Navigation techniques for microsatellites targeted to the Moon
- Paper number
IAC-08.B4.8.9
- Author
Dr. Giovanni B. Palmerini, Universita' di Roma 'La Sapienza', Italy
- Coauthor
Mr. Marco Sabatini, University of Rome "La Sapienza", Italy
- Coauthor
Mr. Fabrizio Reali, Aerospace Engineering School, University of Rome "La Sapienza", Italy
- Year
2008
- Abstract
Interest for lunar missions spread recently, with special emphasis for missions exploited by small spacecraft of the mini- or micro-satellite classes. Many of these missions have been proposed by Universities or small enterprises, and quite often designed with limited resources. The interest itself is driven by the number of foreseen larger missions, which should offer some chance of “hitchhiking” to the Moon. For university (or similarly sized) projects, however, the step between Low Earth Orbiters, many of which already successfully launched, and a lunar mission is a giant one. One of the largest obstacles is given by guidance and navigation performances needed to succeed in mission objectives. Antenna/power constrained amateur ground stations currently used for LEO can not provide sufficient TT&C, and ground segment is a limited and expensive resource. But, microsatellites can not accommodate, for both budget and volume constraints, sophisticated suites of sensors like star trackers. A possible, innovative technique make use of the spillovers of the satellite navigation systems (GPS, Glonass or GNSS at large) signals. Sat-Nav receivers offer a valuable solution from both the points of view of the cost and of the requirements (mass, volume, power) imposed to a limited bus typical of small satellites. Previous work by several authors, including some contribution from the proponents, investigated the available signal level and showed it is suitable, even without a really continuous coverage. In orbit measurements up to extremely high eccentric orbits (not yet in lunar ones) experimentally confirmed these findings. To fix for periods of limited signal availability and grant a continuous navigation, dynamic models which exploit the knowledge of the orbital environment should be introduced in the guidance function of the spacecraft. Otherwise, data fusion with other sensors can be considered. In both cases, specialized filtering is required to increase system performances. The paper aims to discuss the technological readiness of this guidance and navigation concept, deemed as a mandatory component of every small spacecraft mission to the Moon. Two scenarios will be considered, in order to take into account different hitchhiking possibilities, with the primary payload either targeted to orbit the Moon, or aimed to very specific descent trajectories and therefore leaving other passengers far away before. In the first case the shared ride ends in a generic lunar orbit, and the descent phase (for a probe) or the repositioning in a orbit of interest, with relevant manoeuvres, will be exploited on the basis of available navigation data. In the second scenario, the shared ride ends before lunar orbit acquisition, and the task of the microsatellite-based navigation system will be of course more demanding, as many more manoeuvres will depend on. Feasibility and performances analysis have to be carried out on the basis of the covariance analysis for trajectories matching the thrust level typical for a small satellite. Final findings are represented by the figures of the accuracy a microsatellite sharing a ride to the Moon could expect in exploiting its designed trajectory: these figures are certainly a basic point in assessing such a kind of opportunity missions.
- Abstract document
- Manuscript document
IAC-08.B4.8.9.pdf (🔒 authorized access only).
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