Perseverance’s seven minutes of terror

In July/August last year, three spacecraft destined for Mars were launched. One mission was from the United Arab Emirates and the other from China and the USA. A launch window had opened for a few weeks in 2020 and missing it would have meant waiting for two years before the next launch window.
The seven month trips to Mars will end this month. The Hope UAE mission was expected to go into orbit around Mars on February 9, and the Chinese one on February 10
NASA’s Perseverance rover is scheduled to land on the Red Planet on February 18, which is this coming Thursday. Landing on another planet is a very tricky undertaking. Of all the phases of the space trip to Mars, this is the most anxiously awaited one. If it goes wrong, the craft will crash land and the $2.7 billion (about K2 trillion) rover will go to waste.
The trickiest thing about the landing is that it will take place without any human intervention from Earth. It will take just seven minutes from the time the spacecraft hits the Matian atmosphere to the time it rests on the surface. Controlling things remotely from Earth is a technical impossibility within the seven minutes as a signal will take 10.5 minutes to travel one way to Mars and another 10.5 minutes to travel back.
Perseverance was already pre-programmed to go through a number of operations during the seven minutes it will take to land. All the operations will happen automatically. The landing has been dubbed “seven minutes of terror”, like it was in 2012 as the Curiosity rover landed.
Within the seven minutes the craft will have to slow down from 19 500 km/hour at the top of the Martian atmosphere to 3 km/hour just before touching down, then to 0 km/hour as it kisses the ground.
Ten minutes before Perseverance hits the Martian atmosphere, it will separate from the cruise stage which has taken it through space for seven months. A heat shield will protect the rover from the immensely high temperatures that will develop from the friction as the rover descends through the thin atmosphere. Maximum heating will happen approximately 80 seconds after atmospheric entry, resulting in a temperature of 1 300 degrees Celcius. The rover behind the heat shield will only acquire a temperature of about 25 degrees Celcius.
At 240 seconds from atmospheric entry, the heat shield will have slowed down the rover to about 1 600 km/hour, then a supersonic parachute will deploy to slow the craft further. On board the rover is a gadget called the Range Trigger, which will calculate the distance to the destination on the surface and enable the parachute to open just at the right moment.
The heat shield will be shed off at 260 seconds, exposing the rover to the atmosphere of Mars for the first time. Another piece of advanced technology called Terrain Relative Navigation will now use onboard cameras to look at the surface below and compare what the cameras ‘see’ with onboard maps already loaded onto the rover’s computer. This calculation or series of calculations will enable Terrain Relative Navigation identify the exact spot the planners wanted the rover to land on.
In the thin atmosphere of Mars, the parachute can only slow down the rover to 320 km/hour, thereafter the parachute must be discarded so that the rover uses its own rockets for the remainder of the descent. The rockets will start to fire downwards providing an upward thrust that will help to slow down the spacecraft further.
Twelve seconds before touchdown, at an altitude of roughly 20 metres, a skycrane will support the rover on a set of nylon cables before delivering it onto the ground. Just before touchdown, the cables will be severed and the skycrance will fly off to land at a safe distance.
When all these operations happen as programmed, the rover will be on the surface of Mars, ready to embark on an unprecedented robotic manouvres to determine some features of the neighbouring planet. When it has rested long enough, the Ingenuity helicopter will pull off from the rover’s belly to attempt some mechanised flights on Mars.
In 2012, the successful landing of Curiosity sparked hearty jubilations marked by exchanges of high-fives at NASA. This time round, the team will probably be more restrained because of the corona virus pandemic, but you never can tell what will transpire in an atmosphere that is charged with intense joy.
Search Within invites you all to be part of the worldwide audience that will watch the landing on Thursday (9.15pm local time) by visiting nasa.gov/nasalive. Recordings will be available on Youtube after the live broadcast. n