The Alternative Black Arrow

As early as 1958, David Andrews of what was then Armstrong Siddeley Motors put forward a design for an IRBM using HTP and kerosene. The design was essentially a much enlarged Black Knight. Black Knight had a weight of 12000lb with a liftoff thrust of 16,400lb; the IRBM would have a weight of 70,000lb with a lift off thrust of 92,000lb. This was achieved by substituting the large Stentor chamber from Blue Steel for the Gamma chambers in use on Black Knight.

The earlier Black Knights used the Gamma 201 engine with the Gamma chamber derived from the design produced by the Rocket Propulsion Establishment at Westcott; the later 301, more powerful and more efficient, was a substantial redesign using the small Stentor engines. [These may be seen on the page on HTP motors.]. The large chamber of the Stentor could provide nearly 25,000lb thrust, the smaller chamber around 6,400lb at sealevel.

Andrews provided some rather optimistic ranges for his IRBM; given the warheads of the time they were improbable. The design was revived at the time of the Blue Streak cancellation, when the warheads were lighter, but little official interest was shown either time. Given that Blue Streak was cancelled on the basis that it was too vulnerable in silos, this is understandable.

This obviously formed the basis of his later propsed small satellite launcher. Using the same first stage engine, it effectively used a Black Knight second stage and a small HTP third stage. And here is a more detailed view of the design:

Both designs were costed by the R.A.E.: the Bristol Siddeley proposal at M10.5, Black Arrow at M2.9. I'm not sure how legitimate the costings were, but it wasn't as easy as Space Department thought it would be to go from Black Knight to Black Arrow.

The vehicle was nearer Thor Delta size than Scout, which were the comparisons Space Dept. made. It was intended to put 650lbs into LEO; the Prospero satellite by comparison was around 145lbs. It was also acknowledged at the time that Black Arrow took the development of the Gamma engines as far as they could go; the Bristol Siddeley design was capable of being stretched further. It was also realised later in the 60s that the satellites Space Dept. wanted to launch were too large for Black Arrow as it stood - although strap on boosters could have increased its capacity somewhat. [The original Thor Delta could put a nominal 500lbs in LEO in 1961; this was soon increased by use of solid fuel strap ons. By 1963 Scout was capable of orbiting 240lbs.]

However, Space Dept. were also realistic about the budget they would have: Black Arrow might just be affordable, but the Bristol Siddeley design was not, despite its obvious advantages.

The first stage of the Bristol Siddeley design used the PR27 motor - 4 large Stentor chambers - with a thrust of 90,000lbs; a second stage with the Gamma 303 [improved 301] rated at 25,000lbs thrust, and a third stage powered by the PR38 engine at 2-3000lbs. All stages burned HTP and kerosene.

The 4 chambered PR27 motor with 4 Stentor chambers:

and the small PR38 for the third stage:

Ironically, at around the time of the Black Arrow cancellation in 1971, Bruce White of the British Hovercraft Development Co. [ex Saunders Roe] proposed an upgrade to Black Arrow, called SLAVE [which, rather mundanely, stood for Satellite LAunch VEhicle], with the first stage still the two metre diameter of Black Arrow but considerably extended, and with 4 Stentor chambers. The upper stages would be unchanged. This is a retouched version of his design:

Given the decision to cancel Black Arrow, it is easy to see why this got no further.

However, the large Stentor chamber would have made an excellent start for a British satellite launcher, particularly since the Blue Steel missile was now being withdrawn from service!

14th July 1999 revised 15th August 2002

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