Coordinate and Time Support of Flights Between the Earth and the Moon

A. V. Bagrov, S. P. Kuzin, V. A. Leonov

Transactions of IAA RAS, вып. 50, 3–9 (2019)

DOI: 10.32876/ApplAstron.50.3-9

Keywords: navigation beacons, positioning, flight to the Moon, optical active beacons, angular measurements

Abstract

Currently, all problems of the spacecraft positioning in space are solved using the methods based on measurements from the Earth. These measurements are precise enough because the positions of the space objects are measured relatively to a number of geodetic reference points located on the Earth’s surface. However, the positioning becomes less accurate when the distance grows between the object and the reference points. Thus, the accuracy in the positioning of the low-orbit objects is about 1 meter, and it falls by 3, 4 or even 5 orders of magnitude when the objects are near the Moon. A significant increase in the navigation accuracy can be achieved if the astrometric reference points (beacons) are placed both on the Moon and onboard the near-earth navigation satellites. This will fix the coordinate system to one of such beacons on the body of the Moon. It is possible to calculate the position of the center of mass of the Moon from the beacon accurately enough if the selenographic coordinates of the beacon are measured. Also, an active optical beacon onboard the navigation satellite can be observed from the spacecraft which is flying to the Moon. Thus, the exact position of the navigation satellite can be known relatively to the center of mass of the Earth. It gives us the opportunity to calculate the exact spatial position of the spacecraft having measured the distances between the beacons simultaneously by the spacecraft’s onboard star trackers and having solved the “navigation satellite-spacecraft-lunar beacon” triangle. The positioning error of the spacecraft on the entire route of its flight will not exceed 2 km if the accuracy of the onboard star sensors is 1 second of arc. The proposed active optical beacons are planned to be delivered to the Moon by the Luna-25 mission.

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