Delta Differential One-way Ranging Research Articles

Double Asteroid Redirection Test (DART): Navigating to obliteration

DART is NASA’s demonstration of an asteroid deflection using a kinetic impactor. The spacecraft launched aboard a SpaceX Falcon 9 on November 24th 2021, on a direct collision with the binary asteroid system Didymos planned for September 26th 2022. By impacting the small moon, Dimorphos, DART’s objective was to alter the moon’s orbit about the larger asteroid by several minutes.The navigation of a ballistic mission is usually relatively simple. Other than heading to a violent demise, this mission had a number of unconventional aspects which gave the navigation team interesting challenges: a tight propellant budget for part of the mission, no reaction wheels which resulted in a noisy spacecraft with the Nav team having to rely heavily on Delta Differential One-way Ranging measurements to identify off line-of-sight Delta-V, and critical operations in the last 30 days of the mission under a new thrusting control mode regime. Optical navigation was a critical element in the success of this mission, contributing to the determination of the spacecraft and target ephemerides for refined targeting maneuvers. After strategic decisions in the final weeks of the missions, DART could have comfortably hit the larger asteroid, Didymos, which increased the probably of impact with its moon Dimorphos.

Analysis and Demonstration of First Cross-Support Interferometry Tracking in China Mars Mission

Delta-Differential One-Way Ranging (DeltaDOR) is widely used in deep spacecraft navigation, and cross support could enhance navigation accuracy with more interferometry baselines and longer baseline. In China Mars mission Tianwen-1, formal joint cross-support interferometry tracking between China Satellite Launch and TT&C General (CLTC) and European Space Operations Center (ESOC) under commercial contract was conducted around the critical stages of the mission, such as Mars orbit insertion. Cross-support interferometry is a new challenge to CLTC, as the correlator for routine DeltaDOR measurements do not fit for cross support, because of observable definition, blind station clock searching, and so on. This paper discusses the new method and algorithm adopted in joint cross support, especially for spacecraft tone signal processing and clock estimation when correlating with the data of two stations from different agencies. Results of the cross-support interferometry tracking activities are also analyzed. Observables from CLTC and ESOC are consistent with each other, and the difference in observables is in the order of tens of ps. All the baselines are induced to evaluate the accuracy of the spacecraft orbit determined and predicted by CLTC, and the DeltaDOR residuals have a root-mean-square (RMS) better than 0.5 ns (the goal is 1 ns), which could enhance the confidence of the orbit accuracy and the effectiveness of control parameters during critical orbit operation.

Improved Signals for Differential One-Way Range

This article describes the current limiting error source for Delta Differential One-way Range (ΔDOR), provides a means to reduce this error, and lists the benefits to deep space navigation. Particular advantages for Small Satellite class missions are addressed. The key idea is spreading the spacecraft DOR signal with a pseudonoise (PN) code to make the spacecraft signal spectrum closely resemble the spectrum of natural radio sources used for instrument calibration. How spectral differences affect the measurement are discussed. This article describes the general formulation for PN DOR signal design, and the specific X-band implementation of PN DOR on a software defined radio at JPL. Finally, a prototype implementation at Ka-band, providing even better performance, is presented.

Hardware Prototyping and Validation of a W-ΔDOR Digital Signal Processor

Microwave tracking, usually performed by on ground processing of the signals coming from a spacecraft, represents a crucial aspect in every deep-space mission. Various noise sources, including receiver noise, affect these signals, limiting the accuracy of the radiometric measurements obtained from the radio link. There are several methods used for spacecraft tracking, including the Delta-Differential One-Way Ranging ( Δ DOR) technique. In the past years, European Space Agency (ESA) missions relied on a narrowband Δ DOR system for navigation in the cruise phase. To limit the adverse effect of nonlinearities in the receiving chain, an innovative wideband approach to Δ DOR measurements has recently been proposed. This work presents the hardware implementation of a new version of the ESA X/Ka Deep Space Transponder based on the new tracking technique named Wideband Δ DOR (W- Δ DOR). The architecture of the new transponder guarantees backward compatibility with narrowband Δ DOR.

Tropospheric and ionospheric media calibrations based on global navigation satellite system observation data

Context: Calibration of radiometric tracking data for effects in the Earth atmosphere is a crucial element in the field of deep-space orbit determination (OD). The troposphere can induce propagation delays in the order of several meters, the ionosphere up to the meter level for X-band signals and up to tens of meters, in extreme cases, for L-band ones. The use of media calibrations based on Global Navigation Satellite Systems (GNSS) measurement data can improve the accuracy of the radiometric observations modelling and, as a consequence, the quality of orbit determination solutions. Aims: ESOC Flight Dynamics employs ranging, Doppler and delta-DOR (Delta-Differential One-Way Ranging) data for the orbit determination of interplanetary spacecraft. Currently, the media calibrations for troposphere and ionosphere are either computed based on empirical models or, under mission specific agreements, provided by external parties such as the Jet Propulsion Laboratory (JPL) in Pasadena, California. In order to become independent from external models and sources, decision fell to establish a new in-house internal service to create these media calibrations based on GNSS measurements recorded at the ESA tracking sites and processed in-house by the ESOC Navigation Support Office with comparable accuracy and quality. Methods: For its concept, the new service was designed to be as much as possible depending on own data and resources and as less as possible depending on external models and data. Dedicated robust and simple algorithms, well suited for operational use, were worked out for that task. This paper describes the approach built up to realize this new in-house internal media calibration service. Results: Test results collected during three months of running the new media calibrations in quasi-operational mode indicate that GNSS-based tropospheric corrections can remove systematic signatures from the Doppler observations and biases from the range ones. For the ionosphere, a direct way of verification was not possible due to non-availability of independent third party data for comparison. Nevertheless, the tests for ionospheric corrections showed also slight improvements in the tracking data modelling, but not to an extent as seen for the tropospheric corrections. Conclusions: The validation results confirmed that the new approach meets the requirements upon accuracy and operational use for the tropospheric part, while some improvement is still ongoing for the ionospheric one. Based on these test results, green light was given to put the new in-house service for media calibrations into full operational mode in April 2017.

