Lunar Telescopes
The
space telescope on the lunar surface pictured above uses an advanced
walking mobility platform.
Lunar Telescopes |
The
space telescope on the lunar surface pictured above uses an advanced
walking mobility platform. |
| This is my quest, to follow
that star,
No matter how hopeless, no matter how far To fight for the right without question or pause To be willing to march into hell for a heavenly cause And I know if I'll only be true to this glorious quest That my heart will lie peaceful and calm when I'm laid to my rest And the world will be better for this That one man, scorned and covered with scars Still strove with his last ounce of courage To reach the unreachable star -lyrics from "The Man of
La Mancha"
The first, and so far only, lunar astronomical observatory was deployed by the Apollo 16 crew in 1972. The Far Ultraviolet Camera/Spectrograph used a 3-inch diameter Schmidt telescope to photograph the Earth, nebulae, star clusters, and the Large Magellanic Cloud. The tripod mounted astronomicalequipment was placed in the shadow of the Lunar Module so it would not overheat. The Far Ultraviolet Camera took pictures in ultraviolet light which would normally be blocked by the Earth's atmosphere. It had a field of view of twenty degrees, and could detect stars having visual magnitude brighter than eleven. One hundred seventy-eight images were recorded in a film cartridge which the astronauts returned to Earth. The observatory still stands on the Moon today. |
Astronaut John Young and the Apollo Lunar Telescope |
Why is the moon such a good place for astronomy? First of all the moon has no atmosphere. The sky is perfectly black and the stars do not twinkle. Stars and galaxies can be observed at all wavelengths including x-ray, ultraviolet, visible, infrared, and radio. |
| In contrast, the Earth's atmosphere
absorbs light, causes distortion, and totally blocks the x ray, ultraviolet
and certain infrared
and low frerquency radio signals. These limitations prevent scientists
from studying many important phenomena in stars, galaxies, and black holes.
In addition, night time on the Moon lasts about 350 hours. This would permit scientists to watch deep space objects for very long periods, or to accumulate signals on very faint sources such as dim stars, galaxies, or planets around other stars. In contrast the Hubble Space Telescope, NASA's current premier telescope for space research, is in a low earth orbit some 350 km high (the moon is 450,000 km away). Sunrise and sunset are only 90 minutes apart on the HST, meaning that the dark time (the time HST is in Earth shadow) is only 45 minutes long which is a major constrain for astronomers. |
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The moon is a very large, and ultra-stable platform for telescopes of any kind.Unlike orbiting spacecraft, the Moon is a very stable. It has no seismic activity except for meteorite impacts. Average ground motion on the surface is estimated to be less than 1 micron (one millionth of a meter, or about the thickness of a hair). |
| This stability is crucial
for 'opticalinterferometers',
instruments which will be needed to carry out a systematic search of planets
around other stars within our own galaxy. An interferometer is an
array of several telescopes that work together to increase magnification
ability. (Other
galaxies are too far away for visual or radio detection of alien civilizations.)
The Moon is very near to the Earth relative to other planets. Round trip light travel time is about 2.5 seconds. This means a telescope on the Moon can be controlled fromground station with a nearly instantaneous response. (This goes for all kinds of remotely controlled operations, not just telescopes). Finally, a lunar telescope could last almost indefinitely as there is no weather on the moon. Except for rare meteorite hits, a telescope on the moon could last practically forever. The retroreflectors left on the moonby the Apollo astronauts, for example, are still in operation after more than thirty years. A telescope on the moon will remain productive for many decades at low cost. The purpose of the NASA Lunar Telescope Deployment task is to develop and demonstrate telerobotic technologies that enable an unmanned lunar observatory that isconstructed and operated from Earth. Specifically the task is to study an optical interferometric telescope for the moon. |
| A telescope on the moon could also be used for educational purposes. Wendell Mendell, a NASA scientist working in the Exploration Office, supports a lunar telescope for student access. To read his paper, click here. |  |
Types of Telescopes |
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Optical telescopes can be on either the nearside or the farside of the Moon. (The term 'darkside' is not correct because it implies that the Sun doesn't shine there, in fact, the Sun shines on both sides equally.) There is very little atmosphere to scatter light fromthe Sun or Earth, so you could use an optical telescope even during the day. |
| Radio telescopes are best
placed on the farside, to block out the radio noise of Earth and its increasingly
noisy fleet of satellites. Radio bends around small obstacles so it is
harder to block
out. Half a mile from the point where you can no longer see any of Earth
would not be enough.
