80beats » Space

NASA Invites You to “Be a Martian” & Explore the Red Planet’s Terrain

Eliza Strickland — Thu, 19 Nov 2009 18:05:02 +0000

With NASA’s manned space flight program in tumult, it’s an open question when/if human boots will tramp on Martian soil. But the space agency has provided a virtual way for humans to explore the red planet, with its new “Be a Martian” program.

The online project, a collaboration between NASA and Microsoft, enlists the power of crowdsourcing. Users are invited to sort through the hundreds of thousands of photos of Mars that have been sent back by rovers and orbiters. To convince people to spend hours pouring over pictures of dusty Martian landscapes, two tasks have been set up as games where participants can win points and badges. One game asks people to count craters in photos of Mars; the other asks people to match small, high-res photos of the Martian surface with their corresponding locations on a low-res photo taken from a higher altitude [Seattle Post-Intelligencer]. (You’ll need to have Microsoft’s Silverlight application for the games and videos on the site to work.)

By enlisting citizen scientists, NASA hopes to both interest students in space careers and to make real progress in Martian research. “We really need the next generation of explorers,” says Michelle Viotti, from the agency’s Jet Propulsion Laboratory, which oversees Mars missions. “And we’re also accomplishing something important for Nasa. There’s so much data coming back from Mars. Having a wider crowd look at the data, classify it and help understand its meaning is very important” [BBC News].

Image: JPL / Microsoft

Leonid Meteor Shower Set to Light Up the Tuesday Morning Sky

Andrew Moseman — Mon, 16 Nov 2009 15:25:17 +0000

In the wee hours of Tuesday morning, 2009’s edition of the Leonid meteor shower will reach peak viewing time for sky-watchers in North America. Star gazers who lift their eyes to the heavens between 2 a.m. and 4 a.m. will likely be rewarded with a good show of “shooting stars.” A second, briefer, but very intense outburst is expected about 12 hours later — during the early-morning hours of November 18th in Asia [Sky & Telescope]. But that probably won’t last long enough for North Americans to see it when night returns here.

Like other meteor showers, such as the Perseids and the Orionids, the Leonids happen when Earth plows through a trail of debris left in the wake of a comet orbiting the sun [National Geographic News]. This comet, called Tempel-Tuttle, swings through the inner solar system about every 33 years, and last did so in 1998.

On special occasions we’ll pass directly through an unusually concentrated dust trail, or filament, which can spark a meteor storm resulting in thousands of meteors per hour. That indeed is what transpired in 1999, 2001 and 2002 [MSNBC]. This year won’t supply such a bonanza, astronomers predict, but we will see more meteors than average: probably 30 to 300 per hour, depending on where you are.

To get the most spectacular views, of course, you’ll have to venture away from city lights. But you won’t need to haul a telescope. For meteor showers, the naked eye is enough to enjoy the show.

Related Content:
Bad Astronomy: Will the Leonids Roar in 2009?
Bad Astronomy: Leonids ROCK! (Check out the link to the amazing Mt. Hopkins video of a Leonid shower)
80beats: Tonight’s Orionid Meteor Shower Should Be a Beauty, from October
80beats: Study: 20-Million-Year Meteor Shower Turned Earth Warm & Wet

Image: iStockphoto

NASA: Bombing the Moon Provided Definite Evidence of Lunar Water

Andrew Moseman — Fri, 13 Nov 2009 20:53:07 +0000

Bomb and you shall find.

NASA today claimed success in its quest to find water on the moon. “Indeed, yes, we found water. And we didn’t find just a little bit, we found a significant amount,” said Anthony Colaprete, a principal project investigator at NASA’s Ames Research Center [AP].

Scientists had been analyzing data for more than a month since NASA crashed the LCROSS craft into the moon on October 9, which created a tiny crater in the polar region and kicked up a plume of material that had been beneath the lunar surface. NASA worried when the original impact didn’t create the easily visible plume of material that they’d anticipated, but later images showed that the mystery plume had been created and scientists were free to analyze its composition.

The results are clear: both infrared and ultraviolet spectrometers indicated the presence of water, and those readings got stronger over time, which is what you’d expect if you bombed the moon and created a plume full of water.

