Washington | Scientists have designed a prototype system to test for a planned array of 5,000 galaxy- seeking robots, which will provide the most detailed 3D map of the universe and probe the secrets of dark energy, which is accelerating the universe’s expansion.
The Dark Energy Spectroscopic Instrument (DESI) project, being developed by the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) is also expected to improve our understanding of dark matter, the infant universe, and the structure of our own galaxy.
Scientists have developed a prototype dubbed ProtoDESI, a scaled-down, 10-robot system that will help them achieve the pinpoint accuracy needed to home in on millions of galaxies, quasars and stars.
The DESI is planned for the Mayall Telescope at Kitt Peak National Observatory in the US. ProtoDESI will be installed on the Mayall Telescope this August and September. The thin, cylindrical robots that will be tested in ProtoDESI each carry a fibre-optic cable that will be precisely pointed at selected objects in the night sky in order to capture their light.
A predecessor galaxy-measuring project, called BOSS, required the light-gathering cables to be routinely plugged by hand into metal plates with holes drilled to match the position of pre-selected sky objects. DESI will automate and greatly speed up this process.
Each 10-inch-long robot has two small motors in it that allow two independent rotating motions to position a fibre anywhere within a circular area 12 millimetres in diameter. In the completed DESI array, these motions will enable the 5,000 robots to cover every point above their metal, elliptical base, which measures about 2.5 feet across.
That requires precise, software-controlled choreography so that the tightly packed robots do not bump heads as they spin into new positions several times each hour to collect light from different sets of pre-selected sky objects.
The main goal of ProtoDESI is to be able to fix fibres on actual objects and hold them there, said Parker Fagrelius, who is managing the ProtoDESI project at Berkeley Lab.
ProtoDESI’s robots are positioned far enough apart that they would not collide during their initial test run. While DESI’s robots will primarily target galaxies, ProtoDESI will use mostly bright, familiar stars to tune its robotic positioning system and ensure the system is accurately tracking with the motion of objects in the sky.
Mounted next to the positioners is a custom digital camera known as the GFA (for guide, focus and alignment) that will remain targeted on a guide star – a bright star that will aid the tracking of other objects targeted by the robot-pointed fibres.
The robots will initially fix on isolated sky objects so that they do not mistakenly point at the wrong objects. The full robotic array planned for DESI will be segmented in 10 pie-wedge-shaped petals that each contains 500 robots. The first petal will be fully assembled by October at Berkeley Lab and tested through December.
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