Command generation for high gain antenna on lunar orbiter to communicate with deep space network

Abstract

Korea has a plan to launch lunar orbiter by using Korea Space Launch Vehicle (KSLV-II) in 2020. This mission will be the first observatory of Korea to analyze feature of Lunar. The lunar orbiter will take information with mounted payloads such as camera, radiometer, altimeter and detector while orbiting at unrivalled altitude of 100km. The orbiter will communicate with Deep Space Network (DSN) such as receiving command generation and sending collected information through High Gain Antenna (HGA). Lunar Reconnaissance Orbiter (LRO) lunched by NASA in 2008 can be a representative example of lunar orbiter. It communicates with DSN via HGA that is divided with S-band which uses for tracking and command generation of spacecraft and Ka-band that is for transmitting the information of Moon. The data volume through each band are 4.84 Gbits and 460 Gbits per day, and they are hard to transmit once due to data rates

4 kbits/s for uplink and 100 Mbit/s for downlink in order. Therefore, command generations based on tracking information are separated and uploaded 12 times per a day, and the data of lunar information is downloaded to DSN 4 times per a day on average. For communication with DSN during a given time, and increasing data margin, pointing accuracy is required. To point ground stations, 172800 attitude command of azimuth and elevation angle for HGA are generated during a day. Transmitting the generated attitude command with respect to time is under limitation on the amount of traffic. Thus, command generation for HGA is dealt in this thesis based on compression method to reduce the data volume that is necessary to communicate with DSN.