Can We Achieve .99c for Interstellar Travel?

[cjackson]

Is it possible to build a vehicle that can accelerate to .99 C?

How would we go about doing something like this?

If at all possible, how many centuries or millennia is it before this can be accomplished?

Could a Bussard scramjet do it?

How large would a laser/maser/gaser have to be to get the craft up to such speed?

How long would it take from the crew's perspective to cross the galaxy?

How big would the craft be? I imagine a lot of fuel would be required even if you could gather propellant along the way - Bussard scramjet. What kind of fuel would be needed?

Would such a vessel help establish a galactic civilization? Or would time dilation make implausible?

What would it look like?

Are any sort of warp drives completely impossible? If so, which of the following would best for interstellar travel: beamed propulsion, matter/antimatter reaction, Bussard scramjet, or something else?

 

[Ryan_m_b]

Is it possible to build a vehicle that can accelerate to .99 C?

Theoretically yes.

How would we go about doing something like this?

No time soon, it would require fantastic advances in technology that don't look to be anywhere on the drawing board.

If at all possible, how many centuries or millennia is it before this can be accomplished?

Same answer as above.

Could a Bussard scramjet do it?

I take it you mean "ramjet" and no, http://en.wikipedia.org/wiki/Bussard_ramjet#Discussions_of_feasibility".

How large would a laser/maser/gaser have to be to get the craft up to such speed?

http://en.wikipedia.org/wiki/Beam-powered_propulsion" .

How long would it take from the crew's perspective to cross the galaxy?

At .99c time dilation is 0.07 minutes for every minute for an observer at rest. To cross from Earth to the far side of the galaxy (~70kly) would take 4962.168 years from the perspective of the crew. From one side of the galaxy to the other (~100kly) would take 7088.821 years.

How big would the craft be? I imagine a lot of fuel would be required even if you could gather propellant along the way - Bussard scramjet. What kind of fuel would be needed?

That question can't be answered because it depends on technologies that haven't been invented yet e.g. how much mass do you need to hold the necessary stable ecology, industry and society. As linked above ramjets would not work.

Would such a vessel help establish a galactic civilization? Or would time dilation make implausible?

In addition to such a vessel you would also need to be able to terraform otherwise you're not going to have a civilisation. Whether or not it could work as a civilisation is anyone's guess, see the http://en.wikipedia.org/wiki/Fermi_paradox" for further discussion.

What would it look like?

The ship or civilisation? Either question is as unanswerable as a Neanderthal trying to envision Facebook.

Are any sort of warp drives completely impossible?

On the subject of warp drives http://arxiv.org/PS_cache/gr-qc/pdf/9905/9905084v5.pdf" . The "trick" is to change the warp bubble so that it's exterior radius is microscopic yet the interior radius is large enough to accommodate your vehicle (essentially making a warp bubble that's bigger on the inside than on the out). Apparently this would greatly shrink the amount of energy needed to manageable levels. They don't outline how exactly a shell could be build around a ship in such a fashion nor how the ship could leave.

However neither of these approaches fixes the other problems of a warp bubble such as requiring the construction of an exotic matter shell, superluminal signalling to steer/control the bubble and the huge amount of radiation a warp drive subjects you to. There are some interesting (but technical) objections in http://arxiv.org/PS_cache/gr-qc/pdf/0406/0406083v2.pdf" that apparently show that a warp drive would only be capable of very low velocities as well as highlighting other problems.

In summary unless you have a way of making speculative impossible exotic matter, it's not going to happen (and might not even if you could).

If so, which of the following would best for interstellar travel: beamed propulsion, matter/antimatter reaction, Bussard scramjet, or something else?

None of them. For manned interstellar travel beamed propulsion won't be strong enough, M/Am rockets are far too dangerous (your "vessel" is a weapon so powerful that it could easily annihilate the entire surface of Earth countless times over) and the Bussard ramjet won't work.

 

[CosmicEye]

wow ok a lot of questions about 1 thing. First I think its theoretically possible I guess. If we were to have a ship that ran on our current fuel and managed to build it, it would probably take a thousand years to even get to 99%C and also an almost infinite amount of energy. Space is huge. It would take many generations of people to travel even to the closest stars. If we ever discover a wormhole (or if they even exist), that would be a much better bet. ^ I agree with the warp bubble and have heard stuff about it, but who knows exactly how much faster that would be.

