You never started checking my math.

I never claimed a linear relationship between temperature and dm/dt. You made a bad assumtion, I never claimed such a thing.

Okay, my back of the envelope calculations were not the clearest and since you desire better clarity I’ll try to offer you a general formula.

Average Kinetic Energy based on temperature:
KE = (3/2) k T

Kinetic Energy of a nonrelativistic particle:
KE = (1/2) m v^2

Eliminate energy and solve for v you get:

v = sqrt(3 k T / m)

Thrust is the Force on the rocket. Newton’s second law:
F = M a (large M for the rocket mass, small m for ejecta mass)

Thrust = -v dm/dt

-v dm/dt = M a

dm/dt = M a / v

substitute in v and you get:

dm/dt = M * Sqrt (m / 3 k T) * a

So where you falsely assumed a linear relationship between dm/dt and temperature there is really an Inverse square root relationship!

I’m sorry Frank but you’re not even trying . . .

And I’m sorry but Solid Rocket Booster (SRB) Separation occurs at 2:07 in the shuttle’s launch sequence. The Space Shuttle Main Engine then fires until 7:40, it throttles down and cuts out at 8:38.

So in fact my simple calculation is much closer to correct than you pretend, if you’d like a decent undergraduate level text on classical dynamics including a nice section on rocket science I recommend this book.

I’m sorry Frank, I gave you credit for a better understanding of Physics than I should have. As a result I didn’t spell out some of the basics of how a simple rocket engine works.

Q: Why does the heat of the engine core have anything to do with the velocity of the propellant?

A: Unlike what you think when you envision an “The external detonation of large amounts of fuel” what I’m assuming is that you’ve got some sort of bottle that is capable of containing a fusion reaction at a heat equivalent to that of the core of the sun. Particles in this fusion would be moving around with incredible velocities. Velocities that I have calculated for you already in the above. Then I allow you to port this plasma out into space in a linear jet that provides thrust based on a simple conservation of momentum. That’s the thrust equation I’ve shown you. Don't forget that I'm giving for free that there's some way to continue to inject fusion fuel into this reactor core to maintain the reaction at a steady state.

What the space shuttle's solid rocket boosters do is they use combustion rather than fusion to create the heat that forces the propellant out the back of the rocket.

Commentary: You are unwilling to accept that what I showed you actually represents the space shuttle remarkably well. The primary difference being that the shuttle is launched using the combustion of H2 and O2, but ultimately it’s a very hot core that allows a just of hot gas to be shot out the back at a velocity that is determined based on temperature. In fact the dm/dt that this very rough estimation yields is close to the actual space shuttle.

You can’t accept that the space shuttle outputs 9800 kg/s at lift off because that much dm/dt could not be sustained for 510 seconds is a moot point because it is not sustained for 510 seconds. Solid rocket booster separation occurs at 2 minutes and 7 seconds in the flight. In fact I mentioned that above, but you’re stuck on that 510 seconds for some reason.

After the 2:07 SRB separation the Space Shuttle Main engine continues to burn, at a much slower rate, and I haven’t attempted to represent that in any way here. And by claiming a 510 second burn to orbit you’re misrepresenting the essential two stage nature of the Space Shuttle and it’s Launch mechanism.

My question for you:
But I take it you don’t want to accept that this is the type of engine you would have to use. Is it that you instead want to take the fusion reaction and generate electricity with it in order to use a type of particle accelerator and boost your reaction mass to a significant fraction of the speed of light?

Am I correct that that is what you are proposing?

Demerzel, at its core you are proposing that the temperature of the outgas is the singular source of velocity for it. This is not true in any reference frame. Temperature motion of particles goes in every direction, and in aggregate generally sums to zero.

The temperature of the stream is, therefore largely waste energy. So the supposition "If 100% of the forward motion comes from waste energy..." is flawed to begin with. Waste energy isn't giving you any forward motion, that's why it's waste!

You talk about this as if it was somehow a Maxwell's Daemon Drive (which would be awesome). It's not. It's a fusion engine that produces a very large amount of power and squirts it out the back in the form of plasma that is accelerated to high speed (probably with magnets).

The acceleration is modelable in an entirely Newtonian fashion. Energy out the back equals forward acceleration. We need on the order of 10^16 Joules, but we get on the order of 10^14 Joules for every Kilogram of fuel so I'm not worried. With only a 10% efficiency we could get there with a tonne of fuel. We're probably going to want more like 20 tonnes of fuel because getting even a 10% efficiency out of high energy reactions is laughable.

