On Oct. 31, 2018, Parker Solar Probe began its first of 24 solar encounters. This period — which lasts until Nov. 11 — is the time during which the spacecraft is within 0.25 astronomical units, or 23.2 million miles, of the Sun’s center. Parker Solar Probe’s four suites of science instruments are on and collecting data throughout this phase, giving scientists their closest-yet look at this dynamic region of the Sun’s outer atmosphere.
This solar encounter encompasses the first perihelion of the mission, the point at which Parker Solar Probe is closest to the Sun. Perihelion is expected at about 10:28 p.m. EST on Nov. 5. The spacecraft will come within 15 million miles of the Sun’s surface and clock in at a top speed of 213,200 miles per hour relative to the Sun — setting new records for both closest solar approach and top heliocentric speed by a spacecraft. At perihelion, Parker Solar Probe will fly through material at about 3.6 million degrees Fahrenheit — but because material in this region is so tenuous, it doesn’t influence the temperature of the spacecraft. However, the Sun’s intense radiation heats the Sun-facing side of the spacecraft’s heat shield, called the Thermal Protection System, to about 820 F.
For several days around the Nov. 5 perihelion, Parker Solar Probe will be completely out of contact with Earth because of interference from the Sun’s overwhelming radio emissions.
Parker Solar Probe employs a host of autonomous systems to keep the spacecraft safe without guidance from Earth — including automatic retraction of the solar panels to regulate their temperature, attitude control using solar limb sensors that ensures all of the instruments remain in the heat shield’s shadow, and a sophisticated guidance and control system that keeps the spacecraft pointed correctly. This autonomy is key not only during no-contact phases around the 24 planned perihelia but also throughout the mission, when the round-trip light time — the time it takes for radio signals to go back and forth between Earth and Parker Solar Probe — can be up to 31 minutes.
During the solar encounter phase, Parker Solar Probe’s four instrument suites measure the properties of material directly within the Sun’s outer atmosphere. These observations, gathered closer to the Sun than ever before, will help scientists begin to answer outstanding questions about the Sun’s fundamental physics — including how particles and solar material are accelerated out into space at such high speeds and why the Sun’s atmosphere, the corona, is so much hotter than the surface below.
Because of the spacecraft’s distance from Earth and position relative to the Sun, it will be several weeks after the end of the solar encounter before Parker Solar Probe begins transmitting this science data back to Earth.
At about 10:54 p.m. EDT, Parker Solar Probe surpassed 153,454 miles per hour — as calculated by the mission team — making it the fastest-ever human-made object relative to the Sun. This breaks the record set by the German-American Helios 2 mission in April 1976.
Parker Solar Probe will repeatedly break its own records, achieving a top speed of about 430,000 miles per hour in 2024.
On Sept. 25, 2018, Parker Solar Probe captured a view of Earth as it sped toward the first Venus gravity assist of the mission. Earth is the bright, round object visible in the right side of the image.
Two days after Parker Solar Probe flew past Venus toward its rendezvous with the Sun, the spacecraft had drawn close enough to our star that its power-generating solar array wings began to tilt themselves inward – a task directed by the spacecraft itself, based on the rising temperatures – away from the Sun and behind the spacecraft’s heat shield. This is the first time that autonomous, closed-loop solar array angle control based on temperature has taken place on a spacecraft.
This solar array movement, controlled by software within the spacecraft’s main processor, began on Oct. 5, soon after Parker Solar Probe’s distance from the Sun dropped below about 65 million miles.
On Oct. 3, Parker Solar Probe successfully completed its flyby of Venus at a distance of about 1,500 miles during the first Venus gravity assist of the mission. These gravity assists will help the spacecraft tighten its orbit closer and closer to the Sun over the course of the mission.
Detailed data from the flyby will be assessed over the next few days. This data allows the flight operations team to prepare for the remaining six Venus gravity assists which will occur over the course of the seven-year mission.
We like to call Parker Solar Probe the coolest, hottest, fastest mission under the Sun — and fall 2018 will prove why. Here are a few mission milestones to look forward to over the coming months.
Oct. 3, 2018 (about 4:45 a.m. EDT) — Parker Solar Probe performs its first Venus gravity assist. This maneuver — to be repeated six more times over the lifetime of the mission — will change Parker Solar Probe’s trajectory to take the spacecraft closer to the Sun.
Oct. 29, 2018 — Parker Solar Probe is expected to come within 27 million miles of the Sun. This is the record currently held by Helios 2, set in 1976.
Oct. 30, 2018 — Parker Solar Probe is expected to surpass a heliocentric speed of 153,454 miles per hour. This is the record for fastest spacecraft measured relative to the Sun, set by Helios 2 in 1976.
These speed and distance estimates could change after Parker Solar Probe performs its Venus gravity assist on Oct. 3.
Oct. 31 – Nov. 11, 2018 — Parker Solar Probe performs its first solar encounter. Throughout this period, the spacecraft will gather valuable science data. It will not be in contact with Earth because of the Sun’s interference and the orientation needed to keep the spacecraft’s heat shield between it and the Sun. The spacecraft is expected to reach its closest approach on Nov. 5. Like the distance and speed records, this estimate could change after the Venus gravity assist.
December 2018 — Parker Solar Probe will downlink the science data gathered during its first solar encounter.