Table of Contents
1) Introduction
Many have written on this topic, although I don't recall seeing a post discussing this topic on this page.
Some arguments for space development include cheap materials from asteroids, cheap power from solar power satellites, moon colonies, mars colonize, the spirit of adventure, etc. Although I agree with all of the wild eyed dreaminess of these things, the practical economics really just don't work out. Consider our starting point of $5000 - $10,000 / lb of mass into orbit, and it rapidly becomes clear that anything we wish to harvest from space must be REALLY precious to be worth our bother. A pound of platinum or iridium might be worth $12,000 in today’s market but how much might this cost to harvest from a nearby asteroid, at what risk, and compared to what cost to harvest from the Earth?
Right now the commercial demand for space amounts to growing proteins for pharmaceutical researchers, growing exotic materials for materials researchers, telecommunications, weather satellites, and a few miscellaneous reasons. The point is that although these might be profitable ventures, the current investments in these areas are extremely low volume and you're exceedingly unlikely to pay for a robust space infrastructure from marketing low volume capabilities.
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2) Getting to Orbit
If we keep doing things the way we have always done them, we will never develop a robust presence in space.
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2.A) Big rockets cost a lot!
"No duh, am I right?!"
We can actually look at the problem from two directions. It is REALLY expensive to send stuff into space (that's where most of that $10K goes) but it costs almost nothing to bring it back - a few kg of propellant to de-orbit and a heat shield is all it takes.
Several reasons conspire to make space travel so expensive
1) it takes a lot of fuel to get to orbit which makes it costly to go,
2) this very constraint encourages engineers to cram the most capability into every ounce of payload, and
3) sending spacecraft to space is a rare event so each one is one (or perhaps two) of kind.
This means a great deal of research and development goes into each vehicle and all of the very best – most expensive materials electronics, and other systems go into these craft.
But WHY does it take so much fuel to send things into space? In order to achieve Low Earth Orbit (LEO) you must first loft the mass to 100 miles altitude AND then you must accelerate it to ~17,000 miles per hour. You must also accelerate all of its fuel and then incrementally accelerate the reaction mass to accelerate that reaction mass, etc. It ends up being an interesting integral equation. For the Space Shuttle this resulted in
1,620,000 lbs of liquid propellant (Space Shuttle External Tank)
2,200,000 lbs of solid propellant (Space Shuttle Solid Rocket Booster)
to loft 151,000 lbs of orbiter (I include this because the orbiter itself is part of the payload) and 55,000 lbs of orbiter payload. (Space Shuttle)
So it takes nearly 4,000,000 lbs of propellant to loft 206,000 lbs of payload? Since the launch weight is 4,470,000 lbs that leaves 270,000 lbs as "everything else" (such as solid rocket motor casings, external tank, etc.).
That's a ratio of 85.5% fuel, 4.5% "payload", and 10% everything else. At this rate it’s surprising that anyone bothers with it.
Although the conservation of energy (Conservation of Energy) and momentum (Conservation of momentum) equations are strict toll takers whose minimum price must be paid, alternative designs can pay a much less steep toll and achieve the same results.
Some examples are a light gas gun, ram accelerator, and mass driver. In each case the vast majority of the energy required to achieve orbit is imparted by the launching device (the gun, accelerator, or driver). The spacecraft only needs to bring enough additional fuel to circularize or otherwise shape its orbit.
Using any one of these concepts would tremendously decrease the operational costs of space infrastructure. For example to accelerate the same mass (206,000 lbs) to orbital velocity would require this much fuel [m*v(payload) = m*v(fuel) => 206,000lbs*25,000ft/sec = m(fuel)*14,763 ft/sec => 348,827 lbs of LOX + LH2!). Because nothing is ever 100% efficient, let’s use an efficiency of 70%, 348,827 lbs / .65 = 500,000 lbs of fuel. This is << (much less than) the 4,000,000 lbs used by current systems – in fact it is almost exactly 1/8 (12.5%) as much.
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2.B) Some Alternatives
Clearly anyone raised on Star Trek, Star Wars, or any other SF program realizes that Big Dumb Rockets are NOT the way to go. What isn't as clear to everyone is whether we have anything better that we could be using.
