The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission

The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced.     

The Solar Terrestrial Relations Observatory (STEREO) Education and Outreach (E/PO) Program

The STEREO mission’s Education and Outreach (E/PO) program began early enough its team benefited from many lessons learned as NASA’s E/PO profession matured. Originally made up of discrete programs, by launch the STEREO E/PO program had developed into a quality suite containing all the program elements now considered standard: education workshops, teacher/student guides, national and international collaboration, etc. The benefit of bringing so many unique programs together is the resulting diverse portfolio, with scientists, E/PO professionals, and their education partners all of whom can focus on excellent smaller programs. The drawback is a less cohesive program nearly impossible to evaluate in its entirety with the given funding. When individual components were evaluated, we found our programs mostly made positive impact. In this paper, we elaborate on the programs, hoping that others will effectively use or improve upon them. When possible, we indicate the programs’ effects on their target audiences.     

Drag coefficient modeling for grace using Direct Simulation Monte Carlo

Drag coefficient is a major source of uncertainty in predicting the orbit of a satellite in low Earth orbit (LEO). Computational methods like the Test Particle Monte Carlo (TPMC) and Direct Simulation Monte Carlo (DSMC) are important tools in accurately computing physical drag coefficients. However, the methods are computationally expensive and cannot be employed real time. Therefore, modeling of the physical drag coefficient is required. This work presents a technique of developing parameterized drag coefficients models using the DSMC method. The technique is validated by developing a model for the Gravity Recovery and Climate Experiment (GRACE) satellite. Results show that drag coefficients computed using the developed model for GRACE agree to within 1% with those computed using DSMC.     

Extragalactic Abundances of Hydrogen,Deuterium and Helium New Steps,Missteps and Next Steps

Estimates of the deuterium abundance in quasar absorbers are reviewed, including a brief account of incorrect claims published by the author and a brief review of the problem of hydrogen contamination. It is concluded that the primordial abundance may be universal with a value (D/H)P 10-4, within about a factor of two, corresponding to _Bh _0.7 ² 0.0fs2 or 10 2.7 in the Standard Big Bang. This agrees with current limits on primordial helium, YP 0.243, which are shown to be surprisingly insensitive to models of stellar enrichment. It also agrees with a tabulated sum of the total density of baryons in observed components. Much lower primordial deuterium ( 2 × 10^-5) is also possible but disagrees with currently estimated helium abundances; the larger baryon density in this case fits better with current models of the Lyman- forest but requires the bulk of the baryons to be in some currently uncounted form.     

Optimum Alignment of an Inertial Autonavigator

The performance of an inertial autonavigator can only be as good as the accuracy to which the system is initially aligned. Optical methods of alignment can be performed with high precision; however, this technique requires external equipment and is subject to some physical constraints, such as land-based operation. The general problem discussed here is the use of an automatic azimuth alignment technique known as gyrocompassing. In the use of the gyrocompassing technique to obtain azimuth alignment, accuracies are degraded considerably by two dominant error sources, the level axis controlling gyro drift rate and the imperfections of reference or independent velocity information. Consequently, an optimum performance controller is developed for driving the system in this mechanization and is based on a priori knowledge of the second-order statistics of the system error sources. The performance criteria will be to minimize the mean square azimuth error.