Without a wing or a prayer

[Foxster]

Here's a nice little adventure for you: To the Mun surface and back on a wingless single-stage craft.

Here's what you need to do:

1. Build an SSTO with no lifting surfaces at all

2. Use it to get a Kerbal to the surface of the Mun and plant a flag

3. Return the Kerbal safely to the KSC

Easy, uh? You might be surprised!

The winner has the craft with the lowest mass.

A few rules:

1. Stock parts only.

2. No mods (including FAR) except MJ, KER, etc i.e. no mods that add new parts like engines, or alter part properties or game physics.

3. No wings or other lifting surfaces. Thrust-only all the way.

4. You must take every part all the way to the Mun and back. No dropping off bits along the way or separating into 2 or more craft. No refueling.

5. You can use whatever engines and/or jets you like as long as they are stock.

6. Air-hogging is fine.

7. You can make only a single launch from the KSC

8. You must land your craft intact at the grassy area around the KSC.

9. Usual evidence is required of a screenshot in the VAB, orbit around both bodies, on the Mun and back at the KSC and state the dV you had left when you first reached Kerbin obit.

11. If its not obvious from the pictures how the craft works then let me know and/or post a craft file.

12. It's a manned mission and your Kerbal(s) will need a capsule or lander can of some sort i.e. no Dr Stranglelove bomb-riding.

Of course I've had a go, 22.324T, 4613dV left at 70K orbit. Pictures here: http://s395.photobucket.com/user/FoxMouldy/slideshow/Mun%20challenge

I'm pretty sure this can be improved on with less engines and such.

Make it so!

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Leaderboard

1. Tsevion 7.019t http://forum.kerbalspaceprogram.com/threads/107834-Without-a-wing-or-a-prayer?p=1693182&viewfull=1#post1693182

2. numerobis 7.359t http://forum.kerbalspaceprogram.com/threads/107834-Without-a-wing-or-a-prayer?p=1692359&viewfull=1#post1692359

3.

Edited January 25, 2015 by Foxster

[ManlyPotatoe]

Have you considered the K-Prize?

[Foxster]

Have you considered the K-Prize?

Just had a look. Bit easy that though innit?

[KingMufasa]

Should have a challenge for lightest, and heaviest, wouldnt a super heavy SSTO be challenging also?

[Foxster]

Should have a challenge for lightest, and heaviest, wouldnt a super heavy SSTO be challenging also?

Sure. To be honest it would be nice if anyone just had a go at all. Feeling all neglected .

[KingMufasa]

i'll give it a shot tomorrow if i get a chance

[GigaG]

No mods except MJ? How about KER?

[Foxster]

No mods except MJ? How about KER?

I suppose common sense should prevail and the usual criteria for mods apply - if a mod doesn't alter the outcome of the flight by changing part properties or game physics then its fine. So, yes, KER is good.

[Rodyle]

1. Build an SSTO with no lifting surfaces at all

The mk 2 parts give lift nowadays. Do these count as well or do you make an exception for them?

[Foxster]

The mk 2 parts give lift nowadays. Do these count as well or do you make an exception for them?

I'm not much of an aircraft man. I suppose if they don't add much then they are OK.

[numerobis]

They would make a big difference. More important than lift, they halve the drag when you're edge-on -- that means you use a lot less jet fuel and you don't need as many intakes, which means less dry mass in orbit.

I have a 6.2t mission -- no Mk2 parts -- which should work (needs a couple tweaks): I've got 3 km/s on orbit. With Mk2 parts I should be able to cut a few hundred kg.

BTW, do you have capsule requirements, or is this going to be won by putting Jeb in a seat?

[Edit: I said 6.2t but I have no idea how I got that number. It was 7.5t, and I pulled off a parachute to get the mission flown below]

Edited January 24, 2015 by numerobis

[Foxster]

They would make a big difference. More important than lift, they halve the drag when you're edge-on -- that means you use a lot less jet fuel and you don't need as many intakes, which means less dry mass in orbit.

I have a 6.2t mission -- no Mk2 parts -- which should work (needs a couple tweaks): I've got 3 km/s on orbit. With Mk2 parts I should be able to cut a few hundred kg.

BTW, do you have capsule requirements, or is this going to be won by putting Jeb in a seat?

Sounds like we'd best stick to the original rules and so no lifting parts, including MK2 stuff.

You sure 3000dV in Kerbin orbit is going to be enough? I don't think I could manage the transfer to the Mun, the landing and return to the KSC on that, even with aerobraking. I was finding it fairly comfortable with 4500, less than that with aerobraking.

The seat thing - good question. I suppose we'd better say there must be a capsule of some sort, bit unrealistic otherwise. I'll add that rule.

[numerobis]

The naive trip to Mun is 900 for trans-lunar, 1200 to land, 600 to lift off to low lunar, 300 to return, total 3km/s. I typically keep a couple hundred m/s margin on top of that, unless I'm on a challenge.

