A thermal vacuum chamber is a vacuum chamber with a second problem stacked on top: it has to hold vacuum while its internal surfaces swing between cryogenic and elevated temperature, which is the condition that finds every bad material choice.
What makes thermal vacuum different
Thermal cycling moves everything. A joint that seals at room temperature can open when a flange cools and the bolt contracts at a different rate from the flange. A shroud that is rigidly mounted will crack its supports. The design has to allow movement while keeping the vacuum boundary intact, which usually means bellows, slotted mounts and sliding supports rather than a stiff structure.
Materials under thermal vacuum
316L is used for the vessel because it keeps useful toughness at low temperature — the austenitic grades do not suffer the ductile-to-brittle transition that ferritic steels show. Aluminium is used for shrouds where thermal conductivity matters more than strength. Internal fasteners need attention because galling is much worse in vacuum, where there is no oxide to regenerate on the thread.
Ports and feedthroughs
A thermal vacuum chamber carries far more penetration than a process chamber: thermocouple and instrumentation feedthroughs for the shroud and the test article, power feedthroughs for heaters, and optical ports for the instruments that are the whole point of the test. Each is a leak path, so the port count drives both the fabrication cost and the leak test time.
Verification
The vessel is helium leak tested at ambient before the shroud is fitted, and the assembled chamber is re-tested after. A chamber that passes leak testing before installation and fails afterwards is normally a port that was added or a joint that was disturbed, not the vessel itself.
Space simulation specifically
Space simulation adds the requirement that the chamber be large enough that the test article does not see the walls — the shroud has to surround the article without touching it, which sets both the vessel diameter and the internal support structure. That geometry is normally the reason a space simulation chamber is a one-off rather than a standard product.
What we control in-house
- 304 / 316L stainless steel and 6061 / 5083 aluminium fabrication
- Clean-environment TIG welding with full penetration and no micro-porosity
- Helium mass-spectrometer leak testing to 1 × 10⁻⁹ mbar·l/s
- In-house electropolishing and passivation — not subcontracted
- Chamber bake-out to 150–400 °C for UHV outgassing control
- Precision-machined ISO-KF, ISO-K and CF (ConFlat) flanges
- Zeiss CMM verification to ±0.02 mm across large work envelopes
- 12 m gantry CNC machining — 12 m × 4 m × 2 m envelope
- SEMI-referenced documentation and inspection protocols
Frequently asked questions
What is a thermal vacuum chamber?
A vacuum chamber with an internal shroud that can be cooled, typically with liquid nitrogen or a cryocooler, and sometimes heated, so a test article can be cycled between temperature extremes in vacuum. It is used to test spacecraft components, instruments and materials under conditions approximating space.
Why is 316L used for thermal vacuum vessels?
Austenitic stainless steels keep their toughness at low temperature and do not show the ductile-to-brittle transition that ferritic grades do. For a vessel that may see liquid-nitrogen temperatures, that is the deciding property.
What is a space simulation chamber?
A thermal vacuum chamber sized and configured so the test article is surrounded by a shroud without touching it, approximating the radiative environment of space. The requirement to enclose without contact is what drives the vessel geometry and makes most space simulation chambers one-off builds.
How many feedthroughs does a thermal vacuum chamber need?
Typically many more than a process chamber: thermocouples on the shroud and the article, power for heaters, and optical ports for the measurement instruments. Each penetration is a separate leak path, so the port schedule is normally fixed early and the leak test planned around it.
Do you build the shroud as well as the vessel?
We fabricate the vacuum vessel and its ports, and can supply the internal support structure. The shroud and its cooling circuit are usually specified by the customer because the thermal design is tied to the test requirement.
Related capabilities
Need this made to spec?
Send the drawing or the specification and we will come back with a DDP price, lead time and inspection plan.