PARIS — Europe’s Arianespace launch consortium will wait an hour after satellite separation from future Europeanized Soyuz rockets before declaring mission success as a direct consequence of the August failure of the vehicle’s Fregat upper stage, Arianespace Chief Executive Stephane Israel said Oct. 8.
In a conference call on the conclusions of the Soyuz failure review board, and accompanied by board chief Peter Dubock and Arianespace Chief Technical Officer Edouard Perez, Israel said the one-hour delay will give Arianespace enough time to collate data from satellite tracking stations to determine their exact position.
Arianespace and others involved in the Aug. 22 Soyuz launch of two European Galileo navigation satellites spent many minutes in congratulatory speeches after what was presumed to be a success.
It was only several hours later, after the U.S. Air Force’s network of space-object-tracking sensors disclosed that the launch left the two Galileo satellites badly off-target, both in terms of perigee and orbital inclination, that Arianespace announced the orbital-insertion failure.
Israel said the one-hour time lag between satellite separation and mission assessment will be especially useful for Soyuz launches but would not be needed for launches of Europe’s heavy-lift Ariane 5 rocket into geostationary transfer orbit.
The board of inquiry, as expected, concluded that the Fregat upper stage placed the satellites in a useless orbit following a series of events caused by the installation of a hydrazine fuel line too close to a supercold helium pressurization line.
Fregat prime contractor NPO Lavochkin of Moscow used an aluminum clamp to hold the two lines in place. During the long coast phase needed for the Galileo mission between the first and second Fregat engine firing, the clamp acted as a thermal bridge that caused the hydrazine fuel to freeze.
The freezing stopped the supply of fuel to two Fregat attitude-control thrusters, which forced the stage’s inertial reference system to operate outside its usual boundaries and ultimately to fail.
Dubock, a former inspector general of the European Space Agency, said the inquiry board visited Moscow twice, for a total of three days, to convene with Russian authorities at the headquarters of the Russian space agency, Roscosmos.
Roscosmos and the TsNIIMash of Moscow, along with Lavochkin, inspected existing Fregat stages and informed the board that three of the 15 Fregats in the Lavochkin factory were assembled with the helium and hydrazine lines clamped together.
The Russian organizations told the board that nothing in the Fregat production manual advised against such an installation. Dubock said the inquiry board concluded that this was a “design deficiency” that is easily correctable by Lavochkin, which will amend the design instructions to warn against the close proximity of the helium and hydrazine conduits.
In addition, the aluminum clamps would be replaced, in all Fregats, with clamps made of nonconductive material.
Perez said a close inspection of the Fregat stages, aided by photographs brought to the inquiry board by the Russian side, showed 10 different places where helium and hydrazine are in too-close proximity. This, too, will be corrected for future flights.
Dubock and Israel stressed that the error should be viewed as a design omission and not a problem of Russian workmanship or quality control. Dubock said the inquiry board had no issues with Russian cooperation during the investigation.
“They furnished all the information requested and did supplemental work as well,” Dubock said. “I have no complaints about the cooperation they gave us.”
The Aug. 22 mission was the 46th flight of the Fregat upper stage. Dubock said all 45 previous missions had been successes. Of these 45, six featured a similar mission profile as the Galileo launch and thus were subject to hydrazine freezing. But for these missions, he said, it can only be supposed that they were among the majority of Fregats whose helium and hydrazine lines were not clamped together.
Perez said the work in Russia did not include reproducing the exact failure sequence on the ground, which he said would have been difficult. But enough simulations were conducted as to leave little doubt about the root cause.
In light of the board’s conclusions, Israel said Arianespace is ready to prepare a Soyuz-Fregat flight for December.
In principle, this will be for another pair of Galileo navigation satellites. But the European Commission, which owns Galileo, has not decided whether to avail itself of this launch or to wait until sometime in 2015.
Some European government officials argue that the two satellites launched in August are being placed into a more-tenable orbit away from the Van Allen radiation belts. With their orbital perigee raised, the satellites — the first of 22 being built by OHB AG of Bremen, Germany — can be fully tested.
In addition to reducing the risk of further satellites by testing the first two, European government officials said the likelihood of inserting the satellites into the Galileo positioning, navigation and timing network is now viewed as good.
“This will never be the correct orbit, but once we get the perigee raised so that we can communicate with them on a regular basis, we can get them to a point where they know exactly where they are, and then they can be used for navigation,” one government official said. “Nothing is certain yet, but things are looking a lot better than we originally thought. In either case, we’d like to spend the next couple of months testing them rather than launching a second pair in December.”
The European Commission, via the 20-nation ESA, has purchased a mix of heavy-lift Ariane 5 rockets, which can carry four Galileo satellites at a time; and Soyuz rockets to complete the constellation.
A new four-satellite dispenser structure for Ariane 5 is expected to be declared fit for flight this spring.
