The NG-13 Cygnus resupply vehicle has been released from the grip of the Space Station Remote Manipulator System (SSRMS) to begin its EOM (End Of Mission) events. Cygnus will spend two weeks on orbit, deploying a pair of nanosatellites and conducting experiments before ending its life with a destructive re-entry at the end of the month.
NG-13’s mission began with a launch atop the Antares rocket that launched from Wallop’s Pad OA back in February.
Taking just over two days to arrive at the International Space Station (ISS), Cygnus’ berthed mission followed the standard routine of unpacking its array of 3,400kg of cargo – consisting of consumables and scientific experiments to be carried out on the orbital outpost – before reloading the vehicle with trash to join the spacecraft’s ultimate fate via destructive re-entry.
The disposal manifest also included the transfer of the High Definition Earth Viewing (HDEV) payload from the Columbus module to the Cygnus.
HDEV was delivered on SpaceX’s CRS-3 Dragon on April 19, 2014 – and installed on the External Payload Facility of the Columbus module. It exceeded its design life before being shut down last August.
Under the stewardship of Station Commander Chris Cassidy, Cygnus was unberthed – and released by – the SSRMS at 16:08 UTC on Monday, before conducting its departure burns to move it outside of the Keep Out Zone (KOS) to begin its final role as an orbital science platform.
Once into its “free-flying” element of the mission, Cygnus will conduct SEOPS SlingShot CubeSat deployments, part of a significant number of NASA Sponsored secondary payloads.
Cygnus will also conduct the Saffire Next Generation Fire Experiment, which involves two days of operations and an additional eight days of data dumps.
The box of tricks, embedded into the pressurized module of the Cygnus, will investigate the spread of fires in microgravity, while also developing technologies for fire suppression, combustion products monitoring, and post-fire clean-up.
Data obtained from the experiment will be used to validate the modeling of spacecraft fire response scenarios and evaluate NASA’s normal-gravity material flammability screening test for low-gravity conditions.
The data will also help address both the “no ignition” and “no flame spread” criteria involved in passing standard material flammability testing. This will further flesh out data on the materials that can pass the “NASA-STD-6001 Test 1” – where the ignition energy is not sufficient to start the flame spread process.
This will aid the understanding of the development and growth of a realistic fire for future exploration vehicles and determine low-g flammability limits for spacecraft materials. Previous experiments have already fed into the design process for NASA’s Orion spacecraft.
“As the first chance to actually study a realistically scaled fire, the SAFFIRE experiments have provided valuable insight into fire behavior inside a confined low-gravity environment,” said David Urban, SAFFIRE principal investigator.
Cygnus’ EOM will also include the use of the SEOPS WIDAR Hosted payload, with experiments conducted outside of the Saffire operations, given they cannot be performed in parallel, because they both require the use of the Wallops ground station downlink.
NG-13 was set to end on May 25. However, this has been extended to the end of the month via a change request filed during the berthed mission phase.
It noted that the “destructive re-entry for NG-13 was anticipated 31 days after separation from the International Space Station (ISS). However, the authorization issued authorized only two weeks from departure from the ISS.”
A request asked for an additional 16 days after separation, from “ISS + two weeks” to “ISS + 30
days”, noting Cygnus’ onboard fuel allowed for 30 days post-release. The ultimate realignment moved Cygnus’ destructive re-entry to May 29/30, from the previous requirement of ending its mission on May 25.
Re-entry will occur over a safe disposal corridor over the Pacific Ocean.