Author Topic: F9 Second Stage Reusability  (Read 188326 times)

Offline smfarmer11

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Re: F9 Second Stage Reusability
« Reply #320 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.

Offline whitelancer64

Re: F9 Second Stage Reusability
« Reply #321 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...
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Offline wannamoonbase

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Re: F9 Second Stage Reusability
« Reply #322 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. 
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Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #323 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.
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Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #324 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.
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #325 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. 
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Offline MikeAtkinson

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Re: F9 Second Stage Reusability
« Reply #326 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.

Offline hkultala

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Re: F9 Second Stage Reusability
« Reply #327 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.
« Last Edit: 04/12/2017 09:14 PM by hkultala »

Offline sojourner

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Re: F9 Second Stage Reusability
« Reply #328 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..
« Last Edit: 04/13/2017 02:50 AM by sojourner »

Offline rakaydos

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Re: F9 Second Stage Reusability
« Reply #329 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.

Offline sojourner

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Re: F9 Second Stage Reusability
« Reply #330 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.

Online CharlieWildman

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Re: F9 Second Stage Reusability
« Reply #331 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!


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Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #332 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.

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #333 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)

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Offline Rei

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Re: F9 Second Stage Reusability
« Reply #334 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.
« Last Edit: 04/13/2017 10:40 AM by Rei »

Offline MikeAtkinson

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Re: F9 Second Stage Reusability
« Reply #335 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.

Offline wes_wilson

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Re: F9 Second Stage Reusability
« Reply #336 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.



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Offline Steve G

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Re: F9 Second Stage Reusability
« Reply #337 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.

Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #338 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.


Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #339 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.
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