Parker Solar Probe

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Lore & Background

The Parker Solar Probe concept originates in a 1958 report by the Fields and Particles Group, Committee 8 of the National Academy of Sciences' Space Science Board, which proposed several space missions including 'a solar probe to pass inside the orbit of Mercury to study the particles and fields in the vicinity of the Sun.' Studies in the 1970s and 1980s reaffirmed its importance, but it was always postponed due to cost. A cost-reduced Solar Orbiter mission was studied in the 1990s, and a more capable Solar Probe mission served as one of the centerpieces of the Outer Planet/Solar Probe (OPSP) program formulated by NASA in the late 1990s. The original Solar Probe design used a gravity assist from Jupiter to enter a polar orbit which dropped almost directly toward the Sun, but the extreme variation in solar irradiance made for an expensive mission and required a radioisotope thermal generator for power. Following the appointment of Sean O'Keefe as Administrator of NASA, the entirety of the OPSP program was canceled as part of President George W. Bush's request for the 2003 United States federal budget. In the early 2010s, plans for the Solar Probe mission were incorporated into a lower-cost Solar Probe Plus, using multiple Venus gravity assists for a more direct flight path powered by solar panels. In May 2017, the spacecraft was renamed the Parker Solar Probe in honor of astrophysicist Eugene Newman Parker, who had proposed the existence of nanoflares as an explanation of coronal heating as well as having developed a mathematical theory that predicted the existence of solar wind. The solar probe cost NASA US$1.5 billion. A memory card containing names submitted by over 1.1 million people was mounted on a plaque and installed below the spacecraft's high-gain antenna, also containing photos of Parker and a copy of his 1958 scientific paper predicting important aspects of solar physics.

Reader's Guide

The Parker Solar Probe is significant as the first spacecraft to fly into the low solar corona, providing unprecedented data on coronal plasma, magnetic fields, and solar wind acceleration. Its repeated Venus gravity assists allowed it to achieve a record speed of 690,000 km/h in December 2024, making it the fastest human-made object. The mission's thermal protection system, a hexagonal solar shield 2.3 m in diameter and 11.4 cm thick, made of two panels of reinforced carbon–carbon composite with a carbon foam core, withstands temperatures outside the spacecraft of about 1,370 °C (2,500 °F) and keeps the spacecraft's instruments at 29 °C (85 °F). The shield weighs only 73 kilograms (160 lb). The spacecraft systems and scientific instruments are located in the central portion of the shield's shadow, where direct radiation from the Sun is fully blocked. As radio communication with Earth takes about eight minutes in each direction, the Parker Solar Probe has to act autonomously and rapidly to protect itself, using four light sensors to detect direct sunlight and engaging reaction wheels to reposition the spacecraft. According to project scientist Nicky Fox, the team described it as 'the most autonomous spacecraft that has ever flown.' The primary power is a dual system of solar panels; a primary array is retracted behind the shadow shield during close approach, and a much smaller secondary array powers the spacecraft through closest approach, using pumped-fluid cooling to maintain operating temperature. The trajectory required high launch energy, so the probe was launched on a Delta IV Heavy launch vehicle and an upper stage based on the Star 48BV solid rocket motor. The PSP performed its final gravity assist on November 6, 2024, setting the spacecraft on a new orbit passing 6.1 million kilometers (3.8 million miles) from the surface of the Sun. The exact time of closest approach was 11:53 UTC on December 24, 2024, and a beacon signal was received on December 26 showing it had survived the passage through the corona. Detailed telemetry was received January 1, 2025. In 2025, the teams from NASA, Johns Hopkins, and partners were awarded the 2024 Collier Trophy for their achievements.

Did You Know?

• The Parker Solar Probe is the first NASA spacecraft named after a living person, honoring physicist Eugene Newman Parker.
• At its closest approach in December 2024, the probe's speed relative to the Sun was 690,000 km/h (430,000 mph), or 0.064% the speed of light.
• The solar shield is only 73 kilograms (160 lb) but withstands temperatures of about 1,370 °C (2,500 °F).
• A memory card containing names submitted by over 1.1 million people was mounted on a plaque and installed below the spacecraft's high-gain antenna.
• The probe's closest approach to the Sun's surface on December 24, 2024, was 6.1 million km (3.8 million miles), and its beacon signal was received on December 26 confirming survival.