Atomic frequency standards being any of the following: 1. ‘Space-qualified’; 2. Non-rubidium and having a long-term stability less (better) than 1 × 10 – 11 /month; or 3. Non-‘space-qualified’ and having all of the following: a. Being a rubidium standard; b. Long-term stability less (better) than 1 × 10 – 11 /month; and c. Total power consumption of less than 1 Watt.