Artificial Gravity Requirements Evaluation (AGRE) | Rotation Parameter Verification

Purpose

This page defines a neutral evaluation class for rotationally generated gravity at habitat scale. It specifies what must be measured, under what controls, and for how long before a (radius, spin rate, g-level) operating point can be credited as tolerable for long-duration occupancy in any human-rating argument. It is not a mission design, not a product announcement, and not a claim about the answer.

Rotation parameters are routinely carried into habitat concepts as design assumptions: a spin rate selected from a comfort chart, a radius that follows from it, a g-level chosen because it is familiar. The chart values that anchor those choices derive from short-duration ground studies in which Earth's gravity was present throughout. No sustained measurement of human response to a pure rotating-frame gravity field has been made in orbit. Until it has, every rotation parameter in a habitat specification is a hypothesis, and the evaluation defined here is what would turn it into a requirement.

Rotating-frame human factors Partial-gravity dose response In-orbit 1g control Parameters as outputs Uncertainty-quantified

Core idea: "What spin rate is acceptable?" and "how much gravity is enough?" have no validated answers. The honest output of an evaluation is not a defense of any particular geometry — it is the tolerance envelope in (spin rate, g-level) space, with confidence bounds, from which any architecture derives its radius against its own occupancy requirements. The dataset that would define that envelope does not exist in orbit — for this program or for any other.

State of the evidence

Three bodies of evidence bear on rotational gravity. Two exist. The one that governs does not.

Microgravity — exists Decades of continuous orbital occupancy have characterized human physiology over months-long exposures at 0g: bone, muscle, cardiovascular, ocular, vestibular, immune, and behavioral endpoints, with established measurement protocols and countermeasure regimes. This is the field's 0g anchor point.

Ground rotation — exists, confounded Slow-rotation rooms and human centrifuges have produced the spin-rate comfort literature and short-duration adaptation data. In every such study Earth's 1g is superimposed on the centripetal field: the resultant vector is tilted, the net magnitude exceeds 1g, and exposure is measured in hours to weeks. Ground data can bound the problem. It cannot close it.

Sustained orbital rotation — does not exist No human has lived in a rotating habitat in orbit for any physiologically meaningful duration. Brief rotational demonstrations have been flown; none produced sustained exposure or health data. There is no measurement of adaptation, dose response, or long-term tolerance in a rotating-frame gravity field free of Earth's vector.

This gap is a property of the field, not of any one program. Every rotating-habitat concept, at any scale, currently rests on the same absence. The evaluation defined here is the set of measurements that would fill it for all of them.

Partial-gravity animal data from ground centrifuges is hypergravity relative to the 1g baseline the animals otherwise experience; it does not constitute partial-gravity dose-response data. Bed rest and head-down tilt analogs model unloading, not rotation.

Evaluated parameters

Centripetal acceleration in a rotating habitat is g = ω²r. The three quantities form a coupled triple with two degrees of freedom: fix any two and the third follows. Each is constrained by a different discipline, and only one of the three is a free engineering choice.

Parameter	Governed by	Evidence status
Spin rate (ω)	Vestibular tolerance to cross-coupled angular acceleration; Coriolis effects on movement and task performance; adaptation capacity	Ground-derived comfort envelopes only; no sustained in-orbit measurement at any rate
Gravity level (g)	Physiological dose response: bone, cardiovascular, ocular, muscular, and sensorimotor endpoints versus fractional g over long exposure	Two anchor points (0g in orbit, 1g on Earth); no measured points between them, and no in-orbit 1g point
Radius (r)	Structure, mass, cost, and the head-to-foot gradient across standing height and across the radial extent of the habitable volume	Fully determined once ω and g are set; an output, not an input

The engineering consequence is that radius is not a design decision. It is the result of two human-tolerance findings that have not yet been made. The evaluation therefore treats the (ω, g) plane as the object of study and reports radius as a derived quantity.

Kinematic mapping at 1g (computed, not a tolerance claim)

Spin rate	Radius for 1g	Coriolis at 1 m/s walking	Head-to-foot gradient (2 m)
1.0 rpm	~895 m	0.21 m/s² (~2.1% g)	~0.22%
1.6 rpm	~350 m	0.34 m/s² (~3.4% g)	~0.57%
2.0 rpm	~224 m	0.42 m/s² (~4.3% g)	~0.89%
3.0 rpm	~99 m	0.63 m/s² (~6.4% g)	~2.0%
4.0 rpm	~56 m	0.84 m/s² (~8.5% g)	~3.6%

Coriolis acceleration is 2ωv for motion in the plane of rotation; the same walking speed along the rim changes apparent weight by roughly the same fraction, in opposite directions for prograde and retrograde motion. These are kinematic facts. Whether any row of this table is tolerable for years is the unmeasured question.

