1. The short version / what to know first / where this fits in the series

• The gold film is a spacecraft's "blanket, wiring and substrate": thin polyimide film coated with aluminum is stacked into multilayer insulation (MLI), and it is also the base of bendable circuits and thin solar-array substrates Sourced[Ref. 3, 5, 9]
• The enemies narrow down to three: (1) vacuum draws out water and other gases; (2) in low orbit, oxygen atoms (atomic oxygen) erode the surface; (3) ultraviolet light and radiation tint the film and make it brittle. NASA flight experiments report an erosion yield of 3.0 × 10^-24 cm³ per atom for the reference polyimide (Kapton H), and under one set of conditions this works out to a 25 µm film being gone in a few months SourcedOur calculation[Ref. 1]
• Defense is not only "change the material": put a sacrificial layer outside, deposit metal, add a coating, redesign the polymer, and then confirm by testing. For wires, designers also look at behavior after the insulation is damaged, not only normal performance Sourced[Ref. 3, 13, 8]

2. Background: low Earth orbit and the "five enemies"

First, where does polyimide actually sit? Why do satellites and the International Space Station (ISS) not fall to the ground?

The answer is that they keep falling, but move sideways fast enough that they never hit the ground. Imagine firing a cannonball sideways, faster and faster. Beyond a certain speed it moves on over the curve of the Earth before it can land. That is an orbit (Newton's thought experiment). Where the analogy breaks down: in reality a thin atmosphere drags on the craft and uneven gravity nudges it, so real orbits drift slowly.

NASA reports that the ISS flies at an altitude of about 400 km at roughly 7.7 km per second Sourced[Ref. 1]. Assuming a circular orbit at 400 km, one lap takes about 92 minutes, or about 15 to 16 laps a day Our calculation. In other words, the craft passes between sunlight and shadow roughly every 90 minutes.

In this "low Earth orbit" (LEO), space is not "empty vacuum". Even near 400 km a very thin atmosphere remains, and its main component is the oxygen atom we meet below. This series organizes the space environment as five enemies. Polyimide meets all five in the figure below.

3. Where polyimide is used

Polyimide is a thin, light, heat-resistant film. Primary sources confirm its use in the following places on spacecraft.

View original SVG, values and sources

Original SVG reference: Concept diagram (vector drawing). The main places where polyimide film is used inside a satellite. The layout is illustrative and does not show any specific satellite. The basis for each use is given in the table below.

The "main enemies" column is this article's organization of what the sources say (commentary). We did not check how much or what share of spacecraft polyimide is used in each place.

4. Enemy 1, vacuum: water comes out (outgassing)

Start with the most familiar enemy. Polyimide readily absorbs moisture from air. When the craft reaches vacuum, the absorbed water turns to gas and leaves. Not only water: components of adhesives and plasticizers also come out. This is outgassing.

Why is that a problem? The released gas can condense on nearby cold surfaces (lenses, mirrors, sensor windows, solar-cell covers) and fog them or leave a film. So spacecraft materials go through outgassing tests in vacuum chambers on the ground.

What the test measures

NASA describes the outgassing test as measuring the mass lost in vacuum (total mass loss, TML) and the amount that left as gas and then condensed on a separate cold plate (CVCM). The test method is ASTM E 595 Sourced[Ref. 1, 5]. The European standard ECSS-Q-ST-70-02C defines a test on the same principle. Its conditions: condition the sample at (22 ± 3) °C and (55 ± 10) % relative humidity, then hold it in vacuum (10^-3 Pa or lower) at 125 °C for 24 hours and weigh what condenses on a cooled collector at 25 °C Sourced[Ref. 4].

As a screening guide, ECSS-Q-ST-70-02C gives RML < 1.0 % and CVCM < 0.10 % as the minimum screening values for selecting a material. It also says that a material from which water leaves quickly, such as polyimide film, may be accepted with a TML above 1.0 % if its RML is below 1.0 %, provided conditions are met (no equipment colder than -100 °C is involved, no high-voltage equipment is involved, and ground purging with dry gas controls water re-absorption) Sourced[Ref. 4].

