Motivation

Space is a tough environment. Not only is high reliability a necessity (who’s going to go up and poke the reset button?) but space itself brings with it some unique environmental constraints:

• Vibrations, shock, and acoustical stress from launch
• Particle impact from space debris
• Temperature extremes and constant thermal cycling
• Vacuum (i.e. very very low pressure)
• Increased radiation, both ionizing and UV
• Atomic oxygen erosion

So, what can we do to make our satellite function reliably in face of these challenges?

Component Selection

In general, components are rated as Commercial, Industrial, Automotive, Military, Space, and Custom. This list in roughly in order of flight risk (descending), availability (descending), and cost (ascending). As a student team, we must strike a balance between risk and cost, and that tends to land us in the Automotive region.

Automotive components are graded by the Automotive Electronics Council, or AEC. You’ll see on datasheets that a component might be AEC-Q103 rated, for example.

Of the long list of things to look out for in space, the AEC standards only cover temperature and vibration. In general, we want components to be AEC rated (with the exception of Grade 4 which has too narrow of a temperature range). This gives us the appropriate temperature and vibration specification for space.

What about all those other things though? Well, in many cases there isn’t a lot you can do about them except for selling a kidney to get one (1.0) rad-hardened MCU. But there are some smaller things that we can do to enhance reliability:

• For radiation concerns, avoid NMOS where possible, preferring PMOS
• The presence of a vacuum increases the rate of solder whiskering, so use leaded solder
• NEVER EVER USE ZINC OR CADMIUM! It sublimates (goes from solid to gas) in a vacuum, which is super bad.
• Derate all components by 50% for voltage, current, and power, and derate MLCCs by a bit more to avoid capacitance tolerances
  • This is a general rule of thumb, see ECSS-Q-ST-30-11 for every specific case you’d ever want
• Gold plated leads should be around 10 microns or less, for a total gold density of less than 3% in the soldering area. Gold makes joints more brittle, but prevents oxidization, so theres a delicate balance here.