Reaslistically - How far can we travel?

[Roj47]

I am sure I read correctly that China is planning a manned expedition to Mars in the near future.

What I am wondering is - What is the proposed maximum distance a manned module could travel (both to orbit and to land) given our current technology available.

Also what in theory could be accomplished realistically (barring worm holes, finding anti-gravity etc.....).

Anything planned?

Regards

[Mekorig]

Maybe other people, like Waspy, can give you a more detalied info. Has far i know, we can make a ship to make a Mars mission. The problem is the astronauts living in 0-g during a 3 months travel, whith an almost non-existance posibility of rescue in a case or emergency. Has non maned ships, the only limit is time. An example are the voyager probes....

[Startraveler]

There are a lot of factors to consider here. There are psychological questions, there are questions about how to best deflect damaging cosmic rays, etc. I imagine you're talking in terms of chemical propulsion as well but allow me to get a little more speculative than you might have intended by throwing in a small list I put together for another forum of ways we may get around in the future. The focus originally was on how we might start making headway toward interstellar travel but obviously this stuff would also be useful in getting around the solar system.

What we do now

Conventional Chemical Rockets

Obviously we'll either have to move at speeds close to that of light or we'll need to "cheat"--discover warp drive or travel through wormholes, etc. Conventional chemical rockets are limited in that regard because, while they're capable of tremendous thrusts, the speed at which they can eject propellant isn't nearly large enough (such rockets operate on simple Newtonian physics--eject propellant backwards and the rocket will be pushed forward). For example, for a rocket (1/2 or more of the total mass of which is locked up in the propellant--quite a bit will be needed) to reach half the speed of light, it would have to eject its propellant at over 200,000,000 m/s! Sure, we could settle for a lower final velocity so that we wouldn't have to eject our propellant at such enormous speeds but there is a further roadblock: the exhaust velocity of regular chemical rockets is limited to about 5,000 m/s. So those are pretty much out. Unless you have a kind of generational spaceship and you're willing to start the journey so your distant descendants may complete it.

Ion Propulsion

Greater velocities can be reached via the much more efficient ion engine. The basic principle is the same: shoot something out the back, move forward. In this case, a gas (xenon, I think they use) is ionized, accelerated electrically to something like 30,000 m/s and expelled out the back. The accelerations involved are smaller than those of chemical rockets but the velocities ion engines can reach are about ten times what the chem rockets can do. They can operate continuously for long periods of time and so get up to some impressive speeds. The first ion drive craft sent into space was NASA's Deep Space 1, which successfully flew by the asteroid Braille and the Comet Borrelly 6 years ago. An ion engine was also used to get the ESA's SMART-1 to the moon. After a very long, spiralling 13-month journey, it arrived there last year. This method of propulsion may be a good choice for future missions within our solar system but it doesn't look like it's going to get us to other stars any time soon.

Light sails

The idea of light sails is based on the fact that photons have momentum and can exert a force (force is simply a change in momentum). A [big] sail is unfurled and the light from the sun reflecting off it simply pushes it and its payload through space. Not as far out as you might think at first; the very first solar sail was launched last year by the Planetary Society. Unfortunately the rocket failed and we never got to see the sail in action. Anyway, the accelerations aren’t very large but they, like in the ion engines, are continuous and so it adds up over time. It has been proposed that a large, very powerful laser (perhaps one emitting microwaves) could be used to give it a greater push and accelerate it faster. Robert Forward has imagined an unmanned interstellar probe consisting of a sail powered by a maser, which can be accelerated to 20% of the speed of light; the problem is that the proposed lasers consume far too much power. It’s possible these may be used someday to travel between planets and possibly even between stars but if the latter is to become a reality, a way to power the lasers involved must be found. Further reading.

What we'll do in the future

Nuclear Propulsion

The original nuclear propulsion ideas from the ‘60s (like Project Orion) involved actually dropping nuclear bombs out behind the craft and detonating them to accelerate. NASA recently turned back to nuclear propulsion in space a few years ago with its proposed Project Prometheus, perhaps to be used in a Jupiter Icy Moons Orbiter mission (President Bush cut funding for it in the 2006 budget) Prometheus is looking at Nuclear Thermal Propulsion, the use of the tremendous energy released in nuclear fission reactions to heat hydrogen propellant which is then expelled out of the rocket at must greater velocities than can be attained by heating it via regular chemical combustion, and Nuclear Electric Propulsion which uses a nuclear reactor to run ion engines. So this is interesting because it’s realistic. I don’t know the velocities they can [theoretically] get the propellant up to but it's still a long walk to the stars.

