What is the real use of an SSTO?

[Jas1126]

For me it was just something to do. Yes, rockets are FAR more effective but after launching a few hundred or so, I wanted to do new things. I'm sure there are others that experienced similar drive.

In real life SSTOs are a cheap way to get humans and cargo to orbit because they do not throw away spent stages and burn less fuel. The re-usability is key. Unfortunately, KSP has no incentive, at least at the moment, to take advantage of these benefits. A lot of things people do in KSP is just for a cool factor, or simply to say they achieved a difficult task.

"In real life, SSTO's...." There is no such thing. O.o SSTO's are "possible" but have never been constructed.

Edited June 1, 2014 by Jas1126

[R0cketC0der]

One common misunderstanding in this forums seems to be that most people think that SSTO = reusability. To be reusable, a SSTO not only has to get into orbit, but also back from orbit. This makes rocket SSTOs a lot more complicated, because for low lift reentry bodies need about 10% of their own weight to be heatshielding as a rule of thumb. Due to the more gentle reentry that SSTO spaceplanes can use, they don't need as much heatshielding, but they will still need a lot, especially if you want the heatshield to be also reusable. However due to the tviolkovsky equation, you also need a very high fuel fraction. This means that you will need a very high fuel fraction combined with a decent amount of heatshielding, resulting in a very small payload fraction.

[allmhuran]

But you need to launch a bunch of fuel and with a dockingport/grappling unit so it will be expensive for an SSTO too

Sure, but multistage vehicles also throw away their engines. Engines are expensive in real life, I expect they'll be expensive in 0.24 as well. Plus any fuel lines, struts, decouplers, etc. Plus the cost of the launch clamps. I expect having a fuel tanker on standby near the runway for refills will be a cheaper option. With any luck a "refuel" option will also be made available if landed on the runway, further increasing the benefit.

[Monger]

KSP jet engines are lighter, more powerful, and much more efficient than real jet engines, and they can also operate in much thinner air. Combine this with the fact that Kerbin is so small that jet engines can get the SSTO almost all the way to orbit, and it becomes obvious that airbreathing engines are much more useful in KSP than for real SSTOs.

Kerbin's atmosphere is also insanely thick, which results in an enormous amount of friction. KSPs jet engines are largely overpowered to counter this effect.

It's already not that uncommon to get into the outer atmosphere of earth with just a jet engine. Also, ordinary kerosine is much cheaper than liquid hydrogen and liquid oxygen. That's why flying with an airplane is relatively cheap.

[Jouni]

Kerbin's atmosphere is also insanely thick, which results in an enormous amount of friction. KSPs jet engines are largely overpowered to counter this effect.

It's already not that uncommon to get into the outer atmosphere of earth with just a jet engine. Also, ordinary kerosine is much cheaper than liquid hydrogen and liquid oxygen. That's why flying with an airplane is relatively cheap.

Kerbin's atmosphere isn't thick. It's just that our rockets and planes are all badly designed, with about 8 square meters of surface area per tonne of mass, no matter which direction they're facing. This is better fixed with proper aerodynamics instead of ridiculously powerful jet engines that make rocket-based first stages obsolete for payloads less than 100-200 tonnes, if part costs are ever introduced.

The absolute altitude record for a jet aircraft is the 37650 m achieved by a Mig-25 in a zoom climb, which resulted in engine flameout. In KSP scale, with scale height 5 km instead of 8.5 km, this corresponds to around 22 km. The altitude record in sustained flight is the 25929 m achieved by an SR-71, corresponding to about 15.25 km in KSP.

[Tortoise]

Its efficient, especially IRL. But on ksp they are cool as well. You don't worry about staging and dropping debris everywhere. you just refuel and fly whereever you want.

[Kaezan]

im going to build an SSTO to refuel my refueling space station. its a usefull objective

[SkyRender]

SSTOs are fun for getting Kerbals to and from orbit, bus-style. They're not really practical for any sort of operations outside of low-Kerbin orbit (all that extra atmospheric flight hardware is just dead weight in a vacuum), but they're quite nice for getting a ton of Kerbals into orbit. I've managed to get 9 Kerbals to LKO on a fuel load that would barely lift a single Hitchhiker to orbit in rocket mode. (Granted, I WAS using Ferram Aerospace, but I'm also referring to a fuel load that would have gotten that Hitchhiker rocket to orbit in FAR.)

[jfull]

Something nobody seems to be bringing up

SSTO planes are the most compact and lightweight way to get Kerbals to and from the surface of Laythe.

