Space Combat Techniques Discussion

[T.Neo]

Here's the problem with round two: It doesn't work, when your antimatter production facilities are destroyed. Or depleted. Because when you want to have twice the antimatter, for example, you have to go to twice the effort.

My antimatter production figures for interstellar spacecraft are much worse off in terms of actual production... but I allow them years to produce what they produce, and their insane cost is actually warranted (well, it isn't, but from a space exploration view, it definitely is).

Delta-Vee isn't just range. It's also your ability to maneuver AND shortening transit time. Jet fighters are built very maneuverable, and very fast.

Jet fighters and combat spacecraft are not the same thing.

I'm sure I stated somewhere here that an increase in overall dV means an increase in transit velocity. And the same for 'ability to manuver', though if you are talking about manuvers during combat, a fusion or antimatter drive would probably laugh at both.

This re-usable heat sink gives you a tremendous advantage in terms of how long you can keep fighting under repeated thermal laser attack.

It isn't reusable, it is 'open cycle'. You only have a limited amount of coolant onboard.

I think the Delta-Vee advantage of antimatter is being heavily underplayed, and the mass needed for radiators I seriously doubt would offset that advantage, especially using more advanced designs. Also, when I said unleash it in the same amount of time, I mean that the Fusion-fleet only has X amount of Delta-Vee for the whole war. The Anti-matter fleet has 10X amount. Your actual engine burns can last much longer, but you've got 10X as much energy over the course of the war.

Who says you have 10X as much dV and/or energy over the whole war?

I've calculated options for radiators on vehicles with far lower performance, and they are very prohibitive... remember that you are talking about hundreds of terawatts of energy here. The infrastructure needed to deal with that would be massive.

Sure, he can continue to mine Deuterium as the war goes on, but so can you, except you started out with FAR more than he did, perhaps enough so to win the war in the first wave without giving him time for mining new Deuterium to become a significant advantage. Deuterium won't do any good if your refineries on Luna have been leveled, your stations in the outer system have been pulverized, and every other major strategic location has been annihalated by his forces before you could even get halfway to his homeworld. Never mind moving your fleet to defend your asset's, that's simply out of the question when your enemy has ten times the speed (by all three definitions) than you do. Once again, I really, really, really can not over-explain the advantage of having ten times the Delta-Vee of your enemy.

I understand your frustration... because I cannot over-explain the advantage of being able to get energy from nothing (kinda) instead of having to make petajoules of it yourself.

For example... you can manufacture a certain amount of antimatter, but for less advanced and less costly facilities, one could potentially mine the same amount of energy deuterium- or even more, in a similar period of time.

In all these cases and other times I've mentioned single files lines... I don't know if it's written anywhere, but I'll call it the combat-square theory. It goes like this: If you have 2x the forces, you have 4x the advantage.
If you have 1.1x the forces, you have 1.21x the advantage.
The reason is this: Two ships against one both have twice the armament, and twice the number of targets he has to take out. So you've got 2x the "hit points", or hits you can take, AND 2x the firepower.
This is intuitively understood in this way: You won't win by sending your soldiers in a single file line! Even if you vastly outnumber him, 1 v.s. 20, done 40 times, does NOT equal 40 v.s. 20 in warfare.

That is interesting... but I think though, that your suggestion of being able to 'easily attack Earth' (or whoever) also falls under the "single file line" problem. The ships there don't have to meet you halfway to be destroyed, they can meet you (or your weapons) when you arrive. To be destroyed- maybe. But since they're already where you want to go, they don't have to go anywhere themselves.

Also, energy != reaction mass. The antimatter you're having there is used to produce the energy, not to drive the ship. You'll still need propellant, it's not like you could just throw that antimatter out of the thruster.

Yeah. You throw the reaction products out the thruster though, pions- you redirect them with magnetic fields. The exhaust velocity of an antimatter drive is something like 0.33c, which ties into the velocity of the pions when they are formed and how they interact with the magnetic field.

In this case an antimatter thruster is actually a lot like a chemical thruster. The propellant and the fuel (energy source) are the same thing.

When comparing antimatter propulsion to other kinds of propulsion, it is usually better to employ the rocket equation than to compare energy directly.

but what is sure is that the heatsink/radiator could operate at temperatures far, far above any regular radiator, and thus presumably be more efficient, even if it does have to radiate through a transparent wall of a holding container.

But the problem with such a radiator is that it operates at a higher temperature than the equipment you want to cool, which makes it absolutely and utterly worthless.

And sure all these systems for using antimatter take mass, but I think that mass consumption will be tiny compared to the increase of efficiency, unless the extra mass needed is more than 10x what's needed for fusion engines. Don't forget fusion is no small technical problem when it comes to heat and radiation, either.
And the fact that the engine efficiency advantage per mass ratio is much higher, at the end of the day, if I wanted the same Delta-Vee, I could carry MORE weapons and sensors per amount of fuel. But, as things would have it, I'm more interested in strategic/tactical mobility than brute armament. The mobility given by Anti-matter engines versus fusion wins an interplanetary war in any scenario I can think of, and ultimately winning the war is what it's about.

I think, if anything, actual energy conversion efficiency of antimatter is going to be lower than with fusion. A lot of energy with antimatter, is lost to gamma rays and neutrinos. But the higher energy density makes up for it, though. Energy storage wise. But when you have to deal with those gamma rays... :shifty:

I know the technical problems of dealing with waste heat in a fusion engine. They aren't pretty. :uhh:

War isn't about how fancy your technology is. It is about how well thought-out your logistics are. Logistics wins wars. Unfortunately, the logistics of an antimatter vehicle are quite poor.

 

[Eagle1Division]

It isn't reusable, it is 'open cycle'. You only have a limited amount of coolant onboard.

It's re-usable in that you can re-fill it and use it again even after you've dumped out the heat sink material.

Who says you have 10X as much dV and/or energy over the whole war?

The 10x Isp that Anti-matter has compared to Deuterium. Sure, you can have a whole LOT of deuterium compared to antimatter, but you're limited in the Delta-Vee you can get out of a fuel because they cap out to the graph of the natural logarithm in Dv = Ve*ln[R]. So there's a practical limit for R, and the only practical way to get a higher Delta-V is to use a more energetic fuel/reaction mass.

I've calculated options for radiators on vehicles with far lower performance, and they are very prohibitive... remember that you are talking about hundreds of terawatts of energy here. The infrastructure needed to deal with that would be massive.

As I said before, you could run it at a lower thrust to decrease the amount of heat produced per unit of time, so the radiators would have more time to work it off. Also, if you're working past the radiators' capacity, you could store the heat in a heat sink to radiate it later.

I understand your frustration... because I cannot over-explain the advantage of being able to get energy from nothing (kinda) instead of having to make petajoules of it yourself.

For example... you can manufacture a certain amount of antimatter, but for less advanced and less costly facilities, one could potentially mine the same amount of energy deuterium- or even more, in a similar period of time.

You could have a LOT more deuterium, that's certainly true. But, like I said, you're only going to get so much Delta-V from using more of it. Deuterium has a lower Exhaust Velocity and allows for a Higher Mass Ratio.
Antimatter has 10x the exhaust velocity, and using less or smaller ships would allow for a Mass Ratio that's roughly the same.
Your fleet would be smaller, the ships would be smaller, and less combat-capable, but like I said, you'd be able to completely side-step enemy forces, and ultimately win the war because of it.

