Supplier Qualification for Invar Satellite Structure Machining

By Invar Machining editorial team· Published September 26, 2026 · How we write these guides

A satellite program buying an Invar bracket, mount or optical bench structure is not just buying a part that meets print dimensions. It is buying a documented process, because the alloy’s value depends on what happens to it after roughing as much as what the CMM shows at final inspection. Qualifying a shop for this kind of work means checking things a general precision machining RFQ never asks about: material traceability, a first article inspection built around the part’s real sensitivities, and a process record a second source can pick up later if the program needs one. None of this involves invarmachining.com or any matched shop claiming a certification it does not hold. This guide covers what to check, what to ask for, and how to keep the qualification honest.

Why satellite hardware raises the bar past machining capability

A shop that machines Invar 36 competently for an optical instrument on a lab bench and a shop that machines the same alloy for a part going on a satellite are not automatically doing the same job. The material is identical and the cutting parameters are similar, covered in Invar 36 machining parameters, but a flight program adds requirements the lab part never sees: a documented chain of custody for the material, a formal first article inspection, and a process record detailed enough that someone can reconstruct what was done to the part years after it is in orbit. Programs qualify a shop against these requirements, not just against its ability to hold a tolerance.

This is a distinction worth stating plainly on any RFQ headed to a satellite program: cutting the alloy well and documenting the work to program standards are two different capabilities, and a shop can have one without the other. Read how to find a machine shop with real Invar experience for the baseline machining question before layering the documentation requirements on top.

A shop that has never touched a satellite part but runs disciplined process control on other precision work, optical instruments or metrology tooling for example, can often meet a flight documentation requirement faster than a shop with vague space heritage but loose paperwork habits. Ask what the shop actually records on a job, not just what industries it has shipped to before.

Material traceability for flight hardware

Every legitimate lot of Invar 36 or Super Invar ships with a mill certificate confirming chemistry against ASTM F1684. For a lab part, that certificate on file is usually enough. For a flight part, a program typically wants the heat lot traceable through the shop’s own paperwork: the router or job traveler references the specific heat lot, the inspection report ties back to it, and the shop can produce that chain on request, not just at delivery but months or years later if a question comes up during the program’s life.

Traceability level	Typical for	What it covers
Mill certificate on file	General commercial parts	Chemistry per ASTM spec, tied to a heat lot number
Heat lot referenced on router	Most flight structural parts	Certificate plus a documented link from raw material to the specific part serial or lot
Full material pedigree with retained samples	Highest criticality flight parts	Traceability plus a retained material sample or extended documentation package, defined by the program

Ask which level your program actually requires before writing the RFQ. Requesting the top tier for a bracket that does not need it adds cost and lead time without a corresponding benefit. Our material certification guide covers what a standard mill certificate includes and what it leaves out, most notably that CTE is usually a separate, chargeable test rather than a default line on the certificate.

First article inspection built around the part’s real sensitivities

A first article inspection proves the shop’s process produces a part that measures within print tolerance, but for an Invar flight part it should be built around the specific things that make Invar behave the way it does, not just a generic dimensional checklist. That means measuring critical features after a documented soak at 20 °C, per Invar machining tolerances, and recording the stress relief cycle and fixturing approach used to get there, per Invar fixturing and workholding, so the inspection data means something beyond the day it was taken.

A CMM report that shows only pass or fail against the print, with no record of soak time, inspection temperature or the process that produced the part, tells a satellite program very little about whether the part will stay stable. Our CMM inspection report guide covers what a report worth keeping actually contains.

