Author Topic: ICE dropships  (Read 13058 times)

idea weenie

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Re: ICE dropships
« Reply #60 on: 13 May 2019, 22:20:24 »
If all they had was 0.02g, pirate points would be SOP.

Assuming the Earth-Sun L1 point (approx 1.5 million km from Earth) with a .02G constant acceleration to be zero-zero at both start and end, I'm going to provide some numbers.  Note that these numbers are assuming zero turn-around time, which will cause the transit time to increase.

Total distance = 1.5 * 10^6 km = 1.5 * 10^9 m
Accel distance = Total Distance/2 = 750 * 10^6 m
1G = 9.8 m/s^2
.02G = 0.196 m/s^2
Distance-Accel equation:
Distance = V0 + .5 * a*t^2
Starting velocity = 0
Distance = .5 * a*t^2/2
2*Distance/a = t^2
t = SQRT(2*Dist/Accel) = 87,481 seconds or about 24.3 hours for one leg, or about 48.6 hours for accel and decel from planetary orbit to meeting a Jumpship at the Earth-Sun LaGrange point.

The Earth-Moon L1 point is about 320,000 km from Earth, so a .02G engine would take about 11.22 hours to the turn-over, or about 22.5 hours.  From this we can see that having a convenient Moon for L1 points is not as big of an advantage as it would seem.

Two Guns Blazing

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Re: ICE dropships
« Reply #61 on: 14 May 2019, 02:26:32 »
Perhaps it would end up being more cost effective for a lower tech government/entity to simply purchase an existing fusion reactor from a company or faction in the Inner Sphere who could provide and deliver such a thing. The amount of money required to create and maintain an ICE system and its infrastructure could possibly end up being more expensive than simply buying the cool tech from someone else...

Daryk

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Re: ICE dropships
« Reply #62 on: 14 May 2019, 03:53:04 »
A planet-moon LaGrange point won't work, as it doesn't account for the star.  You need the star-planet(moon) point for a jump.

Elmoth

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Re: ICE dropships
« Reply #63 on: 14 May 2019, 04:46:58 »
If all they had was 0.02g, pirate points would be SOP.

I am quite surprised that with the big transit times to the Nadir point pirate points are not MUCH more commonly used. Like, them being the standard jump points for well travelled systems. Jumping to the Zenith or Nadir point for unknown systems is perfectly sensible, but for a system that you know the coordinates of? jump pirate and save a week!

@Daryk: I am fairly sure that in 1000 years they will have the physics models to account for that kind of stuff.


being the OP, I was thinking about the deep Outworlds wastes being somewhat isolated from the inner sphere, but trading (and raiding/warring) among themselves. As such, dropships would be needed. Maintaining a few rickety jumpships sounds OK, but dropships are supposed to be more common and suffer greater casualties in the long run (the wastes have been around for 300 years), so I was looking for a replacement method.

However, the 2100 year is quite significant. There is a general impression that ICE stuff is around because fusion engines are difficult to have and are salvaged for mechs. Now, that fits poorly with the 2100 year for fusion reactors, it is almost medieval tech level for the people living in the 3000's, lostech or no lostech. However, there might be a reason: SMALL fusion engines are almost lostech (and certainly are lostech in the periphery) but big, less efficient designs like those used in huge reactors might be quite common. mech-level reactors or smaller are difficult to come by, and stuff like the ones used in the Gabriel or Sabanah Master are unheard off until the tech renaissance.

That would solve the dropship-level or planetary reactors being available. IIRC it still leaves the Wynn's Roost story in muddy waters, but it is an isolated case that we can attribute to faulty historical records. I think I will take that approach.


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The_Caveman

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Re: ICE dropships
« Reply #64 on: 14 May 2019, 14:37:58 »
The problem with using a LaGrange point as your standard point is that a ship comes out of a jump static with relation to the star, while the LaGrange point moves with the planet. For outer planets and small stars this isn't a huge problem, but for a planet in a fast-moving orbit you're going to burn a lot of fuel catching up. It's like 100 thrust points to catch up to Earth (and you'll actually need to burn more because while you were matching speed you will have drifted outside the L1 point radius) plus the fuel needed to maintain your position.

