We will look in some detail at the light combustion gun and railgun technology. Nextbigfuture believes that railgun technology is the better technological choice.
Magnetic gun technology would be better in the long run
The long run potential of electrically powered magnetic gun is what matters. Light combustion technology is still limited as other chemical technology is nearing its limits. Ultimately magnetic technology can have far better power density than any chemical technology. The argument about light gas guns would be like an argument that repeater crossbows, improved long bows and improved arrow technology are better than flint lock guns. Early cannons would have been inferior to improved ballista's.
The US military does not need either technology to make a difference in any actual likely combat situation. No military conflict with any nation in the middle east will be determined by having exceptional range on large guns. Large and long range guns also would not significantly impact any military scenario involving China or Russia. Improved drones modified for long range bombing would likely be the easiest solution for any situation that might also have long range guns as an option.
Here is a 2007 report on the Navy project for combustion light gas gun technology They built and tested 45 mm (millimeter) combustion light gas guns and built and had some work on 155 mm guns.
The Combustion Light Gas Gun or CLGG has been investigated for over ten years. During this time the research has shown that the technology provides a minimum of 30% more muzzle energy than advanced solid propellant guns which translates to significant advantages in range and/or throw weight. For the Navy Barrage round fired from a 155mm bore CLGG, the predicted range is up to 200 nm (nautical miles), sufficient to provide effective amphibious and in-shore fire support without endangering capital assets. In addition, the CLGG provides:
• The ability to “manufacture” propellant as needed on board ship
• The ability to remotely discharge propellant in damage control situations
• The ability to automatically adjust the propellant charge as needed
The 2006 work built on efforts by continuing to address remaining issues associated with successful system demonstration such as cryogenic propellant handling, multi-shot demonstration, modeling, and proof of principal at 155mm scale. The safe use cryogenic propellant as a viable means to store gaseous propellant before use as well as the subsystems (i.e. projectile, igniter, and auto-loader) required for rapid fire operation is mostly resolved. In addition the hardware for full scale (155mm) demonstration of CLGG technology was largely completed.
The Promised muzzle energy and firing range of the current railgun project could be achieved with the light gas gun
The CLGG System compares favorably to other proposed gun systems with respect to system size, weight, firing rate and operability. The CLGG however, has several distinct advantages over other gun systems, such as:
• Variable range up to 200 nautical miles
• Insensitive, guided projectiles (safer storage and supports more rounds per ship)
• Lower operating costs, including projectile cost
• Easily scalable to support longer sustained rates of firing (i.e. larger H2 storage tanks allow more rounds to be fired at a given firing rate)
• Single H2/O2 production system can support multiple guns of different sizes
Super guns for launching into space are possible but seem inferior to the possibility of a Spacex reusabe rocket
John Hunter of Quicklaunch is working on commercialising the 'Hydrogen Gun', a new form of mass driver which proposes to deliver unmanned payloads to orbit for around 5% of regular launch costs (i.e. $500/lb or US$1,000/kg) and perform 5 launches per day
Ram accelerators have been proposed as a cheap method to get payloads into space. Impulsive launched projectiles need some means to circularize their trajectory for orbit insertion, so rockets, such as those designed in Project HARP, are typically incorporated into the projectiles. Using rockets for upper stages, it is believed that a launch cost of less than $500 (US dollars, 2004) per kilogram can be attained. Using a tether or space tug would further reduce launch costs.
The main competitors to a ram accelerator for direct space launch applications are two-stage gas guns (SHARP), multiple sidewall injection gas guns (JVL), railguns and coilguns. Ram accelerators are currently used primarily for research into supersonic combustion
Railguns have now had far more development and are now being deployed on a pilot basis for Navy ships and army vehicles. Railgun technology will be further boosted by the development of better and cheaper superconductors. Improving capacitor and battery technology will also help enhance railgun capabilities.
Railguns also have the potential to reach far higher speeds if the materials are improved to enable non-destructive launches.
A railgun consists of two parallel metal rails (hence the name) connected to an electrical power supply. When a conductive projectile is inserted between the rails (at the end connected to the power supply), it completes the circuit. Electrons flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.
This current makes the railgun behave as an electromagnet, creating a magnetic field inside the loop formed by the length of the rails up to the position of the armature. In accordance with the right-hand rule, the magnetic field circulates around each conductor. Since the current is in the opposite direction along each rail, the net magnetic field between the rails (B) is directed at right angles to the plane formed by the central axes of the rails and the armature. In combination with the current (I) in the armature, this produces a Lorentz force which accelerates the projectile along the rails, away from the power supply. There are also Lorentz forces acting on the rails and attempting to push them apart, but since the rails are mounted firmly, they cannot move.
By definition, if a current of one ampere flows in a pair of infinitely long parallel conductors that are separated by a distance of one meter, then the magnitude of the force on each metre of those conductors will be exactly 0.2 micro-newtons. Furthermore, in general, the force will be proportional to the square of the magnitude of the current and inversely proportional to the distance between the conductors. It also follows that, for railguns with projectile masses of a few kg and barrel lengths of a few meters, very large currents will be required to accelerate projectiles to velocities of the order of 1000 m/s.
A very large power supply, providing on the order of one million amperes of current, will create a tremendous force on the projectile, accelerating it to a speed of many kilometres per second (km/s). 20 km/s has been achieved with small projectiles explosively injected into the railgun. Although these speeds are possible, the heat generated from the propulsion of the object is enough to erode the rails rapidly. Under high-use conditions, current railguns would require frequent replacement of the rails, or to use a heat-resistant material that would be conductive enough to produce the same effect. At this time it is generally acknowledged that it will take major breakthroughs in material science and related disciplines to produce high-powered railguns capable of firing more than a few shots from a single set of rails. The barrel must withstand these conditions for up to several rounds per minute for thousands of shots without failure or significant degradation. These parameters are well beyond the state of the art in materials science.
A 2003 study of railguns for space launches was made.
The extension of railgun technology to the muzzle velocities ( 7500 m/s) and energies ( 10 GJ) needed for the direct launch of payloads into orbit is very challenging, but may not be impossible. For launch to orbit, even long launchers ( 1000 m) would need to operate at accelerations 1000 gees to reach the required velocities, so that it would only be possible to launch rugged payloads, such as fuel, water, and material. A railgun system concept is described here and technology development issues are identified. Estimated launch costs could be attractively low ( $600/kg) provided that acceptable launch rates can be achieved. Further evaluations are needed to establish the technical and economic feasibility with confidence.
A 10 page IEEE paper, Launch to Space With an Electromagnetic Railgun by Ian R. McNab, Senior Member, IEEE The cost of electricity for a launch will be negligible, as shown below. Barrel life is central to the successful economics for this system. A system might cost $1.3 billion and launch for $500/kg. Recent tests fired 7 pound projectiles at 5637 mph. Lunar escape velocity is 5,324 mph. So the truck sized system is already good enough to launch from the surface of the moon. Classic science fiction "the Moon is Harsh Mistress" by Heinlein could become reality.
Other gun launch systems were reviewed and found lacking:
Only Electromagnetic railguns seem worthy of further study for this application.
This choice was made on the basis that:
• they have already achieved 7 km/s at small scale, and 10.6 MJ at 2–3 km/s (with a test system able to go to 32 MJ) ;
• significant development is being funded for military applications;
• they offer the possibility of achieving the muzzle velocities and energies required;
• the potential cost savings seem significant based on our estimates.
Methods of accelerating large masses in large bore railguns will need to be developed, and some concepts are suggested here.
The muzzle velocity in the range needed for a moon-based launch system have already been achieved in the recent test firings. (about 2.5 km/s). Then it would just be a matter of scaling up energy linearly for heavier masses. (E=MC**2). The 10.6MJ system shot a 7 pound shot. The current 32MJ could fire 21 pounds (10kg) at the desired speed. A 320MJ system could fire 100kg payloads. Using resources available on the moon, this could serve as the forward base for sending material to Mars in support of a manned mission or to supply orbital infrastructure around the earth.
Even a scaled model would have substantial energy requirements: 10 kg at 7 km/s is a muzzle energy of 250 MJ, and with a launcher efficiency of 80%, an energy input 300 MJ would be required. This is comparable to the energy obtained from capacitor modules for the U.S. National Ignition Facility for laser fusion research.
The estimated system cost of $1.3B and a component life of 10 000 launches without replacement yields a cost of about $530/kg into orbit. It is important to note that this does not include the cost of the vehicle itself or operational costs on the Earth or in space, and these items need to be estimated.
The UTSTAR railgun tube.
Railgun launcher parts and sizes for the IEEE designed system
A chart with speed, energy and other variable tradeoffs.
Basically below 7km/s the total energy needed to launch a commercially viable amount of annual payload increases rapidly
The extension of this technology to the muzzle velocities ( 7500m/s) and energies ( 10 GJ) needed for the direct launch of payloads into orbit is very challenging, but may not be impossible. For launch to orbit, even long launchers ( 1000 m) would need to operate at accelerations 1000 gees to reach the required velocities, so that it would only be possible to launch rugged payloads, such as fuel, water, and material. Estimated launch costs could be attractively low ( $600/kg) compared with the Space Shuttle ( $20 000/kg), provided that acceptable launch rates can be achieved.
So triple the muzzle speed and increase power by 1000 times the current test level or 330 times the current 32 MJ system.
A disadvantage of gun launch is that the launch package has toleave the gun barrel at a very high velocity ( 7500 m/s) through the Earth's atmosphere, leading to a very high aerothermal load on the projectile.
However, the current 32 MJ system is only about the size of a truck. So a nice big scramjet that could fly at Mach 10-12 could use a moderately scaled up version of the rail gun current system to fly above most of the atmosphere and then fire hardened payloads into orbit. Then less heat shielding would be needed.
To provide 500 tons/year to orbit would require 2000 launches/year—a little over five per day on average.
The launch package is cargo within a shaped shell with a small rocket.