— Ch. 1 · Origins And Evolution —
Parker Solar Probe.
~7 min read · Ch. 1 of 6
In 1958, the Fields and Particles Group of the National Academy of Sciences' Space Science Board proposed a mission to send a probe inside Mercury's orbit. This early report outlined plans to study particles and fields near the Sun. Decades passed before the idea gained traction again in the 1970s and 1980s. Scientists reaffirmed the importance of such a journey but repeatedly postponed it due to high costs. A cost-reduced version called Solar Orbiter was studied during the 1990s. Later, NASA formulated the Outer Planet/Solar Probe program in the late 1990s. It included three planned missions: the Solar Orbiter, Pluto Kuiper Express, and Europa Orbiter. The original design for the solar probe used Jupiter gravity assists to reach polar orbits close to the Sun. That approach required years of travel and expensive radioisotope thermal generators for power. In 2003, Administrator Sean O'Keefe canceled the entire OPSP program as part of President George W. Bush's budget request. He cited a need for restructuring NASA and refocusing on research and development. Plans resurfaced in the early 2010s under the name Solar Probe Plus. The redesigned mission used multiple Venus flybys instead of Jupiter. It relied on solar panels rather than nuclear power sources. The project received its final funding approval in fiscal year 2009. On the 12th of August 2018, Johns Hopkins University Applied Physics Laboratory launched the spacecraft from Cape Canaveral. The rocket carried a plaque with names submitted by over 1.1 million people. A memory card inside held photos of Eugene Newman Parker and his 1958 scientific paper predicting aspects of solar physics. In May 2017, the spacecraft was renamed the Parker Solar Probe to honor the astrophysicist who had proposed nanoflares and developed theories about solar wind. The total cost to NASA reached US$1.5 billion.
Engineering The Shield
The probe carries a hexagonal heat shield measuring 11 feet (3.4 meters) in diameter and 4.5 inches (11.4 centimeters) thick. It is constructed from two panels of reinforced carbon-carbon composite surrounding a lightweight carbon foam core. This structure withstands temperatures outside the spacecraft reaching approximately 2,500 degrees Fahrenheit (1,370 degrees Celsius). Incident solar radiation at perihelion reaches about 650 kilowatts per square meter, or 475 times the intensity experienced at Earth orbit. Without this shield, direct sunlight would damage the probe within tens of seconds. Four light sensors detect the first traces of sunlight escaping the shield's edge. Reaction wheels then reposition the spacecraft back into shadow automatically. Project scientist Nicky Fox described it as the most autonomous spacecraft ever flown. A white reflective alumina surface layer minimizes absorption of incoming energy. During close approaches, primary photovoltaic arrays retract behind the shield. A smaller secondary array powers the craft using pumped-fluid cooling systems. These systems maintain operating temperatures for both instruments and electronics. If communication with Earth fails during an approach, the probe must act independently to survive. Radio signals take eight minutes each way between the Sun and Earth. The team designed the system so that no human intervention could occur fast enough to prevent overheating. The shield weighs only 160 pounds (73 kilograms). It keeps all internal instruments below 85 degrees Fahrenheit (30 degrees Celsius) despite external heat exceeding 2,500 degrees.