[FPSPACE] Soyuz TMA-11 landing after ballistic entry

[Geert Sassen]

Exactly what I have been wondering about every since: the term 
'overshoot' is used, however a ballistic landing will result in an 
shorter traject and a landing well short of the target, like you say you 
can only get an overshoot if there is an underburn and/or a misalignment 
during retrofire or a late retrofire. Both cases however should easily 
be picked up by tracking stations well ahead of the re-entry blackout.

I presume that the originally mentioned landing '20 minutes too late' is 
wrong and only caused by confusion about the whereabouts of the Soyuz, 
landing 20 minutes late on a ballistic trajectory would mean a big error 
in retrofire! Assuming an error more or less in line with the previous 
landing, the craft must have landed well ahead of schedule, and short of 
the target, not delayed and overshooting its target...

One more item: how does the guidance system respond to an error in 
retrofire (underburn, wrong alignment, or time-error)? Basically a wrong 
alignment should not be possible (the engine will refuse to start or 
switch off as has been seen in the past), but if anything like this does 
happen and the guidance notices the craft to be in a trajectory which is 
too flat (overshooting its landing target), would it compensate for this 
by initiating a ballistic descent (trying to compensate for overshooting 
and getting as close as possible to the target?). If this is true than 
the error must have been in the retrofire, not in the guidance system, 
which leads once again to the question why this was not immediately 
clear from the downlink/tracking?

One final question: how is communication maintained with the craft 
during retrofire and the initial stages of descent? Originally the 
Soviets used to have tracking ships off the African coast (where 
retrofire takes place), however those times are long gone. Presumably 
contact is routed via the ISS? Then, how much telemetry does the ground 
actually receive during these important events, or is it only voice? The 
statement 'the crew failed to report a ballistic descent' worry's me a 
bit as it seems to indicate that there was no other method by which 
groundcontrol could know that a ballistic descent had been initiated, 
this seems quite weird..

Regards,

Geert.


Charles, John B. (JSC-SA2) wrote:
> JimO,
>
> Thanks for the link.  How did anyone really suspect an overshoot?  That
> would imply a late de-orbit burn ignition, an underburn and/or a
> miasalignment, all presumably excluded by real-time downlink.  Or is
> that part of the problem?
>
> John Charles
> Houston, Texas
>
>   
>> -----Original Message-----
>> From: fpspace-bounces at friends-partners.org On Behalf Of 
>> jeoberg at comcast.net
>> Sent: Monday, April 21, 2008 4:20 PM
>> To: fpspace at friends-partners.org
>> Subject: Re: [FPSPACE] Soyuz landing
>>
>> My MSNBC analysis story:
>> http://www.msnbc.msn.com/id/24243569/
>>     
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