Reusable Second Stage Configuration

[SVBarnard]

Alright i dont have the time to read through all these comments so here's my question. How will a rocket engine designed to work in the vaccum of space, work once it enters the atmosphere? I mean how will the Mvac operate once it enters the atmostphere?

Are there any engineering problems to be overcome here?

Also the second stage is going to be reentering head first, how are they going to flip it back over?

[aero]

Alright i dont have the time to read through all these comments so here's my question. How will a rocket engine designed to work in the vaccum of space, work once it enters the atmosphere? I mean how will the Mvac operate once it enters the atmostphere?

Not very well, but it most likely won't be needed.

Are there any engineering problems to be overcome here?

Also the second stage is going to be reentering head first, how are they going to flip it back over?

There are thoughts that it won't, it will touch down nose first with stubby little landing legs and Super Dracos.

Go ahead and take the time to skim the thread, you might find it interesting and find more focused answers to your questions.

[Owlon]

Alright i dont have the time to read through all these comments so here's my question. How will a rocket engine designed to work in the vaccum of space, work once it enters the atmosphere? I mean how will the Mvac operate once it enters the atmostphere?

Are there any engineering problems to be overcome here?

Also the second stage is going to be reentering head first, how are they going to flip it back over?

I think three general ideas have been discussed: the Mvac has a nozzle extension that is either jettisoned or retracted before reentry, leaving a nozzle that works at sea level; the stage lands using a few Superdraco engines; or the stage glides in to a soft landing using wings, similar to the X-37b.

The first idea has the issue of the M1d being substantially overpowered for landing a second stage, though it could be done with a high-g landing.

The second idea is what was actually depicted in the old reusability video, and seems the most plausible to me.

The third idea is completely outside of anything SpaceX has indicated, but doesn't have any fundamental problems I can see.

[wannamoonbase]

Alright i dont have the time to read through all these comments so here's my question. How will a rocket engine designed to work in the vaccum of space, work once it enters the atmosphere? I mean how will the Mvac operate once it enters the atmostphere?

Are there any engineering problems to be overcome here?

Also the second stage is going to be reentering head first, how are they going to flip it back over?

I think three general ideas have been discussed: the Mvac has a nozzle extension that is either jettisoned or retracted before reentry, leaving a nozzle that works at sea level; the stage lands using a few Superdraco engines; or the stage glides in to a soft landing using wings, similar to the X-37b.

The first idea has the issue of the M1d being substantially overpowered for landing a second stage, though it could be done with a high-g landing.

The second idea is what was actually depicted in the old reusability video, and seems the most plausible to me.

The third idea is completely outside of anything SpaceX has indicated, but doesn't have any fundamental problems I can see.

Using as much as possible of what you already have seems like a very SpaceX methodology.  So I expect as much similaririty to Dragon 2 in both hardware and software. 

However it's unmanned so maybe only 1 Super Draco per pod.

Perhaps Get real lean and only use 3 pods and 3 legs. (That obviously requires more software work)

[Robotbeat]

Review:

[Manabu]

What about just making the second stage capable of re-entry but nothing else, and then dock  in the air with a superdraco cluster with fuel and legs to be able to land? Minimizes the payload hit for 2nd stage recovery that way, maybe tipping the total from negative to positive. The precision in the re-entry position is the same required for other landing proposals.

Besides the crazy docking in the atmosphere at terminal velocities during a limited time window, I don't see any problems with my idea. 

[Lars_J]

Besides the crazy docking in the atmosphere at terminal velocities during a limited time window, I don't see any problems with my idea. 

[Sohl]

What about just making the second stage capable of re-entry but nothing else, and then dock  in the air with a superdraco cluster with fuel and legs to be able to land? Minimizes the payload hit for 2nd stage recovery that way, maybe tipping the total from negative to positive. The precision in the re-entry position is the same required for other landing proposals.

Besides the crazy docking in the atmosphere at terminal velocities during a limited time window, I don't see any problems with my idea. 

...

 

[Manabu]

I'm actually half serious: The main thing I like about my idea is that it does scale for big stages like future BFR stages, unlike other ideas that I've seen floating around like fishing a stage in mid-air using a quad-copter or a plane. It surely is much more complicated and risky than bringing those components in orbit with you, but at the same time is more efficient.

The tests flights to develop it will be much more exciting to see than the grasshopper tests! Has anything like that even been tried before? The closest thing I imagine is aerobatic teams displays, where they fly closely together doing various maneuvers.

[Lar]

You just want REALLY exciting test flights.... This has to work right first try and every try or there will be kabooms.

[llanitedave]

So all SpaceX has to do is design a giant, soft, forgiving rocket-powered catchers mitt, and make diving catches every time.

Wouldn't this violate the infield fly rule?

[Manabu]

Well, the test s

You just want REALLY exciting test flights.... This has to work right first try and every try or there will be kabooms.

Well, the stage for testing could be made landing capable, so even if the docking fails both halves can land safely. It will differ from the actual stage to be captured, but the grasshopper also differed from an actual F9 first stage by having larger, more advanced fixed leg, exactly for the enhanced safety on the tests.

Latter they can try to dock with the stage coming from a commercial launch, that would otherwise be expended anyway, like they are doing with the first stage of the latest F9 1.1 launches.

