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March 1 (Reuters) - Space transportation startup Rocket Lab USA Inc on Monday agreed to go public through a merger with a blank-check firm backed by private equity firm Vector Capital, in a deal that values the combined entity at an enterprise value of $4.1 billion.

The move marks the latest in a series of special purpose acquisition companies (SPAC) buying space firms including Richard Branson's Virgin Galactic and rocket startup Astra.

Earlier on Monday, satellite data company Spire Global Inc agreed to go public through a merger with blank-check acquisition firm NavSight Holdings Inc at a $1.6 billion valuation.

The deal with Vector Acquisition Corp will be financed by the $320 million raised by the blank-check firm in its September 2019 IPO and $470 million from private investors including BlackRock Inc and Neuberger Berman.

Founded by New Zealand entrepreneur Peter Beck in 2006 and headquartered in Long Beach, California, Rocket Lab has delivered 97 satellites to orbit.

The company plans to launch a satellite to the lunar orbit for NASA this year as a precursor to the Gateway program, a Moon-orbiting outpost for NASA's lunar mission.

Following the merger, Rocket Lab's current shareholders including Khosla Ventures and aerospace company Lockheed Martin

will own nearly 82% of the combined company.

The transaction is expected to close in the second quarter of 2021, following which the company will be listed on the Nasdaq under the ticker symbol "RKLB".

Morgan Stanley & Co LLC and Deutsche Bank Securities were the financial advisors to Rocket and Vector respectively on the deal.

(Reporting by Sohini Podder in Bengaluru; Editing by Ramakrishnan M.)

((sohini.podder@thomsonreuters.com;))