The dark side of TPF: detecting and characterizing extra-solar Earthlike planets with one or two external occulters

Abstract

One of the major goals in astronomy today is the detection and characterization of extra-solar planets. There are currently many exciting new concepts on the horizon that have the capability to vastly increase our knowledge of extrasolar planets, particularly, planets like our own. The Terrestrial Planet Finder (TPF) program spans several different mission concepts that are all capable of detecting and characterizing Earth-like planets. One such concept under study consists of a telescope spacecraft and separate occulter spacecraft. The external occulters (EO) will be tens of meters in diameter and will be located thousands of kilometers away. This arrangement allows the mission to observe companion planets with a ~4 m telescope by extinguishing on-axis starlight. The operational efficiency of external occulters is constrained by the large separation between the telescope and the occulter spacecraft. Slewing between target stars will consume maneuvering fuel and time. Thus, the efficiency of any single EO mission may be greatly improved by using two or more occulters and optimizing the mission scenario. We explore the design of different size occulters for different objectives in the TPF mission. In one approach, a smaller occulter performs a survey function, while a large occulter performs follow-up searches on prospective planets and fainter celestial objects. The small occulter would have more maneuverability, but have a large inner working angle. The optimized combination of two such occulters may provide the best compromise in the mission's ability to search and characterize extra-solar planets. This paper discusses several potential TPF mission scenarios involving two occulters (one large, one small) and explores the optimization of different scenarios for detection and characterization of Earth-like planets.