TOKYO, March 13 (Reuters) - Japan's Space One will launch its Kairos small rocket on its inaugural trip on Wednesday, in a bid to become the first private firm in the country to put a satellite in orbit.

While Japan is a relatively small player in the space race, the nation's rocket developers are scrambling to build cheaper vehicles to capture booming demand for satellite launches from its government and global clients.

Lifting off from Space One's launch pad in western Japan at 11:01 a.m. (0201 GMT), Kairos will carry an experimental government satellite that can be deployed to temporarily replace intelligence satellites currently in orbit if they come offline.

Kairos, an 18 m (59 ft) solid-fuel rocket, is designed to lift a 250 kg payload to low-earth orbit. Space One had initially planned the launch on Saturday but postponed it after a ship entered the nearby restricted sea area.

Tokyo-based Space One was established in 2018 by a consortium of Japanese companies - Canon Electronics, the aerospace engineering unit of IHI, construction firm Shimizu and the state-backed Development Bank of Japan. Two of Japan's biggest banks, Mitsubishi UFJ and Mizuho, also own minority stakes.

Space One wants to offer "space courier services" to domestic and international clients, aiming to launch 20 rockets a year by the late 2020s, its president Masakazu Toyoda says. The company had already delayed Kairos' inaugural launch window four times but said orders for its second and third planned trips have been filled, including by an overseas customer.

Space One does not disclose Kairos' launch costs, but company executive Kozo Abe said that it is "competitive enough" against American rival Rocket Lab.

Rocket Lab has launched more than 40 Electron small rockets from New Zealand since 2017 at roughly $7 million per flight. Several Japanese companies have used Electron for their missions, including radar satellite makers iQPS and Synspective, and orbital debris-removal startup Astroscale.

Last month, state-funded Japan Aerospace Exploration Agency (JAXA) successfully launched its new cost-efficient flagship rocket H3. JAXA completed a historic "pinpoint" moon landing earlier this year and the H3 is tasked to carry about 20 satellites and probes to the space by 2030.

In 2019, Interstellar Technologies conducted Japan's first privately developed rocket launch with its MOMO series, although without a full-scale satellite payload.

Partnering with the U.S., Japan is seeking to revitalise its domestic aerospace industry to counter technological and military rivalry from China and Russia.

The government last year promised "comprehensive" support for space startups with technology critical for national security, as it seeks to build satellite constellations to ramp up intelligence capabilities.

Japan's defence ministry on Friday said it has struck a deal with Space One to boost its rockets' payload by experimenting with fuel-efficient methane engines. (Reporting by Kantaro Komiya; Editing by Sam Holmes)