Previous space probes had indicated the presence of hydrogen in the lunar polar regions, but researchers hadn’t verified it until now. “LCROSS has now made that definitive discovery,” team member Greg Delory said at the press conference today. The confirmation of scientists’ suspicions is welcome news both to future explorers who might set up home on the lunar surface and to scientists who hope that the water, in the form of ice accumulated over billions of years, could hold a record of the solar system’s history [The New York Times]. For now, though, let’s just enjoy the sweet watery taste of success, and the fact that our whole understanding of Earth’s lone satellite has changed. “This is not your father’s moon,” Delory said.

Image: NASA

Rosetta Photographs a Crescent Earth on Its Way to a Comet Rendezvous

Andrew Moseman — Fri, 13 Nov 2009 16:01:36 +0000

This dazzling picture of our planet, all dark but the cerulean sliver of the South Pole, was a long time coming.

Rosetta, a European Space Agency craft, captured this view of the crescent Earth from about 400,000 miles away. The unmanned probe, which is busy chasing comets, was making its third flypast since it was launched in 2004. The close approach gave it a speed boost to send it on its mission to Comet Churyumov-Gerasimenko [Scientific American].

This will be Rosetta’s final visit to its home planet, having already executed a flyby of the asteroid Steins, a gravity assist with Mars, and two previous swoops past the Earth, gathering images all the way. Now it’s off to the comet.

Rosetta is carrying a fridge-sized lab, Philae, that it will send down to the comet. Anchored by tiny hooks, Philae will look for clues about the Solar System’s primal past, exploring a theory that comets are primitive rubble left over from the making of the Solar System [AFP].

While we bid safe travels to Rosetta, it could tell us something about the Earth itself on this final pass. Scientists notice unexpected behavior in spacecraft that make gravitational assists with our planet: Rosetta itself behaved exactly as expected in 2007 flyby but picked up an extra speed boost of 1.8 millimeters per second on its initial maneuver in 2005, leading some mission scientists to speculate that the Earth’s rotation might be distorting space-time more than they thought. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely groundbreaking news” [MSNBC], says Rosetta flight dynamics specialist Trevor Morley.

Related Content:
Bad Astronomy: Rosetta Takes Some Home Pictures
Bad Astronomy: Earth From Rosetta, from its 2007 flyby.
Bad Astronomy: Rosetta Swings By Mars!
DISCOVER: To Catch a Comet, which anticipated Rosetta, Stardust, and other comet-chasing missions.

Image: ESA

Mars Rover Will Try Daring Escape From Sand Trap of Doom

Eliza Strickland — Thu, 12 Nov 2009 22:27:13 +0000

It’s a terrible thing to have a spirit that is trapped, bogged down, unable to reach its true potential. Just ask NASA–the space agency knows all about it. The Mars rover Spirit has been stuck in the sand since April 23rd, when it drove backwards into a pit of soft sand and came to a dead halt. Since then, NASA engineers have been testing out escape strategies with a mock-up rover and a sandbox in California, and today they announced that they’re ready to begin a careful operation that they hope will extricate the rover. The name of the project: Free Spirit.

Spirit and its partner rover have been exploring Mars for more than five years now, but this sandy area, dubbed Troy, could be the end of the road for Spirit. “If it cannot make the great escape from this sand trap, it’s likely that this lonely spot straddling the edge of this crater might be where Spirit ends its adventures on Mars,” said Doug McCuistion, who heads the Mars exploration program [AP].

On Monday, Spirit’s handlers will send the first commands to the rover. Over days, weeks, and months they’ll order it to slowly rotate its five working wheels and inch back along the path it came in on. Efforts to extract Spirit will continue until at least February. If the rover is not free by then, a review panel may decide whether it’s worth it to keep on trying, McCuistion said [AP]. But even if Spirit is stuck for all time, it may still be able to contribute to our scientific understanding of the Red Planet by studying its soil and atmosphere.

Image: JPL / NASA

Vatican to E.T.: Hello, Brother

Andrew Moseman — Wed, 11 Nov 2009 17:27:04 +0000

Had he lived to what would have been his 75th birthday on Monday, Carl Sagan would’ve seen a surprising new collaborator in pondering whether there’s life out there in the cosmos: the Vatican. The Pontifical Academy of Sciences held a conference of scientists and theologians this week that probed the possibility of extraterrestrial life, and the peculiar religious questions that life on other worlds would raise.

