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The Enigmas on Mars The Amazing Self Cleaning Rovers |
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Spirit Rover ...
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Dust guard will keep Red Planet's colours true 04 April 2006
THE vivid reds and pinks of Mars provide vital clues about the planet's mineral composition. Unfortunately these colours are becoming increasing difficult to pick out in the pictures being sent back by the rovers Spirit and Opportunity. But a clever redesign of a crucial component should mean that colours in the pictures sent back by the next Mars lander should stay true for far longer. The troublesome piece of equipment is a saucer-sized disc covered in patches of brightly coloured polymer that sits near the panoramic camera on the two rovers. By regularly taking photographs of this "calibration target" and comparing the colours with those in photographs taken on Earth, researchers can tell how the dust-filled atmosphere is affecting colours and adjust the images of the landscape accordingly. "The targets take the varying lighting conditions out of the equation," says Mark Lemmon of Texas A&M University, who leads the camera team on NASA's next Mars lander, called Phoenix. Accurate colour calibration allows minerals to be identified from the pictures. But after 14 months on Mars, the calibration targets have become masked by dust. Researchers must use a computer model that estimates and subtracts the effect of dust on the target when processing images and this introducs inaccuracies. Designing a coloured target that does not get clogged by dust is a tricky task. The material it is made from has to be resilient enough to cope with the vacuum of space while on its way to Mars, and then with the harsh conditions on the planet's surface. The target also has to reflect light evenly in all directions without causing glare, and to do this it must be capable of being cratered with 100-micrometre pockmarks. The only material known to meet all these criteria is a slightly sticky silicon-rich polymer called RTV655. The pockmarks trap dust and this, combined with the material's stickiness, has meant the targets have become caked. Using a different material for the targets is not an option. "Materials that have space-qualified properties are very difficult to find," says Firouzeh Sabri, a materials scientist at the University of Florida, Gainesville. To get round the problem, she and colleagues have added a layer of transparent RTV655. This fills the dimples without altering their optical properties. To further improve the target's dust resistance, they have coated this layer with a transparent nanolayer of gold. NASA's Phoenix lander, complete
with the improved calibration target, is due for launch in August
2007.
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The Amazing Self Cleaning Rovers
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| Martian dust devils finally
caught on camera
15 March 2005
Swirling dust devils on Mars have given NASA scientists both a scientific treat and a very welcome power boost. On 10 March, the rover Spirit captured images of two dust devils in one day. It is the first time any have been seen on Mars since first being identified in a single image from the Mars Pathfinder mission in 1997. One of the two appears on two different images from the rover's Navigation Camera, making it possible to track its direction and speed. Furthermore, a separate dust devil has apparently swept the rover clean. The power output of the rover's solar panels had been reduced by almost half because of a year's worth of accumulated dust. But on 9 March, the output shot up to 93% of its initial level, giving it more power for future exploration. Images looking down at the rover's deck show an almost pristine surface, with just a few small tails of dust, compared to the dingy surface seen just a day earlier. The team is still figuring out exactly when the power boost occurred, and whether it was a single event or not. Science team member Geoffrey Landis told New Scientist that the cleaning of the solar panels may have taken place at night. But dust devils occur only in the midday sunlight, he notes, so it may have simply been a strong breeze that cleaned the rover. Too much of a coincidence? Matthew Golombek of NASA's Jet Propulsion Laboratory considers the breeze hypothesis implausible. Golombek, who was the chief scientist of the Pathfinder mission and is another member of the rover science team, told New Scientist: "We wait for months to see a dust devil and finally catch one and there's this big power boost within a day of it? That's too much of a coincidence." The images are far from just a novelty. "We're getting some very interesting science" out of them, Landis said. For example, it is the first time they have had a way to measure wind speeds directly, since there is no anemometer onboard. The two images of the same dust devil show that it was moving at an average speed of 3 metres per second. If more pictures are found that show dust devils, it might be possible to gather meaningful statistics on their frequency and duration. "That would be very exciting," says Landis. But already, as far as atmospheric science is concerned,
this detection "is certainly the highlight of the mission so far", he says. |
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The Case of the Broken Wheel Spirit Rover ..
This three-frame animation aids evaluation of
performance of the right-front wheel on NASA's Mars Exploration Rover
Spirit during a drive on the rover's 2,117th Martian day, or sol (Dec.
16, 2009). Image credit: NASA/JPL-Caltech
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By Duncan Hooper
A broken wheel on a space vehicle has led Nasa to some of the most conclusive evidence yet that Mars may once have been able to support life. When one of the Mars Spirit rover's six wheels stopped rotating, it ploughed a deep trench into the planet's surface, uncovering a patch of soil that was made up of about 90% pure silica. The discovery is significant because the production of the substance would have required the presence of water, a key ingredient in the formation of life. Nasa scientists said yesterday it was a "remarkable" find "which continues to spur the hope that we can show that Mars was once habitable and possibly supported life." The team has already found other indicators of long-ago water, such as patches of water-bearing, sulphur-rich soil, alteration of minerals and evidence of explosive volcanism, while exploring a low range of hills inside a basin named Gusev Crater. One possible origin for the silica could have been interaction of soil with acid vapours produced by volcanic activity in the presence of water, a Nasa spokesman said. Another could have been from water in a hot spring environment. David Des Marais, an astrobiologist at Nasa's Ames Research Centre in Moffett Field, California, said: "What's so exciting is that this could tell us about environments that have similarities to places on Earth that are clement for organisms." The Spirit, and its twin rover Opportunity, completed their three-month prime missions in April 2004, but continue to operate despite showing signs of age. The churning of the soil caused by the Spirit's broken wheel has exposed several patches of bright soil, leading to some of its biggest discoveries at Gusev, including this latest one. Spirit had been working within about 50 yards of latest discovery for more than 18 months before the discovery was made. Steve Squyres, principal investigator for the Mars rovers' science instruments, said: "You could hear people gasp in astonishment." Mr Squyres, of Cornell University, said: "This is a
remarkable discovery. And the fact that we found something this new and
different after nearly 1,200 days on Mars makes it even more remarkable.
It makes you wonder what else is still out there."
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| Mars rover's broken wheel is
beyond repair
03 April 2006
Mission managers have given up hope of fixing a broken wheel on NASA's Spirit rover and will simply have to drag the wheel on future drives. The glitch means NASA must avoid terrain with loose soil as it maps out a route to a safe winter haven for the rover. The rover's right-front wheel stopped turning about two weeks ago - apparently because of a broken circuit in the motor that powers the wheel. The same wheel had experienced a surge in current in 2004 but later returned to normal. But engineers have lost hope that the wheel can ever recover again. Recent tests at a range of voltage levels failed to produce any movement in the wheel. "It's just not responding," says team member Ray Arvidson of Washington University in St. Louis, Missouri, US. He says the wheel will just drag
along as the rover's five other wheels propel it. The loss of the wheel
means engineers must take extra care to avoid terrain with steep slopes
and loose soil, which can cause the rover to slip. "It's just like driving
through snow - you want to avoid the snow banks," Arvidson told New Scientist.
Late last week, such slippage caused mission managers to reverse the rovers course and descend several metres from its climb towards a north-facing slope on McCool Hill. Mission managers are trying to put Spirit on a north-facing slope to maximise the sunlight falling on its solar panels during the Martian winter, which will last for about six months. It is not clear how low the rover's power supply can go before the rover will die, says principal scientist Steve Squyres of Cornell University in Ithaca, New York, US. But he adds: "The more of a northward tilt we get, the more power we'll have. The more power we'll have, the better our chances of survival." Rover managers are meeting this week to discuss those strategies and weigh the advantages and disadvantages of three potential winter havens, all within 100 metres of the rover's current location. The rover began the mission with 900 watt-hours when it landed in January 2004, but the Sun's low angle means it is now operating on about 330 watt-hours of power. That means it can drive for no longer than one hour per day, but Arvidson says mission planners should not simply head for the nearest north-facing slope. "We have to plan not only over the next few weeks but the next few months," he says. "We don't want to drive to a convenient place and have it be a dead-end for science." But he adds that the rover's wheel failure is not entirely bad for the mission. "It's exposing the underlying materials as we go - that's a bonus." |
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| NASA Mars rover limps to the
hills
25 March 2006
A BROKEN wheel has left NASA's Mars rover Spirit in danger of being marooned over winter. "We need to drive like hell and get to the hills before the winter sets in," says Steven Squyres of Cornell University, New York, principal investigator for the rovers. Spirit needs to find a north-facing slope to maximise the sunlight falling on its solar panels during the coming Martian winter. There are hills only 100 metres away, but the broken wheel is making progress slow. Squyres says the rover could ride out the winter on
nearby "lily pads", his term for areas angled towards the sun. That would
ensure survival, but little more. To continue its scientific tasks such
as remote sensing, moving the robotic arm and sending data back to Earth,
Spirit needs more power, and for this it must reach the hills.
