Planet-C

Description

Planet-C, also known as the Venus Climate Orbiter, is a Japanese Space Agency (JAXA) mission to study the dynamics of the atmosphere of Venus from orbit, particularly the upper atmosphere super-rotation and the three-dimensional motion in the lower part of the atmosphere, using multi-wavelength imaging. It will also measure atmospheric temperatures and look for evidence of volcanic activity and lightning. The scientific payload consists of the Ultraviolet Imager (UVI), the Longwave Infrared Camera (LIR), the 1-mm Camera (IR1), the 2-mm Camera (IR2), and the Radio Science (RS) experiment.

Spacecraft and Subsystems

The Planet-C main bus is a 1.6 m x 1.6 m x 1.25 m box with two solar array paddles, each with an area of 1.4 square meters, on opposite (+y and -y) sides and a 1.6 m high gain antenna on the +x side. On the opposite side (-x) from the antenna is a 0.45 m long orbital maneuvering engine. The total launch mass of the spacecraft including propellant will be 480 kg, 34 kg of this will be scientific instruments.

Propulsion is provided by the 500 N bi-propellant (hydrazine and nitrogen tetroxide) orbital maneuvering engine and 12 mono-propellant (hydrazine) reaction control thrusters, eight with 23 N thrust and four with 3 N. The spacecraft is 3-axis stabilized. Attitude control is achieved using 4 reaction wheels, two with 20 Nms momentum capability and two with 4 Nms, which can be unloaded by the reaction control thrusters. Attitude knowledge is obtained using a gyroscopic inertial reference unit, star trackers, sun sensors, and accelerometers.

The solar array panels provide over 1200 W of power in Venus orbit and can rotate about their arms in the y-axis. Power can be used directly or stored in batteries. Communications is via a 20 W X-band (8 GHz) transponder using the 1.6 m slot array high gain dish antenna (for most telemetry data), a pair of medium gain horn antennas mounted on turntables (for housekeeping data downlink when the high gain antenna is not facing Earth), or a pair of low gain antennas (for command uplink). Thermal control is achieved through multilayer insulation, radiators, and heaters designed to keep the inside of the spacecraft below 20 degrees C.

Mission Profile

Planet-C will launch on an M-V rocket sometime in May of 2010 into an Earth phasing orbit with an apogee greater than 200,000 km and will then be put into a Venus transfer orbit. The spacecraft will reach Venus in December 2010 and go into a near equatorial (inclination 172 degrees) 30 hour Venus orbit with an apoapsis of about 79 000 km and a very low periapsis, approximately 300 km above the surface. The mission will last at least 2 Earth years, limited primarily by degradation of the onboard batteries.