Father Jose Funes, director of the Vatican Observatory, became the Catholic Church’s chief evangelist this week spreading the notion that alien life is compatible with Christianity. “This is not in contradiction with our faith, because we cannot establish limits to God’s creative freedom. To say it with St Francis, if we can consider some earthly creatures as ‘brothers’ or ’sisters’, why could we not speak of a ‘brother alien’? He would also belong to the creation” [The Guardian].

The meeting marks another step in the Vatican’s attempt to overcome its historical reputation as unfriendly to science and scientists. The church held a similar scientific conference on evolution earlier this year, and set up a Vatican Museum exhibit to mark the 400th anniversary of Galileo’s observations–and to make up for the church’s 17th century treatment of him. In 1992, Pope John Paul II declared the ruling against the astronomer was an error resulting from “tragic mutual incomprehension” [AP].

But while many Christians have managed to square evolution and astronomy with non-literal interpretations of the Bible, some people think the reconciliation won’t be so easy—like cosmologist Paul Davies, who spoke at the conference. “The real threat would come from the discovery of extraterrestrial intelligence, because if there are beings elsewhere in the universe, then Christians, they’re in this horrible bind. They believe that God became incarnate in the form of Jesus Christ in order to save humankind, not dolphins or chimpanzees or little green men on other planets,” [Washington Post] he says.

Image: flickr/roblisameehan

Spacecraft That Sails on Sunshine Aims for Lift-Off in 2010

Eliza Strickland — Tue, 10 Nov 2009 23:30:19 +0000

It was a fitting tribute to Carl Sagan’s imagination, optimism, and starry-eyed wonder. On Monday, which would have been Sagan’s 75th birthday, the Planetary Society announced that it is pushing ahead with a plan for experimental spacecraft that will ride on sunbeams, powered by solar sails. The first small craft will be sent into orbit in 2010, if all goes well, and will be followed by two others, which may venture farther. Sagan was a founder of the Planetary Society and a big booster of solar sail plans.

Solar sail technology, which has not yet been tested in space, relies on the tiny impacts created by the light particles streaming from the sun as they hit a reflective surface. The force on a solar sail is gentle, if not feeble, but unlike a rocket, which fires for a few minutes at most, it is constant. Over days and years a big enough sail, say a mile on a side, could reach speeds of hundreds of thousands of miles an hour, fast enough to traverse the solar system in 5 years. Riding the beam from a powerful laser, a sail could even make the journey to another star system in 100 years, that is to say, a human lifespan [The New York Times].

The spacecraft that is scheduled for orbit in 2010, the LightSail-1, has been made possible by an anonymous donation to the Planetary Society. The recent donation reinvigorates the Society’s solar sail hopes, which were dashed in 2005 when the Russian Volna rocket carrying its first solar sail prototype, Cosmos 1, failed to reach orbit…. In addition to the Cosmos 1 disappointment, NASA’s NanoSail-D attempt was lost in the third failed flight of SpaceX’s Falcon 1 rocket in 2008 [SPACE.com].

Image: The Planetary Society

NASA’s Plan to Irradiate Monkeys Raises Cruelty Concerns

Brett Israel — Tue, 10 Nov 2009 14:30:10 +0000

If NASA ever wants to send astronauts on long-term space flights, it needs to know how radiation will affect the crew. Testing humans obviously isn’t going to happen, so NASA is funding a round of experiments to study how radiation effects monkeys, the first time monkeys have been used as test subjects by NASA in decades. The point of the experiments is to understand how the harsh radioactive environment of space affects human bodies and behavior and what countermeasures can be developed to make long-duration spaceflight safe for travelers beyond Earth’s protective magnetic shield [Discovery News]. The monkey studies will advance previous radiation experiments with rats and mice and will focus on how radiation affects the monkeys’ central nervous system.

Researchers will expose 18 to 28 squirrel monkeys with a small dose of radiation, similar to what astronauts would receive on a round trip flight to Mars. The monkeys, previously trained to perform a variety of tasks, will be tested to see how the exposure affects their performance [Telegraph] at different times after exposure to gamma rays. The monkeys will not be killed during the experiments, and after testing staff and veterinarians will look after them for the rest of their lives at Harvard Medical School’s McLean Hospital in Boston.

