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I would be interested in getting some feedback on the
feasibility of the idea proposed below.
It's based on the fact that lift for aircraft can be higher than the thrust
for the craft, so why not use this to increase the acceleration produced by
beamed propulsion?
There are a few points I'm uncertain about. First, I was assuming that the
energy delivered to the craft would be much less than the amount emitted at
transmission because of the distances of 100's to 1000's of kilometers.
However, I take it after reading some beamed propulsion papers most of the
beam power will arrive at the vehicle because of focusing.
Still if you did reduce the distance by a factor of 10, could the power arriving at the vehicle be increased by a factor of 100?
Secondly, how much acceleration are the laser and microwave systems expected
to produce?
Thirdly, my analysis was only a preliminary one. The scenario is made more
complicated by the fact the vehicle has to stay oriented to keep the velocity
vector along the centerline of the vehicle. Then we would have to determine if
the control surfaces are sufficient to keep this orientation or would a
portion of the beamed propulsion thrust be needed. Additionally the path would
not be in a straight-line which would complicate the calculation of the thrust
and lift directions.
Here's one scenario in which this could be useful. I was trying to find a trajectory that would minimize the *straight-line* distance to a laser/microwave power trasmitter that nevertheless could provide a long distance of travel for a slow build up of speed. For this purpose I wanted the acceleration in the velocity direction to be low since I wanted the beamed power to provide this acceleration.
The obvious thing to try would be for the craft to travel in a circle and let
the beamed power just slowly build up the speed by the craft's going around
and around in a circle, while the distance to the transmitter stayed constant.
Let's say you wanted the radius to be no more than 100 km say, much shorter
than the 2000 km or so horizontal distance required for the space shuttle. But
if you wanted the final speed to be say 7000 m/s then the radial acceleration
would be v^2/r = 7000^2/100,000 = 49,000,000/100,000 = 490 m/s^2, about 49
g's. But then you're in a worse situation than before because of the high
power required to maintain this acceleration IF this high acceleration were
provided by the beamed power system.
So the idea is not to use the beamed power for this radial acceleration but
instead to provide this by the lifting force. Note that this lifting force
would be radial since it is perpindicular to the velocity vector.
So the idea would be for the beamed power to provide a little more
acceleration than the drag so there would be a slow, gradual build up of
speed around the circle and even at a maximum speed of 7000 m/s, the beamed
power would only have to provide 1/8 the acceleration provided by the lift or
49/8, about 6 g's.
Bob Clark
=========================================================
From: Robert Clark
Date: Fri, Jun 30 2006 6:17 pm
Email: "Robert Clark" <rgregorycl...@yahoo.com>
Groups: sci.astro, sci.space.policy, sci.physics
Subject: Re: Using lift to increase speeds.
William.M...@gmail.com wrote:
> Orbital speed is where centripetal force equals gravity force and is
> given by;
> v = sqrt(GMe/r)
> Which can be derived from the following three equations;
> F = G*m*Me/r^2 - gravitational force
> a = v^2/r - centripetal acceleration
> F = ma - relating mass and acceleration
> a = F/m = GMe/r^2 - gravitational acceleration
> a = v^2/r - centripetal acceleration
> Setting the two accelerations equal
> v^2/r = GMe/r^2
> v^2 = GMe/r
> v = sqrt(GMe/r)
> If we increase velocity by 41.4% we double the centripetal
> acceleration, which means that if we were to fly an aircraft at Mach 33
> we'd need wings to hold it in the atmosphere! Since wings lift
> aircraft all the time against gravity, it seems reasonable to believe
> that wings could hold an aircraft down. Everything would seem quite
> normal to the occupants, except down would be up to them, and the lift
> would be directed toward the Earth's center.
> The vehicle if possible would be capable of circumnavigating the Earth
> in 60 minutes - and delivering payloads to targets anywhere in 30
> minutes or less.
> Would such a craft be possible?
