Author Topic: SpaceX Falcon Heavy Demo - Discussion and Speculation (Read 243635 times)

cppetrie · « **Reply #320 on:** 04/01/2017 02:35 pm »

Quote from: Barrie on 04/01/2017 02:20 pm

Mount a dragon 2 on the payload adaptor upside down. Just land the Dragon 2 as normal with the 2nd stage on top.

That might get the 2nd stage back, but it does nothing to advance 2nd stage reusability since attaching a dragon won't be an option on an actual payload flight. Also seems like the weight distribution is likely to result in the vehicle tumbling and getting destroyed.

Barrie · « **Reply #321 on:** 04/01/2017 03:54 pm »

Quote from: cppetrie on 04/01/2017 02:35 pm

Quote from: Barrie on 04/01/2017 02:20 pm
Mount a dragon 2 on the payload adaptor upside down. Just land the Dragon 2 as normal with the 2nd stage on top.
That might get the 2nd stage back

Really? I thought I was kidding! But if it did work, you would have data and could then set about designing a more functional minimum-hardware version of it.

cppetrie · « **Reply #322 on:** 04/01/2017 04:00 pm »

Quote from: Barrie on 04/01/2017 03:54 pm

Quote from: cppetrie on 04/01/2017 02:35 pm
Quote from: Barrie on 04/01/2017 02:20 pm
Mount a dragon 2 on the payload adaptor upside down. Just land the Dragon 2 as normal with the 2nd stage on top.
That might get the 2nd stage back

Really? I thought I was kidding! But if it did work, you would have data and could then set about designing a more functional minimum-hardware version of it.

Sorry, the sarcasm font on my phone wasn't working. Your suggestion is hardly the most ridiculous legitimate suggestion I've seen on this forum.

docmordrid · « **Reply #323 on:** 04/01/2017 07:31 pm »

It's not like an inverted capsule hasn't been done before (ISRO)

One PICA-X 3 reentry test, comin' right up.

AncientU · « **Reply #324 on:** 04/01/2017 08:16 pm »

Quote

... we're probably going to fly something really silly ...

Eric Berger

Quote

This is why most of us in the space industry who are not competing with Elon, love Elon.

https://twitter.com/SciGuySpace

Yup.

WTF · « **Reply #325 on:** 04/01/2017 08:50 pm »

2nd stage recovery

Three observations, An assumption, and a sequence.

Three observations:
Landing burn is problematic … so do not do it.
Legs are heavy … so do not attach them.
Parachutes are relatively light.

Speculation:
Might have extra fuel in the second stage after dummy payload delivery.

Sequence::

For reentry … after payload delivery, flip the 2nd stage … burn off the hypersonic velocity using that extra fuel available … all the way down to trans-sonic (if not even slower) at an atmospheric density where that vacuum efficient engine is still effective, but not being destroyed by atmospheric conditions.

Then deploy those parachutes … which are stored at the top of the second stage.

And there you are. The vacuum size bell is certainly destroyed upon landing stresses, probably even some of the engine, but the 2nd stage is back.

Seems too easy.

Future enhancements:
Guided parachute to land on barge/land.

Develop a cradle device to catch the second stage keeping that bell and engine intact … with a view toward upscaling it to handle the ITS. 2024 or so is not all that far in the future.

ugordan · « **Reply #326 on:** 04/01/2017 08:56 pm »

Quote from: WTF on 04/01/2017 08:50 pm

For reentry … after payload delivery, flip the 2nd stage … burn off the hypersonic velocity using that extra fuel available … all the way down to trans-sonic (if not even slower) at an atmospheric density where that vacuum efficient engine is still effective, but not being destroyed by atmospheric conditions.

You're suggesting that the 2nd stage do 7 km/s worth of a breaking burn?

WTF · « **Reply #327 on:** 04/01/2017 09:52 pm »

Exactly.

After fuel expended taking dummy payload to orbit (dummy payload being rather light), 2nd stage is much lighter.

Has anyone done the BOE (Back Of Envelope) calculations on that ?

