ISS vs Tiangong: The World’s Two Space Stations Compared
Right now there are exactly two permanently crewed space stations in orbit: the International Space Station and China’s Tiangong. Built decades apart by very different programmes, they are a natural comparison — and, conveniently, they are tracked with the same TLE and SGP4 engine.
The short version: the ISS is roughly four times as massive, carries about three times the pressurised volume and a bigger crew, and has been continuously crewed since 2000. Tiangong is newer, smaller, and was fully assembled in a fraction of the time. Both are naked-eye objects when the geometry cooperates.
Two stations in orbit right now
The ISS first launched in 1998 (the Zarya module), grew through dozens of missions, and has hosted a continuous crew for more than two decades — it is widely regarded as the biggest international laboratory ever flown, operated by the space agencies of the United States, Russia, Europe, Japan, and Canada.
Tiangong ("heavenly palace") is the space station programme of China’s CMSA. It launched in 2021 with the Tianhe core module and was completed in 2022 with the Wentian and Mengtian laboratory modules.
At a glance: the comparison table
| ISS | Tiangong | |
|---|---|---|
| First element launched | 1998 (Zarya) | 2021 (Tianhe) |
| Assembly completed | 2011 | 2022 |
| Partners / operator | NASA, Roscosmos, ESA, JAXA, CSA | CMSA (China Manned Space Agency) |
| Approximate mass | ~420,000 kg (925,000 lb) | ~100,000 kg (220,000 lb) |
| Length (end to end) | ~109 m (356 ft) | ~56 m (182 ft) |
| Solar array width | ~73 m (239 ft) | ~39 m (128 ft) |
| Pressurised volume | ~1,005 m³ (35,500 cu ft) | ~340 m³ (12,000 cu ft) |
| Habitable volume | ~388 m³ (13,700 cu ft) | ~122 m³ (4,300 cu ft) |
| Typical crew | 7 | 3 (up to 6 at handover) |
| Orbital inclination | 51.6° | ~41.5° |
| Typical altitude | ~400-420 km | ~340-450 km (nominal ~390 km) |
| Orbital period | ~93 minutes | ~92 minutes |
All figures are approximate and dates are snapshots — space stations are living machines, and Tiangong in particular is planned to keep growing. Treat the table as a fair comparison, not a specification sheet.
Why the size difference is so large
The ISS was designed in the 1980s and 1990s as a programme spanning fifteen countries, with expansion in mind: modules were added over a decade until the station reached its roadster-like scale. Tiangong was designed, built, and launched as a complete three-module station in a single generation, and it is more comparable in scale to the Mir station of the 1980s than to the ISS.
Mass matters for what each accomplishes: the ISS packs roughly three times the pressurised volume for science, at the cost of being by far the heaviest machine ever flown in low Earth orbit. Tiangong carries less, but flies the way a modern, compact station can — assembled end to end in about eighteen months.
Programmes, partners, and crew
The ISS is a five-way partnership (NASA, Roscosmos, ESA, JAXA, and CSA) representing fifteen nations, and it has a nearly permanent crew of seven. Tiangong is operated by China’s CMSA with a nominal crew of three, expanding to six during crew handovers.
Both stations do microgravity research, host visiting cargo ships, and periodically reboost or manoeuvre. Neither is a competitor on orbit — they are two independent demonstrations of long-duration spaceflight, at different scales and from different programmes.
From the ground: which one should you watch?
Both are naked-eye objects when sunlit and your sky is dark. The practical differences from Earth:
- The ISS is generally the brighter of the two because it is far bigger and its solar arrays act like a bigger mirror — on comparable passes it tends to look noticeably more brilliant.
- Tiangong’s lower inclination (~41.5° vs 51.6°) means it never climbs as high in northern skies; from places like the UK or Canada’s south it stays lower than the ISS, and from very high latitudes passes become rare.
- Both appear as steady, non-blinking stars in straight-line motion — see why the ISS is visible for the timing rules that apply identically to both.
If you want to tell them apart in a single glance, you generally cannot by eye — the giveaway is always the pass prediction: the sky event tells you which object you are watching.
Tracking both with the same engine
Both stations publish TLEs in the same NORAD format, so the same CelesTrak data and SGP4 engine power their trackers on this site. The ISS’s NORAD catalog number is 25544; Tiangong’s is 48274.
Everything on these numbers is a snapshot of recent published figures. Tiangong’s mass and size will grow as planned new modules launch, so expect this comparison to date quickly — check the sources below or the live telemetry for today’s orbit data.
Both stations are live on this site — switch satellites in the tracker dropdown, or use the dedicated Tiangong tracker and the ISS live position page.
You can watch both from one page — open the live Tiangong tracker and the ISS tracker side by side.
Track Tiangong liveSources and further reading
- NASA — International Space Station Facts and Figures (ISS data)
- NASA — Space Station: Facts and Figures archive
- eoPortal — Tiangong space station program (Tiangong data)
