Analysis and simulation of discharging residual rocket Propellants in orbit

To diminish the generation of space debris, the residualpropellants in the storage tank of a final-stage rocket have to bedischarged after the satellite-rocket separation. An analysis shows that thepropellant jets under the discharge conditions, once entering the space,will break up into a number of liquid droplets. The droplets diffuse in thehigh vacuum, while gaseous molecules successively evaporate from the dropletsurfaces. This process yields a rarefied vapor and droplet field around thefinal-stage rocket. This article employs the Lagrange means to tracktrajectories and evaporation processes of the droplets, and employs thedirect simulation Monte Carlo (DSMC) method to calculate motion andcollisions of the gaseous molecules. Macroscopic quantities of interest,such as the flow fields, surface pressure, shear stress and heat flux, etc.,are obtained through statistically averaging the corresponding microscopicquantities. This scheme is validated to simulate a steam plume around awater jet into vacuum，and the calculated Pitot pressure distributions inthe radial direction agree with Fuchs and Legge's measured data . The schemeis then applied to three dimensional rarefied vapor and droplet plumesarising from original and new manners discharging in orbit the residual fuel1,1-dimethyl-hydrazine of a CZ-4B final-stage rocket. The calculation showsthat the original manner may lead to quite large disturbance moments beyondthe rocket attitude-control range, whereas the new manner very smalldisturbance moments within the range. These predictions are supported by theremotely measured data of flights