A spacecraft could fly within 2.72 million kilometres (1.7 million miles) of the Sun in July 2007 as part of a series of new interplanetary space missions being studied by NASA.
The Solar Probe, protected against high temperatures by a large umbrella-like heatshield, would be used to explore the Sun's corona (the halo of gas extending 1.6 million kilometres from the surface seen glowing around the Sun during total eclipses).
Measurements made by a European Space Agency/NASA spacecraft, the Solar and Heliospheric Observatory (SOHO), have indicated that the Sun is more active than originally thought.
The $200 million Solar Probe, to be developed by NASA's Jet Propulsion Laboratory in California, will be launched in November 2003 and will fly outwards towards the planet Jupiter which it will reach in April 2005.
The Solar Probe will be knocked out of the ecliptic plane -in which the planets orbit the Sun - by the intense gravitational force of the giant planet during a retrograde fly-by manoeuvre, so that it will enter a solar polar orbit. The Sun's poles are more active.
Science observations will begin about nine days before the closest encounter begins, when for 36h the Solar Probe will measure the high- speed solar wind over the north pole, the low-speed solar wind zone near the Sun's equator - when it will reach its closest point to the Sun - and the high-speed solar wind zone over the south pole.
The Solar Probe will carry a coronagraph, magnetograph, ultraviolet and plasma spectrometers, an energetic-particle instrument, a plasma-wave sensor and magnetometers. The spacecraft is expected to encounter temperatures of about 1,800íC.
The Solar Probe is one of three craft in the pre-project phase of a new NASA Outer Planets programme, that have been nicknamed the Ice and Fire spacecraft, which will use common instruments, computers, avionics and other technologies to streamline operations and cut costs.
The other craft are the Europa Orbiter and the Pluto Express. The Europa Orbiter will be used to conduct radar-sounding observations of the moon of Jupiter to determine if there really is a liquid ocean under Europa's icy surface and, if so, how thick the ice is.
The Pluto-Kuiper Express will fly past the planet Pluto and its large moon, Charon, in about 2010, and then continue into the outer solar system, to fly through the region of small "ice-dwarf" mini-planets, called the Kuiper Disk, which are thought to be the residue from the formation of the solar system.
The final go-ahead for the Solar Probe, which would be the first of the Ice and Fire missions, is expected to be given in October 2000.
Source: Flight International
