Find out how the rovers Spirit and Opportunity were designed, built, tested, flown, landed, and driven, how they work, and what they've done.

He is author of original zip and companion programs, and author of unzip decompression. He is co-author of GNU gzip and zlib with Jean-loup Gailly.
prepared by Paul Schmidt
 

NASA had good cooperation with the European Space Agency and has been using the radio on their Mars Express orbiter. The U.S. has an instrument on Mars Express and the Europeans have instruments on the Rover. The U.S. and Europe try not to duplicate efforts because they both have limited budgets. Dr Adler started out by showing a view of Earth from space. Earth is really blue and that shows large amounts of liquid water. It is very important to life on earth. A whole ecosystem exists under water using hot springs as energy sources. Any place there is liquid water and a source of energy on Earth we find life. Liquid water is a very good sign of the probability of life as there is usually some sort of energy available.

Next was a picture of Mars, there is no blue. It is grayish and shows darker iron material. There is a little bit of water at the ice cap covered by CO2. Mars is cold and dry with a very thin atmosphere. Liquid water cannot exist on Mars because the surface is colder than the triple point of water. Any water on Mars exists as a gas or a solid. The Viking Orbiter took many detailed pictures back in 1976. The valleys look like they were cut up by liquid water, yet liquid water cannot exist on the surface of Mars. How can this be possible? It appears that there was liquid water on Mars many years ago and that conditions were different then than they are now. On Mars our strategy is to investigate water. The journalists who investigate Watergate said the way to understand it was to follow the money. The way to understand Mars is to follow the water. If you follow the water you will find out a lot about Mars including “What is the potential for life there?”, the climate of Mars, how the water goes in and out of the atmosphere, the geology of Mars, and how water affect Mars rocks and Mars dirt. Water is a resource for human exploration if we want to go there and stay there. There is no known water on the moon, but there is quite a bit of it on Mars.

In 1996-97 we sent Mars Surveyor which found lines on walls that are recent. They found gullies that look like evidence of recent liquid water. In 2001 we sent another orbiter called the Odyssey that made a map using a neutron spectrometer that shows dark blue regions indicating a lot of water is in the ground. The ground is about 50% ice by weight. We don’t know how deep the water goes. The instruments have found more water than was originally expected. The future 2007 Phoenix mission will land near the North Pole and dig into the ground about a meter. It will determine the chemical composition of the ice and the ground.

We get the history of Mars by investigating the layers of ice. The lowlands might have had oceans in the past. The southern part of Mars has a lot of craters while the Northern part is smooth. How did the North become smooth? Possibly by water erosion. Did life originate on Mars then? At about the same time life started on Earth. The 1996-97 Pathfinder was about the size of a micro-wave oven. Pathfinder was an engineering test article and was used to test the air bag system and the ability to rove on Mars. It did not go very far and could not go very far without losing communication. In 2003 we launched the Mars Exploration Rovers that landed in 2004. These were much larger than the Sojourner rover. The Rovers had their own radios and antennas and had a much larger scientific payload. They were roving geologists. The vehicles are larger than people. The Rovers have a lot of telemetry and communications capability. The computer is basically a radiation hardened Power PC. It has a UHF radio that communicates with the orbiters and an X-band radio that can communicate directly with Earth. 94% of the data goes through UHF. The X-Band radio is used to receive commands directly from Earth. There are some small nuclear heat sources to keep the Rover warm.

The batteries are not the life limiter, as far as we can tell. The Rover has both high and low gain antennas. The Rover computer must know which way Earth lies in the sky for direct communication. The low gain antenna has a very low rate but is adequate for emergency use. There are stereo cameras and a science instrument on the mast. There are lower resolution black and white navigation cameras on the front and rear used for steering and auto navigation can be done with them. There is a rock abrasion tool that can drill a few millimeters into solid basalt which helps us see what the rock was like when it was born. On the arm are a microscopic imager and 2 spectrometers that determine a lot about the chemical composition of the rocks.

There were many problems in developing the air bags and the parachutes. Dr. Adler showed a short movie of a parachute test which failed about a year before launch. They got the parachute to work and the Spirit Rover landed successfully on air bags. The Rover drove off and took a picture of the lander after exiting it. He said we always thought “What could go wrong?”. The launch and landing are two very dangerous periods. It was risky driving off the lander. After that they thought they had gone by the really risky times. They were driving around and everything was working great. Then on Sol 18 they didn’t hear from it. This wasn’t too worrisome because there are frequently minor problems with communications especially with the high gain antenna. They waited for the Australian pass but there was still no communication and that was scary. There was something wrong and they didn’t know what it was. There was little contact for 3 days. They received a small amount of data that showed the temperature was going up and the battery was going down and the Rover was not in any kind of state that they understood or knew how to control. They were able to send commands through the radio and reboot the computer and not use flash memory. They were able to determine that the computer was repeatedly rebooting. It was not staying up long enough to put the Rover to sleep so it was continuously running and draining the battery. They were able to slip in commands before the computer rebooted again. They were able to buy time by putting the Rover to sleep and allowing it to recharge its batteries. They watched Opportunity land successfully. They found an error in the software. They were able to get the task trace back after trying for 4 days and fixed the problem. They called this the $18 million task trace award as an estimate of the cost of the lost 4 days of scientific data. Spirit was operational again. Spirit landed in an area where all of the rocks were volcanic and never experienced any water. There were twin hills in the distance, beyond the Rover’s expected range.

