Four months after standing down launch operations of the ICON mission on their Pegasus rocket, Northrop Grumman Innovation Systems is entering the home stretch for a realigned launch on 26 October 2018 at 04:05 EDT (0805 UTC) over the Atlantic Ocean off the coast of Cape Canaveral, Florida.

This week, Northrop Grumman Innovation Systems managers for both ICON and Pegasus sat down with NASASpaceflight’s Chris Gebhardt to discuss what happened back in June as well as the current status of both vehicles in the final weeks before launch.

What happened in June:

In June, Northrop Grumman Innovation Systems (NGIS) began the ferry flight of their Stargazer L-1011 aircraft – with the Pegasus rocket safely encapsulating ICON inside its payload fairing – across the Pacific Ocean from California to the Kwajalein Atoll, where the air-drop launch of ICON was set to occur.

During the first leg of this trip from California to Hawai’i, systems engineers aboard Stargazer noticed an off-nominal reading from one of Pegasus’ new Actuator Control Units.

“This is the first time that we’re using Northrop Grumman-designed Actuator Control Units,” stated Bryan Baldwin, Pegasus Program Manager, Northrop Grumman Innovation Systems, in an exclusive interview with NASASpaceflight.

According to Mr. Baldwin, the previous versions of the Actuator Control Units were installed after ferry flights to the launch location because they couldn’t be powered up prior due to their use of thermal batteries.

“This new unit allows us to power up the electronics separately from the actuators, and so we were actually monitoring the system on the ferry flight over [when] we would not have done [that with the older units].”

With this real-time monitoring, all was reporting well prior to the start of the ferry flight, but over the Pacific between California and Hawai’i, an off-nominal condition presented.

“These are actuators that control the fins [on Pegasus], and part of the feedback loop is a potentiometer that senses the position of the fin,” stated Mr. Baldwin. “And as we were flying over to Hawai’i, the guys were monitoring the system and noticed that there were some position errors showing up on one of the fins.”

This movement of a fin is not possible during ferry flight because the fins are locked in place. Yet the telemetry coming from the Actuator Control Unit said the fin was moving.

After landing as scheduled in Hawai’i, the teams began troubleshooting and tried to duplicate the issue. After a few attempts, they were able to do so, and a review of the data combined with years of experience with Pegasus’ 43 flights to date showed a need to stand down launch operations and return to California for additional tests and repairs.

“Based on the fact that this part was flight critical in the control loop for the fin, we had a condition that we couldn’t accept. So we decided that we needed to fly back and do some troubleshooting and replacement,” explained Mr. Baldwin.

After Stargazer’s return to California, the team found contamination in the Actuator Control Unit that was sending the erroneous readings during the ferry flight. NGIS engineers then tested similar parts from newer builds of Actuator Control Units and were able to verify that those newer parts did not have the same contamination issue.

Those newer parts were installed into Pegasus, and system re-tests showed a fully-functioning system – leading to a clearance to proceed toward launch operations at the end of the month.

During this four month stand down, however, very little had to be done with ICON (Ionospheric Connection Explorer) itself, explained Dave Oberg, Program Manager for ICON, Northrop Grumman Innovation Systems.

“Certainly the top of the list [has been] to keep an active purge on the instruments. Contamination control is one of our primary concerns, and the instruments are very sensitive to that. So we’ve kept an active purge on the instruments.

.@NASA and @northropgrumman now targeting Oct. 26, 2018, for launch of the agency’s Ionospheric Connection Explorer. #NASAICON will launch aboard a Northrop Grumman #PegasusXL rocket from CCAFS in Fla with a 90 min launch window starting at 4 a.m. EDT. https://t.co/GYrMEYwzMk pic.twitter.com/sNykJpXmzw — NASA_LSP (@NASA_LSP) September 21, 2018

“We’ve also kept the battery at a relatively low state of charge so that its lifetime is not degraded while we stand and wait. And really the only other activity we did,” said Mr. Oberg, was “at one point we did a reaction wheel run-in just to guard against the possibility that the grease in the bearings could, through the drive of gravity, pool at the bottom. And so we needed to make sure [the grease] remained distributed” throughout the reaction wheel.

ICON launch status:

With the issue from June now corrected, NGIS teams for Stargazer, Pegasus, and ICON are progressing through their final major pre-flight processing elements.

