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The GALEX spacecraft FROM NASA PRESS KIT Posted: April 24, 2003
The basic satellite design is new, but shares elements in common with several satellites now under development by Orbital Sciences Corp. Much of the flight software is derived from software developed for NASA's Far Ultraviolet Spectroscopic Explorer and for Orbview 4, a commercial imaging satellite. Command and Data Handling Among tasks managed by the computer are Sun avoidance; deployment of the solar arrays; precision determination and control of the satellite's orientation (or "attitude"); thermal management; automated fault detection and correction; communication with the telescope instrument; and acquisition, storage and transmission of science data. A 24-gigabit solid-state recorder stores engineering data from the satellite and science instrument, and science data from the instrument. An uplink card operates independently of the onboard computer and is responsible for receiving, validating and decoding commands from the ground. Commands are routed to three paths for execution: special commands, normal command traffic and stored commands. Special commands operate independently of the onboard computer, thereby bypassing the processing associated with normal command traffic. Special commands are typically used for reconfiguration and/or hard resets for the command and data handling subsystem. They can also be used to place the satellite in a "safe" mode, if this is commanded from the ground. A downlink card is responsible for receiving telemetry data received from various spacecraft subsystems, the science instrument and the solid-state recorder, and preparing them for transmission to ground stations. Electrical Power Power is generated by 2.9 square meters (31.2 square feet) of gallium arsenide solar cells mounted on two fixed wings. Total area of the arrays is 3 square meters (32.2 square feet). Power is stored in a 15-amp-hour nickel-hydrogen battery. The battery can support spacecraft power needs for the 36 minutes of each orbit during which the Sun is eclipsed from the satellite. The power electronics suite consists of three boxes: the battery sensor electronics, the power module, and the power and thermal control electronics. The battery sensor electronics box conditions battery temperature and pressure, and controls battery heaters. The power module converts the voltage from the solar arrays to levels required by various devices on the spacecraft. The power and thermal control electronics box provides overall control of the power subsystem. Thermal Control To control battery temperature, the battery cells are connected to a dedicated radiator by heat-conducting sleeves. A thermal blanket is used to protect the cells from the space environment. Attitude Determination and Control Unlike some spacecraft, the Galaxy Evolution Explorer has no thrusters to adjust its orientation. Instead, it achieves this with four devices called reaction wheels, which use the momentum of spinning wheels to nudge the satellite in one direction or another. Occasionally the reaction wheels accumulate too much momentum, which requries the use of devices called torque bars -- somewhat like large electromagnets -- to push against Earth's magnetic field and cancel out some of the momentum in the wheels. The torque bars are controlled by a device called a magnetometer that senses the orientation of Earth's magnetic field. The satellite's orientation is sensed by a star tracker, while its rotation rates are sensed by gyroscopes. The star tracker is also used to correct slow drifts that occur in the gyroscopes' sensing circuits. Two Sun sensors provide a relatively coarse measure of the Sun's direction when the satellite is in safehold modes. Telecommunications |
Flight data file Vehicle: Pegasus XL Payload: GALEX Launch date: April 28, 2003 Launch window: 7:50-9:50 a.m. EDT (1150-1350 GMT) Mission staging site: Cape Canaveral, Florida Satellite broadcast: AMC 2, Transponder 9, C-band Pre-launch briefing Mission preview - Our story providing an overview of this launch. Launch timeline - Chart with times and descriptions of events to occur during the launch. GALEX spacecraft - A technical look at the Galaxy Evolution Explorer. Telescope - Description of the telescope at the heart of GALEX. Science goals - A look at the GALEX mission objectives. Galaxies - Article on why study how galaxies form. Pegasus XL rocket - Overview of this air-launched rocket. Pegasus directory - See our coverage of previous Pegasus rocket flights. Soviet Space For the first time ever available in the West. Rocket & Space Corporation Energia: a complete pictorial history of the Soviet/Russian Space Program from 1946 to the present day all in full color. Available from our store.U.S. - U.K. - E.U. - Worldwide Viking patch This embroidered mission patch celebrates NASA's Viking Project which reached the Red Planet in 1976.U.S. - U.K. - E.U. - Worldwide Apollo 7 DVD For 11 days the crew of Apollo 7 fought colds while they put the Apollo spacecraft through a workout, establishing confidence in the machine what would lead directly to the bold decision to send Apollo 8 to the moon just 2 months later.U.S. - U.K. - E.U. - Worldwide Gemini 12 Gemini 12: The NASA Mission Reports covers the voyage of James Lovell and Buzz Aldrin that capped the Gemini program's efforts to prove the technologies and techniques that would be needed for the Apollo Moon landings. Includes CD-ROM.U.S. - U.K. - E.U. - Worldwide Get e-mail updates Sign up for our NewsAlert service and have the latest news in astronomy and space e-mailed direct to your desktop (privacy note: your e-mail address will not be used for any other purpose). Mission Report Space Shuttle Flights 1-5: The NASA Mission Reports covers the shuttle through its test flight stage and on to the first operational flight. Includes CD-ROM.Apollo 11 special patch Special collectors' patch marking the 35th anniversary of the historic Apollo 11 moon landing is now available.U.S. - U.K. Gemini 7 Gemini 7: The NASA Mission Reports covers this 14-day mission by Borman and Lovell as they demonstrated some of the more essential facts of space flight. Includes CD-ROM.U.S. - U.K. - E.U. - Worldwide Apollo patches The Apollo Patch Collection: Includes all 12 Apollo mission patches plus the Apollo Program Patch. Save over 20% off the Individual price. U.S. - U.K. - E.U. - Worldwide Mars Rover mission patch A mission patch featuring NASA's Mars Exploration Rover is available from our online.U.S. - U.K. - E.U. - Worldwide Apollo 9 DVD On the road to the moon, the mission of Apollo 9 stands as an important gateway in experience and procedures. This 2-DVD collection presents the crucial mission on the voyage to the moon.U.S. - U.K. - E.U. - Worldwide |
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