OCO-2 (Orbiting Carbon Observatory-2) is the first NASA (National Aeronautics and Space Administration) mission dedicated to studying atmospheric carbon dioxide, specifically to identify sources (emitters) and sinks (absorbers) on a regional (1000 km x 1000 km) scale. The mission is designed to meet a science imperative by providing critical and urgent measurements needed to improve understanding of the carbon cycle and global climate change processes. The single instrument consisting of three grating spectrometers was built at the Jet Propulsion Laboratory, but is based on the design co-developed with Hamilton Sundstrand Corporation for the original OCO mission. The instrument underwent an extensive ground test program. This was generally made possible through the use of a thermal vacuum chamber with a window/port that allowed optical ground support equipment to stimulate the instrument. The instrument was later delivered to Orbital Sciences Corporation for integration and test with the LEOStar-2 spacecraft. During the overall ground test campaign, proper function and performance in simulated launch, ascent, and space environments were verified. The observatory was launched into space on 02 July 2014. Initial indications are that the instrument is meeting functional and performance specifications, and there is every expectation that the spatially-order, geo-located, calibrated spectra of reflected sunlight and the science retrievals will meet the Level 1 science requirements.
This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer
(TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like
planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress
with each of the testbeds is summarized. The current interferometer architecture, design trades, and the viability
of possible reduced-scope mission concepts are also presented.
The NASA Terrestrial Planet Finder Interferometer (TPF-I) and ESA Darwin missions are designed to directly detect
mid-infrared photons from earth-like planets around nearby stars. Until recently, the baseline TPF-I design was the
planar stretched X-Array, in which the four collectors spacecraft lie on the corners of a rectangle with the combiner
spacecraft at the center, all in the plane normal to the direction to the target star. The stretched X-Array has two major
advantages over other configurations: the angular resolution is very high, and the ability to eliminate instability noise. A
direct consequence of the latter is that the null depth requirement is relaxed from 10-6 to 10-5. Implementation of the
planar configuration requires a significant number of deployments, however, including large sunshades and secondary
mirror supports. ESA had been pursuing a non-planar configuration with 3 collector telescopes. Dubbed the 'Emma'
architecture (after the wife of Charles Darwin), this approach brings the combiner spacecraft up out of the plane of the
collectors, and offers significant simplifications in the collector design with minimal deployments. The Emma X-Array
combines the best aspects of each design, bringing together the 4-collector stretched X-Array collector configuration
with the out-of-plane combiner of the Emma geometry. Both the TPF-I and Darwin missions have now adopted the
Emma X-Array as the baseline design, moving a step closer to a single, joint TPF/Darwin mission.
In this paper we assess the planet-finding performance of the Emma X-Array. An optimized completeness algorithm is
used to estimate the number of Earths that can be found as a function of collector diameter. Other key parameters − the
inner and outer working angles and the angular resolution − are also addressed.
For the past several years NASA has been developing the Terrestrial Planet Finder Coronagraph (TPF-C), a space based
telescope mission to look for Earth-like extra-solar planets. By evaluating the cumulative number of habitable zones
observable with a given observation sequence (completeness) we test the relative merits of the baseline 8-m telescope
design and smaller (2.5 - 4 m), less capable TPF-C designs based on various coronagraph technologies as well as
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.
The Terrestrial Planet Finder Coronagraph (TPF-C) is conducting pre-formulation design and analysis studies based on a 8x3.5m elliptical aperture, light-weight primary mirror feeding an internally occulted (Lyot) coronagraph. The primary mirror has challenging static and dynamic performance requirements. We report on recent trade studies and concepts including open- and closed-back mirror blank designs and comparisons of thermal and mechanical performance; aperture shape alternatives to better match the coronagraph application with weight, packaging, and fabrication constraints; and mirror material trades.