some interesting figures for earths early ships
Posted: Wed Jun 21, 2017 2:59 am
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.
-------------------
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.)
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.
-------------------
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.)