Tokyo University's "Microwave Rocket" 48
LiftOp writes "Apparently a group from Tokyo University's Department of Advanced Energy has
used a high-power microwave beam to heat the air beneath a model rocket
, sending it skyward (well, two meters).
Dr. Kimiya Komurasaki, who led the group, seems to be quite a
directed energy
buff; when the rocket eventually gets beyond the air level, a conventional motor could be used to send it further."
high energy ? (Score:3, Interesting)
Re:high energy ? (Score:5, Informative)
Re:high energy ? (Score:2)
And because the dry mass of the rocket is the expensive bit, you haven't pushed up the cost of the vehicle by much.
And air is actually a much worse propellent than rocket fuel; you need many times more energy than the better rocket fuels to get the
Re:high energy ? (Score:1)
Re:high energy ? (Score:5, Insightful)
Yes, I would imagine it does.
If so, wheres the applicable purpose?
Unfortunately when building a rocket to go into space, most of the fuel is spent CARRYING FUEL UP. That's just plain uneconomical. So when one is only lifting the actual payload (and perhaps some small reflector or whatever) there's a *HUGE* energy savings.
There's also the issue of reliability/stress. Things which are being thrown into orbit at high velocities have to be engineered very well to survive the trip. Mass must be shaved, redundancies might be cut to lower costs, etc. Building things on the ground is much easier in these respects... redundancy is much less limited, much less stress is on teh equipment, it's much easier to diagnose repair (because it doesn't have to be all micro-sized, etc). Also miniturizing things can considerably inflate their cost. So keeping as much of the equipment on the ground as you can is a good idea.
There's also safety issues... Most rockets use very dangerous explosive fuels, some of which are environmentally unfriendly. As long as a poor bird doesn't stray into the beam, this should be able as environmentally friendly as possible.
One last answer is that it allows most of the launch system to be reused between launches... Disposable rockets can't do this, and the Space Shuttle doesn't even re-use that much of it's mass... just some of the more complicated bits.
There are of course downsides to this technique (what if the spacecraft drifts off the beam, or the beam is obscured, etc) however I believe that they will eventually be overweighed by the enormous benefits.
It's a good question and not all the answers are obvious. I can't wait for the day where most of the work launching stuff into space is done from the ground.
Cheers,
Justin
Warning: I am not a physicist yet, but I almost have my degree. I also work at the Jet Propulsion Lab
Re:high energy ? (Score:3, Insightful)
From a great special-issue Scientific American a few years back, I think I have an answer for this.
Some of the "heated air" approaches (using microwaves or lasers) depend on a convex reflective surface under the spacecraft, which focuses the energy just below it. If the spacecraft tilts, or drifts to the side, the light from the laser, hitting the underside, gets reflected in a slightly different place. In fact,
Re:high energy ? (Score:1)
Re:high energy ? (Score:2)
D'oh!
Thanks. Obviously, that was posted before I finished my morning cola.
Re:high energy ? (Score:3, Informative)
Reply: If the spacecraft tilts, or drifts to the side, the light from the laser, hitting the underside, gets reflected in a slightly different place. In fact, the simple geometry of the craft's underbelly guarantees that the focal point shifts just enough, in the same direction as the drift, that the next energy burst will nudge the spacecraft back onto the beam. So it's sort of self-correcting.
Of course
Re:high energy ? (Score:1)
Re:high energy ? (Score:1)
This as opposed to fossil fuels, which take quite a bit of time to produce. They are far more efficent than most forms of energy storage, but they are very hard to make, and therefore, not easily renewable. Of course, the sun will eventually burn out, but we might as well grab
Footfall (Score:2, Interesting)
Re:Footfall (Score:1, Interesting)
Google for the Orion Project - 50's concept of using atomic explosions to lift spacecraft
Re:Footfall (Score:2)
Didn't someone do this before? (Score:3, Informative)
The only problem was the projected G Forces were just too much for the human body, from what I remember.
Leik Myrabo (Score:3, Informative)
Re:Leik Myrabo (Score:2)
Re:Leik Myrabo (Score:1)
click here [rpi.edu]
click here [lightcraft...logies.com]
And BTW, this ~is~ the laser powered rocket n1ywb mentioned below. Myrabo pops up on the Discovery channel every couple of years. Unfortunately, his progress has been fairly slow. I read his book back when I was in Junior High. His big problem is using lasers. Both lasers and microwaves have their problems. I think it is a good idea, though, and I wish Dr. Myrabo luck. I recommend the book to NEone who is seriously interested in
Laser powered rocket (Score:4, Informative)
Anyway the laser "rocket" is actually a very lightweight aluminum puck about a foot in diameter, with a some funky curves. They shoot high powered laser pulses up its ass and that superheats the air underneith it, the expansion of which propells the rocket upwards. The pulses fire at about 500Hz so the damn thing sounds like a pulsejet. But at last check it reached an altitude of 71 meters and a flight time of 12.7 seconds. Microwave rocket eat your heart out!
Re:Didn't someone do this before? (Score:2)
I believe the problem they had there was the lack of a suitably powerful laser. They were using C02 lasers in the SciAm tests I believe.
What I wonder is if the deuterium flouride lasers the military has suggested for the MIRACL program would be of use. It seems that the problem with those was that they took a long time to recharge after lasing so perhaps not.
Probabl
The best part of this engine? (Score:3, Funny)
Rocket Equation (Score:5, Informative)
A propulsion system such as this can provide a tremendous reduction in required energy.