Enterprise is fusion and antimatter powered:
A Photoshop of USS Enterprise being constructed at the Newport News Shipbuilding drydock in Newport News, Virginia
Agamemnon is fusion powered:
I personally favor any one of the following four techniques to what we're doing now. I may add a fifth a little later (if you want a teaser - it uses launch lasers and "this is quite an amusing little gizmo. It's really quite cool." - Casanova Frankenstein, Mystery Men).
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2.B.i) Ram accelerator
Is superficially similar to a light gas gun, however, in a ram accelerator the initial acceleration is substantially lessened, begins in front of instead of behind the projectile, and the working fluid is composed of a combustible mixture (such as low temperature O2 + H2). As the project moves through the working fluid, the projectile induces the working fluid, to burn (as in a ramjet engine). The combusting working fluid works on the back of the projectile to accelerate the projectile. As with the mass driver, the ram accelerator can be “tuned” to develop a limited amount of thrust such that, as long as the barrel is long enough, theoretically any acceleration and velocity are possible. Practically speaking even scramjet propulsion isn’t efficient after reaching velocities of mach 18 or so. So although this method could support launching humans into space, it would require some additional rocket propulsion to achieve both orbital velocity as well as to circularize its orbit.
Incidentally, the barrel would need to be about 240 miles long to ensure that humans could tolerate the acceleration! This would be a very costly barrel indeed.
This concept is technologically a little challenging. Some additional scramjet combustion research would ensure that the technique worked as expected, however, a great deal of research has already been accomplished on this technology and the basic concept has been proven quite effective. Furthermore the main cost of this technique would be involved in the construction of the launch tube. Since you could create the barrel of this launcher above the surface of the ground, I expect the construction costs to be significantly less than the costs of the “Chunnel” (the tunnel under the English Channel) or the “Big Dig” the tunnel under the city of Boston.
The launch costs of such a device might be as little as $100/lb of cargo.
More reading:
ram accelerator
SCRam cannon
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2.B.ii) Light gas gun
Use a chemical reaction (air + CH4, air + H2, O2 + H2, etc.) to push a piston. This piston compresses a light-gas (typically H2). This high pressure wave traveling through the light-gas can achieve a very high velocity and is the working gas which pushes the projectile down the “gun” and the region of the barrel in front of the projectile is evacuated (vacuum). Note the working gas is NOT combusted.
The main problem is that (similar to a conventional gun) the projectile experiences exceedingly high acceleration at the beginning of the launch. This acceleration tapers off as the projectile moves down the gun barrel. The main benefit of this technique is that it is both cheap and easy to implement – but the projectile could NEVER support launches of fragile cargo like humans. The main cost to developing a light-gas gun is developing a barrel capable of withstanding the pressures incurred by launches. Since this tube will remain on the ground, developers can use cheap and heavy materials like concrete and structural steel to build the device rather than the materials normally used in aerospace construction (e.g. composites, titanium and exotic aluminum alloys).
Note that it is very likely that SAME launch barrel would work for both the light-gas gun and ram accelerator – meaning you could use one to cheaply launch bulk materials like propellant, LO2, water, and other necessary materials and the other for launching delicate cargos like electronics and humans. The only problem with this is that the gun barrel for the light-gas gun would not need to be nearly as long as that of the ram accelerator.
The technology for the light-gas gun is simple and the construction costs for a dedicated light-gas gun (not usable as a ram accelerator) would be even less than that of the ram accelerator.
Provided that the cargo was insensitive to accelerations up to 6000 gravities, the launch cost might be even smaller than $100/lb.
More reading:
light gas gun
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2.B.iii) Mass Drivers
One method, called a coilgun, uses pulsed electromagnetic fields to accelerate a metal sled down a magnetic track. The system uses electricity as the power source. There is an example of this already running somewhere in Texas where they launch test articles out into the Gulf of Mexico.
Another method called a railgun, uses current flowing from one electrical conductors (rail) through a sacrificial conductive "sabot", and finally back through another electrical conductor (aka rail). The high energies involved first vaporize the sacrificial sabot and then turn that metallic vapor into plasma as the electromagnetic force drives the sled down the track.
A electromagnetic launchers can be adjusted to limit the acceleration of the projectile. Given enough track length (allowing for minimal acceleration), a mass driver could be used to launch fragile cargo (like humans).
This concept is significantly more technically challenging. I’ve seen estimates that state the minimum possible launch cost of ~$500/lb for this launch concept.