Antimatter Propulsion

Matter-antimatter annihilation is the most efficient reaction known— 100% conversion of mass to energy. Secondary charged particles left over (or produced later on) from the reaction would be used as exhaust to push a spacecraft. Alternatively, the reaction could be used to generate heat or electricity to power a variant of one of the propulsion systems already listed (or even a new one) The biggest drawback is that antimatter is difficult to come by and produce; but you wouldn’t need too much. Storage might be a concern but nothing that can’t be handled. Antimatter propulsion is in many ways better than fission or fusion and may very well be a main source of propulsion in the future. Just have to produce it.

Variable Specific Impulse Magnetoplasma Rocket

This propulsion method would include three magnetic cells; a neutral gas (like hydrogen) would be ionized, heated to whatever temperature and density you like via electromagnetic waves, then expelled out the back to provide "modulated" thrust. It has several advantages including: variable specific impulse and thrust at maximum power, high power density, continuous acceleration, high efficiency ion cyclotron resonance heating, the capability for powered mission aborts, and the propulsion system is adaptable to slow, high payload robotic cargo missions as well as fast, lower payload human transfers. Last I heard (which was a while back) VASIMR was having trouble getting funding from NASA and the idea certainly has its critics—not sure what's happening with it now. But the potential seems to be great for this one.

The Bussard Ramjet

Another suggestion is that a ship should scoop up its fuel as it goes; space isn’t completely empty, there are hydrogen atoms scattered here and there. The ramjet would need to be accelerated to a small fraction of the speed of light (I think it’s something like 6%) at which point it begins scooping up those stray hydrogen atoms, feeding them into a fusion reactor, and venting the exhaust out the back (in that respect it resembles the conventional propulsion systems). According to the solution proposed for the February '99 question here, the radius of the scoop should be on the order of 10,000 km to produce a constant 1g acceleration for a 3500-ton vehicle. The scoop is of course not an actual scoop but a magnetic field. The big problems with the idea are the fusion reaction itself and the drag generated by the very particles you’re scooping up (plus the enormous magnetic field you need to generate). Besides, you have to use some other method of propulsion to get yourself up the threshold speed at which the interstellar medium appears dense enough to sustain your nuclear reaction. So this may or may not be practical.

Magnetic Sails

This idea involves a spacecraft generating a magnetic field and utilizing the charged particles in the solar wind similar to the way photons are used in the light sail. The "sail" is in fact simply a magnetic field generated by a superconducting wire and so is much less massive and cumbersome than the actual sail involved in light sailing. In one conception, it begins with an 8-inch magnet generating a small magnetic field; the field expands as plasma is collected from the solar wind and used to generate a successively larger field. Particles from the solar wind hit the "sail" and propel it forward. The drawback: I’m not sure how this could be used for interstellar travel. Further reading from space.com

Now each of the above propulsion methods follows the same basic formula: find a way to accelerate to very large (probably close to the speed of light) velocities and travel in the regular way. Relativistic effects allow you to travel enormous distances because distances shrink if you’re moving fast enough; the downside is that when you return to the earth very large amounts of time will have passed and damn dirty apes may be ruling. Speed is the key. The next ideas are a sharp departure from this formula.

Downright kooky

Transversible Wormholes

Wormholes are shortcuts through spacetime; they may exist naturally, they may not. Most would probably be extremely unstable and short-lived if they do exist. It may someday be possible for us to create artificial wormholes; however, we’d have to actually get where we’re going and drop off a mouth of the wormhole, so the problem of getting there still exists (unless some pre-existing “transit system” already exists—ok, I watched Contact the other night). It just becomes simple to travel back and forth from here to there once you do get there. One of the well-known problems associated with forming a stable wormhole that one could travel through is that it appears some form of exotic negative energy (which you’ll soon notice is a recurring theme with these nutty ideas) is needed to keep it open. Perhaps someday we’ll be able to deal with such things.

Simple intro to wormholes

Warp Drive

In the early ‘90s a physicist named Miguel Alcubierre wrote a paper on developing a kind of warp drive (with those two words right in the title!). The idea is essentially that one could distort spacetime within some volume and (with a ship inside that volume) travel extremely big distances without experiencing the time dilation effects mentioned above. Essentially, space itself expands in front of the “warp bubble” (which is what I’ll be calling that particular volume) and contract behind it, giving it a push from behind and a pull from up ahead. Inside the warp bubble no acceleration is felt, no g-forces (won’t be needing those inertial dampeners just yet) because those inside are locally at rest. Unfortunately no one knows how to produce the distortion in question. More problems with the idea (from this article):

…It violated the strong, dominant, and weak energy conditions of general relativity. The net energy of the warp bubble, as it turned out, was extremely large and negative. For example, a warp bubble 100 meters in radius that might contain a space ship of reasonable size would have a net negative energy that was roughly ten times larger in magnitude than the entire (positive) energy of the visible universe. Another problem was that the walls of the bubble would have to be so thin that they could not be constructed with matter, even "collapsed matter" of nuclear density. It was also found that most of the warp bubble is disconnected from a sizable part of the external negative energy region. Therefore, the surface part of the bubble could not be carried along and would have to be continuously generated externally. The drive could not be self-contained or self-operated.

The article goes on to describe how the work of Chris Van Den Broeck went a long way in showing that maybe the concept wasn’t as hopeless as it seemed at first glance. This idea has always struck me as wonderful: travel across the galaxy and back in a relatively short time with no time dilation. Right out of Star Trek. Even with its problems just the notion itself is amazing.

Another article

Alcubierre’s original paper

Van Den Broek’s

The Krasnikov Tube

This one isn’t so much a propulsion method. Once again I’m going to quote John Cramer (column) because he’s one of the few who takes ideas like this and phrases them in a wonderfully simple way:

Therefore, Krasnikov proposes an alternative: create a space warp behind the space ship as it travels at near lightspeed to some distant star system, and then use the "tube" thus created for the return trip. He suggests a particular "metric", a distortion of space that has an interesting property for the return trip: it gets you back home shortly after you left, no matter how far you go. Perhaps this is best illustrated with an example.

Suppose we have a starship that can travel at speeds that are 0.00005% (5 parts in 10,000,000) less than the speed of light . . .The ship makes a trip to the star system of Deneb. . . approximately 1,630 light-years from Earth. For earth-based observers watching the trip through a telescope, the trip would take essentially 1,630 years. However, because of relativistic time dilation the trip only takes 1.63 years for those aboard the ship.

. . . when the astronauts return from a trip to Deneb, they can expect to find that 3,260 years have passed, everyone they knew is dead, and the world has changed beyond recognition, right? Well, not quite. The Krasnikov Tube that was created in the wake of the spaceship now forms a return pathway within which time "unwinds." Because of the temporal properties of the Krasnikov metric, if the ship travels home at near lightspeed in the space enclosed by this tube, the astronauts can return home just a bit over 3 years after they left.

In effect the Krasnikov Tube is a tunnel through time, connecting the departure time of the ship with the time of its arrival at Deneb. Inside the tube space-time is "flat", i.e., unwarped, but the path limits of light through space-time has been opened out so that it permits superluminal travel in one direction only, e.g., back to the starting point on Earth.

There isn’t much more to say. Krasnikov’s paper

I’m just about out of time so I’ll say once again that this isn’t complete; there are many more fascinating suggestions (I'm sure some are just as out there as the above).

Short of some sort of hibernation chambers, though, I'm not sure human patience can take a conventional chemical trip anywhere but the moon and Mars (not to mention the patience of those on the ground who write the checks).

[Pax Unum]

I am sure I read correctly that China is planning a manned expedition to Mars in the near future.

What I am wondering is - What is the proposed maximum distance a manned module could travel (both to orbit and to land) given our current technology available.

Also what in theory could be accomplished realistically (barring worm holes, finding anti-gravity etc.....).

Anything planned?

Regards

depends what you consider the NEAR future... I haven't heard of anything serious before 2030.

as far as I know, there are not limits as far as distance... the Voyager 1 spacecraft at 8.7 billion miles, is on the verge of slicing into interstellar space, It's the time, Voyager 1 was launched in 1977... the only practical way to reach another solar system, with our current technology, would be to build a colony ship, where the crew raises it's replacements, for several generations.

Ion, Plasma and anti matter drives are being looked into, but who knows when these technologies will be available...

[rice]

well we havent got any astronauts on mars yet...well none that has been reported in nasa.gov or space.com lol...but i think we can make it as far as mars...but the observer satellite/robots i believe can go up to the distance of the kuiper belt until it gets distroyed by the belt by the 800+ objects thats circulating there.

[frogfish]

The biggest drawback is that antimatter is difficult to come by and produce

That's an understatement Its increasingly hard to keep antimatter, and it is very, very expensive to make the most minute amounts...

