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Interstellar Spaceflight: Is It Possible?

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Bannik

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How many of you believe we will ever have the technological capability of venturing out of own solar system? Why or why not?
 
Interstellar Spaceflight: Is It Possible?



With current space travel limited to just a few robotic probes visiting nearby planets, how realistic is it to think about reaching the nearest stars? For the short term, not very – especially when we speak of manned missions. But the long term - 50 or even 100 years - chances are good mankind will have missions, unmanned to start with, traveling to stars in our galactic neighborhood.

Actually, we already have space craft venturing into interstellar space. Pioneer and Voyager probes, 2 each, have reached the sun’s escape velocity and are now forever outward bound. The fastest, Voyager 1, is traveling at 62,000 kilometers per hour (39,000 mph). Even at that tremendous speed it’s painfully slow when interstellar distances are involved. Voyager 1 would take over 17,000 years to get Proxima Centuari, our nearest neighbor at 4.22 light years distance.

With a theoretical speed limit imposed by Einstein's Theory of Relativity at 1,079,252,848.8 km/h, or the speed of light, even the closest stars are very far away indeed.

But if you take in to consideration the rapid pace of technological advancement, things look brighter. The Wright brothers’ first feeble flights advanced to a man on the moon in just 50 years. In less than 100 years, we can travel 1,000 times faster. If this rule holds true for the next hundred years, we will be able to travel to the nearest stars with relative ease.

Predicting this future, however, is not easy. We simply lack even the basic theories to travel at above light speed making the engineering of an interstellar drive even further away. There are however, some interesting ideas on the drawing board that are within current theoretical limits.

A study by NASA in 1998 identified 3 potential propulsion technologies that might enable exploration beyond our solar system. Antimatter, fusion and light sails.

Light sails currently are the most technologically viable of the three. Robert L. Forward, scientist and science fiction writer first proposed them in 1984. The basic idea is to use huge lasers to push an object out of the solar system. Although it sounds strange to think of light pushing an object, photons do exert a very small force over objects they hit. Since the force it small, the object needs to be both large and lightweight – like a sail. It also needs to be reflective as only photons bouncing off an object impart velocity – absorbed photons generate heat. To prevent the heat from building up, the backside of the sail needs to be an effective radiator.


Image from: http://www.itsf.org/brochure/solarsail.html
Because photons exert a tiny force even over a large area, the sail must be large indeed. However, since space is virtually empty, there is very little drag. This means any imparted velocity is incremental – a tiny push over a long period equals one big push.

The sail material could be some form of Mylar – both thin and strong. Steering the sail and aiming the huge lasers, however, are not trivial problems. By huge lasers, think 10 gigawatts shining on a 1 kilometer in diameter sail just to send a 16 gram payload to the closest star. The laser must be precisely aimed on target for as long as possible to get the desired velocities. According to its inventor, this light-powered ship could make it to the next star in only ten years.

This technology also scales up to allow for larger payloads but laser power levels quickly become gargantuan. To send a 1,000 ton ship with a crew to the same destination would require a 1,000 kilometer sail driven by a 10 million gigawatt laser - ten thousand times more than the power used on all the Earth today.

These sails have been tested: On August 9, 2004 Japanese ISAS successfully deployed two prototype solar sails in low Earth orbit. A clover type sail was deployed at 122 km altitude and a fan type sail was deployed at 169 km altitude. Both sails used 7.5 micrometer thick film. They used the force of the sun’s photons as propulsion rather than a large laser.

Faster speed could be achieved by fusion motors. Unfortunately, unlike light sails, fusion has yet to be sufficiently well understood to use as a propulsion device. Not for want of billions of dollars in funding to study it, however. Someday soon we may have the ability to control the same reaction that drives our sun. Fusion liberates tremendous energy from a given mass making it ideal for long voyages when fuel weight becomes the critical factor.

One interesting idea is the Bussard ramjet first proposed in 1960 by the American physicist RW Bussard. Rather than bring fuel, why not get it from space?


Image from: http://www.itsf.org/brochure/ramscoop.html
Although commonly perceived to be empty, interstellar space has a minuscule amount of hydrogen gas - at a density of about one or two atoms per cubic centimeter. Bussard’s idea is to scoop this gas up using electromagnetic force fields that extend outwards in front of the spacecraft. This field would need to be absolutely gigantic – upwards of 50,000 kilometers in diameter. Shipboard superconducting coils would steer interstellar gas towards the ship compressing it until the density was enough to produce usable fuel. In order to start this collection process the ship would already need substantial velocity – on the order of 3 to 4% light speed.

