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DegnanGeoscience Technology Office, Code 920.3NASA Goddard Space Flight CenterGreenbelt, MD 20771 USA1.0 INTRODUCTIONSLR2000 is an autonomous and eyesafe single photon-counting satellite laser ranging station with an expected single shotrange precision of about one centimeter and a normal point precision better than 3 mm. The system will provide co...
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... prototype telescope uses a custom-designed 40 cm diameter off-axis all reflective telescope designed to operate over a wide temperature range (20 to 120 o F). The design (see Figure 2) incorporates various passive elements (invar rods, low expansion optical substrates, etc.) to maintain system alignment and focus over a wide temperature range but also allows for active control of the focus via a computer- translatable lens and CCD camera which can check the focus periodically by imaging stars [3]. The CCD camera is also used to perform periodic star calibrations to compensate for mechanical sag in the mount or telescope. ...
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SLR2000 is an autonomous, unmanned satellite laser ranging station with an expected single shot range precision of about one centimeter and a normal point precision better than 3 mm. The system will provide continuous 24 hour tracking coverage and reduce capitalization, operating and maintenance costs by an order of magnitude relative to current ou...
Citations
... Passive laser tracking of the satellite is an established technique that is made possible by collecting the light scattered off a target illuminated by specially directed laser beam [7]. The Satellite Laser Ranging (SLR) is the reputable international program that through the International Laser Raging Service (ILRS) provides their users with the information on orbital details of the satellites associated with this program [8]. ...
A prototype of an active laser tracking system (ALTS) has been developed with its operation based upon the fundamental principles of the non-linear optical phase conjugation. The key element of the ALTS is the phase conjugate mirror (PCM) that enables to compensate aberrations in the optical cavity and the laser system to operate in atmospheric turbulent environment. Although the current prototype design serves to prove the concept of its operation, i.e. tracking the remote target, when fully integrated, it should be capable to quantify target's 3D state vector and velocity, as well as characterize its maneuvering operations and vibration features. This paper outlines the first field-test execution of the ALTS, and in particular, it discusses the rational, the concept, development of the test plan and some details in its realization.
... The SLR2000 system concept was first proposed in 1994 , but significant funding for the SLR2000 project was not provided by NASA until August 1997. The first detailed overview of the SLR2000 system and technical approach was presented at the 1997 Fall Europto Meeting in London, UK [Degnan and McGarry, 1997], updated at the 11 th International Workshop on Laser Ranging in Deggendorf, Germany [Degnan, 1998] and once again at the 1999 Fall Europto meeting in Florence, Italy [Degnan, 1999]. The reader is referred to these earlier publications and to the subsystem references therein for additional detail. ...
SLR2000 is an autonomous, eyesafe, single photon-counting satellite laser ranging station with an expected single shot range precision of about one centimeter and a normal point precision better than 3 mm. The system will provide continuous 24 hour tracking coverage. Replication costs are expected to be on the order of $1M or roughly an order of magnitude less than that of current manned systems. Maintenance costs will also be substantially lower. Computer simulations have predicted a daylight tracking capability to GPS and lower satellites with telescope apertures of 40 cm. Computer and hardware simulations have demonstrated the ability of our current correlation range receiver and autotracking algorithms to extract mean signal strengths as small as 0.0001 photoelectrons per pulse from daytime solar background noise.
Following several years of study, funding for hardware development became available in July 1997. Early efforts concentrated on the development and test of several "enabling technologies", which included a 2 kHz microlaser transmitter, a quadrant microchannel plate photomultiplier, a 5 psec (1 mm) resolution event timer, a multi-kilohertz range gate generator, and a "smart meteorological station. Following successful completion of these efforts, the overall system detail design was finalized and the facility, tracking mount, and telescope were constructed and tested during the past year. An overview of progress since the 1998 Workshop will be provided. Completion of the prototype SLR2000 system is expected in late 2001, followed by a period of extensive field testing. System replication of the baseline system is expected to begin in 2003.
The unique characteristics of SLR2000, relative to current manned systems, may result in new capabilities for the baseline system or future upgrades. As has already been demonstrated by researchers at the Herstmonceaux SLR station, even low repetition rate photon-counting systems can successfully reproduce the time-averaged satellite impulse response (which is usually a single-peaked function). The high sampling rates of SLR2000 can reproduce this waveform much more quickly and well within the time span of a typical normal point, thereby eliminating a source of systematic range error originating from the satellite "signature". Furthermore, the ability of SLR2000 to sense the satellite position with sub-arcsecond accuracy using the quadrant detector provides an accurate tracking angle in addition to millimeter precision range and further constrains the satellite position.
