Landing a Space Plane...

[rcp27]

... on minmus.

So I set myself the challenge to build a space plane that I can take off and fly to orbit, where I refuel in LKO, then fly it to Minmus and attempt a landing.

My approach goes as follows: circularise in a low minmus orbit, about 15,000m AP. Line up for one of the flats, (I went for the greater flats). start with the plane pointing retrograde in orbit, upside-down (landing gear towards the sky). Burn retro so that my trajectory meets the flats just after the near end. Pitch down so that the nose is pointing 45 degrees up/backwards, still upside down. Deploy landing gear. at about 150m altitude, burn until my vertical velocity is between -5 and -10 m/s. At this point I am doing about 120 m/s. Pitch "down" (nose goes over the top) so that I am in a slight nose-up landing attitude, use RCS to try to keep vertical velocity below 10 m/s, and hold down RCS in retro direction to try to kill as much speed as possible. Touchdown takes place at about 105 m/s. So far, I've attempted it 4 times, but I haven't managed to keep control after touchdown, each time I yaw a bit, a wing tip goes down, makes contact and provides a spectacular fireworks display, but I'm sure it can be done. Anyone else managed this? Is there a better approach? (I nearly wrote "is this a sensible approach", but I don't think anything about this particular endeavour is sensible).

[lordlundar]

Well the thing you have to remember is that you're trying to do a high friction based landing on a low friction based environment. While on Kerbin or any atmosphere based celestial body you're going to have air resistance plus ground resistance to slow yourself down, on a place like minmus you can only rely on the ground friction. You're going to have to rely on your RCS to slow your horizontal velocity (which is what's causing your plane's freakouts upon contact) to a much more manageable level. I would say anything over 65 m/s is too fast for a safe landing. Even lower if you can manage it.

[Scarecrow88]

For space plane to Mun or Minmus, I tend to build a VTOL engine in to the design and land vertically, with 0 horizontal speed.

[RocketPilot573]

I usually just burn retro like a normal lander, then pitch down at the last moment to land on the gears.

[rcp27]

Well, a few more attempts and I got it. Landing speed was about 80 m/s, and I used a silly amount of RCS in retro to stop after something like a 5km landing roll, but I'm down. Now to figure out how to get up again.

[Alshain]

I usually just burn retro like a normal lander, then pitch down at the last moment to land on the gears.

This. You really have 3 options, 1. Creative landing like one of the methods above, 2. VTOL, or 3. adding landing legs around the tail so it can land with the main engines (called a tailsitter, not to be confused with tail dragger)

[rcp27]

I started from the premise that those big flats on Minmus would make a great runway. I wanted to use one of the regular space plane designs that I normally use for things like crew transfer to my LKO space station, so I didn't want to add extras like landing legs or VTOL engines, hence the need for a creative approach. Anyway, the visit has been accomplished, and the plane is now on its way back to Kerbin, with a load of science on board.

[Pecan]

I started from the premise that those big flats on Minmus would make a great runway. I wanted to use one of the regular space plane designs that I normally use for things like crew transfer to my LKO space station, so I didn't want to add extras like landing legs or VTOL engines, hence the need for a creative approach. Anyway, the visit has been accomplished, and the plane is now on its way back to Kerbin, with a load of science on board.

No, you don't have to add legs or VTOL engines - you already have a rocket on the thing so use as you would to land any rocket but once you're almost down drop the nose to settle on the landing-gear.

[cantab]

It's possible to do a rolling landing on Minmus but, as you found, tricky. RocketPilot's approach is probably better - do a fairly conventional landing on the main engines then let the plane flop forward. To take off again you can either roll - a rolling takeoff is much easier than a rolling landing - or if you have enough RCS in the nose you can point skywards first then blast off.

[Alshain]

Yeah, Minmus gravity is so low that if you slow your plane down in a conventional landing to 1m/s while very near the surface and then pitch forward, you won't gain enough speed back to damage anything as you set down on the landing gear.

It's not as easy to do that on the Mun, still possible but you have to be able to turn the craft much quicker because you have to slow down much later.

