* Astronomy

Title: Space-quality data from balloon-borne telescopes: the High Altitude Lensing Observatory (HALO)
Authors: Jason Rhodes, Benjamin Dobke, Jeffrey Booth, Richard Massey, Kurt Liewer, Roger Smith, Adam Amara, Jack Aldrich, Joel Berge, Naidu Bezawada, Paul Brugarolas, Paul Clark, Cornelis M. Dubbeldam, Richard Ellis, Carlos Frenk, Angus Gallie, Alan Heavens, David Henry, Eric Jullo, Thomas Kitching, James Lanzi, Simon Lilly, David Lunney, Satoshi Miyazaki, David Morris, Christopher Paine, John Pea****, Sergio Pellegrino, Roger Pittock, Peter Pool, Alexandre Refregier, Michael Seiffert, Ray Sharples, Alexandra Smith, David Stuchlik, Andy Taylor, Harry Teplitz, R. Ali Vanderveld, James Wu

We present a method for attaining sub-arcsecond pointing stability during sub- orbital balloon flights, as designed for in the High Altitude Lensing Observatory (HALO) concept. The pointing method presented here has the potential to perform near-space quality optical astronomical imaging at 1-2% of the cost of space-based missions. We also discuss an architecture that can achieve sufficient thermomechanical stability to match the pointing stability. This concept is motivated by advances in the development and testing of Ultra Long Duration Balloon (ULDB) flights which promise to allow observation campaigns lasting more than three months. The design incorporates a multi-stage pointing architecture comprising: a gondola coarse azimuth control system, a multi-axis nested gimbal frame structure with arcsecond stability, a telescope de-rotator to eliminate field rotation, and a fine guidance stage consisting of both a telescope mounted angular rate sensor and guide CCDs in the focal plane to drive a fast-steering mirror. We discuss the results of pointing tests together with a preliminary thermo-mechanical analysis required for sub-arcsecond pointing at high altitude. Possible future applications in the areas of wide-field surveys and exoplanet searches are also discussed.

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