Similarly, future two-color versions of SLR2000 could generate satellite impulse responses at multiple wavelengths and provide unambiguous points (e.g., the peaks or centroids of the time-averaged impulse responses) with which to measure the differential time delay introduced by atmospheric refraction, thereby reducing a second systematic error in the range measurement. Such a system would use conventional photomultipliers or SPADs, rather than complex streak cameras, and the measurement of differential delay would not be subject to the ambiguities which result from a lack of temporal correlation between simultaneous multi-photon returns from the same satellite but at different wavelengths.
The temporal spread of optical pulse signals due to reflection from
multiple onboard reflectors is now a critical problem in satellite laser
ranging. The full rate residual profile of single-photon laser ranging
can be used to model the response function of geodetic satellites,
resolving the uncertainty of far-field diffraction. We constructed the
response function model for three types of laser ranging targets already
in Earth orbit, the LAGEOS, AJISAI, and ETALON satellites. The
center-of-mass correction depends on the ranging system and observation
policy at terrestrial stations and varies about 1 cm for LAGEOS and 5 cm
for AJISAI and ETALON.
In this report, we present results of dynamic laser oscillation over a
10 km distance using a coupled-cavity structure assisted by four wave
mixing (FWM). The system consists of a master cavity and a slave cavity
that are coupled together through FWM in a nonlinear medium. The master
and slave laser beams each form two arms of the four wave mixing
structure. The master laser consists of a cavity formed by two highly
reflective mirrors, in which there is a gain medium and the FWM
nonlinear medium. For the slave laser cavity, one of the end mirrors is
the grating formed inside the FWM medium, and the other mirror is the
remote moving target. In this case, this target is a retro-reflector
located on a moving airplane. The laser tracking was completed with a
rotating gimbal mirror system that locked on the target. Successful
lasing field tests at distances over 10 km have been achieved, and
further results can potentially be obtained at longer distances. The
laser oscillations are free running with a pump pulse width of 2-5
milliseconds. Based on the time separations between the pulses from the
master and slave cavities, the target distance can be precisely
calculated.
We performed architecture and design analyses of coupled-cavity laser systems to arrive at a concept for tracking distant objects. We also conducted an experimental study of such a system using a pulsed ruby laser as a prototype for the laboratory tests. Both laser cavities were coupled through the dynamic holographic grating. Special attention was paid to characterization of the coupled-cavity laser system and its operation. In particular, we studied the formation of holographic grating that serves to couple the cavity; the slope efficiency of the master and slave arms and their dependence upon cavity parameters. The resulted experimental data and analyses verified the tracking principle and proved the feasibility of the proposed phase-conjugate double cavity laser system for tracking moving object at distance with high accuracy.
A number of approaches have been suggested in order to develop a passive laser system that can lock on and track a remote object, including satellites. Active laser-based systems have an advantage over passive systems because they can establish communication channels, measure target velocity and spatial coordinates, and/or deliver high optical power levels. We report here on the first experimental realization of a coupled laser system that employs a phase conjugate mirror (PCM) and is capable of adaptively tracking a moving output coupler. Active systems have been demonstrated in the laboratory using phase conjugate mirrors; however, they have generally been limited to locking on to static or very slow moving objects. For tracking remote, high velocity targets, several problems exist including: low returned power, high Doppler frequency shift, and large temporal delays. In this work, we show that laser resonators coupled with a phase-conjugate mirror in a Michelson-type arrangement can be used to overcome some of these limitations and track a remote moving object.
Passively Q-switched, diode pumped, all solid-state lasers are an elegant, yet simple, means to generate single-frequency laser pulses in the nanosecond and sub-nanosecond regions. The majority of the work on these systems has been in the 1-μm region, but recent developments at eye-safe and mid-infrared wavelengths of both diode-pumped lasers and solid-state saturable absorbers will probably lead to practical, passively Q-switched lasers at longer wavelengths. However, longer wavelength material properties are expected to only allow the generation of longer duration pulses. In the 1-μm region, near-term advances are anticipated in the development of higher average power systems operating at multikilohertz pulse rates, with pulse energies exceeding 1 mJ and corresponding improvements at second, third, fourth, and even fifth harmonic wavelengths.
