The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a NASA space probe launched in 2018 to make observations of the Sun's outer corona.
It used repeated gravity assists from Venus to develop an eccentric orbit, approaching within 9.86 solar radii (6.9 million km or 4.3 million miles) from the center of the Sun. At its closest approach in 2024, its speed relative to the Sun was or 191 km/s (118.7 mi/s), which is 0.064% the speed of light. It is the fastest object ever built on Earth.
The project was announced in the 2009 budget year. Johns Hopkins University Applied Physics Laboratory designed and built the spacecraft, which was launched on August 12, 2018. It became the first NASA spacecraft named after a living person, honoring the physicist Eugene Newman Parker, professor emeritus at the University of Chicago.
On October 29, 2018, at about 18:04 UTC, the spacecraft became the closest ever artificial object to the Sun. The previous record, from the Sun's surface, was set by the Helios 2 spacecraft in April 1976. At its perihelion on September 27, 2023, the PSP's closest approach was , reaching this distance again on March 29, 2024.
On December 24, 2024, at 11:53 UTC, PSP made its closest approach to the Sun, coming to a distance of 6.16 million km (3.83 million miles) from the surface.https://parkersolarprobe.jhuapl.edu/The-Mission/index.php Its beacon signal was received on December 26, showing that 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.
History The Parker Solar Probe concept originates in the 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 first three missions of the program were planned to be: the Solar Orbiter, the Pluto and Kuiper belt reconnaissance Pluto Kuiper Express mission, and the Europa Orbiter astrobiology mission focused on Europa.
The original Solar Probe design used a gravity assist from Jupiter to enter a polar orbit which dropped almost directly toward the Sun. While this explored the important solar poles and came even closer to the surface (3 , a perihelion of 4 ), the extreme variation in solar irradiance made for an expensive mission and required a radioisotope thermal generator for power. The trip to Jupiter also made for a long mission, years to first solar perihelion, 8 years to second.
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. Administrator O'Keefe cited a need for a restructuring of NASA and its projects, falling in line with the Bush Administration's wish for NASA to refocus on "research and development, and addressing management shortcomings".
In the early 2010s, plans for the Solar Probe mission were incorporated into a lower-cost Solar Probe Plus. The redesigned mission uses multiple Venus gravity assists for a more direct flight path, which can be powered by solar panels. It has a higher perihelion, reducing the demands on the thermal protection system.
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.How NASA's New Solar Probe Will 'Touch' the Sun on Historic Mission . Meghan Bartels, Space.com. August 9, 2018.Successful Launch of NASA's Parker Solar Probe. SatNews Daily. August 12, 2018. The launch rocket bore a dedication in memory of APL engineer Andrew A. Dantzler who had worked on the project.
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 card also contains photos of Parker and a copy of his 1958 scientific paper predicting important aspects of solar physics.
Spacecraft The Parker Solar Probe is the first spacecraft to fly into the low solar corona. It will assess the structure and dynamics of the Sun's coronal plasma and magnetic field, the energy flow that heats the solar corona and impels the solar wind, and the mechanisms that accelerate energetic particles.
The spacecraft's systems are protected from the extreme heat and radiation near the Sun by a solar shield. Incident solar radiation at perihelion is approximately , or 475 times the intensity at Earth orbit. The solar shield is hexagonal, mounted on the Sun-facing side of the spacecraft, in diameter, thick, and is made of two panels of reinforced carbon–carbon composite with a lightweight carbon foam core, which is designed to withstand temperatures outside the spacecraft of about . The shield weighs only and keeps the spacecraft's instruments at .
A white reflective alumina surface layer minimizes absorption. 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. If the shield was not between the spacecraft and the Sun, the probe would be damaged and become inoperative within tens of seconds. 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. This is done using four light sensors to detect the first traces of direct sunlight coming from the shield limits and engaging movements from reaction wheels to reposition the spacecraft within the shadow again. According to project scientist Nicky Fox, the team described it as "the most autonomous spacecraft that has ever flown".
The primary power for the mission is a dual system of solar panels (photovoltaic arrays). A primary photovoltaic array, used for the portion of the mission outside , is retracted behind the shadow shield during the close approach to the Sun, and a much smaller secondary array powers the spacecraft through closest approach. This secondary array uses pumped-fluid cooling to maintain operating temperature of the solar panels and instrumentation.
