Whats with SSTOs?

[sammoe]

Their basically just rockets with wings... Why is everyone fascinated with them?

[rpayne88]

They are 100% reusable spacecraft. IRL, they would allow us to reach orbit cheaply (in theory, anyway.) The could be flown, landed, refueled, and sent right back into orbit. None have been made IRL. And, no, they are not just rockets with wings. SSTO stands for single stage to orbit. It is incredibly hard to get a payload into orbit without staging. Then factor into the equation things such as stability. It is a milestone to make a successful SSTO in KSP.

[Brotoro]

Not all SSTOs have wings (most of mine don't).

The reusability is important, especially if you need to have vehicles that can ferry passengers up and down from a base on a distant moon/planet… you don't want to have to use a whole new vehicle for each trip because you have thrown away some parts needed to make the trip.

[CalculusWarrior]

You can actually build an SSTO out of a couple of long 1m tanks and an LV-T30, I believe, but it's payload capacity is pretty much nil. Like rpayne88 says, getting a usable payload into orbit is very difficult.

[Hodo]

My fascination with them is simple. They are my primary way of getting payloads of over 50 tons into orbit.

[spikeyhat09]

None have been made IRL.

that is not true. the apollo lunar module was an SSTO craft.

[I_Killed_Jeb]

it's also just a fun challenge op.

[Traches]

As long as you don't count the... 5 stages it took to get it there? If we're picking any body we want, I could get into orbit around an asteroid with a fire extinguisher.

[LeFudge]

Well even the LEM had a descent stage and a separate ascent stage leaving the base behind lol

SSTOs are easily one of the most difficult things to do in KSP

[Galacticruler]

SSTOs are easily one of the most difficult things to do in KSP

Land on Moho is #0 on that list.

SSTOs come in around #3.

[SuperBigD60]

that is not true. the apollo lunar module was an SSTO craft.

I guess it could have been, considering it was able to break orbit and land.

But to get back into orbit it did actually stage once at the beginning. Perhaps we call it a Single Stage FROM Orbit.

And that's on the moon, where its easier to have an SSTO, anyway.

[Vector]

Maybe someday when money is implemented, there will be even more interest in reusing part or all of a spacecraft, rather than just dropping a half dozen mainsails into the ocean.

[CalculusWarrior]

Land on Moho is #0 on that list.

SSTOs come in around #3.

I actually have landed on Moho (just pack a lot of fuel), and still struggle with SSTO's. I think the main difficulties are that you can't simply strap on MOAR BOOSTERS if your ship is underperforming, and they require some skill (so not me) to fly them.

Something that's always put me off from SSTOs (aside from the long, difficult path of creating them) is that in the end, they're fairly useless. A single-stage-to-orbit craft is always going to underperform a staged vessel. I suppose when SQUAD implements the economy to career mode, that's when we'll see more and more SSTO crew transfer vehicles to LKO and other cost-efficient methods of transportation.

[Spatzimaus]

Others have hit most of the high points. The question is whether by "SSTO" people mean spaceplanes; an SSTO rocket plays just like a regular one, albeit with a bit less efficiency. So most of the discussion on SSTOs focuses on the issues of spaceplanes. (And it's implied that we're talking about on Kerbin. Jeb can go single-stage-to-orbit on Minmus/Gilly/Pol using only his jetpack, after all.)

1> It's a challenge. Building something that sheds layers as it goes up is fairly easy, and lets you build as big as you want. Bigger is better with conventional rockets, but with something designed to go single-stage, you often want to stay small. That doesn't mean you can't make ridiculously huge SSTOs (my main heavy lifter, "The Brick", is an 8000-ton SSTO rocket I use to lift my 700-ton space station), but designing an SSTO spaceplane encourages you to prioritize what you REALLY need and learn to construct efficiently.

2> If and when we get an economy, there may or may not be a downside to discarding stages where they can't be recovered. This'll depend on exactly how they structure the system.

3> It's a challenge. (Yes, again.) Spaceplanes are harder to design than rockets. Their resource management is more difficult (IntakeAir), and they have to be balanced around an additional axis. Any sort of symmetry guarantees a rocket's center of mass will remain in front of its center of thrust, but with a spaceplane you also have to worry about center of lift, the location of your control surfaces, and so on. Even how you place ladders is more difficult; landing a spaceplane on an airless moon either requires a VTOL design or the ability to land on your tail.

4> SSTOs, by their very nature, leave no debris to clutter up your space. You can make zero-debris rockets that use multiple stages, but it's inherent to the SSTO concept as well.

5> It's a challenge. (Yup, one more time.) Spaceplanes require a lot more hands-on work to get to orbit, whereas a regular rocket just tips over part way up and circularizes at the top. By going SSTO, you also have to spend more effort managing action groups, since you can't just dump the inefficient stages once you no longer need them.

6> There is NO number 6!

7> Most regular rockets tend to look pretty similar after a while; everyone's used to the basic concept of tapering stages, or an asparagus setup. The specifics might differ, but the basic designs will be similar enough that there's not much point in showing off your own constructions. But go look through the SSTO thread in the Spacecraft Exchange, and you see a bunch of designs that look almost nothing alike.

(To make this more pronounced, the stock rockets are decent starting points, but the stock spaceplanes are lousy. So you're generally starting from scratch once you begin working on your own SSTO spaceplane.)

There are many, many threads on this topic in this forum if you want longer explanations. In the meantime, go have some fun making an SSTO. (Then, once you've succeeded, figure out how to get it to fly to Laythe and back.)

