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Solar and Space Physics: A Science for a Technological Society
94
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
Second Research Recommendation [R2.0] for NASA—Accelerate
and Expand the Heliophysics Explorer Program
The medium-class (MIDEX) and small-class (SMEX) missions of the Explorer program are ideally suited
to advancing heliophysics science and have a superb track record for cost-effectiveness. Since 2001, 15
Heliophysics Explorer mission proposals have received the highest category of ranking in competitive
selection reviews, but only 5 have been selected for flight. Thus there is an extensive reservoir of excellent
heliophysics science to be accomplished by Explorer missions.
The Explorer Program
As noted in a previous NRC report, 8 the Explorer program’s strength lies in its ability to respond rapidly to new concepts and developments in science and to forge a synergistic relationship with ongoing,
larger, strategic missions. The Explorer program (Box 4.7) creates a highly competitive environment in
which teams led by a principal investigator (PI) rapidly capitalize on advances in technology, enabling
cutting-edge science at moderate cost. Over the years, these missions have operated in different management modes, but the common feature is that a PI in partnership with the NASA Explorer Program Office
is tasked to ensure the overall success of the mission and is given the authority to make critical decisions
to control cost and schedule. New Explorer missions are able to pursue the cutting edge of heliophysics
science, because they can make use of emerging technologies that are not available to large facility-class
observatories that have longer development times and a more stringent risk posture. Since the 1990s, the
decision as to which missions are selected is based on the findings of a competitive process that ensures
that the science objectives and implementation approach reflect the frontiers of the field and achieve an
appropriate balance between novel technical capabilities and programmatic risk.
Explorer missions provide outstanding science-per-dollar value and often are capable of achieving
much more than their baseline science mission. For example, before the ACE mission, first the Interplanetary
Monitoring Probes and then the International Sun-Earth Explorers provided crucial measurements of solar
wind properties well beyond their design lifetimes. The IMAGE mission provided breakthrough science
through 5 years of operations (3 years beyond THEMIS’s original design lifetime), including the first simultaneous conjugate observations of the aurora. Two of the five-spacecraft THEMIS magnetospheric Explorer
satellites are now orbiting the Moon, enabling an outstanding expansion of mission science beyond its
original plan. The TRACE solar Explorer was launched in 1998 and obtained unprecedented high-resolution
coronal observations for 12 years. This pattern of Explorers outperforming their as-proposed objectives has
tended to be the rule rather than the exception.
In the course of developing Explorer missions, NASA has built an amazing array of capabilities for
visiting hostile and exotic environments in space and for making measurements of key properties of the
gases and plasma that constitute Earth’s environment. These missions have become arguably more successful and visible to the public in the past decade than ever before. They are scientifically productive
and often tell a story of space exploration that is pertinent to daily life. Their technical achievements and
successful implementation come to fruition at costs not achievable with large flagship missions—and their
findings are often true discoveries.
These achievements come from the competitive spirit that the Explorer program encourages, and the
tight cost-capped implementations that are forced to carry adequate margins from the earliest phases of
8 National Research Council, Solar and Space Physics and Its Role in Space Exploration, The National Academies Press, Washington, D.C., 2003, p. 36.
Solar and Space Physics: A Science for a Technological Society
94
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
Second Research Recommendation [R2.0] for NASA—Accelerate
and Expand the Heliophysics Explorer Program
The medium-class (MIDEX) and small-class (SMEX) missions of the Explorer program are ideally suited
to advancing heliophysics science and have a superb track record for cost-effectiveness. Since 2001, 15
Heliophysics Explorer mission proposals have received the highest category of ranking in competitive
selection reviews, but only 5 have been selected for flight. Thus there is an extensive reservoir of excellent
heliophysics science to be accomplished by Explorer missions.
The Explorer Program
As noted in a previous NRC report, 8 the Explorer program’s strength lies in its ability to respond rapidly to new concepts and developments in science and to forge a synergistic relationship with ongoing,
larger, strategic missions. The Explorer program (Box 4.7) creates a highly competitive environment in
which teams led by a principal investigator (PI) rapidly capitalize on advances in technology, enabling
cutting-edge science at moderate cost. Over the years, these missions have operated in different management modes, but the common feature is that a PI in partnership with the NASA Explorer Program Office
is tasked to ensure the overall success of the mission and is given the authority to make critical decisions
to control cost and schedule. New Explorer missions are able to pursue the cutting edge of heliophysics
science, because they can make use of emerging technologies that are not available to large facility-class
observatories that have longer development times and a more stringent risk posture. Since the 1990s, the
decision as to which missions are selected is based on the findings of a competitive process that ensures
that the science objectives and implementation approach reflect the frontiers of the field and achieve an
appropriate balance between novel technical capabilities and programmatic risk.
Explorer missions provide outstanding science-per-dollar value and often are capable of achieving
much more than their baseline science mission. For example, before the ACE mission, first the Interplanetary
Monitoring Probes and then the International Sun-Earth Explorers provided crucial measurements of solar
wind properties well beyond their design lifetimes. The IMAGE mission provided breakthrough science
through 5 years of operations (3 years beyond THEMIS’s original design lifetime), including the first simultaneous conjugate observations of the aurora. Two of the five-spacecraft THEMIS magnetospheric Explorer
satellites are now orbiting the Moon, enabling an outstanding expansion of mission science beyond its
original plan. The TRACE solar Explorer was launched in 1998 and obtained unprecedented high-resolution
coronal observations for 12 years. This pattern of Explorers outperforming their as-proposed objectives has
tended to be the rule rather than the exception.
In the course of developing Explorer missions, NASA has built an amazing array of capabilities for
visiting hostile and exotic environments in space and for making measurements of key properties of the
gases and plasma that constitute Earth’s environment. These missions have become arguably more successful and visible to the public in the past decade than ever before. They are scientifically productive
and often tell a story of space exploration that is pertinent to daily life. Their technical achievements and
successful implementation come to fruition at costs not achievable with large flagship missions—and their
findings are often true discoveries.
These achievements come from the competitive spirit that the Explorer program encourages, and the
tight cost-capped implementations that are forced to carry adequate margins from the earliest phases of
8 National Research Council, Solar and Space Physics and Its Role in Space Exploration, The National Academies Press, Washington, D.C., 2003, p. 36.