Yes. I speculated about this possibility for the use with beamed
propulsion:
From: Robert Clark
Date: Sat, Nov 19 2005 2:23 pm
Email: "Robert Clark" <rgregorycl...@yahoo.com>
Groups: sci.astro, sci.physics, sci.math
Subject: Math question for the trajectory of beamed propulsion.
http://groups.google.com/group/sci.astr … 32000ef7f7
This would also be applicable to the scenario where electrical power
for propulsion is transmitted though long cables:
From: Robert Clark
Date: Fri, May 27 2005 12:10 pm
Email: "Robert Clark" <rgregorycl...@yahoo.com>
Groups: sci.astro, sci.space.policy, sci.physics,
sci.electronics.design, sci.electronics.misc
Subject: Re: Long cables to power "ioncraft" to orbit?
http://groups.google.com/group/sci.astr … 463e87dde6
The problem is that though the height to orbit might be 100 km, the
horizontal distance travelled might be 2000 km in order to build up
sufficient speed for orbital velocity.
The proposals for beamed propulsion I've seen though do not use
lifting surfaces for the craft:
Riding Laser Beams to Space.
http://www.space.com/businesstechnology … 00705.html
However, the lift to drag ratios at hypersonic speeds suggest we might
be able to increase the thrust and therefore the acceleration by
several times if the craft was designed for aerodynamic lift. See the
graph showing lift to drag ratio versus Mach number here:
Waverider Design.
http://www.aerospaceweb.org/design/wave … ider.shtml
With airplanes you have the thrust directed horizontally to overcome
the drag force against forward motion and the lift provides the force
to keep the airplane aloft. Since subsonic L/D ratios can be 15 to 1
and higher the thrust required from the engines is much less than the
actual weight of the plane.
However, with beamed propulsion a key problem is the dimunition of the
power with distance, which decreases with the square of the distance so
you want to keep the distance short. The idea then in this case using
aerodynamic lift would be to use the thrust produced by the beamed
propulsion to overcome gravity and drag and use the lift force to
provide the higher acceleration to reach orbital velocity in a shorter
distance. Essentially the craft would be pointed upwards so that the
wings/lifting surfaces provide the "lift" in the horizontal direction.
The graph on the "Waverider Design" page shows the L/D ratio can be
about 7 to 8 at hypersonic speeds. For instance if the beamed
propulsion provided a thrust of 1 g to counter gravity plus 4 g's
against drag for a total of 5 g's in the vertical direction, then the
horizontal acceleration could be as much as 8*4 = 32 g's.
Note though it would be important to keep the craft oriented so that
so that the velocity vector is always pointed through the forward
centerline of the craft. When lift and drag calculations are made it's
always in regard to the craft moving so the airstream is flowing more
or less parallel over the wings/lifting surfaces, according to angle of
attack. If instead the airstream was flowing perpindicular to the plane
of the wings the lift would be much less and drag would be much greater
so the L/D ratio would be severely reduced. The aerodynamic control
surfaces would be used to keep the craft properly oriented.
Estimates for beamed propulsion are about 1 megawatt of power to send
1 kilogram to orbit. If say such beamed propulsion provided thrust for
5 g's of acceleration then the lifting force could provide 32 g's, or a
factor of 6 more. So the distance required would be smaller by a factor
6. This means the power required would be smaller by a factor 6^2 = 36.
Then 36 times greater mass could be lifted for the same power. This is
dependent though on how much acceleration beamed propulsion could
provide. If it were 7 g's then the lifting acceleration would be 8*6 =
48 g's, about a factor of 7 more. Then the power required would be less
by 7^2 = 49, and 49 times greater mass could be lifted.
There are apparently megawatt class lasers already in operation:
Mid-Infrared Advanced Chemical Laser (MIRACL).
http://www.fas.org/spp/military/program/asat/miracl.htm
Let's say they are at the 10 megawatt stage now. Then this could
accelerate 10 kilos to orbit. Then with aerodynamic lift it could lift
perhaps 360 kilos to orbit, which is the size of a small sized
satellite.
