You join us again on the adventures of the Opportunity rover on Mars.
It might well have already reached the conclusion of its journey, as it has lost contact with
Earth after a giant dust storm enveloped Mars.
Its solar panels are likely covered in dust, meaning its batteries have run flat.
The 45-day period NASA gave to see if wind would clear the dust off the panels has come
and gone, although they have now extended this waiting period until late January.
We will have to see if there is still life in this rover yet.
In this last episode, Opportunity landed in Eagle crater, investigated Endurance crater,
and headed towards Erebus crater.
To get there was quite a journey.
From Opportunity’s last real waypoint at Endurance crater, it had to travel roughly
5km over unforgiving sand dunes, even getting stuck at one point for weeks in a dune that
became to be known as “Purgatory”.
Thankfully it got free, and as it approached Erebus, mission controllers updated the software
on the rover to prevent wheel slippage from happening in the future.
We left off last time at sol 550 into the mission, sol meaning martian days, just
as the Opportunity rover was in the vicinity of Erebus in October 2005.
As Opportunity approached Erebus, it came to sections of ground where the bedrock was
exposed.
Mission controllers named this section the “Erebus Highway”.
As we know from the last episode, Opportunity’s main mission was to search for signs of water
on Mars, clues of which can often be found in the planet’s rocks.
It used its rock abrasion tool to carve circles into the bedrock, and with its microscopic
camera, it can compare the different structures of the rocks to search for evidence of water.
You’ll notice by here that Opportunity’s tracks are in front of the rover, this is
still the front camera, but sometimes mission controllers drive Opportunity backwards to
even out the wear and tear on the equipment.
Erebus is a very old and eroded crater, filled with sand with only a few outcrops showing.
You may not have been able to tell it’s a crater from the ground perspective because
it is so shallow and eroded, it only really becomes visible from the satellite photos.
It is about twice as big as Endurance crater, at 350 meters in diameter.
Opportunity never actually went inside the crater as there was only more dunes in it.
Instead, it stuck to the rim, avoiding larger dunes as it went.
Even while carefully manoeuvring around these dunes, it hit some soft sand and its wheels
sunk in.
Luckily, the software that was installed only a few weeks previously noticed the wheels
were slipping, and it stopped its drive command.
You see, Opportunity is not controlled in real time by a person on Earth with a joystick.
There is too much of a latency for this, between 6 minutes to 40 minutes, depending on the
proximity of Earth and Mars.
So instead, Opportunity is given drive commands.
Using these same navigational images you are seeing here, and comparing it with satellite
based imagery, mission controllers command Opportunity to drive forward a certain distance,
where it will then take a new photo to show its progress.
The software that prevented Opportunity from getting stuck meant that mission controllers
could get the rover to reverse out without another several week delay.
During Opportunity’s time there, it collaborated with the ESA’s Mars Express Orbiter.
The Mars Express images the surface of Mars from orbit to search for different types of
materials.
Without actually sampling the surface, the data it collects can be hard to interpret.
Opportunity, however, can physically interact with the surface material, confirming whether
what the Mars Express data showed was correct or not, helping them to refine their future
observations.
While Opportunity was near Erebus crater, it was also able to see an incredible transit
of the Sun from Mars’ closest and biggest moon Phobos!
As it was still making its way around Erebus crater, a big dust storm hit, and Opportunity
went dark for a few days.
Very interestingly, you can see the difference the dust storm made to the rover, as the camera
goes from having a clear image to having some dust particles visible.
Also, dust settles on the solar panels, meaning it can’t generate as much electricity.
Very fortunately though, Mars has occasional “cleaning events”, where wind, or even
a dust devil will pass over the rover, blowing the dust off the solar panels and camera.
You can notice this cleaning happen over time too if I speed up the footage.
Look at this fleck of dirt here, and how it disappears over time.
Opportunity doesn’t have means of clearing this dust off by itself, so it has always
relied on these cleaning events happening, which thankfully over the course of the 15
year mission, it did.
Sadly however, during the time at Erebus, Opportunity encountered its first mechanical
fault; its arm was getting stuck all the time as you can see here.
There was a broken wire, although the motor still worked if it was given more power.
After careful deliberation, engineers decided the best thing to do would be to only stow
the arm away while travelling long distances.
Over short distances, it would be kept in a “hover-stow”.
This replica is being used to test how it can travel with the arm out in this “hover-stow”
position, where the arm is out but it bends back at the elbow towards the rover.
They thought it would be better to have the arm stuck while it was out rather than to
try and stow it away, to find it could never be used again, at least it would still be
somewhat functional like this.
Over the course of the mission up until this point, it was also encountering a problem
with a heater for a motor in the arm that wouldn’t turn off.
Engineers managed to get away with switching it off with a T-stat switch, meaning a thermometer
switch would cut power to the heater if the motor got too hot.
But as Martian winter drew near where there would be less sunlight, there wasn’t enough
power to have the heater on all night.
They fixed this by completely disconnecting the batteries at night.
This led to another problem, where there would be very big swings in temperature between
the day and night, meaning the motor would likely wear out faster.
At this point in the mission, this motor stalled altogether.
Engineers temporarily fixed it by applying more current through the motor, although as
a precautionary measure, they stowed the arm outside the rover at night in case the motor
permanently stalled.
You’ll start to notice this in the camera view from now on.
By February 2006, or sol 744, Opportunity visited its last site around the Erebus crater,
called the Payson outcrop.
This outcrop of fine layers shows a diverse range of primary and secondary sedimentary
textures formed billions of years ago.
The structures that were observed here were likely caused between a mix of wind and water
processes.
By Sol 766, Opportunity had left the rim of Erebus and was on its way to the biggest and
most impressive crater yet, Victoria.
It journeyed through large ripple sand dunes, a type of dune we don’t have on Earth!
However, Opportunity tried to stick to paths of exposed bedrock, as these are much easier
to traverse, and it can stop and investigate along the way.
These cobble fields are a bit of a mystery, as we are unsure how they formed like this.
On Sol 833, Opportunity almost got stuck again.
Previously, mission controllers were thrilled by the meters of progress per day Opportunity
had been making towards Victoria, but in this sequence, it took 4 days to get out of this
dune, which they named Jammerbugt, a Danish term for the “bay of wailing”!
Nearly 200 Martian days after it left Erebus, it arrived at Victoria, and what it saw was
amazing.
High ridge walls, a steep slope in and beautiful sand dunes in the centre.
It had already overcome so many obstacles, and this sight is the reward at the end.
And that’s where we will leave our little rover for this episode!
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