The Enstrophy sounding rocket mission will make a multiple-point measurement of the magnetic field which will be used to calculate magnetic-field-aligned current density along the rocket trajectory. Four small (8 cm diameter x 2.7 cm high) autonomous free-flyers (Free-Flyer Magnetometers, or ``FFMs'') will be ejected from the payload, perpendicular to the spin axis of the payload. The free-flyers will measure the magnetic field at 4 points separate from the payload, at relative distances up to 3 km, and will telemeter their data, in bursts, to the ground. Plasma diagnostics on the payload will measure the plasma environment. This will be a winter 1999 nightside launch to approximately 1000 km altitude from the Poker Flat Research Range.
Previous sounding rockets and satellites typically have measured variations in
only along one trajectory in space and time.
``Field-aligned current measurements'' assumed that the
magnetic field varied only in space, and that the currents were sheetlike,
similar to auroral arcs. Since there is strong reason to believe
that the strongest observed gradients in the magnetic field
are actually variations in time (rather than representing spatial variations as the
magnetometer crossed current sheets), it is not known what the highest
field-aligned current densities actually are.
Enstrophy will unambiguously measure spatial gradients. Any 3
FFMs allow for a direct, unambiguous measurement of the local current density.
The highest FAC densities can be determined. These determine which
wave instabilities can occur at higher altitudes; such instabilities
provide at least some of the resistance required to produce the auroral
potential drop and electron acceleration.
The set of 4 FFMs will also allow a measurement of the current
density along two adjacent trajectories, testing the sheetlike nature
of such currents, and showing the filamentation.