This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

24 December 2010

Videos from Mars

From OnOrbit...

A new Mars movie clip gives us a rover's-eye view of a bluish Martian sunset, while another clip shows the silhouette of the moon Phobos passing in front of the sun. America's Mars Exploration Rover Opportunity, carefully guided by researchers with an artistic sense, has recorded images used in the simulated movies.

Link: OnOrbit Article

Link: YouTube Video ("Mars Moon Phobos Eclipse")

Link: YouTube Video ("I'm Dreaming of a Blue Sunset--on Mars")

Article: "Solar Sail Flotilla Could Divert Possibly Dangerous Asteroid"

An illustration of how solar sails might help deflect the asteroid Apophis. Credit: Olivier Boisard

Selections from the article...

A flotilla of solar sail spacecraft could change the course of the asteroid Apophis — which is headed a little too close to Earth for comfort — by shading the space rock from solar radiation, according to a French researcher.

Such a plan could help shift Apophis into a slightly safer orbit by the time it is expected to swing by Earth on April 13, 2036. But experts have warned previously that any efforts to divert the space rock could actually make matters worse.

The preliminary concept idea was proposed at a symposium on solar sails – which are spacecraft powered by sunlight pushing against a sail – a few months ago at the New York City College of Technology in Brooklyn.

"Apophis is a nice target for launching this kind of mission for 20 years from now; not too far, not too close," said Jean-Yves Prado, an engineer at the National Center for Space Study (CNES) in France.

A group of formation-flying solar sails could alter the asteroid's course by eliminating the so-called Yarkovsky effect, a phenomenon described by Russian engineer I.O. Yarkovsky a century ago.

That effect occurs when the sun warms an asteroid more on the sun-facing side than the far side. The rock then emits more thermal radiation on its near side, which creates a bit of thrust and changes its momentum slightly.

"It's really a very small effect and doesn't apply to very small asteroids because the temperature would be quite negligible, so thrust is negligible," Prado explained. "It also does not apply to very large asteroids because they are too heavy."

But for Apophis, which falls just in the middle of that mass range, the effect could make a difference.

The proposed mission would deploy four 441-pound (200 kg) solar sails from a transfer module that used solar electric propulsion to reach Apophis. Previous spacecraft that have used solar electric propulsion include NASA's Deep Space 1 and Dawn probes.

Once deployed, the solar sails would hover a few kilometers above the space rock and fly in formation according to master control by the transfer module, without a direct link between Earth and the individual sails.

The module could also position itself as a small gravity tractor to provide a small gravitational push on Apophis, Prado suggested.

A previous NASA assessment of possible asteroid deflection methods had placed solar sails relatively high in terms of readily available and not-too-complex technology.

Launch windows would become available for such a mission to launch aboard a Russian Soyuz-Fregat rocket in 2016 and 2019, Prado said. He added that a second redundant mission could also launch to ensure success.

Several other solar sail researchers at the symposium raised questions about the mission design. One questioned the need for a chemical propulsion system on each solar sail that would balance out the solar pressure and keep the sails flying in their proper place.

Prado replied that his group had examined the possibility of using solar electric propulsion to also maintain low thrust and keep the solar sails in place, but had ruled it out based on cost.

Another researcher suggested that simply crashing four spacecraft with the mass of the solar sails into Apophis might be simpler.

An earlier, unrelated Russian proposal to nudge the space rock aside has been met with skepticism, in part because any solution might worsen Earth's chances, given the uncertainty regarding Apophis' exact trajectory.

NASA scientists previously pegged the possibility of an Apophis collision with Earth at a low 1-in-250,000 chance in 2036, when Apophis is expected to approach within 18,300 miles (29,450 km) of the planet in 2036.

The asteroid's second near pass by Earth comes in 2068, when it has a three-in-a-million chance (or about 1-in-333,000) of impacting on the planet.

Link: Article

Article: "Experts Push for a NASA Asteroid-Hunting Spacecraft"

A Near-Earth Object Survey spacecraft planned by Ball Aerospace & Technologies Corporation. Placed in a Venus-like orbit, its mission would be to on the prowl for space rocks near Earth. Credit: Ball Aerospace

Selections from the article...

One concept that has already been fleshed out is dubbed the NEO Survey mission, a detailed appraisal done by Ball Aerospace & Technologies Corporation in Boulder, Colo.

Results of a study by Ball Aerospace highlighted how best to meet the George E. Brown objectives for detecting NEOs.

As explained in a Ball Aerospace white paper review provided to, in only 1.6 years, a spacecraft could locate all of the roughly 165 feet (50 meter) diameter, and larger, nearby space rocks that are potentially accessible for human spaceflight, and within 7.5 years could catalogue 90 percent of all NEOs greater than 459 feet (140 meters) in diameter.

"We have more work to do, but what we've created is a very high-quality existence proof. We have a point design based on real engineering with real parts," said Robert Arentz, a Ball Aerospace Advanced Systems Manager.

Arentz told that the NEO survey spacecraft draws upon the firm's heritage of working on NASA's space-based observatories – from the Hubble Space Telescope and the Kepler exo-planet hunter to the Spitzer infrared telescope and the Wide-field Infrared Survey Explorer, along with the company's comet-smacking Deep Impact spacecraft.

The internally funded Ball Aerospace concept has not yet been given a green light by NASA, noted Kevin Miller, a Ball Advanced Systems Manager, but the point design does showcase proven capabilities and an affordable approach, he said. The work uses a recipe "to establish confidence that, yes, this really is a very tractable problem," Miller said.

