Fused silica optical solar reflector (OSR, second-surface silver mirror) OSR
Second-surface silver mirror on a fused silica substrate, optionally overcoated with alumina (aluminium oxide)
An optical solar reflector (OSR) is a second-surface silver mirror on a glass substrate, used on spacecraft radiators to reflect sunlight while radiating heat.
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Low solar absorptance
0.1 -
High infrared emittance
> 0.8 -
Emittance with temperature
0.80 at 300 K to 0.67 at 750 K
Corrosion protection
0.1 -
Thermal vacuum cycling
-40 °C to +120 °C
Recipe, share of the weight
- Si not statedSilicon
- O not statedOxygen
- Ag not statedSilver
- Al₂O₃ not statedAlumina (aluminium oxide)
Best for
Spacecraft radiator surfaces that must reflect sunlight while shedding heat (low solar absorptance with high infrared emittance)
Weakest at
Unprotected silver: a bare silver film blackened within a fraction of a second in the 1968 hydrogen sulfide test, and emittance falls as the surface warms
Risk at a glance
- People None found. Mixed: silica not classified, silver classified
- If it fails High. Corrosion of an unprotected silver film
- Corrosion Severe. A bare silver film blackened within a fraction of a second in the 1968 test.
Quick facts: OSR
| Property | Value | Basis |
|---|---|---|
| Density | 2.2 g/cm³ | 1 sourced value |
| Thermal conductivity | 1.4 W/(m·K) | 1 sourced value |
What is the density of Fused silica optical solar reflector (OSR)?
Fused silica optical solar reflector (OSR) has a density of 2.2 g/cm³. The source and test conditions are listed in the properties table on this page.
What is the thermal conductivity of Fused silica optical solar reflector (OSR)?
Fused silica optical solar reflector (OSR) has a thermal conductivity of 1.4 W/(m·K). The source and test conditions are listed in the properties table on this page.
What is Fused silica optical solar reflector (OSR) used for?
Uses recorded in the sources include Satellite radiator surfaces (second-surface mirror); Commercial rigid OSR tile (SQUID3 SQ-1); Thermal subsystem component (SQ-1 listing).
Why it exists
An optical solar reflector (OSR) is a mirror that reflects sunlight while letting a spacecraft radiator shed its own heat. The 1968 Lockheed study for NASA defined the OSR as a second-surface silver mirror on a fused silica substrate, and this profile covers that design. Modern rigid OSR tiles, such as SQUID3's SQ-1, are sold for satellite radiators, but their datasheet does not name the substrate.
Where it's used
Satellite radiators (1968 NASA definition)
The 1968 study defined the OSR as a second-surface silver mirror on a fused silica substrate, for low solar absorptance and a low ratio of solar absorptance to infrared emittance.
Commercial rigid OSR tile
SQUID3 sells the SQ-1 for satellite radiators and structural panels, in standard sizes of 1 x 1 in and 2 x 2 in.
Recipe
Second-surface silver mirror on a fused silica substrate, optionally overcoated with alumina (aluminium oxide)
The fused silica substrate is made of silicon and oxygen. The reflective layer is vacuum-deposited silver on its back surface, and the 1968 test samples added an optional alumina (aluminium oxide) overcoat on top of the silver.
| Ingredient | Share of the weight | What it does |
|---|---|---|
| Silicon Si | not stated | Main element of the fused silica substrate. Its atomic weight is given as [28.084, 28.086] in the identity note (NIST). |
| Oxygen O | not stated | Second element of the fused silica substrate. Its atomic weight is given as [15.999 03, 15.999 77] in the identity note (NIST). |
| Silver Ag | not stated | The second-surface mirror. Silver reflects sunlight, and the 1968 samples used 1200 A of it on fused silica. |
| Alumina (aluminium oxide) Al₂O₃ | not stated | Optional overcoat over the silver, which the 1968 study tested at 210, 550 and 955 A to protect it from corrosion. |
Weight shares are as printed in the sources.
What it can do
Low solar absorptance
0.1 -
measured
A commercial OSR sample read 0.049 in the 1968 study. Prepared fused silica OSRs averaged 0.044 before ultraviolet exposure and 0.054 after. SQUID3 prints 0.1 for the SQ-1. Each figure carries its own test conditions in the properties.
High infrared emittance
> 0.8 -
measured
SQUID3 prints an infrared emittance above 0.8 for the SQ-1, written as '> 0.8'. The 1968 study printed a total hemispherical emittance of 0.80 at 300 K for the fused silica OSR.
Emittance with temperature
0.80 at 300 K to 0.67 at 750 K
measured
According to the 1968 report text, emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K.
Corrosion protection
0.1 -
measured
In the same hydrogen sulfide test, 210 A alumina over silver moved from 0.055 to 0.064 in one hour, while a bare silver film blackened within a fraction of a second.
Thermal vacuum cycling
-40 °C to +120 °C
SQUID3 claims the SQ-1 passes thermal vacuum cycling from -40 °C to +120 °C. This is a vendor claim with no test report read.
How it compares
Among the figures in this profile, the 1968 fused silica OSR is the measured reference: solar absorptance 0.044 before and 0.054 after ultraviolet exposure, against 0.049 for one commercial OSR sample. Against a bare silver film, which blackened within a fraction of a second in the hydrogen sulfide test, alumina-overcoated silver stayed at 0.064 after one hour with 210 A alumina. The SQ-1 datasheet prints a solar absorptance of 0.1, which is higher than the 1968 samples, but it gives no test method or substrate, so the two cannot be compared directly.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details.
| Measurement | OSR |
|---|---|
| Thermal behavior and safety | |
| Thermal conductivity, fused silica substratePrinted in the Fused Silica Properties table | 1.4 W/m·°C |
| Physical and electrical | |
| Mass density, SQ-1 rigid OSRVendor product table, printed as 400 g/m2 | 400 g/m2 |
| Thickness, SQ-1 rigid OSRVendor product table, printed as 0.3 mm | 0.3 mm |
| Thickness, SQ-1 as listed in SatCatalog | 0.2 to 0.4 mm3 |
| Mass density limit, SQ-1 as listed in SatCatalog | < 500 g/m^24 |
| Density, fused silica substrate | 2.2 g/cm³16 |
| Other measurements | |
| Solar absorptance, SQ-1 rigid OSR | 0.1 -1 |
| IR emittance, SQ-1 rigid OSR | > 0.8 -2 |
| Solar absorptance, commercial OSR (one sample) | 0.049 -5 |
| Solar absorptance, prepared fused silica OSR before ultraviolet | 0.044 -6 |
| Solar absorptance, prepared fused silica OSR after ultraviolet | 0.054 -7 |
| Total hemispherical emittance, fused silica OSR at 300 K | 0.8 -8 |
| Total hemispherical emittance, fused silica OSR at 750 K | 0.67 -9 |
| Solar absorptance, 210 A alumina over silver, before exposure | 0.055 -10 |
| Solar absorptance, 210 A alumina over silver, after 1 h | 0.064 -11 |
| Solar absorptance, 550 A alumina over silver, before exposure | 0.054 -12 |
| Solar absorptance, 550 A alumina over silver, after 1 h | 0.06 -13 |
| Solar absorptance, 955 A alumina over silver, before exposure | 0.054 -14 |
| Solar absorptance, 955 A alumina over silver, after 1 h | 0.059 -15 |
| Refractive index, fused silica substrate | 1.457 -17 |
Why choose it, and why not
Good for
- Radiator surfaces that need low solar absorptance with high infrared emittance. The 1968 OSR had 0.044 to 0.054 solar absorptance, and SQUID3 prints 0.1 with an infrared emittance above 0.8 for the SQ-1.
