Space-quality data from balloon-borne telescopes: the High Altitude Lensing Observatory (HALO)

TL;DR

This paper introduces a novel multi-stage pointing system for balloon-borne telescopes that achieves near-space quality imaging with sub-arcsecond stability, significantly reducing costs compared to space missions.

Contribution

It presents an integrated pointing architecture combining coarse control, nested gimbals, a de-rotator, and fine guidance for high stability in balloon-based astronomy.

Findings

Achieved sub-arcsecond pointing stability in tests.

Demonstrated thermomechanical stability suitable for high-altitude conditions.

Outlined potential for long-duration balloon observation campaigns.

Abstract

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.