Why wouldn’t the hubble space telescope naturally stay pointed in the same direction?

Question

Advanced technology is needed to keep a
telescope, travelling at almost 30 000 km/h
while orbiting Earth, aimed steadily at one
tiny spot for a long time. this is for grad 9 science

Answer 1

It depends on your frame of reference. Relative to the HST's own frame of reference, it IS always pointed the same direction. However, relative motion (or apparent relative motion) between HST and objects it is attempting to observe can be caused by various phenomenon, such as motion of the objects being observed, inertia of the HST, inertia of its fuel, solar wind, micrometeorites, drag, interstellar matter, etc.

Answer 2

The Hubble uses gyroscopes to adjust its position and to move the telescope tube. On the last two service missions those gyroscopes were replaced, currently it only has one working gyroscope. The space telescope has reaction thrusters that fire an inert gas like nitrogen, but the fuel supply for those is limited and they are ONLY used to hold the telescope into its orbit.

When the telescope is making an observation for a long time it is constantly moving, it rotates the earth and the earth is rotating the sun while our sun is rotating in the Milky Way galaxy. Therefore the gyroscopes need to be almost constantly running cancel out these movements to keep it relatively fixed in the sky. It doesn't matter on you frame of reference, it only matters on the telescope's frame of reference compared to the rest of the universe."
Advanced telescopes on earth and some well home made ones have a small motor that turns the tube at the exact counter speed of the rotation of the earth thus holding the tube stationary with the object being observed. This has been done for a long time and it is easy to do.

injanier is correct, but he doesn't explain how the hubble counters all these forces. It uses the reaction thrusters for gross orbital corrections and the gyroscopes for fine adjustments; that's why it needs to be serviced again and soon we only have one gyroscope working on it.

Normally gyroscopes are used for measuring the anglular momentum, but larger ones can direct it.

According to Wikipedia: http://en.wikipedia.org/wiki/Gyroscope
"A gyroscope is a device for measuring or maintaining orientation, based on the principle of conservation of angular momentum. The device is a spinning wheel whose axle is free to take any orientation. This orientation changes much less in response to a given external torque than it would without the large angular momentum associated with the gyroscope's high rate of spin. Since external torque is minimized by mounting the device in gimbals, its orientation remains nearly fixed, regardless of any motion of the platform on which it is mounted.

Answer 3

Although Newton tells us that a body at rest remains at rest, it is in practice rare for anything in orbit to be perfectly still. Any slight perturbation can start the object turning, and without attitude controls there is nothing to stop it. A satellite in low Earth orbit has to cope with atmospheric drag, the gravitational pull of the Moon, tiny fluctuations in local gravity (due to mountains etc), and even the pressure of sunlight. There is also the gravity gradient - the acceleration of gravity is very slightly higher on the part of the satellite closer to Earth. All of these effects are slight, but in the absence of any restraining forces their effects will be seen. Satellites that lose their attitude control systems begin to tumble after a while. And of course, to take a high-magnification picture, the Hubble has to be kept extraordinarily still.