1. Experience of on-board radiation control on Medium-Earth Orbit
SPACEMON: Space Environment Monitoring Workshop 2017
Experience of on-board radiation control on Medium-Earth Orbit
Grigory Protopopov, Pavel Chubunov
Branch of JSC URSC – ISDE, Russian Federation
Noordwijk, The Netherlands. December 13-15, 2017

2. Outline
1 MNOS detector 1.1 detector’s features 1.2 saturation and fading effect 1.3 flight results 1.4 conclusions 2 Heavy ions detector 1.2 test results (ground) 1.3 results and conclusions

3. MNOS dosimeter’s features
Dose sensors: MNOS dosimetry principle (close to radiation effects in electronics)
Range: rad
Mass: <0.4 kg
Power: < 2 Wt
Temperature stabilization (operation point selection)
Metal
Si3N4
SiO2 Si

4. Temperature stabilization
Vgs, V
Isd, uA
An example of i-v curve of MOS transistor in temperature range before irradiation (1) and after 10 krad (2), 20 krad (3) …
There is the point with minimal influence of T on i-v curve

5. Charge accumulation processes
Si3N4-SiO2 Interface domination (unlike for MOS transistor – SiO2-Si Interface domination)
Charge relaxation:
tunneling of electrons from the bulk (dominates, but negative gate voltage is used  electrons tunneling is decreasing)
thermal excitation of electrons (but, T=20±3ºC)
Fading – due to change of i-v curve (not optimal operation point because of power consuming optimization)

6. Calibration of sensitive elements
protons,
electrons,
gamma
T range
Frequency signal vs absorbed dose (gamma)
High linearity

7. Measurements results Orbit: circular ~20000 km
>40 sensors on-board >20 s/c
Results for

8. Dosimeter’s saturation
> rad
Measurements of this detector are not taken into account

9. Fading (relaxation) effect
Time IN and OUT of radiation belt can vary
The effect can be neglected when dose rate > 5 rad/day

10. Annual average experimental and calculated dose rate values
Measurements results
Annual average experimental and calculated dose rate values
Al semi-inf plate 0.65 g/cm2
Russian model and AE9mean give conservative values of dose rate (~1.4 times, if without 2009 – times)
Difference for >20 times

11. Results and conclusions
Differences between experimental and calculated values of absorbed dose can be explained:
- models can not forecast abnormal low electron flux in (relatively short measuring period )
- uncertainty of shielding geometry definition (detectors are partially shielded by moving elements of the spacecraft)
Fading effect can be taken into account (it gives <20% increment), but it should not be taken into account
Saturation effect is observed (out of specification range)

12. Results and conclusions
It is necessary:
to place space radiation monitors on each spacecraft
to use detectors with detailed account of it’s shielding
to carry out thorough detector’s calibration and cross-calibration

13. Heavy ions detector’s features
Sensitive element: SRAM
SEU rate counter (close to radiation effects in electronics)
Mass: <0.6 kg
Power: < 15 Wt
PCB with 4 SRAMs
4 dose detectors
1 SRAM detector

14. SRAM test results SRAM: AT60142F-DC20M
SEU cross section vs LET (Roscosmos test facility, 2010)
SEU cross section vs LET (Belgium test facility, 2006)

15. Results and conclusions
SEE rate detectors had been developed
Small mass and size
Relatively low incident angle sensitivity
Simplicity of SEU detection and SEU rate processing

16. Thank you!
Questions?