Newtonian Aurora

[bean]

It could just be a couple of nuclear missiles minus engines and targeting.  IE. unguided nuclear shells

Yes, you could do that.  However, the yield would have to be in the gigatons.  And the cost of a guidance system is minimal compared to the cost of the nukes themselves.  Not to mention that you can target the nukes for maximum damage.  Hit the big concentrations, and have the rest die off or revert to savagery. 

My comments to the general debate:
1. I've read that something entering the atmosphere at 100 km/s will ablate at around 200 m/s.  This is not a good number for planetary bombardment.  You're sort of restricted to using asteroids.  The best you can hope for with anything smaller is to dump energy into the upper atmosphere.  That's not terribly useful.
2. Passive shrapnel clouds are a bad idea.  See my post on space mines.  (Passive, as in 'constantly there').
3. Nukes.  Enough said.

[jseah]

But like you said, engines take up alot of mass and when they fire, they're visible. 

A 'missile' that is a reentry sheild + warhead is alot smaller and thus much less visible.  At least until it starts reentry, but it's too late by then. 

It could even look like a meteor. 

EDIT: there are enough of those that you can't go shooting them all down.  Although after the first such nuclear holocaust, you bet anything larger than a baseball on course for a colony is going to get shot at. 

[bean]

But like you said, engines take up alot of mass and when they fire, they're visible. 

A 'missile' that is a reentry sheild + warhead is alot smaller and thus much less visible.  At least until it starts reentry, but it's too late by then. 

It could even look like a meteor. 

EDIT: there are enough of those that you can't go shooting them all down.  Although after the first such nuclear holocaust, you bet anything larger than a baseball on course for a colony is going to get shot at. 

How visible the engine is depends on what type it is.  If all you need is a few hundred m/s, then cold gas works well, and is very hard to see.  Note: It is not practical for anything but guidance.
The problem with the meteor idea is that it would probably take a year or more to set up.  You have to come in from an undetectable range, and then change into an orbit that makes the projectile look like a meteor.
Now that I think about it more, even that won't work.  Anything coming toward a city gets shot at, and that goes double for anything that isn't behaving like a meteor (tumbling, etc.).
As for size, given modern technology (which I know isn't true, but nuclear physics don't change) you simply can't fit a nuclear weapon in an object the size of a baseball.  IIRC, that's about the size of a critical mass, not counting any explosives or anything.  You'd probably need something a bit bigger.  And an object that size will likely decelerate high in the atmosphere.  If it doesn't, it's suspicious.  And anything suspicious gets shot at.

[Yonder]

I think I understand your logic here but doesn't it assume that your ship itself is flying a perfect course to the planet at the point of firing your weapon and as a result the error component is only in the aiming? I would have thought that you might expect a similar error in the ships navigation as well which would then introduce the largest error in targetting?

Very true. Probably the best way to look at it is that you have launched your ship towards your target, and then the projectile you shoot is the course correction. In my above example the projectile traveled 66.2 km away from the ship after it was fired, that means that the vector of the firing ship has to pass withing 66.2 km of the target, as the largest course correction you could have would be if the ship fired at a right angle to its course. Doing the math is actually looks like that's the highest precision task of that entire maneuver, the maximum error of 66.2 km from 1e10 km away comes out to 6.62E-9 radians, 220,000 times more accurate than that South African tank cannon. I used to have some info on course corrections for a satellite mission that involved lots of planet flyby's, if I can track that down and do some math I may be able to find a ballpark number for modern space trajectories to go with the modern laser range finder and gun accuracies I found.

Now we certainly wouldn't be able to get the sort of accuracy required in my above example directly out of hyperspace, but if you came out of hyperspace at around 1E10 km, and then course corrected for the next few billion kilometers, shooting at around Uranus or Neptune, then I think you'd be back in business.

Dear All,

New to Aurora forums.  Been playing for a year though.  Some thoughts on the matter of extreme range planetary bombardment.  I don't mean to offend, but though it is an attractive option, isn't it rather impractical?

