Register Register

Author Topic: Fuel Consumption on a HBS inspired campaign.  (Read 1232 times)

Kilderkin

  • Private
  • *
  • Posts: 47
Fuel Consumption on a HBS inspired campaign.
« on: 18 December 2018, 19:29:49 »
Hello Mechwarriors,

For the next campaign me and my game buddy are planning a HBS style game using Campaign Operations as the base. I thought I would go off the deep end when it came to jumping from one system to another. (We're still working out how much a single mission should pay)

I am using a captured modified Trojan dropship. I was wondering should I work out the cost of fuel to get to the destination manually? Or do players use peacetime costs as an average? As an example a journey from Westerhand to Wallacia would be 1.2m cbills in fuel at 29 days burn.  Whereas peacetime costs (assumed 15 days) are 635,000 cbills in fuel. Is this a minimum? Some systems have less days travel than the peacetime costs. Full transport terms for a Trojan is about 580,000 cbills. What would you guys do?

Cheers,


Daryk

  • Lieutenant Colonel
  • *
  • Posts: 10631
  • The Double Deuce II/II-σ
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #1 on: 18 December 2018, 20:13:12 »
Are you using strategic fuel consumption rates, or tactical?  That's probably the basis of the difference in the Campaign Ops numbers.

Kilderkin

  • Private
  • *
  • Posts: 47
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #2 on: 19 December 2018, 07:17:16 »
I am using the ones based in campaign ops. Which I think uses strategic ops as a base and a 1G burn. Believe it goes up to 2G for combat manuevers and doubles the consumption.

I used the same formula for working out peacetime costs for the Trojan 250 tons divided by 88.65 burn days and then times it by 15000 to work out the daily cost. Something like 42000 cbills a day.

In HBStech you just arrive in the system, so don’t think it would be doing 2G manuevers.

Daryk

  • Lieutenant Colonel
  • *
  • Posts: 10631
  • The Double Deuce II/II-σ
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #3 on: 19 December 2018, 18:10:09 »
As you upgrade the Argo, the burns get heavier to shorten the transit time.

Since you seem to be willing to do the math, I'd just calculate your actual burn days and pay the fuel cost for that.

Colt Ward

  • Colonel
  • *
  • Posts: 16891
  • Gott Mit Uns
    • Merc Periphery Guide- Bakunin
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #4 on: 20 December 2018, 15:56:59 »
You will not be wanting to use 2G maneuvers unless . . .

You are in combat, in which case it will not be all day (unless something odd happens)

You are on a contract to relieve another unit and must arrive by X

Dropships pushing 2Gs (or more) are not conductive to mech maintenance, sleeping peaceably, eating or even normal bodily functions comfortably.  If you push the DS trip from the jump point to the planet at 2Gs the whole time your troops are not going to be in the best condition to go into combat.
Colt Ward

Beware the vengeance of a patient man.
Clan Invasion Backer #149

victor_shaw

  • Warrant Officer
  • *
  • Posts: 607
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #5 on: 06 January 2019, 23:18:17 »
You will not be wanting to use 2G maneuvers unless . . .

You are in combat, in which case it will not be all day (unless something odd happens)

You are on a contract to relieve another unit and must arrive by X

Dropships pushing 2Gs (or more) are not conductive to mech maintenance, sleeping peaceably, eating or even normal bodily functions comfortably.  If you push the DS trip from the jump point to the planet at 2Gs the whole time your troops are not going to be in the best condition to go into combat.

Aren't you under zero G's for the 2nd half of the trip unless you have grav-decks?
To the best of my knowledge The ship spends some time in acceleration, then drifts for half the trip.
the second half of the trip involves turning around, then trusting to slowdown, then drifting to the planet, so zero G.

victor_shaw

  • Warrant Officer
  • *
  • Posts: 607
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #6 on: 06 January 2019, 23:35:22 »
Any how.

"The amount of fuel used in traveling is expressed in burn days.
One burn day is equal to the number of tons of fuel used per day
if traveling at 1G of acceleration. To determine the amount of fuel
used during transit, multiply the burn day value by the number of
days of travel and the G-rating. For example, a unit with a burn day
value of 1.84 spends three days crossing a system at 2 Gs. This uses
up 11.04 tons of fuel (1.84 x 3 x 2)".  (Strategic Operations pg. 34)

Alexander Knight

  • Peditum Generalis
  • Battletech Volunteer
  • Major
  • *
  • Posts: 4533
  • O-R-E-O
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #7 on: 07 January 2019, 01:52:23 »
Aren't you under zero G's for the 2nd half of the trip unless you have grav-decks?
To the best of my knowledge The ship spends some time in acceleration, then drifts for half the trip.
the second half of the trip involves turning around, then trusting to slowdown, then drifting to the planet, so zero G.