[FlamedSteak]

I wouldn't call the Apollo LEM a true SSTO. It staged from it's base after landing and did not have the ability to land afterwards, so it wasn't in anyway reusable even from a lunar platform.

[arq]

SSTOs can actually achieve very high payload fractions. If I recall correctly, they can easily surpass 30% without airhogging (compare to 16% for rocket-only asparagus). Of course, a staged jet-assisted launcher would do better yet. Mostly, SSTOs are a way to challenge oneself after regular launches have been mastered.

[1D-1()T]

Others have hit most of the high points. The question is whether by "SSTO" people mean spaceplanes; an SSTO rocket plays just like a regular one, albeit with a bit less efficiency. So most of the discussion on SSTOs focuses on the issues of spaceplanes. (And it's implied that we're talking about on Kerbin. Jeb can go single-stage-to-orbit on Minmus/Gilly/Pol using only his jetpack, after all.)

Wouldn't it be more efficient, since they don't drop parts into the ocean and since they kinda force you to think small and efficient?

[The Destroyer]

Land on Moho is #0 on that list.

SSTOs come in around #3.

ehhhh. Landing on Moho isn't HARD, you simply need to understand to pack lots of fuel... which I've failed to do. The reason I only orbited it so far.

[Ignamious]

An SSTO is WAY Cheaper to operate. Once built the major bills are Phase Maintenance, Fuel and Operation. While staged rockets you have to pay for the stages, fuel, operation, phase maintenance, construction, VAB's, tear down, reconstruction, Transportation of spent stages, inspections, and the list goes on.

yes there are extra costs for the SSTO not mentioned, but many of the costs would be similar to the SR-71 run by the USAF.

one way to show the cost savings of SSTO's is to install the KSP mission packs and KAS. Create and SSTO and use KAS to put your payload into the SSTO with KAS. and bring it to orbit, the return the SSTO and land. refuel it from a tanker, and put another payload in it. You will see how much money you will save with it.

R&D costs will be roughly the same, however there are still engineering hurdles for effective SSTO's. The LASRE and SABRE are both interesting technologies for SSTO. The LASRE is for the cancelled X-33 and the SABRE is for the proposed Skylon.

[Spatzimaus]

Wouldn't it be more efficient, since they don't drop parts into the ocean and since they kinda force you to think small and efficient?

Different definition of "efficient". You're looking at it from an accountant's standpoint, where dropped parts are a waste. I'm looking at it as a mission planner, where unnecessary carried parts are a waste.

An SSTO rocket is carrying a lot of dead weight up to orbit, mainly in the form of empty fuel tanks. Sure, that empty tank only has 1/9th its original mass, but that still adds up to an awful lot when a typical rocket has a ~15% payload fraction. Whereas if it dropped that weight as soon as the tank emptied, it'd use less fuel to get the same capability (or more importantly, get more capability from the same amount of fuel) simply due to the remaining stages' rockets having less mass to accelerate. A true SSTO rocket also wastes quite a bit of weight on engine power; a design that gets the necessary 2.2-2.3 TWR at sea level will have far more engine power than it needs once it gets to near-orbit (not because things weigh less in low orbit, but because most of your fuel will be gone). This is especially true if your design is g-limited, such as lifting a fragile space station. You'll throttle down continuously as you go, to keep the acceleration manageable, and that wastes even more mass since you now could have used a much smaller engine.

And again, the line you quoted was purely regarding SSTO rockets. For those, no, they don't force you to think small, since with rockets you can always scale up. Double the tanks, double the engines, and you double the payload; rockets don't have anything like a spaceplane's size limitations. As I said before, my gigantic booster is an SSTO rocket; its mass is around 8000 tons, designed to lift 700-800 ton space stations in a single launch. I could have done this as a complex asparagus setup, but it's easier to manage as a single entity, and it's fun to see just how big you can get.

It's 29 linked 3.75m KW Rocketry stacks with Griffon XX engines. Any bigger and I wouldn't be able to fit it into the VAB. Here's a screenshot of the Brick-29 (not to be confused with the smaller 5500-ton Brick-21), with my 830-ton space station sitting on top:

(The connection between the station and booster is level with those nose cones, to give you an idea of size.)

[Lohan2008]

it is a challenge to keep space plane level at 16km going at 1000m/s, the objective is to get into a stable orbit. It is another one of those things to check out.

[1D-1()T]

Snipitty snip snip

My jaw just fell to the floor, fell through the floor, to the core of the earth, smashed out the other side and entered solar orbit.

800 TONS! I probably couldn't do that with a normal rocket.

[bsalis]

Plenty of good comments here. Another way of looking at it...

Rocket

SSTO Spaceplane

I know what I would rather be piloting.

[Levelord]

Plenty of good comments here. Another way of looking at it...

Rocket

SSTO Spaceplane

Unity Engine

[Spatzimaus]

800 TONS! I probably couldn't do that with a normal rocket.

You can, it's just not really worth doing unless you're using KW Rocketry to keep the part counts down. I mean, that 8000-ton booster has only ~440 parts; added to the 735 parts of the station, I'm right at the limit of my processor capability when I launch the thing. If I had to use stock tanks it'd take three or four times as many parts for the booster alone, which'd force me to keep things much smaller just to keep my sanity. (Although Whackjob's made an art form of gigantic constructions with mostly stock parts...) The last major barrier to giant constructions, maneuverability, was removed when they switched to the new flywheel system. So I now use 830-ton stations, 400-ton Mun rovers, a 300-ton Kethane-refining lander/depot... and 27-32 ton spaceplanes. Like I said, smaller is a good idea for spaceplanes, and unmanned ion probes, but not much else.