From: George Zack <zack@indra.com>
Subject: Mars Global Surveyor to Aerobrake in Modified Configuration
Date: Wed, 30 Apr 1997 17:39:22 +0100
>Date: Wed, 30 Apr 1997 12:45:46 -0400 (EDT) >From: NASANews@hq.nasa.gov >Subject: Mars Global Surveyor to Aerobrake in Modified Configuration >Sender: owner-press-release@spinoza.hq.nasa.gov >To: undisclosed-recipients:;@spinoza.hq.nasa.gov > >Douglas Isbell >Headquarters, Washington, DC April 30, 1997 >(Phone: 202/358-1753) > >Diane Ainsworth >Jet Propulsion Laboratory, Pasadena, CA >(Phone: 818/354-5011) > > >RELEASE: 97-85 > >MARS GLOBAL SURVEYOR TO >AEROBRAKE IN MODIFIED CONFIGURATION > > NASA's Mars Global Surveyor spacecraft can safely >and successfully aerobrake into its final orbit around >Mars this fall with its one partially deployed solar >panel in a modified configuration, mission managers >have decided. > > No special maneuvers will be conducted to attempt >to force the array to latch, and the focus of the >Surveyor engineering team now will turn to minor >modifications to the critical aerobraking phase that >will circularize the spacecraft's orbit for the >beginning of two years of science operations. > > "After careful analysis of the situation, we've >determined that the solar panel on Mars Global >Surveyor that is not fully deployed presents very >little risk to the mission," said Glenn E. Cunningham, >Mars Global Surveyor project manager at NASA's Jet >Propulsion Laboratory (JPL), Pasadena, CA. > > The decision by NASA's flight team at JPL and its >partners at Lockheed Martin Astronautics, Denver, CO, >was reached after several months of extensive analysis >of spacecraft data, ground-based computer simulations >and a series of very slight spacecraft maneuvers that >were carried out in January and February to >characterize the situation. > > "Thanks to an early launch that gave us an >advantageous trajectory, we will not have to aerobrake >into the Martian atmosphere as fast as we had >originally planned to reach the mapping orbit, and >that will reduce the amount of heating that the solar >panels undergo during this gradual descent," >Cunningham explained. > > "We will rotate the solar-cell side of the panel >that is not fully deployed by 180 degrees, so that it >faces into the direction of the air flow that exerts >drag force on the spacecraft as it dips repeatedly >into the atmosphere," he said. "This way, the >unlatched panel will not be in danger of folding up >onto the spacecraft's main structure, nor will the >panel be at any greater risk of heating up too much." > > The solar panel in question is one of two 11-foot >wings that were unfolded shortly after Surveyor's Nov. >7, 1996, launch from Cape Canaveral Air Station, FL. >Data suggest that a piece of metal called the "damper >arm," which is part of the solar array deployment >mechanism located at the "elbow" joint where the >entire panel is attached to the spacecraft body, >probably was sheared off during deployment in the >first day of flight. The lever that turns the shaft >became wedged in a two-inch space between the shoulder >joint and the edge of the solar panel, leaving the >panel tilted at 20.5 degrees from its fully deployed >and latched position. > > Although the situation was never considered a >serious threat to accomplishing the science objectives >of the mission, the tilted array caused the >JPL/Lockheed Martin flight team to re-evaluate the >aerobraking phase, in which the spacecraft must rely >almost solely on its solar panels for the drag needed >to lower it into a nearly circular mapping orbit over >the poles of the planet. This phase of the mission >will begin a week after Mars Global Surveyor is >captured in orbit around Mars on Sept. 11, and will >last approximately four months. > > Aerobraking was first tested in the final days of >the Magellan mission to Venus in October 1994. The >technique is an innovative method of braking which >allows a spacecraft to carry less fuel to a planet and >take advantage of the planet's atmospheric drag to >descend into a low-altitude orbit. > > Mars Global Surveyor will use an aerobraking >phase much like that used to circularize Magellan's >orbit. The solar wings -- which feature a Kapton flap >at the tip of each wing for added drag -- supply most >of the surface area that will slow the spacecraft by a >total of more than 2,684 miles per hour during the >four-month phase. Surveyor's orbit around Mars will >shrink during this phase from an initial, highly >elliptical orbit of 45 hours to a nearly circular >orbit taking less than two hours to complete. > > Engineers determined that the deployment springs >currently holding the tilted solar panel in its nearly >deployed position will not be strong enough to >withstand the forces of aerobraking. To solve that >problem, they designed a new configuration in which >the tilted solar panel, along with the deployment >springs, will be rotated 180 degrees, using a motor- >driven inner gimbal actuator, and held in position >with force applied by an outer gimbal actuator. >Sequencing software will be modified to turn the >gimbal actuators on before each closest approach to >the planet and off at the conclusion of each drag >pass. > > As a consequence of the new aerobraking >configuration, the more sensitive cell-side of the >unlatched wing will be exposed directly to the wind >flow of atmospheric entry, requiring that aerobraking >be done in a more gradual, gentle manner. Ground >tests have demonstrated that the unlatched solar panel >will have more than adequate thermal margin to >withstand additional heating as the spacecraft >circularizes its orbit for the beginning of science >mapping in March 1998. > > Meanwhile, Mars Global Surveyor continues to >perform very well on its arcing flight path toward the >red planet and its arrival in orbit. A third, very >minor trajectory correction maneuver, planned for >April 21, was deemed unnecessary and canceled. In >addition, science instrument calibrations continue to >go well, and plans are being prepared to take an >approach image of Mars a few days before the July 4 >landing of Mars Pathfinder, which passed Mars Global >Surveyor enroute to Mars on March 14, 1997. > > 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- > ------------------------------------------------------------- George Zack Gilpin County School District RE-1 MS/HS Science Educator Home of the Eagles /Elevation: 9200' AMSL zack@indra.com 10595 Highway 119, Black Hawk CO 80403 303-582-3444 ext 353 http://indra.net/~zack/academics/science/scicenter.html