Tuesday, April 24, 2012

The Moon as a platform for astrophysics

Darks Ages Radio Explorer (DARE), utilizing the radio-quiet of the lunar farside to explore the earliest period on the cosmic time line, 200 million years between the primordial Big Bang and the emergence of the earliest luminous sources and the structure of the present universe. "The lunar Farside is potentially the only site in the inner solar system for high precision radio cosmology.” [NLSI].
Joel Raupe
and from reports

The Moon has been used as a platform for astrophysics research since laser range reflectors were deployed by three of the six Apollo surface expeditions and also as part of the Soviet two Lunokhod robotic rovers. A lunar laser range reflector (LLRR) has now been orbiting the Moon as part of the Lunar Reconnaissance Orbiter (LRO) mission since June 2009.

A welcome added bonus to the LRO mission came after photographing Lunokhod-1. The 1970 mission's French-built LLRR had been lost almost immediately after the rover was parked for the last time in 1970.

Before LRO, with only four arrays bouncing back mere photons from powerful laser pulses from Earth beginning in 1969, the distance to the Moon was measured with increasing accuracy down to a 3 centimeter margin of error. With the addition of the LRO reflector and after definitively locating Lunokhod-1 astrophysicists sharpened  measurements even further, finally with precision enough to rule out the idea that the astounding newly discovered increasing rate of the universe's expansion might be a “local” phenomenon, or a kind of optical illusion.

The Naval Research Laboratory (NRL), together with the Massachusetts Institute of Technology (MIT), has been building on the age old dream of utilizing the “radio quiet” of the Moon’s Farside to peer into the elusive Cosmic Dark Age, the period between the Big Bang and the “Epoch of Reionization,”  when an intergalactic medium composed mostly of neutral gases was “ionized by the emergence of the first luminous sources.”

Continuing with this description supplied by the MIT Haystack Observatory, “The sources may have been stars, galaxies, quasars, or some combination.  By studying  Reionization we can learn a great deal about the process of structure formation in the Universe, and find the evolutionary links between the remarkably smooth matter distribution at early times revealed by (Cosmic Background Radiation) studies and the highly structured universe of galaxies and clusters of galaxies” astronomers can peer more than 10 billion light years into the past.

Exploring that early “Dark Age” will almost certainly require radio telescopes able to detect sources radiating at frequencies red-shifted to wavelengths typical of the noise created by human civilization.

A solution offered by MIT and the NRL suggested an immense antenna farm deployed robotically on the wide floor of Tsiolkovskiy crater. The Dark Age Lunar Interferometer array was discussed in some detail in 2008, when achieving “extended human activity” on the Moon was national space policy.

The NASA Lunar Science Institute (NLSI) reports two of their collaborating working groups are suggesting putting a radio telescope in orbit around the Moon where it can put a significant part of its time exploring this cosmic Dark Age, the Darks Ages Radio Explorer (DARE). The mission concept is one of two ideas being pursued by the Lunar University Network for Astrophysical Research (LUNAR) “addressing the question of how the Moon can be used as a platform to advance important goals in astrophysics,” according to the NLSI.

The other suggestion by the LUNAR group proposes, “technology development for future lunar surface telescopes, which can help detect and characterize Earth-like planets orbiting nearby starts.

“Both approaches leverage the Moon as a science platform. The lunar Farside is potentially the only site in the inner solar system for high precision radio cosmology.”

DARE will use the highly-redshifted hyperfine 21 cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn. The science instrument is composed of a low frequency radiometer, a receiver, and a digital spectrometer. The various sub-systems have been constructed and are in the process of system integration. After check-out, the system will be deployed and tested at the Murchison Radio Observatory in Western Australia—one of the most radio quiet locations on the planet.

The Lunar Radio Telescope Array (LRTA) is a concept for a telescope located on the far side of the Moon where it is protected from radio frequency interference (RFI). It would detect magnetically generated radio emissions to provide insights into the interior structure of planets— information likely to be difficult to obtain by other means.

The Apollo 15 laser ranger reflector, 4x the area of
the LLRR arrays deployed by Apollo 11 & 14, is
the most reliable of the 5 units placed on the Moon.
Furthermore, the Lunar Laser Ranging (LLR) component of the LUNAR team has taken a two-fold approach toward testing theories of gravity. Not only are they continuing precise measurements of the Earth-Moon distance via laser ranging, but they are also leading efforts to develop a next-generation retroreflector package that could be emplaced on the Moon by future missions.

While the three retroflector arrays deployed during Apollo era were an incredible success, the reduced return from the arrays over the years has limited advanced investigation into general relativity. At present, there are a number of stations that can access Apollo 15 arrays but not the Apollo 11 and 14 arrays; the new retroreflectors will have signals that can be accessed by a large number of lunar laser ranging ground stations. A next generation retroreflector would improve precision measurements for gravitational physics and for understanding the lunar interior.

As a classical theory, general relativity and quantum mechanics are fundamentally inconsistent; there must be a breakdown at some level of accuracy in general relativity or a problem with quantum mechanics. A much higher ranging accuracy would improve scientific results in testing the theory of general relativity by more than two orders of magnitude. 

This post was derived in part from the NLSI release,
NLSI Teams Conduct Astrophysics Research

Related Posts:
MIT to lead development of new radio telescope
array on lunar farside
(February 19, 2008)
Naval Research Laboratory to design Farside DALI (March 11, 2008)
What better view? (March 26, 2008)
New model of lunar motion from Apollo LLRR (December 27, 2008)
MacDonald LLR defunded by NSF (June 21, 2009)
The continued importance of lunar laser ranging (August 3, 2009)
Laser Ranging and the LRO (August 12, 2009)
Dust accumulation on Apollo laser reflectors may
indicate a surprisingly fast and more dynamic
lunar exosphere
(February 16, 2010)
Long term degradation of optics on the Moon (March 4, 2010)
A Fundamental Point on the Moon (April 13, 2010)
Acquisition Lunokhod-1 (April 27, 2010)


George Myers said...
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George Myers said...

A spinoff of these retro-reflectors has been a commercial close-range photogrammetry program by one of the researchers, to create 3D "vectors" from photo(s). Another has been in metrology where almost every land surveyor today uses a "total station" which bounces infrared photons off a reflector and calculate 3D coordinate geometry for various purposes. I had the use of an early one and a later one working in archaeology, to record sites and artifacts. With a number of reflectors, the range is in kilometers, without them today 100 meters.