On March 30, 2019, Parker Solar Probe begins the second solar encounter phase of its mission, culminating in its closest approach to the Sun, called perihelion, on April 4 at 6:40 p.m. EDT.
During this solar encounter phase, which lasts until April 10, the spacecraft’s four suites of science instruments are fully operational and storing science data collected from within the Sun’s corona. As designed, Parker Solar Probe will be out of contact with Earth for several days during the solar encounter. This allows the spacecraft to prioritize keeping its heat shield, called the Thermal Protection System, oriented towards the Sun, rather than pointing its transmitter towards Earth. Science data from this second solar encounter phase will downlink to Earth over several weeks later in spring 2019.
Like the mission’s first orbit, Parker Solar Probe will reach a perihelion of about 15 million miles from the Sun’s surface — meeting its own record for closest-ever approach to the Sun, a little more than half the previous record distance of about 27 million miles set by Helios 2 in 1976. The spacecraft’s top speed of about 213,200 miles per hour is also the same as the first solar encounter of the mission. In December 2019, Parker Solar Probe will perform the second of seven Venus gravity assists of its mission, setting up the trajectory that will carry the spacecraft closer to the Sun and to a higher top speed.
Editor’s note: This post was updated on April 3, 2019, to include the time of Parker Solar Probe’s perihelion.
On Jan. 19, 2019, just 161 days after its launch from Cape Canaveral Air Force Station in Florida, NASA’s Parker Solar Probe completed its first orbit of the Sun, reaching the point in its orbit farthest from our star, called aphelion. The spacecraft has now begun the second of 24 planned orbits, on track for its second perihelion, or closest approach to the Sun, on April 4, 2019.
Parker Solar Probe entered full operational status (known as Phase E) on Jan. 1, with all systems online and operating as designed. The spacecraft has been delivering data from its instruments to Earth via the Deep Space Network, and to date more than 17 gigabits of science data has been downloaded. The full dataset from the first orbit will be downloaded by April.
“It’s been an illuminating and fascinating first orbit,” said Parker Solar Probe Project Manager Andy Driesman, of the Johns Hopkins University Applied Physics Laboratory. “We’ve learned a lot about how the spacecraft operates and reacts to the solar environment, and I’m proud to say the team’s projections have been very accurate.” APL designed, built, and manages the mission for NASA.
“We’ve always said that we don’t know what to expect until we look at the data,” said Project Scientist Nour Raouafi, also of APL. “The data we have received hints at many new things that we’ve not seen before and at potential new discoveries. Parker Solar Probe is delivering on the mission’s promise of revealing the mysteries of our Sun.”
The Parker Solar Probe team is not only focused on analyzing the science data but also preparing for the second solar encounter, which will take place in about two months.
In preparation for that next encounter, the spacecraft’s solid state recorder is being emptied of files that have already been delivered to Earth. In addition, the spacecraft is receiving updated positional and navigation information (called ephemeris) and is being loaded with a new automated command sequence, which contains about one month’s worth of instructions.
Like the mission’s first perihelion in November 2018, Parker Solar Probe’s second perihelion in April will bring the spacecraft to a distance of about 15 million miles from the Sun – just over half the previous close solar approach record of about 27 million miles set by Helios 2 in 1976.
The spacecraft’s four instrument suites 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.
On Nov. 16, Parker Solar Probe reported that all systems are operating well in the first detailed performance and health update sent to Earth by the spacecraft since its first solar encounter.
At about 6:00 p.m. EST on Friday, Nov. 16, mission controllers at the Johns Hopkins Applied Physics Lab in Laurel, Maryland, received the report from the spacecraft, which also included information about the data collected by the four instrument suites during its first solar encounter. Parker Solar Probe’s first solar encounter phase took place Oct. 31 – Nov. 11, culminating in its first close approach to the Sun — called perihelion — on Nov. 6 at just 15 million miles from the Sun’s surface, the closest any spacecraft has ever come to our star.
All Parker Solar Probe systems are operating well and as designed. The solid state recorder on the spacecraft indicated that, as planned, the four instrument suites had recorded a significant amount of data, which is scheduled to be downloaded to Earth via the Deep Space Network over several weeks starting Dec. 7. In addition to helping scientists begin to explore fundamental questions about the physics of our star, the data from this initial perihelion — collected closer to the Sun than any before — will help instrument teams calibrate Parker Solar Probe’s instruments and plan future observations.