Bob Clark
============================================================
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So the idea is, if I get this strait to use beamed energy to push a waverider shaped airplane strait up or away from the transmiter, and then use the lift to change this foce into force acellerating the craft in a forward direction? What is the advantage of this? Since you are staying in the atmosphere the drag is going to be increadable, even with a waverider, unless you are plaining to use some kind of exotic plasma drag reduction device, which would probably interfer with the beamed energy. What you seem to be trying to get around is the fact that it takes 30420 kJ/kg to get to orbit. Since you cannot beam that much power in a short rocket launch period of time, you have to:
a) break the laws of physics
or
b) accellerate slowly
Acelorating slowly will be actually way more ineffect than going quick because you will have to stay in the atmosphere and the drag is going to be too high. Even if you are using some kind of wing to change your direction to horazontal, you are not going to be able to produce extra energy, infact there will probably be a loos due to ineffecencies. 10 megawatts are not enough for 360 pounds, you would need to run it for 18 minutes. With a typical hypersonic Cd of 0.1 you have for drag at 25 km up (probably unrealistically high) and an area of a square meter (very small) = (0.5) (0.1) (1) (0.04) (7800) (7800) = 121680 newtons of drag. The energy calculations were considering no drag and needed a constant thrust of about 3000 newtons. I don't think this idea will work the way I understand it.
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So the idea is, if I get this strait to use beamed energy to push a waverider shaped airplane strait up or away from the transmiter, and then use the lift to change this foce into force acellerating the craft in a forward direction? What is the advantage of this? Since you are staying in the atmosphere the drag is going to be increadable, even with a waverider, unless you are plaining to use some kind of exotic plasma drag reduction device, which would probably interfer with the beamed energy. What you seem to be trying to get around is the fact that it takes 30420 kJ/kg to get to orbit. Since you cannot beam that much power in a short rocket launch period of time, you have to:
a) break the laws of physics
or
b) accellerate slowly
Acelorating slowly will be actually way more ineffect than going quick because you will have to stay in the atmosphere and the drag is going to be too high. Even if you are using some kind of wing to change your direction to horazontal, you are not going to be able to produce extra energy, infact there will probably be a loos due to ineffecencies. 10 megawatts are not enough for 360 pounds, you would need to run it for 18 minutes. With a typical hypersonic Cd of 0.1 you have for drag at 25 km up (probably unrealistically high) and an area of a square meter (very small) = (0.5) (0.1) (1) (0.04) (7800) (7800) = 121680 newtons of drag. The energy calculations were considering no drag and needed a constant thrust of about 3000 newtons. I don't think this idea will work the way I understand it.
Thanks for the response. Any feedback helps me flesh out the idea.
The idea is indeed counter-intuitive because it seems to be saying you want there to be drag. This is indeed the case but the reason is because it's using the fact that the lift will be about 8 times this drag according to the data suggesting the hypersonic lift/drag ratio can be 8 to 1 for waveriders.
The nice thing about beamed propulsion is you can provide as much energy as you want (reasonably). For instance, if you need 10 megawatts to launch 360 kilos (not pounds) then you can have your own dedicated gas turbine electricity generator and run it as long as you wish, 18 minutes or whatever. If the drag required 10 times as much energy you just run the generator for 180 minutes.
The cost of gas turbines is in the ten's of millions for megawatt class generators. The fuel cost to run the generator is actually less than what you would pay for electricity off the grid. Look at GE's web site for gas turbines for example. And remember the turbine will be used to provide the power to launch multiple payloads so can quickly pay for itself.
You're calculations are correct for the drag at 25 km:
Drag (physics)
http://en.wikipedia.org/wiki/Drag_%28physics%29
The formula is one-half the coefficient of drag, times the area of the lifting surface, times the air density, times the square of velocity.
However, an altitude of 25km might be alright for a hypersonic scramjet, but you don't have to keep the craft at that low altitude for getting it up to speed when you're using beamed propulsion.
Let's look at the scenario I suggested where the craft is travelling in a circle. Here it is propelled by the beamed power to have thrust that would amount to an acceleration of about 6 g's in the tangential direction and this is supposed to be a little above the drag. But this 6 g's can also be applied to propel the craft upward initially to high altitude. Here we're not trying to get the craft to high speed just high altitude. So we can make it move slowly upward if we wish to keep the drag low.
(You might also want to use a combination of the beamed thrust and the lifting force, especially since the L/D ratio is even better at low speeds. It's just that for the discussion here the calculation of the trajectory is more complicated when it's not moving in a circle.)