A Bussard ramjet could conceivably achieve a constant 1g acceleration that would allow the pilot to make very long journeys. To an Earthbound observer, such a ship would take hundreds of thousands of years to reach the center of the galaxy. But because of relativistic time dilation, only 20 years would pass for the crew on the ship. Imagine – just 20 years to the center of the galaxy! Of course, technical problems remain such as force field drag, shielding the crew from interstellar radiation and the ability to control fusion reactions.

Even farther off technically is the antimatter drive. When matter and antimatter come in to proximity, they annihilate each other releasing even more energy than fusion.

A fusion based propulsion unit could generate 100 trillion joules per kilo of fuel – respectable when considering that it would be 10 million times more efficient than chemical rockets. Matter-antimatter reactions, however, dwarf all other reactions. Imagine a drive could generate 20 quadrillion joules per kilo of reaction mass. That’s enough power form one kilo to supply the world’s needs for about 25 minutes.

Technical problems include lack of fuel – the world supply is a few dozen nanograms a year, fuel handling – you can easily predict the catastrophic results of an antimatter fuel accident - and reaction control.

All these technologies are as far away now as the atomic bomb was to Alfred Nobel – the inventor of TNT. That is to say, not very. We may see the beginnings of an interstellar spaceflight program before the end of the millennium. We will simply need a compelling reason.

To contemplate seriously reaching the nearest stars, we need to understand the hurdles involved. First, there is the enormous cost involved in deploying any of the understood technologies. Second, despite UFO enthusiast’s beliefs, there is no hard evidence that we have ever been visited by alien spacefarers. Third, we know we can send radio waves to these destinations without problems.

With this in mind, it may simply be too expensive and technically difficult to travel in interstellar space. A better solution has been proposed: why not create an intergalactic Internet? Send small, self-replicating research probes to other stars. Once there, they build copies of themselves and continue to explore outwards, relaying a steady stream of information back to Earth.

These self-replicating probes, also known as Von Neumann machines, are named after their inventor, mathematician John Von Neumann (1903-1957). The beauty of this idea is once you manage to construct the first self-replicating machine, the rest is automatic. The probes would expand into space geometrically, spreading rapidly to fill the whole galaxy. Once established, this network could be used for communication and localization of new Earthlike planets to colonize.

As of now, building machines that work well unassisted remain a problematic task for even the best scientists if recent unmanned mission failures are any indication. A self-repairing and self-replicating robotic probe seems distant indeed.

Travel in interstellar space represents a huge challenge to humankind. For now, it remains in the realm of science fiction – but soon, who knows? We may yet live to see the first missions to nearby stars – that is if the last 100 years of history is any guide.

by Chuck Rahls, Copyright 2005 PhysOrg.com



http://www.physorg.com/news8817.html
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Time to resurrect this thread with a report from the 100 Year Starship Symposium. 10 comments so far at link.

Why Humanity Needs to Travel to Other Stars
http://www.space.com/17617-interstellar ... rship.html
by Clara Moskowitz, SPACE.com Assistant Managing Editor
Date: 15 September 2012 Time: 07:01 AM ET

Obtaining the exotic fuels needed for interstellar flight is a major challenge – here a scheme is shown where a spacecraft in low orbit around Jupiter lowers an extremely long tube into the atmosphere, sucking up and processing gases.
CREDIT: Adrian Mann

HOUSTON — Launching a mission to another star could teach us not just about space, but about Earth as well, experts argued here today at the 100 Year Starship Symposium.

"I believe space exploration is a human imperative," said Mae Jemison, the first female African American astronaut. "It didn’t begin in 1957 with Sputnik, it's been a part of us" all along.

Jemison is heading the 100 Year Starship initiative, which aims to mount a mission to another star within 100 years. Toward that end, scientists and thinkers from a variety of disciplines gathered for a public symposium here from Sept. 13 to 16 to discuss the motivations, challenges and possible solutions for pursuing interstellar spaceflight.


"I'm excited for the opportunity we have to pioneer tomorrow's technology and to reimagine our future," former President Bill Clinton, who is the symposium's honorary chair, said via a video address today (Sept. 14). "I only wish I could be here 100 years from now to make the trip."