And transient points (aka "pirate points") may only exist for a few hours at a time.

Unless you're extremely confident about the timetable for your forces infiltrating and exfiltrating from the surface, you run a big risk of not being able to jump when your DropShips come back with a swarm of pissed-off ASFs snapping at their heels. And if you don't have an L-F battery installed, that time savings may be a moot point. You're stuck spending a week recharging your core regardless of how close you are to the planet.

And, what's good for the goose is good for the gander: the closer you show up to the planet, the less time the planet's defenders need to reach your JumpShip and capture/destroy it. An ASF base on a moon is a pretty good deterrent against JumpShips using LaGrange or pirate points. If you arrive at a proximity point (which doesn't have to be the Z/N points) defenders have to plot a much more difficult intercept.

Finally, there is the inherent risk of inner-system points themselves. As gravitational "shallows", LaGrange points love to collect space debris in horseshoe orbits. Unless the system is extremely well mapped you run the risk of saying hello to a 'Mech-sized asteroid while you're hanging out there. Transient points would be even worse, as the gravitational interactions which make them possible would also make the trajectories of local space debris unpredictable.
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Elmoth

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Re: ICE dropships
« Reply #65 on: 14 May 2019, 14:55:33 »
All great and fun. And stuff that regular official BT space magic does not take into account, ever. So I am not sure we should either

The_Caveman

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Re: ICE dropships
« Reply #66 on: 14 May 2019, 15:00:54 »
All great and fun. And stuff that regular official BT space magic does not take into account, ever. So I am not sure we should either

O_o

All that stuff is taken from or rooted in canonical materials. It is very much addressed by the regular space magic.
Half the fun of BattleTech is the mental gymnastics required to scientifically rationalize design choices made decades ago entirely based on the Rule of Cool.

The other half is a first-turn AC/2 shot TAC to your gyro that causes your Atlas to fall and smash its own cockpit... wait, I said fun didn't I?

Maingunnery

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Re: ICE dropships
« Reply #67 on: 14 May 2019, 15:20:48 »


Idea: Launch a manned satellite (w. fusion station keeping drive) on a chemical rocket.
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Elmoth

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Re: ICE dropships
« Reply #68 on: 14 May 2019, 15:56:56 »
O_o

All that stuff is taken from or rooted in canonical materials. It is very much addressed by the regular space magic.
Really? I was unaware of that. Where can I read this stuff? genuinely interested here :) My reading of pirate points and such has always been that they are brief, not that they are more dangerous than the zenith and nadir points.

klarg1

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Re: ICE dropships
« Reply #69 on: 14 May 2019, 16:50:50 »
Really? I was unaware of that. Where can I read this stuff? genuinely interested here :) My reading of pirate points and such has always been that they are brief, not that they are more dangerous than the zenith and nadir points.

The problem with pirate points is that they are transient, and move around based on the motion of planets (and sometimes sizeable moons) within the star system.

The Zenith and Nadir points for the star are stable (relative to the star), and always there, and always work.

If you take the time to calculate what the configuration of the planets at your destination will be when you arrive, pirate points should be as safe as anything else.

If you screw up your calculations for where a pirate point should be when you arrive, you will have a bad day.

Daryk

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Re: ICE dropships
« Reply #70 on: 14 May 2019, 19:30:12 »
Back in college, I remember coming up with a suspiciously convenient 3.45x10-6 value for the maximum gravitational field strength that allowed a jump, but I'll be damned if I can figure out how I came to that conclusion.  I suspect it was related to my astronomy text book, which I no longer have. If that figure was actually canonical, it would simplify a lot of things...

The_Caveman

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Re: ICE dropships
« Reply #71 on: 14 May 2019, 22:51:20 »
I swear there were old rules somewhere for accidentally jumping into an asteroid field as part of a misjump. Maybe MWRPG?
Half the fun of BattleTech is the mental gymnastics required to scientifically rationalize design choices made decades ago entirely based on the Rule of Cool.

