Interstellar Travel

[Asteroid1]

Fusion Technology is the one way we should be able to interstellar travel. Fact or Fiction?!?

[Craig20264]

Pinched From Wiki

Interstellar space travel is manned or unmanned travel between stars. The concept of interstellar travel in starships is a staple of science fiction. Interstellar travel is conceptually much more difficult than interplanetary travel. Intergalactic travel, or travel between different galaxies, is thought to be even more difficult.

Many scientific papers have been published about related concepts. Given sufficient travel time and engineering work, both unmanned and generational interstellar travel seem possible, though both present considerable technological and economic challenges unlikely to be met in the near future, particularly for manned probes. NASA, ESA and other space agencies have been engaging in research into these topics for several years, and have accumulated a number of theoretical approaches.

[Capricorn]

Fusion Technology is the one way we should be able to interstellar travel.

Seem to recall the idea was based on creating a "small" fusion bang at the end of the ship that would push the ship forward.

One idea was to use lasers to compress the material, cause the small bang, get the thrust.

Unless you collected interstellar gas, hydrogen, you would have to carry the full fuel payload. Then you are I suspect into the SF concept of a Busard Ramjet.

This has some relevance but is not the one I was thinking of. Whatever the one I am thinking of had more then one design.

Project Daedalus: A Plan for an Interstellar Mission : Discovery News

By the way check out the dates for these concepts, 1970's I think.

They are not new by a LONG way.

[rfdesigner]

I would imagine the propulsion system is the least of our worries.

Let's say we want to get to Alpha Centuri, 4 light years away.

If we accelerate at 0.1 g until we get half way there, then turn the ship round and decelerate at 0.1g until we arrive at the star it'll take 13 years for a one way trip... I used 0.1g as that produces a maximum velocity of 2*10^8 m/s or 0.66 times the speed of light.. i.e. theoretically possible. I don't know if a super ion drive would ever be capable of delivering this level of thrust, certainly achieving this at relevatistic speeds would be hugely difficult and probably inefficient.

I would argue that we need to work out how to survive in space for that long before we can concider such travel, at the moment apart from the apollo missions, no one has been out of earth orbit, where we've had substantial radiation protection. How do we protect people in interstellar space?.. can we produce suitable fields that can do the job?.. can we produce steerable shields (current technology) but for an entire ship?

The problem with space is that it's full of.. well.. space.

As THHGTTG put it.

You may think it's a long way down to the chemist's, but that's NOTHING compared to space.

Derek

[pete_l]

Fusion Technology is the one way we should be able to interstellar travel. Fact or Fiction?!?

Fiction.

You can't get a fast enough thrust from a fusion motor (or any sort of reaction drive, including ion drives) to attain a practical velocity. The distances involved are simply too great to allow for journeys at the sort of velocity you could reach.

[661-pete]

Then you are I suspect into the SF concept of a Busard Ramjet.

Ah yes. One of the two means of getting about in Known Space (Larry Niven's SF genre) - the other being hyperspace.

The best-known of his stories featuring a voyage by Bussard ramjet is A World Out Of Time (which I highly recommend), in which the protagonist travels from Earth right to the centre of the Milky Way and back again.

Sadly, it doesn't work in Real Life^TM. Practical calculations have demonstrated that the drag on such a craft would exceed the thrust, and it'd probably get - precisely - nowhere...

[Reggie]

I thought the biggest issue would be what would happen to our bodies at those kinds of speeds and of course the stresses it would put on the ships materials? It might never be possible for us to reach other stars (in a single lifetime) but it's possible that we can send data between star systems, which might not be a bad tradeoff if we find anyone to talk to.

[JulianO]

There are some interesting proposals around. I'd heard of project Orion, but not of project Longshot which could get to the nearest star in 100 years or so (unmanned).

[661-pete]

I thought the biggest issue would be what would happen to our bodies at those kinds of speeds and of course the stresses it would put on the ships materials? It might never be possible for us to reach other stars (in a single lifetime) but it's possible that we can send data between star systems, which might not be a bad tradeoff if we find anyone to talk to.

Speed wouldn't be any problem at all - unless the bombardment of your spacecraft by - what would appear to you as - high-energy hydrogen atoms which make up most of the interstellar medium, could lead to a problem. Speed is relative: you would still feel yourself to be at rest: it would be the nearby stars that seem to be rushing past you at high velocity.

