There is now a new rover on the surface of mars. It’s the size of a small SUV and has capabilities that surpass all planetary lander that came before. With a suite of high power cameras, computers and transmitters, Curiosity can capture images of unprecedented resolution and even record high definition video, with the ability to cache images and video to two gigabytes of on board storage before transmitting them back to earth. The rover is also equipped with a suite of analytical instruments, capable of determining the composition of surface materials or drilling and digging for deeper samples.
All of this is made possible by the 125 watt nuclear heat source, the latest generation of plutonium-238 radioisotope thermal generators. Curiosity also has a pair of lithium-ion batteries which are charged by the RTG, enabling it to temporarily consume more than the 125 watt base output of the generator for short periods of time. Previous rovers used solar panels to generate their on board power, and although the highest quality solar panels were used, they could produce up to 140 watts, but only under the best conditions and for a maximum of four hours a day. The rover curiosity produces more than four times the previous two rovers did on their best day, and it does so every day.
So what could be a more amazing technical feat than the rover Curiosity?
Curiosity may be the most capable, most well equipped and largest rover to ever travel to mars, but what is really quite jaw-dropping is that it’s not the only rover operating on the surface of the red planet. It has grabbed most of the attention, and rightfully so, but one of the two twin mars rovers launched back in 2003 is still functional with no signs of stopping. Not even the most optimistic mission planners would have dreamed it would be, and yet it is.
On January4, 2003, the rover Spirit touched down on mars. Three weeks later, its twin Opportunity arrived. The missions were planned to last 90 Martian days, which would be just over three months on Earth. However, given the technical difficulties associated with landing and operating on mars, those involved in the project would have regarded the mission as being an overall success if even if it lasted only half that long. It was, however, hoped that the rovers might outlive their initial planned mission and be able to continue to function and collect data.
In reality, the rovers functioned for several years. The Spirit rover continued to operate on mars for longer than anyone would have predicted. It traversed the martian surface until late 2009, when, having previously experienced problems with traction motors, it finally became stuck in the soil on the side of a crater it had been exploring. NASA attempted to free the rover, but in January 2010, announced that the rover was hopelessly stuck in place and would continue to operate as a stationary research platform. Despite being stuck, Spirit continued to transmit data until March 2010. Further attempts to contact the rover were made, but the effort was ended and the mission declared over in 2011, after an astonishing seven years of operation.
Opportunity, on the other hand, is still functioning and shows no signs of stopping. Over the years, it has experienced its share of problems. The drill used for sampling rock has long ago become dull, and the motors in the robotic arm have repeatedly stalled and frozen, preventing it from being fully stowed. Most significantly, the power systems have degraded, with the batteries no longer holding the charge they once did and the solar panels now covered with dust that reduces their ability to collect sunlight. Still, all major systems have remained functional and the rover continues to move and transmit images and data to earth.
There have been a few close calls, when controllers believed the rover was coming close to being lost. Mission controllers feared that the solar panels might become so dust-covered that the rover would not be able to generate enough power to keep critical systems warm enough to avoid failure or that the complete loss of electrical power might cause the on board computers to shut down completely and be unable to restart. (It’s believed that such lack of power may have been what finally shut down the Spirit Rover, which could not be positioned to optimize its ability to collect solar energy.)
However, in all cases, the solar cells continued to generate enough electricity to keep the rover alive until a “cleaning event” occurred, the term used for wind conditions that help remove dust from the rover. The ability of the martian winds to clean the panels to the degree they sometimes do was a pleasant surprise for controllers and has, in some cases, come just in the nick of time to save the rovers from completely losing the ability to generate sufficient power to keep critical systems running.
As of the most recent updates, Opportunity remains in good overall function. The condition of the solar cells and batteries necessitate that it spend more time recharging and less time in operation than when it started. The cameras and instruments remain functional. The robotic arm is no longer stowed and has limited mobility at some key joints, reducing the ability to reach out and analyze samples. The decay of the cobalt-57 source in on board the Mössbauer Spectrometer has made the instrument unusable.
Opportunity played a minor role in the preparations for the landing of Curiosity, sending UHF signals to receivers as a means of calibrating and testing the systems that would be necessary to communicate with the new rover. Experience gained from both Spirit and Opportunity will be invaluable in controlling Curiosity.
Despite not having the same level of scientific instrumentation or the continuous power supply of Curiosity, the continued value of Opportunity should not be overlooked. A planet can have enormous geological diversity from place to place, and simply being able to make observations from one than one location is of enormous value. Mars offers a virtually limitless number of interesting features for exploration, more than enough to occupy two or more rovers. Opportunity will continue to explore and analyze the martian surface until it eventually, inevitably, fails. How long that might be is anyone’s guess.
Will Curiosity have such amazing endurance?
This question, of course, remains to be seen. It would certainly be amazing if it did, and we can hope for years of operation. There are, however, a few reasons why it might not. The program goal is for the rover to operate for one martian year, which is slightly less than two years on earth. As with previous rovers, it is hoped that it will last some time longer, although simply completing the full two years would return volumes of scientific data and be an engineering triumph.
The radio isotopic generator used by Curiosity will almost certainly not be the limiting factor in the life of the rover. It was designed with a minimum life of fourteen years, and experience with deep space probes has shown RTG’s to be extremely reliable, even long past their original design life. Materials degradation is expected to reduce the output to about one hundred watts in fourteen years, although the unit should continue to produce enough power to run basic rover systems for some time longer. The half life of plutonium-238 has little effect on the power output in this period of time. The reduced capacity of the lithium ion batteries, however, will mean the rover will be unable to draw peak power for operations in years to come. In principle, the rover may be able to continue in reduced power mode for many years to come.
The computing systems and electronics on Curiosity are also likely to have a very long period of operation. Being hardened, solid state and designed for the harsh environment, there is relatively little to go wrong with them. Experience has shown that deep space-rated electronics can function for decades.
More likely, the first systems to fail will be mechanical. The robotic arms, the wheels that propel the rover and even the motors that point the cameras are all subject to mechanical wear and tear, and will have nobody around to replace burned out motors, clean dust from joints or re-lubricate bearings. They may well last for years, but they won’t last forever.
The one thing that might result in a shorter life than Spirit or Opportunity is that Curiosity will spend more time on the move. Earlier solar-powered rovers spent most of their time stationary, charging their batteries for relatively short treks between observation points. When it comes to mechanical wear, the amount of use a motor receives is far more important than the age of the motor. Opportunity has traveled an amazing distance of more than thirty kilometers, more than fifty times its design distance, but it took nine years to reach such a distance. The rover rarely moves more than two hundred meters in a single drive. In a few circumstances, it traveled about a half kilometer in a week, but that’s unusual. When moving, the speed is only about .03 kilometers per hour.
With its RTG power source, the rover Curiosity will be able to spend much more time on the go and less time standing still. It will move faster and is likely to travel far more than thirty kilometers. That may well mean that the motors will degrade in a period of time faster than previous rovers. Of course, we still don’t know for sure. Furthermore, even if the rover eventually loses some or all mobility, it may still be operational for basic observations and measurements.
Even if Curiosity does not last as long as Spirit or Opportunity, it will almost certainly return many times as much scientific data, and that’s ultimately the important thing. The new rover is an amazing piece of scientific equipment, yet the amazing feet of endurance of its predecessors is none the less amazing.
This entry was posted on Friday, August 24th, 2012 at 6:11 pm and is filed under Good Science, Misc, Space. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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