Post by Andrei Tchentchik on Aug 19, 2020 15:31:17 GMT 2
(.#476).- Parker Solar Probe, a NASA probe leaves to graze the Sun.
Parker Solar Probe: a NASA probe leaves to graze the Sun.
Rémy Decourt article
Published on 08/06/2018
Archives
As ESA prepares to launch Aeolus, the most complex Earth observation satellite ever built, NASA will launch a satellite that will approach the Sun like no other spacecraft has done . Parker Solar Probe will carry out the first in situ measurements of the Sun with key answers to fundamental questions about the functioning of our star. Thierry Dudok de Wit, responsible for a magnetic sensor on board the probe, explains his objectives.
Touch the Sun without getting burned. This is the objective of the Parker Solar Probe mission which is due to take off on August 11. For the first time, a probe is sent in contact with the Sun to notably understand "the origin of the heating of the corona and the solar wind", explains Thierry Dudok de Wit, at the head of a team from the Laboratory of Physics and environmental and space chemistry which provided one of the instruments. The four instrumental suites of this probe (Sweap, Wispr, Fields and Isis) from NASA, to which several French laboratories linked to the CNRS have contributed, "will indeed provide unprecedented information, on solar plasma, this molasses of particles and fields electromagnetic that makes up the crown, the origin of the solar wind and the heating mechanism of the crown ”.
Some details on the functions of these four instrumental suites:
• Sweap (Solar Wind Electrons Alphas and Protons): the instruments that compose it will essentially be used to determine the speed, temperature and density of the solar wind;
• Wispr (Wide-fiels Imager for Solar PRobe): placed on the side of the satellite, this camera will not observe the Sun directly, but a part of the crown to study its variations;
• Fields (Fields Experiment): a set of instruments which will each operate in different frequency ranges and will provide information on the electric and magnetic fields in the solar wind;
• Isis (Integrated Science Investigation of the Sun): this set of instruments will measure the high energy particles - electrons, protons, heavy ions - which are produced in particular during solar flares.
Scientific and technical priority of NASA for many years, this project is also considered among "the most innovative and the most exciting by the scientific community federated by the group Sun, Heliosphere, Magnetosphere (SHM) of Cnes". The realization of this probe encountered many technical difficulties and "required a very significant conceptual jump". Given the temperatures to which the probe will be subjected, "around 1,600 ° C", it is obviously a mission with "high risk but with the key an important scientific return". Closer to the Sun, the probe will be only six million kilometers from its surface. At this distance from the Sun, "the radiation emitted by the star is still 500 times greater than that received by a vacationer on a beach".
To observe the Sun so closely, NASA had to adopt an adapted strategy. The probe, moreover, will not remain permanently at this distance: "25 flyovers as close as possible to the Sun, up to 8.8 solar rays from the surface, are planned". These overflights will last three days. A very short duration which is explained by the elliptical orbit on which Parker Solar Probe will evolve but also by its speed.
To date, the Sun has never been studied in situ. Solar Parker Probe will open a new era. © ESA, Nasa, EIT
The first satellite to enter the outer atmosphere of our star.
The probe will therefore be launched into an elliptical orbit around the Sun with a perihelion of 0.045 astronomical units (AU) and an aphelion at 0.73 AU. She will use the gravitational assistance of Venus seven times to reach the solar corona. These successive accelerations added to the powerful gravitational pull of the Sun will make it become "the fastest spacecraft of all time". Closer to the Sun, Solar Parker Probe will fly "at an impressive speed of 700,000 kilometers per hour".
Until now, knowledge about the Sun has come exclusively from studies carried out at a distance, in particular thanks to the ESA Soho satellite and Nasa. With Parker Solar Probe, "we will be able to have in situ measurements, this is a first." By advancing to only 8.8 solar rays, the probe will be in areas where "the streams of particles just emitted from the Sun are still heated and accelerated to form the wind which will then sweep the heliosphere" .
This story of the heating of the crown is an enigma which contradicts the physical intuition which wants, normally, that in "moving away the temperature should decrease. However, it is increasing. And not just a little ”! Indeed, while the surface of the Sun is around 6,000 ° C, it reaches "10,000 degrees in the chromosphere and more than a million degrees in the crown". To explain this process of coronal heating, it is believed that "this energy supply comes in particular from the fluctuations of the magnetic field and the multitude of small invisible solar flares of the Earth". But we are still stuck with hypotheses today because "the measurements of the Sun acquired from Earth or its orbit do not allow ambiguities to be removed". As for the solar wind, what puzzles scientists is why so much matter escapes from the Sun "a million tonnes of matter escapes from the Sun every second" and what are the mechanisms that accelerate the solar wind. The latter appears in two forms, slow, from 300 to 400 km / s, and fast, with a speed of the order of 600 to 700 km / s.
