Integrated Science Investigation of the Sun Energetic Particle Instruments
The official insignia for the mission.
The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a
NASAspace probe launched in 2018 with the mission of making observations of the outer
corona of the
Sun. It will approach to within 9.86
solar radii (6.9 million km or 4.3 million miles) from the center of the Sun, and by 2025 will travel, at closest approach, as fast as 690,000 km/h (430,000 mph) or 191 km/s,
which is 0.064% the
speed of light. It is the fastest object ever built.
memory card containing the names of over 1.1 million people was mounted on a plaque and installed below the spacecraft's high-gain antenna on 18 May 2018. The card also contains photos of Parker and a copy of his 1958 scientific paper predicting important aspects of
On 29 October 2018, at about 18:04 UTC, the spacecraft became the closest ever artificial object to the Sun. The previous record, 42.73 million kilometres (26.55 million miles) from the Sun's surface, was set by the Helios 2 spacecraft in April 1976. As of its
perihelion 27 September 2023, the Parker Solar Probe's closest approach is 7.26 million kilometres (4.51 million miles). This will be surpassed after the remaining
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
eponymous 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
Kuiper belt reconnaissance
Pluto Kuiper Express mission, and the
Europa Orbiter astrobiology mission focused on
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 R☉, a perihelion of 4 R☉), 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 (3+1⁄2 years to first solar perihelion, 8 years to second).
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 also 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 coined the term "
solar wind". The solar probe cost
NASA US$1.5 billion. The launch rocket bore a dedication in memory of APL engineer Andrew A. Dantzler who had worked on the project.
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 650 kW/m2, or 475 times the
intensity at Earth orbit.: 31 The solar shield is hexagonal, mounted on the Sun-facing side of the spacecraft, 2.3 m (7 ft 7 in) in diameter, 11.4 cm (4.5 in) thick, and is made of two panels of
reinforced carbon–carbon composite with a lightweight 4.5-inch-thick carbon foam core, which is designed to withstand temperatures outside the spacecraft of about 1,370 °C (2,500 °F). The shield weighs only 73 kilograms (160 lb) and keeps the spacecraft's instruments at 29 °C (85 °F).
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 were not between the spacecraft and the Sun, the probe would be damaged and become inoperative within tens of seconds. As radio communication with Earth will take about eight minutes in each direction, the Parker Solar Probe will have to act autonomously and rapidly to protect itself. This will be 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 describe 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 0.25 au, 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.
A light bar testing in the
Astrotech processing facility.
The thermal testing of the spacecraft.
PSP during extensive environmental testing.
PSP encapsulated in fairing.
The launch of the probe.
The Parker Solar Probe mission design uses 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 6×10^6 km (3.7×10^6 mi; 0.040 au). The spacecraft trajectory will include 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 is predicted to cause spacecraft charging effects, radiation damage in materials and electronics, and communication interruptions, so the orbit will be highly elliptical with short times spent near the Sun.
The trajectory requires high launch energy, so the probe was launched on a
Delta IV Heavy class
launch vehicle and an upper stage based on the
Star 48BV solid rocket motor. Interplanetary
gravity assists will provide further deceleration relative to its
heliocentric orbit, which will result in a heliocentric speed record at
perihelion. As the probe passes around the
Sun, it will achieve a velocity of up to 200 km/s (120 mi/s), which will temporarily make it the fastest human-made object, almost three times as fast as the previous record holder,
Helios-2. 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.Like every object in an orbit, due to gravity the spacecraft will accelerate as it nears perihelion, then slow down again afterward until it reaches its
How is energy from the lower solar atmosphere transferred to, and dissipated in, the corona and solar wind?
What processes shape the non-equilibrium velocity distributions observed throughout the heliosphere?
How do the processes in the corona affect the properties of the solar wind in the heliosphere?
Determine the structure and dynamics of the plasma and
magnetic fields at the sources of the solar wind.
How does the magnetic field in the solar wind source regions connect to the photosphere and the heliosphere?
Are the sources of the solar wind steady or intermittent?
How do the observed structures in the corona evolve into the solar wind?
Explore mechanisms that accelerate and transport energetic particles.
What are the roles of shocks, reconnection, waves, and turbulence in the acceleration of energetic particles?
What are the source populations and physical conditions necessary for energetic particle acceleration?
How are energetic particles transported in the corona and heliosphere?
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 2,500 °F (1,370 °C). The 2-meter-long (6 ft 7 in) 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.
