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Solar and Space Physics: A Science for a Technological Society
310
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
Voyagers are now deep in the heliosheath, and one or both may cross the heliopause in the next decade.
Although they have performed spectacularly, the Voyager instruments are 1970s-vintage and, for example,
are unable to measure suprathermal heavy ions or interstellar-plasma elemental and ionic charge-state
composition. The interstellar probe 19 would make comprehensive, state-of-the-art, in situ measurements
of plasma and energetic-particle composition, magnetic fields, plasma waves, ionic charge states, energetic
neutrals, and dust that are required for understanding the nature of the outer heliosphere and exploring
our local galactic environment.
Advanced scientific instrumentation for an interstellar probe does not require new technology, as the
principal technical hurdle is propulsion. (Also required are electric power from a low-specific-mass radioactive power source and reliable, sensitive, deep-space Ka-band communications.) Advanced propulsion
options, which could be pursued with international cooperation, should aim to reach the heliopause considerably faster than Voyager 1 (3.6 AU/year). Possibilities include solar sails and solar electric propulsion
alone or in conjunction with radioisotope electric propulsion. 20,21 The panel did not find either the ballistic or the nuclear electric power approach to currently be credible. In summary, to enable achievement
of this decadal survey’s key science goals in the coming decades, the SHP panel believes high priority
should be given by NASA toward developing the necessary propulsion technology for visionary missions
like SPI and interstellar probe.
10.5.2.8 Solar-Sail Propulsion for Heliophysics Missions
Solar sails have long been envisioned as a simple, inexpensive means of propulsion that could provide access to and maintenance of unstable orbits that would otherwise require, if they were possible at
all, large and expensive propulsion systems. Solar sails can use solar photons to propel inner-heliosphere
spacecraft to high velocities (Dv > 50 km/s) and can provide low-thrust propulsion to maintain missions
in non-Keplerian orbits that are not feasible by other means. Solar sails will enable a number of important
heliophysics missions, including the Solar Polar Imager (§10.5.2.6), an interstellar probe (§10.5.2.7), and
a solar wind monitor several times farther upstream than L1. All indications are that solar-sail propulsion
(SSP) is technically feasible and very effective for maneuvering in the heliosphere. 22
Recently, the NASA Office of the Chief Technologist (OCT) selected a small sail-technology demonstration mission for implementation in the near future. However, for future missions like the Solar Polar Imager,
a critical follow-on step will be flight validation of a full-scale (about 150 × 150-m) SSP system. That could
be accomplished by NASA’s Heliophysics Division’s investing about $50 million as “seed money” in the
full-scale SSP development effort over the next decade by partnering with the OCT Technology Demonstration Missions program (or other technology program as appropriate). In addition, investing a modest part
of the seed money (about 10 percent) to fund grants to NASA centers and universities for solar-sail mission
design, trajectory analysis, and so on, would lead to new mission applications for heliophysics exploration.
19 R. McNutt et al., Interstellar Probe, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics),
Paper 195.
20 R. McNutt et al., Interstellar Probe, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics),
Paper 195.
21 L. Johnson et al., Solar Sail Propulsion: Enabling New Capabilities for Heliophysics, white paper submitted to the Decadal Strategy
for Solar and Space Physics (Heliophysics), Paper 122.
22 R.P. Lin et al., Expansion of the Heliophysics Explorer Program, white paper submitted to the Decadal Strategy for Solar and Space
Physics (Heliophysics), Paper 160; E. Moebius et al., NASA’s Explorer Program as a Vital Element to Further Heliophysics Research,
white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 205.
Solar and Space Physics: A Science for a Technological Society
310
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
Voyagers are now deep in the heliosheath, and one or both may cross the heliopause in the next decade.
Although they have performed spectacularly, the Voyager instruments are 1970s-vintage and, for example,
are unable to measure suprathermal heavy ions or interstellar-plasma elemental and ionic charge-state
composition. The interstellar probe 19 would make comprehensive, state-of-the-art, in situ measurements
of plasma and energetic-particle composition, magnetic fields, plasma waves, ionic charge states, energetic
neutrals, and dust that are required for understanding the nature of the outer heliosphere and exploring
our local galactic environment.
Advanced scientific instrumentation for an interstellar probe does not require new technology, as the
principal technical hurdle is propulsion. (Also required are electric power from a low-specific-mass radioactive power source and reliable, sensitive, deep-space Ka-band communications.) Advanced propulsion
options, which could be pursued with international cooperation, should aim to reach the heliopause considerably faster than Voyager 1 (3.6 AU/year). Possibilities include solar sails and solar electric propulsion
alone or in conjunction with radioisotope electric propulsion. 20,21 The panel did not find either the ballistic or the nuclear electric power approach to currently be credible. In summary, to enable achievement
of this decadal survey’s key science goals in the coming decades, the SHP panel believes high priority
should be given by NASA toward developing the necessary propulsion technology for visionary missions
like SPI and interstellar probe.
10.5.2.8 Solar-Sail Propulsion for Heliophysics Missions
Solar sails have long been envisioned as a simple, inexpensive means of propulsion that could provide access to and maintenance of unstable orbits that would otherwise require, if they were possible at
all, large and expensive propulsion systems. Solar sails can use solar photons to propel inner-heliosphere
spacecraft to high velocities (Dv > 50 km/s) and can provide low-thrust propulsion to maintain missions
in non-Keplerian orbits that are not feasible by other means. Solar sails will enable a number of important
heliophysics missions, including the Solar Polar Imager (§10.5.2.6), an interstellar probe (§10.5.2.7), and
a solar wind monitor several times farther upstream than L1. All indications are that solar-sail propulsion
(SSP) is technically feasible and very effective for maneuvering in the heliosphere. 22
Recently, the NASA Office of the Chief Technologist (OCT) selected a small sail-technology demonstration mission for implementation in the near future. However, for future missions like the Solar Polar Imager,
a critical follow-on step will be flight validation of a full-scale (about 150 × 150-m) SSP system. That could
be accomplished by NASA’s Heliophysics Division’s investing about $50 million as “seed money” in the
full-scale SSP development effort over the next decade by partnering with the OCT Technology Demonstration Missions program (or other technology program as appropriate). In addition, investing a modest part
of the seed money (about 10 percent) to fund grants to NASA centers and universities for solar-sail mission
design, trajectory analysis, and so on, would lead to new mission applications for heliophysics exploration.
19 R. McNutt et al., Interstellar Probe, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics),
Paper 195.
20 R. McNutt et al., Interstellar Probe, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics),
Paper 195.
21 L. Johnson et al., Solar Sail Propulsion: Enabling New Capabilities for Heliophysics, white paper submitted to the Decadal Strategy
for Solar and Space Physics (Heliophysics), Paper 122.
22 R.P. Lin et al., Expansion of the Heliophysics Explorer Program, white paper submitted to the Decadal Strategy for Solar and Space
Physics (Heliophysics), Paper 160; E. Moebius et al., NASA’s Explorer Program as a Vital Element to Further Heliophysics Research,
white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 205.