Presently, teams have completed Flight Simulation #4, the last integrated test between ICON and Pegasus before payload fairing installation.

Encapsulation of ICON inside its payload fairing began yesterday, Thursday, 4 October and is expected to take a couple days to complete.

For ICON, Mr. Oberg stated, “just as the fairing is getting re-mated, we’ll do our final checkout and remove any Remove Before Flight items, such as instrument covers and that sort of thing, and then we’ll run a couple of liveness tests. But other than those continuing health verifications, we’ve got no work left. We’re good to go.”

After encapsulation, additional tests will verify that nothing changed with ICON and Pegasus during the fairing installation process; this will be followed by end-to-end testing of the Pegasus rocket’s Flight Termination System.

Teams will then proceed into mating operations of Pegasus to the Stargazer L-1011 aircraft – which is currently scheduled for Sunday, 14 October.

Stargazer will then ferry flight from California to Cape Canaveral, Florida, landing at the skid strip at the Cape Canaveral Air Force Station.

“Once we get [to the Cape], the guys will perform safing operations, get all the equipment in place, get the ground support equipment, air conditioners, those kind of things ready to go,” stated Mr. Baldwin.

“Then we’re going to do what we call a Combined System Test #2, making sure no issues occurred on the ferry over. We’ll exercise our hardware to the degree that we can underneath the airplane. We’ll monitor, we’ll get spacecraft data as well.”

A dress rehearsal will then follow on 22 October ahead of a Launch Readiness Review with NASA and the Eastern Range on 24 October.

Launch location change to Cape Canaveral:

The upcoming launch from the Cape is a dramatic change in location from the Kwajalein Atoll – which had served as the launch location for the 2017 launch campaigns as well as the campaign earlier this year.

In fact, the Cape turns out to have always been a launch option for ICON following a final understanding of the spacecraft’s mass – which came in well under the maximum mass contingency that had to be planned for when selecting the launch location.

“We had our mass estimate at the beginning but had the requirement to carry significant margin on top of that,” said Mr. Oberg. “As the design matured, we never needed that margin, and we came in at the original [mass] estimate. But because [the rocket folks] had to design to the maximum margin mass, that drove” the need to go to Kwajalein instead of the Cape at first.

Basically, Kwaj was needed based on the maximum contingency mass of ICON because Kwaj is closer to the equator than the Cape, and a launch from Kwaj can take greater advantage of Earth’s rotation velocity than can launches from the Cape.

Mr. Baldwin added, “When we first did the proposal, the spacecraft folks had to carry so much mass margin in their design, and at that point, we had to use the maximum mass estimate which made it difficult to do from the Cape.

“So, to be fully compliant with the requirement, we proposed launching out of RTS, the Reagan Test Site [Kwajalein]. But once the spacecraft became more mature and the mass properties were fully understood, we had the opportunity to go back and look at the Cape. And it was doable at that point.”

So why stick with Kwaj in 2017 and June 2018 if the Cape turned out to always be possible from an ICON mass v. Pegasus performance standpoint?

The answer stems from coordination with the two Ranges.

“Typically, you’re coordinating with the Range a couple of years out,” said Mr. Baldwin. “There’s a lot of coordination that goes on. There’s a lot of analysis that gets submitted that has to be reviewed and approved. And it takes a significant amount of time to do that.

“And we figured we would not be able to get all of that done at the Cape. And it was also an additional cost to the customer to change locations.”

So the teams kept Kwaj at first. But that changed after the stand down in June.

“To be perfectly honest, the guys at the 45th [the Eastern Range which controls Cape Canaveral] were very cooperative, very great, good to work with, and they reviewed and did the initial approvals significantly quicker than normal range coordination. So they were very helpful in making a switch possible because typically you’re a couple of years out when you’re making that coordination,” praised Mr. Baldwin.

Launch of ICON on Pegasus from underneath the Stargazer aircraft is currently scheduled for Friday, 26 October at 04:05 EDT (0805 UTC) – five minutes past the opening of the launch window – from a location over the Atlantic Ocean off the coast of Cape Canaveral, Florida.

(This is the first part of a three part series NASASpaceflight will published based on interview material with Northrop Grumman Innovation Systems managers for ICON and Pegasus.)