COMPASS: VLBI Beacons In Support of Lunar Science and Exploration (original) (raw)
Related papers
Relative position determination of a lunar rover using high-accuracy multi-frequency same-beam VLBI
Science China-physics Mechanics & Astronomy, 2010
Multi-frequency same-beam VLBI means that two explorers with a small separation angle are simultaneously observed with the main beam of receiving antennas. In the same-beam VLBI, the differential phase delay between two explorers and two receiving telescopes can be obtained with a small error of several picoseconds. The differential phase delay, as the observable of the same-beam VLBI, gives the separation angular information of the two explorers in the celestial sphere. The two-dimensional relative position on the plane-of-sky can thus be precisely determined with an error of less than 1 m for a distance of 3.8×105 km far away from the earth, by using the differential phase delay obtained with the four Chinese VLBI stations. The relative position of a lunar rover on the lunar surface can be determined with an error of 10 m by using the differential phase delay data and the range data for the lander when the lunar topography near the rover and the lander can be determined with an error of 10 m.
Orbit determination and time synchronisation in lunar orbit with GNSS -Lunar Pathfinder experiment
72nd International Astronautical Congress (IAC), 2021
The internal roadmap for deep space exploration proposed by the International Space Exploration Coordination Group (ISECG) clearly identifies the Moon as the first step towards a larger solar system exploration. In this context, the use of Earth Global Navigation Satellite System (GNSS) signals at Moon altitude has been extensively studied in the past, within and outside the European Space Agency (ESA). This interest has been reflected in "The Interoperable Global Navigation Satellite Systems Space Service Volume" booklet issued by the International Committee on GNSS (ICG). NASA, with their Magnetospheric Multiscale Mission (MMS) mission, has recently demonstrated the reception of GPS signals at a distance which is about halfway between Earth and Moon, marking an important step towards the use of this technology in future lunar operational missions. The very weak signals received in cislunar space and the particular unfavourable geometry with all the signal coming from a similar region of the sky (i.e. high Dilution Of Precision, DOP, values), requires the development of advanced techniques as part of the spaceborne GNSS receiver, both at signal processing level (higher sensitivity) and at navigation filter level. The current approach for deep space Orbit Determination and Time Synchronization (ODTS) relies on-ground-based solutions such as radiometric measurements via Telemetry, Tracking and Command (TTC) link or advanced solutions such as optical links (e.g. laser ranging and optical time transfer) or Very Long Baseline Interferometry (VLBI) techniques. The ground-based approaches suffer from relatively high cost, complexity in the sharing of spare ground resources (e.g. access to deep space network, DSN) and poor performances for real-time on-board ODTS (often in orders of kilometres or tens of kilometres). Based on ESA and NASA analysis presented in several publications, a lunar mission using a spaceborne GNSS receiver could achieve performances around 50-100 m 3D RMS orbit determination and microsecond level time synchronization accuracy with high availability in real time on-board, without the need of frequency ground contact. In this context, ESA is developing a spaceborne receiver that is expected to provide outstanding performances in cislunar space missions and plans to demonstrate this technology as part of the Lunar 1 Paper ID: 64095 oral Pathfinder mission planned to be launched in 2024. To the ESA knowledge, this could become the first ever demonstration of GNSS reception by a satellite in lunar orbit. The present contribution provides details of the experiment (including concept of operations, duration, etc.), the GNSS antenna and GNSS receiver and expected performances, potentially including real hardware in the loop tests with radio frequency constellation simulators and the engineering model of the GNSS receiver.
Science China-physics Mechanics & Astronomy, 2010
Same-beam VLBI means that two spacecrafts with small separation angles that transmit multi-frequency signals specially designed are observed simultaneously through the main beam of receiving antennas. In same-beam VLBI, the differential phase delay between the two spacecrafts and the two receiving antennas can be obtained within a small error of several picoseconds. As a successful application, the short-arc orbit determination of several hours for Rstar and Vstar, which are two small sub-spacecrafts of SELENE, has been much improved by using the same-beam VLBI data together with the Doppler and range data. The long-arc orbit determination of several days has also been accomplished within an error of about 10 m with the same-beam VLBI data incorporated. These results show the value of the same-beam VLBI for the orbit determination of multi-spacecrafts. This paper introduces the same-beam VLBI and Doppler observations of SELENE and the orbit determination results. In addition, this paper introduces how to use the same-beam VLBI for a lunar sample-return mission, which usually consists of an orbiter, a lander and a return unit. The paper also offers the design for the onboard radio sources in the lunar sample-return mission, and introduces applications of S-band multi-frequency same-beam VLBI in lunar gravity exploration and applications during all stages in the position/orbit determinations such as orbiting, landing, sampling, ascending, and docking.
COMPASS Final Report: Lunar Network Satellite-High Rate (LNS-HR)
2012
Two design options were explored to address the requirement to provide lunar piloted missions with continuous communications for outpost and sortie missions. Two unique orbits were assessed, along with the appropriate spacecraft (S/C) to address these requirements. Both constellations (with only two S/C each) provide full time coverage (24 hr/7 d) for a south polar base and also provide continuous 7 day coverage for sorties for specified sites and periodic windows. Thus a two-satellite system can provide full coverage for sorties for selected windows of opportunity without reconfiguring the constellation.