for reducing terminal velocity.

The legs can extend through the heat shield a bit sideways to make the footprint wider. If the CG is far enough forward for a forward entry, it's far enough forward for a stable nose-down landing. Especially with 6 legs.
I'll believe it when I see it. The CG isn't great, not with that heavy Merlin up top. Note the feathered flaps for maintaining COP.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/20/2017 07:58 PM
The legs can extend through the heat shield a bit sideways to make the footprint wider. If the CG is far enough forward for a forward entry, it's far enough forward for a stable nose-down landing. Especially with 6 legs.
I'll believe it when I see it. The CG isn't great, not with that heavy Merlin up top. Note the feathered flaps for maintaining COP.

The CG appears to be slightly forward of the center of the stage once heat shield, thrusters, tanks, and legs are added to the nose. Lets say it's 6 m from the contact plane of the extended legs. If the legs extend out to the diameter of the stage , the inscribed circle will have a radius of about 1.8 m. The static tipover angle is atan(1.8 m / 6 m) = 17 degrees.

Unless landing on the side of a mountain, it will be pretty stable.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/20/2017 08:09 PM
Wait a minute. If it can RTLS without penalty, and if it can fly itself to a pinpoint landing site via grid fins...why not just drop into a net, suspended above the ground? Nets are cheap. Terminal velocity can't be THAT high.

https://www.youtube.com/watch?v=6qF_fzEI4wU (https://www.youtube.com/watch?v=6qF_fzEI4wU)
Title: Re: F9 Second Stage Reusability
Post by: ArbitraryConstant on 04/20/2017 08:48 PM
It's hard to tease this apart, but I think he's talking about increasing payload to orbit by by 'flying' the first stage which has a L/D of 1 at certain (high) speeds. Not clear if the gain comes from going uphill (engine gimbaling), or RTLS landing (less prop needed for boostback because cross range 'flying' with grid fins is increased). TL;DR I don't think this helps S2 landing scenarios.
I parse that as clearly referring to RTLS with greater atmospheric crossrange.

I don't think grid fins are out of the question for S2, just not at initial reentry velocities.
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/20/2017 09:09 PM
Wait a minute. If it can RTLS without penalty, and if it can fly itself to a pinpoint landing site via grid fins...why not just drop into a net, suspended above the ground? Nets are cheap. Terminal velocity can't be THAT high.

https://www.youtube.com/watch?v=6qF_fzEI4wU (https://www.youtube.com/watch?v=6qF_fzEI4wU)

BOE says around 100 m/s, so 25 megajoules into the net. (Big error bars.)
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/20/2017 09:36 PM
EDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...

Erm, that's not how it works. You're working off mass and drag. But you need lift and drag.

An object with a L/D of 4:1 is essentially a crude glider. Think Shuttle orbiter, or jump chute. It doesn't matter how many grid fins you stick on the back of a rocket, it's not going to turn into a glider.
Autorotation works a little differently. I don't know whether the AOA of the grid fins can be adjusted in real-time as readily as the collective and pitch on a chopper, but it's worth investigation.

It still sounds as though you are attributing a L:D to the grid fins themselves, not the stage.
How are you extrapolating from Musk's comments on the first stage to get your numbers for an autorotating second stage?
Title: Re: F9 Second Stage Reusability
Post by: sojourner on 04/21/2017 12:11 AM
I'll believe it when I see it. The CG isn't great, not with that heavy Merlin up top. Note the feathered flaps for maintaining COP.

If you're worried about tipover from wind gusts after landing, then just have it land in a walled off location. A simple, cheap solution that doesn't add weight to the stage.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/21/2017 12:48 AM
You can't use spin stabilization with a empty stage top first, because the CG/CP are too separated and like a top heavy top, it'll tumble on its side.

You can't have the base of the fairing be anything but a PAF, because a) that's how the load paths are communicated to the F9US, and b) because when you encapsulate the payload, its horizontal, and all of the weight of the fairing as a huge offset load, which goes through the PAF along with the payload, meaning it has to be there to integrate a payload. So never draw a fairing without the adapter at the bottom.

You could integrate a portion of the payload as a recovery system - this would make business sense for a large LEO/GSO/GEO payload anyways, since the FH has extreme excess capacity, so using up some of that to recover the F9US would still allow a) unmodified FH/F9US operation, b) deployment of payload(s), and c) allow the additional resources necessary for recovery to be separate from the F9US it was to recover, thus an optional "secondary payload" whose sole purpose was to recover the F9US. Like in the place of the lower payload on Ariane's SYLDA.

The scope of such a "recovery payload vehicle" (RPV?) for development would be like that of a Dragon. You might use it to later recover a large module or spacecraft as well.

Such a vehicle would shift the CG much higher, and might also spin the combined vehicle at a high enough rate as well as a controlled entry, that one could avoid a hypersonic tumble.

It could also have permanent "legs"/other that fit within the confines of the fairing and not interfering with the primary payload(s).

This approach would follow the SX doctrine of optionally reusable or expendable - you'd not wreck the economics of the F9US (actually, you could even improve upon it, because you can get the US back and see just how much you "used" of it, how much margin still remained).

Note that it would only work with missions that could afford the decrease in payload on F9/FH. And ... as you got better at recovery, the performance of this "F9RPV" would decrease the loss incrementally, as we have seen with F9/FH performance figures marching up.

And you don't force your customers to use it, just another option.

Might even allow for BFS experiment recover too. Hows this for an idea?
Title: Re: F9 Second Stage Reusability
Post by: adrianwyard on 04/21/2017 06:04 AM
You can't use spin stabilization with a empty stage top first, because the CG/CP are too separated and like a top heavy top, it'll tumble on its side.
Can you think of another way of explaining why spin stabilization won't work for S2 nose-first? A top does stay upright despite being top heavy so long as it's kept spinning fast enough...
Title: Re: F9 Second Stage Reusability
Post by: BobHk on 04/21/2017 09:24 PM
Can you make the bell of the engine the landing gear and part of the rocket body?  Say, S2 has a gimballed engine with a standard bell 'inside' the rocket body material at the level of the engine is shaped like a bell and also attaches to S1 and is reinforced in 3 areas to act as stiffened landing gear with crush zone adapters.

So two different sized, nested dixie cups at the bottom of S2 (the bigger dixie cup being the diameter of the rocket), both essentially rocket bells.  One outer bell for orbital operations, its stiffened outer area used for landing legs.  The inner bell for landings.  The need for a heat shield is largely obviated by use of the rocket plume during reentry.  Small grid fins and perhaps gas jets could be added, leveraging existing systems in S1 that are already well understood. 

You would not need any changes to the upper parts of S2, the fairings could be jettisoned and recovered as they are now. 

Would this be light enough to have enough fuel left over for landing like an F9 does now?

Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/22/2017 05:02 AM
Can you make the bell of the engine the landing gear and part of the rocket body?  Say, S2 has a gimballed engine with a standard bell 'inside' the rocket body material at the level of the engine is shaped like a bell and also attaches to S1 and is reinforced in 3 areas to act as stiffened landing gear with crush zone adapters.

So two different sized, nested dixie cups at the bottom of S2 (the bigger dixie cup being the diameter of the rocket), both essentially rocket bells.  One outer bell for orbital operations, its stiffened outer area used for landing legs.  The inner bell for landings.  The need for a heat shield is largely obviated by use of the rocket plume during reentry.  Small grid fins and perhaps gas jets could be added, leveraging existing systems in S1 that are already well understood. 

You would not need any changes to the upper parts of S2, the fairings could be jettisoned and recovered as they are now. 

Would this be light enough to have enough fuel left over for landing like an F9 does now?
A few problems here.

First of all, the engine bell is radiatively cooled, so it needs to be exposed in order to not melt. Really.

Next, the engine plume alone won't obviate the need for a heat shield. Not enough fuel, and not effective enough, either.

Finally, the MVac would undergo catastrophic flow separation at SL...and even if it didn't, its TWR is far too high to land on with an empty S2.
Title: Re: F9 Second Stage Reusability
Post by: sevenperforce on 04/23/2017 04:06 AM
Dedicated thread on second-stage reuse configurations in the future: https://forum.nasaspaceflight.com/index.php?topic=42783.0 (https://forum.nasaspaceflight.com/index.php?topic=42783.0)
Title: Re: F9 Second Stage Reusability
Post by: rakaydos on 04/24/2017 01:24 AM
So I've seen a lot of suggestions about landing legs going through the heat shield like Dragon (which has issues of balance) and engines coming out the side like dragon (which has cosign losses).

I havnt seen anyone suggest those same holes used for legs in Dragon be used as Superdraco exaust ports. A hinged cover over each protects the SDs through reentry, and as it slows through the supersonic regime the covers unlatch and the superdracos blow the covers open. (if they dont unlatch, the superdracos STILL blow them open, but additional repairs/replacement of the caps may be needed)

The benifits are twofold- first, you eliminate the cosign losses from disperced thrust plooms. Second, you get the nozzles out of the hypersonic airstream during reentry, which is more of an issue with the cylendrical S2 than the conical Dragon capsule.

Legs can still emerge from the sides, of course- protected under an aeroshell.
Title: Re: F9 Second Stage Reusability
Post by: BobHk on 05/08/2017 11:09 PM


Anyone thought of airbrakes?  Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down.  The brakes deploy from the end (opposite end of the nose that has the heat shielding).  Legs deploy from the nose to land.  You can put the retropropulsive units in the base with the aerobrakes.  The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).

A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net.  What kind of lego model can I make to convince everyone it will work?

Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 05/09/2017 10:46 AM


Anyone thought of airbrakes?  Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down.  The brakes deploy from the end (opposite end of the nose that has the heat shielding).  Legs deploy from the nose to land.  You can put the retropropulsive units in the base with the aerobrakes.  The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).

A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net.  What kind of lego model can I make to convince everyone it will work?

grid fins?
Title: Re: F9 Second Stage Reusability
Post by: Ictogan on 05/09/2017 10:52 AM


Anyone thought of airbrakes?  Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down.  The brakes deploy from the end (opposite end of the nose that has the heat shielding).  Legs deploy from the nose to land.  You can put the retropropulsive units in the base with the aerobrakes.  The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).

A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net.  What kind of lego model can I make to convince everyone it will work?
Developing a non-detaching fairing doesn't make sense given that they are also developing reuse for detaching fairings.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 05/12/2017 02:46 PM


Anyone thought of airbrakes?  Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down.  The brakes deploy from the end (opposite end of the nose that has the heat shielding).  Legs deploy from the nose to land.  You can put the retropropulsive units in the base with the aerobrakes.  The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).

A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net.  What kind of lego model can I make to convince everyone it will work?
Developing a non-detaching fairing doesn't make sense given that they are also developing reuse for detaching fairings.
GTO/LEO?
Title: Re: F9 Second Stage Reusability
Post by: JasonAW3 on 05/12/2017 03:09 PM


Anyone thought of airbrakes?  Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down.  The brakes deploy from the end (opposite end of the nose that has the heat shielding).  Legs deploy from the nose to land.  You can put the retropropulsive units in the base with the aerobrakes.  The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).

A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net.  What kind of lego model can I make to convince everyone it will work?
Developing a non-detaching fairing doesn't make sense given that they are also developing reuse for detaching fairings.
GTO/LEO?

Personally, I'm more in favor of an inflatable decelerator system.  Maximize surface area for lowest mass penalty, to decelerate the system soonest.

     Mind you, it'd be best to make a few high altitude passes prior to final deceleration and landing pass, as this could be used to bleed off velocity in the high upper atmosphere, with minimal external heating, prior to deployment of the inflatable decelerator..
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 06/04/2017 07:41 PM
NASA Considering Using Pre-flown SpaceX Rockets for Cargo Flights - Space.com
https://apple.news/AL8bTtgpdOg6Hgm1ELziJ3g

'Falcon 9 second stage apparently splashed down softly in the ocean southwest of Australia'

Ex-squeeze me, soft landed second stage?  Is this poor reporting or the biggest development since landing a first stage?
Title: Re: F9 Second Stage Reusability
Post by: rory on 06/04/2017 08:00 PM
NASA Considering Using Pre-flown SpaceX Rockets for Cargo Flights - Space.com
https://apple.news/AL8bTtgpdOg6Hgm1ELziJ3g

'Falcon 9 second stage apparently splashed down softly in the ocean southwest of Australia'

Ex-squeeze me, soft landed second stage?  Is this poor reporter or the biggest development since landing a first stage?

Poor reporting, per Chris G:

I noticed this:
Quote
After its work was done on Saturday, for example, the Falcon 9 second stage apparently splashed down softly in the ocean southwest of Australia, Hans Koenigsmann, SpaceX's vice president of build and flight reliability, said during Saturday's press conference.
in this article (http://www.space.com/37083-nasa-considers-used-spacex-rockets.html).

Anyone know if that's true, or rubbish?  I spotted at least one other factual error in the article, so the latter wouldn't surprise me.

He said it was deorbited and reentered SW of Australia.  He said nothing about it splashing down softly, which is most likely complete rubbish.  You can find links to the press conference in the CRS-11 threads.

Thanks, I sort of figured.  I missed the presser due to hosting an (unrelated) party, but figured NSF crowd would be all over it already if Hans had actually said that.

Yeah, Hans said it "deorbited and landed"... but everyone took that to mean it reentered and broke up, not that it actually landed in one piece.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 06/04/2017 08:01 PM
NASA Considering Using Pre-flown SpaceX Rockets for Cargo Flights - Space.com
https://apple.news/AL8bTtgpdOg6Hgm1ELziJ3g

'Falcon 9 second stage apparently splashed down softly in the ocean southwest of Australia'

Ex-squeeze me, soft landed second stage?  Is this poor reporter or the biggest development since landing a first stage?
I don't recall anything being said by Hans during the presser yesterday as mentioned in your link. Definitely worth checking out!
Title: Re: F9 Second Stage Reusability
Post by: TrevorMonty on 06/04/2017 09:48 PM
For US to do soft landing it would need landing engines and heatshield both should be visible.
Title: Re: F9 Second Stage Reusability
Post by: punder on 06/04/2017 10:18 PM
He just said it landed in the Pacific. Nothing about "soft."

Just like most meteorites do...   :D
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 06/04/2017 11:07 PM
For US to do soft landing it would need landing engines and heatshield both should be visible.

A incremental first step might just be control surfaces for atmospheric entry, then a heat Shield, then landing engines.

LEO missions may have margin for second stage development.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 06/04/2017 11:48 PM
For US to do soft landing it would need landing engines and heatshield both should be visible.

A incremental first step might just be control surfaces for atmospheric entry, then a heat Shield, then landing engines.

LEO missions may have margin for second stage development.

But the point is that this mission definitely didn't have a heat shield and definitely didn't do a "soft landing" as the article claims.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 06/04/2017 11:52 PM
The article is based on a misinterpretation BUT we don't actually know the full extent of SpaceX's upper stage experiments. Could include some TPS.
Title: Re: F9 Second Stage Reusability
Post by: macpacheco on 06/05/2017 03:54 AM
What kind of payload capability is expected to be left on the CRS11 mission considering its RTLS profile ?
Could that be enough to try some 2nd stage re-entry tests, if NASA had concurred ?
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 06/05/2017 01:25 PM
Reusability may work with a FH, but wouldn't the extra weight bring down the F9 capabilities too much? 
Title: Re: F9 Second Stage Reusability
Post by: TrevorMonty on 06/05/2017 02:02 PM
Reusability may work with a FH, but wouldn't the extra weight bring down the F9 capabilities too much?
I think F9 can still launch crew dragon and do RTLS with booster while recovering 2nd stage. GTO missions are probably to much but LEO broadband satellites shouldn't be problem.

Sent from my SM-G570Y using Tapatalk

Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 06/05/2017 03:33 PM
Reusability may work with a FH, but wouldn't the extra weight bring down the F9 capabilities too much?

The honest answer is that nobody here actually knows how much second-stage reusability would reduce payload to different orbits.

I believe I heard the estimate of a 50% hit from Musk years ago, but that was likely only a very rough estimate.  SpaceX probably has better estimates now, and possibly very different ideas about how to do it than they did when the 50% payload hit estimate was made.  But it's likely even SpaceX only has a rough idea and won't really know better until they actually do more work on it.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 06/05/2017 05:06 PM
Suggest you think a lot about how SX has "evolved" its LV strategy as it has achieved success, as opposed to how their original roll out was supposed to go.

Originally F1, F5/9 and F9H were supposed to reuse engines (not terrifically differently than SMART reuse), and rollout successively with increasing payload to orbit (thus no need for much beyond M1C engine performance to cover Atlas/Delta families. Then factor in increased reuse.

F1/F5/F9H didn't work out, and one didn't have any reuse. SX also found limits to operations cadence, economics of the market (numerous), and limits to "agile" development (AMOS 6). Bright lights were the degree they could refine F9 into F9R-FT successively, so they stretched it into the "lower" payload range of FH, which is still to fly.

Along the way the flexible reusable/expendable approach (and M1D improvements) has meant that they could span a greater range of missions, while still retaining an economic advantage over rivals (high commonality components). Reuse is primarily a launch frequency rate improvement, as seen with this month's BulgariaSat, incrementally phasing in reuse economics (as well as inspiring rival's Quick Launch response).

SX always goes for the "good enough" solution, then evolves it. (Which, by the way, is why they *won't* do Raptor vehicles other than BFS/BFR BTW.) They will do experiments *after* mission success.

They need F9US largely unchanged - it is key to all F9/FH missions. So how do you factor in US reuse?

You do it above the payload adapter, as a secondary payload, with its own primary payload adapter.

You could either do this incrementally or "all up". Doesn't matter. It is excess payload, just like F9 reusable architecture on an expendable launch. As long as the mission risk isn't significant, you phase in such on various missions, as part of the launch bid process. As they have always done.

The "good enough" approach.

As to reuse economics, like with the booster, the key is to recover the US in a usable form for another mission, and to then see how the economics work to factor it in to your LV strategy, where then the entire LV "evolves" and the LV family takes on different roles to serve the market.

"Good enough" requires a non dogmatic approach. Which is why other providers find it so hard to do.

