Reestimaing the performance of the Unity's fusion drive

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Author Topic:   Reestimaing the performance of the Unity's fusion drive

BKK the Mentat posted 12-10-98 08:26 PM ET
For all you math whizes,genuses,mentats,Unix users,or anyone that enjoys pain, help me out.
Here are the basic catigories of information that I want to know:
Acceleration assuming max velocity ~.1c
Fuel consumption
thust
raw energy release(W)
SPECULATIONS ABOUT THE DRIVE AND LAYOUT OF THE UNITY ITSELF.
also, to perform these calculations, I need to know the ship's mass.
Spoe posted 12-10-98 09:10 PM ET
Hrm, I've been meaning to get around to updating my early calculations to take into account, especially since fuel was a major portion of the initial mass of the ship. Might actually get around to it this weekend...
MikeH II posted 12-11-98 09:27 AM ET
I think we used 100,000 metric tons as the mass of the ship before, without fuel.
I based that on the size and weight of an Aircraft carrier today and estimated.
Anyone know the final predicted size and mass of the ISS? Might help with the densities achievable in space engineering today then we could make a better estimate of mass.
JustAName posted 12-11-98 09:55 AM ET
Remember kids, when using Aircraft Carriers as a means of comparing masses, keep in mind that seaborne technology is significantly more advanced in terms of "mass/density-to-technology" ratios than would be the supposedly new concept of space travel within the confines of the information given in the storyline. In other words, the Unity ain't pretty, just (barely) functional. I'd consider upping the mass.
BKK the Mentat posted 12-11-98 09:59 PM ET
Here's my 2cents worth......
Estimated ship's mass:~185-220,000mt(unloaded superstructure only)
effecency of reactor:~5%
fuel consumption(assumuming 5%ef.and avg. of 15.6 pulses per sec.):1.88avg. acceleration stage:2Kg/sec deceleration:1.76Kg/sec
Total fuel consunption:416,740.3metric tonnes
That's all I can offer until we decide on a standard mass and acceleration rate(or get one from Firaxis; hint hint.
MikeH II posted 12-12-98 06:54 AM ET
I understand your point about the mass JustAName. That was the only thing I could think of which was big enough to compare it with.
Spoe posted 12-12-98 01:48 PM ET
Eh, the first time round I wasn't too worried about the actual mass we used. Why? All the equations were linear wrt mass, so the mass of ship:mass of fuel ratio would be a constant. Basically the only factor that would disrupt this would be the housekeeping load(assuming that they use the fusion drive for electrical power for the rest of the ship), which I assumed to be negligable.
MikeH II posted 12-13-98 07:27 AM ET
Good point.
Heckler posted 12-13-98 08:31 AM ET
BKK noticed one possible discrepancy in your original post.
Acceleration assuming max velocity ~.1c
this should be Acceleration assuming AVERAGE velocity ~.1c
Remember the trip took 40 years, AC is 4 light years, thus overall speed of .1c. I would think that max speed would be .15/.2c to allow for that (proabably .2c assuming constant acceleration to midpoint.) Though max might be lower, if they were able to quickly boost to .12c or so and then coast (to conserve fuel mass) though this is unlikely.
My best guess on Unity's layout
Front Shield, this is to stop as much incoming radiation as possible, would be mostly of use in final portion of voyage where crew is awake and closing on Planet. Due to fact that this would only be a matter of days/weeks at worst they might have done without this.
Drive, Specs as put forward by Zharatov.
Fuel Tanks, put between the Drive and the CryoBays to provide additional radiation shielding to the bays these are proabably doughnut shaped to allow the central drive tunnel to go past them, might be honeycombed with indipendant sections to allow for stabilization
Cryobays, as put forward in the story there were 8 of these one is considered a total loss due to power/computer function loss.
Controll Centers, main and backup centers set for some reason outside the cryobays where they will receive more radiation (evidently the designers didn't care about Garlands Cuhojnes }:-) )
Supply and Science Drones, put last proabably because they were mostly afterthought.