The other half is a first-turn AC/2 shot TAC to your gyro that causes your Atlas to fall and smash its own cockpit... wait, I said fun didn't I?

grimlock1

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Re: ICE dropships
« Reply #72 on: 15 May 2019, 09:07:32 »
Back in college, I remember coming up with a suspiciously convenient 3.45x10-6 value for the maximum gravitational field strength that allowed a jump, but I'll be damned if I can figure out how I came to that conclusion.  I suspect it was related to my astronomy text book, which I no longer have. If that figure was actually canonical, it would simplify a lot of things...

Shouldn't be too hard to reverse that.  SO pg 70 says the trip from Earth to Sol's standard points is 10 AU.  Earth is 1 AU out from the sun, so that gives us a right triangle with a hypotenuse of 10, and a leg of 1.  A2+B2=C2 says that the standard jump points are about 9.95 AU above the ecliptic. Mass of the entire solar system is about 1.99x1030kg.

agravity=Gmsun/r2

Okay, by my math, the acceleration due to gravity at Sol's zenith/nadir point is 5.9 x 10-5m/s2
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cray

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Re: ICE dropships
« Reply #73 on: 15 May 2019, 17:40:45 »
The problem with using a LaGrange point as your standard point is that a ship comes out of a jump static with relation to the star, while the LaGrange point moves with the planet. For outer planets and small stars this isn't a huge problem, but for a planet in a fast-moving orbit you're going to burn a lot of fuel catching up.

You come out static with relation to the jump point, which would be moving with the two or three bodies that formed it. For a planet-moon L1 point, that means you're pretty much following the planet. You'd only need a couple of fuel points to nudge into a halo orbit around the real L1 point.

Really? I was unaware of that. Where can I read this stuff?

Strategic Operations has 2 chapters summarizing hyperspace, life on spacecraft, and other details found in ye olde books like Explorer Corps and DropShips & JumpShips. Strategic Operations also clarifies some things like the functions of pirate points.

Quote
My reading of pirate points and such has always been that they are brief, not that they are more dangerous than the zenith and nadir points.

Transient points are a subset of pirate points. Pirate points, broadly speaking, can be any point other than the zenith and nadir points. That includes the permanent proximity points and all open space beyond the proximity limit of star. Planet-moon and star-planet L1 points are also usually permanent, even if they wiggle around a lot more than standard points. Transient points that come and go tend to be the result of compact, multi-moon systems, like among Jupiter's Galilean moons.
Mike Miller, Materials Engineer

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**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

Daryk

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Re: ICE dropships
« Reply #74 on: 15 May 2019, 18:33:15 »
Grimlock1: From what I remember, my text book had a table of average masses for various classes of stars, and doing the math on each column yielded the number I cited.  I think the science has advanced since then, so the mass numbers are different, which is why I can't reproduce the results.

The_Caveman

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Re: ICE dropships
« Reply #75 on: 15 May 2019, 21:40:34 »
You come out static with relation to the jump point, which would be moving with the two or three bodies that formed it.

Interesting. No wonder the jump computation solutions get exponentially more complicated as you get away from proximity points.

Though it does raise the question, if the computer can synchronize motion with a planet or moon, why can't a ship come out of a jump with arbitrary velocity elsewhere in the system?
Half the fun of BattleTech is the mental gymnastics required to scientifically rationalize design choices made decades ago entirely based on the Rule of Cool.

The other half is a first-turn AC/2 shot TAC to your gyro that causes your Atlas to fall and smash its own cockpit... wait, I said fun didn't I?

Alexander Knight

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Re: ICE dropships
« Reply #76 on: 15 May 2019, 22:39:52 »
Though it does raise the question, if the computer can synchronize motion with a planet or moon, why can't a ship come out of a jump with arbitrary velocity elsewhere in the system?

Hyperspace doesn't work like that?

Liam's Ghost

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Re: ICE dropships
« Reply #77 on: 16 May 2019, 01:06:23 »
Though it does raise the question, if the computer can synchronize motion with a planet or moon, why can't a ship come out of a jump with arbitrary velocity elsewhere in the system?

