| AODA - ATTITUDE AND ORBIT DETERMINATION AVIONICS |
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| The Attitude and Orbit Determination Avionics (AODA) system combines the functions of metrology, attitude determination, and orbit determination. AODA answers the questions: what is the length of the mast, which way are we pointing, and where are we?
AODA has to perform four major tasks: 1) prove that the mast is safely deployed, 2) help align the radar antennas so the beams overlap properly on the ground, 3) help improve shuttle attitude control system performance so the mast won't move around too much, and most importantly, 4) record mast length, shuttle attitude, and orbit data so the earth's land topography can be determined.
AODA consists of a "flight segment" and a "ground segment". The flight segment consists of all the sensors, electronics, computers, and software onboard the shuttle necessary for making measurements. The ground segment consists of all the computers, software, and other hardware needed to support mission operations and data processing.
Global Positioning System (GPS) |
| Orbit determination is provided by the Global Positioning System (GPS). For SRTM, two GPS receivers, developed as part of JPL's Space Receiver program, are connected to GPS antennas located on the outboard radar antenna. |
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Star Tracker Assembly (STA) and Inertial Reference Unit (IRU) |
| The orientation of SRTM has two primary components: the attitude relative to the stars and the relative motion of the outboard radar antenna. The attitude is measured by a Star Tracker Assembly (STA) from Lockheed Martin. The STA consists of a high-performance camera and computer with an onboard database containing a large star catalog. |
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The Inertial Reference Unit (IRU)
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| The Inertial Reference Unit (IRU), from Teledyne, measures attitude changes very precisely. The data from the STA and IRU are combined to get an "absolute fix" of the attitude with respect to the stars by the STA. Then the output of the IRU is used to propagate that attitude through time. |
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ASTROS Target Tracker (ATT) and Optical Target Assembly (OTA)
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| The ATT, located on the inboard antenna, will track three red Light Emitting Diode (LED) targets, called the Optical Target Assembly (OTA), located on the outboard antenna. These measurements will allow AODA to determine the outboard antenna's relative position. |
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Electronic Distance Meters (EDM) |
| Due to limitations in ATT accuracy along its line-of-sight, it was necessary to add additional instruments capable of directly measuring the baseline length (range to outboard antenna). Rather than develop a precision instrument, we took a novel approach and acquired a commercially available surveying rangefinder, known in the industry as an Electronic Distance Meter (EDM). The Leica-Wild DI2002 EDM actually exceeds our performance requirements. |
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| AODA Processing Computers (APC) |
| The AODA Processing Computers (APC) are the brains of AODA. Located in the Shuttle's crew cabin, these two IBM Thinkpad laptop computers will operate the ATT and EDM, guide antenna alignment, provide AODA status displays and command interfaces for the astronaut crew, and record the AODA data.
Some members of AODA team with the flight hardware, March 1999 (left-to-right): Gary Esparza (Integration & Test), Christian Liebe (ATT), Terry Wysocky (APC), John Waters, standing (SIU), Eldred Tubbs, sitting (EDMs), Ed Litty (Management), Riley Duren (System Engineering). The AODA Sensor Panel is above the group, mounted in place of an L-band panel on the face of the main antenna. The STA, IRU, ATT, and EDM are all mounted on this structure. |
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