Which of these (listed below) is the best method for sublight space travel?

[Geschosskopf]

3 hours ago, Bill Phil said:

Assuming it's a laser beam. Particle beams can be deflected by magnetic fields and are actually more efficient than photon beams for propulsion purposes.

And particle beams don't work that well through the atmosphere, so the beam originates somewhere in vacuum.  Which means it can at least obliterate every satellite its owners don't like.

 

3 hours ago, Bill Phil said:

Uh... only if you use laser beams. Microwave beams tuned to a specific frequency and kept at a low enough irradiance will be no more of a threat than normal sunlight. Even if you used laser beams the beam irradiance will not be high. To be honest, this just isn't possible unless you specifically designed the "solar power station" to be a weapon of mass destruction.

But, you've still got to concentrate the energy into a beam (to prevent most of the power from being wasted) and aim it at a relatively small spot on the ground (where this beam can be put to use).  And it has to be considerably more intense than sunlight or ground-based solar panels would do just as well and there'd be no point in putting the panels in orbit.  So no matter how you slice it, you've still got a very power stream of directed energy aimed at Earth.

 

3 hours ago, Bill Phil said:

Another aspect to consider is that the immense power of beams for propulsion is that they're inherently chained to large facilities. Yes, mirrors could deflect the laser beams to hit a target, but doing so will be difficult and will be easily visible. Not to mention the easily visible heat rejection and other unavoidable results of activating the laser beam station. Any and every entity worried about it will keep a lot of firepower trained on the station. As soon as they try something, it'll be turned into slag. 

Unless that firepower is also equally powerful lasers, it'll be too late to stop anything.

[Bill Phil]

1 hour ago, Geschosskopf said:

And particle beams don't work that well through the atmosphere, so the beam originates somewhere in vacuum.  Which means it can at least obliterate every satellite its owners don't like.

Assuming the spot size of the beam is small enough that the area power density is high enough to cause damage.

Not only that but if we had particle beam propulsion and particle beam weapons there would be suitable countermeasures employed to protect assets. For example, we can already shoot down satellites we don't like, but we don't. Why? Because there are consequences. And if such weapons were developed and employed countermeasures would be developed as well. And consider that the beam projector can also be destroyed, quite easily I might add.

1 hour ago, Geschosskopf said:

But, you've still got to concentrate the energy into a beam (to prevent most of the power from being wasted) and aim it at a relatively small spot on the ground (where this beam can be put to use).  And it has to be considerably more intense than sunlight or ground-based solar panels would do just as well and there'd be no point in putting the panels in orbit.  So no matter how you slice it, you've still got a very power stream of directed energy aimed at Earth.

I'm afraid you've misunderstood the point of space based solar power. It isn't about having higher intensity, rather it's about avoiding the interruptions for ground based solar power. Namely, avoiding night time, clouds, and cosine losses. For example, where I live the annual average solar irradiance is something like 200 watts per square meter. Compare this to solar irradiance at 1 AU - nearly 1400 watts per square meter. Just going through the atmosphere cuts into the solar irradiance. (And I live in a place that gets decently hot at that, it's just that night time lowers the average).

You do concentrate the energy into a beam - but a microwave beam. Microwave rectennas can be built to catch the energy of this beam and be spread over a fairly large area, but leave the area beneath them unharmed and still usable. Not only that but you don't need a high intensity beam, nor do you want one. It would be too dangerous. You still get advantages: no night time for the panels in orbit and so on. But you don't want to beam it down at such an intensity that it can actually harm anything.

1 hour ago, Geschosskopf said:

Unless that firepower is also equally powerful lasers, it'll be too late to stop anything.

Why would you use lasers? You could use Casaba Howitzers, slug throwers, missiles. No one said you had to station these weapons far away. A small flotilla of ships standing by is preferable. 

We already have access to immensely powerful systems. Beamed power will be more powerful still and the question of how to control that power is indeed an important one. I'm confident we'll find ways to deal with it.

