Five thousand robots will get busy creating a 3D map of millions of galaxies in 2019.

The Dark Energy Spectroscopic Instrument (DESI) has received US Department of Energy (DoE) approval to move from the design phase to construction, which will start next year.

That includes building the 5,000 10 cm-long, finger-width robots which will have the job of aiming fibre-optic cables at galaxies, stars, and quasars.

DESI's builders have just begun a two-month prototype run of the light collection system in Arizona.

With the project passing “Critical Decision 3”, the DoE has okayed DESI to lay out funds for the robots, and for the 10 spectrographs to measure incoming light from the fibres.

As the Lawrence Berkeley Livermore Lab announcement explains, the array will cycle through its target objects several times an hour, for five years. The scan will cover one-third of the sky.

There are also six million-dollar lenses up to 1.1 metres in diameter, which are ready to get a coating to improve their transparency: they will be stacked to create DESI's “minivan-sized” optical corrector.

Harvard's Daniel Eisenstein, a co-spokesperson for the project, says the map “will reveal patterns that result from the interplay of pressure and gravity in the first 400,000 years after the Big Bang. We’ll be using these subtle fingerprints to study the expansion history of the universe.” ®