[Pax Unum]

but the observer satellite/robots i believe can go up to the distance of the kuiper belt until it gets distroyed by the belt by the 800+ objects thats circulating there.

Voyager 1 has already passed through the Kuiper belt...

[Waspie_Dwarf]

It is far more likely to be the US or Russia which reach Mars in the 2030's than China. China has a long way to catch up and is currently averaging only one manned launch every two years.

The answer to the question, like a lot of things, depends on how much your budget is. If you throw enough money at the problem it would be possible to develope nuclear engines by 2030 that would greatly shorten the flight time. If you soend enough you could build a spacecraft which rotates so that artifical gravity is produced. If you really want to spend money then you could do both.

In reality a far more conventional approach is likely for the simple reason that it is cheaper. This will involve round trip times greater than 2 years. There are health issues with flights this long as bones tend to decalcify. Valeriy Poliyakov currently holds the single flight endurance record. He was launched to Mir on board Soyuz TM18 on the 8th January 1995 and returned on board Soyuz TM 20 on 22nd March 1995. His spaceflight lasted 437 days 17 hr 58 min 16 sec (source: Guinness World Records 2006). He does not seem to have suffered any long term health effects. However more research will be needed into long term effects of microgravity.

Other problems that will be encounter are radiation. Apollo astronauts were exposed to deep space radiation for anly a few days. On a Mars trip this exposure will be for months. Also they will almost certainly encounter solar flares so any Mars ship will need a shielded area to protect them from such flares.

There is no real reason why Mars can not be reached with current technology if enough money is spent, but it will be dangerous. Lives are likely to be lost in such an endeavour.

[Roj47]

There are a lot of factors to consider here.

And all the ones you listed and described are explained very nicely. I have moved notification of this thread in my emails to my favourites sectoin to refer back to.

I was very interested to note that Stephen Hawkins is having some input to the wormhole theory. Personally I can not comprehend the idea, so as the majority of people I would expect I place into the realm of sci-fi.

I hope I understand the mathematics behind it, but I do not hold out much hope.

Will keep trying, and watch in awe should it be proven in my lifetime.

many thanks.

It is far more likely to be the US or Russia which reach Mars in the 2030's than China. China has a long way to catch up and is currently averaging only one manned launch every two years.

The answer to the question, like a lot of things, depends on how much your budget is.

He was launched to Mir on board Soyuz TM18 on the 8th January 1995 and returned on board Soyuz TM 20 on 22nd March 1995. His spaceflight lasted 437 days 17 hr 58 min 16 sec (source: Guinness World Records 2006). He does not seem to have suffered any long term health effects. However more research will be needed into long term effects of microgravity.

There is no real reason why Mars can not be reached with current technology if enough money is spent, but it will be dangerous. Lives are likely to be lost in such an endeavour.

As with all things budget does come into it. I would like to consider the unrealistoc world of unlimited funding.

At a guess - Had I the wealth of Bill Gates I would be pushing in any field to understand and learn while I am around.

I may speak out of turn here, and apologies and no offence intended.

I would suggest that USA has more strigent measures in place for loss of life through these missions and as such may hinder their efforts to Mars.

However as the old children's favourite of the tortoise and the hare....

As I mention above I have this thread save in email notification, but wonder if I can add this thread detail into a folder on here..... any ideas Waspie?

Kind regards to everybody, and the amount of information and thoughts to digest.

[poleshift]

If you soend enough you could build a spacecraft which rotates so that artifical gravity is produced.

Rotating sounds good for its reentry. This concept seems applicable to certain airplane.

Robotic mission will cover the problems you mentioned.

[Antoin]

While i am struggling to understand the "string theory" I have noticed now that I am tainted with the idea that when proven the sting formula would solve all time/space/dimensional travel.. or am I understanding it incorrectly?

antoni

[Startraveler]

That's not quite true. String theory at the very least aims to be a unified theory (that is, one that can successfully put general relativity and quantum mechanics together) and perhaps at the very most aims to be a theory of everything, accounting for just about all physics there is to know. But even if it turned out someday to be the latter, that wouldn't automatically make space travel easier. First of all there's no guarantee that there would be all kinds of new astounding tricks in a complete physical theory that could get us around the universe in no time. And even if there were, there's a tremendous gap between what's theoretically possible and what's practically possible. Right now physical theories can tell us how we might do pretty amazing stuff to get around the universe--the problem is that we just can't possibly do it for practical reasons.

