[Spaceships] Getting A Few Thousand Extra MPS

[Varyon]

Originally Posted by Aldric

I don't understand what the problems would be (according to the rules in Spaceships) with building say an SM+10 fusion drive ship, grabbing an ice rock 10x the size of the ship and heading off with about 4k mps to spare.
Acceleration at the start of the journey might be quite bad (1/11 of what the engines usually provide) but it would improve over time.
If a rock/asteroid is too unstable and possibly not pure enough, you can still build a "ship" made of 20 fuel tanks for about 600M and push that.

If the ice rock were somehow pure hydrogen, that's a 90.9% mass fraction. That's the same as having 18 fuel tanks, for x2.5 to delta-v per tank. At 60 mps per tank, that's a total of 2700 mps delta-v. Without a ramscoop, that means a travel speed of 1350 mps, and ignoring time to accelerate and decelerate, a travel time of 533 years and 4 months. And your rock is unlikely to be pure hydrogen - at best you're looking at more-or-less pure water, which has 3x the acceleration but 1/3rd the delta-v, for a total of 900 mps - at 450 mps travel speed, that's 1,600 years.

You're gonna need a bigger rock...

[Aldric]

Originally Posted by Varyon

If the ice rock were somehow pure hydrogen, that's a 90.9% mass fraction. That's the same as having 18 fuel tanks, for x2.5 to delta-v per tank. At 60 mps per tank, that's a total of 2700 mps delta-v. Without a ramscoop, that means a travel speed of 1350 mps, and ignoring time to accelerate and decelerate, a travel time of 533 years and 4 months. And your rock is unlikely to be pure hydrogen - at best you're looking at more-or-less pure water, which has 3x the acceleration but 1/3rd the delta-v, for a total of 900 mps - at 450 mps travel speed, that's 1,600 years.

You're gonna need a bigger rock...

Not really, 100k tons is all you need if you want 4k mps, since for some reason using an external clamp reduces your ship's acceleration, but not its Delta-V.
It's probably similar to using a smaller component for the engine, which I don't think it's normally allowed, but that's what it ends up being.

[Varyon]

Originally Posted by Aldric

Not really, 100k tons is all you need if you want 4k mps, since for some reason using an external clamp reduces your ship's acxeleration, but not its Delta-V.
It's probably similar to using a smaller component for the engine, which I don't think it's normally allowed, but that's what it ends up being.

I'll have to review the rules in Spaceships, but that's clearly not right. When you link two ships together, delta-v should be recalculated based on the current mass-fraction of "fuel." Otherwise, forget the current Second Stage rules, you'll be far better served just using external clamps to link progressively-larger ships together, at least outside of atmosphere.

[jackcelso]

the really important question is.... is all this math REALLY importante to the game? If the game pass entarely in the destination and the trip must take 100 years... By GM Fiat it will take that time and is done!!

IS there a VERY good reason to all this math?!!!

An alternatie is improve the design of the rockets with a imaginary "extra special geometry that improves the aceleration" or use a later technology than TL 10 as exception in the campain.

Mix types of engines or build a giant eletromagnetic sling shot that will provide the inicial accelarration.... it is a game it is not necessary to respect in full newtons law!! Or declare that you use ion thruster!!

But unless your GAME HISTORY DEPENDS ON that.... just move on. IF you will investigate a murder in the travel this irrelevant... if you will fight a alien race or combat a terrorist abord the ship this calculations are irrelevent....

[Agemegos]

Originally Posted by jackcelso

IS there a VERY good reason to all this math?!!!

I enjoy the maths and physics. Is that a reason good enough?

[Rupert]

And I like playing with design systems and seeing what they'll let you do, and seeing what other people can do with them.

[scc]

Originally Posted by johndallman

Light speed, and Mag-Sails. The beam needs to be on-target at ranges of light-days or light-weeks, given the low acceleration you can get. It isn't a practical solution.

See I'm not assuming that things are limited by what in the rule book. Specifically what I'm thinking is that if a 1 Terra-joule laser beam and Laser Rocket combination can propel an SM+8 at 2g for as long as the plastic remass holds out why doesn't a similarly powerful charged particle beam impacting upon a MagSail provide the same thrust?

Originally Posted by jackcelso

the really important question is.... is all this math REALLY importante to the game? If the game pass entarely in the destination and the trip must take 100 years... By GM Fiat it will take that time and is done!!

