# Stellar Exploration **URL:** \ **Category:** Factual Questions\ **Created:** [November 30, 2004, 10:15pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394 "2004-11-30T22:15:29Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![InvidiousCourgette](https://avatars.discourse-cdn.com/v4/letter/i/e47c2d/32.png) [@InvidiousCourgette](https://boards.straightdope.com/u/InvidiousCourgette)\ **Post date:** [November 30, 2004, 10:15pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/1 "2004-11-30T22:15:29Z")
With current technology, how long would it take for a spacecraft to reach a star outside of the solar system? Would the ship be able to tell us what it had found by sending back a strong enough signal for us to detect? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 30, 2004, 10:40pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/2 "2004-11-30T22:40:31Z")
Well, Voyager 1 left the solar system at [17.4 km/sec](http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970830.html), and the nearest star, proxima centauri, is 4.3 light years distant. At it’s current speed, it’d take Voyager 1 74,122 years to reach it. ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [November 30, 2004, 11:53pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/3 "2004-11-30T23:53:35Z")
I don’t have a cite for this, but I read an article on [CNN.com](http://CNN.com) about four years ago which stated that it is possible to accelerate one ounce of matter to half the speed of light using currently existing ion propulsion technology. (I’m sure it would cost _trillions_ to build even just one, but that’s beside the point). My astronomy professor said that he had read papers which demonstrated the veracity of this position. The only problem is, of course, that we have absolutely no idea whatsoever how to construct a usable probe that weighs only one ounce. However, the same professor also maintained that interstellar spaceflight could be achieved by scaling up currently existing technology, and that it is just an engineering problem, and that if we pumped enough money into it we could start launching small probes to some of the closer solar systems inside of 100 years. In other words, our grandchildren could easily live long enough to see interstellar spaceflight. So, using the half c figure, lets say eight and a half years to the Alpha Centauri system, and four and a quarter years to get the results back. So figure just shy of thirteen years to get data back from a probe heading to the nearest solar system. ---
**Author:** ![fortytwo](https://avatars.discourse-cdn.com/v4/letter/f/f9ae1b/32.png) [@fortytwo](https://boards.straightdope.com/u/fortytwo)\ **Post date:** [November 30, 2004, 11:57pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/4 "2004-11-30T23:57:36Z")
> [@Squink](#): > > Well, Voyager 1 left the solar system at [17.4 km/sec](http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970830.html), and the nearest star, proxima centauri, is 4.3 light years distant. > At it’s current speed, it’d take Voyager 1 74,122 years to reach it. I misread read that as 174,122 years. I’m so relieved it’s only 74,122 years. I could easily have been not paying attention and missed the message when it came. 🙂 ---
**Author:** ![Santos\_L\_Halper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/santos_l_halper/32/1_2.png) [@Santos\_L\_Halper](https://boards.straightdope.com/u/Santos_L_Halper)\ **Post date:** [December 1, 2004, 2:48am UTC](https://boards.straightdope.com/t/stellar-exploration/277394/5 "2004-12-01T02:48:17Z")
In the 1970s, the British Interplanetary Society did an engineering design study on the possibility of building an unmanned spacecraft called [Project Daedalus](http://www.daviddarling.info/encyclopedia/D/Daedalus.html). The design goal was a probe that could reach Barnard’s Star, which is six light years away, in fifty years. This would require accelerating the craft to 12% of the speed of light. It would have an initial mass of 54,000 tons and would be assembled in earth orbit. Note that if the Apollo Saturn V rocket were used to launch the components of Daedalus, it would take about 415 launches! ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [December 1, 2004, 4:31am UTC](https://boards.straightdope.com/t/stellar-exploration/277394/6 "2004-12-01T04:31:00Z")
