Help improving SSTO Space Plane

[GoSlash27]

Wait, wait, how are you making it to orbit with so little fuel

juanml, ruthless attention to efficiency, mostly. My spaceplanes are built to the bare minimum to do the job and flown in the most efficient profile, so the spiraling requirements for more engines fuel and structure are eliminated.

It's surprising how little you actually need to put a payload in orbit! The key is to think in terms of "what do I need to get rid of" instead of "what do I need to add".

Best,

-Slashy

Edited August 23, 2015 by GoSlash27

[panzer1b]

juanml, ruthless attention to efficiency, mostly. My spaceplanes are built to the bare minimum to do the job and flown in the most efficient profile, so the spiraling requirements for more engines fuel and structure are eliminated.

It's surprising how little you actually need to put a payload in orbit! The key is to think in terms of "what do I need to get rid of" instead of "what do I need to add".

Best,

-Slashy

Mine tend to be the opposite, as much overkill as humanely possible......

Since every SSTO that doesnt get to laythge and back (including landing on laythe) is an utter failure for my standards, i pack as much fuel as i can humanely get off the ground.

My latest craft, is almost 30 tons, pushed by a single rapier (and aside from needing a 15 degree downward dive to break the 400m/s barrier, it actually flies somewhat well).

this is my latest SSTL craft, 4550 dV in orbit with ~1.5 tons of dead weight onboard (missiles)!

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the pics are a little outaded, i found a better ascent profile that adds ~200dV to what i had in these pics.

But yes, you are correct that unless ur bat.... insane like me, in general the less fuel and less crap u have on your SSTO, the better it will preform, less lag, and well, if all u care is delivering supplies, then i too dont build monsters like the HK-201 normally.

[Clipperride]

Lots of very useful remarks and suggestions in this thread. I've only been playing/totally obsessed with KSP for a couple of weeks but, by cutting back on things like sleep, I only have about 4000 science worth of tech to unlock.

Being something of an Apollo nut, the rocket side of things all made sense. Now I've come to try my hand at Space Plane's, its a different story.

My current STTO + ½ (with solid rocket boosters to break Mach 1 as quickly as possible from take off), looks a lot like the one David first posted. I keep getting caught in the fuel/weight/thrust vicious circle.

If I could butt in and ask my own question? Should you fly different assent profiles with different weight/class of Space Plane?

[Vegetal]

Usually no. If your plane is too underpowered, it might need a bit of a dive on the 10km region to break the sound barrier, apart from that, it's pretty much the same.

[davidpsummers]

I think that's too much wing. Wings cause both lift and drag, so unless I'm mistaken, you actually want as little wing area as you get away with.

[....]

Also, having the four engines set up that way will also increase drag, I think you'll get better results by using a decoupler in the tail to fit two engines.

[...]

And if you want to toy with something different, four rapiers and two nervs can also put your six kerbals in orbit and leave you with quite a lot of delta-v to spare, even (or specially) if the rapiers aren't given enough oxidizer to push all the way out of the atmosphere.

I needed a wing with a shorter based and I like the wings I don't have to piece together, I stuck it on and it worked. I did suspect I was overkill (a lift of 2x5 was working OK). So I may revisit that. Someone said there was a rule of thumb that you could use 1 rapier for every 15 tons? Is there one for wings like that?

As to using side mounted engines. They are all behind an intake which I need to get air. If I put them on the back, I'm just going to have to add intakes someplace else? (and the radials get no love).

I may look at NERVs. I'm daunted by their weight. Though I could go pure liquid fuel with them....

[Clipperride]

Usually no. If your plane is too underpowered, it might need a bit of a dive on the 10km region to break the sound barrier, apart from that, it's pretty much the same.

Thanks.

Also, when launching rockets, I'm careful to avoid shock waves or heat build up during assent to avoid wasting fuel. I'm in two minds what to do about Space Plane's. On one hand, avoiding shockwaves helps save fuel, but on the other I want to get as much ∆V as possible whilst using air breathing engines. There's the sweet spot between those two extremes?

[selfish_meme]

1 lift per 10 tons , don't quote me

[GoSlash27]

Thanks.

Also, when launching rockets, I'm careful to avoid shock waves or heat build up during assent to avoid wasting fuel. I'm in two minds what to do about Space Plane's. On one hand, avoiding shockwaves helps save fuel, but on the other I want to get as much ∆V as possible whilst using air breathing engines. There's the sweet spot between those two extremes?