 

[Ryan_m_b]

wow ok a lot of questions about 1 thing. First I think its theoretically possible I guess.

It's theoretically possible but that doesn't mean much. It's theoretically possible to rearrange every star in the galaxy, doesn't mean we'll ever have the knowledge, resources and will to do it.

It would take many generations of people to travel even to the closest stars.

If you want people to survive you also have to be able to build:

• A stable ecology
• An industry capable of building and recycling nearly everything
• A social, legal, political and economical model that allows the society on the ship to survive harmoniously for thousands of years

All of these are extremely http://en.wikipedia.org/wiki/Nontrivial" .

If we ever discover a wormhole (or if they even exist), that would be a much better bet. ^ I agree with the warp bubble and have heard stuff about it, but who knows exactly how much faster that would be.

Wormholes suffer from the same problem as warp drives, they require probably impossible http://en.wikipedia.org/wiki/Exotic_matter" .

 

[skippy1729]

Please don't forget that, as you get close to the speed of light, tiny specks of the interstellar medium will impact your ship with the kinetic energy of 20 megaton bombs.

 

[Algr]

Please don't forget that, as you get close to the speed of light, tiny specks of the interstellar medium will impact your ship with the kinetic energy of 20 megaton bombs.

Doesn't this violate relativity? It seems to imply that certain speeds are the universal norm, and others are inherently fast. I thought the universe was supposed to look the same from any vantage point.

 

[Ryan_m_b]

Doesn't this violate relativity? It seems to imply that certain speeds are the universal norm, and others are inherently fast. I thought the universe was supposed to look the same from any vantage point.

It is. From the perspective of the guy on the ship the speck is traveling at 0.99c, the speck sees the ship doing the same. The energy is the result of the kinetic energy that would be the same regardless of who was traveling at that speed.

However only one of them is experiencing time dilation because one of them has been in an accelerating reference frame and the other in an inertial.

 

[Galron]

If you started out from Earth using an ion drive that slowly increased acceleration given enough time it would reach .99c.

You have to also remember time dilation and length contraction for the ship would mean by the time say it arrived at Proxima Centauri it would of aged differently and moved through a shorter space than it would appear to you as an observer who is relatively stationary on Earth.

 

[Ryan_m_b]

If you started out from Earth using an ion drive that slowly increased acceleration given enough time it would reach .99c.

It wouldn't matter if it increased its acceleration, it just needs to have a constant acceleration but there are problems with this:

A) Supplying it with enough fuel to get to 0.99c - taking a http://en.wikipedia.org/wiki/VASIMR" as the best speculative ion drive with a specific impulse of 30,000 seconds you would need ~1000 parts kg fuel for every 1kg of ship

B) Having enough thrust to reach 0.99c in a reasonable time - taking VASIMR again if we assume a 1 tonne ship with 1000 tonnes of fuel then with a thrust of http://en.wikipedia.org/wiki/Ion_thruster#Comparisons" the ship will be capable of an average acceleration of 1e-6 and would reach 0.99c in roughly a million years.

C) All the other engineering issues of energy, waste heat etc

You have to also remember time dilation and length contraction for the ship would mean by the time say it arrived at Proxima Centauri it would of aged differently and moved through a shorter space than it would appear to you as an observer who is relatively stationary on Earth.

What do you mean move through a shorter space? From all reference frames the ship would have traveled the same distance.

 

[PAllen]

It is. From the perspective of the guy on the ship the speck is traveling at 0.99c, the speck sees the ship doing the same. The energy is the result of the kinetic energy that would be the same regardless of who was traveling at that speed.

However only one of them is experiencing time dilation because one of them has been in an accelerating reference frame and the other in an inertial.

This isn't quite true. Each would perceive time for the other running slow, while the ship is in motion. What is true is that when the ship is co-moving again with typical stars again, it will have aged less, and the rocket and a nearby planetary observer agree on this. A good terminology for this is time dilation (relative) versus differential aging (invariant).