The 100 Year Starship project was founded with seed money from the Defense Advanced Research Projects agency (DARPA), and is now being run by Jemison's Dorothy Jemison Foundation for Excellence. The program's leaders aim to recruit not just scientists and engineers, but psychologists, sociologists, religious leaders and philosophers to help solve the problems posed by interstellar travel. [Gallery: Visions of Interstellar Starship Travel]

Because the nearest star is more than 4 light-years away, the fastest spacecraft ever built, Voyager 1, would take 75,000 years to get there. A realistic mission to another star system will require novel propulsion methods, as well as new life support, habitat technology and social structures to support what could be multiple generations of astronauts making the journey.

"We need the full capacity of the people we have on this planet to figure out how to do this," Jemison said. She also stressed the importance of outreach to involve the public in the project. "I know that we would be on the moon right now if we had kept the American public involved. They didn’t leave us, we just left them out. We have to change the idea that space is just for rocket scientists, and nowadays billionaires. It's actually for everybody."

The payoff of such a mission could be felt not just in space but on the ground, she said. For example, one of the leading ideas for how to power a starship is nuclear fusion propulsion. Since fusion is also a potential way to create energy on Earth, the process of inventing such a technology for spaceflight could have applications for our planet, too.

"Just the mere idea of going might transform life on Earth right now," Jemison said.
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The best bet for an achievable technology that will allow interstellar flight is something called a 'sailbeam', also known as a 'beamrider'. This consists of a series of very powerful lasers that do not accelerate the ship directly, but instead accelerate billions of tiny steerable lightsails; these lightsails converge on the ship itself and collide with a magnetic sail spread out in front of it.

The light sails are in theory much more efficient in transferring the energy of the lasers into the momentum of the ship than any other method yet thought of. On arrival at the destination system the magsail can be reconfigured as a brake, using Bussard's ramscoop concept in reverse- which, according to many calculations, is the only thing it is useful for.

Finally, when the ship is moving too slowly for the ramscoop effect to work well, the final drive kicks in - probably a fusion drive. Although antimatter would be more powerful, it is extraordinarily expensive, and might not be available in bulk for many centuries yet.

The 100-year starship people are looking into this scheme at the moment, and reckon it would reduce the total mass of a starship considerably. But it does require the development of very, very big lasers, something that might set warning bells off in the arms limitation camp.
 
Warp Drive May Be More Feasible Than Thought, Scientists Say

http://www.space.com/17628-warp-drive-p ... light.html

HOUSTON — A warp drive to achieve faster-than-light travel — a concept popularized in television's Star Trek — may not be as unrealistic as once thought, scientists say.

A warp drive would manipulate space-time itself to move a starship, taking advantage of a loophole in the laws of physics that prevent anything from moving faster than light. A concept for a real-life warp drive was suggested in 1994 by Mexican physicist Miguel Alcubierre; however, subsequent calculations found that such a device would require prohibitive amounts of energy.

Now physicists say that adjustments can be made to the proposed warp drive that would enable it to run on significantly less energy, potentially bringing the idea back from the realm of science fiction into science.

There is hope," Harold "Sonny" White of NASA's Johnson Space Center said here Friday (Sept. 14) at the 100 Year Starship Symposium, a meeting to discuss the challenges of interstellar spaceflight.

An Alcubierre warp drive would involve a football-shape spacecraft attached to a large ring encircling it. This ring, potentially made of exotic matter, would cause space-time to warp around the starship, creating a region of contracted space in front of it and expanded space behind. [Star Trek's Warp Drive: Are We There Yet? | Video]

Meanwhile, the starship itself would stay inside a bubble of flat space-time that wasn't being warped at all.

"Everything within space is restricted by the speed of light," explained Richard Obousy, president of Icarus Interstellar, a non-profit group of scientists and engineers devoted to pursuing interstellar spaceflight. "But the really cool thing is space-time, the fabric of space, is not limited by the speed of light."

With this concept, the spacecraft would be able to achieve an effective speed of about 10 times the speed of light, all without breaking the cosmic speed limit.

The only problem is, previous studies estimated the warp drive would require a minimum amount of energy about equal to the mass-energy of the planet Jupiter.

But recently White calculated what would happen if the shape of the ring encircling the spacecraft was adjusted into more of a rounded donut, as opposed to a flat ring. He found in that case, the warp drive could be powered by a mass about the size of a spacecraft like the Voyager 1 probe NASA launched in 1977.

