Jan F. McGarry

Initial observations from the Lunar Orbiter Laser Altimeter (LOLA)

As of June 19, 2010, the Lunar Orbiter Laser Altimeter, an instrument on the Lunar Reconnaissance Orbiter, has collected over 2.0 × 10^9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced. These altimetric observations have been used to improve the lunar geodetic grid to ~10 m radial and ~100 m spatial accuracy with respect to the Moons center of mass. LOLA has also provided the highest resolution global maps yet produced of slopes, roughness and the 1064-nm reflectance of the lunar surface. Regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions. LOLAs initial global data sets as well as the first high-resolution digital elevation models (DEMs) of polar topography are described herein.

Free Space Laser Communication Experiments from Earth to the Lunar Reconnaissance Orbiter in Lunar Orbit

Laser communication and ranging experiments were successfully conducted from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in lunar orbit. The experiments used 4096-ary pulse position modulation (PPM) for the laser pulses during one-way LRO Laser Ranging (LR) operations. Reed-Solomon forward error correction codes were used to correct the PPM symbol errors due to atmosphere turbulence and pointing jitter. The signal fading was measured and the results were compared to the model.

LASER RANGING FOR GRAVITATIONAL, LUNAR AND PLANETARY SCIENCE

More precise lunar and Martian ranging will enable unprecedented tests of Einsteins theory of general relativity as well as lunar and planetary science. NASA is currently planning several missions to return to the Moon, and it is natural to consider if precision laser ranging instruments should be included. New advanced retroreflector arrays at carefully chosen landing sites would have an immediate positive impact on lunar and gravitational studies. Laser transponders are currently being developed that may offer an advantage over passive ranging, and could be adapted for use on Mars and other distant objects. Precision ranging capability can also be combined with optical communications for an extremely versatile instrument. In this paper we discuss the science that can be gained by improved lunar and Martian ranging along with several technologies that can be used for this purpose.

Automated tracking for advanced satellite laser ranging systems

NASAs Satellite Laser Ranging Network was originally developed during the 1970s to track satellites carrying corner cube reflectors. Today eight NASA systems, achieving millimeter ranging precision, are part of a global network of more than 40 stations that track 17 international satellites. To meet the tracking demands of a steadily growing satellite constellation within existing resources, NASA is embarking on a major automation program. While manpower on the current systems will be reduced to a single operator, the fully automated SLR2000 system is being designed to operate for months without human intervention. Because SLR2000 must be eyesafe and operate in daylight, tracking is often performed in a low probability of detection and high noise environment. The goal is to automatically select the satellite, setup the tracking and ranging hardware, verify acquisition, and close the tracking loop to optimize data yield. TO accomplish the autotracking tasks, we are investigating (1) improved satellite force models, (2) more frequent updates of orbital ephemerides, (3) lunar laser ranging data processing techniques to distinguish satellite returns from noise, and (4) angular detection and search techniques to acquire the satellite. A Monte Carlo simulator has been developed to allow optimization of the autotracking algorithms by modeling the relevant system errors and then checking performance against system truth. A combination of simulator and preliminary field results will be presented.

Laser pulses from earth detected at Mars

Over 500 pulses transmitted from a ground-based Nd:YAG laser were detected in Mars orbit, at with the MOLA instrument on-board the Mars Global Surveyor spacecraft on September 28, 2005, at distance of 80.1 Mkm.

Geoscience laser altimeter system (GLAS) on the ICESat mission: pre-launch and on-orbit measurement performance

GLAS is a space lidar on NASAs ICESat Mission. GLAS was qualified and delivered and ICEsat is scheduled for launch in December 2002. This talk summarizes the as-built characteristics of GLAS and its predicted measurement performance.GLAS is a space lidar on NASA’s ICESat Mission, which was was launched into a 590 km altitude circular polar orbit on January 12, 2003. This talk will summarize the as-built characteristics of GLAS and its pre-launch and onorbit scientific measurement performance.

The Lunar Orbiter Laser Altimeter (LOLA) on NASA’s Lunar Reconnaissance Orbiter (LRO) mission

We describe the Lunar Orbiter Laser Altimeter instrument on NASAs Lunar Reconnaissance Orbiter mission, scheduled to launch in April 2009, which will provide a precise lunar high-resolution global topographic map using laser altimetry.

Design and performance of a 3D imaging photon-counting microlaser altimeter operating from aircraft cruise altitudes under day or night conditions

The present paper reports on the design and performance of a scanning, photon-counting laser altimeter, capable of daylight operations from aircraft cruise altitudes. In test flights, the system has successfully recorded high repetition rate returns from clouds, soils, man-made objects, vegetation, and water surfaces under full solar illumination. Following the flights, the signal was reliably extracted from the solar noise background using a Post- Detection Poisson Filtering technique. The passively Q-switched microchip Nd:YAG laser measures only 2.25 mm in length and is pumped by a single 1.2 Watt GaAs laser diode. The output is frequency-doubled to take advantage of higher detector counting efficiencies and narrower spectral filters available at 532 nm. The transmitter produces several microjoules of green energy in a subnanosecond pulse at rates approaching 10 kHz. The illuminated ground area is imaged by a 14-cm diameter, diffraction-limited, off-axis telescope onto a segmented anode photomultiplier. Each anode segment is input to one channel of fine range receiver (5-cm resolution), which records the times-of-flight of individual photons. A parallel coarse receiver provides a lower resolution (greater than 75 cm) histogram of all scatterers between the aircraft and ground and centers the fine receiver gate on the last set of returns.

Simultaneous Laser Ranging and Communication from an Earth-Based Satellite Laser Ranging Station to the Lunar Reconnaissance Orbiter in Lunar Orbit

We report a free space laser communication experiment from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in lunar orbit through the on board one-way Laser Ranging (LR) receiver. Pseudo random data and sample image files were transmitted to LRO using a 4096-ary pulse position modulation (PPM) signal format. Reed-Solomon forward error correction codes were used to achieve error free data transmission at a moderate coding overhead rate. The signal fading due to the atmosphere effect was measured and the coding gain could be estimated.

Laser Ranging bBetween the Mercury Laser Altimeter and an Earth-Based Laser Satellite Tracking Station over a 24-Million-km Distance

Using the Mercury Laser Altimeter, a 10-cm laser ranging precision was demonstrated between Earth and the MESSENGER spacecraft over a 24-million-km distance in space.