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Beaming into Space
HobbySpacer writes "At this week's 1st Int. Symposium on Beamed Energy Propulsion in Huntsville a wide range of laser and microwave propulsion schemes are being presented. The big news so far is the announcement by Gregory
Benford of plans for a test of microwave propulsion with the Cosmos Sail, due to fly early next year. The possibilities of using lasers to deflect incoming asteroids & comets are also under discussion."
Wow. I always thought that the likelihood of an asteroid hitting Earth was low, at least low enough that ther are probably better things to spend one's time addressing... say, hunger, AIDS, yadda yadda yadda.
A larger problem is how to lower the cost of missions to allow for an increase their frequency. If this kind of technology c(w)ould be used to allow humans or unmanned craft more time in space to collect data, I think that would be far more useful.
The quote smacks of FUDing. Oooh, look out! A big bad asteroid could it us! You all saw "Deep Impact", right? Well, better fund us so we can make sure that never happens...
"Content's a bitch."
I think you are being way to skeptical here .
Look, you can say all you want but you are talking about something which can basically wipe us. Not to be a controversialist but wherein AIDS and hunger if you aren't there in the first place. Yes, I agree maybe its not top priority as much as the folks quote but its bloody well important. You think even if we spot an asteroid we can do anything about it.....throw a few nukes doesnt solve it. Want us to be sitting ducks and pray ? Maybe you should take a look again about Schu-Levy?
Also how many times will the AIDS+hunger thing come up ? If your view is right then we should stop all technological innovation and start feeding everyone. It doesn't work that way - we should try to fight AIDS, hunger but at the same time its _very_ important to look forward
No offence. Thanks,
vv
One of the nice advantages of Microwaves over
lasers, is that is really easy to make a stearable
beam of Microwaves using the phased array technique. I you make a dipole antenna and feed a
microwave single into it, the signal goes pretty much everywhere, if you put another dipole antenna, next to the first, the two signal interfere results in a more direction beam. If you
have a square grid of antennas, you get a narrow
beam which becomes more focused as the density of
the grid increases.
If all the signals are in phase then the beam goes straight ahead (also straight behind, so you put a microwave mirror, a metal plate behind the antennas at a (half) integer number of wavelength in distances.
To stear the beam, you just put a slight phase difference between each dipole antenna and the ones next to it, so that the phase difference increases with the distance between the each dipole antenna and the first one, thus the beam is stearable electronically. Because there a lots a seperate dipole antenna, the power in each does need to be to large, so you can use fairly ordinary electronic components to produce the beam.
Imagine, building a simple block of antenna, consisting of a 100 by 100 dipole antenna, each
feed by its own 100W oscillator, and with its own
control and stearing computer inside. That should
be fairly cheap to build. Now mass produce these.
Now lets put a hundred of these side by side in a square, you
get a stearable 100 MegaWatt beam and its only 10meter by 10meters big.
You can use this idea to build with conventional
technology a microwave beam as powerful as you like.
Now you don't get much thrust from just reflecting
the energy, 6.7 Newtons per gigawatt. But a constant accelation over time can quickly build up speed in space. You can get a lot more thrust out of the system by using the microwaves to heat a reaction mass, say water in the target craft. I haven't done the calculations, put a powerful enough beam could be used to launch a steam rocket from the earths surface at very little cost.
Your chances of dying as a result of an asteroid hit are similar to your chances of dying from an earthquake or flood. And yet people have flood insurance but no asteroid hit insurance.
The reason for that is that floods and earthquares are local and therefore you can hear about them happining somewhere else and perceive them as a threat. When an asteroids hits Earth there will be no "somewhere else".
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
For propulsion purposes you would need an extremely powerful beam with megawatts of power. Phased array antennas still have pretty strong side lobes. Even if they are attenuated by as much as 40db it would still have enough energy to cook everything in their vicinity. The main lobe of a phased array antenna will still have divergence that will make it ineffective for distances in space.
Masers are coherent and therefore capable of creating an extremely narrow beam with virtually no side lobes. New technologies for masers bring their efficiency from the low single digits to around 50%.
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
That should be slightly under 27000 miles per hour. Furthermore, once it's several thousand miles in altitude it would slowly decelerate and fall back to a circular earth orbit. Thus you achieve earth orbit without the need to propell it horizontally very far. The idea of using the force of photons to push a sail is still out there. It would be more effective to transmit a magnetic dipole of equal phase and polarity from the spacecraft into the microwave and use the repulsion to transmit force through a vacuum.