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1. Space Environment
Lecture 3 – Effects on spacecraft
Particle radiation & Atomic Oxygen
Professor Hugh Lewis
SESA3038 Space Environment

2. Overview of lecture 3
• In this lecture we will continue our high-level look at the key
characteristics of the space environment and their effects on spacecraft
• Here, we will focus on:
– Particle radiation, including looking at a possible effect on spacecraft via
whisker growth
– Atomic Oxygen, focusing on erosion of spacecraft materials
• We will continue our look at the effects of Atomic Oxygen on spacecraft in
lecture 4
Space Environment – Environmental effects

3. Environmental effects
• High vacuum
• Solar radiation
• Particle radiation
• Atomic Oxygen
Space Environment – Environmental effects

4. Effects of particle radiation Space Environment – Environmental effects
• Metals with high vapour pressure
(e.g. cadmium, zinc) grow metallic
whiskers that can cause shorting
• High energy radiation leads to
displacement of atom from crystal
lattice and ionisation
• Semiconductors particularly sensitive,
e.g. solar cells
• On-board software errors by single
particle event

5. Metal whiskers Space Environment – Environmental effects

6. Metal whiskers Space Environment – Environmental effects

7. Metal whiskers Space Environment – Environmental effects

8. Failures from metal whiskers Space Environment – Environmental effects
1998: Hughes (now Boeing) HS601 satellites
experienced on-orbit failures of one side of
redundant satellite control processors:
• GALAXY IV, GALAXY VII and DBS-1
• Disrupted 80% of pager communications in US
Hughes reported:
“…electrical shorts involving tin-plated relay
switches are the most likely cause of the three
spacecraft control processor failures...”
“A team of Hughes engineers and outside experts
confirmed that all three satellites experienced an
electrical short...”
https://www.independent.co.uk/news/satellite-s-failure-leaves-millions-speechless-in-us-1157828.html

9. Effects of particle radiation Space Environment – Environmental effects
• Effects on solar cell performance

10. Effects of particle radiation Space Environment – Environmental effects
• Single Event Upset
• “radiation-induced errors in microelectronic circuits caused when charged particles (usually
from the radiation belts or from cosmic rays) lose energy by ionizing the medium through
which they pass, leaving behind a wake of electron-hole pairs” – NASA
Example of SEU in
Landsat imagery

11. Atomic Oxygen Space Environment – Environmental effects
• Produced by the dissociation of
molecular oxygen by UV radiation
at > 95 km
• Mean free path is long (~100 m)
so the probability of re-
association or the formation of
ozone (O3) is small
• the rate of splitting of O2 to the atomic
Oxygen Species (AO) by UV is faster
than the corresponding
recombination
https://scialert.net/fulltext/?doi=srj.2014.1.13

12. Atomic Oxygen Space Environment – Environmental effects
• AO flux is two orders of
magnitude higher at solar
maximum compared with
minimum
• Energetic collision between
atomic oxygen and spacecraft
leads to the oxidation and erosion
of polymeric surfaces
• Most of the energy comes from the
velocity of the spacecraft
• AO also plays a role in geospace
climate change* Density of the LEO environment particles as a
function of altitude for one year mission length
during mean solar activity

13. Atomic Oxygen erosion Space Environment – Environmental effects
• “Micrometre-scale scanning electron
microscope image of atomic oxygen
erosion of Kapton, typically used in
multi-layer insulation of satellites. The
central pillar of material is due to a
metallic contaminant particle which
serves to preserve the Kapton beneath it,
while the polymer around it has been
eaten away.”
• From:
https://www.esa.int/ESA_Multimedia/Im
ages/2017/05/Atomic_oxygen_erosion

14. Atomic Oxygen erosion Space Environment – Environmental effects
• Erosion:
• Reacts with spacecraft surfaces,
especially:
– Paint
– Mylar and Kapton
– Silver (other metals unaffected)
– Silver is used to measure AO, e.g.
University of Southampton’s
STORM sensor

15. Atomic Oxygen monitor Space Environment – Environmental effects
• Southampton Transient Oxygen and Radiation Monitor (STORM):
• European Materials Exposure and Degradation Experiment on EuTEF (MEDET)

16. Atomic Oxygen monitor Space Environment – Environmental effects
• EuTEF on the Columbus Laboratory on the ISS:

17. Atomic Oxygen erosion Space Environment – Environmental effects
• Example AO erosion:
• Calculate the minimum rate at which the
polyimide Kapton H will be eroded on a
spacecraft at 200 km altitude:
– Reaction efficiency of AO = 3.04 × 10−24
cm3/atom
– Number density of AO at 200 km = 1010
cm-3
– Erosion rate
= 3.04 × 10−24
× 1010
× 8 × 105
cm/s
= 2.4 × 10−8
cm/s
= 0.8 mm/year
Relative velocity (this is
a maximum for this
altitude)

18. Atomic Oxygen erosion Space Environment – Environmental effects
• Can change optical properties
• Changes in absorptivity and emissivity can be significant (Δ > 0.1)
• Example: discolouration of heat pipe assembly:
BEFORE
AFTER