On 10/06/2019 2:54 am, JF Mezei wrote:
On 2019-06-09 09:44, Jeff Findley wrote:

Capsules have an offset CG and that combined with their conical (or
biconic) shape produces lift as they pass through the atmosphere.

How much control do they have during that phase? And if they can control
it, how is that accomplished? would thrusters still be effective in
rotating the capsule to change its centre of gravity?

That's not what he said. The 400ms in time difference would be between
the "ideal" reentry burn time and one which had to be chosen to "miss" a
Starlink.

Thanks you you and Sylvia Else for explaining that part. But I am still
curious on what sort of safety standards will be set. If you have a
satellite passing every 2 minutes, how many seconds AFTER a satellite
has passed will be be safe to descend through that altitude, and what
will be the minimum of seconds BEFORE a satellite arrives that it will
be considered safe to pass through ?

You're not going to get a definite answer to this, because it involves a
judgement about risk.

There are things that can go wrong, such as

a) uncommanded manoeuvres by the satellites (control systems can fail),

b) misfiring on the re-entering spacecraft that wouldn't of itself
endanger the crew, but change the trajectory enough to bring it close to
a satellite,

c) collision avoidance manoeuvres by satellites, that, for whatever
reason, didn't get communicated in advance to the controllers of the
space spacecraft. I note your comment below about a "freeze", but stuff
happens,

d) orbital position errors,

and so on.

Individually, these a likely to be low risks, but they add up. NASA will
need to decide what is an acceptable level of risk, and there is no
unique right answer (we'd all like zero risk, but it's not going to
happen here, or indeed in any other transport technology).


And will there need to be new policies in place to freeze
Starlink/Oneweb"whatever orbits X amount of time before a re-entry
(aka: no adjusting of orbits with their engines) to ensure the
re-entering ship is using accurate orbital data of those satellites when
calculating the precise re-entry time?


Again, look at the landing accuracy of Apollo capsules. This was
achieved partly due to their ability to generate a significant amount of
hypersonic lift.

How much was done with parachutes?

None at all. While steerable parachutes exist, it's hard to justify
them, or the weight of their control systems, on something which is in
any case landing in the sea.

Sylvia.