Title: Re: F9 Second Stage Reusability
Post by: spacenut on 06/05/2017 06:07 PM
If SpaceX uses a lot of carbon fiber in the upgraded 2nd stage, would it not lighten the stage enough to offset some of the 50% drop in payload capability? 
Title: Re: F9 Second Stage Reusability
Post by: IRobot on 06/05/2017 06:21 PM
Then they would end up with a duplicate of tooling for first and second stage. IMO either they remake the whole F9 in carbon (unlikely) or they do nothing.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/05/2017 06:57 PM
Then they would end up with a duplicate of tooling for first and second stage. IMO either they remake the whole F9 in carbon (unlikely) or they do nothing.
That would be very much in keeping with SX's way of doing things. That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
Title: Re: F9 Second Stage Reusability
Post by: Rocket Science on 06/05/2017 07:57 PM
The article is based on a misinterpretation BUT we don't actually know the full extent of SpaceX's upper stage experiments. Could include some TPS.
That and perhaps a different entry and burn profile...
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 06/05/2017 08:47 PM
If SpaceX uses a lot of carbon fiber in the upgraded 2nd stage, would it not lighten the stage enough to offset some of the 50% drop in payload capability?

Carbon fiber isn't a magic bullet.  There are lots of costs and risks associated with changing to carbon fiber, and the upper stage already has a pretty low mass fraction.  There's a limit to how much you could improve payload by switching the main part of the stage to carbon fiber.
Title: Re: F9 Second Stage Reusability
Post by: IRobot on 06/05/2017 09:21 PM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 06/05/2017 09:58 PM
So, would they stretch the stage for more fuel for orbiting and landing, or widen the stage? 

It would be nice if they could make a metholox upper stage with an upper stage Raptor for FH and F9 to not only get reusability, but be able to land it. 
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 06/05/2017 10:18 PM
So, would they stretch the stage for more fuel for orbiting and landing, or widen the stage? 

It would be nice if they could make a metholox upper stage with an upper stage Raptor for FH and F9 to not only get reusability, but be able to land it.
This idea comes up so much it has its own thread...
https://forum.nasaspaceflight.com/index.php?topic=42861.0
Title: Re: F9 Second Stage Reusability
Post by: Lar on 06/05/2017 10:32 PM
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.

Agree. It's why they don't do turbopumps in house either. Hugely difficult to do properly and you need lots of experience... Oh, wait.

I don't think S2 will be composite, but it's not because SpaceX is unwilling to try it.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 06/05/2017 11:59 PM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/06/2017 07:41 AM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Also the landing legs?
We seem to have a disagreement.

I know ULA have a team from the PLF mfg (IIRC they are Swiss) based in the Decatur factory to make theirs but does anyone know if SX mfg in house or not?

Obviously if they do that would be a jumping off point for something as ambitious as the large ITS LOX tank but if they don't that seems like a pretty big leap.

If SX has the capability to do big CF structures in house then F9 US could be done in CF (but I don't think they will. It's another separate mfg and supply chain to maintain).

If they sub contract out then that puts their sub contractor in their critical path for every new US.

I'm sure there are mfgs who are in SX's critical path but I suspect SX have backups for all of them. If they can't deliver (or deliver on time) SX will use the alternate.

The number of mfgs that can do structures that big and that critical (large, highly stressed, cryogenic, high temperature), or are even prepared to attempt to do it, is very limited, possibly only one.   If they don't already have it I expect SX will acquire in house large CF structure capability by the time ITS goes into full scale construction.

Just found this.
https://www.reddit.com/r/spacex/comments/5ul1du
remains_of_the_its_composite_tank_in_anacortes_wa/

and this

https://www.reddit.com/r/spacex/comments/5chddp/pictures_of_the_its_lox_testing_tank_being_taken/

So does SX have an out office in Washington state or could it be Boeing, as the comments suggest?
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 06/06/2017 10:12 AM
According to info I found at reddit they were working with Janicki Industries who work with Boeing as well in the same location.
Title: Re: F9 Second Stage Reusability
Post by: francesco nicoli on 06/06/2017 11:09 AM
I apologize for my limited knowledge (I am an economist, although interested in space- not an engineer :) but I was wondering as follows:
- can the fairing be re-engineered to act as re-entry shield?
- if the above is the case, the payload loss would equal the weight of the fairing, not to be jettisoned (but, rather, kept attached somehow).

* note that I have no idea how much the fairings weight. If it's not too much, then the idea may make some sense since you won't need to bring up anything "extra" (just suffering from the fact you have to bring them up).
my (non-informed) 0.2$
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 06/06/2017 11:30 AM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Also the landing legs?
We seem to have a disagreement.

I know ULA have a team from the PLF mfg (IIRC they are Swiss) based in the Decatur factory to make theirs but does anyone know if SX mfg in house or not?

Obviously if they do that would be a jumping off point for something as ambitious as the large ITS LOX tank but if they don't that seems like a pretty big leap.

If SX has the capability to do big CF structures in house then F9 US could be done in CF (but I don't think they will. It's another separate mfg and supply chain to maintain).

If they sub contract out then that puts their sub contractor in their critical path for every new US.

I'm sure there are mfgs who are in SX's critical path but I suspect SX have backups for all of them. If they can't deliver (or deliver on time) SX will use the alternate.

The number of mfgs that can do structures that big and that critical (large, highly stressed, cryogenic, high temperature), or are even prepared to attempt to do it, is very limited, possibly only one.   If they don't already have it I expect SX will acquire in house large CF structure capability by the time ITS goes into full scale construction.

Just found this.
https://www.reddit.com/r/spacex/comments/5ul1du
remains_of_the_its_composite_tank_in_anacortes_wa/

and this

https://www.reddit.com/r/spacex/comments/5chddp/pictures_of_the_its_lox_testing_tank_being_taken/

So does SX have an out office in Washington state or could it be Boeing, as the comments suggest?
Yes, they brought the landing legs in house.

And YES they do the fairings in-house. They've released multiple pictures of it being done.
Title: Re: F9 Second Stage Reusability
Post by: IRobot on 06/06/2017 12:17 PM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Yeah, but no tanks... Even for ITS they ordered from an external provider. Doing a fairing or interstage is not that hard, compared with fuel/oxidizer tank.

You can do a fairing with a mold with the same skill level required to make a performance sailboat. Interstage and legs can be done in the same way. A fuel tank is not the same. It is not about size, but shape, pressure, valves installation and thermal considerations.
Title: Re: F9 Second Stage Reusability
Post by: spacenut on 06/06/2017 12:39 PM
Don't know if I should bring it up here, or start another thread.  But, if FH can launch Orion to orbit, could a F9 or FH launch a completely fueled second stage as payload.  Then use this to dock with the Orion and service module to send it to cis-lunar space.  Docking equipment would have to be installed on the rear of the Orion/service module and launched with FH.  Then the new 2nd stage could dock with it fully fueled.  No need for fuel transfer from a tanker 2nd stage. 

One must have some type of docking equipment to transfer fuel, why not just a complete new second stage?

How much does a fully fueled second stage weigh? 

Multiples of these dockable 2nd stages could send much larger assembled craft to the moon or Mars. 

Negatives:  A reusable tanker second stage may be cheaper in the long run.  A reusable second stage can also be refueled to land on the moon or Mars while carrying a payload.
Title: Re: F9 Second Stage Reusability
Post by: Jimmy Murdok on 06/06/2017 12:44 PM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Elon is about vertical integration when industry abuse price, they partnered with Toray for CF tanks which make a lot of sense in the same way they do with Panasonic on Tesla batteries and did with Lotus before. They might not do that big number of tanks, so if expert manufacturer of automatic composite production comes in at good price they might catch the opportunity. Avoiding to open a factory is a big save, just need an assembly space.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 06/06/2017 03:25 PM
(fan) SpaceX optimises for cost. So the buy/build decisions are driven by optimizing the trades. Not just initial cost but also delivery times, expected quality, etc.

(mod) It would be helpful if people did a bit of reading and research first, asking if SpaceX does their own fairings when multiple pics of fairing manufacturing are out there may not be the best approach, especially in a thread about second stages. Ditto the "what if they left the fairing attached" which has been discussed many times.
Title: Re: F9 Second Stage Reusability
Post by: rsdavis9 on 06/06/2017 03:39 PM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Yeah, but no tanks... Even for ITS they ordered from an external provider. Doing a fairing or interstage is not that hard, compared with fuel/oxidizer tank.

You can do a fairing with a mold with the same skill level required to make a performance sailboat. Interstage and legs can be done in the same way. A fuel tank is not the same. It is not about size, but shape, pressure, valves installation and thermal considerations.

Just like a copv. which there are 3 per upper stage? and more per booster.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/06/2017 08:53 PM
Yeah, but no tanks... Even for ITS they ordered from an external provider. Doing a fairing or interstage is not that hard, compared with fuel/oxidizer tank.

You can do a fairing with a mold with the same skill level required to make a performance sailboat. Interstage and legs can be done in the same way. A fuel tank is not the same. It is not about size, but shape, pressure, valves installation and thermal considerations.
Indeed. It's not the size, although that does not help.  :(

 The legs and the fairings can be replaced by others if they fail inspection but the tanks are the major structural element of the stage. They carry the internal weight of their contents, the weigh of any object carried on top of them, the thrust from any engine beneath them.

Unlike the legs, interstage or fairings they may have to do this over a range of maybe +400c to below LN2 temperatures for the sub cooled LOX.

That's a very tough combination of factors to get right first time.

I expect SX will be paying close attention to the recent efforts by NASA to build a "fluted core" LH2 tank with direct fiber placement with a robot arm, rather than a special purpose filament winding machine.

I don't think CF is likely for the an F9 US upgrade but I do think that by the time ITS goes into mfg the technology to do this full scale will be in house at SX. However that's a discussion for another thread.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 06/07/2017 12:17 AM
I was wondering as follows:
1) can the fairing be re-engineered to act as re-entry shield?
2)if the above is the case, the payload loss would equal the weight of the fairing, not to be jettisoned (but, rather, kept attached somehow).

Should be relocated to the Q&A thread.

First, what does the fairing/shroud do:

It is a lightweight aerostructure that protects the payload until it is out the sensible atmosphere, where it is jettisoned. Making it lightweight means total payload + US + fairing is optimized for boost stage, jettison means that the orbital stage does not have to accelerate the fairing's weight to orbit.

If you had 1), then it would have to accept reentry loads/thrusts/thermal like a capsule which would reduce the payload to orbit substantially. In 2), it would be much more than the weight of the fairing alone, because you'd have to deorbit and recover the combined vehicle. The "payload penalty" for the fairing as used is just suborbital, not the full cycle.

In the Kistler K-1 reusable LV (unfinished), it's OV is a combination US/"flip top fairing"/heat shield/landing vehicle:
(http://www.kistler.co/images/deploy02.jpg)
Had substantial penalties for reuse, where with a Atlas V class booster and a underexpanded 4x more than MVac US engine could do Falcon 9 1.0  missions, for comparison. This was considered dubious on the economics, because  of the limited capabilities meant too few missions that would have to fly too many times to recover the much higher investment used to build/test/qualify the vehicle.

(Worse, it relied on traditional aerospace vendors for its construction, which bankrupted Kistler before they could construct a single vehicle, because they applied typical overcharge for all components.) Given what we have seen with F9R, either Kistler would have required 150x the finance to endure the same test program (at a time when software/avionics were much less developed), or they would have had to do as SX did vertical integration of systems with about 1.5x the amount of capital while taking about 4-5 years longer before flight.

IMHO, the economics of partial reuse, agile development, and a non dogmatic approach made for a 10x improvement in capital reuse and reinvestment. All of which traditional aerospace (Boeing, LockMart, Orbital, ULA,...) would never do. They didn't care much for Kistler either.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 06/07/2017 03:41 AM
That said they might shift to a CF upper stage if they mfg the big ITS LOX tank in house. Otherwise that would put an outside sub contractor in the critical path for all future upper stages. Something I'm pretty sure SX is very unwilling to do.
I'm pretty sure they will not make the CF in house. CF is hugely difficult to do properly, especially big parts, high quality. You need experience, lots of it! If they want to control the process, the only way to do it is to buy the CF parts manufacturer.
Otherwise they could spend years perfecting that skill and still come short. This is not the same as machining aluminium or 3D printing superdracos. CF and other composite manufacturing is still some kind of an art.
Are you kidding?? Fairing, interstage, legs... SpaceX already does a LOT of in house CF. Fairing is much bigger than the upper stage (not that I think SpaceX will make a CF F9 2nd stage... They won't.).
Elon is about vertical integration when industry abuse price, they partnered with Toray for CF tanks which make a lot of sense in the same way they do with Panasonic on Tesla batteries and did with Lotus before. They might not do that big number of tanks, so if expert manufacturer of automatic composite production comes in at good price they might catch the opportunity. Avoiding to open a factory is a big save, just need an assembly space.
Toray makes the fiber, not the tanks (and nobody else produces CF as good as Toray... And people have tried very hard.).

$20 bucks says they'll bring composite stage production in-house.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/07/2017 06:32 AM
Toray makes the fiber, not the tanks (and nobody else produces CF as good as Toray... And people have tried very hard.).

$20 bucks says they'll bring composite stage production in-house.
No one would take the bet as, based on past experience that's exactly what SX will do once ITS is closer to going into mfg.

But wrt to this thread do you see them going for an "F9 Upper Stage 2.0" in CF?
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 06/07/2017 11:12 AM
But wrt to this thread do you see them going for an "F9 Upper Stage 2.0" in CF?

It seems very unlikely to me that the reusable upper stage "hail Mary" on the FH demo, or the operational upper stage they hope to have by the end of next year will use CF.

Longer term there are several directions SpaceX might go in:

1. Fly F9 and FH with that reusable upper stage until the end of their operational life, then replace with something different (or maybe not replace).

2. Change to use a methalox Raptor variant, with or without composite tanks, but in a conventional upper stage with separate fairing.

3. Change to use a micro-BRF ship with about 20 tonnes to LEO with all composite structure. Then replace the F9 core with a methalox core. Then replace Dragon 2 with a crew variant of the ship.

I think SpaceX will go for the last option. With refueling in LEO that gives 20 tonnes payload or a small number of crew to anywhere in the cis-Lunar space. However this probably won't happen soon, the effort they are putting into fairing recovery indicates that they expect separate fairings to be used for several more years and hundred(s) of F9 launches.

Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 06/07/2017 11:36 AM
As far as I know, the SpaceX requirements for carbon tanks (either for ITS or F9 upgrades) would make them the largest in the world.

This means no-one actually has the experience of making them, so saying they are are going to outsource to the experts, when there is actually no-one with the experience, seems odd. Of course, there are experts in similar fields, but no-one with experience of the specific process required since it's never been done before.

Which means SpaceX may need to do it in house, and learn on the job, or that they outsource to someone else who also has to learn on the job. Either way, there is still a lot of learning to do.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 06/07/2017 01:35 PM
Toray makes the fiber, not the tanks (and nobody else produces CF as good as Toray... And people have tried very hard.).

$20 bucks says they'll bring composite stage production in-house.
No one would take the bet as, based on past experience that's exactly what SX will do once ITS is closer to going into mfg.

But wrt to this thread do you see them going for an "F9 Upper Stage 2.0" in CF?

Agreed, I'd bet that they do move it in house.  Even if that means a new facility somewhere in the continental US.
Title: Re: F9 Second Stage Reusability
Post by: Patchouli on 06/07/2017 06:00 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.
Title: Re: F9 Second Stage Reusability
Post by: Lars-J on 06/07/2017 07:56 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.

More difficulty yes, but not THAT much more.
Title: Re: F9 Second Stage Reusability
Post by: IanThePineapple on 06/07/2017 08:15 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.

More difficulty yes, but not THAT much more.

It would also be pretty easy to just burn at apogee, if of course there's enough fuel left that far into the flight (also if there's enough left to land and to account for boiloff).
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 06/07/2017 08:19 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.

Not really.

A good heat shield is needed anyway for LEO re-entry, and making that heat shield slightly heavier to survive the higher velocity of re-entry from GTO is not a big deal.

And for delta-v perspective: Not much more delta-v is required. The pegiree is what matters for re-entry delta-v, and that is very low also in GTO. Just very slight burn in apogee makes the pegiree drop to low enough that atmosphere does the rest.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 06/07/2017 09:05 PM
The perigee is what matters for re-entry delta-v, and that is very low also in GTO. Just very slight burn in apogee makes the perigee drop to low enough that atmosphere does the rest.

Also critically important is where that perigee will occur, for the cost/possibility of recovery/reuse and flight frequency. Which is not so easy given orbital dynamics, for efficient GTO.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 06/07/2017 09:10 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.


Creating a third stage so that you can recover the second stage misses the point I think? The idea is to reuse everything possible (the trunk is tossed, some rings are tossed but minimize the disposables/consumables other than fluids...)
Title: Re: F9 Second Stage Reusability
Post by: Dao Angkan on 06/07/2017 10:12 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.


Creating a third stage so that you can recover the second stage misses the point I think? The idea is to reuse everything possible (the trunk is tossed, some rings are tossed but minimize the disposables/consumables other than fluids...)

How much spare mass does Dragon usually come down with? I think that some of the trunk could possibly be brought back down in Dragon (maybe solar panels?). Anyway, I think that stage 2 recovery would probably be based on their Dragon recovery expertise.
Title: Re: F9 Second Stage Reusability
Post by: DOCinCT on 06/08/2017 08:25 PM
One thing that occurred to me is a third stage would likely be necessary to be able to consider reusing the second stage on GTO missions.

LEO reentry is hard enough but a direct reentry from reentry high energy orbit would be much more difficult.


Creating a third stage so that you can recover the second stage misses the point I think? The idea is to reuse everything possible (the trunk is tossed, some rings are tossed but minimize the disposables/consumables other than fluids...)

How much spare mass does Dragon usually come down with? I think that some of the trunk could possibly be brought back down in Dragon (maybe solar panels?). Anyway, I think that stage 2 recovery would probably be based on their Dragon recovery expertise.
Maximum of 6,600 lbs, but less due to volume considerations.  Trunk is always discarded' to return the solar panels would require a space walk(s) and opening the hatch in a vacuum. 

I would think they have to decide which end to protect from heating, PAF or Merlin.
Title: Re: F9 Second Stage Reusability
Post by: KelvinZero on 06/08/2017 09:26 PM
Creating a third stage so that you can recover the second stage misses the point I think?
barely on topic note: electric third stages, and reusable tugs that stay in orbit. Obviously that is not a slam dunk. Really just saying here is a wider topic, outside this thread.
Title: Re: F9 Second Stage Reusability
Post by: mikelepage on 06/12/2017 08:34 AM
Suppose the second stage uses up all remaining RP-1 on the entry burn, killing as much velocity as possible just as it's reentering the atmosphere.

