The world's first engineering study of an unmanned spaceship to explore one of the nearer stars was made by a technical group of the British Interplanetary Society between 1973-77. The target selected for the exercise was Barnard's Star, six light years distant from Earth. The team recognised that the work, based on the technology extrapolated to the beginning of the 21st Century, could represent only a first approximation to the solution of starflight.

The results showed it would be a formidable task requiring a massive craft that would dwarf the Saturn V moon rocket, the largest space vehicle yet flown by man. Daedalus, as currently conceived, would weigh some 54,000 tons, nearly 20 times the weight of the Saturn V, carrying nearly 500 tonnes of fully automated payload. Because of the enormous time lag involved in radio communications between the Earth and the ship, a semi-intelligent computer would have to control the entire ship and work out all actions necessary for the exploration phase of the mission.

The result was a two stage, nuclear fusion powered vehicle, unmanned and under autonomous operation due to the distances involved, accelerated to 16% of the speed of light, and armed with a variety of probes, sensors, robotic wardens and intelligent decision making computers. Although the journey could take as long as 40 years, a flyby at such speeds would be over in 70 hours.

Although the study was conducted during the 70's, it's still referred to today, even in NASA, as a baseline study. Any future mission to the stars probably won't look anything like Daedalus, but it gives a good idea of the complexity and scale of task, and the length of time it would take to get to even the closest stars.

No estimate of the cost of such an enterprise could be made, but it would be way beyond the capacity of an individual nation, and would probably need a period of world stability unlike any we have seen to date.

The Daily Galaxy with thanks to Bisbos.com http://www.bisbos.com/space_n_daedalus.html

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Yesterday's headlines reported that China's first space station Tiangong-1 was "in freefall," "hurtling towards Earth" and would "rain molten metal down onto Earth." The eight-ton Tiangong-1 serves as both a manned laboratory and an experimental testbed to demonstrate orbital rendezvous and docking capabilities. It was launched unmanned aboard a Long March rocket in September 2011.

According to astrophysicist Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics who works on Chandra X-Ray Observatory and comments on space launches and space activities, "it's too soon to tell whether Tiangong-1 is out of control. “In the history of the Space Age, uncontrolled re-entries have been common,” McDowell told  the Smithsonian. “And the chance that debris from any one of them hits somebody, it's one in thousands.”

The concerns over Tiangong-1's fate stem from two main sources: a press release the Chinese government published earlier this year and amateur astronomer observations.

This March, the Chinese Manned Space Engineering office (CMSE) announced that the space agency had terminated its data link with Tiangong-1 and would monitor its orbit as it descends into the Earth's atmosphere and burns up, the state-run news agency Xinhua reported at the time. But because the release didn't explicitly state that the CMSE was in control of Tiangong-1, some interpreted it as a sign that all was not well at mission control. In the meantime, amateur astronomers reported witnessing the space lab flicker as it orbited Earth, which some took as evidence that the station was spinning out of control.

Terminating the data link is not evidence of certain death, it just means that they are no longer using the module to collect data, says McDowell. They can also reestablish communication in the future, if necessary. McDowell speculates that CMSE is putting the module into hibernation until after its replacement, Tiangong-2, launches. But the Chinese government's reticence on the matter has further magnified all rumors.

SpaceLab, a craft ten times the size of Tiangong-1, reentered the atmosphere in 1979 and most of it went up in flames over western Australia. “Last year, a couple of farmers in Spain found these metal spheres in their fields,” McDowell says. “That was probably from a two-ton rocket stage left in orbit. It didn't even make the news at the time.”

Tiangong-1 is orbiting at about 215 miles above the ground—a relatively low altitude for an orbital satellite. That makes it easy to spot and could account for some of the worry among amateur astronomers who have noted changes in its appearance. But not only has Tiangong-1 been at this low altitude before, so has the International Space Station (ISS).

ISS and Tiangong-1 both have relatively low orbits, experiencing slight drag from the Earth's atmosphere that causes them to lose altitude over time, McDowell says. But the engineers for both crafts developed ways to ensure they don't fall too low in the sky. The ISS relies on its regular vistors to nudge it back into higher orbit. "They fire their engines and give it a boost," McDowell explains. But Tiangong-1 doesn't receive quite as many visitors and is much smaller, making it more effective for the CMSE to periodicly reposition the space lab using the onboard engine.

In the worst circumstances, the space station wouldn't enter the atmosphere until at least 2017. And reentry isn't something to be feared. “Most likely, some people will see a nice re-entry like a meteor overhead,” McDowell says. “If this were the day Tiangong-1 was re-entering, it still wouldn't be high on my list to worry about.”

The Daily Galaxy via Smithsonian.com

Image credit: With thanks to Adrian Mann/Bisbos.com

A big advantage to our civilization arising early in the evolution of the universe is our being able to use powerful telescopes like Hubble to trace our lineage from the big bang through the early evolution of galaxies. The observational evidence for the big bang and cosmic evolution, encoded in light and other electromagnetic radiation, will be all but erased away 1 trillion years from now due to the runaway expansion of space. Any far-future civilizations that might arise will be largely clueless as to how or if the universe began and evolved.

