Advantages of TSTO piggyback spaceplanes

[foamyesque]

On 2016-08-11 at 6:34 AM, KerikBalm said:

As above.... you can recover a carrier vehicle, but that vehicle needs to be designed to get on a suborbital trajectory that gets it into space. That means you then have the choice between a boost-back, or a boost-forward to take it to orbit... or having it land quite far away from KSC for a bad recovery %.

Especially if you use airbreathers, that boost-back is going to be way more expensive than the boost-forward to get it into orbit. Rapiers in airbreathing can get you to >1,400m/s surface or >1,600m/s orbital considering orbital velocity in low orbit is ~2,300 m/s, the boost-back is clearly inferior to the boost forward... particularly as you need an additional "boost-forward" to get your Ap above 70km for the requisite switching

 

OP was, I thought, asking after a White-Knight style piggyback layout. Getting such a thing to go suborbital in order to recover it basically defeats the entire point of that launch style in the first place. I suppose you could build a conventional SSTO spaceplane and not actually quite fly to orbit and have your payload be the second "stage" and circularize itself, but again, I don't really think that is what was being asked about.

[MedwedianPresident]

3 hours ago, foamyesque said:

OP was, I thought, asking after a White-Knight style piggyback layout. Getting such a thing to go suborbital in order to recover it basically defeats the entire point of that launch style in the first place. I suppose you could build a conventional SSTO spaceplane and not actually quite fly to orbit and have your payload be the second "stage" and circularize itself, but again, I don't really think that is what was being asked about.

"Recoverability" is for RP purposes - by that I don't mean that it needs to be necessarily recovered but that if you switch to the carrier instead of the spaceplane after separation or open the respective autosave, you can land it.

[KerikBalm]

22 hours ago, foamyesque said:

OP was, I thought, asking after a White-Knight style piggyback layout. Getting such a thing to go suborbital in order to recover it basically defeats the entire point of that launch style in the first place.

Well, OP seemed to be talking about in game advantages, and in game, the only way it works due to game engine limitations, is if you get your apoapsis into space.

He has since qualified it as simple role playing. Also, playing with save files, or using a mod that does that for you can make it much more viable, but I was talking stock.

Also, it doens't defeat the whole purpose... space X does the boost back rather than boost forward... because the first stage doesn't get anywhere close to orbital velocity.

I provided a working example of a 2 stage fully recoverable system that beats disposable rockets in terms of funds per ton, using that system. If you go the suborbital route, if you don't do much of a gravity turn, its quite easy to recover, as not much boostback is needed (although a retroburn or lots of brakes will be needed for that steep reentry trajectory... heating isnt' such a problem, just slowing down in time).

Then you get the same advantages as a launch from a realtiely slow carrier plane... a few hundred m/s forwards velocity, but a high start altitude giving the released stage a vacuum Isp and lower total dV requirement.

What you generally lose, is the ability to make much use of airbreathers from such a steep ascent.

If we're talking a rapier or ramjet carrier plane instead of a turbofan one, then you're also losing a lot of forward velocity, because as I mentioned, once going that fast the boost forward is more efficient than the boost back... which isn't true in real life because in real life you would need your boost forward to get you to 8km/sec.

If this is pretending its real life and discussing the advantages, ti should be in the science and spaceflight forums. If its discussing the pro's and con's in KSP - its pretty heavily in favor of the SSTO regime.

It is fun to role play real life in KSP... thats why I made those shuttle style launchers, and that fully recoverable 2 stage design (with an early shuttle concept in mind with a bit of space X thrown in), but I won't discuss the pro's and cons... its role playing, the pro's and cons depend on how you're role playing, rather than the game engine and stats.

[Der Anfang]

What is TSTO?? I never heard of that before.

[foamyesque]

@KerikBalm: If you want to make a jumbo jet go suborbital, be my guest. Me, I'd dispense with the piggyback and just use, you know, winged boosters for a once-around flyback.

 

 

[KerikBalm]

Did you not read my posts? I was advocating for SSTOs, not TSTOs. I was simply saying it could be done if you wanted to... not that you should

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I never claimed they were practical or fund efficient, I was just pointing out that *technically* you can stage before achieving orbit, and recover the spend stage.

 

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boost-back is going to be way more expensive than the boost-forward to get it into orbit. Rapiers in airbreathing can get you to >1,400m/s surface or >1,600m/s orbital considering orbital velocity in low orbit is ~2,300 m/s, the boost-back is clearly inferior to the boost forward... particularly as you need an additional "boost-forward" to get your Ap above 70km for the requisite switching.

"Boost-forward" would be the once around thing you talk about.

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In my TSTO mainly rocket design posted above, I found that I could forgo the separation, and take the whole stack to orbit, with a little more fuel left over... ie it performed better as a SSTO than a TSTO... at least operating within the confines of KSPs mechanics

 

[foamyesque]

44 minutes ago, KerikBalm said:

Did you not read my posts? I was advocating for SSTOs, not TSTOs. I was simply saying it could be done if you wanted to... not that you should

 

And I'm saying that the kind of possible you're describing is incompatible with the kind of design the OP is asking about, and is, therefore, kind of irrelevant, because the best way to implement a recoverable first stage in KSP bears zero relation to a piggyback launcher.

[KerikBalm]

If you're doing a "once around" aren't you doing a SSTO? or nearly so (maybe coming a hundred m/s or so short of orbit and gliding).

Thats incompatible with what the OP is talking about as well, no? also my comment was in reply to GoSlash's comment, not really the OP