As you might expect, the experiment’s funding announcement is causing a stir among animal rights groups like the Physicians Committee for Responsible Medicine (PCRM) and People for the Ethical Treatment of Animals (PETA). PCRM sent an appeal to NASA urging them to halt the experiments, which they are branding as “one giant leap backward for NASA.” They are also arguing that the research is “cruel” since it violates NASA’s own guidelines for animal treatment and that it’s “unnecessary” since long-term spaceflight still seems like a pipe dream. NASA’s animal testing policy, established in 1996, asserts that “the minimization of distress, pain and suffering is a moral imperative” and emphasizes that experimenters must weigh the burdens of animal subjects against potential societal benefits [Scientific American].

In response to the criticism, NASA’s administrator Charles Bolden restated the agency’s commitment to deep space travel and the necessity of radiation testing. Jack Bergman, who will lead the research, said “there’s a long-standing commitment on the part of NASA to deep space travel and with that commitment comes a need for knowing what kinds of adverse effects deep space travel might have, what are the risks to astronauts,” Bergman said. “That’s not been well assessed” [Discovery News]. Bergman will conduct the experiments at NASA’s Space Radiation Laboratory at the Department of Energy’s Brookhaven National Laboratory in New York.

Image: flickr / suneko

Japan Pushes Forward on Plans for a Giant Solar Power Farm in Space

Andrew Moseman — Mon, 09 Nov 2009 22:13:41 +0000

Refusing to cave to the “that’s far too crazy to ever work” crowd, Japan took a step forward this week in the country’s scheme to develop a giant solar power station in Earth orbit. JAXA, the Japan Aerospace Exploration Agency, selected major Japanese firms like Mitsubishi Electric, Fujitsu, and Sharp to help develop the gargantuan project.

JAXA wants a system that can produce 1 gigawatt of electricity by 2030, and at one-sixth the cost Japan currently pays for electricity. The solar cells would capture the solar energy, which is at least five times stronger in space than on Earth, and beam it down to the ground through clusters of lasers or microwaves. These would be collected by gigantic parabolic antennae, likely to be located in restricted areas at sea or on dam reservoirs [AFP]. There the energy would be converted to electricity.

Japan isn’t alone; California utility Pacific Gas & Electric asked for regulatory approval of a similar project in April, though both schemes must confront a mountain of challenges. Sending equipment up to space is one. Operating and maintaining the system cost effectively is another. How about minimizing losses during conversion and transmission of energy [Greentech Media]?

And even if space solar power works, proponents might need to hire some talented public relations professionals: JAXA said the technology would be safe but conceded it might have to dispel fears of laser beams from above roasting birds or slicing up aircraft in mid-air [Sky News].

Image: Institute for Unmanned Space Experiment Free Flyer

A Baby Neutron Star, Swaddled in a Carbon Atmosphere

Eliza Strickland — Thu, 05 Nov 2009 17:51:28 +0000

A supernova that was observed in 1680 by Britain’s first Astronomer Royal, John Flamsteed, has been revealed to have produced a strange little neutron star that will give astronomers insight into how such stars are born and mature. The remains of the supernova, known as Cassiopeia A, have been something of a mystery to astronomers. Supernovae usually leave behind an extremely dense object such as a black hole or neutron star. But for decades no such object was seen at the centre of Cassiopeia A [Nature News]. Now new observations suggest that the 330-year-old neutron star escaped detection because of its odd atmosphere.

Instead of resembling more mature neutron stars, which are surrounded by hydrogen, this baby star is blanketed in carbon gas – a discovery that could provide important new insights into the evolution of neutron stars [Physics World]. The new study, published in Nature, suggests that the star is still extremely hot in the aftermath of the supernova–about 2 billion degrees Fahrenheit. This overheated condition caused a nuclear fusion reaction on the star’s surface that converts all the hydrogen and helium into carbon gas, researchers say. As time goes on, and as the star cools, the researchers think the surface fusion reaction will stop and the star will develop a more traditional hydrogen atmosphere.

Image: NASA / CXC / Southampton / W. Ho / M. Weiss

Laser-Powered Robot Climbs to Victory in the Space-Elevator Contest

Eliza Strickland — Thu, 05 Nov 2009 15:28:50 +0000

A laser-powered robot took a climb up a cable in the Mohave Desert in Wednesday, and pushed ahead the sci-fi inspired notion of a space elevator capable of lifting astronauts, cargo, and even tourists up into orbit. The robot, built by LaserMotive of Seattle, whizzed up 2,953 feet (nearly 1 kilometer) in about four minutes, which qualifies the team for at least $900,000 of the $2 million in prizes offered in the NASA-backed Space Elevator Games.