At this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1)  Also, you still have Helium in COPVs inside the LOX tank, right?

I haven't seen it suggested anywhere: I'm wondering if this excess gas would be what is used to inflate a bouncy castle/life raft/airbag, perhaps with only minor mods to the LOX pumps?  Include an extra outlet that would be used to pump that (pre-warmed) gas into an inflatable structure once the vehicle is subsonic.  That way, the only extra mass to stage 2 would be the inflatable structure itself (plus whatever drogue chute arrangement is chosen to take the craft subsonic).
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/12/2017 08:42 PM
At this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1)  Also, you still have Helium in COPVs inside the LOX tank, right?
SOP is to exhaust the heaviest propellant first, which is normally LOX, it also ensures the engine won't run LOX rich, which will normally damage the engine, unless it's been designed for it.  :(
Title: Re: F9 Second Stage Reusability
Post by: mikelepage on 06/13/2017 04:54 AM
At this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1)  Also, you still have Helium in COPVs inside the LOX tank, right?
SOP is to exhaust the heaviest propellant first, which is normally LOX, it also ensures the engine won't run LOX rich, which will normally damage the engine, unless it's been designed for it.  :(

Ah okay, that makes sense.  But don't you at least have the LOX tank full of pressurised Helium?  Could that be released in ordered to inflate some structure?
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 06/14/2017 07:40 PM
At this point, it would still have fully a pressurised LOX tank, right? (I'm assuming LOX is always in excess to RP-1)  Also, you still have Helium in COPVs inside the LOX tank, right?
SOP is to exhaust the heaviest propellant first, which is normally LOX, it also ensures the engine won't run LOX rich, which will normally damage the engine, unless it's been designed for it.  :(

Ah okay, that makes sense.  But don't you at least have the LOX tank full of pressurised Helium?  Could that be released in ordered to inflate some structure?
Well assuming the tank pressure is 2x or 3x atmospheric pressure you could use the excess to fill something provided you did not need it to resist bending and other loads (F9 is a "semi pressure stabilized structure"). The questions would be a) At this stage in the flight are the loads low enough to not need that stiffening and b)What would you fill with the "excess" Helium? and c) How would you deploy this structure?
Title: Re: F9 Second Stage Reusability
Post by: mikelepage on 06/18/2017 05:42 AM
Well assuming the tank pressure is 2x or 3x atmospheric pressure you could use the excess to fill something provided you did not need it to resist bending and other loads (F9 is a "semi pressure stabilized structure"). The questions would be a) At this stage in the flight are the loads low enough to not need that stiffening and b)What would you fill with the "excess" Helium? and c) How would you deploy this structure?

There's probably not that much "excess" gas is there?  ::) and crashing from terminal velocity (even if subsonic) would need one heck of an airbag.  If you have to perform a landing burn, the heat coming off the engine would probably destroy any inflatable.  And even if it didn't, you'll get seawater corrosion.  On second thoughts, if they're going to try it at all, I imagine it would have to be some combination of what they've already done with the F9 booster and what is planned for BFR.

Better idea (?): it should be easy enough to create a "cradle" for the second stage that could be temporarily installed on a the Vandenberg ASDS for Falcon Heavy launches from the Cape.  It would catch the second stage using the same attachments that the booster stage uses.  If you then install a pair/quartet of grid fins on any second stage where you have the margin, you could then practice cradle landings on a smaller scale.

From a bit of googling, I can see the F9 landing legs (collectively) are estimated at just under 2100kg, where as the grid fins are estimated at only 41kg each (https://www.slideshare.net/quirijnfrederix/the-application-of-grid-fins-on-missiles-and-launch-vehicles).  Even if that's off by an order of magnitude, it seems far more feasible to use grid fins on the second stage than landing legs.  A grid fin plus cradle arrangement seems like a likely "hail mary" attempt that they could perform on the Falcon heavy demo.
Title: Re: F9 Second Stage Reusability
Post by: Peter.Colin on 07/09/2017 01:27 PM
The main problem with re-using the second stage in a similar way as the first stage, is that it compromises the payload to much.
The only way I see you could really deal with this fundamentally is to re-fuel the second stage in orbit.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 07/09/2017 04:43 PM
The main problem with re-using the second stage in a similar way as the first stage, is that it compromises the payload to much.
The only way I see you could really deal with this fundamentally is to re-fuel the second stage in orbit.

Lets put numbers to that.

1. What is F9b5's payload mass to LEO?
2. How do you think does the lighter variant (heat shield and mid-air parachute recovery) weigh?

right now:
#1 on the web site is advertised as 22 tons (so that's a minimum)

For #2, we know the dry mass of S2 is <5 tons.  Let's say a recoverable S2 is +3 tons, split between heat shield, parachute, and structural reinforcements.

So you go down from 22 tons to 19 tons.

If the recovery hardware ended up doubling the weight of S2, payload would go down from 22 to 17 tons.

Remember that SpaceX can always manufacture the expendeble S2 for missions that require it.

Also, remember that LEO missions can be volume constrained, so the mass is free.

---

Things look a lot different for GEO, where the high energy means payload is in the 6-7 ton range, and so suddenly the 3 ton payload hit it very expensive, and a 5 tons hit is basically a non-starter.

---

So my conclusion is that for GEO launches, S2 reusability is not viable, but once frequent LEO launches come into play, S2 reusability on F9 is very viable.

So what will come first?  Lots of LEO launches, or F9's retirement?
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 07/11/2017 08:58 AM
The perigee is what matters for re-entry delta-v, and that is very low also in GTO. Just very slight burn in apogee makes the perigee drop to low enough that atmosphere does the rest.

Also critically important is where that perigee will occur, for the cost/possibility of recovery/reuse and flight frequency. Which is not so easy given orbital dynamics, for efficient GTO.

No need to fly the same stage 2 frequently. Use many upper stages, and wait enough orbits that pegiree is at good position at sea and park a barge there.

The pegiree will anyway be considerably southern than cape, so easiest place probably woud be at pacific, somewhere at near south coast of mexico/something like 1000-1500km south from LA. However, it would take many days for the barge to travel between port and the landing site.

"Just Read The Instructions" would normally be much less utilized than "Of Course I Still Love You" so it would get more work, and spending many days travelling betwen port and landing site would not be so bad. Though this may change when they start launching the big LEO satellite constellations to polar orbits, so they might need additional barges then.

Title: Re: F9 Second Stage Reusability
Post by: envy887 on 07/18/2017 05:33 PM
Envy. You forgot the fact that it delays the development of the next generation vehicle. You also forgot that a reusable second stage might just not work. I would think it's bad investment. But we are again on the wrong thread for this discussion and should defer to not continuing.

That's only relevant if the new vehicle reduces operating costs, and that is what I described as the " opportunity cost of the delay".

A reuse solution specific to the constellation would be worthwhile IMO, if it minimized development costs with mostly existing hardware.

Delaying the next vehicle goes against Musk's Mars goal.  He has only so many years of life to achieve his colony dream. BIG opportunity cost.
And the opportunity cost analysis does not allow for the loss of payload mass, i.e. number of satellites per launch that a Falcon class re-useable upper stage would penalize.  So the cost of Falcon class re-useability is higher than stated.

The lost payload mass could be irrelevant if F9 is volume limited and the recovery hardware takes up volume not otherwise available for payload. And there may be additional capital cost to manufacture an additional 15 upper stages per year.

Delaying the Mars vehicle is an issue. But getting the constellation up faster, cheaper, and earning more revenue for the Mars vehicle could actually accelerate its development.

Posting from here: https://forum.nasaspaceflight.com/index.php?topic=36552.msg1703515
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 07/18/2017 08:07 PM
SpaceX is going through a lot of effort to catch a bloody fairing, since it's a "pallet full of cash".

With rapid reuse of S1, S2 becomes a very large pallet of cash - the largest such pallet on the rocket.

For LEO launch, even doubling the mass of S2 is perfectly acceptable.

The constellation will require tens of identical LEO launches per year.

Why would they not bother?  Especially when this constellation is what is financing the Mars drive?

The only reason is if they think that a new vehicle will take over completely, and then why bother.  But that would be good news from my perspective...
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 07/18/2017 08:57 PM
SpaceX is going through a lot of effort to catch a bloody fairing, since it's a "pallet full of cash".

With rapid reuse of S1, S2 becomes a very large pallet of cash - the largest such pallet on the rocket.

For LEO launch, even doubling the mass of S2 is perfectly acceptable.

The constellation will require tens of identical LEO launches per year.

Why would they not bother?  Especially when this constellation is what is financing the Mars drive?

The only reason is if they think that a new vehicle will take over completely, and then why bother.  But that would be good news from my perspective...

Concur with analysis.

I think there is a better than 50/50 chance we see them attempt to develop the technology.
Title: Re: F9 Second Stage Reusability
Post by: Semmel on 07/18/2017 09:04 PM
Envy, thanks for pulling it over here, I was on mobile and couldn't do it easily (and in the time I had when posting).

Envy. You forgot the fact that it delays the development of the next generation vehicle. You also forgot that a reusable second stage might just not work. I would think it's bad investment. But we are again on the wrong thread for this discussion and should defer to not continuing.

That's only relevant if the new vehicle reduces operating costs, and that is what I described as the " opportunity cost of the delay".

A reuse solution specific to the constellation would be worthwhile IMO, if it minimized development costs with mostly existing hardware.

Ohh ok, I missed that connection. Its a very hard factor to quantify but also quite a relevant one. We simply dont have the insight to know this one way or the other.


Delaying the next vehicle goes against Musk's Mars goal.  He has only so many years of life to achieve his colony dream. BIG opportunity cost.
And the opportunity cost analysis does not allow for the loss of payload mass, i.e. number of satellites per launch that a Falcon class re-useable upper stage would penalize.  So the cost of Falcon class re-useability is higher than stated.

The lost payload mass could be irrelevant if F9 is volume limited and the recovery hardware takes up volume not otherwise available for payload. And there may be additional capital cost to manufacture an additional 15 upper stages per year.

Delaying the Mars vehicle is an issue. But getting the constellation up faster, cheaper, and earning more revenue for the Mars vehicle could actually accelerate its development.

Posting from here: https://forum.nasaspaceflight.com/index.php?topic=36552.msg1703515

SpaceX is going through a lot of effort to catch a bloody fairing, since it's a "pallet full of cash".

With rapid reuse of S1, S2 becomes a very large pallet of cash - the largest such pallet on the rocket.

For LEO launch, even doubling the mass of S2 is perfectly acceptable.

The constellation will require tens of identical LEO launches per year.

Why would they not bother?  Especially when this constellation is what is financing the Mars drive?

The only reason is if they think that a new vehicle will take over completely, and then why bother.  But that would be good news from my perspective...

To both of you (which issue basically the same argument):
Delaying the (subscale) BFR/BFS is a very strong argument against any more tinkering on F9. Shotwell said on many occasions that the team, working on F9, FH and D2 are going to work on BFR once their current work is done. They are clearly manpower limited as well as cash limited. I think, without the development of BFR looming, your arguments are perfectly sensible and would make a good argument for evolving F9 to be fully reusable. With BFR though, I think its not worth doing.

The reason is, that (subscale) BFR/BFS might launch in 4 years. Lets say that tinkering with F9 brings it up to 5 years, thats one year of full steam operation of F9 (and arguably, around 100 launches per year) that are on F9 instead of (subscale) BFR. Even if in these 4 years, F9 becomes fully reusable for LEO missions, that is still a very substantial number of launches that are not reusable.

Also, S2 will not be reusable the instant they try the development. Like on S1, it may take a year or two to get right. So you have to expend quite a lot of S2s anyway. And with the added delay to BFR/BFS, this becomes not worthwile very fast.

Does a reusable S2 accelerate the deployment of the constellation? I dont think so. F9 will more likely be launch pad limited instead of production limited once the production of S1 is reduced in favour of S2. The cadence on A39 shows that the 2 weeks turnaround is required for satellite processing. To get something like 50 launches a year, things have to move towards more parallel processing of payloads. There is also the range that can not support that many launches at moment. There are many many things that need to change in order to get the launch cadence for the constellation and I fear that the least of the problem is the production of S2 (non-reusable).

It seems that a larger vehicle, that can launch more sats at once is advantageous to many smaller launches on more than just launch cost kind of ways. It can also cope much better with weather delays and technical delays.

Title: Re: F9 Second Stage Reusability
Post by: dante2308 on 07/19/2017 07:24 AM
With BFR though, I think its not worth doing.

The reason is, that (subscale) BFR/BFS might launch in 4 years. Lets say that tinkering with F9 brings it up to 5 years, thats one year of full steam operation of F9 (and arguably, around 100 launches per year) that are on F9 instead of (subscale) BFR. Even if in these 4 years, F9 becomes fully reusable for LEO missions, that is still a very substantial number of launches that are not reusable.

Also, S2 will not be reusable the instant they try the development. Like on S1, it may take a year or two to get right. So you have to expend quite a lot of S2s anyway. And with the added delay to BFR/BFS, this becomes not worthwile very fast.

Does a reusable S2 accelerate the deployment of the constellation? I dont think so. F9 will more likely be launch pad limited instead of production limited once the production of S1 is reduced in favour of S2. The cadence on A39 shows that the 2 weeks turnaround is required for satellite processing. To get something like 50 launches a year, things have to move towards more parallel processing of payloads. There is also the range that can not support that many launches at moment. There are many many things that need to change in order to get the launch cadence for the constellation and I fear that the least of the problem is the production of S2 (non-reusable).

It seems that a larger vehicle, that can launch more sats at once is advantageous to many smaller launches on more than just launch cost kind of ways. It can also cope much better with weather delays and technical delays.

Considering that a super-heavy lift spacecraft is a monumental financial and engineering effort predicated on a primary market that does not exist (trips to mars and/or dozens of commercial satellites a month), any delay in that program is disappointing, but perhaps even advisable. An incremental program to prove out a fully reusable architecture on the F9 is fairly sensible, and as meekGee pointed out, potentially economical below GTO. I'd hate to see SpaceX attempt to iterate on a multi-hundred million dollar space dreadnought based only on simulations and fever dreams. They likely don't even have enough revenue to build and launch even one BFR so it isn't clear when it will ever pay for itself.

Secondly, SpaceX's plans are for most of their flights to be to MEO for their own internet constellation. Whatever the infrastructure requirements, they are filing that they intend to put up 1.7 million kg and over 1600 sats up in space over 6 years. We can take that as evidence that they plan to process satellites in parallel. That they need to solve an infrastructure problem doesn't mean that a reusable second stage doesn't help. Those two things are mostly independent. Either way, they will need to be launching hundreds of satellites per year long before BFR gets a static fire and the economics of the BFR are also based on a high flight rate.
Title: Re: F9 Second Stage Reusability
Post by: oldAtlas_Eguy on 07/19/2017 02:55 PM
If SpaceX eliminates the HotFire test on the pad, then the recent demonstration on LC39A is that the minimum turnaround for a pad is 6 days. Ops(Launch) to Ops(HotFire). That makes the launch rate from a single pad with used boosters 1 per week. With 4 pads the max launch rate for the pads recently demonstrated for F9 is a total of 200+/yr. I do not think there will be a limitation because of pads but a limitation because of range scheduling.
Title: Re: F9 Second Stage Reusability
Post by: IanThePineapple on 07/19/2017 02:58 PM
...but a limitation because of range scheduling.

I REALLY hope that the range is updating their system to make it faster to book and have more opportunities during the outage
Title: Re: F9 Second Stage Reusability
Post by: oldAtlas_Eguy on 07/19/2017 04:03 PM
...but a limitation because of range scheduling.

I REALLY hope that the range is updating their system to make it faster to book and have more opportunities during the outage
The key for a fully reusable vehicle is that the limitation is a "soft" one not a "hard" system design (this includes the pads refurbishment requirements between launches and vehicle logistics getting it ready with a payload to launch). The other limitation which is addressed by full reusability is lack of hardware as in US. Without full reusability it will be difficult to do more than 70 per year without greatly expanding the manufacturing infrastructure (this includes plant floor space).
Title: Re: F9 Second Stage Reusability
Post by: deruch on 07/22/2017 08:19 AM
If SpaceX eliminates the HotFire test on the pad, then the recent demonstration on LC39A is that the minimum turnaround for a pad is 6 days. Ops(Launch) to Ops(HotFire). That makes the launch rate from a single pad with used boosters 1 per week. With 4 pads the max launch rate for the pads recently demonstrated for F9 is a total of 200+/yr. I do not think there will be a limitation because of pads but a limitation because of range scheduling.

That assumes that all 4 pads are equally able to support such a sustained, fast turnaround pace.  Based on current designs, this doesn't appear to be so.  IMO, LC-39A is the only pad currently run by SpaceX that is so able, though Boca Chica is likely to as well.  Mostly, this is based on T/E and water suppression system capabilities.  But, also the HIF at LC-39A being wide enough to support fully parallelized integration flows.  Of course, should SpaceX actually run into their launch rate limits, they'll just upgrade those elements that they can/need.
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 07/22/2017 10:01 AM
We know that they have decided to upgrade LC-40 with the same type of TEL as used on LC-39A, except not FH capable. I think the HIF at LC-40 can house 2 cores. Also cores will come largely flight ready from the service facility. Second stages can be prepared elsewhere. So it would be mostly integration at the pad. The calculated 50 a year are likely in reality no more than 35, given a lot of external influences. Less on LC-39A with a lot of government launches. They could still exceed 100/year assuming a sufficiently staffed pad crew.
Title: Re: F9 Second Stage Reusability
Post by: douglas100 on 07/25/2017 03:51 PM
We know that they have decided to upgrade LC-40 with the same type of TEL as used on LC-39A, except not FH capable...

That would be desirable especially if the strongback had throw back to reduce blast damage. But do we actually know this?
Title: Re: F9 Second Stage Reusability
Post by: guckyfan on 07/25/2017 05:53 PM
We know that they have decided to upgrade LC-40 with the same type of TEL as used on LC-39A, except not FH capable...

That would be desirable especially if the strongback had throw back to reduce blast damage. But do we actually know this?

Sorry I have no link. But I am positive it was mentioned in one of the threads.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 08/28/2017 07:44 AM
The key for a fully reusable vehicle is that the limitation is a "soft" one not a "hard" system design (this includes the pads refurbishment requirements between launches and vehicle logistics getting it ready with a payload to launch).
Indeed. The lessons of "single digit hour" swapping of dies on car production lines should inspire everyone in this subject.  It was less what could be done, than what people thought could be done. Once they had an incentive to try, things started to change. Not overnight, but eventually across the whole industry. Thanks to Jon Goff for that (very salient) example.