JazzFan · « **Reply #328 on:** 04/01/2017 10:08 pm »

Quote from: Eagandale4114 on 03/31/2017 07:58 pm

In response to: "serious q: if it fails, what do you have to lose?"

Elon: Good point, odds go from 0% to >0%

Damage to a landing pad or recovery barge is still no laughing matter. SpaceX already has a nice launch backlog.

sdsds · « **Reply #329 on:** 04/01/2017 11:02 pm »

Quote from: ugordan on 04/01/2017 08:56 pm

Quote from: WTF on 04/01/2017 08:50 pm
For reentry … after payload delivery, flip the 2nd stage … burn off the hypersonic velocity using that extra fuel available … all the way down to trans-sonic (if not even slower) at an atmospheric density where that vacuum efficient engine is still effective, but not being destroyed by atmospheric conditions.

You're suggesting that the 2nd stage do 7 km/s worth of a breaking burn?

WTF says yes but I'm not convinced that's exactly what it comes to. What velocity at entry interface could the vehicle survive if the MVac is firing retropropulsively? Naively, the result of running that experiment might be interesting. How deep into the atmosphere can the vehicle get with the engine plume providing a heat shield? Suppose it got so deep that flow separation in the MVac nozzle started causing trouble. What's the state vector (altitude, speed) there? How close to that is a state where parachutes could hope to take over?

rakaydos · « **Reply #330 on:** 04/01/2017 11:46 pm »

Quote from: sdsds on 04/01/2017 11:02 pm

Quote from: ugordan on 04/01/2017 08:56 pm
Quote from: WTF on 04/01/2017 08:50 pm
For reentry … after payload delivery, flip the 2nd stage … burn off the hypersonic velocity using that extra fuel available … all the way down to trans-sonic (if not even slower) at an atmospheric density where that vacuum efficient engine is still effective, but not being destroyed by atmospheric conditions.

You're suggesting that the 2nd stage do 7 km/s worth of a breaking burn?
i

WTF says yes but I'm not convinced that's exactly what it comes to. What velocity at entry interface could the vehicle survive if the MVac is firing retropropulsively? Naively, the result of running that experiment might be interesting. How deep into the atmosphere can the vehicle get with the engine plume providing a heat shield? Suppose it got so deep that flow separation in the MVac nozzle started causing trouble. What's the state vector (altitude, speed) there? How close to that is a state where parachutes could hope to take over?

I recall reading some scholarly work (over my head) about supersonic retropropulsion, a year or two ago, that suggested that a vertical plume actually reduces air drag, in a sort of supercavitation type effect. (it went on to suggest that angled plumes can reverse this effect by effectively increasing how much of the air the rocket interacts with)
I think this implies that silmotanius retropropulsion and air drag based speed reduction just doesnt work out.

Falcon9 does the entry burn, then lets air drag happen, then does the landing burn. Upperstage needs to do a massive entry burn to be anything comparable, and I dont know if it's light enough to make parachutes reasonable afterwrd.

Flying Beaver · « **Reply #331 on:** 04/02/2017 12:14 am »

I'll just throw my 2 cents in to the second stage recovery discussion.

Elon isn't stupid. He wouldn't delay FH's demo just to add landing legs and Super Draco's to the second stage.

In his engineering mind (Cuz I wouldn't be surprised if he didn't talk to the 'making crazy ideas work' team before tweeting) he's thinking of what can be easily done in 6 months time that might make the second stage recoverable. Seeing that his thinking is being put towards FH demo, suggests that the massive fuel margin has something to do with the idea (close on 5km/s Dv).

SpaceX has available the most advanced thermal protection system ever used in spaceflight (PICA-X 3.0). Being extremely light it could be very easily applied to the stage - this, I'm sure, is part of Elon's plan.

Given the recent success of Fairing recovery, with steerable parafoils, Elon's feeling particularly confident in there technology, and seeing the picture of the fairing under chute, probably jogged his mind back to S2 recovery.

So practically thinking, these techs could be integrated into a S2 in time for FH Demo (seeing it's always 6 months away

). Also it probably means RIP MVAC nozzle, but it's not priority.

