Okay, this has been bugging me for quite a while. I think I could quite literally say years. Early on, there came about two different vague types of drives; "speed" drives which are reactionless, don't use fuel for the most part, but have some hardish upper limit on velocity, and "reaction" drives which work more like rockets we know, but with the variables fiddled - much much higher specific impulse and usually higher thrust too. But the question that's lingered is, well, what's the point of reaction drives other than flavor?
So here's a thought - what if speed drives are more limited in acceleration? How limited determines some flavor of things; travel times between planets and so on. Say on both drives that the artificial gravity can counteract 1G, and speed drives are limited to a maximum of 20x their maximum speed in acceleration; so something that maxes out at 0.1C can accelerate at 2G and the occupants only feel 1G, or something that can do 0.2C can max out at 4G, of which the occupants feel 3. Which wouldn't be too comfortable obviously. Some very rough math suggests that that would feel a lot more frontier-ey with things being days apart... for an alternative, maybe 100x their maximum speed in acceleration and artificial gravity cuts felt acceleration to 1/10th. So something maxing at 0.1C can do 10G and occupants feel 1G, something maxing 0.2C can do 10G and occupants feel 2G, etc.
Basic principle though is that reaction drives tend to get used by racers, speed freaks, and combat things because the (uncomfortable, punishing, costly-in-fuel) acceleration is useful, whereas most transportation doesn't accelerate as hard and doesn't need to. Further principle is that if things can accelerate too hard, humans aren't going to be able to react fast enough to be useful pilots, and that takes fun out of things. IMO, 10s of Gs would be pretty tough in realistic sense but probably fine, but changing directions over 100Gs would probably be completely impossible for humans to track.
Thoughts? Someone else willing to do at least brief math of transit times? It was suggested on IRC that one guideline might be Earth-Mars in something car-like (0.1C-ish) in one (albeit long) sitting; I leave agreeing with that or not up to the commentors.
I always figured it was the other way around.Reaction(Acceleration) drives only really need to burn at the start and end of their journeys.... especially if they're pure acceleration models. So for certain big loads they can be more efficient provided you don't worry about getting anywhere fast. 'Speed' drives need to be 'on' constantly burning fuel, or else the spacecraft will just grind to a halt.
Like I said in the channel, most stories written assume a journey time of several hours between planets, not days. And if the average asteroid settlement is days away from help in case things go wrong, pirate attacks suddenly become far more deadlier, and Fenspace gets that bit darker when help is vast distances away.
Hell, even an eight hour journey to Mars in a car would be uncomfortable. Has anyone here ever driven non-stop for that long? Was it uncomfortable fo your too?. Imagine that for two days......
Inertial Dampening is as much a safety feature as anything else, IMHO. Keeps cack-handed idiots from jellifying their friends with an ill-advised 'Watch this!'
________________________________
--m(^0^)m-- Wot, no sig?
I mostly use this for some numbers on flight times:
http://www.projectrho.com/rocket/appmis ... sion_Table. The time is for a mission from Earth to planet X and back... so half it for just getting there.
1g roughly means 2 days from Earth to Mars. To get there within a reasonable "extra long car trip time" (6-8 hours), you would need an acceleration of ~ 50g (four times acceleration means half travel time).
1g would be a week to Jupiter and ~9 days to Saturn... 50g would make this one day to Jupiter and a few hours more to Saturn.
I dunno... the more I think about it the more I kind of like the idea of things taking a bit more time to travel around. To some extent things should feel like a frontier, and maybe this is me as an American, but if I can get from Earth to anywhere else in a matter of an hours, nowhere in the solar system actually is a frontier anymore. Why have a frontier settlement pop up in belts, for example, when you could just pretty easily commute every day from Luna or whatnot?
The idea of just casually driving interplanetary in an any ramshackle vehicle bugs me. In the very early days, why *should* it be easy? If you're trying to go great distances in a tiny space, well, it should be uncomfortable and you should feel like a bit of a loony. Later on, there is at least The Island between for example Earth and Mars, why wouldn't there be other similar waystations?
Everything being too close together in travel time and it's just... too small. There's no need for all sorts of regional groups and factions, no need for multiple groups to try to do defense and policing, etc.
I think the relatively sparse population densities may have something to do with it. In fact, I would dare say that outside of Ceres, 36 Atalante is probably the most populous rock in the Belt, it being the primary base and HQ of the Roughriders and the home of Black Aeronaut Technologies where a number of the more infamous spaceframes of the Fen are mass produced.
