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Hubble Space Telescope
Question and Answer Board

Mark from Bolingbrook
How many changes will be made to Hubble during this repair missions and when will Columbia return from her mission?
There are five major components that will be changed on SM3B. New, more powerful rigid solar arrays will replace the flexible arrays that were originally installed in 1993. A reaction wheel assembly - one of four that drive the motion of the telescope as it rotates from one pointing to the other - will be replaced. The Power Control Unit, the central distribution box that routes electricity throughout the Hubble, is to be changed out. And the Hubble scientific instrument complement will receive a big technology boost with the installation of the Advanced Camera for Surveys and the NICMOS Cooling System. STS-109 is scheduled to be an eleven-day mission with Columbia scheduled to return to the Kennedy Space Center on March 12.
Kathy from Brookfield
How does the Hubble compare in magnification to Mt. Palomar?
The magnifying power of the telescope depends on the optical design of the scientific instruments that are attached to it. Most of the instruments on Hubble contain more than one optical channel, each of which produces different magnification. An instrument with a long focal length gives greater magnification than an instrument with a short focal length. The power of the telescope is also determined by its aperture size or light collecting area and by the sharpness of the images it produces. Although the Palomar 200 inch has four times more light collecting area than Hubble, the Palomar telescope's images are smeared out and distorted by the earth's atmosphere. Above the atmosphere the Hubble is able to produce very sharp and tightly focused images and therefore is able to see fainter, farther and more clearly than the 200 inch.
Kelly from Tucson
How much life does the Hubble have on orbit? Can and will it stay on orbit when a new space telescope is launched?
Hubble is scheduled to continue operating in orbit until at least 2010. However, the final servicing mission by the shuttle astronauts to Hubble is planned for 2004. So, Hubble will have to continue operating without any repair or maintenance for the final six years of its life. The current plan is to attempt to retrieve Hubble and return it to the ground in 2010.
Kathy from Bookfield
Where did the Hubble get its name from?
Hubble was named in honor of the great American astronomer, Edwin P. Hubble. He was born in 1889 in Missouri and studied law at the University of Chicago and at Oxford University in England. However, his first love since childhood was astronomy. He left his law practice to return to Chicago to study astronomy. Hubble and his colleagues were the first to show that our Milky Way galaxy is one of many - that the fuzzy patches of light in the sky that astronomers of the twentieth century called "great nebulae" are in fact other galaxies external to our own. He also discovered that the universe is expanding and derived "Hubble's Law" which describes how rapidly it is expanding. Much of the research done with the Hubble Space Telescope rests on the scientific foundation of Edwin Hubble's work.
Alexandra from Kissimmee
How much does the Hubble payload (including any special equipment/tools the astronauts need to use to repair the telescope) and equipment required for the space walks such as tethers weigh?
The total payload weight is 19,000 pounds. Out of this, 6000 pounds of equipment will be installed in Hubble. The remaining 13,000 pounds consists of the carriers in the payload bay of Columbia which house the equipment being installed, as well as tools, tethers and other equipment. A 19,000 pound payload was originally too heavy for Columbia to haul up to the high altitude of Hubble's orbit. However, the overall shuttle system has been improved and lightweighted in recent years, and this made it possible to execute the entire planned mission with all the necessary equipment.
Olof from Arboga
What is the optimal resolution for the Hubble telescope in the visual range and what is the same for a human eye? Is there a nice metaphor (way to compare) that explains the difference between Hubble and human eye with regard to the above mentioned resolution?
In visible light (at wavelengths near 500 nm) the combination of the Hubble telescope plus its highest resolution cameras achieve an angular resolution of about 0.04 arc seconds. The human eye can resolve objects separated by about 40 arc seconds. In other words the resolution of Hubble exceeds that of the human eye by about a factor of 1000. The science team that developed the new Advanced Camera for Surveys be installed in SM3B points out that the high resolution channel of the ACS should resolve two fireflies separated by about 10 feet at a distance corresponding to the distance between New York and Tokyo.
