Talk:Interstellar travel/Archive for 2012

Supplying the Space Craft with Energy

Another area that is poorly written and lacking in citations is the Energy Requirements paragraph that asserts energy must be carried along. Various proposals exist that do not carry energy along with the primary space craft. One might launch multiple payloads over numerous years well in advance of the primary space craft to allow the primary craft to have a short trip. A ramjet captures interstellar hydrogen. Robert Forward proposed launching the spacecraft using lasers. — Preceding unsigned comment added by 71.141.106.56 (talk) 05:38, 6 December 2011 (UTC)

Regardless of how it is done kinetic energy must be supplied and how it is determined was established as a basic physical law centuries ago.Few seem to realize how gargantuan itis for any conceivable interstellar flight and could even make interstellar travel forever impossible . This can be shown with a specific example.

Kinetic energy is a function of mass and velocity. Assume a spaceship with the mass of the International Space Station 450,000 kg. Further, assume a round trip to our nearest star Alpha Centauri, 4.37-light years distance and a velocity of 20% of that of light , 60-million meters/sec,. which would give a round trip travel time ten times the light distance: 43.7 years This appears to be about the limit for humans existing in an isolated capsule.

Placing these into the basic energy equation e = 0.5*mv^2 gives a result of 8.1E+20-joules. Now, this number is impossible to visualize. However, there is a conversion constant enabling it to be visualized in terms of the unit used to define the energy of nuclear weapons: TNT-tons. The conversion constant as established by the National Institute of Standards and Technology (NIST) is one ton of TNT has an energy of 4.184E+9 joules.(See http://physics.nist.gov/Pubs/SP811/appenB8.html.) Dividing this into the result gives an energy of 193.6-billion TNT-tons. This is equal to the energy of 19,360-ten megaton fusion bombs of which one could destroy a large city..

How far we have to go is shown by noting that the present Space Station, orbiting at 17,239 miles/hour, has a kinetic energy of only 3,390 TNT-tons. And we could not achieve that with a single rocket launch but had to built it in orbit by many visits of the Space ShuttlePaulkint (talk) 16:36, 22 May 2012 (UTC)

- Deep space will have very little interstellar matter to use. "More research required".--173.69.135.105 (talk) 02:13, 27 February 2012 (UTC)

The Hundred-Year Starship study article

I want to know where I report the "The Hundred-Year Starship study" article for the Wikipedia yesterday I change this article with trustful information about the "100 year starship study" ( http://www.100yss.org/ )as you can here, like the official site say this study is about interstellar space travel and not about one way trip to Mars, and then today they rewritten all over again with this ridiculous information that is nothing about 100 year starship study, how to report it? — Preceding unsigned comment added by 187.127.246.78 (talk) 01:29, 23 December 2011 (UTC)

We all know (don't we?) that the challenges of interstellar travel are enormous. I'd look at it from a systems engineering POV: what is required to make it "successful" and what are the *combined* factors and their probabilities that affect success? SE encompasses multiple mission-success factors; such as reliability, maintainability, supportability, risks, performance and technological options that maximize cost-benefit, etc. They must ALL work together to assure mission success.--173.69.135.105 (talk) 02:26, 27 February 2012 (UTC)

article missing critical information-requirements to STOP the vehicle

While the article is basically fantasy, it still should reflect the hard science. The article seems to discuss only the (practically impossible) idea of shooting some payload to another star system but never addresses slowing down/stopping to make that voyage worthwhile in the first place (unless a centuries-later post-launch radio probe is intended). This is a spectacular energy (and mass) requirement and should be detailed - it's there to be had in any mechanics textbook. HammerFilmFan (talk) 07:16, 18 May 2012 (UTC)

A spaceship can be only be “braked” by the reverse of how it was accelerated, issuing a reaction mass opposite to the direction of travel. The kinetic energy is far too large to be dissipated as heat in the atmosphere as is the case with the Space Shuttle.

The amount of reaction mass and its exhaust velocity is determined by the Tsiolkovsky rocket equation A spaceship returning from a 40-year round trip to our nearest star, Alpha Centauri, would be traveling at 21.85% of light or 144,210,000 miles/hr. (This is equivalent to orbiting the earth in less than a second) Assume it is carrying a reaction mass equal to the mass of the spaceship. I calculate based on the rocket equation that the reaction mass would have to be issued with a speed of 58,774 miles/second. That is well over orbiting the earth twice in one second.

