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The propellant tanks on the Apollo 10 Lunar Module "Snoopy" was famously left not full. There is an urban myth that it was done to prevent Gene Cernan and Thomas Stafford from having any funny ideas (i.e. landing on the Moon). NASA's Associate Administrator for Manned Space Flight George Mueller stated that "Snoopy" was an older design and under powered for lunar ascent.

Wikipedia lists the mass for LM-4 and LM-5. What was the mass of each of the 12 completed Apollo Lunar Modules, was there a trend?

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    $\begingroup$ Have you checked "Apollo by the Numbers"? $\endgroup$
    – Organic Marble
    Aug 1 at 2:37

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"Apollo By The Numbers" is a great resource for this, both the complete text and the summary tables document.

The loaded weights of the LM at liftoff generally increased over the course of the program, from 33,278 lbs (15,094 kg) for A11 to 36,262 lbs (16,448 kg) for A17.

Mission LM Dry Weight LM Launch Weight
Apollo 9 9336 32034
Apollo 10 9484 30735
Apollo 11 9287 33278
Apollo 12 9635 33562
Apollo 13 9318 33493
Apollo 14 9407 33685
Apollo 15 10869 36238
Apollo 16 10787 36237
Apollo 17 10884 36262

I'm not sure what added so much dry weight to Apollo 12 (could be an error in the tables -- I've caught errors in ABTN before). After Apollo 13, a fifth battery was added to the descent stage, which added about 130 lbs, but the big step-up in weight was for the final three "J missions", A15 (LM-10), A16 (LM-11), and A17 (LM-12). These missions carried more consumables, in order to support 3-day stays instead of the shorter stays of the early missions, and also carried the Lunar Roving Vehicle.

The LM descent stage was modified for these missions; per Wikipedia:

The descent engine thrust [and more importantly, the fuel efficiency] was increased by the addition of a 10-inch (250 mm) extension to the engine bell, and the descent propellant tanks were enlarged. A waste storage tank was added to the descent stage, with plumbing from the ascent stage. These upgrades allowed stays of up to 75 hours on the Moon.

The dry weight of the J mission LMs was about 1,600 lbs greater than the early LMs.

Regarding Apollo 10:

George Mueller stated that "Snoopy" was an older design and under powered for lunar ascent.

This is not quite right. Snoopy was about 200 pounds overweight, Grumman not having completed their weight-saving program, but the fuel margins were sufficient that the LM would, technically, have been able to land, as explained in this QA. The fuel underload wasn't done to prevent rogue astronauts from landing; it was done so that when the LM staged at high altitude in the Apollo 10 "dress rehearsal", the ascent stage's fuel state would match that of a landing mission which had ascended from the surface.

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    $\begingroup$ The J mission LMs had a larger battery. Battery power was a consumable, but the weight of the battery was supposedly included to the dry weight? $\endgroup$
    – Uwe
    Aug 1 at 4:23
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    $\begingroup$ Although a smaller contributor there was also an increased amount of lunar samples returned on each mission. Apollo 11 - 44 lbs (20kg), Apollo 12 - 75 lbs (34kg), Apollo 14 - 98 lbs (45kg), Apollo 15 - 173 lbs (79kg), Apollo 16 - 210 lbs (95kg), Apollo 17 - 253 lbs (115kg). On early missions the sample weight was offset by the PLSS and other items tossed overboard, but not on the later missions. $\endgroup$
    – Steve Pemberton
    Aug 1 at 11:14
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    $\begingroup$ @StevePemberton the numbers quoted in this answer don't include any samples picked up on the Moon. They are dry vehicle weight and weight as launched from Earth. $\endgroup$
    – Organic Marble
    Aug 1 at 12:37
  • $\begingroup$ @Uwe Yes, the charge of a chemical battery doesn't [significantly] increase its weight, so the battery would only increase the dry weight figure. $\endgroup$
    – Russell Borogove
    Aug 1 at 16:04
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    $\begingroup$ @OrganicMarble - The dry weight and launch weights obviously didn't include the sample weights, but individual ascent stage propellant loads are based among other things on the planned weight of the spacecraft at launch from the Moon. They had a weight budget for samples that increased on each mission and the astronauts used scales to weigh the samples for this reason (NASM article). Increased planned sample weights would have had at least a small effect on LM launch weight, which is what I was pointing out. $\endgroup$
    – Steve Pemberton
    Aug 1 at 20:31

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