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JoshNH4H,
By all means, knock away. I asked people to pick this idea apart and that's what I expect. I'm just trying to explain the concept, as best I understand it and the math involved in the power transmission. Someone else came up with the beamed power idea, I just want to alleviate the distance problem that occurs by trying to launch from a fixed point on the ground. I'm doing a lot of reading because this is far outside what I know anything about. Apparently Tokyo University has done some sub-scale experiments with this concept using those Gyrotrons that Toshiba built. I just found out this evening that they had the same general idea I did regarding using a carrier aircraft. My wife said she thinks she knows which division produces them and will try to obtain a price quote. If these gyrotrons are $10M a pop, then this idea is probably a no-go on initial costs alone.
Although beam aiming could be accomplished in any number of ways, using the vehicle's IR signature is probably the best method.
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Hey kbd512,
I feel like I can neither knock the idea nor comment on its price because there's something fundamental about how it works that I don't understand.
The thing that I don't understand is how the power generated is focused and targeted at the craft.
So if you imagine for a second a solar thermal rocket, which is in some ways similar to beamed propulsion. The issue with this form of rocket travel is that because the Sun is so far away and shines in all directions, sunlight is fairly diffuse and it has been diluted beyond the point of usefulness by the time it reaches the craft.
This is what I don't understand about your idea: You're generating the electricity with gas turbines. You're creating the microwave with commercial high-powered microwave generators. The microwaves heat up metallic elements in the spacecraft that are used to heat and expel Hydrogen.
What means are you using to focus the microwaves to a small angle of emission so that they neither dilute past the point of usefulness nor turn everything in the vicinity to smoldering ashes?
-Josh
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Having done a little bit of googling, it seems that the answer to my question is that the devices you're using are in fact a form of maser, and emit radiation naturally in a relatively tight beam. Is this correct?
-Josh
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JoshNH4H,
A maser could operate over the EHF band, but I don't know what benefit using a maser vs a vacuum electronic device with a linear output (gyrotron) would provide. All experiments I'm aware of have used high power gyrotrons.
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Based on doing some reading, a gyrotron is a type of maser. But the semantics don't really matter.
You said these are catalogue items. Does the catalogue specify the efficiency of the device? How about the angular spread of the beam it produces?
-Josh
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Governments have been trying for years to get sharply focussed lasers or masers to work in our atmosphere. It ain't easy. Otherwise every defence department would have deployed them by now and nobody would be scared of other folks' missiles.
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JoshNH4H,
I always thought masers were using matter, like a gas, to amplify a wave at a frequency specific to a particular type of matter, whereas a gyrotron was an electron gun shot into a cavity resonant at some specific frequency, but I guess a gyrotron is also considered to be a free electron maser. In any event, my understanding is that high efficiency gyrotrons recycle the beam and feed it back into the cavity. The efficiency of a gyrotrons that MIT worked on were improved to greater than 50% using a better cavity and collector design. The catalogue I was looking at was from CPI's Microwave Products Division.
You were right about the efficiency of these things. The 1MW 170GHz Toshiba model's output efficiency is only 60%, but it sustained 1MW output for 800 seconds and .8MW for 1 hour and that was in 2012. A Russian 170GHz design achieved 55% efficiency for 1,000 seconds. The efficiency seems to drop as a function of the pulse duration, but the pulse durations required to achieve orbital velocity are within the capability of current gyrotrons. Basically, we know how to build these things and make them work for durations longer than the acceleration periods required. There's work being done by Karlsruhe Institute of Technology (KIT) on a considerably smaller but still heavy 2MW 170 GHz 45% efficient model for ITER and initial design work is being done on 4MW gyrotrons. That should considerably reduce the number of pieces of hardware that have to be procured.
Here's a link to KIT's Gyrotron:
A single power facility would require 6 Combined Cycle GE 7F's, not the 4 I originally thought it did based on a 1GW output requirement. The total number of gyrotrons required is still 2,000 to output 2GW, but successful demonstration of 2MW continuous wave gyrotrons could cut that number in half. My initial idea was to use two facilities, but air launching the drones 100km inbound to the power facility would keep the drone within 100km of the power facility throughout its acceleration phase. The beam breakdown distance at 300GHz is 200km for a sea level facility. I want to half the distance to the drone and move the power facility to a location that's a mile or two above sea level.
