A Boeing Co. (BA) and Lockheed Martin Corp. (LMT) joint venture working for the government was bared by a U.S. court on Wednesday from dealing with a Russian supplier of rocket engines used to shoot air-force satellites into space.

Elon Musk's Space Exploration Technologies Corp., or SpaceX, won a temporary injunction against the U.S. government and its contractors Boeing and Lockheed operating as United Launch Alliance.

The air force and United Launch Alliance is prohibited "from making any purchases from or payment of money to NPO Energomash", Federal Claims Court Judge Susan Braden said late Wednesday in a temporary injunction.

United Launch Alliance, the air force and NPO Energomash weren't immediately available for comment.

SpaceX is challenging United Launch Alliance LLC's near monopoly on military- and intelligence-satellite launches. It wants the Pentagon to open them to competition.

It drew attention to its rival's use of the RD-180 rockets made by Russia's state-controlled NPO Energomash OAO. U.S. defense officials and lawmakers are uneasy about the air force's reliance on Russian engines in the wake of the Ukraine crisis.

The engines are supplied by RD Amross LLC, a joint venture between the Russian company and a unit of United Technologies Corp. (UTX).

The air force has looked into alternative rocket engines including building them in the U.S. under license or fast-tracking a new domestic design.

Write to Doug Cameron at doug.cameron@wsj.com

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