Space Guns
Jules Verne, the French writer who pioneered the science fiction genre, once wrote, “Anything a man can imagine, another man can create.” But even Verne might be surprised to see that some of the fantastic ideas he imagined 100 years ago are becoming realities today.
Verne was an extraordinary author and his fertile imagination has inspired generations of scientists and engineers. In one of his works, Verne imagined a voyage to the moon enabled by a gigantic space gun. The fictional cannon, called Columbiad, fired a projectile holding three travelers to the moon. Today, a kind of space gun is moving toward true viability and possible commercial application. But first, a little background…
Due in part to the ballooning US deficit, America’s replacement for the shuttle program, Constellation, has been canceled. Once the last space shuttle mission is completed this summer, Americans will be riding on Russian rockets to get to the International Space Station.
However, America will return to space exploration. The reason is simply that space, as my old friend Robert Heinlein pointed out, is the high ground militarily. Americans may be willing to share the high ground. They won’t cede it.
Using conventional technology, the costs involved in extending space exploration to the moon and Mars are prohibitive. Alternatives to conventional rocket launch must be found if costs are to be significantly reduced to allow real exploration and commercialization.
This is great news for commercial space enterprises and their investors. During the Space Race of the 1960s, the United States investigated every possible method to gain an advantage. One was a collaboration between the US and Canadian defense departments. Unlike more conventional (and expensive) rocket-based technology that would become the standard method of access to orbit, this project was based on the use of large guns.
In fact, the gun itself was based on a recycled 16-inch naval gun. Called HARP, the acronym for High Altitude Research Project, the project achieved several speed and altitude records. The final versions of the projectile/vehicle, called Martlet, blasted 180-kilogram payloads out of the barrel at speeds nearing 4 kilometers per second. These reached altitudes of 180 kilometers, after being subjected to a brief and brutal acceleration exceeding 14,000 Gs.
Unfortunately, bureaucratic infighting between the different US service branches, as well as anti-Vietnam War fallout, ended the US/Canadian collaboration. Funding was terminated by 1967.
In the 1980s, the US government revisited the space gun concept, launching the Super High Altitude Research Project (SHARP). Headed by Dr. John Hunter from 1989-1995 and conducted at the Lawrence Livermore National Laboratory, SHARP used technology far advanced over the old HARP project. Instead of cordite explosive detonation, SHARP used gas gun technology. SHARP set records for kinetic energy above Mach 9. It also successfully launched hypersonic scramjet test vehicles for the Air Force between Mach 5 and Mach 9.
Since then, Dr. Hunter has started a new company, Quicklaunch Inc. Its goal is to commercialize the technology he helped develop at Lawrence Livermore.
Hunter and his partners have produced a design for a true space gun. Essentially, it is a long hollow tube 1,000 meters in length. At one end of the tube, hydrogen gas is pumped into chambers at high pressure and then heated. When the launch initiates, the gas is expelled behind the launch vehicle and accelerated at close to 5,000 Gs. Pictures and video are available at his website.
The gun platform would be sea based and mostly submerged. No real estate would therefore be needed to accommodate the launcher. Since the gun would be buoyed by seawater, its launch angle and direction could be easily varied to put payloads into different orbital inclinations and altitudes.
Why use hydrogen as the propellant? All other things being equal, the lighter the molecular weight of a gas, the higher the speed at which sound can propagate through it is. The maximum rate of expansion for a gas is generally equal to the speed that sound waves can move through it. For this reason, since hydrogen is the lightest element, it is the optimal gas. At 11 kilometers per second, it has the highest speed of expansion.
It is an interesting coincidence that the Earth’s escape velocity is also 11 kilometers per second. Because of inefficiencies, the vehicle would exit the gun at about 6 kilometers per second. When the Quicklaunch vehicle would attain sufficient altitude, beyond most of the Earth’s atmosphere, a rocket motor would ignite. This would supply the remaining velocity required to enter orbit. It would also allow directional maneuvering to a docking point.
Does the space gun require esoteric, undeveloped technology to work? We queried Dr. Hunter regarding the technical feasibility of such a launch device, and he told us that it is extremely attainable. Ballistics has been, for the most part, old hat since Isaac Newton. The Quicklaunch space gun isn’t even that extraordinary in terms of the temperatures, pressures and rates of acceleration it develops.
To compare, the final version of the Quicklaunch space gun will develop an internal pressure of 15,000 pounds per square inch and the hydrogen gas in the chamber will reach a temperature of over 2,600 F. The launch vehicle will experience 5,000 Gs of acceleration. While this may sound extreme, you can pop into your local Wal-Mart and for a few hundred dollars purchase a reliable .30-caliber rifle that develops well over 50,000 PSI with propellants that approach temperatures twice those the space gun develops. Working gas guns like those developed at Lawrence Livermore and Sandia labs already do this. This is very “doable” and, in many ways, old-school engineering.
Of course, people cannot be accelerated at this rate. We black out at around 7–9 Gs; 5,000 Gs would quickly kill a human. Quicklaunch’s business plan is for nonhuman payloads. Nevertheless, we were concerned that high rates of acceleration would create serious engineering issues for any payloads it would deliver.
Dr. Hunter explained that conventional artillery shoots projectiles at over three times the acceleration Quicklaunch’s design requires. Yet we have “smart artillery” with such things as delicate electronic components. For years, in fact, we have had GPS-guided artillery shells and rocket-assisted projectiles.
The big question, however, remains: Does a market exist for Quicklaunch’s platform? After all, orbital gun launch has never been done before. Dr. Hunter says that the main business he envisions for Quicklaunch, when it successfully completes a space gun, will be provisioning an orbiting fuel depot.
Any future manned space missions will be propellant intensive. In conventional rockets, 95% of the weight at launch is propellant. Current launch prices range from $5,000-$10,000 per pound, which is incredibly expensive. Hunter estimates that the company will eventually be able to put fuel in orbit for future missions at only 5% of the current cost, $250-500 per pound.
It takes approximately 100,000 pounds of fuel in low Earth orbit for a moon mission. For a Mars mission, it comes out to a million pounds of fuel per person. The business case is pretty clear. At 1/20th the current rates, cost savings of gun-launched fuel would become a huge enabler for space exploration and commercialization.
There is also a market for satellite resupply at geosynchronous orbit. Some of these satellites use neon and other inert gases for their thrusters. Dr. Hunter opines that there is a business potential for a depot for these substances at geosynchronous orbit, but the more obvious market is for a fuel depot in low Earth orbit. That one is the game changer. It would be the staging ground for Mars.
From a military defense standpoint, another advantage of the space gun is responsive launch. If there is a critical need to surveil some point on the globe from space, the space gun could put an observation platform in space on demand within minutes or hours.
Quicklaunch owns this technology. There is significant IP and expertise involved in the space gun technology, and Hunter and Quicklaunch have a monopoly there. Obviously, the timeline to profitability is filled with unknowns. We aren’t ready yet to invest in this sort of enterprise, but we will be someday.
Regards,
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