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> The Stars are not Far, Mars Mission 2071.
FrankTrollman
post Nov 4 2006, 09:21 PM
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So 2071 is the time when Mars gets closest to the Earth as it does every 17 years (the last one was 2003). Using Shadowrun technology and the rules presented in Target: Wasteland, one is able to accelerate at one Gravity (9.8 ms/s^2) pretty much all day. And that's fine, because with one day of accelerating at that speed, and one day slowing down at the same rate, you'd have gone 78 million kilometers.

That's convenient, because that's the distance from the Earth to Mars in 2071. Assuming you have sufficient fuel (and you do, because you are refueling your plasma jet on a stable space platform), you can get to the orbit of Mars in just oer 2 days. You could potentially have a mars mission that lasted less than a week.

Yeppers, that's 86,400 seconds a day, for a mid-point velocity of 847 kilometers per second. That's less than 1/3 of 1% of the speed of light, so you can still handwave off relativistic effects. The best part is that the entire trip (except for a hurlariffic experience at the beginning, middle, and end of the trip) would be spent at acceleration equal to normal Earth Gravity. In short, the plasma jet would propel you through space fast enough that it would feel just like you were sitting in a normal room on Earth.

-Frank
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fistandantilus4....
post Nov 4 2006, 09:25 PM
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New Space Race?
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ChicagosFinest
post Nov 4 2006, 09:30 PM
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Where going to figgure out if those dragon bones are real or not!!! Secondly is the mana on Earth going to get all wacko? What about the two dragons rifts?! Ohh the opportunities galore.
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knasser
post Nov 5 2006, 09:53 AM
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Can SIMs simulate gravity? I presume they can because otherwise you'd never be able to have a SIM of swimming, or falling off something, etc. So the ship may be entering Mars orbit but the pilots are having tea in a virtual living room. Of course the pilot has a shed-load of read-outs in his morning paper. :)

But I'd question the Target Wasteland figures for sustaining that acceleration. I don't have it - what sort of technology provides that? Because assuming the ship were 5,000kg (a tin box with people in it), that's about 3x10^14 joules. You could probably run New York city for an hour off that.
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Demerzel
post Nov 5 2006, 10:43 AM
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See now you're making me dust off Marion and Thornton to brush up on my Transit Orbits...
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Demerzel
post Nov 5 2006, 11:44 AM
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Well, okay. This is a less than simple problem.

Consider the space shuttle orbiter alone weighs more than 100,000kg(wiki) and do you really want to take less than that to Mars?

How much of that should be reaction mass? Let's say 10%. So 10,000kg of fuel. Two days there and two days back that's a dm/dt of roughly 10,000kg/96hours = 0.0289 kg/second.

To get 100,000kg accelerating at 9.8m/s^2 you need 980,000 N Thrust.

Making the horrible assumption of ignoring relitavistic effects that requires the ejectant to be going around .28c.

Not too reasonable even in 2070. Well what if we tack the orbiter sized object onto a 900,000 kg fuel tank and use that much fuel...

900,000 kg / 96 hours = 2.60 kg / second.

Thrust needed is 9,800,000 N.

So now the ejectant is just going roughly .01c but that requires you launch one million kg into orbit...

Keep in mind this is super rough, it's almost 4am and I don't really stand by this as more than back of the envelope calcs.

It throws out earths gravity making it more difficult (This is rocket in free space cals). So it'll be harder by a long shot...

I don't imagine this is the most cost effective way, a much longer trip would allow for significantly less fuel and be way mroe cost effective...
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ChicagosFinest
post Nov 5 2006, 04:29 PM
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In english?
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Konsaki
post Nov 5 2006, 04:46 PM
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To hit that speed based off the weight of the spacecraft, you need more fuel. Adding fuel means adding more weight, and in turn requires more fuel to hit that speed.

It would be more cost efficient to take a few more days to get there and save alot of fuel and money.
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Steak and Spirit...
post Nov 5 2006, 04:55 PM
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QUOTE (Konsaki)
It would be more cost efficient to take a few more days to get there and save alot of fuel and money.

Nonsense! Afterburners, full steam ahead lads! Avast ye, earth-lovers! Watch tha' starboard bow!
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Demerzel
post Nov 5 2006, 05:01 PM
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QUOTE (Konsaki)
To hit that speed based off the weight of the spacecraft, you need more fuel. Adding fuel means adding more weight, and in turn requires more fuel to hit that speed.

It would be more cost efficient to take a few more days to get there and save alot of fuel and money.

But if you put it that way on DSF someone will inevitably say, "Yea? Prove it."