Furthermore, if the intensity of the space warps can be oscillated over time, the energy required is reduced even more, White found.

"The findings I presented today change it from impractical to plausible and worth further investigation," White told SPACE.com. "The additional energy reduction realized by oscillating the bubble intensity is an interesting conjecture that we will enjoy looking at in the lab."

Laboratory tests

White and his colleagues have begun experimenting with a mini version of the warp drive in their laboratory.

They set up what they call the White-Juday Warp Field Interferometer at the Johnson Space Center, essentially creating a laser interferometer that instigates micro versions of space-time warps.

"We're trying to see if we can generate a very tiny instance of this in a tabletop experiment, to try to perturb space-time by one part in 10 million," White said.

He called the project a "humble experiment" compared to what would be needed for a real warp drive, but said it represents a promising first step.

And other scientists stressed that even outlandish-sounding ideas, such as the warp drive, need to be considered if humanity is serious about traveling to other stars.

"If we're ever going to become a true spacefaring civilization, we're going to have to think outside the box a little bit, we're going to have to be a little bit audacious," Obousy said.
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I'm still not convinced that the universe will let a warp drive travel faster than light. Even though the ship inside the warp experiences no time dilation, the ship itself can be used as a FTL messaging system; coupled with Lorentz transformation, this could mean that some frames of reference could communicate with others in their own past light-cone, thus breaking causality.

I would only be mildly surprised if some sort of limited warping of space of this nature were possible- but I would be very surprised if it did not come complete with chronological protection.
 
The Space Sail is becoming reality. Perhaps it will provide a slow starship to Proxima Centauri.

Space sailing soon: A one-kilometer-long electric sail tether produced

January 8th, 2013 in Space & Earth / Space Exploration

The electric sail (ESAIL), invented by Dr. Pekka Janhunen at the Finnish Kumpula Space Centre in 2006, produces propulsion power for a spacecraft by utilizing the solar wind. The sail features electrically charged long and thin metal tethers that interact with the solar wind. Using ultrasonic welding, the Electronics Research Laboratory at the University of Helsinki successfully produced a 1 km long ESAIL tether. Four years ago, global experts in ultrasonic welding considered it impossible to weld together such thin wires.

The produced tether proves that manufacturing full size ESAIL tethers is possible. The theoretically predicted electric sail force will be measured in space during 2013.

An electric solar wind sail, a.k.a electric sail, consists of long, thin (25–50 micron) electrically conductive tethers manufactured from aluminium wires. A full-scale sail can include up to 100 tethers, each 20 kilometres long. In addition, the craft will contain a high-voltage source and an electron gun that creates a positive charge in the tethers. The electric field of the charged tethers will extend approximately 100 metres into the surrounding solar wind plasma. Charged particles from the solar wind crash into this field, creating an interaction that transfers momentum from the solar wind to the spacecraft. Compared with other methods, such as ion engines, the electric sail produces a large amount of propulsion considering its mass and power requirement. Since the sail consumes no propellant, it has in principle an unlimited operating time.

The electric sail is raising a lot of interest in space circles, but until now it has been unclear whether its most important parts, i.e. the long, thin metal tethers, can be produced.

The team at the University of Helsinki is apparently the first one in the world to use ultrasonic welding to join wires together into a tether, says the team leader, Professor Edward Hæggström from the Department of Physics.

A single metal wire is not suitable as an ESAIL tether, as micrometeoroids present everywhere in space would soon cut it. Therefore the tether must be manufactured from several wires joined together every centimetre [Image 1]. In this way, micrometeoroids can cut individual wires without breaking the entire tether.

The tether factory has so far produced ultrasonic welds for one kilometre of aluminium tether

The Electronics Research Laboratory team started studying the production problem four years ago. At the time, the view of international experts in ultrasonic welding was that joining thin wires together was not possible.

However, the one-kilometre-long tether produced now, featuring 90,000 ultrasonic welds, shows that the method works and that producing long electric sail tethers is possible.

The wire is produced with a fully automated tether factory, a fine mechanical device under computer control, developed and constructed by the team itself. [Image 2]. The tether factory at the Kumpula Science Campus in Helsinki, Finland, was integrated into a modified commercial ultrasonic welding device. Ultrasonic welding is widely in the electronics industry, but normally it is used for joining a wire to a base.