I finally found the weight of these JAERI-Toshiba 1MW 170GHz gyrotrons. They weigh about 700kg each, so mounting enough of them to produce usable power in an aircraft of any kind is unlikely. However, they're small and light enough to deliver to orbit using a drone with a 1,000kg payload and the 2MW KIT models are substantially smaller than the 1MW Toshiba-JAERI TA31.
The units that Toshiba produced for ITER were considered to be some of the most efficient available at the time they were built, but MIT's improved cavity and collector designs doubled their efficiency over about 10 years. The Chinese, Europeans, Indians, Japanese, and Russians all submitted gyrotron designs for consideration for the ITER contract and development work continues. I think some Swiss group has a spreadsheet on the net with the ITER contract costs in it. Maybe we can extrapolate what these things would cost using that.
What's the verdict? Workable with more application development funding, or not?
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I'd say probably workable, but more challenging that you've made it out to be. I'm still not sold on the aiming, for example. I would expect losses to be pretty high between geometric dispersion, atmospheric effects, and pointing inaccuracy. It's hard to give numbers, though
-Josh
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Another potential hitch (or at least something that needs to be specified and designed) is how exactly the microwaves are used to heat the elements in the engine that will be used to heat the hydrogen. Will it be an electrical system? Some kind of optical system? How will you deal with the diffusion of the beam on the rocket end?
-Josh
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I think that beamed propulsion is fundamentally a good idea, so I'm going to dig into kbd512's idea a little more to look into its strengths and weaknesses. To start, here's a sequence of events for how a launch would go as I understand it:
Carrier plane launches containing a payload of some number of rockets
100 km West of beaming array, moving in the 100 m/s-200 m/s range, carrier plane releases payload and flies away
Beaming array turns on and focuses on the rocket. Rocket undergoes high acceleration as it moves eastbound over array
Beaming array tracks rocket until it has transferred sufficient energy for rocket to reach orbit
Rocket potentially is tracked by a second beaming array as it moves out of range of the first
Rocket coasts to orbit and fires small thruster for circularization and/or deorbit
In principle, it's a strong concept. This is definitely a workable outline and there are no physical limits that I'm aware of that make it impossible. It's something that I've supported for a long time in principle and I want to see it work. Having said that, my natural inclination is to take an idea and criticize it with everything I've got, to see how well it can hold up.
So let's dig in.
I would say that the single biggest issue for beamed propulsion in general is the losses that happen between the beaming array and the target. Like I said earlier, these losses come in three forms: Geometric dispersion, pointing inaccuracy, and atmospheric effects.
Let's spec this out, to start. The ship will necessarily be fueled by Hydrogen (high Isp with thermal transfer through a solid). Given the estimates I made earlier in this thread, the 1 tonne ship will carry 6,300 kg of Hydrogen. At a density of 70 kg/m^3, this is 90 cubic meters of propellant. If your fuel tank is one sphere, it will have a diameter of 5.6 m and a cross-sectional area of 24.3 square meters. 5.6 m at a distance of 100,000 m is an angle of 0.000056 radians or 0.0032 degrees. This is about the same as the planet Mars, seen from Earth, on average (e.g. not at opposition when Mars is closest). Practically speaking the target area will probably be smaller than this because you'll be aiming at a particular part of the craft.
The portion of the radiation produced by the beaming array that ends up inside this tiny circle is in my opinion the critical parameter to evaluate when looking at beamed propulsion.
As a side note, let's talk about the energy flux involved. 2 GW received power divided by 24.3 square meters is 82.3 MW/m^2, 8.23 kW/cm^2. This is the same flux as a blackbody at almost 6,200 K, i.e. substantially hotter than the Sun. If the actual receiver area is 2 m^2, the equivalent blackbody temperature is 11,500 K. That's not to say that any component will necessarily reach that temperature, but it does show the incredible amounts of energy we're working with.
I have no good way to calculate any of the three loss sources I mentioned above, but just looking at these numbers I'm sorta skeptical that it can be done.