You can save about a hundred m/s with tricks: Gravity assist and lithobreak, basically, and using jets to their full potential (bring Pe up to ~60 km if you can).

[Foxster]

The naive trip to Mun is 900 for trans-lunar, 1200 to land, 600 to lift off to low lunar, 300 to return, total 3km/s. I typically keep a couple hundred m/s margin on top of that, unless I'm on a challenge.

You can save about a hundred m/s with tricks: Gravity assist and lithobreak, basically, and using jets to their full potential (bring Pe up to ~60 km if you can).

Won't your last 300 just get you out of Munar orbit? You will surely want some more to get to the KSC.

If you can do it then paint me impressed

[Rodyle]

They would make a big difference. More important than lift, they halve the drag when you're edge-on -- that means you use a lot less jet fuel and you don't need as many intakes, which means less dry mass in orbit.

Sounds like we'd best stick to the original rules and so no lifting parts, including MK2 stuff.

Eh. Different parts have different drag profiles, might as well say that you can't use certain intakes because they have a lower drag/intake area, or not to use engines because their ISP is too high. I just really prefer the looks of the Mk 2 parts. It makes the SSTO look much sleeker.

[Foxster]

Eh. Different parts have different drag profiles, might as well say that you can't use certain intakes because they have a lower drag/intake area, or not to use engines because their ISP is too high. I just really prefer the looks of the Mk 2 parts. It makes the SSTO look much sleeker.

Umm, OK, but the challenge isn't about making a cute looking craft, its about making an efficient one.

[Rodyle]

Umm, OK, but the challenge isn't about making a cute looking craft, its about making an efficient one.

Yeah, I know. I was more arguing against the "lower drag bit". Jot this down to me not knowing when to hold my gob shut. ^^

[Kesa]

The naive trip to Mun is 900 for trans-lunar, 1200 to land, 600 to lift off to low lunar, 300 to return, total 3km/s. I typically keep a couple hundred m/s margin on top of that, unless I'm on a challenge.

You can save about a hundred m/s with tricks: Gravity assist and lithobreak, basically, and using jets to their full potential (bring Pe up to ~60 km if you can).

I can land on the Mun from trans Lunar for slighty more than 900 m/s (Set Periapsis slighty above ground to brake horizontally). However I can't do a Mun and back mission with 2700 m/s in LKO, but rather with 3000 m/s. 300 m/s to return seems a bit short since LMO is 550 m/s (at least <600 m/s), and Mun escape is about 850 m/s. But It might be as low as 350 m/s.

[numerobis]

7.359t at liftoff.

Single-Kerbal lander can. Drain the monopropellant.

1 turbojet, 6 ram intakes, a full Mk1 tank.

1 48-7s, a pancake.

Lots of cubes and some landing gear.

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The flight plan: use MechJeb's intake management. Fly vertical to 6km, pitch 60 degrees to 10km, pitch 45 degrees to 16km, and after that I was just trying to keep apoapsis from growing too fast -- max of 40km, since that's the top altitude I can go full throttle. About there, I reached orbital velocity, and I pitched down to make the periapsis grow as much as possible. I did two runs, to make sure I used up all my jet fuel (otherwise it's wasted mass for the rocket stage).

That got me to a 45 km x 252 km, and 20 m/s off rockets pulled periapsis out of the atmosphere (to 69,400m). I then split the trans-lunar injection into two burns, because that single 48-7S wasn't pushing much thrust. I made the TLI burn take me to an altitude of 10,000km where I got an encounter, and tweaked it so that the encounter would send my apoapsis to 11,400 km and periapsis up to about 3,000 km. I didn't land that time, I just took the gravity boost and waited for a second encounter. On the second encounter, I circularized to 10km. Unfortunately I somehow didn't get screenshots of all the steps, just the first and last. But that shows that I went from 6.624t to 4.939t, and I was burning a 48-7S, so that's 1009 m/s total from 45x252 at Kerbin to 10x10 at Mun.

I then scouted for a good high landing spot, and then went for it. It took a few tries before my landing spot was flat. Snapped some pictures. 4.939 at the 10x10km orbit, 4.133t on the surface, that's 612 m/s for the landing.

Liftoff was wasteful, 624 m/s from surface to 10km. I should have flown it by hand; Mechjeb went from a heading of 180, pitch nearly 90 on the surface to a heading of 90 and pitch 0 via a heading of 270, because that's SmartASS for you.

Return was 270 m/s. Unfortunately I hit Kerbin at 55 km, which meant it was *many* aerobraking passes before I finally could land. Landing was again tricky, this time due to silliness: on launch I'd pulled my thrust limiter back to 5%, so I could squeeze every last bit of benefit from the turbojet -- but that's a bad place to limit thrust when you're landing!

