SSTO limitations and interplanetary spaceplanes

[Rakaydos]

Aside from their 'kool' look, is there a real practical niche for space planes? Any 2 stage to orbit vehicle will have greater payload/weight and cost effectiveness than a spaceplane. Spaceplanes take longer time to ascent too - I think of those tedious minutes that I waited for my SSTO to claw its way through the atmosphere... No, I stopped building them. I'm on a tight budget and money do matter. Rockets are cheap and reliable.

Jet-powered spaceplanes have a better paylod cpapcity to rocket SSTOs that can return to the launchpad- thus, they corner the market in 100% recovery.

[Wanderfound]

Aside from their 'kool' look, is there a real practical niche for space planes? Any 2 stage to orbit vehicle will have greater payload/weight and cost effectiveness than a spaceplane. Spaceplanes take longer time to ascent too - I think of those tedious minutes that I waited for my SSTO to claw its way through the atmosphere... No, I stopped building them. I'm on a tight budget and money do matter. Rockets are cheap and reliable.

A decent spaceplane can put fuel to orbit for < √1/unit.

[cicatrix]

Jet-powered spaceplanes have a better paylod cpapcity to rocket SSTOs that can return to the launchpad- thus, they corner the market in 100% recovery.

I never talked about rocket SSTOs I use TSTOs, the average payload mass/full mass is 18-20% while an SSTO can give me half of that. I use stage recovery so I don't waste my money completely on first stages. Besides, SRBs are cheap.

[Rakaydos]

I never talked about rocket SSTOs I use TSTOs, the average payload mass/full mass is 18-20% while an SSTO can give me half of that. I use stage recovery so I don't waste my money completely on first stages. Besides, SRBs are cheap.

So, you use a mod that makes spaceplanes less useful. Doesnt mean they arnt useful for other people.

[King Arthur]

For what it's worth, I've found that STS-style space shuttles are the best of both worlds. Good payload capacity and reasonable funds recovery from recovering the spaceplane/shuttle plus any payload(s) or cargo.

I've tried my hand at SSTOs, but the effort spent in designing them to get into space isn't worth it given I've found they always arrive in orbit running on fumes and with little to no practical payload capacity.

[Cirocco]

I've done runway-Duna surface-runway with a 3-man SSTO spaceplane without refuel (no cargo though). There's quite a few things that I learned while doing that project that I can tell you, what exactly do you need help with? Also, feel free to send me a message over the forums for concrete advice/tips/questions, that's probably a bit more structured and easier for the both of us

link to mission report of the Duna Mission: http://forum.kerbalspaceprogram.com/threads/83711-To-Duna-and-back%21-in-a-spaceplane%21-without-refuel%21?highlight=duna+back+spaceplane+refuel

All stock by the way, both the plane and the aerodynamics.

note that that one was made in I think 0.24 and I've learned a few additional spaceplane tricks since then. Coupled with the new parts, I'm sure I could make a better, more efficient one today. I just can't be arsed to do so before the new MkIII parts come out

First and I believe most important tip of all: the order of placement of you engines and air intakes matters. Placing about 2 intakes per engine in the correct order is a lot more efficient than spamming dozens of them. And it looks a lot sleeker as well.

The placement order you want is to first place any air intakes you want a particular engine to use, then place the engine, then place the intakes for the next engine, then place that engine, etc. DO NOT use the symmetry tool.

If you use the above described method, you can eacily go up to 32-34ish km before you need to switch to rocket engines (you'll experience turbulence and will temperarily need to throttle down at about 27km) . This also means you can do circularization purely on atomic engines which will increase your ship's range by several orders of magnitude. Also, never go with more than 3 atomic engines. If you need more thrust then that, you're doing something wrong.

[cicatrix]

So, you use a mod that makes spaceplanes less useful. Doesnt mean they arnt useful for other people.

