JF Mezei wrote:

On 2017-09-23 13:33, Fred J. McCall wrote:

down. I think it's funny that NASA lets astronauts ride on Soyuz,
which relies on power at landing on dirt for them to survive, yet is
being obstructionist to safety certify Dragon V2 for fully powered
landings on dirt.


A rare instance where I agree with you.

But being devil's advocate: At the time NASA started to purchase seats
on Soyuz, it had already proven itself and it ability to land. Also,
they had no choice since Soyuz was also the escape pod in case of emergency.

And during post Columbia stand down and after permanent shutdown of
Shuttle, NASA had no choice either.


True, but doesn't address the issue. Why not let SpaceX prove powered
landing?


Had SpaceX insited on doing land landings for dragon from the get go,
NASA's reaction might have been to not bring back important cargo until
after a few flights when the capsule had proven itself.


Just how much cargo do you think comes back down? Most cargo vehicles
are used to dispose of trash by doing uncontrolled reentries.


But because the option to land on water remained available, NASA saw
this as a much simpler way to get commercial cargo going, and once this
happens, it is easier to just insist on it continuing.


True, but what about all the flights that aren't bringing anything
back? Why obstruct development?


Note: for researchers, landing on land has HUGE advantages as they can
get to experiments much faster.


To some extent, but not all that much.


Question: for a "newbie" company like Space-X, and considering the USA
does not have vast areas of undevelopped land that is flat and easy to
land on, how difficult is it to fairly precicely target a landing site
and what are the implications if re-entry isn't perfect (as has happened
on Soyuz a few times) ?


If you're coming down under power (as opposed to Soyuz which comes
down on parachutes and just uses power to 'soften' the landing enough
to be survivable), you're not going to 'miss' by more than a handful
of meters.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw