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ESA's Herschel and Planck spacecraft were successfully launched on 14 May 2009. Onboard each spacecraft is an SREM radiation monitor to measure the fluxes of energetic electrons and protons encountered by the two missions.

The image shows the first data obtained from the two SREM units after the launch (upper: Herschel, lower: Planck). On their transits to their final operating orbits around the L2 Lagrange point, 1.5 million km from Earth, they passed briefly through the Earth's radiation belts.

This is clearly visible on the left of the graphs when the SREMs measured increases in the rates of high energy particle impacts. "TC1" corresponds to the count rate for both protons above 20MeV energy and electrons above 2 MeV, "TC2" corresponds to the rate of protons above 40MeV and "TC3" corresponds to the rates of protons above 10MeV and electrons above 0.5MeV.

The large cont rates are due mainly to protons of the inner radiation belt and the small "spiky" features in TC3 more towards the centre correspond to electrons of the outer radiation belt, which is very depleted at the moment due to the current very low solar activity.

Once at L2, the SREMs are expected to monitor the galactic cosmic ray background flux, solar particle events that will occur as the new solar cycle increases in activity, and, potentially, particles encountered during occasional passages of the spacecraft through the Earth's "magnetotail".

The observations will be useful for supporting spacecraft and scientific operations but also for use in coordinated analyses of radiation data from SREM units on other missions (Proba-1, Integral, Giove-B and Rosetta).