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[Aqizzar]

Moving to a position of lower gravitiational potential energy is a "drop."

You're talking about an object moving from Neptune's orbit to Earth's orbit.  All three of those objects are orbiting the Sun.  Do you not realize how incredibly wimpy that gravitational pull is in relative terms?  It's wimpy enough that you can't even really call it "falling".

[Azzuro]

Maybe if we had some kind of government-funded but independent terrorist organization? Would that work? Would it be possible to supply a roaming terrorist fleet without the target side finding out?

You already said that to supply a roaming ship, all supplies would necessarily have to be obtained through piracy, which would be improbable at best. To sustain an entire fleet of ships, the problem of supplies is multiplied, but paradoxically, it may be easier to supply a fleet than to supply a single ship. For example, certain ships could act as specialized mini-biospheres, growing food to feed the crew. Other ships could act as solar energy collectors, making the energy needed for weapons and propulsion. However, the problem with this is that if any one specialized ship is destroyed, the "supply web" will eventually fall apart, resulting in the destruction of the primary attack ships as they start to lack critical resources.

In my opinion, if some government wanted to set up a guerrilla campaign in space, the main instrument of destruction should not be ships, but missiles. Assuming that the majority of space traffic would take place in Earth orbit, a single missile launched from a hidden launch site in the wastes of the Sahara or the glaciers of Antarctica could result in complete destruction without the incriminating evidence of an attacking ship having to land. Even better, such missiles could be almost impossible to shoot down without extremely accurate point defenses.

Actually, most of my arguments rely on the fact that space pirates would not have the capital necessary to build an armed ship, and therefore most of them would have the backing of corporations or countries. After all, if you have the resources needed to build and arm a ship for the sole purpose of looting another, it would be foolish to not provide a friendly port for them to dock at.

To restate the clarification that I stated earlier, most historical pirates started out as legitimate trading or military vessels that went rogue/desperate and started stealing from other ships.  As for a friendly port to dock at, privateering and merchant-marine type contracts could certainly come back into vogue; and all it takes is one politically-thorny, lawless port no outside authority wants to deal with for legal and illegal vessels to meet up and barter.  Think a space-Liberia or space-Rio-de-Janeiro.

The same dynamic could occur in any medium, all physical impracticalities of space combat besides.  Which is really the big problem.

Your point about there only needing to be one lawless port for space piracy to flourish is a good one. Indeed, while just one port could present a big problem, I find it unlikely that no outside authority would move to protect their interests. After all, considering the potential billions of dollars being shipped through space, you would think that some of the more unscrupulous corporations would be interested in having their shipments arrive safely. The only situation I can foresee in which your idea can happen is one in which there is some form of treaty banning the attack of space stations. While there would be many groups supporting such an illegal space station, there will undoubtedly be many more wishing to see it gone for good.

Also, to address your point about legitimate vessels becoming pirate vessels, the difference between a merchant galleon and a pirate one was not that much in the days of old. The only difference I can think of offhand was the increased number of cannons and other weaponry. In space terms however, freighters are likely to be large, slow moving ships, with great engine power but slow speed. Fighters however, are likely to be fast and speedy, and agile enough to run round larger ships. To bring back the example of piracy in Somalia, it would be like a supertanker converting itself into a gunboat.

Edit: Ninja'd thrice!

[Azzuro]

Moving to a position of lower gravitiational potential energy is a "drop."

You're talking about an object moving from Neptune's orbit to Earth's orbit.  All three of those objects are orbiting the Sun.  Do you not realize how incredibly wimpy that gravitational pull is in relative terms?  It's wimpy enough that you can't even really call it "falling".

To contribute here, the force of gravity is actually much weak than we think. Just by using a fridge magnet, I can counteract the entire planet's gravitational pull. If you really wanted to shoot cannonballs at Earth, a better way would be to use some kind of electromagnetic mass driver to accelerate projectiles to truly dangerous speeds.

Edit: Whoops, double posted.

[Huesoo]

This is cool, maybe I can become a space merc! Pew Pew!

