VAB SSTOs

[SofusRud]

I would like some advice regarding VAB built SSTO. That is, a craft that uses jets and rocket engines in order to get into orbit, without any wings (look like rocket).

- Turbojets or regular jets?

- Standard gravity turn or should I do it earlier in order to grab as much air as possible?

- if so when?

- how low can my intake air go for two regular jet engines on full power? Turbojets?

- LVT-30, Aerospike, Skipper or a bunch of 48-7Ss?

[giltirn]

Sounds like a tough challenge, if you really want the thing to be a single-stage to orbit vertical launch craft. With a standard spaceplane SSTO you gain pretty much all of your speed while flying horizontally at around 25-30km. With a vertical ascent profile I would be surprised if you got much more than a couple of hundred m/s before you run out of air at 35km, even if you stack hundreds of intakes. This means you are basically building a single-stage rocket that has to haul around a load of dead weight used for only a tiny portion of the delta-V required to achieve orbit.

Edit: Nevertheless, I would definitely use turbo-jets and whatever rocketry setup required to haul that thing from 35km to orbit. Try to spend as much time horizontal as possible between 20km and 30km, completely flat if possible without wings! I think the number is about 0.07 air per turbojet, not sure about jets (likely much more).

Edited September 24, 2013 by giltirn

[SofusRud]

The purpose of the craft is a crew shuttle for my Laythe colony efforts.

I have been basing my design on some SSTOs that Brotoro built a while ago. At the moment I am trying to optimize my design (why I'm asking for input). My current version uses 2 regular jets with 3 ram intakes each, one LVT-30, and can reach a 75km orbit with very little fuel left. However, it can only ferry one guy and has to carry a load of parachutes in order to be reuseable.

Any ideas on how to improve it?

[Dispatcher]

Definitely you want turbos over basic jets. Turbos optimally function at higher altitudes while basics will whine down as they climb. You could still use wings as control surfaces, and when the ship isn't completely vertical the fins provide a little lift too. For space you want an engine which vectors, since control surfaces are useless there. You missed an engine candidate; 2 or 3 Radial 55s. 3 of those are between the performance of the Skipper and the Poodle.

[capi3101]

Well, I have experience building SSTO rockets - pure rockets (hell, the Storax Anacostia 7 started off as an SSTO; I had to chunk that one up to three stages to fulfill the conditions of the challenge).

Let's start with what you have...do you have a screenshot?

Meantime, here's how I'd do it: go with a -45 in the center and three -30s outboard. Forget the jets. If you're ferrying five Kerbals in a Hitchhiker and a Can, that gives you 8.35 tonnes deadweight and payload, 320 Isp. You want 4500 m/s of delta-V to launch to orbit. Work Tsiokolvsky backwards...you need about 50 tonnes of fuel. Two FL-T800s, an FL-T400, an FL-T200 and an FL-T100 per engine should do the trick, and give you 1.43 TWR on launch.

Lemme do the math just to prove I know what I'm talking about:

delta-V = ln (M/Md) * 9.81 * Isp, M = 9Md

4500 = ln(9Md + 8.35/Md + 8.35)*9.81*320

ln(9Md + 8.35/Md + 8.35) = 1.43486

(9Md + 8.35/Md + 8.35) = e^1.43486 = 4.19329

9Md + 8.35 = 4.19329(Md + 8.35) = 4.19329Md + 35.01397

4.80671Md = 26.6639715

Md=5.547239

M = 9Md = 9 * 5.547239 = 49.92515

49.92515 / 4 = 12.48129

(Tank Fuel Suggested: 4.5+4.5+2.25+1.125+0.5625 = 12.9375, * 4 = 51.75 t, + 8.35 tonnes payload/deadweight = 60.1 tonnes)

Thrust = 200 + 215 + 215 + 215 = 845

845 / (60.1 * 9.81) = 1.43 TWR

As far as the flight profile goes then, it's a standard rocket launch. Straight up to 10k then follow the navball. You'll need to throttle back as you burn fuel and get lighter - you won't need all your thrust the whole way up. Throttle back if your gee meter gets out of the green. The 45 gives you steering, the 30s give you power, and you've got enough fuel to make it and then turn around for deorbit. Probably could even include a docking port and a chute or two. And no staging equipment.

You saw how I did the math on this one - it applies to any SSTO, not just rockets.

[arq]

A mainsail under 5-6 x32 tanks should SSTO all by itself. Smaller designs are also possible, but the mainsail is good because it has the highest TWR (meaning it can carry more fuel than any other engine, though the lower ISP will probably hurt you more than this helps). The main place where SSTO's are inferior is in payload fraction - so getting something heavy up will be challenging. Still, bundling enough of these mainsail stacks you should be able SSTO whatever you want without excessive suffering.

[capi3101]

I built what I suggested in my previous post - I went with four LT-30s so I could add a senior docking port, an RCS tank, blocks and some winglets. Started with twelve radial chutes. Got up to a 100k orbit with fuel to spare - enough to deorbit, even. The landing didn't go well, though - the Hitchhiker and Can survived intact, but the rest of the vehicle broke off. Second attempt, went with twenty chutes, just wanted to do a load test so I fired up to 8000 then fell back towards terra firma. Rocket broke again, though I don't know if that would've been a test under actual working conditions or not - she still had a lot of fuel and was therefore a good deal heavier than normal.

I'd be leery of using Mainsails for SSTOs - again, great thrust at launch, but way, way, way too much once you're up out of the atmo, and awful damn heavy in their own right. Skippers are a better alternative, actually - finer control over the throttle.

EDIT: According to the KSP Parachute Calculator, 20 radials should do the trick. I might consider adding a couple of drogues for the hell of it. Some lander legs would probably also be useful.

Edited September 26, 2013 by capi3101

[Guest]

I think your answer will lie in one of two areas, or a combination of them:

1) turbojets with many many intakes per jet engine,

2) nuclear engines.

Both options make much more efficient use of liquid fuel. The nuc required oxidizer, but it is much more efficient that the combustion type engines.

I have not dabbled yet with the Xenon fueled engines, and although they are extremely low thrust, perhaps there might be a option there as well. I don't know as I said I have never even placed one on a craft yet.

[rosenkranz]

Actually, if you look at scott manley's reusable program he used regular jets as they develop more thrust for the short time you're gonna use them

[orangexception]

I don't have one actively, but I've had a few of these.

- Stick to normal rocket launch path.

- 1:1 intake to jet is fine.

- Basic Jets Engines are good. They work well at low alt.

- Use fuel lines to the jet motors. They don't consume a lot of fuel, so just stick them on with structured elements.

- Pack 1x extra liquid fuel tank per 6x jets (or don't they won't eat a ton).

Fly it and figure out when your jets cut out. On your next launch, hit action groups #1 & #2 about 1k short of the cut off altitude.

If your vertical speed drops, then toggle on action group #3 or #4 for a bit.

Action Groups:

This is from my standard action group setup.

SSTO

1 Toggle All Jet Engines

2 Toggle Gimbals & Air Intakes

3 Toggle All Rocket Engines

4 Toggle Main Rocket Engine

Rockets

2 Toggle Gimbals & Air Intakes

3 Toggle All Rocket Engines

4 Toggle Main Rocket Engine

[orangexception]

You can also put a chute on the jets and decouple them, but it adds weight. Closing the intakes works pretty well.

[orangexception]

Another thing to keep in mind. You don't need jets to SSTO. I made a simple rocket last night. 75k orbit w/ a little leftover fuel.

[astropapi1]

Check this out.

Also remember that kerbals attached on ladders so they look down become massless. That's it. My rocket could carry four guys using that exploit.