by Peter W. Merlin, special to Aerotech News
Ever since the Apollo astronauts left their footprints on the lunar surface, humans have focused on Mars as the next exploration goal.
Why then would it make sense to send humans more than 99 percent of the way to such a distant off-Earth destination without putting “boots on the ground?” This is the question Dan Adamo, an astrodynamics consultant focused on space mission operations and architecture, seeks to answer. He has been trying to convince clients, primarily within NASA and in academia, that there is a more logical approach. Adamo believes that Mars and other destinations throughout the solar system may be explored sooner, more efficiently, at less expense, and with less risk through the use of low-latency telepresence. He is suggesting that humans operating in synergy with nearby robotic systems will represent a game-changing space exploration strategy.
Low latency is the key. Until now, the most difficult aspect of using remotely operated robotic probes has been the lag time between sending a command signal from Earth and waiting to learn the results after that command has been carried out. Depending on the relative positions of the two planets it generally takes between five and 20 minutes for a signal from Earth to reach Mars. Typically, science teams prepare a set of instructions using surface imagery from a rover as well as from orbiting reconnaissance satellites. Transmitted commands may have to pass through an orbital relay, and then the team must wait until local sunrise on Mars before the rover executes the command. The robotic rover may then semi-autonomously navigate up to 150 meters across the Martian landscape before halting to await further orders. Data are sent back though the relay to the science team, and the process starts again. Adamo suggests shortening the command chain by basing the operators in Martian orbit, where signal transmission times would be nearly instantaneous.
So, why not simply land humans on Mars and leave the robots out of it? “The thin Martian atmosphere provides no shielding against cosmic radiation,” Adamo explained. “Exposure inside above-surface habitats, space suits, and unpressurized rovers would provide inadequate radiation shielding to support long-duration duty tours.”
Additionally, the Martian soil is composed mainly of magnetic iron oxides that cling to any surface with a slight electrostatic charge, including solar panels and motors. This poses a hazard to machinery and electronics, as well as to human life. Suspended dust particles in the Martian atmosphere contain carcinogenic compounds such as hexavalent chromium and toxic perchlorates. Adamo said extraordinary measures would be required to exclude dust and soil from the interior surfaces and atmosphere of habitat modules. “Most exploration would have to be accomplished using remotely operated rovers anyway,” he explained, “something that could be done from orbit just as easily and more safely.”
The lack of a thick atmosphere also makes safe landings extremely challenging. New technologies will be required to develop a Mars lander capable of both surviving the plunge into the Martian atmosphere and making a successful soft landing. “The one-ton Curiosity rover represents the current state of the art for the mass that we can safely land on Mars,” said Adamo. A lander carrying a crew and supplies would be much heavier, somewhere in the vicinity of 20 metric tons, he added. For long-duration missions the explorers would need to have consumables — oxygen, food, water, etc. — delivered by re-supply landers.
Reduced gravity entails another set of challenges. Millions of years of evolution have optimized humans to live under Earth’s gravitational conditions, and astronauts living in microgravity during long-term space flights have returned with noticeable loss of bone and muscle mass. During transit to Mars this could be offset through the use of rotating habitat modules to simulate Earth-normal gravity. There is no practical way to do this on the Martian surface, however, where gravity is only 38 percent that of Earth.
Another consideration for sending humans to the Martian surface is the possibility, however slim, that explorers could be exposed to native life. With even a slight chance of exposure to extraterrestrial microbes, extreme measures would be required to isolate the crew from contamination. “It’s an ethical barrier,” said Adamo. “We don’t know if there is extant life on Mars, but I don’t think we have any business in the Martian biosphere until we know that.”
It may take decades to conclusively prove or disprove the existence of Martian life. Until then Adamo suggests the best option would be an orbital base beneath the surface of Deimos, the smaller and more distant of two moons orbiting Mars. Like Earth’s moon, Deimos is tidally locked with its parent planet, always presenting the same face toward the Martian surface. The gravitational pull of Deimos is slight, making landing easier than on Mars, and the moon is large enough for construction of a subsurface rotating habitat to provide artificial gravity for inhabitants. Power-generating solar panels positioned at the poles would receive almost perpetual sunlight.
At an orbital distance of slightly under 15,000 miles Deimos is close enough to facilitate near-instantaneous remote operation of robotic rovers, yet far enough away to allow observation of 98 percent of the planet’s surface and allow line-of-sight communications for 60 continuous hours at a time. Using low-latency telepresence would obviate the need for hazardous extravehicular activities requiring space suits and complicate decontamination procedures. Instead, Adamo said, “Human explorers would remain within their shielded habitat, in a shirtsleeve environment.” They would have greater mobility and dexterity for performing tasks and, by using robotic proxies, be exposed to fewer risks.
According to Adamo, this strategy could be used throughout the solar system for exploration of such regions as the asteroid belt and Jupiter’s moons. With low-latency telepresence, he said, “impressive exploration productivity gains are realizable, together with reduced programmatic cost and risk, when compared to more conventional in-person exploration strategies,” which are based on the Apollo program of the 1970s. “These benefits accrue regardless of whether humans orbit above or loiter on or beneath a nearby exploration region.”