SMALLER SATELLITES (LEO AND MICROSATS)

As reported herein, development continues towards producing ever higher power geostationary satellites. As a counterpoint to this trend, the advent of the "little LEO" and "big LEO" systems have given rise to many innovations in spacecraft design and manufacturing aimed at producing smaller satellites at lower cost. Motorola and Loral have created special factories for assembling the relatively large number of LEO satellites for Iridium and Globalstar. Manufacturing is treated as an end to end process, designed for efficient flow, continuous process improvement, and significant reduction in incremental testing, while also meeting high reliability goals.

These new concepts are also being applied to GEO satellites for certain applications. An example is Cakrawarta-1, launched in 1997 for Media Citra INDOSTAR, by Orbital Sciences Corp (OSC). Cakrawarta-1, shown in Figure 3.23, was developed by CTA prior to its acquisition by OSC. The Surrey Satellite Research Center is producing UoSat-12 (about 350 kg or 770 pounds) for Singapore. It carries 38 m resolution multispectral and 10 m monochromatic charge coupled device cameras with sophisticated onboard image processing, together with both VHF/UHF and L/S- bBand satellite communications. This satellite will fly in a LEO orbit. These mini-satellites in the 700 to 1,500 pound class are produced from technology largely within the envelope defined by large GEO satellites, yet may benefit from weight reduction technology aimed at the larger spacecraft. The mini-satellite will also offer opportunity for new technology, an example being an electric thruster produced at the Surrey Center. Matra Marconi has developed a new mini-satellite bus called LEOStar.

Microsatellites continue to be flown, with many carrying experiments. The Air Force Phillips Laboratory plans to fly a series of experimental satellites, some of which may include communications technology experiments. An example of a microsatellite produced by Surrey Satellite Research Center is shown in Figure 3.24. An interesting use of the microsatellite program is to provide an affordable focus for smaller countries to become space faring nations. Such a program, which can also incorporate graduate engineering training at University of Surrey,has been accomplished with Malaysia, Korea, Singapore, and Spain.


Fig. 3.23. Cakrawarta-1 launched for Media Citra INDOSTAR by Orbital Sciences Corporation.


Fig. 3.24. Surrey Space Center's FASat-Bravo microsatellite for Chile.

The Orbcomm satellites are being launched with the expectation of a full constellation of 26 satellites in 1998. These micro-satellites (~98 pounds) provide multiple access with 2,400 bps uplinks and 4,800 bps downlinks to handheld data terminals. Orbcomm will be the first large scale LEO system with a constellation providing continuous coverage. VITA has operated SateLife store and forward satellites for remote medical consultation since about 1992, when UoSAT-3 was launched. Several additional satellites are now used in this network.


Published: December 1998; WTEC Hyper-Librarian