But I want to add a further note on string theory itself. Though it seems to have swept the public and a good portion of the scientific community it might finally be dying down. From what I've seen there are a good many misconceptions about string theory floating around, mostly due to its proponents and popularizers. String theory, contrary to popular belief, is not a well-established or near-universally accepted scientific theory; indeed there's a bit of debate as to whether it counts as a scientific theory at all.

Peter Woit is a mathematician at Columbia who happens to be pretty critical of string theory. He has a blog called Not Even Wrong and recently came out with a book of the same name. There's a review of this book by John Horgan, a science journalist, in the August 2006 Prospect. I want to quote a bit of it (but only a little--its a mostly pay article that I'm getting through LexisNexis):

In his 1988 blockbuster A Brief History of Time, Stephen Hawking nominated string theory as the best candidate for a solution to the riddle of the cosmos. Since then, proponents have continued to sing strings' praises in popular books such as Parallel Worlds by Michio Kaku, Warped Passages by Lisa Randall and the monster bestsellers The Elegant Universe and The Fabric of the Cosmos by Brian Greene (who also hosted a television series about string theory). Moreover, string theorists dominate particle physics in terms of publications, grants and tenured faculty positions-even though they have not produced an iota of evidence for the theory. The MacArthur Foundation has awarded nine fellowships for particle physics since 1981, and eight have gone to pluckers. Of the 22 physicists who have received their doctorates since 1981 and gone on to receive tenure at the leading physics universities-Berkeley, Caltech, Harvard, MIT, Princeton and Stanford-20 specialise in strings. The director of the prestigious Institute for Advanced Study and half of its physics faculty are string theorists.

String theory has always had detractors. Richard Feynman liked to say that string theorists don't make predictions, they make excuses, and his fellow Nobel laureate Sheldon Glashow has compared pluckers to medieval theologians debating how many angels can dance on the head of a pin. I have also criticised string theory in my 1996 book The End of Science and elsewhere. But Not Even Wrong by the mathematician and physicist Peter Woit of Columbia University is the first book-length critique of the theory. Woit first sent the book to Cambridge University Press three years ago, but the publisher rejected the manuscript after pro-string referees panned it. Ironically, Woit then found trade publishers-Cape in the UK and Basic Books in the US-who should help him reach a larger audience.

...

First of all, strings, or membranes, or whatever, are very, very small-as small in comparison to a proton as a proton is in comparison to the entire solar system-and probing these scales requires smashing particles together with enormous force. The large hadron collider, which will be the most powerful accelerator in the world when it comes online next year at Cern, the big particle physics laboratory, is 27km in circumference. Scaling up from this technology, physicists would have to build a particle accelerator 1,000 light years in circumference to probe the micro-realm where strings supposedly shimmy and shake. But even if physicists had such an accelerator, Woit asserts, they still could not confirm string theory because it does not make any precise predictions. Or rather, it makes so many predictions that it cannot be falsified.

Some critics call this surfeit of predictions "the Alice's Restaurant problem," a reference to the refrain of the Arlo Guthrie folk song: "You can get everything you want at Alice's restaurant." "Being able to get anything one wants may be desirable in a restaurant, but isn't at all in a physical theory," Woit comments. In other words, far from answering Einstein's question about whether God had any choice in creating the universe, string theory deepens the mystery of why we find ourselves in this particular cosmos."

...

Witten and other pluckers have often argued that string theory is too "beautiful" to be wrong. But as Woit points out, the term "beauty," when applied to scientific theories, usually refers to elegance, simplicity and clarity, and even proponents of string theory concede that it is hideously complex. Witten himself once told me that he initially found string theory to be "opaque." When pressed, some pluckers suggest that the beauty of string theory stems from the sense it evokes of mysterious, hidden depths. String theory is sometimes called M-theory, and Witten has said that the "M" stands not only for "membrane" but also for "magic" and "mystery." In other words, the aesthetic allure of string theory has less to do with simplicity and clarity than with incomprehensibility.

Maybe someday somehow it'll turn out to be correct; I'm certainly not qualified to say otherwise. But string theory's 40th birthday is not far off and despite the various "breakthroughs" through the years it hasn't amounted to much in terms of physical results. By comparison one of the great theoretical works of all time, general relativity, had seen major experimental verifications before its 4th birthday. One could retort that this is an unfair comparison: string theory(ies) is a different kind of theory because we live in a different kind of time (in terms of where physics is today vs where it was in 1916). But if anything that's the disturbing part.

If nothing else I'm sure this'll all make for a fascinating study in the sociology of science someday.

P.S. Apologies that's a bit off topic.

Edited July 31, 2006 by Startraveler