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[Air & Space Magazine] Defenders of the Planet
« dnia: Styczeń 23, 2018, 20:23 »
Defenders of the Planet
By Elizabeth Howell December 2017 Air & Space Magazine

A new NASA office pledges to save humans from the fate of the dinosaurs.


The Chelyabinsk meteor went undetected until it exploded over Russia in 2013. The 60-foot-wide rock burst with a shock wave that injured 1,500 people and damaged 7,000 buildings across six cities. (M. Ahmetvaleev/ESA)

The first hint of an oncoming collision between a comet and a planet showed up in images from Palomar Observatory in California on March 24, 1993. The International Astronomical Union issued an alert two days later announcing the discovery of the comet, soon to be known as Shoemaker-Levy 9, and describing its odd appearance—it had a long, flattened, dense tail. The alert concluded with an offhand remark on its unusual proximity to Jupiter, causing astronomers to hastily begin mapping the comet’s path.

At the time, Lindley Johnson, a U.S. Air Force major, had just accepted a prestigious assignment to study advanced space operations at the Air Command and Staff College in Montgomery, Alabama. Having already served at the North American Aerospace Defense Command (NORAD) and the Los Angeles-based Space and Missile Systems Center, Johnson was an expert in another type of space collision: He had provided collision-avoidance support for the space shuttle program. The year before he attended the staff college, he had been having conversations with Tom Gehrels, co-founder of the Spacewatch program at the University of Arizona, which used telescopes at Arizona’s Kitt Peak National Observatory to track small objects in the solar system. Talking with Gehrels increased Johnson’s interest in a topic that Shoemaker-Levy was about to elevate to the national conversation and the disaster-movie genre: the hazards that potentially millions of small asteroids and comets moving unseen around the solar system pose to planet Earth.


Arizona still bears the 3,900-foot-wide scar from a 160-foot asteroid. (ESA/NASA)

Today Johnson is NASA’s first Planetary Defense Officer, charged with keeping Earth safe from rocks in the solar system on a path to collide with us. His work at the staff college when Shoemaker-Levy was discovered helped convince Air Force leadership that a potential strike from one of the objects in the solar system was a threat that needed their attention. “Impacts by even a modest-size asteroid, something a couple of hundred meters in size—it would be a catastrophic event unlike anything we ever had to deal with, particularly if it’s near a metropolitan area,” Johnson says. “But the impact of a 400- or 500-meter asteroid anywhere on Earth could be climate change in an afternoon. The amount of debris that would be thrown up into the atmosphere…would cool the weather for many, many months. If it was into an ocean, the amount of superheated water that would be put into the atmosphere would have significant effects on the planet.” As Johnson learned about the dangers, he thought, “If I was in a situation where I could advocate that we do more in this area, that’s what I wanted to do.”

Johnson believed then that the technology existed to prevent an asteroid or comet from striking Earth. In early 1994—on the heels of astronomers’ announcement that Shoemaker-Levy was going to slam into Jupiter the following July—he published a paper describing the means to manipulate the trajectory of an object long before it could collide with the planet. His alarm was met with skepticism. The idea that an asteroid would slam into our planet still “had a bit of a giggle factor,” Johnson says.

Then the world watched in real time as the comet collided with the biggest planet in the solar system. Over eight days, Shoemaker-Levy’s pieces plunged into Jupiter’s atmosphere in spectacular fashion, leaving marks there that lingered for months. At the time, astronomers thought this kind of event would happen once in a lifetime; since then, observations have revealed that impacts on Jupiter big enough to be visible from Earth, like those left by Shoemaker-Levy, have occurred at least five times since 1994, the latest in 2016. Smaller asteroids are estimated to hit the planet dozens of times a year. The Shoemaker-Levy event, Johnson says, “made [believers] out of a lot of folks” who had been scoffing at the danger.

After graduating, Johnson was assigned to Air Force Space Command, where he began advocating for more collaboration with NASA, including a mission that used space surveillance telescopes to search for comets and asteroids called near-Earth objects, or NEOs. In 2003, after 23 years of service, Johnson retired from the Air Force to work at NASA full time. His first job was program manager for the agency’s Deep Impact mission, which sent a spacecraft to study the comet Tempel 1.