There's also another matter that seems problematic: For roughly half of the time, the beam will be coming from in front of the craft. How will it be redirected into the engine? How do you prevent it from vaporizing everything when (not if; it will happen sometimes) you miss? And even if it does actually strike where it's supposed to, how do you turn it into thrust?
Beamed propulsion is really promising, because sending something into orbit only requires $0.90/kg of electrical energy. But with intensities like these it might be somewhat like siren song.
-Josh
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What if we increase the surface area of the receiver substantially? Think of a giant flying wing, or a manta ray. Low frontal area, but plenty of area to receive power.
Use what is abundant and build to last
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Does it have to be directly over it to work? Couldn't an angled beam transfer energy?
Use what is abundant and build to last
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JoshNH4H,
I've been busy trying to close out a project at work and working some crazy hours, so I haven't had time to properly respond. When I'm able to go into more detail, if desired, I will.
The YAL-1 airborne laser laboratory used a low power steering beam aboard the same Boeing 747 aircraft as a target tracker, atmospheric effects assessment sensor (measuring density and air movement through the flight path of the beam in real time), and a power beam collimator that could focus the beam at a point in space beyond the emitter aperture. The power beam emitter in the nose was slaved to that steering beam. It was precise enough to focus the power beam in that point in space using adaptive optics developed by Lockheed Martin that would "bend" the power beam emitter aperture using electromagnetic optics materials such that it would achieve maximum coherency or collimation at the point in space coinciding with the target, rather than at the source emitter. The power beam would burn a small hole in an AIM-9 Sidewinder missile's motor casing to destroy the inbound missile.
YAL-1 was an exceptionally precise and directional weapon, even with atmospheric effects. This is to say that someone right next to the target would experience virtually no radiation from the beam. The microwaves in the area denial system are so precise it can pick a point on a single person's body in a crowd of people. For example, it can simply heat up your hand if you point a firearm at the Police.
To determine with absolute precision where the heat exchanger plate boundary on the drone happens to be, some sort of boundary material with a distinct signature is required so that the steering array can precisely track the drone's plate. The heat exchanger plate is supposed to be a high temperature ceramic. Perhaps the edge of the plate should be some type of refractory metal like Tungsten or a carbide of some sort. It needs to be a thin sheet with embedded temperature sensors connected to the drone's communications avionics so it can transmit temperature data back to the power facility for emergency shutdown of the power beam. If track is lost, the tracking software fails, steering mechanisms fail, or the temperature sensors in the plate boundary detect a heating spike, that information is transmitted back to the power station. If adjustment can be made rapidly and correctly, then it will be and the shot continues, else the power beam shuts down.
A steering laser or maser paints the entire target and starts tracking the plate boundary while the drone is still aboard the carrier aircraft. The carrier aircraft itself can have a secondary target painting system to assist with providing general target location to the power station. Sensors aboard the drone can confirm target track/lock and then transmit the information back to the power station. Real time image processing software precisely defines the distance to edge of the plate boundary, along with atmospheric conditions, to electronically steer the power beam. The beam will be continuously adjusted to collimate in the point in space where the drone is in order to achieve maximum power beam collimation. The software will be a real time system that uses an object database of signature patterns combined with simple AI software that runs on special purpose chips. Additionally, the entire software set must run on separate redundant chips / systems that vote on where the drone's heat exchanger is, much like the Space Shuttle's onboard computers. I'm thinking three steering beams, each equipped with three real time voting system-on-a-chip computers and bi-directional communication with the drone, plus a supplemental system on the carrier aircraft.
This is the basic concept for the adaptive microwave beaming (just like the adaptive laser optics from Lockheed Martin):
Metamaterial bends microwaves into beam
We clearly need different materials for this application, but the link shown above explains the basic concept.
The drone needs a high pressure turbo-pump to feed propellant from the heat exchanger exhaust tubes into the nozzle after being accelerated with thermal energy from the heat exchanger. Also, I think we should revisit the concept of the drone achieving a circular orbit for satellite delivery. If only the payload has to achieve a stable orbit, the propellant mass in the drone's RCS system can be minimized and the quantity of propellant to circularize the orbit of 1t of payload is less than 1t plus the drone's mass.
