How to land a spaceplane on a planet without atmosphere?

[notsobrightguy]

Noob question.

How to do it exactly? Especially when I don't have anu RCS. Do i need to burn retrograde until specific height then turn prograde? Or is there another better method?

Thank you

[diomedea]

Sure you know you're not going to get any lift from wings with your Spaceplane, because no atmo. So, the landing procedure is going to be a lot similar to what a lander would do, hope the spaceplane can make it. In short, you burn retrograde all the time, first to lower your periapsis, then to kill most of your speed, in the end to achieve the suicide burn that will stop the vessel exactly at soil altitude. Only problem, if your main engine is at the back of the vessel (normal with spaceplanes), your vessel has to be able to stand on its rear. If only you had RCS, you may control attitude in final, to have the spaceplane land horizontal.

Your seems one of those very kerbal cases, when a player discovers at the worst moment the vessel they built isn't fit for the mission. Good luck....

[ForScience6686]

Exactly like a lander descent,  except at the last moment,  tilt down to land on the wheels.  you don't have too completely cancel out horizontal speed since you can just roll to a stop.

[Gianni1122]

Like @diomedea said, it is similar to putting a lander on the mun. Kill your forward movement by burning , then use vertical thrust to maintain a controlled descent. 

In other words, a spaceplane with additional engines/thrusters that provide some sort of vertical thrust ability is recommended (basically VTOL). Just make sure the engines you use DO NOT require intake air.

To give you an idea of what you need, here is an example of a VTOL craft and the mod I used to make it:

Edited December 4, 2016 by Gianni1122

[bewing]

It's easy. I do it all the time. You land vertically on your engines, until your plane is standing on its engines on the ground (by burning retrograde like everyone has said). Once you are landed: kill your engines, extend your wheels, and hold down W. The reaction wheels will force the plane to fall forward onto its wheels. Halfway down, you can switch to holding the S key to soften the bounce when the wheels hit the ground. Don't bother with RCS or anything like that. Trying to actually land directly onto your wheels may get you some style points, but it's totally wasted effort.

Edited December 4, 2016 by bewing

[foamyesque]

1 hour ago, bewing said:

It's easy. I do it all the time. You land vertically on your engines, until your plane is standing on its engines on the ground (by burning retrograde like everyone has said). Once you are landed: kill your engines, extend your wheels, and hold down W. The reaction wheels will force the plane to fall forward onto its wheels. Halfway down, you can switch to holding the S key to soften the bounce when the wheels hit the ground. Don't bother with RCS or anything like that. Trying to actually land directly onto your wheels may get you some style points, but it's totally wasted effort.

 

Honestly, it depends on the body. If you do a wheels-down touchdown with some horizontal velocity, you save some deltaV because you can use brakes to kill the final speed without the use of propellant. Some places are easier to do this on than others; Minmus, for example, has giant open flats and very little gravity, and so is easy to do it with. Mun's much trickier. A complimentary approach, or even outright alternative, that is suitable for most of the low-g words (particularly if you're coming in empty) is to have linear or vernor RCS units mounted on the underside of the plane. This lets you kill you your orbital velocity using full-scale engines, either for thrust (e.g. RAPIERs) or efficiency (e.g. nukes), and then control your final descent speed with the RCS thrusters, avoiding the need to change the craft orientation. This will work pretty easily on any body with Munar or less gravity, but is not applicable to Tylo.

Another option is to simply be able to land on your tail, but plane balance and design usually mean that's either unstable or impossible unless you made it explicitly one of your design goals.

[bewing]

1 minute ago, foamyesque said:

Another option is to simply be able to land on your tail, but plane balance and design usually mean that's either unstable or impossible unless you made it explicitly one of your design goals.

Nah. Design always forces your engines to thrust through your CoM. So if you land on your engines, your plane will always be perfectly balanced.

[foamyesque]

24 minutes ago, bewing said:

Nah. Design always forces your engines to thrust through your CoM. So if you land on your engines, your plane will always be perfectly balanced.

 

This is not true of spaceplanes, either as a premise or as a conclusion. Because of the stabilizing effect of the atmosphere, and the gimbal abilities of RAPIERs, it is possible for spaceplane engines to be offset from the CoM by a greater or lesser amount while retaining flight control.

It is also possible, even likely, that engines mounted at the tail are not your only engines and are, to avoid tail strikes, significantly above your CoM and CoT, being balanced by, e.g., wing pods further forward.

Then there's the fact that planes tend to wind up long and with relatively narrow tails, which makes them vulnerable to tilts from ground slope or horizontal momentum.

Edited December 4, 2016 by foamyesque

[juanml82]

3 hours ago, foamyesque said:

Then there's the fact that planes tend to wind up long and with relatively narrow tails, which makes them vulnerable to tilts from ground slope or horizontal momentum.

This. You touch down slow enough so the engines don't break on impact only to find out you were landing on a 17° slope, the plane tilts over and crashes some vital component.

IMHO, if you want to land vertically with a plane, put landing legs in the tail and, if possible, mount the engines on the wings, higher up. You'll have more drag in the atmosphere, but the plane will be simpler to land. Also, add RCS or vernors at the nose. If you begin to tilt over during landing, the higher the rcs pods are, the more torque they'll provide.

[bewing]

You want them to tilt over and fall onto their wheels. You just have to make sure when you land that the wheels are facing downhill. And tails/wings/engines are much sturdier to land on than landing legs.

[notsobrightguy]

Thanks for your suggestions guys!

I'll check them tonight and see which one suit my playing style

Edited December 5, 2016 by notsobrightguy