Jim Green says that when he became the head of NASA’s planetary science division in 2006, Johnson was the agency’s only senior manager working on NEOs. “He was my teacher,” Green says. “I thought, ‘Wow, we can’t do lip service here—we’ve got to step it up.’ ” Several years after the Shoemaker-Levy event, Congress directed the space agency to track down 90 percent of all asteroids one kilometer (two-thirds of a mile) or larger in diameter because, according to scientists, objects that size could cause a planet-wide catastrophe. NASA was falling behind. Thanks primarily to Johnson’s advocacy, says Green, funding for programs to detect and characterize the orbits of NEOs has increased in the last decade more than tenfold, to nearly $50 million. In 2011, through its network of partner telescopes—small observatories spread around Arizona, New Mexico, California, and Hawaii—NASA met its goal for finding most large asteroids.

In 2005, Congress added a second task: to search for asteroids at least 140 meters (460 feet) in diameter. But the assignment was never adequately funded, and Green says the agency won’t meet the 2020 deadline.

Searching a vast, black sky for tiny, dark objects is a particularly difficult challenge. To find the smaller asteroids, Green began looking for a more powerful telescope. In 2009, NASA launched the Wide-field Infrared Survey Explorer, or WISE, a space telescope designed to create an infrared map of the entire sky. Infrared telescopes are particularly good for observing asteroids, which reflect little visible light, but since the atmosphere blocks infrared wavelengths, ground-based telescopes can’t see them. WISE could.

At Johnson’s urging, Green secured funding in 2010 to use the WISE telescope in an asteroid hunt. The WISE investigators had been focused only on stars and other objects outside the solar system; they had been discarding data that showed asteroids, so those wouldn’t be mistaken for stars. The first thing the NEO-hunting team did was scrutinize that discarded data to find images of asteroids. In 2011, WISE completed its primary mission, and its observing team put the telescope into hibernation. Green then was able to allocate money to revive it. In September 2013, NASA began NEOWISE, a four-year mission to use WISE to search for NEOs. Astronomers at NASA’s Jet Propulsion Laboratory proposed a follow-up mission that would launch a new space telescope called NEOCam. It hasn’t officially been selected for launch, but its development continues to receive funding.

After starting NEOWISE, Green says he tried to find whatever money he could to increase asteroid detection and defense. “The Obama administration was very keen on doing this, which we were just delighted with,” but Green also says there was a tension because the administration kept recommending decreases in funding for planetary science while asking that more money be put into the department’s NEO activities subfield.

If the NEO programs were going to justify the increased funds, they needed to be more comprehensive—and more practical. “We needed to move towards a regular structure that went after several aspects—not just detection but mitigation,” says Green. So NASA formed a task group to make recommendations about how to enhance NEO programs: “not just finding things, but culling out potentially hazardous ones and creating notification processes.”


NASA’s first Planetary Defense officer, Lindley Johnson, wants to make sure Earth is prepared for whatever is incoming. Though we can’t move out of the way of a projectile, we can try to move it. (The Aerospace Corporation)

David Schurr came to NASA as Green’s deputy in 2013, and at the time, Johnson was still managing the Discovery program while also juggling NEO activities. Schurr’s first move was to help Johnson re-prioritize—starting with handing Discovery over to someone else so that Johnson could focus on NEOs full time. The planetary science division then proposed an office of support staff for him. “I can’t have this vested all in one person,” Schurr says. “As we ramped the project up into $20 million a year and growing, we also decided it needed to be a formalized, structured program. It needs to have a larger staff.”

These efforts coalesced in 2015 as the Planetary Defense Coordination Office, with Johnson at its head. (This is a different office, by the way, than NASA’s Planetary Protection Office, whose duty is to protect other planets from being contaminated with Earth microbes that might hitch a ride on our spacecraft.) With six program officers, most of whom spend only part of their time working for the office, it manages all of NASA’s programs that detect, track, and characterize NEOs. It also helps develop missions to move asteroids out of Earth’s path and to create strategies for dealing with an impact if one can’t be avoided. The office is the hub for related U.S. agency programs and international efforts. If a threatening asteroid is discovered, it’s Johnson’s responsibility to get that information from telescope staff up through the NASA chain of command and then to the White House and other agencies. The Planetary Defense Coordination Office connects the efforts of hundreds of people spread across the globe concerned with preventing another extinction event, like the one that wiped out the dinosaurs.

