are several different space drives that need little or no reaction mass to function. A tether propulsion system employs a long cable with a high tensile strength to change a spacecraft's orbit, such as by interaction with a planet's magnetic field or through momentum exchange with another object. Solar sails rely on radiation pressure from electromagnetic energy, but they require a large collection surface to function effectively. A magnetic sail deflects charged particles from the solar wind with a magnetic field, thereby imparting momentum to the spacecraft. The Magsail is a large superconducting loop proposed for acceleration/deceleration in the solar wind and deceleration in the Interstellar medium. A variant is the mini-magnetospheric plasma propulsion system and its successor, the Magnetoplasma sail inject plasma at a low rate to enhance the magnetic field to more effectively deflect charged particles in a plasma wind. An E-sail would use very thin and lightweight wires holding an electric charge to deflect these particles, and may have more controllable directionality. As a proof of concept, NanoSail-D became the first nanosatellite to orbit Earth. As of August 2017, NASA confirmed the Sunjammer solar sail project was concluded in 2014 with lessons learned for future space sail projects. Cubesail will be the first mission to demonstrate solar sailing in low Earth orbit, and the first mission to demonstrate full three-axis attitude control of a solar sail. Japan also launched its own solar sail powered spacecraft IKAROS in May 2010. IKAROS successfully demonstrated propulsion and guidance and is still flying today. A satellite or other space vehicle is subject to the law of conservation of angular momentum, which constrains a body from a net change in angular velocity. Thus, for a vehicle to change its relative orientation without expending reaction mass, another part of the vehicle may rotate in the opposite direction. Non-conservative external forces, primarily gravitational and atmospheric, can contribute up to several degrees per day to angular momentum, so secondary systems are designed to "bleed off" undesired rotational energies built up over time. Accordingly, many spacecraft utilize reaction wheels or control moment gyroscopes to control orientation in space. A gravitational slingshot can carry a space probe onward to other destinations without the expense of reaction mass. By harnessing the gravitational energy of other celestial objects, the spacecraft can pick up kinetic energy. However, even more energy can be obtained from the gravity assist if rockets are