Minmus horizontal landing

[esmenard]

My goal is quite simple : land horizontally on Minmus. But fulfilling it is an other level of difficulty. I feel it's possible, but it just seems so hard. Anyway, here is my first try that didn't bounce off right on touchdown : 

Has anyone ever successfully done this ? I would like to know. I have seen someone on the forums, but it was at 60 m/s, not 160 m/s (still very impressing though).

[Gargamel]

Moved to GamePlay Questions. 

 

[RoninFrog]

My suggestion: Slow your horizontal speed waaay down while still descending.  You are going way faster than the landing gear is meant to take (60 m/s is about right).  Slowing down will keep you from flipping, and also give you more time before you mash into the cliff at the end of the lake.

[Cavscout74]

For horizontal landing on any vacuum body, you normally burn off most of your speed until close to the surface & flip horizontal for the touchdown.  Even 60 m/s seems higher than it needs to be.    With Minmus' low gravity, wheel brakes aren't going to do much. 

Now if you are just trying to challenge yourself to see how fast you can land, I'd advise you bring a lot of Monoprop, because your RCS is probably going to be more effective for braking than your actual brakes are.

[Loskene]

Another issue to raise is your craft design doesn't suit your landing profile. You were trying to land with zero pitch but your landing gear is uneven, making your nose gear touch down first and causing SAS to try and level the craft while you're trying to force the rear gear down, combined with the precarious balance on one wheel made the whole thing fundamentally unstable. Plus your landing site is unsuitable for the speed you were going and the braking power the craft has, you'll need retrorockets rather than RCS or wheelbrakes to remove most of the horizontal velocity. Since your plane already has rocket engines, try landing backwards, it might actually be more stable touching down the rear wheels first, and you weren't using those wings to begin with so there's nothing necessitating forward flight. Burn the engines to bleed off horizontal speed, pitch the nose up slightly to stay above the ground, then level off for landing once you're slow enough. If you've eliminated all these issues and still end up flipping or crashing then try practising it from an equatorial orbit (over the Great Flats) rather than polar as well, just in case Minmus' rotation is affecting your touchdown at high speeds. Good luck.

Edited August 16, 2019 by Loskene

[bewing]

@AeroGav likes to do horizontal landings on Minmus. I know he's linked to videos of it before. You get down very close to the surface of the flats, pointed retrograde. Burn the main engines until your velocity is around 30 m/s. Then turn back around and use vernors to soften your impact.

[esmenard]

My challenge was to land on Minmus with only the deorbit burn and the brakes. If I brake using the engines it's a bit pointless for my challenge. But as said @Loskene, I should maybe try having the forward gear higher than the rear gear, so the rear gear touches first. I chose this landing site because at first sight it was the longest flat area.

[Zhetaan]

6 hours ago, esmenard said:

My challenge was to land on Minmus with only the deorbit burn and the brakes. If I brake using the engines it's a bit pointless for my challenge.

You've got my respect for the level of difficulty you've assumed for this.

It may also be advantageous to change some or all of the landing gear to a heavy-duty version; it may be ugly, but it's much more ugly to have your vessel in pieces strewn about Minmus's surface.

Furthermore, I think that you may have some success with a reverse-tricycle design, also known as a tail-dragging plane, where you have the dual landing gear in the front and a single gear in the back.  When you touched down, you had a slight sideslip that, on braking, caused you to flip over to the oblique right.  Overcorrection (which is stupendously easy at 160 m/s) caused you to flip out of control.  This is a problem with any tricycle; deceleration on braking tends to shift the weight forward, and if that weight goes even slightly to the side, then it can cause your vehicle to flip over the leg of the triangle between your contact points--i.e., the wheels on the ground--because those front legs tend to come very close to the centre of mass.  Remember that Minmus's surface acceleration is a little under half of a metre per second squared; most of the force on your craft will be from the deceleration in the forward direction, not the gravity pulling you down, and that makes it easier to flip.  You can change that by reducing your horizontal velocity, but I think your choice of orbit has reduced that to the lowest point possible without a retroburn.  The only other possibility I can think of involves landing in the highlands, not the flats, where you're closer to your apoapsis and thus slower, but of course that appears to save only ten metres per second and further requires you to land on a rougher surface.

With a reverse-tricycle, the centre of mass is much farther away from the front leg of what I will call the 'contact triangle' with the wheels at the vertices, and a slight sideslip won't cause you to flip to the right or to the left, because it still has to flip over the front.

It may, however, still flip over the front.  Any vessel on the ground can spin out of control.  But I hope this helps you.

[Claw]

Additionally, make sure braking is off for the nose gear. From the video, it looks like the nose gear touches down first (meaning there's going to be some bounce) and the brakes come on before the main gear are fully seated. It may be coincidental, but as soon as you turn on the brakes, the nose compresses and the tail slides out (with no main gear on the ground).

You may also want to consider turning off the front upward facing RCS since it's further driving the nose gear into the ground. SAS is probably helpful for keeping the nose straight, but it's also going to keep firing the RCS so it might help if you settle the tail manually or attempt keep the nose off the ground. Once the mains are seated, start tapping the brakes before applying them full. Alternatively, you can tweak down their effectiveness to keep them from biting too hard when you turn them on.

Edited August 17, 2019 by Claw