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Author Topic: Behemoth Slowboat Cargo Ship  (Read 2596 times)

Giovanni Blasini

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Behemoth Slowboat Cargo Ship
« on: 09 September 2021, 18:38:03 »
OK, this is based on the math I did here, on what it would realistically take to slowboat cargo between two star systems in Battletech in the event, as in Herb's setting, that JumpShip travel is lost, but DropShips can still be built.

OK, first off, I gave everyone first-class quarters, to ensure they had sufficient room and amenities for a long flight.  I doubled up on the number of people listed for the crew, which was 9 officers, 55 enlisted/gunners, and 100 bay personnel, for 164 total.  Throwing on 32 marines, that would be 328 + 32 --> 360 personnel, but we're also going to need 12 base personnel, doubled, for the large naval comm-scanner suite I'm adding, so that's 384 total.

Supplies for 384 people, at 60 tons each, works out to 23,040 tons.  I've added 0.21 tons to that, put it in its own insulated cargo bay to represent their supplies, which allowed that bay's mass to round up to an even 26483 tons.  Next up, I put six laser AMS fore and aft, along with a single SCL/1 to function as a communications laser, along with that naval comm-scanner.

I'm left, then, with 36,681 tons of cargo.  The next big question becomes how many tons of spare parts or machinery and feedstock to make spare parts you need.  In that thread, I calculated it at 1% of ship's mass per year, which probably isn't realistic, but I don't recall where the actual rules for that are anymore.

Code: [Select]
Behemoth Slowboat Colony Ship
Type: Civilian Spheriod
Mass: 100,000 tons
Technology Base: Inner Sphere (Standard)
Introduced: 3150
Mass: 100,000
Battle Value: 1,672
Tech Rating/Availability: E/X-X-X-E
Cost: 7,982,653,000 C-bills

Fuel: 8,000 tons (80,000)
Safe Thrust: 2
Maximum Thrust: 3
Heat Sinks: 297
Structural Integrity: 30

Armor
    Nose: 50
    Sides: 50/50
    Aft: 60

Cargo
    Bay 1:  Small Craft (20)        4 Doors   
    Bay 2:  Cargo (Insulated) (23040.21 tons)1 Door   
    Bay 3:  Cargo (12227.0 tons)    1 Door   
    Bay 4:  Cargo (12227.0 tons)    1 Door   
    Bay 5:  Cargo (12227.0 tons)    1 Door   

Ammunition:
None

Escape Pods: 5
Life Boats: 5
Crew:  9 officers, 41 enlisted/non-rated, 5 gunners, 100 bay personnel, 250 passengers, 32 BA marines

Notes: Mounts 15 tons of standard aerospace armor.

Weapons:                         Capital Attack Values (Standard)
Arc (Heat)                   Heat  SRV     MRV     LRV     ERV   Class       
Nose (66 Heat)
6 Laser AMS                  42   2(18)    0(0)    0(0)    0(0)  AMS         
1 Sub-Capital Laser (SCL/1)  24   1(10)   1(10)   1(10)    0(0)  Sub-Capital Laser
RS/LS Fwd (14 Heat)
2 Medium Laser               14   2(18)    1(8)    0(0)    0(0)  Laser       
    1 Large Laser
RS/LS Aft (14 Heat)
2 Medium Laser               14   2(18)    1(8)    0(0)    0(0)  Laser       
    1 Large Laser
Aft (72 Heat)
2 Medium Laser                6   1(10)    0(0)    0(0)    0(0)  Laser       
6 Laser AMS                  42   2(18)    0(0)    0(0)    0(0)  AMS         
1 Sub-Capital Laser (SCL/1)  24   1(10)   1(10)   1(10)    0(0)  Sub-Capital Laser


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Daryk

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Re: Behemoth Slowboat Cargo Ship
« Reply #1 on: 09 September 2021, 18:56:08 »
Nice work!  :thumbsup:

AngryButler with a KNIFE!