Quote from: oldAtlas_Eguy
The other limitation which is addressed by full reusability is lack of hardware as in US. Without full reusability it will be difficult to do more than 70 per year without greatly expanding the manufacturing infrastructure (this includes plant floor space).
Excellent point. While US's remain expendable that's really a hard limit, unless SX is prepared for step change in building out their factory (assuming they have space available, otherwise "acquire new factory space" becomes another line item.  :(  )

I like to recall that Shotwells background is in the mass car market, where 400 engines a year is not a record, it's a production failure that needs fixing.  :(
Title: Re: F9 Second Stage Reusability
Post by: Hotblack Desiato on 12/23/2017 09:05 AM
Just as a fun idea...

It's still somewhat unknown what SX wants to do with the FH demo launch (yes, a Tesla Roadster to Mars...). There have been somewhat cryptic tweets from Musk about second stage recovery, well discussed in this thread.

If SX wanted to hide a test of the second stage recovery hardware, they'd need a launch of a F9 rocket in expendable mode, so there is enough margin to carry the extra mass of the second stage. Just like the Iridium-4 launch yesterday.

Of course, it would be useless for F9, since they'd have to decide whether they should discard the first or the the second stage, and could only be done for the block III first stage in a reflight (as they'd get retired after that anyways). But there is Falcon Heavy around the corner.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 12/23/2017 01:57 PM
We know that they have decided to upgrade LC-40 with the same type of TEL as used on LC-39A, except not FH capable...

That would be desirable especially if the strongback had throw back to reduce blast damage. But do we actually know this?

Sorry I have no link. But I am positive it was mentioned in one of the threads.

We know it's true now.

The other limitation which is addressed by full reusability is lack of hardware as in US. Without full reusability it will be difficult to do more than 70 per year without greatly expanding the manufacturing infrastructure (this includes plant floor space).
Excellent point. While US's remain expendable that's really a hard limit, unless SX is prepared for step change in building out their factory (assuming they have space available, otherwise "acquire new factory space" becomes another line item.  :(  )

I like to recall that Shotwells background is in the mass car market, where 400 engines a year is not a record, it's a production failure that needs fixing.  :(

S2 is smaller than S1. It is not clear to me that more floor space is required, just some reorg. As the number of S1s built goes down, the number of S2 should be able to go up by far more than 1:1...
Title: Re: F9 Second Stage Reusability
Post by: Cheapchips on 01/04/2018 09:37 AM

Once the BFR chomper is flying you could use a single BFR launch to recover multiple Falcon S2's.  Park the S2's in a common orbit and collect them in a batches of three.  I think that fits.  It's certainly within the return weight limits.

It would save money against the projected BFR launch cost if they were reused.

Quite why you'd be flying the Falcon at that point I'm not sure.  I like the perverse nature of it though.  :)

Title: Re: F9 Second Stage Reusability
Post by: oldAtlas_Eguy on 01/04/2018 04:04 PM
We know that they have decided to upgrade LC-40 with the same type of TEL as used on LC-39A, except not FH capable...

That would be desirable especially if the strongback had throw back to reduce blast damage. But do we actually know this?

Sorry I have no link. But I am positive it was mentioned in one of the threads.

We know it's true now.

The other limitation which is addressed by full reusability is lack of hardware as in US. Without full reusability it will be difficult to do more than 70 per year without greatly expanding the manufacturing infrastructure (this includes plant floor space).
Excellent point. While US's remain expendable that's really a hard limit, unless SX is prepared for step change in building out their factory (assuming they have space available, otherwise "acquire new factory space" becomes another line item.  :(  )

I like to recall that Shotwells background is in the mass car market, where 400 engines a year is not a record, it's a production failure that needs fixing.  :(

S2 is smaller than S1. It is not clear to me that more floor space is required, just some reorg. As the number of S1s built goes down, the number of S2 should be able to go up by far more than 1:1...
As a BTW note:
The 70 flights per year assumes the following conditions:
10 total flights per booster
max production of 20 S2 and 20 S1
ratio of 4 S2 for every S1 not built
and 6 FH flights (these cause the used booster flights to increase without requiring additional S2s
=68 flights total

If you could reuse the S2 just once for a total of 2 flights per every S2 and fly each booster 20 times then the total flights possible exactly double to 136. But even if the booster flights is 10 times each the flights could be 100 with 12 FH flights.

So unless the production line increases capability or the S2 is able to be reused the ability to reach above 100 flights per year with F9/FH is not possible.
This points out just how limiting non-fully reusability is hampering flight rate.

Added:
The perspective of using the same manufacturing resource (manpower) as currently on F9 for BFR/BFS where each BFR and BFS flies each 20 times and the manufacturing resource is able to manufacture almost 7 of each per year then the flight rate of BFR/BFS could be as high as 140.

This points further to it not being cost effective to pursue S2 reusability but to hasten the operational status of the next gen system BFR/BFS.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 01/04/2018 05:39 PM

Once the BFR chomper is flying you could use a single BFR launch to recover multiple Falcon S2's.  Park the S2's in a common orbit and collect them in a batches of three.  I think that fits.  It's certainly within the return weight limits.

It would save money against the projected BFR launch cost if they were reused.

Quite why you'd be flying the Falcon at that point I'm not sure.  I like the perverse nature of it though.  :)
F9 second stage fits into the BFS door.
The only situation I can see this being meaningful is if BFR is delayed to the point that BFS testing stalls, and BFS can't quite do SSTO with recovery. Unlikely.
Title: Re: F9 Second Stage Reusability
Post by: crandles57 on 01/24/2018 10:38 PM
Was there some news that there would be no reuse of any recovered second stage it was just about informing design of BFR? If so, anyone got a link?

Oh think I found it
https://www.teslarati.com/spacex-will-attempt-falcon-9-upper-stage-landings-2018-says-shotwell/

Quote
Shotwell clarified that SpaceX would not attempt to reuse Falcon 9’s upper stage, even if recovery efforts succeed.
Title: Re: F9 Second Stage Reusability
Post by: Dave G on 01/28/2018 02:27 PM
Was there some news that there would be no reuse of any recovered second stage it was just about informing design of BFR? If so, anyone got a link?

Also here: https://www.flickr.com/photos/jurvetson/37659376821
Quote from: Fireside Chat with Gwynne Shotwell, Oct 11, 2017
The second stage is not designed for reuse on the Falcon 9 or the Falcon Heavy. However, we do want to bring it back slowly. Currently, it reenters but too hot. On missions with extra propellant, we want to bring it back to see how it behaves, not to recover or reuse. This data will be very valuable.

In addition, recent information coming from SpaceX confirms that they soon plan to stop all new development on F9/FH and concentrate on developing BFR.  The most recent instance of this is here (https://forums.teslarati.com/threads/spacex-talks-moon-mission-as-strategic-stepping-stone-for-mars-colony.5739/#post-12006):
Quote
Josh Brost, Senior Director of SpaceX’s Government Business Development was in attendance at a civil spaceflight conference in Washington D.C. yesterday, January 18, and provided a number of interesting details about SpaceX’s upcoming activities in 2018...

While Brost did not specifically provide any sort of timeline for BFR, aside from a brief statement on its readiness in “a few years,” he did describe in some detail the imminent end of serious Falcon 9 upgrades.

(see tweet image below)

This is arguably the most exciting tidbit provided to us by SpaceX. While it was undeniably vague and rather less than crystal-clear, it can be interpreted as something like this: once Block 5 has been introduced and begun to fly and refly both regularly and successfully, the vast majority of SpaceX’s launch vehicle development expertise will begin to focus intensely on the development and testing of BFR and BFS.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 01/29/2018 04:50 AM
This is consistent with all of their recent messaging.

With BFR/S on the front burner, F9US reusability has very little value.

Right now, SpaceX is capturing the bulk of the launch market, and at a revolutionary cost point (for themselves).

So while everyone else will be stumbling over themselves to reduce margin and still be able to capture some launches, SpaceX will run with very high margins, and dedicated the profit to BFS development - why waste them on a short-lives system?

Title: Re: F9 Second Stage Reusability
Post by: TrevorMonty on 01/29/2018 07:36 AM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.

Title: Re: F9 Second Stage Reusability
Post by: hkultala on 01/29/2018 08:29 AM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.

Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.


Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 01/29/2018 09:13 AM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.

But clearly not important enough for SpaceX to actually do it.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 01/29/2018 10:12 AM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 01/29/2018 10:36 AM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 01/29/2018 12:01 PM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.
Title: Re: F9 Second Stage Reusability
Post by: TrevorMonty on 01/29/2018 01:45 PM
I should of said recoverable not reuseable, as Shotwell stated they don't plan to refly recovered US. Most missions will use current expendable US, only fly recoverable US where mission performance margins can support it.

 While knowledge from capsules and shuttle can be applied to BFS US design, they are still totally different aeroshapes.
The only way to get BFS US design close to right first time is to fly subscale version.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 01/29/2018 01:52 PM
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 01/29/2018 02:22 PM
While knowledge from capsules and shuttle can be applied to BFS US design, they are still totally different aeroshapes.
The only way to get BFS US design close to right first time is to fly subscale version.

F9 upper stage is ALSO totally different aeroshape than BFS.

Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 01/29/2018 02:40 PM
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 01/29/2018 04:39 PM
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.

You are assuming that developing second stage reusability for Falcon will reduce their costs -- enough to justify the development effort.  They are developing recoverable fairings because this reduces their costs (<$5M/launch) and/or streamlines operations.  They are also working toward 24hr turn-around of flown cores.  At this level of granularity, it is easy to see that these activities are more cost-effective lines of development than reusable second stages.

They are soon going to be their own largest customer with Starlink launches... launch costs must already have their full attention, and they seem to be passing on second stage reuse for Falcon.
Title: Re: F9 Second Stage Reusability
Post by: aero on 01/29/2018 04:54 PM
Has anyone here on NSF calculated how many tons of propellant would be needed to do the burns for recovery/landing of stage 2 if it were done similarly to the stage 1 recovery?

Of course, the propellant isn't the only extra mass that would be needed, maybe not even the most significant mass because the stage would most likely need to be strengthened, legs and grid fins attached, a landing engine, etc.

My point is that the extra mass would eat up the second stage payload. Could it even be done that way using all of the mass available now for payload? Add heat shield mass, too.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 01/29/2018 05:22 PM
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.

You are assuming that developing second stage reusability for Falcon will reduce their costs -- enough to justify the development effort.  They are developing recoverable fairings because this reduces their costs (<$5M/launch) and/or streamlines operations.  They are also working toward 24hr turn-around of flown cores.  At this level of granularity, it is easy to see that these activities are more cost-effective lines of development than reusable second stages.

They are soon going to be their own largest customer with Starlink launches... launch costs must already have their full attention, and they seem to be passing on second stage reuse for Falcon.

No, I'm not assuming that or anything else.  I'm not arguing SpaceX will or won't do second-stage re-use, or that it would or wouldn't be financially beneficial for them to do so.

You gave lack of competition as a reason for SpaceX not to work on second-stage reuse.  I merely pointed out that lack of competition doesn't mean there can't be economic reasons for them to work on second-stage reuse.

Maybe the economics of it doesn't favor second-stage reuse.  Maybe there are 100 other reasons not to do second-stage reuse.  All of that is irrelevant to my point, which is just that saying there isn't competition isn't really a good argument against them doing second-stage reuse.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 01/29/2018 08:08 PM
I get what you are saying.  Just think that if they thought there would be significant cost reduction -- for instance, better than recovering fairings for a few million savings per flight -- then they'd be doing it because of their need for lots of flights (and profits, too).

The lack of competition just indicates that they won't grow their launch manifest, and the minimal potential cost reduction -- again bounded by the fairing recovery $$$ -- will be insufficient to stretch the market elasticity.

They are at point of diminishing returns on Falcon and are doing just what you are proposing by building BFR/BFS.
Title: Re: F9 Second Stage Reusability
Post by: JamesH65 on 01/30/2018 12:06 PM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.

Mass, speed, and air drag. US has a limited up mass, it's travelling very fast, often in the wrong direction, it needs to slow down before it hits atmosphere or it will burn up, it need fairly heavy landing gear. All these combined mean it's very difficult to get everything you need in the US to do a return, and still have enough left over mass to actually launch anything. It's not really big enough.

Those ones.

I'm not saying it's impossible, just very difficult to make it worth doing.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 01/30/2018 01:35 PM
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.

Mass, speed, and air drag. US has a limited up mass, it's travelling very fast, often in the wrong direction, it needs to slow down before it hits atmosphere or it will burn up, it need fairly heavy landing gear. All these combined mean it's very difficult to get everything you need in the US to do a return, and still have enough left over mass to actually launch anything. It's not really big enough.

Those ones.

I'm not saying it's impossible, just very difficult to make it worth doing.
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 01/30/2018 03:39 PM
The only way to get BFS US design close to right first time is to fly subscale version.

{{Citation needed}}
Title: Re: F9 Second Stage Reusability
Post by: GWH on 01/30/2018 04:10 PM
Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.

What shuttle proved that reuse of a re-entry vehicle is possible. Shuttle did not prove out the economics of said reuse, in fact it proved out the dis-economies of reuse.

The value in that wouldn't be finding out if its possible, but if it can be done cheaply an routinely. Because just like reuse of the lower stage if you can't do the latter than the former is worthless.  Again, see the space shuttle.

Title: Re: F9 Second Stage Reusability
Post by: freddo411 on 01/30/2018 04:42 PM
Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.

What shuttle proved that reuse of a re-entry vehicle is possible. Shuttle did not prove out the economics of said reuse, in fact it proved out the dis-economies of reuse.


If you are going to claim that the Shuttle orbiter "proved out the dis-economies of reuse" -- FOR ANOTHER DESIGN --, you are going to have to provide a more detailed argument showing the staffing going into the refurb between flights, and what exactly they were spending their time on.   

Note that anytime spent on the SSME isn't a relevant example any longer, because SpaceX (and others) have demonstrated that flight-proven engines can refly with economical levels of refurbishment.

I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.
Title: Re: F9 Second Stage Reusability
Post by: GWH on 01/30/2018 05:25 PM
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights.

In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?

There are certainly ways to this through R&D, actually trying it being one of them. Dragon, while a source of data, does have the benefit of keeping its relatively small primary heat shield being protected for most of it's flight.

Title: Re: F9 Second Stage Reusability
Post by: deruch on 01/30/2018 09:27 PM
US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.

I'm curious what the 1:5 ratio you mentioned is based on?  I thought it was pretty clear that for adding recovery mass to the upper stage, it went 1:1 with payload.  Actually, it may be even a tiny bit worse than that because there is also a minor effect on first stage performance as well.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 01/30/2018 09:48 PM
US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.

I'm curious what the 1:5 ratio you mentioned is based on?  I thought it was pretty clear that for adding recovery mass to the upper stage, it went 1:1 with payload.  Actually, it may be even a tiny bit worse than that because there is also a minor effect on first stage performance as well.
No, not that ratio.  The penalty is 1:1 of course.

But an US that masses 4 tons will put a 20 ton payload in LEO.

So if the US mass goes 2x to 8 tons, payload goes down to 16 tons.

Which is a perfectly fine capability.

And if you really need 20, use an expendable US. (Which you need for GTO anyway)

.. and 2x is a very conservative assumption for heat shield and parachutes.



Title: Re: F9 Second Stage Reusability
Post by: freddo411 on 01/31/2018 04:20 PM
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights.

In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?



It is an unproven assertion so far.   

SpaceX has quite a track record at this point of taking previously difficult, expensive and time consuming tasks (rocket engine refurb, capsule heat shield construction) and re-engineering them into reliable, inexpensive solutions.   I suspect that this is the case because they actually set out to make things into reliable, inexpensive solutions.

We'll just have to wait and see how difficult this ends up being for the TPS on BFS. 
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 02/01/2018 01:01 AM
I wouldn't put it past SpaceX to throw some TPS and a parachute on a 2nd stage for a Falcon 9 launch with a particularly light LEO payload.

SpaceX is king of "we're probably not going to do this thing" then "well, we changed our minds."
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 02/01/2018 11:46 AM
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights.

In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?



It is an unproven assertion so far.   

SpaceX has quite a track record at this point of taking previously difficult, expensive and time consuming tasks (rocket engine refurb, capsule heat shield construction) and re-engineering them into reliable, inexpensive solutions.   I suspect that this is the case because they actually set out to make things into reliable, inexpensive solutions.

We'll just have to wait and see how difficult this ends up being for the TPS on BFS.
Dragon is a good analogy actually..  same diameter, similar mass, a little shorter...  S2 has avionics...

Will require moving the cg and center of drag, adding heat shield, maybe dropping the large nozzle.

None of these are against the laws of physics or even of common sense engineering.

It's just that there are finite engineering resources, and BFS is front burner now.
Title: Re: F9 Second Stage Reusability
Post by: hplan on 02/24/2018 06:22 PM
I wouldn't put it past SpaceX to throw some TPS and a parachute on a 2nd stage for a Falcon 9 launch with a particularly light LEO payload.

SpaceX is king of "we're probably not going to do this thing" then "well, we changed our minds."

Elon seems to be talking about contingency plans in case the BFR takes longer to develop than planned--for example, a bigger fairing.

Let's say it takes 5 more years before BFR is flying commercial payloads. With 50 StarLink launches per year that could be 200 launches before BFR is flying.

That's 200 upper stages -- possibly $2 billion worth.

I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 02/24/2018 06:58 PM
I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.

They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.

How much you believe that is another question.
It can also recover F? second stages from LEO.

This could bring forward reusability by a year or two over a 'pure' BFR+BFS mature system.

There is also the interesting question of how much you believe now the second stage cost derived from the old statement of 'x% of the cost of the stage is saved with reuse'.

Especially in the case where manufacture of the first stage, sharing at least some of the equipment is at least reducing in cadence due to wholesale reuse, it's a mature technology largely.

Has there been any concrete recent statement about second stage costs?
Is it possible they've dropped from 40%  to 20 or lower?

That would drastically change the economics of actually bothering at all.

Title: Re: F9 Second Stage Reusability
Post by: Elmar Moelzer on 02/26/2018 05:12 AM
Has there been any concrete recent statement about second stage costs?
Is it possible they've dropped from 40%  to 20 or lower?

