OA-7 Cygnus re-enters Earth’s atmosphere after 2-month mission
Burning up in a blaze of glory, Orbital ATK‘s OA-7 Cygnus cargo ship re-entered Earth’s atmosphere over the Pacific Ocean on June 11, 2017, ending its nearly two-month-long flight.
The spacecraft, which spent some six weeks attached to the International Space Station, delivered more than 7,300 pounds (3,300 kilograms) of supplies to the outpost and, after unberthing last week, performed a fire experiment.
Once attached, the crew began transferring the cargo, which included various experiments and hardware, such as a new plant growth facility, biology samples, and more. There were also more than 30 CubeSats inside for future deployment from the Kibo module airlock.
After being loaded with trash and unneeded equipment, the spacecraft was detached from the outpost at 9:10 a.m. EDT (13:10 GMT) on June 4. The unberthing came more than a month earlier than originally planned. The schedule for the current Expedition 52 crew opened up when the launch of the CRS-11 Dragon capsule was by postponed by several days.
According to Spaceflight101, station managers on the ground seized the opportunity to have the crew detach the OA-7 spacecraft in early June because crew operations for the rest of the month and into July were expected to be fairly busy with experiments to conduct as well as cargo and crew crafts coming and going.
Cygnus did not immediately de-orbit, however, as it had a fire experiment called SAFFIRE-III to perform. The experiment occurred remotely as to not endanger the space station crew.
The SAFFIRE experiments are the largest flame studies conducted in space. They are designed to better understand flame propagation on various materials in a bid to design safer spacecraft.
For this experiment, a cotton-fiberglass sample, identical to the one for SAFFIRE-I in 2016, was set ablaze. For this run, however, two fans were set at different speeds to measure how airflow can influence flame propagation in zero gravity.
— NASA Glenn Research (@NASAglenn) June 8, 2017
The experiment was performed only hours after departing the space station, at 5:17 p.m. EDT (21:17 GMT). Over the next several days, video and other data from the study were downlinked.
Three more SAFFIRE experiments are being developed to follow up on the results from the first three. According to NASA, the series will focus on the creation and spread of toxic combustion gases.
Other last-minute activities
In the days before Cygnus’ deorbit burn, two pairs of Lemur-2 CubeSats were deployed. These Spire Global satellites will join its larger constellation of ship-tracking and remote sensing satellites. The four are expected to remain in orbit for at least two years.
Cygnus performed three orbit-lowering maneuvers on June 10 to set itself up for its deorbit the following day. Then, at 12:37 p.m. EDT (16:37 GMT), a final 5.5-minute deorbit burn was performed by its BT-4 engine, setting it up for re-entry over the Pacific Ocean and away from major shipping lanes.
Although its mission was almost accomplished, the spacecraft had one more experiment on board called RED-Data2. The study consisted of three soccer-ball-sized capsules designed to survive re-entry, but they are not recoverable.
RED-Data2 has two objectives. The first is to track vehicle parameters – including its location, acceleration, temperature, pressure, etc – to allow for a full digital reconstruction of Cygnus’ atmospheric breakup. This will help engineers better understand how large objects break apart during re-entry. The second is to test new heat shield material.
There are three capsules, each with a different material: a lightweight Conformal Phenolic Impregnated Carbon Ablator called C-PICA, a Conformal Silicone Impregnated Refractory Ceramic Ablator called C-SIRCA, and a modification to the Avcoat shield that will be used by Orion.
With the OA-7 mission completed, Orbital ATK is now shifting its focus toward the OA-8E mission, which is currently targeting launch atop an Antares rocket in September.
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a blog about the International Space Station, called Orbital Velocity.