The issue is setting up the "glide path". Since there is no air, it would be an orbit that is tangential to the "landing strip. So you want to go close to the moon going at more than 3500 mph?
Well, by the time a colony exists, the lunar gravity field should be well mapped so how much more dangerous is approaching within tail hook distance to the surface in a 3500 mph orbit
Quote from: aero on 06/24/2014 06:58 pmWell, by the time a colony exists, the lunar gravity field should be well mapped so how much more dangerous is approaching within tail hook distance to the surface in a 3500 mph orbit wrong, gravity field mapping is a minor/secondary effect. The issue is precision of the "deorbit" burn that sets up the orbit "glideslope" that intersects with the landing field. It can't be done accurately enough to ensure alignment vertically, laterally and short/long. The corrections for the errors end up being orbital corrections in reality. Since it is a low point in the orbit, the corrections are at the worst spot in terms of effectivity. Laterally adjustments are plane changes, long/short adjustments are orbit axis changes. These will be huge in terms of propellant. This makes the concept highly unlikely that it is viable. And there still is the risks flying low that fast.
Certainly valid technical problems to be solved.
Don't forget that as a craft comes down, it starts to form an arc with it's path as it loses speed. To maintain a steady spiral, you'd actually have to add velocity to compensate for the gravitic drag.
The "short" landing problem can be solved using the vertical lift thrusters given sufficiently advanced knowledge of the distance short. The "long" problem looks like a "go around" to me. Isn't vertically just another version of short and long? As for lateral, how much lateral velocity do you suppose the tail hook-arrester cable can accommodate?.
Quote from: JasonAW3 on 06/24/2014 07:56 pmDon't forget that as a craft comes down, it starts to form an arc with it's path as it loses speed. To maintain a steady spiral, you'd actually have to add velocity to compensate for the gravitic drag.What do you mean by "spiral?" The lander inserts into a near circular elliptical orbit with the perilune at and aligned with the landing strip. It does not loose speed until it snags the arrestor cable. It gains a little speed as it looses altitude around the orbit.
Quote from: aero on 06/24/2014 08:06 pmQuote from: JasonAW3 on 06/24/2014 07:56 pmDon't forget that as a craft comes down, it starts to form an arc with it's path as it loses speed. To maintain a steady spiral, you'd actually have to add velocity to compensate for the gravitic drag.What do you mean by "spiral?" The lander inserts into a near circular elliptical orbit with the perilune at and aligned with the landing strip. It does not loose speed until it snags the arrestor cable. It gains a little speed as it looses altitude around the orbit.Basic aeronautics; Gravity is a downward force that also acts as a form of drag.Even without an atmosphere, velocity will be lost due to the lunar gravity. The arc would tend to be like that of a cannon ball. While the cannonball will go farther, gravity will still pull it down in an arc. the speed that it gains is in a downward fashion while forward momentum is bled off by gravity.
Even without an atmosphere, velocity will be lost due to the lunar gravity. The arc would tend to be like that of a cannon ball. While the cannonball will go farther, gravity will still pull it down in an arc. the speed that it gains is in a downward fashion while forward momentum is bled off by gravity.
Quote from: aero on 06/24/2014 07:50 pmCertainly valid technical problems to be solved. The point is there is no ned to solve them. There is no benefit to the idea.
Quote from: aero on 06/24/2014 07:50 pmThe "short" landing problem can be solved using the vertical lift thrusters given sufficiently advanced knowledge of the distance short. The "long" problem looks like a "go around" to me. Isn't vertically just another version of short and long? As for lateral, how much lateral velocity do you suppose the tail hook-arrester cable can accommodate?.And what size are the vertical lift thrusters and how much propellant is needed.A tail hook-arrester cable can accommodate no lateral velocity if the vehicle is not over the strip laterally
Basic aeronautics; Gravity is a downward force that also acts as a form of drag.
Ok, Explain why orbits decay, even around airless moons.