More reading:
mass driver
Railgun
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2.B.iv) Nuclear pulse detonation engines
A given weight of nuclear fuel (fissile material like Plutonium or Uranium) has roughly 10,000,000 times as much energy as the same weight of rocket fuel. That does NOT mean that we could use 10,000,000 times less fuel because the way the conservation of energy and momentum equations work it actually means we could use sqrt(10,000,000) less fuel - which is 1/3162 as much fuel if we used nuclear power.
So why are we doing things the hard way? It's like trying to run a marathon on your hands - a marathon is ALREADY a really tough race, who in their right mind would you want to make it harder?!
Given the numbers I used the above for the Shuttle and applying a 100% nuclear engine solution to the problem, it means we could launch the same vehicle into orbit using only 1207 lbs of fuel (a fuel fraction of 0.5%) - better yet in theory the fuel is much better than this simple equation because we don't have to loft as much of the stuff around for use later.
There are MANY great ideas for utilizing nuclear power, however, most of these would not work that well in a launch vehicle in which high thrust is essential for getting off of the surface of the planet. Two leading contenders are designs which the US has had and worked on since the 1950s & 1960s! These are NERVA and project Orion.
More reading:
Nuclear pulse propulsion
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NERVA
Takes a light weight nuclear reactor, dumps liquid hydrogen onto it, the hot reactor vaporizes the gas, and the engine ejects the superheated gas for thrust. Although it is nuclear powered, only hydrogen gas and no radioactive material is emitted from the engine.
As a launch engine it doesn't quite "cut the mustard". The thrust is a tad too low to permit launching and the engine performance isn't as great as suggested by my idealized numbers above - it's only about 3x (and not 3000x) as efficient in its usage of propellant.
However, NERVA would make a great engine for use as an upper stage, orbital transfers, and even a sustainer engine (what the Space Shuttle Main Engines do). It even could be used for launch in a reusable single stage to orbit vehicle.
More reading:
NERVA
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Project Orion
What would happen if you placed a plate of metal just far enough above a thermonuclear explosion so that it was not vaporized? This experiment was performed (initially by accident) and the results:
"The calculated velocity was sufficiently interesting that the crew trained a high-speed camera on the plate, which unfortunately only appeared in one frame, but this nevertheless gave a very high lower bound for the speed."
That plate of metal was never found and possibly vaporized in the atmosphere due to its high velocity (calculated to be >150,000 ft/sec).
This engine is a design that almost no one has heard about. It takes the most destructive weapon of mass destruction and turns it into the most efficient rocket engine ever devised.
By detonating 800 nuclear bombs, we could launch 8,000,000 tons (16,000,000,000 lbs) of mass into orbit! By using specially engineered bombs (crafted from aneutronic materials) and launching at sea far from human settlements the amount of radiation added to the biosphere could be kept to almost undetectable levels.
Better yet, this type of engine gives the designers any reasonable thrust levels they desire and it would take 2400 tons of fuel (bombs) to launch that 8,000,000 tons of cargo into orbit. This gives a fuel fraction of <0.1% (which reinforces the calculations at the top of this section). Now many people are opposed to the use of nuclear weapons for any reason - yet here's a peaceful use that would rapidly deplete the world's stockpiles of weapons grade radioactive materials. Ironically, if we discover an asteroidal/cometary threat to the world in the next 100 years - it's probable that only a project Orion powered craft could loft the necessary mass, provide the necessary thrust, and fuel efficiency to do anything about it. I personally would like to see us test such a design before the future of all of humanity rests on a successful first launch. Finally, a project Orion craft would release just about the same amount of radiation into the environment whether the craft was launching 800 tons (the theoretical lower limit) or 8,000,000 tons (the theoretical upper limit). Given the downside to this craft (releasing radiation into the environment), I think we ought to launch one to a few of these craft loaded with the full 8,000,000 tons (the mass of a small city) and use the equipment, consumables, and everything else we launched to bootstrap a semi-self sufficient space economy.
More Reading:
Project Orion
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3) Developing space infrastructure
First of all, what do I mean by "space infrastructure?" What the entire world has in orbit at this time is a few thousand satellites of which only a few hundred are working AND we have a space station.
