Precision Attitude Determination for an Infrared Space Telescope Dominic J. Benford †A , Tod R. Lauer B , Robert A. Woodruff C , Roelof W.H. van Bezooijen D , Gopal Vasudevan D A NASA / Goddard Space Flight Center, Greenbelt, MD 20771 USA; B NOAO, P.O. Box 26732, Tucson, AZ 85726 USA C Lockheed Martin Space Systems Company, 12257 S. Wadsworth Blvd., Littleton, CO 80125 USA D Lockheed Martin Advanced Technology Center, 3251 Hanover St., Palo Alto, CA 94304 USA ABSTRACT We have developed performance simulations for a precision attitude determination system using a focal plane star tracker on an infrared space telescope. The telescope is being designed for the Destiny mission to measure cosmologically distant supernovae as one of the candidate implementations for the Joint Dark Energy Mission. Repeat observations of the supernovae require attitude control at the level of 0.010 arcseconds (0.05 microradians) during integrations and at repeat intervals up to and over a year. While absolute accuracy is not required, the repoint precision is challenging. We have simulated the performance of a focal plane star tracker in a multidimensional parameter space, including pixel size, read noise, and readout rate. Systematic errors such as proper motion, velocity aberration, and parallax can be measured and compensated out. Our prediction is that a relative attitude determination accuracy of 0.001 to 0.002 arcseconds (0.005 to 0.010 microradians) will be achievable. Attitude control will have a jitter of around 0.003 arcseconds and stability/repeatability to around 0.002 arcseconds. Keywords: precision pointing, infrared space telescope, attitude determination, attitude control 1. INTRODUCTION Destiny 1 is a simple, direct, low cost mission to determine the properties of dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Its science instrument is a 1.65m space telescope, featuring a near-infrared (0.85-1.7µm) survey camera and slitless spectrometer with a large field of view (FOV) covered by a mosaic of 2k×2k HgCdTe arrays. For maximum operational simplicity and instrument stability, Destiny will be deployed into a halo-orbit about the Second Sun-Earth Lagrange Point. During the first two years of observations, Destiny will detect, observe, and characterize several thousand SN Ia events over the redshift interval 0.4 < z < 1.7 within a fixed survey area that is viewed repeatedly throughout the survey duration. The spectral images must simultaneously provide broadband photometry, redshifts, and SN classification, as well as time-resolved diagnostic data, which is valuable for investigating additional SN luminosity diagnostics. Destiny will be used in its third year as a high resolution, wide-field imager to conduct a weak lensing (WL) survey covering ~1000 square degrees. The large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift will provide independent and complementary constraints on the dark energy equation of state. The combination of SN and WL is much more powerful than either technique on its own. The most stringent requirement for the spacecraft is that the pointing must be accurate to 0.010 arcsec (1σ) in drift and stable to better than 0.030 arcsec in jitter over the 900sec duration of a single integration, and must repoint to the SN survey subfields to within 0.010 arcsec over the two-year survey duration. This can be derived by considering how Destiny will observe SN: by repeatedly imaging an unbiased field near each ecliptic pole, followed by isolating the SN spectra by image differencing. This technique sidesteps all issues of overlap of the SN Ia spectra with that of their host galaxies, and any other concerns about source confusion, but requires that those spurious sources are perfectly subtracted during the image differencing. For each three-month interval, the spacecraft roll angle will be held fixed as the Earth and the spacecraft at L2 orbits the Sun. It will then roll 90° about the ecliptic poles for the next three-month interval (as only one side of the spacecraft can † Dominic Benford: ph: (1) 301.286.8771; Fax: (1) 301.286.1617; e-mail: Dominic.Benford@nasa.gov Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, edited by Jacobus M. Oschmann, Jr., Mattheus W. M. de Graauw, Howard A. MacEwen, Proc. of SPIE Vol. 7010, 70104A, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.789919 Proc. of SPIE Vol. 7010 70104A-1 2008 SPIE Digital Library -- Subscriber Archive Copy