IS☉IS (Integrated Science Investigation of the Sun). The instrument uses two complementary instruments to measure particles across a wide range of energies. By measuring electrons, protons and ions, IS☉IS will understand the particles' lifecycles — where they came from, how they became accelerated and how they move out from the Sun through interplanetary space. The two energetic particle instruments on IS☉IS are called EPI-Lo and EPI-Hi (EPI stands for Energetic Particle Instrument). EPI-Lo measures the spectra of electrons and ions and identifies carbon, oxygen, neon, magnesium, silicon, iron and two isotopes of helium, He-3 and He-4. Distinguishing between helium isotopes will help determine which of several theorized mechanisms caused the particles' acceleration. The instrument has a design with an octagonal dome body supporting 80 viewfinders. Multiple viewfinders provide a wide field of view to observe low-energy particles. An ion that enters EPI-Lo through one of the viewfinders first passes through two carbon-polyimide-aluminum foils and then encounters a solid-state detector. Upon impact, the foils produce electrons, which are measured by a microchannel plate. Using the amount of energy left by the ion's impact on the detector and the time it takes the ions to pass through the sensor identifies the species of the particles. EPI-Hi uses three particle sensors composed of stacked layers of detectors to measure particles with energies higher than those measured by EPI-Lo. The front few layers are composed of ultra-thin silicon detectors made up of geometric segments, which allows for the determination of the particle's direction and helps reduce background noise. Charged particles are identified by measuring how deep they travel into the stack of detectors and how many electrons they pull off atoms in each detector, a process called ionization. At closest approach to the Sun, EPI-Hi will be able to detect up to 100,000 particles per second. The Principal Investigator is David McComas at
WISPR (Wide-field Imager for Solar Probe). These optical telescopes acquire images of the
corona and inner
heliosphere. WISPR uses two cameras with radiation-hardened Active Pixel Sensor CMOS detectors. The camera's lenses are made of a radiation hard BK7, a common type of glass used for space telescopes, which is also sufficiently hardened against the impacts of dust. The Principal Investigator is Russell Howard at the
Naval Research Laboratory.
SWEAP (Solar Wind Electrons Alphas and Protons). This investigation will count the electrons, protons and helium ions, and measure their properties such as velocity, density, and temperature. Its main instruments are the Solar Probe Analyzers (SPAN, two
electrostatic analyzers) and the Solar Probe Cup (SPC). SPC is a
Faraday cup, a metal device that can catch charged particles in a vacuum. Peeking over the heat shield to measure how electrons and ions are moving, the cup is exposed to the full light, heat and energy of the Sun. The cup is composed of a series of highly transparent grids — one of which uses variable high voltages to sort the particles — above several collector plates, which measure the particles' properties. The variable voltage grid also helps sort out background noise, such as cosmic rays and photoionized electrons, which could otherwise bias the measurements. The grids, located near the front of the instrument, can reach temperatures of 3,000 °F (1,650 °C), glowing red while the instrument makes measurements. The instrument uses pieces of sapphire to electrically isolate different components within the cup. As it passes close to the Sun, SPC takes up to 146 measurements per second to accurately determine the velocity, density and temperature of the Sun's plasma. SPAN is composed of two instruments, SPAN-A and SPAN-B, which have wide fields of view to allow them to see the parts of space not observed by SPC. Particles encountering the detectors enter a maze that sends the particles through a series of deflectors and voltages to sort the particles based on their mass and charge. While SPAN-A has two components to measure both electrons and ions, SPAN-B looks only at electrons. The Principal Investigator is Justin Kasper at the
University of Michigan and the
Smithsonian Astrophysical Observatory.
An additional theoretical investigation named Heliospheric origins with Solar Probe Plus (HeliOSPP) starting from 2010 and ending in 2024 has the role of providing theoretical input and independent assessment of scientific performance to the Science Working Group (SWG) and the SPP Project to maximize the scientific return from the mission. The Principal Investigator is Marco Velli at the
University of California, Los Angeles and the
Jet Propulsion Laboratory; he also serves as the Observatory Scientist for the mission.
Parker Solar Probe was launched on 12 August 2018, at 07:31 UTC. The spacecraft operated nominally after launching. During its first week in space it deployed its high-gain antenna, magnetometer boom, and electric field antennas. The spacecraft performed its first scheduled trajectory correction on 20 August 2018, while it was 8.8 million kilometers (5.5 million mi) from Earth, and travelling at 63,569 kilometres per hour (39,500 mph)
Instrument activation and testing began in early September 2018. On 9 September 2018, the two
WISPR telescopic cameras performed a successful
first-light test, transmitting wide-angle images of the background sky towards the
The probe successfully performed the first of the seven planned Venus flybys on 3 October 2018, where it came within about 2,400 kilometres (1,500 mi) of Venus in order to reduce the probe's speed and orbit closer to the Sun.
