What is the point of SSTOs?

[hyperformer]

:huh:I was thinking that, if you were using an SSTO it would be less efficient that using multiple stages. I also think that using action groups for SSTOs is a bit cheating because its like making it have 2 stages, but not.

I do understand that building an SSTO is a really big accomplishment and the after that you go to the planets in a SSTO, but are they really more efficient than a multi-staged space plane?

[foamyesque]

:huh:I was thinking that, if you were using an SSTO it would be less efficient that using multiple stages. I also think that using action groups for SSTOs is a bit cheating because its like making it have 2 stages, but not.

I do understand that building an SSTO is a really big accomplishment and the after that you go to the planets in a SSTO, but are they really more efficient than a multi-staged space plane?

Staging's more efficient in terms of payload fractions and whatnot, but SSTOs are

a. cooler

and

b. theoretically reusable

[Trux]

:huh:I was thinking that, if you were using an SSTO it would be less efficient that using multiple stages. I also think that using action groups for SSTOs is a bit cheating because its like making it have 2 stages, but not.

I do understand that building an SSTO is a really big accomplishment and the after that you go to the planets in a SSTO, but are they really more efficient than a multi-staged space plane?

They are reusable, cheaper and usually more cost effective (In game) than multistage equivalents. As for you believing that using multiple "Stages" in SSTO's are cheating, have a look at the definition of a SSTO - "A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids." That is it...

[ferram4]

A multi-stage spaceplane generally has to deal with a larger Center of Mass shift than SSTOs do, so that's one reason to use them.

Overall, from a fuel perspective, SSTOs are never more efficient than multi-staged vehicles.

From a parts perspective, SSTOs are infinitely more efficient than multi-staged vehicles.

Likely, from a cost perspective (when career mode is added) SSTOs will be a great deal more efficient than multi-staged vehicles.

Finally, how does being able to turn engines on and off as needed in groups have anything to do with staging? You're not losing any parts, so it's not staging in any sense. That's like saying that a car with nitrous installed is a multi-stage vehicle.

[Tada]

I use SSTOs for crew transfer between station over Laythe and Laythe surface colony...

[razark]

b. theoretically reusable

They are reusable

How is a SSTO any more reusable than a staged rocket? You could design a staged rocket such that the stages are recoverable and reused, just as you could build a SSTO that gets scrapped after a mission.

[HoY]

I challenge you to go around kerbin or whatever body you launched from, retrieve your dropped stages and reinstall them on your core and refuel it. Then try to use it again.

Now a SSTO doesn't need to do that. It just gets a quick top up at the pump and off it goes again. Kerbin, mun, Laythe, or where ever it is you are launching from.

[Trux]

How is a SSTO any more reusable than a staged rocket? You could design a staged rocket such that the stages are recoverable and reused, just as you could build a SSTO that gets scrapped after a mission.

Yes theoretically in real life you can go into the ocean and collect your spent stages, however the cost per mission would increase dramatically refurbishing and refueling these. Of course people are now realizing the idea of fly back stages, but they still complicate things.

In KSP the only way to make a reusable vehicle is a SSTO which then refuels either in orbit or on the ground.

[Van Disaster]

I don't actually understand why you'd want a SSTO rocket for a launch platform - as razark said you can recover all the parts anyway if you go for a Falcon Heavy sort of design ( which is working for me with KW parts pretty well ). I'm not talking about shuttles or dedicated vehicles like miners which are their own payload, but something to put a discrete package into space.

Spaceplanes on the other hand don't use fuel to counter gravity drag ( much ), just considerably greater aero drag but with far greater fuel efficiency also. "Multi-stage" spaceplanes are sorta handy if you want to get one in orbit with full rocket tanks ( just put enough fuel in drop tanks to get it circularized ), but I suspect you're talking of Shuttle type vertical launch vehicles - and once again, what's the point in the complexity of making those winged?

Edited May 5, 2013 by Van Disaster
Edited for clarity

[razark]

...the cost per mission would increase dramatically refurbishing and refueling these.

I'd love to see a SSTO vehicle that does not require extensive refurbishment, refueling, testing and retesting, etc. before being launched again. It's really a matter of doing it to several pieces, or doing it to an entire vehicle.

Aside from that, you can have multiple parts ready in stock to go. If you need to swap out a stage, you pull one off the shelf replace it. Not as easy a task when you're using something not designed to come apart.

[Guest]

I think the original impetus was economy

[Trux]

I'd love to see a SSTO vehicle that does not require extensive refurbishment, refueling, testing and retesting, etc. before being launched again. It's really a matter of doing it to several pieces, or doing it to an entire vehicle.