[Rainbow-Dashie]

Like many other things in the game they are pretty much useless just like satellites, space stations, bases, space shuttles, nose cones, fairings, probes, etc. However, these things are fun and cool, and thats why people continue to use them, to enjoy a wonderful game

[Duke23]

I built an ssto just for the challenge of flying it mostly, but I thought it would help once budgets are made in the game. Often I have a relatively large reusable interplanetary ship that physically can't land. So to get the science data back to the surface I either have to hijack the attached lander assuming it has chutes or the escape pod if equipped (and send a replacement) or send up another rocket just for the purpose of a quick rendezvous and deorbit.

A functional ssto makes all that much easier. I can leave it fueled and docked to a station then run over to the big ship to grab data then take it home, refuel again, and send it back up for next time without tons of stages and tons of fuel wasted for no reason. Or just send it up as needed if the large ship is close enough, but usually I leave them in a much higher orbit so I'm not wasting fuel and time next time I leave kerbin orbit.

I mean right now technically none of that matters much, but budgets will have a huge impact imo so I'm trying to go all reusable for frequently used or expensive to operate ships. Theoretically it would cost a lot less for me to run fuel up to the large ship than to send up a new fully fueled ship. Even more benefit if I can ever get my refueling ssto off the ground.

[Wooks]

Virgin Galactic = non SSTO

SpaceX Falcon9 = non SSTO

Skylon = SSTO

2 of 3 reusable crafts isnt SSTOs

Of course SpaceX and Virgin Galactic ships are non SSTO... yet. As many other pointed out the tech is in development and pointing that way, SpaceX and Virgin are developing all the hardware and sooner than later we will have them on runways working at a fraction of the cost of any rocket in the actuar market. The first one to achieve a true SSTO will open the gates of space for all humankind.

I hope SQUAD integrates this into the game in a meaningful way that translates all that message: "SSTO is a lightweight / low cost way to reach orbit with light / medium sized payloads, rockets are for heavy payloads"

[Overfloater]

SSTO's are for delivering crew to any place, transfer all kinds of cargo, hauling asteroids, and-

not dropping off parts of your car when driving home.

[Jouni]

I find Falcon-style reusable rockets much more interesting than SSTOs. The SSTO is essentially the age-old idea that a free man rides his own horse wherever he wants. It's a nice idea, but it doesn't seem to be that much in touch with reality.

SpaceX also tries to achieve cheap spaceflight, but instead of listening to sci-fi authors and test pilots, it's listening to engineers. Reaching orbit is a demanding and highly specialized task that requires a lot of expensive hardware. After reaching orbit, that hardware becomes dead weight, making the ship much worse in everything else. It makes much more sense to drop that hardware before reaching orbit, and to reuse it in the next launch.

[razark]

"In real life, SSTO's...." There is no such thing. O.o SSTO's are "possible" but have never been constructed.

Actually, six manned SSTOs have been launched. They were rocket powered and not reusable.

Each one also required a Saturn V to get to the launch site on the moon.

[Kodiak42]

Although they may be more expensive to build, they're much cheaper because hardware is only purchased once. However, as opposed to staging setup with 100% hardware recovery, the advantage might just be that you can land somewhere, refuel, take off, find some other celestial body, repeat for as many celestial bodies as desired.

For now, in reality, 100% hardware recovery staging is better, but once we start building refueling stations on the Moon, Mars, even Titan, THEN the advantage will be with the SSTO.

[Spatzimaus]

They're similar challenges as reaching orbit or landing on the Mun. Do it a couple of times, and you'll estabilish best practices that allow you to do it again without too much trouble.

Not quite. There are a few fundamental differences between spaceplane design and rocket design that keeps this from being true:

1> With a rocket, bigger is better. If your design is inefficient, just slap more fuel and engines on it; you can take an existing design and just add another giant stage to the bottom. It might not be pretty, but it'll still work. With spaceplanes, you're forced to design more efficiently, since beyond a certain point you just can't scale the design up easily. Smaller is often better, although if you want a design with more capabilities you'll have no choice but to grow. So the difference between a mediocre design and a good one is far larger with spaceplanes.

2> Spaceplanes have more variables to manage, both in the design stage (balancing center of mass with center of lift) and in execution (having to transition from air-breathing mode to rocket mode, managing speed versus terminal velocity, etc.). This makes them much harder to master, and gives more things for a competent designer to tweak.

3> At the moment, there are fewer workable parts for planes than there are for rockets, although certain mods (B9) really help here. This forces you to make design compromises you might not otherwise have to make, which again makes it harder to create a design capable of the things you want.

