MICRO-SATELLITES: SMALLER AND SMALLER

Even as the space powers built ever bigger and more powerful launchers, the 1990s saw, paradoxically, the introduction worldwide of ever-smaller satellites. This development was made possible by electronic microcircuits and more sophisticated computers that permitted satellites to be not only much smaller, but also much smarter – able to do more and more without the intervention of ground control. These new versatile satellites could be launched on smaller, less-expensive rockets (e. g. the American Pegasus) or as piggyback payloads on existing rockets (e. g. Russian Dnepr), thus cutting costs even further. Technically, this new generation could be divided into small satellites (less than 500 kg), micro-satellites (less than 100 kg), nano-satellites (less than 10 kg), and even pico-satellites (less than 1 kg!). The principal developer of “large” small satellites is the DFH Satellite Co., a subsidiary of CAST, which makes three buses: CAST100 (50-250 kg); CAST2000
(300-1,000 kg), and CAST968 (around 400 kg). “Small” satellites have generally been made in the universities.

China was quick to join the micro-satellite revolution. Tsinghua University was the center of micro-electronics in China and hosted the National Aerospace High Technology Space Robotic Engineering Research Centre. The center obtained project 863 funding for the development of micro-satellites and set up the Tsinghua Satellite Technology Company in 1998 as a joint enterprise of China Space Machinery and Electrical Equipment Group, Tsinghua University Enterprise, and Tsinghua Tongfang Company. The engineers there turned to the world leaders in this technology, the University of Surrey in England (Surrey Satellite Technology Limited (SSTL)), to build their first micro-satellite.

China’s first small satellite entered 700-km high orbit on 20th June 2000, lofted by a Russian Cosmos 3M rocket from Plesetsk. The 75-kg micro-satellite, duly called Tsinghua 1, was 1.2 m high with a volume of only 0.07 m3. No sooner was Tsinghua in orbit than it sent back its first photographs of the China Sea. Tsinghua carried a camera system able to image the Earth in three spectral bands with 39-m resolution so as to monitor vegetation, floods, wild fires, desertification, and red tides. Within a month, it had sent back over 100 images, which the university made available free to anyone requesting them. Its design life was 10 years and, according to senior engineers at Tsinghua, Xu Xin, was a serious attempt to close the gap with Indian and Western imaging systems. In orbit, it also took part in rendezvous maneuvers with another Surrey satellite, the 6.45-kg nano-satellite SNAP-1 (Surrey Nano­satellite Applications Platform). Following its success, China announced the establishment of a National Research Centre for Small Satellites and Related Applications. First ground for an 8,000-m2 site was broken on 20th April 2003.

The University of Tsinghua hoped that this would pave the way for a constellation of micro-satellites, also to be developed with SSTL, a fleet of 70-kg disaster-warning satellites. This fleet would comprise satelhtes from China, Algeria, Nigeria, Turkey, and Britain in a high polar orbit. This five-satellite Disaster Monitoring Constellation (DMC) was duly launched, the Chinese one called Beijing 1 or DMC-4. Built by SSTL for Beijing Landview Mapping Information Technology, it was launched on Cosmos 3M from Plesetsk on 27th October 2005 into a 686-km Sun-synchronous orbit. Beijing 1 was 166 kg in weight, carried a 4-m panchromatic camera capable of transmitting real-time data at 40 МВ/sec, and a 32­m multispectral camera with a swath of 600 km. It had a hard disk with 240-GB storage, accessible at any time. By 2007, it had completed a 32-m-resolution cloud – free map of all China, with a 4-m-resolution map of Beijing. Part of the approach of Surrey was that engineers would learn from their participation in such a satellite so that they could apply the same methods to build their own – an example followed in the case of Nigeria. Meantime, as a learning exercise, Tsinghua went on to build Naxing, substantially more sophisticated and the smallest satellite with three-axis stabilization [21].

On 27th June 2011, SSTL signed an agreement with 21 AT (21st Century Aerospace Technology) for a new satellite to be part of a new DMC, the agreement being witnessed by the two respective prime ministers, David Cameron and Wen

Jiabao. It would be a three-satellite constellation to launch on a Russian Dnepr from Dombarovsky, each of the new satellites having a resolution of 1 m (panchromatic imaging) and 3 m (multispectral). The agreement gave 21 AT exclusive access to the images of China for mapping purposes.

China’s first indigenous micro-satellite was the 88-kg Chuangxin, meaning “creation” or “innovation” – a program associated with the Academy of Sciences Knowledge Innovation Program. This was a store-and-forward communications satellite built in the southern part of the country by the Shanghai Academy for Space Technology Engineering Centre for Micro-satellites for the Academy of Sciences and Shanghai Telecom. It was launched in October 2003 piggyback on the CBERS 2 Brazilian-Chinese Earth resources satellite. It was developed to assist in hydrology, meteorology, and disaster relief: Chuangxin works by picking up data from monitoring points, buoys, and meters, collecting data on water, hydrology, and

electric power and then relaying them to a center source. Tracked by terminals in Shanghai, Beijing, Xinjiang, and Hainan, it showed off its digital communications capacities and was unaffected by two strong solar flares and 29 single-particle incidents. The following two Chuangxin, 1-02 and 1-03, were put into orbit on Tansuo 2 and 4, respectively (see above).

China’s first pico-satellite (1 kg) was MEMS, deployed with Yaogan 2. Its purpose was to test accelerometers, micro-gyros, infrared sensors, and a camera for Zhejiang University and the Shanghai Institute of Microsystems and Information Technology. It had 26 sides (18 square faces and eight triangle faces), two antennae, and 17 solar cells of 270 cm2 able to provide 2 W of power. The satellite had no moving parts, attitude control, or propulsion system. S-band telemetry is relayed at 4 kbps at 2,300 MHz, with uplink on 2,100 MHz. It is more than likely that the subsequent Pixing subsatellites detached by Yaogan 11, although heavier at 2.5 kg and 3.5 kg, respectively, are derivatives of MEMS, as they were developed in the same laboratory [22].

Other small satellites have been carried piggyback into orbit. Xi Wang was an amateur small radio satellite deployed from Yaogan 8. A small technology development satellite, Tianxun 1, was launched with Yaogan 12 in November 2011. Meaning “day tour”, it was built by Nanjing University of Aeronautics and Astronautics. It is a 58-kg satellite with a 2.5-kg Earth imaging camera of resolution 30 m built by Suzhou University. Yaogan 14 deployed a small satellite for the National University of Defence Technology. Called Tiantuo 1, or “space pioneer”, it carried an imager, atomic oxygen sensor, and maritime tracking sensor. Between them, these 10 satellites gave China considerable edge in the development of small satellites. Small satellites are summarized in Table 6.12.