One reason why I put the attack on Jenga on a place between Jupiter and the Main Belt was that I needed them out of range of help for a few hours. At the moment most Fen can cover nearly all travel in the solar system with their car within a day... most will be done within a few hours or less.
----
Some more thoughts on numbers.
If 1g (or lets say 10 m/s^2 for simplicity) is a common acceleration in Fenspace, having a maximum speed of 0.1c doesn't make much sense. It would take more than a month to reach 0.1c from zero speed and you would be far out of the solar system (and in the Kuniper Belt) when you reach it.
At 10g you still need 3-4 days to reach 0.1c, and you will still cover ~ 4 lighthours until you reach it, which is nearly enough to get from the Sun to Pluto...
Let me pause here for a moment and note that those two basic schemes I came up with are... the first two basic schemes I came up with. I'm not so much tied to those specific ones (although in general I like the accel drive vs speed drive contrast I came up with) so much as demonstrating ways to tune things. One way or another I would like something figured out; we should have before to a greater extent than we did, because it really does define how things "feel"; longer travel distances are more frontier-ey with more reason to have separate entities spring up, IMO.
So backing up... how long do people think it should take to get places? Say Earth to Mars and Earth to Jupiter... and what other criteria should things have? HRogge figured out right there that with the back of the envelope proposals I came up with, things wouldn't hit their top speeds in the inner system on speed drives, and that may not feel right.
One of the things I used in creating the GURPS Spaceships design was an assumption that getting to the high speeds required an 'upshift'. It was sorta based on extrapolation of the Rules (specifically Rule 5c).
In essence, the extremely high speeds (and associated accelerations) of speed drives relied on a 'gravity warp' (for lack of a better name) screwing with the laws of physics (inertia and momentum for starters). As the Limit implies, the gravity wells of stellar objects disrupt the formation of the grav-warp (with the dry mass of the vehicle being a large factor in the upper bounds of speed inside a gravity well). Thus, to reach the top speeds quoted for speed drives you need to be away from large objects.
This is a good thing, as if a speed drive vehicle could reach top speed in the Earth-Luna area we'd have lots of accidents.
Acceleration Drives are proof that the grav-warp field doesn't need to be the method of propulsion as well, and in this case I can see them being useful for the small and fast (racers and military vehicles) or the large and powerful (bulk cargo haulers).
The Frontier feel comes from the fact that outside Earth-Luna the population of Fenspace is massively spread out. There are only a few places outside planetary systems that have more than about a few hundred people all together in one spot.
Remember, even at closest approach the average car (0.1c max) would take ~3 hours to go from Earth to Mars. Add launch, departure, arrival, and landing you probably have another 2 hours minimum on top of that. This is more like a typical airline flight, not something someone would go "I know, I'll go visit Mars" to themselves on the spur of the moment.
Much. These are Fen we're talking about.
Plus there's the fact you're going to be all by yourself for much of that time, without another vehicle within several lightseconds of you on average. And you don't have much room to move around in a car, which may have cruise control but not an autopilot.
Basically, if you want comfort you'll need a bigger vessel. That means going slower. And given how spread out the Fen are in general (the Main Belt is really bad for this) you're going to need a day for travel each way at least.
Inside planetary systems (Earth-Luna, the Jovian system, Venus and Mars orbital), the gravity wells would slow things down between the bodies and stations, as would ATC.
This effectively spaces people out a lot.
Quote:So backing up... how long do people think it should take to get places? Say Earth to Mars and Earth to Jupiter... and what other criteria should things have?
For an Earth-Mars run, I'd say that travel times ranging from 10-20 hours are perfectly acceptable. Think of it like buying a plane ticket from New York to Sydney - it's quicker than the alternatives, but still long enough to make you think you've accomplished something just by getting there. For an Earth-Jupiter run, I'd say it should take days at least; Jupiter's so much further away, after all.
Of course, this depends on the fencraft in question - a flying car will have much different endurance profiles than a passenger liner, etc. Still, I don't think my general estimates are that far out of line.
Mr. Fnord
interdimensional man of mystery
FenWiki - Your One-Stop Shop for Fenspace Information
"I. Drink. Your. NERDRAGE!"
M Fnord Wrote:For an Earth-Mars run, I'd say that travel times ranging from 10-20 hours are perfectly acceptable. Think of it like buying a plane ticket from New York to Sydney - it's quicker than the alternatives, but still long enough to make you think you've accomplished something just by getting there. For an Earth-Jupiter run, I'd say it should take days at least; Jupiter's so much further away, after all.
Hence, one would expect much more of the interplanetary traffic between the outer planets would be composed predominately of larger craft, certainly large enough that one can stretch one's legs and walk during the trip. Most Fen would prefer to travel in something on the scale of a passenger bus at the smallest if they have to regularly traverse areas between the Belt and Saturn. It doesn't take more than one multi-day trip where your entire universe consists of the interior of your Mini Cooper to drive that point home that being cooped up like that sucks.
Inner system traffic would more likely be composed half and half of cars and considerably larger vehicles, if not actually tipped in favor of cars and similar. Planet to lunar travel is most likely dominated by cars, with the occasional large vessel to ferry items that won't fit into a car's back seat.
--
"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor
JFerio Wrote:Hence, one would expect much more of the interplanetary traffic between the outer planets would be composed predominately of larger craft, certainly large enough that one can stretch one's legs and walk during the trip. Most Fen would prefer to travel in something on the scale of a passenger bus at the smallest if they have to regularly traverse areas between the Belt and Saturn. It doesn't take more than one multi-day trip where your entire universe consists of the interior of your Mini Cooper to drive that point home that being cooped up like that sucks.
"Yes, I know somebody turned a cabin cruiser into a spaceship with some wondergoop. Are you sure you want to do the same thing to your car?"
"I know I want to go into space."
"But can you stay seated for hours? There aren't any rest stops between here and Mars."
"Eimi's got a point, Uncle Noah."
"Fine. We won't do what everybody else is doing. We'll build a 'real' spaceship. It'll take longer, and your father's going to wonder what we're doing ..."
- Eimi Scott, Noah Scott Anderson, and Charles Anderson, January 2008, before designing the
Epsilon Blade
--
Rob Kelk
"Governments have no right to question the loyalty of those who oppose
them. Adversaries remain citizens of the same state, common subjects of
the same sovereign, servants of the same law."
- Michael Ignatieff, addressing Stanford University in 2012
Some more thoughts on Reaction vs. Speed drives.
I think Dartz idea about reaction drives could be both the "racing drives" and "economy cargo drives" could work if the "delta-v" of reaction drives is limited because of their need for reaction mass. You can build very fast drives, but you burn through the reaction mass quickly. Or you just accelerate for some time and then coast most of the journey.
Speed drives would be easier to use because they normally don't use much reaction mass at all (or just a little bit for show). But they could be more limited in terms of acceleration and you need to keep them energized the whole journey.
What do you think?
The big thing about speed drives vs acceleration drives is the speed drives are defined by their top speed... and that the engine has to keep running to maintain that speed rather like star Trek's warp or impuse drive. Those are defined by an absolute speed, rather than their acceleration potential. Ergo their maximum range is defined by that top speed times how long the drive can run between refuelings.
Accelleration drives are just handwaved versions of existing rocketry with higher impulse potential, requiring both acceleration and decelleration, plus a possible 'coast' phase. They require disposable mass as well, either in the form of 'Fuel' for the torch or plain reaction mass that the drive pushes one way in order to make the ship go in the other.
Hear that thunder rolling till it seems to split the sky?
That's every ship in Grayson's Navy taking up the cry-
NO QUARTER!!!
-- "No Quarter", by
Echo's Children
That's pretty much how I always figured things worked Star. One of the reasons I gave my avatar's original ship an acceleration drive was the assumption of it's ability to coast on inertia vs a speed drive.
--
Warning: Some of my best mistakes are yet to be made.
Question!
Why do we need numbers? I mean, handwavium engines move at the speed of plot anyway...
I like to have guidelines... without guidelines, doing a coherent "worldbuilding" is quite hard.
Well, there's two ways to look at why to bother having even approximate numbers in my view.
#1 is that we already have approximate numbers for speeds, they're just kind of confusing and maybe more harm than good. Things will always move at the speed of plot, but I at least have often found it handy to be able to at least do a back of the envelope check of whether something makes sense or if it's at least sorta consistent with what other people are writing. Say, having Earth to Mars be a fairly trivial trip that most vehicles can do in an hour or two, or having Earth to Mars be something that takes the better part of a day and most people do in larger vehicles than cars... either versions are okay, but it feels weird if some people are assuming one and others are assuming the other in what's supposed to be the same universe.
#2 is that I'm an engineer.
Or put a different way, I and my avatar are both engineers, and both of us are into going fast, racing, and so on. And, not that I'm a hugely prolific writer or anything (obviously) but I've actually ended up feeling hamstrung for a long time because I kind of can't really get into this stuff that's a big part of my character in stories, or at least not in any way that's close to how I think. If I can't tell if things are even going to be accelerating slowly enough for humans to react to, it just feels like I can't really write *anything* about that whole category of stuff without stepping on toes by defining precedent, or being wrong.
It may be an edge case, but it's my edge case.
I have run a numbers based on two ideas:
1.) the average Fen car can do 10g acceleration
2.) acceleration is proportional to the squared maximum speed (twice maximum speed, four times acceleration)
The results surprised me a bit...
Funny: time to the target is proportional to the maximum speed *G*
Some examples:
Magn. Midnight (0.2c max, 40g acceleration) can get to Mars in 7 hours... a typical Fen car (0.1c, 10g) can do it in 14 hours... a space station (0.001c, 0.001g) needs 60 days.
Same ships for getting to Saturn: MM in 1.3 days, Fen car 2.6 days, space station 260 days.
Ah.... but handwavium is inherently inconsistent by it's very nature. it's more inconstant than French automotive electronics. Not to mention that different forms of waved speed drives are going to have entirely different kinds of effects with respect to mass, spacecraft shape and field geometry and input power.
Also. We need inertial compensation as a matter of course. Or else, what happens when the speed drive runs out of fuel to power/fuel? Slapstick effect makes it safe for use, even at 100G.
People forget how long an hour is. If helps an hour away and you're being attacked.... it's a very long time when nobody can come to help you. And that's assuming a perfect response time, ideal conditions and the like. Even with things the way they are, most small Belter settlements are still an hour or two away from their neighbours.... and probably further away from somewhere that might actually be able to defend them.
________________________________
--m(^0^)m-- Wot, no sig?
I don't know about you, but around here, in civilized, completely non-frontier Mid-Western America, police response to violent crime is on the order of an hour or more. Belters, living on what they're often thinking of as the edges of the frontier, espousing self-reliance and all the rest, taking longer than that to get an outside response? I'd kind of assume so.
So yeah, it makes response take longer in the early stages of things when there aren't many major settlements outside of the Earth-Luna area, but look at real world frontier places. The time between the very first Fen going Up and OGJ kicking off is 5 years; what was the American West like 5 years after the first settlers had arrived? In the very early going, even with as many problems are solved by the 'wave, shouldn't "pushing the frontier" be pushing the frontier?
I suppose it is a matter of perspective, seen as I'm used to the idea of being able to cross the country in two hours, and would consider a drive to Galway an unusually long one. Being an hour away from home feels like quite a big distance to the Irish mind. I come from a small country. (And find it terribly interesting that Jet is able to get to Mars, in much the same time it takes to drive to Galway. That massive shift in perspective is fascinating)
And, even though the cop-shop is ten minutes walk away, it still takes them hours to turn up. So the fact that they can turn up quickly, doesn't mean they will. The initial 'invasion' is probably long over before the rescue force even departs.
________________________________
--m(^0^)m-- Wot, no sig?
For a matter of perspective, when I was going to university, it was about an hour drive each way when there wasn't any more than normal traffic. I did that 4-5 days a week. Last year, I had a couple incidents of driving more than 6 hours straight each way to go somewhere; one of those was just for a weekend.
KJ Wrote:So yeah, it makes response take longer in the early stages of things when there aren't many major settlements outside of the Earth-Luna area, but look at real world frontier places. The time between the very first Fen going Up and OGJ kicking off is 5 years; what was the American West like 5 years after the first settlers had arrived? In the very early going, even with as many problems are solved by the 'wave, shouldn't "pushing the frontier" be pushing the frontier?
Random Belter: "See this red button? If you press it, it sends a signal directly to the White Tower that Space Patrol should come... if you are lucky, they arrive a day later, if you are unlucky, they ask you back a day later if its really necessary!"
Oh, because I didn't address it... yeah, I think some form of inertia compensation is good and necessary, with both speed and accel drives. I think it might be neat too if on the really fast stuff, it can't cope with all of it; if the Magnificent Midnight or Azu Squadron or whoever is going to noisily tear ass around space, I at least think it should feel like an adventure to the people inside.