So all SpaceX has to do is design a giant, soft, forgiving rocket-powered catchers mitt, and make diving catches every time.

Wouldn't this violate the infield fly rule?

Infield fly rule? I have zero baseball knowledge. Anyway, I imagine that the catching stage could have enough of delta-v to catch a stage that would fall in the sea and bring it to a pad a couple of kilometers away, as it don't have to go to orbit. Haven't done any math though.

[Llian Rhydderch]

Just throwing this out there:  Altius Space Machines (Louisville, Colorado) and MSNW LLC (Redmond, Washington) are doing some preliminary work on a technology concept using a way to transfer momentum to sparse neutral (non-ionized) molecules in near-vacuum upper atmospheres, by ionizing them and injecting very small amounts of plasma into the stream.

The result is much slower deceleration of capsules/rocket bodies/debris/etc. at substantially higher altitudes then of typical atmospheric deceleration, as high as 80 to 150 km in Earth's atmosphere, with much less heat generated, reduced plasma effect on the deorbiting spacecraft, etc.  Moreover, the effective area is, in theory, controllable; effectively an ability to dial in an effective object cross-sectional area that is up to some 10 times the area of the physical spacecraft.  It is termed "magnetoshell aerocapture." 


The TRL is not high on this at present.  Here are a couple of links that describe the concept at a high-level: 

http://www.parabolicarc.com/2014/05/05/altius-space-machines/
Altius' high-level description of Variable-Drag Magnetoshell Aerocapture

Perhaps SpaceX is considering AdTech concepts like these for second stage deorbit. 

One idea to throw out something concrete for how SpaceX might do this:  add a copper wire loop connected to the to the four extensible legs of a F9 resusable second stage and use that as the requisite antenna for generating the magnetic confinement field.  Bury the copper wires on the rocket body during launch through the atmosphere, similar to parachute lines on the Dragon under breakaway tape cover, then cut loose the wires and retract the legs for the post-magnetoshell-use part of the atmospheric descent (the hypersonic/supersonic/transonic transition}, analogous to what they've already done three times with the ocean landing tests on a few of the recent F9 v1.1 flights.  Extend the legs again for landing. 

It's "out there" a bit, and needs a lot of testing.  But SpaceX is not unwilling to think "outside the box" with new concepts.  They might very well be thinking of multiple approaches for bringing second stages back that we've not yet speculated on here on NSF.

[AncientU]

The recent flights have de-orbited second stages off the southern tip of Australia where the flight profile could be monitored.  (Obviously, that's a huge stretch of ocean, so a good splashdown target if nothing else.)  Could SpaceX be gaining preliminary data on de-orbit burn precision in preparation for controlled re-entry of the stages?  Haven't heard even if these returns are monitored...

[sojourner]

I think of all parts of the flight regime, the re-entry of the stage is probably the least problematic design wise.  Magnetoshell aerocapture would have to exhibit some very strong benefits over a more traditional heat shield.

[IslandPlaya]

I think of all parts of the flight regime, the re-entry of the stage is probably the least problematic design wise.  Magnetoshell aerocapture would have to exhibit some very strong benefits over a more traditional heat shield.

Huh?!

[sojourner]

I think of all parts of the flight regime, the re-entry of the stage is probably the least problematic design wise.  Magnetoshell aerocapture would have to exhibit some very strong benefits over a more traditional heat shield.

Huh?!

Compared to COG problems, landing the stage, and retaining a useful payload margin the actual heat shielding of the stage is not a tough nut to crack.

[Robotbeat]

Only true if you're shaped like a capsule. Otherwise, aerothermodynamics (if you're very weight-sensitive) is a very tough nut to crack. None of the usual CFD codes are anywhere near up to snuff or validated and you have to use research-quality code (which is FAR from user-friendly) which isn't nearly as well validated. And the purely analytical solutions are pretty questionable even for ultra-simple geometries like a sphere and cone.

It's solvable, sure, but I think you're thinking it's easier to crack because you haven't seen them actually try to solve it, just seen all the hard work done to make even just first stage recovery work. I see this all the time in the advanced concepts section: because an idea hasn't been tried much and is fairly exotic, all the drawbacks and difficulties are less publicized and less apparent.

[KelvinZero]

Just throwing this out there:  Altius Space Machines (Louisville, Colorado) and MSNW LLC (Redmond, Washington) are doing some preliminary work on a technology concept using a way to transfer momentum to sparse neutral (non-ionized) molecules in near-vacuum upper atmospheres, by ionizing them and injecting very small amounts of plasma into the stream.

Thats our very own Jon Goff

Thanks guys! I've been proposaling the last few days, so hadn't had a time to mention anything publicly about this, but Doug did a good writeup. This is pretty exciting for us!
~Jon

[Llian Rhydderch]

The recent flights have de-orbited second stages off the southern tip of Australia where the flight profile could be monitored.  (Obviously, that's a huge stretch of ocean, so a good splashdown target if nothing else.)  Could SpaceX be gaining preliminary data on de-orbit burn precision in preparation for controlled re-entry of the stages?  Haven't heard even if these returns are monitored...

There was a thread a couple of months ago in which the OP discussed exactly this.  The thread veered off topic and so only a few of the posts which followed addressed this exact subject, but you might find it interesting.  So click the link in the first sentence.