Again, that concept is most applicable to launch of low cost satellites for research or military purposes. The idea is that it's cheaper for the military to use batch production spy and communications satellites replaced with new and upgraded equipment every six months to a year than it is to have to design something to last for a decade or more in a high radiation and debris filled environment. Better sensors and faster communications can go into orbit every six months to a year and the military should capitalize on COTS equipment that's fast and cheap to replace if damaged or destroyed by rail gun, laser, or microwave weapons.
Equipment going to ISS for storage / transfer / assembly requires more onboard RCS, so maybe a modular tankage system that includes extra tanks or larger tanks for that purpose. The use of AF-M315E is all about fast turnaround, minimizing hazards to ground personnel and associated handling costs, and making the propellant tanks as small and light as possible for the task. This is quite literally a heavy duty pickup truck's payload capacity.
I was thinking that the lenticular design of the Pye Wacket was the right way to do this to maximize transonic / supersonic / hypersonic stability and maneuverability, along with maximizing the size of the heat exchanger plate in a craft with minimal equivalent flat plate area, but I could be wrong. A "flying saucer" is just a type of "flying wing", so far as I know. It just happens to be stable in flight across a wide Mach number range. We need every conceivable advantage for this to work at all, let alone work well. All said and done, it's just a highly engineered system for delivery of small payloads.
The heat shield would be the fabric from HIAD, wrapped over aerogel foam cores, and replaced after each flight. Rigidity of the lenticular shape would be provided by a tensioning system that uses a magnesium alloy cylinder that serves as a single attachment point for the LH2 tank, heat exchanger, turbopump, land skid / heat exchanger boundary, and fabric heat shield. Atmospheric maneuvering would be accomplished by "bending" the edges of the vehicle in six or eight sections. To change direction, a servo "pulls" on kevlar straps attached to the heat shield fabric, temporarily deforming one foam segment of the vehicle to control lift. The "bottom" of the vehicle would use the carbide ring as the landing skid and the saucer would "flare up" just like the Space Shuttle to land on the skid. The skid / heat exchanger boundary would be deployed for landing using the tensioning system to push the carbide ring downwards to protect the heat exchanger during landing. The "top" of the vehicle contains the RCS thrusters and payload bay.
The carrier aircraft would have an aiming target for the steering beam immediately ahead of the drone rack. Prior to release, the steering beam follows the aiming target on the carrier aircraft. After release, the carrier aircraft uses its own steering beam to communicate the drone position to the ground, whereupon the steering beam is slaved to the target and confirms a target lock on the released drone. Thereafter, the drone is tracked and powered by the power station. The carrier aircraft will "spin up" the drone's turbine just prior to release using a start cartridge and provide power through a separate umbilical.
So yeah, this is pretty complicated but still possible to do. The target price point should be $100/kg to $250/kg. That's still dramatically better than reusable rockets. The heavier and more sophisticated the aerospace vehicle becomes, the more costly it becomes, without exception.
A 747-400 costs $24K per flight hour, so $36K for a vehicle with 6 of its engines. That's $72/kg right there if the average flight is 2 hours in duration. I'm guessing, of course, but the engines account for most of the maintenance and Roc is brand new. That said, I'm not familiar with composite airframe operational costs. I know that basically when something exceeds fatigue life the entire structure has to be replaced. That could get expensive, but we're far from stressing the airframe to its limit in using only 1/4 of its maximum lift capability.
I'm still wrong about the gas turbines. We need 8 of GE's Frame 9 units to provide the power required and the CC units are $61M per copy, so $488 million for the power station's gas turbines. That's the sticker price for a STS flight. Roc probably cost about $250M to construct, but it's already paid for and uses commodity Boeing 747 avionics, engines, landing gear, and flight control hydraulic systems. With 2MW gyrotrons that cost $1M per copy, that's $1B for the gyrotrons.
