Simulating Reduced Gravity Environments on Earth
Planetary operations demand testing of surface system elements such as rovers, excavators, habitats, deployables, and space suits in planet-relevant gravity. To effectively and affordably simulate reduced gravity effects, Astrobotic Technology and Carnegie Mellon University developed a scalable gravity offload device under a Small Business Technology Transfer award from NASA. Gravity offloading is accomplished by applying a force to counter some portion of Earth gravity to achieve an effective reduced gravity. While this technique sounds straightforward, it demands that the upward-pulling force is always aligned over the center of gravity of the test object. If the pulling force is not aligned, the object will be dragged sideways. For objects that don't move, or only move in circles, a simple seesaw provides a cheap and effective solution. A mobile test object like a planetary rover travels over a surface without any limits on straight lines. This system measures the slight sideways movement of the upward-pulling cable and moves to compensate. The end result is that the test object feels minimal sideways forces while freely roaming under simulated low gravity. The Gravity Offloader is a modified overhead crane with three enhancements: high-speed computer-controlled movement, a variable upward force device, and deflection sensors. The pit itself is 20'x20', filled with a sand mixture that emulates the lunar surface material. The variable upward force device is a modified cable hoist that can be programmed to pull upwards with a force from zero to its design capacity of 330 pounds. To measure the movement of the test object, two weather vane-like sensors are used to determine where to move the crane to compensate and keep the cable hoist directly overhead of the test object. During testing, the Gravity Offloader delivered results that exceeded requirements by a comfortable margin – offload force with average error of less than 5% of the offloaded weight and displacement of the cable with average error of less than 1 degree. The result is an affordable commercial device that is broadly capable of producing any reduced gravity environment and scalable for test objects of any size.