Portraits of Ariane 5: No.7, Gerhard Billig

Gerhard takes us on a behind-the-scenes look at Ariane 5 launches. “Overall, we gave support to 12 Ariane 5 flights, most of them from both Santa Maria and Western Australia stations,” he says. “But first, let’s start at the beginning.”

“A rocket is monitored from liftoff, even a bit before. We want to have station coverage during all significant events, such as an active boost phase or a separation of a payload. Also, a launcher flight can be quite complex with different separation orbits for the different payloads and a deorbit/passivation at the end.

“We need to know what happens during the flight both for the launcher, loaded with fuel and thus potential for damages, and the payload, for instance a satellite. The customer needs to be informed about the status of the separation orbit in order to facilitate the establishing of communications.

“Launches are performed from the European Spaceport in Kourou, French Guiana. They are mostly done into the following typical types of orbits (which require different range tracking networks).

“Geostationary transfer orbits, so an eastward trajectory, from Kourou towards Africa; polar orbits, which go towards the North Pole from Kourou and then come down over Asia and then Australia: and then medium-inclined orbits such as those for Galileo or also for Automated Transfer Vehicles (ATVs) with Ariane 5, where you launched into a north-easterly direction from Kourou, going over Europe, the Arabian peninsula and then over Australia.

“This reception of the launcher signals is done by the launcher tracking downrange network, managed by the French space agency CNES at the European Spaceport. This network consists of several stations, satisfying the trajectories mentioned above and is situated along the path of the rocket. The launch control centre is located here as well, where all the information comes together.

“ESA participates in the launcher downrange network with two ground stations: Santa Maria, on the Portuguese island of Santa Maria (Azores), and New Norcia in Western Australia. ESOC runs and operates ESA’s tracking station network, Estrack, including the two stations mentioned, which played an important role in Ariane 5 tracking.

“The station in Santa Maria was built from scratch in 2007 for medium-inclined orbits and was used for the first time to track the the first ATV, Jules Verne, on Ariane 5 on 9 March 2008. The already existing Perth station in Western Australia was adapted in 2009 and first used in December that year. It provides a dual support: tracking the launcher and, after separation, giving in parallel tracking, telemetry and telecommand to the satellite. Following the closure of the Perth station in 2015, the launcher tracking capability was transferred to the New Norcia site, where a small terminal was built and the existing 35 m deep-space antenna adapted.

“What did it mean to follow an Ariane 5 launch? A launcher has a strong propulsion, therefore a higher potential to do orbit changes compared to a satellite. Concerning this, there are two important aspects in order to achieve a robust setup of the ground network:

“The capability of the antenna to do auto tracking: follow the signal wherever it goes once it has been acquired; then the live trajectory, updated several times per second, sent by the launcher control centre towards all ground stations in the network.

“From a technical perspective, tracking a launcher is quite demanding for a ground station system, firstly because the launcher can be agile, whereas a satellite is mainly ballistic, unless it manoeuvres. In case things go ‘non-nominal’, it can do something not initially foreseen and in this situation it is especially important to keep tracking it to get the data. Secondly, the radio frequency signal seen at ground can fluctuate a lot due to attitude changes, constituting dynamic conditions that the tracking system must cope with. All this implies that it may be quite difficult to follow the signal.

“In launcher tracking, there is only one chance to receive the information: once transmitted it is lost. While most of the launches go nominally, if you're running into any kind of contingency (which could be on the launcher or on the ground station side), you have to be very fast in reacting to ensure that there is no data loss.

“A satellite does another orbit, therefore there is – at least in principle - a second chance to obtain the data. But the ground station is the only way to get information on what the launcher is doing; the only way to understand what went wrong, if indeed it did. The ground stations’ visibility may overlap, but it is not necessary. As I said, visibility is especially required whenever there is an active phase of the launcher.

“Let’s give, as an example, a narrative of an ATV launch with an Ariane 5. Specific for the launches of ATV, the launcher started from Kourou in north-easterly direction over the North Atlantic, before it flew over Europe, with first stage and second stage burns. The involved stations were in Kourou, a boat placed in the middle of the Atlantic until Santa Maria had visibility.

“Further on, there was also a station in Aussaguel, which is close to Toulouse. Then the launcher was shutting down its engine for about half a revolution to reach the apogee, the farthest point away from Earth. During this passive phase there was a big pause without tracking. Then came a second burn over New Zealand to circularise the orbit and separate the ATV to reach the Space Station. This was followed by a de-orbit burn, passivation and splashdown in the sea.

“I have some fond memories of our work following in Santa Maria the Ariane 5/ATV launches. From there we tracked the final part of the first burn of the upper stage. I remember the rocket coming into our visibility 12 minutes after liftoff. It appeared fast since it was travelling quite low, at 120 km approximately, with a relatively high elevation and quite fast in the sky as seen from our ground station. So it was a demanding pass geometry.

“The second ATV launch took place during the night. It is not common to have a clear sky in the Azores, but we were lucky and it was possible to visually see the burn of the launcher. It was really impressive, with a plume appearing to span over half the sky. We tracked the end of the second burn towards the end of the pass, with a relatively low elevation towards the northeast as  the launcher continued farther towards Europe. Basically we could monitor the ‘end of the burn’ from the telemetry, while we were outside seeing the launcher and its plume at the same time, looking like a comet! And then disappearing. It was an impressive experience.

“Personally, Ariane 5 was special because it was my first series of launches, which I was following from Santa Maria as well as from Perth (the station used before New Norcia took over the core spacecraft-acquisition functionality).

“What happened to Ariane 5 launchers when the tracking stopped? If I take a launch into a low Earth orbit, for example for an Earth observation satellite, it would do a couple of burns, usually to deploy a couple of payloads in different orbits. So it burned, reached the orbits, separated the payload(s). This can be quite complex. Once all of this was accomplished, then typically for a low Earth orbit it would do a deorbit burn in order to bring the upper stage safely down typically in an area where there is just a lot of water. This could be the Pacific or Indian Oceans, for example.

“If I have an orbit which goes far away from Earth, like Galileo, or into a geostationary transfer orbit, deorbiting back to Earth would imply too much fuel. The launcher would just be put away in an orbit where it cannot damage active satellites. Before deactivating the launcher, we depleted all the fuel in order to reduce the risk of any kind of explosion should anything happen. Getting rid of all the fuel is called passivation.

“I had the opportunity to watch an Ariane 5 launch in Kourou, only a couple of kilometres away from the launch pad. This was a truly strong experience, I was specifically impressed by the loud sound and noise of the launcher, hitting me kind of unexpectedly when the launcher could already be seen high in the sky.

“For the future, now that Ariane 5 is history, there is Ariane 6 coming and we are preparing the stations to track it. We are looking forward to see what happens in flight. As for any launch, we will be doing lots of tests, preparation and training – technically and operationally - beforehand, in order to be prepared also for contingencies. But there is only so much you can do. This is also the thrilling part, each launch is different. It can be very demanding with lots of problems to solve. Or it can be perfectly nominal and boring in that sense. I have started to like ‘boring’ a lot, actually…”

Ariane 5 had 117 successful launches and placed 239 satellites in orbit. The heavy launcher carried prominent payloads, such as ESA’s comet-chasing Rosetta mission, a dozen Galileo navigation satellites, the James Webb Space Telescope and recently Juice, the explorer of Jupiter and its icy moons.