Combining the second stage and the capsule? A Reuseable spacecraft concept? (Updated)

[DerpenWolf]

Note: Added a few extra things at the bottom of the thread to consider!

OK, so I was thinking about how SpaceX could reuse their second stage so that they could achieve pretty much full reusability (assuming they get the their first stage to be reusable and their capsule can land with its engines). I then thought of the concept that maybe someone could build a rocket in such a manor but instead of having the second stage a separate component they could build it into the capsule. The capsule would land much like the dragon 2 concept, only this would be a decent bit bigger. Heck, maybe if its big enough you could actually refuel the vessel and use it as a moon or mars lander!? Now I doubt this could be done with the falcon 9, however I do think that this is an interesting concept and couldn't quite get it out of my head. I know there are a few problems (such as boil off in orbit if you want to use cryogenic fuel) but I really just want to see what everyone else makes of it.

Also Here are a few images of a VERY crude concept craft I made in KSP.

Edit/More things to think about

You could also remove the capsule and try to add a reusable/opening fairing system for cargo/satellites (Maybe even put a normal capsule inside of the fairing? Also, recognize the movie?)

Another thing to think about is, does it have to be a capsule? You could combine your second stage with a spaceplane.

Edited November 18, 2014 by DerpenWolf

[Kryten]

Rocket engines aren't built to take re-entry.

[FishInferno]

Rocket engines aren't built to take re-entry.

If you look at the spaceX animations, the second stage reenters headfirst to protect the engine

[astropapi1]

Rocket engines aren't built to take re-entry.

Well, that kind of engines aren't, but let me introduce you to a very nice fellow, ROMBUS.

It was a proposed SSTO rocket (with optional drop tanks), which would have used its plug nozzle as a heatshield:

Wish there was more documentation about stuff like this.

[DerpenWolf]

Rocket engines aren't built to take re-entry.

Again, its a very crude concept design, I'm not entirely certain on how to protect the engines or how the engines would be configured. Also no clue what the best way to reenter is

Edited November 14, 2014 by DerpenWolf

[Rakaydos]

Having played with FAR, the biggest problem with reentering nose first to protect the engine, is flipping around at the end. IF youre stable nose first for reentry, it's REALLY hard to swap end for end.

I'd think edge on would be a better option. More surface area to slow it down, and it can roll to even out the heating without changing it's aspect ratio, and easier to "fall off" toward the engine when you switch to propulsive breaking.

[Armchair Rocket Scientist]

OK, so I was thinking about how SpaceX could reuse their second stage so that they could achieve pretty much full reusability (assuming they get the their first stage to be reusable and their capsule can land with its engines). I then thought of the concept that maybe someone could build a rocket in such a manor but instead of having the second stage a separate component they could build it into the capsule. The capsule would land much like the dragon 2 concept, only this would be a decent bit bigger. Heck, maybe if its big enough you could actually refuel the vessel and use it as a moon or mars lander!? Now I doubt this could be done with the falcon 9, however I do think that this is an interesting concept and couldn't quite get it out of my head. I know there are a few problems (such as boil off in orbit if you want to use cryogenic fuel) but I really just want to see what everyone else makes of it.

Also Here are a few images of a VERY crude concept craft I made in KSP.

http://cloud-4.steampowered.com/ugc/43110509156956114/36794AE56F36AFDA2434DFD5190C3864059A7C30/

http://cloud-4.steampowered.com/ugc/43110509156953316/8B74865712F201CD7C9611918624AFA6E045C0A7/

http://cloud-4.steampowered.com/ugc/43110509156958273/E76DEBB2FBEBE983F576848FB6D140549F012391/

I see several major problems with this concept.

1. A built-in second stage can't launch anything but a capsule, such as satellites.

2. If the second stage has problem the capsule needs to be able to separate and land safely on its own. For a typical tailfirst reentry this means that the capsule will require a heat shield capable of bringing it back from LEO, which is never used on the vast majority of missions.

3. A tailfirst reentry will be very difficult, since with the fuel tanks nearly empty the weight of the capsule will move the vehicle's center of mass very far forward. A nose-first reentry has several serious issues, including:

3A: the ideal shapes for a low-drag launch and a survivable reentry are very different.

3B: if your crew are "lying down" during launch, this will be reversed during reentry. This means you have to rotate the seats 180 degrees. The Space Shuttle avoided this problem because the orientation only changed about 90 degrees and being a spaceplane it had a very gentle reentry (<3 gs peak IIRC) compared to a capsule. Even a capsule performing a lifting reentry, which this probably couldn't do.

3C: The front side of your capsule has a bunch of stuff like the windows and exit hatch you REALLY don't want to have facing into a hypersonic airstream (again, the Shuttle's windows were fine because it reentered at a high angle of attack and the front windows were shielded by the nose.