I didn't say SSTOs aren't useful. Well, I say it now

The only two places where they have somewhat questionable advantages are Kerbin and Laythe. And you must carry the dead weight of jets and wings to all other places. I could probably agree that on the direct Kerbin - Laythe - Kerbin route a jet SSTO might have its uses, but this would be about all. Plus you'll need a flat 'runway' to take off and land.

Other use might be Kerbin-LKO-Kerbin but in order to lift a big payload you will need several trips thus burning more fuel in the end.

[Mighty1]

For an extra challenge install the B9 mod. This is not just lots of pretty parts, but a rebalancig of jet power to RL values. Stock turbojets get you to M3, and the B9 jets to M3.2 (1170 m/s). After that speed you have to use rockets. No more getting to orbital speed of jets alone.

[Cirocco]

I didn't say SSTOs aren't useful. Well, I say it now

The only two places where they have somewhat questionable advantages are Kerbin and Laythe. And you must carry the dead weight of jets and wings to all other places. I could probably agree that on the direct Kerbin - Laythe - Kerbin route a jet SSTO might have its uses, but this would be about all. Plus you'll need a flat 'runway' to take off and land.

Other use might be Kerbin-LKO-Kerbin but in order to lift a big payload you will need several trips thus burning more fuel in the end.

Well re-usable SSTO spaceplanes save you money in the fact that you don't discard hardware. Fuel cost is peanuts compared to part cost. That means that, yes, re-usable SSTO spaceplanes don't offer much outside of kerbin's SOI. But they do help in getting stuff into space, which is where about half of your ship's energy goes to anyways. If you can get to orbit cheaper, that helps a TON in reducing costs.

Of course, it's been mentioned many, many, many times before that in the current economics system SSTO spaceplanes indeed don't give that much advantage over disposable rocket systems because the game throws tons of money your way.

Still, there's just something intensely satisfying about flying and designing SSTO spaceplanes. A while ago I was working on desiging a plane with multiple large cargo bays, but the enormous center of mass shifts that come with that were playing merry hell with my design plans. Sure I could just make a smaller plane and do several trips or strap my sattelite payloads to a big rocket and launch em all that way, but it's just a lot of fun trying to come up with creative solutions to the large cargo bay problem.

Mind you now that the new MkIII parts have been announced, I scrapped the project and am just waiting for the new, bigger cargo bays

Edited December 11, 2014 by Cirocco

[Spatzimaus]

Spaceplanes don't scale any better or worse than rockets do; you're just not going to see much of a delta-V improvement as you get bigger. The only way to really extend your range is to go more EFFICIENT, meaning high-efficiency engines (like LV-Ns in stock or even ions) and fewer extraneous parts.

I've posted this quite a few times in this forum, but here's my interplanetary SSTO spaceplane, the Sleazy Weasel:

It's a 32-ton plane using ion engines (the pods on the wingtips) to give interplanetary range; even if it does mean burns of a couple hours. The craft file and more pictures are available in this post in the Akademy Awards thread. It uses a couple mods, but all the things it can do should be possible with stock parts.

As to what it can do? (In stock aero.)

> Without using its ion engines to extend its range, it can take off from Kerbin, fly to Minmus, land there, take off, and return to the KSC runway. No refueling involved.

> With ions, it can fly to Ike, land, take off, land on Duna, take off (using its high-efficiency rockets for the ascent, as the jets obviously don't work), and return to KSC. No refueling involved.

> With a single refueling stop, it can go much further. Recently I took off from Kerbin, flew to Pol, and refueled at an orbital depot I maintain there. Now refilled, it landed on Pol, took off, went to Laythe (using a Tylo slingshot to slow down), landed (see picture above), took off, and returned to KSC (using another Tylo slingshot to speed up on the way back).

With more gravity assists I'm sure you could do quite a bit more.

The point is, once you get a plane to a decent size, allocating a couple tons to add thousands of m/s of dV isn't a big drawback. At that point you can go pretty much anywhere you want.

