Hughes Electronics Corp is suing rival satellite-maker Lockheed Martin Corp for $550m, accusing them of failing to keep the terms of a contract signed three years ago. It claims Lockheed said it would launch four satellites for Hughes’ Space Communications division between 1997 and 2000 for a fixed price, and would offer further launches depending on the availability of rockets. Since 1994, Lockheed has moved more directly into competition with Hughes. The original deal was done through Lockheed’s 51%-owned Russian joint-venture, Lockheed-Krunichev-Energia International and the satellites were to be carried on Russian rockets. But demand for launches has increased over the last year and Hughes now claims that Lockheed wanted to sell it the additional launches at a higher price.