PRECURSOR STUDIES OF RADIO WAVE PROPAGATION AROUND THE MOON
The Moon is the one object that virtually everyone throughout the history and future of Earth has or will have seen and stared at. Doing something inspiring on such a visible heavenly body could impact so many people around the world, giving them new views of our acquaintance in the sky. What could stimulate and expand our imagination more than observing the universe from the Moon? ...to find answers to what humans have always wondered about: How did it all begin... and evolve... to eventually create lives like us? The Moon as a site for astronomy has been proposed since at least the mid-1960s [1,2] when humans began to have access to outer space. The most seriously investigated concept for a Moon-based observatory has always been a very-low-frequency array on the far side for several well-grounded reasons. Setting up an observatory on the Moon could not only give us new views of the universe, but also inspire the billions of people who look at the Moon.
The far side of the Moon offers an ideal site for observations of the universe at the as-yet largely unexplored frequency window of 50kHz-30MHz. In this frequency range, effective observations are possible only from outer space because of absorption and reflection in the Earth’s ionosphere. The Lunar far side always faces away from the Earth, and so has the unique extra advantage that it is shielded from the terrestrial radio interference. Even though the idea of establishing a radio observatory on the Moon seems attractive (and therefore has been investigated a number of times over the past 40 years), several important questions still need addressing before such a project could receive serious funding support. One of these is the exact degree of shielding offered by the Lunar limb. Here we develop a simulation of radio propagation around the Moon to answer some of the key questions.
First Step: A Simple Radio Array
* Simplest & Least Expensive
A simple array of ~10 dipole antennas is probably the most technologically feasible observatory to be placed and operated on the Moon:
An extra reason for the radio observatory to be our 1st step: The unique radio quiet environment will likely not last long once humans begin development around the Moon! Especially important if we want to search for ET!
* Radio Observatory takes the Most Immediate Advantage of the Lunar Environment.
The Lunar far side is recognized as the best site of all for radio astronomy. Even compared to a free-flyer in space [3, 37]:
* Completely New Views of the Universe
Such an observatory will give us a completely new look at the universe by opening up the new frequency window of 50kHz-30MHz.
Taking the First Step
Since 1965, at least 40 pieces of work have been published specifically about radio observation from the Moon. The most comprehensive and recent has been ESA's "Very Low Frequency Array on the Lunar Far Side" (1997), 1-year design study by a team of nine experts . "This study... showed the feasibility of the project within the framework of Phase III of the ESA Moon program: "science from the moon". Before the mission can be started, however, a number of in-situ measurements need to be performed to confirm certain environmental conditions."
Unanswered Questions & Required Measurements
To identify the best sites and to specify the observatory design, it is crucial to address the following questions by making the measurements below :
=> The terrestrial noise levels at various Lunar far-side locations.
=> Electrical properties of the Lunar surface, including permittivity and conductivity, their variation with depth and wavelength.
=> The electron concentration profile above the Lunar surface, both during the day and the night.
=> Detailed surface topology, magnetic fields, and electrical properties at candidate sites.
To help answer these questions quickly (and to better plan precursor missions), radio wave propagation around the Moon is being simulated. We solve the wave equation using the finite difference method on a uniform space-time grid.
Precursor Missions to Plan Now
Ultimately, the performance of a Moon-based observatory is best tested on-site through inexpensive precursor missions with significant scientific returns of their own. Some ideas of proposals for precursor missions to the Moon in the very near future are suggested [24, 26, 28, 29].
To realize the dream of observing the universe from the Moon, it is time for an international team to begin seriously proposing these missions. A simple radio array on the Moon may be just another one small step for man... but it could also be the beginning of a giant leap in the mankind's view of the universe.
I would like to thank Dr Graham Woan for being a very approachable advisor. I would also like to thank the Fulbright Foreign Scholarship Board.
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