[rynak]

I haven't attempted this yet, but will soon. What confuses me about the suggestions is, why full blown VTOL is proposed, when apparently the problem just is horizontal speed? Wouldn't small surface-mounted retro-thrusters do the trick, of compensating for the lack of air resistance?

[Pecan]

I haven't attempted this yet, but will soon. What confuses me about the suggestions is, why full blown VTOL is proposed, when apparently the problem just is horizontal speed? Wouldn't small surface-mounted retro-thrusters do the trick, of compensating for the lack of air resistance?

No-one is suggesting a "full blown VTOL" except as an option that works. What we are suggesting is you use the rocket you already have (to get through space in the first place) just like any other rocket and do (almost) all the landing with it. There are three problems with a retro system such as you propose, i) it's extra mass you don't otherwise need, ii) even on a low-gravity body like Minmus there's a LOT of horizontal speed to lose to get down from orbit, iii) while your retros are slowing you down and your main rocket is facing backwards - you have nothing to kill your vertical descent!

[regex]

LAND ON THE BELL

Because your wings don't work in space.

[rynak]

No-one is suggesting a "full blown VTOL" except as an option that works. What we are suggesting is you use the rocket you already have (to get through space in the first place) just like any other rocket and do (almost) all the landing with it. There are three problems with a retro system such as you propose, i) it's extra mass you don't otherwise need, ii) even on a low-gravity body like Minmus there's a LOT of horizontal speed to lose to get down from orbit, iii) while your retros are slowing you down and your main rocket is facing backwards - you have nothing to kill your vertical descent!

Well, that is a bit taken out of context. The OP and the replies were about the aspect of *landing*, not about lowing one's orbit. He was talking about even in the landing phase still having too much speed, and someone else remarked the lack of air friction, to slow oneself down during landing. That is what the topic was, and what i was replying to, which i suppose is in the range of 200-400ms.

Sure, two micro thrusters would add a bit of mass, but so would any other solution that requires parts. With say 2 micro-thrusters, we're talking less than 0.5t, for a spaceplane which overally probably weights at least 8.0t. It's significant but for a kerbin satellite affordable i think.

The bigger downside i imagine to be that retro-thrusters still don't allow oneself to control vertical speed during landing - which would be a useful benefit of a VTOL-like design (even if just mounting the retros on IR-rotatrons).

[regex]

The bigger downside i imagine to be that retro-thrusters still don't allow oneself to control vertical speed during landing - which would be a useful benefit of a VTOL-like design (even if just mounting the retros on IR-rotatrons).

Uh, wait, you can't rotate your craft while using retro thrusters? I'm confused...

I feel like you're still thinking about the craft flying in an atmosphere when you should be thinking about it flying like any other spacecraft when it's out of atmosphere. The wings on a spaceplane mean precisely nothing (other than dead weight) outside of an atmosphere. Maybe put some landing legs on the back of the craft or try rotating before landing as others have mentioned. Unless you're going for straight cool factor but even then landing outside an atmosphere is a different process than landing within.

[rynak]

If i recall correctly, one is supposed to land with the landing gear facing downwards - it's one of those "this end towards space"-like things. Which means that while close to the ground, its a bad idea to rotate the craft too much.

What wings have to do with any of this, i'm not sure. Your quote says your replying to me, but i think you must be replying to some imaginary person, because you are the first person in this thread to start talking about wings. Or is this a jab to an entirely unrelated and off-topic thread, where i proposed to put winglets on the ends of the first stage of a ROCKET, and you felt insulted by this?

Please stick to the topic, will you?

[Torquemadus]

What we need to do is figure out a way to land vertically and then deploy wheels for horizontal surface travel...

[regex]

If i recall correctly, one is supposed to land with the landing gear facing downwards - it's one of those "this end towards space"-like things. Which means that while close to the ground, its a bad idea to rotate the craft too much.

If you land on the bell you don't have to rotate the craft (you could add landing legs too). Using retro-thrusters does not preclude rotating the craft. Having to rotate the craft near landing is not a huge deal on a small body like Minmus (on Tylo or Moho, yes, you probably want to look into an alternative, but the topic is about landing on Minmus).

What wings have to do with any of this, i'm not sure.

