Has it been proved, mathematically, that an Eve SSTO is impossible?

[Red Iron Crown]

That's one of the few times when it's better to launch west.

[tychochallenge]

are you guys talking without mods? Cause i can definitely SSTO off of Eve with KSPI

[Skorpychan]

Yes, stock.

This needs to be a Challenge, IMO. Because saying anything is impossible is a challenge for the community here.

[Greenfire32]

Forgive my ignorance, but isn't an SSTO an SSTO as long as it's one singular craft?

Doesn't that mean that as long as you don't drop any parts (or stages) there's nothing against saying a craft with 2 liquid fuel engines and 4 ion engines isn't an SSTO?

So....couldn't you just use the 2 big engines to get into orbit and then use the ion engines to get to Eve? It feels like this isn't impossible, but perhaps rather improbable.

[Red Iron Crown]

Forgive my ignorance, but isn't an SSTO an SSTO as long as it's one singular craft?

Doesn't that mean that as long as you don't drop any parts (or stages) there's nothing against saying a craft with 2 liquid fuel engines and 4 ion engines isn't an SSTO?

So....couldn't you just use the 2 big engines to get into orbit and then use the ion engines to get to Eve? It feels like this isn't impossible, but perhaps rather improbable.

The challenge is to get off the surface of Eve to orbit in a single stage, whether with ions or other propulsion. Rockets only are a proven no-go.

[GoSlash27]

First test ran me down to 358 units of xenon (about a quarter tank)when the batteries died.

27 km and 820 M/sec. It was still accelerating well, so I'll restart the test at predawn.

This is definitely the best design so far.

[Greenfire32]

The challenge is to get off the surface of Eve to orbit in a single stage

Ah. I was going the "Kerbin to Eve" route. That would make an Eve-Takeoff-SSTO much more difficult then!

[GoSlash27]

Ah. I was going the "Kerbin to Eve" route. That would make an Eve-Takeoff-SSTO much more difficult then!

I think it's difficult enough as- is

The challenge is SSTO from Eve. Stock parts only. It must work in a stock setup (though you can use mods to design it). No infinigliding, no kraken drives, no GOAP drive. No taking advantage of any other loopholes (known or unknown)in the physics engine. However, liberal use of "zero physics" stock parts is permitted and encouraged.

Edited July 7, 2014 by GoSlash27

[cantab]

Forgive my ignorance, but isn't an SSTO an SSTO as long as it's one singular craft?

Doesn't that mean that as long as you don't drop any parts (or stages) there's nothing against saying a craft with 2 liquid fuel engines and 4 ion engines isn't an SSTO?

You're absolutely right here. However the drawback to such an approach is whenever one set of engines is firing, the other set is dead weight.

That's not usually a problem for jet/rocket SSTOs on Kerbin, because they have plenty of thrust to push the wings needed to lift the extra weight, and they can share the same fuel tanks. But for an ion/rocket SSTO, where the ion stage is so low on thrust, it is a major issue.

[cerberusti]

I was trying for lightest possible eve ascent not long ago and was using an ion powered first stage.

Ion engines will get you high into the atmosphere, but you will need a higher TWR engine to burn to get you suborbital (where you can try to put orbital velocity on with ion drives, or bring more fuel to do so.)

My craft was not single stage (and I have not finished it) but it may be possible to take enough engine and fuel to carry the ion portion along into orbit (especially since it does produce some thrust, so that partially compensates for its weight.) If I get the multistage version working I may give it a try, depending upon what that looks like when I finish it.

Since it requires a fairly high dv rocket be strapped to an ion glider, the part count may be prohibitive without staging.

[GoSlash27]

Okay, that test went a *lot* better. 31.9KM @ 1,276 M/Sec. It looked like it was accelerating nicely when the xenon ran out.

Eliminating drag seems to be the key here, but there's not a whole lot more I can do.

I'm going to try swapping out the small ailerons for the big ones. Same drag, but more lift and mass.

After that, I'm down to eliminating the elevator and finding another way to balance it, then lifting the whole mess on a single control surface, then finally ditching a xenon tank. If it ain't possible by then, then it ain't possible.

[Red Iron Crown]

Be careful calculating drag, it is the drag value times mass. So the large control surfaces have 4x the drag for only 40% more lift compared to the small ones.

[GoSlash27]

Next test

/ I hate ion gliders!

