Preceding chapters in this report discuss how the utility of operational spacecraft to the climate research community can be improved through attention to instrument calibration and characterization as well as to continuity of certain time series of data. The need for an adequate data infrastructure to support processing, archiving, and analysis activities is also explored. This chapter discusses another opportunity to improve the utility of National Polar-orbiting Operational Environmental Satellite System (NPOESS) data for climate researchers—augmentation of planned sensor or system capabilities. In particular, this chapter examines some of the unique challenges associated with the insertion of new technology into operational systems that are conservative by design and whose foremost objective is to provide unbroken service to the primary user communities.
The phase one report of the committee (NRC, 2000a) forms the basis for the present discussion. That report reinforces the findings of several other studies and identifies the programmatic and technological issues to be addressed if an operational system such as NPOESS is to be more responsive to climate research needs. The main impediments are the following:
Lack of a NASA program to facilitate the development of instruments for NPOESS;
Reliance on the use of operational weather data products (as stipulated in the Integrated Operational Requirements Document (First Version) (IORD-1; IPO, 1996) environmental data records) to meet long-term climate monitoring and climate research requirements (which are different from weather-monitoring requirements), adding cost and requirements to the operational system;
Insufficient provision for temporal overlap between replacement instruments, which is necessary to validate and cross-calibrate measurements that span more than one satellite; and
No requirement or specification for long-term instrument stability.
Among other responses to these issues, the phase one report (NRC, 2000a) makes the following recommendations [paraphrased]:
There should be a continuing program for operational satellite improvement that can support joint research and operational activities.
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 history of the Operational Satellite Improvement Program (OSIP) was reviewed in a 1993 publication by the U.S. Congress, Office of Technology Assessment (U.S. Congress, OTA, 1993):
NASA and NOAA have a long history of cooperation in developing spacecraft. An agreement between the two agencies, originally signed in 1973, gives the Department of Commerce and NOAA responsibility for operating the environmental systems and requires NASA to fund development of new systems, and fund and manage research satellites. This NASA line item is known as the Operational Satellite Improvement Program, and was usually funded at an average level of about $15 million per year. Prior to initiating the Geostationary Operational Environmental Satellite (GOES)-Next development, this division of labor seemed to work well. NASA had developed the TIROS and Nimbus research satellites, which carry instruments that were eventually transferred to NOAA operational satellite systems. NASA and NOAA budgets and organizational structure were based to an extent on the agreed-upon division of responsibility.
In the polar-orbiting part of this approach, NASA’s Nimbus spacecraft was used as a science platform (Eden et al., 1993) on which new instruments could be developed and flown as a research or demonstration mission. NOAA’s TIROS (followed by the TIROS Operational System, the Improved TIROS Operational System, and POES) was the corresponding operational spacecraft, whose technology and instrumentation naturally evolved more slowly. The dual path central to the OSIP concept was deemed to be too expensive at the time, and the approach was abandoned in 1985. Nimbus continued to fly for several years as a science program in its own right, but it no longer served as the development platform for the operational system.
technology insertion poses a dilemma: system change is necessary, yet in certain respects it may be undesirable. Any enhancement that appears to be desirable from a science point of view must also be well understood, well qualified, and well documented to qualify as a proposed change. The challenge for NPOESS is to find a way to accommodate technological change in a timely manner, while ensuring that the modified system will sustain operational functionality.
The National Research Council (NRC) has addressed the issue of technology development at NASA in several reports.3 These reports generally have expressed concern about NASA’s commitment to technology development and to technology insertion into NOAA programs.
NOAA itself has always taken a conservative approach to flying new instruments, and the process of introducing new instrumentation has been slow and rigorous by design. This conservatism has a reasonable basis, because instrument changes usually imply subsequent changes in the information products used throughout the weather services and the secondary data processors (commercial users). Any change in the original data may also require a different data processing algorithm, which could disrupt the continuity of corresponding climatology records. (One means of insuring against this risk is to preserve the original data.)
