November 11
MGS successfully launched at 12:00:50 EST in just about perfect weather! (NASA announcement on Thursday, November 7.) MGS stands for Mars Global Surveyor. MGS is a 2300 lb spacecraft that will reach Mars in September of 1997. Global Surveyor will orbit the planet and take data, but it will not land. It is the first of 10 martian probes to be dispatched during the next decade. More Extra Credit This Week. Take the warmup quiz and earn extra points. To get to the quiz click on the blue "warmup quiz" text in the sentence above this line Additional 30 points of extra credit are available in this week's "What's Physics Good For". This week the extra credit questions require a bit more thought. Their point values have been increased to 10 points each. The puzzle and the warmup credits are as usual. To claim the extra credit send an email message to Prof. Novak or go to the Phys 152 communication box. and send your submission from there. Send us your comments. As we try to improve the content and administration of PHYS 152, we rely on the input of our students. No one knows what is wrong with this course better than you. Please use this 100% anonymous opportunity to help us improve the course. To communication box.
What's Physics Good For?
SPACE TRAVEL The MGS Mission The Mars Global Surveyor mission, undertaken by NASA this past Thursday, is a perfect illustration of the physics you have been studying these past weeks. Space missions combine all the most recent advances in physics and technology: mechanics, materials sciences, electronics, computing, optics, and more. The MGS probe will leave the (blue) Earth orbit and move along the (yellow) transfer orbit until it reaches the (red) martian orbit next fall. All this time the probe is orbiting the Sun. Click on the orbit transfer picture on the left to see a larger image of the orbit transfer with the relevant physics data. 1. What would be the speed of the MGS probe if it were to stay in the same orbit as the Earth (the blue orbit in the picture?) Note the position of Mars as the probe starts on its journey towards it. How does this transfer differ from the exercise in last Friday's lab? Once the probe reaches its destination orbit it will be shifted into an orbit around Mars (the "capture orbit" drawn in yellow.) This is the MOI (Mars Orbit Insertion) phase of the mission. Click on the MOI picture on the right to access the larger MOI picture with the relevant physics data. (Compare this with this week's WarmUp.) 2. What will be the acceleration of the probe during the MOI? Why does this probe have to be slowed down as it reaches the higher orbit altitude whereas the GOP satellite in Friday's lab had to be sped up? The orbiter probe is now in a highly elliptical orbit. During the next 100 days the probe will gradually shift to the "mapping orbit" from which it will perform the scientific observations. The slowdown will occur as the probe passes through upper martian atmosphere. At the point the probe will be in a nearly circular orbit at 378 km above the surface of Mars. 3. What will be the speed of the martian probe in the "mapping orbit"? Further study links: 1. 2. 3. 4.
This Week's Puzzle
In your lab last Friday you calculated the speed correction necessary to move a satellite from a low Earth circular orbit to an elliptical orbit that will take it out to the higher orbit. The speed with which the satellite moves as it enters the elliptical orbit is HIGHER than the speed it must have in the high orbit. When the second correction is made to insert the satellite into the high circular orbit , the speed of the satellite has to be INCREASED again. Apparently the satellite loses a lot of its speed as it moves along the elliptical orbit. How do you explain that?		Type your answer to the puzzle in the window and click below. Include your name to get credit.
The first correct response, with the appropriate explanation, wins this week's 152 T-shirt We would encourage you to keep submitting solutions even if you are already a T-shirt winner. Every correct solution entitles you to a virtual T-shirt. The person with the most virtual T-shirts at the end of semester will win a popular Richard Feynman book. So keep at it!
This Week's Trivia	If their heat energy could be converted to electric power, two space shuttle solid rocket motors firing for two minutes would produce enough electrical energy to supply the entire power demand of 87,000 homes for a full day. --source NASA
Puzzle Solutions. Previous editions of This Week...
		Mother Nature doesn't care if you're having fun. -- Larry Niven.

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