Abstract :
[en] We describe one of the secondary payloads of the educational OUFTI-2 satellite under development at the University of Liège, namely the one dedicated to the test of an innovative type of shielding that can protect electronic systems against space radiations, and that is well suited for small satellites. OUFTI-2 is a 1-U CubeSat, the main payload of which is a homemade radio repeater featuring D-STAR amateur-radio communications. We expect OUFTI-2 to be deployed from ISS, with a mission duration of about 6 months.
The impact of space radiations on electronics depends mainly on the orbit/trajectory, mission duration, and possible protections. Such radiations cause well-known undesirable effects such as latch-ups. The protection against such effects is ideally achieved through a combination of device rad-hardening, physical shields, and defensive software. Here, we focus on the use of shields. One limitation with using such shields is the corresponding added volume and weight. The innovative type of shield to be tested aboard OUFTI-2 consists of a multilayer laminate structure, combining doped resin and Wolfram (tungsten) heavy alloy. It has the advantage of being light-weight, robust, and reliable.
The part of the board containing the shields-test payload consists mainly of three identical electronic circuits, resp. without any shield, with a classical 2-mm aluminum shield, and with the new multilayer shield. The 1st part of each circuit is a RADFET (a p-channel MOSFET optimized for ionizing dose measurement), whose threshold voltage ΔV varies with the total dose D in a known way, essentially according to ∆V=A (1-e^(-B D) ), where A and B are parameters depending upon the RADFET used. One measures ΔV. The 2nd part contains 2 op-amp-based circuits. In one, one measures the offset voltage, and in the other the output noise voltage level. One also measures the temperature, T. ΔV, the two op-amp parameters, and T constitute the quadruplet of data measured periodically, and ultimately sent to the ground.
During flight, we will use ΔV and T to deduce D at each sampling time. For each such time, we will also compute the total dose via the ESA SPENVIS simulation software using the known flight trajectory up to that time. Of course, we will also compare the protection provided by both types of shields, and in relation to the absence of a shield. The measurements of the two op-amp parameters will allow us to see how these parameters evolve as a function D.