That would drastically change the economics of actually bothering at all.
This is something I have been wondering about. If S2 and Merlin Vac were originally designed for reuse with all the margins and bells and whistles that come with that. How much could the cost of the second stage be reduced if they decide to completely drop (or shelf) the reuse idea for S2?
Might be able to shave off a little bit of dry weight too...
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 02/26/2018 10:11 AM
I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.

They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.

There are practically about six classes of payload destination:

1) GTO/GEO
2) GPS (12h orbit)
3) Polar Orbits/SSO
4) ISS
5) BEO (interplanetary probes etc)
6) Just anything to be able to say that "we are in space" and stay there for two weeks.

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 02/26/2018 02:56 PM
They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.
<snip>

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.
"Both of these satellites will be deployed in one mission aboard a SpaceX Falcon-9 v1.2 launch vehicle into an orbital plane of 514 km circular at 97.44 degrees inclination. After insertion, the satellite orbits will be raised to the desired mission altitude of 1125 km circular. ".

They have at least some manoeuvring capability. Having the capability to fit somewhat larger tanks to raise from 200km seems wholly plausible, or for very small inclination trims.

SSTO capacity depends on the details of course, BFR/S can sort of manage if large parts of the architecture wholly fail. BFS, everything has to work.

 
Quote
Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload
(Elon - Reddit).

If you take various assumptions that seem plausible, you get answers from 10-40 tons or so to SSTO.
The latter is almost certainly wrong - but note for example that the mass for BFS given at IAC was 85 tons, with massive passenger windows, and in principle removing those and leaving an empty shell may be lighter, so who knows.


The raw numbers for payload are uncertain, but the most basic calculations indicate it can get several Starlink to orbit, and allow them to do interesting things they need to practice for BFS anyway - orbital fuel transfer, ...

Paying for your launch vehicles testing with actual operational uses seems a very Elon thing to do.

As to 28 degrees - well, there is 25 degrees as well - for Texas, or 9 if they go back to Omelek.

It can't do large inclination changes, direct launch to circular (even 1100km) orbit, ...
But can it launch a large subset of Starlink sats, perhaps most if you make different assumptions (that a couple of refuellings are OK, doubling the prop on the sats  ...) - perhaps.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 02/26/2018 04:10 PM
They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.
<snip>

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.
"Both of these satellites will be deployed in one mission aboard a SpaceX Falcon-9 v1.2 launch vehicle into an orbital plane of 514 km circular at 97.44 degrees inclination. After insertion, the satellite orbits will be raised to the desired mission altitude of 1125 km circular. ".

They have at least some manoeuvring capability. Having the capability to fit somewhat larger tanks to raise from 200km seems wholly plausible, or for very small inclination trims.

SSTO capacity depends on the details of course, BFR/S can sort of manage if large parts of the architecture wholly fail. BFS, everything has to work.

 
Quote
Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload
(Elon - Reddit).

If you take various assumptions that seem plausible, you get answers from 10-40 tons or so to SSTO.
The latter is almost certainly wrong - but note for example that the mass for BFS given at IAC was 85 tons, with massive passenger windows, and in principle removing those and leaving an empty shell may be lighter, so who knows.


The raw numbers for payload are uncertain, but the most basic calculations indicate it can get several Starlink to orbit, and allow them to do interesting things they need to practice for BFS anyway - orbital fuel transfer, ...

Paying for your launch vehicles testing with actual operational uses seems a very Elon thing to do.

As to 28 degrees - well, there is 25 degrees as well - for Texas, or 9 if they go back to Omelek.

It can't do large inclination changes, direct launch to circular (even 1100km) orbit, ...
But can it launch a large subset of Starlink sats, perhaps most if you make different assumptions (that a couple of refuellings are OK, doubling the prop on the sats  ...) - perhaps.

Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 02/26/2018 04:34 PM
Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.

Quite.
The 'several hundred' was based on the assumption of one launch site, no capacity to launch to much more than a couple of planes and no large additional fuel on the satellites - basically the absolute worst case. (if it actually can do SSTO with several Starlink sats).
If you've got a spare 10 tons to your optimal launch inclination, you can pretty much launch to any inclination.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 03/03/2018 03:41 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 03/03/2018 04:04 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Starlink satellites can be launched just fine out of the 3.6*3.6m door, and even once BFR is up and running, a very simple turtable will launch a plane a time or so in a very low stress mission with plenty of margin - ideal for development.

BFS+BFRs payload is just too big, and the flight rate is just too high to make a new vehicle make sense, even for Starlink.

(more than about half full - 70 tons - 140 satellites - and you start running into plane change issues on the satellites).

Things may differ if there are many large payloads that won't go out the 3.6*3.6m door.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 03/03/2018 05:15 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Operationally, yes, but financially? BFR's bread is buttered by Starlink's revenues.

Quote
BFS+BFRs payload is just too big, and the flight rate is just too high to make a new vehicle make sense, even for Starlink.

New vehicle? No, but definitely a variation. SpaceX has shown a willingness to experiment and iterate, to opportunistically defer significant projects (FH) in order to obtain more immediate advantages (F9 booster return).

I'm betting that behavior won't change, especially as SpaceX attempts to juggle operational optimization of its existing LVs, construction and deployment of its cash cow, and development of a highly experimental new LV. In the execution of these three we will certainly witness several pivots of varying size and degree (e.g. ITS -> BFR).

I thought you made a strong case for SSTO operation above. If it offers a more economical means to Starlink deployment – and with deployment/replenishment an ongoing need – there's little doubt SpaceX would customize the vehicle for said operation. The chomper variant already demonstrates this willingness.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 03/03/2018 05:43 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Operationally, yes, but financially? BFR's bread is buttered by Starlink's revenues.

By 'new vehicle' - I don't mean a new design of vehicle, I mean that in many cases, a specific BFS may be able to launch the complete Starlink fleet without any additional vehicles being built at all, as especially with BFR, once you've got a plane up at a time, there is little incentive to try for two planes, if in fact you can do rapid reusability.

Making a plane a week of satellites is quite taxing enough.

The savings from making a new BFS-SSTO specifically designed for satellite launching are small, as pretty much any case where this makes sense is diluted if it slows you at all from getting BFR up and running.

Also if it slows you from getting rapid reuse operationally working well for BFS.

Working out cadence on a 'small' launcher like BFS which doesn't have to be stacked, and does not require great infrastructure to launch it could be really valuable insights into designing the launch infrastructure for BFR.
Title: Re: F9 Second Stage Reusability
Post by: Lar on 03/03/2018 11:09 PM
(fan) I could see some equipment in the cargo bay (a turntable dispenser with racks that ratchet each satellite to where it needs to be to be pushed out the cargo door, one after the other, as Speedevil alludes to) but not a new mold line. Not at first. I've said this before and will again, once the basic BFS system is up and running, THEN there may  be variants, but first, no.

(mod) what does this have to do with F9 Second Stage Reusability ?
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 03/04/2018 04:28 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield. Two stage to orbit, if you have capability for extremely rapid integration, is too good to pass up.
Title: Re: F9 Second Stage Reusability
Post by: dglow on 03/05/2018 07:29 AM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 03/05/2018 03:50 PM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 03/05/2018 04:11 PM
[offtopic]


Quote from: speedevil
Quote from: hkultala
of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.

Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.

Starlink has a polar/very high inclination orbit. Polar orbit needs about 400 m/s more than low inclination due not getting the starting velocity from earth rotation.

Definetely not reachable with BFS as SSTO, at least with landing fuel.

Even a low inclination LEO should probably not be reachable with any reasonable payload and landing fuel, reachable only without landing fuel with very small payload.

[/offtopic]
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 03/05/2018 05:20 PM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?
Also because you're not taking very large tanks to very high velocities.

Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.

ABCD: Always Be Counting Down

Title: Re: F9 Second Stage Reusability
Post by: Kansan52 on 03/05/2018 05:43 PM
A recoverable 2nd stage would eat up payload mass. But would Starlink close the business plan? A reusable 2nd stage that put up only 1/2 the number of Starlink sats but could be reused over and over again. It would also have the advantage of easing pressure on the manufacturing line.

Of course if BFR/BFS is not ready in time.

I know they have said no a number of times but they do pivot when the situation presents an opportunity.
Title: Re: F9 Second Stage Reusability
Post by: Negan on 03/05/2018 06:53 PM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.
Title: Re: F9 Second Stage Reusability
Post by: uhuznaa on 03/05/2018 07:40 PM
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.

It would probably be wise to see the projected dry mass and payload capabilities of BFR/BFS (including the theoretical SSTO capability) as the end result AFTER several iterations, with the first "block" having considerably less payload than that. Just as SpaceX didn't build the reusable F9 FT Block 5 right after the Falcon 1 they probably will be happy if the first BFR/BFS will make it to orbit and back undamaged with a very small payload and allows them to look over it to improve the next one they will build.

If there will be a BFS that can do SSTO it might be the third, fourth or fifth iteration but certainly not the first.

Title: Re: F9 Second Stage Reusability
Post by: envy887 on 03/05/2018 07:54 PM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.

Same thing. What's cheaper if you have to launch 12,000 satellites: $3M for 10 tonnes or $5M for 150 tonnes?
Title: Re: F9 Second Stage Reusability
Post by: Elmar Moelzer on 03/05/2018 10:39 PM
It would probably be wise to see the projected dry mass and payload capabilities of BFR/BFS (including the theoretical SSTO capability) as the end result AFTER several iterations, with the first "block" having considerably less payload than that. Just as SpaceX didn't build the reusable F9 FT Block 5 right after the Falcon 1 they probably will be happy if the first BFR/BFS will make it to orbit and back undamaged with a very small payload and allows them to look over it to improve the next one they will build.

If there will be a BFS that can do SSTO it might be the third, fourth or fifth iteration but certainly not the first.
I see it the other way round. The currently projected dry mass and payload capabilities are the beginning and future iterations (like was the case with F9) will be much more capable.
IIRC SpaceX never projected as huge payload capabilities for F9 and engine performance for Merlin as we are seeing today.
Also, what speaks against your conjecture is that Musk mentioned that they would take BFS all the way to orbit (without BFR) for their test flights. Unless my memory is failing me here.
Title: Re: F9 Second Stage Reusability
Post by: Negan on 03/06/2018 12:52 AM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.

Same thing. What's cheaper if you have to launch 12,000 satellites: $3M for 10 tonnes or $5M for 150 tonnes?

Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 03/06/2018 01:19 AM
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?
Title: Re: F9 Second Stage Reusability
Post by: Lar on 03/06/2018 02:40 AM
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?

I.e. Late Stage BFS operations on certain routes....
Title: Re: F9 Second Stage Reusability
Post by: AC in NC on 03/06/2018 03:09 AM
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Can someone unring this bell?  Perhaps reframe what is being discussed?  I think you two are talking past each other.
Title: Re: F9 Second Stage Reusability
Post by: Negan on 03/06/2018 03:11 AM
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?

Based on the following I would use number of estimated trips to determine useful life in this case:

The useful life of identical assets varies by user, and they depend upon the asset's age, the frequency of its use, the condition of the business's environment and the asset's repair policy.
Title: Re: F9 Second Stage Reusability
Post by: Negan on 03/06/2018 03:19 AM
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Can someone unring this bell?  Perhaps reframe what is being discussed?  I think you two are talking past each other.

Only if all <10 ton payloads cease to exist. BFS's useful life will be determined by frequency of use not tonnage to orbit. Depreciation equals cost divided by estimated useful life.
Title: Re: F9 Second Stage Reusability
Post by: AC in NC on 03/06/2018 03:48 AM
Only if all <10 ton payloads cease to exist. BFS's useful life will be determined by frequency of use not tonnage to orbit. Depreciation equals cost divided by estimated useful life.
No one (well speedevil kind of did but tangentially and not seriously) said it does.  As I said, you two are talking past each other arguing unrelated details.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 03/09/2018 03:00 PM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?
Also because you're not taking very large tanks to very high velocities.

Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.

ABCD: Always Be Counting Down



And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 03/09/2018 03:49 PM
And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.

If you've solved stackability, and orbital recovery, three stage is an interesting option.
It allows large payloads to very, very high energies.

But, that is a pretty large 'if'.
Any non-trivial 'zeroth'' stage for almost all useful purposes means a much higher velocity at the next stage burnout, and for it to be far downrange.
About the only exception would be if it was a slow ballistic stage to lift the stage off the pad at low speed, to clear weather, and to allow for use of vacuum engines on the main stage.

But, even if you wanted to do this, you can't, unless your engines are on a considerably wider part of the stage, because you don't have the area.
A 'low' speed at staging, as implied by a two stage vehicle with an energetic second stage means recovery is so much simpler.

F9 - no way would it make sense in the context of reusability.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 03/09/2018 05:54 PM
And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.

If you've solved stackability, and orbital recovery, three stage is an interesting option.
It allows large payloads to very, very high energies.

But, that is a pretty large 'if'.
Any non-trivial 'zeroth'' stage for almost all useful purposes means a much higher velocity at the next stage burnout, and for it to be far downrange.
About the only exception would be if it was a slow ballistic stage to lift the stage off the pad at low speed, to clear weather, and to allow for use of vacuum engines on the main stage.

But, even if you wanted to do this, you can't, unless your engines are on a considerably wider part of the stage, because you don't have the area.
A 'low' speed at staging, as implied by a two stage vehicle with an energetic second stage means recovery is so much simpler.

F9 - no way would it make sense in the context of reusability.

I agree completely.  Especially with the current market.  Just having a reuseable first stage is enough apparently to crush everyone else in the industry.

However, 3 stages could be hugely beneficial. 

A large diameter vehicle, say 12 meters, would provide lots of space for vacuum nozzles.  I like wider and shorter vehicles to minimize tank surface area for subcooled propellants.  The optimum stage zero would be cross-feed, leaving stage 1 fully fueled.  But we know that's not likely to happen.

3 stages just seems like a good way to optimize taking less mass all the way to orbit then having to bring it back.  Taking something to 5+ miles per second just to bring it back to zero is a lot of work.

Edit: None of this is going to happen on F9 or FH, so I'll let it go.  Would be pretty cool though, but they know what they are doing and they can get to a high launch rate and make money with the Block 5 vehicles.
Title: Re: F9 Second Stage Reusability
Post by: hkultala on 03/10/2018 07:43 AM
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield – why?
Greater fuel margins allow for more retropropulsion?
Also because you're not taking very large tanks to very high velocities.

Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.

ABCD: Always Be Counting Down


And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.


Always when thinking about stages, there has to be a plan WHAT the stages are. Not just how many there are.

Reusability for 2-stage LEO is straighforward:

First stage gives some 2km/s staging velocity and can return to the launch site.
Second stage can easily reach LEO with good payload fraction from the staging point, and can then stay in the orbit long enough so that it can return to the launch after the trajectory passes over the launch site later.

Reusability for any other configuration gets more complex:

SSTO to LEO with all the heat shielding etc gets very hard, the stage is very hard to make.

And TSTO to GTO means that
1) Considerable more delta-v needed than for LEO.
1a) First staging has to occur at higher velocity making RTLS vry difficult
1b) Second stage still has to give more delta-v to the payload. doing that while having heat shield etc is getting difficult
2) If the launch site is not at equator, the second stage no longer passes over the launch site. Even if it could land, it could not land to the launch site, unless it spents some propellant for inclination change.

so, three stages might be preferred for reusable GTO/high energy missions.


So, what would the three stages be?

3STO would not be very practical for reusable craft. Where would a suborbital second stage return?

What would seem to make most sense is to have a TSTO + a space tug for high energy orbits.
That would minimize the mass going to the final orbit, and minimize the mass that has to do the inclination change to come back to the launch site.
first stage could easily do RTLS, second stage could return from LEO that passes over the launch site.
And because the delta-v from LEO to GTO is not very much, third stage could even have heat shield and be able to do the inclination change to come back to over launch site.

However, this might not fit to F9 very well. But, for BFR.. would increase the single launch(no refueling)  payload to high energy orbits considerably. Sending a ~5-tonne upper stage to GTO instead of 85-tonne spaceship while the 85-tonne spaceship stays on LEO.

And Blue origin plan looks like this, they have an optional third stage. So normal LEO configuration is TSTO, later high energy configuration adds a third stage. (though they will initially do 2-stage to high energy orbits also before their 3rd stage is ready and before their second stage is reusable)
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/15/2018 11:14 PM
Posted on the TESS thread, but:

Elon: “This is gonna sound crazy, but ...
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon“
https://twitter.com/elonmusk/status/985654333860601856?s=21
Title: Re: F9 Second Stage Reusability
Post by: cppetrie on 04/15/2018 11:15 PM
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.
Title: Re: F9 Second Stage Reusability
Post by: IanThePineapple on 04/15/2018 11:17 PM
I hope we find out when they'll start doing this, but maybe it's just a design in R&D at this point.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/15/2018 11:18 PM
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.
I actually kinda believe it. Not literally a party balloon, but maybe some other large balloon or ball Ute.

TESS is absolutely tiny, so maybe the upper stage has enough performance to spare here.

Just need more COPVs in the upper stage for the greater helium load.
Title: Re: F9 Second Stage Reusability
Post by: yokem55 on 04/15/2018 11:19 PM
Well, they have the helium for it. So, assuming this isn't a crazy joke, they use the giant balloon to generate more drag in the high upper atmosphere to slow the stage more before coming in too hot?
Title: Re: F9 Second Stage Reusability
Post by: HMXHMX on 04/15/2018 11:20 PM
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.
I actually kinda believe it. Not literally a party balloon, but maybe some other large balloon or ball Ute.

TESS is absolutely tiny, so maybe the upper stage has enough performance to spare here.

Just need more COPVs in the upper stage for the greater helium load.

Google "ROOST Bono".
Title: Re: F9 Second Stage Reusability
Post by: cppetrie on 04/15/2018 11:21 PM
Is it clear this post from Elon relates to this specific mission or just something their working on that we might see in the future?
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/15/2018 11:21 PM
You can also in principle inflate the ballute from other sources - for example, there were some plans in the 60s using this to recover stages with reentry heated air.
I don't have details to hand.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/15/2018 11:22 PM
Well, they have the helium for it. So, assuming this isn't a crazy joke, they use the giant balloon to generate more drag in the high upper atmosphere to slow the stage more before coming in too hot?
Yeah, probably a ballute. The default upper stage probably has only about a fifth to a tenth the amount of helium needed to provide its own bouyancy, but plenty to inflate a big ballute.
Title: Re: F9 Second Stage Reusability
Post by: cppetrie on 04/15/2018 11:25 PM
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.
I actually kinda believe it. Not literally a party balloon, but maybe some other large balloon or ball Ute.

