Post-Flight Reconditioning Timeline (2D)

Mission Parameters

Mission duration 180 days

Rehab program intensity 1.0×

In-flight countermeasure adherence 70%

Days since landing (R+) 0 d

Return-to-Duty Status

R+0 — not yet assessed

Predicted clearance

— d

Rate-limiting system

—

How it works

Each physiological system deconditioned by microgravity is modeled as a separate first-order recovery process. If R(t) is the fraction of pre-flight function restored t days after landing:

R(t) = 1 − (1 − R0) · e^(−t / τ)

R0 = fraction already intact at splashdown (1 − deficit)
τ  = recovery time constant (days), one per system

Deficit at landing scales with mission duration and how well in-flight countermeasures (resistive/aerobic exercise) were followed; τ scales inversely with post-flight rehab program intensity. Four tracks are modeled, ordered fastest to slowest:

Cardiovascular / orthostatic tolerance — baroreflex and plasma-volume readaptation, τ ≈ 3–8 days.
Neurovestibular / gait & balance — sensorimotor recalibration to 1g, τ ≈ 6–14 days.
Musculoskeletal strength — antigravity-muscle rebuilding, τ ≈ 25–55 days.
Bone mineral density — trabecular bone remodeling, τ ≈ 250–450 days; real flight surgeons clear crews for full duty before this one finishes, accepting residual fracture risk.

"Return to full duty" in this model is the day the three faster tracks (cardio, vestibular, muscle) all cross a 90% threshold — the rate-limiting system is whichever of those three is still slowest. The top panel plots each system as a lane racing toward the finish; the bottom panel plots the full R(t) curve for all four with a playhead you can drag. This mirrors NASA's real R+0 to R+45 phased reconditioning program, where the astronaut's readiness date is set by whichever system lags, not by the average.

R+0

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Cardiovascular Neurovestibular Musculoskeletal Bone density