Author Topic: Skylab 4 re-entry problem  (Read 2773 times)

Offline deaville

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Skylab 4 re-entry problem
« on: 11/28/2011 06:56 AM »
Looking back over some notes I made at the time of the Skylab 4 mission I came across this -

"The crew had to assume manual control during re-entry when they found that Apollo was not correctly aligned due either to faulty instructions from Houston or to a mistake by the crew in setting up the computer."

Was this difficulty ever resolved? Whose fault was it?
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Offline dks13827

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Re: Skylab 4 re-entry problem
« Reply #1 on: 11/28/2011 11:29 AM »
After CM / Service module sep, Jerry Carr noted with alarm that he had no attitude control, a really bad deal.  Former Thunderbird pilot Bill Pogue said 'Hard over.... Hard over', meaning move the attitude control stick hard over which will fire the thrusters okay.  Turns our that Jerry mis read some switch positions which were in a poorly lighted hard to see area of the panel.  Could have been very bad !!

Offline deaville

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Re: Skylab 4 re-entry problem
« Reply #2 on: 11/28/2011 12:19 PM »
Thanks for response. So it was a crew error.
« Last Edit: 11/28/2011 12:20 PM by deaville »
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Offline kevin-rf

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Re: Skylab 4 re-entry problem
« Reply #3 on: 11/28/2011 12:20 PM »
Excellent human factors story, thanks!
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Offline dks13827

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Re: Skylab 4 re-entry problem
« Reply #4 on: 11/30/2011 10:15 PM »
From time to time you will hear real space guys say:  HARD OVER !!!!

It's kind of a saying amongst the crowd.

It's an example, to me, of the brilliance of the Apollo designers, and they were.  If you need thruster control, you need it bad, no matter what, and you need it now.  Hence, the hard over provision.  The LM also had this also, it had to !!!   It will be interesting to see if the young companies understand and implement this requirement.  Let's ask Jerry Carr if he was glad to have this.
« Last Edit: 12/01/2011 12:05 AM by dks13827 »

Offline Jim

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Re: Skylab 4 re-entry problem
« Reply #5 on: 11/30/2011 11:51 PM »

It's an example, to me, of the brilliance of the Apollo designers,

Your worship of everything Apollo is unfounded.  Nothing special.  The same type of work existed before and after.  Most of the engineering was learned and done on the ICBM program.


Offline Jim

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Re: Skylab 4 re-entry problem
« Reply #6 on: 11/30/2011 11:52 PM »
Same for the Orbiter.  It will be interesting to see if the young companies understand and implement this requirement.

It is not a requirement and the shuttle did not have it.

Offline alk3997

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Re: Skylab 4 re-entry problem
« Reply #7 on: 12/01/2011 01:04 AM »
From time to time you will hear real space guys say:  HARD OVER !!!!

...  Hence, the hard over provision. 

...


I can talk this from a Shuttle requirements standpoint and there was *no* special hardover provision.  In other words moving the RHC fully to the left or right just changed the rheostats (three per axis) to a maximum (or maximum negative) voltage.  The GPCs read the position of the stick (based on the voltages) and adjusted the vehicle accordingly.  Nothing special was done fully over that I can remember.

Now the "wiseness" of doing this is in the human not in the machine.  The GPCs would have allowed you to move the stick "hard over" during first stage.  Not a really wise thing to do unless guidance was out to lunch (which never happened, of course).  If you ever tried to fly first stage in the SMS (or SAIL) you would know how truly impossible that was.  In the simulator the wings didn't break off or the struts crack but that wouldn't have been true in real life.

BTW, in atmospheric flight below Mach 1, a hard over stick position would have resulted in elevon deflections and no jets.  You also stood the risk of a loss of vehicle if you tried that at the wrong time.

So, while you might salute Apollo, this really wasn't a special condition in Shuttle just a natural consequence of having a CSS mode that was available at all times and usable at some times.

Andy

Offline simonbp

Re: Skylab 4 re-entry problem
« Reply #8 on: 12/04/2011 11:01 PM »
Now the "wiseness" of doing this is in the human not in the machine. 

It's always easier to program safety into a human than a machine. :)

I can guess the Apollo case was driven more by the limitations of the GPC, making it more a bug than a feature.

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