Kiss the Sun

Australian Geographic - - Geobuzz -

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

NASA’s high-tech Parker So­lar Probe is trav­el­ling through the Sun’s at­mos­phere.

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