Let's move it to say 75,000m, 75 km. My reference gives the air density at that altitude as 3.5x10^-5 kg/m^3. So the drag force would be less than a thousandth of the amount at 25 km, around 100 newtons. You could then use 1 g of the beamed power or 1 g out of the lifting force to keep the craft at the high altitude while it is being accelerated in the circle.
Actually though you don't want to make the drag too low since that would also make the lifting force low and you wouldn't get enough force to keep the craft in a circle.
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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Okay, I think I have a better idea of what you are talking about now. You are running a laser powered scramjet in a circle and keeping it in a circle by using the lift from wave rider shape. Unfortunately, I don’t think it's going to work. If you cannot increase the radius over 100 km because of focusing and air diffraction you will need 219024 newtons of lift to stay on track at 7800 m/s. Given a hypersonic l/d of 8 your drag must be 27378 newtons, or nine times the theoretically needed thrust. Incidentally, I had the same idea as you awhile back, but was discouraged by the centripetal force requirements for people, which is another issue. Even if the lift of your wave rider can keep you in a circle, the gee's are going to be enormous, probably greater than any electronics can take.
edit: saw another issue, your 10 megawatt output laser can only provide so much thrust, so if the drag is too large you will accelerate until your thrust equals drag and then hold steady. Peak power has a role to play as does the total amount of energy. By the way, how are you planning to change the laser energy into thrust? Laser thermal rocket?
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Yeah, this isn't going to work. The SR-71 Blackbird, at its Mach 3.0-3.5 speed, took about 500km to complete a turn, and its skin was too hot to touch. So hot that it had to be made from Titanium.
Reguardless what schema you use to turn in circles about the transmitter site, the g-forces will always be far too high for a reasonably wide turn radius. 50G is ten times what humans can withstand for any length of time, would pulverise delicate equipment, and probably snap the wings off. The only devices that man uses with any regularity that make 50G turns are anti-aircraft missiles which don't use wings for lift.
The whole reason you are turning is to give you plenty of time accelerate to orbital velocity slowly so that the g-forces are not a problem, right? The solution to this problem is simple: don't turn. Have multiple transmitter sites strung along the equator.
The heating will also be a huge problem, Scramjet airplanes like the X-30 or the X-43, were they to accelerate nearly to orbital velocity using their air-breathing engines, would absolutely need active cooling. This cooling would be provided by the ultra-cold ultra-light hydrogen fuel, which you wouldn't be carrying on a beamed power vehicle. Even if you did, bulky tanks of reasonable mass for it would crumple under the g-forces like an egg shell getting stomped on.
As pointed out, reguardless what method you use to turn, turning requires energy. Lots of energy. The "lift" force is not for free. Surely the added need for energy to provide lift and overcome drag/heating cannot be worthwhile.
An air-breathing engine will be much like a combustion scramjet, except with a "window" to admit microwaves or an absorbant for a laser beam, but is all this trouble really worth not carrying fuel?
Building transmitters powerful enough and cheap enough will be a problem too. Chemical lasers would expend tonnes of expensive/nasty chemicals for every launch (Deterium, Fluorine gas), microwave power is the obvious choice.
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I see only one way to make something like this work, and it's quite speculative. If mutiple microwave transmiters could be placed around the equator and an electric rocket (variant on the mpd/arcjet) could be made powerful enough, then the hypersonic aircraft could tow a wire recttena while using a UV laser/arc heater to reduce the drag.
http://www.physics-math.com/aero/drag_r … 4_0984.pdf
However, this is getting complex and expensive, probably no longer an advantage over a rocket.
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Something like that... it would be difficult to get the vehicle up high enough and make a transmitter with range enough to avoid the need for a floating (and hence difficult to aim with accuracy) transmitter.
One difference though, drop the MPD thruster and stick with microwave/thermal, there is no way to get enough thrust otherwise. Thermal propulsion of some sort is the only game in town for launch. Not too sure about this towed reciever array either.
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Just now getting to read this thread and I am wondering if just creating verticle lift as a first stage but using the beam to create the force to raise the ship, not a plane would be a better way of getting to orbit.