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Re: Behemoth Slowboat Cargo Ship
« Reply #2 on: 09 September 2021, 19:00:50 »
I'm still new to Aerospace stuff but, you might want to devote some cargo space to either some vehicles - preferably ones that are airtight of course - and/or at least a lance of 'Mechs. Simply so you can land on an asteroid and do some mining. Or, once you actually reach the new solar system, a means to start rapidly expanding on the ground beyond merely moving on foot. Or at least, stuck to being on foot until your micro-factories are up and running, and able to build some ultralight rovers.

Giovanni Blasini

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Re: Behemoth Slowboat Cargo Ship
« Reply #3 on: 09 September 2021, 19:13:22 »
I'm still new to Aerospace stuff but, you might want to devote some cargo space to either some vehicles - preferably ones that are airtight of course - and/or at least a lance of 'Mechs. Simply so you can land on an asteroid and do some mining. Or, once you actually reach the new solar system, a means to start rapidly expanding on the ground beyond merely moving on foot. Or at least, stuck to being on foot until your micro-factories are up and running, and able to build some ultralight rovers.

In this case, I was leaning more towards it being a cargo ship that's being used to deliver cargo between two inhabited systems less than 30 light-years apart, where neither ship has the ability to produce JumpShips anymore, but still suppport the ability to produce and maintain DropShips.  It's certainly a valid point, though, and perhaps the easiest way to accomplish that would be to reduce the number of small craft from the rather copious 20 it normally carries down to, say, half that, using the 2000 tons you'd free up to carry the equivalent of a Small Factory station.
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Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #4 on: 09 September 2021, 20:33:17 »
Perhaps this concept is better done with a space station?  It's cheaper and less mass is spent on the engine.

AlphaMirage

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Re: Behemoth Slowboat Cargo Ship
« Reply #5 on: 09 September 2021, 20:45:33 »
It is actually 1.2% of the unit's deadweight mass per year according to Campaign Ops. However, because most of the dropship is cargo I'd say you can get away with what I call 'live weight' which is everything but raw cargo. So that's 40,279 tons in this case or ~483 tons per year in spare parts.

VhenRa

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Re: Behemoth Slowboat Cargo Ship
« Reply #6 on: 09 September 2021, 22:13:37 »
Big question is how far can this ship travel with it's 32 years of supplies [ignoring spare parts]. -does math-

0.6c = 23 LY [39 years real time]
0.7c = 30 LY [44 years real time]
0.8c = 41 LY [52 years real time]
0.9c = 62 LY [72 years real time]

I calculated it at 1% of ship's mass per year, which probably isn't realistic, but I don't recall where the actual rules for that are anymore.

Campaign Operations.

0.1% of ship's mass every month. So 1.2% a year.

Perhaps this concept is better done with a space station?  It's cheaper and less mass is spent on the engine.

Honestly... I am going to have to agree here. You'll lose a bit of time at start because you'll take a it longer to accelerate up to speed... but spacestations don't need as extensive spare parts [0.01% of mass a month!] and can carry a larger fraction of their mass in cargo capacity.
« Last Edit: 09 September 2021, 22:28:35 by VhenRa »

Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #7 on: 10 September 2021, 06:46:17 »
Honestly... I am going to have to agree here. You'll lose a bit of time at start because you'll take a it longer to accelerate up to speed... but spacestations don't need as extensive spare parts [0.01% of mass a month!] and can carry a larger fraction of their mass in cargo capacity.
One "disadvantage" of space stations is that they are usually less fuel efficient.  The natural design points seem to be 49k tons where they require a factor of 4 more fuel.  At the other extreme, a 2.5M ton space station actually requires somewhat less fuel as a fraction of total mass.

The reason for quotes here is that the efficiency of fuel badly breaks known physics.  More realistic versions here require the use of the rocket equation.

One advantage of space stations is grav decks.  Not having simulated gravity for a long period of time seems likely detrimental to health.

VhenRa

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Re: Behemoth Slowboat Cargo Ship
« Reply #8 on: 10 September 2021, 10:27:55 »
That too would be a big advantage, yes.

