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Issues in the Integration of Research and Operational Satellite Systems for Climate Research: II. Implementation
Space should be provided on the NPOESS platforms for research payloads.
These recommendations are discussed further in this chapter.1
In the present context, technology insertion is defined as the introduction of any new and/or improved hardware or software capabilities into an established operational system. Qualifying innovations span a wide range of potential changes and pose varying levels of risk for the operational performance of the system. For example, replacing a computer with a faster model that preserves the form, fit, and function of the earlier model is quite different from changing the operating system of the computer or the data processing algorithm. Any change in design involves risk, but some changes may ripple throughout a system, forcing additional changes to accommodate the first. Additional risk is anathema for an operational system, whose reliability and continuity are the prime considerations. No matter how well justified the augmented capabilities may be from a scientific point of view, any potential change must be examined carefully and conservatively.
Any program with a long time line must face the issue of technology insertion. In past decades, the relatively long lifetime of many of the operational weather satellites and the relative stability of their instrumentation frequently led to obsolescence, and the need for change became a dominant consideration.
The National Oceanic and Atmospheric Administration (NOAA) Polar-Orbiting Environmental Satellites (POES) program essentially began with TIROS in April 1960 and, proceeding through several generations, will fly through 2009 (2011 for the Defense Meteorological Satellite Program (DMSP)). Although there have been several block changes that modified the spacecraft design or exchanged existing instruments for improved or enhanced versions, the POES and DMSP series have been characterized by long periods during which they operated with essentially fixed configurations. Occasionally, these programs made changes and flew special instruments between block changes. These changes included permanent additions as well as one-of-a-kind instrument flights. However, the sponsoring agencies have learned that even apparently simple changes can lead to setbacks.
The Advanced Very High Resolution Radiometer (AVHRR) and the Solar Backscatter Ultraviolet (SBUV) sensor provide examples of the kinds of difficulties that may be encountered. Both instruments were built as a set of several identical flight units. The 3.7 μm band on the first AVHRR was discovered soon after launch to be contaminated with noise, which gave a herringbone pattern in the imagery. Subsequent analyses suggested that there was a design flaw in an amplifier, but funds were no longer available to redesign and rebuild the remaining AVHRRs for future flights. A similar problem occurred with the SBUV. A simple design flaw diminished the scientific utility of the data set for analysis of low-frequency processes (Mark Schoeberl, NASA Goddard Space Flight Center, personal communication, 1998). However, NOAA was unable to provide funding to rectify the problem for future SBUV sensors. These and similar experiences have reinforced the operational agencies’ natural tendency to resist change, and they underscore the need for thorough prequalification of any candidate instrument before it is accepted into an operational payload.
Introducing new technology through block changes is a direct approach to enhancement that avoids the problems caused by introducing new components into an older design. When a block change is associated with recompetition for the program, it also addresses the programmatic and contract issues. However, it does not directly address the issue of continuity of data products and the ability to put a long time series of data on a standardized scale. For short-term weather prediction, new and improved systems may be acceptable if they provide forecasts with higher accuracy. However, for climate research it is necessary to be able to relate the old measurements to the new quantitatively if small trends in critical variables are to be observed over time. Thus,
The committee notes that accommodation of “leveraged payloads” was included in the request for proposals (RFP) for the NPOESS system definition and risk reduction phase (IPO, 1999). Leveraged payloads are those provided by NASA or other agencies and presumably are not necessary to satisfy the core NPOESS requirements. However, they could eventually become part of the operational payload. The RFP also includes the accommodation of the NPOESS Preparatory Project (NPP) mission as a single flight before the NPOESS spacecraft are launched. Implications of the NPP are also discussed in this chapter.