The Orbiting Carbon Observatory (OCO) mission was selected by NASA's Office of Earth Science as the fifth mission in its Earth System Science Pathfinder (ESSP) Program. OCO will make the first global, space-based measurements of atmospheric CO 2 with the precision, resolution, and coverage needed to characterize sources and sinks of this important green-house gas. These measurements will improve our ability to forecast CO 2 -induced climate change. OCO will fly in a 1:15 PM sun-synchronous orbit, sharing its ground track with the Earth Observing System (EOS) Aqua platform. It will carry high-resolution spectrometers to measure reflected sunlight in the molecular oxygen (O 2 ) A-band at 0.76 m and the CO 2 bands at 1.61 and 2.06 m to retrieve the column-averaged CO 2 dry air mole fraction, X CO 2 . A comprehensive validation and correlative measurement program has been incorporated into this mission to ensure that X CO 2 can be retrieved with precisions of 0.3% (1 ppm) on regional scales.

NASA's Interstellar Program was begun in the Spring of 1999 after a year of advanced mission and program planning activities, reported previously in a paper delivered at the 1999 IEEE Aerospace Conference. Summarized here is the progress towards defining the first mission in the Interstellar Program: Interstellar Probe (ISP). This mission will be the first to probe the interstellar medium with a complete set of scientific instruments designed for such exploration and is expected to be a precursor and a significant testbed for technologies being developed for eventual travel to the nearest star. Exploration of the interstellar medium is the objective of the Interstellar Probe mission. The interface between our solar system and galaxy defines the cross over into the interstellar medium and is the minimum target distance, thought to be beyond 125 AU. A mission requirement, therefore, is to reach 200 AU in fifteen years or less with a scientifically capable payload package. Time and distance are key design requirements, and advanced propulsion technology is a key enabler of the Interstellar Probe mission. Another key mission goal is to launch in the 2010 time period; thereby setting associated advanced technology goals of readiness by about 2007. Solar sail propulsion has been baselined for the mission design concept. Key trades are sail technology development requirements as a function of trip time to 200 AU and the payload mass that can be delivered and operated at that distance. This paper provides strawman payload and measurement requirements, technology and mission trade information, and a baseline system design, including a configuration concept. Alternate technology options are described.suggested and outlined in [l]. The Interstellar Probe mission is the subject of this paper. This mission, the first to probe the interstellar medium with a complete set of scientific instruments designed for such exploration, is expected to be a precursor and a significant testbed for technologies being developed for eventual travel to the nearest star.Summarized in this paper is the material developed over a five-month period by a JPL team of missionhystem designers and advanced technology developers for presentation to NASA Headquarters in the summer of 1999. The rationale for the first mission is based on being able to explore new, exciting regions of space with new technology that has recently come onto the scene. The focus is an endto-end missiodsystem design that is integrated and based on technology predicted to be in place by about 2007. Selection of solar sail technology for the baseline design was made based on available information regarding readiness and performance; see [2]. Other propulsion system candidates continue to be considered as options to this baseline. The baseline design is described in an evolutionary manner, with science requirements defined first, mission requirements and baseline architecture next, and then the resulting flight system design. New technology is the basis for the design, and this dri...

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