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Lunar Dust Detector

NSSDCA ID: 1971-063C-09

Mission Name: Apollo 15 Lunar Module /ALSEP
Principal Investigator:Mr. James R. Bates

Description

The purpose of the Lunar Dust Detector Experiment (also referred to as the Dust, Thermal, and Radiation Engineering Measurements package, or DTREM) on the Apollo Lunar Surface Experiments Package (ALSEP) was to assess the long term effects of the lunar environment on silicon solar cells by measuring power output reduction caused by high-energy cosmic particle and ultraviolet radiation damage and dust accumulation, and to measure temperatures, including reflected infrared brightness temperatures in computing lunar surface temperatures. Two other objectives were to determine if pre-irradiation of the cells before deployment and irradiation on the lunar surface followed a simple superposition and if protective cover glass was necessary on the cells.

The DTREM had two components - a sensor package, which comprised a G-10 fiberglass box and solar cells with a mass of 0.159 kg, mounted on the top northwest corner of the central station sun shield, and a printed circuit board, 0.118 kg, located within the central station that interfaced with a preamplifier and the power distribution unit of the ALSEP data subsystem. The sensor package box was 3.63 cm wide, 3.17 cm deep and 4.08 cm high with 0.23 cm thick walls and 1.5 x 2.0 cm apertures in the two opposing narrower walls and the top. The top horizontal aperture was covered by a Kovar sheet. The east-facing aperture was covered by a fiberglass shield and the west-facing aperture was covered by a 3.17 x 2.44 x 0.09 cm fiberglass block which held the external temperature sensor, one of three temperature sensors (thermistors) mounted on the housing, the other two being mounted inside the box.

Three 10-ohm-cm n-on-p structure single-crystal silicon solar cells, each 1 x 2 cm, were mounted on the top horizontal Kovar sheet facing upwards. The power output of each cell varied from 0 to 150 mV. The first cell had a 0.15 mm thick blue filtered glass cover for protection against particles and ultraviolet radiation. The second cell had the same protective glass but was pre-irradiated on the ground with 10E15 electrons of 1 MeV energy. The third cell had no cover glass and was not pre-irradiated. The energy threshold for the covered cells was 175 keV electrons and 4.25 MeV protons and for the uncovered cell 173 keV electrons and 60 keV protons. The short-circuit current was measured by the voltage drop across a precision 1.00 ohm shunt resistor to determine the photovoltaic output. (The resistor was effectively a short-circuit due to the high resistivity of the solar cell.) Only one output quantity was measured per solar cell due to the constraint on telemetry channels.

The external temperature sensor was embedded in the west-facing fiberglass block, embedded 0.03 cm below the outer surface. It comprised a 1.52 cm square winding of a Tylan nickel wire resistor. This high-precision nickel resistance thermometer had a wide dynamic range (84 to 408 K). Nominally 5500 ohms at the ice point, it was connected through the ground and also through a 15000 ohm temperature insensitive precision dropping resistor to the 12 volt ALSEP power line. It was calibrated at three points, ice (273.2 K), steam (373.2 K) and carbon dioxide freezing (194.7 K) and had a drift of less than 0.1 K/yr. The detector was separated from the DTREM structure by 20 layers of aluminized polyester superinsulation film (approximately 0.19 cm) pierced by a pair of thermal isolator standoffs (a stack of 18 0.01 cm thick washers) and nylon bolts, making it a unique thermometer in its degree of isolation from the central station. Its purpose was to measure the reflected infrared surface brightness temperature of the lunar surface. The two internal sensors were also high-precision nickel resistance thermometers, one mounted beneath the Kovar mounting plate and solar cells and one on the inside of the west-facing vertical side of the housing. These measured the internal DTREM temperatures used to calibrate the solar cell output and to help compute lunar surface temperature.

Unlike most ALSEP data, which were sent back to Earth in an ALSEP telemetry stream, the DTREM data were sent back with the central station housekeeping ("Word 33") data. The DTREM would take a set of measurements, cycling through the six sensors, and transmit every 54.34 seconds. Data from this experiment consisted of the photovoltaic output of the solar cells and temperatures measured by the three thermistors (internal temperature, cell temperature, and external infrared temperature) as a function of time. The thermistors were powered by 12 volts dc from the central station and operated continuously, even when the DTREM preamplifiers were turned off. the solar cells generated their own voltages, but required power for signal amplification in the pre-amplifiers. The apparatus used 70 mW of power in "off" mode (to run the thermistors) and 540 mW in "on" mode.

The Dust Detector was originally designed to measure only dust accumulation but was expanded to include the particle, radiation, and temperature studies before the Apollo 11 mission. (The original dust accumulation design was flown on the Apollo 12 mission.) The expanded experiments were flown on the Apollo 11, 14, and 15 missions and were identical to each other except that the Apollo 14 and 15 experiments had a pre-irradiated cell covered by a 0.15 mm glass shield in place of the normal cell covered by 0.51 mm glass on Apollo 11.

The Dust Detector began operation with deployment of the ALSEP on July 31, 1971. The instrument was turned off when ALSEP operations were terminated on 30 September 1977. Performance of the equipment was nominal.

In general the irradiated cells showed a power drop of 1 percent per year and the nonirradiated cell 3.5 percent per year. The uncovered cell had a total power drop of about 16 percent in the first year before leveling off to a decline of roughly 5 percent per year. A major solar particle event in August 1972 caused a drop of approximately 7 percent in the uncovered cell.

Alternate Names

  • Apollo15ALSEP/DTREM
  • DTREM
  • Dust, Thermal, and Radiation Engineering Measurements Package
  • M515

Facts in Brief

Mass: 0.27 kg
Power (avg): 0.5 W

Funding Agency

  • NASA-Office of Space and Terrestrial Applications (United States)

Discipline

  • Planetary Science: Geology and Geophysics

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Brian J. O'BrienCo-InvestigatorDepartment of Environmental Protectionbrianjobrien@ozemail.com.au
Mr. James R. BatesPrincipal InvestigatorNASA Johnson Space Centerjbates@ems.jsc.nasa.gov

Selected References

  • Bates, J. R., and P. H. Fang, Some astronomical effects observed by solar cells from Apollo missions on lunar surface, Solar Energy Materials Solar Cells, 68, No. 1, 23-29, Apr. 2001.
  • Bates, J. R., and P. H. Fang, Results of solar cell performance on lunar base derived from Apollo missions, Solar Energy Materials Solar Cells, 26, No. 1-2, 79-84, Mar. 1992.

Related Information at NSSDCA

Image of EASEP

DTREM (in red circle) on ALSEP central station

Apollo 11 Dust Detector (DTREM) Experiment
Apollo 12 Dust Detector Experiment
Apollo 14 Dust Detector (DTREM) Experiment

Lunar Science
Moon Page

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