[GoSlash27]

Be careful calculating drag, it is the drag value times mass. So the large control surfaces have 4x the drag for only 40% more lift compared to the small ones.

Are you talkin' the drag coefficient or the parasitic drag? That may wreck my plans...

[Red Iron Crown]

The number given in the part spec is not total drag, it is the drag coefficient. The actual drag the part creates is drag coefficient times mass. Not sure if lift works the same way, that might change the part choice a bit.

Disclaimer: I'm not a plane guy at all, my understanding of this may be flawed.

[GoSlash27]

Duly noted. We're all wingin' it right now.

I *am* a plane guy, but not in KSP.

This test was extremely positive, and I think I can top it.

37,034 at 1,611. The big ailerons are an improvement.

I'm gonna run it again.

/ science!

[GoSlash27]

I limited myself to 20 m/sec on the initial climbout to match previous tests, but it wanted to climb. I'm gonna try 40 and see what happens.

[Red Iron Crown]

Are you doing this on Kerbin? Eve is a whole other can of worms.

[GoSlash27]

Yessir.

Kerbin makes a convenient testbed.

My plan is to 1) have an unmanned flight on Kerbin, 2) have a manned flight on Kerbin, 3) have an unmanned flight on Eve, then 4) have a manned flight on Eve. If I can't complete step 1, I'm going to call step 4 impossible.

*edit* I just noticed that the nav ball says "orbit". That's a first...

Edited July 8, 2014 by GoSlash27

[Red Iron Crown]

I'm not sure which is the bigger difference, the greater gravity on Eve, or the thicker atmosphere (more lift, more drag).

[GoSlash27]

I'm guessing the thicker atmosphere. This vehicle has plenty of excess DV on paper (10,545), but it's almost all wasted due to drag. It's also got way more lift than it needs, so it can climb out quicker in a denser atmosphere. The question is whether it has sufficient DV to do over 9000 m/s without wasting too much time climbing. I gotta pass this test first.

Last run was a bust. I got to 30,000 way early, but lost control of the plane. Running it again.

Edited July 8, 2014 by GoSlash27

[zarakon]

See this thread for ion gliders made for Kerbin orbit:

- http://forum.kerbalspaceprogram.com/threads/75704-Reach-for-orbit-with-an-ion-glider%21

Ion SSTO on Kerbin is just barely possible. Maybe. It becomes hard to tell whether infiniglide was a significant factor, even with locked control surfaces, when you have such light craft with a lot of lift.

I don't think you'd get anywhere close on Eve, there's just too much drag. Even on Kerbin, the most important thing is to climb as quickly as possible to get above the high-drag lower atmosphere. The new ion engines suck xenon a lot faster than the old ones did, so it hardly feels like you have infinite fuel.

[RocketPilot573]

My Eve Ion Glider could hardly fly... I don't see anyway it can be an SSTO, Xenon is just too heavy. Though, I wonder, is this possible with FAR?

[GoSlash27]

No dice. I ain't going' to space tonight.

Every time I get near orbital velocity, I lose my longitudinal stability. Perversely, my tail boom seems to be making it worse!

I'm reaching the same kinetic energy as earlier tests with a lot more xenon in the tank and good acceleration. Just a matter of fixing the stability issue, I think. I'll try again tomorrow.

[cerberusti]

Your tail control surface looks slightly off center in the picture. You may also want a vertical tail (or two lifting surfaces at a slight angle if you do not want to waste the lift, but still want some stabilizing force.)

My kerbin ion ssto used small control surfaces (disabled) and reached a 300k orbit with about 400 xenon left in the tank (starting with 1400.) The key is that at some point you will stop climbing normally, when this happens you need to pitch up enough to counteract gravity with the ion engine and still put on forward momentum (lift may still help a little bit.) There is a minimum TWR which makes this possible, at around .25 I needed to be at about 45 degrees initially, but you can slowly pitch back over to horizontal as your velocity removes the need to counteract gravity.

On eve you are probably not going to hit the required twr to keep gaining altitude or speed once aerodynamic flight is no longer possible, but you only need the high twr engine to gain enough speed to make the ion drive sufficient again. This may be possible with 48-7s and a small amount of fuel (lightest engine) or with nuclear engines and a large amount of fuel (best ISP at altitude.)

I may give it a try over the weekend. There will need to be a few test flights to determine how small the booster can be, and I need to get some work done this week.