TESS is absolutely tiny, so maybe the upper stage has enough performance to spare here.

Just need more COPVs in the upper stage for the greater helium load.
I don’t disbelieve it. My response was a poor excuse for a joke. I have no doubt Elon and crew will try all sorts of far fetched stuff to see what happens. That’s part of their culture and what’s made them successful. They are unafraid to fail, careful enough to not risk the primary mission, and clever enough to pull off some pretty crazy-sounding stuff.
Title: Re: F9 Second Stage Reusability
Post by: Bubbinski on 04/15/2018 11:29 PM
I saw that announcement. I was wondering, though, if the 2nd stage recovery attempt would occur on this flight or a later F9/FH flight. I also wonder where the 2nd stage would splash down (or bump down?) if everything works as planned. Maybe in the Pacific? I wonder if Mr. Steven would be used to recover in that case. Or if Atlantic/Gulf of Mexico, what vessels would be available for the recovery attempt in those waters?
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/15/2018 11:29 PM
As I said upthread for FH:
Anything that changes the basic design of the stage, such as adding heat shields, let alone adding thrusters or dropping the tanks, just takes too long. There are lots of things to do, specification, basic and detailed design, simulation, manufacture, testing, installation, changes to software and procedures. It would amaze me if these could be done in less than a couple of years, let alone the 6 months before the FH first flight.

For the FH demo flight the second stage must be fairly close to what will be flown on subsequent flights, so no major changes will be allowed. Even minor changes will be discouraged if they could possibly affect the success of the demonstration.

The only way that I can think of, which does not involve major changes to S2 (not going to happen for FH demo flight) and which will take under 2 years from decision to start to flight, is to use a ballute.

Potentially, deploying a ballute in LEO, then using it to bleed off much of the velocity high in the atmosphere, then capturing the descending stage by helicopter could work.

Wrong about FH, but right about the rest?
Title: Re: F9 Second Stage Reusability
Post by: RedLineTrain on 04/15/2018 11:44 PM
Google "ROOST Bono".

https://www.cafepress.com/+balloon,1959259958
Title: Re: F9 Second Stage Reusability
Post by: tvg98 on 04/15/2018 11:49 PM
Didn't Hans say S2 will be left on heperbolic escape trajectory?
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/15/2018 11:54 PM
Didn't Hans say S2 will be left on heperbolic escape trajectory?
Yeah, so Musk must be talking about some other mission.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/15/2018 11:59 PM
Ballute or similar confirmed:

Phil Plait (@badastronomer) replying to @elonmusk: I’m not sure using helium will help it stay up in space though. #science

Elon replying to @badastronomer: Yeah, but great for creating a giant object that retains its shape across all Mach regimes & drops ballistic coefficient by 2 orders of magnitude

https://twitter.com/elonmusk/status/985668304353116161?s=21
Title: Re: F9 Second Stage Reusability
Post by: yokem55 on 04/16/2018 12:38 AM
Any guesses as to how much a coefficient of drag 100 times lower reduces reentry heating?
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/16/2018 12:46 AM
Any guesses as to how much a coefficient of drag 100 times lower reduces reentry heating?
Perhaps better put as ballistic coefficient (http://ballistic coefficient)?

And ... only a hundred?
(https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/thumbnails/image/1960_projectecho.jpg)

Has been proposed for a JPL Venus mission (https://www2.jpl.nasa.gov/adv_tech/ballutes/Blut_ppr/adm-vnus.pdf).

Potentially kilometers per second delta-v loss. Down to speeds that the booster is already recovered from.
Title: Re: F9 Second Stage Reusability
Post by: Rebel44 on 04/16/2018 12:48 AM
IMO, the best fit for something like this are CRS missions - since they go to LEO (so reentry speed would be lower than GTO launches) and trajectory of polar flights would require keeping 2nd stage alive to too long (first few orbits would take to over deep areas of Pacific - I expect SpaceX to want to try this in shallow waters so that they can recover 2nd stage remains if things don't go perfectly).
Title: Re: F9 Second Stage Reusability
Post by: cppetrie on 04/16/2018 12:53 AM
IMO, the best fit for something like this are CRS missions - since they go to LEO (so reentry speed would be lower than GTO launches) and trajectory of polar flights would require keeping 2nd stage alive to too long (first few orbits would take to over deep areas of Pacific - I expect SpaceX to want to try this in shallow waters so that they can recover 2nd stage remains if things don't go perfectly).
Don’t CRS missions currently dispose of S2 in the Indian Ocean? Where would the stage pass over near the US if they kept it in orbit longer?
Title: Re: F9 Second Stage Reusability
Post by: Rebel44 on 04/16/2018 12:57 AM
IMO, the best fit for something like this are CRS missions - since they go to LEO (so reentry speed would be lower than GTO launches) and trajectory of polar flights would require keeping 2nd stage alive to too long (first few orbits would take to over deep areas of Pacific - I expect SpaceX to want to try this in shallow waters so that they can recover 2nd stage remains if things don't go perfectly).
Don’t CRS missions currently dispose of S2 in the Indian Ocean? Where would the stage pass over near the US if they kept it in orbit longer?

At the end of the 1st orbit, they might get close enough to California coast (some trajectory adjustment might be necessary during deorbit burn).
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/16/2018 01:00 AM
Any guesses as to how much a coefficient of drag 100 times lower reduces reentry heating?
The idea is to make more drag, not less.
As an extreme example, a very thin (2.5um, the thinnest easily available mylar) balloon has a good shot at remaining completely intact through reentry, as it can radiate away all of the reentry heat faster than it's generated.

The second stage is made of metal that is somewhat thicker than foil.
If you have a very thin balloon made of high temperature capable fabric or polymer, this can radiate away a large fraction of the reentry heat, meaning the stage, even if minimally protected sees little of it, because the heat flux into the stage is not enough to damage it, in the short time it's happening.
Title: Re: F9 Second Stage Reusability
Post by: Gliderflyer on 04/16/2018 01:11 AM
Any guesses as to how much a coefficient of drag 100 times lower reduces reentry heating?

Assuming the dry mass of the upper stage is around 3900kg (http://www.spaceflight101.net/falcon-9-v11.html) (8600lb) the ballistic coefficient is:
BC = M/(Cd*A), Cd ~=0.82 for a cylinder, A = 113 ft^2 for a 12 foot diameter circle
BC = 8600/(.82*113)
BC = 93 psf

Two orders of magnitude would be 0.93 psf, which would make a huge difference. That is getting into "just slap some nextel on it (http://spacecraft.ssl.umd.edu/publications/2010/SpaceOps2010ParaShieldx.pdf)" territory.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/16/2018 01:42 AM
Apparently will plop down in a bouncy house:
https://twitter.com/elonmusk/status/985684755877265408?s=21
Title: Re: F9 Second Stage Reusability
Post by: Klebiano on 04/16/2018 01:54 AM
Apparently will plop down in a bouncy house:
https://twitter.com/elonmusk/status/985684755877265408?s=21

Probably on Mr. Steven 2.0
Title: Re: F9 Second Stage Reusability
Post by: docmordrid on 04/16/2018 02:00 AM
Apparently will plop down in a bouncy house:
https://twitter.com/elonmusk/status/985684755877265408?s=21

Probably on Mr. Steven 2.0

Mrs. Steven?
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/16/2018 03:30 AM
Sounds to me like it will take a while to learn to aim it right, since reentry slow-down might be long-ish.

That said, ... WOW... :)

-----
ABCD: Always Be Counting Down

Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/16/2018 03:36 AM
The speed at which SpaceX innovates compared to their competition is ridiculous.

And maybe innovation is not quite the right word. It's not so much generating new ideas but executing on long standing ideas that no one has had the guts or budget to try at scale, finding out what works and doesn't, then refining and iterating until it works.

The closest competition (as far as reuse innovation) is suborbital right now. And SpaceX doing full reuse is basically an afterthought to their grander plans.

No wonder they're valued at $27 billion.
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/16/2018 03:43 AM
It'd almost be worth the delays if the first US crewed flight after Shuttle was done with a reused upper stage recovered via bouncy house.

Anyone remember this?
“@DRogozin: After analysing the sanctions against our space industry I suggest the US delivers its astronauts to the ISS with a trampoline”
Title: Re: F9 Second Stage Reusability
Post by: Nilof on 04/16/2018 04:53 AM
The speed at which SpaceX innovates compared to their competition is ridiculous.

And maybe innovation is not quite the right word. It's not so much generating new ideas but executing on long standing ideas that no one has had the guts or budget to try at scale, finding out what works and doesn't, then refining and iterating until it works.

The closest competition (as far as reuse innovation) is suborbital right now. And SpaceX doing full reuse is basically an afterthought to their grander plans.

No wonder they're valued at $27 billion.

Yep. Ballutes are an old enough idea that they were featured in early 80s Gundam toys for children:

https://www.youtube.com/watch?v=F16AZ55jvw8&feature=youtu.be&t=2m48s

It's about time that someone actually tries it out.

(technically the "ballutes" in the specific clip I found are more like inflatable heat shields but the other kind of ballute also exists in the same toy line)
Title: Re: F9 Second Stage Reusability
Post by: jcm on 04/16/2018 05:06 AM
The speed at which SpaceX innovates compared to their competition is ridiculous.

And maybe innovation is not quite the right word. It's not so much generating new ideas but executing on long standing ideas that no one has had the guts or budget to try at scale, finding out what works and doesn't, then refining and iterating until it works.

The closest competition (as far as reuse innovation) is suborbital right now. And SpaceX doing full reuse is basically an afterthought to their grander plans.

No wonder they're valued at $27 billion.

Yep. Ballutes are an old enough idea that they were featured in early 80s Gundam toys for children:

https://www.youtube.com/watch?v=F16AZ55jvw8&feature=youtu.be&t=2m48s

It's about time that someone actually tries it out.

(technically the "ballutes" in the specific clip I found are more like inflatable heat shields but the other kind of ballute also exists in the same toy line)


It's been tried
http://space.skyrocket.de/doc_sdat/irdt-fregat.htm
Title: Re: F9 Second Stage Reusability
Post by: Robotbeat on 04/16/2018 05:08 AM
That’s an inflatable heatshield, not a ballute.

Armadillo Aerospace actually did use a ballute, I believe of the ram-air type. Near the Karman line.

What Musk may be describing (hard to tell as he is half joking) is a towed ballute inflated with helium.
Title: Re: F9 Second Stage Reusability
Post by: ThePonjaX on 04/16/2018 05:17 AM
The speed at which SpaceX innovates compared to their competition is ridiculous.

And maybe innovation is not quite the right word. It's not so much generating new ideas but executing on long standing ideas that no one has had the guts or budget to try at scale, finding out what works and doesn't, then refining and iterating until it works.

The closest competition (as far as reuse innovation) is suborbital right now. And SpaceX doing full reuse is basically an afterthought to their grander plans.

No wonder they're valued at $27 billion.

To me the most incredible thing is they aren't afraid of ridiculous. A lot of companies start with some crazy ideas but later they "grow up" and start trying to be "serious companies.". So the corporate language is the norm. 

Let say Boeing is going to try the same idea: Boeing announced the development of advanced bla bla technology to slow down and recovery the second stage of his rockets.

but Elon just throw out: We're going to use a party balloon ... bounce castle ... and it's fine and we're ready to believe.
Title: Re: F9 Second Stage Reusability
Post by: Ronsmytheiii on 04/16/2018 05:27 AM
IMO, the best fit for something like this are CRS missions - since they go to LEO (so reentry speed would be lower than GTO launches) and trajectory of polar flights would require keeping 2nd stage alive to too long (first few orbits would take to over deep areas of Pacific - I expect SpaceX to want to try this in shallow waters so that they can recover 2nd stage remains if things don't go perfectly).

The next suitable launch for this type of experiment is likely Idridium NEXT 6/GRACE FO mission, since it is LEO. Plus easily flies over the Pacific targets Elon mentioned.
Title: Re: F9 Second Stage Reusability
Post by: FutureSpaceTourist on 04/16/2018 06:06 AM
Quote
How will you pick where it deorbits? A retrograde burn to pick the final spot?

https://twitter.com/smartereveryday/status/985675157212749824

Quote
We already do targeted retro burn to a specific point in Pacific w no islands or ships, so upper stage doesn’t become a dead satellite. Need to retarget closer to shore & position catcher ship like Mr Steven.

https://twitter.com/elonmusk/status/985731208846831618
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/16/2018 06:26 AM
There's only one reason for them to do this IMO with BFR coming up - they identified second stage production to be a bottleneck for Starlink deployment, and they have doubts about BFR being ready in time.

Starlink has all they need for this to work out: Deployment to LEO, Capacity seems to be volume limited, and they are their own customer, so no red tape from NASA or other customers.

Easiest mission to try this IMO would be the Sun Synchronous Mission this year, because they could recover the second stage after 1 orbit in the pacific. After that, whatever mission they have planned for their Starlink constellation...
Title: Re: F9 Second Stage Reusability
Post by: Cheapchips on 04/16/2018 06:37 AM
There is another reason, which is that they discovered they still had the bandwidth to do it despite the pivot to BFR.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/16/2018 06:44 AM
To me the most incredible thing is they aren't afraid of ridiculous. A lot of companies start with some crazy ideas but later they "grow up" and start trying to be "serious companies.". So the corporate language is the norm. 

Let say Boeing is going to try the same idea: Boeing announced the development of advanced bla bla technology to slow down and recovery the second stage of his rockets.

but Elon just throw out: We're going to use a party balloon ... bounce castle ... and it's fine and we're ready to believe.
Or perhaps because he's impatient and sees no point in not being as direct as possible? It's a simple, striking image that gives a pretty clear idea of what he wants to happen.
There's only one reason for them to do this IMO with BFR coming up - they identified second stage production to be a bottleneck for Starlink deployment, and they have doubts about BFR being ready in time.

Starlink has all they need for this to work out: Deployment to LEO, Capacity seems to be volume limited, and they are their own customer, so no red tape from NASA or other customers.

Easiest mission to try this IMO would be the Sun Synchronous Mission this year, because they could recover the second stage after 1 orbit in the pacific. After that, whatever mission they have planned for their Starlink constellation...
Indeed. It seems quite a lot of effort for a one off mission to study the reentry damage, like Shotwell was talking about. The F9 US is not really a good model of the BFS so it's not clear what lessons you learned getting a US back would transfer over to BFS.

Expending upper stages is the issue if you want to retire the whole F9 mfg line but you suspect it may take longer than planned to bring BFR into service.

A clue to this would be how reluctant SX become to fly missions with any  expendable boosters once all their boosters are block 5.
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/16/2018 07:07 AM
Well, they asked the FCC for a waiver that they did not get with regards to when they have to have their fully operational constellation. That might have triggered them to get those US recovery plans out of the lowest drawer back onto the desk.

Another cross connection - someone noticed crates from Airtech International Inc. at the BFR manufacturing site. I just checked their website and they offer vacuum bagging for composite manufacture. They offer bagging(Polyimide) that is resistant to 426°C, has great tensile strength etc.
Its intended for vacuum...

I think that might make for a mighty strong party balloon.
Title: Re: F9 Second Stage Reusability
Post by: Cheapchips on 04/16/2018 07:19 AM
Will the nozzle survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.
Title: Re: F9 Second Stage Reusability
Post by: groknull on 04/16/2018 07:50 AM
Expending upper stages is the issue if you want to retire the whole F9 mfg line but you suspect it may take longer than planned to bring BFR into service.

Or if it looks like BFR is progressing faster than expected and you want to free up manufacturing resources for BFR production.  S2 reusability would allow the production line to be shut down sooner.  It is likely that S2 reusability R&D has been ongoing.  Maybe one of the ideas just reached the SpaceX try-it threshold.

Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/16/2018 08:31 AM
Well, they asked the FCC for a waiver that they did not get with regards to when they have to have their fully operational constellation. That might have triggered them to get those US recovery plans out of the lowest drawer back onto the desk.
That very much looked to me like routine pushback.
'Oh, that is a regulatory limit that might impact us if everything goes terribly, let's see if we can change it'.

Rather than 'We have real problems with meeting this timeline if everything goes right'.
Title: Re: F9 Second Stage Reusability
Post by: Crispy on 04/16/2018 08:53 AM

Will the nozzel survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

The nozzle *extension* is a very simple thing. Remember when they sent an engineer into the interstage to cut it short with some tin snips?
If they can reliably jettison it, they can easily fit a new one.
Title: Re: F9 Second Stage Reusability
Post by: MikeAtkinson on 04/16/2018 08:59 AM
It could be an annular ballute fitted around the engine, which then hangs the stage nose first. The engine would then be largely protected. Annular ballutes have I believe mass and volume advantages over a sphere.
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/16/2018 09:02 AM
Well, they asked the FCC for a waiver that they did not get with regards to when they have to have their fully operational constellation. That might have triggered them to get those US recovery plans out of the lowest drawer back onto the desk.
That very much looked to me like routine pushback.
'Oh, that is a regulatory limit that might impact us if everything goes terribly, let's see if we can change it'.

Rather than 'We have real problems with meeting this timeline if everything goes right'.
I agree, if Starlink makes the business case as planned, it's in their own interest to put their constellation(s) up quite fast simply to fulfil customer needs, not regulatory requirements. It would have been more of a safety net anyhow.

Maybe they will just do it because they can. If r&d for US-recovery costs anything near what they spent for the first stage, they would need hundreds of of flights to recover those costs. But Gwynne Shotwell said they want to have an upper stage back for research purposes, not for reflight...

Simply trying something for the purpose of trying might still be a possibility, especially if it costs them not too much...
Title: Re: F9 Second Stage Reusability
Post by: Cheapchips on 04/16/2018 09:59 AM

Will the nozzel survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

The nozzle *extension* is a very simple thing. Remember when they sent an engineer into the interstage to cut it short with some tin snips?
If they can reliably jettison it, they can easily fit a new one.

My thought was around cost and ease of manufacture.  Niobium alloy isn't cheap or easy to work with.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/16/2018 10:24 AM
My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.

