WASHINGTON — High winds in the upper atmosphere have led SpaceX to postpone an already delayed Falcon 9 launch by at least three more days, the company announced March 1.

SpaceX Chief Executive Elon Musk tweeted that wind speeds approaching 70 meters per second at an altitude of 10 kilometers led the company to postpone the fourth attempt to launch the SES-9 communications satellite. “Hits like a sledgehammer when going up supersonic,” he said in a tweet describing what he called “extreme high altitude wind shear.”

Because the high upper level winds are forecast to persist through March 3, SpaceX has rescheduled the launch for no earlier than March 4. “Our team will continue working with the Air Force’s Launch Weather Officer to evaluate the best available opportunity for flight in the coming days,” SpaceX said in a statement. Weather forecasts had previously predicted an 80 percent chance of acceptable weather for launch opportunities on March 1 and 3.

The decision to postpone a March 1 launch is the latest setback for a mission whose previous three launch attempts have been delayed. SpaceX postponed a Feb. 24 launch attempt more than a half-hour before the launch window opened, citing a desire to cool the rocket’s liquid oxygen propellant as much as possible.

SpaceX scrubbed a second attempt Feb. 25 with a little more than 90 seconds remaining before launch. The company later said that loading of the supercooled liquid oxygen was going slower than planned, triggering a hold in the countdown that scrubbed that launch attempt.

SpaceX was on track for a third launch attempt Feb. 28 when a ship entered restricted waters off the coast from the Cape Canaveral, Florida, launch site, causing a hold with 90 seconds before launch. SpaceX reset the launch for about a half-hour later, but flight computers aborted the launch when the rocket’s nine main engines failed to generate enough thrust at startup. Musk later said that the rocket’s liquid oxygen warmed up during the delay, contributing to the low thrust problem that scrubbed the launch.

While not an issue for the latest delay, the previous delays in the launch of this mission have been linked to SpaceX’s use of liquid oxygen cooled to near the freezing point. That additional cooling increases the propellant’s density and improves the vehicle’s performance, but does come with handling challenges. However, the use of supercooled liquid oxygen did not pose a problem for the first launch of the upgraded Falcon 9 in December.

The launch postponement is another setback for SES, who had planned to launch SES-9 last fall prior to the June 2015 Falcon 9 launch failure. When launched, the Boeing-built SES-9 will operate at 108.2 degrees east in geostationary orbit. The spacecraft’s 81 Ku-band transponders will provide communications services for parts of Asia, Australia and the Middle East.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...