 

[Ryan_m_b]

This isn't quite true. Each would perceive time for the other running slow, while the ship is in motion. What is true is that when the ship is co-moving again with typical stars again, it will have aged less, and the rocket and a nearby planetary observer agree on this.

Yeah I get this, what was wrong with my explanation? (Not criticising, genuinely interested).

 

[PAllen]

Yeah I get this, what was wrong with my explanation? (Not criticising, genuinely interested).

You said: "However only one of them is experiencing time dilation ". That is misleading.

Also, it is, in fact true, that:

- while moving, the ship perceives the distance to a star as much smaller than appeared before they were up to speed (length contraction; which is why they still measure light from the star as moving at c: shorter distance, smaller elapsed time, compared to Earth bound measurement of lightspeed from the star).

- If you introduce a concept of odometer, there is a perfect symmetry between length and time. Time dilation is relative and once to equivalent clocks are comoving, their rates are the same, but their accumulated time reflects their path through spacetime. Similarly, length contraction is relative, but an odometer measuring integral of apparent distance traveled will be remain different and dependent on path through spacetime. The rocket will perceive it never traveled faster than c, and that it traveled 10 light years in one year because its odometer says it really only traveled e.g. .9 light years.

 

[Ryan_m_b]

You said: "However only one of them is experiencing time dilation ". That is misleading.

I see, of course. I should have explained my point more. Thanks.

 

[Algr]

It is. From the perspective of the guy on the ship the speck is traveling at 0.99c, the speck sees the ship doing the same. The energy is the result of the kinetic energy that would be the same regardless of who was traveling at that speed.

However only one of them is experiencing time dilation because one of them has been in an accelerating reference frame and the other in an inertial.

I wasn't talking about the time dilation, but the "20 megaton bombs." At one speed you get hit by them, and at another you don't. This seems to me to point to a "proper speed of the universe"

 

[Ryan_m_b]

I wasn't talking about the time dilation, but the "20 megaton bombs." At one speed you get hit by them, and at another you don't. This seems to me to point to a "proper speed of the universe"

I don't really see why. The energy has nothing to do with time dilation or relativity, it's simply kinetic energy.

 

[PAllen]

I wasn't talking about the time dilation, but the "20 megaton bombs." At one speed you get hit by them, and at another you don't. This seems to me to point to a "proper speed of the universe"

No, ryan_m_b is completely correct. Speck says rocket moving very fast, hits hard; rocket says speck moving very fast, hits hard.

There is, of course, a frame for any region of space such that the total momentum of matter is zero, and one may describe speed in that frame as speed relative to average matter of the region. However, that is completely irrelevant to the principle of relativity.

 

[Algr]

So there are no galaxies headed for Earth at 99% the speed of light? And no particles? It would only be space ships?

 

[PAllen]

So there are no galaxies headed for Earth at 99% the speed of light? And no particles? It would only be space ships?

Most likely, it will be nothing ever.

[Edit: missed the reference to particles. Particles hit Earth every day with .9999999c. They are called cosmic rays. Occasionally, they are so energetic that one proton carries as much KE as a thrown baseball.

If a 1 gram object had the speed of the fastest cosmic rays, it would hit Earth with an energy of about 1 hundred million gigatons of TNT
]

 

[Lucutus]

[Edit: missed the reference to particles. Particles hit Earth every day with .9999999c. They are called cosmic rays. Occasionally, they are so energetic that one proton carries as much KE as a thrown baseball.

If a 1 gram object had the speed of the fastest cosmic rays, it would hit Earth with an energy of about 1 hundred million gigatons of TNT
]

For Q1 and Q2 below, imagine two objects traveling on a perfect head-to-head collision course.

Q1. Is it possible to calculate the energy released if two 1,0 gram objects, each traveling with the speed of the fastest cosmic rays, would hit each other?

Q2. What would happened if two 1 gram objects, one traveling with the speed of .9999999c and the other at 1c, would colide with each other? Is it possible to calculate the released energy in this impact?

Thanks :)

 

[Ryan_m_b]

For Q1 and Q2 below, imagine two objects traveling on a perfect head-to-head collision course.

Q1. Is it possible to calculate the energy released if two 1,0 gram objects, each traveling with the speed of the fastest cosmic rays, would hit each other?