Theorized in the 1960s and then popularized by Arthur C. Clarke’s 1979 novel “The Fountains of Paradise,” space elevators are envisioned as a way to gain access to space without the risk and expense of rockets. Instead, electrically powered vehicles would run up and down a cable anchored to a ground structure and extending thousands of miles up to a mass in geosynchronous orbit — the kind of orbit communications satellites are placed in to stay over a fixed spot on the Earth [AP].

The LaserMotive vehicle that climbed up the cable (held by a hovering helicopter) was powered by a system that resembles an upside-down solar power mechanism. Laser beams on the ground were fired up at the ascending craft and hit its photovoltaic cells–like those used in solar panels–in a process known as “power beaming.” LaserMotive will have a chance to improve its vehicle’s speed at another trial today, and other teams will also be vying for prizes.

Related Content:
80beats: Japanese Group Pushes for $9 Billion, 22,000-Mile Space Elevator
DISCOVER: Going Up follows U.S. engineers on the space elevator quest

Image: Space Elevator Games. The LaserMotive vehicle gets weighed in.

Don’t Pack Your Bags Yet—New Planet-Finder Hobbled by Electronic Glitch

Eliza Strickland — Wed, 04 Nov 2009 19:09:31 +0000

The quest to find a second Earth–a potentially habitable planet that’s about the size of our home, but that lies in a distant solar system–has hit a snag. The Kepler space telescope was expected to be well on its way to detecting Earth-sized exoplanets by now, but an electronic glitch is slowing it down. The delays are caused by noisy amplifiers in the telescope’s electronics. The team is racing to fix the issue by changing the way data from the telescope is processed, but the delay could mean that ground-based observers now have the upper hand in the race to be the first to spot an Earth twin [Nature News].

Kepler, which was launched in March, uses the transit method to detect exoplanets; it’s watching a patch of 100,000 stars in hopes of detecting the brief dimming of a star’s light, which indicates that a planet has passed in front of the star. Kepler focuses light onto 42 light-detecting chips, called CCDs, each of which monitors stars in a different part of the telescope’s field of view. Each CCD is split into two for the purposes of sending data back to Earth, for a total of 84 data channels. Three of these channels are plagued by electronic noise that makes stars in their field of view appear to flicker – “like it’s changing its brightness at a rapid rate”, says Kepler chief scientist William Borucki [New Scientist]. That’s awkward, since the artificial flickers could obscure the real dimming that occurs during a planet’s transit.

The astronomers reportedly detected the problem during testing before Kepler’s launch, but they judged it riskier to dismantle the satellite at the last minute than to correct the glitch after launch. The noise affects only a small portion of the data, Borucki says, but the team has to fix the software — it would be “too cumbersome” to remove the bad data manually — so that it accounts for the noise automatically. He says that the fix should be in place by 2011 [Nature News].

Still, researchers say that the problem isn’t likely to delay the announcement of an Earth-like planet. For an exoplanet to be habitable to life as we know it, the planet would have to orbit its star at a distance that would keep it at a reasonable temperature and allow for liquid water. An Earth-like planet around a sun-like star would have an orbit roughly similar to Earth’s, and would take about a year to complete one circuit around its star. Astronomers feel the need to record three transits to confirm a planet’s existence–and in three years time, the noise-canceling software should be available. The delays would only affect habitable planets around smaller, cooler stars. The habitable zone for these stars is closer in, where planets could complete the necessary three orbits in about one Earth year. Without the glitch, this kind of planet could in principle be confirmed in 2010 [New Scientist].

Image: Kepler / Ames Research Center

Latest Mercury Pics Reveal Massive Craters & Possible Volcanic Vents

Eliza Strickland — Tue, 03 Nov 2009 22:04:15 +0000

When NASA’s Messenger space probe swung past Mercury on September 29, it snapped this picture of the innermost planet’s barren and strange landscape. The $446 million probe’s third flyby brought it within 142 miles (228 km) of Mercury’s surface to cover more uncharted terrain, leaving 98 percent of the planet now mapped [SPACE.com].

