INSTRUMENT_HOST_DESC |
Instrument Host Overview
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The Apollo 14 Lunar Surface Experiments Package (ALSEP) was carried
on the Apollo 14 lunar module spacecraft. It contained scientific
experiments to be deployed and left on the lunar surface, and other
scientific and sample collection apparatus. The ALSEP central
station located at 3.6440 S latitude, 17.4775 W longitude
[DAVIES&COLVIN2000], was turned on at 17:23 UT on 5 February 1971 and
shut down along with the other ALSEP stations on 30 September 1977.
For more information, see the ALSEP termination report by Bates et.
al (1979) [BATESETAL1979].
ALSEP consisted of a set of scientific instruments emplaced near the
Apollo 14 landing site by the astronauts. The instruments were
arrayed around a central station which supplied power to run the
instruments and communications so data collected by the experiments
could be relayed to Earth. The central station was a 25 kg box with
a stowed volume of 34,800 cubic cm. Thermal control was achieved by
passive elements (insulation, reflectors, thermal coatings) as well
as power dissipation resistors and heaters. Communications with
Earth were achieved through a 58 cm long, 3.8 cm diameter modified
axial-helical antenna mounted on top of the central station and
pointed towards Earth by the astronauts. Transmitters, receivers,
data processors and multiplexers were housed within the central
station. Data collected from the instruments were converted into a
telemetry format and transmitted to Earth. The ALSEP system and
instruments were controlled by commands from Earth. The uplink
frequency for all Apollo mission ALSEP's was 2119 MHz, the downlink
frequency for the Apollo 14 ALSEP was 2279.5 MHz.
A radioisotope thermoelectric generator (RTG, SNAP-27 model) provided
the power to run the ALSEP operations. The generator consisted of a
46 cm high central cylinder and eight radiating rectangular fins with
a total tip-to-tip diameter of 40 cm. The central cylinder had a
thinner concentric inner cylinder inside, and the two cylinders were
attached along their surfaces by 442 spring-loaded lead-telluride
thermoelectric couples mounted radially along the length of the
cylinders. The generator assembly had a total mass of 17 kg. The
power source was an approximately 4 kg fuel capsule in the shape of a
long rod which contained plutonium-238 and was placed in the inner
cylinder of the RTG by the astronauts on deployment. Plutonium-238
decays with a half-life of 89.6 years and produces heat. This heat
would conduct from the inner cylinder to the outer via the
thermocouples which would convert the heat directly to electrical
power. Excess heat on the outer cylinder would be radiated to space
by the fins. The RTG produced approximately 70 W DC at 16 V. (63.5 W
after one year.) The electricity was routed through a cable to a
power conditioning unit and a power distribution unit in the central
station to supply the correct voltage and power to each instrument.
ALSEP Scientific Instruments
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All ALSEP instruments were deployed on the surface by the
astronauts and attached to the central station by cables. The
Apollo 14 ALSEP instruments consisted of: (1) a passive
seismometer, designed to measure seismic activity and physical
properties of the lunar crust and interior; (2) an active
seismometer to study the physical properties of lunar surface and
subsurface materials and the structure of the local near-surface
layers; (3) a suprathermal ion detector, designed to measure the
flux composition, energy, and velocity of low-energy positive ions;
(4) a charged particle lunar environment experiment, designed to
measure particle energies of solar protons and electrons that reach
the lunar surface; (5) a cold cathode ion gauge, designed to
measure the atmosphere and any variations with time or solar
activity such atmosphere may have; and (6) a lunar dust detector,
to measure dust accumulation, radiation damage to solar cells, and
reflected infrared energy and temperatures. See the Apollo 14
preliminary science report (1970) [APOLLO14A1971] for more information
about the ALSEP experiments.
This instrument host description was provided by the NSSDC.
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