Lingering Doubts Drove Europe To Sideline Galileo Launches until Next Year
PARIS — European governments’ decision to forgo a December launch of two Galileo navigation satellites was fueled both by ongoing concerns about the Soyuz rocket following the August failure and by unresolved performance issues on the two satellites stuck in a bad orbit, European government and industry officials said.
Officials said that despite an inquiry board’s conclusion that the Soyuz Fregat upper stage misdirected the two satellites because of an easily fixable design flaw, the inquiry uncovered several other Soyuz issues that will have to be resolved before they will launch.
In addition, each of the two Galileo satellites placed into the bad orbit initially failed to deploy one of its two solar arrays, for reasons that could be due to the bad orbit but may have some other cause. An investigation is ongoing and has come to no conclusion, officials said.
The solar-array deployment anomaly affected one of the arrays on both satellites launched in August. The 20-nation European Space Agency is investigating whether abnormally low temperatures due to the bad orbit could have caused the nondeployment. It took several days for the solar arrays to deploy after ground controllers reoriented them so that the stuck array was facing the sun.
“The investigation is ongoing and there is no conclusion on a root cause,” one official said of the solar-array issue. “Was it a consequence of the bad orbit, or is there an issue with the solar array deployment mechanism? We cannot yet say for sure.”
The two satellites were built by a consortium led by OHB AG of Germany, with electronics payloads provided by Surrey Satellite Technology Ltd. of Britain. They are the first of 22 Galileo satellites under contract to OHB for launch.
Because they are the first of a series,and the European Commission — the executive arm of the 28-nation European Union, which owns Galileo — are loath to put more satellites in orbit before getting to the bottom of the solar-array issue and, in the coming months, testing the satellites’ overall performance.
“So far what we can say is that the satellites are performing very well,” a European government official said. “In fact we are more confident now than we were right after the launch that we can make some use of them inside the Galileo constellation. This will entail some additional costs, which we have not yet assessed, but things do look better than they did after the launch.”
The Europeanized version of Russia’s Soyuz Fregat vehicle, operated from Europe’s Guiana Space Center on the northeast coast of South America, placed the satellites in an orbit with a too-high apogee, too-low perigee and inclination relative to the equator that is far from what was planned.
Bringing them into the correct position would use most of their onboard fuel and is not an option, officials said. But the satellites are under full control and, with some modification to the Galileo network’s ground infrastructure, likely could be used for part of Galileo’s positioning, navigation and timing mission.
The first move for ESA and the German-Italian consortium that now controls the satellites — Spaceopal GmbH of Munich, a joint venture of Germany’s DLR space agency and Telespazio of Italy — is to raise the satellites’ perigee to remove them from their twice-daily passage through the Van Allen radiation belts.
These maneuvers — 10 or 12 per satellite, to be performed not concurrently but on one spacecraft after the other — are scheduled to begin in late October and to end by late November. After that, a series of system tests will be performed.
It will not be before January when early results are available confirming that the satellites work as designed and that launches of the following spacecraft may be scheduled.
A government-industry team comprising European and Russian officials concluded that the Fregat upper stage malfunctioned because a supercold helium pressurization line was installed too close to a hydrazine fuel line, causing the hydrazine to freeze.
The inquiry said it was unable to repeat the failure on the ground because such a test was deemed logistically impossible. But a thorough inspection found that because the Fregat design manual said nothing about separating the helium and hydrazine feed lines, 20 percent of the Fregat upper stages in storage at manufacturer Lavochkin of Moscow had the same defect.
The issue had never posed a problem in 45 Soyuz Fregat launches mainly because the long coast phase during which the hydrazine froze is not part of the flight profile of most Soyuz missions, the inquiry determined.
For the six previous missions that had such a coast phase, the inquiry said, it can only be assumed that since only one in five Fregats was assembled with the lines so close, these previous six flights featured separated lines.
“There are eight or so specific recommendations from the board of inquiry,” a government official said. “They concern some generic issues that need to be addressed by an action plan we expectto present to us.”
The Arianespace launch services company established the inquiry board and has said it has begun implementing the proposed corrective measures with Lavohkin.
A Soyuz Fregat rocket with a different flight profile — carrying four O3b Networks broadband satellites into an equatorial orbit some 8,000 kilometers in altitude — will be using the December Soyuz slot.