The standard rocket propellent is sent out the back via expansion, which doesn't require heat to be produced. If you'll recall, liquid oxygen tanks can become quite hazardous projectiles when breached, and become extremely cold when doing so. The compressed gas decompresses explosively - and consumes heat in the process of phase shifting from liquid to gas.

Your fundamental assumption is without merit. Your very first sentence kills the entire argument. By comparing the motion energy of the temperature of individual particles to... really anything, you're not modelling rocketry at all.

-Frank

A quick fact check shows that fuel is, in fact, 92% of the launch system's mass (give or take; I compared gross weights to empty weights so the estimate could be slightly high).
After the SRBs are jettisoned the shuttle and the external fuel tank actually weigh so much that the thrust from the Shuttle Main Engines provides less force than gravity and the shuttle begins to slow down until it has burned through a certain amount of fuel. By the last 10 seconds it has depleted more than 75% of its mass in fuel and actually has to throttle down to keep the acceleration under 3gs.

Math that shows the shuttle losing more than 75% of its mass while leaving the atmosphere can't be rejected on that fact alone because the shuttle does lose more than 75% of its mass while leaving the atmosphere

I think this argument may have stemmed from the basic premise that I tried to give a simple example of how 1g acceleration for 4 days (2 days out 2 days back) is untenable. Unfortunately it degenerated to a defense of a short and oversimplified counter example.

A good source of info on propulsion is this article on wiki...

I continue to contest that it'll be highly unlikely that you could get 1g of accelleration for something on the order of days... If you want to switch the argument to ion engines we can, but you've got enormous efficiency issues, plus you're talking about scaling a technology to broken proportions.

From that site you linked:

edit: Deleted post - the argument is dead. Just objected to Demerzel's posts that seem correct to me being dismissed as "hangups."

Okay Frank, lets use the example there of a Ion Drive. It’s got an efficiency of 25kW per N of thrust.

So if I have a 100,000 kg (Space Shuttle sized) craft.
1g nearly 10m/s^2 would require 1,000,000 N of force.
25kW/N means 25,000,000 kW, or 25GW OUTPUT from a power generator.

Now if I give you a better than possible efficiency of 50% that means that 25GW of power output is waste heat. Where do you propose that goes? In SR the generators you’re talking about put it in a river or into the ocean. Where is your enormous heat sink?

Wow, who says roleplayers are a bunch of nerds...?

The glowing contrail of plasma would be the output energy from the reaction the waste energy would have to go into some sort of heat reservoir. Basically it would heat your ship. The waste heat is just that waste and you have to do something with it, it is all the energy that you cannot convert to useful work due to the fact that no power generator is 100% efficient.

So basically if I give you a 50% efficient engine, and you need 25GW of power to keep it accelerating at 1g, then you’ve got 25GW of waste heat to deal with.

Water absorbs a huge amount of heat per unit mass compared to the things your ship is likely made of like metal.

If your ship absorbs heat just as well as water, at 25 Celsius, 25 GW of waste energy would heat your ship 62.5 Kelvin per second. How long will your crew survive?

Okay I know what you’re saying that heat will go somewhere, it’s not confined to the ship. But there is no conduction of heat from the ship into space (a vacuum), only radiative heat loss will occur. In order for the radiative heat loss to emit 25GW of energy it would have to be glowing hot.

So you want some sort of huge radiators that will reduce that heat, then you’ve got to add that weight, and increase your power output and in the end you’re going to be talking about an immense amount of heat sink. Also the hotter your heat sink the worse your efficiency.

Basically, your 2 day there and 2 day back at 1g trip is just ridiculous. Take two months to get there and two to get back and there you go, but why are you in this ridiculous hurry?

Well, if you want to get into pure speculative theoretical limits then 2kg of carbon could hold 5.594MJ of heat before melting and if flattened into a 100 square meter sheet could emit (eT)22.041GW at this temperature, where (eT) is the emissivity correction factor of the carbon at this temperature.

The actual mass and specific heat of the radiator doesn't factor into the equation except as they effect temperature. Since a high-temperature radiator is good a low-mass and low specific-heat radiator actually benefits you in some ways.