4. Once in orbit, your vehicle is very heavy and bulky, making docking to a space station unwieldy.

5. During reentry the vehicle will still contain several tons of rocket fuel for landing. This presents safety concerns for a manned craft.

6. On landing, the vehicle is tall and top-heavy (capsule on top, remember?), which makes it vulnerable to tipping over. This may be an acceptable risk in an unmanned vehicle, but not a manned one.

7. Assuming you do land safely, your crew will be descending 3-5 stories of ladder to reach the ground. This is in Earth gravity, and if you're using it as a crew shuttle to a space station they may have suffered bone/muscle deterioration from spending months in microgravity.

Replacing your second stage and capsule with a spaceplane would eliminate some of those problems, but also create new ones, such as the resulting plane being too big to fit in a launch vehicle fairing. How do you keep that stable? Well, what if we replaced the first stage with strapon boosters? We'll make them liquid-fueled, and maintain balance by running the second-stage engines the entire launch and keep the fuel tanks topped off using crossfeeding. Congratulations, you now basically have the Space Shuttle, but with fuel tanks replacing the cargo bay.

[Bill Phil]

Well, problem is that you'll be making a bigger second stage if you're using powered landings.

[problemecium]

Yeah, I too reject the argument that rocket engines can't take reentry. Rocket engines can be made to handle reentry. After all, the inside of the engine handles having superheated exhaust blasted through it. In the end reentry isn't much different, just on the outside.

Also, I propose mitigating the ladder issue by lowering the crew cabin. Nobody wrote a law saying it had to be on the nose - my KSP shuttle (bear with me here) has the crew cabin at the back end (between the engines admittedly, but this can be worked with) so the Kerbals can get out without having to climb five meters of ladder.

Long story short, there will indeed be a lot of difficulties, but I still think this can be done, and that it will pay off if done well.

[Sky_walker]

Yeah, I too reject the argument that rocket engines can't take reentry. Rocket engines can be made to handle reentry. After all, the inside of the engine handles having superheated exhaust blasted through it. In the end reentry isn't much different, just on the outside.

That's why KSP players shouldn't have anything in common with designing real spacecrafts.

Also, I propose mitigating the ladder issue by lowering the crew cabin.

Wise choice of priorities. The ladder.

Nobody wrote a law saying it had to be on the nose - my KSP shuttle (bear with me here) has the crew cabin at the back end (between the engines admittedly, but this can be worked with) so the Kerbals can get out without having to climb five meters of ladder.

Yea... I'm sure astronauts will be super-happy sitting between the engines.

Not to mention the escape system... does it include build-in stargate to get out from under the fuel tanks?

[Kryten]

Yeah, I too reject the argument that rocket engines can't take reentry. Rocket engines can be made to handle reentry. After all, the inside of the engine handles having superheated exhaust blasted through it. In the end reentry isn't much different, just on the outside.

The problem is no engine can actually handle that, at least passively. They either work on consumable coolant (propellant forced through the nozzle walls before burning) or are themselves consumable.

[Aningaaq]

Isn't a convex surface important when entry into an atmosphere occurs? The bell of an engine (or whatever it is called) is concave and almost surely could have strange aerodynamic consequences.

[problemecium]

@Sky-walker: then we add some soundproofing, and yes, of course it has a built-in stargate ;P

@Kryten: the same argument can be made about heat shields - technically they don't survive reentry (or in the case of reusable ones, only a few times). We just need to design a rocket engine that does something like pump coolant along its outer surface or have enough ablative shielding to deal with hot plasma on the outside as well as the inside, at least once. It's obviously a half-baked idea, but so far there's no obstacle that's been brought up that can't be overcome.

[zekes]

That's why KSP players shouldn't have anything in common with designing real spacecrafts.

Wise choice of priorities. The ladder.

Yea... I'm sure astronauts will be super-happy sitting between the engines.

Not to mention the escape system... does it include build-in stargate to get out from under the fuel tanks?

so much sass in this comment I love it.

[Kryten]

@Kryten: the same argument can be made about heat shields - technically they don't survive reentry (or in the case of reusable ones, only a few times). We just need to design a rocket engine that does something like pump coolant along its outer surface or have enough ablative shielding to deal with hot plasma on the outside as well as the inside, at least once. It's obviously a half-baked idea, but so far there's no obstacle that's been brought up that can't be overcome.

True, but the more of these kind of modifications you get, the worse the engine will perform as an actual engine and the less payload you'll be able to carry. You're effectively making it equivalent to a much cheaper expendable engine than it would otherwise be performance-wise, which isn't good for the economic viability of the system.

