After 19 months of mixed fortunes, the second Orbital Flight Test (OFT-2) of Boeing’s CST-100 Starliner—the second of two Commercial Crew vehicles, alongside the in-service SpaceX Crew Dragon—is set to launch from historic Space Launch Complex (SLC)-41 at Cape Canaveral Space Force Station, Fla., during an “instantaneous” window at 2:53 p.m. EDT Friday, 31 July. Assuming a scrub on Friday, the next opportunity for the Eastern Range to launch this mission is at 1:20 p.m. EDT Tuesday, 3 August.
The uncrewed mission will be delivered to low-Earth orbit atop a United Launch Alliance (ULA) Atlas V booster, with an autonomous docking at the International Space Station (ISS) anticipated early Saturday and a parachute-assisted return to Earth five to ten days thereafter. Successful completion of OFT-2 will clear a major hurdle as Boeing readies for its Crew Flight Test (CFT) to the station, which may take place before year’s end.
Friday’s mission also marks the 100th rocket launch from SLC-41, which began a chequered career way back in December 1965 and was most recently used last May to see off an Atlas V laden with the fifth geostationary-orbiting element of the Space-Based Infrared System (SBIRS GEO-5). It witnessed ten launches of the Titan IIIC booster between December 1965 and May 1969, followed by seven Titan IIIE missions between February 1974 and September 1977.
These delivered a mixed bag of satellites for military communications, nuclear detection and surveillance and civilian technology, magnetospheric research and solar science, as well as the twin Viking orbiters/landers, bound for Mars, and the two Voyager deep-space probes. The pad was then deactivated for more than a decade, before launching ten missions for the Titan IV program between June 1989 and April 1999.
More recently, since its maiden flight for ULA in August 2002, SLC-41 has supported 72 Atlas V launches, transporting primarily payloads for national security and defense into orbit. However, it has also lofted a smorgasbord of scientific missions, including Solar Orbiter, the Jupiter-circling Juno probe, five exploratory forays to Mars, the Pluto-bound New Horizons and the OSIRIS-REx sample-gathering voyage to asteroid Bennu.
Hardware preparations for OFT-2 began in earnest back on 23 May 2019, when the Atlas V Common Core Booster (CCB)—tailnumbered “AV-082”—and its Dual-Engine Centaur (DEC) upper stage emerged from ULA’s 1.6-million-square-foot (150,000-square-meter) manufacturing facility in Decatur, Ala.
Both components were loaded aboard ULA’s Mariner vessel for a journey which covered rivers, the Gulf of Mexico and the Atlantic Ocean, before reaching Port Canaveral at dawn on 1 June. Interestingly, AV-082 was initially earmarked for CFT—Starliner’s first launch with humans—but was reassigned to fly the uncrewed OFT-2 when OFT-1 in December 2019 met with serious difficulties and a reflight was ordered.
The Starliner’s road to the ISS has been a long and convoluted one. It first launched atop an Atlas V for OFT-1 mission at 6:36 a.m. EST on 20 December 2019. However, shortly after attaining orbit, an automated timing issue aboard the spacecraft obliged flight controllers to call off its rendezvous and docking and the spacecraft returned to Earth two days later, becoming the first U.S. human-rated capsule to touch down on solid ground when it landed via parachutes and air bags at White Sands, N.M., early on 22 December.
Despite the disappointment of an incomplete mission, OFT-1 successfully demonstrated Starliner’s propulsion systems, communications systems, Guidance, Navigation and Control (GNC), the Environmental Control and Life Support System (ECLSS) and—via a series of in-flight extension/retraction tests—its NASA Docking System (NDS).
Although NASA later noted that an actual ISS docking was not a mandatory requirement to “crew-certify” Starliner, and pointed out that had astronauts been physically aboard OFT-1 they could have taken manual control and likely overcome the automated timing problem, it became increasingly likely as 2020 dawned that a reflight would take place.