As I said, my 2 cents.

guckyfan · « **Reply #332 on:** 04/02/2017 01:58 am »

Doing a reentry method that is in no way applicable to economic reuse is not what I expect from Elon Musk. So IMO it would not involve serious braking using the engines. Not beyond what is needed for deorbit.

meekGee · « **Reply #333 on:** 04/02/2017 02:34 am »

Quote from: guckyfan on 04/02/2017 01:58 am

Doing a reentry method that is in no way applicable to economic reuse is not what I expect from Elon Musk. So IMO it would not involve serious braking using the engines. Not beyond what is needed for deorbit.

Exactly. Slowing down from orbital speed to S1-like speeds (a delta V of about 6 km/sec, maybe 7) takes a mass ratio of 7:1, so the second stage has to start at 35 tons or so after payload separation.

Even if this was somehow possible, it doesn't present a way forward for future reuse.

Aerobraking has to happen. Exactly how, and what happens afterwards, is what's on the table.

SpaceX can aerobrake Dragon. Dragon is similar to S2 in terms of mass and aspect ratio, but dissimilar in shape and location of c.g.

Parachute and heat-shield will help with the c.g.
Maybe an optional drag device can help moving the center of drag backwards.
Active control can help too, either by way of aerodynamics, RCS, or movable mass.

What happens after reentry is "the second problem".
Parachute and air grab?
Landing engine and legs?

Hey - can they help prove out Dragon 2 landings using S2 and superDracos?

butters · « **Reply #334 on:** 04/02/2017 02:41 am »

This mission also has to function as acceptable demo for DoD, which means that one-off mods to the upper stage will be discouraged if not vetoed outright.

Robotbeat · « **Reply #335 on:** 04/02/2017 02:43 am »

Quote from: butters on 04/02/2017 02:41 am

This mission also has to function as acceptable demo for DoD, which means that one-off mods to the upper stage will be discouraged if not vetoed outright.

Upper stage is the one part that is basically unchanged.

meekGee · « **Reply #336 on:** 04/02/2017 02:59 am »

Quote from: butters on 04/02/2017 02:41 am

This mission also has to function as acceptable demo for DoD, which means that one-off mods to the upper stage will be discouraged if not vetoed outright.

Sure, but we went through this cycle several times with S1 and reusability hardware. There is a certain level of modification that is acceptable, and it's still considered "the same stage". Like add-ons. If it flies with an extra parachute tucked away near the top, it probably won't matter. If it flies with a heat shield in front - it's still a pretty small change as far as the up-trip is concerned.

But clearly fairing/no fairing is important enough to matter. So I'm guessing it's up to SpaceX to get approval from DoD for the configuration they want to fly.

biosehnsucht · « **Reply #337 on:** 04/02/2017 07:11 am »

Maybe the dummy payload could be a slightly downsized (to fit in the fairing) mass / aerodynamic simulator of a second stage, and thus the actual second stage isn't being modified ...

sdsds · « **Reply #338 on:** 04/02/2017 07:26 am »

Second stage re-use probably isn't in the cards for Falcon. So physical modifications to the demo flight second stage are unlikely just to run an experiment. But there's available propellant so why not gather what data you can from an experimental retro-propulsive disposal of the second stage? This experiment in no way adds risk to the primary mission of the stage and in no way devalues the significance of the flight for certification of the launch vehicle.

The only cost is developing the firmware that controls the stage during the experiment.

guckyfan · « **Reply #339 on:** 04/02/2017 08:40 am »

OK, after following this discussion I come up with the ultimate Rube Goldberg machine.

A second stage with PicaX on top and on one side. A magical device that keeps it oriented head on for reentry. Forget about landing, declare it a success when it stays in one piece and hits the ocean still sending telemetry data.

On to a fairing for the Airforce demo. Inside the fairing the biggest off the shelf solid upper stage FH can carry and a minimal Dragon on top of it. After payload separation the solid stage accelerates Dragon as much as it can plus Dragon adds whatever delta-v it has, maybe at perigee after a first ellipse. That may not be a full translunar injection but the first Orion also did not achieve that. It goes a long way towards a loop around the moon as a demo.