What exactly is a "Next Generation Lunar Reflector"? Difference in design and performance?

Question

Space.com's 50 Years After Apollo, India Is Carrying a NASA Laser Reflector to the Moon (And It's Only the Start) is a little confusing because it talks about three retroreflectors: - Apollo era retroreflector arrays - Vikram microreflector - Next Generation Lunar Reflector (NGLR)

Question: What exactly is a "Next Generation Lunar Reflector" and how does it differ in design and performance from all other retroreflector designs used or planned for use on or near the Moon? What is it that makes them so Next Generation-esque?

Dell'Agnello is leading the research team on the Vikram microreflector and is a co-investigator working on the upcoming Next Generation Lunar Reflector (NGLR) for NASA's Artemis program. The "next-gen retroreflectors are much more compact and lighter than Apollo's meter-size arrays deployed by Apollo 11, 14 and 15 astronauts," Dell'Agnello added.

The Next Generation Lunar Reflector retroreflector (left) next to its Apollo-era predecessor (right).

Here's a Next Generation reflector: http://trekcore.com/specials/rare/tng_part1/burton_dorn_wheaton_sirtis01.jpg Oops, you said lunar... — Organic Marble, Jul 27 '19 at 02:02
Of all the images I've seen that need scale, that's definitely one of them. — Magic Octopus Urn, Jul 27 '19 at 12:29
@MagicOctopusUrn you can see the Apollo-era retroreflectors in photos in What are these structures on the Lunar Ranging Retro Reflector (LRRR) arrays for? and compare to the size of the boot prints in the lunar regolith. I think they are roughly 20 to 25 mm — uhoh, Jul 27 '19 at 13:09

score 3 · Answer 1 · answered Jul 27 '19 at 02:11

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Because it's bigger? Otherwise seems to be a standard corner reflector. Upon googling I came across this which gives a good description of the differences between the original and TNG reflectors. According to Forbes,

The most important innovation consists of changing from a panel of small cube corner retroreflectors (CCRs) to a single large CCR. The NGLR’s CCR is special fused silica glass that also has fewer internal imperfections than the silica used for the Apollo CCRs.

answered Jul 27 '19 at 02:11

BobT

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Still I wonder why one big one is better than several smaller ones. Per the square-cube law the single big one will be heavier than a set of smaller ones with the same area. The lower imperfections is interesting but that may have been necessary because of the much larger volume and longer path length within the glass, or possibly to make it more robust against the large thermal excursions on the Moon. – uhoh Jul 27 '19 at 06:48
possibly helpful concepts: Planetary Society's LightSail Spacecraft's corner cube reflectors; how large, and corrected for aberration? – uhoh Jul 27 '19 at 13:10
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a panel of small reflectors will have slightly different distances to the source/receiver, so will "blur" the pulse across time @uhoh – Jul 27 '19 at 15:42
@JCRM that's a good point! As noted here time dispersion due to tilt wrt/ incident beam is a big problem. The problem is solved for Earth-bases beams by carefully tilting each array as shown in photos (with lunar lat/long values) in this question but these tilts would be worse than useless for beams from a lunar orbiter. I think that plus effects mentioned in my previous comment may be the answer. – uhoh Jul 27 '19 at 22:25
I've just asked Jitter in timing photons from corner-cube retroreflector arrays on the Moon; does each recorded pulse come from one single cube? – uhoh May 29 '20 at 06:40

What exactly is a "Next Generation Lunar Reflector"? Difference in design and performance?

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