This week the US launched its last DSP satellite: DSP 23.
How well have the DSPs performed? From the article linked in the Topic of this post:
The launch of DSP 23 extends the service of a satellite constellation that has been the nation's eyes in the sky for nearly four decades, providing warnings of tactical and strategic missile launches, nuclear detonations, and other technical intelligence. DSP satellites have operated four times beyond their specified design lives on average, and Flight 23 is expected to serve well into the next decade....
DSP satellites set a high standard for performance. The satellite's longevity has provided an extra 162 satellite-years on-orbit to date, the equivalent of delivering 30 to 50 additional satellites (without the cost of the launch).
While the performance of the first ones launched, beginning in 1970, was a national secret, and very little was known about how the progam matured throughout its development, we will no doubt continue to endure a steady stream of hand-wringing and whining over the DSP follow-on: the Space-Based Infrared System (SBIRS).
As the old saying goes: "Too many people know the price of everything but the value of nothing". Think of DSPs and SBIRS as preventing national blindness.