However, there is a factor which the Interstellar Travel article does not consider. A spaceship, with the mass of the International Space Station and returning from a 40-year round trip to Alpha Centauri, would be hurtling towards earth with an energy at least equal to that of 24,000 ten megaton fusion bombs, one of which could destroy a large city. A failure to decelerate could cause a world wide catastrophe, possibly destroying mankind as the Chicxulub meteor is alleged to have wiped out the dinosaurs.65-million years ago. I cannot conceive this possibility being allowed, however remote — Preceding unsigned comment added by Paulkint (talk • contribs) 14:40, 15 June 2012 (UTC)

These are a very useful points; thanks. The problem of stopping must indeed by taken into account in any real mission design, or proposed spacecraft to accomplish it. Alas, we are nowhere near the level of technology or understanding to be able to go into that much detail. After all, it's only a factor of 2x in velocity, right? — or 4x in energy. At this point we can only grope around for ideas, concepts, and approaches that might get us to where we would like to be, possible pieces useful in some sort of metaphorical jigsaw puzzle. We do display "designs", but really just to kind of benchmark where we are in the process, never as serious proposals.

It might be nice to have a graph of progress for the next century or next millennium, with some "Standard Reference Interstellar Mission" (SRIM; all with the same distance, time, payload mass,..., & cost, as a fraction of planetary GDP), plotting just how far—how many orders of magnitude—each design solution falls short of practicality, versus time, the date it was proposed. Then we could sit back and take the long view of how we are doing. If this sounds hopeless, think how many orders of magnitude of progress we have made had we started such a graph in 1900. So I think we should not be too depressed; I have seen the overall "power" of computer mass storage, defined, say, as a product of (size*speed/cost), improve by around seven orders of magnitude since I graduated in the mid 1970s.

In the same spirit you may indeed wonder about the fuel for returning home. If the first manned trip to a nearby star system takes the better part of a century, I would suppose no return is contemplated. It will not be a tourist trip, nor even a scientific expedition planning to bring home details of the new world. Those folks will be going, planning to stay and settle in. Then, if the ship is a "single stage" rocket vehicle of some kind (orders of magnitude beyond us), we might be able to refuel after establishing ourselves there, and send a ship back to Earth. Obviously this implies the whole affair is not going to be five guys on a joy-ride, but a city-sized space habitat, with everything needed to be self-sustaining at the destination. I would imagine the payload section will be at least the size of an aircraft carrier. (If the ship is multi-staged, or otherwise not immediately reusable, it would have to be restored or rebuilt.)

These considerations affect the whole way we think about the question; eg, as we're not talking about a joyride here, any ship returning "home" will be aiming for the Solar System, not the Earth!

An important consideration in this regard is that, with the vast and rapid improvements we have seen in communications, that star ship will surely be in close contact with Earth civilization, by TV, Internet, etc, subject only to the light-travel time limitation. If then the trip always takes the better part of a lifetime, why would anyone want to make it at all, except to found a human colony? Everything except humans themselves (for now) can be built in place (even new ideas in DNA, as the species evolves). So I think we must, at this stage in our thinking, probably envisage great settler expeditions making single trips out to destination star systems, establishing new outposts which will quickly become civilizations in their own right, the whole thing, a network of kindred civilizations, held together by massive amounts of information, flowing back and forth at light speed.

A thought for this article is, how can we put forth these kinds of considerations in it, to orient the reader as to where we really are in this project, so that fantasy gets connected to reality somehow? The problem with this is to find reasonable references to lay out this reality in a respectable, verifiable way, w/o WP:OR. Do such references exist? We have lots of experts here, who can tell us? Good science fiction might be the answer?

