- One of the most important
and most stressful parts of any Mars Rover mission
is the landing phase, which is commonly referred to
as the Seven Minutes of Terror.
Ola.
My name is Dr. Desiré Whitmore
and I'm a physicist here at the Exploratorium.
Where does the name, Seven Minutes of Terror come from?
Well, seven minutes refers to the time that it takes
for the Mars Rover to enter into the atmosphere,
descend and land on the Martian surface.
This is called the Entry Descent and Landing
or EDL phase of the mission.
Because the earth is so far away from Mars
during the landing of the Rover,
it takes 11 whole minutes for any signal
to reach the Earth from Mars.
This means that we will not know for sure,
if the Rover has touched down
until 11 minutes after it has happened.
So what goes on during these seven minutes,
that could possibly have NASA engineers so worried?
Well first of all, the spacecraft has to slow down
all the way from 12,500 miles per hour,
all the way down to zero miles per hour
in a height of only 80 miles.
Second, the Rover has to land inside of a crater
that is full of obstacles like cliffs and rocky terrain,
all without a driver.
Luckily, NASA has landed previous rovers on the red planet,
and has learned a lot each time
and has continued to make improvements.
The spacecraft itself is made up of five main parts.
At the top is the cruise stage,
which carries the fuel tanks, the solar cells
and other tools necessary to travel to Mars.
Below that is the back shell, which contains the parachute.
Beneath the back shell is the descent stage,
which will help the Rover with its final landing.
And then you have the perseverance Rover itself.
And on the bottom you have the heat shield,
which protects the Rover during entry.
Around 10 minutes, prior to entering the Martian atmosphere,
the craft separates from the cruise stage
and leaves it behind.
It's done its job to get the craft to Mars
and now it is just extra weight.
The aeroshell, which is made of the heat shield
and the back shell spends the next 10 minutes
positioning itself just right
for maximum slow down upon entry.
The best position for entry,
is to have the heat shield in just the right angle
so that the most molecules from the atmosphere
will hit it as it travels.
These molecules will push up against the heat shield
which introduces a drag force
and helps to slow it down a lot.
It starts at a speed of 12,500 miles per hour,
and the drag force will slow it down
all the way to 1000 miles per hour,
which takes about four whole minutes.
Now all of these molecules pushing against the heat shield
also creates friction against it,
which causes it to heat up a lot.
The heat shield reaches a temperature
as high as 1300 degrees Celsius,
which is hot enough to melt iron.
But the Rover, which is inside of the shell,
only gets up to about 25 degrees Celsius,
which is about room temperature here on Earth.
Because the atmosphere on Mars
is so much thinner than the atmosphere on Earth,
there's not enough drag force exerted on the shell
to slow it down to land.
We need something that is able to introduce
much more drag force.
Once the shell slows down to around 1000 miles per hour,
which is about 1.7 times the speed of sound or Mach 1.7,
the aeroshell can deploy it's parachute.
This is the largest parachute ever made
at 70 feet in diameter.
This is the first mission
where the timing of deploying the parachute
is left completely up to the Rover,
based on its position relative to its target.
It has a new technology called Range Trigger.
This will give the Rover
a much smaller area to land in free of obstacles,
and will help to reduce the chance
that it will overshoot or undershoot its target,
cutting down it's time to commute to work site
by as much as a year of precious mission time.
20 seconds after the parachute is opened,
the heat shield is dropped
which allows the Rover to start taking data
using its radar and camera systems.
The brand new terrain relative navigation,
takes photos of the surface of Mars as it is traveling
and it compares them
to maps that are already onboard it's computer
to better understand where it is
and to make course corrections.
The jet pack and the terrain relative navigation
work together to get the Rover to its target location,
making sure to avoid any obstacles
that could be in the way of descent.
When the descent stage has reached an altitude of 65 feet,
it is now time for the sky crane maneuver.
The jet pack can't get too close to the ground
because it will kick up a huge dust cloud,
which could ruin the Rover and all of its instrumentation,
so instead it lowers the Rover down
on a 20 foot rope to the ground.
As soon as the Rover begins lowering,
it uncurls and locks its wheels in place for landing.
(upbeat music)
Once the wheels are firmly on the ground,
the cables are cut and the jet pack flies away
as far as it possibly can to protect the Rover,
and it crashes into the Martian surface
once it runs out of fuel.
All of this will happen in just under seven minutes,
and we on earth will be waiting
for an additional four minutes after landing
to hear back that the Rover has even entered the atmosphere,
so that we can learn about the fate of the Rover
and whether or not its landing was successful.
Stay tuned to learn more about the Perseverance Mission
and its findings on exploratorium.edu/mars.
(upbeat music)