From Economist.com
THE ULTIMATE ENVIRONMENTAL CATASTROPHE
July 23, 2007 ONE of the main weaknesses of the environmental movement has been its unfortunate predilection for using doom-laden language and catastrophic superlatives to describe problems that are serious but not immediately disastrous. But one calamity that truly deserves such a description is almost never talked about. There are tens of millions of asteroids in the solar system, and several thousand move in orbits that take them close to Earth. Sooner or later, one of them is going to hit it. Several have done so in the past. Earths active surface and enthusiastic weather conspire to scrub the tell-tale impact craters from the planets surface relatively quickly, but the pockmarked surface of the moonwhere such scars endure for much longertestifies to the amount of rubble floating in the solar system. Earths thick atmosphere makes it better protected than the moon: asteroids smaller than about 35 metres (115 feet) across will burn up before hitting its surface. Nevertheless, plenty of craters exist. The Earth Impact Database in Canada lists more than 170. Fortunately, such impacts are relatively rare, at least on human timescales. Statisticians calculate that the risk to lives and property posed by meteorite strikes are roughly comparable with those posed by earthquakes. Although the chance of an impact may be small in any given year, the consequences could be enormous. The effect of an impact depends on an objects size and speed. A meteorite a few metres wide could level a city. The largest (a kilometre or more in diameter) could wreak ecological havoc across the entire globe. David Morrison, a NASA scientist, argued at a recent conference that a large meteorite strike is the only known disaster (except perhaps global nuclear war) that could put civilisation at risk. Examples give a more visceral illustration than statistics. The Chicxulub crater, buried beneath modern Mexico, is 65m years old and 180km (112 miles) across. Some think that the ten-kilometre meteorite that created it threw so much dust into the atmosphere that it blotted out the sun and led to the extinction of the dinosaurs. In 1908 a comparatively tiny piece of space-borne rock, 30-50 metres across, exploded above Tunguska, a remote part of Siberia. The blasthundreds of times more powerful than the atom bomb dropped on Hiroshima 37 years laterfelled 80m trees over 2,150 square kilometres. Only blind luck ensured that it took place in a relatively unpopulated part of the world. Astronomers are currently trying to work out whether a 270-metre asteroid named 99942 Apophis will hit Earth in 2036 (probably not, but it would be nice to be sure). Happily for humanity, technology has advanced to the point where it is possible, in principle, to avoid such a collision. In 1998 NASA agreed to try to find and catalogue, by 2008, 90% of those asteroids bigger than 1km in diameter that might pose a threat to Earth. Any deemed dangerous would have to be pushed into a safer orbit. One obvious way to do this is with nuclear weapons, a method that has the pleasing symmetry of using one potential catastrophe to avert another. But scientists counsel caution. A nuclear blast could simply split one large asteroid into several smaller ones, some of which could still be on a collision course. Other plans have been suggested. One is to use a high-speed spaceship simply to ram the asteroid out of the way; another is to land a craft on the rocks surface and use its engines to manoeuvre the asteroid to safety. A subtler method is to park a spaceship nearby and use its tiny gravity to pull the asteroid gradually off course. For now, all such suggestions are theoretical, although the European Space Agency is planning a mission, named Don Quijote, to test the ramming tactic in 2011. These schemes offer consolation, but any effort to deflect an asteroid requires plenty of advance warning, and that may not always be available. NASA has so far catalogued only the very largest, civilisation-killing asteroids. Plenty of smaller ones remain undiscovered, and they could inflict considerable damage. In 2002 a mid-sized asteroid (50-120 metres across) missed Earth by 121,000kmone-third of the distance to the moon. Astronomers discovered it three days after the event. Comets, which originate from the outer reaches of the solar system, are faster moving and harder to track than asteroids, but carry just as much potential for catastrophe. But perhaps the biggest problem is humanitys indifference. Currently only America is spending any money on detection, and even there, politicians have other priorities. Much of the work is done by Cornell Universitys Arecibo radar in Puerto Rico, which is facing federal funding cuts. The telescope costs roughly $1m a year to operate. As an insurance policy for civilisation, the price looks cheap. ADDED NOTE: The Economist was one of the first mainstream journals to recognize the imapct hazard and endore the Spaceguard Survey, in a lead editorial published on September 11, 1993: (http://www.highbeam.com/doc/1G1-14379977.html) Duncan Steel notes that The Economist has a more extensive record of supporting notions of the impact hazard; see also these references/links further down the above web page: http://www.highbeam.com/doc/1G1-122826145.html, http://www.highbeam.com/doc/1G1-15962463.html.
