Voyager RADVS-Exhaust Plume Interference

It is generally accepted that there is virtually no interference between the Surveyor and Apollo LM rocket exhaust plumes and their respective RADVS systems. The obvious tendency to extrapolate the conditions of the Surveyor and Apollo LM vehicle to Voyager would lead to the similar conclusion that no interference problem should exist. However, preliminary calculations on several proposed Voyager descent engines indicate that severe interference with the radar may occur. The essential difference in this case is the back pressure of the Martian atmosphere which confines the plume and introduces shock and mixing layer regions and the associated high gas and electron densities. The extent of the problem was sufficiently serious to impose a major constraint on the preliminary Voyager design. Figure l(a) shows conceptually the Voyager entry and the RADVS controlled soft landing, and Figure l(b) shows two candidate RADVS systems. Only the Surveyor type was studied, however the results are equally valid for either system