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Author Topic:   Closest to the moon without landing
davidcwagner
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From: Albuquerque, New Mexico
Registered: Jan 2003

posted 04-25-2021 11:11 AM     Click Here to See the Profile for davidcwagner   Click Here to Email davidcwagner     Edit/Delete Message   Reply w/Quote
Which Apollo astronauts came closest to the moon without landing?

I read somewhere that the Apollo 15 command module came closer to the moon than the Apollo 10 lunar module.

Ken Havekotte
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From: Merritt Island, Florida, Brevard
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posted 04-25-2021 12:02 PM     Click Here to See the Profile for Ken Havekotte   Click Here to Email Ken Havekotte     Edit/Delete Message   Reply w/Quote
I've always thought Apollo 10/LM-4 with Thomas Stafford and Gene Cernan was just over 9-10 miles above the lunar surface without landing.

But on Apollo 15, if I understand correctly, there was a low pericynthion orbital altitude of 7.6 to 9.6 nautical miles above the lunar surface during one of the DOI burns of Endeavour's SPS engine which included the LM-10/Falcon still attached. What does 7.6 nautical miles equal in 9-10 miles?

Blackarrow
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From: Belfast, United Kingdom
Registered: Feb 2002

posted 04-25-2021 01:49 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
As I recall, there was also the issue of the Apollo 15 CSM/LM passing over the Apennine Mountains, so we need to clarify whether we're talking about "miss-distance" to the highest point below the spacecraft, or are we talking about orbital altitude above the average lunar surface altitude.

I do remember hearing Al Worden talking about passing over the mountains "close enough to count rocks." But I think this needs a technical answer rather than an "anecdotal answer."

Robert Pearlman
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From: Houston, TX
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posted 04-25-2021 02:13 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
According to "Apollo by the Numbers" (SP-2000-4029), prior to the rendezvous with the lunar module ascent stage after the landing, the command module entered an orbit that brought it within 9 miles of the surface.
The 431.0-second firing achieved the initial lunar orbit of 42.5 by 9.0 n mi.
On Apollo 10, however, the lunar module orbited even lower.
The lowest measured point in the trajectory was 47,400 feet (7.8 n mi) above the lunar surface at 100:41:43.
I didn't check the other missions, but maybe the record for Apollo 15 was the lowest altitude for a command module.

Blackarrow
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From: Belfast, United Kingdom
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posted 04-25-2021 05:17 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
The Apollo15 Flight Journal records that at 93:32:50 GET Apollo 15 was in a 58.8 x 7.6nm orbit. But Capcom pointed out that Houston was extrapolating ahead to calculate a low-point of only 33,000 feet at PDI "plus or minus 9,000 feet." The margin of error was due to lunar mascons perturbing the trajectory, and uncertainties about the actual height above the mean lunar surface ("lunar sea level").

I don't believe any of the above figures took account of the height of the Apennine mountains that the spacecraft had to fly over, but based on Capcom's figures, it looks like Apollo 15 beat Apollo 10 (7.6 nm against 7.8 nm) giving another record to Al Worden.

The prediction of "33,000 feet +/- 9,000 feet" (as low as 4 nm) was theoretical: before it came to pass, an orbital trim burn was understandably made to raise the low point to a safer altitude.

I don't know if information exists to determine the height of the CSM/LM above the local terrain at that 7.6 nm point in the orbit, but it would be interesting if someone could determine the actual clearance on crossing the Apennines. Granted, a bit nerdy. But interesting.

Paul78zephyr
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From: Hudson, MA
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posted 04-27-2021 06:07 PM     Click Here to See the Profile for Paul78zephyr     Edit/Delete Message   Reply w/Quote
Was pericynthion even over the mountains?

Blackarrow
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From: Belfast, United Kingdom
Registered: Feb 2002

posted 04-28-2021 12:02 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Good question, and probably the type of highly technical point that very few people could answer. However, I note that the Apollo 14 Flight Journal (in its "Technical Background Information") states:
In the context of an Apollo mission, the altitude at pericynthion is always relative to "RLS": the lunar "Radius at Landing Site." Starting with Apollo 14, the astronauts would spend an extended time, including a sleep period, in an orbit with a pericynthion of less than 10nm (20km). Their restful sleep depended more on adequate ground clearance than height above an abstract mean lunar radius.
I love that last sentence! On its final pass over the landing site before the orbital trim manoeuvre raised pericynthion, Apollo 15 certainly passed over mountainous terrain — I remember the TV views! The landing-site (the point to which Capcom's 33,000 feet +/- 9,000 feet prediction applied) was surrounded on three sides by mountains rising thousands of feet above the landing site.

I leave it to anyone with the necessary skills to prove otherwise, but taking account of that 7.6 nm periapsis announced at 93:32:50 and the presence of the Apennine mountains, it's difficult to avoid the conclusion that Al Worden came closest to the surface of the Moon without landing.

MartinAir
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posted 02-28-2024 01:01 PM     Click Here to See the Profile for MartinAir   Click Here to Email MartinAir     Edit/Delete Message   Reply w/Quote
How about Apollo 17? There are photos of the command module America below the lunar module Challenger and according to this thread the lowest periapsis of 7.1 miles/11.5 km was achieved by this mission.

Blackarrow
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From: Belfast, United Kingdom
Registered: Feb 2002

posted 03-05-2024 09:35 AM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Interesting. But although 7.1 statute miles equals 11.5 kilometers, I suspect the 7.1 miles figure quoted was actually 7.1 NAUTICAL miles (over 8 statute miles, or over 42,000 feet).

All times are CT (US)

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