Feb 2 (Reuters) - Astra, a startup that makes small rockets to send satellites into orbit, is going public at a valuation of $2.1 billion through a deal with blank-check company Holicity Inc , the companies said on Tuesday.

The deal with Holicity is expected to provide up to $500 million in cash proceeds, they said. This includes a $200 million private investment led by funds and accounts managed by BlackRock Inc , the statement added.

Holicity's shares were up about 56% in pre-market trading.

Mergers with blank-check companies, also known as special purpose acquisition companies (SPACs), have become an increasingly popular route to public markets for companies seeking to avoid a traditional initial public offering.

Astra's existing shareholders will own about 78% of common stock of the combined company, the statement said. Ad firm Taboola and electric vehicle maker Faraday Future are just a few of the companies that have joined the SPAC frenzy this year.

The combined company will remain listed on Nasdaq under the symbol "ASTR". Founded in 2016, Astra is based in Almeda, Calif.

PJT Partners acted as financial adviser to Astra, while Deutsche Bank Securities and BofA Securities advised Holicity.

Holicity raised $275 million when it went public last year.

(Reporting by Niket Nishant in Bengaluru; Editing by Bernard Orr)

((Niket.Nishant@thomsonreuters.com;))