If an asteroid is discovered to be on a collision course with this planet, how would Johnson’s team jump into action? Ideally, the members would implement a plan to divert the rock before it reaches Earth. The best potential demonstration of an asteroid-steering mission is the Asteroid Impact and Deflection Assessment mission, or AIDA, an international collaboration to send spacecraft to an asteroid and test the kinetic impact technique—that is, slamming something into a rock to divert its trajectory enough that it bypasses Earth.


A mission like AIDA could test the kinetic impact theory by slamming into a moonlet around the asteroid Didymos. (ESA/Science Office)

The spacecraft is called DART, or the Double Asteroid Redirection Test, which, if approved, would launch in 2020 to reach Didymos, an asteroid that even on its closest approach to Earth, in 2022, will be seven million miles away. Didymos is about 2,400 feet in diameter, and is orbited by a moonlet, 500 feet across. (Discovered in 1996 as part of Tom Gehrels’ Spacewatch program, Didymos is larger than asteroids targeted by the still-unfinished 2005 Congressionally directed search.) DART will approach the pair and slam into the smaller rock. If it works, it will change the moonlet’s orbital period around the larger rock a fraction of one percent, just enough for the change to be detected by ground telescopes. A change that small, mission planners say, may be enough to knock an asteroid off its collision course with Earth. “It’s a dry run for a real-world test,” said Rob Landis, who was the planetary defense coordinator for DART during its early development stage. “It will tell us something about how effective kinetic impactors can be or might be.” (The European Space Agency was originally an AIDA partner, contributing a spacecraft called the Asteroid Impact Mission, or AIM, to accompany DART to Didymos and observe the effect of the impact, but budget constraints forced the agency to withdraw its participation in 2017.)


Arizona still bears the 3,900-foot-wide scar from a 160-foot asteroid. (NASA)

AIDA is based on the best-case scenario: We find an asteroid headed our way, slam a spacecraft into it, and nudge it off course. But what if we discover the asteroid too late to intercept it? Or what if we intercept it, but the nudge doesn’t work? NASA would need a plan to save as many people as possible.

Mitigating the effect of an asteroid impact requires an almost incomprehensibly large action plan, one that begins when there’s just a one percent chance of an asteroid impact. Although that seems low, says Johnson, “if we were to wait until it was certain, it would most likely be too late to adequately prepare.” NASA would inform the White House of any one percenter, updating that information as the asteroid’s orbit is better understood. Once the probability of a hit rises over one percent, NASA, on the president’s order, would inform Congress and appropriate the federal agencies, starting with Federal Emergency Management Agency, if the asteroid had any likelihood of hitting U.S. territory. FEMA’s disaster teams have conducted three exercises with the planetary defense office, using varying times to impact, to practice responses to “the types of hazards and situations that may occur in this unique, low-probability—but high-consequence—disaster,” says Stephanie Moffett, a public affairs officer for the agency. If the impact was likely to be elsewhere, NASA would work with the Department of State, which uses protocol created by the International Asteroid Warning Network, an organization that operates under United Nations approval.

Luckily for us, no searches have turned up asteroids that have even a one percent probability of hitting Earth, but that could change on any day. June 19, 2004, was almost that day, when astronomers at Kitt Peak National Observatory discovered asteroid 99942 Apophis, and calculations of its orbit determined there was a small chance of it slamming into Earth in 2029. Subsequent observations to fine-tune its path eliminated that probability, though it will still pass by at just 19,400 miles away, closer to Earth than the orbit of our geosynchronous satellites. Also worrisome is that its close brush by Earth will slightly alter its course. Astronomers are fairly certain we’re still in the clear, but they’ll be keeping a close eye on it as it approaches for its next pass in 2036, and its return in 2068. If the 1,200-foot rock hit the planet, it would cause an impact about 160 times more powerful than the 1908 Tunguska event, which flattened almost 800 square miles in eastern Siberia.