IS there a VERY good reason to all this math?!!!

An alternatie is improve the design of the rockets with a imaginary "extra special geometry that improves the aceleration" or use a later technology than TL 10 as exception in the campain.

Mix types of engines or build a giant eletromagnetic sling shot that will provide the inicial accelarration.... it is a game it is not necessary to respect in full newtons law!! Or declare that you use ion thruster!!

But unless your GAME HISTORY DEPENDS ON that.... just move on. IF you will investigate a murder in the travel this irrelevant... if you will fight a alien race or combat a terrorist abord the ship this calculations are irrelevent....

I think it's important to me, for some reason. I'd have to re-think part of the back story for any campaign I run based upon this because it changes some things, but I'm just not sure what. While reaction-less engines are possible in this universe, they're very limited and don't actually help here (They do planetary lifts and old school dogfighting and nothing else.)

That said, I'm growing attached to the idea of charged particle beams pushing ships around the solar system, it's opened a story point for me, the start of something of a dark age, where Earth collapses into chaos for environmental reasons, pollution and/or over-population, having just dispatched the last of the early colony ships via primitive hyper-drive and leaving the scattered colony spinners to finish the terraforming of Venus, Luna, and Mars they were in built to carry out

[Varyon]

Originally Posted by Agemegos

I enjoy the maths and physics. Is that a reason good enough?

Same here. There's also the fact that just having things work by GM fiat results in inconsistencies that can break one's sense of disbelief, as well as removes some of the "hardness" from the science fiction (just as having things work by author fiat does for stories). And, finally, sometimes working out how things actually work can give you further ideas. For example, with my gear rifles (rifles that use gears, springs, etc to store energy and impart it onto a projectile, rather than black powder or similar), I could have just waved my hands a bit and have them just work... but actually working out (with help from the forum) how they worked resulted in me figuring out an origin for them. Specifically, the method of action is the same as for a Red Ryder BB gun - a piston compressing air to accelerate the projectile. I recognized this could be based on a fire piston, and realized a potential origin - someone trying to replace a matchlock mechanism with a fire piston one, but then finding the bullet still got accelerated (albeit not nearly enough), even when the powder failed to ignite (due to wet powder, faulty powder, forgetting to load powder, etc), during testing. Further testing and experimentation resulted in a rifle that didn't need black powder, only a few seconds of cranking. Said rifles would be heavier and more expensive than comparable black powder ones, but the increased rate of fire and not needing powder (and reduced fouling of the barrel) makes them competitive with traditional rifles. Without doing the work, that little bit of backstory would have similarly been replaced with the waving of hands.

[Agemegos]

Originally Posted by scc

See I'm not assuming that things are limited by what in the rule book. Specifically what I'm thinking is that if a 1 Terra-joule laser beam and Laser Rocket combination can propel an SM+8 at 2g for as long as the plastic remass holds out why doesn't a similarly powerful charged particle beam impacting upon a MagSail provide the same thrust?

1) Because charged-particle beams diverge owing to electrostatic bloom, and there is no way to reduce the divergence analogous to using enormous objectives for laseer beams.

2) Because the magnetic field of the Sun exerts a Lorentz force on charged particles moving through it, perpendicular to the direction of movement of the particles, so as it varies the beam of charged particles will wander and swerve.

[hal]

Entering Space, Pg 190, gives a formula of

Departure Velocity squared = Max Velocity squared - Escape Velocity squared.

The idea being, to use a gravity assist with our sun, attaining a closest approach of 40,000 km of the sun with a fall from Jupiter allowing the craft to attain 600 km/s at 40,000 km at closest approach. The author points out that the max velocity one can attain is 10 km per second due to twice exhaust velocity of chemical rockets, a ship could leave with a final velocity of 110 k/s.

But, what if you can use a two stage rocket to accelerate towards the sun, separate at 40,000 km above the sun, and then use a mag sail away from the surface of the sun? The single stage vessel after separation would have 1/3 rd the original mass, gain free acceleration via mag sail, and perhaps gain more than the original +10 k/s boost given in Robert Zubrin's scenario?

Could the max bonus be equal to the average delta V gained at 40,000/149,597,871,000 AU and say 1AU? Not sure what the Max velocity is for a mag sail, but I'd guess it to be higher than 10 k/s of chemical exhaust velocity.

Addenda: Max velocity for a mag sail seems to be 375 m/s - making it useless while using a gravity assist or so it would appear.