Travel Time in Space

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Andinel Andinel's picture
Travel Time in Space
So, I've been wondering how fast conventional space travel is in Eclipse Phase with the various engines they list in the core rulebook. From what it seems to me, space travel is so slow that egocasting is the only reasonable means of transport for people who don't want to be stuck on a spaceship for months at a time. Just how long does it take to get from planet to planet? What I'd really like is for a table with travel times for every planet in the solar system.
Tyrnis Tyrnis's picture
Re: Travel Time in Space
While I agree with the sentiment, in practice it just doesn't work very well. The problem would be that distance (and thus travel time) vary dramatically based on orbital position -- Mars ranges from roughly .5 AUs to 2.5 AUs from Earth, for example. The best you could really hope for is a table with maximum distance, minimum distance, and mean distance, but even then it boils down to 'however far the GM decides it is at the time' unless you've all decided on a specific year for your game and want to use a solar system simulation to determine more exact distances.
OneTrikPony OneTrikPony's picture
Re: Travel Time in Space
Arenamontanus provides: :) http://www.flickr.com/photos/arenamontanus/sets/72157624693618421/with/4... Remember to thank him if you get the chance, He did the math and chose the pretty colors. Those are not tables they're graphs called porkchop plots. Look [url=http://en.wikipedia.org/wiki/Porkchop_plot]at this wiki[/url] to learn how to read them if you can't figure it out at first. Like Tyrnis says, if you want to have a table (or porkchop) of travel times you have to decide when you're leaving because that determines where everything is when you arrive. I forget the year A-mont. chose for his plots but it makes a huge difference. Jupiter has an 12 year solar orbit and Saturn's is 32 (iirc) so if you use these graphs you're using these positions for the outer system and effectively declaring what year it is. [edit] also he might have used the mean distance. I don't recall.[] see also; http://www.eclipsephase.com/travel-time-how-long-does-it-take http://www.eclipsephase.com/faceted_search/results/DIY%20space%20travel (the main travel time thread) http://www.projectrho.com/rocket/ (Atomic rockets; massive Geekgasm for the uninitiated rocketeer) http://www.fourmilab.ch/cgi-bin/Solar (an electronic orory of the solar system highly recommended) http://clowder.net/hop/railroad/sched.html (Cosmic train schedule will explain EP's earth/mars, Earth lunar, Earth/mars/main belt cycler ships) http://lunaf.com/english/live-data/saturn-moons-position/ (a map of the orbits of moons arround Saturn) http://www.braeunig.us/space/orbmech.htm (a more in-depth look at orbital mechanics) http://www.clowder.net/hop/railroad/deltaveemap.html (A whimsical look at the minimum amount of fuel it will take to get arround the inner system using [url=http://en.wikipedia.org/wiki/Hohman_transfer_orbit]Hohman Transfer Orbits[/url] looks like you have some reading to do. Say, when you're done would you mind comming back here and explaining it all to me? ;)

Mea Culpa: My mode of speech can make others feel uninvited to argue or participate. This is the EXACT opposite of what I intend when I post.

Arenamontanus Arenamontanus's picture
Re: Travel Time in Space
OneTrikPony wrote:
Arenamontanus provides: :) http://www.flickr.com/photos/arenamontanus/sets/72157624693618421/with/4... Remember to thank him if you get the chance, He did the math and chose the pretty colors.
Thanks for collecting it all into a post!
Extropian
nezumi.hebereke nezumi.hebereke's picture
Re: Travel Time in Space
At the table, I generally say it takes 1 month per AU, round up, and leave it at that.
NewAgeOfPower NewAgeOfPower's picture
Re: Travel Time in Space
nezumi.hebereke wrote:
At the table, I generally say it takes 1 month per AU, round up, and leave it at that.
at 0.5% C (given speed in EP, page 348), a Courier boat would take ~27.72 hours to transit 1 Astronomical Unit. Given acceleration/decel times for Antimatter-pumped hydrogen torches, I'd say about 33 hours total transit time.
As mind to body, so soul to spirit. As death to the mortal man, so failure to the immortal. Such is the price of all ambition.
Arenamontanus Arenamontanus's picture
Re: Travel Time in Space
JSnead gave the numbers he calculated for the ships in the core book earlier, and they make physical sense. I have them in my tables in the naval document. One cannot just divide the distance with the delta-v, since 1) there is an (de)acceleration period, 2) roughly half of the delta-v needs to be used for launch, half for slowing. Still, I earlier calculated that the acceleration burns even to max velocity are on the order of hours, so for most trips they are negligible.
Extropian
bRA1N-b0X bRA1N-b0X's picture
Re: Travel Time in Space
I thought I saw "time travel in space" which means my glasses are horrible and/or faulty recognition software in my mind. However, isn't it "travel time THROUGH space?" I mean, travel time through space requires there to be a defined distance between two points, or else the time taken to get there has no destination to provide a reference and target velocity to calculate that, right? No position to position ratio of location to have velocity that can give comparison by how much distance it chews up by interval of time getting there. IN space to show the rapidity of it THROUGH space, like a tunnel or path betweenSpace travel in time? Space travel through time? I don't know. Not being picky, just felt jipped for thinking this was about time travel. :( Did I just sound stupid? Sorry if I do. double :( WAIT! Another edit to insert something: I get the idea that velocity? speed? is a distance-time ratio. Our cars already have a speedometer and our cars have no idea where we're headed and justify its speed at any point along the way. Dammit, I think I contradicted myself and should go sit in a corner. :( I'm sorry. I'm not very smart...*cry*
NewtonPulsifer NewtonPulsifer's picture
Just to muddle things,
"I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve."- Isoroku Yamamoto
Jaberwo Jaberwo's picture
Correct me if I'm wrong, but
Correct me if I'm wrong, but wouldn't using all you delta v during short phases and the end and the beginning of the journey mean that your spacecraft has an extremly big power output? What I just typed into my calculator: delta v = 200km/s Travel Time Mercury Luna (day 50): about 10 days Insignificant time of acceleration: 1 day = 86400 seconds delta v for acceleration: 100km/s Kinetic Energy of ship after accel (asuming a mass of 1,000,000kg): 0.5*1000mt*(100km/s)² = 5*10^15 J Enegy/time = Power = 58 GW = cooling problems for a 1000mt ship? I don't understand all of this enough to have too much faith in my calculations though. Maybe this is too short for the accel/decel time to be insignificant?
NewtonPulsifer NewtonPulsifer's picture
Jaberwo wrote:Correct me if I
Jaberwo wrote:
Correct me if I'm wrong, but wouldn't using all you delta v during short phases and the end and the beginning of the journey mean that your spacecraft has an extremly big power output? What I just typed into my calculator: delta v = 200km/s Travel Time Mercury Luna (day 50): about 10 days Insignificant time of acceleration: 1 day = 86400 seconds delta v for acceleration: 100km/s Kinetic Energy of ship after accel (asuming a mass of 1,000,000kg): 0.5*1000mt*(100km/s)² = 5*10^15 J Enegy/time = Power = 58 GW = cooling problems for a 1000mt ship? I don't understand all of this enough to have too much faith in my calculations though. Maybe this is too short for the accel/decel time to be insignificant?
That's a very good observation. It's actually worse than that - the propulsive efficiency of a fusion rocket is like 1/7000th. So your power output is actually 7000 times that number. [img]http://upload.wikimedia.org/wikipedia/commons/4/45/Propulsive_efficiency... Notice the efficiency dropping off as exhaust speed increases. A 1 MeV neutron is about 14,000km/sec, so a proton is going to be in that neighborhood too. The reason cooling wouldn't be an issue is because the heat is being continuously dumped out of the rocket. This is one of the reasons He-3/He-3 fusion is favored; because it is such an "engineering friendly" fusion process. The entirety of the output is ionized He-4 particles and protons, which can easily be directed by powerful magnets. You can either directly slow down the He-4 particles with your magnets (generating electricity) or just use the magnets to make sure the (very hot) particles get expelled in the right direction. Presumably the fusion drive would also have fancy near perfect x-ray mirrors (to bounce the x-rays back and forth to reheat the plasma) inside it because He-3/He-3 fusion actually creates more energy as x-rays than it does as charged particles. It does show that even a minor breakdown in your fusion magnetic containment would cause big problems - you'd only be able to thrust up to the amount your ship could shed heat at that point, which is going to be some fraction of 406 terawatts (58GWx7000) (also this assumes the x-ray leakage isn't a big deal). So Eclipse Phase fusion rocket ships must be engineered to be able to prevent the vast majority of that 406 terawatts from impinging on the ship itself at all. EDIT: I just realized, the fusion rockets are supposed to have 1/20th of a gravity of accel, right? That's about .49 meters/sec/sec - so a 100km/sec velocity is going to take about 50,000 seconds. EDIT2: My example also assumes the ship runs purely on fusion fragments. That's probably incorrect - a 1000 tonne ship likely say 50% propellant. Mix that with the fusion output to increase your propulsive efficiency. Get something better than 1/7000th. Also has an effect on your delta-v calcs because you are losing mass in the form of propellant as you go.
"I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve."- Isoroku Yamamoto
Arenamontanus Arenamontanus's picture
I did the calculations back
I did the calculations back in the original massive spacewar thread and also found huge power outputs for acceleration. But as I calculated, it is possible to radiate away enough using radiators to stay solid (see my old http://www.aleph.se/EclipsePhase/EP%20naval%20strategy.pdf for details; I *promise* I will reformat and update it with improved calculations when I get the time) But, yeah, spacecraft in EP are essentially flying nuclear reactors.
Extropian
Jaberwo Jaberwo's picture
I have been working on a
I have been working on a warship for EP, but I have spent so much time on the design that I forgot most of the calculations by now, but they all made sense back then... I just realised that my ship has a similar power level but the thrust is just so much lower. I should probably just present what I have and let you guys check the numbers: http://eclipsephase.com/warship
NewtonPulsifer NewtonPulsifer's picture
Arenamontanus,
Arenamontanus, Are you aware of the errors in your paper already (you mentioned improved calculations)? On page 6 you have a 90 million kg ship at 0.5 m/sec/sec accel (45 million newtons of thrust) only having a 9 gigawatt reactor. That's 200 watts per newton - that cannot be right. That's better than a jet plane.
"I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve."- Isoroku Yamamoto
jhfurnish jhfurnish's picture
To make things a bit simpler...
...someone's already done the work for roleplayers. On RPGNow.com, where in fact you can also get all the EP .pdf's (and where I discovered EP in the first place), there are several resources for sci-fi gamers to make the science a little more tangible or 'hard': This tome will make it easier for you to incorporate 'hard science' into your EP gaming (or any sci-fi gaming for that matter - and would probably be unwelcome in a Star Wars game): http://www.rpgnow.com/product/100018/The-Pumpkin-Suit%27s-Manual%3A-Easy... This one will help you Gatecrashers with making up new alien worlds: http://www.rpgnow.com/product/100391/The-GM%27s-Planet-Building-Handbook Solutions for combat in three dimensions, whether in space, zero-gee or other: http://www.rpgnow.com/product/80714/Three-Dimensional-Combat-Solutions Also available on RPGNow.com are tilesets, map creators, printable paper model kits and even soundtracks and maps for sci-fi settings, all on the cheap. Explore.
nezumi.hebereke nezumi.hebereke's picture
And all three for less than
And all three for less than $8. *bought!*