NEAR![]()
The Near Earth Asteroid Rendezvous (NEAR) mission was the first launch in the
Discovery Program, a NASA initiative for small planetary missions with a maximum
3-year development cycle and a cost capped at $150 million for construction,
launch, and 30 days of operation. The NEAR mission was managed for NASA by the
Johns Hopkins University
Applied Physics Laboratory , Laurel, Maryland. |
XGRS General | Mass: 26.90 kg |
---|---|
Power: 24 W (including DPU) | |
X-ray Fluorescence Spectrometer | Detectors: 3 gas-filled proportional counters;
25-cm2 active aperture area;
25-mm beryllium window, uniformity ~ ±5% ;
Beryllium liner and window support |
Energy range: 1 to 10 keV; Rise-time discrimination to reduce background contamination | |
Energy resolution: <1 keV FWHM @ 5.95 keV | |
In-flight calibration sources: 55Fe | |
Counting rate: Full performance up to 10 kHz | |
X-Ray Solar Monitors | Gas-filled proportional counter with graded shield (resolution <1 keV FWHM @5.95 keV) and solid-state high-resolution solar monitor (resolution <600 eV FWHM @ 5.95 keV). |
Gamma-Ray Spectrometer | Energy range: 0.3 to 10 MeV in 10-keV channels |
Prime detector: 2.5 x 7.5 cm NaI (Tl) scintillator; 8.5% FWHM min resolution @ 662 keV FOV ~ 60° | |
Shield detector: 8.9 x 14 cm BGO scintillator cup shield; 15% FWHM min resolution @ 662 keV | |
Counting rate: Full performance up to 10 kHz |
The X-ray fluorescence experiment used three gas-filled proportional counters, collimated to 5 degrees, observing X-ray line emissions from the asteroid. Balanced filters on two detectors (Al on one and Mg on the other) were used to separate Mg, Al, and Si lines; Ca, Ti, and Fe lines are resolved. The solar monitor used an additional gas-filled proportional counter with a pinhole active area observing the X-ray spectrum of the Sun. A high-resolution, solid-state solar monitor could be alternatively selected.
The gamma-ray spectrometer used a body-mounted NaI scintillator with BGO shield. This unique design eliminated the need for both a long boom and active cooling. This subsystem of the XGRS detected naturally radioactive elements-K, Th, U-by their gamma rays and those of their decay chain products. In addition, it could detect other elements-Fe, Si, O, H-by gamma rays produced by cosmic ray interactions. The gamma rays of interest are typically between 0.2 and 10 MeV.
Page authors: Lorella Angelini Jesse Allen
HEASARC Home | Observatories | Archive | Calibration | Software | Tools | Students/Teachers/Public
Last modified: Wednesday, 29-Jan-2014 14:07:17 EST