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  Mercury - Gemini - Apollo
  Apollo 13: Criticality and timing of engine burns

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Author Topic:   Apollo 13: Criticality and timing of engine burns
TLIGuy
Member

Posts: 20
From: Virginia
Registered: Jul 2013

posted 05-15-2014 06:52 PM     Click Here to See the Profile for TLIGuy   Click Here to Email TLIGuy     Edit/Delete Message   Reply w/Quote
I'm working on a project related to the use of the Omega Speedmaster to time Apollo 13's two critical burns (35 seconds and 5 minutes) as described in the NASA summary of mission events. I need to answer one question and confirm the correct events and the time.

Of the two burns which one is considered most critical?

I also need to make sure I'm identifying the correct events from the NASA chronology of events. I see a number of references to burns and want to make sure I'm identifying the two burn events and times correctly.

Is this the correct event for the 35 second burn?

Midcourse correction ignition to free-return trajectory (LM DPS) at 8:42:43
Is this the correct event for the 5 minute burn?
Transearth injection ignition (LM DPS) at 02:40:39
Again, as always the expertise and help from this forum is greatly appreciated.

Fra Mauro
Member

Posts: 1111
From: Bethpage, N.Y.
Registered: Jul 2002

posted 05-16-2014 07:49 AM     Click Here to See the Profile for Fra Mauro   Click Here to Email Fra Mauro     Edit/Delete Message   Reply w/Quote
The free-return trajectory burn is the most critical since it prevent you from missing the Earth.

uk spacefan
Member

Posts: 109
From: London
Registered: Jan 2007

posted 05-16-2014 10:45 AM     Click Here to See the Profile for uk spacefan   Click Here to Email uk spacefan     Edit/Delete Message   Reply w/Quote
The mid-course correction burn took place approximately five hours after the explosion.

As they approached the moon, the transearth injection burn (for 5 minutes) was to speed up their return home. The 35 second and 5 minute burn details are correct as per the timeline. Although these burns were equally important, the TEI burn would have probably been more critical.

Full details are given from NASA here. Alternatively the mission report can be found here.

moorouge
Member

Posts: 1772
From: U.K.
Registered: Jul 2009

posted 05-17-2014 01:04 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Fra Mauro:
The free-return trajectory burn is the most critical since it prevent you from missing the Earth.

Surely all the burns were equally critical, the failure of any one of them would have prevented a successful recovery. Don't forget the very last one that ensured they were in the re-entry corridor.

Or is it a case of - to misquote George Orwell - all burns are equal but some are more equal than others.

TLIGuy
Member

Posts: 20
From: Virginia
Registered: Jul 2013

posted 05-17-2014 05:42 AM     Click Here to See the Profile for TLIGuy   Click Here to Email TLIGuy     Edit/Delete Message   Reply w/Quote
Thank you all for the help here. I agree that all of the burns would be equally important since the failure of any one of them would have resulted in the inability to return safely.

For my project, I have very limited space to work and can only reference one event so I think I will go with the the 35 second burn since it seems to be the one most outside of this fine community are familiar with.

MadSci
Member

Posts: 190
From: Maryland, USA
Registered: Oct 2008

posted 06-25-2014 11:58 PM     Click Here to See the Profile for MadSci     Edit/Delete Message   Reply w/Quote
Im not sure what your project is, however if you're interested, the original plan was to time the burns with the Command Module Interval Timer, a custom manufactured device resembling a kitchen timer. When Jack Swigert attempted to use it the timer, the knob fell off! This failure resulted in the need to use his watch instead.

I am the current caretaker of the Interval Timer Knob in question. If you're interested in a photo please e-mail me and I'll be happy to provide one.

TLIGuy
Member

Posts: 20
From: Virginia
Registered: Jul 2013

posted 06-26-2014 04:42 AM     Click Here to See the Profile for TLIGuy   Click Here to Email TLIGuy     Edit/Delete Message   Reply w/Quote
Thanks for the additional information. I would like to see the image but your email is not available for contact. I have updated my profile to make mine available. If you have a moment please contact me. Thanks.

mercsim
Member

Posts: 144
From: Phoenix, AZ
Registered: Feb 2007

posted 06-26-2014 09:47 AM     Click Here to See the Profile for mercsim   Click Here to Email mercsim     Edit/Delete Message   Reply w/Quote
Why do people always want to e-mail photos

Why not just post it here for all of us to enjoy?

Ronpur
Member

Posts: 503
From: Brandon, Fl
Registered: May 2012

posted 06-26-2014 11:24 AM     Click Here to See the Profile for Ronpur   Click Here to Email Ronpur     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mercsim:
Why not just post it here for all of us to enjoy?
LIKE!

David Carey
Member

Posts: 379
From:
Registered: Mar 2009

posted 06-26-2014 11:43 AM     Click Here to See the Profile for David Carey   Click Here to Email David Carey     Edit/Delete Message   Reply w/Quote
I believe the item in question, along with other goodies, can be seen here.

A great piece (sorry I didn't pick it up years back) and perhaps MadSci could add an entry to the Apollo 13 artifacts thread.

All times are CT (US)

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