Engineering news
The US space agency has now finalised the four instruments that will travel on board the Solar Probe Plus to study the Sun’s atmosphere. The agency invited researchers to submit their proposals in 2009; a panel then narrowed down the shortlist to the chosen four.
The Solar Probe Plus, set to launch in July 2018, will dive into the Sun’s atmosphere nearly 6.5 million km from the surface – that’s within Mercury’s orbit – to investigate what drives solar winds. These are clouds of highly charged particles released from the Sun’s outer atmosphere – the corona. When they reach Earth, they interfere with its magnetic field, causing problems with electrical equipment.
The small, solar-powered spacecraft will brave our backyard star’s scorching heat and radiation with the help of a 11.5cm-thick thermal protection system. Made of carbon composite, the protective shield can withstand searing temperatures up to 1,377°C. “This allows it to operate near normal spacecraft temperatures,” said Mike Buckley of the Applied Physics Laboratory at Johns Hopkins University in Maryland, who manages the Solar Probe Plus for Nasa.
Sensing the Sun
The probe will sport solar array flaps that will first extend, and then retract, when the craft approaches the Sun. This will minimise the probe’s exposure to the solar surface while generating enough power. Water-cooled with a looped cooling pump, the arrays will operate within the shade the thermal protection system provides.
The spacecraft will be equipped with seven ‘Solar Limb Sensors’ located all around it, to give early warning if it slips out from underneath the protective shield. The probe will then autonomously place itself back.
The Solar Probe Plus has three computers on board: the prime, the hot spare and the back-up spare. In the event that the prime computer fails, the hot spare will take over, “keeping the probe behind the thermal protection system and the solar arrays at the right angle,” said Buckley.
Instrumental information
To understand solar activity better and predict space-weather events, the probe will carry four instruments. The Solar Wind Electrons Alphas and Protons Investigation, led by astrophysicist Justin Kasper of the Harvard-Smithsonian Center for Astrophysics, aims to analyse the most abundant particles in solar wind and measure their velocity and temperature.
Then there is the Integrated Science Investigation of the Sun, led by astrophysicist David McComas of the Southwest Research Institute in San Antonio, Texas. It will measure high-energy accelerations of electrons, protons and ions in the Sun’s atmosphere and compare them to solar wind formations.
The third instrument is called the Fields Experiment. Overseen by plasma astrophysicist Stuart Bale of the University of California at Berkeley, it will measure electric and magnetic fields, as well as shock waves in the solar atmosphere. The device will also monitor density and temperature fluctuations of particles around the Sun. Finally, the craft will carry the Wide-field Imager, led by astrophysicist Russell Howard of the US Naval Research Laboratory in Washington DC. It will complement the rest of the instruments by 3D imaging the corona and solar winds to provide realtime information about radiation conditions.
Don’t expect exciting results any time soon, though. It will be 2025 before the Solar Probe Plus gradually decreases its 88-day orbits to come close to the Sun, hurtling towards the centre of the solar system at 450,000mph. The closest a space probe has previously come to reaching the Sun was in the 1970s, when Nasa’s Helios 1 passed within 28 million miles of the solar surface.