All parts listed in first to last order.
Estimated mass, Proabably close to current day Aircraft Carrier, remember they enjoy an ~50yr. advantage on us in terms of materials.
Spoe posted 12-13-98 05:20 PM ET
Actually, avg velocity would be ~0.1075c(it's actually ~4.3 lyr.
Another thing we can assume from what we are told in the story is that the Unity does not produce the same amount of thrust throughout its journey. If it did, and the mass of the fuel used was not negligable wrt to the mass of Unity(which I believe to be the case from my earlier calculations), then you would expect to see a longer acceleration phase than deceleration.
----
"Controll Centers, main and backup centers set for some reason outside the cryobays where they will receive more radiation (evidently the designers didn't care about Garlands Cuhojnes }:-) )"
Bad assumption here. There is no reason that they would worry about radiation here. With the planned trip, the control centers would only be designed to be occupied at interplanetary speeds at the very beginning and end of the trip. The only reason they are occupied at this point in the timeline was the accident that shut down the drive.
Spoe posted 12-13-98 05:26 PM ET
Er, scratch part of that last -- somehow I skimmed over "Over and over again a burst of energy that rivals an atomic weapon travels through the containment rings, only meters from the edge of the cryobays, and propels us forward. This went on for over six years, accelerating us in the near frictionless environment of space to a coasting speed...". So, looks like 6 years of accel, 14 years of coasting, and then 20 years of decel. Methinks someone wasn't thinking when they put this together.
BKK the Mentat posted 12-13-98 09:42 PM ET
Er...dammit, now i'll have to recalculate everthing!
BTW n the subject of the basic structure of the ship,I think the cryobays may look similar to the type on the colonization ship featured in Red Mars.
Q: Maybe we should try to figure out just how the hell the fusion drive actually works.
BKK the Mentat posted 12-13-98 10:11 PM ET
One question:can any of you describe the ship from CIV2?
JustAName posted 12-15-98 04:53 AM ET
I wouldn't worry about the ship from Civ II...it was cute as a project but it was very modular, and looked as if it couldn't handle even the most neglible force applied to any given section. On the other hand, considering the technology needed to make it work, I CAN picture a huge fusion drive, with pods connected around it to call it a ship. It would be much more structurally stable as well, I imagine.
Spoe posted 12-15-98 04:03 PM ET
Ok, here we go, based on my assumption from above of a 6 yr accel time and a 20 yr decel:
d = 4.3 lyr (distance to AC)
ta = 6 yr (time of accel)
tc = 14 yr (time of coast)
td = 20 yr (time of decel)
aa = acceleration during accel phase
ad = acceleration during decel phase
First, relate aa to ad:
aa * ta = -ad * td
ad = -3 / 10 * aa [1]
Then set up the trip:
d = (0.5 * aa * ta**2) + (aa * ta * tc) + (aa * td + 0.5 * ad * td**2) [2]
Now substitute [1] into [2]:
d = (0.5 * aa * ta**2) + (aa * ta * tc) + (aa * td - 0.15 * aa * td**2)
Substitute in the known values and simplify:
4.3 lyr = 162 yr**2 * aa
Solve for aa:
aa = 0.02654 lyr/yr**2
Then for ad:
ad = -0.007963 lyr/yr**2
This give a coasting speed of:
0.02654 lyr/yr**2 * 6 yr = 0.1593 lyr/yr = 0.1593 c
Now, let's check this against decel:
-0.007963 lyr/yr**2 * 20 yr = -0.1593 c
Checks out.
Spoe posted 12-15-98 04:14 PM ET
Oh, and I meant to add, aa = 0.2521 m/s**2 or approximately 0.026 g. ad is even more negligable at 0.0077 g. Not very much, or even near the maximum performance of the engines(which, IIRC, was figured to be at least 0.1g, given information in the early episodes).
MikeH II posted 12-15-98 04:45 PM ET
Nice work again Spoe.
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Author	Topic: Reestimaing the performance of the Unity's fusion drive
BKK the Mentat	posted 12-10-98 08:26 PM ET For all you math whizes,genuses,mentats,Unix users,or anyone that enjoys pain, help me out. Here are the basic catigories of information that I want to know: Acceleration assuming max velocity ~.1c Fuel consumption thust raw energy release(W) SPECULATIONS ABOUT THE DRIVE AND LAYOUT OF THE UNITY ITSELF. also, to perform these calculations, I need to know the ship's mass.
Spoe	posted 12-10-98 09:10 PM ET Hrm, I've been meaning to get around to updating my early calculations to take into account, especially since fuel was a major portion of the initial mass of the ship. Might actually get around to it this weekend...
MikeH II	posted 12-11-98 09:27 AM ET I think we used 100,000 metric tons as the mass of the ship before, without fuel. I based that on the size and weight of an Aircraft carrier today and estimated. Anyone know the final predicted size and mass of the ISS? Might help with the densities achievable in space engineering today then we could make a better estimate of mass.
JustAName	posted 12-11-98 09:55 AM ET Remember kids, when using Aircraft Carriers as a means of comparing masses, keep in mind that seaborne technology is significantly more advanced in terms of "mass/density-to-technology" ratios than would be the supposedly new concept of space travel within the confines of the information given in the storyline. In other words, the Unity ain't pretty, just (barely) functional. I'd consider upping the mass.
BKK the Mentat	posted 12-11-98 09:59 PM ET Here's my 2cents worth...... Estimated ship's mass:~185-220,000mt(unloaded superstructure only) effecency of reactor:~5% fuel consumption(assumuming 5%ef.and avg. of 15.6 pulses per sec.):1.88avg. acceleration stage:2Kg/sec deceleration:1.76Kg/sec Total fuel consunption:416,740.3metric tonnes That's all I can offer until we decide on a standard mass and acceleration rate(or get one from Firaxis; hint hint.
MikeH II	posted 12-12-98 06:54 AM ET I understand your point about the mass JustAName. That was the only thing I could think of which was big enough to compare it with.
Spoe	posted 12-12-98 01:48 PM ET Eh, the first time round I wasn't too worried about the actual mass we used. Why? All the equations were linear wrt mass, so the mass of ship:mass of fuel ratio would be a constant. Basically the only factor that would disrupt this would be the housekeeping load(assuming that they use the fusion drive for electrical power for the rest of the ship), which I assumed to be negligable.
MikeH II	posted 12-13-98 07:27 AM ET Good point.
Heckler	posted 12-13-98 08:31 AM ET BKK noticed one possible discrepancy in your original post. Acceleration assuming max velocity ~.1c this should be Acceleration assuming AVERAGE velocity ~.1c Remember the trip took 40 years, AC is 4 light years, thus overall speed of .1c. I would think that max speed would be .15/.2c to allow for that (proabably .2c assuming constant acceleration to midpoint.) Though max might be lower, if they were able to quickly boost to .12c or so and then coast (to conserve fuel mass) though this is unlikely. My best guess on Unity's layout Front Shield, this is to stop as much incoming radiation as possible, would be mostly of use in final portion of voyage where crew is awake and closing on Planet. Due to fact that this would only be a matter of days/weeks at worst they might have done without this. Drive, Specs as put forward by Zharatov. Fuel Tanks, put between the Drive and the CryoBays to provide additional radiation shielding to the bays these are proabably doughnut shaped to allow the central drive tunnel to go past them, might be honeycombed with indipendant sections to allow for stabilization Cryobays, as put forward in the story there were 8 of these one is considered a total loss due to power/computer function loss. Controll Centers, main and backup centers set for some reason outside the cryobays where they will receive more radiation (evidently the designers didn't care about Garlands Cuhojnes }:-) ) Supply and Science Drones, put last proabably because they were mostly afterthought. All parts listed in first to last order. Estimated mass, Proabably close to current day Aircraft Carrier, remember they enjoy an ~50yr. advantage on us in terms of materials.
Spoe	posted 12-13-98 05:20 PM ET Actually, avg velocity would be ~0.1075c(it's actually ~4.3 lyr. Another thing we can assume from what we are told in the story is that the Unity does not produce the same amount of thrust throughout its journey. If it did, and the mass of the fuel used was not negligable wrt to the mass of Unity(which I believe to be the case from my earlier calculations), then you would expect to see a longer acceleration phase than deceleration. ---- "Controll Centers, main and backup centers set for some reason outside the cryobays where they will receive more radiation (evidently the designers didn't care about Garlands Cuhojnes }:-) )" Bad assumption here. There is no reason that they would worry about radiation here. With the planned trip, the control centers would only be designed to be occupied at interplanetary speeds at the very beginning and end of the trip. The only reason they are occupied at this point in the timeline was the accident that shut down the drive.
Spoe	posted 12-13-98 05:26 PM ET Er, scratch part of that last -- somehow I skimmed over "Over and over again a burst of energy that rivals an atomic weapon travels through the containment rings, only meters from the edge of the cryobays, and propels us forward. This went on for over six years, accelerating us in the near frictionless environment of space to a coasting speed...". So, looks like 6 years of accel, 14 years of coasting, and then 20 years of decel. Methinks someone wasn't thinking when they put this together.
BKK the Mentat	posted 12-13-98 09:42 PM ET Er...dammit, now i'll have to recalculate everthing! BTW n the subject of the basic structure of the ship,I think the cryobays may look similar to the type on the colonization ship featured in Red Mars. Q: Maybe we should try to figure out just how the hell the fusion drive actually works.
BKK the Mentat	posted 12-13-98 10:11 PM ET One question:can any of you describe the ship from CIV2?
JustAName	posted 12-15-98 04:53 AM ET I wouldn't worry about the ship from Civ II...it was cute as a project but it was very modular, and looked as if it couldn't handle even the most neglible force applied to any given section. On the other hand, considering the technology needed to make it work, I CAN picture a huge fusion drive, with pods connected around it to call it a ship. It would be much more structurally stable as well, I imagine.
Spoe	posted 12-15-98 04:03 PM ET Ok, here we go, based on my assumption from above of a 6 yr accel time and a 20 yr decel: d = 4.3 lyr (distance to AC) ta = 6 yr (time of accel) tc = 14 yr (time of coast) td = 20 yr (time of decel) aa = acceleration during accel phase ad = acceleration during decel phase First, relate aa to ad: aa * ta = -ad * td ad = -3 / 10 * aa [1] Then set up the trip: d = (0.5 * aa * ta*2) + (aa ta * tc) + (aa * td + 0.5 * ad * td*2) [2] Now substitute [1] into [2]: d = (0.5 aa * ta*2) + (aa ta * tc) + (aa * td - 0.15 * aa * td2) Substitute in the known values and simplify: 4.3 lyr = 162 yr2 * aa Solve for aa: aa = 0.02654 lyr/yr2 Then for ad: ad = -0.007963 lyr/yr2 This give a coasting speed of: 0.02654 lyr/yr*2 6 yr = 0.1593 lyr/yr = 0.1593 c Now, let's check this against decel: -0.007963 lyr/yr*2 20 yr = -0.1593 c Checks out.
Spoe	posted 12-15-98 04:14 PM ET Oh, and I meant to add, aa = 0.2521 m/s**2 or approximately 0.026 g. ad is even more negligable at 0.0077 g. Not very much, or even near the maximum performance of the engines(which, IIRC, was figured to be at least 0.1g, given information in the early episodes).
MikeH II	posted 12-15-98 04:45 PM ET Nice work again Spoe.