Interstellar Travel

[Exclipse]

Either there are not, or there are very few "others" in the universe, or interstellar travel is very impractical, or a combination of both exists that prevents us from observing the effects of interstellar travel. IE meeting "others" here, or seeing energy releases possibly associated with more practical IT.

So personally I doubt practical IT will happen in the next 100, for me I need to see photos of other planets from orbit around them to consider it to have happened.

[AngelLestat]

Exclipse: if you use my method, then you will not see nothing, it can not be detected, but you can explore all your 15 light years radius with tons of solar sails, and those solar sails can jump to other stars and keep exploring and sending data, all this without invest any fuel or energy, with printed craft that can be super cheaps once you build 4 or 6 of these. The solar sails can act as repeaters to amplify comunication of those which are at distant stars.

[Voyager55]

Seeing as it's very possible that we won't even land humans on Mars this century (If you're severely pessimistic), i'm going to say no unfortunately

[ChrisSpace]

The topic said interstellar travel in this century, it does not said that you need to reach a star before this century, just start the travel in a practical way.

Okay, that brings our deadline to 2100. While this may seem doable, remember that the second half of the 21st century will be full of climate disasters, economic recessions, wars, resource depletion and other events that will be a significant problem for scientific research. For more information, watch this (

) and read this (http://www.amazon.com/The-Collapse-Western-Civilization-Future/dp/023116954X)

No, fusion has a lot of flaws, the ship even if you try to carry the most lightest instrument and things needed to complete the mission, due to the rocket equation, the ship ends being massive, bigger the ship its, more shielding do you need --> more mass. That ship would perform much worst than the solar sail approach, and it will be thousands of times more expensive.

Indeed, the 4 designs I linked are all very massive and would require hundreds of launches - and billions of dollars - to construct. However fusion propulsion has benefits over solar sails. It can continue to accelerate in deep space far away from a star, and because of this it can go faster than a solar sail. It also can carry a larger payload. A potential 'best of both worlds' approach could be a laser sail. It is like a solar sail except it is powered by a gigantic laser beam. If you look here (https://en.wikipedia.org/wiki/Interstellar_travel) and look at the beamed propulsion section, you can see that laser sail starships can go fast and also carry a large payload.

I think our best options are fusion and laser sails.

[K^2]

I stand by my previous, even in the fantasy (that is what it is, nothing more than a fantasy) matter/antimatter never gets higher than about 0.2c.

Yeah, when somebody accuses you of making up numbers, stand strong, and keep making up numbers as a rebuttal. What can possibly go wrong when you're ignorantly arguing about matter-antimatter rocket with a particle physicist?

Even taking into consideration the lepton production, with bulk of losses caused by μμ' production, you can still get almost 99% of the impulse. In other words, I_SP is still closer to .25 c/g than .24 c/g.

ee' and μμ' production is also the reason that you really can get up to 0.6 c/g using superconductor magnets. This isn't fiction. It's simple, high school physics. Now, TWR in that scheme is going to absolutely suck given current technology, so what we have isn't practical for interstellar. But this is why I'm pointing out that we can probably get higher thrust in the future.

But going back to simply having a led damper and a plasma injector, which is not just something we can build, but something we have built, the TWR is limited by your ability to absorb and radiate heat. Since we're looking at over 2 decades in transit anyhow, acceleration of 0.1m/s² is more than sufficient. That means we need to dissipate 30MW of power per 1kg of mass. At 3,000K, this is trivially accomplished by about 7m² of radiator surface. Tungsten wire with sufficient surface area will take up a tiny fraction of the mass. Similarly, led damper (in thin tungsten shell - molten led is just as good at absorbing radiation) has constant thickness regardless of thrust, so it does not really add to the payload.

The only part of ship's construction that's going to eat into your useful payload is the anti-matter storage tanks. And that becomes less and less significant for larger ships.

