Researchers at NASA Jet Propulsion Labs (JPL) have successfully tested a second-generation “Cobra” fiber positioner for astronomy, consisting of two rotary piezoelectric SQUIGGLE motors from New Scale Technologies. The second-generation design reduced the number of move iterations required to move an optical fiber to its target position for collecting astronomical data. Design improvements include modification of the hard stops to minimize friction and improve robustness. Details and test results were presented at the SPIE Astronomical Telescopes + Instrumentation conference in July in Amsterdam.
A new video of the second-generation Cobra fiber positioner in action is available at
The newly published results highlight JPL’s ongoing development of a spectrograph for the Subaru telescope on Mauna Kea, Hawaii. The Prime Focus Spectrograph (PFS) will have 2,394 positioners, each comprising two SQUIGGLE motors in a theta-phi configuration, able to move an optical fiber to within 5 µm of its target position in six move iterations. The dense-packed hex array of positioners with overlapping patrol areas enables 100% coverage of a large area of the sky.
The ability to quickly move fibers to their target position increases observing efficiency: less time spent positioning the fibers after each move of the telescope means that more time is available for data collection. According to the JPL paper:
“The current estimate is it takes 62 seconds to move the telescope and reacquire the new field of targets with 15 minute exposures. This will allow for approximately 45 fields to be observed per night. This will enable large scale surveys aimed at understanding dark energy as part of the Subaru Measurements of Images and Redshifts (SuMIRe) program… The Cobra system is a key aspect of PFS that will enable its unprecedented combination of high-multiplex factor and observing efficiency on the Subaru telescope.”
The full paper (#8450-41) is available from SPIE at http://spie.org/x648.html?product_id=927161
New Scale’s piezoelectric motors met JPL’s key requirements for the Cobra positioner:
- Small size, allowing more than 2,000 positioners to fit in a close-packed hex pattern with 8 mm center-to-center spacing
- High position resolution and the ability to quickly converge on a target position using open-loop positioning
- High torque to overcome the drag of the optical fiber as it twists during movements, and high holding torque to maintain the target position once reached