Cygnus (spacecraft). Cygnus is an expendable American automated cargo spacecraft designed for International Space Station (ISS) resupply missions. It was initially developed by Orbital Sciences Corporation with financial support from NASA under the Commercial Orbital Transportation Services (COTS) program. To create Cygnus, Orbital paired a pressurized cargo module, largely based on the Multi-Purpose Logistics Module, built by Thales Alenia Space and previously used by the Space Shuttle for ISS resupply, with a service module based on Orbital's GEOStar, a satellite bus. After a successful demonstration flight in 2013, Orbital was chosen to receive a Commercial Resupply Services (CRS) contract. A larger Enhanced Cygnus was introduced in 2015. Orbital Sciences merged into Orbital ATK in 2015; Northrop Grumman purchased Orbital ATK in 2018 and has continued to operate Cygnus missions. A further enlarged Mission B Cygnus is expected to be introduced in 2025.

Cygnus is typically launched using its parent company's Antares rocket from the Wallops Flight Facility in Virginia, however it is able to fly on other launch vehicles. After the failure of an Antares rocket destroyed Cygnus CRS Flight 3 and damaged the Wallops facility, two Cygnus missions were launched with Atlas V rockets in 2015 and 2016. Additionally, two Cygnus missions have launched on the Falcon 9 rocket in 2024 with one more scheduled to launch in 2025, operated by CRS competitor SpaceX.

In addition to Cygnus, ISS resupply missions have been flown by the Russian Progress spacecraft, the European Automated Transfer Vehicle, the Japanese H-II Transfer Vehicle and the American SpaceX Dragon.

Cygnus is the Greek word for swan and the name of a constellation.

Development 

After the retirement of the Space Shuttle was announced, NASA began to look for commercial space launch companies who could fly cargo to the ISS. In early 2006, the agency started its Commercial Orbital Transportation Services (COTS) program, where it would help fund the development of cargo spacecraft after a competitive process. SpaceX and Rocketplane Kistler won contracts in the COTS program, however Rocketplane Kistler failed to meet several financial milestones and on 18 October 2007, NASA announced it would terminate its contract and re-award it after a second competition.

Orbital Sciences Corporation participated in this second round, proposing a largely "off-the-shelf" design. The spacecraft, named Cygnus, would be built around a service module based on Orbital's Star Bus, a satellite bus in use since 1997, which would be attached to a pressurized cargo module built by Thales Alenia Space, which had also built the MPLM cargo module used by the Space Shuttle, the cargo module for the European ATV spacecraft and several permanent modules on the ISS.

Cygnus was awarded a COTS contract worth $170 million in February 2008, which was later increased to $288 million. On 23 December 2008, NASA awarded Orbital Sciences a $1.9 billion contract under the Commercial Resupply Services (CRS) program. Under this contract, Orbital Sciences agreed to deliver up to 20 tons of cargo to the ISS through 2016 in eight Cygnus spacecraft flights.

To propel Cygnus into space, Orbital developed the Antares rocket, which also leveraged lower-cost, off-the-shelf parts and designs. Construction and design of the first stage was subcontracted to Ukrainian companies and used refurbished NK-33 engines, remnants of the Soviet N1 moon rocket. The second stage was the Castor 30, which Orbital had previously used on another rocket project (the Minotaur-C) and was based on a Peacekeeper ICBM first stage.

The first Cygnus flight was originally planned to occur in December 2010, but was repeatedly delayed. The Antares made its maiden flight lifting a payload mass simulator to low Earth orbit on April 21, 2013. On September 18, 2013, Antares successfully launched a Cygnus spacecraft on a flight test to rendezvous with the International Space Station. On 12 January 2014, the first scheduled Cygnus resupply mission arrived at the space station; the capsule carried Christmas presents and fresh fruit for the astronauts. Its arrival was delayed, first by the need to repair the station, and then by frigid weather at the launch site and solar flares that forced postponements.

With the December 2015 launch of Orb CRS-4 on Atlas V, the enhanced version of Cygnus made its debut. While it was planned from the beginning to fly on the fifth mission, the Orb CRS-3 failure and subsequent move to Atlas V meant a delay. However, lessons learned on packing and the extra capabilities of the Atlas allowed payload to be increased to .