IMO, this is NOT space infrastructure - most of what is there doesn't work and the space station is more about science and technological chest beating and actually performs almost no any economic activity. When a satellite fails, we must replace it from Earth. We have no ability to perform on-site repairs, no ability to refuel, deorbit old hardware, or construct new hardware. We support our space presences from Earth and all infrastructure for our space presence only exists on Earth.
So what *I* mean by space infrastructure is assets launched into space that can provide economically useful services and goods. For example, the ability to refuel an existing communications satellite or de-orbit a failed one.
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3.A) Satellite tug
Assuming we have implemented the light-gas gun and we limit the acceleration to 100 g's - we can get by with a launch tube about 19 miles long. We can situate this barrel along the slope of Mauna Kea. Mauna Kea is an extinct volcano, near the equator, which reaches 14,000 feet into the atmosphere, and it already has infrastructure all the way to its top to support observatories.
Once built we start launching anything and everything that might be useful into LEO. Where possible we get paying customers, where it is not possible we start building our own infrastructure - limited only by how fast we can re-evacuate the launch tube between launches (hopefully we can make several launches per day).
We can start with a fuel depot and a satellite tug & servicing unit. The service we'll provide is refueling, re-boosting, or moving other company's satellites for a fee. We wish to make this competitive but our operating costs will be 1/100th that of our competitors. Our fees will mostly include paying back the cost of building the light-gas gun barrel.
Given a little more sophistication, a concept I helped develop while in college, and the correct raw materials we could even construct mechanical parts while in orbit if we elected to start a satellite repair facility. Since many electronic parts are made to withstand high-g loads (e.g. dropped laptops) we may even be able to use our launch infrastructure to shuttle up necessary parts for electronic servicing missions.
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3.B) The new sheriff in town
What isn't widely known outside the space community is LEO has turned into a junkyard. The junk is so pervasive that it is getting dangerous to operate in these orbits and in fact satellite manufacturers have begun to include armor on the satellites that must operate in this region!
What can we do about it?
Why we can clean up the town! Assuming we have both the light-gas gun, satellite tug, and the fuel depot we can introduce a craft somewhat similar to the tug. Make it less sophisticated but include many deflated but giant balloons that we can inflate with a light-weight fluffy substance called an aerogel.
Next we use a high efficiency engine (such as an ion thruster - not discussed here). We then do an orbital plane change change until our balloon is in a retrograde orbit and release it. The balloon won't last long in this orbit but while it lasts it'll intersect a bunch of space junk. Each piece that the balloon hits will be decelerated a bit so that it gets de-orbited. Ironically the same thing will happen to the balloon. The more effective the balloon (intersecting a lot of junk) the faster our balloon will itself de-orbit.
Our junk cleaner satellite can release many such balloons before it too de-orbits and burns up.
We would NOT perform this clean-up for free - this would be a service provided at some cost to various interested parties (including governments).
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3.C) Space tug
What's the difference between our "satellite tug" and our "space tug"? Size and sophistication mostly. The satellite tugs would be used almost exclusively around the Earth (near Earth and Geosynchronous orbits). Meanwhile the "space tug" would be intended for use in interplanetary space and would be intended to work on maneuvering small asteroids and comets.
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3.D) Miscellaneous
Up until this point we have discussed technologies and capabilities centered around the needs of the Earth and Earth based infrastructure. In fact all of the concepts I've discussed do not even require a human presence in space at all! At some point we (as the explorers and colonizers that humans have always been) will want to expand our presence into space.
Given the launch costs (even with something like the light-gas gun or project Orion craft) we will need to begin to build self-sufficient infrastructure in space. An infrastructure which we can collect, process, and directly use most of the basic resources needed to sustain humans in space.
More reading:
Atomic Rockets Home Page
Blogger has nerfed this link, the website name is "projectrho" and can be found with a quick query for "atomic rockets".
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Continue to The Case for Space IV: How to pay our way
- Introduction
- Getting to Orbit
- Developing space infrastructure
- Satellite tug (moving small objects)
- The new sheriff in town (cleaning up)
- Space tug (moving big objects)
- Nuclear power – the ONLY propulsion for interplanetary travel
- How to pay our way
- What does space have to offer?
- Materials
- Free pollution
- Cheap energy
- Tourism
- Science
- Colonization
- Who is our customer?
- Earth can get most of these resources more cheaply or with less risk at home
- Most of the rest of the goods and services are low volume (e.g. tourism) and unlikely to pay for development.
