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Extending our FOV inward to catch the most extreme events would require FOVs of at least 8.3 degrees (LEXI), 15.2 degrees (SMILE), and 20.4 degrees (STORM). At the other extreme, the events with the largest magnetopause standoff distances are probably not of as much interest as they are not dynamically active they are more difficult to observe given the lower neutral density at those distances from the Earth. Of course, the most extreme events with the smallest stand-off distances are the brightest, are of particular interest, and are not well described by the Spreiter relation magnetopause standoff distances as small as 6.3 R E have been observed (e.g., Dmitriev et al., 2016). If we simplify the problem, placing the spacecraft in the plane of the terminator at these orbital distances, then these missions require a FOV of at least 6.1 degrees, 11.0 degrees, and 14.5 degrees, respectively. SMILE is planning an elliptical orbit with an apogee of ∼19 R E, which can observe the subsolar point of the magnetopause from altitudes as low as ∼ 15 R E (Read, private communication). STORM is planning a high inclination circular orbit with a radius of 30 R E. LEXI will be observing from the moon at 60.4 R E. Thus roughly a span of 6.7 R E along the Sun-Earth line will include the magnetopause/magnetosheath for 90% of the time.Ī number of HEOs have been proposed.

Our FOV needs to cover not only the range of interesting R MP but also to include at least the typical width of the magnetosheath, ∼ 3.4 R E (e.g., Farris et al., 1991). The range of stand-off distances from the fifth percentile to the ninety-fifth percentile is 8.6–11.9 R E. The median calculated stand-off distance is 10.5 R E, which is consistent with measured values (e.g., Farris et al., 1991). (3.9) R M P = H 1 / 3 ( 2 π ρ ∞ v ∞ 2 ) − 1 / 6įor the magnetopause stand-off distance ( Spreiter et al., 1966), we can calculate the approximate range of standoff distances.