However, high acceleration would certainly be felt - as would long periods of no acceleration: i.e. weightlessness. Most of the (realistic) proposals for interstellar travel involving accelerating at 1G for half the journey, then decelerating at 1G for the other half. So - assuming your ship maintained its attitude against the thrust - it would feel just like being on Earth...

[angusb1]

If you use an unmanned craft much higher sustained acceleration rates than 1G are attainable. You also don't need to worry about radiation and the crew going mad to the same degree (anyone seen that one where the ship's computer goes mad?).

[pete_l]

If you use an unmanned craft much higher sustained acceleration rates than 1G are attainable. You also don't need to worry about radiation and the crew going mad to the same degree (anyone seen that one where the ship's computer goes mad?).

Sadly, no.

You can't produce constant acceleration indefinitely. If the Fusion technology the OP wants to use powers a reaction drive, then it's governed by the Rocket Equation. That places a fundamental limit on the ultimate velocity. What that limit is will depend on the velocity of the exhaust (even with an ion drive it's < 100,000 m/sec) and the proportion of the rocket that is fuel.

So for an extremely advanced ion drive - far better than we can make today - with an exhaust velocity of 100km/sec and a rocket that is 99% fuel, your final velocity will never be more than 100 * ln(100) = 460km/sec compared with lightspeed of 300,000 km/sec. It'll still take > 2,500 years to get to the nearest star

[661-pete]

If you use an unmanned craft much higher sustained acceleration rates than 1G are attainable. You also don't need to worry about radiation and the crew going mad to the same degree

Sorry: I meant to say manned interstellar flight...

(anyone seen that one where the ship's computer goes mad?).

[HAL]I'm sorry Dave, I'm afraid I haven't seen that movie....[/HAL]

[661-pete]

Sadly, no.

You can't produce constant acceleration indefinitely. If the Fusion technology the OP wants to use powers a reaction drive, then it's governed by the Rocket Equation. That places a fundamental limit on the ultimate velocity. What that limit is will depend on the velocity of the exhaust (even with an ion drive it's < 100,000 m/sec) and the proportion of the rocket that is fuel.

So for an extremely advanced ion drive - far better than we can make today - with an exhaust velocity of 100km/sec and a rocket that is 99% fuel, your final velocity will never be more than 100 * ln(100) = 460km/sec compared with lightspeed of 300,000 km/sec. It'll still take > 2,500 years to get to the nearest star

What about a rocket drive with a light-speed exhaust? I.e. total conversion of mass-to-energy, matter-antimatter annihilations producing a beam of photons.

Of course we would need a Scotty (and an ample supply of di-lithium crystals) to get the thing to work...

[Reggie]

Speed wouldn't be any problem at all - unless the bombardment of your spacecraft by - what would appear to you as - high-energy hydrogen atoms which make up most of the interstellar medium, could lead to a problem. Speed is relative: you would still feel yourself to be at rest: it would be the nearby stars that seem to be rushing past you at high velocity.

However, high acceleration would certainly be felt - as would long periods of no acceleration: i.e. weightlessness. Most of the (realistic) proposals for interstellar travel involving accelerating at 1G for half the journey, then decelerating at 1G for the other half. So - assuming your ship maintained its attitude against the thrust - it would feel just like being on Earth...

thanks pete, that's the human body dealt with, now how about the spacecraft, I know we have materials that are capable of withstanding high heats getting in an out of our atmosphere, how do those materials stand up at high speeds for sustained journeys, I know our spacecraft can make it to the edge of the solar system without dying but we're talking about much larger distances aren't we?

[JulianO]

In one of Arthur C. Clarkes novels in which he has interstellar travel, they have a huge construction made of blocks of ice on the front of the vehicle to act as an absorber of stray particles as they shoot through space. The Songs of Distant Earth I think its called.

[George Jones]

Most of the (realistic) proposals for interstellar travel involving accelerating at 1G for half the journey, then decelerating at 1G for the other half. So - assuming your ship maintained its attitude against the thrust - it would feel just like being on Earth...

And, I think, this would take about 3.5 years to get to Alpha Centauri.

[Rattler]

Of course its possible...have you not seen Star Trek?

Joking aside, a lot of what's been mentioned here I dont fully understand but it's fascinating.

[661-pete]

thanks pete, that's the human body dealt with, now how about the spacecraft, I know we have materials that are capable of withstanding high heats getting in an out of our atmosphere, how do those materials stand up at high speeds for sustained journeys, I know our spacecraft can make it to the edge of the solar system without dying but we're talking about much larger distances aren't we?