Edited December 11, 2014 by Spatzimaus

[TokiTech]

Hello all, i'm new around KSP and been designs and testing SSTO cargo spaceplanes for few days now. My next project is to make an Interplanetary Spaceplanes carrying one Rover that can do return trip to Kerbin with no refuel. Which planet do you think is easiest to achieve this?

[cicatrix]

Hello all, i'm new around KSP and been designs and testing SSTO cargo spaceplanes for few days now. My next project is to make an Interplanetary Spaceplanes carrying one Rover that can do return trip to Kerbin with no refuel. Which planet do you think is easiest to achieve this?

Duna is the easiest

You can get to Eve but landing with a spaceplane on Eve means it would never return.

Aside from that the only other planet with an atmosphere is Laythe.

You can also attempt Dres, Pol and Bop.

Moho/Eeloo is hard due to high energy cost.

[Rune]

You guys are really confusing the poor OP. First things first: the exponential nature of the rocket eqauation means that there is, indeed, a limit to what you can do with a single stage, whether it has wings or not.

Now that limit can be enough to do Duna return missions if you are a good engineer, but that is more tricky. Note that Duna SSTO missions are much harder than Laythe missions where you have an oxygenated atmosphere to run airbreathers and zero need of rocket T/W. In fact, I recommend ions for Laythe, BTW, you can make some ridiculously small interplanetary SSTOs that way: single liquid fuel tank, single turbojet, a couple of ion engines with ample fuel, and that will take a couple of tons to Laythe and back.

But assuming you want to maximize the delta-v of a nuclear-powered spaceplane, how would you go about that? Well, delta-v is all about mass ratio. That is, what percentage of your ship is fuel weight. So you want to minimize airbreathing stuff, and engine weight. The real payload (crew cabin and stuff) should be a really tiny fraction of the ship's takeoff mass. Basically make the SSTO with the least engines you can make that can take up the single nuke and crew cabin, and load it with the biggest amount of fuel that will still allow it to keep climbing over 10,000m.

If you want some engine configurations that should probably work, three jets (so you can make the middle one flame out earlier and have no spins-of-death due to assymetric flameout) and two nukes will probably make for an easy one-person interplanetary SSTO. I have seen people do it with two turbojets and a single nuke, but that is probably trickier since the margin is tighter (the pod is a bigger fraction of the weight). Plus, you need some rocket T/W to take off from Duna (about 0.4).

Rune. Good luck!

[Wanderfound]

Duna is lowest ÃŽâ€V of the interplanetary trips, but the thin atmosphere means that you'll want parachutes or VTOL thrusters for landing. Laythe has an oxygenated atmosphere that makes it as easy to fly on as Kerbin, but you're looking at ~5,000ÃŽâ€V just to get there.

For a Duna demo, see: http://s1378.photobucket.com/user/craigmotbey/Kerbal/Kerboduna/story and http://s1378.photobucket.com/user/craigmotbey/Kerbal/Kerboduna/Kerboduna%20II/story

For Laythe, see: https://www.dropbox.com/s/4v4rkcnvk7pk0rp/Kerbodyne%20Kosciuszko.craft?dl=0 and http://s1378.photobucket.com/user/craigmotbey/Kerbal/Kerbodyne%2025/Kerbodyne%20Kosciuszko/Laythe%20Landing/story

[TokiTech]

Thanks cicatrix, and Wanderfound for the links. So much to learn and i hope i'll make it to Duna in a piece with those reference info. Off to SPH!

[Rune]

Laythe has an oxygenated atmosphere that makes it as easy to fly on as Kerbin, but you're looking at ~5,000ÃŽâ€V just to get there.

Say what? Straight insertion from LKO into a Laythe intercept, a couple km/s or less. Aerobrake for nothing there, then go back to orbit for pretty much the same on turbojets. Then it's the trip back, and that's like a pittance if you drop really close to Jool doing it, perhaps 1.5km/s or two. Doing a Lythe mission and requiring 5km/s of deltaV on transfers? A big waste of fuel.

