An advanced synthesized ultra-stable oscillator for spacecraft applications

Wallis, R.E.; Weaver, Gregory; Reinhart, M.J.; Cheng, Sheng

doi:10.1109/aero.2005.1559386

Cited by 7 publications

(5 citation statements)

References 3 publications

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“…Ten years later, NASA launched the GRACE satellites. These satellites are both equipped with GPS receivers and free-running ultra-stable oscillators (USOs) (Wallis et al 2005). The receivers operate on both frequencies in the presence of anti-spoofing.…”

Section: Grace Data Analysismentioning

confidence: 99%

“…The GRACE USOs have a small frequency/voltage sensitivity, typically less than 1 part in 10 12 fractional frequency change per volt (Wallis et al 2005). Unlike the much smaller temperature variations within the spacecraft, there are large once/rev variations in the battery voltages for the GRACE satellites, with a peak-to-peak difference of 5 V (figure 8).…”

Section: Noise Sources and The Grace Clock Estimatesmentioning

confidence: 99%

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An assessment of relativistic effects for low Earth orbiters: the GRACE satellites

Larson¹,

Ashby²,

Hackman³

et al. 2007

Metrologia

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The GRACE mission consists of two identical satellites orbiting the Earth at an altitude of ∼500 km. Dual-frequency carrier-phase Global Positioning System (GPS) receivers are flying on both satellites. They are used for precise orbit determination and to time-tag the K-band ranging system used to measure changes in the distances between the two satellites. The satellites are also flying ultra-stable oscillators (USOs) to achieve the mission's need for short-term (<1 s) oscillator stability. Because of the high quality of both the GPS receivers and the oscillators, relativistic effects in the GRACE GPS data can be examined. An expression is developed for relativistic effects that explicitly includes the effects of the Earth's oblateness (J 2 ). Use of this expression significantly reduces the twice per orbital period energy in the GRACE clock solutions, indicating that the effect of J 2 can be significant and should be modeled for satellite clocks in low Earth orbit. After relativistic effects have been removed, both GRACE USOs show large (2 ns to 3 ns) once per orbital period signatures that correlate with voltage variations on the spacecraft.

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Section: Grace Data Analysismentioning

confidence: 99%

Section: Noise Sources and The Grace Clock Estimatesmentioning

confidence: 99%

An assessment of relativistic effects for low Earth orbiters: the GRACE satellites

Larson¹,

Ashby²,

Hackman³

et al. 2007

Metrologia

View full text Add to dashboard Cite

show abstract

“…In the paper, presented at the 2005 IEEE Aerospace conference, we discussed our developments for reducing the USO mass to < 0.6 kg and steady state power in vacuum to -0.8 W for its primary operating circuits using Direct Digital Synthesis (DDS) to output 35 channels correlated to the NASA Deep Space Network (DSN) while maintaining all superior USO frequency attributes [5]. Our work with DDS promoted consideration toward using the synthesizer for frequency drift correction in a disciplined oscillator scheme.…”

Section: On-going Work and Future Activitiesmentioning

confidence: 99%

“…These events last in the order of ten to one thousand seconds dependent on the planet's size. 5 Since the phase shift measurement and the noise due to frequency stability are indistinguishable at the receiver, the error in the recovered information is directly related to the source's flicker floor. Also, the span of the flicker floor in time determines the transit period over which valid data can be collected.…”

Section: Disciplining Techniquementioning

confidence: 99%

Developments Toward a Disciplined Timekeeping System for Lunar and Planetary Navigation

Weaver

Kantsiper

2007

2007 IEEE Aerospace Conference

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The future of both lunar and planetary missions will involve the use of an increasing number of orbiters, landers and robotic rovers with ever expanding objectives over greater land area range. The coordination of these individual assets into a system capable of supporting complex exploration activities will necessarily require a local timekeeping system able to directly assist navigation, event synchronization and trunk communication back to Earth.The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has derived a method for disciplining quartz Ultra-stable Oscillators (USO) to extend its superior frequency stability from 10 seconds to nearly 30 days of operating time. This is accomplished through a Kalman estimator that optimally removes the drift of the free running USO. The accuracy of the estimator is improved by periodically comparing the frequency of the USO to an atomic reference, typically located on the Earth, and transferring its accuracy to the timekeeping system via periodic uplink sessions. This is a method most frequently known as 'disciplining an oscillator'. JHU/APL will report on the accuracy of a disciplined USO that maintains better than ±1.5 pt seconds over 30 days and describe our roadmap toward a robust, timekeeping system capable of providing both short-term and long-term frequency stability for lunar and planetary navigation infrastructure and timekeeping.

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“…Accurate position and time estimates are important for a variety of smallsat missions. Examples of missions, which require high performance timekeeping, are deep space missions using one‐way ranging (Imken et al., 2017; Wallis et al., 2005; Weaver & Kantsiper, 2007), small satellite constellations functioning as sensor arrays for astronomy (Engelen et al., 2013; Rajan et al., 2015), low Earth orbit (LEO) constellations for Global Positioning System (GPS) augmentation and improved positioning (Ge et al., 2018; Reid et al., 2018), and Earth observation missions which require accurate position and time information for imagery and science data.…”

Section: Introductionmentioning

confidence: 99%

A low complexity smoothing algorithm for improved GPS point solutions on board LEO spacecraft

2021

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This paper describes a novel approach for reducing the kinematic position and time errors on a GPS receiver in low Earth orbit. For dual‐frequency GPS receivers, point solution errors are dominated by signal‐in‐space ranging errors, which introduce sharp discontinuities in the position and time estimates when GPS visibility changes. These discontinuities may be calculated and removed, greatly reducing the peaks of the errors, at the expense of introducing a slowly varying bias, which is estimated and removed. The paper gives a detailed description of the algorithm and illustrates its use on a GPS receiver using historical ephemerides. To demonstrate real‐world efficacy, GRACE‐FO observations are processed using the proposed approach. Real‐time results show the reduction of the time error standard deviation by 16% to 1.9ns and the reduction of the 3D RMS error by 17% to 1.06m. Maximum real‐time errors are reduced 26% and 32%, respectively. Delayed processing offers greater reductions of errors, near 40%.

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An advanced synthesized ultra-stable oscillator for spacecraft applications

Cited by 7 publications

References 3 publications

An assessment of relativistic effects for low Earth orbiters: the GRACE satellites

An assessment of relativistic effects for low Earth orbiters: the GRACE satellites

Developments Toward a Disciplined Timekeeping System for Lunar and Planetary Navigation

A low complexity smoothing algorithm for improved GPS point solutions on board LEO spacecraft

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