Radiation Environment

Whilst this page was initially written in an effort to estimate the radiation conditions for the C.M.O.S. sensor of the camera, as most of the subsystems contain electrical components, it would be advisable for all subsystems to consider whether they need to make alterations to protect their electronics

A primer on rad hard electronics from Maxwell Tech.: radHardElectronics.pdf

Radiation Definitions

Category Total Ionising Dose T.I.D. (kRad) Single Event Latch-Up S.E.L. (MeV) Single Event Upset S.E.E. (MeV)
Rad hard 100 minimum Up to 120 Up to 120
Rad Tolerant 100 maximum Up to 120 Up to 120
Commercial 3-20 1-120 1-120

Table 1: Standard radiation categories for hardware

The Rad Tolerant category is customize to its orbit. So the figures will vary dependant on each individual mission.

Radiation Environment

To typify the radiation environment that the cubesat will be exposed to, a modelling tool known as SPENVIS was employed. This gives an idea of the environment that the satellite might expect to experience. It is a first order approximation. It is also for a mission duration of one year. This is longer than we expect our lifetime to be, so the satellite meets this specification, it should be fine for our mission duration. In all honesty, whilst this offers a margin on our total dosage, it was mainly because I could only enter integer numbers of years for our lifetime.

Radiation modelling of a 45 degree inclination orbit
Radiation modelling of a 5 degree inclination orbit

Overview of radiation environment information:

The table below is an attempt to condense the information contained in the two links above:

Inclination (o) Model Thickness of Al shielding needed to use Rad tolerant components (approx 50kRad) (mm) Rad Tolerant Aluminium mass per unit area (g.cm-2) Thickness of Al shielding needed to use commercial components (approx 10kRad) (mm) Commercial Aluminium mass per unit area (g.cm-2)
5 Centre of Aluminium Spheres 0.05-0.1 0.014-0.027 0.05-0.1 0.014-0.027
5 Semi Infinite Aluminium Slab 0.05-0.1 0.014-0.027 0.05-0.1 0.014-0.027
45 Centre of Aluminium Spheres 0.3 0.081 0.5 0.135
45 Semi Infinite Aluminium Slab 0.1 0.027 0.3 0.081

Table 2: Approximations of shielding thickness required for Silicon samples at 500km altitude (based on information from SPENVIS)

The information for the 5o inclination orbit is a bit sketchy, because the models both suggest that the total radiation dose over the course of mission with such an inclination would be very very small, and so the first measurement (0.05mm) would reduce the total dosage to a negligible amount. Admittedly, from a radiation point of view, it would be more beneficial to fly a 5o inclination, but with regards to the ground station, and to the range of meteoroids sampled, this would be less advantageous. Even so, from the information on the 45o inclination orbit, an Aluminium plate of 0.5mm thickness would reduce the total dosage to within acceptable levels (over a 1 year mission lifetime) even in the worst case radiation model. Using the mass per unit squared of this plate, and modelling the surface area of the Cubesat as 6 square plates of 10cm size, the total mass given over to shielding would be:

Masstotal shield = 6 x (10 x 10) x 0.135
Masstotal shield = 6 x 13.5
Masstotal shield = 81g

This would also give a total volume requirement of 14cm3, which is just under 1.5% of the total available volume. However, this is just to give an idea of the maximum mass required, and in practice the whole satellite may not be shielded. Also this may interfere with the ADCS coils, and the minimum Aluminium plate thickness may be greater than this.

Sun synchronous orbit

If flying with Floride, a Sun synchronous orbit would be acheived. In this case, a new model of the radiation environment is required. This can be seen here Sun synchronous Radiation Information

Orbit Model Thickness of Al shielding needed to use Rad tolerant components (approx 50kRad) (mm) Rad Tolerant Aluminium mass per unit area (g.cm-2) Thickness of Al shielding needed to use commercial components (approx 10kRad) (mm) Commercial Aluminium mass per unit area (g.cm-2)
Sun synchronous Centre of Aluminium Spheres 0.3 0.081 0.8 0.216
Sun synchronous Semi Infinite Aluminium Slab 0.1 0.027 0.3 0.081

Table 3: Approximations of shielding thickness required for Silicon samples at 500km altitude (based on Sun synchronous orbit information from SPENVIS)

Links

Payload Homepage
Mechanical Structure Homepage
Camera Homepage

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-Share Alike 2.5 License.