totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

1 hour ago, Skylon said:

Would second stage adaptations for reusability compromise structural strength? Will we ever see an upgraded Falcon 9 with better structural integrity so it can actually lift the payload so it says it can, a Falcon 9 Mk6 (to continue the naming scheme) of sorts?

There is already an upgraded payload adapter planned for FH.

[StupidAndy]

since SpaceX is basically rebuilding SLC-40, couldn't they do some Elon magic and upgrade it a bit?

[IncongruousGoat]

1 hour ago, StupidAndy said:

since SpaceX is basically rebuilding SLC-40, couldn't they do some Elon magic and upgrade it a bit?

Not really. As I understand it, the things that were destroyed by the Amos-6 explosion were strictly service structures. Substantial pad upgrades (to allow it to handle FH, for example) would require rebuilding the flame trench, which would be way too expensive for any potential benefit to offset. Also, why would they upgrade it? They already have a perfectly good FH pad at LC-39A, and they're building their own facilities for ITS at Brownsville.

[wumpus]

On 6/11/2017 at 9:49 AM, sevenperforce said:

Falcon Heavy can definitely reuse the second stage, if it takes a performance cut. Heck, Falcon 9 can reuse the second stage, though usable payload drops quite low. It's just something they haven't fully developed.

Spacex has been claiming this, with the usual Elon schedule.  I have my doubts, but the second stage should come down with a lower terminal velocity (only one merlin engine instead of 9, same cross section, same rough shape).  One big issue is landing the thing on a vacuum-optimized engine: I have no idea how much thrust that thing puts out at sea level.

They seemed to have shelved the whole idea indefinitely and recently brought it back.  Possibly they found a return trajectory that they've managed to get a few to survive (even if they never bothered with the other burns and fin control).

[tater]

1 minute ago, wumpus said:

Spacex has been claiming this, with the usual Elon schedule.  I have my doubts, but the second stage should come down with a lower terminal velocity (only one merlin engine instead of 9, same cross section, same rough shape).  One big issue is landing the thing on a vacuum-optimized engine: I have no idea how much thrust that thing puts out at sea level.

They seemed to have shelved the whole idea indefinitely and recently brought it back.  Possibly they found a return trajectory that they've managed to get a few to survive (even if they never bothered with the other burns and fin control).

This got discussed a bit in the old, dead thread (I asked a similar question regarding the vac Merlin). Turns out the video they did years ago shows the answer, they have landing thrusters, they would only use the vac engine for the reentry burn, then land with drakes or something. 

[sevenperforce]

1 minute ago, wumpus said:

Spacex has been claiming this, with the usual Elon schedule.  I have my doubts, but the second stage should come down with a lower terminal velocity (only one merlin engine instead of 9, same cross section, same rough shape).  One big issue is landing the thing on a vacuum-optimized engine: I have no idea how much thrust that thing puts out at sea level.

They seemed to have shelved the whole idea indefinitely and recently brought it back.  Possibly they found a return trajectory that they've managed to get a few to survive (even if they never bothered with the other burns and fin control).

They definitely cannot land on the Merlin, so they'd either need chutes or aux thrusters. But building a custom payload adapter that either integrates or functions as a heat shield would be pretty straightforward. The challenges are passive stabilization during re-entry, to keep the heavy Merlin from flipping the whole stage forward, and the actual terminal landing.

[Rakaydos]

9 minutes ago, wumpus said:

Spacex has been claiming this, with the usual Elon schedule.  I have my doubts, but the second stage should come down with a lower terminal velocity (only one merlin engine instead of 9, same cross section, same rough shape).  One big issue is landing the thing on a vacuum-optimized engine: I have no idea how much thrust that thing puts out at sea level.

They seemed to have shelved the whole idea indefinitely and recently brought it back.  Possibly they found a return trajectory that they've managed to get a few to survive (even if they never bothered with the other burns and fin control).

Current speculation on NSF is a nose landing, to protect the (non retracting) vac bell from supersonic winds.

Basically fitting a "landing module" secondary payload between the second stage and the payload adapter. The (entirely optional) landing module has the primary heat shield, superdraco landing thrusters, and landing legs, bringing the center of gravity foreward of the center of pressure.

Any mission small enough can get a rebate for allowing 2nd stage recovery. those that are too heavy, go with the stock falcon9/heavy

Edited June 12, 2017 by Rakaydos

[kerbinorbiter]

4 minutes ago, sevenperforce said:

They definitely cannot land on the Merlin, so they'd either need chutes or aux thrusters. But building a custom payload adapter that either integrates or functions as a heat shield would be pretty straightforward. The challenges are passive stabilization during re-entry, to keep the heavy Merlin from flipping the whole stage forward, and the actual terminal landing.

