Leading Research for Future
Toward more competitive telecommunications satellites in the all-electric satellite age
Two improvements will be key to Japan’s success in gaining a more competitive position in the global telecommunications satellite market: reduced satellite mass and a greater number of onboard transponders. Progress in these directions will improve both the cost and profitability of telecommunications satellites.
Conventional satellites with chemical propulsion systems have a payload mass ratio of about 20% (ratio of payload mass to the satellite mass at launch). We have been striving to increase the ratio to about 40% by adopting the satellite propulsion systems solely with Hall effect thrusters and designing lighter weight power systems and improving heat-rejection technologies as a means of reducinging total satellite mass.
The autonomous operation of satellites will also enhance Japan's competitive advantage by helping to reduce relevant costs.
The Value of Our Research
In a typical chemical propulsion satellite, the propellant makes up nearly half of the satellite mass at launch. An all-electric satellite, which uses only electric propulsion systems, can significantly reduce the amount of propellant required. Less propellant makes it possible to increase the payload mass ratio by providing more leeway for the number of onboard transponders related to the profitability of communication satellite.
Work in the U.S. and Europe on all-electric satellites has led to the successful development of powerful all-electric platforms to satisfy the increasing electricity demand accompanying the increase in transponders. However, they haven’t succeeded in designing lighter-weight power subsystems to increase the payload mass ratio beyond around 20-to-30% range.
Our research aim is to position Japan's all-electric telecommunications satellites more competitively. We seek to do so by developing Hall effect thrusters and achieving a payload mass ratio of nearly 40% by making the light weight power subsystem (the solar paddles, batteries, and power control unit) the second heaviest component of the satellite after the propulsion system, and so on. This will enable us to gain a competitive advantage over the U.S. and Europe in the number of onboard transponders.
- Realizing an all-electric propulsion system that relies exclusively on Hall effect thrusters and operating the thrusters for 15 years, the typical mission lifetime of a modern commercial telecommunications satellite.
- Applying digital control technologies to get rid of heat spot generation and achieving a specific power of 50 kg/kW by miniaturizing and Lightweight the power control unit and other components of the power subsystem.
- Developing a deployable thermal radiator with a high specific heat rejection capability of 75 W/kg at a temperature of 40°C and flat-plate heat pipe with an effective thermal conductivity exceeding 5000 W/mK to meet the requirements for high-density assembly and improved heat dissipation caused by increased transponders.
- Realizing autonomous station-keeping and orbit maneuvering using GPS receiver capable of operating on geostationary/transfer orbit (conventionally GPS receiver installed on low-earth-orbit satellite only) to accomplish highly accurate, real-time orbit determination in high-altitude orbits. This will reduce operational costs for satellite operators by eliminating the need for ranging ground stations and helping them operate their satellites more efficiently.
- Substantially reducing the weight of the power subsystem by developing high-energy-density batteries (initially with a specific energy above180 Wh/kg; ultimately, with a specific energy above 200 Wh/kg) and much lighter solar paddles (one-third of the conventional weight) with thin-film solar cells.
Hall effect thruster (BBM)
Thin-film solar cell array sheet