Archived posting to the Leica Users Group, 2019/02/16[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
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.