Introduction  The technical fascination with spacecraft rendezvous and docking is unmistakable. The attraction of  watching complex vehicles carrying humans approach, align, collide, attach, park, and structurally anchor  is timeless. For as long as travelers have set off on perilous voyages, onlookers have been mesmerized by  their departure, return or arrival in a foreign port. The vocabulary of spacecraft docking harkens back to the  days of wind-driven ships. Docking, berthing, ports and other mating system terminology are vestiges of  our maritime traditions. The special allure of spacecraft docking is evident in popular culture. Most space  travel motion pictures inevitably include a detailed technical scene depicting how the spacecraft docks or  undocks, complete with the whoosh of a hatch opening and the clunk of the final structural connection to  symbolize the consequence and finality of arrival and departure.  NASA’s newest docking system evolved from systems developed during the Apollo-Soyuz Test Project.  This paper will trace the considerations that drove that evolution to the current design. It will provide an  overview of the NDS architecture, components, and operation, and will recount a few of the key technical  challenges and lessons learned during system development and qualification. System performance as  demonstrated by dynamic testing is also summarized.  Historical Context  NASA makes a distinction between docking and berthing operations. Docking is defined as the process of  connecting two spacecraft without external assistance. Continuing with the maritime analogy, docking  represents the combination of a port and a ship for which the captain in a boat is able to navigate, make  land and tie up to a boat dock without external aid. Berthing, on the other hand, is analogous to the large  ship scenario where a harbor master or pilot boat is required to aid moving the boat into the boat dock.  Wigbert Fehse defines docking and berthing in Automated Rendezvous and Docking of Spacecraft  as  follows [1]:   In the case of docking , the guidance, navigation and control system of the chaser controls the vehicle  state parameters required for entry into the docking interfaces of the target vehicle and for capture.  In the case of berthing , the guidance, navigation and control system of the chaser delivers the vehicle  at nominally zero relative velocities and angular rates to a meeting point, where a manipulator, located  either on the target or chaser vehicle, grapples it, transfers it to the final position and inserts it into the  interfaces of the relevant target berthing port.  In the current International Space Station (ISS) berthing operations, the pilot boat is replaced by the Space  Station robotic arm. Visiting vehicles or other external hardware are plucked from a station keeping position  or removed from a cargo bay, and placed onto an attachment mechanism on the ISS. Berthing allows for a  lighter and less complex attachment mechanism than docking, but requires an external robotic manipulator  to be present at all berth and unberth events. The safe handoff of the payload from the robotic arm to the  berthing mechanism presents technical challenges as well.   In docking, the attachment mechanism includes its own robotic manipulator, known as the Soft Capture  System (SCS), for maneuvering the vehicles after soft capture into final position for hard mate. The SCS  has a capture envelope large enough to accommodate the inaccuracies of the Guidance, Navigation and  Control (GN&C) system. It attenuates the relative motion of the two vehicles, and then slowly brings them  together with enough accuracy to engage the shear features of the interfacing tunnels.  The development of ISS created several different mechanisms for berthing, most notably the Common  Berthing Mechanism. Common Berthing Mechanisms are used to connect the pressurized elements of the  Space Station and allow crew to move between elements. Several other berthing mechanisms are used  around the Space Station to attach the unpressurized truss elements. Despite its array of berthing  mechanisms, NASA lacked a man-rated pressurized docking system design before the development of  NDS. The last US-built docking system, shown in Figure 2, flew in support of the Apollo Soyuz mission.   NASA/CP—2018-219887 472