Crew role in mission control
ATV is an advanced spaceship that approaches the International Space Station automatically. The Space Station crew monitor the automatic rendezvous using independent means nevertheless.
Astronauts are not involved in piloting ATV but they carefully monitor its performance from inside the Russian Service Module on the Station. They can interrupt the spacecraft's approach at any moment if they think their safety is at stake.
Besides its fault tolerant design, ATV controllers in Toulouse monitor ATV by telemetry. The astronauts are additional, independent monitors, but they rely only on a limited number of parameters, mainly related to the spacecrafts position in relation to the Station.
As soon as the radio communication link is established between the unmanned ATV and the Space Station, at a distance between 40 and 50 km, ATV telemetry is displayed to the astronauts. They can initiate the Collision Avoidance Manoeuvre to move the 20-tonne spaceship away from the Station, in the remote case of an anomaly or malfunction.
At a distance of approximately 250 m, during the last half hour of the approach, the astronauts actively check if ATV is behaving normally using a video system. After receiving authorisation from the astronauts, controllers at ATV-CC command ATV to cover the last few metres. The crew carefully checks the ATV's slow-motion approach towards the Station. Should ATV not stay within the virtual approach funnel they can reject it.
To carefully monitor this operation, the crew uses a video screen and a 16-button control panel. Since there is no window to view ATV directly, the astronauts rely on a simple and robust system using two zoom modes of a video camera and an optical alignment device on the front cone of ATV. The crew can monitor, through the video screen, ATV's position and attitude. Essential telemetry data from ATV is also displayed on the screen.
The astronaut's surveillance role is important during this critical moment because they can intervene in the unlikely case of a failure. ATV systems run automatically. At the same time on the ground, the ATV-CC Flight Director can interrupt the approach of ATV, even if the astronauts do not see any showstoppers. Flight controllers have access to more parameters to analyse ATV's behaviour and performance.
The crew can interrupt ATV's approach in four different ways: HOLD, RETREAT, ESCAPE or ABORT, depending 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 m is to report to mission controllers. The spacecraft is still far away enough for ground controllers to take the best decision.
At distances closer than 20 m, the astronauts can send ATV away using the ESCAPE mode if the spacecraft moves outside its approach corridor or in case of problems with 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 as a last level of safety. Any off-nominal scenarios should be automatically handled by any of the four layers of safety which are already implemented - onboard and on ground - for the highly automated ATV.
Astronauts aboard the International Space Station are an extra layer of safety to existing ones. The other four layers include independent monitoring systems and software on ATV and on ground, surveillance and reactions from flight controllers.
After capture by the Station's docking mechanism, the docking seal is tightened and electrical and fluid connections are set up. Following several checks, astronauts open the hatches and can enter ATV's 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 dry cargo, contained in bags, drawers and racks, is handled by the astronauts, supervised by Mission Control in Houston, USA. The cargo can contain maintenance supplies, science hardware, parcels of fresh food and personal items such as letters from family.
Up to two astronauts can work at a time, unloading supplies and conducting experiments, while the hatch remains opened during the whole time ATV is docked.
Air loaded on ATV, is released manually by astronauts from the Cargo Carrier into the Station cabin through the hatch. Fresh water is carried from Earth, and liquid waste from the Station is transfered by valves and flexible hosepipes. Liquid waste can also be loaded with foldable plastic containers. Astronauts steadily fill the cargo section with Station waste and material that is no longer used.
ATV's propellant tanks are connected automatically at docking to the Station's own plumbing and the contents are transfered.
During the attached phase, the crew's only task is to perform hands-on transfer activities; they are not responsible for reboosting, attitude control or refuelling management.
Last update: 4 June 2013