I'm not a gun nut so I can't really contribute to those super technical posts, but I can do rocket science!
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Konsaki
post Nov 5 2006, 05:08 PM
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QUOTE (Demerzel)
QUOTE (Konsaki @ Nov 5 2006, 08:46 AM)
To hit that speed based off the weight of the spacecraft, you need more fuel. Adding fuel means adding more weight, and in turn requires more fuel to hit that speed.

It would be more cost efficient to take a few more days to get there and save alot of fuel and money.

But if you put it that way on DSF someone will inevitably say, "Yea? Prove it."

I'm not a gun nut so I can't really contribute to those super technical posts, but I can do rocket science!

Someone wanted a dumbed down explaination and I figured that was something I'm good at so...
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Dentris
post Nov 5 2006, 05:26 PM
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Chicago Finest:

It means in order to make a rocket flies out in orbit, you need a reactor powerful enough to beat earth gravity (which is 9,8m/s). The journey is likely to burn through the shuttle fuel reserve completly. Now, if you refuel your shuttle in orbit, you can use the same acceleration (9,8m/s) in space, where their is no gravity, which mean your acceleration is exponential (the first second, you travel at 9,8 m/s, the second second, you travel at 19,6 m/s, the third second you travel at 29,4 m/s, etc.) Which mean at the end of a day, you'll be travelling at a speed of 8467 km/s. The next day would be use to decelarate at the same speed and you'll be around Mars within 2 days.

The problem is the amount of fuel needed to achieve this is gargantuan. You'd need 1000 tons of fuel in the shuttle to sustain so much acceleration and deceleration for that much time. It would be a lot more cost-effective to accelerate for a shorter length of time, stop the engines (and continue to travel at a certain speed because there is no friction in space), then decelerate.

I hope i clarified things a little bit.
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Demerzel
post Nov 5 2006, 05:47 PM
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@Konsaki,

I don't mean to diminish your contribution, I'm just excited to get to put my degree in Physics to some use.
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Digital Heroin
post Nov 5 2006, 05:59 PM
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Would I be thoroughly braindead in pointing out that there are alternate possible means of fueling a rocket that no doubt someone will have tried to employ... say nuclear?
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ChicagosFinest
post Nov 5 2006, 06:05 PM
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Ahh so so magical nukes that keep popping up might be put to good use?
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Konsaki
post Nov 5 2006, 06:08 PM
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Why not just have 20 mages cast levitate on the ship until it leaves the mana sphere?
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ChicagosFinest
post Nov 5 2006, 06:10 PM
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and then the nuke blasts to provide fuel
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Konsaki
post Nov 5 2006, 06:14 PM
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Hell, we can use catgirls for the nuclear reaction instead of uranium or other heavy element. Reduce the catgirl population while reducing the radiation output, win/win!
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Dentris
post Nov 5 2006, 06:25 PM
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QUOTE (Digital Heroin)
Would I be thoroughly braindead in pointing out that there are alternate possible means of fueling a rocket that no doubt someone will have tried to employ... say nuclear?

Well, the fuel we are talking about isn't gasoline, but Nuclear Pellets...which mean this is already the alternate fuel source you are talking about.

And no, you are not brain-dead; we weren't explicit enough.
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Digital Heroin
post Nov 5 2006, 06:36 PM
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See, now there's where I go and affirm I am in fact braindead... nuclear pellets? They use them thar tiny bits of plutonium or such today?

*has a tendancy to actually speak with an assumed Georgian accent when feeling dumb, seriously*
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Dentris
post Nov 5 2006, 06:56 PM
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ok, I'm not a rocket scientist myself. All i know is from the excellent GURPS setting called Transhuman Space and from my friend with a doctorate degree in nuclear science.

The nuclear pellets could (theorically) be used as fuel for fusion reactor. By directing a laser into these pellets, creating microexplosions at the atomical level. Right now, this technology is not yet cost-effective, but in the near-future, it could be developed.
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FrankTrollman
post Nov 5 2006, 07:16 PM
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QUOTE
Now, if you refuel your shuttle in orbit, you can use the same acceleration (9,8m/s) in space, where their is no gravity, which mean your acceleration is exponential (the first second, you travel at 9,8 m/s, the second second, you travel at 19,6 m/s, the third second you travel at 29,4 m/s, etc.) Which mean at the end of a day, you'll be travelling at a speed of 8467 km/s.


Well, actually your acceleration is constant,
Your speed is linear,
And your distance travelled is exponential.

But yeah.

QUOTE
The problem is the amount of fuel needed to achieve this is gargantuan. You'd need 1000 tons of fuel in the shuttle to sustain so much acceleration and deceleration for that much time.


Why? We aren't talking Newtonian physics here even if we are needing to come up with Newtons to accelerate our ship. Equal and Opposite Reactions come from energy output, not mass differential. Theoretically we could get our acceleration by throwing individual protons out the back if they were propelled with enough force. The cap of C applies to velocity, not energy. In fact, the cap exists because it would take infinite energy to bring any massed object up to a velocity of C - which coincidentally means that you could have any amount of energy less than infinity on any object with mass - in short there are no hard caps to rocketry.

The difficulty then is to accumulate enough energy in the first place to run your plasma jet, not in carrying enough material to supply particles to your plasma jet. For all we know, the materials for that plasma jet could be 5 kilograms - we aren't using futur tech today so there's no way to know. What we can know (or at least guess), is that the craft probably isn't using something more efficient than Fusion to get that energy, and it's made by humans so it probably isn't going to be getting better than 20% efficiency of that for forward thrust.

So sure, let's assume we have a 100 tonne spacecraft. And we're going to be in essentially constant acceleration for the entire 78 million kilometer journey. That's going to take 9.8 x 78,000,000,000 x 100,000 = 7.6 x 10^15 Joules. That's... a lot.

But it's not an insurmountable lot. A 1 megaton hydrogen bomb (which is about as small as they come) produces 4.18 x 10^15 Joules. So if yoiu have a Fusion reactor (which is what a Hydrogen Bomb is), and you have an efficiency of 20%, and you want to go both ways at 1G, your nuclear drive is going to have to be the equivalent of about 20 megatons (because it's much better to err on the side of caution).

That's the size of a "standard" hydrogen bomb today!

Of course, getting a 20% yield of forward momentum out of your Fusion engine and not, for example, creating a short lived sun around the Earth with you inside - that's a problem. But it's a problem that has been solved with Shadowrun technology. Fusion plants produce power and have for 30 years. They don't simply transform areas kilometers across into plasma while exploding they way they do with current technology.

The 2070s are indeed awesome, and comfortable travel to mars over he Weekend is well within the realm of possibility.

-Frank
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knasser
post Nov 5 2006, 07:23 PM
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QUOTE (ChicagosFinest @ Nov 5 2006, 11:29 AM)
In english?


To keep that sort of accelleration going for that length of time, you're going to need a lot of fuel. And a lot of fuel weighs quite a bit (more properly, has a lot of mass, but this is the simplest the explanation is going to get). So now, your craft is even heavier because of all that fuel, so it needs more energy to push it at those speeds for that long... which means - MORE FUEL!

I was aware of that when I posted, but I kept this out of it until Frank (or someone) answered my question about what sort of power source these ships are supposed to have in 2070, because some sorts of power source are actually off the ship itself, such as lasers fired at it, whilst other sources of power such as nuclear power, have a very good energy to mass ratio, so you don't need to worry quite as much about the problem as you would with regular rocket fuel.

Even if you could focus that much energy in one craft though, the economics are going to make it far far cheaper to take a few months for the journey than to try and burn an entire city's power consumption in a couple of days. In Kim Stanley Robinson's Mars trilogy, he has a ship make the journey in five months, which is considered as fast as economically possible, and that was when there was an urgent need for it. IIRC, anyway.

EDIT: Was writing this before Frank posted his answer. Plasma jets from Fusion reactions answers my question about power source.

@Frank: 9.8 x 78,000,000,000 x 100,000 = 7.6 x 10^16 Joules, not ^15. This brings you to needing around a 90 Megaton bomb equivalent at 20% efficiency. That's way bigger than currently exists, though nowhere near the total that exists. So given the technology (which cannon game seems to support), it's feasible. Still waaaay more cost effective to take a few months instead, though. :)
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FrankTrollman
post Nov 5 2006, 07:33 PM
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17 days. A fusion drive capable of sending you to Mars over the weekend would be producing enough power to power NYC for 17 days.

Of course, conservation of energy never works for you, and forward motion is a fuck tonne easier to get than electrical power. In reality, you're probably looking at a Fusion reactor that could potentially keep NYC going for a week.

-Frank
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Butterblume
post Nov 5 2006, 07:51 PM
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Am I a rocket scientist? I studied computer science, mathematics and physics for a few years and have a good background in chemistry. We even built a few (very small) rockets. (I just mention it to establish that I understand most of what were are talking about :D)

Anyone remember Project Orion?

I first stumbled upon it in the book Footfall by Larry Niven and Jerry Pournelle.
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