While planning for the need to replace other Iridium satellites now on orbit, the final installations of the 66 spacecraft constellation await launch of the last seven spacecraft aboard rockets from China and California, Iridium Vice Chair and CEO Dr. Edward F. Staiano said Tuesday.

Iridium has used three launch vehicle service providers to loft their satellites: Boeing, which has provided a variant of the Delta II booster, Khrunichev, which offers the Proton DM, and the Great Wall Industry Corp., which flies the Long March family.

While Staiano pronounced his company "delighted" with all three providers, he called the Long March "the key to our maintenance plan". That plan, to replace malfunctioning or marginally producing Iridium satellites with new vehicles, plus spares in each of the six different Iridium orbital planes, will begin this summer with the launch of a Long March 2C carrying a pair of the satellites.

"This is a Long March that was planned as a spare," Staiano said. "Our plan is to fly six replacements (satellites) per year."

Staiano also said that extensive planning went into the launch vehicle service purchases, both in terms of the locations needed for launch, plus the sequencing of the launches. Each of the six planes consists of 12 satellites, 11 operational birds plus a single satellite as backup spare.

Staiano told SpaceCast that the Delta carries five, the Long March 2C carries two, and the Proton lifts seven. So it was the flexibility of these vehicles that allow Iridium to mix different launches from different geographic inclinations to assemble each 12 vehicle constellation - and to maintain the arrangement.

One Iridium failed last week, and on an earlier launch another suffered a stuck thruster which sent the spacecraft out of control. The Long March maintenance launch in June will carry a replacement satellite for a spare that has been pressed into service, plus a new spare.

And while the Chinese booster is the primary vehicle for replacements, due to its two-vehicle payload capability, Staiano said that Motorola -Iridium's builder and a major investor in the project -may consider a smaller version of the Boeing Delta. "We will be discussing this with Motorola after the Delta launch next week," Staiano said.