- Thermal control in sunlight. The 1968 study states its purpose as low solar absorptance and a low ratio of absorptance to emittance.
Watch out for
- Bare silver corrodes in sulfur-bearing humid air. In the 1968 test, the alumina overcoat was what protected it.
- Emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K.
- Solar absorptance rose after ultraviolet exposure, by about 1% in the report, from 0.044 to 0.054 on average for prepared samples.
- The SQ-1 datasheet does not name its substrate or test method, so its figures cannot be taken as fused silica data.
A fused silica OSR is a well-documented low-absorptance, high-emittance radiator surface, with measured data on corrosion, ultraviolet and proton exposure from a 1968 study prepared for NASA. The modern SQ-1 product sheet has catalogued figures only, with no named substrate or test method, so the 1968 fused silica design holds the measured detail.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Solar absorptance, SQ-1 rigid OSR | Vendor product table; the datasheet prints the value without a unit, recorded as dimensionless | product SQ-1 Rigid Optical Solar Reflectortest not printed on the datasheet | — |
| 2 | IR emittance, SQ-1 rigid OSR | Vendor product table, printed as '> 0.8' with no test method; recorded as a lower bound and dimensionless | product SQ-1 Rigid Optical Solar Reflectorprinted > 0.8 | — |
| 3 | Thickness, SQ-1 as listed in SatCatalog | Range printed on the SatCatalog details table as 0.2~0.4 mm | product SQ-1 Optical Solar Reflectors as listed on SatCatalog (the page does not separate SQ-1 from SQ-2) | — |
| 4 | Mass density limit, SQ-1 as listed in SatCatalog | Upper limit printed as < 500 g/m^2 on the SatCatalog details table | product SQ-1 Optical Solar Reflectors as listed on SatCatalog | — |
| 5 | Solar absorptance, commercial OSR (one sample) | Laboratory value reported in the 1968 study text, given for comparison with the study's own prepared samples | substrate fused silicacondition initial, before ultraviolet exposuresample count one sample only | — |
| 6 | Solar absorptance, prepared fused silica OSR before ultraviolet | Average of prepared samples as printed in the text; the study says the grades of fused silica did not differ significantly | substrate fused silica, prepared samples (average)condition before 500 equivalent sun-hour ultraviolet exposure at 700 K | — |
| 7 | Solar absorptance, prepared fused silica OSR after ultraviolet | Average of prepared samples as printed in the text (changed from 0.044 to 0.054) | substrate fused silica, prepared samples (average)condition after 500 equivalent sun-hour ultraviolet exposure at 700 K | — |
| 8 | Total hemispherical emittance, fused silica OSR at 300 K | Value quoted in the text of Section 7.2 as printed 0.80; the report's summary says emittance was measured from 400 to 800 K, so this 300 K figure is a text statement | substrate fused silica with vacuum-deposited silver, second surfacetemperature 300 K | Printed as 0.80 in the report text |
| 9 | Total hemispherical emittance, fused silica OSR at 750 K | Value quoted in the text of Section 7.2, as the endpoint of a decrease from 0.80 at 300 K | substrate fused silica with vacuum-deposited silver, second surfacetemperature 750 K | — |
| 10 | Solar absorptance, 210 A alumina over silver, before exposure | Measured value in Table 6-1 (accelerated corrosion test) | coating 210 A alumina overcoat on 1200 A silver on fused silica substratestate before hydrogen sulfide exposure | — |
| 11 | Solar absorptance, 210 A alumina over silver, after 1 h | Measured value in Table 6-1 (accelerated corrosion test) | coating 210 A alumina overcoat on 1200 A silver on fused silica substrateexposure 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity) | — |
| 12 | Solar absorptance, 550 A alumina over silver, before exposure | Measured value in Table 6-1 (accelerated corrosion test) | coating 550 A alumina overcoat on 1200 A silver on fused silica substratestate before hydrogen sulfide exposure | — |
| 13 | Solar absorptance, 550 A alumina over silver, after 1 h | Measured value in Table 6-1 (accelerated corrosion test) | coating 550 A alumina overcoat on 1200 A silver on fused silica substrateexposure 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity) | — |
| 14 | Solar absorptance, 955 A alumina over silver, before exposure | Measured value in Table 6-1 (accelerated corrosion test) | coating 955 A alumina overcoat on 1200 A silver on fused silica substratestate before hydrogen sulfide exposure | — |
| 15 | Solar absorptance, 955 A alumina over silver, after 1 h | Measured value in Table 6-1 (accelerated corrosion test) | coating 955 A alumina overcoat on 1200 A silver on fused silica substrateexposure 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity) | — |
| 16 | Density, fused silica substrate | Printed as 2.20 g/cm3 in the Fused Silica Properties table; describes the substrate, not the OSR stack | temperature not stated on the page | — |
| 17 | Refractive index, fused silica substrate | Printed in the refractive index table at 0.633 um | wavelength 0.633 µm (633 nm)temperature not stated on the page | — |
Corrosion and compatibility
What happens when it meets other materials and environments.
