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Space Radiation Hazards and the Vision for Space Exploration: Report of a Workshop
of forecasting events anywhere in the inner heliosphere that are regions of interest to the Vision for Space Exploration (VSE).
Some global models are beginning to come online now, but they are difficult to tailor to specific events. One clear statement from the workshop is that there is a need for a better understanding of how to relate the observations to the models. The observations have a dual role: (1) they provide the inputs to drive models, and (2) they are required to validate the models (post facto). Some of the anticipated near-term and long-term results from the space physics community are described below.
Near-Term Results (Up to 2015)
For the near-term need (up to 2015), it should be possible to improve predictions of “all clear” periods when there is a very low probability that an SEP event will occur. This is possible with a better understanding of the signatures indicating that a flare or CME is about to erupt. New observations of solar magnetic structures with Solar-B, the Solar Dynamics Observatory, and the ground-based Advanced Technology Solar Telescope and the Frequency Agile Solar Radio Telescope will help in this regard.
Missions such as the Solar Terrestrial Relations Observatory (STEREO) will provide simultaneous data from two different positions off of the Sun-Earth line as interplanetary CMEs propagate outward from the Sun. These data will be useful for developing models that can specify, and in some cases forecast, the SEP environment at a wide range of longitudes in the inner heliosphere. This is an important point since Mars, a future exploration target, is rarely on the Sun-Earth line.
The physics-based models discussed above must be pared down to include only the most essential parameters that are capable of predicting the variability of the space radiation environment. These models must be validated before being transitioned to operational use.
Far-Term Results (After 2015)
Farther out in the future (after 2015), it is desirable to make predictions of solar events weeks before they occur. More than likely this will be possible only with models that use a statistical approach along with a suitable set of in situ and remote sensing measurements from multiple vantage points in the heliosphere. It will be most useful for the VSE if models can predict the following: (1) the onset time for an SEP event, (2) its time-intensity profile, (3) the “spectral indices” of the energy spectrum, (4) the shock arrival time, and (5) the anisotropy in the particle velocity distribution (lower priority).
An effective SEP warning system will require an operational distributed network of observations from the Sun throughout the heliosphere (similar to the distributed network of weather stations on Earth). Near-Sun missions such as Inner Heliosphere Sentinels, Solar Orbiter, and Solar Probe will provide unique measurements to test more sophisticated models. One novel approach for a future mission, presented at the workshop, is to put multiple (~15) spacecraft around the Sun at 1 AU. Spacecraft situated in polar solar orbits, at the Earth-Sun L2 and L3 points, or spacecraft at the Mars-Sun L1 points can provide unique data for a global heliospheric warning system. Remote sensing observations of CME/flare/SEP source regions in the extended corona (2 to 10 solar radii) can provide unique precursor signatures for the severity of radiation events.
Antiochos, S.K., C.R. DeVore, and J.A. Klimchuk. 1999. A model for solar coronal mass ejections. Astrophys. J. 510:485.
Aran, A., B. Sanahuja, and D. Lario. 2006. SOLPENCO: A solar particle engineering code. Adv. Space Res. 37(6):1240-1246.