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Advanced Concepts Studies
Large Lunar Telescope (LLT)
In
response to recommendations by the science community NASA MSFC conducted
several studies of lunar telescopes in the late 1980’s. The Moon is an excellent
place for astronomical observatories because of its pristine deep space
conditions, its slow rotation rate of 0.5 arcsec/ sec and the low gravity,
which eases construction while the need for tethering every part of the
telescope is avoided during the telescope construction. This is an important
factor when compared to a zero gravity assembly of a large telescope where
all residual motion must be compensated.
The LLT is visualized as a 16-m Ultraviolet/Visible/Infrared imaging, optical telescope, operating in the spectral range of 0.1-10 mm. The LLT Project should be rooted in the accumulated experience in lunar-based science, technology, design, engineering, operations, and management acquired with testbeds and precursor telescopes during the early 2000s. A precursor 4 m telescope derived from the central core of the 16 m aperture would serve as a technology testbed for the LLT. The LLT would uniquely combine unprecedented aperture with hours-long integration times, in a superb "seeing" environment. The melding of these factors would ensure that the LLT could produce observations of a very high sensitivity and resolution across the spectrum, giving us an unprecedented grasp of the universe.
A 16-m segmented mirror would form the primary of the 3-mirror, 4-reflection system. Eighteen 4-m hexagonal clusters, each composed of 61 0.5-m hexagonal segments, comprise this primary. Its spherical figure, chosen to simplify the primary mirror element manufacturing, maintenance, and replacement, would be maintained by active correction of all 1098 segments. A tripod would support the 3.2-m secondary 15 m forward of the primary. A 3.2-m active tertiary would replace the central cluster of the primary. The fourth reflection of the light beam (by the secondary) would pass it through a coude system behind the tertiary to the external instrument chamber, whatever the LLT's orientation.
Light weight composites could assure dimensional stability of mirrors and actuator supports under thermal stress. The foundation, base, and alt-azimuth mount could be carried to the Moon for telescope erection. Trades show that power and communication support could best be supplied by a Lunar Base, if it is less than ~10 km distant. A subsurface instrument chamber, shielding instruments from cosmic radiation, would house a UV/Vis Imager, an IR Imager, a UV/Vis Faint Object Spectrograph, a Medium Resolution IR Spectrometer, and a Wide-field Camera. A major shelter could protect the LLT from excess thermal loading, dust, micrometeoroid and ejecta.
The LLT would initially gather scientific data during the construction phase with an initial single primary 4 m mirror cluster plus the secondary and tertiary mirrors. It would evolve to the full science capability by incremental additions of mirror clusters, eventually providing diffraction limited imaging capabilities.
The enormous resolution and sensitivity of the Large Lunar Telescope
could open up new frontiers of astronomy and astrophysics, clarifying
many of the most significant and difficult problems in the physical sciences.
For instance, the structure of all known galaxies would be resolved down
to a level now achieved only in the nearest ones. Exercising its immense
outreach to the most distant regions of the universe, LLT could survey
immense populations of objects never before recorded. It may even image
some of the events which shaped the early stages in creation. Ultimately,
LLT could accomplish one of the most challenging and exciting researches
humans can undertake: directly imaging planets circling neighboring stars
and, perhaps, identifying Earth-type planets which show the spectrographic
signature of life.