In practice, even materials that pass are baked in a vacuum oven after assembly so that the gas is driven out before launch. The same ECSS standard says it is becoming standard practice to bake critical hardware such as structural parts, harnesses, electronics boxes and thermal blankets at the highest permissible temperature for a few days Sourced[Ref. 4]. In NASA's MISSE experiments too, samples that did not meet the outgassing screening levels (TML under 1.00 %, CVCM under 0.10 %) were heat-treated in vacuum before flight Sourced[Ref. 1].

5. Enemy 4, atomic oxygen: the surface is eroded in low orbit

Where do oxygen atoms come from, and what do they do?

The atmosphere in low orbit is thin, but it holds plenty of oxygen atoms (atomic oxygen, AO). According to the NASA report, short-wavelength ultraviolet light from the Sun splits oxygen molecules (O₂) in the upper atmosphere into two atoms. In low orbit (below about 1,000 km) these atoms are the main constituent Sourced[Ref. 1].

In the air near the ground, an oxygen atom quickly bonds with something else and returns to a molecule. At 400 km, however, the mean distance an atom travels before hitting another particle is about 10⁴ m (10 km), so the atoms stay atoms Sourced[Ref. 1].

A spacecraft moving at 7.7 km per second slams into them. From the spacecraft's point of view, oxygen atoms arrive head-on at high speed. The NASA report gives the flux onto a surface facing the direction of travel (a ram surface) as about 5.23 × 10¹³ atoms per cm² per second (at 400 km, averaged over the 11-year solar cycle) and the average impact energy as 4.5 eV Sourced[Ref. 1].

The yardstick called "erosion yield"

How much is eroded? NASA expresses it with the erosion yield: the volume of material lost (in cm³) for each oxygen atom that hits (cm³ per atom). The smaller the value, the harder the material is to erode Sourced[Ref. 1].

Here polyimide holds a special position. The erosion yield of Kapton H, 3.0 × 10^-24 cm³ per atom, has been used as the "ruler" for measuring the total oxygen-atom dose (the fluence) in orbit. The NASA report says Kapton H is used to calibrate fluence because its erosion yield in low orbit is well characterized Sourced[Ref. 1]. A presentation from a Japanese university, prepared for a JAXA workshop, also says that this value was first measured on the 1982 Space Shuttle STS-8 experiment (altitude 225 km) Sourced[Ref. 12]. So polyimide is at once "a material that erodes" and "the reference material for measuring erosion".

Measured: an experiment that put 41 polymers outside the ISS

NASA exposed 41 polymers for about four years on the outside of the International Space Station (the PEACE Polymers experiment of MISSE 2). The samples sat on a tray outside the ISS Quest airlock for 3.95 years, from 16 August 2001 to 30 July 2005, and were retrieved during a Space Shuttle (STS-114) spacewalk on 30 July 2005 Sourced[Ref. 1, 2]. The fluence worked out from the mass loss of the Kapton H samples was 8.43 × 10²¹ atoms per cm² Sourced[Ref. 1].

What happened to MLI: a real case from LDEF

There is a real case that checks the calculation. LDEF (the Long Duration Exposure Facility, a long-exposure experiment launched and retrieved by the Space Shuttle) was in low orbit from April 1984 to January 1990 Sourced[Ref. 12]. Its experiment tray F-9 received 8.32 × 10²¹ oxygen atoms per cm² almost head-on, along with 11,100 equivalent sun hours of ultraviolet light. The Kapton MLI covering the tray lost most of its 0.076 mm (76 µm) outer Kapton layer and of the polyester net beneath it, and its color changed from the bronze of Kapton to the silver of the exposed aluminum coating Sourced[Ref. 3].

By the formula above, 3.0 × 10^-24 × 8.32 × 10²¹ ≈ 2.5 × 10^-2 cm, about 250 µm. That is more than enough to erode a 76 µm outer layer, so it is consistent with the report that "most of the outer layer was lost" Our calculation.

6. Defenses: placement, layering, coatings and material design

If we know it erodes, how do we defend against it? There are four broad ideas.