That is interesting... but I think though, that your suggestion of being able to 'easily attack Earth' (or whoever) also falls under the "single file line" problem. The ships there don't have to meet you halfway to be destroyed, they can meet you (or your weapons) when you arrive. To be destroyed- maybe. But since they're already where you want to go, they don't have to go anywhere themselves.

Sure, you can't go offensive unless they leave their homeworld undefended, or at least thin out their defenses to a point where they'll be overrun by your fleet. But that means that they can't attack, either. It would create a stalemate, and in a sense, a cold war. 50/50 Mutually Assured Destruction. The side that can act and win a head-on engagement is the side certain to lose if he does act.
That is, if they consider "losing" to mean getting their homeworld razed from orbit while a significant portion of their fleet is off en route to your homeworld.

But the problem with such a radiator is that it operates at a higher temperature than the equipment you want to cool, which makes it absolutely and utterly worthless.

Okay, get this, it is possible to cool something off with something hotter than itself. Air Conditioning cools off a house using air that's hotter than the inside. It takes freon, which is at room temperature, then compresses it. When it compresses it, the same amount of heat is stored in a smaller space, so it heats up (I believe the Idea Gas Law states this), while it's compressed and heated up, a system of fans outside cools it off, then it's de-compressed, and when it's de-compressed it becomes much colder than the surrounding environment. You're heating up the 100*F air outside using 60*F air inside the house.

The heatsink/radiator would work in an identical way, only using a different compound, and using a radiator instead of fans to cool the heated compound off. It would start at the same temperature as the rest of the ship, get compressed, now that it's hotter it heats up the heat sink, then gets de-compressed and becomes cooler than it was before. Viola', you've heated up the 15,000K heat sink using the 295K ship.

Once again, you would run the heat sink at the highest temperature engineering constraints would allow, but it would be a plasma, stored using a magnetic bottle. 15,000K is a number I'm using just to illustrate the point. I don't know what temperature modern fusion reactors hold plasma at, but I'd use that as a starting point to determine what a heat sink could hold plasma at.

I think, if anything, actual energy conversion efficiency of antimatter is going to be lower than with fusion. A lot of energy with antimatter, is lost to gamma rays and neutrinos. But the higher energy density makes up for it, though. Energy storage wise. But when you have to deal with those gamma rays... :shifty:

I know the technical problems of dealing with waste heat in a fusion engine. They aren't pretty. :uhh:

Antimatter is less efficient. But it more than makes up for that because of the Ideal rocket equation, when you start working with Mass Ratios higher than 15 or so. Working with antimatter, which increases the Exhaust Velocity, may decrease the engine efficiency, but you still have a much higher, 6-10x I'd estimate despite engineering challenges, 6-10 times as much Delta-Vee for the same mass ratio.

War isn't about how fancy your technology is. It is about how well thought-out your logistics are. Logistics wins wars. Unfortunately, the logistics of an antimatter vehicle are quite poor.

And logistically, antimatter would be very difficult to work with. That's true. But ultimately, the ships will be capable of operating for years at a time just like Fusion ships. And even though they're more expensive, more delicate, and maybe even less combat-capable, being able to sidestep the enemy fleet, pay 3 locations in the outer solar system a visit then turn and either engage their homeworld and their fleet before they're able to even leave their homeworld and arrive anywhere else is such a strategic advantage it would more than make up for that.

 

[T.Neo]

It's re-usable in that you can re-fill it and use it again even after you've dumped out the heat sink material.

Yes, but so is a normal heat sink, for example you can always remove the heat from a normal heatsink via radiators.

The 10x Isp that Anti-matter has compared to Deuterium. Sure, you can have a whole LOT of deuterium compared to antimatter, but you're limited in the Delta-Vee you can get out of a fuel because they cap out to the graph of the natural logarithm in Dv = Ve*ln[R]. So there's a practical limit for R, and the only practical way to get a higher Delta-V is to use a more energetic fuel/reaction mass.

You're going to have a very limited supply of antimatter and have access to far more deuterium. You may only have a limited amount aboard the ship, sure. But it is the logistics of the whole scenario that must be taken into account.

People often think of physics, and physics, and physics. War is not about physics alone. It is primarily about logistics.

I will say again, and again, and again: The logistics of an antimatter rocket in war, are very poor.

As I said before, you could run it at a lower thrust to decrease the amount of heat produced per unit of time, so the radiators would have more time to work it off. Also, if you're working past the radiators' capacity, you could store the heat in a heat sink to radiate it later.

It would need to be a pretty big heatsink.

And lowering your ability to accelerate can be problematic as well...

Okay, get this, it is possible to cool something off with something hotter than itself. Air Conditioning cools off a house using air that's hotter than the inside. It takes freon, which is at room temperature, then compresses it. When it compresses it, the same amount of heat is stored in a smaller space, so it heats up (I believe the Idea Gas Law states this), while it's compressed and heated up, a system of fans outside cools it off, then it's de-compressed, and when it's de-compressed it becomes much colder than the surrounding environment. You're heating up the 100*F air outside using 60*F air inside the house.

But wait... isn't there power needed to do this? I mean, the aircon needs electricity to run.

It'd be extremely annoying when you have to expend terawatts of energy to run your cooling system meant to get rid of terawatts of energy. Then everything snowballs and the whole system fails...

Antimatter is less efficient. But it more than makes up for that because of the Ideal rocket equation, when you start working with Mass Ratios higher than 15 or so. Working with antimatter, which increases the Exhaust Velocity, may decrease the engine efficiency, but you still have a much higher, 6-10x I'd estimate despite engineering challenges, 6-10 times as much Delta-Vee for the same mass ratio.

A mass ratio of 15 in a chemical propelled vehicle is probably better than a mass ratio of 15 in an antimatter rocket. Remember, mass ratio is due to changing factors such as dV and exhaust velocity. A chemical rocket with a mass ratio of 15 can get to roughly 12 000 m/s. An antimatter rocket with a mass ratio of 15, can get to over 0.9 c.

And logistically, antimatter would be very difficult to work with. That's true. But ultimately, the ships will be capable of operating for years at a time just like Fusion ships. And even though they're more expensive, more delicate, and maybe even less combat-capable, being able to sidestep the enemy fleet, pay 3 locations in the outer solar system a visit then turn and either engage their homeworld and their fleet before they're able to even leave their homeworld and arrive anywhere else is such a strategic advantage it would more than make up for that.

Yeah... IF, IF they can do what you say they can.

You're making technical assumptions here, when we haven't even made more than an absolutely tiny amount of antimatter, let alone run a spacecraft off of it...

Again, speed isn't everything. Logistics is everything. An antimatter spacecraft has extremely poor logistics.

It doesn't help much, if you go to engage the Martian ships, get blown up, and then have the Martians come along to Earth a bit later and drop nukes on you.

 

[fsci123]

You have to remember why would we have interstellar war... ANd who we would have it with...

 

[Eagle1Division]

Yes, but so is a normal heat sink, for example you can always remove the heat from a normal heatsink via radiators.

You're missing the point. You can lose heat very quickly by venting the chamber and re-filling it, even the best radiator design is extremely slow compared to just venting the heat into space!
It's not a normal way to lose heat, it's for heat-exchange firefights when you're taking repeated laser blasts at "far" range and your radiators are working at maximum capacity and you're still getting more heat than you can get rid of. Solution: Flush it all out at once, so you can stay in the fight longer.

You're going to have a very limited supply of antimatter and have access to far more deuterium. You may only have a limited amount aboard the ship, sure. But it is the logistics of the whole scenario that must be taken into account.

People often think of physics, and physics, and physics. War is not about physics alone. It is primarily about logistics.

I will say again, and again, and again: The logistics of an antimatter rocket in war, are very poor.

Yes, it's certainly true that an anti-matter fleet would have excruciatingly expensive/difficult logistics compared to a fusion-powered fleet, but in a space war the ships leave home and don't come back until the war is over. No re-fills along the way, just empty space. The Delta-Vee you have in your fuel tanks when you start the war is all you've got for the whole war. The only exception would be if the war went on beyond round 1, and that's highly unlikely, since after round 1 the bulk of any fleet will be destroyed, and it will essentially be decided who's won.

Maybe that's not necessarily true, but assuming you have enough Delta-V to pull a Brochistrone to anywhere in the Solar System (As both Fusion and Antimatter engines do with any meaningful mass ratio), making pit stops, anywhere, anytime, would be a huge, pointless strategic mistake.

It would need to be a pretty big heatsink.

And lowering your ability to accelerate can be problematic as well...

All that depends on how much you decrease the thrust.

But wait... isn't there power needed to do this? I mean, the aircon needs electricity to run.

It'd be extremely annoying when you have to expend terawatts of energy to run your cooling system meant to get rid of terawatts of energy. Then everything snowballs and the whole system fails...

Air conditioning takes power, sure, but with all that waste heat from the engines, there's a huge difference of heat. Carry a small set of traditional radiators to act as the "cold" side, and use the difference of heat to generate electrical power, possibly using something like steam, as nuclear powerplants do to spin turbines. It may not sound like that would work, but consider this: Nuclear, Fission and future Fusion plants, all generate far, far more electricity from the heat difference (reactor core v.s. outside) than it takes to cool them. Such a large difference, in fact, that they can keep themselves cool and power an entire city, too. I don't doubt very much that you could generate enough electricity using the difference of heat in-between the hot engine and a set of decently-sized radiators to run an air-conditioning type system.

Yeah... IF, IF they can do what you say they can.

You're making technical assumptions here, when we haven't even made more than an absolutely tiny amount of antimatter, let alone run a spacecraft off of it...

Again, speed isn't everything. Logistics is everything. An antimatter spacecraft has extremely poor logistics.

It doesn't help much, if you go to engage the Martian ships, get blown up, and then have the Martians come along to Earth a bit later and drop nukes on you.

Didn't you read the scenarios? If they attack, then they garuntee that their homeworld gets nuked. They leave their homeworld undefended, you circle around their fleet, staying out of range and nuke their homeworld and they never even have the chance to engage (or ask them to kindly surrender or be nuked).

If they split their forces, then either the attack force is so small that you can easily win against them (combat square theory), or their defense force is so small you can easily win against them. If they split 50/50 then they're rolling some big dice to hope their defensive force can hold off at home, and according to the combat square theory, they probably won't hold off.

You have to remember why would we have interstellar war... ANd who we would have it with...

So far the scenario I've been doing is one planet against another, both independent nations. That's the best scenario for designing interplanetary warships. Anything else would either be a ground war or civilian ships retrofitted for combat.

 

[Linguofreak]

Didn't you read the scenarios? If they attack, then they garuntee that their homeworld gets nuked. They leave their homeworld undefended, you circle around their fleet, staying out of range and nuke their homeworld and they never even have the chance to engage (or ask them to kindly surrender or be nuked).

No. Your antimatter engine has so much less thrust than their fusion engine that they can fly circles around you. Sure, you have a ton of DV available, but you put that DV on very slowly. Meanwhile, their fusion engines give them more than enough DV for the purpose of getting around the solar system, and as you try to go around them, they cut you off, destroy your fleet (which is a sitting duck to kinetic strikes due to its low maneuverability), go on to your homeworld, nuke it, and possibly even get back to their own homeworld before your fleet would have arrived.

 

[Ghostrider]

All of this discussions are very interesting but why interstellar war? Unless you have Star Wars-like technology that make it feasibly and economically viable it makes no sense to traverse parsecs only to pick up a fight. Might as well find yourself another planet because once you have FTL or any viable interstellar flight capability, it's more economical to get ground elsewhere than waste resource on one particular system. Moreover, at interstellar distances and velocities your ship's detection range will be too small to detect hostiles - and the same is true for the enemy. And even if you detect it what do you do? Change vector to engage? Fire weapons at a target that will be out of range the moment you hit the launch command?

If we must talk space combat, why not limit it to the Terra-Luna space? There's a lot of space just there, pun intended. What about a conflict à la Heinlein's The Moon is a harsh Mistress or Bova's Moonwar where you have a self-sufficient Lunar colony wanting independence from an overbearing Earth? Or a Universal Century setup where you have O'Neill colonies at the Lagrange points, Moon and in various orbits around there either on the loyalist or independence side? That would be nearer to our current technology level and easier to model.

 

[Turbinator]

This trailer belongs here:

 

[T.Neo]

You're missing the point. You can lose heat very quickly by venting the chamber and re-filling it, even the best radiator design is extremely slow compared to just venting the heat into space!
It's not a normal way to lose heat, it's for heat-exchange firefights when you're taking repeated laser blasts at "far" range and your radiators are working at maximum capacity and you're still getting more heat than you can get rid of. Solution: Flush it all out at once, so you can stay in the fight longer.

Then it's a cross between a heatsink and open-cycle cooling.

You then have to refill your heatsink... and this requires mass.

Yes, it's certainly true that an anti-matter fleet would have excruciatingly expensive/difficult logistics compared to a fusion-powered fleet, but in a space war the ships leave home and don't come back until the war is over. No re-fills along the way, just empty space. The Delta-Vee you have in your fuel tanks when you start the war is all you've got for the whole war. The only exception would be if the war went on beyond round 1, and that's highly unlikely, since after round 1 the bulk of any fleet will be destroyed, and it will essentially be decided who's won.

Maybe that's not necessarily true, but assuming you have enough Delta-V to pull a Brochistrone to anywhere in the Solar System (As both Fusion and Antimatter engines do with any meaningful mass ratio), making pit stops, anywhere, anytime, would be a huge, pointless strategic mistake.

Doesn't matter. You might end up producing less dV in antimatter than you do in deuterium anyway, so...

Who says all of the ships would be destroyed? Most of them, sure... but I certainly wouldn't deploy all of my ships, if I didn't have to.

All that depends on how much you decrease the thrust.

The decrease in capability is pretty much proportional to the decrease in thrust. In short, decrease the thrust even slightly, and you will decrease your capability, even if it is only a slight decrease.

