Virgin Galactic says electromagnetic interference (EMI) issues that stalled suborbital tests of its SpaceShipTwo Unity have been resolved, but the spaceplane’s return to flight could be further delayed by a newly discovered maintenance issue on Eve, the company’s WhiteKnightTwo carrier aircraft.
Disclosing the latest hold up to the company’s protracted test effort, Virgin Galactic’s president of space missions and safety, Mike Moses, said a “potential wear-and-tear issue” was discovered last week on the carrier aircraft during the build-up campaign to the next spaceflight attemp tentatively targeted for later in May. Although the specific issue has not been identified, Moses added that the part involved originally was scheduled for attention in the aircraft’s next maintenance schedule later this year.
“However, following this last [post-flight] inspection, we identified an item on our maintenance calendar that needs further study to determine whether we need to take action now, instead of the fall,” he said. “We are still determining what steps may be necessary to address it.”
Speaking at the company’s first-quarter financial results conference, Moses said, “While this may impact our flight test schedule, I want to emphasize that this is the nature of a test flight program, and we’re going to pick the timing before moving forward.”
Virgin Galactic’s last attempt to make the first suborbital space flight from its Spaceport America base in New Mexico was thwarted on Dec. 12, 2020, by an EMI issue that caused the vehicle’s hybrid rocket motor to shut down prematurely shortly after release from the carrier aircraft.
The flight was planned to be the third suborbital flight for Unity since the first successful powered sortie to space in December 2018 from Mojave Air and Space Port, California. It was also to have been the first supersonic and exo-atmospheric test of the SS2’s modified horizontal stabilizer pitch control system, which Virgin developed in 2019 to improve precise flight control and pitch-up performance during the start of the powered ascent phase.
Investigations later revealed that it was EMI from the two flight control computers and associated wiring for the upgraded stabilizer actuation system that interrupted connections to the rocket control system. This triggered a false fail-safe abort signal that shut down the motor around 1 sec. after ignition.
To correct the issue, Virgin Galactic has added hardware filters to suppress the EMI being generated within the flight control computers; improved the shielding around the wire harnesses; and added components to suppress conductivity. “These changes were made to the wires that carry power, as well as the signal wires to transmit measurement data back to the flight control computer,” Moses said.
“As of today, the final installation of the flight hardware is complete, and in end-to-end checkouts we were able to compare the current EMI to previous levels. We can see that we’ve significantly reduced the EMI on the order of 10 to 20 dB—or to a level that is over 90% lower than it was before. We have concluded that we have sufficiently addressed the EMI issue, and that Unity is ready for flight,” he added.
Virgin Galactic CEO Michael Colglazier said, “With this late-breaking maintenance evaluation, we will report back to the market next week with an update on schedule implications to our next flight.” Beyond this, on completion of the first test flight with the upgraded control system, the second flight will include two pilots with “a full cabin of internal spaceflight participants,” he added.
The third flight will include two pilots with Virgin founder Richard Branson in the cabin, while a fourth flight will be conducted in partnership with the Italian Air Force. “It will include three spaceflight participants and multiple payloads, and they will conduct astronaut training, in addition to experiments during the flight. We expect this flight will demonstrate our capabilities for both microgravity research and professional astronaut training,” Colglazier said. “We expect the successful completion of this fourth flight will mark the conclusion of our test flight program. After that, we look forward to moving to commercial service.”
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