In principle, if engine cost was very significant, using F9S1 engines would drop the payload of a ASDS F9 by something like 4-5 tons, assuming no modifications other than any required for vacuum start, and that those modifications were trivial.
However, it's been stated it's only 'some fraction' of a million dollars.
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/16/2018 10:31 AM

Will the nozzel survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

The nozzle *extension* is a very simple thing. Remember when they sent an engineer into the interstage to cut it short with some tin snips?
If they can reliably jettison it, they can easily fit a new one.

My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.
I found a price of 40$/kg for ferroniobium(60-70% Nb). SpaceX might use an alloy that's 10% Hafnium, 1%Titanium, rest Niobium. That alloy was used on the Apollo Service Module.

So it's definitely an expensive material, but not THAT expensive, compared to the rest of the stage. If you estimate the cost of the second stage at 8 million $, at 4t that's an average of 2000$/kg. So I don't think they would mind getting the rest of the stage back even if they loose the nozzle extension ;-)
Title: Re: F9 Second Stage Reusability
Post by: Darkseraph on 04/16/2018 10:44 AM
Off the wall prediction about S2 reuse but here we go:

SpaceX will eventually land F9 second stages back at the launch site or on a droneship using cradle-landing. This will allow them to test this technique for the BFR on a cheaper platform and remove the additional weight of landing legs for S2 recovery.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/16/2018 10:50 AM
Another cross connection - someone noticed crates from Airtech International Inc. at the BFR manufacturing site. I just checked their website and they offer vacuum bagging for composite manufacture. They offer bagging(Polyimide) that is resistant to 426°C, has great tensile strength etc.
Its intended for vacuum...
Well spotted.  What a remarkable operating temp for a plastic (assuming that's in air, not vacuum).

If it's true that it's mainly a case of being thin enough to radiate the heat away then this does sound exactly what you'd need to make this work.

Keep in mind the air pressure at these heights is very low. A couple of psi absolute could be all that's needed to make this thing as stiff as a truck tire inner tube.

It could be an annular ballute fitted around the engine, which then hangs the stage nose first. The engine would then be largely protected. Annular ballutes have I believe mass and volume advantages over a sphere.
This would change everything Protecting the engine was always the challenge for US recovery given either stages tendency to orientate engine first.  You're not quite home and dry as it's unclear if you could get away with just what's on the outside of the stage walls and just put the TPS on the nose, but it'd be a good start.
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/16/2018 11:07 AM
Another cross connection - someone noticed crates from Airtech International Inc. at the BFR manufacturing site. I just checked their website and they offer vacuum bagging for composite manufacture. They offer bagging(Polyimide) that is resistant to 426°C, has great tensile strength etc.
Its intended for vacuum...
Well spotted.  What a remarkable operating temp for a plastic (assuming that's in air, not vacuum).

If it's true that it's mainly a case of being thin enough to radiate the heat away then this does sound exactly what you'd need to make this work.

It should be similar or identical to Kapton, which is a Dupont trademark for polyimide foils...

Quote from: wikipedia
Kapton is used in, among other things, flexible printed circuits (flexible electronics) and thermal blankets used on spacecraft, satellites, and various space instruments.

The James Webb Space Telescopes Sunshield is made from Kapton.
Title: Re: F9 Second Stage Reusability
Post by: AncientU on 04/16/2018 11:42 AM
Maybe what they really want back is the dispensers they will be using for Starlink deployment... might be worth considerably more than the Merlin Vac.  Cannot mention it because of the steep competition for constellation deployment.
Title: Re: F9 Second Stage Reusability
Post by: corrodedNut on 04/16/2018 11:46 AM
Title: Re: F9 Second Stage Reusability
Post by: LouScheffer on 04/16/2018 12:02 PM
Will the nozzle survive this type of entry and bouncy landing?  It uses strengthening rings for launch.  Can they keep those in place instead of discarding them at S2 ignition?

I'd imagine that the nozzel is one of the more extensive and difficult to manufacture element of the 2nd stage, next to the rest of the Mvac.

How about a simple and brute force solution?  Let the stage land engine first in a net, such as on Mr. Stevens.  The thin nozzle extension crumples, so you take it off and bolt on another.  If material cost is a big concern you recycle the old one.

The question is whether that puts too much strain on the regenerative part of the nozzle.   It's not obvious it would, since that part has to be quite strong to deal normal thrust, and the extension will serve as a crumple zone.   And even if you need to strengthen the nozzle, it might be a worthwhile tradeoff.  Finally, you can test this all you want with drop tests from airplanes/helicopters, so it's not crazy expensive to try.
Title: Re: F9 Second Stage Reusability
Post by: Steve G on 04/16/2018 12:26 PM
Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration. The weight penalty would be enormous for the F9, but Falcon Heavy could handle the payload penalty. If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/16/2018 12:46 PM
Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration.
This is at least unclear.
For some configurations, it seems at least plausible that carrying the fairings to orbit is going to weigh considerably more than ballute recovery, perhaps even plus parachute.
The mass of S2 is really quite close indeed to the mass of the fairings, and it's quite plausible they could just reuse wholly the landing solution for the fairings, though it is not optimal.
Title: Re: F9 Second Stage Reusability
Post by: nacnud on 04/16/2018 01:04 PM
If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.

I don't think there will be super dracos involved

Quote
Elon Musk
‏@elonmusk
12h12 hours ago

This is gonna sound crazy, but …

SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon

And then land on a bouncy house.
Title: Re: F9 Second Stage Reusability
Post by: hallmh on 04/16/2018 02:35 PM
My thought was around cost and easy of manufacture.  Niobium alloy isn't cheap or easy to work with.

Even if the nozzle is crushed by the recovery process, they'll still have the alloy to re-work into a replacement - or at the least, for exchange with the supplier as scrap.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/16/2018 02:46 PM
There is another reason, which is that they discovered they still had the bandwidth to do it despite the pivot to BFR.

Another reason would be that the F9/FH family have a long future ahead of them. I think it’s at least 5 years before BFR flys a paying payload. 

The US would likely only be reuseable on low energy, small payload missions, at best.  But that’s enough to make it worth while. Especially if you get the US back then smaller payload launch costs can be even lower than now.

Maybe they get the fairing figured out before jumping to this step. 

Edit: imagine the launch cost for smaller or LEO payloads if they can recover the booster, fairing and US.  My gosh, it could eventually be maybe $20 million or less with time. 

Edit 2: It's likely fair to think that for chance of US reuse that RTLS would give way to ASDS recovery.  Make the booster do as much work as possible and give the US as much margin as possible.  I think this whole idea is marginal at best, but it would be great fun to try.
Title: Re: F9 Second Stage Reusability
Post by: yokem55 on 04/16/2018 04:50 PM
There is another reason, which is that they discovered they still had the bandwidth to do it despite the pivot to BFR.

Another reason would be that the F9/FH family have a long future ahead of them. I think it’s at least 5 years before BFR flys a paying payload. 

The US would likely only be reuseable on low energy, small payload missions, at best.  But that’s enough to make it worth while. Especially if you get the US back then smaller payload launch costs can be even lower than now.

Maybe they get the fairing figured out before jumping to this step. 

Edit: imagine the launch cost for smaller or LEO payloads if they can recover the booster, fairing and US.  My gosh, it could eventually be maybe $20 million or less with time. 

Edit 2: It's likely fair to think that for chance of US reuse that RTLS would give way to ASDS recovery.  Make the booster do as much work as possible and give the US as much margin as possible.  I think this whole idea is marginal at best, but it would be great fun to try.
I think even for larger payloads it should be recoverable. Echo 2 (40 meter diameter mylar) only weighed 256 kg with the pressurant. Granted, adding all the attachment bits to the balloon, some tps on the body of the stage, and a parafoil for final descent adds to that mass, but I can't see it totalling to more than a ton.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/16/2018 04:53 PM
As to why attempt this, suggest you notice that it seems to be an extension of the fairing recover scheme, down to the "bouncy castle/house" part.

Sector leaders of an industry often demonstrate "command of the sector" by going beyond the present need. (Intel, for example, has gone from the Andy Grove days of "being beyond the best in sector" to going to "uh, who cares about Spectre/Meltdown, you'll mostly use our processors or not, we'll be 'good enough' as budget/market/yeild requires" - which is why some analysts as well as me are slowly suggesting to sell off and diversify.)

Why would you want to be a sector leader right now? Well, the former sector leader was ULA, and they don't appear to be competitive on price/frequency/futures, plus they are seen as possessing the joint advantages of Lockheed Martin and Boeing, but have no advantage to show for it, only apparent disadvantage. So the beginnings of a great comic book story, like a Marvel action pic. (Musk has been cast before as Tony Stark.)

Let me talk about how Uber got it's immense valuation. New York taxi medallions have long went for large sums, and San Francisco decided to try to market price them as a tulip industry, expecting wild rises in valuation. Because they could briefly construct a valuation model of large scale, built off of New York's base/history, Uber could similarly value spot drivers in cars with a smartphone equally. By integrating this as a global value (all those drivers possible), they got a huge number that they could show analysts had a reality, and then show that they could grab 5-10% of those drivers in five years, with the potential to get 51% in 10-20 years.

For SX, one can use ULA's economics of Atlas V 551 and Delta IVH as a similar basis, then have the long term economies projected for BFR/BFS, and claim the early Boeing model to dominate civil aviation as space based transport as it's application.

But the problem is how do you connect the dots, to get that huge valuation? You need to go from a current business to that final business, and that you can "command the sector" until you're the only game in town, like Uber.

All they need to do at the moment is demonstrate that they could recycle all the parts of a launch system, such that the theory of "airliner like" reuse could be done. (They don't have to prove economics or practicality - because none of their rivals are within ten years of reaching them in a provable way, and it is reasonable to conclude to analysts that in ten years they stand the best chance of making practical/economical the theory as real.

The space category has always thought of itself as an industry within margins, and Musk as a carney barker.  What if someone erases the margins, and oversells this as a future? (And isn't a Kalanick idiot about it.)

They underestimated their sector, and his scope and sales target. Note - it doesn't have to be real, which is what aerospace engineers always obsess on.

Back to F9US reuse. If he shows a crisped,wet US to park next to the booster out in front of SX in Hawthorne, the analysts will trot by for pics with Musk and them, chat up an insane valuation, and his ability to raise $40-50T goes online at that point. It is SX's equivalent to "Boeing Model 200", while BFS is more like the Model 247. Who needs NASA HSF exploration contracts at that point?

Watch for it.
Title: Re: F9 Second Stage Reusability
Post by: rst on 04/16/2018 05:23 PM
Second stage re-usability would likely incorporate re-using the fairings. Which essentially, we're looking at a mini BFS in configuration. The weight penalty would be enormous for the F9, but Falcon Heavy could handle the payload penalty. If re-usability centers around capturing the fairings with the seaborne net, then the second stage would have to have a heat shield at the front of the stage, protection for the nozzle, and superdrakos for landing. My bet would be the mini BFS, if they even pursue this option.

Elon's recent tweets on the subject say that they'll be trying to get F9 S2 back from orbit by using "a giant party balloon" (presumably a ballute), and then "land on a bouncy house". No sign of a similar strategy for BFS recovery yet...
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/16/2018 05:43 PM
Back to F9US reuse. If he shows a crisped,wet US to park next to the booster out in front of SX in Hawthorne, the analysts will trot by for pics with Musk and them, chat up an insane valuation, and his ability to raise $40-50T goes online at that point.

That valuation seems unlikely - I can sort-of-see >>>50B, but going from that to 50T (All stocks are worth around 70T) seems perhaps a reach.
Even if for the reason that basically all investors would need to sell most of their assets to go in.
Title: Re: F9 Second Stage Reusability
Post by: ChrisWilson68 on 04/16/2018 05:56 PM
I'm not sure why everyone seems to take it as a given that this upper stage recovery is only for LEO missions.

When SpaceX launches a satellite destined for GEO, it doesn't do a direct GEO insertion.  It releases the satellite in GTO.  So the upper stage is in a highly elliptical orbit with its low point pretty close to Earth.  If it inflates a giant balloon of some shape, it can do many passes grazing the atmosphere to lose speed and slow down until it's in a circular low-Earth orbit, and then go for re-entry.

This assumes both the stage and the balloon can last a while in space.  Maybe that's realistic, maybe not, but I wouldn't discount it out-of-hand as impossible.

Edit: fix GEO for LEO typo in first sentence, thanks Kaputnik.
Title: Re: F9 Second Stage Reusability
Post by: Kaputnik on 04/16/2018 06:09 PM
I'm not sure why everyone seems to take it as a given that this upper stage recovery is only for GEO missions.

When SpaceX launches a satellite destined for GEO, it doesn't do a direct GEO insertion.  It releases the satellite in GTO.  So the upper stage is in a highly elliptical orbit with its low point pretty close to Earth.  If it inflates a giant balloon of some shape, it can do many passes grazing the atmosphere to lose speed and slow down until it's in a circular low-Earth orbit, and then go for re-entry.

This assumes both the stage and the balloon can last a while in space.  Maybe that's realistic, maybe not, but I wouldn't discount it out-of-hand as impossible.


I take it you meant to say LEO in your first sentence?
Your basic point stands, though. A longer lived stage could aero brake into a low circular orbit prior to a de orbit burn. Requires some non trivial mods to the stage of course.
Title: Re: F9 Second Stage Reusability
Post by: docmordrid on 04/16/2018 07:13 PM
Once they have Crew Dragon's conformal Trunk solar arrays mastered ISTM using them to extend S2  battery life and prevent RP-1 gelling is low hanging fruit.
Title: Re: F9 Second Stage Reusability
Post by: Nilof on 04/17/2018 07:08 AM
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.

If SX is forced to maintain F9 capability for a time after commercializing BFR, they can keep a Falcon 9 stockpile going for a lot longer if the stockpiled rockets are fully reusable.

By the time the full BFR reaches the point where it has been launched a few times, Falcon 9 will likely have a launch record of a couple hundred launches and it'll probably stay a coveted launch option for any conservative customer, especially if we don't see any more major mishaps.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/17/2018 08:51 AM
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.
If BFR is flying, you can also plausibly delete S2 recovery hardware, and recover with BFS.
This lets you get the full nominal performance of the rocket, while being able to recover it, for customers that want to fly on F9.

I question if this market segment exists though, as anyone really insisting on F9 is likely to want a new one.
Title: Re: F9 Second Stage Reusability
Post by: niwax on 04/17/2018 10:33 AM
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.
If BFR is flying, you can also plausibly delete S2 recovery hardware, and recover with BFS.
This lets you get the full nominal performance of the rocket, while being able to recover it, for customers that want to fly on F9.

I question if this market segment exists though, as anyone really insisting on F9 is likely to want a new one.

Do you mean sending up a BFS to pick up the stranded S2 in LEO and return it to the surface? That's absolutely insane. I love it.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/17/2018 12:09 PM
Do you mean sending up a BFS to pick up the stranded S2 in LEO and return it to the surface? That's absolutely insane. I love it.

Indeed.

To raise another point on S2 reuse - though this would not always technically be reusing the stage, put one on BFS, full, and you can throw about 12 tons very hard at Jupiter or Saturn, with no in-orbit refuelling, or some 30 tons at Mars.
Title: Re: F9 Second Stage Reusability
Post by: rst on 04/17/2018 01:02 PM
So, ummm... anyone have a mass estimate for the ballute-onto-bouncy-house recovery system?

One possibly relevant citation: a study of ballute systems for a somewhat more demanding application -- braking a 7500 kg capsule on a lunar return trajectory:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060018288.pdf

had "total system mass (not including inflation system) with 20% mass contingency" at 550 kg. On the flip side, there's a paper here on a somewhat more worked-out proposal for Cygnus recovery that has a baseline estimate of 482 kg for inflation, inflatable structure, and TPS -- but an additional 830 kg for avionics, instruments and "structure", for a total of about 1.3 mT.

https://websites.isae-supaero.fr/IMG/pdf/137-heart-ippw-9_v04-tpsas.pdf

Either way, this is on the low end for estimates of S2 recovery hardware, but a few hundred kg more or less could make a real difference as to whether you could contemplate using this scheme for missions beyond LEO.
Title: Re: F9 Second Stage Reusability
Post by: Space Ghost 1962 on 04/17/2018 09:18 PM
You don't know the scope of the system yet, so mass estimates could be way off. Also, these systems can have "compressible" systems, so his 100x greater ballistic coefficient needs to be referenced to an altitude and speed. Very different between say deployment, EI, and critical deceleration points.

Also, materials have changed, especially for the shroud lines one might use for this.

And you'd also like to know when/what the low altitude recovery posture is as well, as that's a significant part of the mass budget.

If this approach decelerates high enough, it might not require any heat shields/TPS at all.
Title: Re: F9 Second Stage Reusability
Post by: Comga on 04/17/2018 09:28 PM
Bingo
Remember how this discussion started two days, and three pages, ago:

Elon: “This is gonna sound crazy, but ...
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon“
https://twitter.com/elonmusk/status/985654333860601856?s=21

"bring rocket stage back from orbital velocity" doesn't say anything about surviving or recovering.
"party balloon" does suggest something very light and thin.
It seems to be another low cost SpaceX experiment, and probably light weight.
They will learn from it, whatever happens.
Title: Re: F9 Second Stage Reusability
Post by: rst on 04/17/2018 10:06 PM
"bring rocket stage back from orbital velocity" doesn't say anything about surviving or recovering.

"... and then land on a bouncy house", however, does.  They probably won't expect recovery on the first try (that's not what happened with fairings, and the blooper reel for booster landing attempts is spectacular), but it's clearly the end goal.

https://twitter.com/elonmusk/status/985684755877265408
Title: Re: F9 Second Stage Reusability
Post by: su27k on 04/18/2018 02:36 AM
Additional information:

https://twitter.com/QuinnKupec/status/985736260827471872

Quote from: Quinn Kupec
@elonmusk If you're proposing what I think you are, an ultra low ballistic entry coefficient decelerator, then you and @SpaceX should come see what we have at the @UofMaryland . We've been working on this for awhile and just finished some testing

https://twitter.com/elonmusk/status/986070683426766848

Quote from: Elon Musk
@QuinnKupec @SpaceX @UofMaryland Yeah, exactly! Would be great to hear your thoughts. We’re going to try a few approaches. Can def be done, just about minimizing mass.

https://twitter.com/QuinnKupec/status/986075981004886016

Quote from: Quinn Kupec
Absolutely! That's what we are working on right now! I would love to share with you, or anyone from @SpaceX what we are doing. Please let me know a good way to get you my contact information.

