The Five-hundred-metre Aperture Spherical radio Telescope (FAST), built into a natural karst depression in Guizhou Province, China, is the world's largest single-dish radio telescope. Its site was chosen from hundreds of candidate depressions screened by satellite imagery and GIS mapping between the mid-1990s and 2006, narrowed to a shortlist graded on size, sphericity, bearing capacity, and drainage — before construction of the reflector itself even began, running from March 2011 to the main structure's completion in September 2016.

What makes FAST relevant to erection engineering rather than just astronomy is that its structure is never in a single fixed state, and its site was never a neutral backdrop. The karst depression at Dawodang did structural work no constructed foundation could have matched at this scale — and the erection sequence that followed was solving problems the site had made survivable, not problems the site had created.

500 m
Aperture
4,450
Reflector panels
2,225
Actuator nodes
30 t
Feed cabin
1994–2006
Site-screening window
Stage 1
Site selection: geology doing the structural work
Dawodang was chosen from a large field of candidates largely for its drainage: karst terrain drains through sinkholes and underground channels rather than surface runoff, reducing the pumped-drainage infrastructure the nearly-20-hectare depression would otherwise have required despite Guizhou's heavy seasonal monsoon — a civil-engineering problem the site's geology reduced before any structure was designed. The surrounding karst topography also attenuated line-of-sight radio interference by default; authorities separately relocated roughly 9,000 residents from communities within 5 km as part of the site-clearance and radio-environment programme.
Stage 2
High-altitude sliding assembly of the ring beam
The 500-metre-diameter steel-truss ring beam anchoring the cable net couldn't be assembled flat and lifted into place as one piece, because the rim of a natural depression follows the terrain rather than sitting at a single elevation. It was built and closed at height, in sections, sliding into position along the boundary the depression itself defined.
Stage 3
Cable-net installation to a novel fatigue specification
FAST's cable net undergoes repeated active form-changing, giving it an unusually large fatigue-stress range compared with cable in more conventional applications. Engineers developed steel cable designed for a stress range of approximately 500 megapascals over two million fatigue cycles — more than twice the standard-authorised stress range at the time — a margin engineers judged necessary for the telescope's actual operating cycle.
Stage 4
Feed cabin: a verification lift before the real one
The 30-tonne feed cabin hangs 140 m above the reflector, suspended by six cables (each roughly 600 m long, about 7 t) run off six towers, with an internal Stewart platform correcting positioning to within millimetres. Before the actual cabin was installed, an empty test cabin of identical weight was lifted on 21 November 2015 to verify the suspension system — a dedicated proving lift ahead of committing the real instrument.
A structure with no fixed final shape

Unlike a conventional reflector, FAST's active surface is deformed in real time: 2,225 ground-anchored actuators pull sections of the cable net to reshape the surface from a sphere into a 300-metre working parabola for each observation, then release it. The erection sequence had to deliver a structure engineered to move continuously by design, not settle into a single permanent geometry.

From early site search to completion, the project spanned roughly two decades. Visible construction took about five years. The decision that could not be engineered around afterward was the one nobody was watching.

FAST's construction offers a genuinely different temporary-works problem from any bridge or platform on this site: the cable net is simultaneously the erected structure and the operating mechanism, load-cycled continuously rather than locked off once construction ends — and the site-selection decision that made the whole concept buildable was made a decade before the first cable was strung.

For further reading, see What is Temporary Works & Erection Strategy? and Erection Sequence Risk, which cover the staging logic behind structures whose geometry changes through the build.

Related case studies: SoFi Stadium Canopy · The Sphere · Singapore Sports Hub

Aerial view of the FAST radio telescope's 500 metre spherical dish nested inside a green karst depression in Guizhou, ringed by white lattice support towers
The FAST telescope's 500-metre dish inside the Dawodang depression, Guizhou, China.
Photo: SCJiang / Wikimedia Commons, CC BY-SA 4.0.
Cross-section diagram of the FAST telescope site showing the Dawodang karst depression, the 500 metre ring beam closed at height in sections, the spherical cable-net reflector of 4,450 triangular panels, the 300 metre illuminated aperture reshaped by 2,225 actuators, and the 30 tonne feed cabin suspended 140 metres above the reflector on six cables
Site section — karst depression, ring beam, cable-net reflector with its 300 m illuminated aperture, and the six-tower feed cabin system.
Original diagram — EE&HL Network 2026. Schematic, not to scale.

Sources: Li et al., “Adapting Active Reflector Technology…” (arXiv) — peer-reviewed description of the active reflector system: ring girder, cable-net of roughly 6,670 steel cables, 2,225 crossed nodes used as control points, tie-down cables, actuators and ground anchors; Beam Patterns of the Five-hundred-metre Aperture Spherical Telescope (arXiv) — the 500 m spherical reflector on a 300 m-radius cable-net, adjusted in real time to form a 300 m paraboloid. Published cable counts differ between sources (roughly 6,670 and “nearly 10,000”) and panel counts between about 4,400 and 4,450. Construction completed September 2016; full operation from January 2020.