Within each orbit of the Parker Solar Probe around the Sun, the portion within 0.25 AU is the Science Phase, in which the probe is actively and autonomously making observations. Communication with the probe is largely cut off in that phase.: 4 Science phases run for a few days both before and after each perihelion. They lasted 11.6 days for the earliest perihelion, and will drop to 9.6 days for the final, closest perihelion.: 8
Much of the rest of each orbit is devoted to transmitting data from the science phase. But during this part of each orbit, there are still periods when communication is not possible. First, the requirement that the heat shield of the probe be pointed towards the Sun sometimes puts the heat shield between the antenna and Earth. Second, even when the probe is not particularly near the Sun, when the angle between the probe and the Sun (as seen from Earth) is too small, the Sun's radiation can overwhelm the communication link.: 11–14
After the first
Venusflyby, the probe was in an
elliptical orbit with a period of 150 days (two-thirds the period of Venus), making three orbits while Venus makes two. After the second flyby, the period shortened to 130 days. After less than two orbits (only 198 days later) it encountered Venus a third time at a point earlier in the orbit of Venus. This encounter shortened its period to half of that of Venus, or about 112.5 days. After two orbits it met Venus a fourth time at about the same place, shortening its period to about 102 days. After 237 days, it met Venus for the fifth time and its period was shortened to about 96 days, three-sevenths that of Venus. It then made seven orbits while Venus made three. The sixth encounter, almost two years after the fifth, shortened its period down to 92 days, two-fifths that of Venus. After five more orbits (two orbits of Venus), it will meet Venus for the seventh and last time, decreasing its period to 88 or 89 days and allowing it to approach closer to the
The speed of the probe and distance from the Sun, from launch until 2026
Flybys 3 and 4 occur at the same point in Venus's orbit.
Venus flyby #4
Flybys 3 and 4 occur at the same point in Venus's orbit.
First perihelion to enter the solar corona
Venus flyby #5
Flybys 5 and 6 occur at the same point in Venus's orbit.
Venus flyby #6
Flybys 5 and 6 occur at the same point in Venus's orbit.
Venus flyby #7
^For altitude above the surface, subtract one solar radius ≈0.7 Gm. (A Gm (gigametre) is a million km or about 621371 mi.)
^Details on Venus flybys from Guo et al.: 6 This was published in 2014, four years before the mission began. For a variety of reasons, including the fact that the launch had to be delayed at the last minute, actual details could differ from the ones presented in the work.
^Inbound indicates that the Venus flyby will take place after Parker's aphelion (in the case of the first flyby, after its launch), on its way to perihelion. Outbound indicates that the Venus flyby will take place after Parker's perihelion, on its way to aphelion.
^Inside indicates that the probe will pass in between Venus and the Sun. Outside indicates that the probe will pass beyond Venus from the Sun; the probe will briefly pass through Venus's shadow in those instances.
^The first orbital period of 174 days was the orbit established by the launch and course adjustments, and was the orbit the probe would have taken had nothing further happened to change it. That orbit was, per mission plan, never completed. On the probe's first inbound course towards the Sun, it made its first planned encounter with Venus, which shortened its orbit considerably.
^The altitude is from the source cited,: 6 dated 2014. 2548 km comes to 1583 mi. NASA's  and Johns Hopkins's  press releases (identical), say "...came within about 1500 miles of Venus' surface..." A NASA blog, says, "...completed its flyby of Venus at a distance of about 1500 miles..." Other news reports, presumably taking that information, also provide a figure of 2414 km. But neither the NASA/Hopkins press release nor the blog gives a figure in kilometers. Both the NASA and Hopkins press releases say that the flyby reduced the speed of the Parker Solar Probe (relative to the Sun) by about 10%, or 7000 mph. This altered the orbit, bringing perihelion about 4 million miles closer to the Sun than it would have been without the gravity assist.
^By way of comparison, the planet
Mercury orbits the Sun at a distance varying from about 46.0 Gm (46,001,200 km) at its closest to about 69.8 Gm (69,816,900 km) at its farthest.
^ After the second solar encounter phase, Parker Solar Probe was able to download much more data than NASA had expected. So NASA announced a substantial extension of the third solar encounter phase from 11 days to about 35 days. The observational instruments were turned on when Parker Solar Probe came within 0.45
au on the inbound trip, and are planned to run until the probe reaches about 0.50 au outbound.
^ The third flyby of Venus was the first to pass behind Venus from the point of view of the Sun. The probe was in Venus's shadow, obscured from the Sun, for about 11 minutes, and passed through a so-called "tail" of Venus – a trail of charged particles from the atmosphere of Venus. The probe's instruments were to be turned on to make observations.
