NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) mission was both a lunar science and a technology demonstration mission. The goals identified for LADEE were to determine the composition of the lunar atmosphere and investigate the processes that control its distribution and dynamics, and to determine whether dust is present in the lunar exosphere and reveal the processes that contribute to its sources and variability. LADEE was also developed to serve as a platform for the Lunar Laser Communications Demonstration (LLCD), which had the goal of demonstrating the viability of high-speed optical communication to and from the Moon. LADEE met all of these objectives by operating a robotic spacecraft in a low-altitude, near circular, near equatorial lunar orbit where remote sensing and in-situ instruments measured the Moon's atmosphere and dust environment, and the LLCD demonstrated optical communications at lunar distances. The spacecraft was launched in September of 2013, and spent approximately one month in a transfer orbit before being inserted into lunar orbit in October. It orbited the moon for 188 days, logging time over five lunar synodic months, i.e., "lunations", before being decommissioned via surface impact in April of 2014. LADEE exceeded its baseline mission duration by greater than 40% in terms of time in the science orbit, and greater than 200% in terms of science data return. This paper summarizes the LADEE mission architecture and describes the operational phase of the LADEE mission in detail. The combination of an aggressive science campaign, the demonstration of a new optical communications payload, and the first-use of a new low-cost spacecraft bus resulted in an operational phase filled with challenges, both planned and unplanned. We explain our approach to orbit determination, maneuver planning, attitude planning, activity planning and command sequencing, which yielded exceedingly positive results in the face of a demanding operational timeline consisting of hundreds of interleaved instrument and spacecraft activities. In addition, we discuss the team's identification of, and response to, several in-flight anomalies including a shutdown of the spacecraft's reaction wheels immediately following launch and an on-going unexpected behavior of the on-board star-tracker and attitude state estimation system. Finally, we reflect on the operations experience overall, the successes that LADEE enjoyed, and some suggestions for future lunar missions.

No abstract

The Lunar Crater Observation and Sensing Satellite (LCROSS) spacecraft orbited the earth in an inclined orbit that intersected the moon's south pole on October 9, 2009, resulting in an impact that allowed measurement of the water content in the debris cloud. The main communications requirement was providing robust command and telemetry links for spacecraft operations, including trajectory correction maneuvers and housekeeping. The payload consisted of cameras and spectrometers capable of imaging the visible, near and mid-IR spectrums, requiring 1 Mbps downlink for full science capability at lunar range. This communications performance was delivered by a pair of omni directional antennas coupled with medium gain antennas used for the high-speed science rate. Over the complex flight path that lasted over 3 months, there were many intervals where communications rates were much reduced due to interference between the two omni-directional antennas. Analytical Graphics' Satellite Toolkit was used for modeling the LCROSS spacecraft orbit, its antennas and its attitude with respect to the relevant Deep Space Network ground stations. Link predictions were used to confirm adequate uplink margin for commanding the spacecraft and to recommend downlink data rates supported at the current attitude and range. After initiation of flight operations, a detailed assessment of link performance was performed in order to validate the modeling and to make any necessary improvements. The primary goal was to confirm the accuracy of the modeled omni-directional antenna radiation patterns, particularly the interferometry region. Also of interest was the effect of small attitude motion within the attitude control system dead-band. The capability of predicting variations in link margin based on actual antenna radiation characteristics and dead-band motion greatly improved the accuracy of link margin prediction. Link performance data from actual LCROSS maneuvers are presented to illustrate the methods. Nomenclature dB = decibel IR = infrared Kbps = kilo-bits per second Km = kilometer Mbps = mega-bits per second RF = radio frequency