Tim Furniss/LONDON
Three small NASA spacecraft will explore the earth's dynamic systems early in the new millennium. One of the satellites, called Volcanic Ash Mission (Volcam), will demonstrate the operational and scientific applications of monitoring volcanic clouds and small atmospheric particles, known as aerosols, from a geostationary orbit.
Volcanic clouds are a potential hazard to jet aircraft. There have been several instances of volcanic ash damaging commercial airliners. As well as causing traffic hazards, volcanic eruptions increase the amount of aerosol particles, while ash scatters sunlight in the upper atmosphere, leading to cooler earth surface temperatures.
Under the Office of Earth Science's Earth System Science Pathfinder (ESSP) programme, the information from Volcam would provide better data on the transport of volcanic aerosols in global atmospheric-circulation models of the earth's climate and weather, says NASA.
The estimated mission cost of Volcam is $48 million, of which NASA will provide $45 million and other US Government agencies $3 million. The Volcam mission craft is likely to be flown piggyback on a larger NASA satellite launch.
The two other ESSP missions are the Picasso spacecraft, to study atmospheric aerosols, and CloudSat, to study the effect of thick clouds on the reduction of the earth's radiation budget - a balance of solar energy reaching the earth and lost to space that ultimately controls the temperature of our planet.
Volcam, Picasso and CloudSat will follow three other craft under development. The primary Phase 1 ESSP missions, Vegetation Canopy Lidar (VCL) and Gravity Recovery and Climate Experiment (Grace) were picked for implementation in March 1997.
The VCL is being built by Orbital Sciences for a company launch on a Pegasus booster in February 2000, and the Grace is being built by Loral with DaimlerChrysler Space Systems for a Rokot launch in July 2001.
As well as the VCL and GRACE, a third mission, the Chemistry and Circulation Occultation Mission (CCOM), was selected as an alternative, to be implemented if one of the chosen primary missions hits serious cost, schedule or technical problems during their development. The CCOM would be built by Spectrum Astro and launched on a Pegasus XL.
PROGRAMME CORNERSTONES
The ESSP missions are the cornerstones of a dynamic and versatile programme of small to medium sized, low cost, quick reaction missions, capable of supporting a variety of scientific objectives related to earth science, including the atmosphere, oceans, land surface, polar ice regions and solid earth.
The full name of the Picasso spacecraft - the primary Phase 2 mission - is Picasso-Cena (Pathfinder Instruments for Cloud and Aerosol SpaceborneÊObservations-Climatologie Etendue des Nuages et des Aerosols), a project co-led by NASA's Langley Research Center, Virginia, and the Institut Pierre Simon Laplace of Paris, France. Picasso's instruments will monitor the role of clouds and aerosols and their impact on the earth's radiation budget.
Picasso will use innovative light-detection and ranging instruments to profile the vertical distribution of clouds and aerosols. Another instrument will simultaneously image the infrared (heat) emission of the atmosphere.
During the daylight half of its orbit, Picasso will measure the reflected sunlight in an oxygen-absorption band and take images of the atmosphere with a wide-field camera.
The craft, together with the Earth Observing System satellites, will establish the scientific basis for understanding the dynamics and energetics of the earth's atmosphere in support of short-term weather and long-term climate forecasts. "For the first time, we will be able to construct the three-dimensional structures of the atmosphere to better understand the role of clouds and aerosols in the earth's climate," says Dr Ghassem Asrar, NASA's Associate Administrator for Earth Sciences.
The estimated cost of the Picasso mission, including launch vehicle, is $173.5 million. NASA will provide $117.4 million, with France contributing $56.1 million. The spacecraft will be launched in 2003. Ball Aerospace and Technology of Colorado will be prime contractor and NASA's Goddard Space Flight Center in Maryland will be mission manager.
France's provision of a Proteus spacecraft bus, the infrared imaging system and science analysis support make this mission "-an excellent example of domestic and international partnership towards answering a major climate-related scientific question", says Asrar.
As well as Picasso, NASA has chosen Volcam and a third mission, CloudSat. These will go through extended development and technology assessment before a decision is made on which will be the primary and which the alternative.
The CloudSat mission is focused on understanding the role of thick clouds in the earth's radiation budget. It will use advanced cloud-profiling radar to provide information on the vertical structure of highly dynamic tropical cloud systems. This radar will enable measurements of cloud properties to be made globally for the first time, revolutionising the understanding of cloud-related issues.
The estimated mission cost of CloudSat is $144.6 million, with NASA providing $119.6 million. Collaboration with Canada is being studied for the provision of critical components for CloudSat's cloud-profiling radar.
Source: Flight International
