The SEP transmitter as deployed near the Apollo 17 landing site. Note
the tape holding the solar panels open (AS-17-135-20543).
The SEP receiving antenna on the Apollo 17 LRV. Also visible is the
TGE, geological tools, and sample return bag mounted on the rear (AS-17-141-21511).
Between the astronaut and the tools can be see a pallet of 4 explosive
charges for the Lunar Seismic Profiling Experiment (LSPE).
PI/Engineer: M. Gene Simmons, MIT
Other Contacts: David W. Strangway, U of Toronto
Apollo Flight Nos.: 17
Apollo Exp't No.: S 204
Discipline: lunar geology, geochemistry
Weight: 16 kg (1 kg recorder returned)
Dimensions: receiver box = 23 cm3 (transmitter stood ~knee high
on its legs)
the solar panels that faced the sun ~60 x 25 cm, unfolded from trifold
stowed position
Manufacturer: Raytheon, MIT Center for Space Research
Description/Purpose:
This experiment measured the dielectric constant and loss tangent of
the lunar regolith in situ and also provided information on the subsurface
structure (electrical layering, discrete scattering bodies, and the possible
presence of water) in the region covered by the geology traverses. Electromagnetic
radiation at 6 frequencies from 1 to 32.1 MHz was transmitted from a fixed
crossed-dipole antenna and received through an antenna attached to the
LRV. The basic principal of the unit was interferometry, with reflected
waves and "free space" creating an interference pattern. Useful data was
received only during the traverse from the SEP site to station 2. During
passes of the CSM overhead, the Lunar Sounder Experiment antenna also took
measurements with the SEP on and off.
The experiment consisted of a crossed-dipole antenna that was laid on the ground, a transmitter unit (which stood on 4 legs, needed to be leveled, and had solar panels for power) which generated the signal, and a receiver and receiving antenna (~2.5 m high) on the LRV. The wires which made up the transmitting antenna stretched 35 meters in 4 directions from the SEP central unit - each was 70 m long and were operated sequentially. The receiver included a tape recorder and battery.
Unloading from the LM:
No comments by crew. The Data Storage Electronics Assembly (DSEA) recorder
was transported to the moon inside the LM in stowage area A2. The rest
was stowed in the descent stage..
Transporting by foot or MET: NA
Loading/unloading tools/exp'ts on LRV:
The receiver and receiving antenna were placed on the back of the LRV
during EVA 1 for thermal control and operational convenience even though
they weren't used until EVA 2. A cable for position information was connected
to the navigation unit of the LRV.
Site selection:
A flat area was found for the transmitting antenna ~100 meters east
of the LM. The receiving site was wherever the LRV went on its traverses.
Information on the location of the LRV, obtained from its navigation system,
was recorded on the DSEA. Stereographic photos were used to obtain the
location of the starting point of the SEP experiment profiles to within
1 m. The LRV, with its navigation system, was used to mark straight, orthogonal
lines to be used as guides for deploying the transmitting antenna.
Deploying experiment:
The transmitting antenna was deployed ~100 m east of the LM on EVA
1. The cables were stored on reels until deployed. During the deployment
of the transmitter antennas, the two sets of dipoles were reversed from
the planned orientation (due to the reels being dropped), but this was
corrected in the data reduction process with no loss of data. Also, a problem
was encountered in keeping the solar panels open because of memory in the
panel wiring harness. The A-17 timeline allotted 21 minutes of coordinated
activity of both crewmen to deploy the transmitter in addition to the time
to drive to the site.
Check-out of experiment:
Calibration and synchronization pulses were transmitted.
Operation of experiment:
Nominal during EVA 1. During the rest period between EVA 1 and 2, however,
the temperature of the receiver increased. This was due to dust kicked
up by the LRV compounded by inadequate dust protection for the SEP radiators.
(The LRV had a broken fender on EVA 1, but it was repaired before the 2nd
EVA. The adhesive on the beta cloth cover for the radiator failed, allowing
dust onto the radiator. There was an earlier adhesive failure in the program,
but since that experiment was not scheduled for reflight no corrective
action was taken.) Overheating hampered the operation until the DSEA recorder
was removed in the middle of EVA 3 to prevent loss of data that had already
been recorded. Despite the efforts of the crew to control the temperature,
the receiver became too hot and was turned off by a thermally operated
switch. The transmitter operated nominally throughout the mission. Data
was obtained during EVA 2 on the traverses from the SEP transmitter site
toward station 2 and from station 4 towards the transmitter. Data was not
obtained during the early part of EVA 3 because the receiver switch was
in the standby position rather than "on" as requested by MCC.
Repairs to experiment:
See Operation for temperature control attempts.
The crew resolved the solar panel problem by taping the panel fully open.
Recovery/take-down of experiment:
Terminated at the end of EVA 3. The tape recorder was removed from
the receiver at station 9 and stowed under the LRV seat (for thermal protection)
until it was transferred into the equipment transfer bag and ultimately
into the LM cabin.
Stowing experiment for return:
The DSEA was returned to the LM in an equipment transfer bag and then
placed in storage locker A1L for ascent.
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
Navigating/recognizing landmarks:
The navigational information of the LRV was recorded in the DSEA tape
recorder. This included odometer pulses at 0.5 m increments, computed range
to the SEP transmitter in 100 m increments, and the computed bearing to
the SEP transmitter in 1 degree increments. The data is approximate because
of wheel slippage and was later improved by additional data on the LRV
location based on photographs, crew comments, and long baseline interferometry.
Were there any hazards in the experiment?
i.e. hazardous materials (explosive, radioactive, toxic), sharp
objects, high voltages, massive, bulky, tripping hazards, temperatures?:
No.
Was lighting a problem?: No.
Were the results visible to the crew?:
No. But the receiver did contain a thermometer that was visible to
the crew.
Would you recommend any design changes?:
None made by crew. Choice of adhesive for the beta cloth cover for
the radiator, or new radiator design, would be wise.
Were any special tools required?:
The LRV was used to align the antenna during deployment.
Was the orientation of the experiment (i.e. horizontal/vertical)
important? Difficult?
The transmitting antenna had one dipole oriented N-S, the other E-W.
It was especially important that the arms of the transmitting antenna were
laid out straight and at right angles to each other for analysis of the
data - see site selection.
Was the experiment successful?: Partially.
Were there related experiments on other flights?:
The Bistatic-Radar Investigation on A-14, 15, and 16, and the Lunar
Sounder Experiment of A-17, all orbital radar investigations and not included
in this database, were influenced by the dielectric constant of the regolith.
The Lunar Sounder Experiment penetrated deeper into the subsurface than
the SEP experiment.
Where was it stored during flight?: LM Quad III.
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?: No comments by crew.
Any experiences inside the LM of interest from the experiment/operations
viewpoint?:
No comments by crew.
References:
A-17 Preliminary Science Report
Apollo 17 Mission Report
Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TM X-58131, August, 1974, In JSC History Office.
Apollo 17 Final Lunar Surface Procedures, Vol. 1: Nominal Plans, MSC, 11/6/72.
Apollo 17 Technical Crew Debriefing, 4 January 1973, in JSC History Office.
Apollo Program Summary Report, section 3.2.17 Surface Electrical Properties Experiment, JCS-09423, April, 1975.
Apollo Stowage List - Apollo 17, MSC, 12 December 1972
Personal communication with Eric Jones, 3 August 1993.