The gunsling is a bundle of strong plastic fibers bound with resin in the center of rotation and on the surface adjacent to the projectiles. It rotates like a sling. The projectile slides inside it instead of being attached to the tip of the sling. In addition to the centrifugal force, the projectile is subjected to the Coriolis force, which doubles the kinetic energy of the projectile.
The projectile is fired from a stationary gun into the first gunsling. Upon leaving it, the projectile enters the second gunsling at 3.5 km/s. Each gunsling has the same size, angular velocity, and contributes the same energy to the projectile. Cargo is exposed to the extreme acceleration. No bibliography. The minimum mass is only 100 tons.
Gunslings must be made of a material having high specific strength (strength-to-mass ratio), preferably Spectra fiber. The maximum tip velocity of a non-tapered sling (called characteristic velocity) equals (2tensile_strength/density)0.5. A gunsling made of bare Spectra fibers has the characteristic velocity of 2.5 km/s, which means that a massive, untapered, and perfectly stiff gunsling contributes kinetic energy equal (projectile mass)(25002). Interaction with the moving projectile bends the real gunsling in desirable direction, so the projectile may gain even more energy. The gunslings are slightly tapered to compensate for the mass of the resin. Extremely tapered gunslings are not desirable, because they bloat the total mass of the gunsling relay. A total of six gunslings are needed to accelerate the projectile to the orbital velocity. To eliminate gyro effect and reduce angular velocity of the projectiles, there must be an even number of gunslings rotating in opposite directions.
Geared shafts synchronize the gunslings. Gunsling timing and shape are such that they impart more energy to a slow projectile than a fast one. This effect helps synchronize the projectile with the gunslings.
Direct physical contact between the projectile and a disposable liner ablates both the projectile and the liner. The liner is made of small bundles of Spectra fibers. Dovetail grooves inside the gunsling keep the bundles in place. A knot in the middle of the bundle is inside the groove, while the rest of the bundle is outside the groove and in contact with the projectile. The unconventional design of the liner is necessary to ensure that it is easy to replace and can stretch with the gunsling. The cost of replacing ablated fibers is moderate -- one kilogram of Spectra fibers costs about $50. Nylon fibers can also be used as the liner and are less expensive. However, they are much weaker than Spectra, so they can be used in long gunslings only.
To reduce aerodynamic drag, the gunslings spin inside evacuated chamber supported by a stratospheric blimp which floats at an altitude of 37 km. At this altitude the atmospheric pressure is only 1 percent of the pressure at the sea level. The low pressure reduces stress in the vacuum chamber and atmospheric drag on the projectiles. Plasma windows, gate valves, and silencer shaped baffles reduce air leakage into the vacuum chamber.
A miniature turbojet provides power for the gunslings and resists the force of jet streams. The gunslings are attached to the turbojet via geared shafts and special magnetic clutches. The clutches are made of rare earth magnets. Depending on the torque, the clutch either does not slip, or it slips so much that it transmits almost no power. The purpose of the clutch is to prevent gear damage during projectile launch.
Designing the bearings supporting the gunslings is a challenge, because they have to endure high angular velocity, extreme forces during projectile launch, and the absence of active cooling system. (The ambient air is too thin to carry away the heat.) A dual bearing design solves the problem. Small journal bearings support the gunslings all the time except the moment of projectile launch. The gunsling axle bends during launch thus coming into contact with large bearings.
The projectiles are fitted with protrusions which look like axles. The protrusions match grooves in the gunslings. Their purpose is to reduce angular velocity and centrifugal stress of the projectiles spinning about their center of mass. The projectiles are released at 10 degree angle to the horizon into elliptical orbit having the apogee of about 10,000 km. A solid propellant rocket motor is mounted inside every projectile. When the projectile reaches the apogee, the motor is ignited by a simple delay fuse.
Any freely spinning object will change its axis of rotation until it rotates about an axis having the greatest moment of inertia. Therefore, the projectile must be shaped like a disk to ensure that it rotates about its axis of symmetry after leaving the atmosphere. The apogee rocket motor does not need control electronics because the projectile spins like a gyro. A catcher satellite scoops up the tiny projectiles and assembles them into large structures.
A two-sided gunsling enclosed in a vacuum chamber surpasses the performance of the conventional gunpowder artillery by 2 orders of magnitude -- a 100 kg gunsling can hurl 1 kg projectiles at 4 km/s. To reduce shock stress and recoil, the gunsling simultaneously releases 2 projectiles in opposite directions. Rifled tubes improve aim.
Curator: Al Globus
NASA Responsible Official: Dr. Ruth Globus
If you find any errors on this page contact Al Globus.
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