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Old September 25th 17, 11:06 AM posted to sci.space.policy
Jeff Findley[_6_]
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Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

In article . com,
says...

On 2017-09-24 16:34, Jeff Findley wrote:

From above article:

"The reason we decided not to pursue (powered landings) heavily
is it would have taken a tremendous amount of effort to qualify
that for safety, particularly for crew transport," Musk said.


Ok, so was Dragon gonna do powered re-entry like Stage 1, or be like
Soyuz with lifting re-entry, parachutes and powered "cushion" very near
ground?


No. Parachutes would not have been used for a nominal powered landing.
Parachutes would have been necessary in case of an abort because the
abort burn would have used too much fuel to allow for a powered landing.

I was told it was to be a powered one like stage I, where fuel available
becomes critical. (and validating software a bigger challenge).


It's critical in the sense that you have to budget enough for landing,
but the terminal velocity of the capsule limits the amount of fuel
needed for landing, so it's not hard to make sure you have enough.

So, since it's not as important to Mars as SpaceX once thought it was,


I smell excuse here.


Funny, I saw a clear engineering/management trade-off.

The Mars plans were announced years after Dragon was designed. I suspect
this is more about SpaceX realising that the refurb costs for salt water
landings aren't as high as thought, so it is more economical to land in
water than to spend the extra money to develop/test land landings.

I suspect Mars landing will be different enough to not be applicable to
Earth landings.


We'll see what has changed with the next update from SpaceX on its Mars
plans. It could be that a (relatively simple) powered vertical landing
has been abandoned in favor of something else a tad more complicated.

was a management/engineering trade-off and appears to be SpaceX's
call, not NASA's.


Suspect origimally NASA, then SpaceX realised water landings not as bad
as thought.


Possible.

Yes. Dragon flies a lifting reentry and therefore has some cross-

range
capability. This was also true of both Gemini and Apollo (and Russian
Soyuz and Chinese Shenzhou).


Does "cross range" refer to only left/right, or also forward/backward?
(aka, a narrow elipse or a full circle as possible landing locations?


Roughly speaking, by rotating the capsule, you can direct the lift
vector anywhere along the circle that's normal to the velocity vector.
So in your terms, yes you can direct the lift vector left/right and/or
forward/backward.

Jeff
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