# Satellites and Space Probes

## How they work, how they collect data, and more

The following questions were answered by astronomer Dr. Cathy Imhoff of the Space Telescope Science Institute.

What kind of information do you get from the satellites that monitor our Earth?

We get all kinds of information! Some of the things we can measure using satellites are weather information like rainfall and snow, cloud cover, temperatures, ocean information: temperatures, waves, location of icebergs, and other information: aurorae, ozone layer, influence of the sun on the earth's magnetic field.

How do satellites stay up in space?

As you know, gravity holds on to the satellite. But if you could turn off gravity, the satellite would keep moving — but in a straight line. It would leave Earth. If you stopped the satellite and turned gravity back on, the satellite would fall straight down to Earth. But if you have both gravity pulling down and the speed of the satellite pushing out, the two balance out so that the satellite can go in a circle around Earth.

What was the first space probe like?

The first satellite to be launched into orbit around Earth was Sputnik, which was launched by the Soviet Union in 1957. It was just a little silver ball, less than a foot across, with antennas that sent out a "beep-beep-beep" to let us know that they had been the first into space!

What is the furthest a spaceship could go?

Right now the farthest that we have sent a spaceship that has people onboard has been to the moon. That's only 250,000 miles away. That seems far, but the sun is 93,000,000 miles away!

The furthest unmanned spaceships are the Pioneer and Voyager probes that visited Jupiter, Saturn, Neptune, and Uranus. They have crossed our entire solar system! That's 40 times the distance between Earth and the sun, or 4,000,000,000 miles!

Why does a satellite look like a star?

Satellites are usually several hundred miles up. At that distance they are too small for you to see any detail. You can see them when the sun's light reflects off the metal surfaces of the satellite. The best time to look is in the evening after the sun has set and the sky has gotten fairly dark.

How many satellites are in space? What happened to the ones that left our solar system?

I'm not sure but I would guess hundreds. The ones in low earth orbit (only a few hundred miles up) will eventually be dragged into earth's atmosphere and burn up. The ones higher up will remain there for a long time.

The spacecraft that were sent out to the outer solar system, like Voyager 1 and 2, are still going. They haven't left the solar system quite yet, but when they do they will just keep going. There is not much out there between the stars. It will be cold and dark, and their power will run out. But we put a plaque on each spacecraft, with symbols and pictures. So if someone out there finds the spacecraft, they will have a map to come find us (although the chances are very, very small that anyone will find them, so don't expect visitors anytime soon).

How do spaceships and satellites avoid being hit by meteors? Can meteors be detected by these crafts?

Fortunately most of the stuff in space is really, really small — like dust. These little specks of rock hit spaceships and satellites all the time. On very rare occasions a meteor the size of a grain of sand hits. There isn't much we can do to avoid them, just build the spacecraft to withstand the impact!

The satellite I have been working with once got hit by a tiny meteor. We were taking measurements of a star when suddenly it moved as if someone had smacked it in the side of the head! Fortunately it stayed under control and automatically moved back to its original position. The engineers analyzed what happened and concluded that the satellite had been hit by a small meteor. Fortunately it didn't hurt anything — that we know of.

Does a satellite use film like in a camera?

Most satellites have electronic cameras, so that the images and data that they collect can be sent by radio. This is similar to your TV. A camera records the picture at the TV studio, which is changed to radio waves, sent out on a big antenna (or cable network), and then put back together into a picture on your TV. The type of cameras we use on satellites are not quite the same but it's the same idea. A few satellites do use film cameras. One of the instruments on the last shuttle ASTRO-2 mission uses film. The problem with film is that you have to get it back to earth and develop it before you can look at your pictures!

Are communication satellites considered telescopes? What is the future of telescopes?

The word telescope can be broken into two parts: tele, which means "at a distance" and scope, which means "to look at." So a telescope allows you to look at something at a distance. The telescope collects light, but it does so in a way that allows you to know where the light is coming from, as in a photograph or other image. So a communications satellite is not a telescope because you can't look at something with it. There are special telescopes that let you look at other kinds of light than what our eyes see. There are radio telescopes, X-ray telescopes, infrared telescopes, and ultraviolet telescopes.

In the last several years, astronomers have been doing all kinds of new things with telescopes. We have put telescopes in space, like the Hubble Space Telescope. A telescope in space is above Earth's atmosphere. This lets us see more clearly and also lets us see kinds of light, like ultraviolet and X-rays, that don't go through the atmosphere. Also we've found ways to build bigger telescopes by using lighter materials.

The newest telescopes use something called "adaptive optics." This is a way for the telescope to adjust for the blurring by the air in our atmosphere so that we can see clearer pictures of the sky, without going into space.

• Part of Collection:
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Satellites and Probes
• Skills:
Science