For the future of Mars exploration, the past is prologueby Duane Hyland
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| “Who knew if you had a sharp rock on bedrock that the weight of the rover coming down on it would damage the tire?” Vasavada said. “Now we know.” |
The amount of scientific information that we have already gained from existing missions was reviewed in depth, with special attention shown to the Opportunity and Curiosity rover missions, which have just about settled the debate about water on Mars and the early potential for microbial life. Ashwin Vasavada, deputy project scientist at the Mars Science Laboratory at NASA JPL, summed it up best: “Our evidence shows that Mars had water for thousands, if not millions, of years.”
After the discussion of Mars’ watery past, it was time to look at what future exploration might yield. Those upcoming missions include Mars Atmosphere and Volatile Evolution (MAVEN) mission, which will yield valuable clues to the dissipation of Mars’ atmosphere; the 2016 Mars Insight mission, which will place a stationary lander on the Martian surface to drill beneath the Martian surface to measure seismic activity and core heat; and the 2020 Mars Rover, which will have the capability to cache samples for later return to Earth, allowing for a much more nuanced and in-depth study of them for signs of life. Each of these programs seeks to answer the same basic questions: How did Mars form? What happened to its atmosphere? And was there, at one time, microbial life on the planet?
Each of these missions builds on the heritage of the projects before it, perhaps most literally illustrated with the Mars 2020 mission. Its entry, descent, and landing (EDL) phase lead, Allen Chen, said that it will use both the “skycrane” delivery system and left-over spare parts from the Curiosity Rover mission to mitigate the risk of mission failure. As he succinctly put it, “If it’s not broke, don’t fix it!” Each panelist noted that the ultimate goal of each of the missions is to gather the crucial data needed for successful human exploration of Mars by, or before, 2040.
Other revelations from the session included an amusing discussion of the Curiosity Rover’s tires, which have suffered some damage after two years of rolling across the Martian surface. “Who knew if you had a sharp rock on bedrock that the weight of the rover coming down on it would damage the tire?” Vasavada said. “Now we know. Sand is much better: if you hit a sharp rock on sand, the rover simply pushes the rock down. Hit that same rock on bedrock and it’s problematic.”
“Mars 2020 has learned Curiosity’s lesson and that its tires will be able to withstand those interactions,” Chen emphasized. He also noted that the Mars 2020 rover will employ a much better aerodynamic decelerator, or parachute system, that will help avoid Curiosity’s “slight overshoot” of its landing zone.
Robert Lillis, member of the MAVEN Science Team at the University of California Berkeley, emphasized that MAVEN’s “gull-wing” design will allow it to cruise much more efficiently through the lowest reaches of Mars’ upper-atmosphere—about 120 kilometers above the surface—allowing for a complete examination of the entire upper atmosphere, which was not possible before.
Tom Hoffman, the project manager of the Insight mission, emphasized the role that past rover missions have had on the careful selection of Insight’s landing area, “optimizing our ability to take seismic and heat readings in the best ways possible.”
The threat and opportunity of Comet Siding Spring
For those spacecraft already at Mars, a comet’s close approach with Mars in October is unlikely to endanger them, but the encounter will nevertheless create “30 minutes of concern” for scientists and engineers, reported speakers during the separate “Robotic Mars Explorers Encounter Comet Siding Spring” panel at the AIAA SPACE 2014 forum in San Diego.
| “Multiple studies at JPL, the University of Maryland, and other sites have confirmed that the comet’s dust trail is unlikely to threaten the orbiting systems,” Chodas said. |
On October 19 at 6:32 pm GMT, Comet Siding Spring (2013A1) will approach within about 150,000 kilometers of Mars: about one-third the distance between Earth and the Moon. The comet’s dust will pass over the Martian North Pole, possibly endangering orbiting spacecraft in the region during a 30-minute window. Three spacecraft are currently in Martian orbit: NASA’s Mars Reconnaissance Orbiter and Mars Odyssey, and the European Space Agency’s Mars Express. They will be joined in September by NASA’s MAVEN and India’s Mars Orbiter Mission, which are en route to the planet.
However, concerns about the dust may turn out to be “much ado about nothing,” Paul Chodas, a senior scientist at NASA’s Jet Propulsion Laboratory, said during the panel discussion. “Multiple studies at JPL, the University of Maryland, and other sites have confirmed that the comet’s dust trail is unlikely to threaten the orbiting systems,” Chodas said, adding that “the comet did not begin to ejaculate dust at the critical distance of between 15 and 20 astronomical units from the sun, which would have had to have happened for the dust cloud to fully impact the orbiters’ operations.” He said “the comet’s bulk dust is being ejected at speeds below 1 meter per second,” well below the speeds where it would pose a threat to systems.
Based on the data, researchers have concluded that the cloud will pass up and over Mars, barely skirting a 1-kilometer edge of the orbiters’ operating zone for 30 minutes, prompting Joseph Guinn, manager of the mission design and navigation section JPL, to joke that the situation is not one of “seven minutes of terror, but more like 30 minutes of concern.” Chodas added, however, that if “the models are wrong, it will result in particles ranging in size between 1 millimeter and 1 centimeter, about the size range of a sunflower seed to a grain of rice,” impacting the orbiters like “cannonballs, causing extensive, most likely catastrophic, damage.”
Charles D. Edwards Jr., chief technologist of the Mars Exploration Program and telecommunications engineer at JPL, said that “despite the low risk of impact posed by the dust, NASA ESA and ISRO did develop plans to shield the orbiters during the 30-minute window,” with each agency having plans to adjust the attitudes of their assets, including “hiding” them behind Mars during the window to shield them from any impacts. The mitigation plans are especially critical for MAVEN and the Mars Orbiter Mission, which will arrive on station shortly before the comet’s flyby.
The minimized dust risk means researchers can focus on gleaning valuable scientific data from the fly-by, including Siding Spring’s spin speed, nucleus shape and corona composition, Edwards said. Richard Zurek, chief scientist of the Mars Exploration Program at JPL, said this is “a unique chance to get a first-ever resolution of the nucleus of a long-period comet, especially as the nucleus is thought to be a kilometer wide.”
Additional areas of study, according to Zurek, “will be the comet’s effect on the upper Martian atmosphere, at about 150 kilometers, especially allowing scientists to better understand how atoms potentially escape the Martian atmosphere, as well the potential for the comet’s ejaculate to form cirrus clouds above Mars.” Cameras on the Curiosity and Opportunity rovers will also provide excellent images of the comet.
Zurek concluded the session by warning that the data from the flyby can only come about if the dust models are right, warning that there are “no guarantees here, all the dice are being thrown, but it only takes one particle. The chance is very low, but it’s not zero that we get damage.”