Several European satellite missions are in limbo due to technical and political trouble plaguing the Dnepr rocket, a converted ballistic missile from the Soviet nuclear arsenal.

File photo of a Dnepr rocket launch. Credit: Kosmotras

The Dnepr's missile heritage makes it a responsive and accurate satellite launcher, but the 111-foot-tall rocket has been bitten by political wrangling between Russia and neighboring countries before.

Four European satellite missions are scheduled to launch on three Dnepr flights over the next three months. Two of the missions will blast off from the Baikonur Cosmodrome in Kazakhstan, and another launch will originate from the Yasny space base in southern Russia.

CryoSat 2 is first in the queue, but liftoff of the ice observation craft from Baikonur probably won't occur this month due to the late discovery of a performance issue with the Dnepr's second stage steering system.

The issue stems from the 1,587-pound satellite's large size and unique orbit, which is at an altitude of 447 miles with an inclination of 92 degrees. CryoSat 2's physical dimensions -- 15 feet long and nearly 8 feet wide -- also require the Dnepr's extended payload fairing, adding more mass to the rocket, mission officials told Spaceflight Now.

Kosmotras, the joint Russian-Ukrainian sales firm that markets the Dnepr rocket, informed ESA in February that the liquid-fueled steering engine on the booster's second stage doesn't have the appropriate fuel margins for the mission.

After meeting with Ukrainian engineers in charge of the Dnepr, ESA managers say they are close to resolving the performance issue with the CryoSat 2 launch.

Yuzhnoye, the Dnepr's prime contractor, is reprogramming a flight computer from another SS-18 missile to tweak the mixture ratio of the rocket's second stage vernier steering engine. The change should permit the engine to produce the required thrust, according to Richard Francis, the CryoSat 2 project manager.

"We understand the issues, and we're confident they've got a good handle on it," Francis told Spaceflight Now on Tuesday.

Francis said officials are working on securing a special export license to ship the computer from Ukraine to the launch site in Kazakhstan. Approval for the license could come later this week.

"They really speeded things up because it normally takes 45 days," Francis said. "But they've been banging on the door to get this done, and we appreciate that."

Although a new launch date is still pending, Francis said liftoff probably won't occur before early April.

Two payloads from Sweden and France are scheduled for launch on the next Dnepr rocket from Yasny, Russia. That mission is slated to blast off around April 13, at the earliest.

Artist's concept of the Prisma satellites. Credit: Swedish Space Corp.

The Prisma mission from Sweden includes two spacecraft -- a main satellite and a target -- that will conduct extensive formation-flying, rendezvous and close approach demonstrations using GPS and optical navigation. The French space agency's small Picard satellite will study the sun from Earth orbit.

Political disagreements on drop zones for Dnepr rocket parts have threatened to hold up the launch of Prisma and Picard.

Kazakhstan withheld approval for the rocket to drop its booster stages within its territory, but the Prisma program manager says Russia and Kazakhstan have now tentatively agreed to allow the launch to go forward.

Christer Nilsson, Prisma program manager at the Swedish National Space Board, says representatives from the two countries have agreed on the text of an agreement, and the nations may have already signed a document permitting the launch.

Swedish Prime Minister Fredrik Reinfeldt visited Russian President Dmitry Medvedev on Tuesday, and officials hoped the meeting will accelerate the paperwork. Space issues were on the agenda for the meeting.

This is not the first time disagreements on Dnepr drop zones have held up launch from Yasny. A Thai Earth observation satellite was grounded nearly a year after Uzbekistan and Kazakhstan refused to allow Dnepr rocket stages to fall inside their territories. Kazakhstan finally permitted the launch, which successfully orbited the THEOS satellite in October 2008.

Another Dnepr mission is scheduled for launch in late May with Germany's TanDEM-X, but its official liftoff date depends on the fate of the CryoSat 2 schedule, according to Michael Bartusch, TanDEM-X project manager at DLR, the German Aerospace Center.

TanDEM-X will join another spacecraft already in orbit mapping the Earth to create precise digital elevation models using space-based radars. The satellites will fly in tight formation about 1,000 feet apart.