Would a spaceplane be able to softly land on an airless planet?

Question

Assuming the spaceplane has no vertical (hover)engines, is there a possibility to land a spaceplane on a celestial body without atmosphere in a horizontal way as if it had one? One could lower the periapsis to (close to) 0 altitude and then use the front deorbit engines to further brake the spaceplane once it touches or gets very close to the surface. But wouldn't the craft still be too fast, killing or severly injuring the crew when touching down? Or is there a way one could decelerate it and follow the planet's curvature (by propulsion, beneath orbital velocity) to eventually touch down softly, assuming the craft has enough fuel?

In such case, would rather a high gravity (e.g. Mercury's) or a low gravity (like Ceres') be of advantage for the landing attempt?

Answer 1

Yes But...

This only works if your craft can generate enough thrust to reduce orbital velocity to zero quickly enough that acceleration due to gravity does not produce a crash landing, since you are effectively trying to reduce gravity losses to those that can be absorbed by the undercarriage.

For earth's moon, taking aircraft vertical touchdown speed at 2 m/s and lunar gravity at 1.6m/s this means completing the burn in at most 2 seconds. For a minimal starting orbital velocity of 1.6 kms this involves a burn at more than 800ms2 or 81 G.

Ceres is more reasonable, with surface gravity of 0.28 ms meaning we have 7 seconds to complete the burn, and an orbital velocity of around 300m/s for 42ms2 or 'only' 4G.

In practice, if you were in orbit around Ceres with a space plane capable of 4G you could probable make a conventional descent till close to the surface and land in whatever orientation was convenient on just RCS.

Answer 2

No, you can't. If you want to travel at below orbital velocity at a fixed distance from the centre of mass of some (approximately) spherical body you need a vertical component of thrust. Aeroplanes call this lift and they get it from their wings. In the absence of an atmosphere you must, therefore, have reaction engines which provide a vertical thrust component. From your comment ('I'm assuming the spaceplane has both back engines and front engines (like the shuttle's RCS but stronger), just no vertical engines.) you are ruling these out so what you want to do can't be achieved.

If you allow a vertical thrust component, well, that is how some people landed on an airless moon in the late 1960s and early 1970s, of course. They had only a single high-thrust engine (they also had attitude-control engines but these were relatively tiny) which was gradually turned from acting nearly purely horizontally to acting nearly purely vertically during the descent.

Lower gravity always helps, until it gets so low that tiny mistakes turn into vast leaps or put you back into orbit, or something.

Answer 3

If you ever looked at the photos of the surfaces of Earth's deserts, Mars' plains, Venus' Venera landing site, Jupiter's moons, or some of the recently visited asteroids, you will notice there are few if any areas smooth enough for such landings. Aircraft and spaceplane landing gear are not designed for more than minimal roughness in the landing site. This is partly to save mass, partly because landing gear can't perform miracles of strength, even if they are just skids. Higher speeds mean higher energy collisions with small rocks (whatever their substance), sand drifts, and cavities or craters. All designated rough (unpaved) landing fields on Earth try to minimize these. (Small rocks can bounce and damage or puncture the vehicle skin.) On a distant planet or planetoid, there is no such advance party to clean up the landing site unless a "highway repair" robot lands first. The previous responder is correct, retro thrusting is the only sensible way and the mass allotment is better spent on engines and propellant than the now useless wings. (Mass ratios are unforgiving.) Bear in mind also that on Earth we nearly always conduct long distance travel by changing from one type of vehicle to another, each suited to the type of travel involved. Example: Travel from one's home in NorAm or Eurasia to a research station in Anarctica. If you start in Emporium, Kansas, you won't leave in a Boeing 747 and won't arrive in one either.

Answer 4

It can be done but only if you have a very long, very good runway and your wheel bearings are very, very good. You put your apoapsis low and then put your periapsis at the elevation of your runway. Note that you will need to immediately retrofire when you touch the runway or you'll just take off again. Brakes will not work at all until you have slowed enough that your apoapsis is at the runway and your periapsis is underground.

I'm not aware of any wheels that would work on any substantial world. However, there's a better way to handle this. What's the usual way to do this on Earth? Magnetic levitation. Build a doubled track--instead of simply riding on the rails it rides between two rails. The spacecraft comes in and sets it's periapsis very low as it passes over the track. A vehicle zips down the track at the same speed and releases a cable. The plane grabs the cable, then the cable is reeled back in to bring the plane down to the capture vehicle, then the capture vehicle slows down. Note that you can launch the same way.