An illustration of the Astra 2B satellite orbiting Earth. Photo: Matra Marconi Space

Arianespace has postponed the next launch of its powerful Ariane 5 rocket because of an undisclosed problem with one of two satellites the booster was supposed to carry into space.

The Ariane 506 launch was slated for May 23 from Kourou, French Guiana in South America. But the Astra 2B direct broadcasting TV spacecraft for the Societe Europeenne de Satellites (SES) will not be ready for launch as scheduled. The craft was built by Matra Marconi Space.

The other cargo originally planned to fly with Astra 2B on Arianespace Flight 130 -- the GE-7 communications satellite for GE Americom -- could launch as soon as July. However, a statement released by Arianespace on Tuesday left open the possibility GE-7 might be launched alone by the a smaller Ariane 4 rocket. Flying with some other satellite aboard an Ariane 5 is also an option.

"Arianespace is working with its clients to revise the launch manifest over the near- and medium term, with mission timing and choice of launcher versions depending on the delivery of its customer satellites in French Guiana," the statement read.

The other commercial communications satellites booked to fly on Arianespace this summer include Loral's Europe*Star FM1, PanAmSat's PAS-1R, the Brazilian Brasilsat B4 and Eygpt's Nilesat 102.

Just like last year, Arianespace's flexibility is being tested in the wake of satellite delays. The company, which conducts a majority of commercial space launches annually, was forced to halt rocket flights for several months last year because its customers were experiencing satellite problems.

But a once the flood gates opened and payloads were ready to go, Arianespace reeled off eight launches between August and December.

Artist's concept of Galaxy 4R in space. Photo: Hughes

Meanwhile, Arianespace says all remains on schedule for the launch of Flight 129 next week.

A workhorse Ariane 4 rocket will carry the Galaxy 4R telecommunications satellite into orbit for U.S. operator PanAmSat and builder Hughes Space and Communications.

Liftoff is planned to occur on Tuesday evening during a window of 8:29 to 9:39 p.m. EDT (0029-0139 GMT Wednesday).

The three-stage rocket was rolled from its assembly building to the launch pad on April 3. The Galaxy 4R spacecraft -- already enclosed within the rocket's nose cone -- was expected to be transported to the pad Wednesday.

Galaxy 4R was built to replace its namesake, which spun out of control and failed in space two years ago because of an onboard malfunction. The incident wiped out communications and pager services throughout the U.S. for a time.

Arianespace has completed three successful missions in 2000 -- two using Ariane 4s and one for Ariane 5.