Set the controls for the heart of the sun

By Joseph

Solar Orbiter, a revolutionary spacecraft on a mission to address some of the big questions of solar system science, launched in the early hours of Monday 10th February.

The £1.3 billion project, a collaboration between European Space Agency (ESA) and NASA, is the first of its kind and aims to study the Sun up-close, taking high resolution photographs of the polar regions and helping us to understand how our star creates and controls the plasma bubble enclosing our whole solar system – the heliosphere.

Fitted to an Atlas V rocket that launched from Cape Canaveral, Florida at 4.03am GMT on February 10th 2020, Solar Orbiter is now hurtling towards the Sun.

On its two-year journey, the spacecraft will make use of gravity-assist flybys of Earth and Venus to enter a highly elliptical orbit around the Sun. To slingshot itself out of the plane of the solar system (in which the planets or- bit), the spacecraft will increase the inclination of its orbit using the gravity of Venus, giving us new views of the uncharted polar regions of the sun.

The £1.3 billion project is the first of its kind

NASA Administrator Jim Bridenstine tweeted after the launch: “We have a healthy space- craft! Congratulations to the @ NASA, @esa and @ulalaunch teams on a successful launch of #SolarOrbiter! I’m excited about this incredible mission that will conduct trailblazing science in heliophysics and give us our first images of the Sun’s poles.”

During the mission, Solar Orbiter will make at least 22 close approaches to the Sun. The first close solar pass will take place in 2022 at around a third of Earth’s distance from the Sun, followed by twice yearly solar approaches. Solar Orbiter will be able to observe magnetic activity building up in the atmosphere that can lead to powerful solar flares or eruptions. Researchers will be able to coordinate observations with NASA’s Parker Solar Probe mission (2018-2025) which is performing measurements of the Sun’s extended corona.

The spacecraft has already sent data back to Earth, after its 4.4 metre boom arm was successful- ly deployed. The carbon fibre and titanium arm, which was folded away for launch, carries crucial sensors. Signalling the start of a three-month commissioning phase, in which solar engineers will test each of the ten on-board instruments, the magnetometer took readings throughout the entire boom deployment, beaming its data back to Earth.

Analysis shows that the instrument is working well, distinguishing between the weak interplanetary magnetic field and the electromagnetic fields produced by the spacecraft electronics themselves. This will enable scientists to use the instrument to investigate how the Sun’s magnetic field generates “space weather”, sending out powerful solar flares that can create aurora and have the potential to disrupt technology here on Earth, knocking out power grids and disrupting air traffic and telecommunications.

At its closest approach, Solar Orbiter, which was constructed in the UK by Airbus, will face the Sun from within the orbit of Mercury, approximately 42 million kilometres (26 million miles) from the solar surface. Cutting-edge heatshield technology will protect the spacecraft’s scientific instruments from temperatures of more than 500°C – 13 times the heat experienced by satellites in Earth orbit.

The advanced heat-shield, which took years to perfect and is constructed from titanium, carbon fibre, and aluminium, is designed to dissipate heat while keeping the rest of the spaceship in a protective cone of shadow. Small sliding doors allow sunlight into the instrumentation located directly behind the protective heat-shield, including cameras, whilst protecting them from the harsh conditions.

Solar Orbiter will travel within the orbit of Mercury

To withstand an increase in temperature from 20°C at launch to more than 500°C in flight, the shield was designed to be highly flexible.

As neither paint nor glue would adhere to the shield and remain reliable at high temperatures, engineers instead turned to a chemical treatment originally developed for medical implants. Calcium phosphate (extracted from animal bones) was bonded to the metal, becoming part of the material’s surface, enabling it to withstand the harsh conditions. In testing, the shield was baked for two weeks at over 500°C to ensure that it was fit for the job.

The recent successes are just the start of a very exciting mission, and we’re well on the way to understanding a little more about our parent star.

Image: Molly Murphy

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