Long story short, there is absolutely nothing to prevent us from building an interstellar matter-antimatter powered ship with effective I_SP very close to 0.25 c/g other than antimatter supply problem.

But hey, I'm sure that won't stop you from making up more numbers to convince yourself that you're still right.

[AngelLestat]

Indeed, the 4 designs I linked are all very massive and would require hundreds of launches - and billions of dollars - to construct. However fusion propulsion has benefits over solar sails. It can continue to accelerate in deep space far away from a star, and because of this it can go faster than a solar sail. It also can carry a larger payload. A potential 'best of both worlds' approach could be a laser sail. It is like a solar sail except it is powered by a gigantic laser beam. If you look here (https://en.wikipedia.org/wiki/Interstellar_travel) and look at the beamed propulsion section, you can see that laser sail starships can go fast and also carry a large payload.

I think our best options are fusion and laser sails.

I study beam propulsion before, is a good way but the cost to launch just a few ships would be higher than fusion, it start to have sense if you want to launch ships very often.

There are 3 main issues with beamed propulsion: beam focus, beam accuracy and power needed.

Depending the method of choice, some would be hard to accomplish than others.

To very long distances, accuracy becomes a nightmare, the focus problem is solveable but it rise the total cost by a huge factor, the power needed is also solveable with huge cost, unless we use the Jordin Kare's approach of micro-sail beam, but in that case the extra cost comes in all the micro-sails that you need.

So I will said this rise the cost by a factor of +1000 against normal solar sails.

So if you can launch 1000 interstellar probes for the cost of 1, being just half of fast is not a problem.

Also how much payload you can carry in a solar sails and how fast it can go, it depends on how big you made the sail, so your average density is higher or lower than 0.01g/m2, about how much acceleration a sail can resist, meanwhile you keep the load and masses constant, there is not problem, in fact the jordin kare´s calculation show that it might be possible to accelerate micro sails (which work to push a magsail) from 0 to almost light speed in 1 second.

ee' and μμ' production is also the reason that you really can get up to 0.6 c/g using superconductor magnets. This isn't fiction. It's simple, high school physics. Now, TWR in that scheme is going to absolutely suck given current technology, so what we have isn't practical for interstellar. But this is why I'm pointing out that we can probably get higher thrust in the future.

Why you use /g as a unit of ISP? The unit from what I know is seconds.

In the superconductor magnet approach, there is not chance to increase the efficiency with pair production? The energy would be so concentrated and energetic than 2 gammarays photons crashing between them will produce matter that can be redirected by the magnetic nozzle and increase the chance of pair production with different gammarays.

[bombo1]

we have the technology to travel to the stars, it is just a matter of getting there within a reasonable time. just look at the voyager probe, some day it will reach another star, just not in this millennia or the next, or the next after that...

[sj176]

I don't know about this century, but I think a semi-practical method of interstellar travel will eventually become possible.

[magnemoe]

The last few centuries are pretty unique in human history - we discovered industry, which brought unimaginable progress. Most of the time we're not in a technological revolution of this scale. The last time was when we discovered agriculture!

True, it probably not go on in the same speed, however anybody who grew up before internet, sit back and realize how powerful google is as an tool. Fusion is probably the next change everything item.

[K^2]

Why you use /g as a unit of ISP? The unit from what I know is seconds.

In the superconductor magnet approach, there is not chance to increase the efficiency with pair production? The energy would be so concentrated and energetic than 2 gammarays photons crashing between them will produce matter that can be redirected by the magnetic nozzle and increase the chance of pair production with different gammarays.

I_SP in US Engineering convention is defined as mean exhaust over g, hence being related to c/g for photon drives. And units work out. (m/s) / (m/s²) = s.

You can think of ee' and μμ' production as consequence of intense gamma radation. (It's a bit more complicated than that.) Which is why you can get the aforementioned 0.6 c/g rather than just 0.5 c/g. I've heard claims of going even higher, but at this point we're firmly in sci-fi territory.

