Kiss the Sun
IN AUGUST 2018, NASA launched Parker Solar Probe to skim through the Sun’s super-hot atmosphere. You’d think this would be easy – just launch the spacecraft off the ground, and then drop it at the Sun. But no.
Surprisingly, it takes 55 times more energy to get a spacecraft to the Sun than to Mars. Why? Because, thanks to the Earth’s orbit, Parker has too much energy to simply drop into the Sun. Think about a re-entry vehicle leaving the International Space
Station (ISS) to return to Earth. The
ISS orbits Earth at about 7km/sec. When the re-entry vehicle separates from the ISS, it still has that 7km/sec horizontal speed. This means it doesn’t fall towards Earth – it just keeps orbiting.
So the re-entry vehicle, while pointing backwards to the direction of travel, fires its own rocket engines for four minutes and 21 seconds. That scrubs off a tiny 0.115km/sec from its 7km/sec forward speed. It’s not much, but it’s enough to put it into a lower orbit, where air resistance and gravity does the rest of the work to slow it down. About 53 minutes later, it lands with zero forward speed.
However, there is no air in space between the Earth and Sun. How does Parker Solar Probe scrub off a massive 30km/sec of forward speed? It gives its energy to Venus.
Over its seven-year life, Parker will zip past very close to Venus seven times, and do a Gravitational Slingshot (check it out on Wikipedia). Parker will transfer some of its energy, and forward speed, to Venus. Parker will slow down, and Venus will speed up (by a microscopic amount). Parker will zip past the Sun 24 times, getting ever closer. Each time it passes Venus, it scrubs off more of that 30km/sec forward speed. The last orbit will take it through the Sun’s million-degree atmosphere, at just 6.2 million kilometres from the Sun’s surface.
How will Parker survive that hellish transit? By using probably the best insulator ever made – a specially built shield 11.4cm thick (about as thick as standard home insulation batts). On the sunny side, it can withstand temperatures of 1370°C. But under its protective shade, Parker’s instruments will be at a comfy 30°C. Imagine using this insulation technology on your house!
DR KARL is a prolific broadcaster, author and Julius Sumner Miller fellow in the School of Physics at the University of Sydney. His latest book, Vital Science, is published by Pan Macmillan. Follow him on Twitter: @DoctorKarl