Setting up an astronomical observatory on the farside (the so-called "dark" side) of the Moon has been a dream of astronomers for decades. Such an observatory would have a number of advantages, especially for the field of radio astronomy.
Earth has become one of noisiest objects in the solar system radio-wise. Because the moon is tidally-locked to Earth in its orbit, one hemisphere of it is always facing away from our planet. This face of the moon has been called the "dark" side (erroneously, by the way; it receives just as much sunlight as any other part of our natural satellite) or far side of the Moon.
So the moon can effectively shield a radio observatory from all the interference and noise that comes from Earth. Plus, for fifty percent of its orbit, the farside observatory would also be facing away from the sun, another major source of radio noise. And about one-fifth of the time every twelve years, it would also be facing away from Jupiter (the third radio-noisiest object in the sky) as well as from Earth and the sun, giving it an unprecedented opportunity to observe the cosmos with near-zero radio interference from the solar system at large. The leap in sensitivity and range just from blocking these sources would be as revolutionary for radio astronomy as putting the Hubble Space Telescope above the atmosphere was for optical astronomy.
There are advantages of a farside observatory for optical astronomy as well. The farside of the moon would also be removed from earthlight, and would be turned away from the sun for up to two weeks at a time, allowing for long, continuous precision measurements to be conducted uninterrupted by Earth’s comparatively rapid day-night cycle. Also, the moon would give an unprecedented opportunity to set up an interferometers of large scale, both for radio and optical observation of the cosmos. An interferometer consists of two or more separate telescopes that combine their signals almost as if they were coming from separate portions of a telescope as big as the two telescopes are apart.
Tech Level: 12
In a study conducted by NASA as a Design Project activity during its 1993 summer session at the University of Alabama at Huntsville, the space agency decided on a design called the Very Low Frequency Array (VLFA) for a farside radio observatory, if one should ever be built. The receiver of the array would consist of 280 independent dipole elements distributed over a 17-km circle on the lunar surface. Each element has its own small power supply, signal processing electronics, and data communication capability. Each element sends data to a central station, which combines the signals with appropriate phase relationships to create a virtual antenna with an effective diameter of seventeen kilometers. Because of the effects of the atmosphere and surrounding radio noise, the frequencies the VLFA would study cannot be effectively observed on Earth, opening up a whole new branch of astronomy.
The same study proposed an optical interferometer consisting of three 1.5m-diameter optical telescopes placed on the circumference of a circle of 100 m radius around a central station. Each individual telescope would be calibrated with the moon’s very low level of seismic activity in mind, allowing them to take advantage of the moon’s extreme stability to propagate extremely precise observations and measurements.
The optical telescopes, like their radio-array cousins, would also act as parts of an interferometer. Only a small fraction of the field of view of each of the telescopes is extracted to be sent to the central station. As an interferometer, the three telescopes must track the same object; and measurements by the independent instruments are limited to the field surrounding the primary object.
However, each optical telescope would also be designed to perform as a stand-alone instrument and collect data independently using the remainder of the field of view. Each telescope hosts a different instrument for this purpose: a CCD imager/photometer; an ultraviolet spectrometer; and a polarimeter.
A satellite in halo orbit about the L2 Lagrange point would allow continuous, unbroken communication with the farside instruments and scientists back on Earth.
Maintenance and repair of the instruments would be another matter. Though they would be designed to operate without human interference, and most maintenance could be conducted with specially-constructed teleoperated rovers, human hands would still occasionally be needed. A permanent human presence would probably not be required, but missions to the instruments every few years would probably be prudent. A small habitat cluster close to the observatories would have to be set up to accommodate the repair crews that would occasionally visit. See the articles on Moonbases for exactly what would be required. Because of the enormous cost of sending humans to the moon directly from Earth, human repair crews for a farside repair crew would probably not be economically feasible until after the establishment of a permanent manned base. Sending astronauts from one part of the moon to the other via lander or hopper vehicles would be considerably cheaper than boosting them out of Earth’ gravity well.
SELF-PROPELLED ULTRALIGHT MICROANTENNA (SPUM) INTERFEROMETER
Tech Level: 13
Originally proposed by Buzz Aldrin and John Barnes in their novel Encounter with Tiber, this scheme takes advantage of lunar rover technology to create an extremely large, dynamic radio telescope interferometer in coordination with (or independent of) the VLFA.
The heart of the system are the SPUMs--Self-Propelled Ultralight Microantennas. These are basically light, cheap lunar rovers, similar in size and capability to the Spirit and Opportunity rovers currently deployed on Mars. Once delivered to the Moon, they would each deploy a simple wire-frame antenna about 15 meters across, a structure they would be able to easily handle in the light lunar gravity.
The SPUMs would coordinate themselves with the central VLFA, and position themselves at coordinates that would help to supplement the VLFA’s resolution power. In other words, as they were deployed by the dozens, the SPUMs would turn the VLFA into an even larger and more powerful interferometer. And more, because they could be maneuvered about, the system could be reconfigured as needed for different frequencies and tasks. Aldrin and Barnes envisioned them as being eventually deployed by the hundreds across thousands of square kilometers of the lunar surface, creating an astronomical instrument of profound power and sensitivity. The SPUMs could also function as an interferometer on their own as needed.
The SPUM scheme would most likely be deployed only after a VLFA is set up and a proven technology, hence its slightly higher tech level.
Encounter with Tiber by Buzz Aldrin and John Barnes
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