I believe nasa has done some work on forces of laser pushing a small demonstrator but the problem is the temperature of the laser striking the target and the disipation of its beam reaching the craft.
Now would microwave beamed energy suffer the same problems of convertion to power for whatever engines we might make use of to create the first stage of a rocket.
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There are two ways to used beamed power for launch:
-Use the beam to heat onboard propellant
-Use the beam to heat & expand air to make thrust
In the former, you still have all the trappings of a regular rocket (fuel, tanks for it, pumps) and a specially shaped engine. Using Hydrogen, you can get efficiencies about double normal chemical engines, comperable to simple nuclear engines. You can get full thrust the minute you start the engine, though consumes a huge amount of power.
The other is really only suited for airplanes that spend much of the acent in the atmosphere, since without air you have nothing to push. These would perhaps be more efficent than rockets, but you have to carry wings and deal with air drag. Practical beam-powerd air breathing engines can't "start up" easily until reaching high speeds. The ones used in the NASA demonstration produced very little thrust.
Both methods share the problem that since the Earth is curved, the beam station on the ground can't stay locked on the vehicle for very long, so the vehicle has to accelerate to orbital velocity quickly. This means you have to have an extremely powerful beam generator, the vehicle itself has to have a large engine, and perhaps worst of all the g-forces from the acceleration have to be very high. Multiple beam generators might help, but coordinating, siting, and building them would be difficult.
Both share the problem that the further you get from the transmitter, then more difficult it is to catch the beam. This problem is worse for rockets that acend to altitude fast, while airplanes stay down low longer, though a single beam could remain trained on a rocket longer since an airplane would go over the horizon sooner.
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Yeah, I said electric propulsion because I think the plasma drag reduction device would absoarb the mircowave energy if it was aimed to close, although if the waverider shape is optimised for mach 25 it may be long enough to get by without a towed recctenna. I belive the bigest problem with microwaves is their inability to focus on a tight spot, they need a large reciver
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Okay, I think I have a better idea of what you are talking about now. You are running a laser powered scramjet in a circle and keeping it in a circle by using the lift from wave rider shape. Unfortunately, I don’t think it's going to work. If you cannot increase the radius over 100 km because of focusing and air diffraction you will need 219024 newtons of lift to stay on track at 7800 m/s. Given a hypersonic l/d of 8 your drag must be 27378 newtons, or nine times the theoretically needed thrust. Incidentally, I had the same idea as you awhile back, but was discouraged by the centripetal force requirements for people, which is another issue. Even if the lift of your wave rider can keep you in a circle, the gee's are going to be enormous, probably greater than any electronics can take.
edit: saw another issue, your 10 megawatt output laser can only provide so much thrust, so if the drag is too large you will accelerate until your thrust equals drag and then hold steady. Peak power has a role to play as does the total amount of energy. By the way, how are you planning to change the laser energy into thrust? Laser thermal rocket?
It's not that power transmitters can't send the energy further than 100 km, that's just a distance less than the ones I've seen in beamed propulsion reports. It's also much less than the distance required for the shuttle for example.
Why do you say the theoretically required thrust is 1/9th of 27,378 newtons or about 3000 newtons?
The proposal was only intended for payload launch. The accelerations are indeed too high for people.
Bob Clark
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I believe the acceleration is too high for any mechanical/electronic cargo, and unless the vehicle is built like a submarine or a bunker it cannot possible withstand the acceleration either.
With microwave power, its superior efficiency lets you get away with some loss, so keeping a very tight focus isn't quite as critical.
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Yeah, this isn't going to work. The SR-71 Blackbird, at its Mach 3.0-3.5 speed, took about 500km to complete a turn, and its skin was too hot to touch. So hot that it had to be made from Titanium.
Reguardless what schema you use to turn in circles about the transmitter site, the g-forces will always be far too high for a reasonably wide turn radius. 50G is ten times what humans can withstand for any length of time, would pulverise delicate equipment, and probably snap the wings off. The only devices that man uses with any regularity that make 50G turns are anti-aircraft missiles which don't use wings for lift.
