Originally, since it started in 1963, long before GPS: https://en.wikipedia.org/wiki/Vela_(satellite) https://en.wikipedia.org/wiki/Vela_(satellite) Bundling t

Originally, since it started in 1963, long before GPS: https://en.wikipedia.org/wiki/Vela_(satellite) https://en.wikipedia.org/wiki/Vela_(satellite) Bundling that mission into GPS satellites was an obvious way to save costs and very possibley get better results.