Trajectory
The Parker Solar Probe mission design used repeated gravity assists at Venus to incrementally decrease its orbital perihelion to achieve a final altitude (above the surface) of approximately 8.5 solar radii, or about . The spacecraft trajectory included seven Venus flybys over nearly seven years to gradually shrink its elliptical orbit around the Sun, for a total of 24 orbits. The near Sun radiation environment was predicted to cause spacecraft charging effects, radiation damage in materials and electronics, and communication interruptions, so the orbit is highly elliptical with short times spent near the Sun.
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. Interplanetary gravity assists provided further deceleration relative to its heliocentric orbit, which resulted in a heliocentric speed record at perihelion. As the probe passed around the Sun in December 2024, it achieved a velocity of or 191 km/s (118.7 mi/s) in the heliocentric ecliptic reference frame, which temporarily made it the fastest human-made object, almost three times as fast as the previous record holder, Helios-2.
Launch injection was very close to predictions, but nevertheless required path correction. Trajectory was re-optimized after the launch to save fuel. The first Venus flyby was only 52 days after the launch; three trajectory correction maneuvers were performed in this window.
As described by Kepler's laws of planetary motion, which apply to any object in an orbit, gravity will cause the spacecraft to accelerate as it nears perihelion, then slow down again afterward until it reaches its aphelion. Because of its highly elliptical orbit and the Sun's strong gravity, this effect is particularly pronounced for the Parker Solar Probe. During a perihelion on September 27, 2023, the spacecraft traveled at 394,736 miles per hour (176.5 km/s), fast enough to fly from New York to Tokyo in just over a minute.
Final orbit, possible extensions and end of mission
The PSP performed its final gravity assist on November 6, 2024. It set the spacecraft on a new orbit passing 6.16 million kilometers (3.83 million miles) from the surface of the Sun. A beacon transmission was made and received successfully on December 20 to confirm that the craft was operating normally ahead of the perihelion. The exact time of closest approach was 11:53 UTC on December 24 but the craft was out of contact at this time. A further beacon transmission confirming successful passage was received on December 26.
This final orbit is inside the orbit of Venus and so no further encounters with that planet are planned. PSP will continue in this orbit but requiring adjustment to maintain attitude so that its transmitters point at Earth. Eventually its thrusters will run out of fuel and full functioning will not then be possible. The plan is to then rotate the craft so that its instruments will be exposed to the full radiance of the Sun for the first time. This is expected to ablate and destroy them. The heat shield will remain and is expected to continue to orbit the Sun for millions of years.
PSP's main mission ended in 2025. In 2026, the extended mission was approved into 2029.
Instruments
Parker Solar Probe has four main instruments:
FIELDS (Electromagnetic Fields Investigation). The instrument suite captures the scale and shape of electric and magnetic fields in the Sun's atmosphere. FIELDS measures waves and turbulence in the inner heliosphere with high time resolution to understand the fields associated with waves, shocks and magnetic reconnection, a process by which magnetic field lines explosively realign. FIELDS measures the electric field around the spacecraft with five antennas, four of which stick out beyond the spacecraft's heat shield and into the sunlight, where they experience temperatures of . The antennas are made of a niobium alloy, which can withstand extreme temperatures. FIELDS measures electric fields across a broad frequency range both directly and remotely. Operating in two modes, the four sunlit antennas measure the properties of the fast and slow solar wind — the flow of solar particles constantly streaming out from the Sun. The fifth antenna, which sticks out perpendicular to the others in the shade of the heat shield, helps make a three-dimensional picture of the electric field at higher frequencies. The suite also has three magnetometers to assess the magnetic field. A search coil magnetometer, or SCM, measures how the magnetic field changes over time. Two identical fluxgate magnetometers, MAGi and MAGo, measure the large-scale coronal magnetic field. The fluxgate magnetometers are specialized for measuring the magnetic field further from the Sun where it varies at a slower rate, while the search coil magnetometer is necessary closer to the Sun where the field changes quickly, as it can sample the magnetic field at a rate of two million times per second. The Principal Investigator is Stuart Bale at the University of California, Berkeley.