Remember the spacecraft is travelling entirely through vacuum - or at least near-vacuum. So, if we discount the very tenuous interstellar hydrogen, there is nothing for it to encounter friction against, hence nothing for it to withstand.

In a perfect vacuum a spacecraft could be travelling at any speed you like, relative to any other object, up to just below the speed of light, and not 'feel' anything.

Looking at Wikipedia: it pointed me to quite an interesting article here which seems to sort out a lot of the maths. It appears that, given a pure photon drive (a big 'if'!) and accelerating/decelerating at 1G, our intrepid traveller could get to Alpha Centauri, and land on a planet there (if there are any) if his rocket carries fuel massing 38 times his payload. E.g. if he can keep his hull, drive and life support system down to 1 tonne, he's talking 38 tonnes of fuel - half of which would have to be antimatter. This is less than I thought it would be, but remember: the concept of the photon drive is still very dubious.

And remember, of course, he'd have to build a similar rocket out there to get back...

Time for all the clever guys out there to get inventing!

[pete_l]

Remember the spacecraft is travelling entirely through vacuum - or at least near-vacuum. So, if we discount the very tenuous interstellar hydrogen, there is nothing for it to encounter friction against, hence nothing for it to withstand.

In a perfect vacuum a spacecraft could be travelling at any speed you like, relative to any other object, up to just below the speed of light, and not 'feel' anything.

Looking at Wikipedia: it pointed me to quite an interesting article here which seems to sort out a lot of the maths. It appears that, given a pure photon drive (a big 'if'!) and accelerating/decelerating at 1G, our intrepid traveller could get to Alpha Centauri, and land on a planet there (if there are any) if his rocket carries fuel massing 38 times his payload. E.g. if he can keep his hull, drive and life support system down to 1 tonne, he's talking 38 tonnes of fuel - half of which would have to be antimatter. This is less than I thought it would be, but remember: the concept of the photon drive is still very dubious.

And remember, of course, he'd have to build a similar rocket out there to get back...

Time for all the clever guys out there to get inventing!

Well, there is one thing the rocket would have to withstand: the intertial force of 38 tonnes of fuel and 1 tonne of capsule being accelerated at 1G (and, after crossover, the remaining 20 tonnes being decelerated at 1G).

And space isn't really empty. There's fast moving subatomic particles that makes up cosmic rays - lots and lots of protons, and dust (and maybe even dark matter).

[Dr. Phibes]

At any sort of velocity, the microscopic particles in space would surely turn your multi-billion pound vessel into a very cheap collander?

[Superewza]

Ah yes. One of the two means of getting about in Known Space (Larry Niven's SF genre) - the other being hyperspace.

The best-known of his stories featuring a voyage by Bussard ramjet is A World Out Of Time (which I highly recommend), in which the protagonist travels from Earth right to the centre of the Milky Way and back again.

Sadly, it doesn't work in Real Life^TM. Practical calculations have demonstrated that the drag on such a craft would exceed the thrust, and it'd probably get - precisely - nowhere...

And what are these calculations based on? A ship where the hydrogen is attracted using a giant magnetic field? What if it used some form of peristalsis, movement of the field to direct the propellant (fuel?) to where it needs to be?

[Space Bat]

Hmmmmm

Its not about going fast its about manipulating time

[phat tony]

hi, i am a new member and space travel is something i love to talk about so i came here.

i am a huge fan of most of the suggestions above.

one said that if space was a total vacuum then ships could travel at unlimited speeds.

at this moment in time we can create a vacuum but only inside of a container of some sort. i believe that if we could create a vacuum without that container, and if we done that infront of or around a craft or ship then we would have that total vacuum mentioned before. so a question that could need an answer is how to create that vacuum without a container?.

[phat tony]

hi, me again. i am not a highly educated man but i am always in search of knowledge and answers.

after reading all the above comments i am left with a million questions and i will ask them over time in that search of knowledge.

why are we in such a hurry??, so many of the comments above are asking how we can go faster and only one mentioned how we can go safer. i believe that speed is only important if we want to get there and back in our life time but as we all know we will not be the people doing that journey as we are not astronauts or rich enough, some info would be added to what we know by the journey being done. if we made space travel safer and the lower income people came together then a space civilization would be a better option and ion travel would be safer and cheaper but also fast enough, so why are we in such a hurry??.

[JulianO]

Depends what you mean by fast enough. Do you want to reach the destination in your life time is essentially the issue.