Small satellite space operations
CTA Space Systems has played a premier role in the development of the 'lightsat' programs of the 80's and 90's. The high costs and development times associated with conventional LEO satellite design, fabrication, launch, and operations continue to motivate the development of new methodologies, techniques, and generally low cost and less stringently regulated satellites. These spacecraft employ low power 'lightsat' communications (versus TDRSS for NASA's LEO's) and typically fly missions with payload/experiment suites that can succeed, for example, without heavily redundant backup systems and large infrastructures of personnel and ground support systems. Such small yet adaptable satellites are also typified by their very short contract-to-launch times (often one to two years). This paper reflects several of the methodologies and perspectives of our successful involvement in these innovative programs and suggests how they might relieve NASA's mounting pressures to reduce the cost of both the spacecraft and their companion mission operations. It focuses on the use of adaptable, sufficiently powerful yet inexpensive PC-based ground systems for wide ranging user terminal (UT) applications and master control facilities for mission operations. These systems proved themselves in successfully controlling more than two dozen USAF, USN, and ARPA satellites at CTA/SS. UT versions have linked with both GEO and LEO satellites and functioned autonomously in relay roles often in remote parts of the world. LEO applications particularly illustrate the efficacy of these concepts since a user can easily mount a lightweight antenna, usually an omni or helix with light duty rotors and PC-based drivers. A few feet of coax connected to a small transceiver module (the size of a small PC) and a serial line to an associated PC establishes a communications link and together with the PC constitute a viable ground station. Applications included geomagnetic mapping; spaceborne solid state recorder validation; global store-and-forward data communications for both scientific and military purposes such as Desert Storm; UHF transponder services for both digital data and voice using a constellation; remote sensor monitoring of weather and oceanographic conditions; classified payloads; and UHF spectrum surveillance. Ground processing has been accomplished by automatic unattended or manual operation. Management of multiple assets highlights the relative ease with which two constellations totaling nine satellites were controlled from one system including constellation station keeping. Our experience in small end-to-end systems including concurrent design, development, and testing of the flight and operational ground systems offers low cost approaches to NASA scientific satellite operations of the 1990's.