Whats with SSTOs?

[CalculusWarrior]

Unity Engine

sniptastic

You sir, are fantastic; I nearly fell out of my chair laughing!

[sjwt]

They are 100% reusable spacecraft.

No, They are Single Stage To Orbit, reusable has nothing to do with it, they can be reusable, but as NASA found out, making things reusable can cost more than just building new bits.

Here is a nice SSTO <G>

[doggie015]

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.

Or just one X200-32 tank and the same engine. 5 parts (Capsule, Parachute, Tank, Engine, Decoupler) and you are in orbit and back. Again; minimal to no payload capacity though but good if your computer can't run KSP that well.

On the launchpad (Build shown includes optional ASAS module bringing the part count to 6):

You know what they say about slow and steady (T/W ratio at launch must be about 1.05)...

The power/weight ratio improves dramatically as you lose fuel

Final circularisation burn

Running on fumes here...

.craft file: https://mega.co.nz/#!2YlQCD5I!FB1h00JXKkuxOMJ9NdJHkhd_XPgZyDaJy94q8iHrlDQ

Edited November 25, 2013 by doggie015

[Dante80]

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.)

The problem isn't efficiency, its doing it in style...XD

866tn payload...C:

(a FAR nightmare of course)

The reason for building SSTOs is both for flavor, style and RP reasons (getting a totally reusable space program is an achievement on its own).

Edited November 25, 2013 by Dante80

[ComradeGoat]

Land on Moho is #0 on that list.

SSTOs come in around #3.

Can't agree. Landing on Moho is really not very hard at all. It just needs a long burn with an LV-N to establish orbit.

[liweih]

What I found is jets are so efficienct when you have enough air intakes. Use jet to let your shuttle flying above 40,000m and sliding into the vacumn then let the rocket engine do the final push for a stable obit. The whole thing is simple and beautiful.

[NASAFanboy]

I use something like a grasshopper rocket as a SSTO. It takes off, reaches orbit, releases payload, and lands. The first stage uses jet engines to 250KM, then the jet engines are shutdown and the rocket engines are activated along with a boost of seperatrons. It can get around 15 tons to orbit and back...that's enough for large satellites or probes, or a Shengzhou/Soyuz craft, and enough for a small spacestation module.

I don't use spaceplanes because no matter how well or simple I build them, they won't stop veering off the runway. Heck, "How to bail out of a burning death trap with wings" is a mandatory course for all my Kerbalnauts. And when they do take off, it's a slow trip. I built a spaceplane SSTO and flew it a record total of three times, and put 70 tons into orbit everytime. But it was torture flying that thing, yes, it handled well, but it was slow to orbit... The entire spaceplane and SSTO project got shelved on the basis of "Ain't nobody got time for that" just last week, and I'm back to using staged rockets.

Edited November 25, 2013 by NASAFanboy

[Tank Buddy]

They're a lot more interesting to build and fly, and much more difficult as well.

[fatfluffycat]

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

Rocket

SSTO Spaceplane

I know what I would rather be piloting.

I would want to drive the truck!

[El wonso]

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.

If you are talking strictly about KSP - there is no such thing as unstable orbit.

[Dante80]

If you are talking strictly about KSP - there is no such thing as unstable orbit.

Yes there is, you can orbit Kerbin with a periapsis below 70km in an elliptical orbit. Your orbit will degrade with each pass, gradually bringing you down to the ground after some time.

[El wonso]

Yes there is, you can orbit Kerbin with a periapsis below 70km in an elliptical orbit. Your orbit will degrade with each pass, gradually bringing you down to the ground after some time.

I was going to write, that it is called sub-orbital flight, but it turns out, it actually isn't. Anyway, looks like I was wrong.

btw atmosphere ends at 69km ASL.

[m1xte]

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.

Original question should go "Whats with SSTO space planes?"

Ps.

All oxidiser used under 25km and all engines over 0.8 start TWR is also dead weight.

[Spatzimaus]

Original question should go "Whats with SSTO space planes?"

Fair enough, but some of the same principles still apply. A space plane would be more efficient with drop tanks, or detachable boosters. It wouldn't have to carry quite as much weight during its final boost phase, making it easier to reach a stable orbit. But for the reasons we've discussed, people go SSTO; it's rare to see a non-SSTO spaceplane on these forums.

The bottom line is, SSTO spaceplanes are just more fun. I mean, when I have real work to do I'll use a regular rocket (albeit often my SSTO booster design), but I spend far more time fine-tuning my spaceplane concepts because it's just FUN to tweak them. And getting one to orbit feels like an accomplishment, whereas for rockets it's a couple minutes of trivial effort.

[Ravenchant]

Let me fix that for you

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... No poofters.

[Hodo]

Fair enough, but some of the same principles still apply. A space plane would be more efficient with drop tanks, or detachable boosters. It wouldn't have to carry quite as much weight during its final boost phase, making it easier to reach a stable orbit. But for the reasons we've discussed, people go SSTO; it's rare to see a non-SSTO spaceplane on these forums.

The bottom line is, SSTO spaceplanes are just more fun. I mean, when I have real work to do I'll use a regular rocket (albeit often my SSTO booster design), but I spend far more time fine-tuning my spaceplane concepts because it's just FUN to tweak them. And getting one to orbit feels like an accomplishment, whereas for rockets it's a couple minutes of trivial effort.