To cope with earlier wheel problems, the rover team honed a strategy of dragging a damaged wheel for 90 centimetres, then switching it on for 10 centimetres. "You create a pile of dirt and then drive over it," Squyres says. That won't work now. "We may have to learn to drive all over again." From issue 2544 of New Scientist magazine, 25 March 2006, page 7 |
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| Mars rover's wheel breaks as
winter beckons
20 March 2006
The front right wheel of NASA's Spirit rover has stopped working – just as the approaching Martian winter means it is increasingly urgent that it gets to a northerly facing slope, to maximise the sunlight falling on its solar arrays. "The wheel is not drawing any current at all," says Jacob Matijevic, engineering team chief for the rovers at the Jet Propulsion Laboratory in Pasadena, California, US. It is not the first time a problem has struck Spirit's front right wheel. The same wheel acted up about five months after the rover landed on Mars on 4 January 2004. As the rover neared the Columbia Hills, the troublesome wheel's motor began drawing about twice as much electrical current as each of the vehicle's other five wheels. Mission planners then switched to driving the rover backwards to protect the wheel. Spirit also had fewer driving days when in the hills. After this spell, the wheel started working properly again – probably because the wheel's lubricant redistributed itself, helping the current to return to normal. But now the wheel has completely
stopped turning. On Spirit's 779th Martian day – called a sol and lasting
24 hours and 40 minutes – the motor that rotates the wheel broke down.
Engineers say the "motor brushes" that provide power to the turning part
of the motor may have lost contact.
Both Spirit and its twin, Opportunity, were originally designed to last just 90 sols on Mars. They are currently in their third extended mission and JPL says Spirit's wheels have turned more than 13 million times during the rover's long haul. "It continues to be an exciting adventure with each day like a whole new mission," says John Callas, the new project manager for the rover mission from JPL. "Even though the rovers are well past their original design life, they still have plenty of capability to conduct outstanding science on Mars." But for Spirit right now, the focus cannot be on gathering
scientific data. Instead the team is focused on getting the rover to a
good location to weather the coming Martian winter. Its solar panels are
only producing about 350 watt-hours of electricity these days – only enough
to power about an hour of driving. That is about 15% lower than it was
just a month ago and is less than half the level when the rover first rolled
onto the surface of Mars. The rovers need 280 watt-hours of power to stay
alive.
So Spirit, having finished studying the layered feature dubbed Home Plate, is now aiming to reach the northerly tilting slope of McCool Hill, which lay about 120 metres away on Friday. There its solar arrays will soak up as much sunlight as they can during their second Martian winter. Spirit will drive toward its new target backwards, dragging its broken wheel. With power and driving conditions in their compromised state, planners expect to drive the vehicle about 12 metres per day. Closer to the Equator, at Meridiani Planum, Opportunity started a 2-kilometre drive last week to the large Victoria Crater. It has also suffered wheel problems in the past. |
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| Mars rover Opportunity has wheel
trouble
19 April 2005
The Mars rover Opportunity has lost the ability to steer one of its wheels. While the vehicle can still move, the failure may make it harder to study rocks up close. The rover has six wheels aligned in two rows and each of the four corner wheels has its own steering mechanism. The problem is with the front right wheel, which can still roll but is now stuck at a 7° inward angle. NASA rover project manager Jim Erickson says it is like a car losing its power steering. “At this point, with this one actuator failed, it’s an inconvenience, nothing more,” says rover chief scientist Steven Squyres. But he adds that the failure is a reminder that the rovers will not run forever and that “we should continue to get every bit of science out of these that we can”. On 13 April, the rover was travelling south from the Voyager crater when, at the end of one manoeuvre, the front right wheel stopped. Sometimes this happens when the wheel hits a rock, so ground controllers reversed the rover and tried again to turn the wheel, but the same problem occurred. At that point, engineers decided it was a problem with the wheel’s steering motor and not a physical obstacle. Ground controllers have now disabled the wheel’s ability to steer. A consequence of the failure is that Opportunity’s
ability to make very precise manoeuvres to touch a target sample with its
instrument arm will be reduced. Erickson says Opportunity is likely to
stop to sample rock and soil with the arm before it reaches its current
target - a crater named Erebus.
