PART 2: Challenge Question #1: an answer to Martian baseball
PART 3: Challenge Question #2: unimpressive canyon
PART 4: Testing the Pathfinder at Kennedy Space Center
PART 5: Sand dunes on Mars
Charles Whetsel is a spacecraft systems engineer on the Mars Global Surveyor Project. Currently he is at the Kennedy Space Center preparing for the upcoming MGS launch. He will be available in the Live From Mars chatroom this coming Wednesday, October 30 from 9-10AM Pacific (noon-1PM Eastern). Consider joining us to ask Charles about: - the latest status on MGS (the launch is scheduled just one week after the chat) - what a spacecraft systems engineer really does - how he got from rural Tennessee to NASA's Jet Propulsion Lab - the bike rides he and his wife Anne go on - or other things your students are interested in To best prepare, please have your students read Charles' biography before the WebChat session. It is at:http://quest.arc.nasa.gov/mars/team/whetsel.html
To virtually meet Charles, point your Web browser tohttp://quest.arc.nasa.gov/mars/events/interact.html
and follow the links to the chat room for experts. If you plan to participate in this event, please RSVP to Andrea by sending a brief Email note to firstname.lastname@example.org. This RSVP is very important, since it will allow us to ensure that the chatroom does not become too crowded. Within the next week, a more complete schedule of future guests will be announced. If you want to participate, but the time selected is a problem, please summarize your schedule issues to Andrea so we can try to accommodate your class in future events.
CHALLENGE QUESTION #1: AN ANSWER TO MARTIAN BASEBALL
Last week, we asked: Let's say you have just been appointed Baseball Commissioner for Mars. You would like the game to be similar in difficulty to the game as played on Earth. With that in mind, how far back should you place the center field fence (so that it is just as hard to hit a home run). Assume that a center field fence on Earth is 410 feet from home plate. ANSWER from Alan Federman: As a first approximation, we need to look at the relevant equation: F = MA Force is equal to Mass times Acceleration. The acceleration we are interested in, is due to the gravity field of Mars. Mars gravity is equal to 0.38 of Earth's, so as a first approximation, the "A" on Mars is .38 * 980 cm/s/s = 370 cm/s/s. If the Force of Gravity were the only effect on the ball, 410ft / 0.38 = 1079 feet (or 323 meters). To make the game "play the same" Other factors need to be considered. For example, atmospheric effects. The thin atmosphere means less air resistance so balls will carry further. How fast people can run wearing space suits, would also be a problem. Maybe changing the mass of the players and their equipment is an option. While rain-outs are not going to be a problem, games may need to be called on account of wind or sandstorms! Good Luck, Commish! ANOTHER ANSWER from Bryan Glenn: The old baseball Commish will have quite a problem on his hands placing that fence in the right location. There are actually 2 variables he will have to consider, gravitational differences and atmospheric differences. Both will have a significant impact, but the latter will be much less predictable that the first. When gravitation is compared, Earth's would be +/- 978 cm/sec2, while Mars' is estimated @ 371cm/sec2. 978/371= 2.64, so the 410 ft x 2.64 = 1081ft. That would seem a mighty drive for anyone, if the two atmospheres were comparable. But they are anything but! Earth's gravity and Venus' gravity are almost identical, but if we were putting up a fence on Venus, a 410 ft fence might as well be 2 miles away. Atmospheric pressures on Venus are 100 times that of Earth, so driving a ball through that layer of carbon dioxide smog would require a mighty, mighty bat. Mars' atmospheric pressure is estimated at .005% that of Earth's. Again, some quick calculations should yield the lower atmospheric drag on the bat and ball to determine the "atmospheric" adjustment. But it is not so simple; here again we cannot think of this in Earthly terms. The extreme thinness of the atmosphere and the generally colder temperatures will produce some very "Mars Only" considerations. This thin atmosphere is easily varied by minor climatic events that would produce far less change in Earth's heavier atmosphere. Martian temperature changes could easily produce sudden gusty winds roaring over 100 miles/hour. As winter approaches and more of the CO2 becomes crystallized at the poles, the already thin atmosphere will become even thinner. Parks near the poles will play far differently than those near the Martian equator. Home runs will be even easier to hit then, unless the ball runs into an unexpected 200 mile/hr blast of wind on its way to the fence! Good luck commissioner. Your Martian game will add elements never dreamed of back on good ol' Earth! A special thanks to these folks who sent in their best guesses: Philip and DMackson (Dad) Chris Rowan's students Roxanna Muniz Susan Rico, Mr. Grott's students Mrs. Phaneuf's students Mrs.Grady's students Sandy from St. Anne School Mr.Makar's 3rd Graders, Alden Place Elementary School, Millbrook, NY DMLedet Evan (from Janet Cook's class) Their complete answers will available online on the Web
CHALLENGE QUESTION #2: UNIMPRESSIVE CANYON
Here is this week's Challenge Question: The Valles Marineris is much larger and deeper than the Grand Canyon in Arizona. Yet, if you stood at the rim of the Valles Marineris, it probably wouldn't seem as impressive to the eye. Why? You are invited to send original student answers to us. We will list the names of these folks online and token prizes will be given out to a small number of the students with the best answers. Send your answers to Jan Wee at email@example.com. PLEASE include the words "CHALLENGE QUESTION" in the subject of the email. The deadline for this question is Halloween (October 31).http://quest.arc.nasa.gov/mars/team/beutelschies.html
