Boeing has successfully run the propulsion system for its CST-100 Starliner space taxi through the same test it failed almost a year ago, marking a significant step toward carrying astronauts to the International Space Station.

The thruster firing for Starliner’s launch abort system was part of a series of tests conducted on Thursday at the White Sands Test Facility in New Mexico. A similar test went awry last June, due to an unwanted leak of propellant. No hardware was destroyed, but the problem contributed to delays for Starliner’s first flight.

The current schedule calls for the capsule to be launched on an uncrewed flight to the space station in the August time frame, and for the first crewed flight to take place by the end of the year. Starliner is designed to be launched atop a United Launch Alliance Atlas 5 rocket. (ULA is a Boeing-Lockheed Martin joint venture.)

Starliner’s launch abort system is designed to come into play only in the event of an emergency that calls for the space taxi to be pulled away from the Atlas 5. It makes use of a set of rocket engines built by Aerojet Rocketdyne.

Boeing said Thursday’s tests made use of a flight-like Starliner service module that was equipped with a full propulsion system, including the launch abort engines as well as fuel and helium tanks, a reaction control system, thrusters for orbital maneuvering and attitude control, and all the necessary fuel lines and avionics.

The crucial test involved firing 22 propulsion elements, including the launch abort engines, to simulate a low-altitude abort scenario. In addition, 12 thrusters were fired to simulate a high-altitude abort, and 19 thrusters were fired to simulate in-space maneuvers.

“With the safety of our astronauts at the forefront of all we do, this successful testing proves this system will work correctly and keep Starliner and the crew safe through all phases of flight,” John Mulholland, vice president and program manager of Boeing’s Commercial Crew Program, said in a news release. “The milestone paves the way for the upcoming pad abort test and flights to and from the International Space Station later this year.”

The pad abort test should take place at White Sands this summer.

In addition to Boeing’s Starliner development effort, SpaceX is upgrading its Dragon spacecraft for NASA’s use as a crewed space taxi. SpaceX successfully conducted a pad abort test back in 2015, and launched the Crew Dragon on a successful uncrewed test flight up to the space station and back down to Earth in March.

However, the craft that made that trip was destroyed last month during a follow-up engine test firing, forcing a delay in the schedule for an in-flight abort test and SpaceX’s first crewed flight to the space station. Due to the investigation of the anomaly, SpaceX’s schedule for launching astronauts is currently up in the air.