The planetary defense office already conducted one live trial of its observation systems, when on October 12, 2017, a rock a few dozen feet in diameter called 2012 TC4 came within 27,200 miles of Earth, 10 times closer than the moon. Not long after it was discovered in 2012—but luckily after astronomers confirmed it was not on a collision course—the asteroid, traveling away from us, became too dim to observe. Johnson’s team led the effort to re-establish observations upon its predicted return last summer, and in late July, astronomers at the Very Large Observatory in Chile found it on approach, 38 million miles away. Telescopes around the world coordinated to make careful observations that would tell astronomers more about its exact size and shape, confirm its orbit, and track it as it neared—and passed by—Earth.

Johnson is relieved that so many people are starting to take seriously the threat he’s been warning about for decades. Now that he has a small division at NASA behind him, he hopes a full-scale plan to foil an asteroid on a collision course with Earth—including a spacecraft ready to launch on demand—will be ready in time. “It’s something that, with today’s technology, doesn’t have to be an act of God anymore,” he says. “It’s something we can prevent.” If the sky does fall one day, we’ll be glad we listened.

Source: Defenders of the Planet

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« Odpowiedź #1 dnia: Grudzień 14, 2019, 22:28 »
The Menace of the Asteroids. Part 1: The Risks
By David Darling, on December 10th, 2012 [AS]


Artist’s impression of an asteroid approaching the Earth. Image Credit: Jeff Darling

Of the several hundred thousand asteroids known, about 9,000 are of the near-Earth variety, and of these more than 1,300 fall into the category known as potentially hazardous asteroids (PHAs). To qualify as a PHA, an asteroid must be able to come closer to the Earth than 7.5 million kilometers in its orbit and be larger than 100 to 150 meters in diameter. An asteroid of this size, if it impacted in a sensitive area, could cause significant regional devastation, laying waste to a major city or even an entire state.


The NEO Gaspra is seen in this NASA image. Many NEOs are asteroids such as this one and many are monitored to see how close they come to Earth. Image Credit: NASA

Unless steps are taken to do something about it, the Earth will be hit hard again in the future. Collisions such as the one that happened 65 million years ago, involving an asteroid roughly 10 kilometers across which slammed into what is now Mexico’s Yucatan Peninsula and contributed to a mass extinction, are extremely rare. However, smaller but still potentially devastating impacts happen much more often. As recently as 1908 an object roughly 50 meters across—either an asteroid or part of a comet nucleus—exploded high above the Tunguska region of Siberia, flattening 80 million trees radially outward from the epicenter of the blast. A similar encounter over a highly populated area would cause massive disruption and loss of life.

Our knowledge of the numbers, sizes, and orbits of PHAs has increased dramatically over the past decade or so thanks to a number of dedicated observing programs, such as the Lincoln Near-Earth Asteroid Research (LINEAR) project and Catalina Sky Survey. The results of the most recent survey of near-Earth objects (NEOs), which includes both comets and asteroids, carried out using NASA’s Wide-Field Infrared Explorer (WISE), suggests that 20 to 30 percent of all PHAs have now been found.

No known asteroids pose an immediate threat to our well-being. Astronomers have devised two different scales to categorize the impact hazard posed by PHAs; the simpler of these, called the Torino Scale, assigns a number from 0 (no threat at all) to 10 (certain impact large enough to threaten the future of civilization) to each body. At present, only two PHAs have a non-zero rating, and both these have a rank of only 1. The highest Torino ranking an asteroid has ever earned was 4 in the case of Apophis, but this was later revised to 0 in the light or more accurate orbit calculations.

Still, there are reasons to be concerned. If a sizeable space rock—say half a kilometer across—were found to be on a direct heading for Earth, with only a couple of decades before impact, what could be done about it? There are two main possibilities: destroy or divert. Blowing up an asteroid, say with nuclear weapons, isn’t necessarily a smart idea. It could result in an armada of smaller chunks, still on a collision course, that could cause just as much damage collectively as a single large strike. That’s why most proposed approaches to the problem focus on altering the trajectory of the intruder sufficiently, over time, so that the danger is averted.



