Digital Equipment Corp is expected today to launch the long awaited three-dimensional VAXstation using raster graphics subsystem technology jointly developed under its two-year-old pact with Evans & Sutherland Computer Corp. The new VAXstation is believed to be built around the VAX 8250 processor, be designed for use in VAXclusters and to cost $70,000 to $90,000. Electronic News hears it may use the BI bus, causing problems for existing VAXstation users wanting to transfer their Q-bus expansion products.