We're probably looking at $3B to $4B to make this work, but we'll exceed the payload delivery capability of 3 or even 4 SLS flights in the first year of operations. SLS is $10,000/kg if it costs $1B per flight. It'd be really hard to make the total cost of operations equivalent to 1/10th of the SLS flight costs. We're looking at $25M or less in operational costs to deliver 100,000kg of payload. We can afford to keep using LOX/LH2 or LOX/LCH4 or even LOX/RP1 with prices like that. NASA is dead set on LOX/LH2 as their propellant of choice, but other customers may want different propellants for their engines. The payload could be water and a solar powered electrolyzer to split the water in orbit into LOX/LH2 so that the cryo plant only has to keep the propellant cold just prior to use. ISS could have a water tank and liquid CO2 tank module filled with liquid delivered 1,000kg at a time, a solar power plant and batteries delivered the same way, and upper stages delivered by commodity reusable rockets awaiting propellant fill for missions.
Humans could use the legacy capsule systems until we're sure that the beam won't fry any drones and we build a second or third power station to reduce the acceleration curve. We only send people 2 or 3 at a time, anyway, so an emergency ejection capsule like that designed for XB70 might work. Rockets will still carry the upper stages, habitation modules, and sensitive scientific equipment, but their use is limited to what simply can't ship any other way. A CECE / RL10 only weighs 160kg and is 5 feet long. Mating to the propellant tank is required, but we can afford to ship the tools and test equipment. I'm just thinking out loud here, but if it fits, it ships, and yes, some assembly may be required. StratoLaunch and NASA need to talk to FedEx to learn how to run a shipping business.
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Hey kbd512,
As far as I can tell there are not any inherent problems with your idea, and it lies somewhere along the boundary between current and future technology. I'm not totally sold on the flat heat exchanger thing (that's not typically how thermal engines work and whether you could get adequately high temperatures with conduction seems pretty questionable to me) but I don't doubt that it's something that could be done.
Similar systems have been built and tested at very small scale, but the next step would be a bigger proof of concept. Build an engine, see what kind of Isp you can get. See how well you can aim your gyrotron, and then work on a moving target. See if you can actually get your engine to fire in midair. Build a very small test article and send it to suborbit. Then a bigger one. Then a full scale, partial impulse one. Then head for orbit.
I'm a skeptic by nature, and I'll believe it when I see it. But we won't really know how hard it is until we try.
-Josh
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To be honest, I think the biggest problem with beamed power propulsion is the Kzinti lesson. Governments are not going to take kindly to privately operated directed energy weapons.
Perhaps agreeing to launch outside the range of any targets, say from an (air)ship or atoll, would alleviate these concerns.
Use what is abundant and build to last
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Can you imagine the havoc that could be wreaked by an accurately target-able 2 GW beaming array?
The US might permit it on the condition that the military can take it over for the purposes of missile defense.
-Josh
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On the other hand, private companies operate nuclear reactors. So if the government provides military/police forces to watch the people operating the array, we might allowed to do it.
Or we could put them on an airship, and at a safe distance (say, 500km), the coastguard will board to confirm the array has been disabled. Moving in any closer gets a kill order.
Use what is abundant and build to last
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Or a ship. There shouldn't be much recoil from it. My thinking with an airship, as I've explained before, is that you can get above most of the atmosphere and expand your horizon considerably. Then again, what height are we talking? If it's 10km up, it should stay above the horizon during launch?
Use what is abundant and build to last
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Light pressure on 2 GW is good for about 10 N or so which is pretty minor. Mobile platforms can be affected by other forces though, like wind or waves. The pointing retirement is already aggressively difficult so it seems like a bad idea to add another challenge to it.
-Josh
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JoshNH4H,
All I want to try is a system sized to deliver a 100kg payload to orbit. If it works great, if not, then at least we'd learn quite a bit about atmospheric propagation and directing of high power microwaves. If it does work, then we've discovered our new 24/7 service for delivering small parcels to ISS.
This technology is not an excuse for poor mission planning, but if someone forgets something or something breaks unexpectedly, then it's not the end of the mission. We'd just send a replacement for whatever wasn't accounted for the next day or next week. Roc is not any sort of requirement for this to work, either, and quite possibly counter-productive as a function of operating costs. White Knight One was intended to operate up to 53K and carry a 3,600kg payload. That's sufficient for a 100kg to 250kg payload test. White Knight Two was intended to operate up to 50K with a 17,000kg payload. That's sufficient for 500kg to 1,500kg payloads.