| Environment | Concern | What happens |
|---|---|---|
| Hydrogen sulfide vapour with near 100% relative humidity (accelerated test; ammonium polysulfide in a closed container) | severe | A bare silver film blackened within a fraction of a second in the 1968 test.1 |
| Hydrogen sulfide vapour with near 100% relative humidity, 1 h (alumina overcoated silver) | low | Alumina overcoats kept silver usable in the same test: solar absorptance rose from 0.055 to 0.064 with 210 A alumina.2 |
| Ultraviolet, 500 equivalent sun-hours at 700 K (fused silica substrates) | low | Ultraviolet at 700 K raised solar absorptance only slightly, by about 1%.3 |
| 2 keV protons, up to 5 x 10^17 p/cm2, substrate temperatures of 400, 530 and 700 K | none | No optical damage was seen in the fused silica OSRs under these proton exposures.4 |
| Thermal vacuum cycling from -40 °C to +120 °C (manufacturer claim) | not rated | SQUID3 says the SQ-1 passes thermal vacuum cycling from -40 °C to +120 °C; no test report was read.5 |
| # | Environment | Details | Test conditions |
|---|---|---|---|
| 1 | Hydrogen sulfide vapour with near 100% relative humidity (accelerated test; ammonium polysulfide in a closed container) | The report says this test is probably one of the most rigorous for silver films, and that a bare silver film blackened in a fraction of a second. Table 6-1 has one row marked film failure, with absorptance rising from 0.047 to 0.677; the text layer does not print that row's coating, so it is not used here as a bare-silver value. | exposure closed container, hydrogen sulfide from ammonium polysulfide, near 100% relative humiditycoating bare silver film (one row of Table 6-1 marked film failure) |
| 2 | Hydrogen sulfide vapour with near 100% relative humidity, 1 h (alumina overcoated silver) | Table 6-1 gives absorptance before and after one hour for 210 A alumina (0.055 to 0.064), 550 A (0.054 to 0.060) and 955 A (0.054 to 0.059) over 1200 A silver on fused silica. The conclusions say alumina of at least 500 A is very acceptable, and that in a corrosive environment the attack starts at the exposed substrate edge. | exposure 1 h, closed container, hydrogen sulfide from ammonium polysulfidecoating 1200 A silver on fused silica with 210, 550 or 955 A alumina |
| 3 | Ultraviolet, 500 equivalent sun-hours at 700 K (fused silica substrates) | The report says the OSRs showed a small increase in solar absorptance after the ultraviolet test, which it traced to a change in the transmittance of the fused silica (about 1%). Grades of fused silica did not differ significantly. Prepared samples changed from 0.044 to 0.054 on average; one commercial OSR sample, at 0.049, did not change. | dose 500 equivalent sun-hourstemperature 700 Ksubstrates Suprasil 11, Spectrasil B, Corning 7940 (industrial and UV grade) and G.E. 151 fused silica |
| 4 | 2 keV protons, up to 5 x 10^17 p/cm2, substrate temperatures of 400, 530 and 700 K | The report says none of the samples showed optical damage, and that fused silica showed no change in solar absorptance after the highest proton dose at 700 K, whatever its grade or source. The report also checked the stability of the coating system's spectral reflectance after exposure. | energy 2 keV protonsdose up to 5 x 10^17 p/cm2temperature 400, 530 and 700 K |
| 5 | Thermal vacuum cycling from -40 °C to +120 °C (manufacturer claim) | The datasheet lists this among its features. No cycle count, test report or before-and-after optical values are printed, so this is a vendor claim only. | basis vendor features listproducts SQ-1 and SQ-2 |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
PubChem summarizes ECHA notifications for these materials. Vitreous silica is listed as Not Classified. Silver is listed with H400 (very toxic to aquatic life), and a revised FY2022 entry lists H360 (may damage fertility or the unborn child).
- Silica
- Vitreous silica (EC 262-373-8) is listed as Not Classified. Other silica forms on the same PubChem record are classified, so the form matters.
- Silver
- The main ECHA entry for silver (EC 231-131-3) carries H400. A revised classification for silver, excluding nanoparticles, carries Danger with H360.
- Data limits
- These are aggregated company notifications, not a product safety data sheet. No safety data sheet for the OSR was read.
If the coating is damaged
The 1968 study tested the failure mode that matters most for silver: sulfur-bearing humid air.
- Bare silver
- In the hydrogen sulfide test, the report says a bare silver film blackened within a fraction of a second.
- Edges
- In a corrosive environment the attack starts at the exposed substrate edge, according to the report's conclusions.
Handling and storage
- Preparation
- The report's preparation used a mild hydrofluoric etch of the substrate, then heating to about 500 K before deposition. This profile records no safety data for hydrofluoric acid.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Corrosion of an unprotected silver filmhigh severity | Humid, sulfur-bearing air (hydrogen sulfide vapour in the 1968 accelerated test)The report says a bare silver film blackened in a fraction of a second. The silver is what gives the OSR its low solar absorptance. |
| Attack from exposed substrate edgesmoderate severity | A corrosive environment reaching the uncovered edge of the coatingThe report says in a corrosive environment the attack starts at the exposed substrate edge. |
| Rise in solar absorptance after ultraviolet exposurelow severity | 500 equivalent sun-hours of ultraviolet at 700 KSolar absorptance rose by about 1%, which the report traces to a change in transmittance of the fused silica. |
Side effects on surrounding parts
| Affects | Effect |
|---|---|
| Radiator heat rejection at high surface temperature | Emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K. |
Handling and storage
- The report's preparation used a mild hydrofluoric substrate etch, then heating the substrate to about 500 K before vacuum deposition, for silver adhesion. The report says this treatment did not change solar absorptance.
Mitigations
- Overcoat the silver with alumina of at least 500 A; the report's conclusions call this minimum very acceptable for corrosion resistance in its hydrogen sulfide test.
Supply and geography
How common the raw materials are and where they come from.
Silver (reflective layer)
- Top producers (2025)
- Mexico 24.2%, Peru 13.8%, China 13.1%
- Critical mineral lists
- US: listed
- Recycling
- USGS: about 1,000 tons of silver was recovered from new and old scrap in the United States in 2025, about 11% of apparent consumption.
- Substitutes
- USGS lists substitutes for photographic, surgical, flatware and some battery uses; it does not discuss mirror coatings.
Silicon (fused silica substrate)
- Top producers (2025)
- China 87%, Brazil 3.9%, Norway 2.8%, Russia 0.8%
- Critical mineral lists
- US: listed
- Recycling
- USGS silicon chapter: recycling is "Insignificant."
- Substitutes
- USGS silicon chapter: gallium arsenide and germanium are the principal substitutes for silicon in semiconductor and infrared applications.