1. Aux thrusters would be too heavy 

2. That payload adapter would be a cargo bay

[sevenperforce]

34 minutes ago, kerbinorbiter said:

1. Aux thrusters would be too heavy 

2. That payload adapter would be a cargo bay

The mass of the aux thrusters is really not that high; the tricky thing would be placement and fuel choice. 

The current payload adapter is a big metal ring/cylinder bolted onto the top of the stage. It would need to have TPS added to it. That's all; no cargo bay required.

[cratercracker]

What if we mount 4 solid fuel thrusters ,facing the other side at the second stage.

So my ideas is too reuse second stage too, but now, without cutting down on liquid fuel for the descent burn.

+ it would be better and easier to land on parachutes if you are reusing second stage.

 

Or I am just playing KSP too much..

Edited June 12, 2017 by cratercracker

[KSK]

17 minutes ago, cratercracker said:

What if we mount 4 solid fuel thrusters ,facing the other side at the second stage.

So my ideas is too reuse second stage too, but now, without cutting down on liquid fuel for the descent burn.

+ it would be better and easier to land on parachutes if you are reusing second stage.

Or I am just playing KSP too much..

Afraid so. I'd have thought that the extra fuel required to get those solid rockets into orbit in the first place will negate any fuel you save by using them for the descent burn. SRBs are heavy.

Landing the second stage on parachutes would involve the same problems that landing the first stage on parachutes did. Packing enough parachute to slow that stage down to a survivable landing speed is not trivial. Precision landings by parachute are not easy either.

[wumpus]

1 hour ago, KSK said:

Afraid so. I'd have thought that the extra fuel required to get those solid rockets into orbit in the first place will negate any fuel you save by using them for the descent burn. SRBs are heavy.

Landing the second stage on parachutes would involve the same problems that landing the first stage on parachutes did. Packing enough parachute to slow that stage down to a survivable landing speed is not trivial. Precision landings by parachute are not easy either.

SRBs can be heavy, but if you only need them for a short, high thrust burn they should be wildly lighter than carrying a rocket motor for a short burn.  My kerbal solution would be SRBs (two or three arranged around the center) that would be constructed to match the trust profile you need (KSP gets it wrong: having multiple levels of thrust for SRBs is easier than on liquid rockets.  The difference is you don't get to change the thrust level in flight).  Hopefully you the center of mass is high enough you can mount them so they are still firing after it lands (obviously TWR<1).  Then add some hybrid rockets (easy to make throttleable) for actual control of the landing.

https://www.youtube.com/watch?v=glEvogjdEVY If my eyes got it right, the landing burn was 6 seconds.  That really screams "use a SRB" (assuming the main rocket is right out), although you will need something else for fine control.

 

[KSK]

Fair enough, although I have to say that the landing module that @Rakaydos mentioned is plenty Kerbal enough for me.

 

[Skylon]

Could the second stage use deployable wings? Probably deployed after reentry stress and heating, and with landing gear, skids or landing on a bouncy castle or net kind of thing. Would make it a true falcon.

[magnemoe]

59 minutes ago, wumpus said:

SRBs can be heavy, but if you only need them for a short, high thrust burn they should be wildly lighter than carrying a rocket motor for a short burn.  My kerbal solution would be SRBs (two or three arranged around the center) that would be constructed to match the trust profile you need (KSP gets it wrong: having multiple levels of thrust for SRBs is easier than on liquid rockets.  The difference is you don't get to change the thrust level in flight).  Hopefully you the center of mass is high enough you can mount them so they are still firing after it lands (obviously TWR<1).  Then add some hybrid rockets (easy to make throttleable) for actual control of the landing.

https://www.youtube.com/watch?v=glEvogjdEVY If my eyes got it right, the landing burn was 6 seconds.  That really screams "use a SRB" (assuming the main rocket is right out), although you will need something else for fine control.

Small liquid fuel engines are light, you can integrate them as part of the landing leg structure, think hip joint.
Yes it use of the liquid fuel store but that is also an emergency fuel source if something goes wrong. 

[KSK]

20 minutes ago, Skylon said:

Could the second stage use deployable wings? Probably deployed after reentry stress and heating, and with landing gear, skids or landing on a bouncy castle or net kind of thing. Would make it a true falcon.

I'm guessing 'probably not' at least without a lot of reinforcement and the associated mass penalty.  It doesn't take much to bust up a rocket stage - remember the early 'landing over water' test flights with F9? The booster would land, topple over and break up.

Edited June 12, 2017 by KSK

[wumpus]

1 hour ago, magnemoe said:

Small liquid fuel engines are light, you can integrate them as part of the landing leg structure, think hip joint.
Yes it use of the liquid fuel store but that is also an emergency fuel source if something goes wrong. 

