and one last thing..we talked yesterday about a Physics blog that I thought excellent, well here it is:
arXiv blog
Interstellar Travel Not Possible Before 2200AD, Suggests Study

A new estimate of the amount of energy needed to visit the stars suggests we won't have enough for at least another two centuries

kfc 01/07/2011

* 13 Comments

How soon could humanity launch a mission to the stars? That's the question considered today by Marc Millis, former head of NASA's Breakthrough Propulsion Physics Project and founder of the Tau Zero Foundation which supports the science of interstellar travel.

This is a question of increasing importance given the rate at which astronomers are finding new planets around other stars. Many believe that it's only a matter of time before we find an Earth analogue. And when we do find a place with the potential to host life like ours, there is likely to be significant debate about the possibility of a visit.

The big problem, of course, is distance. In the past, scientists have studied various factors that limit our ability to traverse the required lightyears. One is the speed necessary to travel that far, another is the cost of such a trip.

By looking at the rate at which our top speed and financial clout are increasing, and then extrapolating into the future, it's possible to predict when such missions might be possible. The depressing answer in every study so far is that interstellar travel is centuries away.

Today, Millis takes a different approach. He looks at the energy budget of interstellar missions. By looking at the rate at which humanity is increasing the energy it has available and extrapolating into the future, Millis is able to estimate when we will have enough to get to the stars.

To make his extrapolation, Millis looked at the amount of energy the US has used to launch the shuttle over the last thirty years or so, as a fraction of the total energy available to the country. He assumes that a similar fraction will be available for interstellar flight in future. He then calculates how much energy two different types of mission will consume.

The first mission is a human colony of 500 people on a one-way journey into the void. He assumes that such a mission requires 50 tones per human occupant and that each person will use about 1000W, equal to the average amount used by people in the US in 2007.

From this, he estimates that the ship would need some 10^18 Joules for rocket propulsion. That compares to a shuttle launch energy of about 10^13 Joules

The second mission is an unmanned probe designed to reach Alpha Centauri, just over 4 light years away, in 71 years. Such a ship would be some three orders of magnitude less massive than a colony ship so it's easy to imagine that it would require less energy.

But Millis places another constraint on this mission. Not only must it accelerate towards its destination, it must decelerate when it gets there (although why this isn't a requirement for a colony ship isn't clear).

That changes the the numbers significantly. Millis estimates that the probe would require some 10^19 Joules.

The final step in is to determine when humanity will have this kind of energy available for these kinds of missions. By extrapolation, Millis calculates that the required energy will not be available until at least the year 2196. "This study found that the first interstellar mission does not appear possible for another 2 centuries centuries," he says.

That's necessarily a crude calculation but a sobering one nonetheless. It implies that while we will soon be able to gaze with wonder upon other Earths, it will not be possible to visit them within the lifetime of anybody alive today.

In other words, for the foreseeable future, we're trapped.

Ref: arxiv.org/abs/1101.1066: Energy, Incessant Obsolescence And The First Interstellar Missions

Trips 'n' Travels Amateur Astronomers Usher In New Era Of Discovery, Says Report

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Torbjorn_Larsson_OM

* 3 Days Ago
* 01/07/2011
* 95 Comments

Not trapped, already started

If instead the technology is to colonize our Oort cloud and then the next, we have already started by taking trips out in space.

Such a colonization is AFAIU in principle feasible with today's technology since I've seen claims that the amount of fissionable material in comets will suffice. No need to develop fusion (but it would be a boon), enough hydrogen rich material to protect from radiation and small impactors, and no need for fancy drives. What remains is to show feasibility of inhabiting comets at low gravity and, likely, enough closure of small biospheres (as today's record is a mere 70 % which may be too wasteful).

Unless someone points out a show stopper, we are likely already on our way.

Such a colonizing front would eventually cover the whole galaxy in a reasonable amount of time. If anybody cares, it isn't as if there would be much interest in communication beyond on local environment and techniques. And eventually divergent evolution with speciation would make the common cultural and biological base of little importance. C'est la vie.

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heldervelez

* 3 Days Ago
* 01/07/2011
* 5 Comments

how to survive to the next glaciation ?

