Wheels for Mun landings?

[AaronLS]

It seems like using landing wheels for mun/minmus landings would allow you to save fuel by not having to kill all of your horizontal velocity, and let the brakes do that, plus they can handle some pretty hard landings. I've never seen discussion of mun/minmus landings mention their use though. I imagine you'd have some bouncing, but turning brakes on before touch down will help kill velocity as you touch n go.

Thoughts?

Edited July 7, 2015 by AaronLS

[windows_x_seven]

I don't think that would be particularly useful, since you can't land at 1km/s. IIRC the landing gear's max speed is about 80m/s, so that's vertical velocity and lateral velocity. You'd save not much of delta-v. IMO, it's not hard to tweak the ship to get the delta-v that would be saved without impacting the performance of the ship in stock.

[AaronLS]

Yeh, like I said "not having to kill all", I wouldn't expect to land at 1 km/s, but that makes me realize that it would be challenging to keep your angle of attack very shallow as you burned to slow down. You can burn radially to flatten out the trajectory but that would be a waste of fuel. I know the wheels can handle alot more than the stated max speed, but it's clear to me now why they aren't used.

Thanks.

[cantab]

It's unlikely to save *much* fuel, the Mun's surface is pretty bumpy and you certainly couldn't hit the ground at orbital speed.

On Minmus on the other hand the prospects are better. A rolling takeoff from the flats is definitely possible. A rolling landing relying on brakes would probably have the issue that the wheels won't offer much grip in the low gravity.

[ajburges]

A simpler reason to use wheels on landers is to remove the precision needed when you kill horizontal velocity. The momentum of 10 m/s horizontal is enough to tip your ship on impact. Wheels would just roll with it and reduce the torque applied to your ship.

[Edax]

It seems like using landing wheels for mun/minmus landings would allow you to save fuel by not having to kill all of your horizontal velocity, and let the brakes do that, plus they can handle some pretty hard landings. I've never seen discussion of mun/minmus landings mention their use though. I imagine you'd have some bouncing, but turning brakes on before touch down will help kill velocity as you touch n go.

Thoughts?

I've landed on the mun and minmus with spaceplanes. The most effective way is to kill ALL velocity, so you touch down vertically on the wheels very gently. In low gravity environments, if you try to land horizontally, the wheels will just bump off the ground; you'll get no braking action, and you'll be tossed from the ground at an odd angle that can be difficult to correct. You can compensate by having the thrusters try and keep you on the ground, but it's just safer to burn the extra 70 Delta V for a gentle vertical landing. The advantage of wheels (even just landing gear) is that the spacecraft if moblie on the ground with just a few thruster inputs, and you can easily visit several biomes with all of your science gear with you.

[Vanamonde]

Minmus has some nice flat areas, but trying this on Mun would be dang near suicidal because the terrain is so rough. I'm sure it could be done, but would be much more trouble than it's worth. Unless you just like the challenge.

[Violent Jeb]

I've landed variants on both minmus and Mun with substantial success.

You're right, the impact resistance will allow you to abuse your landing noticeably more than with landing legs. Before they break, they will "pop" which gives an engineer the opportunity to salvage the part.

What I have done is place LY-10's on the "front" and "back" of the craft. This works even if you radially attach them to an upright rocket. Now, you attach Rovemax M1 to either "side, and you have a 4 point wheel system, which is quite balanced. Start with the brakes on.

I have found that you will need MINIMUM 10t craft in order to get sufficient traction on the mun (even more for minmus). The trick is to point your LY-10s so that they face down enough to "push" against the ground. When your landing "legs" also make your craft mobile, the benefits are huge. Crafts can re-position or even make small journeys to nearby biomes. It is definitely worth experimenting with. I had a few designs where the entire craft lands, and a small return vessel sits on top of the wheel-legged rover as well (so you can establish a base and exploration mission at the same time).

I can generally find a smooth mun landing by eyeballing the craters carefully when i create my landing node, to ensure I land on a space between craters; never in ​them.

[Michaelo90]

I tried landing a spaceplane on the Minmus flats once. A bit bumpy but it worked with rcs. Braking was... not really possible

[Khazar]

I use landing gears in almost every craft I build. During landing I have my craft stop just over surface in vertical position and then flip to the side, using vernors (with help of ant engines pointed downwards in case of most heavy crafts). This way I don't have to bother landing exactly where I aimed, I just turn in desired direction and roll towards. I use this both at Mun and Minmus, to brake more efficient I pull up and down or turn sideways if needed. Also its even easier to land at hillsides

[Sharpy]

Yeah, the ability to safely land with good several m/s of horizontal direction is a boon. Ability to drive up to your target instead of performing flight acrobatics is another. My Minmus fuel trucks utilize this.

OTOH the engineer is a necessity. You don't need a high impact speed to bust the tyres if you're dropping a full large Kerbodyne tank from a meter up at Minmus. The wheels safely survive the impact, then simply get squashed under the rapidly decelerating weight.

[Khazar]

I usually land almost dry, can't resist temptation of bringing some more stuff instead of securing some extra fuel reserve for safe landing.

[pincushionman]

I love landing on wheels. I'm a terrible landing pilot, so being able to align along my residual several m/s of horizontal velocity rather than zeroing it all out allows me to concentrate on the vertical speed problem which I am also bad at.

[Skorpychan]

Is it wrong that I'm considering this only so I can ramp off mountains/crater walls to get back into orbit?

[Sharpy]

Nope, not at all. Instead of trying to keep the lander upright, accept and embrace tipping.

[RSwordsman]

Is it wrong that I'm considering this only so I can ramp off mountains/crater walls to get back into orbit?

This is the only thing I thought. Screw landing benefits; taking off is where it's at.

[ajburges]

Is it wrong that I'm considering this only so I can ramp off mountains/crater walls to get back into orbit?

As long as you give it an orange paint job, it's all good.

Definitely an easier gravity turn, but landing unaligned with thrust adds complexity to landing.

[AaronLS]

Following up that I have done this on Minmus with mixed results. The trick is to use reaction wheels to pitch back to dig the rear wheels against the ground and turn their torque up. If you plan descent carefully you can flip up as you near the surface and only kill vertical velocity to make for a softer bounce, and leave the horizontal velocity up to the wheels.

1) Make sure gears are oriented so that after the first bounce you can use ASWD to intuitively correct roll/yaw/pitch.

2) Use navball to make sure you are lined perfectly straight up so that all four wheels touch the ground at the same time to minimize any crazy spinning on bounce.

3) Torque on rear wheels should be higher than front, but not too high as even the rear wheels can cause the craft to flip.

4) After the first bounce, your second bounce should be smoother because you have less vertical velocity remaining. Use your reaction wheels to pitch back to press your rear wheels against the surface.

It's still pretty chaotic with occasional crazy bouncing that results in alot of spinning that you have to stabilize and level out before the next bounce.

Saved me ~40dv. Probably not worth it for just a fuel savings standpoint, and highly risky. At lower speeds the bounces aren't as chaotic and just makes for an easier landing.