The Opportunity lander was on the opposite side of Mars. Opportunity bounced into a hole where there was evidence of water. That outcrop was inspected for about 2 months. There were several indications of water. There was a high concentration of sulfate salts. The only way you get those type of salts is if they have been leached out by water that later evaporated. There were many spaces in the rock that looked as if they had been cut out by water. “Blue berry” spherules were found that were pieces of hematite that is only formed in liquid water. The landing site had been picked because they could detect hematite from orbit, but could not tell if it was formed by water. The tests by Opportunity proved that liquid water had existed at one time at that point on Mars. They moved to another crater and found much more evidence of water and continued to explore the area for the next three months. They drove toward the very large crater Victoria. It took 2 years of driving around this crater to find a way to get in. Opportunity is now at the rim of that crater. They are still looking for a way to get into it.

The Rovers life span has been over 10 times that predicted. It was believed that dust would do in the Rover as solar panels were covered by dust. How long would it survive? On earth you can have a cleaning woman dust off the Rover, but you can’t do that on Mars. Their “dust devil” winds blew the dust off the surface of the solar panel and power went up by 20%. They have been getting a new lease on life every Martian year, something that was unexpected. During design they decided that making the solar panels larger to meet the design life time was less complex and expensive that providing a mechanism to clean off the solar panels. The “dust devils” were unexpected and they have been cleaning the solar panels of both Rovers.

Spirit on Sunday evening was at Sol 976. Its wheels have been digging up white stuff. There has been no corrosion or dust in mechanism. Failures that have occurred have been due to wear. A brush broke off on the front wheel motor and it has been dragging that wheel. Opportunity is still working at Sol 958. Dr. Adler showed a picture of the Victoria crater that was taken by it this morning.

Following the Rovers, the next spacecraft at Mars was the Mars Reconnaissance orbiter that takes pictures with 20-30 cm. resolution which is much higher resolution than previous orbiters. It is in a circular 300 km. polar orbit and it took pictures of proposed Phoenix landing site. The first site had many boulders on it so a different site will be chosen. It has easily spotted the Rovers on the surface of Mars.

The next launch will be in 2008. The Phoenix lander has a 2 meter long arm so that it can dig through ice and analyze water at a landing site near a pole. In 2010 a large Mars Science vehicle will be landed on Mars. Mars launches are made every 26 months as Earth in its orbit periodically laps Mars. The Science Lander doesn’t use solar panels, it has a nuclear power source weighing approximately 50 kg that produces power all of the time. Better planetary coverage is provided because it doesn’t have the limitations of the solar panels that don’t produce power at night and need to be oriented toward the sun. The nuclear power produces heat as well as electricity. The Science lander has much more capable instruments than the current Rovers. It will break off pieces of the rock and bring them into the lander to be analyzed. The design life time is 1 Martian year (22 months) but it could last a lot longer. The Science lander is to be landed by rockets because the air bags don’t scale up well.

It would be better to bring back samples from Mars. No mission has been funded yet. It takes 7 to 11months to get to Mars and then you have to wait for the best spot for return which is a 2 ½ year round trip. Sending people to Mars would have the same time constraints.

There are meteorites that have landed on Earth after impacts on Mars 15 million years ago. Vikings measured the Martian atmosphere and this data was used to prove the rocks were from Mars. A careful look at a rock on Earth from Mars said that it looked like evidence of a live, but the scientific consensus is that is not convincing evidence of life on Mars. It will be much better to get actual samples from Mars.

Artificial intelligence on the Rovers reduces costs in science operations. It takes longer to accomplish things and it can’t do too much that requires ground inputs. It can do quite a bit of automated traveling and position its arm automatically. The team on Earth determines what is going to be done, but the number of people and the amount of time they work has been reduced as the mission has continued. The team tries to come in during the day and it takes longer to get things accomplished on Mars. They are trying to reduce Rover operations costs, as they weren’t expecting them to last this long. The Reconnaissance Orbiter is sending back megabits of data per second.

The Software glitch was explained in more detail. The flash file was a commercial DOS file system which was reused and also used some RAM. There was supposed to be more than enough space available but it ran out of memory and then reset. The flash file was filled and could not be loaded into memory and which resulted in a fatal error during reboot. After 15 minutes the computer rebooted again and since the error was in the reboot cycle it kept returning again on the reboots. The deleted files took up space took up just as much space as the operating files in the flash memory. The maker of the system, Data Products, had made a change to the original and added an additional file so there were double the number of expected files. JPL didn’t track the memory. They expecting to cover any problems by extensive testing. They ran 10 Sols of data in test. During operation on Mars they ran into the problem at 18 Sols. A work-around fix was easy once the problem was discovered. The problem has now been eliminated by a new software load on both Spirit and Opportunity.

Dr. Adler gave an excellent presentation that combined detailed explanations with many spectacular photographs and other useful visual aids. He presented a lot of information in a short period of time. Most of us are unlikely to become Mars explorers, and this was a great opportunity to learn about JPL’s outstandingly successful Mars exploration.

This was second meeting of the LA Chapter year and was attended by about 14 persons.
Mike Walsh, LA ACM Secretary