The fact that you are completely ignoring the "space" part of spaceplane. It's just like any other spacecraft, the fact that it has wings or atmospheric landing gear does not change that fact. If you think of maneuvering it like any other spacecraft the situation in the OP becomes much less of an issue, as others have pointed out in this thread.

Please stick to the topic, will you?

Please don't derail this thread with your overblown outrage stemming from a lack of topic comprehension. Edited February 1, 2015 by regex

[AlexMBrennan]

What we need to do is figure out a way to land vertically and then deploy wheels for horizontal surface travel...

Since Minmus lacks the atmosphere needed to convert forward thrust to upward lift via the use of wings, I am not even sure what you hope to gain by doing this.

even on a low-gravity body like Minmus there's a LOT of horizontal speed to lose to get down from orbit

Not really - you are thinking too much of Earth-like planes. The reason typical airliners land at relatively high speed is that the aircraft will stall and wings will lose lift if you go below a certain speed (which is also why they tend to have thrust reversal to allow them to "brake" with the big engines, or parachutes, etc).

In space, that's not really a concern - you can reduce your horizontal velocity as much as you like before touching down (this is how "traditional" rockets land, after all). And unlike flying a plane on Earth, high horizontal speed does not help you because you cannot convert the speed to lift by pulling the nose up.

Edited February 1, 2015 by AlexMBrennan

[Torquemadus]

Since Minmus lacks the atmosphere needed to convert forward thrust to upward lift via the use of wings, I am not even sure what you hope to gain by doing this.

Space planes can be landed tail-first on low gravity bodies. I fit landing legs around the tail for this purpose. Once on the surface, I can use frictionless wheels and tiny amounts of propellant to travel long distances over the surface. This is handy if I want to spam surface exploration contracts.

When I want to return to Kerbin, I use a hill as a ramp to "ski jump" off the surface. I then manoeuvre the spacecraft conventionally. The wings and landing gear are used to recover to the KSC runway.

[rcp27]

As the originator of the thread, I would like to add one other aspect of this particular challenge I set myself (and have now managed to pull off). There are lots of relatively easy solutions to the problem "land something on Minmus". That's easy, I've done it tons of times with built-for-the-job craft. I also agree that landing tail-first with a space plane is probably the easiest way to solve the problem of getting a space-plane onto the surface of Minmus. These are all well and good, but the challenge I set myself was landing a spaceplane on Minmus, using the flats as a nice open flat runway, in a way that resembles a plane landing on a runway. I wanted to do this not because it's the best way to get a space plane onto the surface of Minmus, but basically because I thought it would be cool. In achieving it, I can confirm it is definitely cool, and Jeb approves. My advice to others trying to achieve the same thing is to keep landing speed to below about 80 m/s, and vertical speed at touchdown below about 10 m/s, and to make absolutely 100% certain that you are absolutely pointed in the direction of travel when you touchdown, because any slight yaw angle will cause your destruction. Also, bring lots of monopropellant or a retro engine to slow down with, because brakes don't work well on Minmus. When taking off again, it is possible to lift off the surface simply by burning your engines on a straight horizontal takeoff roll, but unless you pitch up, chances are from the flats, you will not clear the higher terrain beyond. I thought about driving along the surface to find a nice slope to use as a ramp, but in the end just used RCS to lift the nose and get a trajectory clear of terrain.

[AlexMBrennan]

Actually, I don't think rotation ought to be a problem at all - if I have my ksp constants right, dropping from 50m or less should have your plane land with 7m/s so killing vertical velocity at 50m should give you plenty of time to make sure the wheels are pointing down when you hit the ground at survivable speed.

[Pecan]

Actually, I don't think rotation ought to be a problem at all - if I have my ksp constants right, dropping from 50m or less should have your plane land with 7m/s so killing vertical velocity at 50m should give you plenty of time to make sure the wheels are pointing down when you hit the ground at survivable speed.

(And your earlier post).

Good luck with establishing that 50m orbit in the first place.

Above the flats, that is.

Starting from a 15km orbit.

That's WHY there's a lot of horizontal speed to lose before landing ^^.

@rcp27 - glad you've had fun :-)