Actually no.  The ship spends 1/2 the journey thrusting towards the planet at 1G.  Then it hits turnover and begins decelerating at 1G.  It will have a relative velocity of 0 by the time it intercepts the planet that way.

Colt Ward

  • Colonel
  • *
  • Posts: 16891
  • Gott Mit Uns
    • Merc Periphery Guide- Bakunin
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #8 on: 07 January 2019, 13:11:40 »
You can of course drift for a section in the middle BUT no matter what you will have to have a decel burn, and depending on when you light off will depend on how long/heavy the burn will be when you do it.  Good rule of thumb is you will have to spend as much time in decel burn as you do in accel- 1/3 of the time in transit for accel, 1/3 of the time drifting, and 1/3 of the time decel- if you do it all at a 1g burn.  To use the same example . . . you can spend 1/3 of the time accel, half the time drift, and 1/6 of the time at a 2g+ burn to slow down to enter planetary orbit.

But this messed with other things . . . for instance the reason you stay at 1g both burns and have turnover is that you get pseudo-gravity for nearly the whole trip, jump point to planet (or vice versa), which keeps the troops & crew healthy and allows them to perform tasks that maintain their equipment & the ship.
Colt Ward

Beware the vengeance of a patient man.
Clan Invasion Backer #149

victor_shaw

  • Warrant Officer
  • *
  • Posts: 607
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #9 on: 07 January 2019, 13:13:01 »
Actually no.  The ship spends 1/2 the journey thrusting towards the planet at 1G.  Then it hits turnover and begins decelerating at 1G.  It will have a relative velocity of 0 by the time it intercepts the planet that way.

This goes against the design of the Dropships and physics.
To the physics, 1G is a relative speed not a constant acceleration, if you where to thrust at 1G a day according to the laws of physics the effective gravitational force would increase by 1G per day so the crew would be under increasing G-forces as there is no or little resistance to slow this acceleration in space. So if the trip was 10 days then you would be close to 4-5G's by the time you reached the turnover point. Now if you were to accelerate at a slower speed to reach 1G by the time you reach the turnover point you would not be under 1G of gravitational force until close to the end of the first leg, and under micro to low gravity for most of the trip.

As for the design of the dropship, the dropship/warship plans are shown to have a set up and down to the designs. This is fine if the ships is under 1G for most of the trip then the crew straps in and you deceleration to micro gravity level for the final leg, but if you are deceleration at a constant rate to the planet the gravitational plain would shift and the ceiling would become the floor. As even if you rotate the ship gravity is determined by the direction of moment, not the direction of the thrust.

Now just to be clear, I know this is a fictional universe but is seems in this case the writers are trying to be scientific.
« Last Edit: 07 January 2019, 13:23:43 by victor_shaw »

Alexander Knight

  • Peditum Generalis
  • Battletech Volunteer
  • Major
  • *
  • Posts: 4533
  • O-R-E-O
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #10 on: 07 January 2019, 13:36:43 »
Uh, no.  I don't know where you got that idea about physics but you are completely wrong.

Acceleration of 9.8 meters per second provides 1 G of force for people on board the ship.  At no point during a normal transit are people exposed to more than a 9.8 meter/second change in velocity per second.

Now their speed is far higher than 9.8 meters per second, but that doesn't affect anyone inside the ship.  Example being the Apollo missions flying to/from the moon.  While moving far faster than 9.8 meters/second, they were weightless.

Colt Ward

  • Colonel
  • *
  • Posts: 16891
  • Gott Mit Uns
    • Merc Periphery Guide- Bakunin
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #11 on: 07 January 2019, 13:58:59 »
Now their speed is far higher than 9.8 meters per second, but that doesn't affect anyone inside the ship.  Example being the Apollo missions flying to/from the moon.  While moving far faster than 9.8 meters/second, they were weightless.

