The schedule is set by the slowest part
Ask any programme manager what killed their launch date and the answer is rarely the design. It is the reaction wheel that quoted 30 weeks and shipped at 52, or the rad-hard FPGA that went on allocation. In a supply chain, the long pole — the single longest lead-time item plus everything that must happen after it arrives — sets the earliest possible ship date, and no amount of parallel work elsewhere shortens it.
Typical flight-hardware lead times (2025–26, order-of-magnitude)
| Item | Typical lead | Why so long |
|---|---|---|
| Rad-hard FPGAs / processors | 40–70 weeks | Few fabs, small volumes, government priority allocation |
| Triple-junction solar cells / panels | 30–52 weeks | Two or three suppliers worldwide; capacity booked by constellations |
| Reaction wheels, star trackers | 26–52 weeks | Precision mechanisms, per-unit acceptance testing |
| Propulsion (thrusters, tanks, valves) | 26–60 weeks | Pressure-vessel certification, hot-fire acceptance |
| Space-grade connectors, harness | 12–30 weeks | Commodity parts with non-commodity screening |
| Batteries (space cells) | 20–40 weeks | Cell-lot matching, safety certification |
| Custom structures / machined parts | 8–20 weeks | Fast once the drawing is frozen — but the drawing rarely is |
| Launch slot (rideshare) | 6–18 months | Manifests fill a year ahead |
Two structural facts sit under those numbers. The supplier base is thin — many critical components have two or three vendors on Earth, and some have one. And big buyers crowd out small ones: a mega-constellation ordering 10,000 star trackers gets the line; your two units wait.
Tactics that actually work
- Order long-lead items before the design is finished. Freeze the interface, buy the part, design around it. Buying a reaction wheel you might not use is cheaper than a nine-month slip.
- Put lead time in the trade study. A 20 % better part with 30 extra weeks of lead is usually the worse part.
- Buy spares in the same lot. A replacement from a different lot may need re-qualification; a spare bought with the flight unit doesn't.
- Hold a schedule margin on the long pole specifically, not spread evenly. Vendors slip in proportion to how exotic they are.
- Know your second source before you need it. Next lesson.
The critical path in one formula
Earliest ship = max(lead times) + integration & test + margin
Use the calculator to see how the long pole dominates. Notice that shaving ten weeks off any item other than the longest changes nothing.