Europe's normally highly dependable rocket, the Ariane 5, has had an anomaly during its latest launch.
Europe's normally highly dependable rocket, the Ariane 5, experienced an anomaly during its latest launch.
Contact with the vehicle was lost shortly after its two stages separated, about nine minutes into the flight from French Guiana.
Telemetry from the vehicle was lost shortly after its two stages separated, about nine minutes into the flight from French Guiana.
The rocket was carrying two telecommunications satellites - one for Luxembourg-based operator SES, the other for Abu Dhabi-based Yahsat.
Two hours of uncertainty then followed as controllers tried to determine the status of Ariane and the satellites it was carrying to orbit.
As yet neither spacecraft has made contact with ground controllers.
Radio signals were eventually picked up from the telecommunications spacecraft.
Engineers will now be assessing their health.
Arianespace, the company that operates the Ariane 5 from the Kourou spaceport in French Guiana, issued the following statement late on Thursday, local time:
"The launcher's liftoff took place... at 7:20pm. A few seconds after ignition of the upper-stage, the second tracking station located in Natal, Brazil, did not acquire the launcher telemetry. This lack of telemetry lasted throughout the rest of powered flight.
"Subsequently, both satellites were confirmed separated, acquired and they are on orbit. [The two satellites] are communicating with their respective control centres. Both missions are continuing."
One satellite is owned by Luxembourg-based operator SES, the other belongs to Abu Dhabi-based Yahsat.
The SES satellite, called SES-14, was manufactured in the UK by Airbus at its Portsmouth and Stevenage plants.
The SES satellite, called SES-14, was manufactured in the UK by Airbus at its Portsmouth and Stevenage plants.
The Ariane 5 is the workhorse of European rocketry.
It famously failed on its very first outing in 1996 and had one more complete loss in 2002, before then putting together 82 flights without incident.
"We lost contact with the launcher a few seconds after the ignition of the upper-stage," said Stéphane Israël, the CEO of Arianespace, the company that operates the Ariane 5 at its South American spaceport.
"Up to now our customers do not have contact with the satellites.
"We need now to know if they have been separated and where they are exactly to better analyse the consequences of this anomaly."
It is possible the failure at this stage may only be partial. If the satellites managed to separate from the upper-stage, it is not out of the question that their missions could yet be salvaged.
The SES satellite, for example, has electric propulsion - a slow but very efficient means of raising the spacecraft in the sky. But controllers will first have to make contact and assess the status.
If this is an outright failure it has wide consequences.
A mishap inquiry will inevitably lead to delay for commercial customers who have rides booked on the Ariane 5 in the coming year. Thursday's flight was intended to be the first of a possible seven in 2018.
And this delay would also include some particularly high-profile institutional missions.
These include the next batch of satellites for Europe's version of GPS, known as Galileo. The spacecraft go up four at a time on an Ariane 5.
Then there are the two flagship science ventures on the manifest: Europe's BepiColombo mission to go to Mercury, which is currently booked to fly in October; and the US-led successor to the Hubble Space Telescope, called the James Webb Space Telescope. This near-$10bn payload is scheduled to go into orbit on an Ariane 5 in the spring of 2019.
A failure would also be a frustration to the manufacturing consortium behind the rocket, ArianeGroup, as it battles stiff competition for customers from the American launcher company SpaceX.
The US firm is about to test its latest vehicle called the Falcon Heavy. This will have the capacity to launch the same big telecommunications satellites as Ariane - but also land its boosters back on Earth for re-use.
This recycling of the rocket should allow SpaceX to offer prices to operators that substantially undercut the Ariane 5.
ArianeGroup is looking to respond by introducing a new, low-cost replacement vehicle, the Ariane 6, in 2020.
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
