RE: starship-design: Planetary Landing

[Timothy van der Linden <Shealiak@XS4ALL.nl>]

Lee,

>I'm not an expert on orbital mechanics, but it sounds a great deal like you
>are trying to maintain a variable orbital speed (decreasing with altitude)
>and a constant airspeed all while you are descending vertically. I don't
>think that is possible.

It seems the X-craft can do it. It can hover in the air, move to the left
and right by a slight tilt and go up and down.

>> Sorry, I don't understand why the frame that distributes the
>> forces from the boosters, must be different when instead of
>> boosters, a landing gear is  attached.
>> The boosters push with 1g against the rest of the ship. The
>> landing gear does exactly the same.
>
>The engines/boosters, whatever are typically close to the centerline already
>and require a minimum of structure to transfer thrust evenly to the ship's
>frame.

If the boosters are close to the centerline, then their load has to be
transferred to the sides also. That is, unless most of the mass is along
the centerline and little mass at the edges.
Since most classical rockets are small tubes, there is hardly any other
place to put the boosters. The Shuttle liftoff combination (ie. with
external tank, and solid rocket boosters) has the boosters far from the
centerline of the whole combination.
Furthermore, these new (theoretical?) crafts with aerospike engines seem to
have the exhausts in a line, where the outer edges are far from the
centerline of the craft.
So, I'm not convinced by your comment regarding the distribution of forces.

>Landing gear on the other hand are transferring load from well away
>from the centerline and must withstand additional loading on different
>vectors.

After landing, as long as the starship keeps its nose straight up there
should be no additional forces. But yes, if the starship is tall and the
wind starts play with it, then problems may arise quite fast.

>For small vehicles with relatively small distances between the load points,
>this is not severe. For large vehicles with hundreds of meters between load
>points the load on the structure of the gear can become enormous. This is
>why landing gear on aircraft are designed to act on the same vector as the
>forces being applied to them. I don't see how this would be feasible on a
>starship unless it is considerably broader than we envision.

So far I haven't envisioned a lot regarding shape. Actually we haven't
discussed shapes very often (if at all). Tube models usually are chosen to
minize drag and maximize volume while moving quickly through the atmosphere.

Timothy