“The team is extremely proud to confirm that we have a healthy spacecraft following perihelion,” said APL’s Nick Pinkine, mission operations manager for Parker Solar Probe. “This is a big milestone, and we’re looking forward to some amazing science data coming down in a few weeks.”
During the 11-day solar encounter, the spacecraft executed only one autonomous momentum dump – a procedure in which small thrusters are used to adjust the speed of Parker’s reaction wheels. The rate of spin of the wheels is adjusted to maintain the desired orientation of the spacecraft relative to the Sun. Momentum dumps are expected during solar encounters, as the wheels spin up to counter increasing torque from the gravitational effects of the solar environment. Executing only one dump indicates that the spacecraft is well balanced, minimizing the need for these dumps during future solar encounters, which will save propellant.
Parker Solar Probe’s second perihelion will occur on April 4, 2019. During the seven-year mission, the spacecraft will perform a total of 24 perihelia, with the last three bringing the spacecraft to less than 4 million miles from the Sun’s surface.
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.
Just over a month into its mission, Parker Solar Probe has returned first-light data from each of its four instrument suites. These early observations – while not yet examples of the key science observations Parker Solar Probe will take closer to the Sun – show that each of the instruments is working well. The instruments work in tandem to measure the Sun’s electric and magnetic fields, particles from the Sun and the solar wind, and capture images of the environment around the spacecraft.
“All instruments returned data that not only serves for calibration, but also captures glimpses of what we expect them to measure near the Sun to solve the mysteries of the solar atmosphere, the corona,” said Nour Raouafi, Parker Solar Probe project scientist at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland.
The mission’s first close approach to the Sun will be in November 2018, but even now, the instruments are able to gather measurements of what’s happening in the solar wind closer to Earth. Let’s take a look at what they’ve seen so far.
WISPR (Wide-field Imager for Solar Probe)
As the only imager on Parker Solar Probe, WISPR will provide the clearest-yet glimpse of the solar wind from within the Sun’s corona. Comprising two telescopes, WISPR sits behind the heat shield between two antennae from the FIELDS instrument suite. The telescopes were covered by a protective door during launch to keep them safe.
WISPR was turned on in early September 2018 and took closed-door test images for calibration. On Sept. 9, WISPR’s door was opened, allowing the instrument to take the first images during its journey to the Sun.
Russ Howard, WISPR principal investigator from the Naval Research Laboratory, studied the images to determine the instrument was pointing as expected, using celestial landmarks as a guide.
“There is a very distinctive cluster of stars on the overlap of the two images. The brightest is the star Antares-alpha, which is in the constellation Scorpius and is about 90 degrees from the Sun,” said Howard.
The Sun, not visible in the image, is far off to the right of the image’s right edge. The planet Jupiter is visible in the image captured by WISPR’s inner telescope — it’s the bright object slightly right of center in the right-hand panel of the image.
“The left side of the photo shows a beautiful image of the Milky Way, looking at the galactic center,” said Howard.
The exposure time – i.e. the length of time that light was gathered for this image, an interval which can be shortened or lengthened to make the image darker or brighter – is on the lower end, and there’s a reason: “We intentionally wanted to be on the low side in case there was something very bright when we first turned on, but it is primarily because we are looking so far from the Sun,” explains Howard.
As the spacecraft approaches the Sun, its orientation will change, and so will WISPR’s images. With each solar orbit, WISPR will capture images of the structures flowing out from the corona. While measurements have been made before by other instruments at a distance of 1 AU – or approximately 93 million miles – WISPR will get much closer, about 95% of the way to the Sun from Earth, dramatically increasing the ability to see what’s occurring in that region with a much finer scale than ever before and providing a more pristine picture of the solar corona.
ISʘIS (Integrated Science Investigation of the Sun)
ISʘIS (pronounced “ee-sis” and including the symbol for the Sun in its acronym) measures high-energy particles associated solar activity like flares and coronal mass ejections. (The mission’s other particle instrument suite, SWEAP, focuses on low-energy particles that make up the solar wind.) ISʘIS’ two Energetic Particle Instruments cover a range of energies for these activity-driven particles: EPI-Lo focuses on the lower end of the energy spectrum, while EPI-Hi measures the more energetic particles. Both instruments have gathered data under low voltage, making sure their detectors work as expected. As Parker Solar Probe approaches the Sun, they will be fully powered on to measure particles within the Sun’s corona.
