SPHERES miniature satellites. Researchers test miniature satellites known as Synchronised Position Hold Engage Re-orient Experimental Satellites (SPHERES) on board a KC-135 aircraft. This aircraft can fly in a parabolic (up and down) pattern to simulate effects of weightlessness. SPHERES satellites are designed to fly in formation within the microgravity conditions of the space shuttle or International Space Station. A network of small satellites, such as SPHERES, is thought to be a cheaper and more flexible alternative to using much larger and expensive conventional satellites. SPHERES satellites navigate using small propellant tanks.