Aside from that, you can have multiple parts ready in stock to go. If you need to swap out a stage, you pull one off the shelf replace it. Not as easy a task when you're using something not designed to come apart.

I'd love to see a SSTO full stop. There is no example for you to go by in this case.

[HoY]

Reusability is important if you don't have a VAB to launch every flight from. There are a lot of planets and moons out there, and if you just plan on going to them once and then leaving it doesn't matter how many stages you have. If you want to be able to do multiple flights with the same ships from bodys that don't have a VAB or SPH the spacecraft has to be completely re-useable. And in KSP that means it has to be an SSTO.

Again, if you could literally recover and reuse spent stages you could theoretically use a stages ship more than once. But since you can't...

[HoY]

I have a vertical launch platform that's SSTO, Carrys it's payload in the middle between a large open structural area, and I'm talking about 40t not a satellite. All that holds it there is a docking port and struts (quantum struts for reusability in my case)

It doesn't take a single bit of effort to change the payload. Lighter doesn't effect it one but and it can probably go a couple tonnes heavier.

[razark]

I'd love to see a SSTO full stop. There is no example for you to go by in this case.

True, we have no SSTO to base this on. But we have had reusable spaceships. And SSTOs will be based on the same physics and chemistry that rule normal rockets, so we can work out some reasonable assumptions about future vehicles.

Oh... actually, we do have one example of a SSTO in real life. The Apollo Lunar Lander reached orbit on a single stage. And it was not reusable. Also, it landed on one stage, and lifted off on another. And would not have been able to land again.

[RoboRay]

I also think that using action groups for SSTOs is a bit cheating because its like making it have 2 stages, but not.

Stages are sections of your craft that are discarded in flight, not the ability to turn onboard systems on and off.

[UmbralRaptor]

I was thinking that, if you were using an SSTO it would be less efficient that using multiple stages

Yes, and the effect is quite dramatic with pure rockets. But an airbreathing SSTO can get you >90% of the way to orbit on jets, so staging is a lot less necessary. Why bother to make them even more complex and finicky when you can get a 30% payload fraction?

Non-obvious benefits include recovery gear being built in, and highly precise landings. (None of this ellipse near KSC business, you can land on the runway)

Pure rocket SSTOs lack those, but can be very simple, reliable, and scale up almost infinitely. (Your computer/part count being the limiting factor)

I also think that using action groups for SSTOs is a bit cheating because its like making it have 2 stages, but not.

[Trux]

Oh... actually, we do have one example of a SSTO in real life. The Apollo Lunar Lander reached orbit on a single stage. And it was not reusable. Also, it landed on one stage, and lifted off on another. And would not have been able to land again.

Wikipedia is truly a wonderful thing

[razark]

Wikipedia is truly a wonderful thing

Uhhh. Yes, it is.

I have no idea what you're getting at here. Did you have a point?

[Trux]

No not at all

[StarManta]

It's all about refueling.

With a SSTO, the fuel tank itself is part of the payload you're bringing into orbit. If you can refuel in space (via mined asteroid, lunar base, or whatever), then the empty fuel tank suddenly becomes something worthwhile to carry around with you.

The reason you haven't seen SSTO's in the real-world isn't because we don't know how to make them or anything like that - it's because the empty fuel tanks are dead weight if there's no ability to refuel them. Once we start mining asteroids for rocket fuel, every space agency on the planet will start launching SSTO's within a year.

Reusability is often touted as a strength of SSTO's, but that mindset only applies to "dumb" stages. With modern rockets, staging does not need to be synonymous with discarding the spent stages. Check out SpaceX's planned launch system, for example - it is both staged and completely reusable, because each stage, when jettisoned, has enough fuel left over in it to come to a landing on a landing pad to be reused.

[karolus10]

Point of using SSTO rockets are their re-usability, none of stages are spent and in perfect conditions it could be used multiple times in regular basis.

Also what do You guys think about TSTO (two stage to orbit) shuttle with both stages reusable (fly-back boosters or like grasshopper) ?

[Trux]

Isn't that what the later Falcon rockets are going to be using?

[ComradeGoat]

As others have suggested, SSTO vehicles have an actual use in the game as landers. Yes, you may be able to design a rocket such that the stages can be recovered and reused, but that's of no use whatsoever when you are trying to ferry crew between a colony on Laythe and a space station orbiting it. Use a staged vehicle and you'll be using it precisely once. It will take you two years in game to get another one there from Kerbin.

[SecondGuessing]

Constructing and SSTO is a lot more challenging and fun than constructing a rocket. If your rocket launch fails then the solution is always to either add more rockets or add more struts; with an SSTO you actually have to use some brain power.