The Lure Observatory is located on the 10,000' summit of Mt. Haleakala on the island of Maui in the Hawaiian archipelago. The weather (Mees Observatory weather station) on Mt. Haleakala allows great viewing conditions throughout the year. LURE Observatory was constructed in 1974 as a fixed Lunar Laser Ranging (LLR) station. The Lunar Ranging Experiment (LURE) makes time of flight measurements of very short pulses of laser light between observatories and reflectors on the Moon. Five reflectors were left on the Moon by three Apollo missions and two Russian Federation robot spacecraft. These measurements would allow scientists to determine the distance between the Moon and the Earth to the accuracy of less than 2.0 centimeters (May, 1995). This data is being used to measure movement of the Earth's tectonic plates, to measure the length of day (rate of change of the Earth's rotation), and to determine the Earth's polar motion. The accurate determination of the lunar orbit has also allowed scientists to test portions of Einstein's theory of relativity.
During construction of LURE, provisions were made to accommodate Satellite Laser Ranging (SLR). This effort is similar to LLR, except the targets are reflector equipped artificial Earth satellites. SLR times of flight measurements are also used in the study of plate tectonics, as well as for the accurate determination of the orbit of the target spacecraft. Precise orbit determination is needed to calibrate space borne measurement equipment.
Currently, LURE is tasked to track 16 different artificial satellites. These satellites range in orbit from 400 to 20,000 Kilometers high. The missions of the target satellites include monitoring of Earth resources and climate parameters, measurements of ocean level and temperature changes, measurement of tectonic plate movement, and improvement of the Global Positioning System (GPS). These satellites were developed by the United States (Topex/Poseiden, GPS35, GPS36 and Lageos1), European Space Agency (ERS1 and ERS2), Japan (Ajisai), Russian Federation (Etalon1, Etalon2 and Glonass), France (Stella and Starlette), Germany (GFZ1), and Italy (Lageos2). Jason-1 was launched from Vandenberg Air Force Base in California on December 7, 2001. The launch vehicle was a Delta II, which was shared with another NASA mission, TIMED. Jason-1 was separated first. Jason-1 maneuvered to an orbit very close to Topex/Poseiden.
In 1990, Lunar Laser Ranging at LURE was discontinued. Since 1990, LURE has concentrated on the improvement of the SLR capabilities of the site. LLR continues to be successful at the MLRS (MacDonald Laser Ranging Station), and at several foreign sites.
LURE was constructed as a double domed building, with the Lunar receive telescope in a 9 meter north dome. The laser transmit and satellite receive telescope is located in a 7 meter south dome. Connecting the domes is the computer control room, and observer facilities. Since Lunar ranging is no longer performed at LURE, the north dome was no longer needed. Currently, the 9 meter north dome is being used by the MAGNUM Telescope, from the Research Center for the Early Universe, University of Tokyo. Their research involves using a 2 meter telescope to determine distances to remote active galaxies from multicolor monitoring of their variability.
The (System Configuration) transmit/receive telescope is a coelostat, consisting of a fixed 40 centimeter diameter objective lens, and a flat 65 centimeter pointing mirror. This telescope does double duty as a laser transmitter, and as a laser reflection detector.
The laser is a Continuum manufactured ND:Yag. This laser produces 1 centimeter diameter light pulses of 200 pico-second duration. The laser is capable of operating at a 1 to 10 Hertz rate. Normal operation for LURE is at a 5 Hertz rate. Each pulse contains approximately 140 milli-joules of energy at a wavelength of 5320 Angstroms (i.e. green light).
The pulses of light pass from the laser through a "holey" mirror to a 10 to 1 beam expander, and on to the 40 centimeter objective lens. (The "holey" mirror is a 12.5 centimeter by 7.5 centimeter optical flat mirror with a 1 centimeter diameter "hole" in the center, mounted at an angle in the laser path. This functions as a transmit/receive switch). Operator movement of the beam expander allows the laser divergence to be set anywhere between 4 arc seconds and 30 arc seconds. The objective lens re-collimates the expanded pulse and transmits it to the pointing flat, and out the dome to the target. The laser light that is reflected by the target spacecraft is collected by this same telescope and diverted by the "holey" mirror to an extremely sensitive light detector. A timing device that was started when the laser pulse left the observatory is stopped by the detection of the reflected light. With the application of the velocity of light factor to this time of flight, the distance to the target satellite is calculated. System improvements of the last few years have enabled the raw measurements to most satellites to be made at a sub-centimeter level of accuracy.
Currently, all system control (telescope, laser, domes, etc.) and data collection is accomplished by a PC (Intel 80486 processor) computer running LYNX "real-time" UNIX Operating System. Initial data analysis is performed by a Linux computer and then sent to GSFC via the Internet within two hours of collection. Also, in the near future, a special computer connection to the Honolulu Center for Radar Approach will give LURE the ability to track air traffic above Haleakala. These improvements will make single person operations at LURE possible.
|LURE SLR Personnel|
Project Manager: Dan O'Gara (email: ogara)
Senior Laser Technician: Craig Foreman
|Senior Laser Technician: Tim Georges|
|Electronic Technician: Jake Kambayashi|