Carbon is a poor conductor however so as a heat sink it would be unreliable...

SR2070 technology - how about this: You create a nano-material with strictly controlled bonding forces between the molecules. At specific temperature threshold, they "evaporate" away from the ship. You're in Space so you don't care about the super fine cloud of particles that your ship leaves behind it like an all-consuming fart. It's inherantly degrading, but it's a neat way to get rid of heat and you can make it eight-foot thick if you want. I'm sure SR2070 technology can also come up with a neat little capilliary system to get the heat out to the heat sink "shell".

If we're talking science-fiction (and we are), you could even vary the strength of the bonds in the material as needed with varying current.

My idea is so brilliant that I should patent it, but instead I shall donate it to the public domain, for the greater glory of Dumpshock.

C'mon argue more physics. I want to see digital blood.
If physics classes where this amusing I might have stayed awake through them.

Uh... sure.

Plasma expansion is a refrigerant. The phase shift and volume expansion absorb energy and reduce temperature.

Discuss.

-Frank

I'd like to think the Physics classes I tought while working on my Masters were this fun. I don't think I'd get a majority of votes from my students however.

Oh, and a significant portion of energy popping out of fusion reactions does so in the form of neutrinos, which are close to non-interactive with normal matter. That means that a very large proportion of energy loss comes in a form that does not neat to be thermally dissapated - it's simply a form of radiation which passes harmlessly through your ship in equal measures in all directions.

So the heat sink problem isn't as bad as you might think for looking at the numbr of joules and the efficiency of the propulsion.

-Frank

Well first off, your statement regarding the expanding plasma would work as a refrigerant is true, however what it would be cooling is the core of your reactor and that cooling would have to be compensated by some energy releasing reaction (such as fusion) or else your core would peter out before very long…

Then as to your heat exiting as neutrino statement. Well, energy is lost from the fusion reaction in the form of neutrinos. However the efficiency numbers I used to give you a simple feasibility for your rocket were based purely on the electricity production. Basically if you’re unwilling to use a simple rocket and insist on some sort of ion drive you have to convert the heat energy generated by your energy source (fusion/fission/combustion of methane byproducts from consumption of beans) into electrical energy to create the voltage differential you want to use to accelerate your reaction mass.

Without even talking about the efficiency of your fusion process, just the heat engine necessary to run your power generator has an efficiency limit. The Carnot efficiency is the maximum possible based on thermodynamic principals. Basically if I give you for free a 50% efficient generation process I’m being extremely generous. So without even considering the unusable heat generated in your fusion core (for example those nasty neutrons that cannot be contained in your magnetic bottle because they are neutral and turn your stable isotopes in your ships hull (or your body) into radioactive sources.

Frankly I basically spotted you a fusion rocket with a core as hot as the sun and you said I was being unreasonable. Where in fact if you had that we’d be regularly flying to Saturn to bring back Ice from the rings to use as reaction mass because that would be freakishly amazingly efficient as long as you don’t want to do it all in one day…

The key resource that will allow space travel in our solar system is patience.

Ah there we go.....

okay so the physics lesson was interesting but I thought I might point out something.

If the whole point of going fast was having to do with the comfort of the crew then I can think of a better solution entirely within Shadowrun tech. Just put everyone in a small centrifuge in the center of the ship in long term sleep. Then connect them to the main computer in hot sim. Make sure you have several small independant power sources so they are not in danger easily.

The actual ship may be a large rocket but for the crew it could be the enterprise d. Just give them lots of drones that they can control in VR and they can fix things. Then rotate the crew stifts with the frame rate of on duty personel varying with need of reaction so during the dull portions of the trip you experience time at a fast pace and when you are in danger it goes to normal time. You might only need a few days worth of experience to cover the entire several month trip.

That way there is no negative mental impact and you don't have to waste energy.

If they're in artificial hibernation under artificial gravity for 6 months then they're all going to die from infected bed sores before they reach Mars. If they're in artificial hibernation without artificial gravity for 6 months then they're likely to die of heart failure the second they try to move.

The problem isn't the comfort of the crew. The problem is the massive health problems associated with low gravity environments. The heart doesn't have to work against gravity so it weakens dramatically, for example. Bones become brittle. Muscles lose mass and tone. Really, a low gravity environment is very dangerous to human health and so is 6 months of artificial hibernation.

so you either have some sort of acceleration gel or you have some drones change the sheets. Maybe the bed vibrates to massage their butts.

Hyzmarca, it seems like you are just arguing against the possibility instead of offering alternate ideas. Do you just not like the idea of space travel or do you think it should only occur at a certain tech level where all the problems are solved?

Shadowrun technology provides the ability to keeppeople alive in gravity free hibernation for years - like Roxborough. Unfortunately, it is like Roxborough: your body no longer functions if you ever take it out of the zero gravity holding pattern.

I have no idea how Zero-G life extension is supposed to work, but it does exist in canon Shadowrun. It isn't part of the plan if you intend for the crew to ever accomplish anything at the end of their journey, however.

---

In general, Shadowrun movement is split harshly into the Haves and the Have-nots. On Earth, there are those able to use Movement on their vehicles and transport goods faster using less fuel and in less danger than anyone else. And then there's the people who can't and they have to deal with the fact that the oil has run out and they are stuck with methane vehicles running slow routes.

In space there are people who can afford to make and operate a fusion engine, which costs a crap tonne of and runs off of fuel found on the Lunar surface by Ares' mining station - and there's everybody else who has to come up with ridiculously contrived methods to keep their people alive in space at low gravity for long journeys.

That's how Shadowrun movement works. There is an incredibly limited amount of frieght that is so fast that it might as well be teleported; and then everything else is stuck moving at the slow ponderous speed of a cammel caravan. Literarily this allows players to either skip from one location to the next with what amounts to a cut and a bit of locative subtitles or make a slow and dangerous journey from one land to another overcoming challenges the whole way. Both stories can exist in the Shadowrun world because fast transport exists and yet it is limited in availability.

Not everything in space moves at the fast speed. Only the big things. The expensive things. The things that absolutely, positively, have to make it to Mars by Saturday morning.

-Frank

Ok, I’m no-brainer when it comes to these subjects but when it comes to crew survival there are several options in SR 2070.

The Crew – Medical Solution
Submerge crew in shock-absorbing gel while wearing life sustaining suits (I’m talking a kind of wetsuit here, not a primitive 2006 space suit). Add some basic cyberware for drone control as mentioned earlier.

The suits will include smart materials and myomer muscle bundles that massage the astronauts muscles so that their bodies muscle mass does not degenerate. Then we add Bone Augmentation to strengthen the bones for the long journey and possible some plastic bonelacing as support.

An expert Autodoc system (or even better – a medically trained astronaut that takes care of the crews health AND and Autodoc that can dispense nanites and drugs that can monitor their health.

The Crew – Alternative Cyber Solution
If we go fully extreme we add fully cyborged astronauts with complete limb replacements so that they mostly need spares. This way they can also skip survival suits with massage – An artificial hearth might be good as well since the hearth muscle might be affected by low gravity for an extended time.

The Ship
As I said, I’m no Physics major (or minor for that matter so I’ll just wing it here.

What technology exists in SR4? Particle Accelerator? Fusion Plants? Ritual magic? New materials.

1. The ship has as little metal components as possible and is made of new light smart materials significantly reducing weight (new material for us but have existed for 10-20 years in SR4.)

2. Ritual Magic. Ritual Magic boosts the ship up into the upper atmosphere where it ignites booster rockets (this also reduces weight.)

3. Improvements in engine design have improved fuel economy of booster rockets.

4. The entire crew is rigger trained to handle drones as most EVA will be done by them.

5. No actual landing will take place on mars by humans, a lander with several different drones will be sent down and/or flown over the area.

6. Solar powered High Altitude drones will simply drift over the planet and send data back to earth.

7. Every available sensor technology will be searching the planet for life.


IF a landing is to take place by human crew the cost will increase significantly and the only reason for actually taking such a cost is to se if an awakened individual can sense anything of the planets biosphere.

IF an awakened individual is going on the trip then there is extra costs in case of expert training to NOT use magical abilities in space (think about it, it’s like Unlearning how to breathe – for a mage it is a natural thing to use magic – like walking.)

IF an awakened individual is going it might be required to have a small biosphere onboard (a small area filled with plants perhaps).

IF sending down a mage then they might manage with a small one-man shuttle – thus conserving fuel and space.

Another solution might be to send down awakened animals and monitor them.

why not a probe with that biolum stuff that glows around magic. Then send them all around on drones. Just have enough to get readings of yes/no without the risk to a mage.

There is no need for Rube Goldberg sleep chambers when simulated gravity works just fine.

I still say with blood-god exploit is the best fastest and safest way to go about space travel in SR.


For coolness, people should land on Mars and they should be heavily armed just in case the aliens are hostile. Unmanned probes suck.

In 2064, there had already been at least three landings on Mars, with various levels of secrecy and various numbers of humans onboard since the Awakening. Project Discovery (NASA), Project Cydonis (Ares), and Project Tereshkova (Yamatetsu).

In 2070, Evo has a permanent base on Mars.

In 2071, getting to Mars has never been easier.

-Frank

Easier than ever it may very well be, but a weekend trip it is not.

A 6-month trip is also long compared to what I’d expect out of SR4 level technology. A low-energy transfer orbit will take something like 18 months. The Mars Direct Plan calls for a high-energy transfer orbit that will take 6 months. If you maintain constant acceleration with a reasonable value (more like .01 to .04 g rather than 1g) you can shorten that significantly.

I’m not prepared to take the time necessary to calculate this kind of thing, it’s not a time commitment I’m willing to take on for a DSF argument, besides it’s not like Frank would believe my calculations anyhow. But be a little conservative in your estimate and say it would take 1 to 2 months, the health problems aren’t nearly as huge and likely can be mitigated with SR level medicine, and you’re not abusing science like a red headed stepchild.

Plan ahead and you can send important things like landing craft and extra reaction mass ahead of the trip on a low energy orbit. But let’s consider the past 50 years of advancement in space technology and project that ahead, with a fracturing of nations worldwide global strife and all the problems associated with that . . .

If you are going nuclear at all, and you can do it at .1 G, you can do it at 1 G.

The problem with increasing acceleration is that 10 times the acceleration requires 10 times the energy per kilogram for your journey. That means that you need 10 times the fuel. For a chemical propellant, that's a big deal, because the fuel is the vast majority of the mass. So you need 10 times as much fuel per kilogram and have almost 8 times as much mass and that needs 10 times as much fuel and so on and so forth - ithere's non-fuel mass in there so it doesn't go to infinity, but the total fuel requirements are impractically large.

But Nuclear drives don't work that way. The vast majority of the mass is the reactor itself. The fusionable materials are measured in kilograms, not tonnes. Putting in ten times as much fuel just means you can't take quite as many ham and turkey sandwichs, it doesn't mean that your vehicle is some whole number more massive overall.

That's the breakpoint. Once fuel to get energy out of isn't the primary source of mass, acceleration is pretty much arbitrary all the way up to the point where you'd kill the crew.

Nuclear engines propel the USS Nimitz through water on less than two kilograms of fuel per day, and that's fission. It's 100 tonnes and was built in 1975, I'm sure that in 100 years there has been some progress in this field.

The basic rocketry nightmare - that faster acceleration needs more fuel which means more mass which means more fuel which means more mass.... does not apply to a nuclear engine in any meaningful way. The engine is massive, expensive, and technically difficult. The fuel is expensive, rare, and dangerous - but the fuel isn't massive. It's man-portable if it for some reason came to that.

If you can keep a submarine moving around under water for five years, you can keep a spacecraft going at 9.8 m/s^2 for five days.

-Frank

Wow, I can’t believe you still believe that after all this…

Yes, those are kilotonnes, not tonnes. Sorry, it was supposed to be ktonnes. Sigh.

Anyway, Nuclear Fusion is a state function. The path to completion is irrelevent and the energy output is the same regardless. Maybe the entire reaction is kept in magnetic containment and ejected whole out the back? Maybe the emmitted photns are collected by a pigment and then released as lasers out the back? I don't know.

I don't even care, because fusion power is not possible with the technology of 2006 and it is possible with the technology of the 2070 awakened world. The energy put out by the reaction is predictable and known based on the stability of the isotopes at the beginning and the end. And that energy is many thousands of times greater than what is needed to propel thee craft across the divide of space.

1G isn't a big deal. We can do better than that with our knees, and we do very time we climb stairs. The big deal is maintaining that kind of acceleraton for long distances and time periods. But seriously, when you're using nuclear power, the long time frames and distances are of no concern. The Sun has maintained for billions of years, performing the same reactions for dozens of hours is not the technical hurdle.

-Frank