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Table 1: Reduction of Harvard instrument weights

[[9 row table; 4 column table]]
|Instrument & platform|year|weight(kg)|comments
|CIO/BrO|
|Balloon|1976|450||
|ER-2|1987|175||
|Perseus|1990|35|including power supply and O3, pressure, and  temperature.|
|OH|
|Balloon|1983|1,500|copper vapor laser|
|ER-2|1991|230||
|Perseus|1992|40|diode laser and titanium sapphire|

With respect to scientific instruments, the experience of Harvard University's Atmospheric Research Project illustrates a case in point. Table 1 documents the reductions in weight in successive generations of instruments. The latest versions are designed to be flown interchangeably on unmanned aircraft or small balloons.

Mission requirements

During 1990, with support from the National Science Foundation. Aurora Flight Sciences undertook a study of missions and payloads for a next-generation high-altitude aircraft. The results are documented in [7] and summarized in table 2. For each of the primary performance parameters we have specified a "minimum acceptable value" and a "desired value". An asterisk (*) indicates parameters of secondary importance. Three major conclusions emerged from this study:

1. Using currently available technology, the maximum payload requirement could be reduced to approximately 200 to 250 kg. Most of the instruments that would constitute such payloads do not exist today, but they could readily be developed. The cost almost certainly would be less than 10 million dollars. 

2. The missions cluster into two groups: those that require extremely high altitudes (30 km or above) and those that require extremely long durations (24 hours or greater). The high-altitude requirements are focused on specific locations, so range is determined by the distance from these sites to suitable bases. The long-duration missions require lower observing altitudes (20 to 25 km). Thus the various range and altitude requirements could be satisfied by two different aircraft types. This will much reduce the technical difficulties and overall costs relative to development of a single all-purpose design.

3. Many useful contributions can be made with a payload of 50kg or less. This observation led to initiation of the Perseus program in 1989, whose objective is to provide a platform to satisfy immediate requirements of the science community at a modest cost.

Matching platforms to mission requirements

Examination of the leading scientific questions in global climate change reveals clear conclusions:

Table 2: Summary of mission requirements

[[10 row table; 5 column table]]
|mission|range[km]|duration[hr]|altitude[km]|payload[kg]|
|polar ozone depletion|1,000/20,000|1/50|25/40|50/220|
|atmospheric radiation|*|8/36|11/24|50/150|
|CO2 and CH4|5,000/20,000|*|1/0.01|50/100|
|stratosphere/troposphere exchange|5,000/20,000|*|20/25|100/250|
|tropical photochemistry|5,000/20,000|*|25/30|100/200|
|hurricane reconnaissance|5,000/*|100/200|18/18|50/150|
|SST effects|1,000/20,000|*|25|50/200|
|operational meteorology|5,000/20,000|*|18|50/200|
|satellite ground truth|1,000/*|12/24|25/40|50/220|

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