Now imagine WE'RE all hostile aliens just entering the solar system and about to target earth with extreme range ballistic bombardment.  Remember we would have VERY little pre-existing astrogravitational data on the system.  What? Take time off for detailed survey in a hostile system with active defenders??? Given that our firing location is just beyond the orbit of PLUTO;-

Our problems are, assuming we can even manage to LOCATE EARTH from so far away (what a miracle that was!):-

1) All newtonian sensor data is an image of the past thanks to the speed of light limit.  It takes approx 4 to 7 hours for light to travel from SOL to PLUTO; but EARTH moves at approx 108,000 km/hour around the sun.  Thats like a 430K km to 750K km difference by the time we are pointed at it.  Sure, lets LEAD THE TARGET, but that only takes us to the next problem:-

2) To "lead" the target is difficult given the extreme time lag, because we would need to know the object's EXACT astrogravitational movements, a study that will take years (365. 25 days???) of observation.  But remember, the earth MAY NOT take the EXACT SAME path around the sun for each year due to the following problem:-

3) Predicting the exact planetary orbit given its many variations due to gravitational effects from other solar system bodies and "wobbling" due to LUNA.  Then you need to study the intricate sequence of planetary alignment, but planetary alignments are kinda unique each year so you would need to study and predict ALL the significant solar system bodies to predict their effects on earth orbital variations.

4) Okay now thats done, we ALSO need to factor in the gravitational effects of all those solar system bodies ON THE PROJECTILE, including all other minor bodies that are possibly in the way (planetoids, asteroid belts, comets).  Assuming we've done that, next:

5) What about the effects of solar wind and its unpredictable variations blowing on the projectile? We'd have to study SOL's internal structure, internal convections, solar flares, solar spot activity.  Not to mention that solar wind interaction with the magnetosphere of each major body may have a small effect.  Also, we must assume that:

6) The further away the target is, the more unreliable the sensory data (degree of uncertainty increases with range).  Remeber there are such things, (no matter how minute) as gravitational lensing of light rays, interference from nearby gravity centres, diffraction, echoes, interference from solar wind (and especially actively from defenders), etc.  So we roughly know where a planet WAS to the nearest +/- XXX km, but that may not be precise enough.  

7) Finally we'd have to hope there are no collision whatsoever (not even a glancing blow) with micrometeorites / space dust / comets / asteroids (unlikely) that will put our projectile off course.  Natural stuff are easily avoided (except the space dust and small stuff), but what about:

The last problem is a valid counter-defense in response to any such projectiles that we might launch.  Moving at relativistic speeds, even a collision with a human-seeded "cloud" of floating micro-debris in space early on is enough to veer the projectile sufficiently off-course.  Heck those humans could have already pre-emptively put up millions of square kms of those defensive stuff along the "predicted" optimal line of fire the moment they detected our ships warping in-system.  Remember we're fighting in THEIR territory now, an unfamiliar  battleground they have extensively studied and know very well more than we do.

9) And would you think they'd just let us conduct an accurate system survey in peace? Heck, bouncing all those EM signals in every spectrum off every major solar system body , blasting and lighting us up with all sorts of EM/sensor energy.  Putting up false "ghost images".  Partial cloaking of earth itself? I'm sure that'd have a profound effect on the accuracy of any survey.

Better we crack out those MK III 100 MSP self-guided drone missiles with the 999 radiation yield dirty warheads??? At least their courses are self-correcting with minimal sensor time-to-target (plus other interferences to be avoided) lag.