ASTRONAUTS ON ASTEROIDS? NASA TOYS WITH IDEA By Leonard David, MSNBC
July 30, 2007 GOLDEN, Colo. - NASA's Constellation Program including the deployment of the Orion crew vehicle replacing the space shuttle will first be assigned to international space station flights, then propel humans and cargo to the Moon. Expeditionary missions to Mars and beyond will follow. But there's ongoing discussion of mounting a piloted mission to an asteroid a voyage by astronauts to a near-Earth object. These proponents feel certain of the scientific payoff from reaching, first-hand, an asteroid perhaps even becoming able to exploit these chunks of celestial flotsam to further humankind's plunge into the cosmos. Space technologists argue that a NEO trip could be a valuable shakeout of people, equipment, and procedures prior to hurling astronauts beyond the Moon to the distant dunes of Mars. For others, NEOs are viewed as downright dangerous, in terms of a head-on collision between Earth and a space rock. It's best to get to know these incoming beasts ahead of time. Internal looks by a small group of NASA "NEOphytes" have projected that a human trek to one of those mini-worlds may involve two or three astronauts on a 90 to 120-day spaceflight, including a week or two week stay at the appointed asteroid. Dispatching astronauts to a NEO is a sensible idea, said Harrison Schmitt, Apollo 17 astronaut, geologist and current chair of the NASA Advisory Council. In fact, the Exploration and Space Operations subcommittees of the NAC were briefed July 18 by NEO study team members from the NASA Johnson Space Center, although there has been no Council action on the topic. Schmitt told Space.com: "I think examination of a NEO mission and the development of the stand-by monitoring systems, plans, protocols and procedures for the diversion of a potentially Earth-impacting asteroid would be very prudent activity for the U.S. to undertake." Additionally, Schmitt said that a NEO mission would be a potentially important demonstration of the versatility and capability of the Constellation systems and a "gap-filler" before any Mars landing mission. "So far, the arguments for asteroid science and resources are interesting, but not well-developed or potentially as historically or politically persuasive as a demonstration of long-term Earth defense," Schmitt said. At this point in time, NASA has not issued any formal requirements to augment the Orion spacecraft to handle a piloted NEO mission, explained John Stevens, Director of Business Development for the human spaceflight line of work at Lockheed Martin Space Systems, near Denver, Colorado. However, the company builder of the crew-carrying Orion spacecraft - internally funded two years worth of studies to flesh out technologies to support a diversity of destinations, Stevens said. For sojourns to a near-Earth asteroid, he said, future block upgrades to Orion are necessary. "It's not that difficult from an architecture point of view to fly by an asteroid and then come back," Stevens said. But pulling off a rendezvous and docking with such an object, then rocketing back to Earth, requires more propulsion oomph, he noted, along with the need for larger living quarters for transiting crews, as well as recycling hardware to handle oxygen and water needs. Also, any roundtrip Earth-to-NEO-to Earth is an extended flight, way beyond that required for Moon travel. So that brings up crew psychological-sociological issues. "It's a concern...but we don't know how much of a concern," Stevens advised. Stevens said that the near-Earth object human mission can be viewed as an intermediate step between a Moon mission and a Mars mission. "In terms of complexity and the length of time that you have to stay out...it does represent a good stepping stone between the kinds of missions you do at the Moon and the kinds of missions that you next bite off...which is the Mars mission," he said. DigitalSpace, a privately held company based in Santa Cruz, California, has just released a design simulation of a notional crewed mission to an as-yet identified asteroid. "This visualization is DigitalSpace's design concept for the mission, produced as an independent effort for the benefit of an internal NASA feasibility study completed in 2007," said Bruce Damer, founder of the company that provides leading edge Internet content and tools for communication, collaboration, and visualization. The NASA study was performed to show that such a mission is possible with the new Constellation architecture, Damer said. DigitalSpace received input from numerous experts inside and outside NASA to produce the NEO mission visualization. "It is important to note that this is not a NASA concept, nor has NASA given it any kind of technical blessing...it is a design created by the DigitalSpace team to stimulate discussion in the space community," Damer emphasized. Indeed, many in the space community see any pilgrimage to an asteroid by either robots or astronauts as having multiple benefits. Learning