Its not they would be more efficient, they would be a pain in the but to design. Once you have a working theory on space plane SSTOs, or even SSTOs in general why would you go and throw all that out to be able to drop, drop tanks or detachable boosters. The balancing before the drop and after would be a nightmare.

[Spatzimaus]

The balancing before the drop and after would be a nightmare.

Not really. Take my own spaceplane design for example:

Those ion pods at the ends of the wings (which are what I use for traveling to Laythe) are perfectly balanced with the center of mass, because the entire design is basically coplanar. I could put pretty much ANYTHING at those wingtips and it'd balance just fine; in previous versions I'd put separating ion-powered probes and such out there. It wouldn't take any effort to put a drop tank or a booster at those locations and drop them as necessary. And that's with a design that's not INTENDED to drop stuff off; it wouldn't be hard to make a Y-shaped plane that mounted droppable fuel tanks between two aft prongs of fuselage.

It'd be even easier for a design using boosters that separate after you left the atmosphere, since you could use top/bottom symmetry instead. Four SRBs, for instance, mounted on radial separators above and below the wings? Those'd make it far easier to reach orbit with most of your fuel supply intact. Or imagine a Space Shuttle-style design where your spaceplane rides a much bigger fuel tank/booster combo most of the way up. Any of these would make your design more efficient, in terms of how much fuel it reaches orbit with.

All that being said, it's just not that hard to make a basic SSTO in KSP once you know what you're doing; it's the initial learning phase that's difficult. And if you can do that, then there's little reason to debase yourself by adding detachable bits, at least until we get some sort of economic system that encourages that sort of thing.

[inigma]

Besides, they just look so darn sporty:

Here's one of mine. Capable of undocking from 120km station, landing at the KSC helipad VTOL, and flying back up with a friend and re-docking at 120km without refueling.

The SSI Neutron:

As someone hinted above, I'd rather go into space in one of those.

Or my single seat sport shuttlecraft, the SSI Ion:

Javascript is disabled. View full album

Edited November 26, 2013 by inigma

[Hodo]

Not really. Take my own spaceplane design for example:

Those ion pods at the ends of the wings (which are what I use for traveling to Laythe) are perfectly balanced with the center of mass, because the entire design is basically coplanar. I could put pretty much ANYTHING at those wingtips and it'd balance just fine; in previous versions I'd put separating ion-powered probes and such out there. It wouldn't take any effort to put a drop tank or a booster at those locations and drop them as necessary. And that's with a design that's not INTENDED to drop stuff off; it wouldn't be hard to make a Y-shaped plane that mounted droppable fuel tanks between two aft prongs of fuselage.

It'd be even easier for a design using boosters that separate after you left the atmosphere, since you could use top/bottom symmetry instead. Four SRBs, for instance, mounted on radial separators above and below the wings? Those'd make it far easier to reach orbit with most of your fuel supply intact. Or imagine a Space Shuttle-style design where your spaceplane rides a much bigger fuel tank/booster combo most of the way up. Any of these would make your design more efficient, in terms of how much fuel it reaches orbit with.

All that being said, it's just not that hard to make a basic SSTO in KSP once you know what you're doing; it's the initial learning phase that's difficult. And if you can do that, then there's little reason to debase yourself by adding detachable bits, at least until we get some sort of economic system that encourages that sort of thing.

While most of this works in normal KSP, when using FAR those things add so much additional drag that it isn't worth taking them. If you are going to add additional stages to turn it into a horizontally launched rocket with jet support, then you may as well just build a rocket.

[Brofessional]

Stacking intakes via part clipping doesn't count.

[csanders]

My SSTO

[AstroDoc]

Now that the accountants are having their say (missions need costing to make a profit), SSTOs make a big difference

I'm playing a game on version 0.25. I wanted a cheap solution to the recurrent problem of needing to rescue Kerbals who get stuck in orbit. I don't like seeing Kerbals in chairs being toasted on re-entry, so I wanted pod.

So here is a basic functional spaceplane. I've tweaked it to have '72' fuel and '55' oxidiser on takeoff, and the pod has no crew on takeoff. Mass 2.71 t. Cost 11885. I can rescue the Kerbal and bring him back to the runway, get 11821 Kerbal currency back on recovery, for a final rescue cost of 64 Kerbal currency. The KSP accountants are very enthusiastic

AstroDoc

Edited October 29, 2014 by AstroDoc

[Farex]

They are 100% reusable spacecraft. [....] It is a milestone to make a successful SSTO in KSP.

Exactly this! Up until 0.24 I never bothered with them because I kind of thought them to be useless and to be honest I never ever build a successful SSTO. But everything changed when 0.25 attacked. New Parts that look nice, let's try out SSTOs and now I am certainly a SSTO Supporter

[Frank_G]

I would want to drive the truck!

Yeah, a truck with 22.000.000 horsepower... who cares about re-usability

[Richy teh space man]

SSTOs are great fun, designing something that can get to orbit in one piece and then flying it.

Also, with economics now playing a role, they also have a place in having an efficient space program where money can be tight.