You can’t just take a Raspberry Pi into space in your pocket or an old soft scoop ice cream tub. It’s too spiky for one thing. What you need is a block of aluminium the size of your head and some mad milling skills to make the best Pi case ever. Dave Honess explains:
The latest update to the Astro Pi project is the unveiling of the Astro Pi aluminium flight case that British ESA Astronaut Tim Peake will be using on the ISS. This will not be available to the public to buy because we’re only making a small number of them. We may however, in due course, release an object file so schools with a 3D printer can print one themselves.
The Astro Pi flight case.
The case is made from 6063 grade aluminium which is standard for aerospace applications. The image below was taken from the CAD software that we used to model it.
This is the top view showing the opening for the LED matrix and joystick along with a quad of buttons with an adjacent pair. The face on the right is used to attach it to a Bogen arm so that the Astro Pi can be held in place, for example if the crew want to aim the camera out of the cupola window.
The hole next to the joystick is to allow air to flow inside and reach the temperature, pressure and humidity sensors.
The design may surprise you because it’s so big a bulky. It satisfies the safety requirements that ESA and NASA have in place for small payloads aboard the ISS though!
This is not a 3d rendering!
The most important of these requirements is touch temperature. There is a rule that any surface, that the crew can touch, must not reach or exceed 45 degrees Celsius. Our Jonathan Bell and SSTL’s Nimal Navarathinam did extensive thermal simulations to work out the requirements. That’s really hard maths to you and me! The CAD heavy lifting was done by Jonathan Wells who runs an industrial design consultancy local to us in Cambridge.
In space the process of convection doesn’t happen. On Earth the air warmed by a Pi CPU will rise as colder air is pulled down by gravity. On the ISS the air warmed by a CPU just stays there and bakes it. So the case has been designed for thermal dissipation in mind. There is a guaranteed level of airflow within all of the ISS modules which makes this possible.
Those pillars on the base each dissipate about 0.1 Watts of heat. All of them combined with the surface area of the case ensure that the Astro Pi can never get anywhere near 45 degrees. Inside the case the Raspberry Pi is thermally joined to the aluminium by way of a heat conductive boss / slug.
The view above shows the hole for the camera module in the middle too. So make a mental note that the camera faces in the opposite direction to the LED matrix when in flight configuration. You can also see the corner bolts that hold the two halves of the case together.
The ISS crew are also really fond of bungee cords, the kind you might use for camping or mountaineering with those hooks on the ends, and so the four corner columns have holes to allow bungee cords to be used to lash the Astro Pi to whatever they want.
The case is made from a solid block of aluminium and a serious set of skills are required to turn it into what you see above. We’re using a company based in Derby called Pentaxia for this. They’re a great company and have been hugely accommodating of our needs. Below is a picture of their main shop floor. The machines on the right were the ones used to make the case.
So that’s about it for now. The only thing left to tell you is that we’ve now reached and successfully passed phase two of the flight safety process with ESA. So it’s only phase three to go now before we get the mighty flight safety certificate that says we can go on the Soyuz rocket with Tim! Between now and the phase three review all the testing will occur at SSTL and Airbus Defence and Space.
Here is a brief summary of the tests we have to do:
RTC (real time clock) Battery
- Measurement of open circuit voltage and loaded voltage
- Vacuum exposure test (450 mmHg for 2 hours)
- Post vacuum inspection for leaks and deformation
- Post vacuum measurement of open circuit voltage and loaded voltage
- Operation checks (verify it boots and functions correctly)
- Power integration test (using an ISS mains AC inverter)
- Thermal test (stress the Astro Pi to cause maximum current consumption / heat dissipation and measure touch temperature)
- Vacuum thermal test (same as the above but in a vacuum)
- Off gassing assessment (determination of off gassing products from materials and assembled articles to be used inside the ISS modules)
- EMC test
- Vibration test (Soyuz launch vehicle conditions)
Keep an eye on social media over the coming weeks for as it happens updates!
Thanks for reading.