A phone box-sized spacecraft has accelerated past the 42-year-old record for Fastest spacecraft as it flies towards the Sun.
Parker Solar Probe – jointly operated by NASA and the Johns Hopkins University Applied Physics Laboratory – went past the record at 2:54 a.m. GMT on Tuesday 30 October (10:54 p.m. Monday 29 October EDT).
Seven hours later the probe had reached a speed of 69.72 km/s (kilometres per second, which translates to around 250,992 km/h or 155,959 mph) relative to the Sun.
That’s fast enough to travel from New York to London in about 1 minute 20 seconds (assuming someone got the atmosphere out of the way) and beats the previous record of 68.6 km/s (246,960 km/h; 153,453 mph) set by the US/German Helios 2 probe in 1976.
Although the probe has broken the fastest of all speed records, going fast is just a side-effect of the mission’s main goal, which is to get its array of scientific instruments as close to the Sun as possible.
This leads us to another of the Parker Solar Probe’s records, broken on Monday 29 October at 6:04 p.m GMT/UTC (1:04 p.m. EDT): Closest approach to the sun. As of 10:00 a.m. GMT/UTC (5:00 a.m. EDT) on the following day, the probe was 40,350,600 km (25,072,700 mi) from the Sun’s surface and closing fast, beating another of Helios 2’s records from 1976.
The Parker Solar Probe will continue to accelerate and close in on the sun until around 3:30 a.m. GMT on 6 November (11:30 p.m. 5 November EST), when it will reach “perihelion” – the closest point in its orbit, and begin its long swing back out past the orbit of Venus. At perihelion it will be travelling at 95.3 km/s (343,080 km/h; 213,180 mph) around 24.1 million km (14.9 million miles) from the Sun’s surface.
Why so fast?
Well, it’s to do with how fast we’re all travelling right now.
Earth orbits the sun at a speed of around 30 kilometres (18.6 miles) every second. This speed represents the enormous amount of energy required to resist the Sun's gravitational pull and stay in a stable orbit (this is why we're not on fire right now). To move closer to the sun, a spacecraft has to lose some of this energy.
The simplest way to reach the Sun directly from Earth would be to launch a spacecraft in the opposite direction with enough power to cancel out the energy it carried from Earth's orbit – effectively coming to a stop and then "falling" inwards towards the Sun.
There is no rocket available that can get away from Earth with that much power, however. Even the massive Delta IV Heavy (above) that launched the Parker Solar Probe on 12 August 2018 falls well short. For this reason, the solar probe mission had to be planned around a series of "gravity assists" that would chip away at the spacecraft's orbital energy.
Each of these assists will see the probe use Venus’ gravitational pull to drain some more of its orbital energy. It conducted the first of these manoeuvres on 3 October, passing within 2,429 km (1,509 miles) of the surface of Venus and, as this was only 52 days 1 hour and 13 minutes after its launch, breaking the record for Fastest interplanetary journey in the process.
Over the next seven years the Parker Solar Probe will repeat this manoeuvre six more times, losing a little bit of orbital energy with each pass.
Over time its orbit around the Sun will become shorter, but also more elliptical, meaning that the probe will be travelling progressively faster at perihelion (the closest point to the Sun) and slower at aphelion (furthest point from the Sun). By the time of its 22nd perihelion on 24 December 2024, it will be moving at a projected speed of around 200 km/s only 6.2 million km (3.8 million mi) from the surface.
Tomorrow, the probe will begin the observation phase of its orbit, turning its instruments – protected by a 4.5-inch-thick (11.43 cm) carbon-composite heat shield – towards the Sun.
Over the next 11 days the Parker Solar Probe will endure temperatures of 1,377 C (2,500 F) to gather a vast trove of data on the behaviour of our parent star, measuring heat currents on the surface and investigating the origins of the stream of charged particles known as the solar wind.
This unprecedented close-up view of the behaviour of a star will hopefully provide answers to many long-standing questions in the fields of solar physics.