Small, lower-cost spacecraft to study the distribution of Earth's forests and the variability of its gravity field have been competitively selected by NASA for development under a new Office of Mission to Planet Earth program, called Earth System Science Pathfinders (ESSP). NASA's Jet Propulsion Laboratory has been named a partner in the gravity mission and in an alternate atmospheric chemistry mission.
JPL will conduct the mission design and instrumentation on the Gravity Recovery and Climate Experiment (GRACE), led by Dr. Byron Tapley of the University of Texas at Austin. GRACE employs a satellite-to-satellite microwave tracking system between two spacecraft to measure the Earth's gravity field and its time variability over five years. Such measurements are directly coupled to long wavelength ocean circulation processes and to the transport of ocean heat to Earth's poles. GRACE includes major international cooperation with participation from Dr. C. Reigber, co-principal investigator from GeoForschungsZentrum (GFZ) in Potsdam, Germany.
JPL has also been selected as a partner in a proposed mission to better understand how atmospheric circulation controls the evolution of key trace gases, aerosols and pollutants over time. This mission was chosen as an alternate, should one of the primary missions encounter serious cost, scheduling or technical problems in its early development phases. Called the Chemistry and Circulation Occultation Spectroscopy Mission (CCOSM), this project would be led by Dr. Michael Prather of the University of California at Irvine.
The first mission to fly as part of the Earth System Science Pathfinders program is the Vegetation Canopy Lidar (VCL) mission, led by Dr. Ralph Dubayah of the University of Maryland, College Park. The mission seeks to provide the first global inventory of the vertical structure of forests across Earth using a multibeam laser-ranging device. VCL will enable direct measurement of tree heights, forest canopy structures and derived parameters such as global biomass, with at least 10 times better accuracy than existing assessments.
"These exciting missions will deliver their first science results in a little over three years, remarkably fast for such capable spacecraft," said William Townsend, acting associate administrator for the Mission to Planet Earth program at NASA Headquarters, Washington, DC. "At the same time, they will cost-effectively complement NASA's Earth Observing System (EOS) program by addressing emerging research questions that will further expand our scientific knowledge of the Earth.
"Science value per dollar was the top criteria in this selection," Townsend added. "We also spent a great deal of effort validating the realism of the proposers' cost estimates and their technical readiness. For all of these reasons, the alternate mission should be considered a very real option should one of the selected missions unexpectedly encounter major difficulties."
"It also is important to note that the three selected missions collectively address all four major science research priorities of the U.S. Global Change Research program: land cover change, atmospheric chemistry, and both seasonal and long- term climate change," said Dr. Ghassem Asrar, Earth Observing System chief scientist at NASA Headquarters.
The ESSP selections were made from a group of 12 proposals that were evaluated in the second phase of a rigorous, two-phased selection process that began less than eight months ago with a July 1996 announcement of opportunity. This original announcement generated 44 proposals, which were initially reviewed for scientific merit. The review resulted in 12 proposals that met the requirements for the second phase of the ESSP evaluation.
As with NASA's Discovery program of small, focused space science-oriented spacecraft, the underlying philosophy of ESSP is to achieve maximum science value while complementing existing or planned flight missions. In the "principal investigator" (PI) mode for implementing ESSP, the single PI and his or her team are ultimately responsible for developing the flight mission hardware from selection to a launch-ready condition within 36 months, with minimal direct oversight from NASA. The PI and mission team are responsible for accomplishing the stated scientific objectives and delivering the proposed measurements to the broader Earth science community and general public as expediently as possible.
The laser mapping technique to be used by VCL, which was pioneered by NASA in aircraft experiments several years ago, should help resolve a major uncertainty in the scientific understanding of the global carbon cycle, particularly the role of terrestrial ecosystems in sequestering the atmospheric carbon dioxide produced by industrial activities and automobile exhausts. At the same time, the multibeam VCL lidar instrument will generate a vast array of reference points for future surveys of land topography, including the planned NASA-Department of Defense Shuttle Radar Topography Mission in 1999-2000. VCL measurements should also have practical commercial applications in forestry management.
The total mission life-cycle cost to NASA of VCL is $59.8 million, including the launch vehicle. VCL will be launched in spring 2000 on a Pegasus launch vehicle. Industrial partners in VCL include CTA Space Systems, McLean,VA; Fibertek Inc., Herndon, VA; and Omitron Inc., Greenbelt, MD, with participation by scientists at NASA's Goddard Space Flight Center, Greenbelt, MD, and several U.S. universities.
GRACE will provide a framework for studying the gravitational signatures of gigantic, continent-sized underground water reservoirs, or aquifers. It also will provide a never-before-available perspective on global ocean circulation and the time variability of Earth's overall external shape, or geoid. This fundamental data set could enable great improvements in existing ocean radar altimetry data sets, and retrospective improvements of seasonal to inter-annual climate change estimates.
Through an innovative teaming arrangement, GRACE's German partner, GFZ, will provide mission operations and a Russian booster for a spring 2001 launch, greatly reducing the direct total cost to NASA, which is $85.9 million. In addition to JPL, other partners include Loral Space Systems, Palo Alto, CA, and Dornier of Germany to build the spacecraft.
The Chemistry and Circulation Occultation Spectroscopy Mission would make at least 18 months of measurements of the vertical distribution of more than 30 diagnostic trace gases and aerosol properties. Such data will provide never-before-available chemical and physical boundary conditions from which to model the behavior of the chemistry of Earth's atmosphere, such as the mixing of pollutants in the lower atmosphere. Measurements to be acquired by CCOSM will be used in conjunction with general atmospheric circulation models to assess the effectiveness of the Montreal Protocol (i.e., the banning of chlorofluorocarbons and other potentially harmful gases) on controlling the depletion of atmospheric ozone.
In addition to JPL, partners in CCOSM include Lockheed- Martin Infrared Imaging Systems, Lexington, MA, and Spectrum Astro Inc., Gilbert, AZ.
In addition to the funding support for the science team associated with each mission, NASA has set aside 10 percent of the annual budget for the ESSP program to support innovative use and analysis of the observations resulting from the ESSP missions. The intent is to utilize these funds to support science data analysis and research investigations through an open solicitation and peer review process once data from the ESSP missions become available. NASA intends to solicit another set of ESSP missions in the fall of 1998.
The ESSP program is a new element of NASA's Office of Mission to Planet Earth, a long-term, coordinated research enterprise designed to study the Earth as a global environmental system.
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