NOAA is not a space agency; in the past it has relied on NASA to develop instruments and spacecraft. In recent years, NOAA’s alliance with the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) has added an international dimension to the technology insertion question. Economics, reduced budgets, and increased awareness of the global nature of the issues has engendered more international cooperation, both scientifically and programmatically, with European and Asian countries. However, the means of technology insertion for these operational missions is still not well determined. Indeed, there appears to be a gap between the development of instruments in the science stream and the application of instrumentation in the operational stream. For example, the NASA Earth Science Enterprise has expressed its intention to rely on international partners to fulfill certain of its NASA science goals (P. Morel, NASA presentation, 1999). Such international exchange may be sound financial policy in this age of reduced budgets, but it does not necessarily lead to enhanced instrumentation on the operational satellites of either Europe or the United States. For example, it was originally agreed that the Meteorological Operational satellite (METOP; supplied by EUMETSAT) would provide morning coverage for NPOESS, and in exchange there was meant to be shared instrumentation between METOP and NPOESS. At this time, however, planned METOP flights through 2017 will not include NPOESS operational instruments. There have been no substantive discussions between the pertinent agencies regarding the insertion of new instrument capabilities that might follow from the international scientific cooperative programs.
Without making a major block change, how can new instruments be introduced directly on the operational platforms? Technological insertion of a new instrument outside a block change has a precedent on POES with SBUV and the Earth Radiation Budget Experiment (ERBE). However, the policy that would determine the future of such new instruments is not clear. Are they to be adopted as part of the operational program, or are they to be replaced by a different experiment on the next flight? Resources for the operational platforms are limited and usually committed well in advance; there does not seem to be enough excess capacity (“margin”) to support many concurrent experiments. There are lessons to be learned from the POES experience. If the NPOESS program is to be used to support the science community as well as the operational weather agency, then a careful assessment of the pertinent science requirements must be made in the early phases of development. A possible solution to this dilemma is a continuing program of missions where “preoperational” measurements and technologies can be tested without disrupting the operational programs. This approach is in the spirit of the OSIP or Nimbus model.
The insertion of technology raises issues of hardware and software capability and capacity. Once a major system design such as NPOESS has been finalized, it is increasingly difficult to accommodate change. Hence, advance planning that anticipates change and technology insertion over the life of the program is essential. Such planning should be part of the NPOESS system definition and risk reduction (SDRR) phase and continue into the subsequent stages of design. To the extent that instrumentation innovations from NASA science programs might become candidates for NPOESS, NASA and the Integrated Program Office (IPO) must incorporate planning for technology insertion in the near term. Highlights of the technical issues to be considered are described in the following sections.
Defining Available Program Resources
Technology insertion always will be subject to limitations. Any downstream change in the on-board technology must fit within the spacecraft resources (mass, power, data bandwidth, data volume, etc.) that may remain over and above the requirements of the baseline system. To estimate resource availability, it will be necessary to
consider all system elements from the program level through the space segment down to the individual instruments. For the introduction of enhancements, it may even be necessary to consider sensor subsystem attributes, such as frequency bands and data streams. For example, the AVHRR on the current POES was enhanced (over the VHRR instrument) by adding a new channel. Even this change, as simple as it might appear to have been, encountered a resource limitation in the downlink data rate that restricted the data flow from the AVHRR to the same number of channels as the older version. For the satellite and payload combination, it is difficult to increase resource demand within the design envelope of the spacecraft and launch vehicle. Because the spacecraft liftoff mass usually is matched to launch vehicle capacity, it may take a major redesign of either the spacecraft or the launch vehicle to accommodate an increase in mass or volume. For the ground segment, usually it is possible to add capacity during the operational life of the mission, but even this may require difficult choices, such as changes to remote site antennas and processing equipment. Ground segment changes are to be avoided because, in general, many facilities worldwide would be affected.
Characteristics of the Available Spacecraft
Just as the measurement characteristics of instruments must satisfy the requirements imposed by meeting science objectives, so must the host spacecraft be able to support the requirements of the instrument payload. The science community, through its participation in the NPOESS science team, should provide guidance to the IPO on the magnitude of the spacecraft resource margins necessary to support planned or potential new instruments. This will require that the IPO and its contractor maintain a status report on the resource margins for use in the technology insertion process.
For any innovation being considered, the resource needs and requirements of the candidate technology insertion, measurement enhancement, or new instrumentation must be compared with the margins and limitations determined by the spacecraft characteristics. For an existing operational design—such as that for NPOESS—there will be virtually no possibility of substantive changes to the spacecraft and its standard payload. An additional constraint is that NPOESS is being designed for a relatively long (7-year) lifetime.5 Indeed, if the design has little room built in for enhancement, many potentially interesting innovations can be ruled out. Clearly, NPOESS and its payload should be designed from the outset with sufficient margin in its critical parameters to support the insertion of new or enhanced measurement capabilities.
The committee anticipates calls from the scientific community, and perhaps also tangible interest from the operational community, for the addition of new, enhanced, or more reliable measurement capabilities over the lifetime of the NPOESS system. In anticipation of these events, a process and infrastructure should be defined now to review proposed technological or measurement innovations and oversee their acceptance when warranted. The IPO was responsible for the generation of the original NPOESS operational requirements (IPO, 1996), so there is already in place a process that should provide for multiservice approvals and signoffs of revisions to those requirements. Requirements for enhanced measurement capabilities that would respond to the needs of the climate science community would have to be developed and approved through that process.
The NPOESS RFP for the SDRR phase (IPO, 1999) provides for leveraged instruments, which are to be developed by other (non-IPO) organizations and then offered to the IPO at zero (or nominal) cost. The RFP specifies that the contractor develop a process to accommodate the leveraged instruments that are accepted for flight. The IPO’s inclusion of this task in the SDRR statement of work, an effort that the committee supports, indicates that the IPO recognizes the need to incorporate additional instruments, and it sets a precedent that could help in the formulation of a review and selection process for future technology insertion. Leveraged instruments
can be developed by either domestic or international agencies. If successful, NASA’s Instrument Incubator Program (IIP), which is designed to prove the value of new measurement concepts by aircraft or suborbital implementation, could be followed by a satellite-based mission, selected, for example, through Earth science flight programs such as the Earth System Science Pathfinder. Another possibility for a leveraged instrument is the radar altimeter, which appears in the straw-man manifest for the 0530 satellite and which the IPO has said it favors being contributed by the French, in contrast to its strategy for facility instruments such as the atmospheric sounder, whose development it funded directly.6 A lesson that could be drawn from the IPO’s position in this instance is that the development and qualification of any new measurement capability for scientific purposes would have to be funded from non-IPO sources, unless that instrument were deemed to be critical to the NPOESS mission. Because important science issues may not be addressed by this approach, vision and well-coordinated interagency planning are needed to sustain suitable instrument development in synchronization with NPOESS flight opportunities.
Programmatic issues for an explicit technology insertion element include those related to cost and schedule. There will be direct costs associated with planning for and accommodating system contingencies (margins), staffing in the IPO for the science dimensions of NPOESS, and associated schedule impacts and indirect costs. If NPOESS is to be successfully extended from an operational system to a system that can encompass climate research objectives, then the partners in the IPO, primarily NASA and NOAA, must allocate (or reallocate) funds accordingly. The SDRR contractor’s costs will probably have to increase to accomplish these future tasks, an increase that the government would have to factor into the overall costs and funding or find other ways to accommodate. The time required to develop, select, and qualify potential research payloads cannot be allowed to compromise operational needs.
Unlike its predecessors, which have relatively short design lifetimes, the NPOESS satellites are meant to have a 7-year lifetime. While a 7-year design life is a laudable objective for an ongoing operational facility, the launch and replacement schedule as well as the physical resources of the spacecraft will inhibit technology insertion. Having longer intervals between launches implies also a larger number of instrumentation innovations worthy of flight, yet there will be fewer opportunities to insert them.
Management of the Process
If the NPOESS satellite series is to be enhanced in response to climate science requirements, the leadership and management responsible for doing so need to be identified. The IPO, on behalf of its three principal stakeholders (NOAA, the Department of Defense (DOD), and NASA), is coordinating convergence toward an operational polar-orbiting weather satellite system, but the climate and research requirements are outside its primary mission. No single organization represents the needs of climatology.7 If such an organization were created, it could provide insight and oversight, but the responsibility for NPOESS would, with good reason, remain with the IPO. Therefore, the science and operational mandates of NPOESS would have to be coordinated at the highest levels of the three sponsoring agencies.
NASA’s Earth Science Enterprise is committed to continue funding small, short-duration missions to study Earth, including climate-related variables of its ocean and atmospheric environments. However, such missions are ill-suited to long-term climate studies (NRC, 2000b). As noted in a number of places in this report and elsewhere, polar-orbiting operational weather satellites (no matter how long their missions) are not equipped to meet the needs of climate science. These two themes could be harmonized if suitable and coordinated leadership were exercised.
Note that to date, there is no agreement between the IPO and the French for the NPOESS altimeter.
See the “Organizational Issues” section in Appendix B of this report.
Coordination of Instrument and Spacecraft Development Schedules
Consider a situation where the NPOESS spacecraft have spare on-board resources that have been identified for scientific use. If no additional Earth observation satellites are identified for demonstration of new instrumentation, the only opportunities to insert the new technology into the NPOESS program would be during routine replacement flights. Once the NPOESS system is fully in place,8 the replacement cycle for each of the two IPO satellites will be at nominal 7-year intervals, with an average launch frequency of one every 5 years. If historical trends continue,9 spacecraft will probably last longer than their design lifetime, so that replenishment opportunities will be further delayed. Instrument development and procurement must be synchronized with the spacecraft procurement cycle, which in general is paced by the scheduled ready-to-launch date. The actual launch date may be delayed by several years because of the continued operation of the on-orbit spacecraft.
Technology insertion into the space segment is a discrete process that culminates only when a spacecraft is launched. As discussed above, the expected time between launches is likely to lengthen as the program matures and early-life design problems are eliminated. The IPO has stated that failure of one of the NPOESS mission-critical instruments (see Table 3.1 in Chapter 3) will require a replenishment launch.10 Experience has shown that instruments frequently degrade gradually, perhaps losing a channel rather than failing completely. NOAA, as the cost-conscious operator of POES, has been tolerant of instrument degradation and has a complex, and not explicitly stated, decision process for deployment of a replacement spacecraft. The decision factors include the availability of alternative data sets, the specific data loss, the weather parameters affected, and the availability of a replacement spacecraft ready for launch. Under current policy, the fact that an instrument provides data that are important to a climate science record has no bearing on the replacement launch criteria. Partial failure may have only a small impact for operational weather purposes but may induce degradations that are far more significant for scientific purposes. Thus, the IPO’s replacement strategy could have a serious impact on the science community.
In general the IPO has not announced a formal replacement policy in response to the failure of a non-mission-critical payload instrument. The committee has expressed concern about the loss of continuity in data collected from such secondary instruments, which may play a more significant role for climate and other science studies than they do for weather. It seems that the current IPO policy is to not order a launch if a secondary instrument fails, as long as the mission-critical instruments remain viable.
The complementary question is what happens when the spacecraft is replaced early (in response to the failure of one instrument) and the other instruments are still performing satisfactorily. The histories of POES and DMSP indicate that it is difficult to maintain operational status for spacecraft that have failed partially at the same time as their replacements are also in orbit. The main problems are conflicts at the downlink data readout and command and control stations, and the additional burden on all ground facilities and personnel. If additional NPOESS spacecraft are to be operated after a replacement launch, additional resources (including funds) will be necessary.
A CONTINUING NPOESS SYSTEM AUGMENTATION PROJECT
NASA and the NPOESS IPO are formulating final plans to build, launch, and operate an NPP satellite as a bridge mission between the current POES/DMSP and the future NPOESS series. The goals and objectives of the NPP mission are to validate critical and new instruments, algorithms, and processing for NPOESS, as well as to provide continuity for selected science and climate measurements. The NPP was conceived as a bridge between science and operations. Experience has shown that proving in practice the value of a candidate research instrument is often the crucial step in developing it for operational use. A satellite program such as NPP can provide just such an opportunity.
The dichotomy between operational and research systems suggests that a separate and continuing series of spacecraft would be a useful adjunct to NPOESS. Such a program could support short-term studies, serve as a technology development testbed for instruments and spacecraft, and help to ensure continuity of noncritical measurements. Unfortunately, NPP may be only a one-time opportunity, as NASA has no plans to continue it. Nevertheless, the concept of an ongoing bridging capability between the scientific and operational arenas is very appealing. This should be closely tied to the IPO.
NASA views the NPP as a means of continuing certain EOS measurements and as a demonstration platform for selected NPOESS instruments. The mission is in the concept-development stage, and not all the requirements are fixed. The next stage, in which the level 2 and level 3 requirements will be developed, will provide more detail. The timing of the mission is important for the continuity of data. EOS-AM (Terra) and EOS-PM (Aqua) will complete their expected mission lives in 2006 and 2007, respectively. NPOESS does not launch until 2009, and this could be delayed if the POES system survives beyond its predicted lifetime (which is probable, based on past performance). METOP-1 launches in 2003, but it does not include new NPOESS instruments.
The flight of NPP is planned for 2005 (IPO, 1999) with the Advanced Technology Microwave Sounder (ATMS), CrIS, VIIRS, and possibly a fourth instrument. The NPOESS program development and risk reduction (PDRR) phase calls for a study of system enhancements to ensure the system’s readiness to accept NPP data. The NPP data will not be processed exactly like the NPOESS data, although the front-end processing will be similar. There will be a best-effort attempt to produce environmental data records (EDRs). The EDR algorithms produced from the NPP are expected to converge to production quality, but the time required for the products may be greater than the 3 hours required for NPOESS products. This approach is being taken by the IPO to facilitate and speed the development of the Integrated Data Processing Segment that is planned to process data from NPOESS satellites.
The NPP system architecture also incorporates a science data system that will produce science data records (SDRs) and climate data records (CDRs). This research side of the NPP data system is expected to support a number of science projects through the announcement-of-opportunity process. This is the bridge from EOS to NPOESS. The CDRs and the SDRs will need to be defined as the program matures.
The details of NPP data processing will be developed in the next few years as the NPP and NewDISS (New Data and Information System and Services) designs mature. The committee is in favor of this early proof of concept and validation of the instruments, algorithms, and processing systems. With a flight planned for 2005, NPP precedes NPOESS by a sufficient margin to allow correcting any problems in the ground system before NPOESS becomes operational.
NASA STRATEGIES AND PLANS FOR TECHNOLOGY DEVELOPMENT
Earth Science Enterprise Technology Development Plan
Goals and Themes
In 1999, NASA’s Earth Science Enterprise (ESE) published its technology strategy (NASA, 1999). A summary provided in the Introductory Letter states as follows: “To insure timely technology availability, the Enterprise has established a strategically driven technology development program with two primary objectives.
The first is to accomplish the defined ESE missions more efficiently and effectively, and the second is to enable new fundamental and applied research programs essential for meeting the long-term Enterprise goals.”
These goals are to be accomplished through the Technology Development Plan, which includes both near- and long-term projects with a flow of promising developments into ESE missions. The Instrument Incubator Program and the ESE core technology initiatives are also being developed to meet ESE needs. The New Millennium Program (NMP) is the space demonstration segment of the approach. It was originally conceived as a technology improvement program for deep-space missions but has been expanded to include Earth observation.11 The NMP includes six areas of technology (listed below), which can be applied to any type of spacecraft if the projects are chosen correctly. It is the choice of demonstration projects that makes the results more or less specific to a class of systems (e.g., deep space or near Earth observation).
In situ instruments and microelectromechanical systems,
Instrument technology and architecture, and
Modular multifunctional systems.
The goal statement12 for the instrument technology and architecture (IT&A) group promises as follows:
The Instrument Technologies and Architectures IPFT is focusing on the identification, development, and validation of revolutionary technologies that will enable new science measurement capabilities in the 21st century, or that will provide current capabilities at a significantly lower life-cycle cost. The emphasis on reducing overall science mission cost, while increasing the science return through increased mission frequency, results in a strategy of miniature microspacecraft and instrument systems. Consequently, technologies that contribute to system requirements of lower power, mass, and volume while maintaining or enhancing performance and reliability are of particular interest. Special attention will be given to technologies that enable the development of highly integrated, multi-function observational systems.
The New Millennium Science Working Group has identified and defined science measurement capabilities in support of the programs of Mission to Planet Earth, Solar System Exploration, Origins, Structure and Evolution of the Universe, and the Sun-Earth Connection. These capabilities are used as a guide for identifying and selecting IT&A technology candidates for flight validation by the NMP.
However, concerns have been raised about the direction of the NMP, specifically that there has been an overemphasis on microsatellites, and the related technologies may not be applicable to NPOESS-type missions, which are concerned with more conventional Earth observation. The committee does recommend that technology development should continue and, specifically, that part of the effort should be focused on reducing cost. Both nonrecurring and recurring costs need to be addressed, but in a long-term operational program recurring costs are most important because of the number of copies that will be procured. Additional effort is needed to develop instrument technologies that reduce the costs and development times. Larger instruments, such as those in the EOS program, have a development time of about 10 years. It takes about 60 months to go from a phase B concept to a flight instrument, but the time from initial concept to flight can be highly variable and quite long. Shortening this time would greatly reduce the costs and provide a faster return of science data, which is the goal of all the new NASA initiatives.
The overall goals were discussed by the Jet Propulsion Laboratory program manager, E. Kane Casani, in an interview for Space News (Space News, 1996).
This information was available in November 1999 from the Jet Propulsion Laboratory Web site at <http://npm.jpl.nasa.gov/tec/index>.
The site provides information about NMP, but the information is subject to change.
NASA’s ESE has generated three interlinked themes (NASA, 1999), which are captured as ESE’s level I requirements:
Development of instruments and information systems to support coupled Earth systems studies;
Development of information system architectures to greatly increase the number of users to tens of thousands over 5 to 7 years; and
Development of partnerships with industry and operational organizations.
There are also concerns about both the schedule and the decision process in the NMP. The present schedule does not suit NPOESS needs and it is not clear if it can be shortened to have an impact on NPOESS. It is also not clear who makes the decisions on what technology will be pursued. A technology subcommittee of the ESE Earth System Science and Applications Advisory Committee is said to be the guiding body, but as this report was written its membership was not known and it was not clear how the subcommittee would interact with the operational programs. The NASA contribution to NPOESS is technology, and the needs of NPOESS must be addressed by the goals of the ESE program.
The ESE plan is to have demonstration instruments and other technologies ready in the 2003 to 2009 time frame. This is rather late if the aim is to get them into the first NPOESS flight cycle. However, this schedule does depend on when the first flight actually occurs. Although economics may favor a delay, that is, use of the POES/ DMSP spacecraft for as long as they are available (potentially to 2014), it will be necessary to start developing NPOESS early to be prepared in case it must fly as early as 2007. This reduces the probability that the ESE initiatives will have an impact on NPOESS. The climatology community favors earlier flight of NPOESS to ensure overlap with the long-term POES data sets (AVHRR, Microwave Sounding Unit, etc.).
The ESE Technology Development Plan appears to be coherent and to make sense for ESE’s mission types. However, the committee is concerned that missions have not been fully defined in terms of the interaction between science objectives and enabling technology. Furthermore, as of February 2000, mission funding had not been clearly delineated, nor had the Technology Development Plan been implemented.
The committee is concerned that NASA/ESE’s current approach to mission implementation is too ad hoc and could lead to a fragmented collection of small missions.13 The committee makes a distinction between small missions and small satellites, because a larger mission can use several small satellites (or one). A system consisting of many small satellites flying in formation and using data fusion may not be a small mission. The general position of the committee is that a mix of mission sizes and satellite sizes is required and that each mission must be addressed on its own merits (NRC, 2000c).
Integration with NPOESS
It is noteworthy that the ESE Technology Development Plan does not provide for transitioning the technology from scientific status to operational status. This fact is central to the question of technology insertion into NPOESS in support of climate or other scientific objectives. Even if a new technological innovation is proven to be feasible, there are currently no plans to carry it forward once NASA’s scientific missions have ended. One of the three divisions of the IPO, the Technology Transition Division, is led by NASA. There is little linkage between that office and the NASA office that drafted the ESE technology strategy. In spite of its name, the Technology Transition Division is responsible mainly for contractor oversight of the operational instruments now being developed for NPOESS.
The NASA plan also addresses spacecraft hardware and operations. It gives a general impression of the direction ESE expects spacecraft systems to take. A heavy emphasis on formation flying of small spacecraft, including instrument calibration and data fusion considerations, portends the use of smaller spacecraft, but not necessarily single-spacecraft small missions. Although smaller spacecraft can reduce certain costs, they do not necessarily reduce overall mission cost, a point discussed in the report The Role of Small Satellites in NASA and NOAA Earth Observation Programs (NRC, 2000b), which recommended that NASA continue to use a mix of mission and spacecraft sizes to maintain a balanced approach.
NASA’s ESE will also support research into ways to simplify the methodology for the design and building of spacecraft. This is a commendable goal that has been neglected somewhat in the past. Previous attempts to use modular systems did not fare well and the costs were often higher than those for conventional methods.
In addition, ESE is looking into how to greatly reduce resource requirements (mass, power, etc.), a necessary condition if smaller spacecraft are to be used and the payload fraction increased. The committee believes that instrument development must also be part of this effort. While there are lower limits on the size of instruments to achieve a certain resolution and signal gathering, other aspects of instruments are amenable to size reduction.14
Other areas of development include increased autonomy, on-board data fusion and inter-instrument data comparisons with autonomous and adaptive strategies, and advanced communications. On-board data fusion is an area that will require cooperation from the science community. Past efforts to perform data processing on the spacecraft have met with resistance from the science community. The science community in general and the climate research community specifically require the raw data records so that retrospective processing can be performed as knowledge of the sensor, models, or physics improves over time. With on-board processing there is concern over loss of data and loss of ability to reprocess the data when better algorithms are developed. In the interplanetary missions, data compression and processing have been accepted, because the difficulty of transmitting large volumes of data overrides the other issues.
