After being part of the International Space Station (ISS) for over four months, Northrop Grumman Corp.’s NG-17 Cygnus cargo ship—named in honor of the late shuttle astronaut and environmental scientist Piers Sellers—departed the orbital outpost early Tuesday, bound for a destructive re-entry later this week. Cygnus was robotically detached from its berth on the Earth-facing (or “nadir”) port of the station’s Unity node overnight and, an hour later than originally intended, was set into free flight at 7:07 a.m. Tuesday. Laden with unneeded equipment and trash, Cygnus will harmlessly burn up in Earth’s atmosphere, high above the Pacific Ocean, on Wednesday, 29 June.
This morning’s departure occurred several days later than planned, following a delayed attempt last week to execute a “limited reboost” of the ISS using Cygnus’ propulsion assets. It marks the first all-up demonstration of an enhanced Cygnus capability as a standard service for NASA. Back in July 2018, the OA-9E Cygnus’ main engine was test-fired for about 50 seconds to raise the station’s altitude by about 295 feet (90 meters). The OA-9E test marked the first propulsive reboost of the ISS by a commercial spacecraft.
NG-17’s limited reboost was initially targeted for 18 June but was postponed a couple days to refine its duration and magnitude following an earlier Debris Avoidance Maneuver (DAM). However, the planned five-minute and one-second “burn” on the 20th was aborted after only five seconds.
Northrop Grumman and NASA teams noted that the root cause of the abort was “understood” and was apparently terminated sooner than intended as a conservative measure, “due to system parameters that differed from Cygnus flight operations”. A second attempt was undertaken on the 25th, which successfully ran to its intended burn duration and served to raise the ISS altitude by 0.1 miles (0.16 kilometers) at apogee and 0.5 miles (0.8 kilometers) at perigee.
With Tuesday morning’s departure, and a planned Wednesday re-entry over an uninhabited region of the Pacific Ocean, NG-17 wraps up more than four months in orbit. Launched at 12:40 p.m. EST last 19 February, it ferried more than 8,300 pounds (3,700 kilograms) of equipment, payloads and supplies to the ISS.
Less than two days later, at 4:44 a.m. EST on the 21st, Expedition 66 astronaut Raja Chari—assisted by crewmate Kayla Barron—grappled Cygnus with the station’s 57.7-foot-long (17.6-meter) Canadarm2 robotic arm. Mission controllers at the Johnson Space Center (JSC) in Houston, Texas, then commanded Canadarm2 to rotate and install the cargo ship onto the Earth-facing (or “nadir”) port of the Unity node.
Key payloads heading uphill aboard NG-17 included an investigation developed by BioServe Space Technologies of Boulder, Colo., which seeks to examine the effects of a drug on breast and prostate cancer cells. Under microgravity conditions, cells can grow in a three-dimensional model, rendering it simpler to characterize their structure, gene expression and cell “signaling” and response to the drug.
Another experiment, supplied by Colgate-Palmolive, utilizes three-dimensional models of engineered human skin cells on a porous membrane to evaluate cellular and molecular change in the peculiar space environment. It forms part of a wider campaign to rapidly assess new products to protect skin from the aging process. Although it is difficult to examine such change on Earth because the process develops over several decades, in microgravity changes in skin which mimic aging are noticeably accelerated.
Elsewhere, the Japan Aerospace Exploration Agency (JAXA) has sponsored a solid-state lithium-ion battery, capable of safe and stable operations under extreme temperatures in a high-vacuum environment. Made from solid, inorganic and flame-retardant materials, the new battery does not leak liquid and can function across wider temperature ranges, making it safer and more reliable than previous designs.
Other experiments include a technology demonstrator for a new suite of hydrogen sensors for the ISS Oxygen Generation System (OGS) and the eXposed Root On-Orbit Test System (XROOTS), which employs hydroponic and aeroponic techniques to grow plants without soil or other growth media.
Within hours of Cygnus’ arrival in February, the Expedition 66 crew began unloading these payloads and putting experiments to work. NASA astronauts Barron, Tom Marshburn and Mark Vande Hei began unpacking samples from science freezers aboard NG-17 and transferred them to research racks aboard the ISS. Marshburn set about activating the Colgate-Palmolive study, whilst Vande Hei readied the station’s Life Science Glovebox (LSG) on 24 February to observe the BioServe-provided tumor cells.
In recent weeks, Expedition 67 astronauts Kjell Lindgren, Bob “Farmer” Hines, Jessica Watkins and Italy’s Samantha Cristoforetti worked extensively on the XROOTS botany experiment, replacing seed cartridges and tending to growing radishes and mizuna beans. And as May wore into June, Cygnus’ role morphed from a cargo delivery ship into one of “taking out the trash”, as unneeded equipment and hardware was loaded into its cavernous Pressurized Cargo Module (PCM).
Following last Saturday’s successful limited reboost of the ISS, Hines and Watkins wrapped up cargo operations aboard Cygnus on Monday and Cristoforetti helped to disconnect power and ventilation systems, before closing the cargo ship’s hatch. It was robotically detached from the Unity nadir port overnight and held in the grasp of Canadarm2, pending its release and departure.
Originally scheduled for 6:05 a.m. EDT Tuesday, that release was postponed by one hour, to better set up Cygnus’ trajectory to keep it clear of conjunctions and enable an improved communications capability after departure. With Watkins providing commentary from the station’s multi-windowed cupola, Piers Sellers’ robotic namesake entered free flight at 7:07 a.m. EDT. Twenty minutes later, it left the vicinity of the ISS, as Watkins hailed its “new and important capability” of reboosting the station “that Sellers helped build”.
And as NG-17 heads for tomorrow’s destructive dive into the atmosphere, it is important to recall Sellers not only as a respected climate scientist in his own right, but as a veteran NASA astronaut. Selected by NASA in May 1996, he flew three shuttle missions in October 2002, July 2006 and May 2010, executed six sessions of Extravehicular Activity (EVA), totaling more than 41 hours, and logged over 35 days in orbit.Missions » ISS » COTS » CYGNUS »