Regards,
Sam

You don't need to sit around watching the Earth's orbit for a year to know where it's going to be. From a snapshot of the current positions and velocities of the solar system bodies, you can then just propagate out their positions from that point forward. Gravity is a well understood force, and can be easily modeled. Almost immediately after arriving in a new system you will have a very accurate measurement of that Star's mass due to measuring the change in velocity of your ship, giving you the gravity acceleration, and from their (and the distance to the sun) you have the mass.
You can similarly, trivially, and almost immediately measure the mass of any planet with a moon you find, by observing the acceleration on the moon. A slightly more thorough examination would let you find the barycenter that that planet and its moons were rotating around, which would give you the mass of all of the bodies.
The only thing that would give you trouble is a planet with no moons, in that case the only way to measure its mass (except for using our sensors which somehow actively probe and detect the gravity of all objects, which I am pretending we don't have) is to examine the wobble of the sun, which does take time. While you gather that data you'll just have to use a placeholder mass based on its size and type.
So shortly (how shortly depends on how long it takes you to find all the planets, in Aurora this has always been done instantaneously upon entering a new system) you have all the information you need to propagate all of the non-trivial gravity effects for every body in the entire system. The last bit you need is the star's luminosity so you can calculate light pressure, as well as the velocity and density of the hydrogen in the solar wind. Direct observation of the star will quickly give you that.
With this information you can begin propagating the positions of all of the planets and moons in the solar system over time. Accurately, and quickly.
I have to stress again that we do this today. We have thousands of satellites up there right now, and a lot of them have to stay in fairly particular places, or we have to know where they are, or where they are going to be. We don't have to wait until they are there, we can look at where they were in the past, and then calculate their trajectory including all of the affects that you have mentioned (and more) that you seem to think are impossible or difficult to account for.
This program: http://www.agi.com/products/by-product-type/applications/stk/stk-for-space-missions/ is one which is used to do those sorts of calculations, this is a list of the forces that it models when calculating a satellite's (Earth-orbiting) trajectory.
1. Two-body gravity
2. Gravity correction for the irregularities of the Earth's gravity field, primarily due to it being an oblate spheroid, but also due to the fact that it doesn't have a continuous density over the entire volume. This is accomplished by using corrections calculated by earlier space missions which meticulously measured the gravity over Earth. Depending on the gravity file the Earth is broken up into a couple dozen or several thousand sectors.
3. Drag, which is based on density which can be calculated in a variety of ways. The better models take into account the current strength of the magnetic field, the current solar activity, and some other variables to model how the atmosphere balloons outwards as it heats up during the day. If you really care you can also use high-altitude weather forecasts to compensate for windspeed when calculating the drag.
4. Third-body gravity from the sun and moon, and if you're really anal, Jupiter and Venus. You could do the others if you wanted to, but there is really no point.
5. The solar radiation pressure from the light emitted by the sun, as well as the solar wind. Of course this also entails modelling when you are being shaded from the sun by the Earth or the Moon.
6. The light coming from the Sun is only part of the battle, there is also a lot of light that bounces off the Earth and pushes you, and you have to measure how much light that was using the shape of the Earth and a model of its albedo.
7. It also models radiation pressure of the light being emitted by the Earth, as in the IR light being emitted as black body radiation.
8. Then you have outgassing, the mass that is from a satellites surface that throws it off course. The largest offenders of these are fuel or cryogenic tanks, which always have some amount of leakages.
9. Lastly the satellite might even have an engine, which also has to be modeled when it fires.

We've had the ability to model all of that stuff for more than 20 years, and the problem we are talking about here is way simpler, since we really just care about the sun and planet gravity. SRP is meaningless for a dense slug, and we won't be near any bodies long enough to worry about Drag or gravity field irregularities.

[Mel Vixen]

As for size, given modern technology (which I know isn't true, but nuclear physics don't change) you simply can't fit a nuclear weapon in an object the size of a baseball.  IIRC, that's about the size of a critical mass, not counting any explosives or anything.  You'd probably need something a bit bigger.  And an object that size will likely decelerate high in the atmosphere.  If it doesn't, it's suspicious.  And anything suspicious gets shot at.

It depends on the material (uran plutonium ...) you use and how much preasure your explosives can create if you use a nuclear shaped charge (normally its a hollow ball of your nuclear material with multiple explosive packages on its oute side). Iirc and i am no nuclear physicist higher pressures meant that you need less material for the critical mass.
The davy Crocket nuclear shell was 53 kilograms by a length of 40 cm and a diameter of 27cm (in 1950). You have a low yield though. Said shell goes to 1 Kilotons.
I would guess a shell about the size of a soccer-ball would be possible if you have modern tech and some tinkering spirit. Dont forget till 2003 it was forbidden in the USA to research mini-nukes so that we didnt see any such small nukes isnt that surprising for me.

There was also the idea (some say a idea from the ####es) of using two shaped charges (the same kind as in heat ammunition just with uranium) facing each other with tritium/deuterium in between. The high pressure and energy of the 2 uranium-streams hitting each other would have been enough to generate a short but brief fission+fusion reaction (fizzle) that boosted the yield of the explosion. Still the yield would be far lower then the yield of "Little boy". Depending on what you want to hit say just critical infrastructure like powerplants, train-stations, water-reserves or whatever it would be enough.