We have a challenging task, as keeping thin wires repeatedly in the precisely correct position is hard, says Timo Rauhala who works in the laboratory.

Approximately three metres of tether is currently produced per hour. Its quality is verified optically with a real-time measurement that inspects the connection of every individual joint. In the future, the production speed is to be raised and the weld quality will be assured during the production process
.
The products of the tether factory will soon see action in space. The first opportunity will be the ESTCube-1 satellite, an Estonian small satellite to be launched in March 2013. ESTCube-1 will deploy a 15-metre long tether in space and measure the ESAIL force it is subjected to. This is ground-breaking as, so far, the theoretically predicted electric sail force has not yet been experimentally measured.

Next in turn will be the Aalto-1 small satellite from the Aalto University, to be launched in 2014, which will deploy a 100-metre long tether.

The deployed tethers are kept straight in space by the centrifugal force, the magnitude of which is five grams in a full-scale electric sail. The wire-to-wire welds of the ESAIL tether produced at the University of Helsinki will tolerate a pull of 10 grams.

More information: www.electric-sailing.fi/

Provided by University of Helsinki

"Space sailing soon: A one-kilometer-long electric sail tether produced." January 8th, 2013. http://phys.org/news/2013-01-space-one- ... ether.html
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Starship troupers
http://www.economist.com/news/science-a ... -not-deter

If starships are ever built, it will be in the far future. But that does not deter the intrepid band of scientists who are thinking about how to do it
Oct 26th 2013 |From the print edition

SPACE, as Douglas Adams pointed out in “The Hitchhiker’s Guide to the Galaxy”, is big. Really big. It is so big, in fact, that even science fiction struggles to make sense of it. Most sci-fi waves away the problem of the colossal distances between stars by appealing to magic, in the form of some kind of faster-than-light hyperdrive, hoping readers will forgive the nonsense in favour of enjoying a good story.

But there are scientists, engineers and science-fiction writers out there who like a challenge. On October 22nd a small but dedicated audience gathered at the Royal Astronomical Society (RAS) in London to hear some of them discuss the latest ideas about how interstellar travel might be made to work in the real world. The symposium was a follow-up to a larger shindig held earlier this year in San Diego.

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Starship research is enjoying something of a boom. “A few years ago, there was only one organisation in the world working on interstellar travel,” Jim Benford, a microwave physicist and former fusion researcher, told the conference. “Now there are five.” The following day many of the speakers at the event would visit the British Interplanetary Society (BIS, the venerable organisation of which Dr Benford spoke) to discuss design details for a starship named Icarus.

Starship research has always been a small field, full of iconoclasts and dreamers fitting the activity around their “proper” jobs. Serious work in the field dates back to 1968, when Freeman Dyson, an independent-minded physicist, investigated the possibilities offered by rockets powered by a series of nuclear explosions. Then, in the 1970s, the BIS designed Daedalus, an unmanned vessel that would use a fusion rocket to attain 12% of the speed of light, allowing it to reach Barnard’s Star, six light-years away, in 50 years. That target, though not the nearest star to the sun, was the nearest then suspected of having at least one planet.

How final a frontier?
After Daedalus, interest flagged. Lately, though, several developments have given the field a shot in the arm.

The internet has made it easier for like-minded dreamers to get in touch. Astronomers have discovered thousands of alien planets (including, possibly, one around Alpha Centauri B, which at 4.4 light-years away is part of the star system that actually is closest to the sun), and this exoplanet boom has caught the public’s imagination, as well as giving starship researchers a list of destinations. The rise of the private space industry, which aims to slash the cost of getting into orbit, brings hope that the sort of orbital infrastructure which would be needed to build a starship might one day be developed. And the involvement of DARPA, an arm of the American defence department, which is sponsoring a long-term project to develop the sorts of technology a starship might require, has brought money and attention.

The chief problem, as Adams noted, is distance. During the cold war America spent several years and much treasure (peaking in 1966 at 4.4% of government spending) to send two dozen astronauts to the Moon and back. But on astronomical scales, a trip to the Moon is nothing. If Earth—which is 12,742km, or 7,918 miles, across—were shrunk to the size of a sand grain and placed on the desk of The Economist’s science correspondent, the Moon would be a smaller sand grain about 3cm away. The sun would be a larger ball nearly 12 metres down the hall. And Alpha Centauri B would be around 3,200km distant, somewhere near Volgograd, in Russia.

