Na 1990s, Air Force Research Laboratory (AFRL) bidoro HyTECH mmemme maka hypersonic propulsion. Pratt & Whitney natara nkwekọrịta site na AFRL iji mepụta engine scramjet nke na-ebute mmepe nke SJX61 engine. SJX61 engine bụ nke mbụ maka NASA X-43C, nke a kagburu. E jiri engine ahụ mee ihe na AFRL's Scramjet Engine Demonstrator program na ngwụsị afọ 2003. A na-ahọpụta ụgbọ elu nnwale ụgbọ elu scramjet X-51 na 27 Septemba 2005. Ajụjụ: Gịnị bụ ọdịnihu nke NASA X-43C?
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