[bean]

It depends on the material (uran plutonium ...) you use and how much preasure your explosives can create if you use a nuclear shaped charge (normally its a hollow ball of your nuclear material with multiple explosive packages on its oute side). Iirc and i am no nuclear physicist higher pressures meant that you need less material for the critical mass.
The davy Crocket nuclear shell was 53 kilograms by a length of 40 cm and a diameter of 27cm (in 1950). You have a low yield though. Said shell goes to 1 Kilotons.
I would guess a shell about the size of a soccer-ball would be possible if you have modern tech and some tinkering spirit. Dont forget till 2003 it was forbidden in the USA to research mini-nukes so that we didnt see any such small nukes isnt that surprising for me.

And a soccer ball is a bit bigger then a baseball.  Though I do question strategic warheads of that size.  Antimatter, on the other hand...
What happened in 2003?

There was also the idea (some say a idea from the ####es) of using two shaped charges (the same kind as in heat ammunition just with uranium) facing each other with tritium/deuterium in between. The high pressure and energy of the 2 uranium-streams hitting each other would have been enough to generate a short but brief fission+fusion reaction (fizzle) that boosted the yield of the explosion. Still the yield would be far lower then the yield of "Little boy". Depending on what you want to hit say just critical infrastructure like powerplants, train-stations, water-reserves or whatever it would be enough.

I've heard some stuff about the #### program, but I'm not sure that was exactly how it worked, and I don't think it scales down that well.  Maybe I'll look it up later.

Very true. Probably the best way to look at it is that you have launched your ship towards your target, and then the projectile you shoot is the course correction. In my above example the projectile traveled 66.2 km away from the ship after it was fired, that means that the vector of the firing ship has to pass withing 66.2 km of the target, as the largest course correction you could have would be if the ship fired at a right angle to its course. Doing the math is actually looks like that's the highest precision task of that entire maneuver, the maximum error of 66.2 km from 1e10 km away comes out to 6.62E-9 radians, 220,000 times more accurate than that South African tank cannon. I used to have some info on course corrections for a satellite mission that involved lots of planet flyby's, if I can track that down and do some math I may be able to find a ballpark number for modern space trajectories to go with the modern laser range finder and gun accuracies I found.

This is what I was talking about with the sensors.  You can't expect yourself to be on a perfect intercept course.  You have to determine your relative velocity experimentally, and that takes time, particularly with a passive sensor.  Is putting a guidance system in the projectile really too much to ask?
As for corrections, I'll look them up in the morning.  However, expect them to be absolutely negligible over a few days, particularly as most of that time is spent in deep space.

[Mel Vixen]

And a soccer ball is a bit bigger then a baseball.  Though I do question strategic warheads of that size.  Antimatter, on the other hand...
What happened in 2003?

True put extrapolated into the future with TN tech i could see kiloton tennisballs. Every explosive is usefull exspecaily one that can obliberate a block of houses while being the size of an soccer or even baseball, its just a tool thought. Such small weapons could work well in planetary warfare if it ever gets refined.

In 2003 the US-senat removed alaw that did forbid the research and development of mini-nukes the congress though watered that down to just research. I forone think that nukes at all should be forbidden so i am not happy about it either way.

[scoopdjm]

I should have been more clear.  I was comparing them to missiles.
A missile has to go out and kill its target.  A fighter has to accelerate to get to the target, decelerate to a stop, then kill the target and go back to the mothership.
The statement about "less manuverable" also applied as compared to missiles.  The extra mass of the human and his stuff hinders acceleration. 
At medium distance, you can either evade or you can't, and there's no reason that a conventional ship couldn't if a "fighter" can.
I'm in favor of drones, but what makes a fighter is recoverability.  That tacks on delta-V somewhere in the system.

well a few points on fighters one is that technically you could use theorized nuclear engines to easily power them (once miniaturized) assuming that, like conventional jet engines of today, they do not rely on a flow of particles to move the fighter. Secondly on regards to maneuverability, multiple nose and wing thrusters easily mitigate the effects of using a conventional maneuvering flap (like all planes today). Thirdly what do you think fighters are? Spacious luxury craft? They're already 98% engine.

