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Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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Hubble Buzz!

Image of Hubble Space Telescope HST SM3A stands for Hubble Space Telescope Servicing Mission 3, Part 1. This important mission is a special tune-up to keep the telescope healthy for the next 10 years.

A Space Shuttle crew blasts through the atmosphere of Earth and into space to reach the telescope. When the Shuttle reaches the telescope, the astronauts use the Shuttle's robotic arm to catch it in mid flight and perform a 370 mile (595.33 Kilometers) high house call. They attach Hubble to a pivoting, turntable-like ring inside the Shuttle's cargo bay.

Installation of RSUsOnce Hubble is firmly anchored to the Shuttle, they grab their tools and equipment and leave the Shuttle to replace equipment and upgrade the telescope.

Hubble's Light Meal

FoodHubble can view the deepest areas of space and record pictures of stars, nebulae, galaxies, and planets. In a way, Hubble "eats" light, digests the information and sends it to us as pictures.

The Earth is very bright and reflects the Sun's light. That light and other things in Earth's atmosphere act like junk food. Ground telescopes fill up on atmospheric junk food, which makes them unable to see as far or as clearly as a telescope in space.

Space is like an all-natural, light meal! A space telescope can be Earth-light free and devour the good stuff like black holes! Hubble can see light from stars and other space objects without filling up first on Earth's light. These deep space lights become clearer and more defined with every new instrument and improvement to Hubble.

Two is better than one!

Because Hubble has no spares, it is very important to service the telescope before another gyro breaks. NASA planned the third Hubble check-up for the year 2000.

To make sure Hubble keeps delivering great pictures, NASA decided to divide duties for the Third Servicing Mission into two separate missions: A and B.


What is Safe-Hold?

Your mom says it is past your bedtime. Dad says you have school tomorrow. But you want to stay up late. After a while, you can't keep your eyes open. When you try to open your eyes to see the TV, you are just too tired to make sense of the fuzzy pictures! Even getting a glass of water is tough when you are sleepy! You can't even find the sink!

Hubble is just like you! The same thing happens to Hubble when not enough of its gyroscopes work. Hubble goes into Safe Mode or Safe Hold, which is like sleeping. Its eyelid (aperture door) now covers Hubble's eye(lens). Without at least three gyros working, Hubble can't keep its eye open or focus clearly on the sky. Hubble is completely healthy, just merely "sleeping" until it has enough working gyroscopes.

When the astronauts replace the old gyros for new ones, Hubble will be able to open its eyes and see! Hubble can then focus on and snap photos of targets like stars. Hubble can tell clouds of gas swirling around deep space, "SAY CHEESE!"


Hubble's Groove in Space

Hubble moves around the Earth in a path called an orbit. The Earth holds you to the ground, by a force called gravity. This same force pulls on Hubble, even hundreds of miles up.

If you swing a yo-yo around in a circle, the string keeps it from flying off. The Earth's gravitational pull is like a string that holds Hubble in its orbit.

  • Hubble orbits the Earth about every 96 minutes, or every 1 � hours. That is 24,901.55 miles (40,066.59 Kilometers)!
  • Every minute, Hubble travels 276 miles (444.08 Kilometers)! The fastest human ran a 3-minute mile. Hubble moves 828 times faster!
  • Friction causes the decline of speed. A bike moves faster than a runner, because less surface area (the amount of tire versus the amount of foot) touches the ground. The ground actually slows you down, whereas, in the vacuum of space, there is very little friction to hold back Hubble's speed.
Spiral Galaxy M100
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Hubble, without a spare...
(gyros, Rate Sensor Units)

Just like keeping a spare tire in a car, it's smart to have spare gyros on Hubble if others break. The gyros are part of a system that points the telescope at stars. Gyros sense and report the telescope's position. Hubble has six gyros, and three of these are spares.

RSUsUntil November 13, 1999 Hubble had been using all three spares right now because the first three gyros broke. Another one broke on November 13th and now it only has two. Astronauts will walk into space to deliver six new gyros to Hubble. These gyros are packaged in three new Rate Sensor Units, with two gyros in each unit.


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Content Last Updated: 12/27/99