17 ms·
To get a spacecraft there it would take: Accelerating at 1g the 1st half, and decelerating at 1g the 2nd half, the traveler would experience 7.3 years of time.
by e0m 10y ago
To get a spacecraft there it would take:
Accelerating at 1g the 1st half, and decelerating at 1g the 2nd half, the traveler would experience 7.3 years of time. For observers it would take 41.8 years at a max speed of 0.998c
If you had a near perfect hydrogen -> helium fusion engine, it'd take about 6 million tons of fuel (about the mass of the Pyramids of Egypt or 2,000 Saturn V rockets)
- pm90 10y agoWhat if we used engines powered by nuclear energy (fission or fusion)? Could we reduce the amount of fuel, since the energy density is so much higher?
- jdormit 10y agoWe don't have any spacecraft that can go that fast, do we?
- JorgeGT 10y agoNo. If I'm not mistaken we're in the order of magnitude of 0.0001c.
- dexwiz 10y agoNo, but we probably could with enough fuel. The bigger issue is space dust. Hitting it at relativistic speeds would be like flying into a cosmic shotgun for the entire journey.
- deleted 10y ago[deleted]
- aaronblohowiak 10y agoCould that cause accidental fusion?
- delecti 10y agoAssuming this [1] is reasonably accurate, very much yes. It proposes fusion occurring at speeds as "slow" as 0.9c. [1] https://what-if.xkcd.com/1/ https://what-if.xkcd.com/1/
- deleted 10y ago[deleted]
- snerbles 10y agoA large mass of water ice would make a decent ablative shield.
- CoolGuySteve 10y agoAccording to this paper, you can travel around 0.5 c before the radiation caused by colliding with interstellar hydrogen kills you: http://www.scirp.org/journal/PaperInformation.aspx?paperID=23913 http://www.scirp.org/journal/PaperInformation.aspx?paperID=2... "Going slow to avoid severe H irradiation sets an upper speed limit of v ~ 0.5 c. This velocity only gives a time dilation factor of about 15%, which would not substantially assist galaxy-scale voyages. Diffuse interstellar H atoms are the ultimate cosmic space mines and represent a formidable obstacle to interstellar travel."
- gech 10y ago
- pshposh 10y agoI've read about laser systems for sending unmanned crafts at high speed: http://www.space.com/29950-lasers-power-tiny-interstellar-spacecraft.html http://www.space.com/29950-lasers-power-tiny-interstellar-sp...
- deleted 10y ago[deleted]
- josho 10y agoIf I understand our capabilities correctly we can't even escape the solar system without using gravity assist boosts from other planets, let alone sustaining thrust for a long period. http://solarsystem.nasa.gov/basics/chapter4-1 http://solarsystem.nasa.gov/basics/chapter4-1
- deleted 10y ago[deleted]
- narag 10y ago"Capabilities" seems a little ambiguous to me. Is it what we have done or what we could do? Using those boosts is a way to achieve the same results, only cheaper. Yes, it's slower than building a big ass rocket, but it seems people that sign the checks are in no hurry. Also if I'm not mistaken, Voyager probes were not even intended to live so long or leave the system. If there were a reason to send a probe to another star as soon as possible and no matter the cost, there would be a way, maybe not fast, maybe very expensive, maybe something weird, but it would be done.
- aaronblohowiak 10y agoI think we do if you look at it in terms of acceleration. As I understand it, In space there is almost 0 friction so "fast" is more about acceleration than "top speed". In this view, 1g isn't that fast.
- xigency 10y agoAbout as "fast" as a helicopter at a stable altitude, or to fit with the no-atmosphere bit, a stationary jetpack or lunar lander (on Earth).
- wallace_f 10y agoDoesn't energy required to accelerate keep exponentially increasing, though? ke = mv^2
- aaronblohowiak 10y agoEnergy is relative to a frame of reference, and IIUC 1g acceleration of the space vessel is in The vessel's frame of reference, not earth's.
- DanBC 10y agoHow much fuel would it take to get 6 million tons of fuel off Earth into the interstellar ship?
- VikingCoder 10y agoStep one, find an asteroid with ice...
- surrey-fringe 10y agoYou have a path from earth to a planet 40 lightyears away. There is a planet every K meters that can house a fuel tank to serve as a checkpoint. Let F be the amount of fuel to take a ship between two adjacent planets. Let 0 be the first and L be the last checkpoint. Suppose a rocket can hold 3F. Go to A, deposit F, and return 2 times. Next rocket goes to B, stopping at A each way to take F -- do the B trip two times. Now you have two tanks at B and none at A. Repeat like binary addition till you fill L-2 with F, then repeat for L=L-3 to L=0. Now each checkpoint except the last and next-to-last has 1F. A final ship can make the trip to the planet, build a civilization, find a fuel source and return with pics.
- phkahler 10y agoIf you make the fuel on Mars it will take less effort to get it into orbit. It's also a bit further up the suns gravity well.