[Steve Walmsley (OP)]

I just realised the targeting is more complex than I thought because the railgun projectile will have the momentum of the firing ship as well as its own velocity, which complicates the calculations. Time to learn some new maths I think

Steve

Finally got this sorted out. I can now predict the correct launch angle for the shot (or if the shot isn't possible) based on the heading and speed of the two ships and the speed of the projectile, taking into account the momentum of the firing ship being added to that of the projectile. The eventual solution was based on a combination of suggestions on here, on the sfconsim-l board and on the stackoverflow forum.

Essentially I looked at the shot from the frame of reference of the firing ship (idea from Isaac Kuo on sfconsim). By giving the target ship the combined vectors of both ships, I could predict the angle of a shot from a stationary firing point against a moving target using a quadratic equation provided by Jeffrey Hantin on the stack overflow forum. Then I took the x,y velocities of that shot (which is firing at the wrong place because in reality the actual target ship isn't moving with the combined vectors of both ships) and combined them with the x,y velocities of the firing ship to give me the actual x,y velocity of the projectile, including velocities from both launch angle and firing ship momentum. The addition of the firing ship momentum will now send the projectile into the path of the target ship.

This means I am going to track the projectile on the map like a missile so you can see its progress. It also means it might hit something else instead, including your own ships if you aren't careful about firing position (line of battle reborn?). If the processing overhead gets too high because of the number of projectiles I might look at this again.

Steve

[bean]

well a few points on fighters one is that technically you could use theorized nuclear engines to easily power them (once miniaturized) assuming that, like conventional jet engines of today, they do not rely on a flow of particles to move the fighter. Secondly on regards to maneuverability, multiple nose and wing thrusters easily mitigate the effects of using a conventional maneuvering flap (like all planes today). Thirdly what do you think fighters are? Spacious luxury craft? They're already 98% engine.

1. What do you mean, do not rely on the flow of particles?  There are no reactionless drives planned as far as I know.
2. And maneuverability is far more then pointing the nose.  It's related to acceleration.
3. Supporting a human is going to tack on at least 5 tons, if not more.  And it means you absolutely have to get it back.

There are only two situations I can see any type of fighter being practical, and neither applies here:
1. A war breaks out that neither side is prepared for, so they throw some parts together to make what is basically a fighter. It's likely to be manned.
2. You have a highly effective engine that is too expensive to use in missiles.  (Fusion torches spring to mind.) Instead, you use a lancer, which is almost certainly unmanned.

Steve:
Just have them go away if they miss.  Space is so vast that the chances of a hit are negligible, particularly if the ship in question has any form of radar.  Unguided projectiles will be harmless unless they can hem the target in, while a good guided round will either hit or be out of fuel, not to mention being "dumb".

[Mel Vixen]

Well one could theorize that transnewtonian elements could be used to generate gravity fields/wells. Given that you can generate this field at some point in space you achive movement of your ship by generating a strong field somewhere right in front of you. But that gets to scifi for me. Thats the same category as riding waves of spacedistortions etc.

I could see fighters as computercontrolled drones. Like the vulturedroids in the Star wars sequells these guys thought were remotecontrolled and slowed down in the reactiontime if there were to many droids running on the same mainframe. Iirc thats why a six year old shrimp could kill that battleship.

[bean]

Well one could theorize that transnewtonian elements could be used to generate gravity fields/wells. Given that you can generate this field at some point in space you achive movement of your ship by generating a strong field somewhere right in front of you. But that gets to scifi for me. Thats the same category as riding waves of spacedistortions etc.

Steve has given no indication that he's even considering this. 
Oh, and jet engines do rely on the flow of particles.  They just get most of the particles from the surrounding air.  I know you weren't the one who suggested it, but I thought I'd clear it up.

[UnLimiTeD]

If a fighter ever were to be manned, I'd expect it to be a brain hotwired to a computerframe.^^

[scoopdjm]

Steve has given no indication that he's even considering this. 
Oh, and jet engines do rely on the flow of particles.  They just get most of the particles from the surrounding air.  I know you weren't the one who suggested it, but I thought I'd clear it up.