Edit: Some googling results in a paper about this from UMD: Applications of Ultra-Low Ballistic Coefficient Entry Vehicles to Existing and Future Space Missions (http://spacecraft.ssl.umd.edu/publications/2010/SpaceOps2010ParaShieldx.pdf)

Also a reddit post explaining the image: https://www.reddit.com/r/UMD/comments/8ctmv4/elon_musk_responds_to_a_umd_students_tweet/dxiarto/

Quote
Shout-out to the UMD Nearspace team and the Balloon Payload Program! The orange payload in the image is called TARDIS, and it essentially works like an upside-down umbrella, opening up wide when falling back to earth to decelerate. Quinn's been working on this for over a year, by now
Title: Re: F9 Second Stage Reusability
Post by: Rocket Surgeon on 04/18/2018 03:40 AM
Does any one have any good sources for the mass of steerable parafoils and/or the mass of the second stage? From the sounds of it, this system will use either a huge ballute to reduce peak heating to below 500oC (well below the melting temperature of Aluminium and removing the need for a heat shield) or a smaller deployable heat shield like HIAD*.

Regardless, I would be willing to put money down on them using a steerable parafoil and landing on Mr Steven like the the fairings for the last 5-10km, though if they go for the ballute they would probably have to cut if free.

I don't think they'd be able to steer accurately enough with out a parafoil to catch the second stage, so that would limit how big the rest of the system can be.

*My guess would be the former one as that more matches Elon's description, would weigh less, and would interfere less with the current design. If heating could be limited to below 400oC, the design could be rather simple and lightweight, using off-the-shelf materials like Kevlar and Mylar.

PS: I remember there being a thread discussing this sort of system for second stage recovery a few years ago, is that just me?
Title: Re: F9 Second Stage Reusability
Post by: Swedish chef on 04/18/2018 07:03 AM
PS: I remember there being a thread discussing this sort of system for second stage recovery a few years ago, is that just me?

Perhaps you are thinking of the fairing reuse thread? Lots of information on steerable parachutes in that thread.
https://forum.nasaspaceflight.com/index.php?topic=37727.1520
Title: Re: F9 Second Stage Reusability
Post by: OxCartMark on 04/18/2018 01:39 PM
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient is going to make this approach susceptible to wide variances in how far down range the touchdown point is relative to the point you retro fire to begin re-entry.  Hundreds of miles of variation(??).  Unless you have a way to adjust the drag (size, geometry) of the party balloon on the fly (preferably both increases and decreases) and a very current atmospheric model to adjust the initiation point of the re-entry.  A variable balloon and a late well informed decision on when to fire the engines.

And, let's not forget to what degree a simple balloon (if that's what it is) will shrink in size due to atmospheric pressure increase in going from "space" to some more airy portion of the atmosphere, so there may need to be some intermediate step between balloon and parafoil to get through the mid altitudes.

Seems that a framed solution such as an umbrella or a sheet with structure made of inflated tube ribs would meet the need better than a strict balloon.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/18/2018 01:41 PM
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient
I'm 99.9999% sure that what's meant is the ballute increases the drag lots, by presenting a larger area.

This causes the heat per square meter of balloon to drop, as the kilos per square meter goes from about 100kg/m^2 to about 1.
It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.
Title: Re: F9 Second Stage Reusability
Post by: OxCartMark on 04/18/2018 02:18 PM
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient
I'm 99.9999% sure that what's meant is the ballute increases the drag lots, by presenting a larger area.

This causes the heat per square meter of balloon to drop, as the kilos per square meter goes from about 100kg/m^2 to about 1.
Your statement matches my thinking 100% up to that point.

It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.
No doubt once it hits the top of the atmosphere (which is a squishy border but high up in this case because of the very low loading) that'll be the case but the large variability occurs before that time in the re-entry, when the speed is very high and the atmospheric density is just a slight bit more than negligible.
Title: Re: F9 Second Stage Reusability
Post by: nicp on 04/18/2018 02:55 PM
Surely if it's possible to get the second stage down to sea level in one piece without using much retro-propulsion (party balloons, ballute, whatever you wanna call it) the same must be true of the first stage. Just keep enough fuel to land it, no need for any burn except to get it into the right place.
Or am I being dense?
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 04/18/2018 03:01 PM
Surely if it's possible to get the second stage down to sea level in one piece without using much retro-propulsion (party balloons, ballute, whatever you wanna call it) the same must be true of the first stage. Just keep enough fuel to land it, no need for any burn except to get it into the right place.
Or am I being dense?
For downrange recovery, and very large balloon, maybe, but it will be a bit more difficult because the stage is longer.

But you can't do RTLS with balloons, and the boostback burn is the main  consumer of propellant.

-----
ABCD: Always Be Counting Down

Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/18/2018 03:28 PM
It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.
No doubt once it hits the top of the atmosphere (which is a squishy border but high up in this case because of the very low loading) that'll be the case but the large variability occurs before that time in the re-entry, when the speed is very high and the atmospheric density is just a slight bit more than negligible.

Assuming reasonable knowledge of the atmosphere, and that a little fuel can be retained - for say a 1 second burn - 300kg or so, this gets you 250m/s or so delta-v, and firms up the entry position considerably.
If you can choose the inflation position of the ballute, this also helps.
Title: Re: F9 Second Stage Reusability
Post by: Bananas_on_Mars on 04/18/2018 03:45 PM
I remember that with the fairings there has been speculation about a bouncy castle on the fairing itself, instead of the fairing landing inside a bouncy castle that's waiting on the ocean, that you have to hit...

I've been thinking about a Zorbing Ball (https://en.m.wikipedia.org/wiki/Zorbing) around the stage, providing the drag on reentry(maybe through partial filling?, partial lift (helium filled, party balloon)+ drag on descent, fully inflate to serve as an airbag to cushion the landing on the ocean(bouncy castle). How big would such a Ball be to limit terminal velocity to maybe 60km/h? What i'm proposing here might a all-in-one solution for EDL.
Title: Re: F9 Second Stage Reusability
Post by: rst on 04/18/2018 03:59 PM
Does any one have any good sources for the mass of steerable parafoils and/or the mass of the second stage? From the sounds of it, this system will use either a huge ballute to reduce peak heating to below 500oC (well below the melting temperature of Aluminium and removing the need for a heat shield) or a smaller deployable heat shield like HIAD*.

Second stage dry mass is widely estimated at between 4 and 5 mT (to which you'd have to add a bit to account for residual propellant, etc.).  As to masses of ballute systems, well... some dude posted pointers to a couple of relevant design studies (HIAD for Cygnus return and a more speculative study about lunar capsule return) a bit upthread at post 665, which came in at between 500 and 1500 kg depending on what you count (one had a fairly elaborate structural mount for the furled HIAD) to which you'd have to add mass of a separate parafoil system for terminal descent, if you add one.  Pointers to those papers again:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060018288.pdf
https://websites.isae-supaero.fr/IMG/pdf/137-heart-ippw-9_v04-tpsas.pdf

ETA: also see subsequent comments from Space Ghost about how differences between these proposals and whatever SpaceX deploys (details so far unknown) could make these estimates off.
Title: Re: F9 Second Stage Reusability
Post by: Norm38 on 04/23/2018 04:41 PM
Saw this on YouTube today, thought I'd post it.  Didn't hear anything new for the regulars, but may be good for the non-engineers.

https://www.youtube.com/watch?v=6kY2SvyDcbg
Title: Re: F9 Second Stage Reusability
Post by: Comga on 04/29/2018 02:03 PM
Saw this on YouTube today, thought I'd post it.  Didn't hear anything new for the regulars, but may be good for the non-engineers.

Nah
I would bet against each of this guy’s guesses and interpretations.
It’s not “obvious”. It doesn’t “have to be”.
SpaceX is not going to rig up some complex structure like HIAD or whatever
They can’t surround the second stage in airbags. It’s too big and they couldn’t be well distributed
All of his borrowed video snippets are irrelevant.

edit: typos
Title: Re: F9 Second Stage Reusability
Post by: deruch on 04/29/2018 03:51 PM
Saw this on YouTube today, thought I'd post it.  Didn't hear anything new for the regulars, but may be good for the non-engineers.

Nah
I would bet against each of this guy’s guesses and interpretations.
It’s not “obvious”. It doesn’t “have to be”.
SpaceX is not going to rig up some complex structure like HIAD or whatever
They can’t surround the second stage in airbags. It’s too big and they couldn’t be well distributed
All of his borrowed video snippets are irrelevant.

edit: typos

If they were going to only try to recover the engines/thrust structure ala an orbital SMART, they might go with something like a HIAD.  For a full 2nd stage, they'll try other things.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/30/2018 01:37 PM
I think like many SpaceX development projects they will work in steps and take incremental steps from the least amount they think is possible and work up to finding out what is the minimal needed.

I can see them trying as a first step to just re-enter and not fly to a controlled path or recover.

After all that seems like the largest technical challenge.

As for the bouncy house, that's how fairing recover was described and EM said that Mr. Steven could catch a returning Dragon.  So maybe the SpaceX navy would be catching Upper stages as well.

Should be interesting to watch.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 04/30/2018 02:29 PM

Nah
I would bet against each of this guy’s guesses and interpretations.
It’s not “obvious”. It doesn’t “have to be”.
SpaceX is not going to rig up some complex structure like HIAD or whatever
They can’t surround the second stage in airbags. It’s too big and they couldn’t be well distributed
All of his borrowed video snippets are irrelevant.
True.
Just  the KE alone (27 mega m/s Vs 5 mega m/s) makes it 29x harder in energy dissipated before we get to the potential energy of the increased altitude.

I comes down to this.
1) You want the engines in the rear.
2) A rear heavy object wants to flip heavy end forward.
3) Too much side load and the (very) lightweight tank walls collapse.

How you keep the loads along the stage, and the engines pointing backward, are the crux of the problem.


Now a really big skirt (with minimum TPS) just above the engine bay can
a) Radically increase drag in the high (near vacuum) atmosphere so the stage is moving much more slowly before it descends to the thicker low atmosphere. big deceleration. Small(ish) heating.
b) Keep the light end (with a thick, simple PICX heatshield) pointing into the airstream.

As long as it last long enough to get into the air density where the grid fins can work then your home dry.

But the exact details are very tricky and clearly SX have learned some new science since 2014 when Musk last visited this issue.
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 04/30/2018 03:32 PM
But the exact details are very tricky and clearly SX have learned some new science since 2014 when Musk last visited this issue.

Maybe they just have enough performance margin for some LEO missions to make an attempt.

Block 5 is over kill for many possible missions, may as well make use of that when possible to experiment.

Plus if they manage to make it work they could lower the costs of such missions even further.  That would be an interesting market option.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 04/30/2018 03:40 PM

Nah
I would bet against each of this guy’s guesses and interpretations.
It’s not “obvious”. It doesn’t “have to be”.
SpaceX is not going to rig up some complex structure like HIAD or whatever
They can’t surround the second stage in airbags. It’s too big and they couldn’t be well distributed
All of his borrowed video snippets are irrelevant.
True.
Just  the KE alone (27 mega m/s Vs 5 mega m/s) makes it 29x harder in energy dissipated before we get to the potential energy of the increased altitude.

I comes down to this.
1) You want the engines in the rear.
2) A rear heavy object wants to flip heavy end forward.
3) Too much side load and the (very) lightweight tank walls collapse.

How you keep the loads along the stage, and the engines pointing backward, are the crux of the problem.


Now a really big skirt (with minimum TPS) just above the engine bay can
a) Radically increase drag in the high (near vacuum) atmosphere so the stage is moving much more slowly before it descends to the thicker low atmosphere. big deceleration. Small(ish) heating.
b) Keep the light end (with a thick, simple PICX heatshield) pointing into the airstream.

As long as it last long enough to get into the air density where the grid fins can work then your home dry.

But the exact details are very tricky and clearly SX have learned some new science since 2014 when Musk last visited this issue.

An inflatable radically changes the COP/COM equation, the engine location becomes less critical.

With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Title: Re: F9 Second Stage Reusability
Post by: speedevil on 04/30/2018 04:08 PM
With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Stagnation temperatures drop to 800C and heat flux at that temperature goes way down, meaning some things might not need protection at all for the several tens of seconds of peak heating.

Excited to see what it actually is.
Title: Re: F9 Second Stage Reusability
Post by: kraisee on 05/02/2018 01:58 AM
With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.

With some fried PINEAPPLE, that'll make for a delicious snack after they land. :)

Oh...

Ross.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 05/02/2018 07:32 AM
An inflatable radically changes the COP/COM equation, the engine location becomes less critical.

With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Certainly shifts the CoP. Not so sure about the Centre of Mass. AFAIK the consensus remains the engine bay will be the heaviest section of the stage.

To lower the ballistic coefficient 100x needs a skirt about 16.5m (54 feet)  in width.

That's a pretty substantial unfurling task. Not impossible, but tough. If it can be made like those emergency slides aircraft use you could get quite a lot of area in a fairly small space, using inflatable tubes to stiffen it.
Title: Re: F9 Second Stage Reusability
Post by: matthewkantar on 05/02/2018 12:22 PM
Quote from Elon Musk in a comment below the recent Instagram photo of the fairing descending under a parachute: "No, the upper stage engine is designed for vacuum operation only. We will either bring it in hot and fast Dragon style with a heat shield on front or slower with a giant party balloon."

I guess they are still in the concept phase of design on this. 
Title: Re: F9 Second Stage Reusability
Post by: wannamoonbase on 05/02/2018 12:33 PM
Quote from Elon Musk in a comment below the recent Instagram photo of the fairing descending under a parachute: "No, the upper stage engine is designed for vacuum operation only. We will either bring it in hot and fast Dragon style with a heat shield on front or slower with a giant party balloon."

I guess they are still in the concept phase of design on this. 

They have existing heat shield capabilities, I believe they’ll start there. 

Edit: Spelling.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 05/02/2018 01:27 PM
An inflatable radically changes the COP/COM equation, the engine location becomes less critical.

With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Certainly shifts the CoP. Not so sure about the Centre of Mass. AFAIK the consensus remains the engine bay will be the heaviest section of the stage.

To lower the ballistic coefficient 100x needs a skirt about 16.5m (54 feet)  in width.

That's a pretty substantial unfurling task. Not impossible, but tough. If it can be made like those emergency slides aircraft use you could get quite a lot of area in a fairly small space, using inflatable tubes to stiffen it.

A toroidal ballute around the engine would probably be easier than a skirt, but a simple spherical towed ballute hanging off the bottom of the stage would probably be easiest.
Title: Re: F9 Second Stage Reusability
Post by: john smith 19 on 05/02/2018 04:21 PM
An inflatable radically changes the COP/COM equation, the engine location becomes less critical.

With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Certainly shifts the CoP. Not so sure about the Centre of Mass. AFAIK the consensus remains the engine bay will be the heaviest section of the stage.

To lower the ballistic coefficient 100x needs a skirt about 16.5m (54 feet)  in width.

That's a pretty substantial unfurling task. Not impossible, but tough. If it can be made like those emergency slides aircraft use you could get quite a lot of area in a fairly small space, using inflatable tubes to stiffen it.

A toroidal ballute around the engine would probably be easier than a skirt, but a simple spherical towed ballute hanging off the bottom of the stage would probably be easiest.
Like a sort of space "sea anchor" ?

One problem with that would be the mounting. I'd think you'd want to put it as close to the center as possible but that's occupied by the engine. So off center you've got a force tugging the off its line, or you need say a 3 or 4 point attachment arrangement around the nozzle to equalize loads. Again, tricky to deploy reliably. A smaller ballute, one per mounting point, might be easier, but now you need all of them to inflate or you get the the uneven loading.

Just remembered. 800c is probably in the range of the Dunlop developed woven metal "airmat" technology. Unfortunately I don't know of any plastics that go above 400c (IIRC 300-350c is pretty challenging for regular use).

OTOH probably well within the range of a layer of flexible PICAX, which SX should have access to.
Title: Re: F9 Second Stage Reusability
Post by: envy887 on 05/02/2018 05:35 PM
An inflatable radically changes the COP/COM equation, the engine location becomes less critical.

With a 100x increase in ballistic coefficient, you don't need PICA-X. Stagnation temperatures drop to ~800 C or lower and easily into the working range of COTS ceramics and metals or a coating of SPAM.
Certainly shifts the CoP. Not so sure about the Centre of Mass. AFAIK the consensus remains the engine bay will be the heaviest section of the stage.

To lower the ballistic coefficient 100x needs a skirt about 16.5m (54 feet)  in width.

That's a pretty substantial unfurling task. Not impossible, but tough. If it can be made like those emergency slides aircraft use you could get quite a lot of area in a fairly small space, using inflatable tubes to stiffen it.

A toroidal ballute around the engine would probably be easier than a skirt, but a simple spherical towed ballute hanging off the bottom of the stage would probably be easiest.
Like a sort of space "sea anchor" ?

One problem with that would be the mounting. I'd think you'd want to put it as close to the center as possible but that's occupied by the engine. So off center you've got a force tugging the off its line, or you need say a 3 or 4 point attachment arrangement around the nozzle to equalize loads. Again, tricky to deploy reliably. A smaller ballute, one per mounting point, might be easier, but now you need all of them to inflate or you get the the uneven loading.

Just remembered. 800c is probably in the range of the Dunlop developed woven metal "airmat" technology. Unfortunately I don't know of any plastics that go above 400c (IIRC 300-350c is pretty challenging for regular use).

OTOH probably well within the range of a layer of flexible PICAX, which SX should have access to.

That's the idea. Why wouldn't an off-center mounting work? There's no reason the stage has to be pointed directly into the airflow. A slightly off-center mount would cause the stage to tip away from the tow rope so that the nozzle bell would clear it.

A 400 C material might work if the heat flux is low enough that you can dissipate it radiatively. Many highly stressed materials operate in environments beyond their melting temperatures (jet turbine blades), and sometimes beyond their boiling temperatures (regeneratively cooled rocket engines).

If you need more temperature resistant materials, a thin layer of woven ceramic might work. Like 3M Nextel (https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Nextel-Fabric-AF-62/?N=5002385+3292678376&rt=rud) with a melting point of 1800 C. It's 980 g/m^2 so 1,300 kg of it would cover the hot half of a 30 m sphere.
Title: Re: F9 Second Stage Reusability
Post by: meekGee on 05/03/2018 06:38 PM