Catastrophic failure modes of NASA's proposed Ares I crew launch vehicle's upper stage fuel tank are being simulated and the space agency is seeking to place contracts for modelling services.The failure modes being investigate by NASA include propellant tank baffle failure leading to a mixing of the liquid oxygen (LOX), liquid hydrogen (LH2) propellants and their respective pressurisation gases, oxygen vapour and helium tank venting due to over-pressurisation-induced cracking that leads to combustion in an air-rich environment and flight instability caused by propellant sloshing from steady and unsteady vehicle acceleration. The point of greatest danger for sloshing-induced instability is where gravitational forces become small along the trajectory."Simulations at various points in the vehicle trajectory that are characterised by very different vaporisation and combustion characteristics [are required]," says NASA, which will provide upper-stage crack location and size data for computational fluid dynamics simulations.
The agency is also requiring up to five failure scenarios to be modelled where LOX and LH2 at different temperatures and pressures mix transiently through a failed bulkhead leak. The scenarios will also have to reflect the subsonic, supersonic and hypersonic flight regimes.