Earth 2.0 discovered? - Page 1
Forum section: electronics / general

author: firewalker
author_rank: Super Contributor
timestamp: July 23, 2015, 05:19:53 pm
content: http://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earthAlexander.

author: mtdoc
author_rank: Super Contributor
timestamp: July 23, 2015, 05:54:35 pm
content: Woo Hoo! A potential new world to escape to!

author: firewalker
author_rank: Super Contributor
timestamp: July 23, 2015, 05:57:08 pm
content: Alexander.

author: SeanB
author_rank: Super Contributor
timestamp: July 23, 2015, 06:23:19 pm
content: Are we taking the telephone handset sanitisers along in the ship as well?

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 23, 2015, 06:34:18 pm
content: More like we're on Kepler-452b v 1.5 cost reduced edition.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 23, 2015, 06:53:53 pm
content: No thanks, since it's older than our Earth, will be full of even more filth and free loaders.

author: retrolefty
author_rank: Super Contributor
timestamp: July 23, 2015, 07:08:57 pm
content: 1,600 light years away, guess they would have to pack a lunch to get there.

author: Mephitus
author_rank: Regular Contributor
timestamp: July 23, 2015, 07:11:14 pm
content: Quote from: SeanB on July 23, 2015, 06:23:19 pmI thought we where all leaving because of a mega-donkey that was going to, I dont know, eat us or something terrible like that?Or maybe its like my wife tells me, in that its doomed or something. Oh well, back to my market research to see if people want fire that can be inserted nasaly

author: mtdoc
author_rank: Super Contributor
timestamp: July 23, 2015, 07:23:52 pm
content: Quote from: retrolefty on July 23, 2015, 07:08:57 pmDamn. I guess we better get working on that warp drive then, becausethe state of charge of our current battery is not looking good.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 23, 2015, 07:30:09 pm
content: The article states 1400 light years. So even at warp 9.9 using the original series calc it would take 527 days to get there.

author: SeanB
author_rank: Super Contributor
timestamp: July 23, 2015, 07:33:16 pm
content: Quote from: dr.diesel on July 23, 2015, 06:53:53 pmWe can sell them shiny beads and TB loaded blankets though.............

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2015, 08:22:07 pm
content: Quote from: retrolefty on July 23, 2015, 07:08:57 pmIf the spacecraft can travel fast enough, that won't be a problem. Thanks to time dilation it should be possible to cover that distance within a human life time, in the frame of reference of the spacecraft of course.

author: firewalker
author_rank: Super Contributor
timestamp: July 23, 2015, 08:56:46 pm
content: It is warp drive. The spacecraft remains still. Also, according to Star Trek TNG, the warp speed is not linear. Warp 9.9 could be around 1000 times the speed of light, if I am not mistaken.Alexander.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 23, 2015, 09:07:04 pm
content: Quote from: firewalker on July 23, 2015, 08:56:46 pmUsing the TNG calc it would take 78 days to travel 1400 light years.EDIT: ^ at warp 9.9

author: JackP
author_rank: Regular Contributor
timestamp: July 23, 2015, 09:07:20 pm
content: Sorry, but doesn't time slow down as you approach the speed of light, thus one can never exceed it?

author: tom66
author_rank: Super Contributor
timestamp: July 23, 2015, 09:27:59 pm
content: Quote from: JackP on July 23, 2015, 09:07:20 pmYes, and mass increases towards infinity, as does kinetic energy ...The only way (according to current physics) to travel faster than the speed of light would be to physically warp space (aka warp drive) ... this isn't really travelling faster than light but instead manipulating the universe to make the distance traveled shorter. See also: wormholes.

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2015, 09:47:29 pm
content: Quote from: JackP on July 23, 2015, 09:07:20 pmYes but that's also why travelling huge distances would be possible if a spacecraft to reach near the speed of light, without exceeding it.

author: JackP
author_rank: Regular Contributor
timestamp: July 23, 2015, 10:23:36 pm
content: Fair point - although who knows what might be left back home when you return...

author: zapta
author_rank: Super Contributor
timestamp: July 23, 2015, 10:56:19 pm
content: Earth 2.0 is a major regression from 1.0. Should go back to the drawing board.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 01:47:04 am
content: Quote from: dr.diesel on July 23, 2015, 09:07:04 pmTNG had warp 10 as a sort of "speed of light" though, whereas TOS could go over warp 11!!!!!!Quote from: tom66 on July 23, 2015, 09:27:59 pmNo, not at all. "Warp drives" move the space-time around the ship itself, the "warp bubble" would indeed move faster than light*, the vessel would just remainn stationary within that area of space-time. Wormholes would actually decrease he distance, but through a totally different mechanism.*There's no known speed limit for space-time, hence expansion.

author: Deathwish
author_rank: Unknown
timestamp: July 24, 2015, 02:08:16 am
content: I'm staying here, there's an extra 20 days a year there that management will make you work.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 02:14:29 am
content: Quote from: Deathwish on July 24, 2015, 02:08:16 amYou never know, the UK has a serious lack of public holidays. They might let you take one of those 20 extra days off.

author: Deathwish
author_rank: Unknown
timestamp: July 24, 2015, 02:16:33 am
content: MM if you believe that you will believe the moon is made of cheese, when have management ever given days of to the masses, or do I read too much Dickens ?.