Marty from Cuyahoga Falls
Hubble will be receiving new solar arrays which look physically different from those replaced during the first servicing mission. Can you explain what the "improvements" are? Are they for life? reliability? efficiency? Did the engineering changes for these solar arrays come as a result of the space station engineering?
The new solar arrays are 30 percent smaller than the arrays they replace and their beginning-of-life power is about 20 percent higher than beginning-of-life power of the older arrays. The new solar cells are made of a material called gallium arsenide. The older arrays are made of silicon. The new arrays are rigid and less susceptible to vibration and structural distortions produced by the extreme and rapid changes of temperature in orbit than the old, flexible arrays. This helps Hubble remain jitter-free as it takes its ultra-sharp pictures of distant stars and galaxies. The new arrays were purchased directly off the assembly line of the Iridium series of communications satellites. The smaller size of the new arrays produces less atmospheric drag (yes, there is a very low density atmosphere even at Hubble's altitude). This will help Hubble remain higher for a longer period of time. The older solar arrays had degraded in power output with time. The new arrays will provide Hubble with ample electrical power for the rest of its life.
Tom from Levittown, NY
I always thought that due to Columbia's increased weight, the payload it was capable of launching was not as great. If that's true, were any modifications done on Columbia for the STS-93 mission which launched the heaviest shuttle payload to date?
There was a restriction on how much payload Columbia could take into orbit because of the additional 8,000 pounds. I told you it carried back in the rear-end and as a result it could not carry some of the heavier payloads. We did a lot of modifications to all of the vehicles and continue to do so with the best of my knowledge to reduce the weight, but I'm not exactly familiar on that particular flight weight-wise but I don't think that it was the heaviest payload.
Dennis from Ft. Lauderdale
I've watched the Hubble pass overhead many times during the early evening. Considering the speed of its orbit, how is it able to focus on an object for an extended period of time? Does it temporarily lose track when its on the opposite side of the Earth?
Hubble is inertially pointed. It really doesn't "care" that it is in orbital motion around the Earth. Its internal gyros keep it pointed in the same direction on the sky (which only tiny amounts of drift) over an entire orbit, regardless of whether the target being observed is in view or blocked by the intervening earth. According to Newton's First Law, one would have to apply a force to Hubble to make it rotate away from its inertial pointing. There are weak forces acting on Hubble in orbit (due to the change in the Earth's gravitational tug over the length of the telescope, atmospheric drag, etc.). But these only produce a slow drift in the pointing direction. Hubble's point direction is maintained with even greater stability when two of its three fine guidance sensors are locking onto guide stars. This is necessary to preserve the fine clarity of Hubble's images. The fine guidance sensors are themselves complex optical devices mounted within the telescope. Guide stars are selected for each Hubble target and are relatively bright stars closely spaced on the sky to the primary target Hubble is observing.
Liz from Brookfield
What are the best results from Hubble since its installation in the space 12 years ago?
There are so many that it's hard to summarize all of them in a short space. But a "top ten" list would surely include the Hubble Deep Field, which is the deepest image ever obtained of the universe. It penetrated back in time to detect objects that emitted the light we see when the universe was less than one billion years old (the present age of the universe is believed to be about 14 billion years). Also, Hubble made the first measurement of the mass of a supermassive black hole at the center of a galaxy (it was about 3 billion times greater than the mass of the sun) and has since shown that supermassive black holes are present at the center of almost every galaxy (including our Milky Way). Hubble has revealed the detailed forms of dust rings and disks around newly-born starts that contain the raw material from which planets may be formed. Such protoplanetary systems are very common in our galaxy, suggesting that many stars possess systems of planets. Finally, Hubble (in partnership with several ground-based telescopes) has provided strong evidence that the current rate of expansion of the universe is speeding up, driven by mysterious "repulsive gravity" that physicists call "dark energy." The nature and source of dark energy is not known and it is one of the most important problems in the physical sciences today.
NASA's John F. Kennedy Space Center