(Besides which, an effect called 'libration' means that Earth wanders slightly
in the sky over
the course of a month.)
Data communications from the lunar observatory to Earth would be done by laser through a lunar satellite to further avoid noise. Astronomers could control the telescopes through the international computer networks from their own offices on Earth. A one-meter transit telescope is shown in the image above. It is mounted to arobotic lunar lander on the surface of the Moon. The Moon is a uniquely suitable platform for astronomy, which could include extreme ultraviolet images of Earth's magnetosphere (permitting study of solar wind interaction), the first far ultraviolet sky survey, and first-generation optical interferometers and very long wavelength radio telescopes. The instrument illustrated above is a Lunar Ultraviolet Telescope Experiment (LUTE), which takes advantage of thestable and atmosphere-free lunar surface, and uses the Moon's rotation to survey the ultraviolet sky. The lander is an "Artemis" - class lander capable of delivering up to 200 kilograms to the lunar surface. The "Artemis" robotic lunar lander is designed for cost-effective delivery of payloads to the Moon to study lunar geology, astronomy, and as a precursor to human lunar expeditions. |
It is an artist's concept depicting a possible scene of an observatory on the far side of the moon. The artwork is part of NASA new initiatives study which surveyed possible future manned planetary and lunar expeditionary activity. |
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| The objective
of the lunar observatory
case study is to understand the
effort required building and operating a long-duration
human-tended astronomical observatory
on the moon's far side.
Some scientists feel that the lunar far side, quiet, seismically stable and shielded from Earth's electronic noise, may be the solar system's best location for such an observatory. The facility would consist of optical telescope arrays, stellar monitoring telescopes and radio telescopes, allowing nearly complete coverage of the radio and optical spectra. The observatory would also serve as a base for geologic exploration and for a modest life sciences laboratory. In the left foreground, a large fixed radio telescope is mounted on a crater. The telescope focuses signals into a centrally located collector, which is shown suspended above the crater. The lander in which the crew would live can be seen in the distance on the left. Two steerable radio telescopes are placed on the right; the instrument in the foreground is being serviced by scientists. The other astronaut is about to replace a small optical telescope that has been damaged by a micrometeorite. A very large baseline optical interferometer system can be seen in the right far background. Scientists at the NASA Goddard Space Flight Center's Laboratory for Astronomy and Solar Physics are working to develop an advanced technology telescope on the Moon for astronomical research. The goal is to produce a robotic telescope that can be deployed in the near future (3-5 years), at very low cost, and without need for human presence. To read about their plans for a future Lunar Astronomy Mission visit their site! The Goddard design as shown in the picture below is an experimental telescope that weighs about the same as the two month old kitten named Pacobel on the right. It is composed of a graphite fiber cyanate ester resin composite which is very lightweight. Ultra-lightweight composite mirrors could reduce the cost of an unmanned telescope on the Moon from $1 billion dollars to as low as $50 million. Lightweight optics are of major importance in weight and cost reduction.
The purpose of the mirror in a telescope is to collect and focus the light, the rest of the telescope is used to support and point the mirror with precision, and to collect data. If the mirror can be made lighter, then the rest of the system can become much lighter also. The telescope costs less and becomes easier to move around, whether in space or on the ground. By using the same materials throughout, the telescope minimizes distortion due to differential thermal expansion effects (parts made of different materials expanding at different rates) as the temperature changes. Questions to think about:
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