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
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spore: profile
id: fused-silica-optical-solar-reflector
spore_version: 0.2
family: optical-coatings
name: Fused silica optical solar reflector (OSR, second-surface silver mirror)
abbreviation: OSR
role: Low-absorptance, high-emittance radiator surface for spacecraft
category: coatings
type: optical-solar-reflectors
summary: |
An optical solar reflector (OSR) is a second-surface silver mirror on a glass substrate, used on spacecraft radiators to reflect sunlight while radiating heat. In a 1968 Lockheed study for NASA, prepared fused silica OSRs had a solar absorptance of 0.044 on average before ultraviolet exposure, rising to 0.054 after 500 equivalent sun-hours of ultraviolet at 700 K. The same study printed a total hemispherical emittance of 0.80 at 300 K, falling to 0.67 at 750 K. A commercial SQUID3 SQ-1 OSR is listed with a solar absorptance of 0.1 and an infrared emittance above 0.8, but its datasheet does not name the substrate.
best_for: Spacecraft radiator surfaces that must reflect sunlight while shedding heat (low solar absorptance with high infrared emittance)
weakest_at: 'Unprotected silver: a bare silver film blackened within a fraction of a second in the 1968 hydrogen sulfide test, and emittance falls as the surface warms'
identity:
formula: Second-surface silver mirror on a fused silica substrate, optionally overcoated with alumina (aluminium oxide)
source: nasa1968
where: 'Section 2 (program objectives: OSR defined as a second surface mirror of silver on a fused silica substrate); Section 2.4.3 (alumina overcoat)'
note: 'NIST standard atomic weights for the substrate elements: silicon Si [28.084, 28.086]; oxygen O [15.999 03, 15.999 77]'
tags:
applications:
- thermal-control
properties:
- benchmark: solar_absorptance
label: Solar absorptance, SQ-1 rigid OSR
value: 0.1
unit: '-'
scope: material
conditions:
product: SQ-1 Rigid Optical Solar Reflector
test: not printed on the datasheet
method: Vendor product table; the datasheet prints the value without a unit, recorded as dimensionless
status: ground
source: squid3-sq1-datasheet
where: Product table, row SQ-1, column SOLAR ABSORPTANCE (alpha)
- benchmark: infrared_emittance
label: IR emittance, SQ-1 rigid OSR
value: 0.8
bound: lower
unit: '-'
scope: material
conditions:
product: SQ-1 Rigid Optical Solar Reflector
printed: '> 0.8'
method: Vendor product table, printed as '> 0.8' with no test method; recorded as a lower bound and dimensionless
status: ground
source: squid3-sq1-datasheet
where: Product table, row SQ-1, column IR EMITTANCE (epsilon)
- benchmark: areal_mass_density
label: Mass density, SQ-1 rigid OSR
value: 400
unit: g/m2
scope: material
conditions:
product: SQ-1 Rigid Optical Solar Reflector
method: Vendor product table, printed as 400 g/m2
status: ground
source: squid3-sq1-datasheet
where: Product table, row SQ-1, column MASS DENSITY
- benchmark: thickness
label: Thickness, SQ-1 rigid OSR
value: 0.3
unit: mm
scope: material
conditions:
product: SQ-1 Rigid Optical Solar Reflector
method: Vendor product table, printed as 0.3 mm
status: ground
source: squid3-sq1-datasheet
where: Product table, row SQ-1, column THICKNESS
- benchmark: thickness
label: Thickness, SQ-1 as listed in SatCatalog
value: 0.2
value_high: 0.4
bound: range
unit: mm
scope: material
conditions:
product: SQ-1 Optical Solar Reflectors as listed on SatCatalog (the page does not separate SQ-1 from SQ-2)
method: Range printed on the SatCatalog details table as 0.2~0.4 mm
status: ground
source: satcatalog-osr
where: Details table, row Thickness
- benchmark: areal_mass_density
label: Mass density limit, SQ-1 as listed in SatCatalog
value: 500
bound: upper
unit: g/m^2
scope: material
conditions:
product: SQ-1 Optical Solar Reflectors as listed on SatCatalog
method: Upper limit printed as < 500 g/m^2 on the SatCatalog details table
status: ground
source: satcatalog-osr
where: Details table, row Mass density
- benchmark: solar_absorptance
label: Solar absorptance, commercial OSR (one sample)
value: 0.049
unit: '-'
scope: material
conditions:
substrate: fused silica
condition: initial, before ultraviolet exposure
sample_count: one sample only
method: Laboratory value reported in the 1968 study text, given for comparison with the study's own prepared samples
status: ground
source: nasa1968
where: Section 6.3 (Ultraviolet environmental test results), paragraph on the commercial OSR
- benchmark: solar_absorptance
label: Solar absorptance, prepared fused silica OSR before ultraviolet
value: 0.044
unit: '-'
scope: material
conditions:
substrate: fused silica, prepared samples (average)
condition: before 500 equivalent sun-hour ultraviolet exposure at 700 K
method: Average of prepared samples as printed in the text; the study says the grades of fused silica did not differ significantly
status: ground
source: nasa1968
where: Section 6.3, paragraph on prepared test samples
- benchmark: solar_absorptance
label: Solar absorptance, prepared fused silica OSR after ultraviolet
value: 0.054
unit: '-'
scope: material
conditions:
substrate: fused silica, prepared samples (average)
condition: after 500 equivalent sun-hour ultraviolet exposure at 700 K
method: Average of prepared samples as printed in the text (changed from 0.044 to 0.054)
status: ground
source: nasa1968
where: Section 6.3, paragraph on prepared test samples
- benchmark: total_hemispherical_emittance
label: Total hemispherical emittance, fused silica OSR at 300 K
value: 0.8
unit: '-'
scope: material
conditions:
substrate: fused silica with vacuum-deposited silver, second surface
temperature: 300 K
method: Value quoted in the text of Section 7.2 as printed 0.80; the report's summary says emittance was measured from 400 to 800 K, so this 300 K figure is a text statement
status: ground
note: Printed as 0.80 in the report text
source: nasa1968
where: Section 7.2 (Emittance relationships), page 7-2
- benchmark: total_hemispherical_emittance
label: Total hemispherical emittance, fused silica OSR at 750 K
value: 0.67
unit: '-'
scope: material
conditions:
substrate: fused silica with vacuum-deposited silver, second surface
temperature: 750 K
method: Value quoted in the text of Section 7.2, as the endpoint of a decrease from 0.80 at 300 K
status: ground
source: nasa1968
where: Section 7.2 (Emittance relationships), page 7-2
- benchmark: solar_absorptance
label: Solar absorptance, 210 A alumina over silver, before exposure
value: 0.055
unit: '-'
scope: material
conditions:
coating: 210 A alumina overcoat on 1200 A silver on fused silica substrate
state: before hydrogen sulfide exposure
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1 (Corrosion of alumina overcoated silver), 210 A row, Before Exposure column