[Geschosskopf]

On 9/21/2019 at 9:08 PM, Bill Phil said:

I'm afraid you've misunderstood the point of space based solar power. It isn't about having higher intensity, rather it's about avoiding the interruptions for ground based solar power. Namely, avoiding night time, clouds, and cosine losses. For example, where I live the annual average solar irradiance is something like 200 watts per square meter. Compare this to solar irradiance at 1 AU - nearly 1400 watts per square meter. Just going through the atmosphere cuts into the solar irradiance. (And I live in a place that gets decently hot at that, it's just that night time lowers the average).

Orbital solar collectors can't avoid the dark.  If you put them in geostationary orbit so they can connect to the same ground station, then they'll be in the dark a some amount of the time.  If you put them in any other orbit, they'll not only be in Earth's shadow some of the time, but you'll also need long chains of ground stations all around the world under their paths.  Ignoring the diplomacy needed to allow such sharing, each such ground station is a discrete target requiring a pretty tight beam and the ability to switch it rapidly from 1 station to the next without scorching the space in between.

 

On 9/21/2019 at 9:08 PM, Bill Phil said:

You do concentrate the energy into a beam - but a microwave beam. Microwave rectennas can be built to catch the energy of this beam and be spread over a fairly large area, but leave the area beneath them unharmed and still usable. Not only that but you don't need a high intensity beam, nor do you want one. It would be too dangerous. You still get advantages: no night time for the panels in orbit and so on. But you don't want to beam it down at such an intensity that it can actually harm anything.

Hmm.  I just cooked my supper with microwaves running on 110V and less than the 20A the associated breaker trips at.  And that's fairly weak even by household standards, which includes HVAC, clothes dryers, etc., but is still enough to burn animal and plant matter in seconds to minutes.  So basically, it doesn't take much microwave energy for very long to be quite harmful to stuff on the ground.

And therein lies the problem.  If you widen the beam coming down, lowering its intensity to a less-than-popcorn setting, you need a vast forest of rectennae, each of which is only absorbing a less-than-popcorn amount of power to the grid.   And each is a discrete entity so all the photons that pass between them are wasted, doing nothing but cooking whatever's there.  This doesn't seem worth the bother for a number of reasons---cost, complexity, resistance loss, waste of most of the wide beam you paid to put in orbit, etc.  Not to mention the EMP-like effect and RFI this would create all over the target area.  To avoid these problems, you have to concentrate the beam, which creates other problems.

 

On 9/21/2019 at 9:08 PM, Bill Phil said:

Why would you use lasers? You could use Casaba Howitzers, slug throwers, missiles. No one said you had to station these weapons far away. A small flotilla of ships standing by is preferable. 

Because the country with the big lasers obviously wouldn't allow foreign powers to position conventional artillery within its borders close to said lasers.

 

On 9/21/2019 at 9:08 PM, Bill Phil said:

We already have access to immensely powerful systems. Beamed power will be more powerful still and the question of how to control that power is indeed an important one. I'm confident we'll find ways to deal with it.

We already have.  If's called "we ain't doing that".  Anybody who takes a step in that direction MUST be viewed by everybody else as potentially making a world-dominating weapon, because it could easily be used as such.  This is why we don't have bases on the Moon.  It's better not to go there than to give us something else to fight over.  I mean, look at all the hassle currently going on over Iran's nuclear program.

[kerbiloid]

And even with ideal rectennae, the beam should pass through 8 km thick air.
Even 1% of losses in air means a constant 10 MW torch above a 1 GW rectennae area.

A nuke powerplant dissolves the heat waste in water. A beam receiver can't, as the losses happen before the beam reaches it.

Edited September 23, 2019 by kerbiloid

[Bill Phil]

53 minutes ago, Geschosskopf said:

Orbital solar collectors can't avoid the dark.  If you put them in geostationary orbit so they can connect to the same ground station, then they'll be in the dark a some amount of the time.  If you put them in any other orbit, they'll not only be in Earth's shadow some of the time, but you'll also need long chains of ground stations all around the world under their paths.  Ignoring the diplomacy needed to allow such sharing, each such ground station is a discrete target requiring a pretty tight beam and the ability to switch it rapidly from 1 station to the next without scorching the space in between.

