People have been shooting things into space since the 1940s, but in every case this has involved using rockets. This works, but it’s incredibly expensive with the cheapest launch costs hovering around US$2,000 per pound. This is in part because almost every bit of the rocket is either destroyed or rendered unusable once it has put the payload into orbit. Reusable launch vehicles like the SpaceX Grasshopper offer one way to bring costs down, but another approach is to dump the rockets altogether and hurl payloads into orbit. That's what HyperV Technologies Corp. of Chantilly, Virginia is hoping to achieve with a “mechanical hypervelocity mass accelerator” called the slingatron.
Invented by Derek Tidman in the 1990s, the slingatron replaces rockets with a more sophisticated version of the sling famed in the story of David and Goliath, and still used today by enthusiasts to hurl pumpkins across fields.
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A sling works by spinning in a circle about the user’s head. The thong on the sling keeps the stone in place and the slinger spins it faster and faster before releasing it. The limiting factors are the speed of the slinger’s arm and the strength of the thong. The slingatron uses a slightly different principle. If it tried to spin the entire machine fast enough to hurl a projectile into orbit, the forces generated would tear the slingatron to bits. Instead, as its name implies, it acts more like a cyclotron, which is a very simple particle accelerator.
A cyclotron is a flat, hollow metal cylinder inside of which is a vacuum. There are also a pair of magnetic or electrostatic plates of opposing charges. An atomic particle, such as a proton, is introduced into the center of the cyclotron and is attracted to the negative plate. The polarity of the plates flips and the proton rushes toward the other plate. As the frequency of the flipping is increased, the proton moved faster and faster in a series of ever widening spirals until it reaches the rim of the cyclotron and shoots out a window at extremely high velocity, though the machine itself never moves.
The slingatron achieves the same result mechanically. Instead of using charged plates or spinning around, a spiral tube gyrates in circles around its axis. It is similar to the way someone swirls wine in a glass, so that the wine spins around the glass although the glass itself doesn't spin at all. If the glass is swirled at a low frequency, the wine swirls in a leisurely fashion, but by increasing the frequency slightly, the wine is soon shifting up the sides of the glass and slopping over the brim.
Inside the slingatron is a spiral tube, or a series of connected spiral tubes, depending on the design, that gyrates on a series of flywheels spread along its length. As the slingatron gyrates, a projectile is introduced into the tube and the centripetal force pulls the projectile down it. As the projectile slides through larger and larger turns of the spiral, the centripetal forces increase as the the frequency of gyrations increases to up to 60 cycles per second. By the time the projectile shoots out the muzzle in the rim of the slingatron, it is traveling at kilometers per second.
Friction is an obvious problem with such a setup, but this is reduced at first by a Teflon skin, which rapidly wears away, and then by means of a substance, such as a polycarbonate, with a low boiling temperature, wrapped around the projectile. As the projectile spins around inside the tube, the substance vaporizes and forms a frictionless layer of gas. In addition, unlike conventional payloads, the projectile needs a heat shield for leaving the atmosphere.
The goal is to build a slingatron big enough to fire a projectile at 7 km/s (15,600 mph, 25,000 km/h), which is enough to put it into orbit. Actually, it will have to be traveling faster than that when it leaves the muzzle because it has to travel through the atmosphere, where it will lose some velocity. There’s also a need for a small rocket on board for final orbit insertion and course corrections, which highlights the strengths and weaknesses of the idea.
With rapid turnarounds and thousands of launches per year while all of the launch system remains on Earth, the developers say the slingatron promises lower costs for getting payloads into orbit. Unfortunately, the G-forces involved are tremendous with the projectile subjected to up to 60,000 times the force of gravity.
It’s questionable whether any rocket system could survive such stresses and there’s certainly no chance of a slingatron being used on a manned mission because it would turn an astronaut into astronaut pudding. Only the most solid state and hardened of satellites built along the lines of an electronic artillery shell fuse would have a chance of survival. The developers say that a larger slingatron would reduce the forces, but even with a reduction by a factor of 10,000, it would still be restricted to very robust cargoes. This makes it mainly attractive for raw materials, such as radiation shielding, fuel, water, and other raw materials.
Currently, there have been three one-meter (3.2 ft) prototypes built ranging from a tabletop demonstrator to a semi-modular design capable of firing a 0.5 lb (226 g) projectile at 100 m/sec (328 ft/sec). HyperV Technologies Corp. has launched a Kickstarter campaign that aims to raise $250,000 to build the modular Slingatron 5, which will be 5 m (16.4 ft) in diameter. It is designed to launch a 0.25 lb (113 g) projectile at 1 km/s (0.62 mi/sec) and later be capable of launching a one-pound (453 g) payload at 2 km/s (1.24 mi/s). Eventually, the team hopes this will lead to a full-scale version capable of launching a payload into orbit.
In addition to the Slingatron 5 demonstrator, the developers also hope to host the Slingatron Applications Workshop to discuss further applications of the technology and related topics.
The video below outlines how the slingatron works.