The Perrseus helium influx budget is an end-of-life requirement, not a ceiling that must hold continuously throughout the mission. Designing the package to hold the budget as a throughout-ceiling over-constrains getter capacity and seal design for no qualification benefit, and the distinction changes which measurement is decisive.
6 models deliberated; a human Commander held the room but did not steer. Sealed 2026-08-21T16:12:42.715Z. Engine lucentfire-roundtable/v1 (live).
The question put to the room
The Perrseus helium influx budget is an end-of-life requirement, not a ceiling that must hold continuously throughout the mission. Designing the package to hold the budget as a throughout-ceiling over-constrains getter capacity and seal design for no qualification benefit, and the distinction changes which measurement is decisive.
What survived
- With no helium sink in the package (NEG pumping speed for He is zero), P_He(t) is monotone non-decreasing, so a throughout-life *pressure* ceiling at the EOL limit is the identical constraint at zero extra cost — the thesis is vacuous under that reading.
- The thesis's claim that a throughout-ceiling over-constrains *getter capacity* is false for helium: NEG He capacity is zero at any price, so any penalty falls entirely on seal permeation, wall thickness and bond area.
- If the budget is silently upgraded to a pointwise instantaneous rate cap Q(t) ≤ Q̄, it genuinely over-constrains seals — ~1.4× versus ~40× required tightness for an identical physical outcome — but no retrieved Perrseus text writes the requirement that way.
- In a Perrseus‑like µUHV cell with only non‑evaporable getters, helium has effectively zero pumping and its partial pressure increases monotonically with the time‑integral of the leak rate, so the end‑of‑life helium pressure is the maximum over the mission.
- An influx budget physically constrains the time‑averaged leak rate over the mission, not the instantaneous rate at every moment; imposing a pointwise leak‑rate ceiling at the mean budget value can strongly over‑constrain seal permeation relative to what the integrated budget requires.
- Getter capacity and design are irrelevant to the helium term because standard NEGs do not pump helium; qualification for the helium budget must rely on ultra‑low leak‑rate characterization via rate‑of‑rise measurements and activation‑energy‑based thermal extrapolation.
- For an unpumped, monotonically accumulating species like helium, a throughout-life pressure ceiling is physically identical to an end-of-life pressure requirement.
- Interpreting the helium budget as a continuous ceiling on the instantaneous leak rate would significantly over-constrain the package's seal design due to temperature variations, but this interpretation is not explicitly required by the retrieved program text.
What the room could not place
- Show the sensor's He failure mode is dose-integrated rather than instantaneous-pressure — then even the EOL reading is the wrong observable.
- So the distinction is real for hydrogen and vacuous for helium — and the thesis is stated about the helium budget.
Seal (sha-256, single-writer): a146f84b1e793c23a9eddbf39a910a4e28e004b61ecf537e6c018622f848b21f
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