On its way to the ISS
In March 2008 the European ATV (Automated Transfer Vehicle) space freighter named Jules Verne will travel for the first time to the International Space Station (ISS). After being launched by an Ariane 5 from the European spaceport Kourou in French Guiana, Jules Verne will undergo extensive tests of its capabilities in orbit for about 16 days. For all of the four anticipated subsequent ATVs, the flight to the ISS up to the time of docking takes between two and four days.
100 minutes after launch, the ATV is on its own
Approximately six minutes after lift-off the EPS V upper stage and the ATV are separated from the burned out first stage of the Ariane 5. The upper stage ignites and takes the heavy payload into an elliptical orbit between 140 and 260 kilometres altitude. A second ignition of the upper stage causes the elliptical orbit to stabilise and become circular at a height of around 260 kilometres. Approximately 70 minutes after launch, the Ariane's re-igniteable upper stage is separated from the ATV. A brief braking manoeuvre then directs it into Earth's atmosphere where it burns up shortly afterwards. The control centre in Toulouse now activates the ATV. This begins with unfolding the solar panels and directing them towards the Sun. All necessary on-board systems are switched on one by one. Approximately 100 minutes after launch, the ATV is already an autonomous spacecraft. Monitored by the control centre in Toulouse, it is first navigated via GPS (Global Positioning System). By igniting its main engines several times the Jules Verne approaches the orbit of the ISS which at present is at a height of 340 kilometres.
Jules Verne tests flight safety to the ISS
Prior to docking at the space station, ESA needs to extensively test the space freighter and demonstrate its technical capabilities in space. Among other things, this involves a manoeuvre in collision avoidance during which a faulty final approach to the ISS is simulated. In the event of such a command, which can be issued by the Earth station or by the ISS astronauts, the ATV is supposed to abort its flight and fly to a defined waiting position outside the ISS safety radius which is a good two kilometres away. Here all of the ATV's systems are tested by the engineers in the control centres using telemetry before a new attempt at docking is made. The ATV can undertake a total of three docking attempts before the fuel required for this runs out.
ATV - Approaching the International Space Station
ATV's automatic approach to the ISS
The first contact between the ISS and the ATV takes place at a distance of around 30 kilometres from the space station by way of the Russian KURS system. This is a radar connection to the Russian ISS service module Swesda, which remains switched on until the craft has docked. In addition, it is now that the ATV's GPS comes into use in order to increase the level of positional accuracy during ATV navigation. If all the values on the ATV onboard computer seem correct, Earth control issues the command for a so-called 'homing'. This indicates the closer approach of the ATV to the ISS to a distance of 3500 metres away, which takes place during a half an Earth orbit and for which the ISS needs around 45 minutes. At this position all values and data are checked again.
What follows takes around 40 minutes. The relative speed, as compared to the ISS, is at this time only around seven centimetres per second. At a distance of around 700 metres the ATV's optical sensors take over the navigation. In the process infra-red lasers from the so-called 'telegoniometer' sense corresponding target reflectors on the outer shell of the Russian service module. Using the reflections the ATV onboard computer is able to calculate the relative position of the ATV in space and correct it using its 28 control jets.
The last 20 metres are navigated via a video system which was previously monitoring the telegoniometer. The telegoniometer is used to monitor the procedure during the final metres. The docking adapter's mechanical torque moment sensor, which is extended during this process, is used to dock and anchor the ATV to the ISS at a relative speed of around three centimetres per second. This is followed by a certain damping phase in order to allow the vibrations created to subside. Only then is the docking process brought to a close with the interface seal, locking, pressure equalisation and impermeability check. It takes around five hours from the time of first contact via the KURS system to docking.
Propellant to raise the ISS altitude
From sleep mode to the reboost manoeuvre
Now the airlock to the ATV is opened so that the astronauts can unload the freight. The Jules Verne transports 5.5 tonnes of goods and fuel to the ISS. The fuel for the Russian service module is automatically transferred from tank to tank at the push of a button via the docking ring. After docking and opening the airlock the ATV enters a type of 'sleep mode' in order to save resources. The vehicle receives a portion of the electrical current from the ISS during this time.
The ATV can also be used to boost the orbit altitude of the ISS. In order to carry out an orbit lifting manoeuvre for the ISS during the mission the ATV must be fully reactivated prior to it. According to the current plan this re-boost manoeuvre is scheduled to take place in April at the earliest.