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NASA's MAVEN spacecraft in orbit on Mars has begun a series of ground-towing maneuvers with the planet's atmosphere to lower its orbit as the craft prepares for its additional task of serving as a relay station. communication for NASA's next March 2020 rover to be launched next year.
The orbit descent operation comes four years after MAVEN's arrival on the red planet and the instruments of the craft continue to reveal the interaction of the Mars atmosphere with the solar wind, which has recently led to the resolution of a case of stolen electrons.
Lowering MAVEN's orbit:
The MAVEN spacecraft (Mars Atmosphere and Volatile Evolution) has been in orbit on Mars since 22 September 2014 after a 10-month cruise in the interplanetary vacuum between Earth and Mars.
Launched on November 18, 2013 by a United Launch Alliance Atlas V rocket from Cape Canaveral Air Force Base in Florida, the mission had a main duration of a land-based year.
Like almost all NASA missions, MAVEN has largely survived its expected life thanks to robust engineering and NASA's project from the beginning of using the satellite as a communications relay and making additional scientific observations on the Martian atmosphere once its main mission is over.
In fact, the MAVEN team carefully manages the propellant supply for its thrusters to allow it to continue operating until 2030.
A mission duration of this duration has not yet been approved, but there are many historical precedents – such as Mars, Mars Odyssey, Curiosity, Opportunity, orbiter reconnaissance. – for the US Congress to approve the funding of Martian orbiter and rover mission extensions. as long as they continue to work.
For MAVEN, currently in one of its mission extensions, NASA is preparing to transfer part of the main task of the spacecraft to a stronger and stronger communication link with the recently arrived InSight lander , the veteran rover Curiosity and the future rover March 2020 – The cousin of Curiosity.
"The MAVEN spacecraft has done a phenomenal job in teaching us how Mars has lost its atmosphere and bringing other important scientific information about the evolution of the Martian climate," said Jim Watzin, director of the Mars Exploration Program. NASA. "We are recruiting her now to help NASA communicate with our future Mars mobile and its successors."
To ensure this strong communication link, NASA lowers the apoareion of MAVEN: the farthest point of the surface in its orbit of Mars.
When the craft was inserted for the first time in the Martian orbit in September 2014, it entered a highly elliptical orbit of 6,200 km by 150 km. During its first scientific research, the controllers on Earth periodically lowered the distance from MAVEN (approach point closest to the Martian surface in its orbit) from 150 km to 125 km.
the #MAVEN The aerobraking campaign began on February 11th. The goal of the campaign is to reduce the apoapsis (the furthest point) from a highly elliptical orbit of 6,030 km to nearly 4,500 km. This will give about 7 orbits a day and will multiply the relay possibilities for #March surface assets. pic.twitter.com/N7xmYVFnaj
– MAVEN Mission of NASA (@ MAVEN2March) February 14, 2019
MAVEN's on-board thrusters and on-board thrusters were then used to re-establish the operational orbit of the craft over 6,200 km by 150 km after each of these scientific dives, providing an opportunity to experience the atmosphere Martian in ways never before possible and add to MAVEN's main mission.
These troughs are now very useful, serving as a kind of training tricks on how the team is currently lowering MAVEN's orbit by using an aerobraking with the Martian atmosphere rather than throwing propellants.
In this case, the use of friction with the Martian atmosphere is a common practice to gradually reduce the appearance of the MAVEN orbit while avoiding to dive the spacecraft too low in the atmosphere to the point where the heating damage the orbit.
An additional benefit, especially for NASA's long-range plans for MAVEN, is that aerobraking preserves on-board fuel reserves and is in fact the most efficient way to modify the orbit of a spacecraft.
Closer to Earth, NASA is also using the aerobic technique to lower the orbits of Van Allen's radiation belt probes, as reported by NASASpaceflight last month.
For MAVEN's aerobatics, the mission's control team ordered a firing of the aircraft's propellers in mid-February to reduce the distance traveled from 150 km to 125 km – the same altitude used for its operations. scientific immersions in the atmosphere of the Red Planet.
Aerobics plan for MAVEN with original orbit as of February 10, 2019 (left), the aerobackage process (center) and the post-aerobic orbit at the reduced altitude and at the shorter orbit period (left). (Credit: NASA / Kel Elkins and Dan Gallagher Scientific Visualization Studio)
The lower orbit defines MAVEN for about 360 scans with the Mars atmosphere over the next 10 weeks. By early May 2019, the aerobic marking process will be complete and the MAVEN apoareion will be approximately 4,500 km long, or just under 2,800 miles.
