NASA is going to launch its next science mission, named Parker Solar Probe, on 11th August 2018. The spacecraft will eventually get within 4 million miles of the surface of the sun. It will fly through an intensely hot atmosphere, the corona.
To put this in context, if the Sun was at one end of a yardstick and Earth on the other, the spacecraft will reach within 4 inches of the Sun’s surface. It will help us understand why particles, heat and energy flow outward into the solar system.
Parker Solar Probe will travel through temperatures more than a million degrees Celsius and will be exploited to extreme sunlight. So from where does it get its extraordinary capability? What prevents the spacecraft from melting like an ice cream.
Well the answer lies in its autonomous system and special heat shield that protects the spacecraft from intense heat, while allowing the coronal matter to ‘touch’ the probe. Let’s find out in details what keeps the instruments safe.
1. Temperature Vs. Heat
Temperature and heat are two different entities. High temperatures aren’t always responsible for transferring heat to another object. Temperature in outer space could reach tens of thousand of degrees without transmitting much heat to a specific material. But, why?
Actually, temperature depends on the speed of particles, whereas heat measures the amount of energy particles transfer. Particles moving at very fast speed generate high temperature, however, if the number of particles is low, they won’t transmit much energy (less heat).
Same happens to Parker Space Probe: since the space is mostly empty and corona isn’t much dense, the spacecraft encounters fewer particles (coming out of the Sun) and does not accumulate heat on excessive level.
More specifically, the heat shield facing towards the Sun will reach nearly 1400°C, despite traveling through temperatures of millions of degrees Celsius.
2. The Protecting Shield
Obviously, 1400°C is still incredibly hot. To put this into context, volcano eruption lava goes up to 1200°C. In order to work optimally at such high temperatures, the spacecraft is built with a Thermal Protection System that is 11.5 cm thick and 240 cm in diameter. It keeps the equipment temperature (on the other side of the shield) in a safe range (about 30°C).
Spacecraft’s Heat Shield | Credit: NASA
This shield is built with a carbon composite foam sandwiched between two carbon plates. To reflect the maximum amount of heat, the sun-facing plate has a white ceramic paint, and it’s capable of withstanding temperatures up to 1650°C.
3. Faraday Cup For Measuring Solar Wind
An instrument called Faraday cup is one of two modules on spacecraft that is not protected by the Thermal Protection System. It’s placed over the heat shield to calculate the electron and ion fluxes, and flow angles in the intense solar environment.
Engineers have used advanced technologies to make this instrument survive in the harsh conditions. It’s made of Titanium-Zirconium-Molybdenum sheets (melts at 2349°C) and tungsten chips (generates electric field for cup and has a melting point of 3422°C).
4. Electronic Wiring
Conventional wires would melt at such extreme conditions. Therefore, engineers created niobium wires and sapphire crystal tubes to support the wiring of Faraday cup.
5. Cooling System
Without protection from excessive radiation, solar panels can overheat. So it’s important to put solar panels behind the heat shield and allow limited Sun rays to pass through. However, the more it gets close to the star, the more protection it needs. That’s why solar arrays are equipped with a cooling system, which contains –
- A heated tank and two radiators to keep coolant (deionized water) from frosting.
- Fins made of aluminum to increase the cooling surface.
- Pumps for circulating coolant.
For coolant, they’ve used 3.7 liters of pressurized deionized water. It can keep the system cool for temperatures ranging anywhere between 10°C and 125°C (in this case, the boiling point of pressurized water is more than 125°C).
6. Autonomous System
Image credit: NASA
Since the spacecraft will be far away from the Earth, it would take several minutes to send a signal from the ground. But, what if it encounters a critical error that needs to be corrected immediately?
For such scenarios, engineers have integrated an autonomous system that can keep spacecraft safe and on the right trajectory. It’s equipped with numerous sensors that can notify computer (without any human involvement) to correct its position if anything goes wrong. The system has been rigorously tested, so that it can make right decision on the fly.
It’s a 7 year mission, and during this period, the probe will revolve 24 times around the Sun. On each closest approach to the star, it will examine the corona and sample the solar wind.
The mission will answer three main questions:
- Why atmosphere of the Sun is hotter than its surface?
- How the solar wind of charged particles is born?
- What causes coronal mass ejections?
The answers would help scientists understand how stars beyond our solar system function.