Tiny Eve ascent vehicle, 6.23 tons, KSPX + MechJeb

[tavert]

The inline Rockomax 48-7S in KSPX is quite powerful. Little bit heavier than the radial 24-77, but significantly better specific impulse more than makes up for it. From the 0.21 preview streams it looks like quite a few of the KSPX parts are coming to stock, apparently including the half-ton FL-T100 fuel tank as well. If these parts have the same stats in stock 0.21 as they do in KSPX right now, then it'll open up a whole new set of tiny design possibilities. Like so:

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This relies on glitchy ladder physics, rather than a seat, since this way is lighter and the Kerbal's mass effectively gets ignored by the physics engine. There's only enough delta-V to make it to orbit from the highest mountains on Eve, around 6400 meters altitude.

Edited July 23, 2013 by tavert

[magnemoe]

That is verry impressive. Far lighter than mine lighest who uses balloons

[tavert]

Thanks! So other than the FL-T100 tank having a different texture in stock 0.21 than it did in KSPX, everything looks the same so this should work nicely as a stock design now. The aircraft landing gear are still massless, and ladder forces are still reactionless. Now to just add an ion transfer stage and a jet lifter stage, see if I can do a stock Eve round trip in 10ish tons before someone else gets the same idea...

[magnemoe]

My first advice would be to replace the aircraft landing gear with an standard one you drop on takeoff.

That way it would look less than an exploit, the ladder is pretty much ok as other has used it before the seats came.

Point is to take credit for making the lightest stock Eve accent craft.

[tavert]

I could do that, but that adds decoupler and landing leg mass so is no longer absolutely lightest. I see no reason to do so until the aircraft gear actually have mass. Other people have built small (around 20ish tons IIRC) Eve ascent vehicles using ladders pre-0.20, but I believe all of those had the ladders mounted parallel to the thrust axis instead of perpendicular. When the Kerbals are standing on part of the craft, the collision does actually exert a reaction force so the Kerbal's mass counts as payload and takes more fuel. The perpendicular mounting ends up using less fuel, but only by exploiting buggy physics. So if I'm exploiting one glitch, no reason not to exploit massless parts too while I'm at it. It's nowhere near as bad as infiniglide or the FTL egg though, which can get off Eve without any fuel at all...

[metaphor]

Looks interesting. I was going to build a stock one with a proper seat instead of the ladder and no massless landing gear. Around 25 tons to go from Kerbin to Eve and back, but with the new update coming I didn't bother trying it out. With the new half-size fuel tank and small inline engine it should look kinda like yours though.

[tavert]

Yes, I remember that from Reddit comments. 2 jets isn't enough to lift 25 tons vertically, the TWR from MechJeb assumes the jets are at full thrust which doesn't happen until 1000 m/s. And that ascent vehicle is somewhere in the range of 1500-2000 m/s short of what you'll need from 6400-6500 meters landing site, even with the entire jetpack I don't think it would make it.

Eve's terrain has been redone, the mountain I used to use isn't as tall any more. I think I found a better one, but need to go check it out, the new mountains may be too steep to land at.

[tavert]

So the highest mountain on Eve that I've found in 0.21 is 7400 meters altitude. It's pretty steep right at the peak, but with either MechJeb targeting precision or luck/practice getting you pretty close, you can land above 7000 meters without too much trouble. That additional altitude allowed me to get rid of the extra set of FL-T100 tanks on my first stage and get to within 40 m/s of orbit with a 4.9-ton ascent vehicle, well within jetpack range or maybe even just by fine-tuning the ascent parameters. I reconfigured the landing setup in a clever way (not using aircraft gear for once), that also lets me decouple the parachutes so they don't add dead weight to the first ascent stage.

[Sandermatt]

Do you know the coordinates of this 7400 meters spot?

[tavert]

Do you know the coordinates of this 7400 meters spot?

It's really close to 25 south, 158.5 west. And it turns out it's 7400 meters if you have your terrain settings on low (specifically maxSubdivision in settings.cfg), otherwise it's more like 7540 meters.