Of course there is always the possibility (probability?) of some revolutionary scientific or technological breakthrough, that will change everything. Some of these clearly need to be mentioned, being based on potentially real cracks in the wall of problems. Wormholes would be one, and the possibility of simply sending the information content in a human by light beam or radio, and re-assembling the body and brain there (by quantum teleportation, I guess) might be another. The article needs to be broad enough to say as much as we reasonably can about such things, which after all, may very well sweep all the grubby nitty-gritty in the present nuclear rocket section out the door. Wwheaton (talk) 22:40, 4 September 2012 (UTC)

Beamed propulsion feasibility

The section in the interstellar travel article on beamed propulsion states “Beamed propulsion seems to be the best interstellar travel technique presently available, since it uses known physics and known technology” However, in fact, beamed propulsion is hopelessly incapable of supplying the required energy. This is shown by calculating that energy in terms of electrical power. It has been established above that the required energy for a 20-year voyage to Alpha Centauri by the International Space Station is 9.66E+20 joules. Now, the Institute of Standards and Technology defines one watt-hour of electricity as having the energy of 3.6E+3 joules Dividing that into the above kinetic energy result results in a value of 2.69E+17 watt-hours. Based on this, it would require the full output of a 1000-megawatt power station for over 30,000 years to generate this much energy and the output of some 1500-such stations to do it in 20-years, all this power to be transmitted though a single laser.Paulkint (talk) 15:39, 15 September 2012 (UTC)

I think the sentence is correct. It only claims that beamed propulsion could be said to be the "best" method, not that it is feasible. Nanobear (talk) 16:03, 15 September 2012 (UTC)

I agree that the sentence is inappropriate as it stands, because the claim that it "seems to be the best interstellar travel technique presently available" is too strong to make in a Wikipedia article as a matter of opinion, without external support. Nuclear rockets (especially fusion with an ion-electric drive) also use known technology and physics, with no scientific miracles required, and it is my personal opinion that some kind of a solution along those lines is more likely. Besides the raw power requirement of the laser (space-based, surely), to form the beam and focus it on the departing ship (to a distance at least 2 light yrs, for Alpha Cen) appears to require a diffraction-limited transmitting optical aperture of many km diameter. Then to maintain a reasonable acceleration we would need to collect the beam at the ship with a reflector of roughly similar aperture. And then we really do need to stop (unless this is just a scientific fly-by, which is surely ridiculous, considering the massive size of the project−again my opinion), meaning the ship will not be only a crew capsule, and ultra-light optical reflector, but also still some kind of nuclear rocket (that is to say, very massive considering its fuel).

I think beaming is remarkably effective, and a useful item to keep in mind for our toolbox, but if we are thinking of an all-up system design, it fails rather badly. We could list its shortcomings in the article, but it would seem to be OR without a reference. I would instead just propose to drop that sentence. Wwheaton (talk) 07:57, 16 September 2012 (UTC)

The sentence seemed to be one of the main conclusions in Forward's article, so I think it's well-sourced. Maybe the "best" claim is indeed too strong for an encyclopedia article. How about changing it to "one of the best methods"? In any case, I think it's important to mention that beamed propulsion is one of the most promising methods. Nanobear (talk) 13:34, 16 September 2012 (UTC)

I agree it is remarkably effective and needs to be mentioned, I am just skeptical that it can be more than one piece helping us towards an overall solution. I have not seen Forward's article, but I am worried that the "primary sail" mentioned must be both diffraction-limited in its parabolic surface accuracy (in order to maintain focus on the decelerating payload), and yet also strong enough to maintain this precise form, while still having the very low mass per unit area needed to be accelerated in the first place. Instead of a sail, it becomes an optical surface. Let's just suppress the "best methods" and substitute "one of the best ideas"? It clearly deserves further thought as a way forward. Wwheaton (talk) 16:29, 16 September 2012 (UTC)

I've been doing a bit of looking around about Beamed propulsion. We have a WP article on the subject, which includes various terrestrial and aerospace applications as well as a limited section in the interstellar context, which however includes more recent references than Forward's older (1984) one. Landis 1989 has extended and criticized Forward's work. Ideally we should consider creating an improved article specialized to the Interstellar case from the present "Beamed propulsion" article, improving it, and then linking out from our article for most of the details. I can't do much of this any time soon, but might be able to to update the references a bit from what we have here. Wwheaton (talk) 21:33, 16 September 2012 (UTC)

Construction costs

Ceyssens et al (2011) and the more rigorous Moir and Barr (2005) both seem to assume a generation ship. What would be involved in using those construction cost estimates for a sleeper ship? —Cupco 18:39, 21 September 2012 (UTC)