Direct imaging of terrestrial and Jupiter-size planets about other stars is a major goal of NASA's Origins Program and should be as well for the next generation of spaceborne telescopes. In this paper, we discuss a free-flying occulter to augment the design and imaging capability of space-based telescopes. The Umbral Mission Blocking Radiating Astronomical Sources (UMBRAS) space mission would consist of a Solar-Powered Ion-Driven Eclipsing Rover (SPIDER) and possibly one or two metrology platforms. The UMBRAS spacecraft would be semi-autonomous, with their own propulsion systems, internal power (solar cells) , communications, and navigation capability. The spacecraft (the telescope, SPIDER, and any metrology platform) would define a reference frame for aligning the telescope and the SPIDER with the observed target.When stationed at distances of 1 ,000 to 15,000 km from a telescope, the occulter will enable an 8 m telescope to image very faint sources as close as 0.15" from the target stars. Three of the Doppler-detected planets about nearby stars are at this separation and could be directly imaged with this observing technique. It would be possible to image giant planets as close as 5 AU from parent stars at distances from the Sun as great as 30 pc. With this technique, terrestrial-size planets could be detected around nearby stars within the next decade. We briefly discuss the diffraction effects caused by the occulter and a preliminary proof-of-concept design for the UMBRAS spacecraft. Finally, we suggest types of observations other than planet finding that could be performed with UMBRAS.

We describe a 1-meter space telescope plus free-flying occulter craft mission that would provide direct imaging and spectroscopic observations of Jovian and Uranus-sized planets about nearby stars not detectable by Doppler techniques. The Doppler technique is most sensitive for the detection of massive, close-in extrasolar planets while the use of a free-flying occulter would make it possible to image and study stellar systems with planets comparable to our own Solar System. Such a mission with a larger telescope has the potential to detect earth-like planets.Previous studies of free-flying occulters reported advantages in having the occulting spot outside the telescope compared to a classical coronagraph onboard a space telescope. Using an external occulter means light scatter within the telescope is reduced due to fewer internal obstructions and less light entering the telescope and the polishing tolerances of the primary mirror and the supporting optics can be less stringent, thereby providing higher contrast and fainter detection limits. In this concept, the occulting spot is positioned over the star by translating the occulter craft, at distances of 1,000 to 15,000 km from the telescope. Any source within the telescope field-of-view can be occulted without moving the telescope.In this paper, we present our current concept for a 1-m space telescope matched to a free-flying occulter, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS) space mission. An UMBRAS space mission consists of a Solar Powered Ion Driven Eclipsing Rover (SPIDER) occulter craft and a matched (apodized) telescope. The occulter spacecraft would be semi-autonomous, with its own propulsion systems, internal power (solar cells), communications, and navigation capability. Spacecraft rendezvous and formation flying would be achieved with the aid of telescope imaging, RF or laser ranging, celestial navigation inputs, and formation control algorithms.Al Schultz is an Instrument Scientist at the Space Telescope Science Institute (STScI). He has worked at STScI for ∼12 years. Since launch, Dr. Schultz has supported HST operations in PODPS, which is now part of OPUS, the GHRS, STIS, NICMOS, and WFPC2 instruments. (Send correspondence to schultz@stsci.edu; Telephone: 410-338-5044)High-Contrast Imaging for Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Proc. of SPIE Vol. 4860 57 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Large space-based telescopes have specific design requirements which offer challenges to the instrument designer. The optical design and detector fabrication are frozen years before the launch date. The Umbral Mission Blocking Radiating Astronomical Sources (UMBRAS) space mission design consists of a Solar-Powered Ion-Driven Eclipsing Rover (SPIDER) and possibly one or two metrology platforms. The ultimate goal of UMBRAS is to provide pseudocoronagraphic capability for direct imaging of extrasolar Jovians and other brighter, distant substellar companions.In this paper we discuss operational considerations for the free-flying occulter. Operations consist of maneuvering the SPIDER between targets, alignment with the space-based telescope line of sight to the target, and stationkeeping. Target-to-target maneuvers need to be optimized to conserve propellant. A reasonable balance needs to be determined between target observation rate and the number of targets that are observable during mission lifetime. Velocity matching of the SPIDER with the telescope is essential to mission performance. An appropriate combination of solar electric and cold-gas thrusters provides the ability to match velocities using positional information derived from communication and ranging between telescope, occulter and any metrology stations.Desirable features of using an external coronagraphic vehicle include the ability to obtain coronagraphic data with any instrument on the telescope -imaging, spectroscopic, or interferometric.

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We present a novel coronagraphic imaging technique and design for space-based telescopes. The Umbral MissionBlocking Radiating Astronomical Sources (UMBRAS) is a space mission design consisting of a free flying occulter, the Solar Powered Ion Driven Eclipsing Rover (SPIDER), and possibly one or two metrology platforms. The UMBRAS spacecraft operate in conjunction with a space-based telescope. The size of the occulting SPIDER is dictated by the size of the telescope with which it will work. The goal of UMBRAS is to provide "paleolithic" (i.e., non-focal plane) coronagraphic capability to enable direct imaging of extrasolar Jovian planets and other bright substellar companions such as brown dwarfs.We discuss two aspects of the operation of a free flying occulter: acquisition of targets and station keeping. Target acquisition is modeled after the onboard schemes used by Hubble Space Telescope (HST) science instruments. For UMBRAS, the onboard commanding sequences would include imaging the field using instruments on the telescope, locating the target and the occulter in the field, and accurately positioning the occulter over the target. Station keeping consists of actively maintaining the occulter position in the telescope line of sight to the target.Velocity matching of the c)cculter with the space-based telescope is essential to mission performance. An appropriate combination of solar electric and cold gas thrusters provide the ability to match velocities using position information derived from communication and from ranging data between telescope, occulter and any metrology stations.The accuracy requirements for target acquisition and station keeping depend upon the science requirements, the occultation geometry, and the sensitivity of the science to changes in occultation geometry during an exposure sequence. Observing modes other than the ideal centered occultation of a target will be discussed.