Functional requirements (requirements-style)

ID	Function	Requirement
AGRE-F-001	Parameter-space coverage	The evaluation shall measure human and system response at no fewer than three distinct g-levels between 0g and 1g inclusive of a 1g reference, at a defined spin rate or rates, such that results are reported as a function of g-level and not at a single presumed operating point. ≥3 g-bands1g reference
AGRE-F-002	Coriolis effects	The evaluation shall measure the effect of Coriolis acceleration on gait, balance, stair and ladder transit in the radial direction, reach accuracy, object handling, and timed manual task performance, prograde and retrograde, at each evaluated band, on arrival and after adaptation. Gait & reachRadial transitTask timing
AGRE-F-003	Cross-coupled acceleration	The evaluation shall measure vestibular response to head movements in pitch, yaw, and roll relative to the spin axis at the evaluated spin rate: motion-sickness incidence and severity, gaze stabilization, postural stability, and illusory-tilt reports, acutely and across the adaptation period. Head-movement restriction shall not be used to suppress the measurement. Head movementMotion sicknessUnrestricted
AGRE-F-004	Gravity gradient	The evaluation shall measure physiological and perceptual response to the head-to-foot gravity gradient across standing height, and to the larger gradient encountered during radial movement between decks, including orthostatic response on standing and on radial transit. Standing heightInter-deckOrthostatic
AGRE-F-005	Adaptation & re-adaptation	The evaluation shall measure time to functional adaptation on entering rotation, time to re-adaptation on leaving it (to a microgravity hub and to Earth), and any performance or symptom decrement during each transition, with defined functional endpoints and repeated transitions per subject. Adaptation timeRe-adaptationRepeated transitions
AGRE-F-006	Inter-band transitions	The evaluation shall measure crew response to movement between g-bands within the rotating structure, including dual-adaptation state, transition frequency effects, and any limit on permissible transitions per day or week, sufficient to define a transition protocol. Dual adaptationTransition protocol
AGRE-F-007	Partial-gravity dose response	The evaluation shall measure bone (density and microarchitecture), cardiovascular (structure, function, and orthostatic tolerance), and ocular (intraocular pressure, optic nerve, retinal, and refractive) endpoints as a function of g-level over exposures of not less than six months per subject, with pre-flight and post-flight baselines and in-flight interval measurements. Muscular, sensorimotor, and immune endpoints are recommended. BoneCardiacOcular≥6 months
AGRE-F-008	In-orbit controls	The evaluation shall include a 1g control population and a microgravity control population resident in the same vehicle, sharing radiation environment, atmosphere, lighting, diet, schedule, and instrumentation, such that rotation and g-level effects are separable from spaceflight effects generally. 1g in orbit0g hubShared confounds
AGRE-F-009	Spin transients	The evaluation shall define the angular-acceleration envelope, duration, and permitted crew activity states for spin-up and spin-down, and shall measure crew response and fluid, structural, and balance-system behavior during planned transients and in a simulated unplanned spin-down. Crew exposure during transients shall be treated as a measured quantity, not an assumed non-event. Spin-up / downUnplanned caseCrew exposure
AGRE-F-010	Bioregenerative systems	The evaluation shall measure crop germination, gravitropic orientation, growth rate, gas exchange, root-zone water and nutrient distribution, pollination, and harvest yield at each evaluated g-level against the in-orbit 1g control, in the rotating frame with Coriolis present, for at least one full crop cycle per species evaluated. Full crop cyclePer bandRoot-zone fluids
AGRE-F-011	Fluid & thermal behavior	The evaluation shall characterize buoyancy-driven convection, two-phase flow, free-surface and tank slosh behavior, pressure head and Coriolis-induced asymmetry in radial plumbing, pump and separator performance, and thermal stratification at each g-level and during spin transients, with results reported against the corresponding 1g and 0g predictions. ConvectionTwo-phaseRadial plumbing
AGRE-F-012	Mechanical dynamics	The evaluation shall characterize spin-axis stability under crew movement, consumable transfer, and biomass growth; wobble and precession onset and damping; active balance-system authority and response time; structural load cycling; and the performance of the despun-hub interface and docking under rotation. Mass redistributionWobble dampingHub interface
AGRE-F-013	Instrumentation	Rotation state, centripetal acceleration, and vibration shall be continuously recorded at each evaluated band, and every human endpoint shall be time-tagged against that record. The measurement set for each human endpoint shall be defined in advance, with in-flight capability sufficient to acquire it at the stated interval. Continuous g recordPre-defined endpoints
AGRE-F-014	Power & uncertainty	Primary endpoints, effect sizes of interest, subject numbers, and exposure durations shall be defined before the campaign such that a null result is interpretable, and every reported quantity shall carry a stated confidence interval and an accounting of subject-selection, confound, and measurement uncertainty. Pre-registeredInterpretable nullUncertainty budget
AGRE-F-015	Standards traceability	All human endpoints, limits, and acceptability criteria shall trace to the current human-system standard (NASA‑STD‑3001 or successor), and a verification matrix shall link each requirement on this page to its verifying measurement, analysis, or test. NASA-STD-3001Traceability matrix
AGRE-F-016	Parameter output	Results shall be reported as a tolerance envelope in (spin rate, g-level) space with confidence bounds, and as the derived radius range that envelope implies, such that rotation parameters are an output of the evaluation. No specific radius, spin rate, or g-level shall be presumed acceptable in advance of results. Tolerance envelopeRadius as output