Strategic Operations also goes into this. Going from memory (because laziness), coming out of your jump at any velocity but stationary relative to your destination point adds a bunch more variables that makes the jump impossible to plot. You can, however, come out with a different facing. And you can jump while moving relative to your starting point.
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The_Caveman

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Re: ICE dropships
« Reply #78 on: 16 May 2019, 01:20:57 »
Obviously it's to keep someone from using a K-F drive as a weapon of mass destruction (otherwise you could turn any JumpShip into a planet-killing R-bomb). Maybe they hardwired the computers in-universe to prevent exactly that ;)
Half the fun of BattleTech is the mental gymnastics required to scientifically rationalize design choices made decades ago entirely based on the Rule of Cool.

The other half is a first-turn AC/2 shot TAC to your gyro that causes your Atlas to fall and smash its own cockpit... wait, I said fun didn't I?

idea weenie

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Re: ICE dropships
« Reply #79 on: 16 May 2019, 19:06:07 »
A planet-moon LaGrange point won't work, as it doesn't account for the star.  You need the star-planet(moon) point for a jump.

You just need a volume where the total gravity is below the limit.  The fairly easy math is to calculate the L1 point of the plant and moon, then shift it towards the sun until the sun's gravity is offset by the planet and moon's gravity.  It should not affect the rough travel times I did by more than 1 percent
« Last Edit: 17 May 2019, 23:38:59 by idea weenie »

cray

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Re: ICE dropships
« Reply #80 on: 16 May 2019, 20:16:03 »
Though it does raise the question, if the computer can synchronize motion with a planet or moon, why can't a ship come out of a jump with arbitrary velocity elsewhere in the system?

Nope, per p. 131-132 StratOps. You have to arrive stationary with respect to the destination jump point's motion.

Now, about facing…yes, question? What? No, they can’t
do that. All right, for those of you who didn’t hear, the question
was, “Since JumpShips can adjust their velocity during a
jump, can they pop out of a jump point with some extra velocity?”
That’s a good question, but the answer is no. A forming
hyperspace field is very sensitive to gravitational gradients and
there’s a deliberate feedback process to help the drive’s controller
know if the hyperspace field forming at the destination is
matching the velocity of the destination jump point. If it’s not,
the hyperspace field will be moving through a changing gravity
field, which makes it nearly impossible to form the hyperspace
field correctly.


Good news: you don't have to be stationary when you jump. You can go screaming into a jump point, though there's a modifier on the roll.

You just need a volume where the total gravity is below the limit.  The fairly easy math is to calculate the L1 point of the plant and moon, then shift it towards the sun until th son's gravity is offset by the planet and moon's gravity.  It should not affect the rough travel times I did by more than 1 percent

Right. Pirate points aren't exactly at L1 points - they ignore the centrifugal force that goes into determining Lagrange points. But adding a third body's gravity isn't too hard.
Mike Miller, Materials Engineer

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**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

Daryk

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Re: ICE dropships
« Reply #81 on: 16 May 2019, 21:16:59 »
Says someone clearly up on their differential equations...  :D

Three body problems (of the dynamic sort) are anything but simple...

cray

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Re: ICE dropships
« Reply #82 on: 16 May 2019, 21:22:50 »
Says someone clearly up on their differential equations...  :D

Back when I tried it I just did a quick approximation at a single point in time. Let the people who use lots of math handle the DiffEqs. ;)
Mike Miller, Materials Engineer

**"A man walks down the street in that hat, people know he's not afraid of anything." --Wash, Firefly.
**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

Daryk

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Re: ICE dropships
« Reply #83 on: 16 May 2019, 21:42:09 »
Stars are so massive compared to planets, a moon won't move the null field point much, really.  The easiest way to simplify a problem like that is to find the center of mass of the planet-moon system, and use that as the starting point with the star.  For the earth-moon system, the center of mass is inside the earth.  If you assume the earth-moon relationship is "normal", you're going to be out of luck for most planet-moon pirate points.

idea weenie

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Re: ICE dropships
« Reply #84 on: 17 May 2019, 23:49:15 »
Stars are so massive compared to planets, a moon won't move the null field point much, really.  The easiest way to simplify a problem like that is to find the center of mass of the planet-moon system, and use that as the starting point with the star.  For the earth-moon system, the center of mass is inside the earth.  If you assume the earth-moon relationship is "normal", you're going to be out of luck for most planet-moon pirate points.

