The SWEAP investigation consists of three separate instruments and a central
electronics box most of the instruments within sweep sit on either side of the
spacecraft stare out over the entire sky and make maps of all the different
particles and what energies they're moving at what types of particles they
are the purpose of sweep is to measure the bulk of the solar wind and a solar
atmosphere one of the biggest questions we want to resolve with Solar Probe is
how the corona in the solar wind are heated in order to do that we need to
see if there are waves that are coming from the Sun and depositing energy
within the solar atmosphere in the solar wind so we have a series of sensors
across the spacecraft that will collect individual particles electrons fully
ionized hydrogen helium which we call protons and alphas and other minor ions
and make maps of the number of particles as a function of their speed and energy
and type we take those maps on the ground and we can interpret them to
figure out the temperature the density the pressure of the solar wind and the
solar atmosphere on the RAM side of the spacecraft so that's in the shadow of
the heat field in the direction that Solar Probe is moving around the Sun we
have Span A. Span A looks ahead of the spacecraft it has an electron and an ion
instrument and they can see the entire sky on that side of the spacecraft on
the other side the anti ram side of the spacecraft we have Span B which
basically looks behind our direction of motion Span a and Span B are each able
to take an inventory of electrons coming from any direction in the sky their
fields of view stitch together like the seams on a baseball the spans combined
to give us a field of view that covers nearly the entire sky and we have one
large gap in our field of view and it's produced by the heat shield at the front
of the spacecraft so we have the Solar Probe Cup is the
final instrument within SWEAP. The Solar Probe cups sits on a strut it looks
around the heat shield and faces directly into the Sun when our solar
wind or solar atmosphere comes blowing into the cup
if those particles which are charged don't have enough energy they get
reflected out by that electric field we've set up the particles with enough
energy to make it past the could feel come in and strike a plate
and we record the current all we have to do in an individual measurement is sweep
in voltage and measure the number of particles that can make it in as a
function of the voltage that's sweep when we interpret it lets us figure out
the average speed direction energy temperature density of individual
populations of particles