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2015, 02:20:13 am
content: Quote from: Mechanical Menace on July 24, 2015, 01:47:04 amThe "warp bubble" doesn't move, you form it, travel a bit to reach the end of the bubble, collapse, reform, repeat.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 02:26:44 am
content: Quote from: miguelvp on July 24, 2015, 02:20:13 amNah that wouldn't be warp drive as we think of it. The space-time within the warp bubble you purpose would have to have different physics from normal space-time to allow you travel at faster than light within it for that to get you around any faster than you could otherwise. Acceleration could be easier though.Quote from: Deathwish on July 24, 2015, 02:16:33 amI was actually thinking they may need an extra leap day once every 17 years. That's the extra day off

author: digsys
author_rank: Unknown
timestamp: July 24, 2015, 02:45:54 am
content: All sci-fi aside, we're dying out on this planet, and not really that far off (geo scale)AN EVEN IF someone DID come up with a warp drive, NO women would go anyway !!"Great new dear, we found a new world to move to, but you'll weigh 60% more and .. and .. dear? hello? where'd you go?"

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2015, 02:59:15 am
content: Quote from: digsys on July 24, 2015, 02:45:54 amThat's just silly, there are women that go to space and crave it as much as their lunatic male astronauts.Do you think after we Europeans invaded the American continent women didn't come along to the new world?As for dying out on this planet, well, we shouldn't go there because I see a storm coming.

author: BillWojo
author_rank: Regular Contributor
timestamp: July 24, 2015, 03:57:48 am
content: There you go, believing that Einstein guy again.BillWojo

author: rs20
author_rank: Super Contributor
timestamp: July 24, 2015, 04:20:27 am
content: Quote from: tom66 on July 23, 2015, 09:27:59 pmIt's not possible for an object to travel faster than the speed of light -- but from an outside "stationary" observer, the clocks onboard the spacecraft (and the lives of the people on board) get slower and slower due to time dilation. Thus, it is perfectly possible to travel 1000 light yearswhile only ageing10 years. Google "why do muons reach the earth's surface"; it's the same story -- muons are formed in the atmopshere, and the lifetime of a muon * the speed of light is less than the distance from the upper atmosphere to the ground. Yet they survive the trip. How? Time dilation from our point of view, length contraction from the muon's point of view.Now, to be fair, I've think I've read that this "hack" isn't actually exploitable because somehow accelerating that fast will take more time than the amount of time you save through time dilation (and not just because we don't have engines that good, IIRC it is a fundamental, theoretical limitation? Maybe?). But the bottom line is, if you somehow end up travelling at 99.99xxx% the speed of light, you will potentially be able to travel thousands of light years (from an outsider's perspective) before you die.

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2015, 04:39:59 am
content: A constant 1 g acceleration is all that is needed to travel all the known universe in one lifetime, but we can't do that just yetEdit: according to "Magic Universe: A Grand Tour of Modern Science" by Nigel CalderSo you get there and come back and suddenly the apes have taken over Earth 1.0

author: TerraHertz
author_rank: Super Contributor
timestamp: July 24, 2015, 09:11:36 am
content: Relevant:http://xkcd.com/1555/Also, FWIW, my hunch is that the light speed limit is a deliberate design element in this Universe, and there aren't any loopholes. Not to get into arguments about 'creators'.A light speed limit has an interesting and probably very beneficial consequence: No naturally evolved species-based civilization can spread in space. Only transcended self-engineering individual entities can do so, since they are able to adapt their form to survive very long interstellar transit times, and the serious attrition that would occur over hundreds or thousands of years traveling through dust and pebble filled space at some significant fraction of the speed of light.This is the answer to the Fermi Paradox, and why it isn't a Paradox at all - just a question with an intellectually very uncomfortable solution. We don't see any evidence of large scale 'interstellar empires' for a simple reason: There are none. Not anywhere in the entire Universe, ever, at any time. Nor will there ever be.Notice I'm using the definite term. That's because there is a simple logical proof.http://everist.org/texts/Fermis_Urbex_Paradox.htm(A short SF story. Not the proof, just based around it.)Not sure if I've posted that here before. It's a funny coincidence to have cause to post it today; never mind why.

