Glossary of terms related to the NEAR mission
- ACS
- Attitude Control System
- AEC
- Automatic Exposure Control
- AGC
- Automatic Gain Control
- AIU
- Attitude Interface Units. There are two computers used for handling spacecraft commands, one of which is used (mainly for redundancy, in case one fails, there is a backup). There are also two Attitude Interface Units; they link the flight computer to the attitude (spacecraft pointing) control system, which includes gyroscopes, a star camera, accelerometers (for measuring how fast the spacecraft moves and turns in each direction) and the spacecraft thrusters.
- AOS
- Acquisition of Signal
- APL
- The Applied Physics Laboratory in Laurel, Maryland. Part of the Johns Hopkins University. NEAR was built and managed by APL.
- AU
- Astronomical Unit, the average distance from the Earth to the Sun. 149,597,870 km (92,955,808 miles). Astronomical Units are a common unit used for distances in solar system.
- BGO
- Bismuth Germanate
- Bi-propellant
- Oxidizer and fuel, for NEAR these are Nitrogen Tetroxide, N2O4, and Hydrazine, N2H4, which are self-igniting when mixed.
- BPS
- Bits per Second
- C&DH
- Command and Data Handling
- CDU
- Command Detector Unit
- CRC
- Cyclic Redundancy Code
- DPU
- Data Processing Unit
- DSM
- Deep Space Maneuver.
- DSN
- Deep Space Network, the JPL-administered network of interplanetary tracking stations in Goldstone, Calif.; Madrid, Spain; and Canberra, Australia. 34 meter is the diameter of the radio antenna used. "high gain" means that NEAR's 1-meter high-gain antenna is pointed at the Earth and used for the communication.
- ESB
- Earth Swingby, 23 Jan 98
- Earth Safe Mode
- In Earth Safe Mode, the spacecraft is placed in a power safe configuration with an emergency mode downlink. The solar panels are pointed directly at the Sun, and the medium gain antenna is placed on the Earth. The underlying assumption in Earth Safe Mode is that the Guidance & Control subsystem retains knowledge of the location of the Earth, and that the telecommunications subsystem is operational.
- EEPROM
- Electronically-Erasable Programmable Read-Only Memory
- Eros
- An asteroid which is the destination of the NEAR spacecraft. Eros is one of the Near-Earth asteroids.
- FC
- Flight Computer. NEAR has 2 flight computers.
- G&C
- Guidance and Control
- GSFC
- NASA/Goddard Space Flight Center
- HGA
- High Gain Antenna. This is the dish antenna on the NEAR spacecraft.
- HVPS
- High Voltage Power Supply
- IMU
- Inertial Measurement Unit
- JPL
- Jet Propulsion Laboratory, in Pasadena, CA.
- LGA
- Low Gain Antenna
- LHC
- Left hand Circular
- LOS
- Loss of Signal
- LSW
- Least Significant Word
- LVA
- Large Velocity Adjustment, as in LVA thruster.
- LVS
- Low Bus Sense (Voltage)
- MAG
- Magnetometer. One of the instruments on NEAR.
- MET
- Mission Elapsed Time. Used to schedule or time-tag mission events. MET starts at 1996 Feb 16 13:54:08.337 UTC. That is on the day before the launch, which occurred at 1996 Feb 17 20:43:26 UTC. (see Time for systems of time). Here is a JavaScript NEAR MET calculator.
- MGA
- Medium-Gain Antenna (Fan Beam)
- MOC
- Mission Operations Center. People, processes, and facilities for planning, control, and assessment necessary for conducting the mission.
- MOPS
- Mission Operations. Acitivites of the MOC.
- Monopropellant
- Single component propellant. On NEAR this is Hydrazine and is used for the smaller thrusters.
- MSI
- MultiSpectral Imager (the main camera). One of the instruments on NEAR.
- MSW
- Most Significant Word
- NEAR
- The Near Earth Asteroid Rendezvous spacecraft, the first spacecraft launched in NASA's Discovery Program of low-cost, small-scale planetary missions.
- Near-Earth asteroid
- Most known asteroids are found between the orbits of Mars and Jupiter, within the so-called main belt. A few asteroids venture outside of the main belt, and some approach to within 120 million miles of the Sun. Earth is 93 million miles, or 1 AU (Astronomical Unit), from the Sun. The asteroids that come within 1.3 AU of the Sun are called Near-Earth asteroids because they come very close to Earth's orbit.
- NIS
- Near-Infrared Spectrometer . One of the instruments on NEAR.
- NLR
- NEAR Laser Rangefinder. One of the instruments on NEAR.
- NTO
- Nitrogen Tetroxide (N2O4), a propellant gas
- OpNav
- OpNav stands for Optical Navigation, and means that images are obtained of Eros against the star background. These are measured (just like plates of asteroids and stars are measured to update asteroidal occultation predictions) to help determine where NEAR is relative to Eros, that is, to help navigate the spacecraft (since these observations are used in the overall orbit determination, based also on measurement of NEAR's radio signals, which is then used to plan thrusting maneuvers to target NEAR to Eros).
- PRF
- Pulse Repetition Frequency
- PRI
- Pulse Repetition Interval
- RHC
- Right Hand Circular
- RS
- Radio Science. NEAR's radio transponder is used for navigation and science.
- R/T
- Real-Time
- RWA
- Reaction Wheel Assembly
- S/A
- Solar Array
- S/C
- Spacecraft
- SDC
- Science Data Center. Stores science data received from the spacecraft and provides retrieval and analysis software for the science teams.
- SPICE
- A means for providing ancillary observation geometry data and related tools used in the planning and interpretation of science instrument observations returned from planetary spacecraft. For more details see http://pds.jpl.nasa.gov/naif.html
- SSR
- Solid State Recorder, used for storing data before it is transmitted back to Earth. NEAR has 2 SSRs.
- ST
- Star Tracker
- Sun Safe Mode
- In Sun Safe Mode, the spacecraft is placed in a power safe configuration with an unmodulated carrier downlink. The solar panels are pointed directly at the Sun, and the spacecraft is rotated to sweep the fan beam antenna through the hemisphere facing the Sun and Earth. Every 10 hours, redundant components of the telecommunications subsystem are exercised.
- TCM
- Trajectory Correction Maneuver. TCM-18 means it's the 18th trajectory correction maneuver that we have planned since NEAR was launched.
- Time
- Systems of Time are discussed at http://tycho.usno.navy.mil/systime.html
- XGRS
- X-ray/Gamma-Ray Spectrometer. One of the instruments on NEAR.
