RE: starship-design: Planetary Landing

["L. Parker" <lparker@cacaphony.net>]

Timothy,

> Sorry, I meant only that part when the X-craft land, ie. when the nose
> points up. The starship doesn't use aerobraking, it slows
> down to say 1000
> km/h of radial velocity and keeps zero velocity with the
> horizontal plane
> of each particular part of the atmosphere. (Landing on a
> north or southpole
> would be ideal.) During the whole descend time its trusters would be
> pointed downwards like the X-craft during landing.

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.

>
> 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. Landing gear on the other hand are transferring load from well away
from the centerline and must withstand additional loading on different
vectors. Simply put, the frame of the ship must be able to support itself
plus the weight of the ship, the landing gear must support itself, the
frame, the weight of the ship attached to the frame, and additional loads
cause by the fact that all of this weight is now applied on a vector that is
at an angle to the centerline of the landing gear.

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.

>
> The same frame that distributes the forces coming from the
> boosters will be
> used to distribute the forces of the landing gear. No large amounts of
> additional weight are needed.

Except the weight of the landing gear...


Lee