1. Put a sacrificial layer outside: in the LDEF MLI, even when the outermost Kapton layer eroded, the inner layers remained and the blanket stayed functional. It is reported that on the inner Kapton layers, coated with aluminum on both faces, the aluminum stayed attached and protected the Kapton from the space environment Sourced[Ref. 3].
2. Use a tough fabric for the outer cover: the Space Station WP-2 standard blanket, which used that result, has an outer cover of Beta cloth (glass-fiber fabric) aluminized on its inner face, and an inner cover of 0.076 mm double-aluminized, perforated Kapton. The inner reflector layers are 0.0076 mm double-aluminized Kapton separated by Dacron (polyester) net. These constructions are as described in the NASA report Sourced[Ref. 3]. The report says the blanket is expected to last 30 years in low orbit, but that is a design expectation, not a record of performance Not yet confirmed.
3. Coat the surface: the protective SiOx film on Kapton H (silicon dioxide or close to it) developed for Space Station Freedom was meant to protect the substrate from oxygen-atom impact Sourced[Ref. 14]. However, NASA reports that if the film has scratches, pinholes or surface roughness, the polymer underneath can erode under the film (undercutting) and a thin polymer film can fail, even though the coating itself resists oxygen atoms Sourced[Ref. 13].
4. Change the material itself: the BSF series from NIPPON STEEL Chemical & Material is a polyimide with siloxane (silicon-oxygen chains) built in as blocks. Its catalog says that oxygen atoms react to form a SiO₂ layer on the surface that prevents erosion, and that the SiO₂ layer regenerates after damage by reaction with oxygen atoms (self-healing) (manufacturer's stated explanation) Sourced[Ref. 11].

For BSF, the catalog lists the following exposure tests by JAXA as flight heritage: exposure on the Japanese Experiment Module Kibo in 2009 (8.5 months), a thermal-control-material exposure test (SDS-4) from 2012, ExHAM in 2015 to 2016, and the Super Low Altitude Test Satellite "Tsubame" (SLATS) in 2017 to 2019 (this is a manufacturer's account; we did not confirm numerical data in JAXA's primary documents) Sourced[Ref. 11].

7. Enemy 2, UV and radiation: tinting and brittleness

Polyimide film is amber (gold) to begin with. That color is tied to how much sunlight the film absorbs (its solar absorptance, α). For a film on the outside of MLI, a larger α means it warms in sunlight, which changes the thermal design. In space, moreover, ultraviolet light and particle radiation (electrons and protons) can cut polymer chains and add color-causing groups (chromophores), so α can rise over time (commentary; the test results follow below).

A quick glossary. α (solar absorptance) is how much of the Sun's light a surface absorbs. ε (emittance) is how well a surface gives off heat as infrared. For both, a larger number means a stronger property. ECSS-Q-ST-70-09C defines methods to measure them, including by spectrometer Sourced[Ref. 21].

A test under simulated space radiation

A research team including Boeing simulated, in a vacuum chamber on the ground, five years near the Sun-Earth Lagrange points (L1 and L2). The thin films tested (12.5 µm thick, aluminized on one side) included Kapton E and HN, UPILEX-S and the colorless polyimides CP-1 and CP-2 Sourced[Ref. 6]. The results follow.

All Sourced (Russell et al., AIAA-2001-1414 [Ref. 6]). Test conditions: ultraviolet about 1000 equivalent sun hours, protons 1.0E15 per cm² (40 keV), electrons 8.0E15 per cm² (40 keV).

Polyimide is not the only polymer facing this on the outside. The outer layer of the Hubble Space Telescope's MLI is aluminized Teflon FEP; after about 19 years in orbit, NASA reports that the retrieved outer layer was highly embrittled and fractured like glass at strains of 1 to 8 % Sourced[Ref. 15]. Any polymer sent into space is designed on the assumption that it will change with years, and that is common to all of them.

8. What happens in wire insulation: arc tracking

So far we have talked about films. Polyimide is also used as wire insulation, because it is light, heat-resistant and tough against abrasion. In this use, however, a different issue arose: not the material's "normal performance" but its behavior after a fault.

