Advanced space rubidium atomic frequency standard for satellite navigation

A Comprehensive Overview of Atomic Clocks and their Applications

“…It is worth noting the recent developments of ion-based compact high-performance clocks, and the developments of the rubidium pulsed clocks, and cold atom clocks for space-based navigation and scientific missions. 24,[42][43][44][45][46] The next section covers further details of the space based atomic clocks and overview of various navigation systems that contribute to Global Navigation Satellite Systems (GNSS).…”

“…Presently, the best onboard clocks onboard a navigation satellite system are passive hydrogen masers 49 that are in-orbit in ESA's Galileo navigation system. The passive H-masers are however bulky in comparison to rubidium standards: 24,45 having a volume of 28 dm 3 (3 dm 3 for Rb), mass of 18 kg (4 kg for Rb) with a power consumption of 80 W (18 W for Rb). On the other hand, the laboratory clocks like primary Cesium (Cs) fountains and optical clocks exhibit excellent stability of σ Y (t) ~1x10 -13 τ -1/2 , but are bulkier occupying a room space and expensive.…”

“…These atomic clocks give a precise frequency and therefore timing output which helps to locate the precise position for navigating. 13,[42][43][44][45] Usefulness of atomic clocks is not only limited to earth, but beyond the earth's orbit for deep space tracking and navigation. 46,51,52 The lamp pumped Rb clocks are used in almost all Global Navigation Satellite Systems (GNSS).…”

“…The atomic signal typically has a Lorentzian line shape and the stabilisation of the quartz oscillator to the center of this reference signal, realises the clock. 13,15,35,45,57 The theoretical basics and further details of Double-Resonance (DR) spectroscopy and clock are explained in the references. 13,15,35,36,57 Figure 6 shows 87 Rb and 85 Rb energy level schemes representing the Rb discharge lamp, filter cell and resonance cell, respectively.…”

“…Typical DR atomic signal of a Rb clock has a Lorentzian shaped curve 24,35 with a narrow linewidth of 1kHz or lower, and a signal contrast of up to 30%-if it is a laser pumped clock 36,57 or typically a contrast of up to 2.5% for a lamp pumped clock. 13,45 At the heart of a conventional rubidium atomic frequency standard, atomic rubidium in vapor phase and buffer gases are contained in a glass enclosure, called vapor cells. Buffer gases help to prevent the polarized Rb atoms from colliding on to the cell walls and reduce the mean free path of a Rb atom to less than the microwave photon's wavelength of few centimeters, thereby giving rise to narrow resonance lines, this is known as Dicke narrowing.…”