Small satellites have a tremendous potential in the civilian, scientific as well as military arenas having applications in diverse fields like communications, remote-sensing, meteorology, cartography, disaster management, and search and rescue

Microsatellites—or miniaturised satellites or small satellites, as these are sometimes referred to—represent a revolutionary breakthrough in satellite development. This ‘generation-next’ of satellites offers many advantages over conventional satellites. Small in size, these are cheap and have a rapid development cycle, allowing microsat-ellite projects to be completed in schedules as tight as one to three years. Their lighter weight and small size also permits these to be launched from smaller launch vehicles and, as demonstrated lately, multiple microsatel-lites can be inserted into orbit simultaneously using a single launch vehicle.

The credit for having launched maxi-mum microsatellites in orbit goes to the Russians who successfully launched 13 sat-ellites aloft one rocket in April 2007. India joined this elite club a year later on April 28, when a PSLV-C9 launch vehicle successfully introduced 10 satellites into space simul-taneously. Where the Indians scored over the Russians was that while the payload of the Indian mission was 829 kg, the Russian mission had a payload of only 300 kg.

On one hand, the low manufacturing and launch cost of small satellites make them ideal for testing advanced technologies for future satellite applications. Even failure of an experimental technology does not impose as much cost/time penalty as a full-fledged conventional satellite. On the other hand, their small size makes them quite complex with highly miniaturised rugged components. Nevertheless, small satellites have a tremendous potential in the civilian, scientific as well as military arenas having applications in diverse fields like communi-cations, remote-sensing, meteorology, car-tography, disaster management, and search and rescue.

Classification of satellites

Being a relatively new field, no standard classification of this class of satellites has been universally accepted as yet. They are variously called small satellites (SmallSat), cheap satellites (CheapSat), microsatellites (MicroSat), mini-satellites (MiniSat) and nano-satellites (NanoSat). The US Defence Advanced Research Projects Agency refers to these as light satellites (LightSats) and the US Naval Space Command as SPINSats (Single Purpose Inexpensive Satellite Systems). Nevertheless, in recent years, a generic method of classifying satellites, including small satellites, has been generally accepted. This is as follows:
• Large satellites: greater than 1,000 kg
• Medium satellites: 500 to 1,000 kg
• Small Satellites

- Mini satellites – 100 to 500 kg
- Micro satellites – 10 to 100 kg
- Nano satellites – 1 to 10 kg
- Pico satellites – 0.1 to 1 kg
- Femto satellites – less than 0.1 kg

Nano-satellites and Pico-satellites are also sometimes referred to as cube satellites (CubeSats) due to their little-bigger-than-matchbox size with one side of the satellite being approximately 10 cm. This category of small satellites has generated probably the greatest interest out of the category of small satellites.

Military perspective

Militarily, small satellites, especially micro and nano-satellites, hold tremendous poten-tial. Conceptually it is feasible to launch hundreds of small satellites almost simul-taneously by small size solid-fuel rockets. These are thus ideal for launch-on-demand applications which may be critical for future military space operations. Micro and nano-satellites can also be used effectively in anti-satellite (ASAT) roles. Microsatellites carrying hard-kill or soft-kill payloads can be manoeuvred close to the target satellite and activated at the desired time. China is said to be developing ASAT systems using ‘parasitic’ satellites capable of attaching themselves to target satellites without detec-tion and lying dormant till the need arises.

Microsatellites are best deployed in net-worked local satellite groups or distributed constellations which offer many advantag-es. Firstly, such networks/constellations are highly survivable. Even if one or more com-ponents satellites of such a constellation are damaged, unserviceable or ‘taken-out’, the constellation can continue functioning effectively using other satellites. Secondly, the combined processing power of satellite constellations may equal or even surpass bigger satellites. Thirdly, the target handling capability of a satellite constellation will be much more than a single satellite and they can cover more area. Last, but not the least, is the flexibility inherent to a network for carrying out multiple tasks simultaneously. Consequently, microsatellite constella-tions can be designed to support the entire spectrum of space-based C4ISR operations, such as surveillance, navigation, commu-nications, remote-sensing, electromagnetic intelligence (ELINT), and so on.

Trend worldwide

Due to their launch-on-demand capabil-ity, small satellites offer a few more tactical advantages. Microsatellites swarms can be launched over the area of interest at short notice, lending these an edge over conventional satellites that have to be pre-positioned after detailed planning as their orbital manoeuvre capability is restricted. Such satellites are more ‘military friendly’ as these can be placed over the target area in the correct time, space and duration like any other military weapon or sensor. Besides, these can provide highly flexible and survivable communication, naviga-tion and surveillance networks with build in redundancy over the tactical battle area. Perhaps due to this very reason several countries are pursuing military oriented microsatellite programmes.

In the US, interest in small satellites for military applications was kindled with the launch of Defense Advanced Research Projects Agency (DARPA)-sponsored 52 kg Global Low Orbiting Message Relay experimental satellite by the Space Shuttle in 1985. Thereafter, a large number of DARPA, National Aeronautics and Space Administration, US Navy and Air Force sponsored microsatellites have been launched by the US. Most of these were for communications, ELINT, Earth observation and experimental purposes. The former Soviet Union was known to have used con-stellations of small satellites of the COSMOS series for tactical communications. France, too, is said to be developing experimental electronic ELINT microsatellites called ESSAIM. Four of them, each weighing 120 kg, will be in LEO at 680 km and monitor radio communications. In 2004, France launched its first micro-satellite DEMETER (Detection of Electromagnetic Emission from Earthquake Regions) designed to record disturbances in the ionosphere due to earthquakes, volcanic eruptions and tsuna-mis. Most members of the EU, UK, Canada, Brazil and India, too, are engaged in small satellite research and development.