Two torso phantoms, one vest: Artemis I puts a number on crew radiation shielding

Run the two headline figures backwards and they land in the same place. A 60% cut worth 193 cruise days implies an unshielded August 1972-type event of about 322 days; an almost 40% cut worth 131 days implies about 328 ^[14][15][1]. Behind Orion's hull the two historic storms deliver close to the same total effective dose, and the vest is still half again as useful against one as against the other. Event size cannot be the variable; the energy distribution of the protons is, and that is the parameter a garment designer never gets to pick.

StemRad's own framing supplies the conversion into dose. If a three-year Mars round trip equals or exceeds the 600 mSv career limit ^[4], the cruise floor is about 0.55 mSv per day, which makes the vest worth at least roughly 106 mSv in a 1972-type event and 72 mSv in a 1989-type one, or 18% and 12% of a career ^[3]. Set that against Oren Milstein's other number, that one major solar particle event can deliver more than a third of the 600 mSv limit, and therefore more than 200 mSv ^[3][2]. The two statements only reconcile if the cruise is worse than the limit: about 0.62 mSv per day, or roughly 680 mSv over three years ^[4]. The uncertainty runs the wrong way.

None of this was measured in a storm. Artemis I met no solar particle event, and what Orion actually flew through was the inner Van Allen belt, whose protons cover a similar energy range ^[12]. The team built digital twins of both phantoms, the vest, the detectors and the spacecraft shielding, generated hundreds of billions of virtual particles and found close agreement with the flown dosimeters ^[13]. So the demonstrated result is that the model reproduces a real belt exposure. The 60% and 40% are that model's answers about two events no phantom has ever worn a vest through ^[14].

The operational claim is a separate thing, and it comes from one party. Jordan Houri of StemRad says the vest matches the most robust shelter configuration while letting the wearer move around the cabin and keep working ^[10], against a status quo of barricaded supplies or standing where the hardware is thickest ^[9]. That is the comparison that decides whether a vest is manifested, and it has not been published by anyone outside the company.

Which raises mass. The team is working to reduce it and is looking at flying lighter empty vests to be filled with recycled polyethylene after launch ^[16]. That idea is worth more than the percentages, because high-density polyethylene earns its place through hydrogen content ^[11] and this version moves shielding mass off the launch manifest onto material already aboard, assuming the feedstock inventory is really there. Milstein's stated payoff is longer careers ^[17]; the organ-by-organ thickness map ^[6] and the choice of female phantoms, made because women carry the higher predicted cancer risk ^[8], are what give that argument sex-specific flight data instead of an assertion.