Author Topic: F9 Second Stage Reusability  (Read 99475 times)

Offline MikeAtkinson

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Re: F9 Second Stage Reusability
« Reply #200 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.

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #201 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.
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Offline Elmar Moelzer

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Re: F9 Second Stage Reusability
« Reply #202 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.

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #203 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.
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Offline uhuznaa

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Re: F9 Second Stage Reusability
« Reply #204 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.

Offline envy887

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Re: F9 Second Stage Reusability
« Reply #205 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.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #206 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?
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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"...
« Last Edit: 04/07/2017 03:07 PM by Rocket Science »
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Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #207 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.
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Offline Lar

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Re: F9 Second Stage Reusability
« Reply #208 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.
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Offline launchwatcher

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Re: F9 Second Stage Reusability
« Reply #209 on: 04/07/2017 09:07 PM »
Elon's latest 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%.

Offline mme

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Re: F9 Second Stage Reusability
« Reply #210 on: 04/07/2017 09:28 PM »
Elon's latest 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.
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Online AncientU

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Re: F9 Second Stage Reusability
« Reply #211 on: 04/07/2017 09:42 PM »
Elon's latest 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)
« Last Edit: 04/07/2017 09:49 PM by AncientU »
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Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #212 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.
« Last Edit: 04/07/2017 09:57 PM by guckyfan »

Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #213 on: 04/07/2017 10:01 PM »
I think they were further along on s2 reusable design(maybe hardware) when Elon canned it.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
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Offline RonM

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Re: F9 Second Stage Reusability
« Reply #214 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.

Offline rakaydos

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Re: F9 Second Stage Reusability
« Reply #215 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."

Offline philw1776

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Re: F9 Second Stage Reusability
« Reply #216 on: 04/07/2017 10:28 PM »
Elon's latest 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".
« Last Edit: 04/07/2017 10:29 PM by philw1776 »
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Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #217 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.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline punder

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Re: F9 Second Stage Reusability
« Reply #218 on: 04/07/2017 10:56 PM »
Elon's latest 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.

Offline Helodriver

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Re: F9 Second Stage Reusability
« Reply #219 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.

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