It has to be roughly as powerful as the onboard engine throttled down to limit (40%?).  It can be light, but I'd still expect a 7 second SRB to be a lot lighter than a fuel engine + fuel.

Also I think its "deployable wings" would be similar [probably identical] to the [first stage] Falcon's paddles.  From what I understand, even scaled composites has given up on deployable wings for re-entry (they might recommend such a scheme for the first stage booster).

[Rakaydos]

2 hours ago, wumpus said:

It has to be roughly as powerful as the onboard engine throttled down to limit (40%?).  It can be light, but I'd still expect a 7 second SRB to be a lot lighter than a fuel engine + fuel.

The dry mass of the upper stage, according to wikipedia, is about 4000 kilos. (4 tons)

Thrust of a single SuperDraco, same source, is 71 kilonewtons. 4 of them are enough to land a 6.4 ton (dry) Dragon 2 (though it carries 8 superdracos for redundancy) with 1.4 tons of hypergolic fuel, enough for 25 seconds of operation.

Wolfram Alpha calculates 4 superdracos would land a drymass dragon 2 at just over 4 g (clearly, it's gong to be a bit less because there's still fuel it's burning, but that's the ballpark for landing speed)

Lets assume a worst case, where stripping the Dragon's pressure vessel and all the draco maneuver thrusters saves no mass at all, and everything else is exactly the same as the dragon 2. That gives a 7.8 ton "landing module" to take out of Falcon 9 FT's 10.8 ton reusable LEO mass, or 7.8 tons from Falcon heavy's 63.8 tons to LEO or 26.7 tons GTO.

Assuming these worst case numbers, an off the shelf (read as- Cheap) recovery system is marginally useful for Falcon 9 FT (though Block 5 has better LEO numbers, I didnt see them on wikipedia), but amazing on Falcon Heavy.

[kerbiloid]

Or return/landing/ullage small engines on kerosene from the big ones and peroxide from a small rank, with rcs engines on peroxide and kerosene, too. Like i'm doing for my KSP reality.

rank = tank, hate autocorrection and can't edit from pad

Also this gives a mini-shuttle on kerosene, lox and peroxide, with turbojets on kerosene

[Rakaydos]

58 minutes ago, kerbiloid said:

Or return/landing/ullage small engines on kerosene from the big ones and peroxide from a small rank, with rcs engines on peroxide and kerosene, too. Like i'm doing for my KSP reality.

rank = tank, hate autocorrection and can't edit from pad

Also this gives a mini-shuttle on kerosene, lox and peroxide, with turbojets on kerosene

The merlin is too powerful, and the Kestrel isnt in production. Also a GTO return may involve a longer wait time than LOX can handle. The Superdraco, on the other hand, is just the right power and already in production.

SpaceX has more to worry about than a kerbal player.

Edited June 13, 2017 by Rakaydos

[kerbiloid]

Superdraco requires udmh+at, two more substances in their own tanks, incompatible with the main engine. While using kerosene, which is already onboard + htp which makes it hypergolic, allows to add just one small tank with htp and to choose whether you will burn all kerosene in a one-way flight, or reserve a little to return and land.

So, unless the falcon is udmh+at, this looks like a lesser evil.

[Rakaydos]

10 minutes ago, kerbiloid said:

Superdraco requires udmh+at, two more substances in their own tanks, incompatible with the main engine. While using kerosene, which is already onboard + htp which makes it hypergolic, allows to add just one small tank with htp and to choose whether you will burn all kerosene in a one-way flight, or reserve a little to return and land.

So, unless the falcon is udmh+at, this looks like a lesser evil.

you may notice that Raptor isnt flying yet. neither is BE4, or the SLS engines.

Designing a new engine is not a lesser evil compared to adding more tanks. especially if the extra tanks add flexibility by being removable if you arnt landing on a mission.

Edited June 13, 2017 by Rakaydos

[kerbiloid]

They've already designef a bunch, and this one would be the smallest between them, non-cryo and maybe even not turbopumped. While tanks cost weight.

[Rakaydos]

2 minutes ago, kerbiloid said:

They've already designef a bunch, and this one would be the smallest between them, non-cryo and maybe even not turbopumped. While tanks cost weight.

They've already designed the Superdraco. Part commonality saves cost. If it ends up weighing an extra half ton for separate tanks, that just comes out of the reuse mass budget. The Falcon Heavy, especially, can afford the cost.

[KerbalNetwork]

SpaceX is going to launch another Falcon 9, scheduled to launch in 4 more days (June 17) with onboard payload Bulgaria Sat. 

The rocket's going to be launched at Kennedy Space Center, LC-39A, the one that Saturn V has launched from.

I did a quick research, and found out that it's Bulgaria's first "geostationary communications satellite"

Edited June 13, 2017 by KerbalNetwork