A few days ago, @Space_Pete sent in a query via Twitter asking about the Multi-Layer Insulation issue that occurred with ATV Jules Verne in 2008 and how this had been addressed for ATV Johannes Kepler. His question referred to a problem that occurred during the ATV-1 mission when, after launch, portions of the MLI – the brilliant, white thermal blanket that covers the ATV – came lose from several mooring points and, basically, just flapped free.
The absence of thermal protection over portions of the ATV’s Integrated Cargo Carrier (the portion of ATV that carries the cargo) allowed heat to leak to space and caused some on-board heaters to work more than expected. Because the thermal and power situation remained acceptable, however, this was not considered a problem and the mission continued normally.
We passed the question over the ESA’s Nico Dettmann, Head of the ATV Production Programme, who sent in this reply.
The Jules Verne Multi-Layer Insulation (MLI) partially detached from its fixation points because of a ‘ballooning’ or ‘pillowing’ effect of the MLI blankets. The depressurisation rate during lift off was underestimated. As a result, the air captured in the MLI compartments – basically, underneath the blanket – could not escape fast enough, leading the MLI to ‘balloon’ up. The MLI attachment points were not designed to withstand the resulting forces of the ballooning and partially detached.
Both the ballooning and the detachment were clearly visible in the photos taken from the ISS cameras when Jules Verne arrived at the station of docking.
What, however, was really impressive was that we knew already before we got the pictures what had happened – and we could predict very accurately where the MLI had detached. Shortly after Jules Verne separated from its Ariane booster, mission controllers noted higher-than expected heater activations at some areas of the Integrated Cargo Carrier – the cargo-carrying portion of ATV – which could only be explained by degraded insulation.
Despite the fact that we didn’t like at all what had happened to the MLI, we obtained a very good confirmation of the precision of our thermal models – and since the loss of heat remained within acceptable limits, the ATV mission continued without mishap.
To address this problem with the second ATV, Johannes Kepler, teams at ESA and our industry partners worked very diligently and we completely redesigned the concept of the venting holes – holes in the thermal blanket that, as the name implies, allow air to escape as the ATV is lofted into space. With our new design, we performed a series of rigorous tests that included a complete depressurisation as happens in flight; in addition, we modified the way the MLI blanket portions overlap each other and we increased the number of attachment points.
Last but not least, we repeated the thermal vacuum test to esure that the thermal properties of the modified MLI remained inside the vessel’s requirements. We learned some pretty valuable lessons and we’re very confident that ATV-2 won’t experience this problem again.