In order to meet the George E. Brown requirements to find 90 percent of all NEOs larger than some 460 feet (140 meters) within 7 years, the NEO Survey mission would cost roughly $638 million. The catalog it would yield is a superset of the targets that NASA human spaceflight planners would find of interest for piloted excursions to selected space rocks.

Given a go, the NEO hunter from start to launch should take around 42 months to develop, Arentz added.

But there are technological challenges in building the NEO survey spacecraft.

Dealing with solar radiation is one. The heat load from a location so near the sun means the spacecraft would need a large thermal shield and cryocooler hardware. Also, the telescope's photon-gathering array requires highly advanced engineering.

The key is to prevent the intense solar radiation at Venus from reaching the telescope. This is done by careful design of the spacecraft's solar array and use of two thermal shields between the main array and the telescope.

The spacecraft design, Arentz said, is based largely on the Kepler planet-hunting spacecraft design to reduce cost and risk.

And, if two NEO-hunting spacecraft were placed in roughly opposite locales in a Venus-like orbit, this would allow a binocular view of space rocks, and scientists could chart them with an even greater degree of tracking accuracy.

Link: Article ("Experts Push for a NASA Asteroid-Hunting Spacecraft")

09 December 2010

Paper: "Moving an asteroid with electric solar wind sail"

Sini Sanvia Merikallio has an updated paper based upon her winning entry for the SGAC 2009 Move An Asteroid technical paper competition. Related to the technology discussed in the paper, there is a European Union (EU) project working on the electric solar wind concept that will have a kickoff meeting this week. Paper highlights follow...

Moving an asteroid with electric solar wind sail

S. Merikallio and P. Janhunen
Finnish Meteorological Institute, Po. Box. 503, FIN-00101, Helsinki, Finland

Astrophys. Space Sci. Trans., 6, 41-48, 2010
© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.

Abstract. The electric solar wind sail (E-Sail) is a new propulsion method for interplanetary travel which was invented in 2006 and is currently under development. The E-Sail uses charged tethers to extract momentum from the solar wind particles to obtain propulsive thrust. According to current estimates, the E-Sail is 2-3 orders of magnitude better than traditional propulsion methods (chemical rockets and ion engines) in terms of produced lifetime-integrated impulse per propulsion system mass. Here we analyze the problem of using the E-Sail for directly deflecting an Earth-threatening asteroid. The problem then culminates into how to attach the E-Sail device to the asteroid. We assess alternative attachment strategies, namely straightforward direct towing with a cable and the gravity tractor method which works for a wider variety of situations. We also consider possible techniques to scale up the E-Sail force beyond the baseline one Newton level to deal with more imminent or larger asteroid or cometary threats. As a baseline case we consider an asteroid of effective diameter of 140 m and mass of 3 million tons, which can be deflected with a baseline 1 N E-Sail within 10 years. With a 5 N E-Sail the deflection could be achieved in 5 years. Once developed, the E-Sail would appear to provide a safe and reasonably low-cost way of deflecting dangerous asteroids and other heavenly bodies in cases where the collision threat becomes known several years in advance.

Link: Full Article (PDF, 7229 KB)

Link: Supplement (3828 KB)

Link: Paper Reference

06 December 2010

Article on ATLAS (for the Asteroid Terrestrial-impact Last Alert System)

Selections from the article on ATLAS (for the Asteroid Terrestrial-impact Last Alert System)...

An early warning system that could give Earth a week's notice or more before a space rock destroyed a city would cost only $1 million per observatory, its leading proponent suggests.

Given current technologies, this lead time would not be enough to mount a mission to deflect the incoming object, but it could be enough to evacuate the area under threat.

Astronomer John Tonry at the University of Hawaii mentioned a near-miss in 2009 as he stressed the need for an early warning system against cosmic impacts.

According to estimates by Tonry and other researchers, the rate of impact by asteroids at least 460 feet (140 meters) long is just once per 20,000 years or more — but the smaller the rock, the larger the risk. A roughly 160-foot-long (50 meters) object like the one that devastated the Tunguska area in Russia in 1908 is likely to impact Earth about once every millennium, while a 65- to 100-foot-long asteroid (20 to 30 meters) should strike once every century.

The National Research Council estimated a 160-foot-long object would cause an average of 30,000 deaths.

Tonry details his analysis in a paper set to appear in the January issue of the Publications of the Astronomical Society of the Pacific.

The network the researchers propose, dubbed ATLAS (for the Asteroid Terrestrial-impact Last Alert System), would consist of two observatories roughly 60 miles (100 km) apart that together would scan the visible sky twice a night. Each observatory would house four relatively small telescopes some 10 inches (25 cm) in aperture, as well as a camera for each telescope. The distance between the observatories would provide a way of separating nearby and distant moving objects, and the system would be able to help pinpoint the location and time of an impact to a few miles and a few seconds.

Each telescope and each camera would cost roughly $50,000. The software would take up the lion's share of expenses, bringing the cost for each observatory to $1 million. Tonry also projected $500,000 annually for staff, maintenance and other operating costs. He and his colleagues have submitted a $3 million proposal to NASA to build two observatories and operate them for two years.

ATLAS could provide three weeks' warning for 460-foot-long objects and one week's notice for 160-foot-long impactors. The smaller the object, the less warning there would be; a 65- to 100-foot-long asteroid might draw two or three days warning, while 33-foot-long objects might get one.

As currently proposed, ATLAS would detect more than half the impactors longer than 160 feet, and nearly two-thirds of those 460 feet long. The chances of detection go up with more telescopes, Tonry said, which would allow ATLAS to compensate for cloudy weather or lack of coverage in the Southern Hemisphere. Still, ATLAS' detection rate would never go higher than roughly 75 percent, since it could spot objects coming from the blinding direction of the sun.

Link: Article

Link: ATLAS website
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