Boeing engineers are close to resolving concerns with the mass and aerodynamic shape of the company’s CST-100 Starliner commercial crew carrier, and officials are optimistic the spaceship will be ready to deliver astronauts to the International Space Station in early 2018.

NASA safety advisors on Thursday lauded hardware milestones on Boeing and SpaceX commercial crew capsules, but said multiple technical issues, including problems with parachutes, must be resolved before the human-rated ships are ready to carry astronauts, adding that both companies continue to pursue schedules that appear to be unachievable.

NASA’s Mars 2020 Perseverance mission resumed normal operations Friday after cold temperatures forced the spacecraft into space mode soon after a successful launch from Cape Canaveral.