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• The measurement platform must be robust in its execution of flight profiles through the region under study on carefully selected trajectories with guidance algorithms that blend real time data interpretation with preflight objectives. • The measurement platform must provide unperturbed, simultaneous, in situ observations of such disparate variables as radiance divergence, free radicals, condensations nuclei, trace-gas fluxes, etc., over extended horizontal and vertical segments of the atmosphere. • The measurement platform must be deployable to remote locations at minimum cost. • The measurement platform must be available to a large community of scientists with a minimum amount of bureaucratic complexity and at per-flight-hour costs that encourage innovation. • The concept of a single aircraft design is as inappropriate to the future as the concept of a highly restricted number of vehicles. Both are made obsolete by the demands of science as well as by recent technological developments in aeronautics, propulsion, guidance, and control. • The platform must venture into and successfully negotiate passage through regions of considerable danger; severe weather; deep into winter polar regions at high altitude; extended missions (≈days) over open ocean, ice pack, jungle regions at low altitudes, etc. When these requirements are viewed in concert, they demand an evolution (albeit rapid) of a family of platforms that not only maintain balance with respect to instrument versus platform development but also minimize technical dislocations in transitions from one platform to another. For example, while a "universal" requirement for stratospheric ozone studies is to deliver a payload of 250 kg to 30 km with a range of 20,000 km, critical scientific objectives can be satisfied with 70 kg payloads at 25 km, with a range of 2,000 km. Instruments and propulsion modules from more modest endeavors should be directly transferable to the larger platform that evolves from the smaller prototype. We introduce this concept explicitly in the discussion of three aircraft currently under development. Perseus A is a lightweight unmanned aircraft designed for near-term delivery of 50 to 70kg payloads to 25 to 30 km altitudes, using on board oxygen storage to allow operation of a modified existing engine. Perseus B uses the same airframe and control system, but replaces the closed-cycle engine with a turbocharged version, allowing transport of payloads up to 200 kg at altitudes of 18 to 25 km for durations of several days. Theseus is designed to carry three of the Perseus instrument sections to higher altitudes or for longer ranges, using a new airframe but two of the Perseus propulsion systems. Perseus A Since May of 1989, the Harvard Atmospheric Research Project and Aurora Flight Sciences have been developing Perseus, a lightweight unmanned aircraft designed specifically for atmospheric research. The effort evolved from Harvard's long-standing program in the chemistry of atmospheric ozone, which has relied on both laboratory experiments and in situ sampling by balloons and the NASA ER-2. The in situ data taken to date include the series that conclusively implicates chlorofluorocarbons in the formations of the Antarctic ozone hole [1] [2]. The program has thus been highly effective, but at the same time it has been constrained by limitations of the instrument carriers. In particular, the ER-2 has a ceiling of about 20km, which is below the bulk of atmospheric ozone, and moreover it cannot reach many areas of interest (e.g. high polar latitudes) because of necessarily conservative safety rules. Balloons can reach higher altitudes and can fly from more remote sites, but lack of trajectory control and risk to payloads make them unacceptable for many missions. Harvard sought a new aircraft that would overcome the limitations of each platform and combine their best features. These requirements developed just as a group from MIT was finishing the Daedalus human-powered aircraft project, which culminated in April 1988 when Kanellos Kanellopoulos flew 115 km from Crete to Santorini. The aerodynamic and structural methods used for Daedalus were directly applicable to high-altitude flight, and several of the Daedalus engineers therefore took up the Harvard problem. Perseus, as II-6
