NASA's Way Out EVs
By Bill Moore
"The top speed of our vehicle is approximately the land cruising speed of a slug," chuckled a jubilant Kobie Boykins as we continued our dialog just a few hours before the Mars Exploration Rover 'Spirit' rolled cautiously off the lander that had been its home for hundreds of millions of miles on the journey from Earth to Mars.
Then just a few days after our telephone conversation, 'Spirit' suddenly became the robotic equivalent of autistic, virtually shutting down and only briefly sending tiny streams of computer-coded gibberish. JPL scientists have been working around the clock to try to understand what happened and why, even as a second rover named "Opportunity" rapidly approaches the planet, its target a 1000 feet higher plain called Meridiani that satellite images suggest is rich in Hematite, a mineral usually associated with water.
Naturally, given the inexplicable problems with "Spirit" after such a brilliant start to its mission, the concern is that whatever ails it may also be secretly lurking in Opportunity's electrical, mechanical or software systems. So, there's a race on to track down "Spirit's" problem so that Opportunity can be prevented from prematurely shutting down, as well.
But in those more halcyon days at the end of Sol 11 in Spirit's mission, Boykins was excited to talk about the pair of golf cart-sized EV's the JPL engineering team had built. "The vehicle has on board smarts, so it can drive itself, for the most part. So, the rover moves for approximately thirty seconds and then stops and take pictures of its surroundings, makes sure that its safe, and then moves again. There's no land speed records that we're going to set in terms of what we've got here on the surface of Mars," he told EV World.
The operational range of each rover is fairly limited. Boykins estimates the maximum is about a kilometer. This is dependent on many factors, including the amount of Martian dust that will gradually accumulate on each vehicle's solar panels, which somewhat resemble insect wings. "It is totally dependent on how much sun we get," he stated, noting that as Mars moves further away from the Sun in its orbit, the amount of available daily sunlight will also diminish, reducing the power output of the 140 watt solar arrays. The goal of reaching a series of small hills approximately five kilometers east of the Gusev Crate landing site is well beyond the range of 'Spirit' even on its best day.
However, for NASA and JPL, the capabilities of the rovers are a magnitude greater than that of the previous rover sent to Mars in 1997. Little Sojourner could operate only 10 meters away from the Pathfinder lander, in part because it didn't have sufficient power to do so and also because it used Pathfinder as its communications relay back to Earth.
Really Remote Control
At more than 125 million miles away from Planet Earth, JPL engineers cannot "joystick" control of either rover because commands take at least nine minutes to reach Mars. So, both MERs were designed with some limited intelligence, what Boykins compares to that of a "flea."
"What we do is send it commands that say, 'We want you to go to this rock.' The vehicle is smart enough to say, 'Here is my path to that rock,' and it will drive towards that rock.
"If the rover detects a potential obstacle, it is intelligent enough to try and figure a way around it," Boykins explained. When its not sure how to solve the problem, it will wait for NASA to give it the necessary instructions. Those instructions may simply involve temporarily turning off the hazard avoidance system because the space agency has determined that no real threat exists because the on board system was simply confused about where it was or what it was looking at. Or it may involve sending a series of intermediate way points to help the rover circumnavigate the obstacle or hazard.
Curious Soil Anomalies
Once 'Spirit" successfully rolled off Columbia Memorial Station, as the lander is now known, the mystery of the "Magic Carpet" soil deformation has only deepened. The soil appears to have characteristics that resemble a crust of brine left behind after an ancient salt lake -- which satellite data strongly suggests the Gusev Crate may once have been -- had evaporated.
At the time of our discussion, JPL wasn't certain what constitutes the soil on this part of Mars, but Boykins said that NASA science teams and their university counterparts had postulated numerous soil possibilities before sending the vehicles on their months-long mission. The rover engineer team tested their vehicle on different soil combinations from loose sand to hard pack dust, "to see what would happen." Tests also included taking the rover out to random locations in the Southern California desert and letting the navigation team back in Pasadena control the vehicle as if it were on Mars.
Of course, Mars isn't sunny California. It's a frozen, desiccated planet with only the hint of an atmosphere made up mostly of carbon dioxide. The processes that formed soils there probably bare little resemblance to the weathering processes of wind and rain here on Earth . The mystery of the "Magic Carpet" and subsequent extreme close-up/near microscopic images of the soil around the site strongly hint that we have a lot to learn about the "dirt" that makes up this distant neighbor.
Given the level of uncertainty about what NASA rovers might encounter in their target zones, JPL engineered the rovers so they could adapt somewhat to different soil conditions, including giving each rover the ability to adjust what Boykins calls its "buoyancy." This means adjusting the size the tire patch of each wheel somewhat akin to increasing or decreasing the tire pressure on a Jeep. The "fatter" the tire patch, the less likely the wheel will get stuck in soft sand. This is accomplished on the twin MERs by increasing or decreasing the width and diameter of each wheel slightly.
Fear of Fire, Free of Freezing
From Boykins' perspective the biggest concern for the safety of the rovers is temperature. Both vehicles have to withstand a firey descent through the planet's atmosphere and then almost immediately each is plunged into bitter, sub zero conditions that can fluctuate a hundred degrees in a Sol's time.
"The two biggest risks for this vehicle were the entry and descent landing, which we accomplished. And number two is actually getting off the lander."
