howclose.to
Earth & Space · Updated July 2026Momentum · steady ↔

How close are we to closed-loop life support?Can a space habitat recycle everything?

or, simply: Can a space habitat recycle everything?or, precisely: How close are we to closed-loop life support?

Water recycling is near exploration grade in orbit, but oxygen, food, waste and maintenance have never been closed together beyond Earth.The space station recycles almost all its water, but a self-sustaining habitat still has to close air, food and waste loops at the same time.

We are here

ESA selects five circular studies - Five studies target biomass reuse, air quality and resource-efficiency gaps in circular space habitats. Next up - Gateway targets first launch (expected 2027).

01 · Where we stand

State of playWhere closed-loop life support stands right now

The current stage, the honest metric, and the single threshold that gates the next stage. Each threshold is a falsifiable claim with a named next test.How far up the ladder we've climbed, the honest verdict, and the one thing blocking the next step.

The five stagesMaturity ladder
Deployed
Out in the real worldDeployed at scale
Scaling
Making it cheap enough at scaleScaling toward competitive cost
Engineering← HERE
Building one that pays for itselfEngineering a system that pays back
Lab demo
Shown to work in a labDemonstrated in the laboratory
Theoretical
The idea is worked out on paperTheoretical basis established
The honest verdictVerified state

The space station recycles almost all its water, but a self-sustaining habitat still has to close air, food and waste loops at the same time.Water recycling is near exploration grade in orbit, but oxygen, food, waste and maintenance have never been closed together beyond Earth.

47Best result so farISS Sabatier average estimate
100SCOR stretch goal · target, not achieved
Blocking the next stepBlocking threshold

Recover three quarters of the oxygenSeventy-five-percent oxygen recovery Next test: An integrated flight demonstration must sustain oxygen recovery above 75% while managing methane and carbon deposits.

The verdict, in five rungsHow far up the ladder↓ next — the thresholds & the gap
01 · The evidence

The thresholds that gate the next stageWhat has to happen next

Each threshold is a falsifiable claim with a named next test; the gap chart shows how far today's metric sits from the goal.Each row is one thing that has to be proven — and how far today's number is from the target.

Exploration-grade water recoveryRecycle nearly all the water✓ Achieved · Jun 2023
100%
Proven byNASA demonstrated 98% total water recovery aboard the ISS.
Seventy-five-percent oxygen recoveryRecover three quarters of the oxygenIn progress
63%
Next testAn integrated flight demonstration must sustain oxygen recovery above 75% while managing methane and carbon deposits.
Three-quarter food regenerationGrow most of the foodIn progress
73%
Next testRepeat for at least one year with 75% or more of a complete diet, stable crop yields and explicit accounting for stored inputs.
Integrated off-Earth closureRun the whole loop in spaceEarly
0%
Next testDemonstrate combined air and water regeneration beyond low Earth orbit; no dated staple-food-loop flight is committed.
THRESHOLDS - Thresholds for Closed-Loop Life Support.
Scale
Metabolic oxygen recovered from exhaled CO2 over time, with measured values, projected values, and a goal at 100 %.020406080100Metabolic oxygen recovered from exhaled CO2 · %Year2017GOAL 100 · SCOR stretch goal · target, not a…SCOR exploration threshold · target, not achievedISS Sabatier average estima…~53 % to goal
NOTE - NASA describes 47% as an average estimate for ISS Sabatier hardware. The 75% threshold and 100% stretch goal are programme targets, not flight results; water, food and total-material closure use different boundaries.
02 · How we got here

The record behind the verdict

Major events set large; context events set small but never hidden. Everything below the TODAY rule is a schedule, not a result.

1911-19711 event1 shown

Miniature Earths imagined

Miniature Earths imagined begins with plants proposed for spacecraft. The result established the next question for the field.

1911
Plants proposed for spacecraftTheory
Konstantin Tsiolkovsky proposed that carried plants could absorb wastes continuously and return food.
Konstantin Tsiolkovsky
1972-19903 events1 shown

Sealed habitats become experiments

Sealed habitats become experiments moved the field from bios-3 closes human loops to melissa idea takes flight. The results narrowed the next question without closing it.

1972
BIOS-3 closes human loopsExperiment
Three people occupied the 315 m³ BIOS-3 ground habitat for 180 days with regenerated air and water and some plant-grown food.
Institute of Biophysics, Krasnoyarsk
1979
NASA establishes CELSS
NASA established a programme spanning food production, waste management, atmospheric regeneration, water purification and system control.
NASA
1991-20074 events2 shown

Ecologies reveal hidden instability

Ecologies reveal hidden instability moved the field from biosphere 2 crew enters to integrated test reaches 91 days. The results narrowed the next question without closing it.

