CAD software supports a heavenly business

It’s surprising what you find. A small company in Birkenhead is making large astronomical telescopes as commercial products, and it’s doing so by harnessing modern 3D CAD and analysis software to turn complex design into good manufacturable product fast and efficiently. Critical to delivering optimum performance, it also ensures that modifications are verified and reflected in all drawings automatically – and it’s cutting design cycles by 75%. Telescope Technologies (TTL) started out as a joint venture between the Royal Greenwich Observatory and John Moores University in 1995. Following the demise of the former, it was taken over fully by the latter and turned into a business making ‘affordable’ telescopes. Four instruments are currently going through, each with a 2m mirror and a price tag of £4.5 million. Target market is institutions and countries wanting an instrument capable of supporting serious research, but unable or unwilling to pay out the 10 times or greater costs of more leading edge instruments. Right first time As in all manufacturing, right first time design, reduced time to market and thus remote view and mark-up have been crucial to TTL’s commercial success. These are not trivial designs; nor are they easy build projects. Each telescope is protected by a clamshell structure that has to fold down to release warm air quickly when observation begins at night. Beyond that, the tracking system has to follow objects to an accuracy of 0.2 arc seconds, even in Force Seven gales. And the 1.25 tonne mirror is supported by an array of 36 pneumatic pads, the pressures of which have to be varied to compensate for distortions caused by gravity as the instrument is tilted. Optical design for the telescopes is via a specialist program called Zemax, but most of the rest is being undertaken using commercial packages. MSC’s Working Model 4D, for example, provides first cut static and motion analysis. Its Visual Nastran is used for initial, quick analysis and ANSYS for in-depth finite element analysis (FEA). This latter includes the study of mirror and structure deflections and displacements, shape optimisation, general stress analysis and so on. When it comes to mechanical engineering, that’s all undertaken using Autodesk. TTL began with Mechanical Desktop 2 and AutoCAD in 1999, and moved on to Mechanical Desktop 5 in 2001. Recently, the company went up to Inventor 6 for 3D modelling which, according to mechanical engineer Alec Waters, has cut the time to design large assemblies by 75%. Waters says Inventor was chosen because of its compatibility with TTL’s existing .dwg drawings, its “acceptably low” price and its easy graphical user interface. He also cites its browser-to-model relationship, adaptability, artistic control, use of fastener libraries and I Parts, accurate calculation of masses and inertias, and the way it updates drawings in response to changes. TTL is also looking at Autodesk Streamline Release 4, an enhancement for Inventor that has been available in the USA for some time, but is new to Britain. With Streamline, it will publish versions of the CAD model as XML files so users can log in remotely and view and mark up models without Inventor software. As well as visualising components and assemblies, users can make 2D and 3D measurements, and investigate bills of materials (BoMs) and file properties, according to assigned rights. For TTL, with product assembly so far from the design offices, Waters says this will be particularly useful. The current Liverpool Telescope, for example, is being assembled on a mountain top in La Palma, while the next three are to be put together in Pune, India, on Maui in Hawaii and in Australia. As for the future, Waters expects projects to include more orders for the 2m mirror models and possible construction of very large (and expensive) instruments with single mirrors up to 8m across, or combinations of mirrors resulting in a 50m effective diameter. He says sales of these will be helped by using 3D Studio Max which allows 3D models to be photo-realistically rendered and animated.