NASA’s Wide-Field Infrared Explorer (WISE) spacecraft was used to conduct a survey of Near-Earth-Objects, some of which could pose a threat to the Earth. Image Credit: NASA

Source: https://www.americaspace.com/2012/12/10/the-menace-of-the-asteroids-part-1-the-risks/

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« Odpowiedź #2 dnia: Grudzień 14, 2019, 22:28 »
The Menace of the Asteroids. Part 2: Defending Earth
By David Darling, on December 11th, 2012 [AS]


Artwork showing a large asteroid impact with the Earth. Image Credit: Don Davis / NASA

A 500-meter-wide asteroid has just been discovered that will almost certainly collide with the Earth in 2030. No one knows yet where it will strike—on land or at sea—but its potential for regional devastation is high. The question is: what, if anything, can be done to stop it?

Fortunately, this shock announcement isn’t true: nothing is heading our way as far as we’re aware. But it’s very possible, given that only about a quarter of all the potentially hazardous asteroids out there have yet been detected, that some big dumb object has our name on it. So, having some form of planetary defense system in place makes a lot of sense.

Approaches to dealing with the threat of asteroid (or comet) impacts fall broadly into three categories that we can call the three D’s: duck, destroy, or deflect. “Duck” means we’d do our best to get out of the way of the impact zone by evacuating the area or, in the most extreme case of a planet-wide disaster, retreating to purpose-built underground shelters. Needless to say, this would be a last-ditch measure if other strategies had failed or not even been attempted.



A gravity tractor being used to alter the trajectory of an asteroid. Image Credit: Dan Durda

Another option would be to try to blow up a threatening asteroid into smaller pieces using, for example, powerful nuclear weapons. The problem with this is that many of the fragments might continue on the same course and strike the Earth anyway, subjecting us to the equivalent of a blast of lead shot no less damaging than a single bullet.

By far the best solution would be to gradually alter the motion of the problem asteroid so that it missed. This could involve deflecting the object sideways so that it no longer intersected the Earth’s orbit, or speeding up or slowing down the intruder so that it arrived at the wrong time to collide. Direct methods, involving short, sharp shoves from explosions or kinetic impactors, might be necessary in the case of a short-notice threat, but would probably not work well against many near-Earth asteroids which are of the “rubble-pile” variety, made of loose aggregations of boulders.

The preferred strategy of most experts is to use an indirect, slow-acting method. For example, the asteroid could be given its own propulsion system in the form of chemical rockets, ion engines, or a mass driver attached to its surface. These would fire over an extended period of time and allow fine control over the asteroid’s trajectory.

A more subtle method would be to park a large, massive spacecraft over the asteroid to serve as a gravity tractor or space tug. Because the spacecraft and asteroid would mutually attract one another, the spacecraft would only need to counter the force toward its much more massive companion, using some kind of long-duration thruster, such as an ion engine, to cause a net movement of the asteroid toward the spacecraft and thus slightly alter its heading. Other approaches have also been suggested, including wrapping an asteroid in a sheet or reflective material to use the pressure of solar radiation to nudge the asteroid out of harm’s way.


Source: https://www.americaspace.com/2012/12/11/the-menace-of-the-asteroids-part-2-defending-earth/

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« Odpowiedź #3 dnia: Grudzień 28, 2019, 01:45 »
NASA mission to track near Earth objects takes shape
by Jeff Foust — December 26, 2019 [SN]


The fiscal year 2020 funding bill provided $35.6 million to start work on the NEO Surveillance Mission, a successor to the proposed NEOCam space-based infrared telescope to search for near Earth objects. Credit: NASA/JPL

SANTA FE, N.M. — A revamped NASA mission to search for near Earth objects from space has secured funding to start development as the agency works out details about how it will be managed.

The fiscal year 2020 “minibus” spending bill signed into law by President Trump Dec. 20 that provides $22.63 billion for NASA includes $35.6 million to start development of the Near Earth Object (NEO) Surveillance Mission. That mission would fly a small space telescope with an infrared camera to discover and track NEOs, helping identify any that pose an impact risk to the Earth.

