Second try of Akatsuki – JAXA’s probe will try another rendezvous with Venus on 7th December 2015

After failed try five years ago, JAXA will perform another attempt to move Akatsuki into Venus Orbit.

Venus as second planet from the Sun and is third brightest object in our sky. Its brightness is at –4,6m. Distance between Earth and Venus varies in the range 40 million to 259 million kilometers. Due its dimensions and surface it is similar to Earth. Mean radius is at 0.9499 Earths, surface is at 0.902 Earths. Gravity at the surface level is at 0.904 g. Discovered places on Venus are covered with rocks and dust. Atmosphere consists mostly of carbon dioxide, pressure at atmosphere is 92 bar, and temperature on the surface is 460 °C. Due the extremely unfriendly conditions for manned missions, Venus was not in the center of attention during planning probe missions. First Soviet Wenera-1 probe launched in 1961, failed to send gathered data due the problems with communication. American probe Mariner-2 reached Venus and measured density of Venus atmosphere. Following probes from Wenera and Mariner series were gathering data about temperature, density and composition of atmosphere and surface of Venus. First pictures were taken by Wenera-9 and Wenera-10 spacecrafts. Until 2010 various probes were reaching Venus including Magellan radar mapping satellite, Venus Express and first Japanese Venus probe called Akatsuki which should reach Venus orbit in the same time as Venus Express launched by ESA. Unfortunately Akatsuki due failed attempt to recovery contact after occultation by Venus and stayed on heliocentric orbit.

JAXA attempts to use Akatsuki again gave results. After five years, probe reached Venus, and on 7th December 2015 will be again able to inject into orbit. It is impressive, that after five years of space wandering Akatsuki remains fully operational. Probe was developed as climate observer - the aim is inter alia confirming presence of lightings and seismic activity. Akatsuki was designed as medium spacecraft with mass at 500 kg, where 34 kg are designated for scientific equipment; dimensions are 1.6 m x 1.6 m x 1.25 m. Probe is in the shape of a cuboid with two solar arrays at 1.4 m each. Arrays are equipped with motors which are positioning arrays to sun - they are providing 1200 W of power. Akatsuki is equipped with propulsion fueled with hydrazine and nitrogen tetroxide - main engine has thrust at 500 N, twelve additional control thrusters are fueled only with hydrazine; eight of them are giving 23 N and four are providing 3 N of thrust. Spacecraft has 196 kg of propellant. Communication with Earth is provided by 8 GHz transponder working on X band with power at 20 W. It is utilizing 1.6 m dish antenna and two turn able low gain antennas for communicating when dish is not faced to the Earth. Scientific capacity was extremely filled with research instruments. IR1 camera is imaging on 0.90 micron wavelength (day) and 0.91, 0.97, 1.01 wavelength (night). Camera detective array is Si-CSD(charge sweeping device)/CCD with active cooling, weight is at 3.7 kg with power consumption at 9.4 W. IR1 main objective is to find active volcanos or hot lava on the surface. IR2 camera is imaging on 1.73, 2.26, and 2.32 micron wavelength, it is also actively cooled. Power consumption is at 50 W and mass is 9 kg. Camera is designed to cloud observations which will be useful in creating map of Venusian winds. Next instrument is UVI. It is emitter of UV rays which will be measured after scattering from clouds at 65 km altitude. Goal of this experiment is identification of UV rays absorber. Atmosphere of Venus has strong ability of absorbing solar radiation due heavy sulfur oxide clouds (UV in range 200 nm- 320 nm) and unidentified absorber (for over 320 nm UV values). UVI weighs around 3.4 kg with power consumption at 9.4 W. Longwave Infrared Camera (LIR) is instrument designed for measuring temperature of upper layer of clouds. Resolution of the sensor is 320 x 240 pixels (pixel size is 37 micron). LIR weight is at 3.7 kg with power consumption at 29 W. All four cameras are controlled by Sensor Digital Electronics Unit (DE). This unit is responsible for gathering RAW data, arithmetic data processing and compression, preparing telemetry data for downlink. DE is also controller for cameras, which sets exposure, gain and adds filters. Another instrument is LAC - Lightning and Airglow Camera - imaging sensor designed especially for taking images of lightings. It will image single lightings with frequency at 50 Hz; airglow will be recorded in 20 s intervals. Viewing angle is 16 degrees; utilized sensor is multi-anode avalanche photo-diode (APD) with resolution 8 x 8 with 2 mm square pixel. Weight of the LAC is 1.5 kg. Last part of scientific equipment is Radio Science (RS). It is designed to measure density, atmospheric temperature and electron density in ionosphere. RS will utilize signal generated by 8.4 GHz transponder. Signal will be received on Earth and basing on its variation various parameters of atmosphere will be recognized.

On 7th December Akatsuki will try to inject itself on elliptical orbit, 299 km to 80,467 km away from Venus’s surface. Last correction of trajectory took place on 2 August 2015. For now JAXA can only wait - another try is possible after next 5 years...