- Ultimately space development is the target customer for most resources
- What does our customer want?
- Little conventional economic demand for what space has to offer
- Go forward
- Early development (e.g. light-gas gun would likely be very profitable)
- Middle development (e.g. satellite tug would also likely be profitable)
- Later development’s risk and length of payback may require some investor altruism!
- Some of this development *may* require the investment of a country or the world.
- Current designs offer no opportunity for most people to ever get to space.
- Conclusions and Summary
1) Introduction
Many have written on this topic, although I don't recall seeing a post discussing this topic on this page.
Some arguments for space development include cheap materials from asteroids, cheap power from solar power satellites, moon colonies, mars colonize, the spirit of adventure, etc. Although I agree with all of the wild eyed dreaminess of these things, the practical economics really just don't work out. Consider our starting point of $5000 - $10,000 / lb of mass into orbit, and it rapidly becomes clear that anything we wish to harvest from space must be REALLY precious to be worth our bother. A pound of platinum or iridium might be worth $12,000 in today’s market but how much might this cost to harvest from a nearby asteroid, at what risk, and compared to what cost to harvest from the Earth?
Right now the commercial demand for space amounts to growing proteins for pharmaceutical researchers, growing exotic materials for materials researchers, telecommunications, weather satellites, and a few miscellaneous reasons. The point is that although these might be profitable ventures, the current investments in these areas are extremely low volume and you're exceedingly unlikely to pay for a robust space infrastructure from marketing low volume capabilities.
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2) Getting to Orbit
If we keep doing things the way we have always done them, we will never develop a robust presence in space.
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2.A) Big rockets cost a lot!
"No duh, am I right?!"
We can actually look at the problem from two directions. It is REALLY expensive to send stuff into space (that's where most of that $10K goes) but it costs almost nothing to bring it back - a few kg of propellant to de-orbit and a heat shield is all it takes.
Several reasons conspire to make space travel so expensive
1) it takes a lot of fuel to get to orbit which makes it costly to go,
2) this very constraint encourages engineers to cram the most capability into every ounce of payload, and
3) sending spacecraft to space is a rare event so each one is one (or perhaps two) of kind.
This means a great deal of research and development goes into each vehicle and all of the very best – most expensive materials electronics, and other systems go into these craft.
But WHY does it take so much fuel to send things into space? In order to achieve Low Earth Orbit (LEO) you must first loft the mass to 100 miles altitude AND then you must accelerate it to ~17,000 miles per hour. You must also accelerate all of its fuel and then incrementally accelerate the reaction mass to accelerate that reaction mass, etc. It ends up being an interesting integral equation. For the Space Shuttle this resulted in
1,620,000 lbs of liquid propellant (Space Shuttle External Tank)
2,200,000 lbs of solid propellant (Space Shuttle Solid Rocket Booster)
to loft 151,000 lbs of orbiter (I include this because the orbiter itself is part of the payload) and 55,000 lbs of orbiter payload. (Space Shuttle)
So it takes nearly 4,000,000 lbs of propellant to loft 206,000 lbs of payload? Since the launch weight is 4,470,000 lbs that leaves 270,000 lbs as "everything else" (such as solid rocket motor casings, external tank, etc.).
That's a ratio of 85.5% fuel, 4.5% "payload", and 10% everything else. At this rate it’s surprising that anyone bothers with it.
Although the conservation of energy (Conservation of Energy) and momentum (Conservation of momentum) equations are strict toll takers whose minimum price must be paid, alternative designs can pay a much less steep toll and achieve the same results.
Some examples are a light gas gun, ram accelerator, and mass driver. In each case the vast majority of the energy required to achieve orbit is imparted by the launching device (the gun, accelerator, or driver). The spacecraft only needs to bring enough additional fuel to circularize or otherwise shape its orbit.
Using any one of these concepts would tremendously decrease the operational costs of space infrastructure. For example to accelerate the same mass (206,000 lbs) to orbital velocity would require this much fuel [m*v(payload) = m*v(fuel) => 206,000lbs*25,000ft/sec = m(fuel)*14,763 ft/sec => 348,827 lbs of LOX + LH2!). Because nothing is ever 100% efficient, let’s use an efficiency of 70%, 348,827 lbs / .65 = 500,000 lbs of fuel. This is << (much less than) the 4,000,000 lbs used by current systems – in fact it is almost exactly 1/8 (12.5%) as much.
