John Doe wrote:

One message I saw here had the pressure begin to drop prior to
undocking. I would ASSUME that it began to happen when the closed the
hatches and vaccumed the vestibule, at which point they may have noticed
an imperfect seal.


The leak was noticed prior to undocking; apparently there is a test
where they enter the reentry module and seal the hatch to the orbital
module, then lower the pressure in the orbital module to make sure the
hatch joining the two maintains pressure integrity before they separate
from the station. In this case it apparently showed a loss of pressure,
but Russian mission control assumed it was a screw-up on their part, and
told them to separate from the ISS anyway.
The logic of that decision is very suspect, especially given what
happened afterwards.

This is a soyuz that stayed on station for 6 months. So any leaks would
have been noticed during this time.

IF the leak happened in the hatch between the orbital module and vacuum,
The crew could have closed the hatch between the re-entry module and the
orbital module and be safe. (but without toilet and space to move around)



This seems to be a leak in the orbital module/reentry module hatch.

One has to consider that if the leak was detected prior to undocking, it
probably was probably slow enough that they decided to proceed with
undocking. It was probably felt that delaying undocking to debug the
leak wasn't worth it based on the leak rate.



The question one should ask oneself is _why_ the hatch is leaking.
If you don't know that, then there is no guarantee that it might get
considerably worse when you fire the explosive bolts to separate the
orbital module after retrofire.

So the big question is whether they lived with the leak and made use of
orbital module until it was separated, or if they closed the hatch and
stayed in re-entry module all the time. (perhaps repressurising the
orbital module once to make use of the toilet).



As long as the two modules were joined and the hatch between the two
modules was open, the leak wouldn't be noticeable.
That's why it manifested itself again after the orbital module was
separated, and reentry began.


It was probably a very minor glitch that appears to be more serious than
it was because of the "secrecy" about it. Russians should be man enough
to release the detailed information about this glitch to end any speculation.



They're probably concerned that their decision to allow to allow the
Soyuz to separate from the ISS despite the leak indication would look
flawed...as indeed it was.

Pat