Van Laak of NASA's Johnson Space Center summarized the problem with Kapton wire at the 1994 NASA workshop on wiring. According to the presentation, as aerospace electrical systems grew, new requirements arose (smaller conductors, thinner insulation, higher heat resistance and abrasion resistance), and Kapton wire spread because of its heat resistance and abrasion resistance. At the same time, it brought in a new failure mode that was not fully recognized then. This is "arc tracking": it involves the formation of conductive char, and starting from an initiating event, insulation damage, an arc can travel along the wire and spread, so that a whole wire bundle (harness) can lose function Sourced[Ref. 8]. The presentation records a failure history of more than 500 arc-propagation events in defense applications and more than 5 at NASA (our reading of the extracted text of the slides). A NASA Headquarters investigation concluded that the risk is a credible threat to the Space Shuttle Orbiter, and the presentation also sets out the rationale for continuing to fly for the time being.

9. Colorless polyimide and the solar sail

For uses that call for a "thin, light, large film", polyimide is especially attractive. The best-known case is the solar sail, a sail pushed by the pressure of sunlight.

IKAROS: a membrane 7.5 µm thick

JAXA's Small Solar Power Sail Demonstrator IKAROS (launched on 21 May 2010) had a square membrane 20 m on the diagonal, made of polyimide 7.5 µm (0.0075 mm) thick. Thin-film solar cells of amorphous silicon, 25 µm thick, were attached to the membrane (pre-launch leaflet design values) Sourced[Ref. 9]. According to JAXA's operations log, regular operations ended on 26 January 2011 and verification of navigation by the sail and of power generation by thin-film solar cells was reported as achieved. After that, during the period when power is insufficient because of the distance from the Sun (7 months of its 10-month orbit around the Sun), it goes into hibernation; at its fifth hibernation in May 2015 it was about 110 million km from Earth, and no anomaly had been found Sourced[Ref. 10]. We could not confirm its status after May 2015.

What changes when polyimide is made colorless

For uses that need to reflect sunlight or need a transparent substrate, nearly colorless polyimides have been studied. On the colorless polyimides LaRC-CP1 and CP2 developed by NASA Langley, NASA's Spinoff magazine (1998) says SRS Technologies was the only company licensed by Langley to produce them Sourced[Ref. 25]. Why colorless versions are hard to make (coloring by charge transfer) is covered in our explainer on polyimides. What we want to confirm here is that in space, "colorless" is only a starting point, and that we must also look at what happens after ultraviolet light and radiation (A materials engineer's view 4 in Chapter 7). In MISSE 2, the erosion yield of CP1 (colorless) was 1.91 × 10^-24 cm³ per atom, smaller than that of Kapton H (3.00 × 10^-24) but not zero (Fig. 6) Sourced[Ref. 1].

10. Limits, and what could not be confirmed

• Quantity in actual use, and the latest status: we could not confirm statistics on how much polyimide is used in which part of which spacecraft. The evidence is mainly experiments from the 1980s to the 2000s such as LDEF and MISSE, which may differ from today's spacecraft designs
• Radiation dose by orbit: we do not give numbers for polyimide degradation in geostationary orbit or in the radiation belts. The simulation in Chapter 7 mimics the solar wind near L1 and L2
• Aging of the IKAROS membrane: we could not find published data measuring how its membrane changed under ultraviolet light and radiation
• Space heritage of BSF and similar materials: this rests on the manufacturer's catalog; we did not confirm quantitative data in JAXA primary documents
• Current wire requirements: we rely on a 1994 presentation and a 1990 test report and did not check current NASA or ESA wiring requirements
• The text of the standards: we did not confirm the test conditions or requirements of the ISO standards (paywalled), or the test conditions of ECSS-Q-ST-70-04C and 70-06C. For ECSS-Q-ST-70-02C we checked the relevant passages of the publicly available PDF
• ASTM: we did not open ASTM's site. For ASTM E 595 and E 2089 we give only the number, title and what is measured, as written in NASA reports

11. How to read the yardsticks and standards

Space materials cannot be chosen from a table of properties alone. What matters is how well a ground test reproduces the real space environment. The yardsticks fall into four groups: (1) what comes out in vacuum (outgassing: TML, RML, CVCM); (2) what erodes in low orbit (erosion yield); (3) how the material changes under ultraviolet light and particles (changes in α, ε and tensile properties); and (4) whether it stays bonded through repeated temperature swings (thermal-vacuum cycling). Each measures only one environmental factor, whereas in space they act together (synergy). A yardstick is a tool for comparing and screening materials; it does not directly predict lifetime in orbit.