[DJ]

The idea that industry in space will naturally spawn space piracy is just ludicrous for at least the first few conceivable centuries of developed space travel.  We've had air travel for a century, and the volume and worth thereof increases exponentially all the time.  We don't have air-piracy do we?  (More's the pity, but the point stands.)  I's just not feasible to hijack aircraft, because of all the physical dangers involved, but more importantly because communication is such that you'd be instantly identified and responded to.  Space would pose much the same situation.

I don't think any of these are the actual reasons for lack of air piracy. Cars don't pose any of these problems, yet we don't see much road piracy. My theory is that there's something wrong with modern-day rum. And who's to say that rum won't get better again by the time we get to commercial space travel?

[SmileyMan]

You're talking about an object moving from Neptune's orbit to Earth's orbit.  All three of those objects are orbiting the Sun.  Do you not realize how incredibly wimpy that gravitational pull is in relative terms?  It's wimpy enough that you can't even really call it "falling".

Well, my physics degrees were quite a few years back, but I think I'd have been informed if G had changed

Energy is force times distance, and although the force may be small, the distance is really, really, really big.  Also, the force is relative to mass, and the Sun is quite heavy.  There's no friction forces to convert the energy gain to hear, so it all stays as kinetic energy.

Gravitational potential enegy between two objects is given by E = -G.m1.m2/R (the minus is to keep anally retentive physicists happy)

G is 6.6743e-8 in units that aren't important.
m1 (the Sun) is 1.9891e+30 kg.  That's a lot of mass
if we set m2 to 1kg, then we can have a convenient Energy-per-unit-mass value for a particular orbit.
R is 4.5034e+9 m for Neptune distance, and 1.4960e+8 m for Earth distance.

Plugging those values in, we find that the G.P.E at the two orbital distances from the Sun is:

E/m(g,Nep) = -2.9480e+13 J/kg
E/m(g,Ear) = -8.8742e+14 J/kg

To transfer from one to the other, we will lose (as potential energy, therefore gain as kinetic energy) a magic figure of:

E/m(g,Ear-Nep) = 8.5794e+14 J/kg

Or 858 terajoules for each kg of mass.  That's about 10 fission bombs.

[Aqizzar]

All I know is potential energy is not explosive force.  Sure, gravity will eventually pull an object from Neptune's orbit to Earth's orbit.  It would take millions of years due the incredibly low acceleration.  Nobody's doubting the physics, we're (or at least I'm) just saying that's it's silly to attribute the danger of a missile between planetary orbits to solar gravity.  A good shove would impart more energy in the same time, so just stick an engine on it and forget all that gobbledygook about gravity.

My theory is that there's something wrong with modern-day rum. And who's to say that rum won't get better again by the time we get to commercial space travel?

It is one of the dirty secrets of anthropology that for most of recorded history, humanity was drunk off its collective tits.  If everyone went around swilling homemade palm rum and scurvy toxin all the time, your daily commute would be far more entertaining and likely to be pillaged.

[SmileyMan]

A good shove would impart more energy in the same time, so just stick an engine on it and forget all that gobbledygook about gravity.

Ah, I never said it was a practical weapon.  In fact, you'll see that my design involves an initial mass driver.

The missile would be detectable, hence my undetectable solution to the initial problem posed.

It occurs to me that you could make the weapon system more devastating by putting it in a retrograde solar orbit, noncoincident with any of the planets.  That way, your projectiles would have the planetary system's own kinetic energy on their side as well......

[Soadreqm]

I don't think any of these are the actual reasons for lack of air piracy. Cars don't pose any of these problems, yet we don't see much road piracy. My theory is that there's something wrong with modern-day rum. And who's to say that rum won't get better again by the time we get to commercial space travel?

There used to be train piracy and horse piracy, before the era of efficient police forces. You obviously aren't going to have piracy in any medium if you have enough cops. Which we do on the ground.