Note: quantitative thresholds (acceptable symptom incidence, permissible bone-loss rate, minimum adaptation performance) are architecture-dependent and are set by the program's human-rating requirements. None are asserted here; asserting one in advance of the evaluation would presume its conclusion.

Verification approach

Gradient One is the platform defined to close these requirements. A single rotating structure at a fixed spin rate places microgravity, lunar-gravity, Mars-gravity, and 1g bands in one vehicle, under one radiation environment, one atmosphere, one lighting schedule, and one instrumentation suite. That configuration is what AGRE-F-001 and AGRE-F-008 require: multiple g-levels measured simultaneously against an in-orbit 1g control, with spaceflight confounds shared across all bands.

Requirement group	Closure on a first campaign
F-001, F-007, F-008, F-010	Closable in full at the platform's spin rate: g-level dose response with in-orbit controls, per band
F-002 to F-006, F-009	Closable at the platform's spin rate; spin-rate sensitivity not resolved by a fixed-rate vehicle
F-011 to F-013	Closable in full; system behavior is measured on the vehicle itself
F-014 to F-016	Closable as campaign design and reporting requirements

Platform geometry, gravity bands, and architecture are described on the Gradient One page and are not restated here.

Open items

A first campaign of the kind described above would produce the field's first sustained rotating-frame dataset. It would not close the following:

Spin-rate sensitivity. A fixed-rate platform measures g-level response at one spin rate. Separating the effect of ω from the effect of g requires either a spin-rate change campaign on the same vehicle or a second platform at a different rate. Until then the tolerance envelope has one measured column.
Exposure beyond campaign duration. Six-month to one-year exposures bound near-term missions. Multi-year and career-length residency, and any effects that emerge only after long exposure, remain extrapolations.
Population generalization. Campaign subjects are few, screened, and trained. Extension to a broader adult population, to older residents, and to individuals with the range of vestibular and cardiovascular baselines a general population carries is unmeasured.
Reversibility. Whether measured changes at partial g reverse on return to 1g, and on what timeline, requires post-exposure follow-up of duration comparable to the exposure.
Radial extent of the habitable volume. A band on a truss samples a narrow radial range. A habitat whose occupied volume spans tens of meters radially presents a gradient across decks that a band campaign does not fully exercise.
Countermeasure interaction. Whether exercise and pharmacological countermeasures developed for microgravity are needed, helpful, or counterproductive at partial and full rotational g is a separate question from the dose response itself.
Long-duration coupling with other systems. Interaction between rotational gravity and chronic radiation exposure, closed-loop life support, and psychological factors over years is outside the scope of a first campaign.
Developmental biology. Human development under rotational or partial gravity is out of scope for this evaluation and for any near-term campaign. No requirement on this page addresses it, and no habitat specification should assume it.