Lesson 6 of 6 · Outgassing, exposure & test evidence
Choose materials for the environment they will meet
9 minute lesson · 3 checks along the way
Your goal for this lessonCompare material tests using stated environments and measurements, and separate a promising result from an unsupported lifetime guarantee.
Follow a linked name to explore its archive card. “Back to your lesson” brings you to the same part of the reading.
Words with a dotted underline open a short definition right here in the lesson.
Space is a collection of environments
A material that works in a room may behave differently on the outside of a spacecraft. Low , changes, radiation, reactive particles, and impacts can act together. Their importance depends on orbit, orientation, shielding, and mission duration. Low Earth orbit is not the same environment as a sheltered instrument inside a lunar lander, so “space-proof” is too vague to be a useful material requirement.
Vacuum can encourage volatile substances to leave surfaces or the bulk of a material, a process called . Those do not necessarily vanish harmlessly: some can deposit on cooler optical surfaces and change their performance. Engineers consider cleanliness, material selection, and controlled preparation alongside mechanical strength. A strong adhesive can still be unsuitable near a sensitive mirror if its released material compromises the optical path.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Separate different damage mechanisms
In low Earth orbit, can react with exposed surfaces and erode susceptible materials. It is different from the oxygen molecules normally emphasized in breathing air. Ultraviolet and charged-particle radiation can change material properties, while repeated thermal expansion and contraction can stress bonds and joints. A protective coating that addresses one mechanism must still survive the others and remain attached to its substrate.
During STS-82, Mark Charles Lee and Steven L. Smith repaired insulation on the Hubble Space Telescope after degradation had become visible. The photograph connects material behavior to a real observatory’s maintenance. It does not establish the exact chemical contribution of each exposure mechanism. Laboratory measurements and returned or monitored samples help distinguish erosion, embrittlement, contamination, and mechanical damage instead of treating every visible crack as evidence for the same cause.
During STS-82 in February 1997, Mark Charles Lee works from the robotic arm while Steven L. Smith assists with repairs to the Hubble Space Telescope’s damaged insulation. NASA photograph STS082-325-034 documents the work. Visible damage motivates inspection and testing, but the photograph alone does not separate the chemical and mechanical causes of degradation.
Look closely
Could this single image tell us which environmental exposure caused a particular crack?
See what to notice
No. The image records appearance and maintenance activity. Distinguishing ultraviolet exposure, particle effects, temperature cycling, and mechanical stress requires material histories and suitable measurements or controlled comparisons. Several mechanisms can contribute to one failure.
Work through a decision
Compare losses with the denominator stated
In an invented screening test, equal-area coupons made from the same polymer start with identical thickness and each weigh 10.0 grams. Coupon A loses 0.2 grams; coated coupon B loses 0.05 grams under the same specified exposure. Their mass losses are 2 percent and 0.5 percent, respectively. B loses one quarter as much mass, a 75 percent reduction relative to A. These numbers are illustrative, not a report of a flown material.
That result favors B for this particular mass-retention test, assuming adequate measurement precision and controlled conditions. It does not prove a four-times-longer mission life: erosion rate may change, coating defects can grow, and optical or mechanical failure can occur before a chosen mass-loss threshold. A better follow-up repeats the comparison, measures uncertainty, and tests the relevant property after combined exposures. Keep a to distinguish handling or instrument drift from exposure effects.
Check 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Translate a requirement into evidence
For an optical instrument, specify acceptable contamination and image performance; for a thermal blanket, specify the retained optical and mechanical properties. Record the vacuum level, temperatures, radiation or particle exposure, duration, and viewing direction. NASA’s Materials International Space Station Experiment compares exposed materials using environmental records and postflight analysis. A ground chamber can isolate mechanisms, while flight exposure adds combinations that are difficult to reproduce completely.
Finish a material decision by stating what passed and what remains untested. A sample that survives ten cycles has evidence for those ten cycles under those conditions, not a blanket guarantee for every destination. An engineering team can combine controlled tests, validated models, and prior flight experience to justify a service life. The same particle, -transfer, and energy ideas from earlier lessons explain why each part of that evidence matters.
Check 3 of 3
10 pointsUse the reading above. You can try again without losing points.
Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
Go to the source
Explore the evidence behind this lesson. These optional readings and videos open in a new tab.