The most metal of rockets has gone into the great mosh pit in the sky

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  United Launch Alliance's Delta IV Heavy rocket lifted off for the final time on Tuesday. [credit: United Launch Alliance ]

I've got a guilty secret that I can now share—I loved the Delta IV Heavy rocket.

No, I didn't love the price, which was preposterous, at times approaching $400 million. This precluded Delta from having any other customers than the US government. I didn't love the low flight rate, just 16 missions in 20 years. This prevented the rocket's operator, United Launch Alliance, from ever approaching anything remotely like efficient operations.

But there were two things I adored about the Delta IV Heavy rocket, which made its final launch on Tuesday. I loved watching it take flight. And I love that, warts and all, it demonstrated that private companies could develop a heavy lift rocket. The Delta booster, although the product of decades of traditional space development, offered a glimpse of the commercial launch future that we're living in today.