Why miniaturise satellites?
The space age was heralded by a small satellite called Sputnik 1 - a metal sphere, 58cm across, that was launched into low earth orbit (LEO) by the Soviet Union in 1957. Sputnik did very little besides broadcasting radio pulses, but it triggered a space race that eventually saw the Apollo Space Programme take the first humans to the moon in 1969, using the largest rocket (111m) ever built - the Saturn V. The infrastructure required to operate these vehicles was equally gargantuan and the cost per launch topped $3 Billion in current terms. The Apollo missions are estimated to have cost some $170 billion in total.
Mass Range: 1kg to 10kg
Prevailing Standard: The CubeSat (Typical Electrical Specification: PC/104
Main Proponents: California Polytechnic State University and Stanford University
Standardisation Date: 1999
Useful Volume: 10x10x10 cm (1U)
Variations: 1.5U (10x10x15), 2U (10x10x20), 3U (10x10x30), 6U (10x20x30), 12U (20x20x30)
It took 30 years to bring the mind-set of the space industry back to small satellites. In 1999 Prof. Robert Twiggs, from Stanford University, proposed the diminutive CubeSat standard measuring around 10cm on each side that could fit into the ballast compartments of conventional satellite launchers. Their mass is limited to 1.33kg which classifies them as nanosatellites (1 to 10kg), and the cost associated with launching them is of the order of $100,000 per CubeSat.
This was an especially important development in astronautics because it democratized the use of space and allowed universities around to world to participate in space engineering without the multimillion dollar budgets that are typically associated with such endeavours. Some consider smaller satellites as a way to address the space debris problem that results when too much material is launched into long-lived orbits. Other feel that the proliferation of small satellites will exacerbate the problem. The debate ranges on, but in the meantime, NASA and the ESA have each embarked on their own CubeSat missions as a means of containing costs. Over 100 CubeSats
have been launched to date, mostly by Universities, and the concept is quickly morphing into a flourishing business.
Mass Range: 100g to 1000g
Prevailing Standard: The PocketQube (Typical Electrical Specification: PQ60)
Main Proponents: Morehead State University and Kentucky Space
Standardisation Date: 2009
Useful Volume: 5x5x5 cm (1p)
Variations: 1.5p (5x5x7.5), 2p (5x5x10), 3p (5x5x30)
Wren224x205stadoko Eagle2224x205download Qubescout-S1224x205
The PocketQube is another order of magnitude in miniaturisation proposed by Prof. Twiggs during his time at Morehead State University in Kentucky. It divides a CubeSat into 8 equally sized cubes, about 5cm on each side. The mass is typically limited to 250g, classifying them as picosatellites (100g to 1kg). The current cost of launching these into LEO, is about a quarter that of launching a typical CubeSat, but it brings with it some new challenges associated with the very small size. However, it is expected that this new form factor will dominate the market in a few years as space engineering seeks to reduce cost further by taking advantage of the latest developments in mobile phone technology. The Wren, Eagle2 and Qubescout-S1 pictured above were among the first four PocketQubes to be launched in 2013 aboard the Italian UniSat 5 microsatellite.
Mass Range: 10g to 100g
Prevailing Standard: The SunCube
Main Proponents: Arizona State University
Standardization Date: 2016
Useful Volume: 3x3x3 cm (1F)
Variations: 2F (3x3x6), 3F (3x3x9)
A 3F SunCube Femtosat (left), and a CubeSat-Sized x27 SunCube deployer by Arizona State University
Following the same trend, femtosatellites were proposed as a means of reducing costs further. The SunCube is an attempt to standardize devices and deployers at this scale, with the aim of fitting 27 such devices into a deployer the size of a CubeSat. It was proposed by Prof. Jekan Thanga and his associates at the Arizona State University and hopes to bring launching cost down to $3000 per launch. This would be a cost accessible to most schools and classes and could have a big impact in the long run. However, at these scales, the cost of components small enough to fit in a 3x3x3cm volume, and more significantly the 100g mass budget, starts to rise. It is as yet unclear whether the cost of materials and assembly would exceed the cost of launch for anything more than the simplest systems. Further research is needed, but with a published standard, the first such devices are set to appear on the miniature satellite landscape.
Mass Range: 1g to 10g
Prevailing Standard: No standard yet (feasibility study)
Typical Embodyments: Satellite on a chip
Main Proponents: Surrey Space Centre - University of Surrey
Attosatellites take the weight limit down to under 10g, and within this onerous constraint we can only speak of single PCBs called sprites and the revered idea of the satellite-on-a-chip. These devices are not standardized yet and are typically deployed from within one of their larger brothers. They have very limited means of attitude control and negligible protection from the space environment and increasing their lifespan is just one of the many unsolved problems requiring research. That said, these devices are ideal for creating massive constellations of extremely low cost satellites, where the lifespan of the individual is irrelevant compared to that of the group. The ability to send hundreds, or even thousands, of such devices into space opens a new range of possibilities not feasible by any other class of satellite.
PCB Sprites and the Satellite-on-a-chip address the problem of cost in different ways. They both offer launching costs of the order of a few dollars a piece, considering that hundreds of them may be fit into a single CubeSat. However, the manufacturing cost structure is very different. PCB Sprites, are fairly cheap to develop and replication cost is quite low, but the complexity is limited to the size of commercial off the shelf components that may be had. Chip-on-Board techniques hope to improve this aspect somewhat at the expense of slightly higher production cost.
The satellite-on-a-chip is another interesting idea that directly leverages the huge strides made in integrated circuit manufacturing technology. The cost of design and development can be extremely high. However, as with all integrated circuits, by using the standard CMOS planar manufacturing process the cost of replication can be reduced to a few cents per device. Therefore, if the application requires thousands, or even millions, of members in a constellation this is probably the way to go. The surface of the chip can house the solar cells, power converters, sensors, memory, processors, communications, RF electronics and even simple actuators. Depending on the frequencies used, some types of antenna may also be integrated. The world is still waiting for the first major deployment of these devices.