[magnemoe]

managed to get an stock version of this down to 20.5 ton, it includes an 4.5 ton decent tank who is overkill but 2x90 liter was to lite with the old landing location.

This was able to get back to orbit from 6500 meter attitude.

Landing location and resulting orbit.

The 6500 meter location is close to equator and its not an peak but an pretty flat area, mechjeb used 180 liter deorbiting but this could be done far cheaper using mechjeb aerobrake nodes to get close.

Lander

It uses 8 45 liter tanks around an center, two radial ants and two oscar tanks for upper stage, has two 180 liter tanks with two 20Kn engines on each as an first stage, they are placed on top of the aspargus and uses seperatrons to kick them away then empty, can land on parashutes only but the 6.5 m/s landing kills all the landing legs, but leaves all engines intact.

I uses an extra 40 kg probe core to simulate the kerbin in seat weight.

[tavert]

managed to get an stock version of this down to 20.5 ton

The only thing non-stock about this in 0.21 is MechJeb. The Eve ascent part only needs to be 5 tons if you use the ladder trick. By using a seat, you're going up in mass, not down. Here's a craft that should be able to do the entire Eve round trip, if you're patient enough for 5 hours of ion burns (which I'm not).

[magnemoe]

The only thing non-stock about this in 0.21 is MechJeb. The Eve ascent part only needs to be 5 tons if you use the ladder trick. By using a seat, you're going up in mass, not down. Here's a craft that should be able to do the entire Eve round trip, if you're patient enough for 5 hours of ion burns (which I'm not).

Nice rover design, hope you have an ladder to get up to the cockpit

I found out about the benefit of using an ladder, It let me drop the 2*180 liter tanks and I uses an 2*90 liter for deorbit, still a bit heavier than yours but I like the extra margin.

[Sirine]

Just drop by and say "Hi'.

[magnemoe]

I having serious problems with getting ladder launches to work anymore.

I worked well in my grand tour 2 trip for both the Eve and Tylo landings, however then trying to repeat the trip it fails, has tested multiple times. The problem is that kerbal is unbalancing the lander then the engine is started up again to circulate, this even happen with the same upper stage as used for the previous Eve landing, has changed from 8 to 6 side tanks and engines but they has long burned out at this time.

Both missions was done in 0.21.

Worse an test launch to Kerbin orbit did not cause any problems during circulation. I dropped tanks to get the same situation as during Eve launch. With 3 or more engines running it look like the gimbal was able to handle the unbalance, with one engine I get some drift mechjeb is unable to correct.

At reignite the lander is not controllable with more than 10% trust. Trying to move the kerbal, even droping ladder and grabbing it again does not help.

Anybody else had weird issues like this?

This design look like work.

http://imgur.com/Sp6Hghj

One strut out then one rotated 90 degree upward, a stack on them then two out to stop kerbal from gliding off.

This leaves the kerbal standing on the middle of the probe core.

Edited August 26, 2013 by magnemoe

[tavert]

If the ladder is parallel to the thrust axis, then the Kerbal will shift around and eventually collide with some piece of the ship. Those collisions do seem to impart a reaction force and can lead to major imbalances. With the perpendicular ladders I've had to keep an eye on the Kerbal and adjust the positioning on the ladder occasionally to keep it centered, but things only get out of control if I let a Kerbal-ship collision happen and persist.

[magnemoe]

Yes, I had this kerbal hits edge of ladder many times during the testing and execution of grand tour2, they gave the ship an sideway kick and then stabilized.

Tylo lander is basically the two upper stages of an Eve lander with two drop tanks for decent, during decent it had multiple burns without problem.

It might help that you use an shorter ladder, mine might be a bit long. However it look like the vertical ladder works nice, the top look like an nice place to put an seat on top of an decoupler.

[magnemoe]

Tested the new design, worked perfectly on Kerbin however its unstable in Eve atmosphere. the off center struts make an off center drag.

Ship rotated and stabilized after dropping the first and second set of boosters but the kerbal fell off.

Has to test the 9 engine design again to see if I was just lucky.

Adding an seat on top worked fine, made decent faster and would not affect accent. Has the benefit of automatically deploying kerbal on ground after landing.