After a two-and-a-half day cruise to the International Space Station, the NG-13 Cygnus resupply craft from Northrop Grumman has arrived at the orbital outpost with a host of scientific experiments and equipment.

The arrival comes just 18 days after the previous Cygnus departed the Station and marks the shortest time between two Cygnus missions to date.

Reflecting on this milestone, Frank DeMauro, Vice President and General Manager of Northrop Grumman’s Space Systems Division, said, “One of the things NASA asked for was not only to accelerate this launch to early February, but then they wanted NG-12 on board the ISS for as long as possible to obtain as much disposal cargo.

“And because on the last mission we demonstrated the ability to have two Cygnus vehicles in orbit at the same time, this was not an issue.”

With just 18 days between departure and arrival of two Cygnus spacecraft, the launch-to-launch cadence at just three months was also a new record for Northrop Grumman.

On the surface, this might not seem significant given other launch providers ability to launch missions just a few days apart from each other.

But for Northrop Grumman and their Cygnus vehicles, a nominal launch cadence is about once every six months for NASA in terms of resupply of the International Space Station.

Furthermore, months have previously separated the departure of one Cygnus from the arrival of another.

This short turnaround from the Station perspective of Cygnus missions stems not only from NASA’s request to accelerate the launch of NG-13 but also to delay the departure of NG-12.

Originally, NG-12 had been slated to depart in mid-January so it could perform all of its two-week-long post-Station activities and reenter the atmosphere prior to the then-scheduled 9 February launch of NG-13.

But the need to reschedule three spacewalks from November and December 2019 into January 2020 constrained Station crew operations.

Additionally, NASA decided they wanted NG-12 to remain longer so the crew could pack additional disposal cargo into the craft.

All of this led to a late-mission timeline change for NG-12, extending its stay until the final day of January.

“The key thing here was the flexibility of both the spacecraft and the team to respond to those kinds of changes so late in the game.,” said Mr. DeMauro to NASASpaceflight.

“Staying on the Station longer is just a matter of replanning what events are going to happen when. When departure happens, we get plenty of notice of that, and even with a late change, we can modify our processes, update our flight dynamics models on when the reentry will occur at the end of the mission.

“So when things change, we have a great ability to modify on short notice.”

#DefiningPossible with cargo delivery in space. After leaving the @Space_Station today, NG-12 #Cygnus will remain in orbit until late Feb. pic.twitter.com/AiOhDp0Vr1 — Northrop Grumman (@northropgrumman) January 31, 2020

Part of this modification included an extension to the Federal Communications Commission (FCC) operating permit to extend NG-12 from a two-week post-Station flight to a one month flight profile, something that was made easy by communication processes already in place between Northrop Grumman and the FCC.

That left the biggest challenge as the now-overlapping flights of NG-12 and NG-13.

“That was [really] just a planning exercise because the systems were in place to operate two Cygnus vehicles at the same time. They were proven during the last mission,” related Mr. Demauro.

“NASA had great confidence in coming to us and saying ‘We’d like to change the plan. How do we go about doing that?’ And our team was able to respond quickly and put that updated plan in place.

“There was no heartburn with it or worry about it. A customer asked for flexibility, and we could provide it.”

The updated plan also required no changes to Cygnus and Antares processing on the ground prior to the NG-13 launch, with Mr. DeMauro noting that it was simply a matter of resources to meet the integration and test flow needed to obtain the 9 February targeted launch date, which then eventually slipped due to a Ground Support Equipment issue and a weather violation to an eventual launch on 15 February.

“It’s so gratifying to see the work we’ve done over the last several years — and really over the entire program for Antares and Cygnus to prepare ourselves for these types of situations — to enable us to be responsive to our customer and to see a customer taking advantage of that. That’s just really great from our perspective,” said Mr. DeMauro.

A large part of that gratifying work is the demonstration of flying two Cygnus spacecraft in orbit at the same time during the NG-11 and NG-12 missions last year.

Part of Northrop Grumman’s goal with Cygnus is to offer it as a free-flying science platform that can continue to conduct experiments after its standard 3-month mission at the Station is over.

This would see the craft continuing to operate an orbit for a full year from launch to re-entry.

In order to do that, Northrop Grumman needed to be able to demonstrate the ability to fly two Cygnus spacecraft at the same time, and they achieved this in October, November, and December 2019.

What’s more, Mr. DeMauro revealed to NASASpaceflight that Northrop Grumman saw no significant issues, in fact no major issues at all, during that demonstration.

“There were no big lessons learned or anything that made us stop and say ‘we have to change that.’”

In fact, according to Mr. DeMauro, the big lesson learned was that the teams really didn’t have to change anything, that everything went very smoothly thanks to the years of work put into simulating and preparing all the ground and spacecraft systems for overlapping flights.

Exactly when Cygnus will again remain on orbit for a prolonged period after it departs the International Space Station to serve as a free-flying science platform is currently unknown.

However, Mr. DeMauro noted that short duration free-flying science experiments are taking place on NG-12 as it awaits the close of its mission at the end of the month.

Moreover, the NG-12 Cygnus was used as a science module in and of itself and as an extension of the Station’s science capabilities, hosting dedicated payloads that were not transferred from the craft to the orbital outpost.

This capability will continue on NG-13 now that it has arrived at the Station.

NG-13 will remain at the ISS until late-April or early-May, after which it will perform a fire in space experiment to continue testing new construction and composition elements to help combat the spread of fires that may ignite on future spacecraft.