NASA Docking System

The NASA Docking System (NDS) is a spacecraft docking and berthing mechanism being developed for future US human spaceflight vehicles, such as the Orion Multi-Purpose Crew Vehicle and the Commercial Crew vehicles. The NDS is NASA’s implementation of the International Docking System Standard (IDSS), an attempt by the International Space Station Multilateral Coordination Board (MCB) to create an international spacecraft docking standard. NDS is also known as the international Low Impact Docking System (iLIDS).

Two International Docking Adapters (IDA) will be attached to the ISS' Pressurized Mating Adapters (PMA), one at Node-2 forward, the other at Node-2 zenith. These will convert the Androgynous Peripheral Attach System-95 (APAS-95) to the NASA Docking System. The IDAs were scheduled to be delivered to ISS by the Dragon spacecraft on separate Commercial Resupply Services missions in 2015. IDA-1 was lost when CRS-7 was destroyed during launch in June 2015.

Design
The NDS docking mechanism is androgynous, the first system to use low impact technology and the first system to allow both docking and berthing. It supports both autonomous and piloted dockings and features pyrotechnics for contingency undocking. Once mated the NDS interface can transfer power, data, commands, air, communication and in future implementations will be able to transfer water, fuel, oxidizer and pressurant as well. The passage for crew and cargo transfer has a diameter of 800 mm.

In form and function NDS bears some resemblance to the APAS-95 mechanism already in use on the PMAs attached to the International Space Station, but is not completely compatible with it.

History
In 1996, Johnson Space Center (JSC) began development of the Advanced Docking Berthing System, which would later be called the X-38 Low-Impact Docking System. After the X-38 was canceled in 2002, development of the mating system continued, but its future was unknown. In 2004, President George W. Bush announced his Vision for Space Exploration and NASA's 2005 Exploration Systems Architecture Study was created in response, recommended the use of the Low Impact Docking System (LIDS) for the Crew Exploration Vehicle (which was later named Orion) and all applicable future exploration elements. The Hubble Space Telescope received the Soft-Capture Mechanism (SCM) on STS-125. The SCM is meant for unpressurized docking, but uses the LIDS interface to reserve the possibility of an Orion docked mission. The docking ring is mounted on Hubble's aft bulkhead. It may be used for safely de-orbiting Hubble at the end of its service lifetime. In February 2010, the LIDS program became modified to be compliant with the IDSS and became known as the international Low Impact Docking System (iLIDS) or simply the NASA Docking System (NDS). In May 2011, the NDS critical design review was completed and qualification was expected to be completed by late 2013.

In April 2012, NASA funded a study to determine if a less complex docking system could be used as the NASA Docking System that both met the international community’s desire for a narrower soft capture system ring width, as well as providing the ISS a simpler active docking system compared to the then-planned design. Boeing's proposal was the Soft Impact Mating and Attenuation Concept (SIMAC), a design originally conceived in 2003 for the Orbital Space Plane (OSP) Program.

A leaked NASA internal memo from November 2012, stated that SIMAC had been chosen to replace the previous design and that the majority of the work on the NASA Docking System would be shifted from NASA JSC to Boeing. Following this change the IDSS was modified, so the new design of the NASA Docking System is still compatible with the standard. In August 2014, Boeing announced that the critical design review for the redesigned NDS had been completed.

IDA-1 was part of the payload on SpaceX CRS-7 in June 2015, but was destroyed when the Falcon 9 rocket exploded during ascent. IDA-2 is scheduled to launch on SpaceX CRS-9.