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2.B) Some Alternatives
Clearly anyone raised on Star Trek, Star Wars, or any other SF program realizes that Big Dumb Rockets are NOT the way to go. What isn't as clear to everyone is whether we have anything better that we could be using.
Enterprise is fusion and antimatter powered:
A Photoshop of USS Enterprise being constructed at the Newport News Shipbuilding drydock in Newport News, Virginia
Agamemnon is fusion powered:
I personally favor any one of the following four techniques to what we're doing now. I may add a fifth a little later (if you want a teaser - it uses launch lasers and "this is quite an amusing little gizmo. It's really quite cool." - Casanova Frankenstein, Mystery Men).
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2.B.i) Ram accelerator
Is superficially similar to a light gas gun, however, in a ram accelerator the initial acceleration is substantially lessened, begins in front of instead of behind the projectile, and the working fluid is composed of a combustible mixture (such as low temperature O2 + H2). As the project moves through the working fluid, the projectile induces the working fluid, to burn (as in a ramjet engine). The combusting working fluid works on the back of the projectile to accelerate the projectile. As with the mass driver, the ram accelerator can be “tuned” to develop a limited amount of thrust such that, as long as the barrel is long enough, theoretically any acceleration and velocity are possible. Practically speaking even scramjet propulsion isn’t efficient after reaching velocities of mach 18 or so. So although this method could support launching humans into space, it would require some additional rocket propulsion to achieve both orbital velocity as well as to circularize its orbit.
Incidentally, the barrel would need to be about 240 miles long to ensure that humans could tolerate the acceleration! This would be a very costly barrel indeed.
This concept is technologically a little challenging. Some additional scramjet combustion research would ensure that the technique worked as expected, however, a great deal of research has already been accomplished on this technology and the basic concept has been proven quite effective. Furthermore the main cost of this technique would be involved in the construction of the launch tube. Since you could create the barrel of this launcher above the surface of the ground, I expect the construction costs to be significantly less than the costs of the “Chunnel” (the tunnel under the English Channel) or the “Big Dig” the tunnel under the city of Boston.
The launch costs of such a device might be as little as $100/lb of cargo.
More reading:
ram accelerator
SCRam cannon
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2.B.ii) Light gas gun
Use a chemical reaction (air + CH4, air + H2, O2 + H2, etc.) to push a piston. This piston compresses a light-gas (typically H2). This high pressure wave traveling through the light-gas can achieve a very high velocity and is the working gas which pushes the projectile down the “gun” and the region of the barrel in front of the projectile is evacuated (vacuum). Note the working gas is NOT combusted.
The main problem is that (similar to a conventional gun) the projectile experiences exceedingly high acceleration at the beginning of the launch. This acceleration tapers off as the projectile moves down the gun barrel. The main benefit of this technique is that it is both cheap and easy to implement – but the projectile could NEVER support launches of fragile cargo like humans. The main cost to developing a light-gas gun is developing a barrel capable of withstanding the pressures incurred by launches. Since this tube will remain on the ground, developers can use cheap and heavy materials like concrete and structural steel to build the device rather than the materials normally used in aerospace construction (e.g. composites, titanium and exotic aluminum alloys).
Note that it is very likely that SAME launch barrel would work for both the light-gas gun and ram accelerator – meaning you could use one to cheaply launch bulk materials like propellant, LO2, water, and other necessary materials and the other for launching delicate cargos like electronics and humans. The only problem with this is that the gun barrel for the light-gas gun would not need to be nearly as long as that of the ram accelerator.
The technology for the light-gas gun is simple and the construction costs for a dedicated light-gas gun (not usable as a ram accelerator) would be even less than that of the ram accelerator.
Provided that the cargo was insensitive to accelerations up to 6000 gravities, the launch cost might be even smaller than $100/lb.
More reading:
light gas gun
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2.B.iii) Mass Drivers
One method, called a coilgun, uses pulsed electromagnetic fields to accelerate a metal sled down a magnetic track. The system uses electricity as the power source. There is an example of this already running somewhere in Texas where they launch test articles out into the Gulf of Mexico.
Another method called a railgun, uses current flowing from one electrical conductors (rail) through a sacrificial conductive "sabot", and finally back through another electrical conductor (aka rail). The high energies involved first vaporize the sacrificial sabot and then turn that metallic vapor into plasma as the electromagnetic force drives the sled down the track.
