Enabling the Next Generation of Space-Based Astrophysics Observations

The next generation of space telescopes will require platforms than can provide pointing stability on the order of 1 - 2 mas/axis1 1 over time periods of up to an hour. In many cases, the attitude measurements for these ultra-stable platforms will be provided by a Fine Guidance Sensor (FGS) collocated with the science instruments. Utilizing the main telescope aperture, which is expected to be +3.2 m, enables the use of guide stars as dim as 17th Mv, producing measurement noise < 8 mas/axis 1, 80% of which is rolled off by the low bandwidth of the controller. But this addresses only the measurement half of the stability problem without looking at the control portion. Many of the observatories will be operated in an Earth-Sun L2 Halo orbit2, where disturbance torques will be small (< 1 mNm) and the required control authority during science data collection will also be small. This paper presents an architecture that uses a set of low force, high specific-impulse electro-spray thrusters for attitude control. Line-of-sight motion due to thruster noise is less than 20 as/axis 1, assuming a thrust noise level of 80 nN/thruster 1, giving these observatories the stability required to produce groundbreaking astronomical research.