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Mission Omissions.

Your "Space Missions in 2018" summary (S&T: Jan. 2018, p. 16) omits some space weather and other missions. I noticed that these missions were also absent from the list the previous year, and since there have been no corrections, I thought it time to send this information.

The most notable omissions are NASA's Van Allen Probes, two satellites studying Earth's radiation belts, as well as the Magnetospheric Multiscale (MMS) mission, four spacecraft moving through Earth's magnetosphere in highly elliptical orbits.

According to the list at science.nasa gov/missions-page, TWINS and Geotail, other space weather missions, are also still operational. Other missions on this list that are still operational are MESSENGER, AIM, and GRACE, as well as other Earth observation satellites. I have used GRACE data for space weather studies on how much auroral currents heat and expand the thermosphere. I also use data from TIMED, another NASA mission that is presently operational.

There are also ESA's three Swarm satellites ( swarm) that I'm currently using for space weather research, mainly for measuring auroral currents and atmospheric density.

Daniel Weimer

Blacksburg, Virginia

"Camille Carlisle replies: Thank you for pointing out these omissions. I went back through my notes and found MMS and Geotail on my original list, but somehow they never made it into the spreadsheet used to create the illustration. I'll make sure we include them when creating next year's list.

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Title Annotation:FROM OUR READERS
Author:Weimer, Daniel
Publication:Sky & Telescope
Article Type:Letter to the editor
Date:Jul 1, 2018
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