1. What do you mean, do not rely on the flow of particles?  There are no reactionless drives planned as far as I know.
2. And maneuverability is far more then pointing the nose.  It's related to acceleration.
3. Supporting a human is going to tack on at least 5 tons, if not more.  And it means you absolutely have to get it back.

There are only two situations I can see any type of fighter being practical, and neither applies here:
1. A war breaks out that neither side is prepared for, so they throw some parts together to make what is basically a fighter. It's likely to be manned.
2. You have a highly effective engine that is too expensive to use in missiles.  (Fusion torches spring to mind.) Instead, you use a lancer, which is almost certainly unmanned.

Steve:
Just have them go away if they miss.  Space is so vast that the chances of a hit are negligible, particularly if the ship in question has any form of radar.  Unguided projectiles will be harmless unless they can hem the target in, while a good guided round will either hit or be out of fuel, not to mention being "dumb".

1. A jet engine doesn't rely on atmospheric molecules to go (except for the oxygen required for ignition) therefore it is just as effective, if not more so, in space. 2. Yes quite, hence wing thrusters which can counter-act the forward force of the engine when changing direction, it would be a bit sloppy but it would theoretically work. 3. Take a que from starwars' tie-fighters the cabin doesn't necessarily have to maintain some form of homeostasis if the pilot's suit can. Now for your statements on the practical uses of fighters: a fighter is a reusable weapon with alot more damage potential then missiles, also fighters act as good defense ships, easily destroying when gathered en masse. secondly if you designed a highly expensive and/or advanced engine you wouldn't use it on a measly fighter it would go to a stealth ship or something very important or experimental. Also id like to added something someone said earlier in the topic, a fighter doesn't just stop at a ship and attack it, think of it like strafing runs every time it's ready to attack it makes a run.  To Bryon now: do mean for the use of combustion or for the purpose of thrust from pushing off of them?

[Yonder]

1. A jet engine doesn't rely on atmospheric molecules to go (except for the oxygen required for ignition) therefore it is just as effective, if not more so, in space.

If you take a jet engine, and remove the "requirement of oxygen to ignite" you have a rocket engine. I am with Byron in being confused as to how either jet or rockets are supposed to accomplish thrust without "particle flow".

2. And maneuverability is far more then pointing the nose.  It's related to acceleration.
3. Supporting a human is going to tack on at least 5 tons, if not more.

2. To expand on that, maneuverability for a "real" spaceship would be based on how quickly you could point your engine in the direction you need it (what Scoop was referring to) and then how powerful that engine is. In NA we are ignoring facing, meaning that only the second factor is important.
3. 5 tons is probably more than is really necessary for a high tech fighter. The F22 is 19tons empty, and I highly doubt that a fifth of that is life support. A high altitude fighter really has all of the life support considerations as a space ship as well, aside from radiation, and that's not too much of a penalty because high-performance electronics are even more vulnerable to radiation than humans are, so you need to shield against it regardless. In a 200-300 ton fighter the mass devoted to life support would be pretty inconsequential, the real new consideration is that you are now limited to 6-7 gs, for any length of time, and 9-10 for very short bursts. That's a pretty huge constraint on something that relies on acceleration to survive. (Of course 250 years into the game when you have genetically engineered fighter pilots that can withstand 70g's... Lol, although 250 years in the game your fighters may very well need more than that to be competitive).

This is what I was talking about with the sensors.  You can't expect yourself to be on a perfect intercept course.  You have to determine your relative velocity experimentally, and that takes time, particularly with a passive sensor.

I quoted an actual textbook citing today's sensor technology and used that in my example, it also just doesn't take that much time to determine this stuff.

Is putting a guidance system in the projectile really too much to ask?

It kinda sounds like you are just throwing up all sorts of objections because you really want every single projectile to have a guidance system. I know that projectiles with guidance systems are better. If you go back a couple pages I did lots of math showing how much your range was extended by launching projectiles that were guided. I am with you on the guided projectiles. That said, there are some times when you don't need guided projectiles. All I'm saying is that when you are shooting at a target that is 6378 km across and can't dodge out of the way, you don't need guided projectiles. I'm not standing here and claiming that you can snipe a 20m fighter with 10g's of acceleration from Pluto with dumb slugs, I will let you take care of that with your missiles.