[jrphilps]

Do you think we will be capable of interstellar travel within this century? If so how? And if not, why?

No, I don't think interstellar space travel is going to be a possibility in the 21st century, or even the 22nd. The sheer amount of energy required is a hard limit: Sending humans even to nearby stars is a task for type 1 civilisations.

This century will be spend colonising the moon, with manned explorations to the inner planets, and probes to the surfaces of the outer planets (and their satellites). Theres no rush to get to the stars, humanity must learn to crawl before it can walk.

Edited May 23, 2015 by jrphilps
Wrong address

[ChrisSpace]

I study beam propulsion before, is a good way but the cost to launch just a few ships would be higher than fusion, it start to have sense if you want to launch ships very often.

There are 3 main issues with beamed propulsion: beam focus, beam accuracy and power needed.

Depending the method of choice, some would be hard to accomplish than others.

To very long distances, accuracy becomes a nightmare, the focus problem is solveable but it rise the total cost by a huge factor, the power needed is also solveable with huge cost, unless we use the Jordin Kare's approach of micro-sail beam, but in that case the extra cost comes in all the micro-sails that you need.

So I will said this rise the cost by a factor of +1000 against normal solar sails.

So if you can launch 1000 interstellar probes for the cost of 1, being just half of fast is not a problem.

Okay, but how will a sail purely pushed by the sun speed up enough? once it gains a few tens of kilometers per second in outwards velocity, it will move away from the sun so fast it cannot be pushed much further. If the sail swings really close to the sun, that might help a little, but its close-range flyby would be very short and would again not last long enough to accelerate to the speeds required. So what's your solution? How do you think solar sails can achieve interstellar speeds?

[shynung]

I_SP in US Engineering convention is defined as mean exhaust over g, hence being related to c/g for photon drives. And units work out. (m/s) / (m/s²) = s.

You can think of ee' and μμ' production as consequence of intense gamma radation. (It's a bit more complicated than that.) Which is why you can get the aforementioned 0.6 c/g rather than just 0.5 c/g. I've heard claims of going even higher, but at this point we're firmly in sci-fi territory.

So, about 18,000 kiloseconds?

[K^2]

Theoretically, based on some estimates I've seen for a magnetic nozzle. I have not looked at these numbers too closely, but there is nothing fantastic about it, other than field strength and fuel itself. The 0.25 c/g I've mentioned earlier, or about 7.5Ms, you can get without doing anything fancy.

[AngelLestat]

I_SP in US Engineering convention is defined as mean exhaust over g, hence being related to c/g for photon drives. And units work out. (m/s) / (m/s²) = s.

You can think of ee' and μμ' production as consequence of intense gamma radation. (It's a bit more complicated than that.) Which is why you can get the aforementioned 0.6 c/g rather than just 0.5 c/g. I've heard claims of going even higher, but at this point we're firmly in sci-fi territory.

Ah ok, Now I check again the Keane and Zhang analysis and it seems that I missunderstood some numbers.

0.6c sounds super good, even 0.25c is a lot higher than fussion, the only problem with low ISP in antimater propulsion that the ships requires more radiators to release the excess of heat.

Okay, but how will a sail purely pushed by the sun speed up enough? once it gains a few tens of kilometers per second in outwards velocity, it will move away from the sun so fast it cannot be pushed much further. If the sail swings really close to the sun, that might help a little, but its close-range flyby would be very short and would again not last long enough to accelerate to the speeds required. So what's your solution? How do you think solar sails can achieve interstellar speeds?

Yeah, does calculation was already done it by many researchers, like mattoff, zubrin, adam crowl, etc. Each one with different parameters on sail density and sun periapsys.

http://crowlspace.com/?p=1882

http://crowlspace.com/?p=1585

http://nextbigfuture.com/2013/02/carbon-nanotube-sheets-for-solar-sails.html

With CNT or graphene, temperature is not an issue no matter how close you want to be, first because graphene can stand 3000 degrees, at that temperature even if you absorb all the radiation (which you dont, because the surface is reflective), you will be able to release the same amount as heat.