- benchmark: solar_absorptance
label: Solar absorptance, 210 A alumina over silver, after 1 h
value: 0.064
unit: '-'
scope: material
conditions:
coating: 210 A alumina overcoat on 1200 A silver on fused silica substrate
exposure: 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity)
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1, 210 A row, After 1 hr Exposure column
- benchmark: solar_absorptance
label: Solar absorptance, 550 A alumina over silver, before exposure
value: 0.054
unit: '-'
scope: material
conditions:
coating: 550 A alumina overcoat on 1200 A silver on fused silica substrate
state: before hydrogen sulfide exposure
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1, 550 A row, Before Exposure column
- benchmark: solar_absorptance
label: Solar absorptance, 550 A alumina over silver, after 1 h
value: 0.06
unit: '-'
scope: material
conditions:
coating: 550 A alumina overcoat on 1200 A silver on fused silica substrate
exposure: 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity)
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1, 550 A row, After 1 hr Exposure column
- benchmark: solar_absorptance
label: Solar absorptance, 955 A alumina over silver, before exposure
value: 0.054
unit: '-'
scope: material
conditions:
coating: 955 A alumina overcoat on 1200 A silver on fused silica substrate
state: before hydrogen sulfide exposure
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1, 955 A row, Before Exposure column
- benchmark: solar_absorptance
label: Solar absorptance, 955 A alumina over silver, after 1 h
value: 0.059
unit: '-'
scope: material
conditions:
coating: 955 A alumina overcoat on 1200 A silver on fused silica substrate
exposure: 1 h in hydrogen sulfide vapour (ammonium polysulfide, near 100% relative humidity)
method: Measured value in Table 6-1 (accelerated corrosion test)
status: ground
source: nasa1968
where: Table 6-1, 955 A row, After 1 hr Exposure column
- benchmark: density
label: Density, fused silica substrate
value: 2.2
unit: g/cm3
scope: material
conditions:
temperature: not stated on the page
method: Printed as 2.20 g/cm3 in the Fused Silica Properties table; describes the substrate, not the OSR stack
status: ground
source: pmoptics-fused-silica
where: Fused Silica Properties table, row Density
- benchmark: thermal_conductivity
label: Thermal conductivity, fused silica substrate
value: 1.4
unit: W/m·°C
scope: material
conditions:
temperature: not stated on the page
method: Printed in the Fused Silica Properties table
status: ground
source: pmoptics-fused-silica
where: Fused Silica Properties table, row Thermal Conductivity
- benchmark: refractive_index
label: Refractive index, fused silica substrate
value: 1.45702
unit: '-'
scope: material
conditions:
wavelength: 0.633 µm (633 nm)
temperature: not stated on the page
method: Printed in the refractive index table at 0.633 um
status: ground
source: pmoptics-fused-silica
where: Refractive Index table, row 0.633 um
corrosion:
- environment: Hydrogen sulfide vapour with near 100% relative humidity (accelerated test; ammonium polysulfide in a closed container)
headline: A bare silver film blackened within a fraction of a second in the 1968 test.
effect: The report says this test is probably one of the most rigorous for silver films, and that a bare silver film blackened in a fraction of a second. Table 6-1 has one row marked film failure, with absorptance rising from 0.047 to 0.677; the text layer does not print that row's coating, so it is not used here as a bare-silver value.
rating: severe
conditions:
exposure: closed container, hydrogen sulfide from ammonium polysulfide, near 100% relative humidity
coating: bare silver film (one row of Table 6-1 marked film failure)
source: nasa1968
where: Section 6.2 (silver film stability), discussion before Table 6-1
- environment: Hydrogen sulfide vapour with near 100% relative humidity, 1 h (alumina overcoated silver)
headline: 'Alumina overcoats kept silver usable in the same test: solar absorptance rose from 0.055 to 0.064 with 210 A alumina.'
effect: Table 6-1 gives absorptance before and after one hour for 210 A alumina (0.055 to 0.064), 550 A (0.054 to 0.060) and 955 A (0.054 to 0.059) over 1200 A silver on fused silica. The conclusions say alumina of at least 500 A is very acceptable, and that in a corrosive environment the attack starts at the exposed substrate edge.
rating: low
conditions:
exposure: 1 h, closed container, hydrogen sulfide from ammonium polysulfide
coating: 1200 A silver on fused silica with 210, 550 or 955 A alumina
source: nasa1968
where: Table 6-1 and Section 8.1 (film deposition, corrosion resistance)
- environment: Ultraviolet, 500 equivalent sun-hours at 700 K (fused silica substrates)
headline: Ultraviolet at 700 K raised solar absorptance only slightly, by about 1%.
effect: The report says the OSRs showed a small increase in solar absorptance after the ultraviolet test, which it traced to a change in the transmittance of the fused silica (about 1%). Grades of fused silica did not differ significantly. Prepared samples changed from 0.044 to 0.054 on average; one commercial OSR sample, at 0.049, did not change.
rating: low
conditions:
dose: 500 equivalent sun-hours
temperature: 700 K
substrates: Suprasil 11, Spectrasil B, Corning 7940 (industrial and UV grade) and G.E. 151 fused silica
source: nasa1968
where: Section 6.3 (Ultraviolet environmental test results) and Section 8.3 (OSR ultraviolet exposure)
- environment: 2 keV protons, up to 5 x 10^17 p/cm2, substrate temperatures of 400, 530 and 700 K
headline: No optical damage was seen in the fused silica OSRs under these proton exposures.
effect: The report says none of the samples showed optical damage, and that fused silica showed no change in solar absorptance after the highest proton dose at 700 K, whatever its grade or source. The report also checked the stability of the coating system's spectral reflectance after exposure.
rating: none
conditions:
energy: 2 keV protons
dose: up to 5 x 10^17 p/cm2
temperature: 400, 530 and 700 K
source: nasa1968
where: Section 6.4 (Proton radiation test results) and Section 8.2 (Proton environment)
- environment: Thermal vacuum cycling from -40 °C to +120 °C (manufacturer claim)
headline: SQUID3 says the SQ-1 passes thermal vacuum cycling from -40 °C to +120 °C; no test report was read.
effect: The datasheet lists this among its features. No cycle count, test report or before-and-after optical values are printed, so this is a vendor claim only.
rating: unknown
conditions:
basis: vendor features list
products: SQ-1 and SQ-2
source: squid3-sq1-datasheet
where: Features list
risks:
hazards:
- text: PubChem lists vitreous silica (EC 262-373-8) as Not Classified under GHS, aggregated over 1682 reports by companies from 17 notifications to the ECHA C&L Inventory.