The "Spirit" mission (MER 1) successfully overcame both of these hazards, at least initially, only to be stymied by something totally unforeseen. As I write this, "Opportunity" is entering is descent phase and is slated to land on Mars in about three hours. So, by the time you read this, we'll know the fate of this spacecraft.
Given the often planet-wide dust storms that within days can shroud almost the entire surface of Mars, I asked Boykins about the potential threat posed by a Martian wind storm. Surprisingly, this is one of the lesser concerns.
It turns out that Mars' atmospheric pressure is so low -- roughly one-tenth that of earth -- that by Boykins' estimate, a 40 mph wind on Mars has the effective force of a 5 mph breeze on Earth.
[Author's note: In examining two pairs of photos from the "Spirit" PanCam, I did detect the presence of what appears to be a mote of dust on the left lens. By superimposing in Photoshop two images taken by the same lens but panned several degrees apart, I concluded that what appeared to be distance object floating above the horizon was either a speck of dust on the lens or a possible pixel failure. It wasn't -- to my disappointment -- a distant Martian UFO.]
Changing the subject for a moment and with the understanding that Boykins is an engineer, not a scientist or geologist, I asked him about the curious lopsided nature of Mars topography where the majority of what appear to be meteor impact craters are located primarily in the Southern Hemisphere.
His response was that there are about as many theories on what caused this disparity as there are scientists proposing them. All have plausible elements, but no one explanation has gained credence in the scientific community.
"In engineering there is right answers and then there's a great answer. In the scientific community there's lots of good answers and whoever you listen to, people have different opinions." He acknowledged it is obvious that the southern hemisphere got "beat up" a lot more than the northern hemisphere. "The range of reasons why vary so widely that if you talked to any expert, they'd give you three different answers. They would give you a good answer. Then they'd give you their answer, and then they would give you the answer de ju."
Will the Next Rover Be a Nuclear Volkswagen Beetle?
Regardless of the outcome of the current Mar's missions, NASA and JPL have already begun a pre-engineering study of what the successor(s) to "Spirit" and "Opportunity" are going to be. Boykins told EV World that the first conclusion that's been reached is that succeeding rovers need to be larger, about the size of a VW Beetle, so they can cover more terrain, operate longer and perform more experiments.
The current MER's were limited in size because they had to fit in landers that used air bags to safely get the craft down on Mars. These vehicles now have pretty well reached the limits imposed by air bag landing systems. Succeeding missions will have to come up with new strategies, probably some form of smart landing system that replies on rocket breaking and guidance. The challenge here, however, is designing an extremely fast and smart collision avoidance system because Earth-based ground controllers won't be able to make last minute landing decisions and corrections. The lander will have do that all by itself.
Once safely on the ground, a larger vehicle could easily clear most one meter-sized obstacles are appear typical of the terrain found at most of the sites on which previous missions has successfully landed. Boykins sees the real engineering challenge as getting the ratio of the pure structure vs the amount of instrumentation carried into a more equitable balance. Right now that ratio is about 70/30: seventy percent of the rover's mass is supporting structure and mechanics, while thirty percent of the mass is dedicated to the scientific payload. He said NASA would like to see that ratio move closer to fifty-fifty.
Another important reason for moving beyond the air bag bounce-down landing is that it limits exploration to a 30 degree swath of lowland sites around the planet's equator. Eventually, we'll want to explore the more remote and rugged parts of the planet, which is impossible using current technology.
As NASA investigates sending larger robotic missions to the surface of Mars, how to power them also becomes an issue. Boykins said there are an number of possible systems beyond solar electric power. One that is being consider -- and is certain to generate a lot of controversy -- is powering the vehicle with some type of small nuclear power plant that can generate heat to keep the vehicle powered up through the cold Martian nights. NASA has powered spacecraft before with nuclear fuels, but sending such a vehicle down onto a distance planet poses both environmental and political risks, especially given the long string of Mars mission failures.
Sending Man to the Mission-Killer Planet
The Bush Administration has proposed reorganizing NASA to focus its efforts on two missions: establishing a base on the Moon and eventually sending a manned mission to Mars, perhaps before 2030.
Given the continuing rapid improvement in robotics technology, I asked Boykins at what point does it make sense to send a manned mission to Mars given the attendant risks?
For him, the first reason to establish such a lofty -- not to mention expensive -- goal is to inspire the current generation of young people, elementary-aged children, among whom may be some of the first humans to stand on that distant world. The motivational benefits of that goal are important, in and of themselves.
Beyond that, there are things humans can do that robots will probably never be able to do, at least in the foreseeable future. For Boykins, a human mission would represent a quantum leap in science, not only in what can be learned once the mission is there but also in terms of the technology necessary to get mankind there and back safely.
"It's an evolutionary step in the study of Mars," he concluded. "It will happen, it's just when will it happen?"
One final note: one of the rocks photographed by "Spirit" intrigued me. It appears to be about the size of a human fist and has a very curious, squarish hole "cut" into an unusually straight surface. In a subsequent email, I asked Kobie if the geology team could take a closer look at it. He graciously wrote that he would pass on my request to them. Unfortunately, 'Spirit" ceased working properly a short time later, so it may be a very long time before we find out what made that strange hole.