Railgun - note atmospheric shock wave forming in front of & vaporized incandescent sled trailing the projectile
A electromagnetic launchers can be adjusted to limit the acceleration of the projectile. Given enough track length (allowing for minimal acceleration), a mass driver could be used to launch fragile cargo (like humans).
This concept is significantly more technically challenging. I’ve seen estimates that state the minimum possible launch cost of ~$500/lb for this launch concept.
More reading:
mass driver
Railgun
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2.B.iv) Nuclear pulse detonation engines
A given weight of nuclear fuel (fissile material like Plutonium or Uranium) has roughly 10,000,000 times as much energy as the same weight of rocket fuel. That does NOT mean that we could use 10,000,000 times less fuel because the way the conservation of energy and momentum equations work it actually means we could use sqrt(10,000,000) less fuel - which is 1/3162 as much fuel if we used nuclear power.
So why are we doing things the hard way? It's like trying to run a marathon on your hands - a marathon is ALREADY a really tough race, who in their right mind would you want to make it harder?!
Given the numbers I used the above for the Shuttle and applying a 100% nuclear engine solution to the problem, it means we could launch the same vehicle into orbit using only 1207 lbs of fuel (a fuel fraction of 0.5%) - better yet in theory the fuel is much better than this simple equation because we don't have to loft as much of the stuff around for use later.
There are MANY great ideas for utilizing nuclear power, however, most of these would not work that well in a launch vehicle in which high thrust is essential for getting off of the surface of the planet. Two leading contenders are designs which the US has had and worked on since the 1950s & 1960s! These are NERVA and project Orion.
More reading:
Nuclear pulse propulsion
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NERVA
Takes a light weight nuclear reactor, dumps liquid hydrogen onto it, the hot reactor vaporizes the gas, and the engine ejects the superheated gas for thrust. Although it is nuclear powered, only hydrogen gas and no radioactive material is emitted from the engine.
As a launch engine it doesn't quite "cut the mustard". The thrust is a tad too low to permit launching and the engine performance isn't as great as suggested by my idealized numbers above - it's only about 3x (and not 3000x) as efficient in its usage of propellant.
However, NERVA would make a great engine for use as an upper stage, orbital transfers, and even a sustainer engine (what the Space Shuttle Main Engines do). It even could be used for launch in a reusable single stage to orbit vehicle.
More reading:
NERVA
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Project Orion
What would happen if you placed a plate of metal just far enough above a thermonuclear explosion so that it was not vaporized? This experiment was performed (initially by accident) and the results:
"The calculated velocity was sufficiently interesting that the crew trained a high-speed camera on the plate, which unfortunately only appeared in one frame, but this nevertheless gave a very high lower bound for the speed."
That plate of metal was never found and possibly vaporized in the atmosphere due to its high velocity (calculated to be >150,000 ft/sec).
This engine is a design that almost no one has heard about. It takes the most destructive weapon of mass destruction and turns it into the most efficient rocket engine ever devised.
By detonating 800 nuclear bombs, we could launch 8,000,000 tons (16,000,000,000 lbs) of mass into orbit! By using specially engineered bombs (crafted from aneutronic materials) and launching at sea far from human settlements the amount of radiation added to the biosphere could be kept to almost undetectable levels.
Better yet, this type of engine gives the designers any reasonable thrust levels they desire and it would take 2400 tons of fuel (bombs) to launch that 8,000,000 tons of cargo into orbit. This gives a fuel fraction of <0.1% (which reinforces the calculations at the top of this section). Now many people are opposed to the use of nuclear weapons for any reason - yet here's a peaceful use that would rapidly deplete the world's stockpiles of weapons grade radioactive materials. Ironically, if we discover an asteroidal/cometary threat to the world in the next 100 years - it's probable that only a project Orion powered craft could loft the necessary mass, provide the necessary thrust, and fuel efficiency to do anything about it. I personally would like to see us test such a design before the future of all of humanity rests on a successful first launch. Finally, a project Orion craft would release just about the same amount of radiation into the environment whether the craft was launching 800 tons (the theoretical lower limit) or 8,000,000 tons (the theoretical upper limit). Given the downside to this craft (releasing radiation into the environment), I think we ought to launch one to a few of these craft loaded with the full 8,000,000 tons (the mass of a small city) and use the equipment, consumables, and everything else we launched to bootstrap a semi-self sufficient space economy.
