Analysis: Plug-and-play satellites

E&T reports from the CEAS 2009 European Air and Space Conference in Manchester, organised by the Council of European Aerospace Societies.

Developments in micro-miniaturisation, packaging and power subsystems have allowed engineers to reduce the size and mass of satellites capable of accomplishing missions formerly reserved for much larger spacecraft. One example is the Disaster Monitoring Constellation (DMC), whose baseline satellites produce images of similar resolution to those of the Landsats of the 1980s (around 30m), but weigh less than 100kg - rather than the 2,000kg of the Landsats.

Luca Maresi from the European Space Agency's research and technology centre (ESTEC) gave the example of the SPOT 'Vegetation' payload which accounted for 128kg of the spacecraft's mass budget. ESA is now proposing an entire spacecraft that is smaller than that payload, weighing just 28kg, he said.

Maresi also highlighted some encouraging trends in image resolution and cost. Comparing Landsat-1, launched in 1972 with a resolution of 100m, with SPOT-1 (10m in 1985) and Ikonos-1 (1m in 1999), he concluded that "the resolution of imaging satellites has improved by a factor of 10 every 12 years or so". Moreover, he added, the cost per square kilometre of image decreases by approximately one order of magnitude every seven years.

This is because complex multi-spectral instruments can now be built using CMOS detectors that do not require complex analogue electronics, he explained, which simplifies design, assembly and test. In addition, complex optical systems are now "within reach of small budgets", he said, "thanks to single point diamond turning technologies", while detectors such as micro-bolometers make IR systems possible without the need for complex cooling systems.

Although smaller satellites tend to have lower reliability than their larger brothers, and have technical limitations in terms of power handling and communications capabilities, Maresi identifies them as "disruptive technology". As with other disruptive technologies such as electric cars, he explained, "established players will find themselves in a situation in which they rapidly need to adapt technologies, company values and processes". The effect of new entrants can be disruptive to the point of causing serious difficulties for established players, he added.

One development guaranteed to shake up incumbent space systems manufacturers is the concept of the "plug-and-play satellite". Fredrik Bruhn, from ÅAC Microtec (a spin-out from Sweden's Uppsala University), explained how "Space Plug and Play Avionics (SPA)" was developed to enable "virtually anyone" to develop payloads and subsystems. Specifically, ÅAC has developed what it calls a 3D-System-in-Package (3D-SiP) technology that offers "extreme endurance" to vibrations and large temperature ranges.

In essence, this involved designing electronic modules for specific subsystem tasks - such as attitude control, telemetry and command, or payload management - to fit into a standard, stackable tray. The subsystems trays required for a specific satellite mission can then be stacked to form the spacecraft platform, to which solar arrays, communications antennas and payload sensors can be attached. The key, says Bruhn, is "to make the electronics module - the silicon - act as both structure and thermal subsystem", thus saving weight on dedicated structural and thermal components.

The technology was demonstrated in orbit in January 2009 by the Japanese SpriteSat-1, a mission designed to monitor lightning effects known as sprites in the upper atmosphere.

According to ESA's Johan Kohler, the way the modules in a plug-and-play satellite are designed to stack together "eliminates the 'dead mass' of a separate wiring harness, connectors, and so on". If this makes a spacecraft seem more like a PC, then the visionaries behind plug-and-play have done their job.

It is, however, more than a vision, as the US Air Force Research Laboratory has demonstrated with its 35kg PnPSat-1, a demonstrator for what the US military terms Operationally Responsive Space (ORS) - put simply, the ability to launch a satellite quickly. According to Bruhn, the goal is to have a satellite built from "off-the-shelf parts" and operational in six days. He showed a speeded-up movie of engineers building a PnPSat in August 2008: it took them four hours, but Bruhn says they now have it down to two.

Of course, it's one thing to build a satellite in the lab, quite another to launch it into orbit. However, when asked whether the recognised lack of launch opportunities represents a logjam in the ORS process, Bruhn was dismissive: "The US military can do it", he said. For future commercial versions, he speculated that companies such as Virgin Galactic will offer flights for small payloads. While the jury is still out on that, there is no denying that plug-and-play satellites open, at the very least, a niche market for scientific as well as military payloads.

Kohler's team, for example, has studied the possibility of a "near-Earth object inspection probe called NEOMex" (NEO Micro Explorer) as "a strawman mission" to guide technology development. Whether or not something like NEOMex actually gets built will depend, as much as anything else, on its price. Although Kohler admits that an intended mission cost of $6m had yet to be achieved, such an order-of-magnitude cost reduction could herald the opening of a new space age.

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