Design 

The Cygnus spacecraft consists of two basic components: the Service Module (SM) and the Pressurized Cargo Module (PCM).

The SM was based on prior products developed by Orbital including the GEOStar and LEOStar (collectively known as Star Bus) satellite buses and the Dawn spacecraft. It has a gross mass of , 32 thrusters for attitude control and one BT-4 main engine fuelled with  of hypergolic propellants, hydrazine and nitrogen tetroxide. The SM is capable of producing up to 4 kW of electrical power via two solar arrays.

The PCM is manufactured by Thales Alenia Space in Turin, Italy. The first "Standard" PCMs had a length of , a payload capacity of , and a pressurized cargo volume of .

The fourth and all subsequent Cygnus spacecraft are the "Enhanced" variant. These have a stretched PCM with a length of , a payload capacity of , an increase of 32%, and a pressurized cargo volume of , an increase of 19.5%. To launch the added weight, Orbital used the more powerful Castor 30XL solid-fuel rocket as a second-stage.

Starting in mid-2025, a further enlarged "Mission B" Cygnus will be introduced with a length of , a payload capacity of , an increase of 19.5%, and a pressurized cargo volume of , an increase of 15.5%.

During a typical CRS missions, Cygnus maneuvers close to the International Space Station, where the Canadarm2 robotic arm grapples the spacecraft and berths it to a Common Berthing Mechanism, typically the nadir port of the Unity module.

Cygnus does not provide cargo return capability. However, it can be loaded with obsolete equipment and trash which will burn up as the Cygnus makes a destructive reentry.

An earlier proposed version of Cygnus would have replaced the PCM with the Unpressurized Cargo Module (UCM), based on NASA's ExPRESS Logistics Carrier, and would have been used to transport unpressurized cargo, such as ISS Orbital Replacement Units. Another proposed variant would have replaced the PCM with the Return Cargo Module (RCM), which would have allowed Cygnus to return cargo to Earth.

In August 2023, Northrop Grumman announced a further enlarged Mission B version of Cygnus, with a  stretch to the payload module and payload mass increased to . This version is expected to enter service with the NG-23 mission in 2025 (the first to use the new Antares 330 launch vehicle).

Lunar Gateway module variant 
In August 2019, NASA decided to sole source its design for the Minimal Habitation Module (Habitation and Logistics Outpost, or HALO) of the Lunar Gateway to Northrop Grumman Innovation Systems, which offered a minimalist  by  design based directly on the Enhanced Cygnus, as well as a larger  by  design having radial docking ports, body-mounted radiators (BMRs), batteries and communications antennas added on the outside. Northrop Grumman Innovation Systems opted to build the minimalist design, which offered the advantage of component compatibility and expedited testing of life support systems on existing Cygnus spacecraft. On 5 June 2020, NASA awarded Northrop Grumman Innovation Systems a $187 million contract to complete the preliminary design of HALO. NASA will sign a separate contract with Northrop for the fabrication of the HALO, and for integration with the Power and Propulsion Element (PPE), being built by Maxar.

Missions 
The following list includes only missions that have flown and six planned missions.  one more mission is planned to be launched on the Falcon 9 rocket from Cape Canaveral Space Launch Complex 40, and three from Wallops on an Antares 330. Cygnus is the only cargo freighter to launch on four different launch vehicles: the Antares 100 series, Atlas V, Antares 200 series and Falcon 9 Block 5. Each mission is named for a notable member of the Human spaceflight community.

See also 
 Space Shuttle retirement
 Comparison of space station cargo vehicles

References

External links 

 Cygnus spacecraft – Northrop Grumman
 Orbital Sciences news page for Cygnus (archived)
 Thales Alenia Space page for Cygnus  (archived)
 Computer animation of the Standard Cygnus delivering cargo to the ISS – YouTube

 
Cargo spacecraft
American spacecraft
Supply vehicles for the International Space Station
Vehicles introduced in 2013
Northrop Grumman spacecraft
Orbital Sciences Corporation
Commercial spaceflight