From: Jan Wee <jwee@mail.arc.nasa.gov>
Subject: Mars Global Surveyor Solar Panel Will Not Hinder Mission Goals
Date: Wed, 27 Nov 1996 14:54:56 -0600
Dear discuss-lfm members, FYI -- news about the MGS Solar Panel! Jan Wee >Subject: Mars Global Surveyor Solar Panel Will Not Hinder Mission Goals > >Douglas Isbell November 27, 1996 >Headquarters, Washington, DC >(Phone: 202/358-1753) > >Diane Ainsworth >Jet Propulsion Laboratory, Pasadena, CA >(Phone: 818/354-5011) > >RELEASE: 96-250 > >MARS GLOBAL SURVEYOR SOLAR PANEL WILL NOT HINDER MISSION GOALS > > Mission engineers studying a solar array on NASA's Mars >Global Surveyor that did not fully deploy during the >spacecraft's first day in space have concluded that the >situation will not significantly impair Surveyor's ability to >aerobrake into its mapping orbit, or affect its performance >during the cruise and science portions of the mission. > > The solar panel under analysis is one of two 11-foot >(3.5-meter) wings that were unfolded shortly after the Nov. 7 >launch and are used to power Global Surveyor. Currently, the >so-called -Y direction array is tilted 20.5 degrees away from >its fully deployed and latched position. > > "After extensive investigation with our industry >partner, Lockheed Martin Astronautics, using a variety of >computer-simulated models and engineering tests, we believe >the tilted array poses no extreme threat to the mission," >said Glenn Cunningham, Mars Global Surveyor project manager >at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "We >plan to carry out some activities in the next couple of >months using the spacecraft's electrically driven solar array >positioning actuators to try to gently manipulate the array >so that it drops into place. Even if we are not able to >fully deploy the array, we can orient it during aerobraking >so that the panel will not be a significant problem." > > Diagnosis of the solar array position emerged from two >weeks of spacecraft telemetry and Global Surveyor's picture- >perfect performance during the first trajectory maneuver, >which was conducted on Nov. 21. The 43-second burn achieved >a change in spacecraft velocity of about 60 miles per hour >(27 meters per second), just as expected. The burn was >performed to move the spacecraft on a track more directly >aimed toward Mars, since it was launched at a slight angle to >prevent its Delta third-stage booster from following a >trajectory that would collide with the planet. > > Both the telemetry data and ground-based computer models >indicate that a piece of metal called the "damper arm," which >is part of the solar array deployment mechanism at the joint >where the entire panel is attached to the spacecraft, >probably broke during the panel's initial rotation and was >trapped in the two inch space between the shoulder joint and >the edge of the solar panel, Cunningham said. > > Engineers at JPL and Lockheed Martin Astronautics, >Denver, CO, are working to develop a process to clear the >obstruction by gently moving the solar panel. The damper arm >connects the panel to a device called the "rate damper," >which functions in much the same way as the hydraulic closer >on a screen door acts to limit the speed at which the door >closes. In Global Surveyor's case, the rate damper was used >to slow the motion of the solar panel as it unfolded from its >stowed position. > > Engineers have been re-evaluating the aerobraking phase >of the Global Surveyor mission, which begins in September >1997 after the spacecraft is captured into an elongated orbit >around the planet using its on-board rocket engine. The >solar arrays are essential to the aerobraking technique and >will be used to drag the spacecraft into its final, circular >mapping orbit. First tested on the Magellan spacecraft at >Venus, aerobraking allows the spacecraft to carry less fuel >to a planet and take advantage of its atmospheric drag to >gradually lower itself into the correct orbit. > > "Since we launched early in our window of opportunity, >we will not have to aerobrake as fast to reach the mapping >orbit, and this reduces the amount of heating that the solar >panels are exposed to," Cunningham said. "In the event that >our efforts to latch the solar array properly in place are >not successful, this reduced heating should allow us to tilt >the array in such a way to prevent it from folding up and yet >still provide enough useful aerobraking force." Additional >analysis and testing will be performed over the next several >months to verify this hypothesis. > > Meanwhile, Mars Global Surveyor continues to perform >very well as it completes its first two weeks in space, with >on-going science instrument calibrations being performed this >week. At the same time, the Mars Relay radio transmitter has >been turned on for a post-launch checkout. Radio amateurs >around the world are gearing up to participate in a radio >tracking experiment in which they will become receiving >stations for the low-power beacon signal transmitted by the >Mars Relay radio system. > > Mars Global Surveyor is approximately 3.4 million miles >(5.5 million kilometers) from Earth today, traveling at a >speed of about 74,000 miles per hour (119,000 kilometers per >hour) with respect to the Sun. > > Mars Global Surveyor is the first mission in a sustained >program of robotic exploration of Mars, managed by JPL for >NASA's Office of Space Science, Washington, DC. > > -end- > >Note to Editors: A line-drawing of Mars Global Surveyor >showing the current position of the solar panel in its fully >deployed position, including a blow-up which shows the area >in which the broken deployment mechanism is located, can be >found under "News Flashes" on JPL's World Wide Web home page >using the following URL: http://www.jpl.nasa.gov > >