Duna on the other hand, has two km/s just to get out of it into orbit, and that is supposing you know how you are landing you plane of the game's thinnest atmosphere, which usually implies a separate system eating into the mass ratio further. And a pretty big rocket T/W imposition that translates into an even worse mass ratio.

I'm actually looking for a very old thread from the first time someone did the whole Laythe thing without oxidizer... can't seem to find it.

Rune. It was doubly impressive because it was with the old crappy ions.

[m4rt14n]

Interesting Rune.

[Wanderfound]

Say what? Straight insertion from LKO into a Laythe intercept, a couple km/s or less. Aerobrake for nothing there, then go back to orbit for pretty much the same on turbojets. Then it's the trip back, and that's like a pittance if you drop really close to Jool doing it, perhaps 1.5km/s or two. Doing a Lythe mission and requiring 5km/s of deltaV on transfers? A big waste of fuel.

Duna on the other hand, has two km/s just to get out of it into orbit, and that is supposing you know how you are landing you plane of the game's thinnest atmosphere, which usually implies a separate system eating into the mass ratio further. And a pretty big rocket T/W imposition that translates into an even worse mass ratio.

I'm actually looking for a very old thread from the first time someone did the whole Laythe thing without oxidizer... can't seem to find it.

Rune. It was doubly impressive because it was with the old crappy ions.

The ~ was there for a reason. LKO to Jool is 2,000-3,000m/s of ÃŽâ€V, depending upon patience and finesse; aerocapture from interplanetary speeds can be done at Jool, but is tricky to get right if you're using DRE and spaceplanes (i.e. no ablative heatshield). Jool to Laythe is another 1,600m/s or so, and again can be finished with an aerocapture, but is again likely to require a bit of thrust from a novice pilot: the margin between escape velocity and reentry burn-up is rather thin. Trying to go directly from Kerbin to Laythe without the Jool aerobrake is well beyond most non-veteran Kerbonauts.

Do it perfectly, and you can manage an LKO to Laythe orbit trip (even with DRE in play) for <4,000m/s of ÃŽâ€V, but a first-timer is very unlikely to do it perfectly. OTOH, build it right and it's fairly easy to get a spaceplane to LKO with better than 5,000m/s of ÃŽâ€V still in the tanks.

[Spatzimaus]

Duna is lowest ÃŽâ€V of the interplanetary trips, but the thin atmosphere means that you'll want parachutes or VTOL thrusters for landing.

If your design is well-balanced and has decent wing area then it can just glide down onto Duna without chutes or VTOL engines. That's what I did, anyway. The landing can be a bit rough in an unpowered glide, but it's manageable. That might depend on mods, though; I use the landing gear in the B9 mod, which are handy for a number of reasons (drive like rover wheels, can rotate, can have a longer extension, don't have that annoying light) but I also think they can take quite a bit more impact force than the stock wheels as they're not as rigid. It also helps that on my plane I placed the aft wheels on a somewhat flexible mount, to absorb even more force.

As for engine configuration, the basic model for engines is pretty straightforward; you need the equivalent of one turbojet per ~10 tons, at minimum (I'd aim for 7-8 tons per) just to ascend at a decent speed. You also need something like an LV-N, something with good fuel efficiency and enough thrust for low-orbit maneuvers. Ions are great for interplanetary burns, as long as you're willing to wait a couple hours (or if the design is small enough that x4 physics acceleration won't rip it apart). And depending on design you'll often need some low-efficiency rocket with enough raw thrust to get you through that awkward transition from jets to low orbit, although the rocket half of a RAPIER works just fine for that as long as you only use it sparingly.

My lastest design, the one I posted above, has four RAPIERs (really don't need more than 2, but there's no longer a real difference between turbojets and RAPIERs), two LV-N equivalents (from a mod, they're radial hybrid ion engines), and two stock ion engines. Mass is 32 tons, so that should give you an idea of what amounts you need for each size.

