Developing PiSAT: A Miniature Payload Control System
The miniaturisation of components on board a small satellite is crucial. In fact, weight and space are vital factors in the design of any project, whether it’s an Earth-orbiting satellite, a high-altitude balloon, a ground-based robot, or anything in between. Recent advances in computer miniaturisation have removed many of the constraints posed in payload development and people in the space industry – including Spacelink Solutions – now have the opportunity to create small, lightweight satellite and payload control systems that can be built and customised to a client’s needs and specifications.
PiSAT is a new project being undertaken by Spacelink Solutions that utilises the technology and features of the Raspberry Pi, a credit-card sized computer. Not only is the size and weight of the Raspberry Pi a distinct advantage in satellite development, but it also has much more computing power compared to previous custom-built flight hardware.
“You can get to 10 to 20 kilometres up, which, functionally, from a lot of points of view, is space,” said Eben Upton, the developer of Raspberry Pi, who envisages the device being used by schools in science projects. “From a child’s point of view, it’s got almost all of the cool stuff of being in space, with a millionth of the cost of actually going into orbit.”
The first milestone of the PiSAT will be to construct a system that can be used on board a high-altitude balloon. The initial features of this phase of PiSAT are likely to include:
- Temperature, pressure, and altitude sensors
- Camera control for photography
- GSM/GPRS communications for transmitting data and GPS location
- Backup radio beacon transmitting basic data on shortwave bands
At this point, as well as having a functioning and customisable payload control system, the first phase of PiSAT will form the basis of the next milestone: developing a system that can be used in space. Spaceflight poses its own unique variety of challenges that are different to flying a payload “in-atmosphere” such as extremes of temperature and cosmic radiation.
Throughout the whole process there will be the ongoing development and testing of software to make each aspect of PiSAT work, and work well. Software modules will be required to automate data acquisition, for example, so that the experimenter does not have to worry about whether or not the payload’s camera is taking enough images, or if the sensors are returning incorrect altitudes. As the software gathers data from the PiSAT, that data must then be packaged up and transmitted to a ground station (this could be as simple as a text message to a mobile phone).
The end result of the software development process will be a robust and well-tested collection of modules that can be used easily on any version of the PiSAT, without much need for tinkering or writing new code.
Upton has considered the use of the Raspberry Pi on board a CubeSat, a low-cost satellite system built using off-the-shelf components. “A CubeSat typically has got a bunch of solar cells and batteries and some radio hardware, maybe a heater to keep it warm in the Earth’s shadow,” he said. “There’s a variety of bits and pieces of hardware in there, and you need some processing element to control those. Now, Raspberry Pi is a little bit overcooked for that. But once you’ve got it there, you could potentially think about doing imaging as well.”
Check back regularly to keep up to date with the development of PiSAT. If you are interested in purchasing a PiSAT system for your high-altitude balloon project, please contact us.