Time to acceleration is also going to be a pain... honestly you might want something like an Argo... something halfway between the two.

Daryk

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Re: Behemoth Slowboat Cargo Ship
« Reply #9 on: 10 September 2021, 17:17:44 »
BTs magical fusion rockets have ALWAYS violated the rocket equation (even with relativistic corrections, the energy requirements exceed matter/anti-matter annihilation).

idea weenie

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Re: Behemoth Slowboat Cargo Ship
« Reply #10 on: 10 September 2021, 19:18:05 »
For a multi-year mission like this I'd want to use rules that reduce fuel consumption based on current mass of the craft.  So it starts at 100,000 tons, has a burn-day consumption rate of 19.75 tons.  After the Dropship has burned off 1 ton of fuel, I'd want to recalculate the fuel consumption rate as technically the vessel is a 99,000 ton craft, with a burn-day rate of 9.77 tons/burn-day, or half the fuel demand.  If the vessel's mass ever gets down to 49,999 tons, I would want to recalculate the fuel consumption again since it is now 2.82 tons/burn-day.

DevianID

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Re: Behemoth Slowboat Cargo Ship
« Reply #11 on: 10 September 2021, 19:22:23 »
Yes the transit drives are a big offender.  The tactical fuel use is actually pretty close to what is actually possible, and if we pretend strategic transit drives are not real the tactical drives would be considered close to peak efficiency.  In fact, because the writers stopped making brackets as tonnage increases, even tactical fuel use breaks physics on the higher end of tonnage.  Warships are the most obvious as the bracket of 5 pts is from 110k to 249k, then it's 2.5 pts from 250k to ?  If the next logical bracket at 500k was 1 pt per ton, then .5 at 1000k, and .25 pt at 2+ million tons we would be fine.

It is entirely possible to travel using only tactical drive fuel usage, but the current ships are not designed to do so.  Same with using an existing ship like the behemoth. 

For slowboating, if you are not going to land on the surface a purpose built speed 1/2 'dropship' is best I think.  You also added on a bunch of superfluous things like naval comms and high power lasers for communication.  If this is a luxury passenger liner that makes sense, but for cargo look at what the 'Alien' transport looked like... Very low tech future, very rugged, no frills and no high tech equipment, coupled with a skeleton crew.  The Canterbury from the expanse was another good example for shorter trips.

Daryk

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Re: Behemoth Slowboat Cargo Ship
« Reply #12 on: 10 September 2021, 19:38:35 »
I agree tactical fuel consumption mostly works... it's the strategic that's most problematic, and that's what we're really looking at for a "slow boat".

Giovanni Blasini

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Re: Behemoth Slowboat Cargo Ship
« Reply #13 on: 10 September 2021, 20:44:51 »
I agree tactical fuel consumption mostly works... it's the strategic that's most problematic, and that's what we're really looking at for a "slow boat".

Strategic even works fine up to about 800 tons.  Beyond that it's problematic.
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Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #14 on: 10 September 2021, 21:25:21 »
Strategic even works fine up to about 800 tons.  Beyond that it's problematic.

My calculations (here's the link again) suggest that strategic only works to ~50 tons (if you see a flaw, I'm very interested). 

Using that calculation, you need to use ~3.6% of mass per burn-day.  For tactical fuel consumption this implies, dropships in 1600-1899 and 2000+ tons violate physics.  For capital craft, tactical fuel violates physics at 8000+ tons.

It is pretty feasible to reach .03c using actual fusion physics.  Combining that with an automated repair systems has some possibilities---you might be able to reach (say) 25 light years although it will certainly take quite a long time.

Giovanni Blasini

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Re: Behemoth Slowboat Cargo Ship
« Reply #15 on: 10 September 2021, 22:08:10 »
My calculations (here's the link again) suggest that strategic only works to ~50 tons (if you see a flaw, I'm very interested). 

Interesting.  Last time someone ran the numbers, strategic fuel usage at 1.84 tons/burn-day/G worked out to being problematic at 800 tons, not 50.  That's figuring 846,720 m/s delta-v after a 24-hour burn, with a specific impulse of around 2.3 million seconds?
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Natasha Kerensky

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Re: Behemoth Slowboat Cargo Ship
« Reply #16 on: 10 September 2021, 23:58:18 »
0.6c = 23 LY [39 years real time]
0.7c = 30 LY [44 years real time]
0.8c = 41 LY [52 years real time]
0.9c = 62 LY [72 years real time]

I didn’t check, but I assume the calculations above include a deceleration phase so our interstellar Behemoth can actually deliver cargo and is not limited to high-speed flybys.

At these speeds, interstellar dust grains become high explosives.  She’ll need some serious physical shielding to protect against these ongoing collisions.  Project Daedalus from the British Interplanetary Society assumed a beryllium shield weighing 50 tonnes for a vehicle that only massed some 3K tonnes dry.  The same ratio applied to our interstellar Behemoth yields a shield weighing 1667 tons.  But Daedalus topped out at only 0.12c, so the shield for our interstellar Behemoth will be some multiple of that 1667 tons, depending on its actual velocity and the time spent at that velocity.
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DevianID

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Re: Behemoth Slowboat Cargo Ship
« Reply #17 on: 11 September 2021, 00:59:18 »
At 1000 tons, 10^-3 for 80 points of thrust comes out to 1 ton of fuel being 80 points, using your fusion energy data which I wont check.  A 1k ton dropship gets 60 points per ton, meaning they are a little less efficient.  The brackets all work until we get to the last bracket, which breaks conventions with the others as it goes from 40k ton 100k tons all at 10 points per.  So after 80k tons the dropships break your calculations, due entirely to the writers not finishing the chart with a break point at 60k-80k and 81k to 100k.  So dropships arnt as bad with missing chart entries as warships, but both have issues with the fuel chart being unfinished.

For incoming dust, is it possible to ionize it and scoop it up for fuel/reaction mass instead of trying to shield it?  Shielding just isnt feasable if you need 50k tons of shield for a 3k ton ship.
« Last Edit: 11 September 2021, 01:44:09 by DevianID »

cawest

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Re: Behemoth Slowboat Cargo Ship
« Reply #18 on: 11 September 2021, 01:00:59 »
green space would cut down on your food needs and help with crew health maybe temporary inflatable rooms.  i can see having one or two small craft bays for working on small craft, but you could attached a few more on the outer hull to save space and volume.  i also would add 2-500 tons of tools to help with repairs. 

VhenRa

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Re: Behemoth Slowboat Cargo Ship
« Reply #19 on: 11 September 2021, 02:11:36 »
I didn’t check, but I assume the calculations above include a deceleration phase so our interstellar Behemoth can actually deliver cargo and is not limited to high-speed flybys.

At these speeds, interstellar dust grains become high explosives.  She’ll need some serious physical shielding to protect against these ongoing collisions.  Project Daedalus from the British Interplanetary Society assumed a beryllium shield weighing 50 tonnes for a vehicle that only massed some 3K tonnes dry.  The same ratio applied to our interstellar Behemoth yields a shield weighing 1667 tons.  But Daedalus topped out at only 0.12c, so the shield for our interstellar Behemoth will be some multiple of that 1667 tons, depending on its actual velocity and the time spent at that velocity.

Yes, those calculations include that.

idea weenie

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Re: Behemoth Slowboat Cargo Ship
« Reply #20 on: 11 September 2021, 03:08:53 »
I didn’t check, but I assume the calculations above include a deceleration phase so our interstellar Behemoth can actually deliver cargo and is not limited to high-speed flybys.

At these speeds, interstellar dust grains become high explosives.  She’ll need some serious physical shielding to protect against these ongoing collisions.  Project Daedalus from the British Interplanetary Society assumed a beryllium shield weighing 50 tonnes for a vehicle that only massed some 3K tonnes dry.  The same ratio applied to our interstellar Behemoth yields a shield weighing 1667 tons.  But Daedalus topped out at only 0.12c, so the shield for our interstellar Behemoth will be some multiple of that 1667 tons, depending on its actual velocity and the time spent at that velocity.

Is that 50-ton shield based on the mass of Daedalus, or on its diameter?  I.e. if you make the Daedalus twice as wide, tall, and long you will get a vessel 8* the mass, but only 4* the cross-section.  Would that larger Daedalus need a 200-ton or 400-ton Beryllium shield?

(I'm leaving alone the increased mass due to higher speeds)


Another detail that nobody has brought up yet - replacement crew.  Will the ship need natal support for the crew en-route (and on the way back), or will the crew be given a 20+ year supply of birth control?  Likely the former, if the ship has to make a round trip.

Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #21 on: 11 September 2021, 08:34:59 »
Interesting.  Last time someone ran the numbers, strategic fuel usage at 1.84 tons/burn-day/G worked out to being problematic at 800 tons, not 50.  That's figuring 846,720 m/s delta-v after a 24-hour burn, with a specific impulse of around 2.3 million seconds?
A specific impulse of 2.3 million seconds implies that a ton of fuel accelerates 1000 tons of mass for 2300 seconds (~=38 minutes) at 1g.   My calculations suggested slightly over 40 minutes is possible, although it's not super clear how close engineering can get to the theoretical maximum.  So, yes, that's consistent.  Natasha Kerensky also brought up Project Daedelus which projects a .12c flyby (i.e. no slowing down) with a 2-stage fusion approach.  This also seems consistent with .03c ignoring the rocket equation with a plan to decelerate.

At 1000 tons, 10^-3 for 80 points of thrust comes out to 1 ton of fuel being 80 points, using your fusion energy data which I wont check.  A 1k ton dropship gets 60 points per ton, meaning they are a little less efficient.  The brackets all work until we get to the last bracket, which breaks conventions with the others as it goes from 40k ton 100k tons all at 10 points per.
At 1600 tons, it's 50 fuel points/ton which precisely matches 80 fuel points/ton at 1000 tons.  At 1700 tons, it should be just 47 fuel points/ton (but is 50).  At 1800 tons, it should be 44 fuel points/ton (but is 50).  At 1900 tons it should be 42 (but is 40, so it works).  At 2000 tons, it's 40 fuel points/ton (which works).  At 2100 tons, it should be 38 (but is 40).  Nothing larger works, which we can check by looking at the beginning of each fuel efficiency step.  3000 tons should be 27 (but is 30), 20000 should be 4 (but is 20), 40000 should be 2 (but is 10).  And at 100000 tons, it should be .8, but is 10.  So overall tactical fuel efficiency starts out ok and becomes an order of magnitude aphysical on the largest dropships.

One thought here is that you can make slowboating much more feasible with corpsicle technology.  On page 313 of aToW, there is a 'Stasis Tube' which does this.  My understanding of the very abbreviated rules is that freezing for a very long time just implies you lose either a point of BOD or INT.  That's not great, but it's at least sometimes survivable.

killfr3nzy

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Re: Behemoth Slowboat Cargo Ship
« Reply #22 on: 11 September 2021, 09:47:40 »

Honestly... I am going to have to agree here. You'll lose a bit of time at start because you'll take a it longer to accelerate up to speed... but spacestations don't need as extensive spare parts [0.01% of mass a month!] and can carry a larger fraction of their mass in cargo capacity.

Could you reduce the acceleration (and perhaps even deceleration) periods with a tug?

DevianID

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Re: Behemoth Slowboat Cargo Ship
« Reply #23 on: 11 September 2021, 13:58:46 »
I thought btech stasis was like interstellar stasis, where you sleep for years in a induced coma but still age; people live a bit longer in btech so losing your 40s and 50s to travel 20 years isn't as debilitating

idea weenie

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Re: Behemoth Slowboat Cargo Ship
« Reply #24 on: 11 September 2021, 14:01:33 »
One thought here is that you can make slowboating much more feasible with corpsicle technology.  On page 313 of aToW, there is a 'Stasis Tube' which does this.  My understanding of the very abbreviated rules is that freezing for a very long time just implies you lose either a point of BOD or INT.  That's not great, but it's at least sometimes survivable.

Handbook: Major Periphery States also has notes about Stasis Tubes.  For those interested, it takes 24 hours to enter or leave, and one year of real time is one day inside.

These slowboats could be set up with a revolving crew, where different personnel take turns being asleep and waking up for a few days/weeks to let their bodies repair themselves.  Atomic Rockets' Slower Than Light page has a section about cryosleep, but it dealt with timeframes longer than the trip.  Off-hand, I'd say that the crews would be cycled through for less time than it takes for the injuries to start happening, they are kept awake for long enough for their bodies to repair themselves, then are put back under.

So if the penalties start happening after 2 years, and it takes 1 month to recover, then on average you'd have ~1/25 of your crew awake at any time (exact numbers may vary). 

One idea for this sort of slowboat would be using Quarters (with their inherent life support capabilities) to build up a stockpile of Life Support, and when it is time to wake up the extra crew the the cargo bays get converted to Bays to handle the extra personnel.  This also allows for good drama, where the crew might need to wake up extra people to solve an issue, but they also know they have a limited supply of oxygen and food where each extra mouth makes that supply get used up faster.  Can they solve the problem before they have to start drawing straws, or do they risk putting someone into cryo-sleep whose skills might be needed later?

VhenRa

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Re: Behemoth Slowboat Cargo Ship
« Reply #25 on: 12 September 2021, 07:21:22 »
Could you reduce the acceleration (and perhaps even deceleration) periods with a tug?

I don't think a station will stand up to such a higher acceleration. Structure isn't built for such accelerations. Maybe you might be able to get it up to half a G? [Based on 1 SI?]

Half a G will shave a bit of time off, yes.

Deceleration... would require a tug to travel with you. That or placing a tug in the path of your slowboat, having it accelerate up to meet you, dock and then start the deceleration phase. That is kinda absurd tbh.

Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #26 on: 12 September 2021, 08:17:36 »
From the viewpoint of fusion physics, you wouldn't use a tug since it has a large mass cost. Instead, a much larger station with ample cargo capacity could carry the smaller station.   The larger station would accelerate until 1/4 of it's fuel is burned, unload the cargo, decelerate, accelerate back home, and then decelerate to 0 at home.  This might allow the smaller station to begin expending fuel with a baseline velocity of .01c, allowing it to achieve a higher cruise velocity of .04c.  Slowing down could use the same process in reverse.

Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #27 on: 13 September 2021, 07:45:48 »
I found a bug in the equation which implies we should imagine at most 50 thrust points per .1% of fusion mass. 

Using the rocket equation and .01% of mass/month for spare parts on a space station, this suggests a 10 light-year range at .025c. 

Using a giant space station (2.5 megatons) to carry this one as cargo up to a high initial velocity, release, then return to base (and vice-versa on the receiving end) helps quite a bit because the giant station need not carry so much spare parts.  This enables at least doubling the cruise velocity to .05c and hence the range to 20 light-years.

Giovanni Blasini

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Re: Behemoth Slowboat Cargo Ship
« Reply #28 on: 13 September 2021, 11:48:30 »
Is that with realistic fusion rockets, or rules as written fusion rockets?
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Lagrange

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Re: Behemoth Slowboat Cargo Ship
« Reply #29 on: 13 September 2021, 12:52:19 »
Is that with realistic fusion rockets, or rules as written fusion rockets?
Err... neither.  This is for 'allowed by known physics' fusion rockets.  That's not likely realistic (which is almost surely worse), and it's certainly not 'rules as written' (which is dramatically better).

I had an idea though: a big chunk of mass is going to maintenance during the cruise period.  Maybe we could get around that by using the mothballing rules? If the majority of the mass was mothballed during the centuries of cruise, then significantly more mass could be devoted to thrust.