But the rover should be able to travel without too much trouble. In February 2005, NASA transmitted a software package to the rovers giving them the ability to determine how well they are staying on course and to correct their steering for themselves if they did lose the function of a wheel. If the steering on the wheel has permanently failed, the rover could drive with just three other wheels directing the vehicle. In addition, the team may opt to steer the rover like a tank, with the three left wheels turning one way while the three right wheels turn the other. “I have always said my goal is to wear these things out,” Erickson says. But NASA managers still hope to get a lot more from the rovers before they roll to a final halt. Opportunity and Spirit landed on Mars in January 2004. The pair were given a further 18-month mission extension on 5 April 2005. Spirit is now heading toward an outcrop of bedrock, named Methuselah, spotted this weekend in photos taken by one of its cameras. “We found the biggest and most spectacular outcrop of bedrock that Spirit has ever seen in those images,” Squyres says. He says there are fine layers visible in the bedrock, with “hints of interesting structuring”. Spirit should arrive at the rock later this week. |
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| Mars rovers enjoy a new lease
of life
06 April 2005
The missions of the twin Mars rovers Spirit and Opportunity - which have already surpassed all expectations - have been extended by a further 18 months. NASA officials announced on Tuesday that the rovers will be allowed to roll on well beyond the end of their second extension, which has just expired |
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| SUMMARY
15 March 2005: Spirit
But on 9 March, the output shot
up to 93% of its initial level,
giving it more power for future exploration.
The team is still figuring out exactly when the power boost occurred, and whether it was a single event or not. Science team member Geoffrey Landis told New Scientist that the cleaning of the solar panels may have taken place at night. But dust devils occur only in the midday sunlight, he notes, so it may have simply been a strong breeze that cleaned the rover. Matthew Golombek of NASA's Jet Propulsion Laboratory considers the breeze hypothesis implausible. Golombek, who was the chief scientist of the Pathfinder mission and is another member of the rover science team, told New Scientist: "We wait for months to see a dust devil and finally catch one and there's this big power boost within a day of it? That's too much of a coincidence." 19 April 2005: Opportunity The rover has six wheels aligned in two rows and each of the four corner wheels has its own steering mechanism. The problem is with the front right wheel, which can still roll but is now stuck at a 7° inward angle. NASA rover project manager Jim Erickson says it is like a car losing its power steering. 20 March 2006: Spirit The front right wheel of NASA's Spirit rover has stopped working But now the wheel has completely stopped turning. On Spirit's 779th Martian day – called a sol and lasting 24 hours and 40 minutes – the motor that rotates the wheel broke down. Engineers say the "motor brushes" that provide power to the turning part of the motor may have lost contact. 25 March 2006: Spirit To cope with earlier wheel problems, the rover team honed a strategy of dragging a damaged wheel for 90 centimetres, then switching it on for 10 centimetres. "You create a pile of dirt and then drive over it," Squyres says. That won't work now. "We may have to learn to drive all over again." 03 April 2006: Spirit Mission managers have given up hope of fixing a broken wheel on NASA's Spirit rover and will simply have to drag the wheel on future drives. The rover's right-front wheel stopped turning about two weeks ago - apparently because of a broken circuit in the motor that powers the wheel. The same wheel had experienced a surge in current in 2004 but later returned to normal. [It]900 watt-hours when it landed in January 2004, but the Sun's low angle means it is now operating on about 330 watt-hours of power. That means it can drive for no longer than one hour per day |
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