Blackstar: the US space conspiracy that never was?
Two-stage ultrasecret vehicle wows the crowds
The X-33 (pictured right) was another expensive US project which ended on the scrapheap. The single-stage-to-orbit concept cost the taxpayer an estimated $912m up to its 2001 cancellation.
Among the X-33's innovative technologies was its linear aerospike engine, also apparently deployed on the Blackstar orbiter.
Aerospike programme manager for Boeing Rocketdyne, Mike McKeon, explained to Space.com that the main difference between an aerospike engine and conventional jet plant was the nozzle shape: "In the bell shape, gas expands at the end of the nozzle. A bell nozzle is most efficient at one altitude."
An aerospike engine, on the other hand, is shaped like a "V" and uses a "series of small combustion chambers shoots [the hot gases] down the ramp on the outside using the atmosphere on the other side to act as the engine bell".
Building engine nozzles is a study in tradeoffs – an engine must operate at a wide range of altitudes, but can operate at peak efficiency in only a narrow range. At higher altitudes, gasses could expand farther and produce better performance if a bell-shaped nozzle was longer, but conventional nozzles can't grow longer, thus the compromise in performance.
The aerospike's plume is open to the atmosphere on one side, allowing it to expand, while it pushes against the ramp allowing it to operate efficiently at different altitudes.
Aerospike engines also allow "vectored thrust" without the need for moving mechanical nozzles, as they can simply adjust thrust from multiple combustion chambers to provoke the required change in direction.
The fuel for the aerospike, AWST claims, is "believed to be a boron-based gel having the consistency of toothpaste and high-energy characteristics, but occupying less volume than other fuels".
This is not an unusual concept - the US developed an ethyl borane fuel for the Valkyrie project - a so-called "zip fuel" - since "the common jet fuels of the time were recognised as being too heavy for the power they yield to push an aircraft beyond Mach 2 without constant use of afterburners".
The idea is pretty simple: boron-doped fuels produce more bangs for your bucks for less weight. Unfortunately, they're also highly toxic and leave "a heavy deposit on anything in its path, with turbine blades being particularly vulnerable".
That's the technology, but who built the Blackstar? AWST says: "One Pentagon official suggests that the Blackstar system was 'owned' and operated by a team of aerospace contractors, ensuring government leaders' plausible deniability. When asked about the system, they could honestly say, 'we don't have anything like that'."
One contractor named is Boeing, which "on 14 Oct, 1986... filed a US patent application for an advanced two-stage space transportation system", as well as "patent Number 4,802,639, awarded on 7 Feb, 1989, [which] details how a small orbiter could be air-dropped from the belly of a large delta-winged carrier at Mach 3.3 and 103,800 foot altitude".
AWST concludes: "Although drawings of aircraft platforms in the Boeing patent differ from those of the Blackstar vehicles spotted at several USAF bases, the concepts are strikingly similar."
McDonnell Douglas is also fingered. AWST claims technicians at a company plant in St Louis in the late 1980s and early 1990s "said much of the XOV's structure was made of advanced composite materials". They were, one unnamed techie says, "incredibly strong, and would handle very high temperatures".
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