- mjmahone17 10y agoAre we willing to use a railgun, with a rocket burn at apogee? (So one-half orbit from the starting point: without the burn, the object will hit the ground when it completes its orbit). If so, a lot less than is needed by pure rocket burns, where you have to carry all of the mass used to accelerate to orbital velocity.
- dgudkov 10y agoThe best way would be to use a space elevator pipe for this. But it's still not feasible.
- narag 10y ago
- kcorbitt 10y agoThat actually sounds... more plausible than I would have expected. Like, doable with technology I can imagine being within reach in the next 50 years even if we don't achieve any currently-unforseen breakthroughs.
- blueprint 10y agoWhich begs the question, why haven't we at least even tried to have done anything like this already? Do we really need to repeatedly spend comparable amounts of money on yet another dramatic TV special about humans traveling to Mars, as narrated by a favored celebrity? We really are running out of time. And it almost seems like it's pre-determined to happen. :\
- raspasov 10y agoIt sounds like you have a startup idea on your hands : )
- blueprint 10y agoYou've no idea. But for the first step, I need to find one or two very truthful physics grad students / electrical engineers who feel some responsibility for Earth or saving themselves. You wouldn't happen to know someone?
- autokad 10y ago2000 saturn v rockets sounds possible
- colordrops 10y agothe fusion bit not (yet) so much though
- Beltiras 10y agoThat's 2000 chemical rockets. The example talks about a perfect Hydrogen-Helium conversion.
- hcarvalhoalves 10y agoWhat's the math behind your estimations? Doesn't sound so unfeasible.
- ohitsdom 10y agoUpvote for doing the math, but we're going to have to ditch traditional chemical rockets for this kind of trip. Fortunately, we're making progress on alternatives. https://arstechnica.com/science/2017/02/nasas-longshot-bet-on-a-revolutionary-rocket-may-be-about-to-pay-off/ https://arstechnica.com/science/2017/02/nasas-longshot-bet-o...
- ahh 10y agoNote that he's not giving a figure for a chemical engine, but a fusion engine (sometimes termed a "torchship" due to the absurd power involved.) That would be strictly more efficient than VASIMR or similar. The figure would be even more ludicrous with a LOX/LH2 engine. (I did not check his math, however.)
- JumpCrisscross 10y ago> about...2,000 Saturn V rockets Or about 670 BFRs [1]. It would take 6 cycles of tripling size and/or performance to get a single system with enough thrust to meet your 7/42 year schedule. The Saturn V first flew in 1967 [1]; SpaceX plans to launch its Interplanetary Transport System (ITS) in 2022 or 2024 [2]. That's an expected 60 years to triple performance. [1] http://waitbutwhy.com/2016/09/spacexs-big-fking-rocket-the-full-story.html http://waitbutwhy.com/2016/09/spacexs-big-fking-rocket-the-f... [2] https://en.wikipedia.org/wiki/Saturn_V https://en.wikipedia.org/wiki/Saturn_V [3] https://en.wikipedia.org/wiki/Interplanetary_Transport_System#SpaceX_tentative_calendar_for_Mars_missions https://en.wikipedia.org/wiki/Interplanetary_Transport_Syste...
- tim333 10y agoThough that kind of performance is probably not going to come about from improvements to chemical rockets but moving to fusion. There are some promising developments on fusion reactors (see Breakthrough in Nuclear Fusion? - Prof. Dennis Whyte https://www.youtube.com/watch?v=KkpqA8yG9T4 https://www.youtube.com/watch?v=KkpqA8yG9T4) Guess something like that with the 100 million C gas doing the propulsion maybe?
- kristopolous 10y agoThere may have to be some clever system where you don't take a lot of fuel with you. Imagine a type of particle accumulator and aggregator - call it cosmic flypaper. If you're going say 100 km/s, things seemingly insignificant and rare you may be able to collect a lot of pretty quickly.
- Arizhel 10y agoIt sounds like you're talking about the Bussard Ramjet. It collects interstellar hydrogen gas for use in fusion engines. The problem is that it's unlikely there's enough hydrogen floating around for it to really work.
- deleted 10y ago
- drewrv 10y agoHonestly that amount of mass seems doable (the hard part being a near perfect fusion engine of course). Just curious about your calculations though. Did you take into account the fact that you could eject spent helium and therefore lower your mass in transit? Assuming most of the mass is fuel, I would imagine by the time you're arriving there would be very little mass left to decelerate.
- VikingCoder 10y agoHow many Saturn V rockets have we launched in total?
- marssaxman 10y agoThirteen: the last was Skylab.
- actsasbuffoon 10y agoIt would take 37 days at warp 6 (assuming we're using the new warp factors established in The Next Generation). I have no idea how much dilithium crystal would be required though.
- John23832 10y agoWhy can't I up vote more?
- MrZongle2 10y agoMost likely several hundred quatloos' worth, I'm guessing. :D Edit: Oh, HN, you are so humor impaired sometimes.
- fsloth 10y agoVoting is a mechanism to signal whether the comment adds anything to the discussion. Star Trek references really don't add anything to an actual scientific discovery. I would much rather read actual engineering rather than entertainment driven thought.