That funding will come from the agency’s planetary science funding line, which received more than $2.7 billion in the bill. Neither the bill nor the accompanying report specified funding for NASA’s overall planetary defense programs, which include ground-based telescopic searches for NEOs as well as the Double Asteroid Redirection Test (DART) mission under development to the asteroid Didymos. NASA sought $150 million for planetary defense in its original budget proposal, but did not identify any specific funding for the NEO Surveillance Mission.

That was in part because NASA decided only in September to pursue the NEO Surveillance Mission. Thomas Zurbuchen, NASA associate administrator for science, said at a Sept. 23 meeting of the agency’s Planetary Science Advisory Committee that NASA would fund development of the mission as a “directed” one, led by the Jet Propulsion Laboratory, rather than competed through the Discovery program of planetary science missions.

NEO Surveillance Mission is the successor to NEOCam, a similar mission concept that was one of the finalists in the most recent round of the Discovery program. While NASA did not select NEOCam in early 2017 for development, it did provide funding to allow work to continue on its infrared detectors.

Zurbuchen said at the meeting that the reason for going from NEOCam to NEO Surveillance Mission was because the goals of the mission were not strictly scientific. The mission is designed to meet a congressionally mandated goal to identify all NEOs at least 140 meters in diameter, which represent those large enough to do damage on a regional or global scale in the event of an impact.

“The only reason we want every 140-meter object is not because we need it to do all the science,” he said. “It’s because we want to understand whether one of them is on a collision course over time to Earth.”

The mission, which has an estimated cost of $500–600 million and launch date of 2025, has congressional support beyond the funding provided in the appropriations bill. A NASA authorization bill introduced in the Senate in November directs NASA to build and launch by the end of fiscal year 2025 “a space-based infrared survey telescope that is capable of detecting near-Earth objects equal to or greater than 140 meters in diameter.”


The decision to pursue the NEO Surveilliance Mission as a directed mission raised questions in September about the role the NEOCam team would play on it, including its principal investigator (PI), Amy Mainzer, who earlier this year moved from JPL to the University of Arizona. “I expect the former PI of NEOCam to have a really crucial role,” Zurbuchen said in September.

In a Dec. 10 statement, the University of Arizona said that Mainzer would serve as the survey director for the mission. The university would have overall scientific leadership for the mission, including responsibility for building the infrared camera and supporting operations after the spacecraft’s launch. JPL will manage the project, with several companies and universities also partnering on the mission.

“This mission would answer a fundamental question: Are there asteroids or comets out there that can cause harm to the Earth over the next century?” Mainzer said in the university statement.


Source: https://spacenews.com/nasa-mission-to-track-near-earth-objects-takes-shape/

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« Odpowiedź #4 dnia: Czerwiec 11, 2020, 22:28 »
Scientists propose new solution against asteroid threat
Source: Xinhua| 2020-06-01 17:07:36|Editor: huaxia

BEIJING, June 1 (Xinhua) -- Chinese scientists have proposed a new solution to defend Earth from asteroid strikes, according to a study recently published in the journal Scientific Reports.

There are more than 18,000 near-Earth asteroids, of which about 800 are more than one kilometer across. If one of these large objects were to hit Earth, a global catastrophe would result.

Planetary defense technologies including nuclear explosion, kinetic impact, laser ablation, ion beam traction and gravitational drag have been developed to reduce the risk of potentially hazardous asteroids.

Experts from the National Space Science Center (NSSC) under the Chinese Academy of Sciences proposed a concept of enhanced kinetic impact to push a hazardous asteroid away from the orbit that crosses Earth's path by hitting it with space rocks.

In this technique, an unmanned spacecraft will be launched to collect more than one hundred tonnes of rocks from a near-Earth asteroid with which to strike an asteroid that poses a threat to the planet.

In simulations designed by researchers, the new method was more effective at deflecting an asteroid than a classic kinetic impact.

The new technique is not constrained by the limitation of ground-based launch for artificial impactor, promising to significantly increase the effect of planetary defense against large asteroids, said Li Mingtao of the NSSC, one of the authors of the study.
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Source: http://www.xinhuanet.com/english/2020-06/01/c_139105354.htm

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