As to the original question, of what use there is for SSTO spaceplanes when rockets are freely available and there's no cost benefit to reusability? Here are a few answers:

> Trips to other planets/moons. An SSTO design can fly there, land, take off, refuel in orbit, and come home. Any design that has to ditch parts during an ascent can't do that. All you have to do is ensure you have a network of fuel depots at strategic locations (especially if you're going to Laythe or Tylo). This is an advantage of SSTO designs in general, and not spaceplanes in particular; when I did my Grand Tour way back when, it was in a non-plane SSTO. That last one deserves special mention; as others have said, you can land, take off, refuel, land somewhere else, take off again, etc. ad nauseum with a SSTO design. While there's no actual gameplay benefit to doing a Grand Tour as opposed to dozens of specialized missions, it's a bit point of bragging rights.

> Precision landings. A capsule that uses parachutes to land is unlikely to land exactly where you want it to, unless you really abuse quickload until you get it right. A design with atmospheric control surfaces has much more control over its landing point on any body with air, so if you're trying to return to KSC's airstrip it's much, much easier in a plane. (Also, on Laythe a "brick" design is likely to splash in the ocean or land on a severe slope and tip over. Controlled landings there are very important.)

Beyond that, they look cool and when we get an economy they'll have a distinct advantage. In the meantime, though, they're mainly for the challenge.

[spudcosmic]

Reuseable stages with chutes to land and using docking ports/klaws. ROCKETS ALWAYS WIN

Yes but parachute landed stages are more prone to being damaged upon landing, but even more so is the cost of recovering the spent stage from the ocean many kilometers away. With an SSTO you can land it back at the space center and the only cost is a little bit of refurbishing and refueling. Over all bringing payloads up with an SSTO is many times more cheaper than using a rocket.

[GoSlash27]

An SSTO from Kerbin to LKO doesn't get you much of anything. You can always build more rockets and you never have a fuel shortage.

But consider the logistical problem of dealing with other planets where you can't do that.Every liter of fuel you burn and every piece of equipment you jettison had to be shipped in from Kerbin, landed on the surface, and possibly assembled on the surface.

An SSTO simplifies that job and makes possible what would otherwise be impossible.

Regards,

-Slashy

[ArmchairGravy]

I don't really have a practical use for them. I build them for the challenge. I can launch a rocket to LKO and be docked in the time it takes for a spaceplane to break 20k altitude. That being said the spaceplane I made from a science lab and used to bring down the results from my Jool expedition gave me a nice feeling of accomplishment. Spaceplanes are one of those points for style kind of thing for me.

[Jouni]

Not quite. There are a few fundamental differences between spaceplane design and rocket design that keeps this from being true:

We were talking about SSTOs, not spaceplanes. While spaceplanes don't scale up that easily due to the lack of bigger wings, scaling up SSTOs in general is just a matter of adding more fuel and more engines.

I played quite a lot with SSTOs when I had a Laythe colonization project back in 0.23. My designs eventually converged into utilitarian ones that take off vertically and do parachute-assisted powered landings:

This tug was involved in some funny episodes, such as pushing an unattached payload back to orbit.

In the current aerodynamic model, there's little point in adding wings to SSTOs. With better aerodynamics, spaceplanes could actually be useful by saving a lot of engine mass.

[Aghanim]

Try doing SSTO spaceplane in Realism Overhaul. I still cannot do that after a lot of testing

[magnemoe]

This is an 7 man ssto.

http://imgur.com/waotD51

The upper stage is an ecape system based on the dragon2 as the hitchhiker module had issues with parashute landings, it also make an good baseline ship for travel out to Minmus with an larger fuel tank and a drop tank below.

Rocket itself is rated for 11 ton payload to LKO.

http://imgur.com/94vSSvi

18 ton to LKO SSTO, an longer version with four recoverable SRB is rated to 40 ton to LKO.

http://i.imgur.com/E2Q6jmN.png

120 ton to LKO SSTO, with 12 SRB it takes 200 ton, this is my heavy lifter.

I also have an small jet assisted one who can take one kerbal or two ton to LKO.

Use them for simplicity, in 0.235 its no need to build the launcher around the payload, just put it below and add 4 struts and you can launch.

Edited June 2, 2014 by magnemoe

[MarvinKitFox]

Terminology:

SSTO: Single Stage To Orbit.

note the absence of the words "plane","airbreathing","reuasable","Horizontal takeoff"

one jumbo-64 with an SLS motor strapped to it is SSTO. Heck, its SSTE (Single Stage To Escape)

Spaceplane: Implies Horizontal takeoff. Implies Airbreathing. Implies reusable. Usually implies fly-back-to-runway-landing but this is more optional.

SSTO =/= Spaceplane!

[sumrex]

I could see the appeal of an SSTO with a contract system. If you threw away a 747 every time it flew like you do with a rocket prices would be astronomical. I imagine budgets will make them very attractive.