[Landge]

In the past SSTO spaceplanes were near impossible for me to achieve LKO. So instead of sending SSTO planes to Laythe, I attached regular jet planes to rocket boosters.

Journey to Laythe 0.22 Mission Album

Those were meant for strickly oneway aerial survey of the islands with refueling depots.

Recently with 0.25 new Mk2 parts I have built a true SSTO that can reach Mun and back but needs LV-909s for VTOL assist and requires refueling in Mun orbit.

Now whether it will get to Laythe on it's own I don't know yet. This is still experimental. I'm working on an orbital carrier that is launched separately from the VAB that will allow

the SSTO a means of reaching Laythe without using the SSTO's own fuel supply except for deorbit and ascent.

I posted this recently in the What did you do in KSP today thread. I'm still fine tuning the design. I haven't even named them yet.

Here are picks I took last night of my latest test flight after docking in LKO...

The SSTO is now equipped with the full array of science gear.

The mobile lab is located on the orbital carrier.

So far I have different cargo load outs depending on what RP element the mission needs. Cargo, science (as shown), and satellite deployment.

Edited December 11, 2014 by Landge

[Wanderfound]

VTOL isn't compulsory for Duna, but it does make it a lot easier, especially if using FAR. Thinner atmosphere = higher stall speed; bumpy ground = bad for fast landings. A bit of VTOL (doesn't need to be 1G Kerbin-grade, a few Vernors will do) allows a landing at Kerbin-normal low speeds.

[Rune]

The ~ was there for a reason. LKO to Jool is 2,000-3,000m/s of ÃŽâ€V, depending upon patience and finesse; aerocapture from interplanetary speeds can be done at Jool, but is tricky to get right if you're using DRE and spaceplanes (i.e. no ablative heatshield). Jool to Laythe is another 1,600m/s or so, and again can be finished with an aerocapture, but is again likely to require a bit of thrust from a novice pilot: the margin between escape velocity and reentry burn-up is rather thin. Trying to go directly from Kerbin to Laythe without the Jool aerobrake is well beyond most non-veteran Kerbonauts.

Do it perfectly, and you can manage an LKO to Laythe orbit trip (even with DRE in play) for <4,000m/s of ÃŽâ€V, but a first-timer is very unlikely to do it perfectly. OTOH, build it right and it's fairly easy to get a spaceplane to LKO with better than 5,000m/s of ÃŽâ€V still in the tanks.

Oh yeah, you can waste quite a bit of delta-v by doing things such as going into Jool orbit prior to going to Laythe of course. But managing a Laythe intercept is actually easy as you come into the Joolian system, and DRE is very much not stock. In stock, you can belly-flop into an atmosphere at 10km/s and you will be perfectly fine. I was referring to stock, of course. Where, incidentally, I don't find it anywhere near easy to get 5km/s out of a SSTO in LKO orbit, unless it is sporting ion engines, and then Duna is out by definition. I mean, this thing has 4.5km/s and it is mostly just fuel, with the single pilot, nuke, and only two jets:

Delta-v wise it could go to either Laythe or Duna... but the delta-v budget to Duna is tighter, and even though it has the TWR to take off in there... well, it doesn't have enough lift to land safely. Adding a chute or VTOL system would cut into the deltaV, of course.

Rune. I don't think I have any SSTD, actually, I know I could build one, but I haven't... yet.

Edited December 11, 2014 by Rune

[Wanderfound]

6,293m/s ÃŽâ€V in LKO, with a not-very-big and not-very-specialised ship I threw together in a few minutes:

But, of course: FAR. Choice of aerodynamics model has a substantial influence on spaceplane possibilities.

[m4rt14n]

Why would anyone want SSTD? Space STD

[Rune]

Why would anyone want SSTD? Space STD

Hahahaha. I meant Single Stage To Duna! But I totally see your point