The whole reason you are turning is to give you plenty of time accelerate to orbital velocity slowly so that the g-forces are not a problem, right? The solution to this problem is simple: don't turn. Have multiple transmitter sites strung along the equator.
The heating will also be a huge problem, Scramjet airplanes like the X-30 or the X-43, were they to accelerate nearly to orbital velocity using their air-breathing engines, would absolutely need active cooling. This cooling would be provided by the ultra-cold ultra-light hydrogen fuel, which you wouldn't be carrying on a beamed power vehicle. Even if you did, bulky tanks of reasonable mass for it would crumple under the g-forces like an egg shell getting stomped on.
As pointed out, reguardless what method you use to turn, turning requires energy. Lots of energy. The "lift" force is not for free. Surely the added need for energy to provide lift and overcome drag/heating cannot be worthwhile.
An air-breathing engine will be much like a combustion scramjet, except with a "window" to admit microwaves or an absorbant for a laser beam, but is all this trouble really worth not carrying fuel?
Building transmitters powerful enough and cheap enough will be a problem too. Chemical lasers would expend tonnes of expensive/nasty chemicals for every launch (Deterium, Fluorine gas), microwave power is the obvious choice.
The energy for the lift force is coming from the same place as it does for subsonic airplanes and supersonic jets. The thrust for these cases is never enough to hold the airplane aloft. The weight is always several times the thrust provided by the engines. The force to raise the aircraft is provided by the lift.
The turn radius for the SR-71 Blackbird was about 150 km at Mach 3, which means a circle 300 km across. But remember all aircraft when turning use a banking maneuver. This allows some of the lift to keep the airplane aloft while some of the lifting force contributes to the turn.
I'm proposing having the wings be 90º to the horizontal. This means the entire lifting force is used for the turn. The thrust to keep the vehicle aloft could be taken by 1 g from the beamed propulsion thrust. Normally, an airplane won't bank at 90º because you want to make a level turn where you're not losing altitude. However, if you've seen aerobatics you'll observe these aircraft can make much tighter turns when they're banked at 90º. The control surfaces for these aerobatic craft are designed to be able to provide sufficient vertical upward direction to the craft to keep the craft aloft. It may be since you only need 1 g of upward thrust, control surface here as well could keep the craft aloft.
Also, I'm considering having the proportions of the craft change as you increase in Mach number. From the hypersonic waverider page you see the shape is for a much slimmer craft to achieve high L/D ratio at the higher Mach numbers. This would be analogous to the swept wings on the F-14 fighter/bomber. Then you might have a "bending body" as well as a lifting body where it curves in the middle so the entire body becomes a control surface.
The proposal is not to launch manned craft. The g forces are too high. Electronics such as on satellites can be hardened to survive thousands of g's, much more than the tens to hundreds of g's required here. This has been demonstrated by gun launched missiles and rockets.
The waverider shape is that of a flattened cone. There are not wings sticking out. This would make it much easier for the airframe to survive the g forces.
Some versions of beamed propulsion do use hydrogen as fuel. In these cases this could be used for cooling. The space shuttle survives the high temperatures of reentry at Mach 25 at least for a few minutes by using lift. This would also be used in this proposal. Thermal protection materials now are more advanced than when the shuttle was designed to extend the length of time these materials can withstand the high temperatures.
You would indeed reduce the power and cost for each transmitter if you had several of them strung out some distance apart. But this would involve a total cost more that just using a single transmitter.
The purpose of the proposal was to reduce the power and cost required for a transmitter for beamed propulsion, which is too high for a moderately sized satellite. I believed using this proposal, the megawatt sized lasers already in existance have sufficient power to launch medium sized satellites.