Once the apoareion has reached 4,500 km, the controllers will use a small amount of propellant and MAVEN propellers to go up the craft up to 150 km so that MAVEN does not encounter the Martian atmosphere on the aircraft. following orbits.
The new 4,500 x 150 km orbit will reduce MAVEN's orbital period from 4.5 hours to 3.5 hours and increase the number of orbits per day from 5.3 to 6.8, allowing for more frequent communications with Curiosity and InSight.
As the main reason for the lowering of MAVEN's orbit is the communication with NASA's next rover, March 2020, this mission is continuing on schedule for the scheduled launch launch, July 17th. 2020, at the opening of the interplanetary launch window between Earth and Mars. mission launch site at Cape Canaveral Air Force Base, Florida.
The Mars 2020 rover, which will carry a more familiar name like Curiosity, is expected to be launched on a United Launch Alliance Atlas V rocket and its 541 configuration with a 5-meter payload fairing, four robust rocket engines and a top-floor upper engine .
The launch window extends from July 17 to August 5, 2020. In case of omission for any reason, the launch of the mission should wait another 26 months, until September 2022, for the next interplanetary window Earth -March.
Taking off at the scheduled time at the opening of the window, the March 2020 rover will land via a skycrane winch that will land in the Jezero Crater, March 18, 2021.
Most importantly, MAVEN's new orbit does not prevent the continuation of its extraordinary scientific mission on Mars, and the craft will continue to study the structure and composition of the upper Martian atmosphere and how it interacts with the wind. solar.
MAVEN and the case of stolen electrons:
Over the past four years, MAVEN has conscientiously put into orbit on Mars, its ultraviolet imaging spectrography instrument (IUVS) has periodically detected a lightening of ultraviolet light from hydrogen in the upper atmosphere of March.
This lightening would take place a few hours before the ultraviolet light levels return to normal.
By analyzing what they saw, the teams discovered that these clearings occurred at the same time as MAVEN's solar wind ion analyzer (SWIA), which detected an increase in the number of improved solar wind protons ( hydrogen atoms freed from their unique electrons by the intense heat of the plant). Sun) bombarding the planet.
Animation of proton aurora on Mars. (Credits: NASA / MAVEN / Goddard Space Flight Center / Dan Gallagher)
The mystery here is that this type of ultraviolet lightening – a dawn – should be impossible for two reasons: 1) the protons should not be able to exceed the arc shock of Mars' magnetic shield which deflects the solar wind around the planet, and 2) protons can not emit light because they lack electrons, a key element of auroral light emissions.
To return to the Sun where the solar wind originates, the star of our solar system continuously emits this flow of particles, mainly electrons, protons and alpha particles. Due to the intense heat in the solar corona, only one electron can be removed from the hydrogen atom, thus creating a proton.
Periodically, the Sun launches a tantrum and launches an explosion of protons at a speed of 3 million kilometers per hour (3 million km / h). Depending on the trajectory of these ejections, they can sometimes collide with the planets.
Back on Mars, the red planet – like Earth – is surrounded by a large cloud of hydrogen. It turns out that this cloud of hydrogen is the answer to the two mysteries of how proton-based ultraviolet aurora should not be possible on Mars.
"The answer [is] flight, "said Justin Deighan of the University of Colorado's Laboratory of Atmospheric and Space Physics, Boulder. "As [the protons] approach to Mars, [they] to turn into neutral atoms by stealing electrons from the outer edge of the vast hydrogen cloud surrounding the planet. "
MAVEN observations of a proton aurora. In the upper panel, the natural variability of the solar wind results in occasional and dense flows of protons from the solar wind bombarding Mars. Basically, the observations made by the MAVEN IUVS show an increase in ultraviolet emissions of the atmosphere as the solar wind intensifies.
(Credits: NASA / MAVEN / University of Colorado / LASP / Anil Rao)
The magnetic damper of Mars can only repel charged particles (like protons), but neutral atoms can cross it, which responds to the first mystery of how protons cross the damper of the planet.
The stolen electrons also respond to the second part of the mystery because the protons themselves can not emit light, but the atoms (the protons coupled to an equal number of electrons) can.
When these atoms transformed into neutral atoms spread in the Martian atmosphere, some of their energy is emitted in the form of ultraviolet light.
Curiously, this discovery allowed MAVEN to continue to build a history of the past and present climate of Mars, a key element of its main scientific mission.
"The Martian proton aurora is more than a light show," said Jasper Halekas of the University of Iowa, head of the SWIA instrument. "They reveal that the solar wind is not completely diverted around Mars, thus showing how the protons of the solar wind can sneak past the shock of the arc and affect the energy deposition by the atmosphere and even on improving the hydrogen content in this atmosphere. "
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