The Presence Gate

The three tests

How the Presence Gate decides crewed, contested or uncrewed.

The gate reads the constraint and hazard fingerprints at each canonical site and asks three questions.

• Return to help - how long a sick crew member or a failed life-support loop takes to reach a hospital or a spares depot. Earth orbit answers in hours; cislunar space and the Moon in days; every other destination in months, years or decades.
• Dose to the career limit - days of unshielded surface exposure before NASA's 600 mSv career limit, alongside the best shielded figure the site allows. ESA, Roscosmos and the Canadian Space Agency use 1 Sv, and a US terrestrial radiation worker is permitted more over a career than three astronaut lifetimes. The cap is policy, set to force rotation, and it moves a destination only at the margin.
• Need for hands, or a mandate - whether the work at the site is human-shaped, and whether anyone wants people there for their own sake.

Verdicts

Twelve sites, one verdict each.

Observed Building Projected Modeled Confidence scale

Reading the verdicts

Return time sorts the map; dose only reorders it.

Crewed with an ambulance: Earth Orbit, Cislunar Space, the Moon

The International Space Station has been continuously crewed since November 2000 and China's Tiangong since 2022. Cislunar space and the Moon keep a return measured in days. NASA's first crewed landing is now Artemis IV in 2028, after Artemis III was rescoped to a crewed docking test in LEO, and China plans its own landing with Mengzhou and Lanyue on the Long March 10 before 2030. The binding test at the Moon is dose on the surface, and a few meters of regolith answers it: about 6.3 years to the career limit for a buried resident at 5 m, with time outside setting a floor no shielding lifts.

Crewed by mandate: Mars

Mars fails the ambulance test - a crew waits up to 26 months for a return window - and passes anyway, because Mars is the one destination where people are the point. The program is a second, independent instance of human civilization, measured by time to independent operation and by how few failure modes it shares with Earth. Its dose fits: about 0.64 mSv/day at the surface by MSL RAD, roughly 920 days to the 600 mSv limit before shielding.

Crewed in principle: Venus

Venus at 50-55 km passes every environmental test on the page - about 1 bar, 0.90 g, near-Earth temperature, and roughly half of Earth's atmospheric shielding overhead. It fails on reasons: no water, no hydrogen outside the acid clouds, nothing to export, and a return window every 19 months. The crewed marker records an aerostat capability that no program is building.

Contested: the Belt

Ceres sits on the line. A five-year mission with 300-day transits lands near 1.1 Sv - almost twice NASA's cap and at the edge of the 1 Sv limit the other agencies use. Crew would live at Ceres-synchronous orbit, 722 km up, in a spun habitat shielded with Ceres water, running surface machines at millisecond latency. The gate that binds is the ship: 300-day transits need a 10-20 MWe nuclear-electric vehicle rejecting heat at about 800 K, and nothing at that scale has flown.

Uncrewed: Mercury

Mercury's industry is thin-film collectors, mass drivers and beam operation, and none of it needs hands. Solar particle fluence at 0.39 AU runs about 6.6 times Earth's; extreme coronal mass ejections have pushed the magnetopause down to the surface on MESSENGER's record; and Earth never leaves the Sun's glare as seen from Mercury. ESA and JAXA's BepiColombo reaches orbit in November 2026; no crewed Mercury program exists in any country.

Uncrewed until megawatt-class nuclear propulsion: the outer system

Callisto's dose fits a career - 0.35-0.64 mSv/day behind a berm, 2.6-4.7 years to the limit - and its return time does not: about three years one way, and a crewed mission closes at neither dose limit below roughly 200 W/kg of propulsion specific power. Titan has the most benign surface in the solar system after Earth, needing oxygen and insulation and no pressure vessel, and sits six years from help. Triton and Pluto sit decades out. China's Tianwen-4 Callisto orbiter, ESA's JUICE and NASA's Europa Clipper and Dragonfly are all machines.

Uncrewed by physics: Interstellar

A Breakthrough Starshot-class sail is gram-scale and accelerates at thousands of g. Nothing alive rides it.

What moves a verdict

Four developments that would move destinations across the gate.

• Megawatt-class nuclear-electric propulsion - moves the Belt to crewed and Callisto to contested. NASA's SR-1 is the nuclear-electric pathfinder; Kilopower's KRUSTY test in 2018 is the last flight-relevant reactor result.
• Regulating off-Earth industrial workers as radiation workers - makes multi-year residence legal at the Moon and Callisto with no hardware change.
• Partial-gravity biology - a ring of about 18 m radius in orbit would settle whether 0.16 g and 0.38 g are enough; a bad answer pushes every low-gravity site toward spun stations.
• Beamed departure from Mercury - a collector array pushing and braking ships inside 1.3 AU shortens inner-system transits and with them every return time on this page.

Record

Provenance.