The problem with the Daedalus ship is that it relies on fusion, which we haven’t really gotten to work all that well yet. . . . [Project Orion](http://www.islandone.org/Propulsion/ProjectOrion.html) is something we could do today. All you need are some nuclear weapons. The biggest problem simply has to do with how _big_ space is. (You might think that’s its a long walk to the chemist’s, but that’s just peanuts to space. . . .) Let’s say, hypothetically, that we developed something like cold fusion, which is a lot of power in a really small container, and we could build a spaceship that could travel at 1g continuous acceleration, it’d still take roughly 100 years to reach the closest star (other than Sol). Now, if our cold fusion power plant allows us to build a ship that can travel at almost the speed of light for the entire journey, thus cutting the trip down to around 4 years, but the necessary acceleration to accomplish this would be so great as to turn the crew into jelly in approximately .0000000013 nanoseconds. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [December 1, 2004, 10:50am UTC](https://boards.straightdope.com/t/stellar-exploration/277394/7 "2004-12-01T10:50:22Z")
An H-bomb is a pretty efficient way of turning a little mass into a lot of energy. The problem is: what exactly do you _do_ with all this energy? In space, a nuclear explosion is actually just a very very bright _light_ - it has little _propulsive_ ability - and the same would be true of antimatter annihilation, which would merely be more _efficient_. Now if you had a large plate coated in something which expanded when heated, _this_ could provide the actual propulsion. Hey presto, we have [orion spacecraft](http://en.wikipedia.org/wiki/Project_Orion). These are perfectly theoretically possible with today’s technology: A craft built in space containing a million nukes could feasibly reach 0.1c (a tenth of light-speed) within a few months, **thus reaching Alpha Centauri in 45 years**. “Tomorrow’s” technology might bring us further towards lightspeed, perhaps allowing us to get anywhere in [this map](http://www.anzwers.org/free/universe/250lys.html) in a lifetime (250 years), assuming some slowing down of the aging process or time dilation effects (which only become significant past 0.95c). Further? _Ever_? I think not. We may talk of warp space or wormholes, but the energies and forces inherent in these things are simply unimaginable. It would be fairer to ask: _Will we ever build a spaceship which can fly **through the sun**?_ We had better hope that somewhere on that map is a habitable planet. For What It’s Worth, SETI tells us that nobody on the map is _transmitting_ anything, and the number of candidate _stars_ (let alone planets) is only a small subset. ---
**Author:** ![aahala](https://avatars.discourse-cdn.com/v4/letter/a/a88e4f/32.png) [@aahala](https://boards.straightdope.com/u/aahala)\ **Post date:** [December 1, 2004, 12:03pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/8 "2004-12-01T12:03:52Z")
The responses seem to be narrowing in on the correct answer. It’s 50-250 years, raised to some power. Now all we need to do is find the exponent. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 1, 2004, 12:21pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/9 "2004-12-01T12:21:33Z")
> [@](#): > > The responses seem to be narrowing in on the correct answer. > > It’s 50-250 years, raised to some power. Now all we need to do is find the exponent. I’m not sure what you’re saying… If you have 50-250 years, and you want to get a time as your final answer, the only possible exponent you can raise that to is 1. Or would you expect a voyage to take square years, or cubic years? And to address some of **SentientMeat** ’s points, time dilation becomes significant below .95 c. At .87 c, the dilation factor is 2, which means that the passengers would only age 125 years (within a possible lifespan) for a voyage which takes (relative to an Earthbound observer) 250 years. But why are we restricting ourselves to a human lifespan? The relevant timescale here is the lifespan of the _species_, not of an individual. It took rather more than a single lifespan to get from the Olduvai Gorge, across Asia and half of Africa, over the Bering Land Bridge, and down both Americas to the tip of Chile. But humans did it. Why, then, could we not take a similar span of time to reach the other side of the Galaxy? And for those speculations on warp drives, worm holes, and the like, it does not take an insanely large amount of energy to produce a wormhole. Quite the opposite, in fact: It takes an insanely small amount of energy, one less than zero. Give me a single negative gram of anything, and I’ll give you a warp-drive starship. We’re just not sure if it’s possible to get that negative gram. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [December 1, 2004, 12:36pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/10 "2004-12-01T12:36:41Z")
