Here's a 6 minute video explaining the sprint missile for those unaware and interested (rather fascinating technology for the 70s) https://www.youtube.com/watch?v=3dl9Ovwmnxw
For those that need a little teaser to be incentivized to click on the YouTube link, here's the title of the video 'Super Pointy Sprint Missile - 0 to Mach 10 in 15 Seconds - 100Gs & 6000°F'
If you have any interest in aerospace at all and have never heard of the Sprint, take a gander, it's a spectacular edge case in engineering.
After that has a good mixture of technical and political limitations.