Bob Clark
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I said thrust of 3000 newtons for a total flight time of 18 minutes, refering to my last example. If you are not changing the radius of the circular path past 100 km, I don't think it's possible simply because of the energy required to keep a circular path. You can see for yourself right here http://hyperphysics.phy-astr.gsu.edu/HBASE/cf.html. The calculator is handy for doing things quickly. The frontal drag with a l/d of 8 is still 219024 newtons. If you are using a laser themal rocket so as to use hydrogen to cool the craft a reasonable specific impulse would be 900 to 1200 sec, that would be with a rotating drum of hafnium carbinaide pellets. if we taak a middle value of 1000 sec that gives us a rough exahust velocity of 10000 m/s. To throw 20 kg of hydrogen out the back, roughly enough to equal drag uses x watts - x = (0.5)(20)(10000)(10000) the wattage nessisary is 1 gigawatt, too much to beam realistically, and that only equals the drag. Plus using hydrogen fuel you are going to need a lot throwing 20 kg out a second. With a 360 kg payload you need (2.71^[7800/10000])(360). Thats 783.46 kg of fuel which has to be added into the centripical foce equation meaning that the drag must be higher still, though most of it will be gone at topspeed. An airbreathing engine is probably unworkable because of the heating. That 219024 newtons of drag is turned into heat, and over a long acelleration due to the finite power of the trasmiter will probably melt most ceramics. The only way you can use long accelloration is if you have low low drag.
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I said thrust of 3000 newtons for a total flight time of 18 minutes, refering to my last example. If you are not changing the radius of the circular path past 100 km, I don't think it's possible simply because of the energy required to keep a circular path. You can see for yourself right here http://hyperphysics.phy-astr.gsu.edu/HBASE/cf.html. The calculator is handy for doing things quickly. The frontal drag with a l/d of 8 is still 219024 newtons...
I think you interchanged lift and drag here. The radial acceleration is a = v^/r = 7800^2/100,000 = 608.4 m/s^2. So for a 360 kg body, the force would be 219,024 newtons. This is what would be provided by the lift force. So with an L/D ratio of 8 to 1, the drag would be 1/8th of this or 27,378 newtons.
Bob Clark
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Yes you are right I pasted in the wrong number. The total power output would only need to be a meissly 100 megawatts to equal drag, throwing out about 2 kg of hydrogen a second. Unfortunatly that''s still a lot of drag and a huge amount of beamed energy. You have another problem with laser energy "70 seconds maximum lase duration" is a quote from the webpage you posted a link to. That's not much time to go from 0 to mach 25.
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The energy for the lift force is coming from the same place as it does for subsonic airplanes and supersonic jets. The thrust for these cases is never enough to hold the airplane aloft. The weight is always several times the thrust provided by the engines. The force to raise the aircraft is provided by the lift.
The turn radius for the SR-71 Blackbird was about 150 km at Mach 3, which means a circle 300 km across. But remember all aircraft when turning use a banking maneuver. This allows some of the lift to keep the airplane aloft while some of the lifting force contributes to the turn.
I'm proposing having the wings be 90º to the horizontal. This means the entire lifting force is used for the turn. The thrust to keep the vehicle aloft could be taken by 1 g from the beamed propulsion thrust. Normally, an airplane won't bank at 90º because you want to make a level turn where you're not losing altitude. However, if you've seen aerobatics you'll observe these aircraft can make much tighter turns when they're banked at 90º. The control surfaces for these aerobatic craft are designed to be able to provide sufficient vertical upward direction to the craft to keep the craft aloft. It may be since you only need 1 g of upward thrust, control surface here as well could keep the craft aloft.
Also, I'm considering having the proportions of the craft change as you increase in Mach number. From the hypersonic waverider page you see the shape is for a much slimmer craft to achieve high L/D ratio at the higher Mach numbers. This would be analogous to the swept wings on the F-14 fighter/bomber. Then you might have a "bending body" as well as a lifting body where it curves in the middle so the entire body becomes a control surface.
The proposal is not to launch manned craft. The g forces are too high. Electronics such as on satellites can be hardened to survive thousands of g's, much more than the tens to hundreds of g's required here. This has been demonstrated by gun launched missiles and rockets.
The waverider shape is that of a flattened cone. There are not wings sticking out. This would make it much easier for the airframe to survive the g forces.
Some versions of beamed propulsion do use hydrogen as fuel. In these cases this could be used for cooling. The space shuttle survives the high temperatures of reentry at Mach 25 at least for a few minutes by using lift. This would also be used in this proposal. Thermal protection materials now are more advanced than when the shuttle was designed to extend the length of time these materials can withstand the high temperatures.