The third objective concerns "the study of high energy particles (electrons, protons, helium nuclei, etc.) which, during eruptions of the Sun are accelerated at speeds close to the speed of light". The same physical mechanisms act elsewhere in the universe, but on much larger scales, for example during supernovae. In this sense, "the solar corona is a magnificent laboratory of astrophysics".
Finally, by venturing into unknown territory, scientists expect to discover "new and unexpected phenomena". This has happened every time "a probe has ventured into an unexplored region of the Solar System, in this case in the near solar corona".
One of many test sessions to ensure that the probe will function normally as close to the Sun as possible. © Nasa
Unsurprisingly, the probe will be equipped with a heat shield designed to withstand temperatures of 1,600 degrees. This shield built on the base of the front shields of the space shuttle will gradually degrade until it can no longer effectively protect it. That said, it is "sufficiently large to withstand the best during the 25 orbits of the initial mission (until 2025-2026)". If most of the instruments are protected from solar radiation by this shield, this does not prevent them from being affected by the proximity of the Sun. Thus, for example, the ultraviolet radiation from the Sun will tear electrons from the shield which will “form a cloud around the front face of the satellite. This will create a drag and disrupt the measurements. ”
As for the solar wind, which can blow up to more than 700 kilometers per second, "it will hardly brake the probe because it is very tenuous". In addition, it escapes from the Sun in a spiral and "will not come from the front, but will come from the side, so that its observation will not be hampered by the shield".
Limiting the amount of data that can be collected is the main compromise accepted by scientists for the accomplishment of the mission. As close as possible to the Sun, the solar panels will be folded down to be housed behind the heat shield. Batteries will take over to operate the satellite and the instruments which, as they pass, will record a total of around 90 Gigabits of data. Unfortunately, a non-negligible part of this data will be lost because everything cannot be downloaded to the ground. The elliptical orbit of the probe will indeed bring it so far from the Earth that contact with ground stations will not be permanent.
F I N .
Parker Solar Probe: a NASA probe leaves to graze the Sun.
Rémy Decourt article
Published on 08/06/2018
Archives
As ESA prepares to launch Aeolus, the most complex Earth observation satellite ever built, NASA will launch a satellite that will approach the Sun like no other spacecraft has done . Parker Solar Probe will carry out the first in situ measurements of the Sun with key answers to fundamental questions about the functioning of our star. Thierry Dudok de Wit, responsible for a magnetic sensor on board the probe, explains his objectives.
Touch the Sun without getting burned. This is the objective of the Parker Solar Probe mission which is due to take off on August 11. For the first time, a probe is sent in contact with the Sun to notably understand "the origin of the heating of the corona and the solar wind", explains Thierry Dudok de Wit, at the head of a team from the Laboratory of Physics and environmental and space chemistry which provided one of the instruments. The four instrumental suites of this probe (Sweap, Wispr, Fields and Isis) from NASA, to which several French laboratories linked to the CNRS have contributed, "will indeed provide unprecedented information, on solar plasma, this molasses of particles and fields electromagnetic that makes up the crown, the origin of the solar wind and the heating mechanism of the crown ”.
Some details on the functions of these four instrumental suites:
• Sweap (Solar Wind Electrons Alphas and Protons): the instruments that compose it will essentially be used to determine the speed, temperature and density of the solar wind;
• Wispr (Wide-fiels Imager for Solar PRobe): placed on the side of the satellite, this camera will not observe the Sun directly, but a part of the crown to study its variations;
• Fields (Fields Experiment): a set of instruments which will each operate in different frequency ranges and will provide information on the electric and magnetic fields in the solar wind;
• Isis (Integrated Science Investigation of the Sun): this set of instruments will measure the high energy particles - electrons, protons, heavy ions - which are produced in particular during solar flares.
Scientific and technical priority of NASA for many years, this project is also considered among "the most innovative and the most exciting by the scientific community federated by the group Sun, Heliosphere, Magnetosphere (SHM) of Cnes". The realization of this probe encountered many technical difficulties and "required a very significant conceptual jump". Given the temperatures to which the probe will be subjected, "around 1,600 ° C", it is obviously a mission with "high risk but with the key an important scientific return". Closer to the Sun, the probe will be only six million kilometers from its surface. At this distance from the Sun, "the radiation emitted by the star is still 500 times greater than that received by a vacationer on a beach".