[Superluminaut]

OK, so I was thinking about how SpaceX could reuse their second stage so that they could achieve pretty much full reusability (assuming they get the their first stage to be reusable and their capsule can land with its engines). I then thought of the concept that maybe someone could build a rocket in such a manor but instead of having the second stage a separate component they could build it into the capsule. The capsule would land much like the dragon 2 concept, only this would be a decent bit bigger. Heck, maybe if its big enough you could actually refuel the vessel and use it as a moon or mars lander!? Now I doubt this could be done with the falcon 9, however I do think that this is an interesting concept and couldn't quite get it out of my head. I know there are a few problems (such as boil off in orbit if you want to use cryogenic fuel) but I really just want to see what everyone else makes of it.

Also Here are a few images of a VERY crude concept craft I made in KSP.

http://cloud-4.steampowered.com/ugc/43110509156956114/36794AE56F36AFDA2434DFD5190C3864059A7C30/

http://cloud-4.steampowered.com/ugc/43110509156953316/8B74865712F201CD7C9611918624AFA6E045C0A7/

http://cloud-4.steampowered.com/ugc/43110509156958273/E76DEBB2FBEBE983F576848FB6D140549F012391/

SpaceX already has a plan to reuse the second stage. Its just like your plan except it doesn't keep the capsule attached.

[Duxwing]

@Sky-walker: then we add some soundproofing, and yes, of course it has a built-in stargate ;P

@Kryten: the same argument can be made about heat shields - technically they don't survive reentry (or in the case of reusable ones, only a few times). We just need to design a rocket engine that does something like pump coolant along its outer surface or have enough ablative shielding to deal with hot plasma on the outside as well as the inside, at least once. It's obviously a half-baked idea, but so far there's no obstacle that's been brought up that can't be overcome.

Or the engines could just retract.

-Duxwing

[Starman4308]

If it were to be sent to the ISS, you could include a heatshield with the payload, and have ISS personnel fix the heatshield onto the bottom before sending it home.

I suppose one might be able to make a robotic system to do the same, but it's a complicated procedure to take something from the top and secure it to the bottom.

[magnemoe]

Could you have an port in the heat shield for the engine, like the wheels on the space shuttle.

Not sure if you would need an serious heat shield on the pod: If second stage engine fails to ignite you are traveling as fast as first stage who don't need one.

Higher up and you should be able to rotate and reenter using the second stage heatshield before separating pod.

You would have to rotate the pod anyway but this might be by itself because of drag and center of mass.

Other objections like high center of gravity still apply.

Another issue might be that the LOX in the upper stage is not storeable over long time, you could not dock for months to a space station and double as an lifeboat.

[Armchair Rocket Scientist]

Could you have an port in the heat shield for the engine, like the wheels on the space shuttle.

It's possibly but it would be rather difficult and might not be the best idea. A better option for reentering tail-first with an upper stage would be an inflatable heat shield that came up around the engines.

Not sure if you would need an serious heat shield on the pod: If second stage engine fails to ignite you are traveling as fast as first stage who don't need one.

Higher up and you should be able to rotate and reenter using the second stage heatshield before separating pod.

The issue isn't either of those situations. The issue is a turbopump explosion 95% of the way through the burn which shreds the second-stage heat shield (which is near the engines). Now you've got a crippled spacecraft traveling just below orbital speed. Reentering on a destroyed heat shield is suicide, and with the engines out there's no way of getting into orbit.

[problemecium]

Alternately, we could pack extra delta-V into the ship maybe and have it slow down to a nice lazy velocity before reentering, and then just float down on a giant blimp.

Blimps, yo. I went there ;P

[NERVAfan]

Not to mention the escape system... does it include build-in stargate to get out from under the fuel tanks?

The issue isn't either of those situations. The issue is a turbopump explosion 95% of the way through the burn which shreds the second-stage heat shield (which is near the engines). Now you've got a crippled spacecraft traveling just below orbital speed. Reentering on a destroyed heat shield is suicide, and with the engines out there's no way of getting into orbit.

If the rocket engines can be made/proved to be reliable enough, maybe it wouldn't have a launch escape system. Depends who is building it and what risk they are willing to accept.

[Nibb31]

I can't see any government flights doing away with a launch escape system any time soon. And for the foreseeable future, the government is the only customer for a manned spacecraft. Even if space tourism does emerge, it doesn't make sense to build a spacecraft that doesn't cater to your biggest customer.

Anyway, I don't think a reusable upper stage is going to be practical any time soon. I think a better design might be something like Dragon V2, without the trunk but with a disposable fuel tank instead of the second stage, and uprated SuperDracos (or maybe ressucitated Kestrels) doing the job of the Merlin 1D-Vac.

The Merlin has 800kN of thrust, and the Dragon's SuperDracos can provide nearly 600kN (8x73kN) of thrust, but with a much lower Isp. On the other hand, this design would be much lighter because you would save the weight of the Merlin and the trunk and at least one set of staging equipment.

[NERVAfan]

I can't see any government flights doing away with a launch escape system any time soon.

Any government, or just US/NASA?

[Nibb31]

Any government, or just US/NASA?

Have you seen any other governments buying flights from private operators?