Martian Chronicles XII: Flying SORTS
Three spacecrafts are now hurtling toward the Red Planet to look for evidence that it might once have been wet enough to sustain life. Orbital projections of where Europe’s Mars Express and the two NASA Mars Exploration Rovers (MER) are right now, can be continuously monitored over their half-year journeys. Experiments performed by the MERs will help to determine whether water might have once existed in volume on the red planet.
SORTs: Surface Operations Readiness Tests
Scientists and engineers use a bank of computers at the Jet Propulsion Lab to send commands to a full-scale rover located in a large chamber with a simulated martian surface. They do not see the test rover. The commands are sent blindly, just as they will be when the rovers are on Mars. Computer software offers a simulated 3-D view of the rovers and their martian landing sites. Only after the test is complete is the MER team allowed to view the actual rover model and how it responded to their instructions.
Groups of instructions that tell the rovers where to go and which tasks to complete are called "sequences." Throughout the seven months of cruise, scientists and engineers are designing and building sequences that will be tested in a SORT. There are nominal sequences that cover routine tasks, and there are contingency sequences that act as back-up should the rovers be unable to complete their original duties.
Each SORT focuses on a different aspect of landed operations. An "impact to egress" SORT covers the critical time from touch down through egress when the rovers leave their landers. There is a lot to do. After the long journey to Mars and the impact of landing, the health of the rovers and their science payload must be checked. The first MER-view images of Mars are acquired and sent back to Earth. Pancam and Mini-TES take their first panoramas. These are 360-degree surveys of the terrain. From these images, scientists select interesting targets for further study and a drive direction for the rovers. Egress from the lander is a risky maneuver that must be carried out very carefully. Then, after the rovers are on solid martian ground (or, in this case, simulated martian ground in the test chamber), images are taken to assess the safety of the drive off the landers.
Other SORTs include "surface approach," which helps the team understand how to approach a target rock and position the rover arm when it deploys, and "anomalies" SORTs that serve up a week’s worth of difficult situations.
Another Earth-based activity during the cruise phase of the mission is similar to a SORT, but is not a blind test. A full-scale model of the rover is transported to a Mars-like location here on Earth and is sent a string of commands. MER scientists and engineers watch the rover as it responds to the commands. The more that is learned about the way the rover and its science instruments move, the easier it will be to understand how to build sequences for the rovers.
–Pamela Smith, Cornell
The two Mars Exploration Rovers are targeting what imagery indicates might have been ancient dry lake beds and other geologically interesting sites in early 2004.
The Martian Chronicles series gives an inside view of what it takes for scientists to deliver a complex mars mission. The journal entries are from Cornell’s Steve Squyres, the Principal Investigator for the Mars Exploration Rovers’ scientific package called Athena. The chronicles begin sequentially from the beginning of July 1999, four years before launch, and will culminate in the dramatic landing of the twin rovers on Mars in January 2004. The expected mission time roaming the red planet is ninety days, from January to April.
As Spirit and Opportunity speed toward Mars, more than three hundred scientists and engineers here on Earth will learn how to act in unison to master the art of commanding two very complex robots to do science on another world.
The chronicles include an insider’s view of hardware tests and site selection to problem solving and science planning on the surface of Mars.
September 27, 2003
Well, we survived the latest operations readiness test. It wasn’t easy. As I mentioned last week, this test was focused mostly on the period we call "Impact Through Egress".
This is the period of time that begins when the lander comes to rest, and that ends when we’ve got six wheels in the dirt. The test went amazingly well, all things considered.
Impact Through Egress is one of the most complicated parts of the mission. The rover lands in a tightly folded-up configuration, and over a period of several days it has to unfold, take a look around, stand up, and find its way off the lander and down onto the martian surface.
We did all of that in this test, and we successfully drove the rover off the lander right on schedule.
Of course, this was an easy test compared to what’s to come. At this point we’re just trying to get all the basics down, so the test conductors didn’t throw too many nasty surprises our way. (There were several nasty-looking rocks right in front of the rover that we had to find a way around, though.) Future tests promise to be trickier. And who knows what the actual landings on Mars will bring.
|A simulated image of the Mars rover carrying the Athena science instruments against the horizon of the Mars rust-colored sky. As Cornell’s Project Scientist, Steven Squyres, wrote about their simulations: "We’ve just finished a ten-day test using the rover to simulate twenty martian days. The guys took their baby out to a site somewhere out in the American Southwest, and we drove it from JPL just like we’ll drive the real MER rovers when they’re on Mars. The "landing site" was fantastic, with no vegetation, great rocks, and many geologic puzzles for us to solve. Very Mars-like! In our twenty "sols" of operations, we drove the rover more than 200 meters, made a bunch of detailed measurements of the chemistry of the rocks, and took a lot of spectacular pictures."
October 4, 2003
Out of the frying pan and into the fire. It feels like we just finished our last Operations Readiness Test, and now it’s time to start the next one. This one is going to be a killer.
Every other test that we’ve done (and every other test that we’re going to do) involves running just one rover at a time. But once we get to Mars we’re going to have to be able to operate both Spirt and Opportunity simultaneously. So in this test, we’re going to try running two rovers at once.
We’ve got all the hardware we’ll need, and we’ve got enough people. The question is whether or not it’ll all work when we try to make it happen. We’ll find out real soon. The test starts next Monday and runs for two weeks…
October 18, 2003
If it’s 3:00 AM in Los Angeles, what time is it at Gusev Crater? That’s the kind of problem we’re wrestling with this week. We’re into the fourth martian day of our latest Operations Readiness Test.
In this test we’re simulating the process of landing the Opportunity rover at Meridiani Planum at the same time that we’re operating the Spirit rover at Gusev crater.
Both rovers operate on Mars time, of course, and the martian day is 24 hours and 39 minutes long. That’s bad enough, but it gets worse. The two landing sites are in two different locations on Mars, and the local martian time at the two sites is completely different.
So, for example…
Right now, as I type this, it’s 3:00 AM at the Jet Propulsion Laboratory. It’s 4:35 AM in Gusev crater, and it’s 4:33 PM at Meridiani Planum. At 3:00 AM Pacific time tomorrow it’ll be about 3:56 AM in Gusev crater, and about 3:54 PM at Meridiani Planum. And so forth.
It gets really confusing.
Anyway, the test is going really well. We’ve had a few hiccups, most of them because this time the people running the test have begun introducing some anomalies… little challenges (and some big challenges) of the sort that we could encounter in flight. Overall, though, it’s going very well. I just wish we didn’t have to keep such strange hours…
October 25, 2003
Is there life on Mars? Could humans build a new off-Earth settlement on the red planet? Like the Earth’s little brother, Mars has long fascinated sky-watchers. NASA’s new plans for exploration of Mars include the Athena Payload: instruments and tools for a Mars rover.
Equipped with the Athena Payload, the twin rovers of NASA’s Mars Exploration Rover project will be robotic field geologists, exploring Mars’ climate history and searching for signs of water and life. So suit up, strap in, and prepare to blast off with Athena: roving soon on a planet near you.