Historical research guide · 0333 · 2010
DIRD Materials for Advanced Aerospace Platforms
DIA / AAWSAP contractor
In one minute
The Defense Intelligence Agency commissioned this survey for its Advanced Aerospace Weapon System Applications programme and issued it on 12 January 2010. Its subject is the unglamorous half of advanced flight: what an aerospace platform is actually made of. The author works through launch vehicles, reusable crew modules and rocket engines in turn, and the argument stays the same throughout. Design and materials have to be chosen together — the National Aerospace Plane was launched as a Mach 12 reusable strike vehicle, became materials limited, and was cancelled in 1993 after about $750 million of federal research money, because the mission requirements were fixed before anyone asked what could be built. Friction stir welding now joins the high-strength aluminium alloys that fusion welding ruins, and the shuttle’s external tank is made that way. Titanium threaded with silicon carbide fibre more than doubles the strength of the matrix at no weight penalty. And a reusable single-stage-to-orbit craft needs a metallic heat shield that also carries load — a materials problem still open.
Connection
Chapter 1 reads the thirty-eight AAWSAP reference documents as one government stocktake of what an advanced aerospace vehicle would need, and this is the volume about the airframe itself. It is also chapter 13’s bottleneck stated by a government reviewer with no exotic physics anywhere in view: what gets built and what does not is decided by which materials exist.
From the source
Any clean-sheet design must start from an honest assessment of what the construction materials can do, because the alternative has already been paid for: the National Aerospace Plane was launched as a Mach 12 reusable strike vehicle, rapidly became materials limited, and was cancelled in 1993 after about $750 million in federal research spending plus a substantial private investment.Introduction, p. iv
Friction stir welding joins the high-strength aluminium alloys — 7075, 7050, 2024, 2050 — that conventional fusion welding either cracks or leaves badly weakened, by driving a rotating tool through the seam so friction softens the metal without melting it; the space shuttle’s external propellant tank is an aluminium-lithium alloy made this way, and welded rather than bolted joints are a considerable weight saving on a structure that size.Launch Vehicles, pp. 2-3; Figure 1
A reusable single-stage-to-orbit vehicle will need metallic materials for the thermal protection system and for much of the rest of the hot structure, and the weight only closes if the heat shield and the load-bearing structure are designed as one thing rather than stacked; the report sorts ten candidate material classes by operating temperature and by the property that limits the design.Reusable Single-Stage-to-Orbit Vehicles, Table 1, p. 10
Titanium reinforced with long silicon carbide monofilaments more than doubles the strength and stiffness of the matrix alloy with no increase in density — 276 ksi (1,902 megapascals) ultimate tensile strength and 226 gigapascals Young’s modulus at 4.43 grams per cubic centimetre — yet work stopped after about $500 million of United States government investment, because a single supplier held the fibre and chose not to sell it.Ti Matrix Composites, Table 2, p. 14; pp. 15-16
Ceramic matrix composites are the class that holds the greatest promise of defeating the temperature limits of current metals — silicon carbide fibre in a silicon carbide matrix reaches as much as ten times the toughness of the unreinforced ceramic and serves to about 1,400 °Celsius — but once the matrix microcracks the environment reaches the fibre-matrix interface, and there is at present no way to estimate the reduced toughness as a function of service life.Ceramic Matrix Composites, pp. 18-19
The industry’s zero-tolerance rule for the oxygen-hardened alpha case that forms on hot titanium sheet has never actually been tested: essentially no effort has been made to find out whether it can be tolerated at a modestly reduced stress, the SR-71 flew above 300 °Celsius for 34 years with no known alpha-case issue, and the Air Force Materials and Manufacturing Directorate is starting a project to answer the six questions the report sets out.Ti Alloys, pp. 12-14
The way in
https://documents2.theblackvault.com/documents/dia/AAWSAP-DIRDs/DIRD_05_Materials_for_Advanced_Aerospace_Platforms.pdfHow to cite it
DIA / AAWSAP contractor (2010) DIRD Materials for Advanced Aerospace Platforms https://documents2.theblackvault.com/documents/dia/AAWSAP-DIRDs/DIRD_05_Materials_for_Advanced_Aerospace_Platforms.pdf