BOX 7-1 Ariane Passivation

The Ariane 1 through Ariane 4 are three-stage launch vehicles with cryogenic third stages. The third-stage liquid-oxygen and liquid-hydrogen tanks use a common bulkhead. On average, 120 kg of liquid hydrogen and 160 kg of liquid oxygen remain after third-stage engine cutoff.

Passivation measures for the third stage ensure full depletion of the residual propellant. Venting of the tanks begins when pyrotechnic devices fire to activate the pressure relief valves and venting pipes that were installed for this procedure. Depletion is timed so that the pressure difference between the two tanks meets the bulkhead design requirement throughout the procedure.

cause of rocket body breakup. In several cases, debris has been generated by the explosion of residual propellant for the auxiliary engines used to maintain three-axis control during transfer orbit segments and to provide axial acceleration prior to rocket body reignition. Propellant venting and depletion burns also can be used to avert such explosions. Finally, batteries and other pressurants rocket bodies are sources of energy that can lead to breakups. These can be passivated in the same manner as they would be on spacecraft.

Reducing the Creation of Debris from Degradation

The products of spacecraft surface deterioration include paint flecks and other surface materials that come loose from a space object under the influence of the space environment. Very few of these items are large enough to be cataloged; the vast majority are small. The few cataloged objects believed to be released due to surface degradation have had high ratios of cross-sectional area to mass and have experienced relatively rapid orbital decay. The vast numbers of small particles released due to surface degradation are also suspected to have high ratios of cross-sectional area to mass and thus fairly short orbital lifetimes (as discussed in Chapter 3). However, since a typical paint fleck may have a mass of only 10-6 gram, the deterioration of even minor amounts of surface material can rapidly replenish the orbiting population. As discussed in Chapter 4, these particles can cause surface degradation and can also potentially damage unprotected spacecraft components such as optics, windows, and tethers.

Much has been learned from LDEF and other experiments about the

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