The things that limit how much you may close to the sun are:

-if you are too low, you should dodge the magnetic fields (mainly black spots).

-sun atmosphere, it will not decelerate, but the particles may damage the sail or instruments.

-acceleration (g-force) This may be the main concern.

Acceleration is a problem for humans because is not constant in each atom of our bodies (with the gravity field exception).

A solar sail by other hand, as it can be visualize as a 2d structure, all atoms are under the same acceleration, so in theory should not be a problem.

Adam crowl calculation with lower densities than mines using quarter wave CNT:

At 0.0045 Au, the acceleration is 8000 G aprox, 0.11c max speed

At 0.019 something as 1000 G aprox, 0.056c max speed.

Lets imagine that one small part of the sail is 1% less reflective than the average.

95% to 94%.

Density: 0.01g/m2

Periapsys: 0.007 au.

Power by m2 at periapsys: 1360w * (1 / 0.007)² = 27877551 w/m2

Force by m2: 2*27877551/c = 0.18 N (95% aprox) --> 94%? --> 0.18N - (0.49% because the force is absortion + reflection) = 0,179N

Acceleration 95% reflection: 0.18N / 0.00001kg = 1800 G -->94%? --> 1790 G

So we have 10G of difference between sail sections, So the real speed limit for a solar sail depends in how average is the reflectivity and the mass distribution.

If we add the strenght of graphene plus my idea to active mass distribution and control with magnetic rails and superconductors may be possible.

The superconductors will be in the sail shadow, and they will be reflective. Not sure how to get and keep the power needed to manage the magnetic rails.

A different method to keep the acceleration constant for longer time once we gain distance:

(the angles will be different of course in direction of our prograde at periapsys)

You launch a heavy solar sail that goes to jupiter, use gravity assist and returns to the sun at high speed, that sail will reflect and bounce (for longer time because it has speed) the radiation that receive the sail probe multiplying the force depending the number of bounce you achieve, we can add extra solar sails at the side to increase the radiation over the probe.

The first sails does not steal energy (shadow) to the sail probe because the sun is so big in comparison that it will not matter.

[Bill Phil]

Let me just ask:

What does a starship need?

[baggers]

Let me just ask:

What does a starship need?

Let's be precise:

What sort of starship?

[Bill Phil]

Let's be precise:

What sort of starship?

Just a general starship.

Let's say one that can get to another star within a human lifetime.

[SargeRho]

Every probe we've sent on a solar escape trajectory so far is technically a starship.

If we're talking about getting to a nearby star in a human lifespan, aside from the "basic" systems of a spacecraft, you need a propulsion method to get you to at least 5% of the speed of light (Alpha Centauri, almost 100 years of flight at that speed), as well as some way to power the craft for duration of the trip. A "simple" Fission reactor could probably do the trick of keeping the vessel powered for the trip.

At the destination you can just use solar power.

At those speeds, you will need a method of protecting your spacecraft from impacts. An erosion shield, or a magnetic field and a laser could do the trick.

You will probably want to slow down at the destination, too, so you need something like a magnetic sail to help you slow down.

If you're going with a crew, you'll also need extra radiation shielding, and perhaps some form of hybernation.

[baggers]

It's an evidence, be we need too:

- a communication system able to send back home a signal. (like "TOUCHDOWN§§§§§§§§" ^^): it's probably a very big antenna for a signal able to travel 5 ligth-years, and even be catch back at earth.

- A good solar powered engine that can do some interplanetary travel. (a ion engine with enought "fuel")

- an AI at least able to :

- interstellar fligth control

- slow down and interplanetary fligth control (in a planetary system not well know): like, insert into orbit of all planets one after the other and do some survey.

