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Wednesday, 28 July 2021

What’s changed since Boeing’s last attempt to send Starliner to the space station


Boeing will try again to dock its Starliner spacecraft to the International Space Station this week during an unpiloted flight test to the orbiting laboratory. It’s the last critical step before NASA gives the company the OK to fly astronauts.

Since the first attempt to conduct an orbital flight test without crew to the space station in 2019 a lot has changed within the company of Boeing and with the CST-100 Starliner program.

Friday’s planned launch will send the Starliner on the second orbital test flight, known as OFT-2, to the ISS. The spacecraft will launch on a ULA Atlas V rocket from Cape Canaveral Space Force Station Complex-41. After liftoff, Starliner will dock at the ISS about a day later. The capsule will then undock on Aug. 5 and land in New Mexico the same day.

In December 2019 during the OFT-1 launch, the Atlas V rocket performed flawlessly but a computer timing error with Starliner caused the spacecraft to miss a critical maneuver that would have sent the vehicle on its way to catch up with the ISS. Instead, Starliner returned to Earth less than 48 hours later. An extensive independent investigation was conducted by Boeing and NASA to determine the root cause of the software error.

Two years later, Boeing commercial crew program manager John Vollmer said the spacecraft and its teams are ready to get it right.

“We have spent the 18 months really trying to ring this vehicle out to have a lot of confidence that this flight will be successful,” he said Tuesday during a pre-launch news conference at Kennedy Space Center. “We will learn something out of this flight, there’s no doubt, but we want it to be a successful flight, and that the learning is something that we incorporate back to make this a safer, more robust vehicle.”

Since the botched first attempt, Boeing hired Jinnah Hosein to be the first software engineering vice president at the company. Hosein, a former SpaceX employee, participates in monthly software reviews and provided input on Starliner’s software as well as making recommendations across all Boeing products, according to Vollmer.

Boeing incorporated all flight software update recommendations from the independent review team as well as additional updates.

Vollmer said the biggest changes were to the communication software code. When things fell apart in 2019, Boeing had difficulty communicating with the spacecraft when it sent commands to correct the issues.

“We found that the communication was not as robust as we would have desired on our first flight. So we spent some effort modifying that code, mostly antenna pointing algorithms, some fault detection and recovery algorithms that we changed,” Vollmer explained. “We also added an algorithm so that if we lost (communications), that the system would automatically reset and go search for (communications). And then we added an algorithm that made sure that post-separation that we had an antenna that was pointed back at Earth so that we could get communication from that antenna.”

Despite the previous flight not meeting all of its mission goals Boeing still came away with valuable data allowing engineers to make additional upgrades to the flight software ahead of this do-over.

This time, Starliner and the ULA Atlas V rocket will have an emergency abort system active. For the OFT-1, the system was not active, according to NASA’s Commercial Crew Program Manager Steve Stitch.

“We’ll have the abort system active so if anything were to happen, it would separate Starliner and land the vehicle,” Stitch said. “We are going to practice the abort weather for this flight but we won’t make those mandatory constraints. In other words, we’ll just use the launch weather for this flight.”

In the event something were to go wrong the abort system would send the spacecraft away from the rocket to safety.

Another change this time around is the price tag for the launch. Boeing opted to repeat the orbital flight test on its own and is footing the bill, including for the costs associated with the supplies flying to the ISS in Starliner. About 400 pounds of experiments and supplies for the ISS are riding along for OFT-2.

“Boeing decided on their own to fly a second orbital flight test before they go embark upon the crewed mission and so NASA did not pay for the cargo delivery at all for this flight,” Stitch said.

While there won’t be human astronauts on this launch, Rosie, a mannequin will be going along for the ride. But this time, she won’t have the same duties as the last attempt. Instead of placing sensors on her, the data will be collected from the spacecraft seats, according to Vollmer, essentially making Rosie a fancy space weight.

“We took a little bit different approach with Rosie this time,” Vollmer said. “Last flight, she was fully censored, and we used those sensors and they were very valuable data that we got back. This flight, Rosie’s there, but she is essentially ballast. And we are taking measurements we put sensors in the seats and other locations in the vehicle as we found that we thought that would be more valuable since we’d gotten the data from Rosie on the first flight. So a little bit different approach, but she’s still there.”

The most critical part of the Starliner mission will be the steps it was unable to complete last time: docking and undocking with the ISS.

“The part that we’re really focused on here is going into the approach ellipsoid and testing the rendezvous Vesta sensor system that’s necessary to get in close to ISS and track the docking interface, docking with the International Space Station,” Stitch said.

Starliner will dock using the docking system provided by NASA but the spacecraft’s computers control the docking sequence.

After docking, there is a laundry list of other systems to be tested including opening the hatch, power transfers with the space station and exchanging data while Starliner is attached to the ISS.

With Boeing, ULA and NASA teams confident in the spacecraft all eyes will be on the weather leading up to Friday’s instant launch window at 2:53 p.m.

Three days ahead of liftoff weather officers with the 45th Weather Squadron are predicting a 40% for favorable weather. If the launch delays there is another opportunity on Aug. 4.

If all goes well Boeing could launch a crew of NASA’s astronauts later this year on the crewed test flight (CFT).

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