"Our main motivation was understanding the Earth's place in the context of the rest of the universe," said study author Peter Behroozi of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, "Compared to all the planets that will ever form in the universe, the Earth is actually quite early."

Earth came early to the party in the evolving universe. According to the new theoretical study, when our solar system was born 4.6 billion years ago only eight percent of the potentially habitable planets that will ever form in the universe existed. And, the party won't be over when the sun burns out in another 6 billion years. The bulk of those planets -- 92 percent -- have yet to be born. This conclusion is based on an assessment of data collected by NASA's Hubble Space Telescope and the prolific planet-hunting Kepler space observatory.

The NASA researchers say that future Earths are more likely to appear inside giant galaxy clusters (the massive cluster galaxy-cluster-macs-j0717 below) and also in dwarf galaxies, which have yet to use up all their gas for building stars and accompanying planetary systems. By contrast, our Milky Way galaxy has used up much more of the gas available for future star formation.

Looking far away and far back in time, Hubble has given astronomers a "family album" of galaxy observations that chronicle the universe's star formation history as galaxies grew. The data show that the universe was making stars at a fast rate 10 billion years ago, but the fraction of the universe's hydrogen and helium gas that was involved was very low. Today, star birth is happening at a much slower rate than long ago, but there is so much leftover gas available that the universe will keep cooking up stars and planets for a very long time to come.

"There is enough remaining material [after the big bang] to produce even more planets in the future, in the Milky Way and beyond," added co-investigator Molly Peeples of STScI.

Kepler's planet survey indicates that Earth-sized planets in a star's habitable zone, the perfect distance that could allow water to pool on the surface, are ubiquitous in our galaxy. Based on the survey, scientists predict that there should be 1 billion Earth-sized worlds in the Milky Way galaxy at present, a good portion of them presumed to be rocky. That estimate skyrockets when you include the other 100 billion galaxies in the observable universe.

This leaves plenty of opportunity for untold more Earth-sized planets in the habitable zone to arise in the future. The last star isn't expected to burn out until 100 trillion years from now. That's plenty of time for literally anything to happen on the planet landscape.

The results appeared in the Monthly Notices of the Royal Astronomical Society.

The Daily Galaxy via NASA/Goddard Space Flight Center

Image credits: NASA and CfA -the artist's conception at the top of the page depicts an Earth-like planet orbiting an evolved star that has formed a stunning planetary nebula. David A. Aguilar (CfA)

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Astronomers from KU Leuven, Belgium, have shown that the interaction between the surface and the atmosphere of an exoplanet has major consequences for the temperature on the planet. This temperature, in turn, is a crucial element in the quest for habitable planets outside our Solar System.

In the quest for habitable planets outside our Solar System astronomers are currently focusing on rocky planets of M dwarfs - stars that are smaller than our Sun. In our universe, there are many more M dwarfs than there are sun-like stars, making it more likely that astronomers will discover the first habitable exoplanet. Most planets orbiting these M dwarfs always face their star with the same side. As a result, they have permanent day and night sides. The day side is too hot to make life possible, while the night side is too cold.

Last year, KU Leuven researchers showed that planets with permanent day sides may still be habitable depending on their 'air conditioning' system. Two out of three possible 'air conditioning' systems on these exoplanets use the cold air of the night side to cool down the day side. And with the right atmosphere and temperature, planets with permanent day and night sides are potentially habitable.

Whether the 'air conditioning' system is actually effective depends on the interaction between the surface of the planet and its atmosphere.

The graphic above shows the wind, temperature, and surface-atmosphere friction on a planet 1.45 times the size of the Earth in a 1-day orbit around an M dwarf. The two topmost figures show the wind and the temperature in the upper layers of the atmosphere. The two figures in the middle show the wind and the temperature on the surface of the planet. On the left-hand figures, the surface-atmosphere friction equals that on Earth. On the right-hand figures, there is ten times as much friction between surface and atmosphere than is the case on Earth. Both scenarios have a different impact on the climate of a planet: the climate represented in the right-hand figures is more habitable.
CREDIT

"We built hundreds of computer models to examine this interaction. In an ideal situation, the cool air is transported from the night to the day side. On the latter side, the air is gradually heated by the star," said lead researcher Ludmila Carone. "This hot air rises to the upper layers of the atmosphere, where it is transported to the night side of the planet again."

But this is not always the case: on the equator of many of these rocky planets, a strong air current in the upper layers of the atmosphere interferes with the circulation of hot air to the night side. The 'air conditioning' system stops working, and the planet becomes uninhabitable because the temperatures are too extreme.

"Our models show that friction between the surface of the planet and the lower layers of the atmosphere can suppress these strong air currents," added Carone. "When there is a lot of surface friction, the 'air conditioning' system still works."

The KU Leuven researchers created models in which the surface-atmosphere interaction on the exoplanet is the same as on Earth, and models in which there is ten times as much interaction as on Earth. In the latter case, the exoplanets had a more habitable climate. If planets with a well-functioning 'air conditioning' system also have the right atmosphere composition, there's a good chance that these exoplanets are habitable.

The Daily Galaxy via KU Leuven, Belgium

Image credit: to of page, NASA/JPL 

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