You will probably want to slow down at the destination, too, so you need something like a magnetic sail to help you slow down.

Will it be enought to slow your ship down from 15.000.000m/s (interstellar speed) to a more "interplanetary speed" (like, 15.000m/s) and even "orbital speed" for some survey?

Edited May 24, 2015 by baggers

[SargeRho]

It can probably slow it down enough to allow for an extended fly-through of the system.

[K^2]

the only problem with low ISP in antimater propulsion that the ships requires more radiators to release the excess of heat.

I wouldn't classify it as the "only problem," but it's the biggest one, yeah. But as I've indicated, for "very short" interstellar hauls, it's still within capability of existing materials.

[PB666]

we have the technology to travel to the stars, it is just a matter of getting there within a reasonable time. just look at the voyager probe, some day it will reach another star, just not in this millennia or the next, or the next after that...

Right, voyager is in interstellar space, but it will take 40,000 years to pass within 1 ly of the nearest star, meaning that it will continue to travel in interstellar space until some clever computer scientist figures out when it might pass into the 'atmosphere' of some star.

- - - Updated - - -

True, it probably not go on in the same speed, however anybody who grew up before internet, sit back and realize how powerful google is as an tool. Fusion is probably the next change everything item.

Well thats not exactly the poster child of progress. Rye cultivation began during the period between LGM and the younger dryas (~12,000 a). The first wheat cultivars were cultivated and domesticated about 10,000 years ago, the wheat we know as bread wheat was domesticated about 8000 years ago. So what we consider the development of the fertile crescent acutally begins in Europe and ends several thousand years later were agriculture is doomed as a consequence of upstream water hoarding, decreased pan evaporation rates in the Indian ocean as a consequence of chaff burning and global warming. And of course we can look at all these regions now and then ask the question where technology is going to lead eventually to those that create it. If we want to go back as far as pottery, that's roughly 16 to 18 thousand years ago in the Sea of Japan region (notable home of the worlds most maniacal nuclear state).

Now put these techno-savey on a ship, say 50 to 1000 years and lets reask the question, is this likely to succeed. You have to get the socialization right before you can attempt such ventures.

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True, it probably not go on in the same speed, however anybody who grew up before internet, sit back and realize how powerful google is as an tool. Fusion is probably the next change everything item.

Google is a powerful, its also a powerful weapon. Identity theft as we know it now would not be possible without an internet. When you talk about the Usenet, google and deja-vu all but destroyed it, not because of the competition, but because it allowed any nepharious idiot could had just enough sense to use a web browser to begin posting crap. I use duck-duck. Think about google in a time of war between the US and any major world power. Step one, use all the financial information you have parsed together from from the internet step two shut down the western financial systems. War over.

Consider that antimatter will have the same growing pains as any technology. The first useful rocket was the V2, so where is actually that going to go.

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This century will be spend colonising the moon, with manned explorations to the inner planets, and probes to the surfaces of the outer planets (and their satellites). Theres no rush to get to the stars, humanity must learn to crawl before it can walk.

Sustainable lunar colony, no. Manned exploration of inner planets, possible, missions less than 5 years.

There is really no reason to have a colony on the moon, limiting resources are magnitudes more expensive on the moon than on earth.

The first question to ask is why

Why would I have a space station at L2 - astronomical observatory on a much larger scale.

Why would I have a space station in LEO - space science (microgravity).

Why would I have a production facility on the moon (with DV > 1000 m/s to get stuff into orbit, when we already have the materials we need floating around in orbit).

Lunar colonization - 15 days of light and dark (not suitable), except a small region of the moon. Requires a power supply capable of sustaining all aspects of living. (no microgravity, lower concentrations of hydrogen, carbon, and low molecular weight atoms - essentially all the elements concentrated in organic matter).

A lunar station is useful for scientific reasons only, until it is buried 10M below the surface it is not suitable for long term survival of humans. Colonies have mini-gravity may have consequences of growth on children and heart health, they require expensive importation of almost all the biological elements, the will need to maintain a constant pressure differential of 100 kPa, the will have to manage carbon dioxide flux between photosynthetic and not photosynthetic organisms. 220,000 miles away from the nearest hospital.

A colony that includes minors would not get an IRB unless those minors had some life-limiting condition.

[magnemoe]

Right, voyager is in interstellar space, but it will take 40,000 years to pass within 1 ly of the nearest star, meaning that it will continue to travel in interstellar space until some clever computer scientist figures out when it might pass into the 'atmosphere' of some star.

- - - Updated - - -

Well thats not exactly the poster child of progress. Rye cultivation began during the period between LGM and the younger dryas (~12,000 a). The first wheat cultivars were cultivated and domesticated about 10,000 years ago, the wheat we know as bread wheat was domesticated about 8000 years ago. So what we consider the development of the fertile crescent acutally begins in Europe and ends several thousand years later were agriculture is doomed as a consequence of upstream water hoarding, decreased pan evaporation rates in the Indian ocean as a consequence of chaff burning and global warming. And of course we can look at all these regions now and then ask the question where technology is going to lead eventually to those that create it. If we want to go back as far as pottery, that's roughly 16 to 18 thousand years ago in the Sea of Japan region (notable home of the worlds most maniacal nuclear state).

Now put these techno-savey on a ship, say 50 to 1000 years and lets reask the question, is this likely to succeed. You have to get the socialization right before you can attempt such ventures.

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did not understand the reply. Yes middle east is less fertile than it was, i might add goats who eat anything and increase erosion. An serious problem in dry areas.

Still you have to be careful then farming in dry areas, wetter are much easier.

Note that this is not an new effect, majority of it was done before modern time then nobody knew or could do much.

Google is a powerful, its also a powerful weapon. Identity theft as we know it now would not be possible without an internet. When you talk about the Usenet, google and deja-vu all but destroyed it, not because of the competition, but because it allowed any nepharious idiot could had just enough sense to use a web browser to begin posting crap. I use duck-duck. Think about google in a time of war between the US and any major world power. Step one, use all the financial information you have parsed together from from the internet step two shut down the western financial systems. War over.

Identity theft=Impersonation others and is as old as large cities where you could not know an faction of the people.

If idiots did not post on the net they would rather talk crap in pubs.

Consider that antimatter will have the same growing pains as any technology. The first useful rocket was the V2, so where is actually that going to go.

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Sustainable lunar colony, no. Manned exploration of inner planets, possible, missions less than 5 years.

There is really no reason to have a colony on the moon, limiting resources are magnitudes more expensive on the moon than on earth.

The first question to ask is why

Why would I have a space station at L2 - astronomical observatory on a much larger scale.

Why would I have a space station in LEO - space science (microgravity).

Why would I have a production facility on the moon (with DV > 1000 m/s to get stuff into orbit, when we already have the materials we need floating around in orbit).

Lunar colonization - 15 days of light and dark (not suitable), except a small region of the moon. Requires a power supply capable of sustaining all aspects of living. (no microgravity, lower concentrations of hydrogen, carbon, and low molecular weight atoms - essentially all the elements concentrated in organic matter).

A lunar station is useful for scientific reasons only, until it is buried 10M below the surface it is not suitable for long term survival of humans. Colonies have mini-gravity may have consequences of growth on children and heart health, they require expensive importation of almost all the biological elements, the will need to maintain a constant pressure differential of 100 kPa, the will have to manage carbon dioxide flux between photosynthetic and not photosynthetic organisms. 220,000 miles away from the nearest hospital.

A colony that includes minors would not get an IRB unless those minors had some life-limiting condition.

Agree here, an moon base would be primary mining.

[Rakaydos]

Moon base would be primarally mining, particularly if you set up a lagrange elevator so you dont have to launch mass into orbit, just lift it to Lagrange.