Life on Earth is not a miracle. It is a 100% probable event.

Then an EarthLike planet must be full of Life.
The 'terraforming ' science must evolve.
Biology must evolve.

The author is short-sighted because it sees only in accordance with current conditions: 'moving adults'.
But nothing prevents us from moving frozen embryos to be developed and educated in the future.

So, instead of displacing 500 people,
We could move thousands/millions of people TO BE BORN and educated in the future, near the target, progressively, without a vivid memory of a 'Lost Eden'.
Some educators must deeply sleep until needed in each journey.

And we must move forward, without delay, because, as we soon will aknowledge, the Earth is in a process of Constant Global Cooling. (*)
We will be subjected to further glaciations, and shortage of energy.

(*) It exists a paper to be, that will turn this issue unquestionable, following this one:
http://arxiv.org/abs/astro-ph/0208365
A relativistic time variation of matter/space fits both local and cosmic data
--
And the sun is not dead, quite the opposite, and occasionally gives a sneeze. Oh, we still do not know this, we think it is quite so calm. I'm sorry.

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rarnold

* 3 Days Ago
* 01/07/2011
* 4 Comments

Technology and Step Functions

The development of technology and its impact on available energy density has not followed any linear progression in the past, but rather has increased non linearly. Why does the study presume via linear extrapolation otherwise?

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gerardomarina

* 2 Days Ago
* 01/07/2011
* 8 Comments

Re: Technology and Step Functions

maybe i'm not correct but will venture to say is log normal base 10 -> 10^1, 10^2, 10^3 transforms into 10, 100, 1000 right?

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UncleAl

* 3 Days Ago
* 01/07/2011
* 170 Comments

Nonlinear in energy

Spaceflight is change in momentum (p = mv) but thrust is E = (mv^2)/2. Project vs. energy is not as depicted in the log charts. The slope is much steeper for fast traverse. Modified charts are then eloquent: Humanity remains mudfeet barring a drastic alteration of physics.

Reaction mass was ignored. A self-contained vessel cannot be both fast (mv) and efficient ((mv^2)/2). It requires both outrageous amounts of reaction mass and huge contained energy. Matter-antimatter annihalation is optimistic by at least a factor of two: hadron-antihadron annihalation (99.97% of atomic mass is nuclear) loses 50% of its E = mc^2 as neutrinos that provide no directional thrust.

An open cycle craft (e.g., Bussard ramjet) is no better than marginal even if the technology existed. Traveling at 10% of lightspeed and hitting a 1 microgram interstellar grain is a world of hurt: 215 grams of TNT detonating in a 0.001 mm^3 volume.

Physics seeks to quantize all interactions. The appropriate force-mediating vector boson here is the fundon, the quantum of grant funding. The fundon is promoted out of the vacuum with money. Theory is always prefered to experiment because virtual mud always packs tighter than real gems.

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mark1qhorsey

* 3 Days Ago
* 01/07/2011
* 2 Comments

Re: Nonlinear in energy

Any inter-steller mission must by default gather its source of propulsion energy 'along the way'. One consideration is to 'extract' mass, as well as gravity-well energy from objects in the Oort cloud and to then collect the mass for conversion into reaction mass. With this notion (which is implicit in previous comments) mapping the Oort cloud for suitable 'fuel mining' objects - both massive and offering gravity wells - would be a nice step. Also, all impinging mass - micro-meteorites - are potential fuel if captured without damage (i.e., in a giant foam farm?). It's a wonderful challenge!

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mark1qhorsey

* 3 Days Ago
* 01/07/2011
* 2 Comments

Re: Nonlinear in energy

Two additional thoughts - I reference M. Xu et al., Science 330:1364 (2010) for a candidate early technology 'viscoelastic foam., and of course, graphene/carbon nanotube structures that may be able to store electrical energy in tremendous amounts necessary to provide for mass conversion to reaction mass.

