Crew role in mission control
The ATV is an advanced spaceship, which automatically performs final approach with the ISS. Nevertheless, the Space Station crew, before welcoming the arrival of its cargo, monitor the automatic rendezvous using independent means.
The crewmembers are not involved in the auto-piloting of the ATV, but they carefully monitor its performance from inside the Russian Service Module. They can interrupt the spacecraft's approach at any moment if they consider their safety is at stake.
Beside the multiple-fault tolerant capability, the ATV ground controllers in Toulouse have the full monitoring capability of the ATV by telemetry. The ISS crew acts as an additional and independent level of monitoring, but they rely only on a limited number of parameters, mainly related to the vehicle motion in relation to the Station.
As soon as the radio communication link is established between the unmanned ATV and the ISS, at a distance starting between 40 and 50 km, selected ATV telemetry is displayed to the crew. The astronauts can initiate the Collision Avoidance Manoeuvre (CAM) on their own to move the 20-tonne spaceship away from the Station, in the remote case of a major anomaly or malfunction, showing up on their consoles.
At a distance of approximately 250 metres, in the last half hour of the approach, the crew actively checks if the ATV behaves normally using the ISS Russian Segment (ISS/RS) video system. After the authorisation from the crewmembers, the controllers at the ATV-CC command ATV to cover the last few metres. The crew carefully checks the ATV's slow motion towards the ISS takes place in the rendezvous safety corridors. Should the ATV not stay within this virtual funnel they can reject it during the final approach.
To carefully monitor this operation, the crew uses a video screen and a 16 pushbutton control panel. Since there is no direct window view in the ATV direction, they rely on a simple and robust visual method using the two zoom modes (wide and narrow) of the video camera and an optical alignment device on the front cone of ATV. The crew can monitor, through their video screen, the position and attitude of the ATV. Essential telemetry data from the ATV is also displayed on the screen.
Their surveillance role is important during this critical moment because they know they can intervene in the improbable case of multi-failure scenario which exceeds the design requirements. However they do not need to handle the ATV systems. They run automatically. At the same time on the ground, the ATV-CC Flight Director can also interrupt the approach of ATV, even if the crew does not see any showstopper. The flight controllers have a greater visibility of all the parameters to analyse in real-time the behaviour and performance of the ATV.
The crew can interrupt the ATV approach in four different ways: HOLD, RETREAT, ESCAPE or ABORT. The action to be taken depends on the type of anomaly.
The main action to be taken by the crew in case of failures occurring at distances further away than 20 metres is to report to mission controllers. The space vehicle is sufficiently far away for the ground controllers - having access to all data and not just a limited selection, to take the best decision.
At distances closer than 20 metres, the crew can send the ATV away using the ESCAPE mode if the ATV moves outside the approach monitoring corridor or in case of malfunctions of the safety system. ABORT has the same effect as ESCAPE but uses independent software and hardware. It is used as a last resort should the main ATV computers or piloting hardware fail completely.
Layers of safety
If there is a serious problem during rendezvous, the crew can act only as a last level of safety. That is because any off-nominal scenarios should be automatically handled by any of the four layers of safety which are already implemented - on board and on the ground - for this highly automated spacecraft.
The human presence on board represents an extra layer of safety to the existing ones. The other four layers include independent monitoring systems and software already aboard the ATV and on the ground, the surveillance and the possible action from the flight controllers.
After the capture by the Station's docking mechanism, the docking seal is tightened up and electrical and fluid connections are set up. Following several checks, the crew opens the hatches and can enter the ATV pressurised cargo section. The European cargo vehicle is now an integral part of the International Space Station and remains attached for up to six months.
The transfer of the dry cargo, contained in bags, drawers and racks, is handled manually by the astronauts or cosmonauts, with the supervision of the Station's inventory by Mission Control in Houston. The payload is composed of maintenance supplies, science hardware, and parcels of fresh food, mail and personal items such as family tapes and DVDs.
Up to two astronauts can work, unloading supplies and conducting experiments, while the hatch remains opened between the ISS and the ATV.
The air loaded in the ATV, is released manually by the crew from the Cargo Carrier into the Station cabin through the hatch. For fresh water carried from Earth to ISS, and for Station liquid waste transfer back to the ATV, crewmembers use valves and flexible hosepipes. Liquid waste can also be carried away with foldable plastic containers. The crew steadily fill the cargo section with the Station's waste and material that is no longer used on the Station.
Meanwhile, the ATV's propellant tanks have been connected automatically - at docking - to the Station's own plumbing, to transfer their contents to the ISS.
During the attached phase, the crew's only task is to perform hands-on transfer activities; they are not responsible for re-boost, attitude control and refuelling management. Although during Jules Verne flight, which is a demonstration mission, the crew may be asked by the ground to monitor these activities the first time they are performed.
Last update: 2 March 2011