ghs: []
source: pubchem-silica-ghs
where: 'Safety and Hazards, GHS Classification, ECHA entry ''Silica, vitreous (EC: 262-373-8)'' (CID 24261)'
- text: 'Other silica forms on the same PubChem record are classified, so the substance name matters: amorphous silica (EC 601-216-3) carries Warning with H315 (56.3%), H319 (56.3%) and H335 (56.3%), aggregated over 2540 reports; cristobalite (EC 238-455-4) carries Danger with H350 (12.6%): May cause cancer.'
ghs:
- H315
- H319
- H335
- H350
source: pubchem-silica-ghs
where: 'Safety and Hazards, GHS Classification, ECHA entries ''AMORPHOUS SILICA (EC: 601-216-3)'' and ''Cristobalite (EC: 238-455-4)'' (CID 24261)'
- text: 'PubChem gives the main ECHA entry for silver (EC 231-131-3) as Warning with H400 (70.4%): Very toxic to aquatic life, aggregated over 2154 reports by companies from 36 notifications.'
ghs:
- H400
source: pubchem-silver-ghs
where: 'Safety and Hazards, GHS Classification, ECHA entry ''Silver (EC: 231-131-3)'' (CID 23954)'
- text: 'PubChem lists a revised classification for silver (excluding nanoparticles), FY2022, as Danger with H360: May damage fertility or the unborn child.'
ghs:
- H360
source: pubchem-silver-ghs
where: Safety and Hazards, GHS Classification, entry 'Silver (excluding nanoparticles) - FY2022 (Revised classification)' (CID 23954)
failure_risks:
- mode: Corrosion of an unprotected silver film
trigger: Humid, sulfur-bearing air (hydrogen sulfide vapour in the 1968 accelerated test)
consequence: The report says a bare silver film blackened in a fraction of a second. The silver is what gives the OSR its low solar absorptance.
severity: high
source: nasa1968
where: Section 6.2 (silver film stability), discussion before Table 6-1
- mode: Attack from exposed substrate edges
trigger: A corrosive environment reaching the uncovered edge of the coating
consequence: The report says in a corrosive environment the attack starts at the exposed substrate edge.
severity: moderate
source: nasa1968
where: Section 8.1 (film deposition conclusions)
- mode: Rise in solar absorptance after ultraviolet exposure
trigger: 500 equivalent sun-hours of ultraviolet at 700 K
consequence: Solar absorptance rose by about 1%, which the report traces to a change in transmittance of the fused silica.
severity: low
source: nasa1968
where: Section 8.3 (OSR ultraviolet exposure)
side_effects:
- text: Emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K.
affects: Radiator heat rejection at high surface temperature
source: nasa1968
where: Section 7.2 (Emittance relationships), page 7-2
handling:
- text: The report's preparation used a mild hydrofluoric substrate etch, then heating the substrate to about 500 K before vacuum deposition, for silver adhesion. The report says this treatment did not change solar absorptance.
source: nasa1968
where: Section 8.1 (film deposition)
mitigations:
- text: Overcoat the silver with alumina of at least 500 A; the report's conclusions call this minimum very acceptable for corrosion resistance in its hydrogen sulfide test.
source: nasa1968
where: Section 8.1 (film deposition)
uses:
- application: thermal-control
device: Satellite radiator surfaces (second-surface mirror)
example: The NASA 1968 study defines an optical solar reflector as a second surface mirror of silver on a fused silica substrate, for low solar absorptance and a low ratio of solar absorptance to infrared emittance.
source: nasa1968
where: Section 2 (program objectives), definition of OSR
- application: thermal-control
device: Commercial rigid OSR tile (SQUID3 SQ-1)
example: SQUID3 says the SQ-1 may be used as a surface material on satellite radiators and structural panels, with standard sizes of 1 x 1 in and 2 x 2 in.
source: squid3-sq1-datasheet
where: Applications section and product standard sizes
- application: thermal-control
device: Thermal subsystem component (SQ-1 listing)
example: SatCatalog lists the SQ-1 under the Thermal Subsystem, with component type Optical Solar Reflectors and status In Production.
source: satcatalog-osr
where: Overview table, Subsystem, Component Type and Status rows
supply:
- subject: Silver (reflective layer)
producers:
- country: Mexico
share_percent: 24.2
year: 2025
- country: Peru
share_percent: 13.8
year: 2025
- country: China
share_percent: 13.1
year: 2025
critical_lists:
- list: USGS 2025 Final List of Critical Minerals (silver added in the 2025 list)
listed: true
recycling: 'USGS: about 1,000 tons of silver was recovered from new and old scrap in the United States in 2025, about 11% of apparent consumption.'
substitutes:
- USGS lists substitutes for photographic, surgical, flatware and some battery uses; it does not discuss mirror coatings.
source: usgs-mcs2026-silver
where: World Mine Production and Reserves table, 2025e column (world total 26,000 t; shares calculated by Space Mushroom against that total); Recycling; Substitutes; critical list statement
- subject: Silicon (fused silica substrate)
producers:
- country: China
share_percent: 87
year: 2025
- country: Brazil
share_percent: 3.9
year: 2025
- country: Norway
share_percent: 2.8
year: 2025
- country: Russia
share_percent: 0.8
year: 2025
critical_lists:
- list: USGS 2025 Final List of Critical Minerals (silicon added in the 2025 list)
listed: true
recycling: 'USGS silicon chapter: recycling is "Insignificant."'
substitutes:
- 'USGS silicon chapter: gallium arsenide and germanium are the principal substitutes for silicon in semiconductor and infrared applications.'
source: usgs-mcs2026-silicon
where: World Production table, silicon metal, 2025 column (thousand metric tons, silicon content; world total 4,600 printed as rounded; shares calculated by Space Mushroom against that total). The chapter's world-resources statement names silica in natural forms, such as quartzite, as the source of silicon. This is a silicon-metal statistic, not a fused-silica production figure; none was found.
documents:
- title: SQ-1 and SQ-2 Optical Solar Reflectors datasheet (SQUID3 Space, Version 2024/10)
type: datasheet
url: https://satcatalog.s3.amazonaws.com/components/1449/SatCatalog_-_SQUID3_Space_-_SQ-1_Optical_Solar_Reflectors_-_Datasheet.pdf?lastmod=20260119070530
year: 2024
- title: Low Solar Absorptance and Emittance Surfaces Utilizing Vacuum Deposited Techniques (Lockheed final report 4-06-68-1, NASA NTRS 19680015854)
type: report
url: https://ntrs.nasa.gov/api/citations/19680015854/downloads/19680015854.pdf
year: 1968
- title: 'Mineral Commodity Summaries 2026: Silver'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silver.pdf
year: 2026
- title: 'NIST Atomic Weights and Isotopic Compositions: silicon'
type: database
url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Si&all=all&ascii=html
- title: 'Mineral Commodity Summaries 2026: Silicon'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
year: 2026
- title: 'PubChem: Silica (CID 24261), GHS classification (ECHA notifications)'
type: database
url: https://pubchem.ncbi.nlm.nih.gov/compound/24261
year: 2026
- title: 'PubChem: Silver (CID 23954), GHS classification (ECHA notifications)'
type: database
url: https://pubchem.ncbi.nlm.nih.gov/compound/23954
year: 2026
gaps:
- No flight, thermal-vacuum or on-orbit test data for an OSR found in the sources read; the 1968 results are laboratory measurements and the SQ-1 thermal-vacuum claim has no test report.
