I recall that the old animations that were used by the TV networks during the Apollo missions often showed a kind of "double plume" for rocket engines firing in a vacuum. There was a relatively strong "central plume" directed out along the engine axis, but also a much wider "inverted umbrella" plume spreading out from the engine bell.

Now, of course I realize that an artist's conception doesn't necessarily correspond to reality (thank goodness!), but I'm wondering if there may be a bit of truth in those animations. No doubt they used technical consultants and tried to get the effect right. Perhaps some of Von Braun's people were involved, or engineers from Rocketdyne.

In any case, I can speculate a bit on what might be happening here. There would be a boundary effect at the lip of the engine bell, a point of discontinuity where the exhaust gasses are no longer constrained by the nozzle. This might lead to a bit of turbulence along the margin of the exhaust flow, sending a small fraction of the plume out to the side.

This roundabout argument is to suggest that the "blow-dry" model of dust removal may just have some merit! [img]/phpBB/images/smiles/icon_biggrin.gif[/img]


<font size=-1>[ This Message was edited by: Donnie B. on 2002-11-05 10:30 ]</font>