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 1958 April 02
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The Raven motor thrust interrupter unit, as tested on SL06 (BFSR Fig.5.44 / Dorling (1959), figure 43)

One of the pieces recovered from SL06
(BFSR Fig.5.46 / National Archives of Australia: D8891, N58/1363)

Summary: The main purpose of this proving flight was to test a part called a 'thrust interrupter unit' or 'motor cut-down' device, designed to disable the motor by blowing out a sealing plug at the opposite end of the motor to the exhaust throat.

Preparation: This was originally intended to be the last of the proving flights, but as SL05 had been delayed, and the preparations for SL06 had proceeded without problem, it was launched beforehand.

Flight: Wednesday 2nd April 1958 dawned fine and cloudless, with visibility at 15 miles (24 km), and launch occurred at 8.02 am. The Raven 1A motor powered SL06 for just 26 seconds, and then the motor thrust was interrupted as planned.

Recovery: The head was separated from the motor by the cut-off operation and fell to the ground 3 miles (4.8 km) downrange, although unexpectedly the residual thrust from the motor meant the case travelled much further, to 35 miles (56 km) downrange.

Result: Although the thrust interrupter worked well on this occasion, it was not long before it caused the first Skylark failure, when in June 1958 SL18 crashed after launch, and the interrupter had to be redesigned.

Comparison of the predicted and actual trajectories for SL06, with and without the thrust interrupter unit. (BFSR Fig.5.45 / Dorling (1959, figure 46)

(i) Brand, R. H. (2014), Britain's First Space Rocket, pp.98-100 & 612.
(ii) Dorling (1959), The First Six Skylark Firings, pp.46-57. (RAE Technical Report GW530, Oct.1959)
(TNA:PRO DSIR 23/27687)

                       New Forest Electronics Tel. +44 (0) 1425 650089                 Issue 3.109    13 May 2024