- The SQUID3 datasheet and SatCatalog page do not name the substrate of the SQ-1; the 1968 fused silica design is not assumed to be the SQ-1 construction. The SQ-1 areal mass and thickness are not used to infer a material.
- SatCatalog lists the form factor of the same product as both All and Rigid/Flexible; the datasheet lists SQ-1 as Rigid and SQ-2 as Flexible.
- Solar absorptance and infrared emittance from SQUID3 carry no unit and no test method; recorded as dimensionless with the caveat in method.
- The 1968 report gives OSR emittance at 300 K and 750 K only in the text (0.80 and 0.67); the emittance figures (Figs. 6-1 to 6-4) and the full temperature curve were not read in this run.
- Table 6-2 (solar absorptance after ultraviolet, by grade) is not legible in the text layer; only the text averages are used.
- The Table 6-1 row marked film failure has no legible coating label, so it is not used as a bare-silver absorptance value.
- Hazard data come from PubChem ECHA notification summaries only; no safety data sheet for silver or vitreous silica was read in this run, and the PubChem entries are aggregated company reports, not a single product classification.
- 'Outgassing: SQUID3 claims a low outgassing requirement (ASTM E-595) but prints no total mass loss or collected volatile condensable material values.'
- Silicon production shares are from the silicon-metal table, not from fused-silica feedstock; no fused-silica or quartz-glass production statistic was found. Silver EU critical raw materials status was not read in this run.
- Refractive index was read at one wavelength (0.633 um) from the pmoptics table; no temperature dependence was printed.
- No images were fetched or read; no media entries.
sources:
satcatalog-osr:
title: 'SatCatalog: SQ-1 Optical Solar Reflectors (SQUID3 Space) component page'
url: https://www.satcatalog.com/component/sq-1-optical-solar-reflectors
year: 2026
kind: web
license: SatCatalog web page (cited, not reproduced)
squid3-sq1-datasheet:
title: SQ-1 and SQ-2 Optical Solar Reflectors datasheet (SQUID3 Space, Version 2024/10)
id: SQUID3 datasheet, Version 2024/10; hosted on SatCatalog
url: https://satcatalog.s3.amazonaws.com/components/1449/SatCatalog_-_SQUID3_Space_-_SQ-1_Optical_Solar_Reflectors_-_Datasheet.pdf?lastmod=20260119070530
year: 2024
kind: datasheet
license: vendor document, linked not reproduced
nasa1968:
title: Low Solar Absorptance and Emittance Surfaces Utilizing Vacuum Deposited Techniques (Greenberg and Vance, Lockheed Palo Alto Research Laboratory, final report 4-06-68-1)
id: NASA NTRS 19680015854; Lockheed report 4-06-68-1; contract NAS 2-3063
url: https://ntrs.nasa.gov/api/citations/19680015854/downloads/19680015854.pdf
year: 1968
kind: report
license: public domain (NASA)
pmoptics-fused-silica:
title: Fused Silica, PMOptics property page (Fused Silica Properties table and refractive index table)
url: https://www.pmoptics.com/Fused_Silica.html
kind: web
license: supplier web page (cited, not reproduced)
usgs-mcs2026-silver:
title: Mineral Commodity Summaries 2026, Silver
id: USGS MCS 2026, February 2026
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silver.pdf
year: 2026
kind: report
license: public domain (USGS)
nist-atomic-weights:
title: NIST Atomic Weights and Isotopic Compositions for Silicon and Oxygen
id: NIST Standard Reference Data, stand-alone compositions pages (Si, O)
url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Si&all=all&ascii=html
kind: database
license: public domain (NIST)
usgs-mcs2026-silicon:
title: Mineral Commodity Summaries 2026, Silicon
id: USGS MCS 2026, February 2026
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
year: 2026
kind: report
license: public domain (USGS)
pubchem-silica-ghs:
title: 'PubChem: Silica (CID 24261), Safety and Hazards, GHS Classification'
id: PubChem CID 24261 (ECHA C&L Notifications Summary)
url: https://pubchem.ncbi.nlm.nih.gov/compound/24261
year: 2026
kind: database
license: PubChem record (cited, not reproduced)
pubchem-silver-ghs:
title: 'PubChem: Silver (CID 23954), Safety and Hazards, GHS Classification'
id: PubChem CID 23954 (ECHA C&L Notifications Summary)
url: https://pubchem.ncbi.nlm.nih.gov/compound/23954
year: 2026
kind: database
license: PubChem record (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-11-01'
review:
status: draft
method: assistant
checked_values: 20
unreachable: 0
caveats: 3
note: 'Read by an AI assistant on 2026-11-01: SatCatalog page, SQUID3 SQ-1 datasheet, NASA 1968 report (text layer and Table 6-1), USGS silver and silicon chapters, PMOptics fused silica table, NIST atomic weights, PubChem silica and silver GHS records (read through the PubChem JSON view, since the web pages returned a browser check).'
story:
recipe:
line: The fused silica substrate is made of silicon and oxygen. The reflective layer is vacuum-deposited silver on its back surface, and the 1968 test samples added an optional alumina (aluminium oxide) overcoat on top of the silver.
parts:
- name: Silicon
symbol: Si
role: Main element of the fused silica substrate. Its atomic weight is given as [28.084, 28.086] in the identity note (NIST).
- name: Oxygen
symbol: O
role: Second element of the fused silica substrate. Its atomic weight is given as [15.999 03, 15.999 77] in the identity note (NIST).
- name: Silver
symbol: Ag
role: The second-surface mirror. Silver reflects sunlight, and the 1968 samples used 1200 A of it on fused silica.
- name: Alumina (aluminium oxide)
symbol: Al₂O₃
role: Optional overcoat over the silver, which the 1968 study tested at 210, 550 and 955 A to protect it from corrosion.
risk_groups:
- title: For people
level: 0
verdict: 'Mixed: silica not classified, silver classified'
lead: PubChem summarizes ECHA notifications for these materials. Vitreous silica is listed as Not Classified. Silver is listed with H400 (very toxic to aquatic life), and a revised FY2022 entry lists H360 (may damage fertility or the unborn child).
points:
- label: Silica
line: Vitreous silica (EC 262-373-8) is listed as Not Classified. Other silica forms on the same PubChem record are classified, so the form matters.