author: PE1RKI
author_rank: Regular Contributor
timestamp: July 24, 2015, 10:46:27 am
content: im gonna ask Q to snap his fingers and poof me over there instantly.

author: Deathwish
author_rank: Unknown
timestamp: July 24, 2015, 10:56:16 am
content: Quote from: PE1RKI on July 24, 2015, 10:46:27 amYou should know you can't trust Q, you would probably end up in Rura Penthe

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 11:26:12 am
content: Quote from: TerraHertz on July 24, 2015, 09:11:36 amProbably someone has done already the calculations, but I think anO'Neill cylinder(not named after Jack O'Neill from Stargate) could be used as a generations space ship to travel to other solar systems. Would need some enhancements compared to the original design, like an ion thruster and a fusion reactor to power it and to provide sun light and energy, but it should be physically possible.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 11:53:43 am
content: Quote from: FrankBuss on July 24, 2015, 11:26:12 amBut would they be human as we think of it by the time they get there and someone gets back or follows after them? Would the earthbound group still be human? How would the two branches have diverged in biology, technogy and culture? How would the other groups who went other places compare with "us" and each other? Just look at how cultures on earth have differed after they settled in different places over smaller time scales and distances, and they were all dealing with roughly the same environment on the same planet. Now imagine how much bigger the problems of meeting up with the rest of humanity would be compared to our less than amazing history in that situation.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 24, 2015, 11:55:53 am
content: Quote from: FrankBuss on July 24, 2015, 11:26:12 amOf course it's physically possible. Special Relativity is well established, but there are still people that either don't believe it, or simply don't understand it. There's no travel impediment to colonizing wherever we wish to colonize. It's more a matter of needing a bit better technology and the actual desire to do it. Truthfully, we could probably do it with the technology we already have, but that second part is insurmountable. We can't even get anyone excited about maybe going back to the Moon.

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 12:33:10 pm
content: I don't think culture would change much, and of course not biology, because it would only travel for a few hundreds of years (subjective time) to reach any point in our galaxy. Communication with Earth during the voyage would be possible, too. But latency for internet would suck. Fortunately some people thought about it already:Interplanetary Internet. But would need some enhancements for intersolary internet.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 12:49:41 pm
content: Quote from: FrankBuss on July 24, 2015, 12:33:10 pmHow about once they reach their destination? And they may only experience a few hundred years but those not travelling at those sort of speeds wouldn't.

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 12:53:37 pm
content: Right, would be really fascinating to see the Earth changes in a 10x timelapse or faster.

author: EEVblog
author_rank: Unknown
timestamp: July 24, 2015, 01:24:09 pm
content: Quote from: rs20 on July 24, 2015, 04:20:27 amThe problem of course is one of mass, and the energy required to get up to any decent speed.

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 01:59:17 pm
content: It would be difficult, but possible. Anyone who wants to calculate it? Should be possible withthe rocket equation. And we should assume that a fusion reactor is possible (the sun demonstrates it), because then we could use water from a dwarf planet like Ceres, to avoid the required energy to transport it outside the earth gravity. And the ship should have an ion thruster, because of the high effective exhaust velocity. A good question would be how long subjective time do you need with such a ship to travel to a planet 1,400 lightyears away, if your ship is made of 99% fuel (deuterium) ?

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 02:23:43 pm
content: Quote from: FrankBuss on July 24, 2015, 01:59:17 pmDo they have enough thrust to produce enough g through acceleration/deceleration to keep the travellers happy and healthy? Say the 6m/s2I've heard people suggest would be enough? I know they're efficient but I could imagine some problems scaling them up to there.Also remember you don't just need the energy for ion-thrusters but some gas to use as a propellent. Xenon is expensive and you'd need more of it than you would deuterium even if we could make small efficient fusion reactors*.A big friendly rocket burning hydrogen and oxygen obtained in space would probably be the place to start. A Bussard ramscoop could even be used to collect more fuel while travelling.*The added weight for neutron shielding would be a problem too.

author: continuo
author_rank: Frequent Contributor
timestamp: July 24, 2015, 03:11:35 pm
content: Voyager 1 will pass Gliese 445, a red dwarf star, in aboutfourty thousendyears from now. The distance to our sun is approx. 17 lightyears. Seventeen... It's so depressing...

