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FIELD JOURNAL FIELD JOURNAL FIELD JOURNAL FIELD JOURNAL

Blowing in the Wind

by Greg Wilson

December 9, 1996

The last couple of years, since coming to NASA's Ames Research Center and Arizona State University, I have been working with Dr. Rob Sullivan on the Mars Pathfinder Windsocks. These little aluminum cones and counterweights are connected to a strut by a gimbal-joint, allowing both vertical and horizontal movement. Three of these assemblies are attached at different heights above the surface to the meteorological mast on Mars Pathfinder. When in operation on the surface of Mars later next year, the Martian winds will blow on these windsocks and cause them to deflect. These deflections will be recorded by the Imager for Mars Pathfinder (IMP) and sent back to Earth. It is anticipated that the wind speed will be slowest near the surface and increase with height. The way the wind speed varies with height can tell us a lot about the interaction of the atmosphere and the surface.

How I got involved in all of this was that each of these windsocks is slightly different and needed to be calibrated under Martian conditions in the Mars Surface Wind Tunnel here at Ames. Rob, who also works at Arizona State University in Tempe, AZ, came out to Ames numerous times to test different windsock configurations under both Earth and Martian conditions. Sometimes these tests would go on almost 24 hours per day! With the final configuration and calibration complete, we sent the windsocks down to the Jet Propulsion Laboratory for further testing and integration with the spacecraft.

A couple weeks later the phone rang and it was Rob. "Greg, we have a problem 55 seconds into the final 60-second shake test at JPL. The #2 windsock failed. We have three weeks to solve the problem, calibrate, and get them to JPL or we are off the spacecraft." This began the longest and hardest three weeks of my life. At one point Rob and I logged over 100 hours of wind-tunnel operation during a six-day period. Needless to say, we have been close friends ever since.

So you can imagine how I felt last week when the Delta II rocket carrying Mars Pathfinder (and the windsocks) lifted off! Rob and I, along with other project scientists and some cool teachers from Idaho and Washington spent the early hours of Tuesday and Wednesday morning at Jetty Park, which is about 1.5 miles south of the launch pad. We all had a great time both nights, although, the night of the launch we were thinking about some teachers who had to miss it. The launch was awesome! At one point in the trajectory, the rocket was heading toward the Moon, and just above it to the north was Mars! After the rocket was out of sight, we went back to our hotel rooms and waited to hear word that the spacecraft was in communication with the Deep Space Network.

While at the Cape, I attended the ninth Pathfinder Project Science Group meeting. At these meetings we talk about current status of scientific experiments and planning for the landed phase of the mission. Obviously everything on the spacecraft was ready to go, but many more operational issues/problems still needed to be worked through. During the first operational readiness test, a few computer problems were encountered. For example, the computer reset right before lander separation. In the simulation, the reset resulted in the lander not separating, the heat shield not coming off, parachutes not opening, etc. And while this is a serious problem, a senior project scientist commented that the maneuver was called "litho-braking" with the analogy to Mars Global Surveyor's "aerobraking" as a way of slowing down when getting to Mars. Everyone got a good laugh out of it, which should give you the idea that we all like to have fun even though the work we do is very serious. Reset assured that every detail is being looked into.

Back at the Mars Wind Tunnel, we are reducing the data for the sand dune experiment. The results look very interesting and will be presented at the Lunar and Planetary Science Conference in Houston, Texas in March 1997. I have also been trying to figure out why during a dust storm, large particles get charged positive and small ones negative. Very interesting.

Future work involving the windsocks will be and "end-to-end" test where we will take a mast mock-up and the flight-spare windsocks out into the desert somewhere and take images of it just like IMP will do on Mars. At the same time we will take wind velocity measurements from a 10-meter tower. We will take this data home, convert windsock deflection images into wind speed and direction measurements and compare it with the 10-meter tower data.

On the personal side, nothing new is really happening. I just want to say "Hi" to all my new teacher friends in Idaho and Washington and wish everyone a happy holiday season and a great new year!


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