The images taken and the data recorded during the flyby are the last that will be acquired until Messenger finally slips into orbit around Mercury in 2011. The probe has now completed about three-quarters of its swooping 4.9-billion-mile journey that will eventually bring it into orbit.

Researcher Brett Denevi explains that this enhanced color shot shows a bright area surrounding an irregular depression, with steep sides and an odd shape, “all of which are hallmarks of something like a volcanic vent,” Denevi said [SPACE.com]. The double-ring basin in the center of the photo measures about 180 miles in diameter. It appears to be a relatively young impact crater–researchers believe it formed about 1 billion years ago–and the smooth stuff on the crater floor may be even younger volcanic material.

Image: NASA

Bonk! Hard Landing Dents New NASA Rocket Booster During Test Flight

Brett Israel — Mon, 02 Nov 2009 20:21:47 +0000

NASA’s Ares I-X experimental rocket completed its first test flight—but the successful endeavor ended on a sour note. The rocket’s first booster stage, which splashed down in the ocean as planned six minutes after launch, was found to be significantly dented when divers reached the mammoth cylinder to prep it for retrieval [Scientific American]. A malfunctioning parachute system caused the hard splashdown, according to mission manager Bob Ess. However Ess argued that it’s not a real cause for concern, since test flights are intended to reveal and work out the technology’s glitches.

The Ares I-X was a prototype for the controversial Ares I rocket that may carry astronauts to the International Space Station and beyond once the space shuttle is retired. The rocket’s design calls for the first booster stage to be retrieved after each flight for reuse. While NASA’s main objective on the test flight was to evaluate the rocket booster’s power, the test of the new parachute system was one of several major objectives of the Ares 1-X test flight [Spaceflight Now]. Despite the test flight’s overall success, the parachute system’s failure is a black eye for the $450 million project, since the heavy Ares I booster rocket will be difficult to ease back down to Earth. The booster is being retrieved from the Atlantic Ocean to determine what exactly went wrong with the parachute system.

80beats: Liftoff! NASA’s New Rocket Takes to the Sky in a Successful Test Flight
80beats: New NASA Rocket May Not Be “Useful,” White House Panel Says
80beats: NASA’s Lanky Ares Rocket Gets Ready for a Test Flight

Image: NASA

For a Real Blast, Strap a Nuclear Reactor to a Spaceship

Eliza Strickland — Fri, 30 Oct 2009 21:26:31 +0000

The Russian space agency has proposed a powerful new way to get a spacecraft to Mars or beyond: just put a big ole nuclear reactor on board.

The head of the agency, Anatoly Perminov, just proposed this new class of nuclear-powered spaceships for manned missions to explore our solar system. “The project is aimed at implementing large-scale space exploration programs, including a manned mission to Mars, interplanetary travel, the creation and operation of planetary outposts” [AP], Perminov wrote in an online statement. He suggested that preliminary designs could be completed by 2012, and said it would then take about nine years and $600 million to build the spacecraft. Some experts call these numbers utterly unrealistic, but Russian President Dmitry Medvedev insists that the government is very serious about the project.

The idea of a nuclear-powered spacecraft is not entirely new. Some NASA space probes that venture into the outer reaches of the solar system (where solar panels are less effective) make use of a mild type of nuclear power, in which the gradual decay of radioactive plutonium isotopes generates electricity. But such systems can only produce a few hundred watts of electricity. In contrast, the craft that Perminov proposes would be powered by a nuclear fission reactor, where uranium atoms are split to produce energy. Perminov said the new nuclear-powered ship should have a megawatt-class nuclear reactor, as opposed to small nuclear reactors that powered some Soviet military satellites. The Cold War-era Soviet spy satellites had reactors that produced just a few kilowatts of power and had a life span of about a year [AP].

A megawatt-class manned spaceship is an ambitious idea, but Igor Lisov, a Russian aerospace expert, says he doesn’t believe it will ever be built. “Both the US and the USSR tried very hard to master this technology, but neither ever got to the point of building something that could be used,” he says. Environmentalists point to a long list of accidents with Soviet nuclear-powered satellites, including the crash of Kosmos-954 over northern Canada, which spread radioactive debris over a wide area [The Christian Science Monitor]. A nuclear-powered spacecraft would primarily pose an environmental threat if something went wrong during takeoff or re-entry into the atmosphere, but experts also worry about astronauts’ radiation exposure from the reactor.

Image: NASA