Among the Various Type of Cargo That ATV Transports to the International Space Station

Among the various type of cargo that ATV transports to the International Space Station there is also gas, used to reequilibrate the air composition on board ISS and to maintain the internal pressure to adequate level.

ATV can bring to ISS three types of gas: air, oxygen and nitrogen. The last two are utilized in case the gas percentages in the internal air are not in equilibrium, air is used to reestablish the correct pressure level. In fact every time astronauts exit the Station to perform extra vehicular activities (EVA) a certain amount of air is lost in space and it is necessary to replace it.

Here you can see the ATV3 Gas Control Panel, that allows the delivery of air and oxygen (ATV3 transports 33 Kg. of air and 66 Kg. of oxygen). The gas is transferred directly in the ATV cabin through the dispenser that is located in the lower part of the panel and it is then distributed in the ISS thanks to the air distribution caused by the fans located in the various modules (remember that in microgravity air does not move as on Earth unless it is moved on by appropriated fans). Every gas delivery is carefully planned on ground, where the ECLSS (Environmental Control Life Support System) specialists control the pressure parameters and the air composition e decide when it is time to raise the pressure or improve the air mix. They define the ∆P to be reached (expressed in millimeters of mercury – mmHG) and estimate the needed time to obtain that result. The activity is performed by the crew who must open the valves, monitor the transfer and close the valves when the required ∆P has been obtained. An estimation of the quantity of gas to be delivered (in kg.) is done in advance and will be confirmed after the delivery. This information is also important to plan the next deliveries. Every ATV gas delivery is carefully monitored by the ATV Flight Control Team located in Toulouse, but not only. In fact at the Altec Engineering Support Room, normally dedicated to the Columbus engineering support, we have now a dedicated console connected to ATV-CC where we receive the ATV telemetry data from ATV-CC and from which we can connect to the Station voice loops to follow the activity.

The first gas delivery from ATV3 was performed on the afternoon of April 6th 2012. Normally this would have been an holiday for Altec and its employees (since it was Good Friday) but this doesn’t stop the ATV team (composed by Mauro Signetti from TAS-I and Liliana Ravagnolo and Davide Monge from Altec) to renounce to half a day of holidays to support the activity.

The astronaut charged of the activity was Andre’ Kuipers, that beeing the european astronaut on board now is mainly involved in the ATV operations. The ISS Flight Control planned a gas delivery from Gas Line 1 (that contains air) able to raise the Station pressure of 10 mmHG. The estimation of the delivered gas quantity was 13,5 Kg.

Initial pressure, measured by Andre’, was 732 mmHg., valves were opened at 13.13 GMT. Planned pressure (742 mmHG) was reached around 15.11 GMT, after about two hours, matching perfectly the time estimations from Flight Controllers. No problems at all, everything went smooth and perfectly nominal.

Next ATV3 gas delivery is planned for Thursday April 19th, when a second gas delivery from Gas Line 1 (air) is planned, again with a ∆P of 10 mmHG. The main difference is the time duration that is considerably longer (from 11.05 to 16.05 GMT, 5 hrs.) because the internal pressure in the tank is now lower and for gas law the delivery spped will be lower and the needed time longer. We will be again on console in Altec to follow the activity and will keep you informed on how it will go.