Conventional rockets, which carry their own fuel are large consumers of energy, as not only must they lift a payload into space but all the fuel as well. The total weight of a rocket including fuel is given by an exponential function known as the rocket equation. Stated simply, a rocket of mass m0 requires fuel of mass m1 to lift it; that fuel of mass m1 requires more fuel of mass m2 to lift it; the fuel of mass m2 requires fuel of mass m3; and so on, ad infinitum. The rocket equation is given by
m = m0 exp(Vf/Vex)
where m is the total required mass, m0 is the mass of the payload, Vf is the final velocity, and Vex is the exhaust velocity of the combusting fuel.
This exponential increase in initial mass can be huge. For example a low earth orbit requires a change in velocity, Vf, of about 8 km/s. Kerosine and liquid oxygen provide an exhaust velocity of about 2.5 km/s. Thus, m/m0 = exp(Vf/Vex) = 24.5. It would take 25 times the original weight of a given payload mostly in fuel to achieve a low earth orbit with kerosine and liquid oxygen! Assuming a payload of 1000 kg and an energy density of 10^7 J/kg for the fuel, the total energy would be E = (25*10^3 kg)(10^7 J/kg) =~ 250 GJ!
The wonderful thing about rockets that don't carry fuel with them is that there is no exponential dependency on initial mass. The energy required is simply the orbital energy, given by half the gravitational potential energy (derivation mercifully omitted) of the payload, given by E = -(G m0 M)/2r. The energy in this case, omitting concerns of efficiency, would be
E = (6.67*10^-11 Nm^2/kg^2)(5.98*10^24 kg)(1000 kg)/(2*6400 km) =~ 30 GJ
The savings in energy is almost a factor of ten!
Michael. [michael-forman.com]
P.S. - Lots of derivations late at night. Be merciful in the event of errors.
Re:Rocket Equation (Score:2, Interesting)
That's not actually true at all. For a few reasons:
a) some (a lot) of the energy ends up in moving the exhaust around (for example you have to throw it downwards to get thrust from it- unlike the case where you carry the fuel with you the propellent has to end up moving downwards, since it was stationary when you met it).
b) gravity
Re:Rocket Equation (Score:3, Insightful)
Good points.
However, the original post is a first-order approximation of the required energy. It is meant to highlight that one system's required fuel weight is exponential while the other's is not. Let's not let excessive details (which apply similarly to both vehicles) obfuscate the elegant simplicity of the rocket equation.
Your statement that a reduction in fuel by a factor of ten is not possible is very wrong. For a given orbit, provided exhaust velocities are equal, a rocket which does not car
Re:Rocket Equation (Score:1)
Re:Rocket Equation (Score:2)
The problem is that because it is such a heavy atom when you heat it, it ends up moving very slowly. By conservation of momentum, your rocket ends up moving much more slowly than if you had used hydrogen, or even nitrogen for the same mass of fuel (the fuel would be much denser, but still, it turns out to be a big, big loss).
Re:Rocket Equation (Score:2)
What statement? I said your calculation that you would only need 10% of the energy was bogus; and I stand by that. In externally powered airbreathing rockets as we are discussing here, the energy and the fuel are unrelated; or are only related by the trajectory you've chosen to use.
For a given orbit, provided exhaust velocities are equal, a rocket which does not carry its fuel will always use less fuel.
Trivially tr
Re:Rocket Equation (Score:2)
I don't think I'm going to hold my breath on this. You don't appear to know the difference between energy and fuel, and waving your hand like:
Let's not let excessive details (which apply similarly to both vehicles) obfuscate the elegant simplicity of the rocket equation.
Really doesn't cut it w
Re:Rocket Equation (Score:2)
Sir, it's bad form for a scientist to tell people that they don't know what they're talking about. If I am incorrect, exercise the option of teaching rather than insulting.
Anyway, since I don't want you holding (or refusing to hold your breath), I did a little research. For those, who are still interested, below is a wonderful set of links to websites that discuss the rocket equation. The second is my favorite. Enjoy!
Teachin' Science [mit.edu]
Rocket Equation Applet [spacetethers.com]
Wolfram [asi.org]
Michael. [michael-forman.com]
Re:Troll?? (Score:2)
microwave (Score:2, Interesting)
Re:microwave (Score:1)
that sounds dangerous. i don't want the same microwaves that cook my food(or even waves in the same spectrum) being beamed from over head just so i don't have to replace the batteries in my pda. it is stuff like this that makes me trust technology less and less.
i know that was off topic, but it is my two cents.
on topic, perhaps they could use a swarm of these(say
Yes it has been done already (Score:1)
I remember reading about this several years ago in a magazine. This is just one of the many articles ou there on the subject. I know they have sent the object up a couple hundred feet untethered.
There was also another article that used microwave power to gernerate a sort of force field around the nose of a space craft to remove drag and possible the shockwave. (Somethig spike was the name). Just some cool technologies that
Microwaves are problematic (Score:2)
Normally when microwaves are used for sending signals, for example satellite TV or point-point transmission, most of the power ends up missing the receiver, but the receiver amplifies the signal using power from the mains.
When you have a rocket, there's obviously no power cord ;-), so you need the vehicle to catch as much of the microwaves
Re:Microwaves are problematic (Score:1)
Re:Microwaves are problematic (Score:2)
Nah. Doesn't work. You have to be approximately 1 wavelength away for that to work, in this case we would be millions of wavelengths.
and once the "Rocket" is high enough, why not use more than one transmitter... have the transmitters arranged in consecutive circles.
Provided the rings are within a wavelength of each other; yup. Otherwise, nope; you get a horrible diffraction grating effect and most of the power slops around and probably takes out bystanders.
phtttt (Score:1)
network! (Score:1)
Microwaves to lauch objects? NOT (Score:1)