Chemical rockets simply cannot generate enough energy to cross such distances in any sort of useful time. Voyager 1, a space probe launched in 1977 to study the outer solar system, has travelled farther from Earth than any other object ever built. A combination of chemical rocketry and gravitational kicks from the solar system’s planets have boosted its velocity to 17km a second. At that speed, it would (were it pointing in the right direction) take more than 75,000 years to reach Alpha Centauri.

Nuclear power can bring those numbers down. Dr Dyson’s bomb-propelled vessel would take about 130 years to make the trip, although with no ability to slow down at the other end (which more than doubles the energy needed) it would zip through the alien solar system in a matter of days. Daedalus, though quicker, would also zoom right past its target, collecting what data it could along the way. Icarus, its spiritual successor, would be able at least to slow down. Only Project Longshot, run by NASA and the American navy, envisages actually stopping on arrival and going into orbit around the star to be studied.

But nuclear rockets have problems of their own. For one thing, they tend to be big. Daedalus would weigh 54,000 tonnes, partly because it would have to carry all its fuel with it. That fuel itself has mass, and therefore requires yet more fuel to accelerate it, a problem which quickly spirals out of control. And the fuel in question, an isotope of helium called 3He, is not easy to get hold of. The Daedalus team assumed it could be mined from the atmosphere of Jupiter, by humans who had already spread through the solar system.

A different approach, pioneered by the late Robert Forward, was championed by Dr Benford and his brother Gregory, who, like Forward was, is both a physicist and a science-fiction author. The idea is to leave the troublesome fuel behind. Their ships would be equipped with sails. Instead of filling them with wind, an orbiting transmitter would fill them with energy in the form of lasers or microwave beams, giving them a ferocious push to a significant fraction of the speed of light which would be followed (with luck) by an uneventful cruise to wherever they were going.

Without fuel, the ships could be small, and therefore easy to accelerate. They might even be able to stop at their destinations by employing the solar wind of the target star to slow themselves down, using a second, so-called magnetic sail. The basics of the technology already exist: microwave sails have flown in laboratories. And the transmitter could be reused, which would make such ships cheaper than one-shot nuclear rockets.

Because it’s there
“Cheaper”, though, is a relative term. Jim Benford reckons that even a small, slow probe designed to explore space just outside the solar system, rather than flying all the way to another star, would require as much electrical power as a small country—beamed, presumably, from satellites orbiting Earth. A true interstellar machine moving at a tenth of the speed of light would consume more juice than the entirety of present-day civilisation. The huge distances involved mean that everything about starships is big. Cost estimates, to the extent they mean anything at all, come in multiple trillions of dollars.

That illustrates another question about starships, beyond whether they are possible. Fifty years of engineering studies have yet to turn up an obvious technical reason why an unmanned starship could not be built (crewed ships might be doable too, although they throw up a host of extra problems). But they have not answered the question of why anyone would want to go to all the trouble of building one.

Ian Crawford, an astronomer at Birkbeck College, London, pointed out that sending a robotic probe to another star would be much better, scientifically, than studying it through telescopes. He even presented a checklist of the instruments such a mission should carry, and of the questions—in stellar physics, planetary science and general astronomy—it could be designed to answer. But for many of those attending such conferences, “because we can” would be reason enough to try.

Several speakers at the RAS agreed that a starship would not be feasible until such time as human beings had spread through most of Earth’s solar system, and possessed an economy able to command the resources of more than one planet. Whether that day will arrive is an open question. Gregory Benford said that Thomas Jefferson, America’s third president, guessed it might take a thousand years for the American frontier to advance to the Pacific Ocean. Humans are bad at prediction, Dr Benford argued, and often things thought on the edge of possibility happen faster than anyone would have believed.

Of course, the past is not necessarily any guide to the future, and the magnitude of the problems involved in space exploration dwarf any earthly analogy. Gregory Benford may be wrong. But he and his fellow starship designers are, by necessity, an optimistic bunch.
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Obtaining the exotic fuels needed for interstellar flight is a major challenge – here a scheme is shown where a spacecraft in low orbit around Jupiter lowers an extremely long tube into the atmosphere, sucking up and processing gases.

This is nonsense!

What are you going to 'suck' it with? A pump? But the spacecraft is already in vacuum!

So why doen't the vacuum of space 'suck' all of Jupiter's atmosphere away?
Because the massive gravity of the planet holds it in place. Jupiter's atmosphere is already as high as it can get under vacuum.

