The Expedition 65 crew aboard the International Space Station (ISS) will bid farewell to a long-serving cargo ship on Tuesday, as an almost identical vehicle undergoes final preparation for its own launch, targeted No Earlier Than (NET) 10 August from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va.
Northrop Grumman Corp.’s NG-15 Cygnus—launched last 20 February during Black History Month and named in honor of “Hidden Figures” mathematical genius Katherine Johnson—will be robotically unberthed from the Earth-facing (or “nadir”) port of the station’s Unity node and cast into free flight at about 12:25 p.m. EDT Tuesday. Elsewhere, preparations are entering high gear for the NG-16 Cygnus, which will remain attached to the station into the early fall.
Following its smooth arrival at the sprawling multi-national outpost on 22 February, laden with 8,400 pounds (3,800 kg) of payloads, equipment and supplies, NG-15 took up residence for more than four months. And with Tuesday’s departure, it will have spent 127 days berthed at the station, eclipsing last winter’s NG-13 mission by a couple of weeks for the longest single ISS stay by a U.S. uncrewed visiting vehicle.
But NG-16 does not hold the empirical record for the longest Cygnus mission, for the NG-11 cargo ship—although only attached to the station for 109 days between April and August 2019—also enjoyed a lengthy period of post-unberthing free flight and totaled 233 days in space before it was finally deorbited the following December.
Shortly after arrival on 22 February, NG-15 was accessed by the Expedition 64 crew and time-critical payloads and cold bags were removed from the ship’s Pressurized Cargo Module (PCM). Cargo transfer operations were completed by 28 February. NG-15’s presence has enabled a remarkable amount of science and technology research aboard the station, spanning both Expedition 64—which ended in April—and the ongoing Expedition 65.
One notable payload is the second flight of the Hewlett Packard Enterprise (HPE) Spaceborne Computer, which demonstrates the usefulness of high-performance, commercial off-the-shelf hardware for long durations aboard the ISS. The first Spaceborne Computer rode to orbit aboard SpaceX’s CRS-12 Dragon in August 2017 and operated without incident for 615 days, before it was returned to Earth aboard the CRS-17 Dragon in June 2019.
It functioned near-flawlessly on its first mission, despite unpredictable levels of high radiation and unique power and cooling conditions. It also achieved the significant milestone of running one teraflop, which equates to more than a trillion calculations in a single second; for comparison, this is over 30 times faster than an average laptop and closely approximates the performance of a ground-based supercomputer.
However, efforts to activate Spaceborne Computer-2 in early March met with significant delay, when the Expedition 64 team experienced difficulties with a tool needed to secure the payload into its Expedite the Processing of Experiments for Space Station (EXPRESS) rack. A new tool was launched the following month on the Crew-2 mission and the computer was successfully installed and brought to life on 29 April. It is expected to remain in active operational service for two years, before returning to Earth.
Original plans for NG-15 to depart in late May were pushed back to late June. Beginning in late May, efforts to transfer unneeded materials and trash aboard Cygnus got underway and Final Cargo Loading ahead of departure was completed last Tuesday, 22 June.
Overseeing Tuesday’s unberthing from the ISS will be Expedition 65 astronaut Megan McArthur. Following departure, the NG-15 vehicle will support the release of multiple CubeSats via SlingShot and NanoRacks deployment mechanisms, prior to deorbit and a destructive re-entry.
Looking ahead, NG-16 is slated to launch no earlier than 10 August, having been moved to the right in part to accommodate the scheduled 30 July target for the second Orbital Flight Test (OFT-2) of Boeing’s CST-100 Starliner. One payload flying uphill on NG-16 is the second ISS Roll-Out Solar Array (iROSA) modification kit.
The next scheduled U.S. Extravehicular Activity (EVA) is presently scheduled for late August and will see astronauts install the “mod kit” onto Power Channel 4A of the station’s P-4 truss. According to the current manifest, the next two pairs of iROSAs will be launched on the CRS-25 and CRS-26 Dragon cargo missions, provisionally scheduled for NET April and September 2022.
As previously detailed by AmericaSpace, three pairs of iROSAs—totaling six new solar arrays, each some 60 feet (18.2 meters) long when fully unfurled—will augment (and “shadow”) six of the station’s eight “legacy” Solar Array Wings (SAWs) and furnish an electrical power hike of 20-30 percent. Installation of the first pair of iROSA arrays on the P-6 truss was completed last Friday, following a challenging three-spacewalk marathon by Expedition 65 astronauts Shane Kimbrough and Thomas Pesquet.
The next two pairs of iROSAs will be installed to cover Power Channels 4A and 3A on the P-4 and S-4 trusses, respectively. They will be followed by the final two iROSAs, which will be fitted to Power Channel 3B on the S-6 truss and Power Channel 1A on the S-4 truss.