All I know is potential energy is not explosive force.  Sure, gravity will eventually pull an object from Neptune's orbit to Earth's orbit.  It would take millions of years due the incredibly low acceleration.  Nobody's doubting the physics, we're (or at least I'm) just saying that's it's silly to attribute the danger of a missile between planetary orbits to solar gravity.  A good shove would impart more energy in the same time, so just stick an engine on it and forget all that gobbledygook about gravity.

You obviously give it a starting shove to send it to the right direction, and get it off whatever orbit you are currently in. And potential energy IS explosive force. Any energy can be. When a moving object is brought to halt by friction, most of the energy is converted into heat. If that happens fast enough, and there is enough energy, you get explosions. We are making an artificial meteorite*. If our kinetic projectile survives atmosphere without slowing down too much, it will turn whatever it hits into a huge crater.

If you could build a railgun the length of the difference between the orbits of Earth and Neptune, using that would obviously be better. Since you can't, letting gravity accelerate your missile for you sounds like a pretty decent idea to me. Especially since it's going to do that ANYWAY.
*Or something like that, anyway. I can't remember the terminology. Meteorite, or a meteor, or possibly a meteoroid. Not a meteorologist.

[Il Palazzo]

It occurs to me that you could make the weapon system more devastating by putting it in a retrograde solar orbit, noncoincident with any of the planets.  That way, your projectiles would have the planetary system's own kinetic energy on their side as well......

Sounds like some seriously infeasible energy or time investment would be required to lose all that angular momentum and go retrograde. Besides, correctly aiming the thing from anywhere else than near-earth space seems like a fantasy to me. You'd need some trajectory correction device + energy source on the "mass packet", which would in turn make it detectable.

[Aqizzar]

And potential energy IS explosive force. Any energy can be. When a moving object is brought to halt by friction, most of the energy is converted into heat. If that happens fast enough, and there is enough energy, you get explosions. We are making an artificial meteorite*. If our kinetic projectile survives atmosphere without slowing down too much, it will turn whatever it hits into a huge crater.

Well yeah, I get that big things hitting friction fast enough produces what is essentially an explosion.  But we're talking very large objects traveling at an appreciable fraction of lightspeed.  Not exactly anything you'd be firing from a coilgun.

Besides, correctly aiming the thing from anywhere else than near-earth space seems like a fantasy to me. You'd need some trajectory correction device + energy source on the "mass packet", which would in turn make it detectable.

We did exactly this plenty of times with the Voyager probes.  Slinging a satellite through several planetary orbits to alter velocity and trajectory is no mean feat, but it was done with 1980s computers and rocketry.  If NASA had wanted it to slam into a planet, they certainly could have.  Heck, they're pretty good at slamming satellites into planets even when they don't want to.

[Il Palazzo]

We did exactly this plenty of times with the Voyager probes.

Exactly, we did that with space crafts, not inert mass packets. Probes are equipped with micro-rockets and batteries, so they're easily detectable. They also have the advantage of not being exactly in a hurry to finish their maneuvers, which is why they can have just these tiny engines. And if your space weapons platform don't have the advantage of launching an essentially stealthy alternative to CBMs, then I don't see what's it has going for it, that'd justify the cost of putting it in space in the first place - as compared to just building more missiles. Not the cost-effectiveness surely.

[SmileyMan]

*Or something like that, anyway. I can't remember the terminology. Meteorite, or a meteor, or possibly a meteoroid. Not a meteorologist.

We're making a meteoroid.  If it hits the atmosphere, the visible trail will be the meteor (not the body itself).  If it hits the ground and there's anything left, that leftover will be a meteorite, in the same way that goblinite is what is left after a seige.

Anyway, who cares - NEW VERSION TO PLAY!

[Il Palazzo]

I probably shouldn't talk, as I've contributed to this myself, but lately it seems that every discussion involving space devolves into some variant of "rods from space" nerdturbation.

[Aqizzar]

I probably shouldn't talk, as I've contributed to this myself, but lately it seems that every discussion involving space devolves into some variant of "rods from space" nerdturbation.

Yeah, I don't understand this forum's sperglord fascination with "rods from God" or whatever they're calling it now either.  I think we just weren't on the same page about maneuvering spacecraft.