Live From Mars was active July 1996-December 1997.
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 firstname.lastname@example.org. PLEASE include the words "CHALLENGE QUESTION" in the subject of the email.
Why does the Pathfinder get to Mars earlier, even though it leaves later?
And how can the Pathfinder have an exact arrival date even though its liftoff date may vary?
Answer from Cheick Diarra:
There is a good reason for MGS's more looping path. The arrival velocity depends on the type of trajectory. The more looping trajectory provides a slower arrival velocity. Since MGS is an orbiter, NASA wants it to arrive at Mars with as little speed as possible. This is because it will need to be slowed down with a retro burn to be captured by Mars's gravity. That maneuver is called the Mars Orbit Insertion maneuver, or MOI for short. The slower MGS is going relative to Mars, the smaller the retro burn. And a smaller retro burn means less fuel (and weight and dollars). So that is why MGS is on a more looping trajectory which will allow for a slower arrival speed. MPF, on the other hand, is not going into orbit, so it can arrive at a faster speed, and thus its more direct route to Mars.
To help understand why a more looping trajectory results in a slower arrival speed, consider a golf ball being putted on a slanting green toward the hole. A golfer can hit the ball hard right toward the hole and the ball will arrive relatively quickly. Or else, the ball can be putted more gently toward the uphill side of the hole; in that case, the ball will loop down towards the hole and arrive at a slower speed.
Finally, about the issue of the fixed arrival date for MPF. When we travel to Mars, we have the opportunity to do Trajectory Correction Maneuvers (TCMs) that let us correct not only our aim point at Mars arrival but also the time of arrival. Early on, NASA decided July 4 would be a good day to arrive. This was partially historical. In 1976 when the Viking spacecraft went to Mars, it was expected to land on July 4 for national reasons (July 4 is America's Independence Day). But when Viking arrived, there was a raging dust storm that prevented this scheduled landing so the team missed a July 4 landing and decided to remain in orbit until July 20 (July 20 is the anniversary of the first Apollo landing). So this time NASA has decided that Pathfinder should land on July 4. The TCMs for Pathfinder will be performed to remain true to the July 4 landing date.
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Answer from Bill Gutsch:
Answer from Bill Gutsch
Answer from Bill Gutsch
Assume that a center field fence on Earth is 410 feet from home plate.
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, 410 ft / 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 farther. 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!
When gravitation is compared, Earth's would be +/- 978 cm/sec2, while Mars's gravitation is estimated at 371 cm/sec2. 978/371 = 2.64, so the 410 ft x 2.64 = 1081 ft. That would seem a mighty drive for anyone if the two atmospheres were comparable. But they are anything but!
Earth's gravity and Venus's 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's atmospheric pressure is estimated at 0.6% 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 carbon dioxide 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!