|
||||
|
|
||||
|
|
||||
|
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. 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. - E.U. - Worldwide Inside Apollo mission control
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.U.S. The ultimate Apollo 11 DVD This exceptional chronicle of the historic Apollo 11 lunar landing mission features new digital transfers of film and television coverage unmatched by any other.U.S. - U.K. - E.U. - Worldwide Next ISS crew
Own a little piece of history with this official patch for the International Space Station's Expedition 11 crew. We'll ship yours today!U.S. 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). Creating Space Creating Space groups together the history, the vehicles and the models into logical and meaningful categories. This book is equally valuable to space enthusiasts, modellers, and space historians.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. 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. - E.U. - Worldwide Inside Apollo mission control
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.U.S. The ultimate Apollo 11 DVD This exceptional chronicle of the historic Apollo 11 lunar landing mission features new digital transfers of film and television coverage unmatched by any other.U.S. - U.K. - E.U. - Worldwide Next ISS crew
Own a little piece of history with this official patch for the International Space Station's Expedition 11 crew. We'll ship yours today!U.S. |
||||
|
MISSION STATUS CENTER INDEX | PLUS | NEWS ARCHIVE | LAUNCH SCHEDULE ASTRONOMY NOW | STORE ADVERTISE © 2008 Pole Star Publications Ltd |
|||||