- mrleiter 10y agoSimply: this is not reddit. Voting happens based on the content of information added by your comment. Not a joke or a wordplay, unfortunately.
- bsmith89 10y agoFor anyone (like me) who wants to adjust the parameters while not having to deal with calculus, this[1] "Space travel calculator" works great. [1]: http://nathangeffen.webfactional.com/spacetravel/spacetravel.php http://nathangeffen.webfactional.com/spacetravel/spacetravel...
- logicallee 10y agoIf we had a near-perfect hydrogen -> helium fusion engine, why would we want to stop at 2,000 saturn V rockets of mass? Hydrogen is cheap AF. Also why would we only want to stop at helium, why not fuse any further? Also why would you want to stop at 1g acceleration - why not 1.5g or 2g, say? Surely living in 2g environment is okay for that period? However presumably there is no good reason for us to go there. Just because there are planets doesn't make it worth the trip.
- noselasd 10y ago> you had a near perfect hydrogen -> helium fusion engine, it'd take about 6 million tons of fuel (about the mass of the Pyramids of Egypt or 2,000 Saturn V rockets) That is assuming constant energy consumption to sustain 1g, but unfortunately that's not the case, the closer you get to the speed of light, the more energy you'd need to sustain 1g, and this becomes unrealistic long before you are anywhere close to the speed of light.
- panic 10y agoYour speed doesn't affect the laws of physics you experience.
- dragonwriter 10y agoIts probably more clear to say that a constant 1G acceleration in the local reference frame takes constant fuel, but produces a progressively smaller acceleration (asymptotically approaching zero as speed in the fixed frame approaches c) in the fixed reference frame you were launched in (or of the point you are trying to reach, the logic is equivalent) because relativity.
- deleted 10y ago[deleted]
- pavanky 10y agoWhat do you consider a spacecraft though. What is the payload mass ?
- gydfi 10y agoThat actually sounds pretty achievable. Difficult, but all within the boundaries of known physics and existing human lifetimes.
- pbhatia 10y agoIs that just for the rockets? We would definitely need much more than that considering we would also need to carry at least a city's worth of infrastructure, supplies, settlers, etc.
- theossuary 10y agoI'm pretty sure he meant a probe. Not a good idea to send a bunch of people to a planet we don't know is habitable (and probably isn't).
- stouset 10y agoAt 0.125g/cm^3 of density, this amounts to a cube of liquid helium about 350 meters per side (43.5 million cubic meters).
- flukus 10y agoIs there any reason to accelerate to the half way point? Accelerating to .99c is much faster and would use much less fuel. It also wouldn't make the travel time much different, to the outside observers anyway.
- deleted 10y ago[deleted]
- andreareina 10y agoIf you accelerate beyond the halfway point you're not going to be able to stop in time.
- flukus 10y agoI mean you can stop well before half way. 2 years at 1g will get you to .97c and drastically cut the fuel requirements.
- bubersson 10y agoAt first I was confused about if the star is 39 light years from earth, how come it would take just 41.8 years from the observer perspective (assuming me looking out of the window). But with pen and paper I see that you would be accelerating the first year up to speed of light, then 40 years at almost speed of light and then one year decelerating. What is the efficiency of some current hydrogen -> helium fusion engine?
- isolli 10y agoIsn't 0.998c unrealistic?
- hansbo 10y agoI don't understand how it could be less than 39 years for the traveler. Time dilation is a thing, but being less than 39 years would mean the traveler observed the planet approaching faster than the speed of light, which should be impossible. Or does space contract as well?
- simias 10y agoThat's correct. You wouldn't be able to do the roundrip expedition in less than 78 years from an observer's standpoint so you still can't transmit information faster than the speed of light, however from the explorer's point of view it might take a lot less time to do that as you get closer to c. If you travel at the speed of light (assuming you're a photon or something) then time stops "existing" altogether and you are simultaneously at the point of origin, destination and everywhere in between. At least that's my understanding of it. I find it both exciting and depressing at the same time, it means that you could potentially make a rountrip to the center of the milky way and back within a human lifetime but by the time you'll be back everybody that remained on earth would be long dead and nothing would be the same anymore. If those types of travels become common then society would stop existing on a single timeframe. It's pretty mind boggling.
- jlebrech 10y agowouldn't it be better to plot a course where pitstops could be made at gas giants?
- hkjgkjy 10y agoFor others who don't know how much an American ton is, 6 mil of them = (5.44 * (10^9)) kilograms.
- credit_guy 10y agoI didn't get the same result. I used the relativistic rocket equation [1], and the change in rapidity from 0 to 0.998c is about 3.5, which means a total change of rapidity of about 7 (static to full speed and then back to static). Assuming perfect hydrogen->helium fusion engine (specific impulse=0.12c) the ratio between initial mass and final mass is 10^25. For comparison the mass of the earth is about 0.6*10^25, or in other words, if you want to send only 2kg of load to this star, you need fuel as much as the mass of the earth. [1] https://en.wikipedia.org/wiki/Relativistic_rocket https://en.wikipedia.org/wiki/Relativistic_rocket