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OCR for page 55
7
Technology Requirements
PROVED DISTURBANCE COMPENSATION SYSTEMS
(DISCOS)
Major unprovements are needed in the DISCOS in order to
achieve enhanced performance in the laser gravitational radiation
observatory. These would include both reduction in the distur-
bance level below the 10~~°/T2g/~-spectral amplitude expected
for the initial laser gravitational radiation antenna in space and
extension of this performance to periods longer than 104 s.
MODERATE-POWER FREQUENCY-STABIIIZED LASERS
Frequency-stabilized single radial and longitudinal mode la-
sers will be useful in many areas of fundamental physics and in as-
tronomy carried out in space. The gravitational wave observations
proposed by this study as well as the optical interferometry being
considered by the Task Group on Astronomy and Astrophysics will
require moderate-power 100- to 1000-mW lasers that will function
trouble-free for periods of years. For space applications, it is im-
portant that the lasers be efficient; the ratio of the optical output
power to the pump power should be larger than in conventional
laboratory systems.
ss
OCR for page 56
56
A good candidate laser system is the Nd:YAG solid-state
laser pumped by laser diodes. Solid-state laser systems using
neodymium (Nd) in other host lattices may prove to be even bet-
ter candidates. The development of high-performance moderate-
power lasers is not a major military concern (to the task group's
knowledge) and would benefit from funds provided by the space
program.
CRYOGENIC CAPABIIITY TO TRANSFER HELIUM IN
ORBIT
Low-temperature experiments such as the Infrared Astronomy
Satellite (IRAS), Gravity Probe B (GPB), the Cosmic Background
Explorer (COBE), and the Shuttle Infrared Telescope Facility
(STRTF) are limited by the lifetime of the liquid helium in the
spacecrafts' dewar. A very important capability to develop for the
future is the ability to transfer liquid helium in space, especially to
eject a transfer for low-temperature free flyers. Ultimately, this
should be a routine service function of the Space Station, but it
could be extremely useful if developed earlier for the Shuttle.
DEVELOPMENT OF CLOCKS
The hydrogen maser now has a long-term stability of better
than 10-~5. An biller version of this clock was flown several years
ago on Gravity Probe A to measure the gravitational red shift
to an uncertainty of 10-4 in a suborbital highs. The hydrogen
maser is the logical candidate to use in the second-order red shift
experiment proposed for the Starprobe mission. Building a space-
worthy improved hydrogen maser is an important technological
development program for NASA.
The present development of trapped ion clocks is not as far
along as the hydrogen maser but holds the possibility of stabili-
ties of 10-~7 to 10-~. The continued development of these clocks
opens the possibility of a sensitive test of the strong principle of
equivalence by intercomparison of clocks with different mixtures
of electronic and nuclear energy terms. The intercomparison could
first be carried out on Earth, where the solar gravitational poten-
tial changes over the course of the year due to the Earth's eccentric
motion about the Sun, and later on a spacecraft to sample a larger
change in the solar field.
Representative terms from entire chapter:
gravity probe