Q2. What would happened if two 1 gram objects, one traveling with the speed of .9999999c and the other at 1c, would colide with each other? Is it possible to calculate the released energy in this impact?

Thanks :)

I'm pretty sure (but not absolutely sure) you could just calculate the energy by each and add it up. So;

1 gram object traveling at 0.9999999c (299792428m/sec) would release 44,937,749,943,067.6 joules of energy or ~45 petajoules. So the collision of two grams would be ~90 petajoules

 

[Lucutus]

I'm pretty sure (but not absolutely sure) you could just calculate the energy by each and add it up. So;

1 gram object traveling at 0.9999999c (299792428m/sec) would release 44,937,749,943,067.6 joules of energy or ~45 petajoules. So the collision of two grams would be ~90 petajoules

I used a joule to kiloton converter on the internet, if this converter is true the combined force would be about 21,48 kilotons.What about Q2? Is it possible to calculate the energy if one of the two one gram objects were traveling at 1c, and the other 1 gram object were traveling at 0,999999c?

And, finally, my Q3 =)
Is it possible to calculate the energy of a collision if both 1 grams objects were traveling at 1c?

I ask these Q2 and Q3 because I have a vaguely memory that I read that calculations states that the energy would be infinitive when reaching 1c. Or is it only the energy needed to accelerate an object two 1c that becomes infinitive?

Best regards
Mattias

 

[Maximilan]

I know that your goal is speed; but what about slow and steady?
What if Helium 3 could be used as a fuel source, and plotting courses to moons with robotic mining missions that would set up robotic mining colonies - no humans. These "colonies" would be the galaxtic "gas stations" for future missions when technology has caught up to speed (pardon the pun) to possibly carry humans :)

 

[Ryan_m_b]

I ask these Q2 and Q3 because I have a vaguely memory that I read that calculations states that the energy would be infinitive when reaching 1c. Or is it only the energy needed to accelerate an object two 1c that becomes infinitive?

Best regards
Mattias

It takes infinite energy to accelerate an object with mass to c.

I know that your goal is speed; but what about slow and steady?
What if Helium 3 could be used as a fuel source, and plotting courses to moons with robotic mining missions that would set up robotic mining colonies - no humans. These "colonies" would be the galaxtic "gas stations" for future missions when technology has caught up to speed (pardon the pun) to possibly carry humans :)

You've done the hard part, coming up with the idea, now just to solve the easy part, the engineering!

That's a little bit of sarcasm there because without overcoming the huge technical hurdles ideas like this are just interesting fantasies.

 

[Maximilan]

You've done the hard part, coming up with the idea, now just to solve the easy part, the engineering!

That's a little bit of sarcasm there because without overcoming the huge technical hurdles ideas like this are just interesting fantasies.

LOL .. yeah, I was trying to blend in so I could ask a Sci-Fi question :)

But nations are seriously considering this in the near future: http://www.explainingthefuture.com/helium3.html

 

[Ryan_m_b]

LOL .. yeah, I was trying to blend in so I could ask a Sci-Fi question :)

But nations are seriously considering this in the near future: http://www.explainingthefuture.com/helium3.html

Lol, first show me working fusion on the ground, then show me a working http://en.wikipedia.org/wiki/Fusion_power#D-3He_fuel_cycle", then show me a nuclear fusion propulsion system. After all of that let's examine the geopolitical, socioeconomic and scientific/technological situation at that point in history and then we can have a meaningful discussion about He3 mining.

I don't mean to sound flippant but discussing the role of He3 mining in future space exploration is not just putting the cart before the horse its putting the cart before the wheel.

 

[Maximilan]

Lol, first show me working fusion on the ground, then show me a working http://en.wikipedia.org/wiki/Fusion_power#D-3He_fuel_cycle", then show me a nuclear fusion propulsion system. After all of that let's examine the geopolitical, socioeconomic and scientific/technological situation at that point in history and then we can have a meaningful discussion about He3 mining.