- label: Silver
line: The main ECHA entry for silver (EC 231-131-3) carries H400. A revised classification for silver, excluding nanoparticles, carries Danger with H360.
- label: Data limits
line: These are aggregated company notifications, not a product safety data sheet. No safety data sheet for the OSR was read.
- title: If the coating is damaged
lead: 'The 1968 study tested the failure mode that matters most for silver: sulfur-bearing humid air.'
points:
- label: Bare silver
line: In the hydrogen sulfide test, the report says a bare silver film blackened within a fraction of a second.
- label: Edges
line: In a corrosive environment the attack starts at the exposed substrate edge, according to the report's conclusions.
- title: Handling and storage
points:
- label: Preparation
line: The report's preparation used a mild hydrofluoric etch of the substrate, then heating to about 500 K before deposition. This profile records no safety data for hydrofluoric acid.
why: An optical solar reflector (OSR) is a mirror that reflects sunlight while letting a spacecraft radiator shed its own heat. The 1968 Lockheed study for NASA defined the OSR as a second-surface silver mirror on a fused silica substrate, and this profile covers that design. Modern rigid OSR tiles, such as SQUID3's SQ-1, are sold for satellite radiators, but their datasheet does not name the substrate.
uses:
- where: Satellite radiators (1968 NASA definition)
line: The 1968 study defined the OSR as a second-surface silver mirror on a fused silica substrate, for low solar absorptance and a low ratio of solar absorptance to infrared emittance.
- where: Commercial rigid OSR tile
line: SQUID3 sells the SQ-1 for satellite radiators and structural panels, in standard sizes of 1 x 1 in and 2 x 2 in.
can_do:
- label: Low solar absorptance
benchmark: solar_absorptance
line: A commercial OSR sample read 0.049 in the 1968 study. Prepared fused silica OSRs averaged 0.044 before ultraviolet exposure and 0.054 after. SQUID3 prints 0.1 for the SQ-1. Each figure carries its own test conditions in the properties.
- label: High infrared emittance
benchmark: infrared_emittance
line: SQUID3 prints an infrared emittance above 0.8 for the SQ-1, written as '> 0.8'. The 1968 study printed a total hemispherical emittance of 0.80 at 300 K for the fused silica OSR.
- label: Emittance with temperature
benchmark: total_hemispherical_emittance
value: 0.80 at 300 K to 0.67 at 750 K
line: According to the 1968 report text, emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K.
- label: Corrosion protection
benchmark: solar_absorptance
line: In the same hydrogen sulfide test, 210 A alumina over silver moved from 0.055 to 0.064 in one hour, while a bare silver film blackened within a fraction of a second.
- label: Thermal vacuum cycling
value: '-40 °C to +120 °C'
line: SQUID3 claims the SQ-1 passes thermal vacuum cycling from -40 °C to +120 °C. This is a vendor claim with no test report read.
compare: 'Among the figures in this profile, the 1968 fused silica OSR is the measured reference: solar absorptance 0.044 before and 0.054 after ultraviolet exposure, against 0.049 for one commercial OSR sample. Against a bare silver film, which blackened within a fraction of a second in the hydrogen sulfide test, alumina-overcoated silver stayed at 0.064 after one hour with 210 A alumina. The SQ-1 datasheet prints a solar absorptance of 0.1, which is higher than the 1968 samples, but it gives no test method or substrate, so the two cannot be compared directly.'
compare_rows:
- label: Solar absorptance (lower is better)
benchmark: solar_absorptance
- label: Infrared emittance (higher is better)
benchmark: infrared_emittance
- label: Total hemispherical emittance at 300 K and 750 K
benchmark: total_hemispherical_emittance
handling:
- Keep the silver away from sulfur-bearing humid air. A bare silver film blackened within a fraction of a second in the 1968 test.
- Overcoat the silver with alumina of at least 500 A. The 1968 conclusions call this minimum very acceptable.
- For silver adhesion, the 1968 preparation etched the substrate with a mild hydrofluoric acid treatment and then heated it to about 500 K before deposition.
good_for:
- Radiator surfaces that need low solar absorptance with high infrared emittance. The 1968 OSR had 0.044 to 0.054 solar absorptance, and SQUID3 prints 0.1 with an infrared emittance above 0.8 for the SQ-1.
- Thermal control in sunlight. The 1968 study states its purpose as low solar absorptance and a low ratio of absorptance to emittance.
watch_out:
- Bare silver corrodes in sulfur-bearing humid air. In the 1968 test, the alumina overcoat was what protected it.
- Emittance falls as the surface warms, from 0.80 at 300 K to 0.67 at 750 K.
- Solar absorptance rose after ultraviolet exposure, by about 1% in the report, from 0.044 to 0.054 on average for prepared samples.
- The SQ-1 datasheet does not name its substrate or test method, so its figures cannot be taken as fused silica data.
verdict: A fused silica OSR is a well-documented low-absorptance, high-emittance radiator surface, with measured data on corrosion, ultraviolet and proton exposure from a 1968 study prepared for NASA. The modern SQ-1 product sheet has catalogued figures only, with no named substrate or test method, so the 1968 fused silica design holds the measured detail.
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.
| # | Source | Type | Year | Used for |
|---|---|---|---|---|
| SatCatalog: SQ-1 Optical Solar Reflectors (SQUID3 Space) component page | web | 2026 | 3 values | |
| SQ-1 and SQ-2 Optical Solar Reflectors datasheet (SQUID3 Space, Version 2024/10) | datasheet | 2024 | 6 values | |
| Low Solar Absorptance and Emittance Surfaces Utilizing Vacuum Deposited Techniques (Greenberg and Vance, Lockheed Palo Alto Research Laboratory, final report 4-06-68-1) | report | 1968 | 23 values | |
| Fused Silica, PMOptics property page (Fused Silica Properties table and refractive index table) | web | 3 values | ||
| Mineral Commodity Summaries 2026, Silver | report | 2026 | 1 value | |
| NIST Atomic Weights and Isotopic Compositions for Silicon and Oxygen | database | 0 values | ||
| Mineral Commodity Summaries 2026, Silicon | report | 2026 | 1 value | |
| PubChem: Silica (CID 24261), Safety and Hazards, GHS Classification | database | 2026 | 2 values | |
| PubChem: Silver (CID 23954), Safety and Hazards, GHS Classification | database | 2026 | 2 values |
Updated