Ball screw jacks selected for radio telescope dishes

As part of the University of Cambridge's School of Physical Sciences, the Cavendish Laboratory has a world renowned history of discovery and innovation in physics. Power Jacks was selected by the Cavendish Laboratory to engineer an actuator to drive the elevation for the antenna dishes on the Arcminute Microkelvin Imager (AMI), a twin-array radio telescope (spanning 13.5-18GHz) operated by the astrophysics group at the Cavendish Laboratory.

The AMI is designed to find and visualise very faint cm-wave structures on scales 750mm (30inches) to 3000mm (10ft) on angular scales of 10 minutes of arc (1/6 of a degree) to 30 seconds of arc (1/120 of a degree) at a very fast surveying speed, and observe the Cosmic Microwave Background, the radiation left over from the Big Bang. These observations tell the scientists a great deal about how much matter content there is in the universe and how the universe evolved. The principal operation of the AMI is to carry out surveys for clusters of galaxies, to image these clusters in detail and to search for topological defects, which were created a tiny fraction of a second after the Big Bang.

Sited at the Mullard Radio Astronomy Observatory, near Cambridge, the twin-array radio is made up of a Small Array (SA), consisting of ten 3.7m diameter antennas and a Large Array (LA) consisting of eight 13m diameter antennas. Both arrays employ Fourier transform correlators, each with a total bandwidth of 4.5GHz.

Ball screw jacks

Power Jacks supplied ten 50kN metric ball screw jacks in a translating screw configuration and with a stroke of 1050mm. These ball screw jacks operate in normal UK outdoor conditions and allow the antenna to operate at wind speeds of up to 50mph. The ball screw jacks also allows the AMI to achieve a pointing accuracy of better than half a minute of arc (1/120 of a degree).

The screw jacks are mounted on a special trunnion base at their gearbox and clevis end on the lead screw. The ball screw is protected from the elements by a bellows boot and has a safety stop nut to protect the screw jack from accidental overtravel.

Previous the Cavendish Laboratory had used Power Jacks screw jacks for the tilt mechanism on a 3m table for a Very Small Array (VSA) telescope, which was operated successfully for eight years from the Mount Teide Observatory in Tenerife.

The metric ball screw jacks on the AMI have now been in operation for over five years and the Cavendish Laboratory has been using Power Jacks products since 1999. Dr Keith Grainge, Project Manager for both the AMI and VSA telescopes, says: "We are entirely satisfied with the quality of service and products supplied by Power Jacks."

Already the Cavendish Laboratory has published seven research papers based on observations from the AMI, and work on the results from the main cluster surveys is well underway. The VSA telescope project has now finished, with its results on observations of the Cosmic Microwave Background published in a series of 21 papers.

Follow the link for more information about Power Jacks' metric ball screw jacks.