[Leica] It went to the moon!

[Brian Reid]

This both a startling coincidence and some partly faded memories. While 
writing this, I think I figured out what is going on; I'll explain it at 
the end.

I spent 5 years of my life (1968-1973) working on the planning and 
building of the Lunar Surface Gravimeter for Apollo 17, which was part 
of ALSEP (Apollo Lunar Surface Experiment Package). It was a research 
project of Dr. Joseph Weber of the University of Maryland, where I was 
employed. Dr Weber was trying to detect gravity waves, and he proposed 
to put one gravimeter on the moon and another on earth and look for 
events in which both instruments saw the same gravity disturbances.

A gravimeter is basically a very sensitive scale with a fixed weight 
made of tungsten. If the scale shows a change in weight, and the thing 
you're weighing hasn't changed, then obviously gravity has changed. They 
were invented in the 1930s for oil exploration, and are still in use for 
that purpose.

The actual gravimeter portion of the LSG was built by Lacoste and 
Romberg Inc of Austin Texas. It has since merged to form Micro G-Lacoste 
Inc: http://microglacoste.com/about/
Here is a copy of the instruction manual for it that has been preserved 
by a university in Germany:
http://userpage.fu-berlin.de/geodyn/instruments/Manual_Lacoste_GDl.pdf

We added a lot of electronics to the Lacoste and Romberg device, so it 
could be used remotely. My role in the project was primarily software 
and telemetry, but in 1971 I needed to fill in for an engineer whose 
wife had just had their first baby, and I designed and drafted the masks 
for the 3-layer round circuit board that sat at the top of the unit to 
interface to the telemetry. When it came back from fab I installed it in 
a prototype and helped test it. It did a great job of transmitting data 
about the gravity on the 3rd floor of the Physics building at the 
University of Maryland. When it went off to Houston I never saw it 
again.

The LSG was successfully taken to the moon and deployed by Eugene 
Cernan. There is a description here, with a photograph of it sitting on 
the surface of the moon:
https://en.wikipedia.org/wiki/Apollo_Lunar_Surface_Experiments_Package#Apollo_17

Alas, it didn't work because the research engineers back at the 
University of Maryland (I'll name no names here) forgot to adjust the 
design to be calibrated for the moon's gravity and not the earth's 
gravity, and the dynamic range of the servomotor was not enough to 
compensate for this. I had participated in the calibration of the thing, 
which was done by driving it up and down a mountain near Roswell, New 
Mexico for about a week, taking measurements at each end of the trip. 
When a gravimeter is used in oil exploration, you don't care about 
absolute gravity values, you only care about changes. But when a cruise 
missile is flying, it cares a lot about the absolute strength of 
gravity, so the US Air Force got very involved in the calibration 
process for gravimeters used in survey work; they had originally 
calibrated the mountain (with pendulums) that we drove endlessly up and 
down.

Recovered memory: there were actually two gravimeters onboard Apollo 17. 
The teams involved hated each other. Our LSG was part of ALSEP, the 
experiment package. The main mission also included the Traverse 
Gravimeter Experiment (TGE) which is described here: 
https://www.hq.nasa.gov/alsj/a17/a17-TGE.html. The TGE was built by 
Draper Labs, part of MIT. It rode on the back of the rover, which ALSEP 
devices did not. I'm guessing that your involvement was with the TGE and 
not the LSG. I know it wasn't LSG because I knew everybody on the LSG 
project well, and didn't know you. I had over the years forgotten about 
the second gravimeter onboard Apollo 17. Now it all comes back.

NASA claims (https://www.hq.nasa.gov/alsj/a17/a17-TGE.html) that the TGE 
was used 26 times and "delivered excellent results". I don't know any 
un-official lore about it because I wasn't part of that group; in 
particular, I don't know anything about it being thrown off the rover. 
They were having serious problems with the rover because of a damaged 
fender.

I took my family to Washington DC for a vacation in 1994 and I was 
stunned to see one of the backup LSG devices on display in the Air and 
Space Museum. I was thrilled to be able to point at it through the 
window and tell my children "I helped build that".

I have no idea why I didn't take any pictures of it while I was working 
on it. I had my first Leica by then (a IIIf). Mostly I took pictures of 
people; I guess I didn't consider a lump of aluminum alloy to be 
photogenic.