How to you build a spacecraft and an experiment to survive plunging into
the atmosphere of a star? This page provides some background on
what we can do on Earth to prepare for a solar encounter.
Both SPP and the SWEAP instruments
will be exposed to a new and harsh environment, with
surfaces experiencing high temperatures and intense particle
fluxes. At closest approach the Sun will be more than twenty times
larger and 500 times brighter than it is at Earth.
Our most important
demonstration for SWEAP was to prove that the components
of our instruments exposed to sunlight would survive
these conditions. But how can you re-create the inferno of the
solar atmosphere on Earth?
For our project we use the largest
in the world to simulate encounters with the Sun.
In order to test our design, we worked with the
Processes, Materials and
(PROMES) laboratory in Perpignan, France.
PROMES is run by the National
Centre for Scientific Research (CNRS) and features the largest solar
furnace in the world. One one side of a mountain 64 giant mirrors
slowly move and track the Sun as it moves across the sky. The mirrors
reflect sunlight onto the side of the main building, which is
shown in the picture above. As you can see, the side of the building
is curved and covered with thousands of small mirrors, each tilted
at a slightly different angle in order to focus the sunlight onto
a small spot in the side of a vacuum chamber located in the top fo the
The furnace dumps one megawatt (1 MW) of
sunlight onto the entrance to a quartz-windowed vacuum chamber
in the tower. The
chamber includes a particle accelerator that can reproduce solar wind
ion fluxes, a UV light source to reproduce the portion of the solar
spectrum blocked by the atmosphere, and diagnostic equipment including
mass spectrometers and optical pyrometers to monitor mass loss and
surface temperatures. Instrument components were imaged with a
microscope (SEM), placed in the chamber and heated beyond 1400C, and
then removed and re-imaged.
Later that year samples
at the furnace were raised to 2500C (more than 1000C hotter than we will
ever experience in the solar atmosphere) and simultaneously exposed to an
ion beam four orders of magnitude more intense than the solar wind at
closest approach, again with no problems.