Week of August 12th The spacecraft arrived at Kennedy Space Center. It was pouring rain. We waited until the rain stopped to roll the container that the spacecraft is in into the airlock. We then wiped down the exterior of the container with alcohol to clean off any dirt and to kill any biological material. Mars Pathfinder has to be very clean from a biological standpoint so it does not contaminate Mars. Spores from Earth life are actually hardy enough to withstand the flight through space. After the container is cleaned, the top was taken off and the spacecraft was moved to a workstand using an overhead crane. Meanwhile, the rest of the electronic equipment used to test the spacecraft was craned up to the test complex, which is on the second floor. It is very nerve racking watching million dollar equipment swinging in the air 20 feet from the ground. This equipment used to create commands, process telemetry, and provide power to the spacecraft. It is connected via long cables which pass through the wall and down into the cleanroom. This allows us to do most of our electrical testing without having to put This allows us to do most of our electrical testing without having to put on cleanroom clothing, which are called bunny suits (because they make you look like a big bunny without ears). Week of August 19th Testing started. We found several problems with our Flight Software during our testing at JPL so we decided to repeat our complete Mission Mode test down here in Florida. This test started with launch, went through the cruise to Mars, the descent to the surface, and then the Day 1 activities. This went pretty smoothly until the (simulated) entry to the Mars atmosphere. We were feeding data into the accelerometers to make the spacecraft think that it was entering the atmosphere and slowing down. There is software onboard that is supposed to read this data and figure out when to fire the parachute. This software never produced an answer. The telemetry showed that the parachute fire signal was sent based on the backup timers and not the software algorithm. We spent a couple of days (and nights) troubleshooting this before we found the bug in the software. The rest of the test went smoothly Week of August 25th The mechanics then opened up the Lander and took the petals off. We are doing this so that we can install fresh batteries for launch. We also have to put in the Radio-isotope Heater Units (RHUs) on the Rover. These are devices containing a very small amount of Plutonium that give off heat to keep the Rover warm. We also installed a small amount of Radioactive Curium in the Alpha-Proton X-Ray Spectrometer (APXS) instrument on the Rover. This instrument uses the radioactivity in the Curium to give off alpha particles. When placed against a rock, these particles will hit the molecules in the rock, which in turn will release x-rays, Protons, and other alpha particles. The instrument looks at all three of these and determines what elements are in the rock. We also took off the thermal enclosure on the Lander so that we could replace an antenna switch. During one of the last tests at JPL, we broke it due to a bug in the software which applied power to it for much longer than it was designed for. We had a spare so we swapped it for the broken one. We then ran a series of tests to make sure that everything under the thermal enclosure was working properly before we put the enclosure back on.http://quest.arc.nasa.gov/mars/team/wilson.html
October 10, 1996 After two weeks of summer vacation in Germany and England, it was time to get back to work and the Planetary Aeolian Laboratory. I really like to travel, but it was time to get back to science and a full summer of research, presentations, and proposal writing. Upon returning home and getting over jet-lag, I had to prepare the Mars Wind Tunnel for a series of experiments involving wind flows of sand dunes. Dr. Haim Tsoar, a geography professor from Israel, and a world authority on sand dunes, would be spending two months at the laboratory, and together we were hoping to explain why we don't see a particular sand dune type on Mars. The dune type we were interested is called a linear dune, and they happen to be the most common form here on Earth, but we don't see them on Mars. Why? We think is has something to do with the thin atmosphere of Mars, so with the help of Dr. Bruce White, a fluid mechanics professor at University of California, Davis, we developed a matrix of experiments where we simulated different Martian atmospheric conditions and wind directions. Hopefully this would answer our questions, but developing the instrumentation need to measure the flow field in all the locations was going to be difficult. We started by attaching in a grid pattern very pieces of light string (tuffs) to the dune model in the tunnel. When the tunnel was turned on, we could see the flow directions and Haim explained to me the mechanism for how linear dunes were formed. If these mechanisms were not present on Mars, it would explain why we don't see them. While this was going on, I had to prepare at talk on the physics of wind erosion and dust generation for a presentation in Lubbock, Texas. Not only did this take time away from the dune experiment, but I would be traveling for a whole week. I was nice in Lubbock. I spent 5 years there during my graduate studies, and it was really great to see my old instructors and advisors. The talk went well, but I couldn't help but worry about the experiments going on at the lab, and how we were going to get the measurements we wanted. I think being a scientist is a lot different than other jobs because you are always thinking about science and how to solve problems. When I got back to the lab, Haim was tired of the "tuffs" and want to make measurements of the shear stress at different locations on and around the model. You see, it is the shear stress (energy of the wind) that moves sand grains and make sand dunes, and measuring this would help prove our theories. We normally measure shear stress by measuring the wind velocity gradient near the surface with a pitot tube, but this technique does not work in separated flow, which was occurring down- wind of the dune model. I said, "Houston, we have a problem!" Until one day, I was walking down the hall of this building, and I saw a poster on the wall of this super sonic (faster than the speed of sound) airplane wing and a simple technique of measuring skin friction on it. After doing some math, I learned that shear stress can be calculated from skin friction measurements. So I went to talk with Dr. David Driver, the author of the poster, and he was more than happy to help me. The technique worked really well, except for the fact that the small dust particles really mess up the measurements. Solution, wash out the entire wind tunnel and put a big air filter on it. This was not a fun job. But it was well worth it. And while the experiment is not complete yet, and Haim is back in Israel, we are really excited about the things we are going to learn and the many applications we have for this new technique. While all this was going on, proposals to do science with Mar Pathfinder were quickly becoming due. I worked on the wind tunnel experiment during the day, my nights and weekends were spent working on my proposal. I think it would be really exciting to operate a spacecraft on the surface of another planet, so I didn't mind giving-up a lot of my personal time to try to make it happen. Well, as of October 10, the proposal is all done and in the mail. It is time to sleep and relax a little. I still have the dune experiment to complete, other proposals to write, and other trips to take. As for now, I'm going to go backpacking in Kings Canyon, California this weekend with another planetary geologist here at Ames and my girlfriend.
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