Clipperride,

The basic idea is you get it to the "ludicrous speed altitude" over Mach 2 in a shallow climb and "damn the torpedoes". Don't worry about shock waves or heating. Just get all the speed you can before the air breathers give out. This process begins at 16 km altitude for jets and 18 km for RAPIERs. and ends somewhere over 20 km.

Best,

-Slashy

[Vegetal]

Clipperide, I made an SSTO rocket once, and experimented with different gravity turns. It wasn't scientific, but the best results (Most dV once in LKO) came from a very shallow climb, flames all over. You might want to rethink your ascent, in spaceplanes especially, the ideal ascent will always involve a lot of heat.

[A_name]

If I could butt in and ask my own question? Should you fly different assent profiles with different weight/class of Space Plane?

I'm taking the freedom to copy+paste part of Slashy's response to a similar question in another thread (which will probably be more useful too):

#2: Spaceplanes all follow the same basic profile regardless of size, but it must be adjusted for the thrust to drag, engine type, and t/w of the closed cycle engine.

First step is to get it supersonic at around 10km altitude. Jets have an easier time doing this than RAPIERS. If you have high thrust- to- drag, you may blow through Mach 1 in a steep climb. If you have a very low t/d, you may need to do it in level flight or even a dive. But in any case, it should happen around 10 km altitude.

Next, get to your acceleration altitude and build speed in a gentle climb. For jets, this is about 16 km. For RAPIERS, it's about 18km. Get the nose down and let it build speed in a shallow climb. velocity is cheap here, so get all you can before you're over 20 km.

Once you're over 20 km and the air breathing is no longer adding velocity, you switch to rockets. If you have powerful and inefficient rockets you want to climb steeply to get over 43km and out of the drag as rapidly as possible. If you have weak and efficient engines, it's important to limit your climb rate so that your apoapsis remains at least 45 seconds ahead. Otherwise, you will fall back ballistically before you've had enough time to establish orbit.

These are the important checkpoints. Some SSTO designs can burn right through them in a single climb and others stairstep very slowly, but they all hit these marks.

[ajburges]

I find that some of my RAPIER designs have insufficient lift while high, full, and subsonic. It winds up being more fuel efficient to break Mach 1 ASL to support a faster, more aggressive climb. Double the fuel consumption rate, quarter of the time.

Remember, you only need enough lift to land while near empty and to climb while full. The v² relationship will give you plenty of lift everywhere else. The less lift, the less drag.

[GoSlash27]

I find that some of my RAPIER designs have insufficient lift while high, full, and subsonic. It winds up being more fuel efficient to break Mach 1 ASL to support a faster, more aggressive climb. Double the fuel consumption rate, quarter of the time.

Remember, you only need enough lift to land while near empty and to climb while full. The v² relationship will give you plenty of lift everywhere else. The less lift, the less drag.

Up to a point. IME you still want enough lift so that you can exceed 20 km altitude at 5° AoA. If you don't have that, then you're actually producing *more* drag than you would with more wings.

Best,

-Slashy

[Clipperride]

Some great information thanks. Instead of keep hijacking this thread, I'll start my own (all input gratefully received!)

[TronX33]

I on;t know, maybe more wings? that seems like a lot of weight for just 2 Big-S delta Wings

[A_name]

I on;t know, maybe more wings? that seems like a lot of weight for just 2 Big-S delta Wings

I beg to differ. It's surprising how little wing you need with Mk2 parts which provide plenty of body lift. Especially if your TWR is near or greater than 1 at takeoff or shortly after when your jets start to pick up. I've made Mk2 spaceplanes that only need the standard Wing Streaks as main wings and some Winglets at the back as horizontal stabilizers. Of course, this one is particularly long, but still, I think it could even do with less wing. The standard Delta Wings would probably be enough.

My advice for people building spaceplanes: Use as less wing as possible and save in drag and weight.

What I do is to start out with the smallest wings that will fit reasonably on my design. Then I hit the runway and try to take off. Only if I'm unable to sustain flight will I add more wings. Try this method, you'll be surprised how little wing you actually need.

[Nothalogh]

you'll be surprised how little wing you actually need.

Yep, it's amazing what can actually fly