On 4 December 2019, the first four research papers were published describing findings during the spacecraft's first two dives near the Sun. They reported the direction and strength of the Sun's magnetic field, and described the unusually frequent and short-lived changes in the direction of the Sun's magnetic field. These measurements confirm the hypothesis that
Alfvén waves are the leading candidates for understanding the mechanisms that underlie the
coronal heating problem. The probe observed approximately a thousand "rogue" magnetic waves in the solar atmosphere that instantly increase
solar winds by as much as 300,000 miles per hour (480,000 km/h) and in some cases completely reverse the local
magnetic field. They also reported that, using the "beam of electrons that stream along the magnetic field", they were able to observe that "the reversals in the Sun's magnetic field are often associated with localized enhancements in the radial component of the plasma velocity (the velocity in the direction away from the Sun's centre)". The researchers found a "surprisingly large
azimuthal component of the plasma velocity (the velocity perpendicular to the radial direction). This component results from the force with which the Sun's rotation slingshots plasma out of the corona when the plasma is released from the coronal magnetic field".
Parker discovered evidence of a
cosmic dust-free zone of 3.5 million miles (5.6 million kilometres) radius from the Sun, due to vaporisation of cosmic dust particles by the Sun's radiation.
On April 28, 2021, during its eighth flyby of the Sun, Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated the
Alfvén surface; the probe measured the solar wind plasma environment with its FIELDS and SWEAP instruments. This event was described by NASA as "touching the Sun".
On 25 September 2022, the first discovery of a comet was made in images from the Parker Solar Probe. The comet is named PSP-001. It was found by Peter Berrett, who participates in the NASA funded Sungrazer project. PSP-001 was discovered in images from 29 May 2022, part of the spacecraft's 12th approach to the Sun.
Since this discovery, a further 18 sungrazer comets have been discovered in the images taken by the Parker Solar Probe, including two non-group comets.
WISPR first light image. The right portion of the image is from WISPR's inner telescope, which is a 40-degree field of view and begins 58.5 degrees from the Sun's center. The left portion is from the outer telescope, which is a 58-degree field of view and ends about 160 degrees from the Sun.
The view from the probe's WISPR instrument on Sept. 25, 2018, shows Earth, the bright sphere near the middle of the right-hand panel. The elongated mark toward the bottom of the panel is a lens reflection from the WISPR instrument
Photo from the WISPR shows a coronal streamer, seen over the east limb of the Sun on Nov. 8, 2018, at 1:12 a.m. EST. The fine structure of the streamer is very clear, with at least two rays visible. Parker Solar Probe was about 16.9 million miles (21.2 million km) from the Sun's surface when this image was taken. The bright object near the center of the image is Mercury, and the dark spots are a result of background correction.
When Parker Solar Probe was making its closest approach to the Sun on June 7, 2020, WISPR captured the planets Mercury, Venus, Earth, Mars, Jupiter and Saturn in its field of view
Photo taken by the probe during its second
Venus flyby, July 2020
As Parker Solar Probe flew by Venus on its fourth flyby, its WISPR instrument captured these images, showing the nightside surface of the planet
As the probe passed through the Sun's corona in early 2021, it flew by structures called
MESSENGER, Mercury orbiter (2011–2015) with sun shield
Sunshield (JWST) – Main cooling system for the infrared observatoryPages displaying short descriptions of redirect targets
Solar Orbiter, Sun-observing space probe developed by the European Space Agency (ESA) launched on 10 February 2020
^Mission planning used a perihelion of 9.5
R☉ (6.6 Gm; 4.1×10^6 mi), or 8.5 R☉ (5.9 Gm; 3.7×10^6 mi) altitude above the surface, but later documents all say 9.86 R☉. The exact value will not be finalized until the seventh Venus gravity assist in 2024. Mission planners might decide to alter it slightly before then.
abSee data and figure at
"Solar Probe Plus: The Mission". Johns Hopkins University Applied Physics Laboratory. 2017.
Archived from the original on August 22, 2017. Retrieved June 17, 2017. This article incorporates text from this source, which is in the
^"Parker Solar Probe Heads Toward Second Venus Flyby". Parker Solar Probe News Center. Johns Hopkins University Applied Physics Laboratory. November 20, 2018.
Archived from the original on December 26, 2019. Retrieved December 23, 2019. Gives the time as "1:14 p.m. EST" and the distance of the flyby as "within 1870 miles". This article incorporates text from this source, which is in the
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ).
Cubesats are smaller. Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).