To observe the Sun so closely, NASA had to adopt an adapted strategy. The probe, moreover, will not remain permanently at this distance: "25 flyovers as close as possible to the Sun, up to 8.8 solar rays from the surface, are planned". These overflights will last three days. A very short duration which is explained by the elliptical orbit on which Parker Solar Probe will evolve but also by its speed.
To date, the Sun has never been studied in situ. Solar Parker Probe will open a new era. © ESA, Nasa, EIT
The first satellite to enter the outer atmosphere of our star.
The probe will therefore be launched into an elliptical orbit around the Sun with a perihelion of 0.045 astronomical units (AU) and an aphelion at 0.73 AU. She will use the gravitational assistance of Venus seven times to reach the solar corona. These successive accelerations added to the powerful gravitational pull of the Sun will make it become "the fastest spacecraft of all time". Closer to the Sun, Solar Parker Probe will fly "at an impressive speed of 700,000 kilometers per hour".
Until now, knowledge about the Sun has come exclusively from studies carried out at a distance, in particular thanks to the ESA Soho satellite and Nasa. With Parker Solar Probe, "we will be able to have in situ measurements, this is a first." By advancing to only 8.8 solar rays, the probe will be in areas where "the streams of particles just emitted from the Sun are still heated and accelerated to form the wind which will then sweep the heliosphere" .
This story of the heating of the crown is an enigma which contradicts the physical intuition which wants, normally, that in "moving away the temperature should decrease. However, it is increasing. And not just a little ”! Indeed, while the surface of the Sun is around 6,000 ° C, it reaches "10,000 degrees in the chromosphere and more than a million degrees in the crown". To explain this process of coronal heating, it is believed that "this energy supply comes in particular from the fluctuations of the magnetic field and the multitude of small invisible solar flares of the Earth". But we are still stuck with hypotheses today because "the measurements of the Sun acquired from Earth or its orbit do not allow ambiguities to be removed". As for the solar wind, what puzzles scientists is why so much matter escapes from the Sun "a million tonnes of matter escapes from the Sun every second" and what are the mechanisms that accelerate the solar wind. The latter appears in two forms, slow, from 300 to 400 km / s, and fast, with a speed of the order of 600 to 700 km / s.
The third objective concerns "the study of high energy particles (electrons, protons, helium nuclei, etc.) which, during eruptions of the Sun are accelerated at speeds close to the speed of light". The same physical mechanisms act elsewhere in the universe, but on much larger scales, for example during supernovae. In this sense, "the solar corona is a magnificent laboratory of astrophysics".
Finally, by venturing into unknown territory, scientists expect to discover "new and unexpected phenomena". This has happened every time "a probe has ventured into an unexplored region of the Solar System, in this case in the near solar corona".
One of many test sessions to ensure that the probe will function normally as close to the Sun as possible. © Nasa
Unsurprisingly, the probe will be equipped with a heat shield designed to withstand temperatures of 1,600 degrees. This shield built on the base of the front shields of the space shuttle will gradually degrade until it can no longer effectively protect it. That said, it is "sufficiently large to withstand the best during the 25 orbits of the initial mission (until 2025-2026)". If most of the instruments are protected from solar radiation by this shield, this does not prevent them from being affected by the proximity of the Sun. Thus, for example, the ultraviolet radiation from the Sun will tear electrons from the shield which will “form a cloud around the front face of the satellite. This will create a drag and disrupt the measurements. ”
As for the solar wind, which can blow up to more than 700 kilometers per second, "it will hardly brake the probe because it is very tenuous". In addition, it escapes from the Sun in a spiral and "will not come from the front, but will come from the side, so that its observation will not be hampered by the shield".
Limiting the amount of data that can be collected is the main compromise accepted by scientists for the accomplishment of the mission. As close as possible to the Sun, the solar panels will be folded down to be housed behind the heat shield. Batteries will take over to operate the satellite and the instruments which, as they pass, will record a total of around 90 Gigabits of data. Unfortunately, a non-negligible part of this data will be lost because everything cannot be downloaded to the ground. The elliptical orbit of the probe will indeed bring it so far from the Earth that contact with ground stations will not be permanent.
F I N .
