The twin Voyagers are the only man-made objects to have entered interstellar space. However, while they have left the heliosphere, they have not yet left the boundary of the Solar System which is considered to be the outer edge of the Oort Cloud. Upon passing the heliopause, "Voyager 2" Plasma Science Experiment (PLS) observed a sharp decline in the speed of solar wind particles on 5 November and there has been no sign of it since. The three other instruments on board measuring cosmic rays, low-energy charged particles and magnetic fields also recorded the transition. The observations complement data from NASA's IBEX mission. NASA is also preparing an additional mission, Interstellar Mapping and Acceleration Probe (IMAP) which is due to launch in 2024 to capitalise on Voyager observations.