I don't mean to sound flippant but discussing the role of He3 mining in future space exploration is not just putting the cart before the horse its putting the cart before the wheel.

http://fti.neep.wisc.edu/pdf/wcsar9304-1.pdf

http://www.lpi.usra.edu/decadal/leag/DecadalHelium3.pdf

Prototype Reactor:
"A commercial fusion reactor has never been built, but a prototype called the International Thermonuclear Experimental Reactor (ITER) has just begun construction in Cadarache, France. The plan is to generate the needed 100 million degree plasma by the year 2016, but a power plant that can supply electricity might not come online for another 20 years after that." reported by msnbc.com http://www.msnbc.msn.com/id/2617994...-science/t/how-moon-rocks-could-power-future/

Fusion Propulsion:
"Fusion is the only option that potentially achieves the most important regime for Solar-System travel: exhaust velocities of 105 to 106 m/s at thrust-to-weight ratios of 10-3. Such levels of performance allow both fast human transport and efficient cargo transport. There is no doubt that one of the most difficult problems that a peaceful world will face in the 21st century will be to secure an adequate, safe, clean, and economical source of energy. Existence of lunar helium-3, to be used as fuel for fusion reactors, is well documented; verified from numerous Apollo and Luna mission samples, current analyses indicate that there are at least 1 million tonnes embedded in the lunar surface. The helium-3 would be used as fuel for fusion reactors." Fusion Technology Institute of Wisconsin http://fti.neep.wisc.edu/research/dhe3

Robotic Mining Technology:
http://technology.infomine.com/robomine/

 

[Ryan_m_b]

I should have been clearer, I meant fully mature technology or peer-reviewed research, not mission statements or opinion pieces. I'm well aware of the current state of projects like ITER but that is a far cry from even being proof of principle of what you have described.

Yes He3 is on the moon and yes there are large quantities but without fully realized technology we cannot meaningfully discuss the situation. We cannot examine the economical viability of mining without knowing exactly how much the efforts will cost, what the alternatives will be and what political and social factors will be in play. Looking at what we do know I am sceptical that anyone will make the effort to mine He3 for nuclear fusion fuel, the aforementioned first generation nuclear fusion reactors (based on ITER if it is a success) can be used to breed He3. I doubt we will ever get to the stage where sending vast robotic industries to the moon and other bodies is cheaper than simply having a number of dedicated 1stgen fusion reactors for breeding on Earth.

 

[JeffKoch]

...but a power plant that can supply electricity might not come online for another 20 years after that...

Our fathers and grandfathers said the same thing in the 1940's, but every time we get a little closer we find another very complex unanticipated collective phenomenon that makes it more difficult than we thought. I think our great great grandchildren would agree that fusion almost certainly will not play a significant role in the future of power generation, instead we will refine other, more elegant approaches.

 

[Drakkith]

Our fathers and grandfathers said the same thing in the 1940's, but every time we get a little closer we find another very complex unanticipated collective phenomenon that makes it more difficult than we thought. I think our great great grandchildren would agree that fusion almost certainly will not play a significant role in the future of power generation, instead we will refine other, more elegant approaches.

I disagree. We have made steady progress for the last 60+ years in confinement time and power using multiple confinement methods. Saying that it will never be a source of significant power generation seems to imply that we haven't made any progress. (to me at least) While it might not be a NEAR future approach, I have very little doubt that we will eventually reach power production.

What about Q2? Is it possible to calculate the energy if one of the two one gram objects were traveling at 1c, and the other 1 gram object were traveling at 0,999999c?

And, finally, my Q3 =)
Is it possible to calculate the energy of a collision if both 1 grams objects were traveling at 1c?

I ask these Q2 and Q3 because I have a vaguely memory that I read that calculations states that the energy would be infinitive when reaching 1c. Or is it only the energy needed to accelerate an object two 1c that becomes infinitive?

As has been said, getting to 1c is impossible. No matter how much energy you poured into an object, it would not approach c. However it's momentum would approach huge amounts near 1c.

 

[Maximilan]

Our fathers and grandfathers said the same thing in the 1940's, but every time we get a little closer we find another very complex unanticipated collective phenomenon that makes it more difficult than we thought. I think our great great grandchildren would agree that fusion almost certainly will not play a significant role in the future of power generation, instead we will refine other, more elegant approaches.

WOW! Your grandpa knew about Helium 3 fusion prototypes being built before even Nuclear was on the block? Einstein must have been jealous. PLUS you got a time machine! Dang you da man - let me guess your ancestors were from Nibiru right?