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 03:43:03 pm
content: I did aquick table with some calculations, everyone can edit it online to test different numbers. I was too optimistic. Using available technology, like liquid oxygen/hydrogen rockets, you would need 63,000 years to reach the next solar system, Alpha Centauri, 4.37 light years away. Speed would be only 20,000 m/s and can't be much faster without really a lot more fuel than the 1/100 ratio. If you want to use a Stanford torus ship, with 1.8 km diameter, it would have a mass of 10 million tons, so the required water (for times 100) would fill a square tank of 1,000 m side length. To reach Earth 2.0 in 1,400 light years distance, you would need 20 million years. A Stanford torus might be repairable for a 63,000 years travel, but not for 20 million years. So would require some intermediate stops, or better rocket motors.PS: I didn't calculate the stop maneuver, would be a fly-by at full speed, or required mass for the rocket motor and time to accelerate etc., and you would need some more fuel for the artificial sun etc., so it would require even more years, this was an optimistic calculation.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 04:33:05 pm
content: Quote from: FrankBuss on July 24, 2015, 03:43:03 pmOne of the reasons I thought about getting the artificial gravity from constant acceleration for a year and half or so* (depending on the distance you're wanting to go), with a couple of weeks (in it's time frame) zero g while turning around to start decelerating. You wouldn't need a ship that is so big by necessity as you wouldn't need rotating sections or a population that can keep going for multiple generations. Orders of magnitude smaller crew needed, simpler smaller vessel. Still need a lot of fuel but what you can scoop up in transit would actually have an impact on a smaller vessel.*At a constant 6m/s^2 you'd be at 99.999 the speed of light in just a smidgin over 18 months, assuming you start from a dead stop.EDIT: You could even use the separate stages idea in reverse. send a fuel tank ahead and catch up with it when the ship and it are at the same speed. last chance for that would be the "zero g" section of the flight though.

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2015, 04:46:22 pm
content: Quote from: FrankBuss on July 24, 2015, 03:43:03 pmHelios 2 reached 70,220 m/shttps://en.wikipedia.org/wiki/Helios_(spacecraft)

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 04:55:01 pm
content: I don't think you can accelerate for 18 months. Even the best known experimental ion thruster has a specific impulse of 6,000, which is 58,839 m/s exhaust velocity, which results in a final speed of 270,000 m/s (for a fuel/payload ration of 100). Would require still 4,800 years to Alpha Centauri. You would need a new thruster technology.But at least for a good start velocity you can use a slingshot maneuver, maybe they did this with Helios, too.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 05:30:41 pm
content: Quote from: FrankBuss on July 24, 2015, 04:55:01 pmI'm not thinking ion thrusters but hydrogen-oxygen rockets. Ion thrusters just wouldn't work for manned missions (yet, maybe never) without massive intergenerational ships. And yes no ones run a rocket motor for 18 months none stop but I bvet that'd be easier to achieve.But no matter how you do the constant acceleration (and ignoring things like Alcubierre drives) I really think that's our best bet for travelling the galaxy. I picked the 6 m/s^2 as I've heard that's a nice balance between what would be possible on today's tech (money no object admittedly) and what would keep people healthy.Anyone got an idea how the time dilation would effect how the travellers experience acceleration one it becomes noticeable enough? If they're running 2 times slower than a stationary observer would they only need 1/2 of the acceleration from the observers point of view to feel the same g?

author: FrankBuss
author_rank: Unknown
timestamp: July 24, 2015, 05:41:24 pm
content: I'm not an expert, and maybe my spreadsheet is wrong, but the rocket formula says, even with a mass ratio of pay load to fuel of 1 billion to 1 you can only reach 100,000 m/s (and it increases slowly because of the logarithm). No way to go faster without higher exhaust velocity of the rocket motor, regardless how expensive it is. Relativistic effects are not very important at this speed.

author: apis
author_rank: Super Contributor
timestamp: July 24, 2015, 07:48:56 pm
content: Quote from: miguelvp on July 24, 2015, 04:39:59 amThe apes are already in charge actually.

author: McBryce
author_rank: Super Contributor
timestamp: July 24, 2015, 07:59:22 pm
content: I don't think propulsion is the biggest problem. Even if you do manage to get up to the required speeds, at those speeds you have zero chance of avoiding some random rock floating around in space. You'd have to pre-sense and pre calculate a path which I doubt is possible. Hitting even a tiny rock at those speeds would release serious energy.McBryce.

