The Parker Solar Probe probe, its speed record and the technique to reach interstellar space

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The Parker Solar Probe probe, its speed record and the technique to reach interstellar space





The Parker Solar Probe probe, its speed record and the technique to reach interstellar space


Last November 5, 2018 at 03:28 UTC the probe Parker Solar Probe (PSP) of NASA made its first step through the perihelion, that is, the point closest to the Sun in its orbit. Many probes in solar orbit go through the perihelion and it is not news, but in the case of the PSP it is for two reasons. First, because it has become the human artifact that has most approached the Sun. Indeed, the PSP has passed only 24.8 million kilometers from the photosphere, the visible "surface" of our star. At the same time, and respecting the laws of Kepler, PSP broke the speed record of a spaceship around the Sun, reaching 95.33 km / s, or 343 190 km / h. Does not it impress you? Well think that it is nothing more and nothing less than 0.032% of the speed of light. As you hear it.



Fast and hot (NASA).



Previously, on October 29, the PSP exceeded the Sun distance record set by the German probe Helios 2 (Helios B) on April 16, 1976, as well as the speed (68.6 km / s), reached on April 16, 1976. Of course, when we talk about speeds of space vehicles, we must be very careful with the reference system. The Parker Solar Probe is by far the fastest ship in orbit around the Sun if we measure its speed with respect to the Sun's center, that is, in a heliocentric coordinate system; and has also surpassed the speed record of the Juno probe around Jupiter, of almost 59 km / s (which is still the highest planetocentric speed of a probe) and that of the Soviet probe VeGa 1 when it flew over Halley's comet at 79 , 2 km / s (and that continues being the highest speed of overflight reached by a probe). However, if we measure the speed with respect to Earth, in a geocentric reference system, the PSP has not yet broken the record of 98.9 km / s (356,040 km / h) established by Helios 2 in 1989. The record of the German probe is being a harder bone to crack than expected.



Parker Solar Probe (NASA).



The probe Parker Solar Probe was launched on August 12, 2018 at 07:31 UTC by a Delta IV Heavy rocket from Cape Canaveral to study the solar corona on-site. But, despite using the second most powerful rocket in service in the United States and employing a superior stage of Star-48V solid fuel, the PSP was not placed in its final scientific orbit. For this, the PSP must perform seven Venus overflights in order to further reduce its perihelion. The first of these nearby perihelios, some 6.2 million kilometers from the Sun, will not take place until December 2024. By then, the Parker Solar Probe will surpass its own record of speed and proximity to the Sun on several occasions. In total, the primary mission of the PSP should last 6 years and 11 months, which will allow the probe to carry out 24 turns around the Sun. The final scientific orbit will be very elliptical, with a perihelion very close to the Sun -6, 2 million kilometers, as we have already pointed out- and an aphelion of some 110 million kilometers -near the orbit of Venus-, which will allow the probe not to spend much time in the torrid solar corona.



The Helios probe still has the speed record of a probe with respect to Earth, but not for long (Wikipedia).



As we can see, getting closer to the Sun is difficult. It is not about "dropping", because you have to take into account that any probe that we launch from the Earth already has an important energy simply by the fact of turning around the Sun along with our planet. In fact, the speed reached by the PSP when leaving the Earth was only slightly lower than that obtained by the New Horizons probe heading for Pluto. At its launch, the New Horizons became the fastest human object to leave the Earth (45 km / s from the Sun, 16 km / s from Earth), although it is better to reflect this data in terms of energy characteristic or C3. For the New Horizons the C3 was 157.8 km2 / s2, while the C3 of the PSP reached 153.8 km2 / s2. Or, to put it more simply, energetically it is the same to send a probe to the vicinity of the Sun than to Pluto. And that originally the PSP had to be a much more ambitious mission that was going to approach up to 2.1 million kilometers from the Sun (3 solar radios). In that case it would not have been enough to make several Venus overflights to reach this orbit, so the probe would have to have traveled first to Jupiter in order to use the gravity of the Jovian giant to reduce its perihelion.



Original trajectory of the Solar Probe with a gravitational assistance with Jupiter to reach the Sun (NASA).





Orbits of the Parker Solar Probe (NASA).



Interestingly, getting close to the Sun is not only necessary to study our star closely, but it is also one of the best methods to get away from it and reach the interstellar medium. The Sun constitutes the largest mass of the solar system and, therefore, is the best option to perform a gravitational assist maneuver in the face of an interstellar mission. If this maneuver is also accompanied by an impulse from a propulsion system during the passage through perihelion, the magic of the Oberth effect will allow hyperbolic excess velocities high enough to send a probe to the interstellar medium (if we wish to travel to another star it is necessary to use some additional propulsion system). For example, a probe that acquires a Delta-V of 14.6 km / s at a distance of 4 solar radios will achieve a speed of 20 AU per year (that is, three million kilometers per year), enough to reach a distance of 500 AU in 25 years.



Interstellar waves (here similar to the New Horizons) with a STAR-48B stage for a gravitational assist maneuver in the vicinity of the Sun. Depending on the distance of the perihelion the probe would carry one or two thermal shields (Ralph McNutt / APL).



Naturally, the probe should be protected from the enormous temperatures. The PSP has a thermal shield that protects it from the 438 ºC reached in this last perihelion, but an interstellar probe should be closer to the Sun and, therefore, its temperature would be much higher. For this, the ideal would be to incorporate one or two disposable shields - in the interstellar medium they are not necessary - during the passage through the perihelion. That is why the experience of the Parker Solar Probe is important for the future, when we want to launch a mission to the interstellar medium ... or to an object that moves away from the Sun as' Oumuamua.

[youtube https://www.youtube.com/watch?v=FjdZU0whkug?feature=oembed&w=500&h=281]

References:



https://planetaryexploration2061.epfl.ch/files/content/sites/planetary-exploration-2061/files/McNutt.pdf

https://www.nasa.gov/feature/goddard/2018/parker-solar-probe-reports-good-status-after-close-solar-approach/

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