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Old 11-06-2019, 12:09 PM
gary
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Massive mascon detected beneath the Moon's South Pole-Aitken basin. Metal asteroid?

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Originally Posted by Baylor University
A mysterious large mass of material has been discovered beneath the largest crater in our solar system—the Moon's South Pole-Aitken basin—and may contain metal from the asteroid that crashed into the Moon and formed the crater, according to a Baylor University study.

"Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground. That's roughly how much unexpected mass we detected," said lead author Peter B. James, Ph.D., assistant professor of planetary geophysics in Baylor's College of Arts & Sciences.The crater itself is oval-shaped, as wide as 2,000 kilometers—roughly the distance between Waco, Texas, and Washington, D.C.—and several miles deep. Despite its size, it cannot be seen from Earth because it is on the far side of the Moon.
Story here :-
https://phys.org/news/2019-06-mass-a...st-crater.html
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Old 11-06-2019, 07:55 PM
Dennis
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Thanks for that Gary – I assume that none of the Apollo missions that landed successfully on the Moon’s surface overflew this mascon.

Otherwise, I assume it might have affected their pre-programmed descent profiles, as the LM Guidance and Navigation Computer would not have factored in the effects of such a larger mass?

Cheers

Dennis
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Old 11-06-2019, 10:41 PM
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billdan (Bill)
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That's a very big crater (2,000Km wide), considering the Moon itself is less than 3,500Km wide. Smaller than the width (E to W) of Australia.
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Old 12-06-2019, 11:59 AM
gary
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Quote:
Originally Posted by Dennis View Post
Thanks for that Gary – I assume that none of the Apollo missions that landed successfully on the Moon’s surface overflew this mascon.

Otherwise, I assume it might have affected their pre-programmed descent profiles, as the LM Guidance and Navigation Computer would not have factored in the effects of such a larger mass?

Cheers

Dennis
Hi Dennis,

As they were on free-return trajectories, it would have meant their lunar
orbital insertions were approximately along the Earth-Moon plane.

As you will recollect, mascons came as a surprise to Apollo planners
during the Lunar Orbiter missions between 1966 and 1967. It increased
the error radius of the Apollo landing sites if they weren't accounted for.
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Old 12-06-2019, 01:05 PM
Dennis
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Quote:
Originally Posted by gary View Post
Hi Dennis,

As they were on free-return trajectories, it would have meant their lunar
orbital insertions were approximately along the Earth-Moon plane.

As you will recollect, mascons came as a surprise to Apollo planners
during the Lunar Orbiter missions between 1966 and 1967. It increased
the error radius of the Apollo landing sites if they weren't accounted for.
Thanks Gary, I remember that Apollo 11 was a little long on the planned descent line, as the LM was travelling a little faster than expected.

I think that subsequent Apollo Missions had the CSM fire its thrusters when the CSM and LM separated in lunar orbit, whereas on Apollo 11, the LM fired its thrusters at separation which "might" have accounted for the slight increase in approach speed.

Cheers

Dennis

Cheers

Dennis
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Old 12-06-2019, 01:45 PM
gary
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Quote:
Originally Posted by Dennis View Post
I think that subsequent Apollo Missions had the CSM fire its thrusters when the CSM and LM separated in lunar orbit, whereas on Apollo 11, the LM fired its thrusters at separation which "might" have accounted for the slight increase in approach speed.
Plus from Apollo 12 onward, they added different pre-computed offsets to
each of the landing site targets based on what they then knew about the
mascons from Lunar Orbiter data analysis.

The LM Apollo Guidance Computer (AGC) program suite, which was
named "LUMINARY", was not changed so I gather they would simply
enter landing target coordinates according to those derived after applying
the offsets to the nominal target coordinates.

You will recollect Apollo 12 landed within 180 metres of Surveyor 3.
An impressive feat given the distance from the Earth to the Moon.
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