Measured doses
Doses Measured From ISS to the Surface of Mars
Daily dose equivalent, measured by instruments on site.
| Where | Daily dose | Note | Rated |
|---|---|---|---|
| Earth, natural background | About 0.007 mSv/day | About 2.4 mSv a year | Observed |
| ISS · NASA and partners | About 0.5-0.9 mSv/day | About 80-160 mSv per six-month stay | Observed |
| Lunar surface · Chang'e-4 LND | 1.37 mSv/day | First lunar-surface measurement, 2019 | Observed |
| Mars cruise · Curiosity RAD | 1.8 mSv/day | Measured inside the cruise stage, 2011-2012 | Observed |
| Mars surface · Curiosity RAD | 0.64 mSv/day | Gale crater; 0.21 mGy/day absorbed dose | Observed |
Galactic cosmic rays set the steady dose and shielding barely dents them. Solar particle events come in storms of hours to days; the August 1972 storm fell between Apollo 16 and Apollo 17 and would have been dangerous to a crew on the surface.
Limits
A Mars Round Trip Exceeds NASA's Career Limit
Career dose limits against a Mars mission.
| Limit | Dose | Note | Rated |
|---|---|---|---|
| NASA career limit | 600 mSv | One limit for all ages and sexes since 2022 | Observed |
| ESA and Roscosmos career limit | 1,000 mSv | Agency standards | Observed |
| Earth occupational, ICRP | 20 mSv a year | Averaged over five years | Observed |
| Mars round trip with a surface stay | About 1,000 mSv | Over NASA's limit on the transfer legs alone | Modeled |
Anyone whose job crosses the pressure boundary is a radiation worker, spending a finite career dose to do the job. On one modeled profile, 3 m of regolith over the habitat and 10% of work time outside, the dose-limited career for outside work is about 4.2 years; on a construction-heavy profile with less shielding and 15% outside, about 2.6. Trained people become a depleting stock - see The Human Layer.
Classifying crews as radiation workers under occupational rules is a policy decision that costs nothing to make. Under the same risk models a given dose carries less lifetime risk later in life, which pushes early crews toward experienced mid-career specialists. The radiobiology to set a real ceiling cannot be done on Earth: no accelerator reproduces the full mixed field of cosmic rays.
Shielding
Shelter Area, Not Dose, Sets the Cost
Mass of shielding for a storm shelter against a whole habitat.
| Shield | Area or depth | Mass | Rated |
|---|---|---|---|
| Solar storm shelter, small | 20 m2 of floor | About 40 t of shielding | Modeled |
| Whole-habitat storm shielding | 450 m2 | About 900 t | Modeled |
| Galactic cosmic rays | Buried habitat | About 2-3 m of regolith | Modeled |
A small shelter the crew moves into during a storm costs a twentieth of shielding the whole habitat. Hazards beyond radiation are on Hazard Fingerprints.
The body
Bone, Muscle, Eyes and the Missing Partial-Gravity Data
Measured on long-duration station crews; partial gravity is the gap.
| Effect | What happens | Rated |
|---|---|---|
| Bone loss | About 1-1.5% of hip bone density a month in microgravity | Observed |
| Muscle loss | Up to 20% in leg muscles over months without exercise | Observed |
| Eyes | Spaceflight-associated neuro-ocular syndrome: swelling of the optic disc, flattening of the eyeball | Observed |
| Fluid shift | Fluid moves toward the head; face swells, legs thin | Observed |
| Partial gravity | No data between Apollo's three days at 0.17 g and 1 g on Earth | Modeled |
NASA's Twins Study, Scott Kelly in orbit for 340 days against Mark Kelly on the ground, found most changes reversed within months of return. A child developing at 0.38 g on Mars has no return to make - see Settlements.
For pregnancy, radiation is the shieldable problem. Malformation thresholds sit near 100-200 mGy, not reached under regolith, so a maternity area beneath a few meters of shielding is affordable because it is small. The unshielded early sign would be lower fertility, not birth defects.
Dust stays airborne about 2.6 times longer at 0.38 g, and Mars dust carries about 1% perchlorate, which blocks thyroid iodine uptake. Filtration and iodine supplements are part of health infrastructure.
China
China Made the First Lunar-Surface Dose Measurement
Chang'e-4 carried a German-built dosimeter to the far side.
| Program | Data point | Rated |
|---|---|---|
| Chang'e-4 LND · CNSA and Kiel University | 1.37 mSv/day on the lunar far side, 2019; 2.6 times the ISS rate | Observed |
| Tiangong · CMSA | Six-month crews since 2021; Shenzhou-13 stayed 183 days | Observed |
Contested
Deliberately Not Claimed
The load-bearing uncertainties, tagged with the confidence they actually earn.
Cancer risk per sievert is extrapolated. It comes mainly from atomic-bomb survivors exposed to gamma rays, not the heavy ions in cosmic rays.
Partial gravity may or may not protect. Whether 0.38 g or 0.17 g is enough to hold bone and muscle is unknown; a rotating partial-gravity test in orbit would answer it.
Record
Provenance and Data Sources
- Confidence
- Observed for flown, fielded or measured - Building for hardware and programs in development - Projected for announced plans - Modeled for original analysis
- Status date
- Q4 2026
- Data
- Curiosity RAD; NASA-STD-3001; ICRP; NASA Twins Study; ISS dosimetry
- China
- CNSA Chang'e-4 LND; CMSA Tiangong
- Weakest link
- Heavy-ion radiobiology