Air conditioning takes power, sure, but with all that waste heat from the engines, there's a huge difference of heat. Carry a small set of traditional radiators to act as the "cold" side, and use the difference of heat to generate electrical power, possibly using something like steam, as nuclear powerplants do to spin turbines. It may not sound like that would work, but consider this: Nuclear, Fission and future Fusion plants, all generate far, far more electricity from the heat difference (reactor core v.s. outside) than it takes to cool them. Such a large difference, in fact, that they can keep themselves cool and power an entire city, too. I don't doubt very much that you could generate enough electricity using the difference of heat in-between the hot engine and a set of decently-sized radiators to run an air-conditioning type system.

I'm pretty sure that an airconditioner takes in more energy than it removes. What you are trying to do is run the airconditioner off the heat within the air in the room.

The difference is that a fission/fusion plant on Earth, has the whole Earth to dump its heat into.

And a fission plant outputs maybe... a gigawatt. And masses more than the entire spacecraft fully fueled (probably). Here you are working with power on the magnitude of terawatts, with infrastructure that masses at best, several hundred tons. This is at extremely high temperature. And you must also prevent the rest of the ship from rising to this temperature...

Didn't you read the scenarios? If they attack, then they garuntee that their homeworld gets nuked. They leave their homeworld undefended, you circle around their fleet, staying out of range and nuke their homeworld and they never even have the chance to engage (or ask them to kindly surrender or be nuked).

If they split their forces, then either the attack force is so small that you can easily win against them (combat square theory), or their defense force is so small you can easily win against them. If they split 50/50 then they're rolling some big dice to hope their defensive force can hold off at home, and according to the combat square theory, they probably won't hold off.

I think you're underestimating the ease at which a planet can be attacked on a massive scale.

For one, there are a lot of targets on a planet. A spacecraft can only carry a limited number of weapons. Nukes also do not "slag continents" or anything of the sort. Even in a mass-scale, total nuclear war between the world powers of today, while being massively destructive to targeted population centers, would leave other parts of the world untouched- or almost untouched, save for low amounts of radioactive fallout.

Furthermore there are countermeasures that can be put in place- such as for example, anti-warhead missiles. And you can even have warships in orbit, for example, that can battle an invading fleet. They do not have to go far, because the enemy is coming to them. Since they lack unholy super-engines, they are less expensive to produce, so they can be built in larger numbers. And/or have better weapons and protection.

No. Your antimatter engine has so much less thrust than their fusion engine that they can fly circles around you. Sure, you have a ton of DV available, but you put that DV on very slowly. Meanwhile, their fusion engines give them more than enough DV for the purpose of getting around the solar system, and as you try to go around them, they cut you off, destroy your fleet (which is a sitting duck to kinetic strikes due to its low maneuverability), go on to your homeworld, nuke it, and possibly even get back to their own homeworld before your fleet would have arrived.

We can't save decisively that antimatter engines will have tiny thrust. We know, that it is extremely difficult to have an antimatter spacecraft that achieves high acceleration. But I don't see how it would be impossible, even with the design of an antimatter beam-core engine, if done correctly (Mass flow in a 10 meganewton beam-core engine would be something like 100 grams/second).

Fusion also has big problems with waste heat, but has things somewhat better than fusion does.

All of this discussions are very interesting but why interstellar war? Unless you have Star Wars-like technology that make it feasibly and economically viable it makes no sense to traverse parsecs only to pick up a fight. Might as well find yourself another planet because once you have FTL or any viable interstellar flight capability, it's more economical to get ground elsewhere than waste resource on one particular system. Moreover, at interstellar distances and velocities your ship's detection range will be too small to detect hostiles - and the same is true for the enemy. And even if you detect it what do you do? Change vector to engage? Fire weapons at a target that will be out of range the moment you hit the launch command?

Yeah. I can really only see interstellar war occuring between two parties in the same system. In other words, someone who has traveled to the system and then set up home there, and then wants to fight for whatever reason.

I really don't see why aliens would want to pick a fight with us. If they ever did it'd be because they'd have some very odd, stupid logic. And if they intended to invade Earth with any level of success, they would probably have to set up a base elsewhere in the system first.

This trailer belongs here:

Oh no... not Shattered Horizon.

If we must talk space combat, why not limit it to the Terra-Luna space? There's a lot of space just there, pun intended. What about a conflict à la Heinlein's The Moon is a harsh Mistress or Bova's Moonwar where you have a self-sufficient Lunar colony wanting independence from an overbearing Earth? Or a Universal Century setup where you have O'Neill colonies at the Lagrange points, Moon and in various orbits around there either on the loyalist or independence side? That would be nearer to our current technology level and easier to model.

Interesting idea, but: it's slower, smaller, and less exciting.

The caveman in me wants BIG! SHINY! DANGEROUS! SPACESHIP!

Arghghg!

Now where's my atlatl...

 

[fsci123]

Well if you wanted to destroy an alien country/ies on another planet across interstellar space all you go to do is accelerate a few tungsten rods to .9c instead of a huge spacecraft with crew... And they will be devastated...

 

[T.Neo]

Try accelerating anything to 0.9c with a coilgun. Then try to hit a target the size of a continent, light-years away, with an inert projectile... :uhh:

A 50mm thick, 1000 mm long tungsten rod hitting something at 0.9 will only have around a megaton of energy, anyway. A few here and there won't do much.

And the whole conflict won't be a very exciting one either... :shifty:

 

[Eagle1Division]

All of this discussions are very interesting but why interstellar war? Unless you have Star Wars-like technology that make it feasibly and economically viable it makes no sense to traverse parsecs only to pick up a fight. Might as well find yourself another planet because once you have FTL or any viable interstellar flight capability, it's more economical to get ground elsewhere than waste resource on one particular system. Moreover, at interstellar distances and velocities your ship's detection range will be too small to detect hostiles - and the same is true for the enemy. And even if you detect it what do you do? Change vector to engage? Fire weapons at a target that will be out of range the moment you hit the launch command?

If we must talk space combat, why not limit it to the Terra-Luna space? There's a lot of space just there, pun intended. What about a conflict à la Heinlein's The Moon is a harsh Mistress or Bova's Moonwar where you have a self-sufficient Lunar colony wanting independence from an overbearing Earth? Or a Universal Century setup where you have O'Neill colonies at the Lagrange points, Moon and in various orbits around there either on the loyalist or independence side? That would be nearer to our current technology level and easier to model.

Interplanetary, not interstellar. Similar scenario but with Mars rather than Luna, and if it was a rebellion they'd be using weaponized civilian vessels. After all, even if it was a civil war, there'd be no point for a military unless the government of Earth was really oppressive or there's more than one nation.

Doesn't matter. You might end up producing less dV in antimatter than you do in deuterium anyway, so...

With 10x the Isp, I seriously doubt that. The whole purpose of using antimatter would be to get a higher Delta-V than your enemy, so if you used it you'd use enough to accomplish that goal. Deuterium can allow for a higher mass ratio, but that bigger "R" will only help so much, and then adding more just doesn't help anymore, and you run into engineering constraints. The only other option for increasing Delta-V at that point is to increase Exhaust Velocity, and that's done with antimatter.

Who says all of the ships would be destroyed? Most of them, sure... but I certainly wouldn't deploy all of my ships, if I didn't have to.

