CAPE CANAVERAL, Fla. (Reuters) - A joint venture between Boeing Co BA.N and Lockheed Martin Corp LMT.N will conduct the final design review for its new flagship Vulcan rocket within months, it said on Wednesday, as the aerospace company heads for a showdown with Elon Musk's SpaceX and others in the launch services market.

FILE PHOTO: The Boeing logo is pictured at the Latin American Business Aviation Conference & Exhibition fair (LABACE) at Congonhas Airport in Sao Paulo, Brazil August 14, 2018. REUTERS/Paulo Whitaker

The final design review is a crucial milestone as the company, United Launch Alliance (ULA), tries to move into full production ahead of a first flight in spring 2021 after slipping from its initial 2019 timetable.

“The design is nearly fully mature,” ULA systems test engineer Dane Drefke told Reuters during a tour of Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida.

The companies are vying to develop rockets to carry satellites into orbit in what the Satellite Industry Association lobby group estimates is a roughly $5.5 billion satellite launch services market.

ULA has started cutting and building hardware and has begun structural and pressure testing at its Decatur, Alabama factory. Engineers were also modifying the Florida launch pad and tower to accommodate Vulcan.

ULA’s legacy Atlas and Delta rockets have been synonymous with America’s space missions for decades. But the Colorado-based company has waged a cost-cutting campaign in recent years that included job cuts and trying new production methods as it faces mounting competition from SpaceX.

Musk has upended the industry with reusable rocket technology that has slashed the cost of space transportation.

And Amazon.com Inc AMZN.O founder Jeff Bezos' Blue Origin said last week it will fly its still-in-development New Glenn rocket in 2021 - the same year as Vulcan.

While ULA’s rockets burn up during each voyage, making for reliable but costlier missions, the company is charting a strategy of returning the first-stage engine to Earth under a parachute and plucking it out of mid-air with a helicopter.

ULA does not envision more job cuts and has been adding engineers in Florida and elsewhere, it said on Wednesday.

“We are now optimal-sized,” Drefke said, adding that ULA will be hiring more engineers as it moves into production.

The Vulcan, which will be powered partly by Blue Origin’s U.S.-built BE-4 engine, is central to ending U.S. reliance on Russia’s RD-180 engine for national security missions.

ULA confirmed new purchases of at least five more RD-180s in recent months for non-military missions, like commercial satellite launches.

Meanwhile, Blue Origin has hit “a few minor setbacks” during rigorous BE-4 testing but was “progressing nominally” and was expected to live up to delivery targets, Drefke said.

Blue Origin did not immediately respond to a request for comment.