A High Visibility Close Call (HVCC) Review revealed a worrisome number of technical and organizational root causes for the difficulties encountered by the mission. In March 2020, an joint NASA/Boeing Independent Review Team (IRT) highlighted three principal anomalies, two of which were classified as “software coding errors”.
Specifically, Starliner had incorrectly synched its Mission Elapsed Timer (MET) with the Atlas V before the onset of the Terminal Countdown, leading it to presume that it was at a different point in its mission following separation from the booster and failed to perform its maneuvers at the proper time. And another issue might have impaired the successful separation and disposal of its service module at the mission’s end.
Prompt “ground intervention” prevented a Loss of Vehicle (LOV) incident in both of these software anomalies. A third issue revolved around an unanticipated loss of Space-to-Ground Communications, where an intermittent forward-link issue impeded flight controllers’ efforts to command and control the spacecraft.
This was traced to Radio Frequency (RF) interference with Starliner’s communications system. Had astronauts been aboard OFT-1, the ability of Mission Control to establish reliable voice communications with the crew might have been adversely impacted.
In its overview, NASA outlined 80 recommendations to be addressed with Boeing after the conclusion of the HVCC process. Areas of focus fell into five broad categories. Twenty-one related to testing and simulation, emphasizing the need for greater hardware and software integration testing, performance of an end-to-end “run-for-record” test before each flight, reviews of subsystem behaviors and limitations and the identification of simulation and emulation gaps.
Ten pertained to assessment of all software requirements with multiple logic conditions to ensure full test coverage. Thirty-five others required modifications to Change Board documentation, bolstering the numbers of participants in peer reviews and test data reviews and and “increasing the involvement of subject matter experts in safety-critical areas”. Seven dealt with the need for changes to the NASA/Boeing safety culture, whilst another seven focused upon updates of the Starliner software coding issues which caused the MET and service module separation problems.
Following the investigation, Boeing committed to review and correct the software coding for the MET and service module disposal burns, strengthened its review processes and enhanced the fidelity of its testing to ensure overall “product integrity”.
Early in April 2020, the company announced plans to fly an uncrewed OFT-2 at no cost to the U.S. Government, although that mission—originally targeted for last fall—has met with significant delays, which saw it pushed it firstly into early January 2021, then late March, then early April and eventually to 30 July.
In the meantime, testing of spacecraft systems continued unabated, with parachute trials at White Sands during the second half of 2020 under “dynamic abort conditions and a simulated failure”. And just last January, Boeing reported that it had formally requalified Starliner’s flight software load, ahead of OFT-2.
That work involved an intricate series of static and dynamic tests in the Avionics and Software Integration Lab (ASIL) in Houston, Texas, which validated software performance in tandem with the recommended flight hardware across “hundreds of cases, ranging from single-command verifications and comprehensive end-to-end mission scenarios with the core software”. Originally targeting a 29 March launch, this date was initially moved forward to the 25th, then back to no sooner than 2 April.
This additional delay was caused by a need for additional time for hardware processing. Avionics units aboard the spacecraft required replacement following a power surge due to a Ground Support Equipment (GSE) configuration issue.
But with a packed manifest of visiting vehicles through the summer—including Russian and U.S. crew exchanges and coming-and-going science-loaded cargo missions—a further push of the beleaguered mission from April to the end of July proved inevitable.
Finally, last month, stacking operations of the Atlas V got underway. On 17 June, the Launch Vehicle On Stand (LVOS) milestone was completed, when the 107-foot-long (32.5-meter) CCB was rotated to a vertical configuration atop the Mobile Launch Platform (MLP) inside the 30-story Vertical Integration Facility (VIF).
Stacking progressed through the installation of two Aerojet Rocketdyne solid-fueled AJ-60 boosters on 6 and 8 July, before the Offsite Vertical Integration (OVI) structure—which includes the Centaur, the interstage and the launch vehicle adapter—was added on the 9th. Finally, a week later, the OFT-2 Starliner spacecraft itself was added, topping-off the Atlas V at an impressive 172 feet (52.4 meters).