On Earth, we can suck water up with a pump, but only if the column of water is less than about 30 feet high. Any higher, and the water vapourises, 'breaking' the vacuum.

To pump water higher than 30' it's best to use a pressure pump at the base of the column, pushing the water upwards. This presumably would work for Jupiter's atmosphere too, but the energy requirements might be exhorbitant.

And if the orbiter's speed is higher than that of the surface of the atmosphere, as it probably would be, there'd be drag on the pipe which would probably pull the orbiter out of the sky! :shock:

An idea that needs more work! ;)
 
The pipe would also have to be made of unobtainium.
 
Unobtainium! I believe the largest source of that is the MacGuffin Mine in Badidillybong, Odaidaho.
 
I missed this earlier- the problem of 'sucking' material out of Jupiter's atmosphere is a tricky one, but it doesn't seem to be impossible. Of course you couldn't do it with a vacuum cleaner hose, as that article seems to imply, but I suspect that this is journalistic oversimplification - there are various ways and means to extract material from the gas giants.

First you need an atmosphere scoop, to concentrate the very thin outer layers of the gas giant. This could be a relatively simple funnel, so that the atmosphere is concentrated into a somewhat denser state.
Here's an image of one concept -
http://commons.wikimedia.org/wiki/File: ... oncept.png

The drag created by the scoop's large cross-section would tend to de-orbit the scoop, so some sort of thrust needs to be applied to the scoopship, until it is in equilibrium. This particular design used solar power to power ion drive motors; this would be quite a weak propulsion system, since solar energy is quite weak near Jupiter.

Other methods of obtaining power for the scoopship include fusion (you are collecting fusable material after all, but this would probably require some sort of on-board fuel processing which would be a weight penalty) or magnetic field extraction (using an electrodynamic tether to extract electricity direct from Jupiter's massive magnetic field).

The tether solution might be the one that this article is attempting to describe - a scoop lowered on a tether would collect energy from the field as it orbits, providing enough energy to prevent the ship from entering the atmosphere while also powering the elevator that lifts the compressed gas along the tether to the collection point at the counterweight end.

I suspect that the most important consideration would be escape velocity. The escape velocity of Jupiter is very, very high- this might make extraction from Saturn, Neptune or Uranus more attractive. Uranus has the lowest escape velocity of any of these worlds, so might be the most economically valuable planet in the Solar System, in the long run.
 
Scooping gas from Uranus would be easier, I believe.
 
The late Paul Birch of the BIS had the idea that the best place to mine would be the Sun itself; it has a massive atmosphere, and emits plenty of energy that could be used for the extraction. Of course the scoopship would need to withstand very high temperatures, and would need to be made of very high melting point materials like diamond or tungsten.

Once extracted the compressed gases could be propelled to the point-of-use by solar powered spacecraft.
 
Mythopoeika said:
Scooping gas from Uranus would be easier, I believe.
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The escape velocity is a crucial factor in operations like this, as I'm sure you'll appreciate. :D
 
eburacum said:
Mythopoeika said:
Scooping gas from Uranus would be easier, I believe.
Click to expand...
The escape velocity is a crucial factor in operations like this, as I'm sure you'll appreciate. :D
Click to expand...

And of course, you should always take into account the size of aperture involved. ;)
 
Mythopoeika said:
Scooping gas from Uranus would be easier, I believe.
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You should go and sit on the naughty step for that!
 
Researchers at Nasa's Eagleworks Laboratories say that they are still discovering signals of thrust which cannot be explained in their latest tests of the highly controversial electromagnetic space propulsion technology EmDrive.

The EmDrive is the invention of British scientist Roger Shawyer, who proposed in 1999 that based on the theory of special relativity, electricity converted into microwaves and fired within a closed cone-shaped cavity causes the microwave particles to exert more force on the flat surface at the large end of the cone (i.e. there is less combined particle momentum at the narrow end due to a reduction in group particle velocity), thereby generating thrust.

His critics say that according to the law of conservation of momentum, his theory cannot work as in order for a thruster to gain momentum in one direction, a propellant must be expelled in the opposite direction, and the EmDrive is a closed system. However, Shawyer claims that following fundamental physics involving the theory of special relativity, the EmDrive does in fact preserve the law of conservation of momentum and energy.

