WASHINGTON — Vector, one of a number of companies developing small launch vehicles in response to growing small satellite demand, announced June 29 that it closed a $21 million funding round.

The Tucson, Arizona-based company said Sequoia Capital, a venture capital firm based in Silicon Valley, led the Series A funding round. Two other funds, Shasta Ventures and Lightspeed, also participated in the funding round.

Vector announced the round after closing a $4.5 million bridge round in April, intended to support company operations until it could close the Series A round. The company had, prior to the bridge round, raised $2.25 million, as well as winning Small Business Innovation Research awards from NASA and DARPA.

“Securing this round of funding is not only a testament to the industry’s confidence in our team and launch vehicle technology, but is also a significant validation of the entire microsatellite launch industry,” said Vector Chief Executive Jim Cantrell in a statement announcing the funding round.

Vector said it will use the funds to accelerate testing of its Vector-R small launch vehicle. A full-scale prototype of that vehicle flew a successful low-altitude test flight May 3 in California’s Mojave Desert. That flight was planned to go to an altitude of less than 1,400 meters as part of an incremental testing strategy.

Vector plans to do a second test flight of Vector-R later this summer, from the future site of Spaceport Camden on Georgia’s Atlantic coast. Cantrell said in an early May interview that the launch would take place in “about two months,” or early July, but the company did not provide a more specific launch date in its statement.

Cantrell said in May that Vector planned “an incremental development approach that gradually adds more and more complexity and performance to the vehicle as we go along,” with five or six test flights planned, culminating in an orbital launch.

Investors were swayed by the progress Vector had made since the company was formally established last year. “We’ve been impressed with Vector’s achievements in just 14 months, and are thrilled to partner with such credible veterans of the space industry,” said Bill Coughran, partner at Sequoia, in the statement.

“Vector is poised to strike on the increasing demand we see in the market,” said Rob Coneybeer, managing director and co-founder of Shasta Ventures, in the same statement. “We see Vector as being far ahead of the competition.”

However, one other company working on a small launch vehicle has flown higher than Vector. Rocket Lab, a U.S.-New Zealand company, launched its first Electron rocket May 25 from its New Zealand launch site. While the rocket failed to reach orbit, it did reach space on its suborbital flight, and the company said the rocket’s first stage performed as planned.

Rocket Lab Chief Executive Peter Beck told Bloomberg Businessweek recently that the company believes it “has now solved the orbit issue” and plans to resume test launches in the next six weeks.

Virgin Orbit is also expected to start ramping up test activities for its LauncherOne small launch vehicle later this year. David Caponio, mission manager at Virgin Orbit, said in a June 14 panel discussion at the Small Payload Rideshare Symposium in Laurel, Maryland, that modifications to the company’s Boeing 747 aircraft should be completed in about a month. The first “pathfinder” LauncherOne vehicle, which will be used for ground and flight tests, is also nearing completion, he said.