NASA and Boeing have decided to bring Boeing’s CST-100 Starliner spacecraft back to a landing at White Sands Missile Range in New Mexico tomorrow. Landing is set for 7:57 am Eastern Standard Time. Starliner is conducting an uncrewed test flight and was unable to dock with the International Space Station (ISS) because a timing error placed it in the wrong orbit. Other test objectives are being met and landing will be one of them.

At a media teleconference today, NASA Administrator Jim Bridenstine emphasized that not all test objectives carry the same weight, and entry, descent, and landing (EDL) is among the most important. He wants the Boeing and NASA teams “focused like a laser” and on their “A game” tomorrow.

Starliner will follow a path across the Pacific Ocean, up over the Baja Peninsula and west of El Paso, Texas into its landing site at White Sands. Starliner is the first U.S. space capsule designed to land on land instead of splashing down in the ocean like Mercury, Gemini, Apollo and SpaceX’s Crew Dragon. It descends under parachutes and uses airbags to cushion the landing. (The airplane-like space shuttle was a completely different design and landed on runways.)

White Sands is the primary landing site for Starliner not just for this test flight, but in the future. Boeing has three alternate landing sites at Dugway Proving Ground Utah; Edwards Air Force Base, California; and Wilcox Playa, Arizona.

Starliner was successfully launched by a United Launch Alliance (ULA) Atlas V rocket yesterday, but a timing error on the spacecraft resulted in it ending up in the wrong orbit.

Jim Chilton, Boeing Senior Vice President for Space and Launch, said at today’s teleconference they now have a better understanding of what happened, but are still working on why.

The Atlas V flies Starliner on a unique trajectory designed to keep g-loads down for the crews that will be flying in it and to ensure there are abort options during ascent. It separates from Starliner while the spacecraft is still suborbital. Starliner then fires its own engines to reach orbit and continue to the ISS.

A Mission Elapsed Timer (MET) on Starliner triggers the engine firing. Yesterday, it was set to the wrong time. Consequently, Starliner thought it was at a different point in the mission timeline and began firing its Orbital Maneuvering and Attitude Control (OMAC) engines to adjust the spacecraft’s attitude to where it thought it should be, using up propellant. By the time flight controllers on the ground were able to communicate with Starliner, the fuel was depleted to the point where it could not finish the trip to the ISS. The spacecraft otherwise is in good shape and flight controllers placed it into an orbit to set it up for landing at White Sands within 48 hours.

Starliner was supposed to conduct an Orbital Insertion (OI) burn and it was not clear yesterday whether that burn took place or not. Chilton said today Starliner did not conduct the OI burn that was planned. Instead, once flight controllers could communicate with it, the engines had turned on and off so many times that the decision was made to just do a series of short engine burns to get it into orbit, albeit lower than planned.

Another mystery yesterday was why flight controllers were not able to establish a link with the spacecraft more quickly to tell it what to do. They communicate with Starliner via NASA’s geostationary Tracking and Data Relay Satellite System (TDRSS), which provides near-global coverage. Initially they thought the anomaly happened at a rare moment when one of the satellites was not accessible. Now, however, it appears that the problem was Starliner’s movements as it tried to correct its attitude, which meant its antennas were not pointing at TDRSS correctly. Basically the communications problem was also the result of the timing error.

Two more engine burns were made yesterday to raise the orbit to get into the proper position for tomorrow’s landing. It is currently in a 250 x 250 kilometer circular orbit.

The pressing question is why the MET was set to the wrong time. Today, Chilton called it a “data retrieval” error with the software.

Our spacecraft needs to reach down into the Atlas V to figure out what time it is, where is the Atlas V in its mission profile, and then we set the clock based on that. Somehow we reached in there and grabbed the wrong spot. … We reached in and grabbed the wrong coefficient. More to learn there, but it’s not more complicated than that. And we started the clock at the wrong time. — Jim Chilton, Boeing

He stressed that the problem was not with the Atlas V, but Starliner. He and the Boeing team are “surprised” because extensive integrated software testing prior to launch never identified that as a possibility. Starliner’s software is written by Boeing.

Although rendezvous and docking with ISS was one of the major test objectives, he and Bridenstine drew attention to other objectives that are being met, including successful launch and, hopefully, landing.

What this all means for the next step in Boeing’s effort to launch astronauts into space is yet to be determined. Boeing is developing Starliner as a public-private partnership with NASA, which will purchase services from Boeing to send NASA astronauts to ISS. NASA requires Boeing to conduct this uncrewed OFT and then a Crew Flight Test (CFT) before certifying the system for operational use.

Whether NASA will require Boeing to redo the OFT may depend more on how the landing goes tomorrow than what happened already. Bridenstine stresses that if a crew had been aboard Starliner they could have overridden the automated systems and the outcome could have been quite different.

Chilton expressed confidence that the timing error during ascent will not recur during descent, and that Starliner’s three parachutes will deploy correctly. During a Pad Abort Test at White Sands last month, one of the three parachutes did not deploy because a pin was not inserted correctly in the rigging. Chilton and NASA Commercial Crew Deputy Program Manager Steve Stitch said they have verified that these parachutes will not have the same problem.