After landing I noticed I have the equivalent of an FL-T100 remaining. So you could break 7t with a minor change to my spacecraft. I'd also recommend making the landing gear have a wider base, and lowering the center of gravity, to ease landings.

Tricks I used:

0. throttle back aggressively and do two passes to get every possible benefit from the jets.

1. gravity assist to reduce deltaV to get to Mun.

2. land at the highest altitude you can to reduce landing and liftoff deltaV requirements.

3. landing gear and cubes to allow landing hard (I did 10 m/s, but with a wider base you could land harder).

4. no parachutes, just use a jet to land.

You could beat me by packing a bit less fuel. Otherwise, use an ion engine for the deep space burns.

[Foxster]

Very nice, numerobis. There's definitely some stuff there I don't know about yet. Like gravity boosts.

I'd had another go at this and got it down around 14t but your's blows that right out of the water. So congrats and you are the winner (so far).

[numerobis]

OK, how much did the gravity assist get me?

Normally from a 70x70 Kerbin orbit it costs 864 m/s to get to the Mun SoI, and 280 m/s to circularize there at 10 km altitude. Total: 1144 m/s.

It cost me 989 m/s from a 252x70 Kerbin orbit, using a gravity assist. Not directly comparable yet...

From a 70x70 Kerbin orbit, while doing your TLI burn, you pass through an apoapsis of 252km after burning 133 m/s. So we can say that from a 252x70 orbit, the usual Hohmann transfer to Mun would cost 1011 m/s.

The gravity assist saved me a whole 23 m/s !!!11eleventy!

I bet one could do better; my gravity assist flew by at high altitude, and I didn't really know what I was doing.

[Tsevion]

Alrighty, I went and tried to come up independently with the most efficient vehicle for this possible... what I came up with ended up being very similar to numerobis, although slightly better at only 7019kg. Main savings were using a smaller tank and less fuel for the jet stage, and only using 4 intakes instead of 6. Totally different layout and fuel-tank choice, but the same engines, and the same amount of fuel for the rocket engine. I did a somewhat useless second pass with the jets (mostly to burn off extra jet fuel), that could likely be eliminated, and less fuel could be brought in a possible smaller tank for the jet, grabbing a small amount of additional savings. Obviously an unmanned mission could be done cheaper and smaller, but already lugging the weight of the Jet engine around is likely the most expensive part.

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[numerobis]

Good idea using the FL-T200 for jet fuel; to use all my fuel I had to fly a little less efficiently, might as well just pack less fuel and use a slightly lighter tank for it.

This implies we can break 6.5t with this design, using my flight path to save an FL-T100, and your improved jet stage.

- - - Updated - - -

Calculating, with ions I think it should be possible to get below 4t. The configuration is:

Turbojet to get to orbit.

Ion to lift Pe out of atmosphere, go to Mun, and return.

48-7s to land on Mun and lift off.

The key is in the lunar landing and liftoff; you burn more fuel there than everywhere else combine. My calculated solution tells me that I can get there in 3.98t assuming perfectly-sized tanks. I can't build that in reality, best is about 4.01t.

But what my calculation forgets is that the ion engine can help out during the landing, and provide 6% or more of the thrust during that burn. Plus, I assumed fairly high losses on liftoff and nothing special for the trans-lunar burn. So I bet if I skimp on fuel for the other stages, I could fly this thing with about 3.95t or so.

[Foxster]

Considered using Vernor Engines for the non-ion thrust? They are massless and Mechjeb will use them as engines if there's no other thrust. Have to careful to turn them off when steering and they seem act a tad weird but I did put a tiny craft to orbit with them after the jet had died.

Downside is that the ISP is not great.

[numerobis]

Doesn't seem like the thruster mass is a big deal, it's the Isp. But that got me thinking: what if I use an LV-1. It has way less thrust, but combined with the ion it's about enough to land. That would shave off 70kg dry mass, but more importantly, it means the ion engine is a large part of the thrust on landing (a third of it), which means Isp on landing is much improved.

Running the numbers: The LV-1 plus ion engine has Isp 420s. When I use that for the landing and liftoff burns, I can reduce the overall mass a lot, to 3.55t. The two engines together get just enough thrust to land: the 6 kN gives TWR 1.13 at the start of landing, TWR 1.3 on landing (and on liftoff), so maybe I'm being aggressive when I claim to be able to use just 600 m/s on each of landing and takeoff.

But wait, the ion engine is 2 kN now? Then maybe we can just have three ion engines on board? Then my script is telling me we could have a launch mass of just 3.18302t (assuming perfectly-sized tanks). We'd have TWR 1.26 at the start of landing, but because the Isp is so wonderfully high, we'd only get up to 1.28 when we hit the ground. So I think we'd hit a bit hard; probably should pack either a bit more Xenon, or an RCS thruster and a smidge of monopropellant just for the final landing.

It'll be a while before I can fly this, but can anyone beat 3t?