1991
Biosphere 2 crew entersExperiment
Eight people began a two-year material-closure experiment whose farm supplied about 80% of their nutritional needs.
Biosphere 2
1993
Biosphere oxygen crashesSetback
Oxygen fell from 21% to 14% in 16 months as soil respiration and concrete chemistry defeated ecosystem balance.
Biosphere 2
1995
Lunar-Mars tests begin
NASA began four integrated crew tests with one person, 11.2 m² of wheat and a sealed chamber for 15 days.
NASA Johnson Space Center
2008-20173 events1 shown

Recycling reaches orbit

Recycling reaches orbit moved the field from iss recycles urine to lunar palace runs 105 days. The results narrowed the next question without closing it.

2014
Lunar Palace runs 105 days
Three people completed 105 days with oxygen and water recycled and 55% of food regenerated inside the ground habitat.
Beihang University
2018-20285 events2 shown

Closing separate loops

Closing separate loops moved the field from lunar palace reaches 370 days to gateway targets first launch. The results narrowed the next question without closing it.

2018
Lunar Palace reaches 370 daysExperiment
A ground test reported 100% oxygen and water regeneration and 98.2% defined material closure over 370 days.
Beihang University
2018
European loop reaches ISS
ESA's Advanced Closed Loop System launched to recycle about half of crew carbon dioxide and save about 400 L of launch water yearly.
European Space Agency
2024
ESA selects five circular studiesWe are here
Five studies target biomass reuse, air quality and resource-efficiency gaps in circular space habitats.
European Space Agency
2027
Gateway targets first launchDeploymentTarget
Gateway's PPE-HALO stack is scheduled no earlier than 2027; HALO is a partial habitat, not a self-sustaining loop.
NASA and Gateway partners
2017-20282 events0 shown

Events outside the declared eras

Events outside the declared eras moved the field from scor pursues more oxygen to artemis iv adds life support. The results narrowed the next question without closing it.

2017
SCOR pursues more oxygen
NASA introduced SCOR to raise metabolic-oxygen recovery above 75%, with 100% as a stretch goal.
NASA Johnson Space Center
2028
Artemis IV adds life supportDeploymentTarget
Gateway assembly with Artemis IV is scheduled no earlier than September 2028; JAXA is supplying life-support hardware for Lunar I-Hab.
NASA, JAXA and Gateway partners
— end of record · 18 shown, 0 hidden —
18 events · below the TODAY rule = scheduled, not done
03 · The data behind the verdict

Why the meters read the way they do

The learning curves and comparisons that justify each threshold's percentage. Every series is measured, with the source event linked in the timeline above.

Water reaches 98% recovery, but flight oxygen is 47%; food and material remain ground-bound.Water is near closed; a complete life-support loop is not.One solid bar = observed closure share · grey ladder = separate loop boundaries · dashed rule = target or ideal boundary · percent of flow, food or material · 2014–2023 · not one combined scoreOne bar = observed closure share · dashed rule = target or ideal boundary · separate flight and ground tests · 2014–2023
Observed closure across four life-support loopsWater recovery aboard the International Space Station has reached 98%. Average estimated flight oxygen recovery is 47% against a greater-than-75% NASA target. Ground tests regenerated 55% of food and reported 98.2% material closure under defined boundaries. These measurements are not one combined score.0%25%50%75%100%WaterISS · flight · 202398% exploration goal98%measured recoveryOxygenISS Sabatier · flight estimate>75% SCOR target47%average estimateFoodLunar Palace 1 · Earth · 201475% dossier threshold55%food regeneratedMaterialsLunar Palace 365 · Earth · 2018100% ideal boundary98.2%defined closure98.2% is a defined ground-test boundarynot 98.2% off-Earth autonomy
NASA · Beihang / Lunar Palace · AS OF JUL 2026
04 · What it unlocks

If the remaining tests pass

Downstream capabilities, drawn dashed because they depend on results not yet in.

Closed-Loop Life SupportMulti-year Mars missionsReduce the tonnes of water and oxygen that crews must carry beyond practical resupply range.Permanent off-world habitatsTurn lunar or Martian bases into settlements that can survive missed cargo flights.Resilient Earth systemsApply compact water, waste and controlled-agriculture loops in remote or resource-scarce communities.
05 · Sources

Where every number comes from

10 sources — every figure on this page traces to one.

  1. NASA SpaceCraft Oxygen Recoverynasa.gov
  2. NASA ISS 98% water-recovery milestonenasa.gov
  3. NASA Lunar-Mars Life Support Test resultsntrs.nasa.gov
  4. NASA ISS life-support operational lessonsnasa.gov
  5. ESA Advanced Closed Loop Systemesa.int
  6. ESA MELiSSA historyesa.int
  7. Lunar Palace 365 resultssciencedirect.com
  8. Lunar Palace 105 studyjournals.sagepub.com
  9. Biosphere 2 oxygen-loss analysisagupubs.onlinelibrary.wiley.com
  10. NASA Gateway schedule and life-support rolesnasa.gov