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2015, 08:13:23 pm
content: Quote from: McBryce on July 24, 2015, 07:59:22 pmOnce you are clear of the solar system there is not much out there to hit. You will have to slow down before entering the destination system though.

author: McBryce
author_rank: Super Contributor
timestamp: July 24, 2015, 08:15:47 pm
content: "Not much" is still more than zero. It would only take one impact to end the mission, so you need to be 100% sure that there's nothing in the way.McBryce.

author: continuo
author_rank: Frequent Contributor
timestamp: July 24, 2015, 09:06:55 pm
content: That's why you shape your Juggernaut like a needle and cover the front with a few hundred meters of ice. Will also protect you against hard radiation, which will be a real problem once you approach a significant percentage of the speed of light...

author: calexanian
author_rank: Super Contributor
timestamp: July 24, 2015, 10:06:03 pm
content: Quote from: SeanB on July 23, 2015, 06:23:19 pmNo. remember that we already sent them in the other ship to that primitive planet with all the Hairdressers and middlemen insurance salesmen and but that ding bat captain in charge of the ship.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 24, 2015, 10:22:12 pm
content: Quote from: McBryce on July 24, 2015, 08:15:47 pmAcceptable losses. We're happy to accept a certain number of people dying for the benefits brought by a lot of things, even if we don't admit it openly often. When everybody involved is aware of and willing to take the risks it's tragic when that impressive failure happens, but the proverbial happens and at least they were concious of taking the risk and happy to do so. Most who die as a socially acceptable statistic don't really have that luxury.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 05:34:11 am
content: Quote from: FrankBuss on July 24, 2015, 05:41:24 pmI'm not sure I understand. Why does the exhaust velocity matter? Force is force. I'm sure I could find a reference frame where my exhaust velocity of ANY rocket is significantly negative, but the rocket still moves forward all the same.

author: FrankBuss
author_rank: Unknown
timestamp: July 25, 2015, 06:00:15 am
content: Quote from: John Coloccia on July 25, 2015, 05:34:11 amSee the derivation part of the formula:https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation(basic Newton mechanics). Only the exhaust velocity and the mass ratio matters. That's the beauty of the forumula. It doesn't matter how many motors you have and how fast it accelerates. If you know the mass ratio of ship with fuel and ship without fuel, and the exhaust velocity, then you know the final speed. And because it is the log of the mass ratio, you need either a really reaaaaally high mass ratio, or a high exhaust velocity, which is linear in the formula.

author: FrankBuss
author_rank: Unknown
timestamp: July 25, 2015, 06:29:09 am
content: And of course, you can't trick the formula. Say if you fly with vx, then you could start the engine again and add dv. To reach vx you need vx=ve*ln(m0/m1). Then you need dv=ve*(m1/m2) for the second start to reach v=vx+dv. Butvx+dv=ve*ln(m0/m1)+ve*ln(m1/m2)=ve*(ln(m0/m1)+ln(m1/m2))=ve*ln((m0*m1)/(m1*m2))=ve*ln(m0/m2)This would be a nice "fundamental friday" episode, if Dave were teaching physics instead of electronics.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 01:07:12 pm
content: Quote from: FrankBuss on July 25, 2015, 06:00:15 amI understand now. I never knew about the "rocket equation". It's just different way of breaking down the actual forces involved without having to do all that messy calculus.But the kinds of drives you would consider, such as matter/antimatter drives, achieve exhaust velocities of .5c or better. Plug that into your spreadsheet (1.5*10^8 m/s), and you'll see that the weights involved are quiet modest and achievable.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 25, 2015, 01:24:10 pm
content: OK am I right in thinking that to to get up to relativistic speeds no single propulsion method we have now would do it in regards to manned space flight? Those that would be better for starting the journey have a lot of thrust but too small an exhaust velocity once you reach certain speeds to keep accelerating, but the higher exhaust velocity/lower thrust options would help there?

author: EEVblog
author_rank: Unknown
timestamp: July 25, 2015, 01:31:43 pm
content: Quote from: McBryce on July 24, 2015, 07:59:22 pmAnd don't forget the energy required to slowback down too! Everyone seems to forget that that little technical detail. It's the reason why the New Horizons probe couldn't orbit Pluto, it was going to fast and didn't have the fuel to slow down.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 01:52:12 pm
content: Quote from: Mechanical Menace on July 25, 2015, 01:24:10 pmThe short answer "yes." The longer answer is "it depends what you mean by relativistic speeds."Time dilation by velocity:%Speed of light | Dilation fraction (divide the "rest" observer time by this)0 | 110 | .995 <-- Pretty much the upper bound with a nuclear fusion based propulsion system.25 | .96850 | .7575 | .6690 | .4395 | .3199 | .14As you can see, there's little gain relativity-wise unless you are going honkin' fast. At half the speed of light, the trip to Alpha Centauri 4.5 light years away would take 9 years for the folks back home, and 6.75 years for the traveler. This of course discounts acceleration/deceleration time. If you could accelerate your behemoth starship at a solid 1G, it would take 176.8 days to get to 50% the speed of light, which means on the Alpha Centauri trip, you'd have already traveled 1.14 trillion km (.12 LY), and of course if you'd need similar room to stop.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 02:01:03 pm
content: Quote from: Mechanical Menace on July 25, 2015, 01:24:10 pmThat's what confused me too. The exhaust velocity is an input to the equation, but not because you need a high exhaust velocity to achieve high speeds. Force causes acceleration, not exhaust velocity, but knowing the exhaust velocity, you can calculate the change in momentum because you know THIS much stuff was tossed out the back THIS fast.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 25, 2015, 02:12:48 pm
content: Quote from: HP-ILnerd on July 25, 2015, 01:52:12 pmThe speeds where Lorentz contractions and time dilation become noticeable to the casual observer and/or dominant effects. About 85% the speed of light sound about right?Quote from: John Coloccia on July 25, 2015, 02:01:03 pmYeah, I get that. But lets say I'm in space throwing tennis balls to accelerate. As I start to get faster to keep up the same rate of acceleration I need to throw more tennis balls at the same speed at once. I then get to the point where I'm throwing say 20 tennis balls at once and it seems I start to hit diminishing returns no matter how many balls I throw at once. It seems at that point the best option would be to throw 1 ball 20 times as fast or am I getting that wrong?