Velocity would be a better word than speed, and why I used accel/decel- along with the rough break down on timing when putting in a drift period.  And the ship is thrusting to create 1g of pseudogravity- not creating real gravitational fields.  Everyone just uses it as a reference b/c that shorthand is how its used in fiction.  Ships are also built like skycrapers, where up is the bow, rather then like blue water ships where forward is the bow.
Colt Ward

Beware the vengeance of a patient man.
Clan Invasion Backer #149

victor_shaw

  • Warrant Officer
  • *
  • Posts: 607
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #12 on: 07 January 2019, 14:25:04 »
You do realizes that even in your example the crew would be weightless for the second half of the journey?
And if I am wrong (which I probable am)and movement is not the cause of the G forces.
Then the deceleration burn would also not cause the "acceleration force" needed to create the effect of gravity.



Colt Ward

  • Colonel
  • *
  • Posts: 16891
  • Gott Mit Uns
    • Merc Periphery Guide- Bakunin
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #13 on: 07 January 2019, 16:20:09 »
No, you get pseudo-gravity in both directions because of inertia . . . in the first half your body is getting pushed along with everything else in one direction and its wanting to keep the velocity it had 1 second ago- which pushes you down against where the thrust is coming from.  When you hit turn over you have zero-g (really probably micro) because the thrust has cut off while the ship sings about.  I imagine it could get disorienting if you pushed off into the middle of a room during turn over you could watch the ship swing around you as it reorients to place the thrusters 'down' at where the planet would be in X hours.  When the thrust cut back in however, depending on how much, you could 'fall' to the deck . . . or if its a gentle transition back to 1g, slowly float down to the floor.

So during the decel burn, just like in the accel burn, your body is wanting to keep the velocity it had in the previous second while the ship is thrusting against the velocity thereby slowing the ship from its former high point during turn over.

In either case, for a '1g burn' from the thruster the amount of thrust is constant but your velocity accelerates or decelerates depending on where you are in the journey.
Colt Ward

Beware the vengeance of a patient man.
Clan Invasion Backer #149

Daryk

  • Lieutenant Colonel
  • *
  • Posts: 10631
  • The Double Deuce II/II-σ
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #14 on: 07 January 2019, 19:36:32 »
Colt has it right overall (with a typo or two).  I'll break out my 20+ year old physics degree if necessary to further explain.

AdmiralObvious

  • Master Sergeant
  • *
  • Posts: 210
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #15 on: 08 January 2019, 14:57:38 »
Thrust can be measured in multiple ways. Relative to fuel consumption, or relative to raw power measured in a metric of measurement I forgot (I'm leaning towards Joules though). Edit: Nope, it's Newtons.

Acceleration is measured in G force, and depends on the thrust to weight ratio of the ship you're pushing. High G thrust is for faster acceleration. People, assuming they're all strapped into crash seats can take 5 G of acceleration for a little while if you REALLY need to use your DeltaV.

Basically everything in space is based on relative velocity. Once you stop accelerating, you don't have to deal with the forces of gravity that are related to the thrust. Ideally, the whole ship and everything in it accelerated with it, and didn't smash against the back of the vessel during the acceleration. Otherwise, everything is going with the ship and once you stop accelerating, you won't notice the difference in velocity.

If you do your insertion right, you shouldn't even need to do a burn to keep orbit around the planet, though that's generally pretty difficult to do.

Jump drives are a whole different can of worms though, but in theory, there is absolutely no "acceleration" as a result of a jump.
« Last Edit: 08 January 2019, 15:40:03 by AdmiralObvious »

Colt Ward

  • Colonel
  • *
  • Posts: 16891
  • Gott Mit Uns
    • Merc Periphery Guide- Bakunin
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #16 on: 08 January 2019, 16:21:32 »
Colt has it right overall (with a typo or two).  I'll break out my 20+ year old physics degree if necessary to further explain.

Lol . . . I could explain with more detail, maybe not to your level, but then I would look like-



During Land Nav training in basic I got called on for how to plot a course when you did not have a compass.  Then when I started getting into how the sun shifted with equinox & solstice the DS interrupted- "That's more info than these dummies need!"  Which is why I said my explanation was a rule of thumb.
Colt Ward

Beware the vengeance of a patient man.
Clan Invasion Backer #149

Daryk

  • Lieutenant Colonel
  • *
  • Posts: 10631
  • The Double Deuce II/II-σ
Re: Fuel Consumption on a HBS inspired campaign.
« Reply #17 on: 08 January 2019, 18:38:21 »
Lol... As I recall, I got an A in Celestial Navigation, but that was a LONG time before I had to do anything with Land Navigation... Let's just say I passed that sufficiently to deploy in country... :)

 

Register