Crewed Stations

The ISS

The International Space Station: 25 Years of Continuous Human Presence

The most expensive object ever built, and the only place humans have lived continuously for a quarter century.

The International Space Station has been continuously crewed since November 2, 2000 — over 25 years. A five-partner program (NASA, Roscosmos, ESA, JAXA, CSA), it spans 109 m tip to tip, masses approximately 420,000 kg, contains 916 m³ of pressurized volume, and generates roughly 215 kW from its solar arrays. The ISS orbits at ~400 km in a 51.6° inclination, completing an orbit every 90 minutes. Total program cost (assembly, operations, and logistics through 2024) exceeds $150 billion, making it the most expensive single object ever constructed.

The ISS has hosted over 3,800 experiments, served as the proving ground for orbital manufacturing research (ZBLAN, bioprinting, crystal growth, semiconductor experiments), tested long-duration human spaceflight physiology, and demonstrated international cooperation in orbit. It requires periodic reboost to counteract atmospheric drag. As a research platform it remains productive; as infrastructure it is aging — module seals, radiators, and power channels are degrading.

Deorbit. The ISS is authorized through 2030 with deorbit planned for 2031. SpaceX holds a $843 million contract to build the US Deorbit Vehicle, which will perform the controlled reentry of the station into the South Pacific — the largest controlled reentry in history. Russia has signaled intermittent participation through decommissioning. The deorbit timeline depends on structural integrity assessments; the station has experienced air leaks in the Russian Zvezda module’s service tunnel that remain under monitoring.

Tiangong

Tiangong: China’s Space Station and Its Expansion to Six Modules

Assembled in 2021–2022, already expanding. By the time the ISS deorbits, Tiangong will be twice its current size.

China’s Tiangong space station was assembled across 2021 and 2022 and has been continuously crewed since. The current T-shaped configuration comprises three modules: the Tianhe core module and the Wentian and Mengtian laboratory modules, totaling approximately 90 tonnes and ~110 m³ habitable volume. The station generates ~100 kW peak power and supports a permanent three-person crew rotated every six months via Shenzhou spacecraft, with crew handovers expanding to six during transitions.

Expansion. In June 2026, China announced plans to double Tiangong’s size. Phase 1 adds a new 20-tonne multifunctional module docking with Tianhe to form a cross shape — adding docking ports, experiment space, storage, and EVA staging. Phase 2 adds two more experiment modules (Lab Module III and Lab Module IV) to reach a six-module “double-T” configuration of approximately 180 tonnes. The expanded station increases permanent crew capacity from three to six. Xuntian, the 2 m space telescope (see Space Telescopes), launches in 2027 and co-orbits with Tiangong for docking-based servicing.

Science output. Tiangong has deployed 267 scientific and application projects. In 2025 alone: 86 new in-orbit experiments, 1,179 kg of science materials delivered, 105 kg of samples returned, 150+ TB of data generated. The containerless electrostatic levitation platform has produced 565 experimental records across metallic alloys and ceramics. The Shenzhou-23 mission (May 2026) includes the first year-long crew member stay in the Chinese program.

Tiangong is operated by CMSA (China Manned Space Agency). It does not host NASA astronauts — the Wolf Amendment (US law since 2011) prohibits bilateral cooperation between NASA and Chinese government space organizations. ESA, UNOOSA, and several national space agencies have cooperation agreements with CMSA; international researchers have flown experiments on Tiangong.

Commercial successors

NASA’s Commercial LEO Destinations Program and the Post-ISS Stations

NASA is transitioning from owner-operator to tenant. Four companies are building what it will rent.

NASA’s Commercial LEO Destinations (CLD) program funds privately operated space stations to replace the ISS. The model: NASA purchases services (crew time, research racks, cargo logistics) from commercial operators rather than building and operating its own station. Phase 1 awarded $416 million in 2021 to three teams for design work. Phase 2 awards of $1–1.5 billion, selecting at least two providers, are expected in 2026. In March 2026, NASA introduced the “Ignition” framework, which may have private developers supply modules to a government-anchored hub rather than each flying a fully independent station.

