Reali-Slim bearings help minimise telescope size and weight

Lightweight, high-performance bearings from RA Rodriguez are among the components in the PoGOLite (Polarised, Gamma-ray Observer) that will be relaunched later this year from the Esrange Space Centre in Sweden. Its mission will be to study high-energy light (X-rays) emitted by heavenly bodies such as neutron stars, pulsars and black hole systems. And for this purpose the telescope will be lifted into space by a helium-filled balloon so that it can travel on stratospheric winds across Sweden, Norway, Iceland, Greenland, Canada and Russia, returning to Sweden 20 days later.

Keeping the payload to a minimum without compromising performance has been a key issue in the design of the PoGOLite altitude control system (ACS). The Swedish company DST was responsible for this element, and it sought components whose design would contribute to savings in weight and space.

These design criteria are key selling points for Kaydon thin-section bearings, making them a standard choice in the aerospace sector. As well as supplying these products in the UK and Ireland, the RA Rodriguez is also responsible for the Scandinavian market. It was therefore the company DST contacted to source these proven, lightweight and high-performance bearings.

Overall payload weight is critical because PoGOLite needs to reach the greatest possible altitude. This is because X-rays are absorbed by the Earth's atmosphere, so increasing the ascent potential of PoGOLite meant that more accurate findings can be assured. It is ultimately hoped that the study will show a clear polarisation of X-rays, revealing a new observational window through which scientists can study the universe.

Elevation angle

Although the altitude control system is just one part of the vessel payload, it needed to be as compact and lightweight as possible. DST therefore specified 50 and 70mm Kaydon angular-contact bearings for accurate control of the elevation angle of the telescope. The elevation bearings carry the full mass (700kg) of the telescope and are able to survive the 10 'g' shock resulting from the launch of the parachute during landing. Furthermore, DST specified 90 and 180mm Kaydon angular-contact bearings for the critical azimuthal motion of the gondola. Hence these azimuthal bearings carry the entire mass of the gondola (2000kg) and are able to survive the 10 'g' shock during landing. The main reasons for choosing these particular bearings are the high requirements on small mass and size, low friction for accurate positioning and high axial capacity.

Key benefits of the Kaydon angular-contact bearing chosen by DST are its ability to support radial and unidirectional thrust loads, but there are Kaydon bearings to suit wide-ranging load requirements and, indeed, for special applications too. Choices include bearings that are resistant to corrosion, high temperatures and chemicals, as well as those for nuclear and clean room applications.

PoGOLite's maiden test flight of in July 2011 proved to be a great success in terms of telescope performance. However, the vessel failed to reach the required 42km altitude, not through any fault in ACS design or too great a payload, but simply because the balloon had developed a helium leak. The relaunch is now scheduled for mid-summer 2012.

To find out more about the lightweight, high-performance bearings and other products supplied by RA Rodriguez, go to www.rarodriguez.co.uk.