(https://img.novosti-kosmonavtiki.ru/153825.jpg) (http://spaceflight101.com/spacecraft/wp-content/uploads/sites/18/2016/08/TanSat-1.jpg)Image: TanSat Collaboration
TanSat, Tan being the Chinese word for Carbon, is China's first mission dedicated to Carbon Dioxide detection and monitoring using a payload of two instruments to track the atmospheric CO2 concentration and variability.
Funded by the Ministry of Science and Technology, the TanSat project was initiated in January 2011 to develop a small satellite mission for the detection of CO2 using a high-resolution spectrometer for the measurement of Carbon Dioxide via its near-infrared absorption bands, and a Cloud and Aerosol Polarimetry Imager to correct errors in the spectroscopic data caused by suspended aerosols and clouds.
The 500-Kilogram TanSat spacecraft has the main objective of measuring the atmospheric column-averaged CO2 dry air mole fraction with a precision better than four parts per million over the Chinese and international territory. Scientific goals of the mission include understanding the global CO2 distribution, variations over time and its role in climate change phenomena.
(https://img.novosti-kosmonavtiki.ru/153828.jpg) (http://spaceflight101.com/spacecraft/wp-content/uploads/sites/18/2016/08/TanSat-5.jpg)Image: TanSat Collaboration
Responsible for the overall management of the project is the Chinese Academy of Sciences, the satellite platform is developed by the Shanghai Institute of Microsystems and Information Technology, and the payloads are manufactured at the Changchun Institute of Optics, Fine Mechanics and Physics. The ground segment for the mission is managed by the National Satellite Meteorological Center.
The University of Leicester and the University of Edinburgh, UK participate in the mission as an international partners.
TanSat is tasked with a mission of at least three years, operating from a Sun Synchronous Orbit with an equator crossing at 13:30 local time and a revisit cycle of under 16 days. Measurements can be made as nadir, sun-glint and target observations with in-orbit calibration features to guarantee the accuracy of CO2 retrievals.
(https://img.novosti-kosmonavtiki.ru/153824.jpg) (https://img.novosti-kosmonavtiki.ru/153824.jpg)Image: TanSat Collaboration
As a large developing country, China has the world's highest levels of Greenhouse Gas emissions and the Chinese government identified the need for reducing GHG emissions, requiring access to spaceborne data on CO2 sources and sinks.
As a primary driver in climate change, Greenhouse Gases have been an important aspect of scientific study and a number of spacecraft to measure their distribution and temporal variation have flown in recent years including hosted instruments on weather satellites and dedicated missions such as ESA's Greenhouse Gases Observing Satellite and NASA's Orbiting Carbon Observatory.
To contribute to the study of CO2 in Earth's atmosphere, the China Academy of Science initiated in 2011 a five-year program to study the Carbon Budget and Relevant Issues and provide the information needed by policy-makers for informed decisions furthering a sustainable development plan to reduce GHG emissions.
The TanSat spacecraft utilizes a box-shaped satellite platform supporting the payload deck on the +X panel of the vehicle with a common instrument boresight to +Z which will constantly be facing the Earth. A pair of solar arrays are installed on the Y-panels of the satellite and constantly point to the -X direction when the satellite is in its duty attitude.
(https://img.novosti-kosmonavtiki.ru/153827.jpg) (http://spaceflight101.com/spacecraft/wp-content/uploads/sites/18/2016/08/TanSat-4.jpg)Image: TanSat Collaboration
The overall dimensions of TanSat are 150 by 180 by 200 centimeters in its stowed configuration with a launch mass of approximately 500 Kilograms including a 10-Kilogram propellant supply to support orbit maintenance over a three-year primary mission. With its solar arrays deployed in orbit, TanSat measures 7.4 meters from tip to tip.
The Electrical Power System of the spacecraft hosts two three-panel solar arrays with a total surface area of 10 square meters to ensure an end-of-life power generation of 1790 Watts. Power is fed to a central Power Control Unit that distributes a regulated 28-Volt power bus to the various satellite subsystems and manages the state of charge of a Li-Ion battery unit with a total capacity of 80 Amp-hours.
TanSat uses a three-axis stabilization system with a variety of attitude sensors and actuators. Attitude Determination is provided by a pair of star trackers in use as the primary attitude sensors, collecting imagery of the star-filled sky that are then compared with an onboard catalog to deliver accurate attitude data to the onboard computers. Data on body rates is captured by two gyros in use during de-tumbling and slew maneuvers while a pair of three-axis magnetometers delivers data on the magnetic field vector for the actuation of magnetic torque rods. Three sun sensors are available for attitude determination in a satellite safe mode to ensure proper sun-pointing of the solar arrays for power generation.
(https://img.novosti-kosmonavtiki.ru/153826.jpg) (http://spaceflight101.com/spacecraft/wp-content/uploads/sites/18/2016/08/TanSat-2.jpg)Payload Deck & Star Trackers – Image: TanSat Collaboration
Attitude actuation is provided by four reaction wheels to deliver a stable pointing capability for measurements in an Earth-pointed attitude.
Momentum is unloaded from the reaction wheels by four magnetic torque rods and four hydrazine monopropellant thrusters can assist in attitude control during de-tumble after launch and in safe mode. The thrusters are also in use for orbit adjustments and regular maintenance maneuvers to maintain the 13:30 equator crossing time to within 15 minutes over the course of the three-year mission. The four 1N thrusters reside on the -X panel of the satellite and are fed from a 20-liter hydrazine tank filled with 10kg of propellant at the start of the mission.
TanSat's attitude determination system delivers attitude solutions with an accuracy better than 0.03 degrees while the attitude actuators point the spacecraft to within 0.1 degree of the commanded orientation.
(https://img.novosti-kosmonavtiki.ru/153833.jpg) (http://spaceflight101.com/spacecraft/wp-content/uploads/sites/18/2016/08/W020151209501890506398.jpg)TanSat Payload Module – Photo: CIOMP
TanSat makes use of a centralized data handling system featuring an onboard computer that is in charge of all satellite functions from commanding of all subsystem activities, flight dynamics control, attitude data processing, payload data management and storage, telemetry control to thermal and power control. A CAN bus provides connectivity between the main computer and the payload controller as well as all other subsystems.
Command uplink and health data downlink is accomplished with an S-Band terminal supporting full-duplex communications at a 2kbps uplink and 8.192kbps downlink data rate.
A high-speed X-Band system is employed for the downlink of payload data at a rate of 64Mbps. Two antennas support the X-Band system, one pointed directly nadir (+Z) and one canted by 25 degrees to maximize downlink time when the satellite is in sun-glint observation mode, avoiding an attitude change for communications sessions. A 128 GBit onboard storage device holds collected payload data for downlink – typically within eight hours of acquisition.