Re: Mars Global Surveyor Solar Panel Will Not Hinder Mission Goals

Subject: Re: Mars Global Surveyor Solar Panel Will Not Hinder Mission Goals
Date: Thu, 28 Nov 1996 07:50:34 -0800

Dear Jan,   THnaks for alerting us to this news release.  Since I dont' 
watch TV (CNN probably had the pictures already), I was imagining a one 
sided GS spining helplessly around Mars.  Now I see it's actually just a 
couple of inches out of alignment.  PHEW!  That's easy to work around.  I'll 
share this with my class on Monday.  Hope you have/had a nice Thanksgiving!  

On 11/27/96 14:54:56 you wrote:
>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: