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Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions (2000)

Chapter: Appendix E Material Provided by Space Studies Board Discipline Committees

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Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
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E

Material Provided by Space Studies Board Discipline Committees

Two of the assignments for the Space Studies Board discipline committees (see Appendix C) were to identify examples of ongoing and planned missions in different sizes that address near-term (10 years) and far-term (10 to 20 years) science objectives in the discipline, and to identify criteria for evaluating the mix of missions chosen for the portfolio. This appendix presents the material submitted by the board’s discipline committees in response to the assignment. In addition, each discipline summary includes a table showing a nonexhaustive set of ongoing and planned missions (including international missions) and their scientific objectives or parameters, life-cycle costs, size (as defined by NASA for the study), status, and estimated lifetimes.

EARTH SCIENCE

Arguments for a Portfolio of Mission Sizes

There are powerful arguments for having a broad portfolio of mission sizes to achieve near-term (10 years) and far-term (10 to 20 years) goals in Earth science. In each application, the scientific objectives and the specific mission goals will generally dictate the size range of the spacecraft. The need continues for the capabilities offered by several larger platforms such as NASA’s Earth Orbiting System Chemistry Satellite (EOS-CHEM) mission: multiple instruments, extensive redundancy, and long lifetimes. Smaller missions aimed at well-focused and relatively short-term objectives allow for separate new starts to maintain pace with emerging scientific interests and needs. NASA’s Earth System Science Pathfinder (ESSP) program is an excellent example of this small mission paradigm.1 Smaller spacecraft can also reduce the time to “first science,” if the instruments are already available (i.e., no development is required).

1  

The ESSP program was initiated by NASA in 1996. The program is intended to apply the spirit of FBC to the Earth Science Enterprise. Proposals submitted by the community in response to announcements of opportunity must offer principal-investigator-led, end-to-end flight missions within tight constraints. The proposed missions must also have (1) a significant and well-focused science objective, (2) a cap on the cost to NASA, typically $120 million, (3) minimal reliance on unproven or high-risk technology, (4) time to launch of less than 3 years, and (5) flight mission duration of nominally 2 years. NASA’s plan is to conduct ESSP opportunities every 2 years or so, selecting 2 missions each round.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Larger Spacecraft

The principal arguments in support of larger spacecraft are (1) beneficial aggregation of instruments and (2) accommodation adequate to support large instruments. Increased science requirements or the need for more comprehensive data sets lead to significant growth in several instruments central to Earth science applications.2 This growth is driven by increases—sometimes by large factors—in the required spatial resolution, number of spectral bands, and signal amplitude resolution (bits per sample).3 These and similar enhancements call for larger apertures, higher data rates, greater power load, more severe thermal control requirements, and more stringent pointing requirements, among other things. The demand from the scientific community for increased performance has outstripped the ability of technology to keep pace.4

Smaller Spacecraft

The principal arguments in support of smaller spacecraft are that (1) they suffice to meet modest, well-focused objectives, (2) they minimize the time to science, and (3) they reduce the cost of achieving certain science objectives. A significant corollary is that with more new programs, there is a greater potential to increase the number of investigators and students involved from start to finish in space-based Earth observation. Small satellites, and by implication less complex missions, tend to be most effective when directed toward well-focused, short-term objectives. They can provide a rapid response for some missions if the required instruments have already been developed, presumably through a separate, adequately funded preparatory program. The concept of small satellites may also, however, connote higher risk and development shortcuts.5 “Cheaper” should be interpreted as “more cost-effective” rather than “short-changed” if the faster-better-cheaper (FBC) philosophy is to have value in the long run. Small satellites also have the reputation of being short-lived, although there is no intrinsic reason for this to be so.6 New technology coupled with cost-effective design and implementation practices would make multiple small satellite options appealing alternatives to large, multi-instrument systems for certain science applications. However, these faster-better-cheaper and (sometimes) smaller missions must not be invented ad hoc but should fall within a comprehensive long-term science plan.

2  

Space Studies Board, National Research Council, Earth Observations from Space: History, Promise, Reality, National Academy Press, Washington, D.C., 1995.

3  

As noted in Chapter 3, research advances in long-term weather forecasting and the development of climate computer models have increased the requirements for horizontal and vertical resolution for temperature and moisture atmospheric profiles. The need for 1-km vertical resolution will necessitate larger instruments.

4  

SSB, Earth Observations from Space, 1995.

5  

See Space Studies Board, National Research Council, The Role of Small Satellites in NASA and NOAA Earth Observation Programs, National Academy Press, Washington, D.C., 2000, p. 54, which discusses the risks involved in employing small satellites:

The small satellite approach carries with it several risks concerning scientific return:

1. Rapid development missions are often focused on “small” problems. Missions are not designed for long life and are sometimes viewed as “one shot” opportunities.

2. Missions employing small satellites are more likely to be developed as part of a program of technology demonstrations as opposed to a program in which the science return is paramount.

3. Small missions require a well-defined focus to keep them simple and the cost low. This approach may not work well for scientific studies that require measurements of many processes.

4. Data processing and distribution may be related to relatively lower priority, thus making it difficult for nonproject scientists to gain access to the data. This problem could be exacerbated in the case of missions led by a principal investigator (PI) should research investigations become centered on an individual’s personal scientific interests.

5. With more single-sensor missions, the proportion of funds spent on satellite hardware and launch vehicles will increase. Such funds might otherwise be spent on scientific research.

6  

For example, one of the early and very small Transit navigation satellites maintained full operational status for 22 years.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

A satellite should be as large as necessary, but no larger than needed to carry out its mission; the overall program should be funded sufficiently, but no more than necessary to complete its tasks. Objective cost trade-offs can be used to determine the right size for a spacecraft.7

If budget is the dominant consideration, low-cost missions generally bear higher risk, both in development and in operation, as was made all too clear by Lewis and Clark and the more recent Mars missions.8 If reliability is compromised by a lack of redundancy or for other cost-reduction reasons, the spacecraft life may be curtailed. Some of the smaller, cheaper programs have been successful (e.g., QuikSCAT), but in general, short schedules and mission success depend on the availability of previously developed instruments and a baseline spacecraft as well as efficient and effective mission management and operations.9

Need for Long-Term Measurements

Programs such as the Earth Observing System (EOS) that have long-term science objectives (the measurement of climate variables, for example) cannot be replaced by short-term limited missions. Long-term and broad-based systematic measurements require a long-term commitment. Such a commitment could be met by a mix of satellite sizes if well-planned and coordinated.10 The SSB’s Committee on Earth Studies recently completed an analysis of issues related to the transitioning of NASA research satellite instrumentation for NOAA’s operational use and conducted a workshop on joining the Integrated Program Office (IPO)/NPOESS and NASA/Earth Science Enterprise capabilities for climate research. Among the conclusions, the Committee on Earth Studies notes that climate studies require long-term measurements, revision and independent validation of the algorithms, ability to reprocess older data, and good characterization and calibration of instruments.11

7  

SSB, Earth Observations from Space, 1995, p 134.

8  

The Small Spacecraft Technology Initiative (SSTI) was developed by NASA’s Office of Space Access and Technology to advance the state of technology and reduce the costs associated with the design, integration, launch, and operation of small satellites. In July 1994, TRW and CTA Space Systems were each awarded a contract by NASA to design and launch small Earth-observing satellites, one named “Lewis,” the other named “Clark.” Both contracts called for substantial infusion of new technology into both payload and spacecraft bus and for delivery of the satellites to launch in only 24 months following contract start. Both missions were unsuccessful. In the case of Lewis, the satellite development was completed within the allotted 24-month period and, after a 1-year delay before its Athena-I (LMLV-I) launch vehicle was deemed flight-ready, the satellite was successfully placed into its initial orbit in August 1997 and was subsequently lost. The Clark mission suffered excessive schedule delays and projected cost growth, ultimately leading to termination of the contract.

9  

“The often complex evaluation of whether the use of a small satellite is appropriate is driven by mission-specific requirements, including those related to the policy and execution of the program, fiscal constraints, and the scientific needs of the end users. Considering the many issues involved, the design of an overall mission architecture, whether for operational or research needs, requires a complete risk-benefit assessment for each particular mission. For some missions, a mixed fleet of small and large satellites may provide the most flexibility and robustness, but the exact nature of this mix will depend on mission requirements” (SSB, The Role of Small Satellites, 2000, p. 5).

10  

An excellent example is provided by ongoing measurements of atmospheric ozone, particularly over Antarctica. TOMS, the Total Ozone Mapping Spectrometer, has flown on four different spacecraft since 1978. TOMS was one of several instruments on three previous large satellites, but the current mission is a small (295 kg) Earth probe. Since TOMS is only a 35-kg instrument, that option works well. From a climate point of view, however, ozone is only part of the story. Climate, or the trend in long-term weather, depends on atmospheric gases and particulates, clouds, moisture, temperature, and their circulation and interaction with the surface, especially the sea’s surface. Climate observations must track all of these key variables for many years. Several of the instruments required are considerably larger than can be accommodated on a small spacecraft.

11  

Issues raised by the integration of research and diverse climate measurements into the operational NPOESS have been studied by the SSB Committee on Earth Studies. Its phase I report, Issues in the Integration of Research and Operational Satellite Systems for Climate Research: I. Science and Design, emphasizes the potential science value of operational weather observations and examines the fit between NPOESS and the climate requirements with respect to a set of eight environmental variables. Issues in the Integration of Research and Operational Satellite Systems for Climate Research: II. Implementation, which is forthcoming, focuses on technology and related spacecraft issues.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Example of a Portfolio of Mission Sizes

Examples abound in the Earth sciences of a wide variety of Earth-observing missions and their satellites. Selected Earth observation missions drawn from NASA’s current plan12 are provided in Table E.1. Missions shown in the table are meant to be representative of the current and projected mix of satellite sizes.

Terra, the first satellite in the EOS program to be launched, and its companions, EOS-PM (now Aqua) and EOS-CHEM, are survivors after a decade of recurrent revisions of NASA’s EOS plans. All three are large13 satellites, with a design life of 5 or 6 years. The original EOS plans for these missions spanned 15 years, to be implemented by a series of three nearly identical satellites in each sequence. All were to share a large common bus, which promised certain economies of scale to reduce their aggregate cost; however, the common-bus approach has been abandoned. Landsat-7 has a long history, the Landsat series having been returned to NASA after a complicated path originating at NASA in the 1970s, passing first to the commercial world, next to NOAA, and then back to NASA. It is part of a sequence of Earth-imaging systems that provide an important source of data for environmental and land process studies. Whether Landsat-like observations will continue beyond Landsat-7 is under discussion.

The weather satellites GOES, POES, and NPOESS are first and foremost operational weather satellites. Their data, which now span more than 40 years, provide the most important space-based record of climate and environmental variables. These data are and will continue to be in demand for scientific studies. The NPOESS Preparatory Project satellite appears to be unique, providing a one-time opportunity to validate new technologies and instruments of interest for NASA research and NOAA’s operational activities. UARS, launched on the space shuttle in 1991, continues to provide an important series of upper atmospheric observations. Its large size is as much a reflection of the relatively unconstrained mass limitations of the shuttle as it is a consequence of its mission. The Ocean Topography Experiment (TOPEX)/Poseidon and Jason-1 are the two currently funded precision ocean altimeter missions in which the United States has a major role. SeaWiFS, an instrument flown in a precedent-setting commercial partnership with the private sector, provides an important source of ocean color data.14 EO-1, the first of the New Millennium satellites,15 is designed primarily as a technology demonstration platform; science (if any) is secondary.

The Gravity Recovery and Climate Experiment (GRACE) (ESSP-2) is a good example of the faster-better-cheaper system encouraged by the ESSP program. Total mission costs are about twice those billed to NASA, thanks to major foreign contributions. GRACE would not be possible without extensive prior developments, including a large science base and an existing spacecraft design, Challenging Minisatellite Payload (CHAMP), for a European mission. Note also that the science objective of GRACE cannot be met by one satellite, as it takes two satellites to capture the level of detail in Earth’s gravity field to be mapped by GRACE. In turn, a twin-satellite mission would not be feasible, technically or financially, without the motivation afforded by the spirit of FBC.

12  

Available at <http://www.earth.nasa.gov/missions/2002/index.html>.

13  

Small, medium, and large are meant to convey total system cost, as defined by NASA. Because such numbers are often controversial and the cost may be complicated by extensive international participation, spacecraft mass is also listed, where known, to provide an objective indication of the size of each satellite.

14  

NASA’s coastal zone color scanner (CZCS), hosted on a Nimbus-7 satellite in the 1970s, first proved the importance of such data. Neither CZCS nor its equivalent was adopted by NOAA as an operational instrument.

15  

The New Millennium program is a technology demonstration program to validate technology in spaceflight that will lower the risks to future science missions using the technologies. The program draws on existing government-funded research and development efforts.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

TABLE E.1 Selected Earth Science Missions

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

ONGOING

QuikSCAT

Ocean winds, sea ice storm patterns

Small,

970 kg,

$95 million

Ongoing

1999-(2-yr design)

SeaWiFS

Ocean color (commercial system)

N/Aa

Ongoing

1997

TRMM

Tropical rainfall

Medium,

$296 million

3,600 kg,

Ongoing

1996-

POES

Meteorology/weather (original TIROS–NASA)

Large,

2,250 kg

Several in orbit

1960-2010 (2-yr design)

GOES

Meteorology/weather (original SMS–NASA)

Large,

2,100 kg

Several in orbit

1974-

UARS

Upper atmosphere (10 instruments)

Large,

6,800 kg,

$750 million

Ongoing

1991-

TOPEX/ Poseidon

Ocean altimetry

Large,

2,500 kg,

$450 million

Ongoing

1992-(5-yr design)

Landsat-7

Medium-resolution, multiband Earth imager

Large,

2,200 kg,

$447 million

Ongoing

1999-(5-yr design)

Terra (EOS-AM)

Earth and atmospheric study

Large,

5,190 kg,

$1.2 billion

Ongoing

1999-(5-yr design)

PLANNED

ESSP-2 (GRACE)

Gravity field mapping (two spacecraft constellation) and cooperation with Germany

Small,

NASA, $86 million;

Germany, $45 million

Planned

2001 (2-yr design)

EO-1

Technology: land mapping instruments

Medium,

530 kg,

$162 million

Planned

2000

ICESat

Laser altimetry measuring ice-sheet topography and temporal changes, cloud and atmospheric

Medium,

$227 million

Planned

July 2001

Jason-1

Ocean altimetry

Medium,

Planned

2001

500 kg, (5-yr design)

$160 million (French-led mission; NASA contribution, $94 million)

Aqua (EOS-PM)

Earth and atmospheric study

Large,

3,120 kg,

$880 million

Planned

2001 (6-yr design)

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

EOS-CHEM

Tropospheric chemistry

Large,

2,970 kg,

$670 million

Planned

2002 (5-yr design)

NPP

Flight of opportunity, plus new instruments

Large,

Estimated $800 million: (5-yr design) $500 million from NASA; remainder from DOD and NOAA

Planned

2005

NPOESS

Meteorology/weather

Large, $ N/Aa

Planning

2008-2020 (10-yr design)

aNA, not available.

Criteria for Evaluating the Mission Mix

Previous Space Studies Board reports identified several criteria that can be used for evaluating the balance of missions in the Earth science portfolio.16 In addition to being assessed on their individual scientific merit, missions are assessed based on the extent to which they do the following:

  • Address the high-priority scientific goals;17

  • Serve the needs of the U.S. Global Change Research Program;

  • Reflect the need for sustained, long-term observations as well as for short-term, focused research;

  • Respond to the need to facilitate the transition from research to operations;

  • Incorporate and justify appropriate new technology without being technology-driven;

  • Involve the science community in overall planning;

  • Allow for increased risk in individual, specialized missions;

  • Balance spacecraft design against instrument reliability and mission time horizon; and

  • Recognize the need for stable funding for a diligent, sustainable, and productive program.

Several of the criteria underscore the need for long-term planning in the space-based Earth science program, as stated in two Space Studies Board reports:

The planning process should be an orderly one that is aimed at minimizing the continual changes. The process also must include more attention to intricate issues associated with … ensuring the continuity of key long time-series measurements.18

and

16  

Space Studies Board, National Research Council, “Report of the Task Group on Assessment of NASA’s Plans for Post-2002 Earth Observing Missions,” letter to Ghassem Asrar, associate administrator, Office of Earth Science, NASA, April 8, 1999, pp. 5-9.

17  

Board on Sustainable Development, National Research Council, Global Environmental Change: Research Pathways for the Next Decade, National Academy Press, Washington, D.C., 1999.

18  

Space Studies Board, National Research Council, “Report of the Task Group on Assessment of NASA’s Plans for Post-2002 Earth Observing Missions,” letter to Ghassem Asrar, associate administrator, Office of Earth Science, NASA, April 8, 1999, p. 15.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

… the CES [Committee on Earth Studies] believes that the needs of research in the Earth sciences and applications should not be continually deferred until the development of new, unproven technologies. The prospect of lower cost is always attractive, but the practice of placing new technology developments ahead of the conduct of basic and applied research has been disruptive to the Earth sciences for more than two decades.19

PLANETARY SCIENCES

Arguments for a Portfolio of Mission Sizes

The Space Studies Board’s strategy report for the planetary sciences, An Integrated Strategy for the Planetary Sciences: 1995-2010, covers a diversity of topics and objectives, including studies of protoplanetary disks, planetary systems about other stars, primitive bodies, the origin and evolution of life, the surfaces and interiors of solid bodies, and planetary atmospheres, rings, and magnetospheres.20 The scientific, technical, and operational aspects of planetary exploration require a range of mission sizes.21,22 Large missions are necessary to approach future high-priority scientific goals such as a sample return from a comet nucleus or from the surface of a planet or satellite, a comprehensive survey of a giant planet (with atmospheric and satellite probes), and extensive exploration of Mars in preparation for human missions.23 Small missions are critical for continuing the introduction and infusion of new technology and for addressing very tightly focused scientific goals. The current mix of planetary-science missions seems to reflect this balance. However, there is a growing emphasis on medium-size missions that is affecting the balance.

Example of a Portfolio of Mission Sizes

Table E.2 shows examples of planetary science missions that span the range of sizes. It includes planned missions as well as missions that are currently operating. Many of the ongoing and planned missions are medium-size missions (or nearly so) in the Discovery line. The few low-cost missions are either at the low end of Discovery (e.g., Contour) or are non-NASA or international missions for which the total costs are uncertain (e.g., Nozomi). Some missions (e.g., Europa Orbiter and Pluto-Kuiper Express) have officially been classified as large missions, but they are near the medium-size cap of $350 million. Many larger missions are either conglomerate missions (Mars Sample Return) or missions involving international collaboration (e.g., Rosetta or Mars Express), whose costs are uncertain.

19  

SSB, Earth Observations from Space, 1995, p. 134.

20  

Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, pp. 3-6.

21  

“… Priority scientific investigations [identified by the Integrated Strategy] can be addressed by the full gamut of techniques, including small (inexpensive) and large (expensive) robotic probes, ground- and space-based observatories, and laboratory studies and theoretical modeling” (SSB, Integrated Strategy, p. 186).

22  

“Many diverse objects across the solar system must be studied to achieve the broad goals of planetary and lunar exploration [outlined by COMPLEX]. An effective program for lunar and planetary exploration also dictates a mix of mission sizes, ranging from comprehensive missions with multiple objectives, such as Galileo and Cassini, down to relatively low cost missions, such as those in the Discovery program” (SSB, The Role of Small Missions, 1995, p. 27).

23  

“The long travel times between Earth and the outer solar system require long-lived components, specialized power systems, and complex, high-powered communications. This implies that, with current technology, any mission sent beyond the asteroid belt must be very capable. In addition, many [priority studies] require concurrent coordinated observations between the different components of a particular planet or comet (e.g., simultaneous in situ and remote-sensing observations of Titan’s atmosphere by Huygens and Cassini, respectively). Thus, COMPLEX believes that many solar system missions, especially those to the outer solar system, cannot be adequately accomplished by reconfiguration of large spacecraft into one or more small spacecraft” (SSB, Integrated Strategy, pp. 182-183).

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

TABLE E.2 Selected Planetary Exploration Missions

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

ONGOING

NEAR

Asteroid rendezvous

Medium,

503 kg,

$224 million

Ongoing

1996

4-yr cruise

1-yr operations

Mars Global Surveyor

Mars mapping mission

Medium,

1,030 kg,

$273 million

Ongoing

1996 5 years

Nozomi

Atmosphere and ionosphere of Mars; U.S. contributed NMS instrument

Medium,

Japanese-led mission; U.S. contribution,

$6 million

Ongoing

Launched 1998

Stardust

Collect comet material

Medium,

380 kg,

$205 million

Ongoing

February 1999 7 years

Galileo

Jupiter orbiter and probe

Large,

$1,425 million

Ongoing

Launched 1988, in orbit 1995-

Cassini

Saturn system including Titan probe

Large,

5,650 kg,

$2,550 million

Ongoing

October 1997,

over various timescales up to 11 years

PLANNED

Contour

Imaging and spectral maps of three comets

Small,

489 kg,

$144 million

Planned

2002

6 years, 3 flybys

Genesis

Solar wind sample return

Medium,

648 kg,

$216 million

Planned

January 2001

2-yr operations

Messenger

Mercury Orbiter

Medium (Discovery),

$339 million

Planned

Launch 2004

1-yr orbital operations

Deep Impact

Image subsurface of a comet

Medium,

600 kg,

$240 million

Planned

Launch January 2004

1.5 years

Mars 2001 (orbiter and lander)

Mars geochemical mapper

Large,

1,460 kg,

$415 million

Planned

2001,

3-yr orbiter

Europa Orbiter

Europa search for oceans

Large,

1,600 kg, $460 million

 

Planned

Launch in 2003,

6 years

Mars Sample Return (1 French orbiter, 2 U.S. landers)

Mars sample return

Large,

1,800 kg each,

$1,100 million

Planned

2005 and 2007 launches, sample return in 2010

Rosetta (ESA mission, NASA providing 4 instruments)

Comet lander and surface investigation

Large total (U.S. contribution, $39 million)

Planned

January 2003

10-yr cruise plus landed operations

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

Mars Express (ESA mission; NASA providing components of ASPERA-3 (Energetic Neutral Atoms Analyzer) plus other: radio frequency section, transmitter, antenna subsystems for the radar instruments)

Interaction of solar wind with Mars atmosphere

Large total (U.S. contribution, $6.6 million for ASPERA, $27 million for other contributions)

Planned

June 2003 3 years

Pluto-Kuiper Express

Surface and atmosphere

Large,

225 kg,

$354 million

Planned

2004 More than 9 years

Criteria for Evaluating the Mission Mix

The following criteria are proposed for evaluating the current mix of missions for solar system exploration:

  • Addresses high-priority scientific goals;

  • Optimizes science return for the money spent;

  • Exhibits compatibility between mission goals and scale;

  • Demonstrates a balanced-risk strategy;

  • Considers future application of new technologies;

  • Shows balance between technology and science;

  • Involves community in mission/instrument/technology selection;

  • Promotes stable funding and continuous planetary exploration;

  • Is consonant with Deep Space Network (DSN) and mission operations and data analysis (MO&DA) support;

  • Uses diverse modes of mission implementation (principal-investigator-led, university-industry-NASA team, NASA-led); and

  • Incorporates education and public outreach.

SPACE AND SOLAR PHYSICS

Arguments for a Portfolio of Mission Sizes

Solar and space physics are mature sciences in which exploration, discovery, and observations have been carried out in space for more than four decades. The disciplines are now essentially beyond the exploration and discovery phases, although—remarkably—discoveries are still made. The disciplinary maturity requires that future missions must address sophisticated questions that require a coordinated and novel approach—typically involving multiple instruments and even multiple spacecraft—to measure the many physical variables involved and to separate spatial from temporal physical effects. In the past, the disciplines were driven by science questions and priorities and not by mission size per se. That approach—science-driven missions—led naturally to a portfolio of mission sizes that included small, medium, and large missions. As explained below, the diversity and maturity of Sun-Earth Connection (SEC) science and current scientific priorities, even though they are being implemented using FBC principles, continue to necessitate medium-size and occasionally large missions. Thus,

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

the new SEC Roadmap sets forth a community science plan that requires Explorers (small missions), Solar-Terrestrial Probes (medium-size missions), and Frontier Probes (medium and large missions) for implementation. Interdisciplinary missions to the planets (space physics and planetary science) would most likely require large missions (more than $350 million) unless conducted through the Discovery program.

Example of a Portfolio of Mission Sizes

Table E.3 includes an array of currently operating and planned missions in space and solar physics. Some of the missions are important both for addressing science questions and for understanding current space weather conditions.

TABLE E.3 Selected Space Physics Missions

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

ONGOING

IMP-8

Near-Earth solar wind monitor

Small (Explorer),

$ n/a

Ongoing

Launched 10/25/73; far into extended-phase operations

SAMPEX

Observations of solar energetic particles, cosmic rays, precipitating relativistic electrons

Small (SMEX),

$80 million

Ongoing

Launched 7/3/92; continues to 2003

FAST

Electron and ion acceleration, plasma dynamics above auroral zone

Small (SMEX),

$74 million

Ongoing

Launched 8/21/96, 1-year primary plus extended mission as permitted

SNOE

Nitric oxide density and variation in Earth’s upper atmosphere

Small (UNEX),

$12 million

Ongoing

Launched 2/26/98

TRACE

Solar magnetic structures, heating of solar atmosphere, flare onsets

Small (SMEX),

$72 million

Ongoing

Launched 4/1/98, 1-year primary phase, in extended phase

Geotail

Magnetotail dynamics, the near-Earth neutral line, and the magnetopause

Medium,

$150 million (Japanese-led mission)

Ongoing

Launched 7/24/92, 2-year primary and extended phase through 2002

ACE

Interplanetary particles, composition, energy spectrum, solar wind plasma

Medium (Explorer),

$215 million

Ongoing

Launched 8/25/97,

3-year primary plus

2-year extended mission

Wind

Comprehensive measurements of solar wind plasmas, fields, and radio waves upstream of Earth

Large,

$360 million

Ongoing

Launched 11/1/94,

extended to 2003

SOHO

Measurements of solar electromagnetic emissions, the solar interior, the inner heliosphere, and the solar wind (ESA-led mission)

Large,

$430 million, cost is U.S. portion only for instruments, launch, and tracking and missions support

Ongoing

Launched 12/2/95, now in extended phase through 2005

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

Polar

Energy flow into magnetosphere and the ionosphere in polar regions

Large,

$420 million

Ongoing

Launched 2/25/96, extended to 2003

PLANNED

HESSI

Solar flare high-resolution spectroscopy and imaging (3 keV to 2 MeV)

Small (SMEX),

281 kg,

$76 million

In development

Launch 7/4/00, planned 3-year lifetime

IMEX

Dynamics of inner magnetosphere and storms

Small (UNEX),

350 lb,

$13 million

Under study

Launch 8/00

IMAGE

Imaging magnetospheric plasma, boundary layers, and auroras

Medium (MIDEX),

536 kg,

$154 million

Waiting for launch

Launch 3/15/00,

2-yr primary plus extended phase

TIMED

Energy flow and dynamics in the 60- to 180-km region of Earth’s atmosphere, by remote sensing

Medium (STP),

$208 million

In development

Launch 7/01,

2 years of operation

Solar B

Solar magnetic field evolution at photosphere, lower corona

Medium,

875 kg,

$154 million (Japanese-led mission)

Phase A/B

Launch 2003

STEREO

Observe stereoscopically CMEs and solar energetic particles from the photosphere to Earth

Medium (STP),

$318 million (2 spacecraft)

Phase A/B

Launch 2004 on a Taurus

Magnetospheric Multiscale

Turbulence, reconnecting plasma entry at plasma boundaries

Medium (STP),

$ N/Aa

STD in process

Launch 2005 on a Delta 7325

Global Electrodynamic Constellation

Plasma and electrodynamic coupling in Earth’s upper atmosphere/ ionosphere

Medium (STP),

$ N/A

STD in process

Launch 2007 on a Delta 7325

Magnetotail Constellation

3-D dynamic imaging of the outer magnetosphere

Medium (STP),

$ N/A

STD in process

Launch 2008 on a Delta 7325

Solar Polar Imager

Solar polar fields, origin of solar wind and activity cycle

Medium (Frontier Probe),

$ N/A

Under study

Launch 2010

Solar Probe

Coronal heating, acceleration mechanism of solar wind

Medium (Outer Planets),

$156 million

Planning, under study

Launch 2010 (?)

Interstellar Probe

Explore outermost heliosphere and interaction with local instellar medium

Large (Frontier Probe),

$ N/A

Under study

Launch ~2010

CLUSTER II

3-D study of plasma using 4 identical spacecraft at magnetospheric boundaries and magnetotail, separating space and time variations

Large (ESA/NASA mission, NASA contribution $14.3 million to replace the U.S. instruments)

In development

Launch June and July 2000 (by 2 Soyuz rockets)

aN/A, not available.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Criteria for Evaluating the Mission Mix

The recent Roadmap exercises conducted by the Sun-Earth Connection theme reflect the portfolio of mission sizes recommended by the solar and space physics science communities to address current scientific priorities.24 Determined and pragmatic efforts were made in these exercises to adhere to NASA’s expectations of FBC and NASA’s budgetary trends, with the result that most of the missions recommended were made to fit into the Solar-Terrestrial Probe (STP) program. An STP is capped at $250 million and has an anticipated launch rate of about one every 18 months. Quoting from the 1997 Roadmap document:

The majority of the candidate missions described in the Roadmap would be implemented under NASA’s STP program, which offers a continuous sequence of flexible, cost-capped missions designed for the systematic study of the Sun-Earth system. The strategy embodied in the STP mission line is to use a creative blend of in-situ and remote sensing techniques and observations, often from multiple platforms, (i) to provide understanding of solar variability on time scales from a fraction of a second to many centuries, with an underlying activity cycle of approximately 11 years; and (ii) to determine cause (solar variability) and effect (planetary and heliospheric response) relationships over vast spatial scales. The latter objective generally requires innovative multi-spacecraft and/or missions operating concurrently.25

A portfolio of missions to carry out the scientific objectives in space and solar physics is reflected in Table E.3, which shows that both ongoing and planned missions span the full spectrum of small, medium, and large sizes. Small and medium missions in the plan have focused scientific objectives. Certain other scientific requirements can be met only by large missions: a long observation time line (solar variations or sunspot cycle effects); multiple instruments of high resolution (microphysics of particles and fields); highly stable platforms (for remote observations); vast physical parameter ranges in the operating environment (heliospheric observations outward to interstellar space); interdisciplinary missions (planetary missions to investigate both the planet and its environment); and use of multiple spacecraft or constellations (to separate spatial and temporal effects or to make complementary observations simultaneously).

ASTRONOMY AND ASTROPHYSICS

Arguments for a Portfolio of Mission Sizes

The importance of having a mix of mission sizes and costs to pursue space astronomy and astrophysics has long been recognized by the astronomy and astrophysics community. For example, the previous astronomy and astrophysics survey committee (the Bahcall committee) noted in its 1991 report, The Decade of Discovery in Astronomy and Astrophysics, that a vigorous program in space astronomy and astrophysics requires a proper mix between small, moderate, and large missions.26

The goals identified by the Bahcall committee and NRC strategies27 are broad and diverse and can be answered in a cost-effective way only through a coordinated program. In addition to suiting the scientific and physical requirements, a mix of mission sizes provides for continuity and follow-up in the various subfields of space astronomy and astrophysics. To achieve that diversity, the Bahcall committee recommended that the Explorer program be substantially expanded to allow flying six Delta-class astronomy and astrophysics Explorer missions and five SMEX-class missions for astrophysics during the 1990s.28 Most of the Delta-class missions would fall into the medium cost category.

24  

NASA, Office of Space Science, Sun-Earth Connection Roadmap: Strategic Planning for 2000-2025, 1999.

25  

NASA, Sun-Earth Connection Roadmap: Strategic Planning for the Years 2000-2020, 1997.

26  

National Research Council, Astronomy and Astrophysics Survey Committee, The Decade of Discovery in Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1991, pp. 15-16.

27  

See, for example, Space Studies Board, National Research Council, A New Science Strategy for Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1997.

28  

National Research Council, The Decade of Discovery, 1991, p. 23.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Example of a Portfolio of Mission Sizes

Table E.4 lists current and planned missions in astronomy and astrophysics. As shown, there are several small and medium missions under development; few are currently operating.

TABLE E.4 Selected Astronomy and Astrophysics Missions

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

ONGOING

SWAS

Submillimeter spectrum molecules in star-forming regions

Small,

$97 million

Ongoing

December 1998-present

ACE

Particles, isotopic, elemental composition of planetary and interstellar space

Medium,

$203 million

Ongoing

August 1997

2-5 years

FUSE

Far-UV spectrum, deuterium, H2, hot gas

Medium,

$204 million

Ongoing

June 1999

3 years

HST

Optical, UV, and near-IR observations

Large,

$9.1 billion (including operations, data analysis, and use of shuttle)

Ongoing

April 1990-present

Compton Gamma Ray Observatory

Gamma-ray astrophysics

Large,

$ N/Aa

Ongoing

April 1991-present

Chandra X-ray Observatory

X rays, supernovae, compact stars, AGNs

Large,

$2,800 million

Ongoing

July 1999

5+ year lifetime

XMM European-led mission with U.S. guest observer program

X rays to faint flux limits

Large,

$ N/A

Ongoing

December 1999

PLANNED, Short-Term

HETE-2

Gamma-ray bursts/fast response

Small,

125 kg,

$23 million

Planned

2000

5-2 years

MAP

CMBR anisotropy <1 deg

Small,

800 kg,

$149 million

Planned

Fall 2000

2 years

GALEX

UV surveys/galaxy evolution

Small,

280 kg,

$76 million

Planned

2 years

CATSCAT

Origin and nature of gamma-ray bursts

Small (UNEX),

$ N/A

Planned

July 2001

CHIPS

EUV spectrum, hot local ISM

Small,

$12 million

Planned

April 2002

1 year

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×

Spacecraft

Parameters/Goals

Mission Size/Mass/ Life-Cycle Costs (real $)

Status

Time Scale of Observation

Swift

Gamma-ray bursts

Medium,

1,270 kg,

$163 million

Planned

2003

3 years

FAME

All-sky stellar astrometry

Medium,

1,030 kg,

$162 million

Planned

2004

5 years

GLAST

Gamma rays/AGNs, bursts, pulsars, supernovae remnants

Medium,

4,500 kg,

$330 million

Planned

September 2005

5 years

SOFIA (aircraft)

Suborbital infrared/star, planet formation

Large,

$1,351 million (including 20 years of operations)

Planned

November 2002

20 years

GP-B

Gyroscopes/test general relativity

Large,

3,300 kg,

$556 million

Planned

Fall 2001

SIRTF

Infrared/brown dwarfs, protoplanetary disks, AGNS, distant galaxies

Large,

905 kg,

$880 million

Planned

December 2001

2.5-5 years

ACCESS

Cosmic ray experiment

Large,

$ N/A

Planned

2005

PLANNED, Long-Term

SIM

Optical interferometer/parallax, proper motion, planet detection

Large,

5,000 kg,

$900 million est.

Planned

June 2006

5 years

NGST

Near-IR/high-redshift galaxies

Large,

3,300 kg,

$1,700 million

Planned

2008

5 years

LISA

Interferometer/gravitational radiation with contributions from several countries

Large,

$ N/A

Under study

2009

6 years

Constellation-X

X rays (imaging and spectroscopy)

Large,

$ N/A

Planned

2010

3-5 years

TPF

IR interferometer/planet detection, processes related to star and planet formation, AGNs

Large,

$ N/A

Planned

2011

>5 years

FIRST/Planck

Image the anisotropies of the cosmic background radiation field over the whole sky

Large,

$ N/A (ESA missions with NASA contributions)

Planned

2003 for FIRST,

2007 for Planck

aN/A, not available

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Criteria for Evaluating the Mission Mix

Mission selection criteria were well described in a 1986 report by the NASA Advisory Council29 and are excerpted below:

  • Scientific merit

    • Significance of the scientific objectives

    • Potential for new discoveries and understanding

    • Generality of interest;

  • Programmatic considerations

    • Feasibility and readiness

    • Infrastructure requirements

    • Cost effectiveness

    • Institutional implications; and

  • Societal and other implications

    • Potential for stimulating technological development

    • Contributions to scientific awareness of the public

    • Contributions to international understanding

    • Contributions to national pride and prestige.

To evaluate the mix of mission sizes, the criteria need to be weighted according to the mission costs. For example, a large mission would need to have a very broad impact while a small mission might be selected to pursue a narrow science problem and to stimulate technological development. More risk could be accepted with medium-size and small missions.

29  

NASA Advisory Council, Space and Earth Science Advisory Committee, The Crisis in Space and Earth Science: A Time for New Commitment, 1986, pp. 55-58.

Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 71
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 72
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 73
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 74
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 75
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 76
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 77
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 78
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 79
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 80
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 81
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 82
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 83
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 84
Suggested Citation:"Appendix E Material Provided by Space Studies Board Discipline Committees." National Research Council. 2000. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions. Washington, DC: The National Academies Press. doi: 10.17226/9796.
×
Page 85
Next: Appendix F Acronyms and Abbreviations »
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Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions addresses fundamental issues of mission architecture in the nation's scientific space program and responds to the FY99 Senate conference report, which requested that NASA commission a study to assess the strengths and weaknesses of small, medium, and large missions. This report evaluates the general strengths and weaknesses of small, medium, and large missions in terms of their potential scientific productivity, responsiveness to evolving opportunities, ability to take advantage of technological progress, and other factors that may be identified during the study; identifies which elements of the SSB and NASA science strategies will require medium or large missions to accomplish high-priority science objectives; and recommends general principles or criteria for evaluating the mix of mission sizes in Earth and space science programs. Assessment of Mission Size Trade-offs for NASA's Earth and Space Science Missions considers not only scientific, technological, and cost trade-offs, but also institutional and structural issues pertaining to the vigor of the research community, government-industry university partnerships, graduate student training, and the like.

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