The ORLAN-M spacesuit is the main means to support cosmonaut extravehicular activities (EVA).
A spacesuit of the semi-rigid type is the most fitting for the EVA on operation of the permanent orbiting station (OS). The semi-rigid spacesuit with an integrated self-contained life support system is optimal for repeated work in the open void for a long time.
There are several modifications of such spacesuit. All of them have a number of advantages making their use successful in long-term missions. The following advantages can be attributed to them: - quick unaided donning/doffing of the suit; - usage of a single standard size of the suit for cosmonauts with various anthropometric characteristics; - possibility to maintain the suit in the orbit without its return to the Earth; - easy replacement of replaceable and failed components.
Proceeding from the necessity to use the spacesuit on-board the SALYUT OS for a long time and maintain it by cosmonauts themselves, the first modification of the ORLAN spacesuit (assigned with index "D") was developed. The ORLAN-DM, the next modification of the spacesuit, was the intermediate stage prior to utilization of the ORLAN-DMA spacesuit, which was operated in the SALYUT-7 OS and in initial phase of the MIR OS operations.

The ORLAN-D and ORLAN-DM spacesuits were connected to the on-board systems with electric umbilicals, which supplied the electric power to the suits systems, supported radio communication and transferred the telemetric information on suits` functioning and cosmonaut physical state. The suit connection to the on-board station with the electric umbilical was quite an acceptable solution for cosmonaut EVA on the OS surface near the airlock.
The most significant modification of the semi-rigid ORLAN type spacesuit was assigned with the index "DMА". This modification made it possible to increase the time of self-contained operation up to 6 hours. Moreover, there were made a number of principle changes in the suit design. Unlike the ORLAN-DM, the ORLAN-DMА spacesuit could be used on the MIR OS without the electric umbilical connecting it to the OS on-board systems. For this purpose, the ORLAN-DMА spacesuit was equipped with two safety tethers and a dedicated removable unit containing an electric power source and units of radio-telemetric system/ antenna-feeder device. The radio antenna proper was built in the spacesuit outer protective garment.
The ORLAN-М, the fourth modification of the spacesuit, was used for the EVA from the MIR OS. The MIR OS existed over 15 years. In order to keep the station operable, to conduct various research and repair activities, 46 Russian and foreign cosmonauts performed 78 paired EVAs from the orbiting station with the total duration exceeding 700 man·hours. Moreover, the ORLAN-M supports international crew EVAs, even nowadays being the only orbit-based spacesuit at the International Space Station (ISS). The ORLAN-M supports EVAs from both the ISS Russian segment and ISS common airlock. Currently, the ORLAN-MK, a new modification of the ORLAN spacesuit, is under testing. Its major novelty is an on-board computer system.

The 21KC unit makes it possible for a cosmonaut suited in the ORLAN-DМА to transfer with 6 degrees of freedom The 21KC design takes into account the specific features of the ORLAN-DМА semi-rigid spacesuit and uses the advantages of its design concept. The maneuvering controls are arranged on two rotation booms. The working medium for 32 jet thrusters of the unit is air containing in two 28-liter bottles under a pressure of 35 MPa.