A formal Flight Readiness Review (FRR), chaired by NASA Associate Administrator for Human Exploration and Operations, Kathy Lueders, was concluded on 22 July and produced a definitive “Go” to press ahead with the 30 July launch attempt.
In the meantime, efforts aboard the space station entered high gear, as Crew-2 astronauts Shane Kimbrough, Megan McArthur, Aki Hoshide and Thomas Pesquet took a 51-minute free flight on 21 July, during which they relocated Dragon Endeavour from the forward-facing port of the Harmony node to the space-facing (or “zenith”) port.
This opened up the forward port for Starliner’s arrival. Last week, Expedition 65 crewmen Hoshide, Kimbrough and Mark Vande Hei undertook On-Board Training (OBT) tasks to refresh themselves on procedures for the approach, docking and undocking of OFT-2.
Weather conditions for launch remain marginal, with only a 40-percent chance that Mother Nature will play ball on Friday afternoon. “South to southwest flow, combined with a plume of deep moisture over the area, will lead to a typical summer pattern of afternoon showers and thunderstorms over the Space Coast,” noted the 45th Weather Squadron at Patrick Space Force Base in its L-3 update on Tuesday. “Isolated convection is expected to develop along the East Coast sea-breeze early each afternoon, before the boundary pushes slowly inland and storms increase in coverage through the day.
“This pattern of showers and storms favoring the eastern half of the peninsula is expected to hold through much of the upcoming week,” it was added. “Given the time of day of the launch on Friday, a weather-related violation is likely during Friday’s countdown, due to isolated to scattered showers and thunderstorms in the vicinity, particularly west, of Space Launch Complex 41.” It was noted that infringement of the Cumulus Cloud, Surface Electric Fields and Lightning Rules were the principal violating factors.
Powering off SLC-41 with a combined thrust of 1.6 million pounds (725,000 kg), the Atlas V will discard its twin boosters about two minutes into flight and the single RD-180 engine of the CCB will shut down at 4.5 minutes after liftoff. This will set the stage for a seven-minute “burn” by the Centaur’s twin RL10A engines, which will propel Starliner towards orbit with a combined impulse of 45,200 pounds (20,500 kg).
A little less than 15 minutes after leaving Cape Canaveral, the spacecraft will separate and enter free flight at an apogee of 112 miles (180 km) and a perigee of 45.2 miles (72.7 km), inclined 51.6 degrees to the equator.
Assuming an on-time launch, OFT-2 will embark on a day-long transit to the ISS, with docking scheduled for about 3:06 p.m. EDT Saturday and hatch opening around 9:35 a.m. EDT Sunday. According to NASA, Starliner will remain attached to the space station for between five and ten days, before executing an autonomous undocking, departure and re-entry and parachuting to a landing in the Western United States.
Current projections call for an undocking on 5 August and a return to Earth later that same day, although Commercial Crew Program Manager Steve Stich has noted that Starliner can “stay up as long as we need, relative to weather”.
Flying in the commander’s couch aboard Starliner will be “Rosie the Rocketeer”, a Boeing anthropometric test device, who will be instrumented with multiple sensors to gather data from the seat pallet which holds all of the crew seats in place.
Also heading uphill aboard OFT-2 are about 475 pounds (215 kg) of NASA equipment, payloads and supplies for the incumbent Expedition 65 crew. This includes about 328 pounds (148 kg) of clothing, hygiene items, sleeping bags and food, together with crew care packages, six Radiation Area Monitors and a commemorative U.S. Flag.
And returning to Earth on Starliner is approximately 575 pounds (260 kg) of NASA cargo, including reusable Nitrogen Oxygen Recharge System (NORS) tanks and results from NASA-Glenn’s Preliminary Advanced Colloids Experiment (PACE) and BioServe’s BioCell investigation.