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NEAR Laser Rangefinder (NLR)

NSSDCA ID: 1996-008A-04

Mission Name: NEAR Shoemaker
Principal Investigator:Dr. Maria T. Zuber

Description

The NEAR Laser Rangefinder (NLR) system is an incoherent, direct detection laser ranger and is part of the engineering subsystem primarily used for spacecraft navigation. It will also be used as a laser altimeter to determine the range to points on the surface and hence the shape of the asteroid. It is mounted in a fixed position on the instrument deck of the spacecraft. The NLR operates by transmitting a laser pulse to the surface of the asteroid, receiving the reflection of the pulse from the surface, and recording the round-trip travel time, giving the distance. The primary scientific objectives of the instrument are to determine the size, bulk shape, and surface topography of the asteroid 433 Eros. This information will be combined with data from the multispectral imager and the radio science experiment to study the asteroid's internal structure, bulk composition, and geologic and cratering history.

The NLR is a bistatic system, composed of a separate transmitter and receiver. The transmitter consists of a diode pumped, neodymium doped yttrium-aluminum-garnet (Nd:YAG) laser. The laser wavelength is 1.064 micrometers with a divergence of 235 microradians and a pulse energy of 15 milliJoules. The pulse duration is 12 nanoseconds and the frequency is commandable among 0.125, 1, 2, and 8 Hz. The receiver consists of a reflecting telescope bore-sighted with the multispectral imager. The telescope has a baffle/door aperture, and focuses onto an enhanced hybrid silicon avalanche photodiode detector. The receiver aperture is 8.9 cm. The detection threshold is commandable to eight different settings. There are two commandable range gates.

The NLR is controlled by a rad-hardened microprocessor with Mil-Std 1553 bus standard interface. Round trip timing is done by a custom gallium arsenide time-of-flight chip. The instrument is designed for measurements within 50 km for low albedo, diffusely reflecting surfaces and has an accuracy requirement of 6 m. The range quantization level is 31 cm. NLR acquisition of the asteroid should occur at about 150 km. Peak operating power is 20.7 W. Data rates are commandable between 6.4 and 51 bps. The NLR also has an in-flight calibration mechanism consisting of a 100 m long spool of optical fiber. A small portion of each laser pulse is sent through the spool, emitted at the other end, and detected by the receiver to provide a continuous end-to-end calibration of the timing.

Alternate Names

  • NEARShoemaker/NLR
  • NLR

Facts in Brief

Mass: 5 kg
Power (avg): 16.5 W
Bit rate (avg): 51 kbps

Funding Agency

  • National Aeronautics and Space Administration 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. Maria T. ZuberTeam LeaderNASA Goddard Space Flight Centerzuber@tharsis.gsfc.nasa.gov

Selected References

  • Cole, T. D., et al., The NEAR-Earth Asteroid Rendezvous laser altimeter , Space Sci. Rev., 82, No. 1-2, 217-253, 1997.
  • Zuber, M. T., et al., The NEAR laser ranging investigation, J. Geophys. Res., 102, No. E10, 23761-23773, Oct. 1997.
  • Cole, T. D., et al., The Laser Rangefinder on the Near Earth Asteroid Rendezvous spacecraft, Acta Astronautica, 39, No. 1-4, 303-313, 1996.
  • Cheng, A. F., et al., In-flight calibration of the Near Earth Asteroid Rendezvous Laser Rangefinder, Icarus, 148, No. 1, 572-586, Jan. 2000.
  • Cheng, A. F., et al., Small-scale topography of 433 Eros from laser altimetry and imaging, Icarus, 155, No. 1, 51-74, Jan. 2002.
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