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Time To Uranus, Average Spacecraft Speed
Name: Deb
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A
Question:
As part of a class project, we are trying to
determine how long a trip to Uranus would take via automobile,
airplane, and space ship. I have searched many web sites but
cannot come up with any answers other than to take the
approximate distance between Uranus and Earth (1.69 billion
miles) and then divide that distance by the approximate general
speed each vehicle would go. Am I on the right track or is there
something I am missing? If I am on the right track, what is the
approximate speed of a space/rocket ship?
Replies:
A spacecraft's velocity depends on how quickly it was launched, then
on a combination of the gravity of the Sun, Earth, and whatever body
it is approaching. Often a spacecraft will speed up as it
slingshots close by a planet as it is on its way to another
planet. New Horizons will speed up as it passes Jupiter on its way to Pluto.
David Levy
Deb,
As a first approximation you are on the right track, and if all you
really want is to get some numbers indicating the difference it
would take to travel that long distance at different speeds then
what you are doing is good enough. I do not know if you need to add
the complications that come from a more "accurate" or realistic
measurement. Here are some of the complications that come
immediately to mind: (1) the speed of the vehicle must necessarily
change over the course of the travel, the speed will be different
when boosting out of the Earth's gravity, in space - since the
vehicle is no longer being boosted by rockets and is essentially
using whatever remaining forward momentum it had to get to Uranus -
it is continually being slowed by the decreasing effect of the Sun's
gravity; this makes calculation of the vehicle's speed difficult;
(2) the trajectory of the vehicle is not straight between Earth and
Uranus, not only are both planets moving; the Earth's momentum is
transferred to the vehicle, but the target landing may not be the
shortest distance between the two planets or the two orbits; (3) the
vehicle may be "slingshot" through another planet like Jupiter or
Saturn, using the gravitational effect of this planet to boost the
vehicle, and so on. I leave it up to you to decide how much of these
real world complexity you want your students to consider.
Greg (Roberto Gregorius)
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Update: June 2012
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