Square Combat Theory, if I hold ships back, I'm severely hurting my chances of victory. If I send 4 ships and keep 2 back against an enemy who's sending all 6 ships, then I'd fight 2 battles:
4v6 and 2v6.
Combat capability:
16v36 and 4v20. (Assuming your 16 destroyed an enemy 16 in the first battle.)
Add it all together and it comes down to:
(16+4)v(36+20)
20v56

Sending only some of the fleet is a very bad idea. The numbers here aren't certain to happen, but they're the most likely to happen.

Current wars are a little different, because combat-square theory applies for whatever number of combatants are all in firing range and LOS of eachother all at once. In modern or modern-historical wars, combat usually occurs with each vehicle/soldier only seeing a few other at a time, so the total size of the deployed army doesn't matter much.
But with space warfare I'm working on the assumption that the fleets will all be in firing range of eachother, more or less, at once, since weapon ranges extend well beyond twice the diameter of Earth, and the combat will either be along an interplanetary course intercept or in orbit of another world. And LOS isn't much of a question.

Hmm... On a smaller scale, it seems what would happen is the defending side would put their fleet in the lowest orbit possible, so that ground-based defenses and their vessels come in range of the enemy all at once, so they're "combat capability" on the combat-square theory would be highest. Also make them more difficult to detect b/c of clutter.

The decrease in capability is pretty much proportional to the decrease in thrust. In short, decrease the thrust even slightly, and you will decrease your capability, even if it is only a slight decrease.

Wait... Do you mean combat capability? I don't see really how that would effect that on a tactical level, which is what combat capability is. Sure, there's evasive maneuvers, but how much of a difference will a small amount of acceleration make? And what fore? Evasive action from kinetics?
Personally I really don't think kinetics belong in space warfare, there's just no purpose when their effective ranges are far, far, far shorter than the "near" range of any respectable laser. It's like carrying a 16in gun on a modern warship with cruise missiles.
Granted, I do like the idea of kinetic CIWS for anti-missile PDS. As a last-ditch resort, a simple high ROF spinning-berral, multi-thousand round/minute gun is very nice to have. Doesn't take much power, relatively lightweight, drops off the excess heat in shells, and if it's FlaK you don't even have to get a direct hit to KO the missile. No range limitations in space, either, except effective accuracy, and accuracy by volume works to a certain range, but still it remains very, very Close-In.
Then again, CIWS guns are being replaced by RAM missiles in the current navy. Perhaps a point-defense missile system would work better?...
(This is in the scenario that lasers are swamped with inbound missiles at longer ranges.)

I'm pretty sure that an airconditioner takes in more energy than it removes. What you are trying to do is run the airconditioner off the heat within the air in the room.

The difference is that a fission/fusion plant on Earth, has the whole Earth to dump its heat into.

And a fission plant outputs maybe... a gigawatt. And masses more than the entire spacecraft fully fueled (probably). Here you are working with power on the magnitude of terawatts, with infrastructure that masses at best, several hundred tons. This is at extremely high temperature. And you must also prevent the rest of the ship from rising to this temperature...

And you have all of space to radiate your heat into. It's the same thing except you use radiators instead of convection to lose heat. Sure, conventional radiators are a slower way of losing heat, but the key is they aren't there to dump all the heat, they're there just to create enough temperature of difference to create a power supply to run the plasma radiators.

And anyways, that's just a different idea. I seriously doubt we'll be stuck with the same technology used today when we're so far in the future there's whole 'darn cities on another world. How long did it take them to come up with the idea of a liquid droplet radiator? Which is supposed to be 5x or so as efficient. What will they have in the next 100 years? 15x efficiency?

Also you have to look at a few other factors. A current RL nuclear powerplant doesn't have to be light. Perhaps I should parallel a submarine's nuclear reactor instead?
A nuclear reactor generates heat and uses difference of heat to do work and create electrical power. Except, instead of a fission reactor core, we're talking an antimatter reactor, a lot more difference of heat, a lot more power. Remember, the power-generating radiators don't need to radiate all the heat, just enough to create enough difference of heat to generate enough electricity to run the real radiators.

EDIT: Okay, let me clear this up; I'm not trying to break a law of thermodynamics. I'm not using this system to turn heat into electricity, it's turning heat gradient into electricity, what I'm doing is putting all the heat in one spot, which takes energy, I know it will create more heat, but the much higher rate of radiation because that one spot is so much hotter, will mean as a whole the ship cools down faster, despite the fact there's a little more heat.

I think you're underestimating the ease at which a planet can be attacked on a massive scale.

For one, there are a lot of targets on a planet. A spacecraft can only carry a limited number of weapons. Nukes also do not "slag continents" or anything of the sort. Even in a mass-scale, total nuclear war between the world powers of today, while being massively destructive to targeted population centers, would leave other parts of the world untouched- or almost untouched, save for low amounts of radioactive fallout.

Furthermore there are countermeasures that can be put in place- such as for example, anti-warhead missiles. And you can even have warships in orbit, for example, that can battle an invading fleet. They do not have to go far, because the enemy is coming to them. Since they lack unholy super-engines, they are less expensive to produce, so they can be built in larger numbers. And/or have better weapons and protection.

True, and worse than that for my case are lasers, which would be far more effective at shooting down RV's than the modern interceptors.
However, this case can be made for either side.
The difference in-between the two sides is that I get to attack his homeworld before the battle in-between fleets, Fusion-team has to wait until after the battle to attack AM team's homeworld, at which point they'll either be weaker, so they'll have a harder time overcoming defenses, or will have lost altogether.

We can't save decisively that antimatter engines will have tiny thrust. We know, that it is extremely difficult to have an antimatter spacecraft that achieves high acceleration. But I don't see how it would be impossible, even with the design of an antimatter beam-core engine, if done correctly (Mass flow in a 10 meganewton beam-core engine would be something like 100 grams/second).

Fusion also has big problems with waste heat, but has things somewhat better than fusion does.

This really makes me wish I could sit down and actually design the ship. I'll have to get to work on that as soon as I can. Will still probably be awhile...
First I'll see about conventional radiators myself, since I have no idea what kind of output the heatsink/radiator would have.

Before that, though, it would be most interesting to see what the combat ranges would be...

 

[T.Neo]

With 10x the Isp, I seriously doubt that. The whole purpose of using antimatter would be to get a higher Delta-V than your enemy, so if you used it you'd use enough to accomplish that goal. Deuterium can allow for a higher mass ratio, but that bigger "R" will only help so much, and then adding more just doesn't help anymore, and you run into engineering constraints. The only other option for increasing Delta-V at that point is to increase Exhaust Velocity, and that's done with antimatter.

You're arguing from a purely physics-based perspective, I'm factoring in the fact that the antimatter actually has to be produced.

To put things in perspective, the amount of fusion fuel you'd need to run the fusion powerplant to run the antimatter factory, will probably exceed the amount of fusion fuel needed by a fusion spacecraft to achieve the same dV.

Square Combat Theory, if I hold ships back, I'm severely hurting my chances of victory. If I send 4 ships and keep 2 back against an enemy who's sending all 6 ships, then I'd fight 2 battles:
4v6 and 2v6.
Combat capability:
16v36 and 4v20. (Assuming your 16 destroyed an enemy 16 in the first battle.)
Add it all together and it comes down to:
(16+4)v(36+20)
20v56

Sending only some of the fleet is a very bad idea. The numbers here aren't certain to happen, but they're the most likely to happen.