You would indeed reduce the power and cost for each transmitter if you had several of them strung out some distance apart. But this would involve a total cost more that just using a single transmitter.
The purpose of the proposal was to reduce the power and cost required for a transmitter for beamed propulsion, which is too high for a moderately sized satellite. I believed using this proposal, the megawatt sized lasers already in existance have sufficient power to launch medium sized satellites.
You make it sound like lift is some free force that isn't subject to the normal laws of thermodynamics, which is obviously not the case. You must simply have a poor understanding of the thermodynamics of flight. All energy for all motion must ultimately come from propulsion.
Having a vehicle that "changes proportions" would be extremely difficult given how hypersonic aircraft must be carefully shaped or a vehicle with wings sticking out that withstand 50G's without snapping off isn't happening. Even hiding behind the shockwave, I doubt that even swing wings' delicate structures would be sufficently protected either.
Having to design all systems to withstand ~50G+ is insane, it is possible to do this but it just isn't practical, anything delicate would simply not survive, not just electronics. Remember, they must not survive only one acceleration, but many if your vehicle is to be reuseable. Missles and cannon shells, obviously, do not. Even providing that your vehicle could withstand it, placing these restrictions on the payload is crazy for the limited bennefit your scheme has.
A "waverider" shape without wings sticking out couldn't get off the runway at subsonic speeds, and if you are going to use rocket/jet power of some sort for takeoff how will you develop fuel tanks able to resist the incredible g-forces while not being fantastically heavy?
And the cooling problem is a serious problem, your vehicle must stay in the atmosphere until it approaches orbital velocity to take advantage of lift, there are no materials known or near at hand that could possibly protect the vehicle completly passively. Active cooling is absolutely required, and active cooling of a "reconfigurable" vehicle would be fantastically difficult.
Comparisons with Shuttle are simply wrong, Shuttle's speed drops substantially before it ever reaches the lower atmosphere, plus it decelerates fairly quickly to lower Mach numbers. During the early part of decent, it doesn't use aerodynamic lift from its wings at all, instead coming down "belly first." Your vehicle, on the other hand, will be accelerating to these speeds while still in fairly dense atmosphere and do so gradually as you have stated previously in your proposal.
Putting asside all the details for a moment, taking in the big picture and not getting bogged down on any little things...: How can any of this be worth it? Big vertical fins for spiraling acent? Superhigh g-forces to stay near a transmitter? Cooling the vehicle in the lower atmosphere at orbital velocities? Rediculous restrictions on delicate hardware? All this, for what? To reduce the power requirements for a transmitter a little?
This is all endemic of going to a rediculous amount of trouble to save a little headache (a common affliction with aerospace engineers, see Bob Zubrin), when it will obviously be much harder to make such a vehicle then it would to build a bigger/network of smaller transmitters. For goodness sakes, just build more/bigger transmitters! A network of smaller ones solves so many problems, no turning, more time to accelerate (less power each), reduced line-of-site problems.
Laser power is also definatly out, the "megwatt class" lasers you cite are usually chemically powered and are not very practical for launch use. Not to mention they are far too small, you need gigawatt-class power levels for such a vehicle, since a good amount of it will never become propulsive force and you have to lug your entire multi-use-50G-Mach 25-withstanding airplane to orbit with the satellite. Phased-array microwave transmission is the obvious choice: efficient, easy to focus, easy to deploy, no moving parts.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I wonder if beamed energy propulsion might be a good fit with an Airship to Orbit concept. First to power ion wind and then to push it up.
I might launch the ATO bigelow fashion atop Ares and coat it with some UV material to give it a super thin shell.
it my be that Leiks craft is the only way to us beamed energy.
Frankly--its best to just stick with big rockets.
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I think that making the airship to orbit use beamed energy would be more trouble than it's worth. Stringing transmitteres around the equator would be a huge amount of truble and a 6 km ship dosent turn well.
Ad astra per aspera!
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You are probably right.
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We have been talking recently of just this topic in how do we get power to something that is moving and or for how to connect not directly for the intent of supplying energy for use.
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