According to Eagleworks engineer Paul March, who explained the lab's findings on the Nasa Spaceflight forum on 31 October, the researchers built a second generation version of the EmDrive and took steps to reduce and mitigate any possible magnetic or thermal interference, in order to try to discover just where the unexplained, anomalous thrust signals were coming from.

http://www.ibtimes.co.uk/emdrive-fu...ints-breakthrough-interstellar-flight-1527184
 
Let us not forget that we already have a craft in instellar space - according to Wiki,

"In September 2013, NASA announced that Voyager 1 had crossed the heliopause on August 25, 2012, making it the first spacecraft to enter interstellar space.
https://en.wikipedia.org/wiki/Voyager_program

Voyager 2 is about there too, and other deep space probes like Pioneers 10 and 11, and New Horizons, are getting there.
 
I worry about the rocks. The further one travels, the more rocks you are going to 'encounter', big and small. Anything for serious and reliable interstellar (and even solar system) travel will need tough multi-compartmentalized ships with strictly enforced protocols on how many of the multi-person crew can be in one compartment at one time or adjacent compartments. You might even want to travel a pair of said ships on a long journey.

Then there's the armored hull, the repairs, the redundant systems etc...never mind getting it to go fast.

For me, getting into orbit quickly, reliably and cheaply is the first major problem to solve. Once this can be done , suitable vehicles can be assembled in orbit. So some kind of modular constructions method might be handy as well.

"Mars? You'll need two command pods, three living pods, two engine pods and a couple of green house units... "
 
That's why the best spaceship would be in a hollowed out asteroid.
Also, you'd need some kind of huge magnetic shield out in front of the spaceship, to divert rocks away.
 
When you’re travelling at one-fifth the speed of light, even a small collision can hurt. Now we know exactly how much. A team working on a project to send tiny spacecraft to the stars have calculated the damage that hitting just a speck of dust could do.

Breakthrough Starshot is an ambitious plan to launch probes weighing little more than a few grams at interstellar speeds using lasers. The goal is to reach the Alpha Centauri star system in just 20 years, and hopefully send back pictures of any planets that might be lurking there. Unconfirmed reports from German newspaper Der Spiegel suggest the discovery of one such world around the star Proxima Centauri is due to be announced later this month.

When billionaire Yuri Milner announced the Breakthrough Starshot project earlier this year, he said a team of scientific advisers had identified around 20 challenges that would need to be tackled for a successful mission, and stumped up $100 million to fund this research. The full mission will likely cost many billions.

Now Avi Loeb at Harvard University, who heads Milner’s scientific team, has completed the first of these studies, looking at the effects of collisions with the interstellar medium of dust and gas. “We did a thorough analysis, taking all the relevant physics into consideration,” he says. “We didn’t see any showstoppers.”

Little ping, massive energy
Normally, a speck of dust would bounce harmlessly off a spacecraft, although slightly larger micrometeoroids are known to cause trouble for telescopes and the International Space Station. But Breakthrough Starshot wants to send their probes travelling at a fifth of the speed of light, meaning the kinetic energy released by even a tiny ping will be massive. ...

https://www.newscientist.com/articl...id=SOC|NSNS|2016-Echobox#link_time=1472040798
 
I think it is possible. Elon Musk is doing awesome things with rocketry. And it is crucial we find other habitable planets or terra-form our closest planetary neighbors. I'm personally holding out hope for a moon base for my grandkids.
 
Xanatic* said:
The first peer-reviewed paper on the EM-drive has been published by NASA. So far it's looking good.

http://arc.aiaa.org/doi/10.2514/1.B36120
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The thrust from these test objects is tiny, if it exists at all; so far all the results have been within the range for experimental errors. You'd need a huge powerplant to get the acceleration a tiny rocket could give. I'm not particularly hopeful that this drive would get us to the Moon, let alone the stars.
 
eburacum said:
The thrust from these test objects is tiny, if it exists at all; so far all the results have been within the range for experimental errors. You'd need a huge powerplant to get the acceleration a tiny rocket could give. I'm not particularly hopeful that this drive would get us to the Moon, let alone the stars.
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Like I said before, best to stick one in a tiny micro cube satellite and see if it moves consistently in one direction - experimental error becomes irrelevant if they actually move in space. You could even ship a couple to the ISS and do some experiments. If they actually move constantly in the right direction, EM works. If they don't, well, then it doesn't. Job'd be done then one way or the other.
 
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