Current wars are a little different, because combat-square theory applies for whatever number of combatants are all in firing range and LOS of eachother all at once. In modern or modern-historical wars, combat usually occurs with each vehicle/soldier only seeing a few other at a time, so the total size of the deployed army doesn't matter much.
But with space warfare I'm working on the assumption that the fleets will all be in firing range of eachother, more or less, at once, since weapon ranges extend well beyond twice the diameter of Earth, and the combat will either be along an interplanetary course intercept or in orbit of another world. And LOS isn't much of a question.

I was referring to a scenario where I had a sizable number of ships more than the enemy; in that case, while the chance of winning might be smaller by sending more ships, you still have a good chance, as well as a reserve of spacecraft that can be employed alongside other defences if the enemy decided to attack, or a basis for a renewed fleet for a second wave.

Hmm... On a smaller scale, it seems what would happen is the defending side would put their fleet in the lowest orbit possible, so that ground-based defenses and their vessels come in range of the enemy all at once, so they're "combat capability" on the combat-square theory would be highest. Also make them more difficult to detect b/c of clutter.

That sounds like a worthwhile idea.

Wait... Do you mean combat capability? I don't see really how that would effect that on a tactical level, which is what combat capability is. Sure, there's evasive maneuvers, but how much of a difference will a small amount of acceleration make? And what fore? Evasive action from kinetics?
Personally I really don't think kinetics belong in space warfare, there's just no purpose when their effective ranges are far, far, far shorter than the "near" range of any respectable laser. It's like carrying a 16in gun on a modern warship with cruise missiles.
Granted, I do like the idea of kinetic CIWS for anti-missile PDS. As a last-ditch resort, a simple high ROF spinning-berral, multi-thousand round/minute gun is very nice to have. Doesn't take much power, relatively lightweight, drops off the excess heat in shells, and if it's FlaK you don't even have to get a direct hit to KO the missile. No range limitations in space, either, except effective accuracy, and accuracy by volume works to a certain range, but still it remains very, very Close-In.
Then again, CIWS guns are being replaced by RAM missiles in the current navy. Perhaps a point-defense missile system would work better?...
(This is in the scenario that lasers are swamped with inbound missiles at longer ranges.)

Don't bash kinetic weapons. We've actually tested kinetic kill vehicles, but we've never built a laser of the sort you often see being discussed in space warfare.

Of course the ability to manuver makes a difference! Just compare the overall abilities of a vehicle that can accelerate at 0.01g, to a vehicle that can accelerate at 1g... there, it is not even about advantages in combat, but an overall tactical advantage over the while mission.

And you have all of space to radiate your heat into. It's the same thing except you use radiators instead of convection to lose heat. Sure, conventional radiators are a slower way of losing heat, but the key is they aren't there to dump all the heat, they're there just to create enough temperature of difference to create a power supply to run the plasma radiators.

And that isn't my point. Convection and conduction are far more efficient ways of transferring heat than radiation. That's why a nuclear powerplant has things far better than a spacecraft does.

And anyways, that's just a different idea. I seriously doubt we'll be stuck with the same technology used today when we're so far in the future there's whole 'darn cities on another world. How long did it take them to come up with the idea of a liquid droplet radiator? Which is supposed to be 5x or so as efficient. What will they have in the next 100 years? 15x efficiency?

Efficiency doesn't correlate directly to years. Technological advancement is not magic- the liquid droplet radiator is one concept that allows an increase in efficiency. Just because that concept came around doesn't mean that 100 years down the line someone is going to find some magical new concept that changes everything radically.

Of course, it's entirely possible that someone wil come up with some new and novel technological scheme. But you can't garuntee it. Unless you can come up with it yourself, handwaving that something is there without actually explaining it, is fantasy. We're not fantasising. We're speculating.

Also you have to look at a few other factors. A current RL nuclear powerplant doesn't have to be light. Perhaps I should parallel a submarine's nuclear reactor instead?

Also not my point. The power/mass ratio of a submarine nuclear reactor is also far lower than that which is being discussed here.

EDIT: Okay, let me clear this up; I'm not trying to break a law of thermodynamics. I'm not using this system to turn heat into electricity, it's turning heat gradient into electricity, what I'm doing is putting all the heat in one spot, which takes energy, I know it will create more heat, but the much higher rate of radiation because that one spot is so much hotter, will mean as a whole the ship cools down faster, despite the fact there's a little more heat.

So you're basically saying you can run an airconditioner entirely off the heat difference between the inside and the outside of a room?

Do you have any equations or mathamatical framework for your concept?

True, and worse than that for my case are lasers, which would be far more effective at shooting down RV's than the modern interceptors.
However, this case can be made for either side.
The difference in-between the two sides is that I get to attack his homeworld before the battle in-between fleets, Fusion-team has to wait until after the battle to attack AM team's homeworld, at which point they'll either be weaker, so they'll have a harder time overcoming defenses, or will have lost altogether.

I'm confused here... could you rephrase that?

This really makes me wish I could sit down and actually design the ship. I'll have to get to work on that as soon as I can. Will still probably be awhile...
First I'll see about conventional radiators myself, since I have no idea what kind of output the heatsink/radiator would have.

Before that, though, it would be most interesting to see what the combat ranges would be...

You want to design a ship? :lol:

I spend most of my time... designing... ships. It isn't good for my blood pressure or my self esteem. :dry:

 

[jedidia]

I think the Delta-Vee advantage of antimatter is being heavily underplayed, and the mass needed for radiators I seriously doubt would offset that advantage, especially using more advanced designs.

Everyone thinks that until they do the math. Ask T.Neo, he could write a song about it... or probably a whole epic.

Once again, I was pulling IR out of the air. Presumably you'd use the best transparent material you could over the optimal wavelength to radiate the most heat and absorb the least.

That is pretty much how a radiator works. There's nothing stealthy about it. take a look at the black body radiation spectrum to understand why trying to get rid of high heat in a low spectrum is a very bad Idea. (Hint: A body at high heat practically DOESN'T radiate at long wavelengths!)

I'm really sorry I'm no good with the precise ranges

This is pretty much the problem: Unless you're really good with the precise ranges, your guesstimates have the bad habit of being really far of. Again, listen to what T.Neo tells you (allthough he's a bit hard on himself... everyone wakes up like he did when they do the math for a design the first time...). The latest point you'll scrap your idea is when you come up with solid figures for the mass of your heatsink. I promise!

but what is sure is that the heatsink/radiator could operate at temperatures far, far above any regular radiator, and thus presumably be more efficient, even if it does have to radiate through a transparent wall of a holding container.

If you mean to convert low heat into high heat, for better radiating efficiency, a heatpump might be worth some math to see if it holds up, but I can tell you three things right away:

1. It won't help in creating a stealth ship.
2. If you're driving antimatter (or any propulsion system, really), it's NOT the low heat that's your problem. It's the very high heat (indeed too high) from your drive.
3. low heat is produced by A/C systems, computers, apliances and even the humans living onboard. As I said, using a heatpump to get it into the high-heat circle to avoid having additional low-heat radiators might be worth a quick calculations, but the first thing I must wonder: where goes the heat produced by the heat-pump?