The committee recognizes the consequences and risks of technology insertion on the operational performance of the system. Its findings on technology insertion are as follows:
Operational agencies naturally tend to resist change; any candidate technology enhancement to increase the science content of data products must satisfy rigorous prequalification before being accepted into an operational payload.
The challenge for an operational meteorological satellite system such as NPOESS is to find a way to accommodate technological change in a timely manner while ensuring that the modified system sustains operational functionality.
In general, the means for insertion of technology into operational missions is not well determined. Indeed, there appears to be a gap between the development of instruments in the science stream and their adoption in the operational stream.
If the NPOESS program is to be used to support the science community as well as the operational weather agency, the pertinent science requirements must be carefully assessed in the early phases of the program.
Technology insertion always will be subject to limitations. Any downstream change in the on-board technology must fit within the spacecraft resources (mass, power, data bandwidth, data volume, etc.) that may remain over and above the requirements of the baseline system.
It is likely that the development and qualification of any new measurement capability that might be required for scientific purposes would have to be funded from non-IPO sources, unless that instrument were
deemed to be critical to the NPOESS operational mission. Clearly, vision and well-coordinated interagency planning are needed to sustain the development of suitable instruments in synchronization with NPOESS flight opportunities.
Unlike the relatively short design lifetimes of their predecessors, the NPOESS satellites will have a 10-year design lifetime. While such a long life is laudable for an ongoing operational facility, it impedes the process of technology insertion.
If an instrument provides data that are important to a climate science record, under current policy this fact has no bearing on the launch of an NPOESS replacement spacecraft. Partial failure, even of a mission-critical instrument, may have such a small impact for operational weather purposes that it does not trigger a replacement launch. However, the same small fault could induce degradations that would be far more significant for scientific purposes.
An opportunity to prove in practice the value of a candidate instrument is often a pivotal step in the effort to translate a scientific measurement into an operational tool. A satellite program such as NPP could provide such opportunities.
It is noteworthy that the ESE Technology Development Plan does not provide for transitioning the technology from scientific status to operational status. This fact is central to the question of technology insertion into NPOESS in support of climate or other scientific objectives. Even if a new technological innovation is proven to offer unique scientific value and is shown to be technically feasible, there are no current plans that would guide its transition to NPOESS.
A study of the use of small satellites (NRC, 2000b) noted the advantages of using a mixed fleet of missions, rather than trying to achieve all operational, research, and technological objectives with one type of spacecraft. Although there are resources for additional sensors on the NPOESS spacecraft, opportunities to include small spacecraft with one or two sensors should also be pursued. Such spacecraft could even be placed in nonpolar orbits to maximize their contribution to both weather and climate measurements.
The committee’s findings all point to the need to maintain an open and flexible system that can accept new technology, which includes new instruments. The desire to use the operational meteorological system for research places demands on both the IPO (for the operational use) and NASA and NOAA (for climatology research use). Because of the ongoing competition for the NPOESS total system performance requirements contract, it was not obvious to the committee which issues are being addressed, and the following more specific recommendations are intended to provide guidance. On the climate research side there is no designated agency, but NASA and NOAA are the stakeholders. NASA has a vested interest in using NPOESS to satisfy some of its plans, and NOAA has responsibility for the long-term archiving of data to support the needs of the climatology community.
The IPO should identify a person or group to review the NPOESS system requirements and the design to ensure that both the IORD and the contractor approaches will support flexibility and change.
NASA should provide a list of science requirements (presumably from the Science Plan) and climate requirements that are candidates for implementation on NPOESS.
The IPO should plan for the insertion of new or enhanced measurement capabilities into NPOESS that would likely have to be funded from non-IPO sources.
NASA ESE should implement its Technology Development Plan with firm plans linked to missions and ensure that any necessary NPOESS enabling technologies are covered in the plan.
NASA and the IPO should devise an approach to support accepting additional experiments on NPOESS.
It is essential that the process of incorporating research requirements into NPOESS be started now and be allowed to influence the program development and risk reduction phase that is in progress, without disrupting the primary NPOESS mission. Opportunities for change after the launch will be limited by the longer satellite lifetime and longer intervals between launches.
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