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 02:18:27 pm
content: Quote from: Mechanical Menace on July 25, 2015, 02:12:48 pmGive or take. See my updated post. I inadvertently posted it before I was finished. :/

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 02:19:39 pm
content: Quote from: EEVblog on July 25, 2015, 01:31:43 pmYou turn around and thrust the other way.I also don't think space debris is a particularly huge concern. Practically speaking, space is empty. It only starts getting crowded where you have a lot of gravity to collect things together. Also, if you build your vehicle in space and don't care about how expensive it is to build, you can build it to take quite a beating. You won't survive slamming into a big rock, but I don't see interstellar dust being a real problem.I think the biggest impediment is that no one actually cares about doing it for real, but if we DID want to do it for real, I'm pretty confident we could do interstellar travel. It might not be the safest mode of transportation, and it may even take multiple generations to get where you're going, but these are philosophical concerns, not engineering or scientific concerns.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 02:28:48 pm
content: Quote from: Mechanical Menace on July 25, 2015, 02:12:48 pmF=MA....that's all there is to it. There is no velocity term in there. Your reference frame moves with you!The implicit assumption in the rocket equation, and really the point of it, is that it assumes all of your mass is getting dragged along with you. That means that the exhaust velocity term is really an acceleration term, because you ultimately have to accelerate the mass TO the exhaust velocity because the mass is assumed to be at rest IN YOUR REFERENCE FRAME. But it's even simpler than that because he simply uses transfer of momentum to figure it all out, but ultimately it's a consequence of F=MA.

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 02:31:29 pm
content: When you are doing a good percentage of C space becomes very crowded. Though you might only have 100 or so protons ( elemental Hydrogen) per cubic kilometre, when you are doing a shedload of those per second all those little atoms add up to some serious erosion and a massive radiation source as you are essentially sitting in a proton accelerator like the LHC, and with a lot more energy being pushed at you.Bussard ramjet anybody? Just need to figure out how to make some really big monopole magnets to use for the compressor, and then you can get enough H to do plain compression fusion to power the ship and drive. To brake turn around, it still works, though you will need a lot of fuel to speed up to speed and the same amount to stop. Bussard got fusion running in a magnetically confined plasma, using gas densities similar to space vacuum. His biggest problem was the magnets required having finite volumes and his test chamber being too small for bigger more efficient ones.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 02:44:31 pm
content: Quote from: John Coloccia on July 25, 2015, 02:28:48 pmCareful, there. "A" in F=MA is deltaV/deltaT. If deltaV is very large (relativistic), things start behaving oddly. I.e., M doesn't behave like a constant anymore.There's inevitable issues trying to shoehorn Newtonian mechanics into Relativity. It's where unfortunate notions like "Relativistic Mass" wander in to be frowned on. Relativistic momentum (which only uses a rest-mass term) avoids the problems.