Of course, I speculated on how far one might go in a lifetime only to illustrate the limits of what one human might accomplish given that they would have to spend their _entire existence_ in a lonely sterile prison, rather than hopping from Star Trek M Class planet to planet in a fortnight or so. Generational ships or unmanned missions could acheive far greater coverage. Similarly, I speculated that getting the necessary negative energy might well require vast _positive_ energy expediture, practically speaking. Certainly, all the proposed means of actually acheiving negative energy I have ever seen appear to require vast cosmic strings or manipulations of spacetime only possible with black holes or the like. ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [December 1, 2004, 1:12pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/11 "2004-12-01T13:12:44Z")
The Thread title _should_ read “ **Inter** stellar exploration”. _Stellar_ exploration would be the study of a star by entering its photosphere. A good trick if you have SPF 10,000,000,000. ---
**Author:** ![InvidiousCourgette](https://avatars.discourse-cdn.com/v4/letter/i/e47c2d/32.png) [@InvidiousCourgette](https://boards.straightdope.com/u/InvidiousCourgette)\ **Post date:** [December 1, 2004, 1:19pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/12 "2004-12-01T13:19:48Z")
Thanks for all the answers. It makes for interesting reading. I liked **SentientMeat** ’s [star map](http://www.anzwers.org/free/universe/250lys.html). If you click around it explains that > [@](#): > > Even our fastest space probes would take sixty thousand years to travel this distance. (the distance to Proxima Centauri) - which agrees well with **Squink** ’s figure. It also says that we have sent or are sending 4 probes out of the solar system - Pioneer 10 and 11, and Voyager 1 and 2. Unfortunately, > [@](#): > > we will probably lose contact with all of them within twenty years I guess even if we develop better propulsion systems, inter-stellar communication is going to be a tricky nut to crack as well. On **preview** , okay **Bosda** , I have been gotcha ya’ed. 🙂 ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [December 1, 2004, 2:16pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/13 "2004-12-01T14:16:54Z")
> [@](#): > > inter-stellar communication is going to be a tricky nut to crack as well. I think the loss of contact with Voyager/Pioneer is more to do with their power contraints. A million-nuke ship could presumably generate a focussed gigawatt beam audible at Earth’s [Arecibo](http://en.wikipedia.org/wiki/Arecibo_radio_telescope) telescope from anywhere in the entire galaxy (assuming the beam is aimed properly). ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [December 1, 2004, 3:06pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/14 "2004-12-01T15:06:29Z")
> [@Tuckerfan](#): > > Let’s say, hypothetically, that we developed something like cold fusion, which is a lot of power in a really small container, and we could build a spaceship that could travel at 1g continuous acceleration, it’d still take roughly 100 years to reach the closest star (other than Sol). At 1g acceleration, you’d get to about 0.7c in a year (you’d get close to c if Newtonian physics applied; the relativistic equations for continuous acceleration are a bit hairier). The final velocity you can reach (limited by your delta-v for acceleration and deceleration, and also by the effects of the interstellar not-quite-vacuum) is a more significant contraint than the crew’s acceleration tolerance. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 1, 2004, 3:12pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/15 "2004-12-01T15:12:22Z")
> [@Washoe](#): > > I don’t have a cite for this, but I read an article on [CNN.com](http://CNN.com) about four years ago which stated that it is possible to accelerate one ounce of matter to half the speed of light using currently existing ion propulsion technology. Color me dubious. Squeezing enough energy out of a one ounce package to accelerate Hoover Dam (5,500,000 tons) to 2,600 mph (m[sub]1[/sub]v[sub]1[/sub] = m[sub]2[/sub]v[sub]2[/sub]) would be a hell of technological feat! Google _does_ turn up your claim, but not at any site I’d consider reliable. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [December 1, 2004, 3:37pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/16 "2004-12-01T15:37:22Z")
Without looking it up, I’d be willing to bet that the total spacecraft size would be much larger than one ounce. Probably they mean the _payload_ would be one ounce, sitting on top of a vast amount of fuel (just like the Apollo spaceships were a lot smaller than the total Saturn V assembly, only more so). It’s not enough to design an engine that can boost at 0.01 g or whatever it is long enough to reach half the speed of light, you’ve also got to have enough propellant to allow you to continuously accelerate long enough to reach that speed. Similarly, for an Orion type starship, quite a lot of the initial mass of your interstellar cruiser is going to be hydrogen bombs; only a fraction of it will be spacecraft (and only a fraction of _that_ will be crew quarters or cybernetics banks or instruments and so on, after subtracting out the pusher plates and radiation shielding and so on). The problem of most of your spaceship being fuel could be gotten around by using a light sail design or (more speculatively) some sort of interstellar ramjet. ---