First article element	Generic dimensional FAI	Invar-specific FAI for flight hardware
Measurement conditions	Ambient shop temperature, unspecified soak	Soak at 20 °C for a stated time, recorded on the report
Process record	Not usually attached	Stress relief cycle, fixturing method and finishing sequence attached
Timing	Single measurement at delivery	Delivery measurement, sometimes a repeat after a stated interval for drift-sensitive parts
Material reference	Alloy named on the print	Heat lot number referenced and tied to the mill certificate

Second-source qualification for a flight program

Most satellite programs eventually need a second source, whether for schedule risk, cost or a production ramp. Qualifying that second shop for Invar hardware is its own exercise, covered in depth in second-source qualification for an Invar part, and the short version matters here too: a second shop that hits the same print dimensions with a different stress relief cycle or fixturing approach has not automatically produced an equivalent part. The program needs the same process history from the second source that it collected from the first, compared feature by feature, not just a passing first article.

Certifications: what programs typically ask for, and what we do not claim

Satellite and aerospace programs commonly ask a shop about AS9100 quality system certification, and programs handling export-controlled data or hardware ask about ITAR registration. We do not hold or claim either of these for invarmachining.com, and we do not verify or guarantee that a matched shop holds them either. If your program requires a specific certification or registration, confirm it directly with the shop, in writing, before releasing flight hardware or export-controlled drawings. That verification is between the buyer and the shop, and it belongs earlier in the process than the first purchase order.

The same caution applies to any claim a shop makes about prior space heritage. Ask for specifics, such as the program name if it is not restricted, the part type and the year, rather than accepting “we have shipped space hardware before” as sufficient. A shop that answers with detail is usually the one that actually did the work; a shop that answers vaguely is worth a follow-up question before the drawing goes out.

A hypothetical qualification example

A program needs an Invar 36 optical bench bracket for a small satellite bus, quantity six units across two spacecraft, with a possible second batch of twelve a year later. The program qualifies a primary shop through a first article: material traceability to a specific heat lot, a documented stress relief cycle at 330 °C for 90 minutes, fixturing described and photographed, and CMM data taken after a 20 °C soak. The first article passes and the program accepts the source.

For the second batch, the program requests a second shop as schedule protection. The second shop’s first article also passes dimensionally, but its stress relief cycle runs at 320 °C for two hours, a different but individually reasonable process. Because the program documented the first shop’s cycle, the difference is visible and gets recorded rather than discovered later if a dimensional question comes up on a delivered unit. Neither cycle is wrong. The value is in knowing they differ.

This is illustrative, not a specific case, and every real program sets its own acceptance criteria for what counts as an equivalent process.

What to put on the qualification package

• The governing spec and UNS number, referenced against the Invar specs reference, so there is no ambiguity about which alloy variant is being quoted
• The traceability level required, from a certificate on file up to full pedigree with retained samples
• The specific first article requirements: soak time, inspection temperature, and which features are datum-critical
• Whether a second source will eventually be qualified, so the primary shop knows to document its process in a form that transfers
• Any certification or registration your program requires, stated as a requirement for the shop to answer directly, not assumed

Getting matched

Send your drawing and your qualification requirements through our RFQ form. We match it with up to three shops that machine Invar and Super Invar structural hardware, and each shop answers your traceability and documentation questions directly, since that verification has to happen between your program and the shop rather than through us. For the sourcing side of a satellite optical bench specifically, see sourcing Invar optical benches for spacecraft programs, and for questions about Super Invar mounts on temperature-controlled payloads, see Super Invar instrument mounts for satellite payloads. Back to the space and satellite hardware overview for the full picture of how Invar and Super Invar are used across a spacecraft program.

Frequently asked questions

Reviewed against

• ASTM F1684, Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications
• Wikipedia, AS9100

Values in this guide are typical handbook figures for planning. The mill certificate for your heat lot and the shop's quote for your geometry govern.

Keep reading

• Second-Source Qualification: Requalifying an Invar Part at a New Shop · Choosing a Supplier
• Invar Mill Certifications: What a Certified Material Report Should Show · Choosing a Supplier
• Reading an Invar CMM Inspection Report: What Each Number Means · Process
• How to Find a Machine Shop That Has Really Machined Invar · Choosing a Supplier

All choosing a supplier guides