What is an ultra-small satellite?
An ultra-small satellite, so-called micro or nano-satellite, is one weighing less than 100kg in total mass. In this article, I will discuss specifically satellites of under 50kg. R&D on ultra-small satellites is being advanced at a remarkable pace across the world. In Japan, the laboratories of the University of Tokyo and Tokyo Institute of Technology started first to develop cansats weighing several 100 grams and lately succeeded in on-orbit demonstrations of 1kg-class cubesats for the first time in the world. Since then, activities on the satellites have started a trend. Today, energetic and promising young people from many universities and technical colleges have entered the world of the ultra-small satellite. As a result, new fields of space engineering are being explored.
The activities include planning satellite missions, as well as analysis, design, manufacture, testing, launch site work, operation, documentation, management and a variety of international coordination and contracts. In this way, young people gain R&D experience on space systems that are actually functioning in the space environment. The activities are not limited to education, but range from early demonstration of the most advanced technologies to science missions using ultra-small satellites. Looking at this from a different angle, it means that, since reduction in satellite size increased mission flexibility and diversity, we become able to use the ultra-small satellites for education. At the same time, there are severe technical restrictions peculiar to small satellites. Even so, these satellites offer training opportunities to discover, pursue, and resolve new research themes in practice in space.
In space development in the past, a huge budget was required to obtain demonstration opportunities in space even with space-science research projects. Size specialization would add considerable meaning because even laboratory level can contribute to space development. Furthermore, Japan, as a leading country, plays an important role in this contribution. These activities have been recognized inside and outside of Japan and, for this reason, a preferential budget has been allocated to R&D on ultra-small satellites in the last couple of years. It is expected that, by building an all-Japan framework and gathering the power to realize revolutionary results, we could lead the world and contribute to society.
Ultra-small satellites in the past
As an example, let me introduce briefly some activities related to ultra-small satellites conducted mainly at Matunaga Laboratory, the Department of Mechanical and Aerospace Engineering, the Graduate School of Science and Engineering at Tokyo Institute of Technology.
(1) CUTE-I: Development of the world’s smallest 1kg satellite. Launched on June 30, 2003, by Russian Rockot rocket. Currently still operating more than eight years after launch.
(2) Cute-1.7+APD: Developed jointly by science and engineering laboratories. Launched on February 22, 2006, by M-V-8 rocket and successfully operated. Entered the atmosphere in October 2009.
(3) 3kg-class Cute-1.7+APD II: Developed jointly by science and engineering laboratories. Launched on April 28, 2008, by India’s PSLV rocket. Currently still operating more than three years after launch.
(4) R&D on the ground control system for ultra-small satellites.
(5) R&D on a separation mechanism for ultra-small satellites: Conducted on-orbit demonstration four times. Performed launching demonstration by the three launches above and TSD (Titech Satellite Deployer) on July 10, 2005, by M-V-6 rocket
(6) A small separation camera for the Small Solar Power Sail Demonstrator IKAROS: Conducted design cooperation, assembly tests, separation analysis and system integration of the separation mechanism. Successfully photographed the entire IKAROS including its fully deployed membrane in orbit in June 2010.
(7) 50kg-class advanced technology demonstration and polarized X-ray observation satellite TSUBAME: Now under R&D. Launch planned for December 2012.
Fig. 1 shows the world’s smallest 1kg Cubesat CUTE-I of 10 cm on a side. Compared to a micro-satellite of 50kg and 10 cm on a side that was classified as ultra-small satellite at that time, this was a breakthrough that required reduction by two orders of magnitude, specifically 1/50 in weight and 1/125 in volume. Ultra-small satellites must be reduced in weight by limiting their mission, but still need features as a space system operating in outer space. It can be said that cubesat is the ultimate result that is created by pursuing what technologies are really needed to make satellite. The success of CUTE-I showed those who were interested in space but hesitant to act, a route leading to the development, launch and operation of satellites on their own. CUTE-I is still operating more than eight years after its launch.