This really makes me wish I could sit down and actually design the ship.

By all means, do so. project RHO gives you practically everything you need. Just don't get too disapointed when your design doesn't work out when presented in solid numbers. It happend to all of us at least once.

 

[T.Neo]

Yeah, I definitely have to agree with jedidia here. Always- and I mean always crunch the numbers before you make any assumptions (or assertions).

Let's start with producing antimatter vs mining deuterium straight-out;

Let's say we have 4 000 0000 m/s dV requirement. The ship masses... let's say... 1000 tons. The mass ratio is 1.0408. This means you will require roughly 40 tons of propellant. Roughly 50%- 20 tons- will be antimatter. Antimatter has an energy density of roughly 8.987e10 MJ/kg.

We will need roughly 1.797e15 MJ worth of antimatter. We can assume 1% efficiency for the antimatter factory- essentially, 1% of the energy fed into the factory in the form of electricity, becomes antimatter. Even this low figure is probably far beyond our current capabilities. I think I may have heard energy-antimatter conversion efficiencies if 0.001%, using current technology optimised for antimatter production rather than scientific study (this number was supposedly from Robert Forward), but I can't verify this.

We will thus need 1.797e17 MJ of energy. Let's say that we are generating this via a fusion reactor running D-D. I'm not sure what percentage of that energy goes into the heat cycle for the reactor; let's say... 80%, as a total thumbsuck. Roughly a third of the energy is lost to neutrons, but we can capture at least some of them in the coolant water. Let's assume that the heat engine cycle run off the reactor is 40% efficient, and the electrical generator is 90% efficient (again, thumbsuck), leading to a total fusion-electricity efficiency of roughly 30%. This means we need roughly 6e17 MJ of fusion fuel.

My crude, reverse-engineered calculations show an energy density of roughly 87 452 000 MJ/kg for D-D fusion. To put that into perspective, highly enriched Uranium (as used in nuclear weapons) has an energy density of 88 250 000 MJ/kg, and D-T fusion has an energy density of around 576 000 000 MJ/kg. The 'low' energy density of D-D fusion is more than made up for by the fact that it does not require an exotic fuel such as rare He3 or unstable Tritium.

This means (if I'm correct, which I might not be), that other requirements of the fusion reaction notwithstanding, you will need roughly 6 860 000 tons of Deuterium to produce 20 tons of antimatter. Yeah. Now, you could have futuristic ways of extracting the energy from the fusion... more efficient ways... but the big problem is the actual creation of the antimatter. If the fusion reactor could convert all of the fusion energy into electricity and feed it into the particle accelerator, you would still need over two million tons of deuterium.

Now, a D-D fusion rocket isn't the best option, you lose energy via neutrons, etc. I have heard an exhaust velocity of 7 800 000m/s for a D-D fusion rocket (without any seperate propellant injection, so this is usually going to be a high ISP, low thrust drive, unless you give it unholy ulterations and push it into the realm of producing tens of terawatts of thrust power). This results in a mass ratio of 1.67 for a 4000 km/s capable ship. This is 670 tons of propellant for a 1000 ton ship, though the amount of deuterium needed in total to power such a drive might be higher or lower than this figure.

Still, as can be seen, the pure fusion figure is far lower than the figure needed to produce the smaller quantity of antimatter. As I said, an antimatter drive would be a complete logistical nightmare.

 

[Eagle1Division]

That is pretty much how a radiator works. There's nothing stealthy about it. take a look at the black body radiation spectrum to understand why trying to get rid of high heat in a low spectrum is a very bad Idea. (Hint: A body at high heat practically DOESN'T radiate at long wavelengths!)

That's not the stealth idea. The stealth idea is similar, but it works off the "radiate all your heat in one direction", except instead of radiating all the heat in one direction, you take that idea to the logical extreme and radiate it in a narrow beam. Granted, it will mean your ship can do very little tasks because it's inefficient - and it won't help exhaust at all - but at least en route, during the cruise phase, the ship could be difficult to detect, at least enough so to get close enough to whatever strategic asset you're after. (much like a Sub to attack a carrier.)
You have a large radiating surface area, but a reflective chamber (which I realize can't reflect perfectly, yes.) focus it into a beam.

The first Delta-V burn could be done with a booster, from a low orbit around your home world. LOS means they don't see the burn, and the booster can detach and carry all the Engine heat with it, if you want it to be re-usable you can have it turn around and do another Delta-V burn to stay in orbit - and make it so the enemy can't use it's vector to guesstimate the now-separated stealth craft's vector.

The beam-radiator would be for cruise phase, only, when the ship isn't producing much heat anyways.

And finally, if it was manned, or just if you wanted the central craft to survive, you have a platform carrying your weapons payload detach from the main craft, and fire at a pre-programmed target and time. Weapon palate fires and destroys target by getting at very close range, and you drift off, hopefully undetected.

Sure, they'll detect you when you're several AU out and you do another burn to go home, but by then you're safely out of range. That's if you're pulling a brochistrone. If you're not, then you can just ride your orbit back near your homeworld, and do a course correction burn there, switching to normal radiators, safely away from the enemy world.

This is pretty much the problem: Unless you're really good with the precise ranges, your guesstimates have the bad habit of being really far of. Again, listen to what T.Neo tells you (allthough he's a bit hard on himself... everyone wakes up like he did when they do the math for a design the first time...). The latest point you'll scrap your idea is when you come up with solid figures for the mass of your heatsink. I promise!

Haha, I've never really been that attached to the heatsink idea, anyways...

By all means, do so. project RHO gives you practically everything you need. Just don't get too disapointed when your design doesn't work out when presented in solid numbers. It happend to all of us at least once.

Hmm. I guess radiators aren't in the "thermodynamics" section. Oh well, reading it will be good for me, the first time was what got me into Freefall, Orbiter, Rocket Science and other wonderful things. Maybe the second time will introduce me to even more good stuff

@T.Neo
Well, I never doubted that antimatter was far more inefficient than fusion. My point was that if it ever came to a sort of arms race of Delta-V, Antimatter would be the solution, because it offers a way to get more Delta-V than any fusion engine ever could. And then use that extra Delta-V to get a strategic/tactical advantage and win against an enemy.

For a better sense of scale at those final figures, every STS mission and the Saturn V's have consumed about 294,360 tons of LOX, LH-2, RP-1 and Ammonium Perchlorate combined. Which means that that's a LOT of Deuterium, but a large dedicated facility and complex could pull it off.

Looking at the Delta-V range, though, I'm beginning to think that the Extra Delta-V advantage at a lower thrust wouldn't be entirely worth it. Accelerating at 1 m/s^2 for a Delta-V of 2,000 kms means accelerating over a distance of 2,000,000,000 km, and that wouldn't even be a high mass ratio, so that's without the Delta-V arms race.

After pages of debate and many hours of posting, I think fusion finally wins - but on the point that working at a low thrust, as would be required to keep from overheating, astronomical distances are needed to accelerate to the Delta-Vee capability of the enemy vessels.