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gdnordley

* 2 Days Ago
* 01/07/2011
* 1 Comment

Re: Nonlinear in energy

Human interstellar travel will take a lot of energy. I usually think in terms of a thousand-ton starship moving at a gamma of two (useful time dilation, nice round number). The relativistic expression is E = m c^2 (gamma - 1), which gives us about 1E23 J. The most obvious source for this amount of energy is space based Solar. As it far exceeds the needs of even a rather profligate Terrestrial population, I think the energy source would need to be built specifically for interstellar flight, so the past history of energy expansion is probably not relevant. Imagine someone in 1880 trying to predict the amount of automobile use in 2000 based on the historical rate of road paving, or oil production, extant at the time.
For star travel, key technology could be the ability of robotic manufacturing technology to turn asteroid material into copies of itself and solar power stations. As an oversimplified example, suppose one can build a factory that copies itself and makes a 1GW solar power station every year. This would not be a huge feat of artificial intelligence; I think the smarts of a honeybee would do the trick. Some in-situ resource acquisition and use technology would need to be invented or improve on. But the replication rate may even be conservative. Robots don't sleep and you don't need heavy equipment to move stuff in space. Given that scenario, the total energy collected in one year would reach 1E24 Joules in 26 years. Allowing a ten year development program, a starship could be launched in about 36 years from the word go.
It is part of the art of comparative mission studies to shape the final conclusion by careful selection of the study groundrules. Serious and honest investigators check their conclusions for their sensitivity to assumptions. For instance, in the above, if the multiplier is 1.5 factories/stations per year, it takes 44 years to reach 1E24 J. If it is 2.5, the time is 20 years. I like the latter idea because, it isn't impossible that those of my generation will often be alert and reasonably functional in their 90's. I might live to see the launch.
When projecting decades into the future, one has to apply a bit of "Kentucky windage" to the technology base. While that involves some intellectual risk taking, we know that projections made on the basis of existing technology limitations and practices will certainly be wrong. In the case of interstellar travel, we should at least anticipate inevitable advances in robotics, ultrastrong materials such as graphene, and superconductors, then factor these into designs for radiation protection, sails, in-situ resource use, life support systems, etc... Magnetic sails, for instance, would be most useful in slowing down from relativistic velocities, which is one reason not to be too bothered by deceleration energy. People are not going to the stars in the starships we could build today with the energy infrastructure on planet Earth.
Gerald Nordley-7 Jan 2011

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smoker

* 2 Days Ago
* 01/07/2011
* 14 Comments

Rubbish

If we accelerate at 1G then we would be travelling at an appreciable fraction of light speed before we left the solar system. Io and Titan contain all the fuel we need for inter-stellar flight.
There are many many people who would be glad to take a one way trip.

What's the problem ?

Destination.

No one wants to go on a meaningless one way trip.
But given a viable planet, there is no holding back. I would go just for the trip, £$%^ the planet !

Ignorant people causing parochial policies.
If this had been the aim from the start of the space age, then we would be nearly there by now !

(unfortunately, it would be another xx years before we found out if they had made it !)

Imagine the news on the day that we received a message from another star system... and the signal was human. I would be happy to die knowing we had actually made it,and the door was now open.

There is no try ...

pps. Why can't the publisher of this web site spot spelling mistakes and blatant grammatical errors ?

"He assumes that such a mission requires 50 tones per human occupant ..."
Is that a metric "tone"?

Reply

intuition

* 2 Days Ago
* 01/07/2011
* 11 Comments

Push V. Pull

Rather than pushing with thrust is it possible to pull a craft towards a source?

Reply

rbrtwjohnson

* 2 Days Ago
* 01/08/2011
* 8 Comments

Interstellar spacedrives

I think space colonization, in a foreseeable future, will depend on development of energy-efficient spacedrives.

Reply

intuition

* Today
* 01/09/2011
* 11 Comments

Re: Interstellar spacedrives

Agreed, but would not the most efficient drive be one which directs energy already contained within space?

Reply

rbrtwjohnson

* Today
* 01/09/2011
* 8 Comments

Re: Interstellar spacedrives

I think we need to learn more how to harness energy already contained within space.
Do you know some technology already available that can do that?

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The Physics arXiv Blog produces daily coverage of the best new ideas from an online forum called the Physics arXiv on which scientists post early versions of their latest ideas. Contact me at KentuckyFC @ arxivblog.com

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