More Reading:
Project Orion
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3) Developing space infrastructure
First of all, what do I mean by "space infrastructure?" What the entire world has in orbit at this time is a few thousand satellites of which only a few hundred are working AND we have a space station.
IMO, this is NOT space infrastructure - most of what is there doesn't work and the space station is more about science and technological chest beating and actually performs almost no any economic activity. When a satellite fails, we must replace it from Earth. We have no ability to perform on-site repairs, no ability to refuel, deorbit old hardware, or construct new hardware. We support our space presences from Earth and all infrastructure for our space presence only exists on Earth.
So what *I* mean by space infrastructure is assets launched into space that can provide economically useful services and goods. For example, the ability to refuel an existing communications satellite or de-orbit a failed one.
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3.A) Satellite tug
Assuming we have implemented the light-gas gun and we limit the acceleration to 100 g's - we can get by with a launch tube about 19 miles long. We can situate this barrel along the slope of Mauna Kea. Mauna Kea is an extinct volcano, near the equator, which reaches 14,000 feet into the atmosphere, and it already has infrastructure all the way to its top to support observatories.
Mauna Kea
Once built we start launching anything and everything that might be useful into LEO. Where possible we get paying customers, where it is not possible we start building our own infrastructure - limited only by how fast we can re-evacuate the launch tube between launches (hopefully we can make several launches per day).
We can start with a fuel depot and a satellite tug & servicing unit. The service we'll provide is refueling, re-boosting, or moving other company's satellites for a fee. We wish to make this competitive but our operating costs will be 1/100th that of our competitors. Our fees will mostly include paying back the cost of building the light-gas gun barrel.
Given a little more sophistication, a concept I helped develop while in college, and the correct raw materials we could even construct mechanical parts while in orbit if we elected to start a satellite repair facility. Since many electronic parts are made to withstand high-g loads (e.g. dropped laptops) we may even be able to use our launch infrastructure to shuttle up necessary parts for electronic servicing missions.
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3.B) The new sheriff in town
What isn't widely known outside the space community is LEO has turned into a junkyard. The junk is so pervasive that it is getting dangerous to operate in these orbits and in fact satellite manufacturers have begun to include armor on the satellites that must operate in this region!
What can we do about it?
Why we can clean up the town! Assuming we have both the light-gas gun, satellite tug, and the fuel depot we can introduce a craft somewhat similar to the tug. Make it less sophisticated but include many deflated but giant balloons that we can inflate with a light-weight fluffy substance called an aerogel.
Next we use a high efficiency engine (such as an ion thruster - not discussed here). We then do an orbital plane change change until our balloon is in a retrograde orbit and release it. The balloon won't last long in this orbit but while it lasts it'll intersect a bunch of space junk. Each piece that the balloon hits will be decelerated a bit so that it gets de-orbited. Ironically the same thing will happen to the balloon. The more effective the balloon (intersecting a lot of junk) the faster our balloon will itself de-orbit.
Our junk cleaner satellite can release many such balloons before it too de-orbits and burns up.
We would NOT perform this clean-up for free - this would be a service provided at some cost to various interested parties (including governments).
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3.C) Space tug
What's the difference between our "satellite tug" and our "space tug"? Size and sophistication mostly. The satellite tugs would be used almost exclusively around the Earth (near Earth and Geosynchronous orbits). Meanwhile the "space tug" would be intended for use in interplanetary space and would be intended to work on maneuvering small asteroids and comets.
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3.D) Miscellaneous
Up until this point we have discussed technologies and capabilities centered around the needs of the Earth and Earth based infrastructure. In fact all of the concepts I've discussed do not even require a human presence in space at all! At some point we (as the explorers and colonizers that humans have always been) will want to expand our presence into space.
Given the launch costs (even with something like the light-gas gun or project Orion craft) we will need to begin to build self-sufficient infrastructure in space. An infrastructure which we can collect, process, and directly use most of the basic resources needed to sustain humans in space.
More reading:
Atomic Rockets Home Page
Blogger has nerfed this link, the website name is "projectrho" and can be found with a quick query for "atomic rockets".
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Continue to The Case for Space IV: How to pay our way