**Author:** ![MMI](https://avatars.discourse-cdn.com/v4/letter/m/53a042/32.png) [@MMI](https://boards.straightdope.com/u/MMI)\ **Post date:** [December 1, 2004, 3:42pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/17 "2004-12-01T15:42:37Z")
From some NASA pages, assuming a 900 year trip time to the Centauri Cluster (our nearest neighbor), the propellant mass required for various propulsion systems: Chemical rocket: (assuming ISP 500 s) 10^137 kg – more mass than the universe contains Fission rocket: (assuming ISP 5000 s) 10^17 kg - roughly a billion supertankers Fusion rocket: (assuming ISP 10,000 s) 10^11 kg - a mere thousand supertankers Ion/Electric propulstion (assuming ISP of 50,000 s) 10^5 kg, 10 railway cars full ( A separate slide on project Orion shows that ISP projected was between 1000 and 10000 so figure accordingly) The slide concludes that a propellant free method is required. [http://www.nasa.gov/centers/glenn/research/warp/warp.html](http://www.nasa.gov/centers/glenn/research/warp/warp.html) (overall presentation) [http://www.lerc.nasa.gov/WWW/PAO/images/warp/warp06.gif](http://www.lerc.nasa.gov/WWW/PAO/images/warp/warp06.gif) (fuel requirements) [http://www.lerc.nasa.gov/WWW/PAO/images/warp/warp10.gif](http://www.lerc.nasa.gov/WWW/PAO/images/warp/warp10.gif) (project orion) ISP is a measure of a rocket (or jet) “fuel efficiency” the units (in english) are (pounds-force)(seconds)/(pound mass of propellant) (thrust and duration for a unit of propellant mass) - the unit isn’t actually seconds but that is a convenient shorthand. More “practical” than a rocket might be something like Robert Forward’s “StarWisp” which would be a light sail/antenna sail powered by solar powered microwave lasers (of a power considerably above that currently available). The instrumentation would have to be integrated into the spacecraft with a total mass of 16 grams, but the journey would be at 1/5 c so trip time would be on the order of a couple of decades. [![](https://www.nasa.gov/centers/glenn/images/content/84516main_warp11.gif) ](https://www.nasa.gov/centers/glenn/images/content/84516main_warp11.gif) ---
**Author:** ![Loopydude](https://avatars.discourse-cdn.com/v4/letter/l/e56c9b/32.png) [@Loopydude](https://boards.straightdope.com/u/Loopydude)\ **Post date:** [December 1, 2004, 5:42pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/18 "2004-12-01T17:42:19Z")
I know I’m always flogging the antimatter horse, but I think the ability to aquire, contain, and safely manipulate large (meaning on the order of hundreds of kilograms) stores of antimatter is probably necessary before practical interstellar travel will be possible. Having antimatter even as a primer for what would be otherwise very mundane-looking fission bombs, to be used in an old design like Project Orion, _greatly_ decreases the mass of the fuel you need to carry. Not only that, since you can fine tune the mass of the explosive to provide whatever size explosion you want with an antimatter primer, even simple fission bombs become much more versatile. Antimatter also makes a good primer for fusion reactions, and it’s great for generating plasmas that can be used in ion propulsion. Getting lots of antimatter will require practical fusion here on Earth. Production of antimatter is an enormously expensive process in terms of energy input, but if that energy is essentially free (and considering the fact that our capacity for antimatter production has been growing geometrically since we began generating it for experiments), the sky’s the limit. ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [December 1, 2004, 6:17pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/19 "2004-12-01T18:17:33Z")
> [@Loopydude](#): > > I know I’m always flogging the antimatter horse… **edited by Bosda** You are? :eek: Is flogging the antimatter horse an act of animal cruelty? Is flogging the antimatter horse an act of anti-cruelty? Does the anti-horse _enjoy_ his anti-flogging? If so, does this make **Loopy** an animal abuser or an animal lover? Does **Loopydude** enjoy anti-flogging the anti-horse? If so, is **Loopydude** an animal lover? In a nice way? And, what about Naomi? 😃 ---
**Author:** ![Loopydude](https://avatars.discourse-cdn.com/v4/letter/l/e56c9b/32.png) [@Loopydude](https://boards.straightdope.com/u/Loopydude)\ **Post date:** [December 1, 2004, 6:37pm UTC](https://boards.straightdope.com/t/stellar-exploration/277394/20 "2004-12-01T18:37:02Z")
Depends on if it’s got negative mass (which I don’t think it does). If so, flogging is the only way to get close. [Next page](https://boards.straightdope.com/t/stellar-exploration/277394.md?page=2)