Mars Global Surveyor Solar Panel Will Not Hinder Mission Goals

From: Jan Wee <>
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
>     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: