On 19-03-03 16:54 , Jeff Findley wrote:
In article ,
says...

"Jeff Findley" wrote in message
...

From what I understand, Dragon 2 has a triply redundant computer system
so any computer hardware problem shouldn't be an issue. I'd bet the
updated computer hardware on Dragon 2 is at least somewhat based on what
was done with Dragon, which has been successful in terms of its software
used to approach and station keep near ISS so that the SSRMS can grab
it.


The difference is that Cargo Dragon is docked via a robotic arm, whilst Crew
Dragon docks via the airlock. That's a significant difference. Also, the
astronauts don't have any control over Crew Dragon, it's completely
autonomous. If something goes wrong, there's nothing they can do to prevent
a catastrophe.

I watched the docking on NASA TV this morning. The crew were definitely
monitoring the approach and even had a display from the Dragon 2 on one
of their laptops. Could they have commanded an abort from that laptop?
I don't know, but it wouldn't surprise me if they could command a hold
or even an abort.

The SpaceX commentary to the docking video makes it quite clear that the
ISS crew can and did command Crew Dragon. At least the following
commands were described as being given from the ISS to Crew Dragon,
during this approach and docking:

- command to turn on the blinking white nav light

- command to retreat from the 150 m waypoint to 180 m

- command to turn on the continuous (non-blinking) white docking light

- command to set the approach speed, when Crew Dragon was again approaching.

In addition, the ISS crew's ability to command abort was clearly stated.

However, when Crew Dragon is docking and very close (one or two meters,
if I remember correctly) there seems to be a "crew hand-off point" at
which ISS crew commanding stops and Crew Dragon is left to dock
autonomously. But it was not clear to me if this is just a procedural
rule, or technically prevented in some way.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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