The arrangement of this table is Our calculation (our own reordering). Standard numbers, titles and status were checked on the official pages of ECSS, ISO and NASA (checked 17 October 2026). For ASTM we give only the numbers and titles written in NASA reports; we did not open ASTM's site. ISO texts are paywalled, so we limited ourselves to titles and scope.

Cautions in reading (for materials engineers)

• Ground tests and flight results are different things: atomic oxygen applied from a ground plasma differs from space in energy and particle types. That is why results are corrected as a ratio to polyimide (Kapton H) [Ref. 2, 12]
• Qualification and acceptance are different: ECSS-Q-ST-70-17C (durability testing of coatings) separates the kinds of tests for the evaluation, qualification and acceptance stages Sourced[Ref. 26] (an example of a standard aimed at coatings). Material-selection tests and per-unit acceptance tests are different matters
• Check whether a standard is a recommendation or a requirement: ISO 15856 is guidance that gives recommended methods. An ECSS standard becomes a requirement when a project's contract says it applies, and it is tailored (the standard pages say it "may be tailored"). NASA-STD-6016 is shown as not a NASA mandatory standard
• Manufacturer's values and third-party measurements are different: the space heritage of specialty products such as BSF rests mainly on the manufacturer's documents. We did not confirm numbers in JAXA primary documents

