Two stage. Launched 7 June 1961 20:50. Apogee 362 miles.
BK17 was another two-stage vehicle but with a lighter low-drag eroding head to give higher re-entry speed. The first stage performance was very good. The kerosene level sensor and HTP probes worked well and propellant usage in flight was determined. Visual observation and camera records of re-entry were confusing, but it soon became clear that the second stage had not functioned correctly. The head and tape recorder were recovered, and subsequent analysis of head tape record and body telemetry indicated that second stage separation occurred at re-entry and not at the end of first stage burning. It was possible to deduce from the records that the failure of second stage separation at first stage burn-out was due to failure of one of the two explosive bolts. In later vehicles explosive bolts and associated circuits were duplicated. At re-entry the second stage was torn off, followed by second stage burning.
The tape of the recorder in the head ran out before re-entry. In subsequent heads, the speed of the tape in the tape recorder was reduced so as to run for a longer period and ensure recording re-entry.