You are not looking for the center of mass, you are looking for a point where the gravity of two objects cancels out.  Note that that the center of mass between the Earth and the Sun is about 280 miles from the center of the Sun, yet the Earth-Sun L1 point is ~1,500,000 km from Earth.

(Center of mass is proportional to the distance between two objects, while gravity strength is inversely proportional to the square of the distance between two objects.  Very different)

As for the calculations, I'd expect a Jumpship or Dropship's computer can run the calculations to figure out the pirate point.  You have semi-live coverage of the system, you know where the planet is, and you can look up in records if the planet has a moon.  If not sure, you just pop to the planet-sun jump point.  Depending on time delay between destination and observation (i.e. if 10 light-minutes away), you can just have the computer move the bodies forward by half an hour, and plot the Pirate Point coordinates based on that data.  Assuming you can do the math in less than 20 minutes, you will get the Pirate Point coordinates, and can pop to the destination easily.  After arriving, it is the helm officer's job to park the Jumpship in a halo orbit around the L1 point (and out of the jump limit).

Who knows, the Star League probably had something where you plugged in the mass of the star, distance to the star, the target planet's current orbital distance, the target planet's nearest/largest moon, angles between them, and it would provide the relative coordinates for the navigator to use taking into account all the math.  Unfortunately, that computer program was lost with the fall of the Star League.

The_Caveman

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Re: ICE dropships
« Reply #85 on: 18 May 2019, 01:54:41 »
A general solution to the three-body problem would be Star League kind of magic ;)
Half the fun of BattleTech is the mental gymnastics required to scientifically rationalize design choices made decades ago entirely based on the Rule of Cool.

The other half is a first-turn AC/2 shot TAC to your gyro that causes your Atlas to fall and smash its own cockpit... wait, I said fun didn't I?

Daryk

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Re: ICE dropships
« Reply #86 on: 18 May 2019, 07:25:08 »
True that!

Idea Weenie, you're right on the center of mass bit, but again, you have to take the star into account.  You can't simply ignore it.

idea weenie

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Re: ICE dropships
« Reply #87 on: 19 May 2019, 12:57:07 »
True that!

Idea Weenie, you're right on the center of mass bit, but again, you have to take the star into account.  You can't simply ignore it.

You're not.  You calculate the plane where the gravity for the planet and moon balance out.  You then move the pirate point along that plane towards the local star, calculating gravity between the sun and the angles of the gravity between the planet and local moon.  It takes a bit of time, but it can be done.  You could technically calculate points in 1,000 or 10,000 km increments, and once the gravity of the sun is greater than the gravity of the planet and moon, you move the point back until it balances.  You could then move that point up and down relative to the plane, to see if you can figure a better spot for the three body gravity solution to balance out.

Very repetitive, very boring, so a computer program would be good.  Figuring out the equation for plugging in the distances/angles/locations would make this a lot easier.

Daryk

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Re: ICE dropships
« Reply #88 on: 19 May 2019, 17:07:28 »
Numerical methods are the only way to solve 3-body (or more) problems.  Only 2 body problems can be fully solved.  My main point is the L1 point between the planet and moon isn't a valid jump point.  The moon only slightly shifts the star-planet jump point toward the planet.

Slightlylyons

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Re: ICE dropships
« Reply #89 on: 20 May 2019, 00:47:13 »
Only L1 points between a star and planet are in gravitational equilibrium.

Edit: The Jupiter Trojans have shipyards because they are outside of the Suns proximity limit, not because they are L4 or L5 points.
« Last Edit: 20 May 2019, 00:49:36 by Slightlylyons »