author: EEVblog
author_rank: Unknown
timestamp: July 25, 2015, 02:53:18 pm
content: Quote from: SeanB on July 25, 2015, 02:31:29 pmYup, and ships are big.Even at 1/10th light speed which would be phenomenal, the nearest exoplanet istwo generations (40 years)away:https://en.wikipedia.org/wiki/List_of_nearest_terrestrial_exoplanet_candidatesMost others are several hundred years travel time.That's one boring arse existence for those who want to go.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 02:58:39 pm
content: Quote from: HP-ILnerd on July 25, 2015, 02:44:31 pmI know that, and you can take special relativity into account if you want to, but the question was about having to toss stuff out faster because you're traveling faster. The answer to that is no. So for example, when you're zipping towards some galaxy at .999c, it takes the same amount of force to toss a baseball from the back of the ship to the front of the ship as it did in orbit around the Earth. Your reference frame always travels with you, and by and large that's why there is no V term in physics, just like there are generally no (X,Y,Z) coordinates. Yes, V terms do show up in some specific equations, but it's really a dV term where some arbitrary reference frame is considered to be at rest.In fact, the most striking realization of this is with the Twin Paradox....how does it know which twin to age and which one to keep young? Trying to figure this out just looking at the velocities involved is what leads to the paradox.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 25, 2015, 03:01:45 pm
content: Quote from: SeanB on July 25, 2015, 02:31:29 pmEven below the speeds where the ramjet would work the ramscoops could pick up additional hydrogen fuel (for rocket or fusion stages) and propellants for say plasma thrusters. May not be as efficient as ion thrusters but they are nowhere near as picky when it comes to propellants. Some forms work really well with lithium and/or nitrogen which are both a bit easier to come across than xenon but what little xenon you come across could still be stored.Now with the fusion ramjet straight doing mainly hydrogen hydrogen fusion it would produce a lot more high energy neutrons than easier to achieve reactions (say on the ships fusion reactors) so even more shielding would be needed around the fusion chamber than around any straight up fusion reactor.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 25, 2015, 03:29:54 pm
content: Quote from: SeanB on July 25, 2015, 02:31:29 pmBut that's an engineering problem, not a technology problem. You can even send a scout ship just in front of you to clear the way. You might even end up with a shockwave that will tend to deflect other incoming particles to begin with. Clearly, this isn't an impossible problem. It's a cost problem...how much shielding do you need, and who's going to pay for it? You assemble your craft in space, and get the pieces up there 1kg at a time if you have to.If you look at what's actually required, what you will find is the biggest impediment to doing it for real is that no one actually wants to do it for real. Yes, people would do it with a Star Trek style warp drive, but the resources required to do it for real now are such that no one is interested. Oddly enough, the case may have been different 50 years, but today we just don't have the interest.

author: mtdoc
author_rank: Super Contributor
timestamp: July 25, 2015, 04:44:32 pm
content: Quote from: John Coloccia on July 25, 2015, 03:29:54 pmAnd we no longer have the excess resources and productive capacity.50 years ago we were still in an era of productive growth. In the 1980s we transitioned to an era of destructive growth (borrowing from the future). That era is about to end as we transition into an era of cannibalistic growth - where any economic growth is derived from salvage and repurposing of existing infrastructure and materials.Though it's fun to imagine and discuss the challenges of interplanetary space travel (which we were all brought up to believe was inevitable) the reality, IMO, is that it will remain a fantasy.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 25, 2015, 05:02:36 pm
content: Quote from: mtdoc on July 25, 2015, 04:44:32 pmInterplanetary isn't a fantasy. It has been done quite a few times. We just gave up on sending people when it became obvious you don't have to go that far to be able to end all life on earth. Why put nukes on the moon when you can hit anywhere on the planet with a sub orbital missile?Interstellar space travel will remain a fantasy for one reason, what was once a common place time scale for getting there and back was longer than most jobs or even marriages last now.QuoteProductivity per person is higher than it's ever been, it's just that now only the top 5-10% reap the benefits of that increased productivity. Everyone else is punished for it with lower wages compared to when we were less productive in dollar value (inflation adjusted) to the employer per hour worked.QuoteSo there was a time after a sharpened stick was the height of technology when we didn't rip down the old for materials to make the new?

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 05:35:39 pm
content: Shielding is easy for neutrons, you just need enough water ice. You might lose a few kilometers per decade from the front from ablation, but there is a lot of water ice ( may not be pure, but you can pull out the impurities as building materials) and a lot of iron as well for shielding out in orbit around the outer planets, and past Mars.We just have to GET OUT THERE!

author: mtdoc
author_rank: Super Contributor
timestamp: July 25, 2015, 05:51:45 pm
content: Quote from: Mechanical Menace on July 25, 2015, 05:02:36 pmYes, of course, I was referring to interplanetary travel with people.QuoteI don't disagree, but productivity per worker is not the same as excess productive capacity on a societal level which I was referring to and which depends largely on the availability of excess, inexpensive, and easily extractable resources (the key being oil)QuoteYes, but we are quickly approaching a time where virtually all new production is derived from salvage of previously used materials, with all the thermodynamic and net loss of energy consequences that implies.

author: Zero999
author_rank: Super Contributor
timestamp: July 25, 2015, 06:16:34 pm
content: Quote from: miguelvp on July 24, 2015, 02:59:15 amIt was a joke. Perhaps I was the only one who got it?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 25, 2015, 06:37:43 pm
content: A lot of things have changed since spaceflight was everyone's dream and seemed inevitable. In the 1950s and early 1960s the productive core of the population of the developed world had just been through a worldwide conflict. For someone who has lived a decade or more with the realization that death tomorrow is a very real possibility the dangers of space were not as daunting as they are for those who have grown up in a world where a toy with unpadded edges is considered an unacceptable risk.The difficulty of space has also sunk in. Many people in the 1950s and 1960s had witnessed the transition from horse and buggy to automobiles, the invention of the aircraft and the transition from a flight of a few dozen meters to supersonic flight and transcontinental distances. There was a widespread belief that everyone would be commuting by air in the near future. It seemed inevitable that a new fuel, or new materials technology would put spaceships in everyone's back yard in a decade or two. We have now seen that for space you have to do a lot of big things right every time to succeed. Even SpaceX is finding that the path is difficult.And finally, I agree in a way with mtdoc. We are transitioning to a spoils economy. The vast majority of people don't think in terms of creating wealth, they think in terms of how to get some of the wealth that is out there. I am not as sure as mtdoc seems to be that this is driven by fundamental physics, but it is very real.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 10:29:08 pm
content: The overriding problems in interplanetary manned travel are lift cost and trip time. Trip time is easily addressable, but more efficient propulsion systems are inevitably leveraged to add mission mass and sacrifice trip time because of high lift cost. Even New Horizons utilized an Atlas V plus a convenient Jupiter gravity assist instead of (or in addition to) a much larger Delta IV Heavy booster saving on the order of a $100 million on the mission cost.As long as lift costs remain high (and this is an ancient debate) space travel will be relegated to expensive "missions" rather than more modestly priced "travel."This is why SpaceX (and now it's competitors, even ULA) are looking to reusable technologies to reduce lift cost. When 0.3% of the cost of a Falcon 9 mission is propellant, and 80% of the cost is the first stage, being able to reuse the first stage even 1 time is a big deal. Every factor of two you reduce launch cost is a really big deal, every order of magnitude is a really huge deal.Consider also the cost of non-reusability on interplanetary flight. If you are forced, due to high lift costs, to spend a more efficient engine on increasing mission mass rather than decreasing mission time, amortizing the cost of a vehicle becomes problematic.If the orbital re-phase to Mars is ~18 months, and your reusable craft can only make one six month trip per re-phase, even discounting other mission duration parameters, it would mean it would still take you over a decade to amortize the per mission cost by a factor of 10. I.e., (NRE+lifetime operational costs)/number of missions. Under those circumstances, you can never even approach the several paying trips per day airlines get to have a reasonable ROI for a vehicle. In fact with current launch costs, there's nothing in space that can get you an ROI at all.As an aside, real estate matters too. The ISS is in a ridiculous orbit so as to accommodate the Russians. The high inclination means you have two launch opportunities per day from any useable launch location, and from Canaveral only one is useable per day because launching Southeast takes you over inhabited islands. If you had an equatorial space station, and an equatorial launch site, you getsixteendirect rendezvous opportunities per day. With a proper reusable SSTO (Holy Grail), even if you were taking your time such a spacecraft could fly several mission per day to move people and cargo to this station. No two-day chase downs needed.Interplanetary space travel combines the worst aspects of ships (long trip time) and planes (high costs) and amplifies them. Both can be mitigated, but it will always be the most expensive form of travel. However, it is not in any way inconceivable that it might become affordable for individuals to become part of a colonization effort, nor is it inconceivable that it can become profitable for the users of spacecraft, not just the launchers of them.As I said, this debate is ancient. The problems have been well known since almost the beginning.Here's a swank paper from Los Alamos National Labs from way back in the 90's that addresses mission mass, radiation protection and trip time in a completely realistic manner. No Warp Drive necessary.http://fas.org/sgp/othergov/doe/lanl/la-ur-97-3361.pdfThe amazing thing for me, is that SpaceX's recent serious drive for reusability seems to be spurring their competitors to develop it too. It's like I smell springtime in the air. The smell of the giant private-space disaster from the 90's (Kelly,Kistler,Roton, etc.) is finally going away. I think I have a hint of what it must have been like back in the late 50's and 60's when anything seemed possible.If Lockheed can pull off that fusion reactor they described last fall as advertized (i.e., the size and power) then the whole solar system is available to manned exploration and colonizing the moon or mars becomes (by today's standards) almost easy. Assuming (of course) low lift costs.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: July 26, 2015, 09:52:15 am
content: Quote from: HP-ILnerd on July 25, 2015, 10:29:08 pmThat's the main thing that's holding us back in my opinion. But I honestly think that as soon as someone can afford to get some form of base mining and manufacturing equipment up there it won't be as big a deal. I don't see the point of building a massive space ship on Earth instead of in high orbit, pulling in space junk and asteroids for raw materials.