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The Terrestrial Planet Finder - Occulter (TPF-O) mission has two Spacecraft (SC) buses, one for a formation-flying
occulter and the other for a space telescope. These buses supply the utilities (support structures, propulsion, attitude
control, power, communications, etc) required by the payloads: a deployable shade for the occulter and a telescope with
instruments for the space telescope. Significant requirements for the occulter SC bus are to provide the large delta V
required for the slewing maneuvers of the occulter and communications for formation flying. The TPF-O telescope SC
bus shares some key features of the one for the Hubble Space Telescope (HST) in that both support space telescopes
designed to observe in the visible to near infrared range of wavelengths with comparable primary mirror apertures (2.4 m
for HST, 2.4 - 4.0 m for TPF-O). Significant differences from HST are that 1) the TPF-O telescope is expected to have a
Wide Field Camera (WFC) that will have a Field of View (FOV) large enough to provide fine guidance, 2) TPF-O is
designed to operate in an orbit around the Sun-Earth Lagrange 2 (SEL2) point which requires TPF-O (unlike HST) to
have a propulsion system, and 3) the velocity required for reaching SEL2 and the limited capabilities of affordable
launch vehicles require both TPF-O elements to have compact, low-mass designs. Additionally, it is possible that TPF-O
may utilize a modular design derived from that of HST to allow robotic servicing in the SEL2 orbit.
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