Writing: Input Wanted Limits of detection and interception in space

[GTOM]

I write about a world, where Moon fight against Mars, and there is a postapocalyptic Earth. Can it be realistically justified, that mine metals on asteroid belt and transfer them to Moon isnt much more expensive than lift them from Earth?

Pro : Crates can be launched electromagnetically from asteroids, no need for expensive rockets.
Con : Isnt it just as easy for Mars to intercept those crates?

Question : if a crate doesnt emit much heat after launch, and not many kilometers big like a comet, can the martians calculate its exact trajectory and hit it with a simple missile? (If ships arent nearby.)

What could be cheap countermeasures? Use decoys? (Empty crates.) Attach ion thrusters to crates, just a few km/s deltaV and low acceleration is fine to make the course unpredictable? Automated defence systems? Since in my world Earth is ruined due to rebel AI, no strong AIs.

 

[.Scott]

There would be at least two significant advantages in having Lunar enterprises source minerals from the asteroid belt rather than Earth.
1) The specific impulse required of the rocket system would be much smaller. In fact, given enough patience, solar-powered ion thrusters could be used.
2) Many of the minerals are likely to be more easily collected from asteroids.

Regarding the intercept: The best trajectory from the asteroid belt to Earth and Moon would give you a good starting point in search of these cargo ships. And, if ion thrusters are used, they would be active during a large portion of the cargo's path. An active ion thruster system will have emissions that can likely be detected by telescopes on or near Mars. And Mars could deploy satellites with telescopes and missiles to orbit near the asteroid belt (about the Martian orbit) to get an early detection and possible kill of these cargo treks. Although noble gases are generally used for electrostatic ion thrusters, a large commercial operation ferrying heavy patient loads (ie, no human passengers) might find some other element more economical - such as iron or carbon. In any case, such engines would have signature emission bands that would make them easy to identify.

The intercept itself should pose no technological problem - especially if the cargo ship keeps it thrusters running. It's path will be very predictable and with due planning, delivery of the effector should be very reliable against such a massive target.

It is also possible for a missile to hi-jack a shipment - by rendezvous and then redirecting the cargo propulsion system. If this is done, team Mars might arrange for the shipments to crash into preselected regions of Mars for their own eventual use.

 

[GTOM]

There would be at least two significant advantages in having Lunar enterprises source minerals from the asteroid belt rather than Earth.
1) The specific impulse required of the rocket system would be much smaller. In fact, given enough patience, solar-powered ion thrusters could be used.
2) Many of the minerals are likely to be more easily collected from asteroids.

Regarding the intercept: The best trajectory from the asteroid belt to Earth and Moon would give you a good starting point in search of these cargo ships. And, if ion thrusters are used, they would be active during a large portion of the cargo's path. An active ion thruster system will have emissions that can likely be detected by telescopes on or near Mars. And Mars could deploy satellites with telescopes and missiles to orbit near the asteroid belt (about the Martian orbit) to get an early detection and possible kill of these cargo treks. Although noble gases are generally used for electrostatic ion thrusters, a large commercial operation ferrying heavy patient loads (ie, no human passengers) might find some other element more economical - such as iron or carbon. In any case, such engines would have signature emission bands that would make them easy to identify.

The intercept itself should pose no technological problem - especially if the cargo ship keeps it thrusters running. It's path will be very predictable and with due planning, delivery of the effector should be very reliable against such a massive target.

It is also possible for a missile to hi-jack a shipment - by rendezvous and then redirecting the cargo propulsion system. If this is done, team Mars might arrange for the shipments to crash into preselected regions of Mars for their own eventual use.

So you advocate piracy. Although i think that rather requires ships. With all theese difficulties, is it still reasonable that mine on Earth isnt cheaper?
(Well they have to face attacks on Earth too, but rather from guerillas.)

 

[.Scott]

What is cheaper depends on what you want and how much of it you want.
In most cases, the best source of minerals for Lunar enterprises will be the moon.
If it's only several hundred tons of something that is cheap on Earth and rare on the moon (say bananas), then have Elon move it for you. But if you are looking for a mineral that's rare on the moon, then it's likely rare on Earth as well. And if you need thousands of tons of it, that will likely strain your post-apocalyptic space-faring infrastructure.

I don't imagine that either the "missiles" or the cargo vessels are going to be manned. In most cases, once intercepted, "taking" the cargo without the vessel would present problems. So, I think that "hijacking" rather than "piracy" would be the first tactic.

But there are some inherent problems for the Mars colony. Failing to control the cargo would leave it in an orbit that would "visit" Mars now and then - presenting a hazard to that planet. Striking the cargo for the purpose of shattering it would ultimately result in intense Martian meteor showers - a planet where such meteors often make it to the surface with lethal force.

Deliberate countermeasure that could be employed by the Lunatics (or whatever you call your Moon dwellers) might be to deliberately destroy the ion thrusters when a cargo vessel was high-jacked. Or, worse yet, hide a secondary ion thruster robot in the cargo that could be deployed after the hijacking to deliberately create a Martian hazard. So, an attempted theft might follow this line: Mars intercepts the cargo with a robot, disconnects the cargo thrusters from cargo navigation, then directs the cargo to a safe crash site on Mars. Moon waits for the cargo to approach Mars; destroys it primary hijacked thrusters remotely; engages the secondary thrusters; and directs the payload into the Martian capital.

 

[GTOM]

What is cheaper depends on what you want and how much of it you want.
In most cases, the best source of minerals for Lunar enterprises will be the moon.
If it's only several hundred tons of something that is cheap on Earth and rare on the moon (say bananas), then have Elon move it for you. But if you are looking for a mineral that's rare on the moon, then it's likely rare on Earth as well. And if you need thousands of tons of it, that will likely strain your post-apocalyptic space-faring infrastructure.

I don't imagine that either the "missiles" or the cargo vessels are going to be manned. In most cases, once intercepted, "taking" the cargo without the vessel would present problems. So, I think that "hijacking" rather than "piracy" would be the first tactic.

But there are some inherent problems for the Mars colony. Failing to control the cargo would leave it in an orbit that would "visit" Mars now and then - presenting a hazard to that planet. Striking the cargo for the purpose of shattering it would ultimately result in intense Martian meteor showers - a planet where such meteors often make it to the surface with lethal force.

Deliberate countermeasure that could be employed by the Lunatics (or whatever you call your Moon dwellers) might be to deliberately destroy the ion thrusters when a cargo vessel was high-jacked. Or, worse yet, hide a secondary ion thruster robot in the cargo that could be deployed after the hijacking to deliberately create a Martian hazard. So, an attempted theft might follow this line: Mars intercepts the cargo with a robot, disconnects the cargo thrusters from cargo navigation, then directs the cargo to a safe crash site on Mars. Moon waits for the cargo to approach Mars; destroys it primary hijacked thrusters remotely; engages the secondary thrusters; and directs the payload into the Martian capital.

i think such dirty tricks are good justification that redirect cargo should be trusted to manned ships (together with no strong AI).