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FIELD JOURNAL FIELD JOURNAL FIELD JOURNAL FIELD JOURNAL

Equipment Tests on the Lander

by Guy Beutelschies

Week of September 2, 1996

We finished up our tests on the equipment underneath the thermal enclosure. One of the activities was to install a fresh silver zinc battery. This was a potentially dangerous operation because the battery is very powerful. If someone accidentally touched the pins on the power connector, it would release enough current to injure or even kill them. This is similar to touching a live wire in your house without the protection of fuses or circuit breakers. We also tested the telecommunications equipment. This is used to receive commands and send down data from the spacecraft after we launch. A bunch of us went out on Friday night and ended up at a restaurant that had Karaoke singing. If you've never heard a bunch of engineers singing, you're lucky. We went waterskiing the next day.

Week of September 9

The mechanics put the thermal enclosure back on and mounted the high-gain antenna and the camera on top of it. We then started our tests to make sure that those devices work as expected. The high-gain antenna actually moves to point at Earth. We moved it through its entire range of motion to see if it would hit any part of the lander. Turned out it did! One of the engineers did not take into account how far a particular screw head came out from a nearby bracket. The antenna would have just grazed the top of the screw, which would have messed up the pointing. We did a quick analysis on the screw and determined that we could remove a small amount of material from it without affecting how it holds the bracket in place. So we got a file and filed down the screw just enough so the antenna would not hit it.

Another test we did was to make sure that when we pointed the camera and the antenna, they actually pointed to where we specified. To do that we sent commands to point them in a certain direction and then used a set of instruments called theodolites. These are basically small telescopes that give very accurate information about where they are pointed. They are often used by surveyors that you see out on the city streets. We pointed the theodolites at several points on the lander to determine a reference coordinate system. We then pointed the theodolites at several marks on the surface of the antenna, which told us where the antenna was pointed relative to the rest of the lander. We will use this information to make sure that the antenna points at Earth when the lander is sitting on Mars.

We repeated this procedure on the camera so that we know exactly where the camera is pointing relative to the commands we gave it. This information will be used to determine where objects (like rocks) inside an image are located in relation to the lander. The rover people are very interested in this information because they plan on using those pictures to tell the rover where interesting rocks are located and how to get to them.

The mechanics then connected the petals to the lander. That allowed us to run tests on the equipment located on the petals. The first test was to shine light on the solar arrays to make sure that they were hooked up correctly. We made sure that they were indeed providing power to the rest of the lander. We then put the opaque covers back on to make sure that the lander did not turn on when we weren't expecting it.

Another test we ran was to verify the atmospheric structures instrument mast. This mast lies flat against the petal on the way to Mars and then pops up once we are on the surface. It has temperature sensors to tell us what the temperature is at points from right next to the ground up to about four feet above the ground. It also has a wind sensor on the top of it to tell us wind speed and direction. The atmospheric structures instrument also has a pressure sensor located on the base petal. This will track the pressure changes like a barometer to see how it changes during the day.

We also verified that the radar altimeter was working correctly. This device is used as we are descending through the atmosphere to tell us when we are about to hit the ground. It signals the airbags to inflate to cushion our landing.

Part of our week was taken up by hurricane preparations. Hurricane Fran was heading right toward us so we made plans to evacuate. The hurricane turned north and missed us at the last minute.

That weekend, a couple of us played in a mud volleyball tournament in a nearby town to benefit the March of Dimes. They basically dug several pits and filled them with water, which soon turned into mud. We didn't win.

Week of September 16

We were now ready to close the petals so that we can install the airbags. Before we did this, we wanted to do a full inspection to make sure that everything was ready. We even called down experts from the Jet Propulsion Laboratory to help us. We all went into the cleanroom and stood around the lander, looking at each piece of it very closely. We found a couple wires on the bridle (which connects the lander to the backshell) were too close to part of the lander structure. We were worried that during launch these wires could be broken by rubbing against that structure. This is bad because those wires carry the signal to fire the retro-rockets, which slow us down right before we hit the surface. We spent a couple of days rerouting those wires.

We got to see a shuttle launch. It was at 4:00 in the morning so we had to get up real early. It was worth it, though. The ground rumbled and the sky lit up like it was day.

Several of us went on a charity 5K run for cancer research in Orlando, which is about an hour from Kennedy Space Center. It was raining so we didn't break any records. We also tried surfing over the weekend. The waves were too weak for any long rides but it was fun anyway.

Week of September 23

The mechanical team installed the airbags, which took most of the week. All the electrical team had to do was to open and close the petals whenever the mechanics asked. This gave us a chance to test out the actuators used to move the petals, and the airbag retraction actuators, which are used to pull the airbags close to the lander after they are deflated.

We went on another 5K run, this time right at Kennedy Space Center. The race was run right on the runway that the shuttle lands on. Luckily, no shuttles landed during the race.


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