This lecture discusses the environmental effects of radiation, temperature, and vacuum on humans in space. It covers the different types of radiation in space and their health impacts on astronauts. Temperature must be kept within a narrow range for human survival, requiring spacesuits in vacuum conditions. The document also presents a calculation for determining the time available for emergency egress from a spacecraft if it loses pressure through a leak. It provides an example calculation for a 10 m3 spacecraft with a 1 cm2 hole.

1. Space Environment
Lecture 6 – Effects on humans
Radiation, temperature & vacuum
Professor Hugh Lewis
SESA3038 Space Environment

2. Overview of lecture 6 Space Environment – Environmental effects
• In this lecture we will continue our look the key environments affecting
human spaceflight. In this lecture, we will focus on:
– Radiation
– Thermal and high vacuum
– We will also look at a simple calculation for the time needed for a
spacecraft (e.g. the ISS) to lose pressure in the event of a leak
• We will look at countermeasures that can be employed to reduce or remove
these effects in a later lecture

3. • Launch
• Zero ‘G’
• Radiation
• Thermal
• High vacuum
Environmental effects Space Environment – Environmental effects

4. Radiation types:
• Ionizing:
• X-ray, Gamma-ray, high-energy particles
• Non-ionizing:
• Ultra-violet
Radiation definitions:
• Roentgen:
• Related to the amount of ionization caused in air (= 2.58 × 10−4 C in 1 kg of air)
• ‘Rad’ or ‘Gray’:
• Unit of absorbed dose: 100 rad = 1 Gray ≡ 1 Joule/kg
Radiation Space Environment – Environmental effects

5. Some types of radiation cause more damage to
biological tissue than other types
• QF – Quality Factor:
• Also called relative biological effectiveness
• Rad × QF = rem
• Gray × QF = Sievert
• 1 Sv = 100 rem, 1 cSv = 1 rem
Radiation Space Environment – Environmental effects
Source Dose rate
galactic radiation 0.3 cSv/day
radiation belts 1-30 cSv/hr
solar flares 1000cSv/hr
Mean dose on Earth is 0.25 cSv/year.
The maximum permissible dose is 30
cSv/year

6. Astronaut radiation risks:
Radiation Space Environment – Environmental effects

7. Astronaut radiation risks:
Radiation Space Environment – Environmental effects
Organ Exposure in 51.6 degree Orbit at 190 N.M. Altitude and Solar Minimum Activity
https://www.researchgate.net/publication/255039258_Estimate_of_Space_Radiation-Induced_Cancer_Risks_for_International_Space_Station_Orbits

8. Astronaut
radiation impacts:
Radiation Space Environment – Environmental effects

9. Humans cannot survive in the vacuum of space
Skin temperature has to be kept within a narrow range:
Typically greater control required for humans than for spacecraft subsystems
• Humans require spacesuits to work in vacuum
Thermal and vacuum Space Environment – Environmental effects

10. How much time is
available for egress
if there is a loss of
pressure?
Vacuum Space Environment – Environmental effects

11. How much time is available for egress if there is a
loss of pressure?
To leak from an initial pressure of 𝑃𝑃𝑖𝑖 to a final
pressure of 𝑃𝑃𝑓𝑓 the time required is:
Where:
• 𝑇𝑇 = the (constant) spacecraft temperature
• 𝐴𝐴 = the area of the hole
• 𝑉𝑉 = the volume of the spacecraft
Vacuum Space Environment – Environmental effects
𝑡𝑡 =
0.086𝑉𝑉 ln
𝑃𝑃𝑖𝑖
𝑃𝑃𝑓𝑓
𝐴𝐴 𝑇𝑇
http://www.geoffreylandis.com/higgins.html

12. For a spacecraft with:
• 𝑇𝑇 = 300 K
• 𝐴𝐴 = 1 cm2
• 𝑉𝑉 = 10 m3
The time it takes to leak from an initial pressure of
𝑃𝑃𝑖𝑖 = 1 atm to a final pressure of 𝑃𝑃𝑓𝑓 = 0.5 atm is
Vacuum Space Environment – Environmental effects
𝑡𝑡 =
0.086 10 ln 2
10−4 300
= 344.2 sec ≈ 6 min

13. Recap of lectures 5 and 6 Space Environment – Environmental effects
• In these lectures we took a high-level look at the key environments
affecting human spaceflight. These were
– The launch environment
– The Zero ‘G’ or microgravity environment
– The radiation environment
– The thermal and high vacuum environments
• We also introduced a simple calculation for the time needed for a
spacecraft (e.g. the ISS) to lose pressure in the event of a leak (we will look
at the solution to the end-of-lecture activity at the beginning of the next
lecture)
• Our next two lectures will focus on the countermeasures that can be
employed to reduce or remove these environmental effects

14. Calculate the time needed for emergency egress from
the ISS with:
• 𝑇𝑇 = 293 K
• 𝑉𝑉 = 916 m3
• 𝑃𝑃𝑖𝑖 = 1 atm
If a debris impact causes a circular hole with diameter
2 cm and the astronauts lose consciousness once the
atmospheric pressure falls below 60% of nominal
Activity Space Environment – Environmental effects