12. Glossary

13. References

1. de Groh K. K. et al. (NASA Glenn) "MISSE PEACE Polymers Atomic Oxygen Erosion Results", NASA/TM—2006-214482 (November 2006) — ntrs.nasa.gov/citations/20070002707
2. Stambler A. H. et al. (NASA Glenn) "Ground-Laboratory to In-Space Atomic Oxygen Correlation for the Polymer Erosion and Contamination Experiment (PEACE) Polymers", NASA/TM—2011-216904 (January 2011) — ntrs.nasa.gov/citations/20110006367
3. Smith C. A., Hasegawa M. M., Jones C. A. (McDonnell Douglas Aerospace) "Space Station WP-2 application of LDEF MLI results", LDEF Materials Results for Spacecraft Applications (NASA Marshall, conference paper, December 1993) — ntrs.nasa.gov/citations/19940026511
4. ECSS ECSS-Q-ST-70-02C "Thermal vacuum outgassing test for the screening of space materials" (15 November 2008; checked on the ECSS page and PDF) — ecss.nl/standard/ecss-q-st-70-02c-thermal-vacuum-outgassing-test-for-the-screening-of-space-materials/
5. NASA Goddard Outgassing Database (searchable test results; checked 17 October 2026) — outgassing.nasa.gov/
6. Russell D. A., Connell J. W., Fogdall L. B., Winkler W. "Effects of Electrons, Protons, and Ultraviolet Radiation on Thermophysical Properties of Polymeric Films", AIAA-2001-1414 (2001; NASA Technical Reports Server) — ntrs.nasa.gov/citations/20010072172
7. St. Clair A. K., Slemp W. S. (NASA Langley) "Evaluation of colorless polyimide film for thermal control coating applications" (1985) — ntrs.nasa.gov/citations/19850007585
8. Van Laak J. (NASA Johnson) "Kapton wire concerns for aerospace vehicles", First NASA Workshop on Wiring for Space Applications (presentation, September 1994) — ntrs.nasa.gov/citations/19950009630
9. JAXA Small Solar Power Sail Demonstrator "IKAROS" leaflet (membrane dimensions and material; pre-launch design values) — global.jaxa.jp/activity/pr/brochure/files/sat28.pdf
10. JAXA IKAROS project topics (operations from 2010 to 2015; checked 17 October 2026) — global.jaxa.jp/projects/sas/ikaros/topics.html
11. NIPPON STEEL Chemical & Material Atomic-oxygen-tolerant polyimide film "BSF series" catalog (manufacturer document, in Japanese; edition 2510) — nscm.nipponsteel.com/display/pdf/2510_BSF%E3%82%AB%E3%82%BF%E3%83%AD%E3%82%B0(%E5%92%8C%E6%96%87).pdf
12. Yokota K., Tagawa M. (Kobe University) "Impact of the SLATS mission on space-materials degradation research" (in Japanese), JAXA 5th workshop on utilizing very-low-altitude satellites (24 January 2020) — satnavi.jaxa.jp/ja/wp-content/uploads/sites/3/2019/12/09_slatsMaterial-tagawa.pdf
13. Banks B. A. et al. (NASA Glenn) "Issues and Consequences of Atomic Oxygen Undercutting of Protected Polymers in Low Earth Orbit", NASA/TM-2002-211577 (2002) — ntrs.nasa.gov/citations/20020062043
14. Banks B., Sovey J., Mirtich M. (NASA Lewis) "SiOx Protective Coat For Polyimide Sheet", NASA Tech Briefs 15(4) (April 1991) — ntrs.nasa.gov/citations/19910000163
15. de Groh K. K. et al. "Analyses of Hubble Space Telescope Aluminized-Teflon Multilayer Insulation Blankets Retrieved After 19 Years of Space Exposure" (2015) — ntrs.nasa.gov/citations/20150002706
16. Finckenor M. M., Albyn K. C., Watts E. W. (NASA Marshall) "Atomic Oxygen Exposure of Polyimide Foam for International Space Station Solar Array Wing Blanket Box" (2006) — ntrs.nasa.gov/citations/20060020185
17. ISO ISO 15856:2010 "Space systems — Space environment — Simulation guidelines for radiation exposure of non-metallic materials" (edition 1, August 2010; reconfirmed in 2026; checked on the ISO page) — iso.org/standard/45843.html
18. ISO ISO 15104:2025 "Space systems — Environmental testing for spacecraft thermal control materials" (edition 1, January 2025; checked on the ISO page) — iso.org/standard/84447.html
19. ECSS ECSS-Q-ST-70-06C "Particle and UV radiation testing for space materials" (31 July 2008) — ecss.nl/standard/ecss-q-st-70-06c-particle-and-uv-radiation-testing-for-space-materials/
20. ECSS ECSS-Q-ST-70-04C "Thermal testing for the evaluation of space materials, processes, mechanical parts and assemblies" (15 November 2008) — ecss.nl/standard/ecss-q-st-70-04c-thermal-testing-for-the-evaluation-of-space-materials-processes-mechanical-parts-and-assemblies/
21. ECSS ECSS-Q-ST-70-09C "Measurements of thermo-optical properties of thermal control materials" (31 July 2008) — ecss.nl/standard/ecss-q-st-70-09c-measurements-of-thermo-optical-properties-of-thermal-control-materials/
22. ECSS ECSS-Q-ST-70-71C Rev.1 "Materials, processes and their data selection" (15 October 2019) — ecss.nl/standard/ecss-q-st-70-71c-rev-1-materials-processes-and-their-data-selection-15-october-2019/
23. NASA NASA-STD-6016 "Standard Materials and Processes Requirements for Spacecraft" (Version C with Change 1; dated 30 September 2021, changed 15 November 2023; checked on the NASA Standards page) — standards.nasa.gov/standard/NASA/NASA-STD-6016
24. NASA Johnson "Kapton wire arc track testing: Per test procedure KWATT BB01" (report on tests performed in 1990; NASA Technical Reports Server) — ntrs.nasa.gov/citations/19910012114
25. NASA "Thin Film...Large Payoff", Spinoff 1998 (on LaRC-CP1 and CP2 and the license) — ntrs.nasa.gov/citations/20020065031
26. ECSS ECSS-Q-ST-70-17C "Durability testing of coatings" (1 February 2018) — ecss.nl/standard/ecss-q-st-70-17c-durability-testing-of-coatings/

14. Claim-to-source audit

Last updated: 17 October 2026 / Sources are limited to primary materials (NASA technical reports, the NASA Goddard database, the official pages of ECSS, ISO and NASA, JAXA public materials and manufacturer catalogs). Flight measurements are values under the conditions reported and do not carry over to other orbits or periods. Calculated values are illustrative values made for this article and are not predictions of real spacecraft lifetime. We could not confirm the quantity of actual use, aging of the IKAROS membrane, JAXA primary data on BSF, current wiring requirements, or the test conditions in the standards' texts, so we do not state them.