Okev

The OKEV microsatellite is a student project to design a scientific mission, which uses hyperspectral wide field imaging in exploring marine and coastal environments. In order to better utilize the hyperspectral instrument it was suggested to place OKEV in orbit with an existing “On – going” constellation of Earth remote sensing satellites. OKEV operates in a circular sun synchronous Earth repeating orbit (altitude 705 km, inclination 98.2º) as part of the AM-Train formation, which consists of 4 currently in orbit satellites: Landsat 7, EO-1, SAC-C, and Terra. OKEV crosses the equator at 10:07 local time. It is six minutes after EO-1 and usually four minutes before SAC-C. The several simulations for OKEV’s orbit calculation, analysis and visualization were fulfilled using Satellite Tool Kit (STK-5.0) produced by Analytical Graphic, Inc. (AGI).

OKEV satellite design guidelines included: using trade studies to iterate spacecraft designs and components; and selecting COTS equipment whenever possible while injecting advanced technologies. OKEV satellite presents an aluminium structure composed of prism and pyramid parts and is stabilized about all three axes using an integrated momentum biased system with some acquisition modes. TAMAM’s magnetotorquers provide the system with efficient momentum discharge capability. The redundant attitude sensor set includes a 3-axis magnetometer, a star tracker and a block of FOGs. System nadir pointing capability is about 1°.

The satellite employs cold-gas reaction thrusters designed by RAFAEL for manoeuvres and has redundant on-board computers for command and data handling. Thermal control is provided by a combination of passive methods. Communications (mission and telemetry) with ground station use innovative S-bands link. Electrical power, provided by body-mounted Si solar cells and Li-Ion batteries, exceeds 63 W averages including more than 15% margin. OKEV design accommodates mean mission duration of 5 years. For the OKEV launch the Russian relative low cost, high performance and reliability launchers (DNEPR, KOSMOS, START, ROCKOT and TSIKLON) were be chosen. Its docking systems are compatible with OKEV structure and mechanical interface.

The OKEV payload is a remote sensor of the Earth and the Earth’s atmosphere operated in the hyperspectral mode – WFIS (Wide Field Imaging Spectrometer). WFIS wide field of view is 120º. WFIS has a contiguous scanning range of 400-2500 nm, a spectral resolution of 3.3 nm, and 632 possible bands. OKEV can utilize only 20 different bands at each operational session due to memory constraints and limited ground station access times. The satellite total mass is less than 85 kg including 20 kg of WFIS mass.

Results of OKEV orbital dynamic computations are presented in the article published in AGI’s May 2004 In-View newsletter, as an example of successful STK application www.agi.com/invriew: