Author Topic: F9 Second Stage Reusability  (Read 66106 times)

Offline watermod

  • Full Member
  • ***
  • Posts: 339
  • Liked: 84
  • Likes Given: 99
Re: F9 Second Stage Reusability
« Reply #40 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?


Offline su27k

  • Full Member
  • ****
  • Posts: 487
  • Liked: 274
  • Likes Given: 33
Re: F9 Second Stage Reusability
« Reply #41 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...

Offline Ludus

  • Full Member
  • ****
  • Posts: 663
  • Liked: 221
  • Likes Given: 94
Re: F9 Second Stage Reusability
« Reply #42 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.

Offline Space Ghost 1962

  • Senior Member
  • *****
  • Posts: 2088
  • Whatcha gonna do when the Ghost zaps you?
  • Liked: 1807
  • Likes Given: 1292
Re: F9 Second Stage Reusability
« Reply #43 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.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26063
  • Minnesota
  • Liked: 6072
  • Likes Given: 4490
Re: F9 Second Stage Reusability
« Reply #44 on: 04/01/2017 05:45 AM »
You can waste performance on the Falcon Heavy demo mission.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Clueless Idiot

  • Member
  • Posts: 12
  • USA
  • Liked: 1
  • Likes Given: 0
Re: F9 Second Stage Reusability
« Reply #45 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.

Offline dorkmo

  • Full Member
  • ****
  • Posts: 619
  • Liked: 280
  • Likes Given: 733
Re: F9 Second Stage Reusability
« Reply #46 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

Offline MKremer

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 3901
  • Liked: 11
  • Likes Given: 468
Re: F9 Second Stage Reusability
« Reply #47 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).

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2697
  • Liked: 372
  • Likes Given: 319
Re: F9 Second Stage Reusability
« Reply #48 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.
Waiting for joy and raptor

Offline MP99

Re: F9 Second Stage Reusability
« Reply #49 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

Offline MP99

Re: F9 Second Stage Reusability
« Reply #50 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
« Last Edit: 04/01/2017 08:47 AM by MP99 »

Offline Alastor

  • Full Member
  • **
  • Posts: 209
  • Liked: 106
  • Likes Given: 233
Re: F9 Second Stage Reusability
« Reply #51 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! :-)

Offline robert_d

  • Full Member
  • **
  • Posts: 243
  • Liked: 31
  • Likes Given: 93
Re: F9 Second Stage Reusability
« Reply #52 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.
 

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2697
  • Liked: 372
  • Likes Given: 319
Re: F9 Second Stage Reusability
« Reply #53 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.
Waiting for joy and raptor

Offline nacnud

  • Extreme Veteran
  • Full Member
  • ****
  • Posts: 1761
  • Liked: 101
  • Likes Given: 83
Re: F9 Second Stage Reusability
« Reply #54 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.

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6028
  • Germany
  • Liked: 1485
  • Likes Given: 1209
Re: F9 Second Stage Reusability
« Reply #55 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.

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2697
  • Liked: 372
  • Likes Given: 319
Re: F9 Second Stage Reusability
« Reply #56 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.
Waiting for joy and raptor

Offline nacnud

  • Extreme Veteran
  • Full Member
  • ****
  • Posts: 1761
  • Liked: 101
  • Likes Given: 83
Re: F9 Second Stage Reusability
« Reply #57 on: 04/01/2017 02:27 PM »
Entering nose first, shuttlecock style?

Offline alang

  • Full Member
  • *
  • Posts: 149
  • Liked: 40
  • Likes Given: 2
Re: F9 Second Stage Reusability
« Reply #58 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.

Offline saliva_sweet

  • Full Member
  • ****
  • Posts: 405
  • Liked: 335
  • Likes Given: 1013
Re: F9 Second Stage Reusability
« Reply #59 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.
« Last Edit: 04/01/2017 04:13 PM by saliva_sweet »

Tags: