some interesting figures for earths early ships

[glitterboy2098]

ok so in the Invasion comics series, the B-story was the story of mars base Sera, and near the end of it you have an oberth showing up at mars.

this had gotten me curious awhile back, so i'd decided to crunch a few numbers, to see what kind of trip said ship would have been making, based on the RPG's stats.

blue is my more recent additions.. this was part of a train of thought thing i wrote awhile back but didn't post.

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ok, so i dug out my macross saga book and tried to figure out what the travel times o the ARMD and Oberth would be to mars.

the ARMD has a max velocity of 249,900 kmh, or in easier to use form, 69.4 kps
the Oberth has a max velocity of 274,400 kph, or 76.2 kps.
(note they both have long decimals but i'm rounding)

while this is about 5x the best top velocities our current rockets can do, and roughly comparable to some of our space probes after multiple speed boosting flyby's, the fact is this isn't all that high. however, the real measure is gonna be acceleration. because robotech drives seem to be able to operate for long times constantly. if we knew the acceleration in G's we could calculate how long it would take to reach specific places i nthe solar system using constant thrust (accelerate halfway there, decelerate on the other half)
sadly the RPG does not give us details from which we can easily base the acceleration, the way it does with the Zentreadi, ASC, and Master's vessels. which suggests that the ARMD drives are pitifully weak compared to interstellar ships.

thankfully, the internet provided a tool i could use to figure that out..
http://www.transhuman.talktalk.net/iw/TravTime.htm
this calculator was created for the transhuman space RPG, which used semi-realistic physics and ships that traveled by constant thrust. and it had a "trip to mars" setting.

so i set the distance to earth-mars, and enabled turnover (since this is not a flyby i'm looking for)
i then played around with various settings to find the level of thrust an ARMD or Oberth would require to make the trip. using the maximum velocity figure to ensure the speed at turnover didn't exceed the listed velocities in the RPG.

the result?

ARMD = 0.0015 G's for a trip of 101 days, 0 hours, 38 minutes, max velocity at turnover 64kps
Oberth = 0.002 G's for a trip of 87 days, 11 hours, 48 minutes. max velocity at turnover 74 kps.

so about 3.4 months for an ARMD, and 2.9 months for an Oberth.
(note that their "combat" thrust is probably higher, the upper speed limit is a function of exhaust velocity and overcoming inertia. but we'd still be looking at rather small thrust levels)

we actually can calculate the maximum thrust, it is just trickier. the ARMD says that it can reach full interplanetary speed of 249,900 kmh/69.4 kps in 24 hours. assuming that 24 hours is a specific value as opposed to a rough estimate, that would mean;
69.4 kps x 1000 = 69,400 mps
24x60x60 = 86,400 seconds

69,400 mps/86,400 seconds = 0.8032407 meters per second^2. or about 0.08 g's.

the Oberth works out as (76.2x1000)/86,400 = 0.881944 meters per second^2. or about 0.09 g's.

note that accelerating faster up to the max velocity will not actually get you to mars faster.. the maximum velocity is the main factor here.


the main issue this raises is endurance. while these ships clearly have the reactor and remass endurance to make these trips, the RPG's values for crew supplies ("expendables") is 6 months for the ARMD and 3 months for the Oberth.

lets be generous and assume that oxygen and water are recycled and thus not counted expendables for this purpose, but things like food are. the RPG says these values are for standard crew and troop compliment, so a minor solution presents itself, that of reducing the crew compliment to minimum levels on long voyages. though this would seem contradictory to the fact that somehow the UEG built fairly large and complex bases on mars, suggesting they moved a lot of workers. and with round trips (much less time at destination) always being longer than the onboard expendables an issue rears its head.

but one that might not be insurmountable. i can think of several things that could reduce the issue to manageable size.

first, use of automated delivery vehicles to pre-position stocks of food and other expendables at the destination for resupply. (similar to the early stages of the Mars Direct plan of real life, where the return vehicle and supplies for the stay on mars and the return are sent out before the manned mission even is assembled.) these could be launched well in advance using conventional heavy lift vehicles, and programmed to sit in orbit until the ship arrives to transfer the supplies. and they would not require powerful drives of their own, being able to use lower energy coasting orbits. so launch a resupply package or two two to three months before the ARMD or Oberth sets off and it'll be sitting in orbit waiting on the ship's arrival. (this method also helps explain why the base can be so large.. they only need the oberths and ARMD's to ferry the personnel around, the materials and tools needed to build the base (those that can't be sources in-situ on mars) would likely have been sent on cargo rockets well ahead of time.)

second, reduction of crew size and loading of additional supplies. leave behind as many people as you can without sacrificing the mission at hand, and fill the corridors with boxes of canned goods if need be. the ARMD is in a better position for such, given that it has a rather large contingent of pilots and mechanics for it's airwing. leave behind several squadrons and their mechanics, and fill the resulting freed up mass and deck space with supplies. Oberths would suffer more, not having much crew that can be cut, or any onboard airwing . though removing several of the large ICBM like anti-ship missiles to gain working mass for additional supplies to be carried onboard may have been a common option.

(it is worth noting that gravitational slingshots and oberth maneuvers would not be much help here. while they would certainly allow the ship to gain even more velocity than its drives normally would allow, they are very reliant on the positions of the planets, and windows where they would help would only open up every few decades. and the only options for an earth mars trip are making a swingby of venus (which actually adds more time to the trip's first leg) or of the sun itself (which could get dicey depending on how close you have to get) so such methods are only really useful if you have to get to mars when it is at opposition and on the far side of the sun from earth at the time. and you'd spend a lot of that trip coasting since you liekly wouldn't have enough fuel otherwise. it is much easier to launch at a time mars is reasonably close and use constant thrust.)



oh, and since i know you'll be curious.. the SDF-1 works out to an acceleration of 0.1G's, and could make the trip in 12 days, 8 hours, 57 minutes. (clearly the SDF-1 was not able to make 'best time' on the way to earth..)
the zentreadi flagship hits 0.25g's, allowing it to make the trip in 7 days, 19 hours, 48 minutes
and the Zent Destroyer hits 0.21g's, letting it do the trip in 8 days, 12 hours, 55 minutes.

so basically the Zent ships have twice as much acceleration as the SDF-1 and can reach places in roughly two thirds the travel time.
(and the SDF-1 is about ten times better in acceleration than the ARMD and Oberth class. not quite as bad as i'd figured they'd be.)

[ShadowLogan]

oh, and since i know you'll be curious.. the SDF-1 works out to an acceleration of 0.1G's, and could make the trip in 12 days, 8 hours, 57 minutes. (clearly the SDF-1 was not able to make 'best time' on the way to earth..)

Based on nothing but show cues based on the "Pluto" to Saturn leg of the return voyage home, the SDF-1 could have been far sooner than the show had happen just in terms of distance covered and aloted time.

thankfully, the internet provided a tool i could use to figure that out..
http://www.transhuman.talktalk.net/iw/TravTime.htm
this calculator was created for the transhuman space RPG, which used semi-realistic physics and ships that traveled by constant thrust. and it had a "trip to mars" setting.

Per the old MS Space Simulator Manual (pg170) for the program that worked on Newtonian Physics (math looks to be identical between the Manual and your website link):
Time (for turnover) = (2*SqRt of (Acceleration * Distance)) / Acceleration
Time (no turnover) = (SqRt of (2*Acceleration * Distance)) / Acceleration

watch your units.

Provided to give more options in terms of distance.

ARMD = 0.0015 G's for a trip of 101 days, 0 hours, 38 minutes, max velocity at turnover 64kps
Oberth = 0.002 G's for a trip of 87 days, 11 hours, 48 minutes. max velocity at turnover 74 kps.

And if you set it to actual values of .082G and 0.090G you end up with ~13 days #hrs, #minutes, max velocity 474-496kps for the respective ships. A far cry from the months trip time mentioned in Invasion #5 for an Orberth (RT Infopedia limits ARMD to Earth-Lunar distances, Mars transit for Orberth). This likely implies these particular ships can't accelerated in the manner being looked at.

It should also be noted that the calculator uses the median distance between Earth and Mars, but orbital motion can shrink or expand the distance between the two planets which would impact travel time.

the main issue this raises is endurance. while these ships clearly have the reactor and remass endurance to make these trips, the RPG's values for crew supplies ("expendables") is 6 months for the ARMD and 3 months for the Oberth.

They don't clearly have the remass endurance to perform constant acceleration for Earth-Mars trips as it is suggested they "top out" given the text in both ships lists it as "Interplanetary speed [of varying values] can be attained within 24hours of sustained acceleration".

Interestingly using the median Earth-Mars distance (from you weblink) of 280million km, and assuming the ARMD/Orberth accelerated to maximum velocity (and held it) would have enough consumables for either of them to make a trip to Mars in ~42-47days, well within the stated endurance of either ship. So consumables are not an issue. And the 40+days would seem to work with the stated "months" trip time in Invasion#5 from certain POV.

[glitterboy2098]

ARMD = 0.0015 G's for a trip of 101 days, 0 hours, 38 minutes, max velocity at turnover 64kps
Oberth = 0.002 G's for a trip of 87 days, 11 hours, 48 minutes. max velocity at turnover 74 kps.

And if you set it to actual values of .082G and 0.090G you end up with ~13 days #hrs, #minutes, max velocity 474-496kps for the respective ships. A far cry from the months trip time mentioned in Invasion #5 for an Orberth (RT Infopedia limits ARMD to Earth-Lunar distances, Mars transit for Orberth). This likely implies these particular ships can't accelerated in the manner being looked at.

and at turnover said ship would be moving at 474kps, which is way way too high considering we're told the ARMD max's out at 69.4

the calculations i did were done with the limit that it not exceed the maximum velocity attainable.

and removing limits to get an ideal case scenario does not allow you to then claim the analysis is flawed.

It should also be noted that the calculator uses the median distance between Earth and Mars, but orbital motion can shrink or expand the distance between the two planets which would impact travel time.

very true, but i have yet to find a calculator program that will do multiple position versions. if i can find accurate values for the distances i might be able to use the custom distance option in the program. i have been considering using it to find the time to reach 2010 TK7, which is a planetoid located in the earth-sun L4 trojan point. it's constant relative position to earth seems like it could be useful for something like a research center or solar system observation point.

the main issue this raises is endurance. while these ships clearly have the reactor and remass endurance to make these trips, the RPG's values for crew supplies ("expendables") is 6 months for the ARMD and 3 months for the Oberth.

They don't clearly have the remass endurance to perform constant acceleration for Earth-Mars trips as it is suggested they "top out" given the text in both ships lists it as "Interplanetary speed [of varying values] can be attained within 24hours of sustained acceleration".

actually max velocity is more a factor of drive exhaust velocity, not fuel load in this case. we are told and shown they can make the trip by the RPG and comics, ergo, it is not the fuel load that is limiting them.

macross saga sourcebook, pg 140, "atmosphere": ARMD carriers are unable to to enter atmosphere, and are restricted to operations in earth orbit and nearby planetary bodies such as the moon and mars"

the Oberth has the exact same entry, aside from the ship class changing, on pg137. further we are shown one having made the trip from earth to mars in the mars base sera comic.

interestingly using the median Earth-Mars distance (from you weblink) of 280million km, and assuming the ARMD/Orberth accelerated to maximum velocity (and held it) would have enough consumables for either of them to make a trip to Mars in ~42-47days, well within the stated endurance of either ship. So consumables are not an issue. And the 40+days would seem to work with the stated "months" trip time in Invasion#5 from certain POV.

again though, you are ignoring the maximum velocity limit. (which is a factor of drive exhaust velocity, or rather a complex relationship between exhaust velocity and the ability to impart additional energy to the ship)

we are told they can make the trip, and it is not treated as an exotic case, ergo we know they have the fuel and thus the delta-V to do it. so the max valocity has to be a limitation of the rocket technology they possess, not the design of the ship.

also, 87.5 days = about 3 months.
42-47 = about 1.4 months.
(using a 30 day month)
87.5 days is more likely to be described as "months" in general speech. 1.4 is more likely to be rounded down or expressed as "over a month". (and the shorter figure assumes traveling at full military power the whole way, and, again, ignores the maximum velocity limit.)

[ShadowLogan]

and at turnover said ship would be moving at 474kps, which is way way too high considering we're told the ARMD max's out at 69.4

True, but that is a consequence if you want to use constant thrust for the entire trip. The main issue with the RPG (and other canon specs) is it doesn't do a good job of modelling space flight. Cutting the acceleration is certainly an option, but one is then left with why they don't just run it at the stated max accel to reach maximum velocity and then coast for a period of time since that would seem to deliver them to their destination faster than if you try to accelerate slower to said velocity to try and arrive at a months long trip to match dialogue.

That means either:
-the RPG is incorrect in its speeds (technically the canon stats in the old RT.com infopedia avoiding listing speed, and IINM the 2E RPG gives it a much larger crew size)
-the dialogue's implied trip time is not entirely "trip time", but also "prep time" to get a ship ready (fueled, staffed, loaded with any special equipment they might need for the S&R, etc)
-the dialogue could also mean that the Mars-Earth distance at that particular time was larger than the median assumed (without a more specific date I couldn't tell you, in 2005 Mars ranges from over 300million to about 100million distance depending on the date, I looked at Jan/June/Dec 22nd each month)
-it depends on how "months" in the bit is being portrayed. Is a specific calendar period April-June (for ex, it is possible to construct a 40+ day trip to cover 3 months), or a generic sense regardless of calendar period
-the aide was not being precise in his statement and was giving a rough figure to work from (as it was sort of "on the spot" assessment, so could be off depending on how he arrived at it)
-likely though is some combination of the various dialogue aspects I suspect

very true, but i have yet to find a calculator program that will do multiple position versions. if i can find accurate values for the distances i might be able to use the custom distance option in the program. i have been considering using it to find the time to reach 2010 TK7, which is a planetoid located in the earth-sun L4 trojan point. it's constant relative position to earth seems like it could be useful for something like a research center or solar system observation point.

More likely than not you're going to have to make one on your own.

The math that went into your website link is used elsewhere (see previous post) and can be duplicated pretty easily at the programming level (or even spreadsheet). The main stumbling block is finding the distance between two desired locations, which is certainly possible (for ex: http://space.jpl.nasa.gov/), though may not be as complete (previous link doesn't really have the L4 location covered for ex). so might require more research on the users part depending on desired locations.

actually max velocity is more a factor of drive exhaust velocity, not fuel load in this case. we are told and shown they can make the trip by the RPG and comics, ergo, it is not the fuel load that is limiting them.

True, but to get max velocity from any drive you need a sufficient propellant load. They ship(s) just do not have the stated propellant endurance for the type of flight profile you are looking at is what I am saying.

again though, you are ignoring the maximum velocity limit. (which is a factor of drive exhaust velocity, or rather a complex relationship between exhaust velocity and the ability to impart additional energy to the ship)

No actually I am not. I am taking the maximum velocity the ship is stated to be able to achieve and using the (websites stated) median distance to determine travel time by solving for t in v=d/t, which is t=d/v. When I say "held it", I mean that nothing acts to alter the velocity. In which case by the RPG listed speeds you still end up with trip times in the 40day range.

[glitterboy2098]

and at turnover said ship would be moving at 474kps, which is way way too high considering we're told the ARMD max's out at 69.4

True, but that is a consequence if you want to use constant thrust for the entire trip. The main issue with the RPG (and other canon specs) is it doesn't do a good job of modelling space flight. Cutting the acceleration is certainly an option, but one is then left with why they don't just run it at the stated max accel to reach maximum velocity and then coast for a period of time since that would seem to deliver them to their destination faster than if you try to accelerate slower to said velocity to try and arrive at a months long trip to match dialogue.

That means either:
-the RPG is incorrect in its speeds (technically the canon stats in the old RT.com infopedia avoiding listing speed, and IINM the 2E RPG gives it a much larger crew size)
-the dialogue's implied trip time is not entirely "trip time", but also "prep time" to get a ship ready (fueled, staffed, loaded with any special equipment they might need for the S&R, etc)
-the dialogue could also mean that the Mars-Earth distance at that particular time was larger than the median assumed (without a more specific date I couldn't tell you, in 2005 Mars ranges from over 300million to about 100million distance depending on the date, I looked at Jan/June/Dec 22nd each month)
-it depends on how "months" in the bit is being portrayed. Is a specific calendar period April-June (for ex, it is possible to construct a 40+ day trip to cover 3 months), or a generic sense regardless of calendar period
-the aide was not being precise in his statement and was giving a rough figure to work from (as it was sort of "on the spot" assessment, so could be off depending on how he arrived at it)
-likely though is some combination of the various dialogue aspects I suspect

or occams razor. your assumptions are wrong.

i have demonstrated they can achieve it in the exact book stats, save for the food issue. which can be easily fixed as pointed out in the original post. we are told that the ships can make the trip using the stats they have, and the fact you can actually make that work makes me wonder why you are insisting that the statement or the stats are wrong.

very true, but i have yet to find a calculator program that will do multiple position versions. if i can find accurate values for the distances i might be able to use the custom distance option in the program. i have been considering using it to find the time to reach 2010 TK7, which is a planetoid located in the earth-sun L4 trojan point. it's constant relative position to earth seems like it could be useful for something like a research center or solar system observation point.

More likely than not you're going to have to make one on your own.

The math that went into your website link is used elsewhere (see previous post) and can be duplicated pretty easily at the programming level (or even spreadsheet). The main stumbling block is finding the distance between two desired locations, which is certainly possible (for ex: http://space.jpl.nasa.gov/), though may not be as complete (previous link doesn't really have the L4 location covered for ex). so might require more research on the users part depending on desired locations.

actually max velocity is more a factor of drive exhaust velocity, not fuel load in this case. we are told and shown they can make the trip by the RPG and comics, ergo, it is not the fuel load that is limiting them.

True, but to get max velocity from any drive you need a sufficient propellant load. They ship(s) just do not have the stated propellant endurance for the type of flight profile you are looking at is what I am saying.

again though, you are ignoring the maximum velocity limit. (which is a factor of drive exhaust velocity, or rather a complex relationship between exhaust velocity and the ability to impart additional energy to the ship)

No actually I am not. I am taking the maximum velocity the ship is stated to be able to achieve and using the (websites stated) median distance to determine travel time by solving for t in v=d/t, which is t=d/v. When I say "held it", I mean that nothing acts to alter the velocity. In which case by the RPG listed speeds you still end up with trip times in the 40day range.

you are going to have to find a better arguement than "because i say" for the remass issue, because the book stats certainly don't back you up. we are told they can make the trip to mars, and we are told they have 36 months of fuel onboard for their reactors. which indicates that they probably do have the remass for long burns.

so the velocity limit has, logically, got to be an issue with the capabilities of the drives themselves rather than reaction mass or delta-V issues.


and just because a ship does not lose velocity in space once it gains it does not override the fact that your assumptions ignore the hard velocity limit in the stats, or the reality that a ships ability to accelerate is governed by the complex physics of how a drives exhaust velocity imparts a change in velocity to the ship, and that after a certain point drives just fail to impart enough energy to change the velocity of the ship, even if they are running full tilt.

[glitterboy2098]

A point I thought might need explaining. The reason I bring up the food\expendable supplies issue is basically this;
While both can actually make the trip to mars with their normal supplies, they don't have enough afterwards to support operations while there, and enough for the trip back. The ARMDs could cover both legs of the round trip, there and back.. But that would not leave much time while at mars.

This is made worse by the way the orbital windows are. Since we used a median distance, these figures (or slightly shorter) would apply for the 6 to 7 months when earth and mars are on roughly the same side of the sun. The rest of the earth year mars would be even farther away and take longer to get to. (Often much longer, given the need to detour around the sun on a long arc)
So while you could make a full round trip in a single window, that would only leave you a few days or weeks at mars, assuming you left right as the window opened. For flights transferring people around this would probably work fine, but it leaves very little margin for error or delays.
And if you don't leave for mars right away when the window opens, get delayed on starting the return, or need to spend more than a few days in mars orbit, you are looking at either needing to load 5 plus months of food for the return trip (longer distance and long periods coasting) or waiting in mars orbit for 6 months to a year for the orbital window to open up again.

Frankly it is a good thing humanity got all those zentraedi warships to study and dissect, because without the better sublight drives that came out of that, humanity would continue to find it real hard to get around in space. (Even with fold drives)

[taalismn]

A point I thought might need explaining. The reason I bring up the food\expendable supplies issue is basically this;
While both can actually make the trip to mars with their normal supplies, they don't have enough afterwards to support operations while there, and enough for the trip back. The ARMDs could cover both legs of the round trip, there and back.. But that would not leave much time while at mars.)

"Forget about having that second slice of toast, Murphy; we're ALL tightening our belts on this mission."

[glitterboy2098]

my own preference is two fold.. assume that the ships being sent have had their crews reduced in size as much as possible without impacting safety or performance, and that earth has been sending unmanned and automated supply packages to mars, launched by those big old heavy lift rockets we see in macross saga and the canon comics. each is huge and probably rivals the saturn-V in terms of payload, so sending up a capsule full of food and other supplies, with a small plasma rocket attached to kick it into an earth-mars orbit, is clearly possible. would work best if the drive replicated the Oberth or ARMD routes i listed, but anything less than 6 months would suffice.

heck, that might be why sera still had valid supplies years after it was abandoned. not only would you have the stuff that was there when that zent scout arrived (minus whatever the oberth that arrived during that incident might have taken on with the base's crew in the evacuation before the final confrontation) but you could have had several shipments of supplies on the way for the base that arrived in the months and years afterwards. earth had some pretty capable AI-drone tech by then, going by the show, and the comic shows the base as having a fair amount of automation involved (logical) so the payloads could have reentered, landed, and been stored away in the hangers without human intervention. the UEDF probably had always planned to go back, given how intact the base was, but the 1st war seems to have happened first.

[ShadowLogan]

or occams razor. your assumptions are wrong.

Well the simplest explanation though amounts to:
-poor research on the part of various people involved (we know this happens in RT "stats" and "use", both at the RPG level and HG product level)
-the sources are not compatible (2008 canon infopedia information vs 2008 2E RPG SB, there are differences in the non-game mechanic information)

makes me wonder why you are insisting that the statement or the stats are wrong.

Because you don't seem to be considering all the variables that would be at play here.

you are going to have to find a better arguement than "because i say" for the remass issue, because the book stats certainly don't back you up. we are told they can make the trip to mars, and we are told they have 36 months of fuel onboard for their reactors. which indicates that they probably do have the remass for long burns.

And with other examples in the 2E RPG books it can be shown that reactor endurance doesn't equate to actual propulsion burn time without breaking the laws of physics when trying to tie in various sources (show depiction, RPG stats, infopedia).

Have you looked at how much "re-mass" is going to be needed by the Orberth and/or ARMD for this if we assume constant 28 or 36month (all months assumed to be 30days) burn at maximum acceleration per the book? I just did the math, the amount of mass being expelled at 100,000sec ISP (typical for a fusion rocket engine IINM per NASA) for a fusion drive requires millions of tons of material for Orberth/ARMD to be able to accelerate that long (the ships are only thousands of tons "provisioned and armed"). That means the reactor's "fuel" mass alone if called upon to do this "breaks" things. Even if I use your 0.002G accel cruise for the stated reactor endurance on the Orberth (and value for ARMD) the result is greater than the stated "provisioned and armed" mass of the respective ships (provisioned IMHO would include fuel), though in this case we are talking about 100s of 1000s of tons of material. Better, but still "breaks".

Yes if we assume the Fusion Drives on Orberth/ARMD have higher specific impulses (ISP) we can reduce the resulting required mass, but nothing indicates the fusion drives in RT are going to have specific impulses greater than NASA is stating a fusion rocket will have (and I know I've seen fusion rocket engine ratings higher than NASA figure, but the NASA figure is the one I've see the most often). At full RPG listed accel. you'd need to be approx x66times more ISP just to get into the "break even" zone (ie fuel mass = listed mass at provisioned/armed level), for your lower assumed figures (~1.35x).

This basically means that the 2E RPG ships lack the propellent (re-mass) to use their ship's reactors to accelerate for the stated endurance (either the 2E RPG figure, or your lower figures). Granted we could open it up to something like a Bassard Ramjet that would scoop up material, but nothing indicates the ships in question can or do something like that.

Without an idea on how much more energetic PC/Reflex would be in place of Fusion systems, I can't rate the ship examples I have without putting the assumptions on that value front and center.

[ShadowLogan]

Actually the math gets even worse. I had to go looking for the density of SLMH, which allowed me to estimate how much volume would be necessary if this is a pure SLMH system (no reason it has to be, but). I have to revise my earlier assessment slightly, by the 2E RPG and the resulting math they can pack in enough SLMH for the fusion engines for a 24hr burn, but they could not possibly come close for the full stated endurance of the reactor to provide propulsion using just reactor waste. glitterboy2098's numbers result in an even worse result.

Simple Ideal "Brick" Volume for the ships (I just treat the ships a a simple rectangular brick, if you object to this volume assement, please feel free to calculate your own volume for the respective ships, but keep in mind if it can't work with the simplified version the more detailed version is highly unlikely):
Orberth: 4,318,080m^3
ARMD: 10,406,000m^3

Orberth is supposed to have a 28month endurance for the reactor:
At the RPG's listed acceleration (0.090G) and assuming 100,000sec ISP fusion drive it would need for constant propulsion:
-for 24hrs: ~9,716metric tons (occupying ~13,880m^3) of SLMH re-mass
-for 28 MONTHS endurance: ~8,161,669metric tons (occupying ~11,659,528m^3) of SLMH re-mass
At gb2098's listed acceleration (0.002G) and assuming 100,000sec ISP fusion drive it would need for constant propulsion:
-for ~87.5days: ~563,866metric tons (occupying ~805,523m^3) of SLMH re-mass
-for 28 month endurance: ~5,443,200metric tons (occupying ~7,776,000m^3) of SLMH re-mass

ARMD is supposed to have a 36month endurance for the reactor:
At the RPG's listed acceleration (0.082G) and assuming 100,000sec ISP fusion drive it would need for constant propulsion:
-for 24hrs: ~12,317metric tons (occupying ~17,600m^3) of SLMH re-mass
-for 36 MONTHS endurance: ~13,302,855metric tons (occupying ~19,004,079m^3) of SLMH re-mass
At gb2098's listed acceleration (0.0015G)
-for ~101days: ~683,283metric tons (occupying ~976,118m^3) of SLMH re-mass
-for 36 month endurance: ~7,306,329metric tons (occupying ~10,437,613m^3) of SLMH re-mass

NOTES:
-IF the 100,000sec ISP for a fusion drive is replaced with a 1,000,000sec ISP drive (x10 better, or what ever modifier you desire), you can reduce the amounts needed by a factor of 10 (so instead of 9,716metric tons it's now ~971.6metric tons).
-gb2098's endurance times in the equations are taken to their listed precision in the calculations, I just did not re-write them here
-all mass and volume figures have been truncated and drop anything to the right of the decimal point
-SLMH was chosen as the reactor fuel based on other fusion systems available in the books