EPI-Lo’s initial data, on the left, shows background cosmic rays, particles that were energized and came rocketing into our solar system from elsewhere in the galaxy. As EPI-Lo’s high voltage is turned on and Parker Solar Probe gets closer to the Sun, the particles measured will shift toward solar energetic particles, which are accelerated in bursts and come streaming out from the Sun and corona.
On the right, data from EPI-Hi shows detections of both hydrogen and helium particles from its lower-energy telescopes. Nearer to the Sun, scientists expect to see many more of these particles — along with heavier elements — as well as some particles with much higher energies, especially during solar energetic particle events.
“The ISʘIS team is delighted with instrument turn-on so far,” said David McComas, Professor of Astrophysical Sciences at Princeton University and principal investigator of the ISʘIS instrument suite. “There are a few more steps to go, but so far everything looks great!”
The FIELDS instrument suite aboard Parker Solar Probe captures the scale and shape of electric and magnetic fields in the Sun’s atmosphere. These are key measurements to understanding why the Sun’s corona is hundreds of times hotter than its surface below.
FIELDS’ sensors include four two-meter electric field antennas — mounted at the front of the spacecraft, extending beyond the heat shield and exposed to the full brunt of the solar environment — as well as three magnetometers and a fifth, shorter electric field antenna mounted on a boom that extends from the back of the spacecraft.
The data above, gathered during the boom deployment shortly after the spacecraft’s launch in August, shows how the magnetic field changes as the boom swung away from Parker Solar Probe. The early data is the magnetic field of the spacecraft itself, and the instruments measured a sharp drop in the magnetic field as the boom extended away from the spacecraft. Post-deployment, the instruments are measuring the magnetic field in the solar wind — illustrating the very reason such sensors need to be held out far from the spacecraft.
In early September, the four electric field antennas on the front of the spacecraft were successfully deployed — and almost immediately observed the signatures of a solar flare.
“During its commissioning time, FIELDS measured its first radio burst from a solar flare,” said principal investigator Stuart Bale, of the Space Sciences Laboratory at the University of California, Berkeley. Such bursts of radio waves can be detected during solar flares — enormous eruptions of energy and light — and are associated with the energetic electrons that flares release. This radio burst was captured by the FIELDS electric field antennas, shown above with measurements from NASA’s Wind spacecraft (on the top) for comparison.
“FIELDS is one of the most comprehensive fields and waves suites ever flown in space, and it is performing beautifully,” said Bale.
SWEAP (Solar Wind Electrons Alphas and Protons)
The SWEAP suite includes three instruments: Two Solar Probe Analyzers measure electrons and ions in the solar wind, while the Solar Probe Cup sticks out from behind Parker Solar Probe’s heat shield to measure the solar wind directly as it streams off the Sun. After opening covers, turning on high voltages and running internal diagnostics, all three instruments caught glimpses of the solar wind itself.
Because of Parker Solar Probe’s position and orientation, the science team expected that Solar Probe Cup would mostly measure background noise at first, without picking up the solar wind. But just after the instrument was powered on, a sudden, intense gust of solar wind blew into the cup, visible in the data as the red streak. As the spacecraft approaches the Sun, such observations will be Solar Probe Cup’s bread and butter — and will hopefully reveal new information about the processes that heat and accelerate the solar wind.
The two Solar Probe Analyzers (SPAN) also caught early peeks of the solar wind. During commissioning, the team turned the spacecraft so that SPAN-A — one of the two SPAN instruments — was exposed to the solar wind directly. It captured about 20 minutes’ worth of data (right), including measurements of solar wind ions (top) and electrons (bottom). While SPAN-A and its sister instrument, SPAN-B, will measure solar wind electrons throughout the mission, the spacecraft’s orientation now means that SPAN-A will likely go several more years before it captures such ion measurements again. This is because solar wind electrons can be measured from any direction, as their low mass and high temperature make their motion much more random, while the much heavier solar wind ions follow a relatively direct path out from the Sun.
“SWEAP’s solar wind and corona plasma instrument performance has been very promising,” said Justin Kasper, principal investigator of the SWEAP instrument suite at University of Michigan. “Our preliminary results just after turn-on suggest we have a set of highly sensitive instruments that will allow us to do amazing science close to the Sun.”