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The conversationFeb 17, 2021 1:57:44 PM IS
This month has been a busy month for exploring Mars. Several countries it sent missions to the red planet in June last year, taking advantage of a launch window. Most have now i arrive after his eight-month trip. In the next few days, NASA will perform a direct entry from the Martian atmosphere to land the Perseverance rover in the Jezero crater of Mars.
Perseverance, about the size of a car, is the largest payload on Mars so far, literally weighs a ton (on earth). After landing, the rover will look for signs of ancient life and collect samples for it will eventually be returned to Earth.
NASA will make a direct entry of the Martian atmosphere to land the Perseverance rover in the Jezero crater of Mars. Image Credit: NASA / JPL-Caltech
Mission will use hardware similar to 2012 Mars Science Laboratory (MSL), which landed the Curiosity rover, but will have certain improvements, including the improved accuracy of the rover’s landing.
Curiosity’s trip provided a wealth of information about what kind of environment Mars 2020 might face and what technology it would need to survive.
Mars: a strangest land
As Mars is a hostile and remote environment with an atmosphere above 100 times thinner than Earth, there is a bit of atmosphere for the incoming spacecraft to use to reduce speed aerodynamically.
Rather, surviving the entry to Mars requires a creative combination of aerodynamics, parachute, retro-propulsion (using engine thrust to decelerate for landing), and often a large airbag.
A profile of the entry, descent and landing phase of Mars 2020 Image Credit: NASA / JPL-Caltech
Furthermore, the Martian weather models are not updated in real time, so we don’t know exactly what environment a probe will face during entry. Unpredictable weather events, especially dust storms, are one of the reasons why landing accuracy suffered in previous Missions
NASA engineers call the Entry, Descent and Landing (EDL) phase of Mars Entry missions the “seven minutes of terror”. In just seven minutes there are countless ways input can fail.
Thermal protection
The 2012 MSL spacecraft It was equipped with a 4.5 meter diameter heat shield that protected the rover during its descent through the atmosphere of Mars.
Entered the Martian atmosphere around 5,900 m per second. This is hypersonic, which means it is more than five times the speed of sound.
Mars 2020 will be similar. It will rely heavily on its thermal protection system, which includes a front heat shield and a rear heat shield, to prevent hot flow from damaging the rover stored inside.
At hypersonic speeds, the atmosphere of Mars won’t be able to get out of the way of the spacecraft fast enough. As a result, a strong shock wave will form in front.
In this case, the gas in front of the vehicle will rapidly compress, causing a large pressure and temperature jump between the shock wave and the heat shield.
The hot post-shock flow heats the surface of the heat shield during entry, but the heat shield protects the internal structure from this heat.
Shown in the image are the Mars 2020 rear shell heat shield (foreground) and the main PICA heat shield (background). Image Credit: NASA / JPL-Caltech
Since the MSL 2012 and Mars 2020 missions use relatively larger payloads, these spacecraft have a higher risk of overheating during the entry phase.
But MSL effectively avoided this problem, in large part thanks to a specially designed heat shield that was the first Mars rover to use NASA’s Phenolic Impregnated Carbon Ablator (PICA). material.
This material, which is also used by the Mars 2020 spacecraft, is made of chopped carbon fiber embedded in a synthetic resin. It is very light, can absorb immense heat, and is an effective insulator.
Guided entry
All entries prior to the 2012 MSL mission had not been guided, which means they were not controlled in real time by a flight computer.
Instead, spacecraft were designed to crash into “input interface”(125km above the ground) in a particular way, before landing where the Martian winds would carry them. With this came a great landing uncertainty.
This artist’s impression shows thrusters controlling the angle of the spacecraft during MSL 2012’s Mars entry. Mars 2020 will use the same technique. Image Credit: NASA / JPL-Caltech
The landing uncertainty area is called landing ellipse. NASA’s Viking Mars missions in the 1970s had an estimated landing ellipse of The 280x100km. But both MSL and now Mars 2020 were built to surpass previous efforts.
The MSL mission was the first guided entry to Mars. An improved version of the Apollo Guidance Computer It was used to control the vehicle in real time to ensure a precise landing.
With this, MSL reduced its estimated landing ellipse to The 20×6.5km and i ended up landing alone 2 km from your target. With a bit of luck, Mars 2020 will achieve similar results.
Shown in the photo are several NASA landing sites on Mars, including the proposed Perseverance landing site. Perseverance is expected to land in a relatively less clear area Image Credit: NASA / JPL-Caltech
Supersonic skydiving
A parachute will be used to slow down the Mars 2020 spacecraft enough to make final landing maneuvers.
With a 21.5 million in diameter, the parachute will be the largest ever used on Mars and will have to deploy faster than the speed of sound.
The descending spaceship after the parachute has deployed. Image Credit: NASA / JPL-Caltech
Deploying the parachute at the right time will be critical to achieving an accurate landing.
A new technology called “range triggerIt will control the deployment time of the parachute, based on the relative position of the spacecraft to the desired landing site.
Next generation navigation
Approximately 20 seconds after the parachute is opened, the heat shield will separate from the spacecraft, exposing the perseverance to the Martian environment. Its cameras and sensors can start collecting information as it gets closer to the ground.
The rover is specialized terrain relative navigation The system will help you land safely by diverting you to a stable landing surface.
Perseverance will compare a preloaded map of the landing site with images collected during its rapid descent. You should then be able to identify landmarks below and estimate their position relative to the ground with an accuracy of about 40 m.
The terrain relative navigation is far superior to the methods used for past Mars entries. Older spacecraft had to rely on their own internal estimates of their location during entry.
And there was no way to effectively recalibrate this information. They could only guess where they were with an accuracy of about 2-3 km when they got close to the ground.
The final touchdown
The parachute carried by the Mars 2020 spacecraft can only slow it down to about 320 km per hour.
To land safely, the spacecraft will drop the parachute and rear shell and use ground-facing rockets to get down to the last 2,100m. This is called “retro-jet”.
The Perseverance rover is being placed on Martian soil by the aerial crane Image Credit: NASA / JPL-Caltech
And to avoid the use of airbags to land the rover (as was done in pre-MSL missions), Mars 2020 will use the “skycrane” maneuver; A set of cables will slowly lower the perseverance to the ground as it prepares for autonomous operation.
Once Perseverance detects that its wheels are secure on the ground, it will cut the cables connected to the drop vehicle (which will fly and crash somewhere in the distance).
And with that, the seven minutes of terror will be over.
Chris James, Member of ARC DECRA, Center for Hypersonics, School of Mechanical and Mining Engineering, The University of Queensland
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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