04-06-2014, 08:14 PM | #1 |
Join Date: Mar 2013
|
[Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
OK, I'm working on a so far hard Sci-fi setting and I've got two planets that are 400 AU apart, +/- 44 AU. Now according to my math that means that at a velocity of ~300 mps it will take a ship 4 years to move between the two planets.
My problem is that I want there to be somewhat regular trade between them (In fact one's supposed to be settled from the other). Now the basic issue here is drives, the tentative TL for the setting is TL9, but I'm thinking that most of the freighters use older systems, such as Ion Drives. No I'm thinking that lithobraking can be used at the journeys end to slow the ship down, but that still leaves me trying to figure out how to get the ship moving that fast. Boosters/upper-stage's are just sort of wrong for the setting, there's supposed to be a lot of traffic so it doesn't work out. Catapults could work, but how long would a human usable one be? Increasing the amount of delta-v is out, at least for Ion Drives, from what I can see the specific thrust they get is Spaceships is twice as high as it should be. Mag-sails are an option, but both they a Ion Drives have an acceleration problem, though I might be able to get by that with Mag-sails. So what do you suggest I do? |
04-06-2014, 08:43 PM | #2 | ||||
Join Date: Feb 2007
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Quote:
Quote:
Quote:
Quote:
|
||||
04-06-2014, 09:12 PM | #3 | |||
Join Date: Jun 2006
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Quote:
Quote:
Quote:
It's very optimistic for an ion drive though. If you are going to do this with a ship that is only half fuel tank, you'll need an exhaust velocity of about 0.1% of c, which if you are accelerating it electrically means dropping your ions through on the order of 10 million volts. You're going to need an impressive power plant.... Realistic space flight is like that. It takes a long time to go anywhere, and 400 AU is a *tremendous* distance even on the scale of solar systems. It's an odd one too - 55 light-hours - several times the separation even widely separated binaries, but amazingly close for independent stars.
__________________
-- MA Lloyd |
|||
04-06-2014, 09:55 PM | #4 | |||
Join Date: Mar 2013
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Quote:
Quote:
Quote:
Can you think of what else you need to know? |
|||
04-06-2014, 11:35 PM | #5 |
Join Date: Feb 2005
Location: Berkeley, CA
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Any meaningful fraction of 300 kps will vaporize any conceivable TL 9 ship, as they basically turn the kinetic energy of your ship into heat, and 300 kps is 45 gigajoules per kilogram, which is likely somewhere upwards of 1,000 times the energy required to turn the ship into an expanding cloud of vapor.
|
04-06-2014, 11:36 PM | #6 |
Join Date: Aug 2007
Location: Vermont, USA
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Lithobraking can only be done once low orbit speeds are achieved or from the low speeds of interplanetary transfer orbits, not from effectively interstellar speeds. In GURPS Spaceships terms, it's just a Soft-Landing System.
A single GURPS Spaceships magsail* can achieve 375 mps in 712 days (1.9 years) over the span of 124 au (assuming maglines out that far). The remaining 276 au will then take 792 days cruise time (2.2 years). I'm not sure how long aerobraking would take, but it's going to be at least half a year and possibly multiple years, if it's even possible from those speeds. Since this is a binary system, it might be better to just use the magsail for braking -- then it's 436 days for a 152 au cruise, plus 712 days for accel and decel each (1,860 days total = 5.1 years). Adding more magsails can cut the accel and decel times down by hundred of days each. For example, with 6 magsail systems the accel/decel time is 119 days each over 21 au, with a 1,027-day cruise over 358 au, for a total travel time of 1,265 days (3.5 years). Adding more magsails only takes a few weeks off the time. Adding an advanced fusion pulse drive (20 mps/tank) to burn after the magsail maxes out its velocity can cut down the cruise time depending on how many fuel tanks you want to give it. The best combination of 12 propulsion systems (sails, drives, and fuel tanks) I could find was 5 magsails and 6 fuel tanks which gave a total travel time of 1,011 days (2.8 years). But if you only want to commit 6 systems to propulsion, it's better to go all magsails. * a realistic magsail probably leaks plasma so would require fuel tanks that projections give only 6.8 mps/tank. Last edited by munin; 04-06-2014 at 11:40 PM. |
04-07-2014, 12:41 AM | #7 |
Join Date: Mar 2013
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
6 Magsails is probably a bit high, but I was thinking of boosting their performance. And I'm thinking of dropping the distance between the two stars down to somewhere around 136 AU, which should make things bette
|
04-07-2014, 01:37 AM | #8 | ||
Join Date: Aug 2004
Location: Alameda, CA
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Quote:
Quote:
People would travel in suspended animation. Like that Mars exploration/colonization proposal, it will be a one-way trip, at least initially. Round trips would be rare. or possible, but awkward. The twin effect happens without approaching relativistic speeds. For example, Joe leaves planet A for planet B for 12 years leaving behind a wife and two small children. While in space, he is suspended animation. When he gets back, he has aged four years while his wife and kids have aged 12. To remedy this the spouse and kids could be put in suspended animation during the travel times without leaving planet A.
__________________
Fraser: "Could you elucidate, sir?" Welsh: "No, no. Not since the late sixties." Ray: "That's Canadian for explain." --- from "due South" episode Seeing Is Believing |
||
04-07-2014, 01:39 AM | #9 |
Untagged
Join Date: Oct 2004
Location: Forest Grove, Beaverton, Oregon
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
Suspended animation has never been proven to work. That would push the TL to 9 or 10. If that's allowed, then all sorts of THS type engines become possible.
__________________
Beware, poor communication skills. No offense intended. If offended, it just means that I failed my writing skill check. |
04-07-2014, 02:07 AM | #10 |
Join Date: Mar 2013
|
Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
flyingwombat, the problem is more that an Ion Drive only provides 3 MPS per fuel tank, and a 4 year trip, one way, needs 300 MPS
|
Tags |
interstellar trade, magsail, space, spaceships |
|
|