PART 1: Answering the Challenge
Last week, in CQ #5: BRUSH UP ON YOUR GREEK, we asked: There's a letter in the Greek alphabet that's very important both to launching NASA's current Mars missions and to getting to Mars. What's that letter and explain how it is used. ANSWER: Both Mars Pathfinder and Mars Global Surveyor were launched aboard Delta II rockets from Cape Canaveral, as seen during LFM program 101. "Delta V" is what rocket scientists (including the Navigation teams who were featured during program 102) call the "change in velocity" that keeps a spacecraft on course for a distant planet. Trajectory correction maneuvers fine tune the route by a combination of precise timing, and carefully controlled "burns" providing additional velocity in specific direction.
NEW CHALLENGE FOR THE WEEK
CQ #6: COMPARATIVE ANALYSIS Teachers have been telling us (referring back to the vocabulary of CQ #1) that they think it's very useful for students to compare Earth's "geology" and Mars' "areology." Now, a more open-ended question, which will require and receive some subjective, but fair, judgments from our PTK/Live From Mars CQ staff! What five features make Mars most like Earth? And, what five features make Mars most unlike Earth? We hope students will come up with some geologically correct answers, but also with some clever, provocative and tongue-in- cheek comparisons! You are invited to send original student answers to: firstname.lastname@example.org. Please include the words CHALLENGE QUESTION in the subject line of your email. The kids' names will be listed online and token prizes will be given to those will the best answers. Answers are due within seven full days of Challenge Question posting. (e.g. If a CQ is posted on April 24, answers are due by midnight PDT on May 1.) A list of answers from all students who submitted them will be posted on the Live From Mars Web site soon.
APRIL WEBCHAT SCHEDULE
An apology: Due to a scheduling error, the April 23 WebChat with Guy Beutelschies, test director for the Mars Pathfinder spacecraft, was canceled. Guy will reschedule for sometime in May. The May chat schedule will be posted next week. Tues. April 29, 10 a.m., PST: Bridget Landry, deputy uplink systems engineer, Mars Pathfinder, Jet Propulsion Laboratory, Pasadena, Calif. Bridget teaches computers on the ground to speak the same language as the Mars Pathfinder.
MARS TEAM JOURNAL: A Snake Swallowing a Gopher
by Bridget Landry [Editor's note: Bridget is a deputy uplink systems engineer on the Mars Pathfinder team. She takes complex, but general computer programs and makes them understand all the commands that the Pathfinder knows.] April 18, 1997 In virtually every project (costuming or scientific) that I have been involved in, the work doesn't come in a steady stream. There is a long period where there isn't much actual work being done, because you're waiting for people "upstream" from you to do their thing, or you haven't been able to define the questions you want to ask. And then, suddenly, something crystallizes and this HUGE amount of work surges through the pipeline. I refer to this as "a snake swallowing a gopher": it is an enormous amount of data/work/whatever and it can almost be tracked visibly as the lump makes its way through the system. This was one of those weeks. We have a five-day test coming up next week, which will simulate the first five sols on Mars. On the basis of previous tests, there were a lot of changes to be made to the existing imaging sequences, and these had to be ready, not only for the test, but in time to be run through our testing system BEFORE the test. This made it an incredibly long week for many of us, but I feel good about the work we've done. I think we're well on our way to having at least the first few days fleshed out. There are always a few things that we want to tweak, but, in the main, I think we're in pretty good shape for our test. And now I'm going home to sleep!
ANOTHER INTERESTING MARS SITE
If you're interested in following the Pathfinder and Surveyor spacecraft as they make their way toward Mars, go to:http://mars.catlin.edu
GLOBAL SURVEYOR FLIGHT STATUS
[Editor's note: This status report was prepared by the Office of the Flight Operations Manager, Mars Surveyor Operations Project, NASA Jet Propulsion Laboratory.] Friday, April, 18 1997 No major mission activities occurred this week onboard the Mars Global Surveyor spacecraft. Back at the Jet Propulsion Laboratory in Pasadena, California, the project management has made a decision not to attempt any more efforts to free debris that is currently keeping the -Y-side solar array slightly out of position. This solar panel is currently deployed and fully functional, but is 20.5 degrees from its proper position. The flight team believes that the position discrepancy was caused when a damper shaft in the array's deployment mechanism broke shortly after launch. This damper is a device that was installed to minimize the mechanical shock of deployment by slowing the motion of the array during deployment. The flight team theorizes that the broken shaft caused the damper arm to wedge into the hinge joint connecting the solar panel to the spacecraft. An important aspect of this position discrepancy is that the solar panels will be used at Mars not only to produce electrical power, but also to help the spacecraft attain its final mapping orbit. Over the course of a four-month period following Mars orbit insertion, Surveyor will be dipped into the upper Martian atmosphere on every orbit. During these atmospheric passes, air resistance generated by the solar panels will slow the spacecraft and gradually lower its orbit. Surveyor will use this "aerobraking" technique to lower the high point of its orbit from an initial 56,000 kilometer altitude to just under 400 kilometers. For the last few months, the flight team has been considering several options to free the debris and allow the panel to latch and lock into its proper position. One idea involved a short firing of Surveyor's main rocket engine to provide a small force to dislodge the damper arm. However, such efforts will not be necessary because an extensive analysis has indicated that aerobraking with the -Y solar panel slightly out of position is feasible with a few minor modifications to the original plan. One of the minor changes involves rotating the panel into a position where the front side will face into the air flow instead of the back side. This orientation will keep the unlatched panel from folding up on itself when it encounters the air flow during aerobraking. Because the front side contains the silicon cells that produce electricity, it is more fragile than the back side and cannot tolerate as much heating from the air flow. As a result, the flight plan will be modified so that Surveyor aerobrakes at a slightly slow pace than previously planned. After a mission elapsed time of 162 days from launch, Surveyor is 76.20 million kilometers from the Earth, 44.32 million kilometers from Mars, and is moving in an orbit around the Sun with a velocity of 24.59 kilometers per second. This orbit will intercept Mars 146 days from now, slightly after 6:00 p.m. PDT on September 11 (01:00 UTC, September 12). The spacecraft is currently executing the C6 command sequence, and all systems continue to be in excellent condition.
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