about NEOs offers much in both scientific and practical terms. That's the perspective offered by Clark Chapman, a planetary scientist at the Southwest Research Institute's Department of Space Studies in neighboring Boulder, Colorado. The reasons are many, Chapman said: Because there are many of them, because they are made of materials both common and exotic compared with materials available near the Earth's surface, and because they have negligible gravity...they are an obvious source of raw materials for future human exploration of outer space. Tooling up for NEOs is already being tackled by specialists at Ball Aerospace & Technologies Corporation, also in Boulder. They have been looking into a small, low-cost landing probe design that could characterize both the surface and interior of small solar system objects, such as an asteroid. The device is about the size of a basketball and weighs just a few pounds, said Dennis Ebbets, Senior Business Development Manager for Ball Aerospace's Space Science division. He and staff consultant, Richard Reinert, along with Rich Dissly, Ball's Deputy Director for Solar System Advanced Systems, suggest that several of the probes could be hauled to a target object and deployed individually. Once released, these non-propulsive surface probes would freefall onto an asteroid's surface and begin transmitting results from their respective locales. The probes are outfitted with deployable panels to ensure self-righting to begin their errands. Each self-energized probe might employ tiny imagers, accelerometers, x-ray spectrometers, sample collection and analysis gear perhaps even utilize small explosive charges to create seismic waves that help gauge an asteroid's internal structure. While asteroid surface probes could be deployed from an automated spacecraft, they are also a "perfect candidate" to be toted onboard a human expedition to a near-Earth object, Ebbets told Space.com. Ebbets said asteroids deserve attention to help figure out what they are, where they come from, why they are different, and why there are families of these objects that are the same. Additionally, "there's a non-zero chance of being hit by one of these things," Ebbets noted. He said he was a big fan of dropping a transponder onto an asteroid that's been branded as a potential troublemaker. "Putting a transponder on it would be an excellent thing to do," Ebbets added. "You can get a very, very accurate orbit...predict years into the future whether it's on a collision course with us or not." Along with the need to come to grips with scalawag asteroids that could harm Earth, SwRI's Chapman senses other NEO exploration outcomes. "Though I am a space scientist strongly oriented toward the cost-effective robotic exploration of the solar system, I also grew up on science-fictional accounts of human expansion into the cosmos, and I endorse that more expensive but ultimately inevitable direction for human exploration," Chapman said. Chapman said that it makes sense to him that NEOs could be used as "way-stations" to Mars. "Human visits to NEOs can go part-way toward understanding the challenges of going to Mars, yet not invoke the most serious challenges," he said. Regarding concerns in some quarters that efforts to send humans to NEOs may be a distraction from the main, early focus of sending humans to the Moon, Chapman said: "In the current environment where the 'Vision' dominates NASA and the budget tends to restrict what we might do under the umbrella of the 'Vision' to the narrowest aspect of the 'Vision'...the focus must be on the Moon." But Chapman continued by noting that the dreams of people worldwide who want to expand their long-delayed expectations of going into interplanetary space, NASA assisted by the budgetary processes in the Congress must find a way to do more than just return to the Moon. "I happen to believe that scientific exploration of the Moon...could be extremely significant. And the Moon is much more easily explored and developed than Mars, which must remain a longer term challenge. But NEOs offer a special, practical, and inspiring challenge that we should keep on the table," Chapman explained to Space.com. In the context of the hazard of destructive impacts by NEOs on the Earth, Chapman said that "everything we can learn about the physical nature of NEOs can incrementally enhance our chances of dealing effectively with one, should one be discovered that seriously affects us." He explained that robotic exploration of such a NEO would be essentially as good as human exploration of that threatening object. "But the generic exploration of NEOs even if solely in the goal of getting to Mars can have side benefits not only for understanding the range of issues we might have in dealing with a threatening NEO, but also in learning how we might mine the resources of NEOs for future use in human exploration of the solar system," Chapman concluded. ADDED NOTE: The DigitalSpace website is http://www.digitalspace.com/projects/neo-mission/index.html. |
