How and Why NASA’s Parker Solar Probe Will Touch the Sun
12 September 2018
Nasa is playing Star Trek; going where no-one has gone before.
For nearly five billion years, the sun has been watching us from above. Now NASA is on its way to take a closer look and brush the face of our home star.
The Parker Solar Probe rocket lifted off from Cape Canaveral, Florida. The probe is set to become the fastest-moving manmade object in history.
To crack longstanding mysteries about the Sun's behaviour.
The sun is always changing, it’s always in motion, it goes through periods of incredible violence and calm. It’s an incredibly dynamic star. On earth the sun has powered life on Earth for billions of years, and it has anchored theologies and fueled myths throughout human history. For centuries, astronomers have tried to study our star. But no matter how hard scientists have tried, they haven’t been able to crack its code.
Named after 91-year-old astrophysicist Eugene Parker, who first identified the supersonic stream of particles called the solar wind.
Among the most basic questions the mission aims to answer what accelerates that solar wind, thing that could even help with nuclear fusion experiments on Earth.
The spacecraft will also be studying the storms that sometimes erupt on the sun’s surface and sling huge blobs of material into space called coronal mass ejections. And why the corona is 300 times hotter than the surface of the sun.
When these charged clouds slam into Earth, they produce beautiful auroras, but they are also dangerous for astronauts and can disrupt communications systems and power grids.
The spacecraft is wearing a special, 4.5-inch-thick heat shield that will protect the four suites of onboard instruments from the sun’s intense heat. Made of carbon composites, the shield is a sandwich-like design that incorporates foam, mesh, and plates of material.
Most of the instruments sit on the main body of the spacecraft and are well in the shadow provided by the heat shield.
Once the spacecraft will run out of fuel it will start to turn, and at that point, parts of the body that are not designed to see the full solar environment will then melt.
And the spacecraft will ultimately become one with the sun.
The earth travels very fast, at about 108,000 km/h (67,000 mi/h) always sideways relative to the sun.
If you launch a rocket from Earth, straight toward the Sun, it won't lose that sideways speed and so it will miss the Sun. The only way to get the rocket to go right into the Sun is to cancel all that sideways motion. Leave even a little bit and it will miss the Sun and enter a new orbit.
To cancel Earth's motion, you have to launch the spacecraft backward as fast as Earth is hurtling forward. To do so Nasa is using one of the most powerful rockets available and additional gravity assists from Venus over a period of several years. So now, rather than speeding up the spacecraft as in a typical gravity assist, Venus slows down its sideways motion but Parker Solar Probe will gain a great deal of overall speed thanks to the Sun's gravity.
Over the course of seven years, Parker will make 24 loops around our star to study the physics of the corona, the place where much of the important activity that affects the Earth seems to originate.
The probe will dip inside this tenuous atmosphere, sampling conditions, and getting to just 6.16 million km (3.83 million miles) from the Sun's broiling "surface".
"I realise that might not sound that close, but imagine the Sun and the Earth were a metre apart. Parker Solar Probe would be just 4cm away from the Sun. It will also be the fastest man-made object ever, travelling at speeds of up to 430,000mph [690,000km/h] - New York to Tokyo in under a minute!" explained Dr Nicky Fox, the UK-born project scientist who is affiliated to the Johns Hopkins Applied Physics Laboratory.
The European Space Agency has its own version of Parker.
Solar Orbiter, or SolO as it's sometimes known, is undergoing final assembly and testing in the UK. It is expected to launch in 2020, arriving at its closest position to the Sun towards the end of Parker's planned seven years of operations.
SolO will go to within 42 million km of the Sun's surface. That's further away than Parker but it will still need an impressive shield.
“Once Parker runs out of fuel it will start to turn, and at that point, parts of the body that are not designed to see the full solar environment will then melt, and the spacecraft will ultimately become one with the sun.
The Parker Solar Probe concept originates from a predecessor Solar Orbiter project conceived in the 1990s. Similar in design and objectives, the Solar Probe mission served as one of the centerpieces of the eponymous Outer Planet/Solar Probe (OPSP) program formulated by NASA. The first three missions of the program were planned to be: the Solar Orbiter, the Pluto and Kuiper belt reconnaissance mission Pluto Kuiper Express, 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 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).
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."
The cancellation of the program also resulted in the initial cancellation of New Horizons, the mission that eventually won the competition to replace Pluto Kuiper Express in the former OPSP program. That mission, which would eventually be launched as the first mission of the New Frontiers program, a conceptual successor to the OPSP program, would undergo a lengthy political battle to secure funding for its launch, which occurred in 2006.
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 Parker Solar Probe in honor of astrophysicist Eugene Parker, coiner of the term "solar wind". The solar probe cost NASA US$1.5 billion.
The Parker Solar Probe will be 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. The solar shield is hexagonal, mounted on the Sun-facing side of the spacecraft, 2.3 m (7.5 ft) in diameter, 11.4 cm (4.5 in) thick, and is made of reinforced carbon–carbon composite, which is designed to withstand temperatures outside the spacecraft of about 1,370 °C (2,500 °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, 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 sun light coming from the shield limits and engaging movements from fly 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.
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 6×106 km (3.7×106 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 science phase will take place during those 7 years, focusing on the periods when the spacecraft is closest to the Sun. 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 manmade object, almost three times as fast as the current record holder, Helios-B. 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 aphelion.
- Trace the flow of energy that heats the corona and accelerates the solar wind.
- Determine the structure and dynamics of the magnetic fields at the sources of solar wind.
- Determine what mechanisms accelerate and transport energetic particles.
To achieve these goals, the mission will perform five major experiments or investigations:
- Electromagnetic Fields Investigation (FIELDS) – This investigation will make direct measurements of electric and magnetic fields, radio waves, Poynting flux, absolute plasma density, and electron temperature. It consists of two flux-gate magnetometers, a search-coil magnetometer, and 5 plasma voltage sensors. The Principal investigator is Stuart Bale, at the University of California, Berkeley.
- Integrated Science Investigation of the Sun (IS☉IS) – This investigation will measure energetic electrons, protons and heavy ions. The instrument suite is composed of two independent instruments, EPI-Hi and EPI-Lo. The Principal investigator is David McComas, at the Princeton University.
- Wide-field Imager for Solar Probe (WISPR) – These optical telescopes will acquire images of the corona and inner heliosphere. The Principal Investigator is Russell Howard, at the Naval Research Laboratory.
- Solar Wind Electrons Alphas and Protons (SWEAP) – 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, a Faraday cup). The Principal Investigator is Justin Kasper at the University of Michigan and the Smithsonian Astrophysical Observatory.
- Heliospheric Origins with Solar Probe Plus (HeliOSPP) – A theory and modeling investigation to maximize the scientific return from the mission. The Principal Investigator is Marco Velli at UCLA and the Jet Propulsion Laboratory (JPL).
EXTRA REFERENCES: Wikipedia, Nasa
|Written by: Luis Clement|