Pilotage non linéaire en temps minimum d'un engin spatial propulsé

Spacecraft missions may call upon great amplitude changes of attitude within a minimum of time. With a view to define an absolute performance criterion for the spacecraft and, if need be, to guide the research towards the definition of piloting algorithms, it is necessary to determine the open loop optimal control. A numerical method, based on the Pontryagin Maximum Principle, has been defined to carry out this study. It has been applied to the non linear problem of the three-dimensional piloting of a rigid powered spacecraft in atmosphere-free vacuum.     

Global Gravity Field Recovery Using Solely GPS Tracking and Accelerometer Data from Champ

A new long-wavelength global gravity field model, called EIGEN-1, has been derived in a joint German-French effort from orbit perturbations of the CHAMP satellite, exploiting CHAMP-GPS satellite-to-satellite tracking and on-board accelerometer data over a three months time span. For the first time it becomes possible to recover the gravity field from one satellite only. Thanks to CHAMP'S tailored orbit characteristics and dedicated instrumentation, providing continuous tracking and on-orbit measurements of non-gravitational satellite accelerations, the three months CHAMP-only solution provides the geoid and gravity with an accuracy of 20 cm and 1 mgal, respectively, at a half wavelength resolution of 550 km, which is already an improvement by a factor of two compared to any pre-CHAMP satellite-only gravity field model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of heavy particle irradiation and diet on object recognition memory in rats

On long-duration missions to other planets astronauts will be exposed to types and doses of radiation that are not experienced in low earth orbit. Previous research using a ground-based model for exposure to cosmic rays has shown that exposure to heavy particles, such as ⁵⁶Fe, disrupts spatial learning and memory measured using the Morris water maze. Maintaining rats on diets containing antioxidant phytochemicals for 2 weeks prior to irradiation ameliorated this deficit. The present experiments were designed to determine: (1) the generality of the particle-induced disruption of memory by examining the effects of exposure to ⁵⁶Fe particles on object recognition memory; and (2) whether maintaining rats on these antioxidant diets for 2 weeks prior to irradiation would also ameliorate any potential deficit. The results showed that exposure to low doses of ⁵⁶Fe particles does disrupt recognition memory and that maintaining rats on antioxidant diets containing blueberry and strawberry extract for only 2 weeks was effective in ameliorating the disruptive effects of irradiation. The results are discussed in terms of the mechanisms by which exposure to these particles may produce effects on neurocognitive performance.     

Isotopic Signatures of Volatiles in Terrestrial Planets - Working Group Report

Variations in the isotopic ratios of volatile elements in different reservoirs on the terrestrial planets carry information about processes that operated on the planets since their formation. Comparisons between primordial planetary compositions, to the extent they can be determined, may help us understand the planetary formation process. This working group report summarizes our knowledge of terrestrial planet volatile inventories. This revised version was published online in August 2006 with corrections to the Cover Date.     

Journey to the Moon: Recent results,science, future robotic and human exploration

The upcoming fleet of lunar missions, and the announcement of new lunar exploration initiatives, show an exciting “Journey to the Moon”, covering recent results, science, future robotic and human exploration. We review some of the questions, findings and perspectives given in the papers included in this issue of Advances in Space Research.     

Impact analysis of the transponder time delay on radio-tracking observables

Accurate tracking of probes is one of the key points of space exploration. Range and Doppler techniques are the most commonly used. In this paper we analyze the impact of the transponder delay, $i.e$. the processing time between reception and re-emission of a two-way tracking link at the satellite, on tracking observables and on spacecraft orbits. We show that this term, only partially accounted for in the standard formulation of computed space observables, can actually be relevant for future missions with high nominal tracking accuracies or for the re-processing of old missions. We present several applications of our formulation to Earth flybys, the NASA GRAIL and the ESA BepiColombo missions.