SAN, FRANCISCO/HOUSTON ¨C Elon Musk¡¯s Space Exploration Technologies Corp. capped a record-setting year Sunday when it launched a rocket carrying a new GPS III satellite for the U.S. Air Force, after delaying the mission several times because of a technical issue involving its rocket sensors and bad weather.

The Falcon 9 rocket lifted off from Cape Canaveral Air Force Station in Florida at 8:51 a.m. local time carrying the Lockheed Martin-built satellite. SpaceX first won U.S. Air Force certification for national-security space missions in spring 2015, breaking the lock on sensitive satellite launches long held by United Launch Alliance, a joint venture between Boeing Co. and Lockheed Martin Corp. The GPS III will go into medium Earth orbit roughly 1 hour and 56 minutes after liftoff, according to the SpaceX press kit.

This was SpaceX¡¯s 21st launch of the year, up from a record 18 in 2017. The company has been able to cut costs and win market share by designing its rockets for reusability. This time, however, SpaceX won¡¯t attempt to land Falcon 9¡¯s first stage after the launch, the company said in its press kit, citing mission requirements.

ULA has flown eight missions in 2018, and a ninth is scheduled for no earlier than Dec. 30 from Vandenberg Air Force Base on California¡¯s central coast.

¡°SpaceX has had a phenomenal year no matter how you slice it,¡± Luigi Peluso, an aerospace and defense consultant at AlixPartners, said in a phone interview. ¡°In 2019, the big race is who is going to be the first company to put humans into space and bring them back. You¡¯ve got SpaceX, Boeing, Virgin Galactic and Blue Origin all vying.¡±

SpaceX, along with Boeing, has a contract to ferry American astronauts to the International Space Station as part of what¡¯s known as the Commercial Crew program with NASA, but the time-line for the first flights has slipped repeatedly. The agency¡¯s current schedule has SpaceX¡¯s first uncrewed demonstration flight Jan. 17 and its first flight with astronauts on board in June.

Hawthorne, California-based SpaceX¡¯s valuation has climbed as it has racked up successful missions, making it the third-most valuable venture-backed startup in the U.S. after Uber Technologies Inc. and Airbnb Inc. The Wall Street Journal reported Tuesday that SpaceX is poised to raise another $500 million by selling stock at a $30.5 billion valuation, citing people familiar with the transaction.