Yeah, solar collectors can't avoid the dark from happening. But they don't experience night time, they experience eclipses. These only happen during specific times of the year, and for minutes at a time. Easy to deal with from a practical standpoint, just add slightly more capacity and then use storage systems.

55 minutes ago, Geschosskopf said:

Hmm.  I just cooked my supper with microwaves running on 110V and less than the 20A the associated breaker trips at.  And that's fairly weak even by household standards, which includes HVAC, clothes dryers, etc., but is still enough to burn animal and plant matter in seconds to minutes.  So basically, it doesn't take much microwave energy for very long to be quite harmful to stuff on the ground.

And therein lies the problem.  If you widen the beam coming down, lowering its intensity to a less-than-popcorn setting, you need a vast forest of rectennae, each of which is only absorbing a less-than-popcorn amount of power to the grid.   And each is a discrete entity so all the photons that pass between them are wasted, doing nothing but cooking whatever's there.  This doesn't seem worth the bother for a number of reasons---cost, complexity, resistance loss, waste of most of the wide beam you paid to put in orbit, etc.  Not to mention the EMP-like effect and RFI this would create all over the target area.  To avoid these problems, you have to concentrate the beam, which creates other problems.

...

Microwave ovens are entirely different from a microwave beam for transmitting.

You see, microwave ovens are designed to heat water and other molecules common in foodstuffs. This means that they operate at one of many frequency those molecules are sensitive to, usually one of the optimum frequencies. A microwave beam for power transmission will operate at the optimum safe frequencies for that purpose - which means that no, they will not (and likely can not, aside from photon collisions) cause anything within the beam to cook. Not to mention that you're talking 2.2 kilowatts of power spread over a rather small area for a microwave oven. The design irradiance for a microwave beam transmission system would be much smaller and less dangerous, not to mention less likely to cause dielectric heating.

The rectenna can intercept nearly the entirety of the beam energy, and can do so efficiently. 

It appears as though you have not devoted much time to researching microwave beam power transmission. I suggest you do so, there are numerous interesting aspects to look into, but nothing has been found to be game breaking - save for the cost of putting payloads in orbit.

1 hour ago, Geschosskopf said:

Because the country with the big lasers obviously wouldn't allow foreign powers to position conventional artillery within its borders close to said lasers.

I was under the impression we were discussing laser facilities stationed in space. Such facilities on Earth would, again, just be massive targets - practically useless for warfare. All they could shoot down would be spacecraft and some aircraft, but missiles and artillery could easily take it out from beyond visual range.

1 hour ago, Geschosskopf said:

We already have.  If's called "we ain't doing that".  Anybody who takes a step in that direction MUST be viewed by everybody else as potentially making a world-dominating weapon, because it could easily be used as such.  This is why we don't have bases on the Moon.  It's better not to go there than to give us something else to fight over.  I mean, look at all the hassle currently going on over Iran's nuclear program.

Then why are there numerous government backed programs around the world trying to develop space based solar power systems? I mean, they're probably not going to result in anything, but the intent is there. The answer is simple: space based solar power is not a military threat, and can never be (as soon as it is it'll be dealt with). The beam energies for such systems are not and can not be significant threats. This is because power generating beams are inherently different from weaponized beams.

Beams for propulsion carry a much larger threat with them but they also make easy targets due to them being large facilities. And yet even then there is research, both theoretical and practical, into beamed propulsion.

The only way to truly travel at significant fractions of the speed of light (above gamma = 2) will require beamed propulsion of some sort, as rockets are simply not up to the task due to the rocket equation.

(Either that or some kind of Robert Forward gravitational accelerator, which is "indistinguishable from magic", but could actually work, if the assumptions turn out true)