posted 03-28-2017 01:38 AM
Frank Borman's Apollo 8 mission originally was scheduled to be the Apollo 'E' mission and it would have been a repeat of the Apollo 'D' mission flown by Jim McDivitt's crew. The only difference is that the Apollo 'E' mission would be flown in a 4,000 apogee orbit.
Would the 4,000 mile apogee orbit have allowed a high velocity re-entry, therefore simulating the reentry of a command module returning from the moon?
David C Member
Posts: 1039 From: Lausanne Registered: Apr 2012
posted 03-28-2017 12:07 PM
The short answer is "yes, but..."
A normal de-orbit burn from that altitude wouldn't achieve lunar return velocities. However, the SPS was capable of providing a sufficient ΔV (delta-V) increment, provided they didn't plan much else for it. Or an SPS burn could have been combined with a steeper entry angle.
Another thing is that in an incremental test program, they probably didn't "need" to reach a full lunar return velocity, just an intermediate figure between that and normal Earth re-entry. The first lunar mission would achieve the full lunar return data point. If you follow that logic further and bear in mind the Apollo 4 results, you can see why this wound up not being required.
I don't know what the actual plan was, and I suspect the final trajectory had not been computed when the flight was cancelled.
Headshot Member
Posts: 891 From: Vancouver, WA, USA Registered: Feb 2012
posted 03-28-2017 04:27 PM
NASA planned several high altitude orbital missions as alternative missions for Apollo 11, if they had been unable to reach the moon due to various circumstances. These missions ranged from 35,000 nautical mile to 200,000 nm apogees.
These alternative are described on pages 44-45 of the Apollo 11 Vol. I Mission Reports. I do not know if similar high altitude alternatives were planned for Apollo 10.
Jim_Voce Member
Posts: 273 From: Registered: Jul 2016
posted 03-30-2017 12:47 AM
Thank you. The Apollo 8 questions comes up because noted, just as there was an "alternate" mission for Apollo 11, there was an "alternate" mission plan for Apollo 8 in which it would have gone into a 4,000 mile apogee orbit if the Saturn stage could not break out of earth orbit. I do not know if they intended to reach partial or near return velocity speeds but would like to know.
Does anyone know what the G-load would be for a ballistic reentry if the "dip" and "skip" reentry technique didn't work at translunar velocities on Apollo 8's return?
David C Member
Posts: 1039 From: Lausanne Registered: Apr 2012
posted 04-02-2017 02:13 PM
Can you be a bit more definitive about what you mean by "didn't work"? Apollo didn't have a reversionary ballistic mode. Do you mean the spacecraft L/D wasn't as predicted, roll control failure, poor G&N resulting in being out of the corridor (in which case do you mean undershoot or overshoot), stable II attitude, etc.?
Jim_Voce Member
Posts: 273 From: Registered: Jul 2016
posted 04-04-2017 01:12 AM
Basically, I was asking what the G-loads would have been at reentry for Apollo 8 if Apollo 8 had been forced to make a ballistic reentry.
David C Member
Posts: 1039 From: Lausanne Registered: Apr 2012
posted 04-04-2017 06:27 AM
Okay, that's not a very meaningful question because a complete answer partially depends on the failure scenario. It's not the same situation as having specifically designed a capsule to perform a ballistic entry from a translunar trajectory.
For an Apollo size, mass and shape re-entry vehicle with L/D = 0 (I'll assume because the crew didn't load it properly and offset the center of gravity), you're theoretically looking at around 11g. However, the main reason for Apollo's lifting entry design is that G&N could not assure the required vacuum perigee altitude range for successful ballistic entry within structural and heating limits.
In other words in this scenario the load factor could range from very low (no capture) to well over 20g and structural failure.
As an aside, the well known Soyuz ballistic re-entry mode is a different situation. Although the Soyuz CA L/D ratio is very similar to the Apollo CM, the entry is from a much lower velocity and capture is assured after successful retrofire. My understanding is that it's effectively a guidance mode failure whilst the CA remains properly loaded and controllable.
oly Member
Posts: 971 From: Perth, Western Australia Registered: Apr 2015
posted 04-04-2017 07:33 AM
Up until recent times, there was a very good YouTube video that was part of the late 60's early 70's NASA educational series that covered reentry of Apollo in great detail. It showed the effect of velocity, entry angle, capsule c/l and CofG and also gave good detail of the roll control used to vary the g-load/heating and also downrange and cross range variation.
The link I had for this video is now dead, I will search for another link unless anyone else is aware of a live one. It covers what you want.
David C Member
Posts: 1039 From: Lausanne Registered: Apr 2012
posted 04-04-2017 08:37 AM
This MPAD film on YouTube is pretty good. It describes the exo-atmospheric skip out design profile. However, in practice every manned Apollo lunar mission actually flew a more conservative lifting no-exit profile (although skip out was an available option).
But I'm guessing it's not the one you mean.
oly Member
Posts: 971 From: Perth, Western Australia Registered: Apr 2015
posted 04-04-2017 09:16 AM
No that is not the video I remember but seems to be of the same style and narration. The video in question seemed like it was made after the Apollo 11 flight. But I like this video too, thanks.
posted 03-28-2017 01:38 AM
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