I would've never guessed it, but apparently this would mean accelerating continuously over astronomical distances. Space is big, very big, I thought Delta-V burns would take only a very small amount of the total transit distance. But apparently space isn't big enough! :blink:

You want to design a ship? :lol:

I spend most of my time... designing... ships. It isn't good for my blood pressure or my self esteem. :dry:

Oh, I have, and I am! Hmm... I guess those would belong in the "projects" section?
Blood pressure and self estseem... Sometimes I wonder what the other high schoolers are thinking when I have pages of Hohmann transfer Delta-V requirements, Mass ratios, Exhaust Velocities, masses of various moons of jupiter, and a card full of orbital equations spread out over my desk. :lol:

 

[fsci123]

That's not the stealth idea. The stealth idea is similar, but it works off the "radiate all your heat in one direction", except instead of radiating all the heat in one direction, you take that idea to the logical extreme and radiate it in a narrow beam. Granted, it will mean your ship can do very little tasks because it's inefficient - and it won't help exhaust at all - but at least en route, during the cruise phase, the ship could be difficult to detect, at least enough so to get close enough to whatever strategic asset you're after. (much like a Sub to attack a carrier.)
You have a large radiating surface area, but a reflective chamber (which I realize can't reflect perfectly, yes.) focus it into a beam.

The first Delta-V burn could be done with a booster, from a low orbit around your home world. LOS means they don't see the burn, and the booster can detach and carry all the Engine heat with it, if you want it to be re-usable you can have it turn around and do another Delta-V burn to stay in orbit - and make it so the enemy can't use it's vector to guesstimate the now-separated stealth craft's vector.

The beam-radiator would be for cruise phase, only, when the ship isn't producing much heat anyways.

And finally, if it was manned, or just if you wanted the central craft to survive, you have a platform carrying your weapons payload detach from the main craft, and fire at a pre-programmed target and time. Weapon palate fires and destroys target by getting at very close range, and you drift off, hopefully undetected.

Sure, they'll detect you when you're several AU out and you do another burn to go home, but by then you're safely out of range. That's if you're pulling a brochistrone. If you're not, then you can just ride your orbit back near your homeworld, and do a course correction burn there, switching to normal radiators, safely away from the enemy world.



Haha, I've never really been that attached to the heatsink idea, anyways...



Hmm. I guess radiators aren't in the "thermodynamics" section. Oh well, reading it will be good for me, the first time was what got me into Freefall, Orbiter, Rocket Science and other wonderful things. Maybe the second time will introduce me to even more good stuff

@T.Neo
Well, I never doubted that antimatter was far more inefficient than fusion. My point was that if it ever came to a sort of arms race of Delta-V, Antimatter would be the solution, because it offers a way to get more Delta-V than any fusion engine ever could. And then use that extra Delta-V to get a strategic/tactical advantage and win against an enemy.

For a better sense of scale at those final figures, every STS mission and the Saturn V's have consumed about 294,360 tons of LOX, LH-2, RP-1 and Ammonium Perchlorate combined. Which means that that's a LOT of Deuterium, but a large dedicated facility and complex could pull it off.

Looking at the Delta-V range, though, I'm beginning to think that the Extra Delta-V advantage at a lower thrust wouldn't be entirely worth it. Accelerating at 1 m/s^2 for a Delta-V of 2,000 kms means accelerating over a distance of 2,000,000,000 km, and that wouldn't even be a high mass ratio, so that's without the Delta-V arms race.

After pages of debate and many hours of posting, I think fusion finally wins - but on the point that working at a low thrust, as would be required to keep from overheating, astronomical distances are needed to accelerate to the Delta-Vee capability of the enemy vessels.

I would've never guessed it, but apparently this would mean accelerating continuously over astronomical distances. Space is big, very big, I thought Delta-V burns would take only a very small amount of the total transit distance. But apparently space isn't big enough! :blink:



Oh, I have, and I am! Hmm... I guess those would belong in the "projects" section?
Blood pressure and self estseem... Sometimes I wonder what the other high schoolers are thinking when I have pages of Hohmann transfer Delta-V requirements, Mass ratios, Exhaust Velocities, masses of various moons of jupiter, and a card full of orbital equations spread out over my desk. :lol:

Well antimatter shoots out most of its energy in gammarays which require unobtanium in order to get some energy out of it... PLuss antimatter is super hard to store and you may end up destryoing your ship if a power outage occurs...

Ive been deisgning ships since i was 5 even though they were total monkey they were something...:rofl:

 

[Eagle1Division]

Well antimatter shoots out most of its energy in gammarays which require unobtanium in order to get some energy out of it... PLuss antimatter is super hard to store and you may end up destryoing your ship if a power outage occurs...

Ive been deisgning ships since i was 5 even though they were total monkey they were something...:rofl:

Only if you use antiprotons. Positrons have a different energy release upon interaction with matter.
Read about it here.

Haha, yes, back when "realistic" was saying "this gun goes here, the engines go here and they're really big."
Anyways, those ships are probably about as realistic as the ships from Star Wars and most other big-screen Sci Fi...

 

[Eli13]

Well, I would say that mine are a little less than that. Mine were spaceships with space shuttles that could take you to pluto in a second. Then they would blow up some random ship by it and... Boom! i was done. Off topic there sorry.

 

[T.Neo]

Which means that that's a LOT of Deuterium, but a large dedicated facility and complex could pull it off.

A large and complex facility could also move the Earth...

If you gave me a long enough lever...

After pages of debate and many hours of posting, I think fusion finally wins - but on the point that working at a low thrust, as would be required to keep from overheating, astronomical distances are needed to accelerate to the Delta-Vee capability of the enemy vessels.

I would've never guessed it, but apparently this would mean accelerating continuously over astronomical distances. Space is big, very big, I thought Delta-V burns would take only a very small amount of the total transit distance. But apparently space isn't big enough!

The problem here, though, is that you're trying to get to astronomical speeds, to cross these astronomical distances. Low acceleration isn't really a problem, you can still do very fast low acceleration brachistochrones. But with a combat spacecraft, you want an ability to have high acceleration, to give you an edge in manuvering.

I wouldn't discount high acceleration capability. It is just extremely difficult, not impossible. For example nuclear pulse propulsion is promising- Daedalus is an example of a high-rate pulse ship that achieves a pretty good thrust/mass and a high exhaust velocity. It has a gigantic engine bell, but seemingly no heat radiators, which is pretty odd for such a powerful spacecraft. Something tells me that something is going on within the Daedalus design that is either (a) wrong, or (b) very interesting. Considering that Daedalus was designed by people far smarter than me, I'm tending towards the latter...

Oh, I have, and I am! Hmm... I guess those would belong in the "projects" section?
Blood pressure and self estseem... Sometimes I wonder what the other high schoolers are thinking when I have pages of Hohmann transfer Delta-V requirements, Mass ratios, Exhaust Velocities, masses of various moons of jupiter, and a card full of orbital equations spread out over my desk.

What most highschoolers are thinking about? Sex. :lol:

I can certainly relate. What with all the Delta-V requirements and mass ratios and exhaust velocities and moon-masses and equations...

What do I do for a hobby? Why, I design spaceships.

I never say that to anyone though. They'd probably think I'm crazy. Maybe that's because I am.