Good Speed, Parker Solar Probe!

By Jason Schreiner, Planetarium Coordinator

Image Credit: Johns Hopkins Applied Physics Laboratory/Steve Gribben

In 1957, Eugene Parker proposed some radical new theories on the nature of our home star, the Sun. Six decades later, his dreams of unlocking the secrets of the Sun are becoming a reality. In the early hours of August 12, 2018, the Parker Solar Probe lifted off aboard a Delta IV Heavy rocket from Cape Canaveral Air Force Station Space Launch Complex 37. Its seven-year journey will push the limits of human engineering, breaking numerous records to confirm and reach beyond Dr. Parker’s hypotheses on the solar wind, the corona, and the magnetic interactions between the Sun and Earth.

Vehicle Assembly Building and Venus. Image Credit: Jason Schreiner/MOAS

The Launch

The launch of the Parker Solar Probe (PSP) marks only the tenth Heavy version of the Delta IV rocket to be utilized. Requiring a large specific orbital energy to achieve its goals, the car-sized probe sat in a mostly empty capsule atop the enormous rocket with the two additional boosters all strapped together. A rocket with this much energy was necessitated by the orbital mechanics of the mission to fight against the momentum of Earth’s orbit and fall inwards to the center of the solar system. (More on this later.) To aid this expedition even further, controlling the weight of the spacecraft was of vital importance. A lighter craft can attain higher speeds, so every bit of excess was shaved off when possible. The Parker Solar Probe is a lean, mean, speed machine.

Image Credit: Delta IV Heavy rocket in the final stages of preparation. For a sense of scale,
look closely for two United Launch Alliance workers. Image Credit: Jason Schreiner/MOAS

Image Credit: Jason Schreiner/MOAS

 

Image Credit: Jason Schreiner/MOAS

 

Image Credit: Jason Schreiner/MOAS

 

Image Credit: NASA/Bill Ingalls

At precisely 3:31 a.m. on August 12, 2018, the 236 ft tall, 1,616,000 lb. rocket blazed through clear skies. The RS-68A engines burned the cryogenic liquid hydrogen and liquid oxygen fuel, leaving a blindingly bright trail. With 2.2 million foot-pounds of thrust, the trio of engines departed the Florida coast and arced east over the Atlantic Ocean, to ever greater heights and a rendezvous with scientific immortality.   

The Mission

Since we all live within the Sun’s atmosphere as it extends far into space, it is vital that we understand how it functions. Solar weather can have a massive impact on Earth’s technology, especially on satellites in space, on our radio transmissions at the surface, and on our electrical grid, as well as the immediate safety of our astronauts. To achieve the scientific goals of better understanding solar behavior, five major investigations will take place during the expedition. 

1. Electromagnetic Fields Investigation (FIELDS) will make direct measurements of the electric and magnetic fields, radio waves, plasma density, and electron temperature.
2. Integrated Science Investigation of the Sun (IS☉IS) will measure energetic electrons, protons, and heavy ions.
3. Wide-field Imager for Solar Probe (WISPR) will take optical images of the corona and inner heliosphere.
4. Solar Wind Electrons Alphas and Protons (SWEAP) will count electrons, protons, and helium ions and measure their velocities, densities, and temperatures.
5. Heliospheric Origins with Solar Probe Plus (HeliOSPP) will be a theory and modeling investigation to maximize the scientific return from the mission.

Image Credit: NASA's Scientific Visualization Studio

An unprecedented mission such as this requires a level of heat shielding technology never seen before. The side facing the Sun must endure temperatures upwards of 1,400 degrees Celsius (2,552 degrees Fahrenheit). This high-tech Thermal Protection System is the culmination of years of trial and error, research and analysis by the engineers at the Johns Hopkins University Applied Physics Laboratory. Without their immense efforts and the resultant heat shield, the entire mission would not be viable. Composed of complex layers of white ceramic, tungsten, carbon-carbon, and 4.5 inches of carbon foam, the core of which is 97% air, the shield will insulate the instruments from exposure to the intense solar thermals and keep them near room temperature. Kevlar blankets will also protect the craft from “hypervelocity dust,” tiny particles moving at incredibly high speeds which can (and will) damage the spacecraft.

The Trajectory

While it may seem relatively easy to send a mission to the Sun rather than the far reaches of our solar system, this is not the case. Gravitationally speaking, the trajectory is actually rather difficult. In fact, it takes about 55 times more energy to reach the Sun than Mars. Keeping in mind that the Earth is constantly in motion around the Sun, think of our orbit like water spiraling around a drain. As a spacecraft launches from Earth, it conserves the angular momentum imparted by our planet, so it would naturally continue along that roughly circular path around the Sun. In order to travel towards the Sun, however, a series of braking maneuvers must be performed to bleed off some of that speed and fall inwards to the center of the solar system. Over the course of seven years, the Parker Solar Probe will make seven passes by Venus for a gravitational assist. Most often, gravitational assists are associated with stealing a little of a planet’s momentum to increase a spacecraft’s velocity as it passes. However, in the case of the PSP, the gravity “assist” is more of a “desist” since the purpose is to remove some inherent speed of the probe from Earth’s angular momentum. 

By giving Venus some of its momentum, the probe’s orbit will gradually shrink, resulting in a closest pass of only 3.83 million miles from the Sun. With the Earth at a distance of about 93 million miles from the Sun, the probe will be only 4% of that distance away from the Sun’s surface.

While the probe may require a reduction in velocity to direct itself towards the Sun, nobody will be able to claim it is a slow spacecraft. The reality will be quite the opposite. While the scientific data collected from this mission will revolutionize humanity’s understanding of the Sun, an equally exciting prospect is the incredible speed that the spacecraft will achieve along the way.  

As the Parker Solar Probe approaches the center of the solar system, the Sun’s ever-present gravitational force will continue tugging on the spacecraft, pulling it to faster and faster speeds. Not only will the Parker Solar Probe become the new record holder for the fastest object ever made by humans, on December 19, 2024, it will obliterate the current record of 44 miles per second, set by spacecraft Helios-B in 1976. The PSP will reach a truly blazing velocity of 120 miles per second, beating Helios-B almost three times over. That’s fast enough to travel from Philadelphia to Washington, D.C. in one second. This velocity is so high, it requires two graphs to fully appreciate.

A "high speed" object such as a typical airline passenger plane, cruising at 560 miles per hour,

does not even register when compared to the Parker Solar Probe's extreme velocity.
Image Credit: Jason Schreiner/MOAS

Traveling at 432,000 miles per hour, the PSP will face immense heat and radiation like no other spacecraft before. Braving the plasma, magnetic fields, and charged particles to touch the face of the Sun, it will gather precious data to help us better understand our place in the solar system, aid in space-weather prediction, and potentially keep us safe from future solar phenomena. As is the case with most groundbreaking experiments, the Parker Solar Probe will surely lead to even more new questions than it will provide answers, but further expanding our knowledge of our home star, our solar system and the entire universe.

Launch of the Parker Solar Probe on a Delta IV Heavy rocket from Launch Compex 37 in Cape Canaveral, FL on August 12, 2018 at 3:31 am.
Taken with a Canon 70D attached to an 8 inch Meade Schmidt-Cassegrain telescope from the roof of the Vehicle Assembly Building.
Distance: about 6 miles. Video Credit: Jason Schreiner/MOAS