Vast — Haven-1 and Haven-2. Haven-1 is a single-module station (45 m³ habitable volume, crew of four for two-week missions) targeting Q1 2027 launch on Falcon 9 — potentially the first standalone commercial station in orbit. Haven Demo, a pathfinder, launched in 2025. Full-scale life-support testing underway in Long Beach, California. Former NASA astronaut Andrew Feustel is lead astronaut. Haven-2 is the CLD bid — a nine-module station launched on Falcon Heavy and Starship, with the first module operational by 2028 if selected. No artificial gravity (microgravity research is the NASA requirement). Vast’s long-term goal is the first artificial-gravity station. Added to NASA’s Private Astronaut Mission (PAM) program February 2026.

Axiom Space — Axiom Station. The only CLD contender with crewed ISS experience — four Axiom private astronaut missions to the ISS to date. Axiom’s plan: attach modular segments to the ISS starting with Axiom Module 1 (AxM1, targeted 2026–2027), then detach as a free-flying station before the ISS deorbits. Subsequent modules add a research lab, crew quarters, and an observatory with a cupola larger than the ISS cupola. $350 million raised in February 2026. NASA contract for at least one habitable module (2020). Axiom’s architecture relies on the ISS as scaffolding — it does not need to launch a complete station from scratch.

Starlab Space — Starlab. Joint venture between Voyager Space and Airbus Defence & Space. A single-launch station with a large habitation and laboratory module plus a service module for power and propulsion. Phase 1 CLD award ($160M to Nanoracks-led team, now Starlab Space). Targeting 2029 launch. Less public detail than Vast or Axiom.

Blue Origin / Sierra Space — Orbital Reef. Described as a “mixed-use business park 250 miles above Earth.” Built around Sierra Space’s LIFE inflatable habitat module (830 m³ target volume, crew of 10). Phase 1 CLD award ($130M). The partnership experienced public friction between Blue Origin and Sierra Space in 2023. Human-factors testing underway with life-size mockups. Sierra Space’s Dream Chaser spaceplane (first uncrewed ISS mission launched 2025) is part of the cargo architecture.

Northrop Grumman. Phase 1 CLD award ($125.6M) for a station concept retrofitting existing Cygnus-derived technology. Less publicly visible than the other three programs.

Station comparison

Crewed Space Stations: Current and Planned

What is in orbit, what is coming, and when.

The gap

The Station Gap: Can Commercial Stations Launch Before the ISS Deorbits?

The ISS retires in 2031. The earliest commercial station targets 2027. The gap in between is the risk.

The central concern in the crewed-station transition is timing. The ISS is authorized through 2030 and is planned for deorbit in 2031. The earliest commercial station (Haven-1) targets Q1 2027 as a single-module platform with limited capability. Axiom’s first module targets 2026–2027 attached to the ISS. Full-capability commercial stations — ones that can host long-duration crews, support manufacturing payloads, and serve as NASA research platforms — may not reach operational readiness until 2029 or later.

If the ISS deorbits on schedule and no commercial station is fully operational, there will be a period in which the United States has no crewed platform in LEO. Tiangong will continue operating (and expanding) throughout this period. The gap would end the continuous US human presence in orbit that began in 2000 and leave China as the only nation operating a crewed space station. This scenario is one reason NASA structured the CLD program to support multiple competitors — reducing the risk that a single program’s delay leaves no US station available.

The counter-argument: the ISS can be extended beyond 2030 if needed (it has been extended before, repeatedly). Structural concerns (Zvezda air leaks, aging power channels) constrain how long the extension is practical, but the decision is political as much as technical. The cost of operating the ISS through 2030 is roughly $3–4 billion per year — funding that NASA wants to redirect to Artemis and deep-space programs.

Crew transport

Crew Transport to Low Earth Orbit: How People Get There

Three vehicles carry crew to orbit today. A fourth is in testing.

SpaceX’s Crew Dragon dominates crewed access to the ISS. Boeing’s Starliner completed a troubled crewed flight test in 2024 (CFT, Butch Wilmore and Suni Williams) that extended from eight days to eight months due to thruster issues; operational certification timeline remains uncertain. Soyuz continues to fly ISS crew rotations and seat-swap agreements with NASA. Shenzhou operates independently for Tiangong with no Western integration. No private company other than SpaceX currently offers operational crewed orbital transport.