Experiment Operations During Apollo EVAs

Experiment: Traverse Gravimeter Experiment

Acronym: TGE

The TGE experiment as operated on the surface (AS-17-142-21730). The unit is sitting on the surface directly "above" the geological scoop, which is in the foreground. It was also operated without removing it from the LRV.
See also the TGE mounted on the LRV.

PI/Engineer: Manik Talwani, Columbia Univ.
Other Contacts:
George Thompson, Brian Dent/Stanford Univ.

Apollo Flight Nos.: 17
Apollo Exp't No.: S 199

Discipline: space physics, lunar geology, lunar gravimetry

Weight: 14.6 kg
Dimensions: 50.8 x 27.9 x 24.8 cm

Manufacturer: MIT/Draper Lab

The primary goal of the TGE was to make relative gravity measurements at a number of locations in the A-17 landing area and to use these to obtain information about the geological substructure. A secondary goal was to obtain the value of the gravity at the landing site relative to an accurately known value on Earth. The gravity sensor used was a Bosch Arma D4E vibrating string accelerometer. It was a double-stringed instrument. The sensor was mounted on a gimbaled frame. Two vertical pendulums mounted on the frame sensed departures from vertical through comparator circuits, which drove motors to level the unit - up to 20 seconds was required in the normal mode and between 90 - 130 seconds in the bias mode (instrument inverted). The TGE could be leveled only if it was initially placed in a position less than 15 degree; from level. The entire unit was housed in a cylindrical box with a flat rear surface. It had 3 feet, a handle for carrying, and a cover over the display/control panel. It was battery powered.

Unloading from the LM: With ALSEP pallets.

Transporting by foot or MET: NA

Loading/unloading tools/exp'ts on LRV:
It rode on the geopallet at the back of the LRV. Between EVA periods, the unit was placed in the shade with the radiator open.

Site selection:
The field geology stations on the planned traverses were used to obtain the TGE measurements. Several measurements around the LM were also made.

Deploying experiment:
Measurements were made both with the TGE mounted on the LRV and with it placed on the surface. One reading was made at the start and end of each EVA.

Check-out of experiment:
Several runs near LM, and on and off the LRV, were performed to check the operation of the instrument.

Operation of experiment:
A network of gravity measurements at 12 sites spread across the valley floor (and 1 gravimeter bias measurement) were obtained during EVA's on A-17. Six measurements (and the bias) were made on EVA 1, seven on EVA 2, and 4 on EVA 3, spread out among several stations and near the LM (some were duplicates.) A measurement was initiated by depressing the "GRAV" button. The cycle started by leveling, then went into the measurement mode. To obtain the bias measurement, a separate button was pushed, and a similar sequence ensued. It had to be left undisturbed during its operating cycle. The reading was displayed on the display and stayed on for 20 sec. It could be redisplayed by pushing the "READ" button once the crewman had time to read it. A toggle switch selected ON or STANDBY for power conservation.

 The TGE team strongly wanted to impose a constraint which would not allow the LRV TV camera to be aimed during the gravimeter's operating cycle because of vibrations. The geology team was just as strongly opposed to not being able to see what the crew was doing every minute at a station, or not being able to see some potentially interesting rock and directing the crew's attention to it. The gravimeter team was hard pressed to specify exactly what constituted an "unacceptable" vibration level. A great deal of analytical work went into trying to prove what the vibration levels would be, and it was finally necessary to instrument an engineering model of the LRV with accelerometers in the vacuum chamber. The vibration from the moving camera proved to be negligible and the "constraint" went away.

Repairs to experiment:
None required. Note that the pallet on which the TGE sat in the LRV swung open before measurement 25 and the resultant banging of the pallet may have caused problems resulting in an erroneous reading.

Recovery/take-down of experiment: Left on the surface.

Stowing experiment for return: NA

Loading/unloading samples on LRV: NA

Loading of exp't/samples into the LM: NA

Stowing of package once in the LM: NA

Sampling operations - soil, rocks: NA

Trenching: NA

Raking: NA

Drilling: NA

Navigating/recognizing landmarks: NA

Were there any hazards in the experiment?
i.e. hazardous materials (explosive, radioactive, toxic), sharp objects, high voltages, massive, bulky, tripping hazards, temperatures?
Power was supplied by a 7.5 V battery.

Was lighting a problem? No.

Were the results visible to the crew?
Yes. A display panel read out gravity and oven temperature values.

Would you recommend any design changes? No comments by crew.

Were any special tools required? No.

Was the orientation of the experiment (i.e. horizontal/vertical) important? Difficult?
Yes, level was important, but the astronaut only had to have it level to 15 degree, the instrument did the rest.

Was the experiment successful? Yes.

Were there related experiments on other flights?
There was a stationary Lunar Surface Gravimeter (S 207) on A-17. Also, orbital measurements of mascons were made during several manned and unmanned missions. The accelerometers of all LMs which landed measured a value of lunar g after landing.

Where was it stored during flight? LM Quad III, experiment pallet.

Were there any problems photographing the experiment? No

What pre-launch and cruise req'ts were there?
power, thermal, late access, early recovery?

What was different between training and actual EVA? No comments by crew.

What problems were due to the suit rather than the experiment?
Operating the unit on the surface, as opposed to on the LRV, was difficult because it was very low and the suit made it hard to lean over and press the buttons. Cernan tended to put it down near the LRV so that he could lean on it to reach the experiment, or if on a slope, stand down-slope. Leaning on a scoop might have worked, too.

Any experiences inside the LM of interest from the experiment/operations viewpoint? No


A-17 Preliminary Science Report

 A-17 Mission Report

 Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TM X-58131, August, 1974, In JSC History Office.

 Apollo Program Summary Report, section 3.2.16 Traverse Gravimeter Experiment, JCS-09423, April, 1975.

 Apollo 17 Technical Crew Debriefing, 4 January 1973, in JSC History Office.

 Apollo Stowage List - Apollo 17, MSC, 12 December 1972.

 Glenn Mamon, "A Traverse Gravimeter for the Lunar Surface", MIT Draper Labs, Cambridge, MA, August 1971, in the JSC History Office.

 Personal communication, Jack Sevier to Thomas Sullivan, 5/93