We can scale the power facilities as the gyrotron technology matures, adding gas turbines for power as we prove out the basic design for specific payload classes. There are currently designs for 10MW class gyrotrons. That would mean just 100 gyrotrons per GW of emitted power. That seems a lot more workable than using 1MW or 2MW class gyrotrons.
If we only carry liquids like water or rocket propellants to start with, then we can fry the drone and its payload if something goes wrong. Later on when we're more confident about where the drone will end up, we can start sending solid payloads.
I wanted this facility located in the Rocky Mountains to protect NORAD without using rail guns. A hypersonic 155mm projectile is not something we want landing on an office building. The results would be catastrophic. Public opinion regarding these missile defense systems will be adversely affected if we accidentally kill our own people with any of them. The microwave systems are not subject to interference from atmospheric turbulence and are somewhat less susceptible to ionization from water vapor than lasers would be.
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All this talk of improved rocket nozzles had me thinking about what we could realistically expect to accomplish. Even if the claims are dead-on correct and we'll save 30% of the fuel mass required to deliver the same payload to orbit, that's still not nearly enough. In order to truly become an interplanetary species, launch costs must plummet to levels far below what a 30% fuel savings would ever provide.
We need an electromagnetic launch system and microwave power transmission system that, in combination, can provide the power required to achieve orbit, leaving nearly all of the associated infrastructure on the ground. While we certainly should endeavor to get the most from conventional rocket engines, we still haven't addressed the incredible cost of operating massive aerospace vehicles on a routine basis.
At some point, we need to put the infrastructure in place to drastically reduce the size and weight of these vehicles, to something approaching a fighter jet, while carrying a payload in the same tonnage class as a prototypical modern fighter jet (5t to 10t). If this launch system can provide flight rates similar to those of fighter jets, then a single squadron of such vehicles would deliver as much tonnage to orbit in a year as humanity has managed in the entire history of space launch.
As of the end of 2017, humanity had collectively delivered just over 13,000t to orbit over the entire history of space flight. A pair of Arleigh Burke class destroyers is in the 16,000t to 18,000t range. A squadron of rail gun / HPM powered launch vehicles, each flying once per day with 10t payloads, could deliver 43,800t per year. Even if the sortie rate was half of that, we're still talking about more delivered tonnage than humanity has ever managed to put in orbit over more than half a century of space flight. With a pair of such facilities, one on each coast, we could deliver a tonnage equivalent to an aircraft carrier each year. That kind of tonnage would enable us to construct colonies on other worlds. If the Europeans and Chinese also constructed a pair of such facilities, we could begin to think about mass movement of people and goods between planets. The yearly Hydrogen consumption of each facility to support such flight rates would be in the 22,000t range. The US produces about 10 million tons of Hydrogen per year, so this would amount to about 1/227th of yearly production. The Hydrogen production sector is expected to see a global 18.6% year-over-year growth through the next few years, so there's more than enough fuel to go around.
Long term, electrification of the launch infrastructure is the only way to sustainably maintain a presence on other worlds, never mind shifting our populations between the moon, Mars, and Venus to support economic and population expansion.
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After we're in LEO, we need to start serious experimentation with electrodynamic tethers to adjust orbits without the need for massive quantities of propellants. The propellants that are used in space need to be high-efficiency, most likely for electric thrusters, and limited to injecting into transfer orbits to other planets. To the extent practical, the major portion of the power supply for these vessels need to be in Lagrange Point orbits, such that the power supplies for these ships can be sized for human habitation, rather than propulsion requirements.
Obviously this requires a lot more infrastructure in space, but that's also how modern terrestrial civilization operates here on Earth, so there are infrastructure parallels that must first exist in space. We have constructed a vast amount of infrastructure to support our human endeavor. The same will be true for any space-faring civilization, which I presume we want to become.
Given 100,000t of mass per year to work with, we can begin to construct the types of ships we see in our favorite sci-fi movies, or in other words, the sorts of ships that have the mass and redundancy to reliably and routinely move people between interplanetary destinations.
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