Local correlation and orbit determination for DOR signals in Chang’E-3

The X-band Delta-Differential One-way Range is first formally used in Chang’E-3 spacecraft, and will be continually used for other Chinese future deep space navigation. We have carried out researches on each DOR tone using local correlation method which is quite different from the conventional VLBI correlator. The CE-3 signal interferometry processing is completed with this method. High precision Delta-DOR group delay and radio source correction are obtained for orbit determination. The phase noise of local correlation is significantly smaller than that of the VLBI conventional correlator. The ephemeris from local correlation is about 20 m different from the precise ephemeris of CE-3 project, and the corresponding equivalent residual delay is about 0.4 ns. Experiment result shows that local correlation is more suitable for weak signal processing, and it can be used for the future Chinese lunar and other deep space exploration projects.

Astra: Interdisciplinary study on enhancement of the end-to-end accuracy for spacecraft tracking techniques

Navigation of deep-space probes is accomplished through a variety of different radio observables, namely Doppler, ranging and Delta-Differential One-Way Ranging (Delta-DOR). The particular mix of observations used for navigation mainly depends on the available on-board radio system, the mission phase and orbit determination requirements. The accuracy of current ESA and NASA tracking systems is at level of 0.1mm/s at 60s integration time for Doppler, 1–5m for ranging and 6–15nrad for Delta-DOR measurements in a wide range of operational conditions. The ASTRA study, funded under ESA's General Studies Programme (GSP), addresses the ways to improve the end-to-end accuracy of Doppler, ranging and Delta-DOR systems by roughly a factor of 10. The target accuracies were set to 0.01mm/s at 60s integration time for Doppler, 20cm for ranging and 1nrad for Delta-DOR. The companies and universities that took part in the study were the University of Rome Sapienza, ALMASpace, BAE Systems and Thales Alenia Space Italy. The analysis of an extensive data set of radio-metric observables and dedicated tests of the ground station allowed consolidating the error budget for each measurement technique. The radio-metric data set comprises X/X, X/Ka and Ka/Ka range and Doppler observables from the Cassini and Rosetta missions. It includes also measurements from the Advanced Media Calibration System (AMCS) developed by JPL for the radio science experiments of the Cassini mission. The error budget for the three radio-metric observables was consolidated by comparing the statistical properties of the data set with the expected error models. The analysis confirmed the contribution from some error sources, but revealed also some discrepancies and ultimately led to improved error models. The error budget reassessment provides adequate information for building guidelines and strategies to effectively improve the navigation accuracies of future deep space missions. We report both on updated error budget for radio-metric observables and the system configurations proposed for the upgrade of ESA's tracking and orbit determination systems.

Orbit determination for Chang’E-2 lunar probe and evaluation of lunar gravity models

The Unified S-Band (USB) ranging/Doppler system and the Very Long Baseline Interferometry (VLBI) system as the ground tracking system jointly supported the lunar orbit capture of both Chang’E-2 (CE-2) and Chang’E-1 (CE-1) missions. The tracking system is also responsible for providing precise orbits for scientific data processing. New VLBI equipment and data processing strategies have been proposed based on CE-1 experiences and implemented for CE-2. In this work the role VLBI tracking data played was reassessed through precision orbit determination (POD) experiments for CE-2. Significant improvement in terms of both VLBI delay and delay rate data accuracy was achieved with the noise level of X-band band-width synthesis delay data reaching 0.2–0.3 ns. Short-arc orbit determination experiments showed that the combination of only 15 min’s range and VLBI data was able to improve the accuracy of 3 h’s orbit using range data only by a 1–1.5 order of magnitude, confirming a similar conclusion for CE-1. Moreover, because of the accuracy improvement, VLBI data was able to contribute to CE-2’s long-arc POD especially in the along-track and orbital normal directions. Orbital accuracy was assessed through the orbital overlapping analysis (2 h arc overlapping for 18 h POD arc). Compared with about 100 m position error of CE-1’s 200 km200 km lunar orbit, for CE-2’s 100 km100 km lunar orbit, the position errors were better than 31 and 6 m in the radial direction, and for CE-2’s 15 km100 km orbit, the position errors were better than 45 and 12 m in the radial direction. In addition, in trying to analyze the Delta Differential One-Way Ranging (DOR) experiments data we concluded that the accuracy of DOR delay was dramatically improved with the noise level better than 0.1 ns and systematic errors better calibrated, and the Short-arc POD tests with DOR data showed excellent results. Although unable to support the development of an independent lunar gravity model, the tracking data of CE-2 provided evaluations of different lunar gravity models through POD. It is found that for the 100 km100 km lunar orbit, with a degree and order expansion up to 165, JPL’s gravity model LP165P did not show noticeable improvement over Japan’s SGM series models (100×100), but for the 15 km×100 km lunar orbit, a higher degree-order model can significantly improve the orbit accuracy. Chang’E-2, VLBI, orbit determination, lunar gravity field

Applications of Delta Differential One-way Ranging (ΔDOR) to Lunar Exploration Program

相对差分单向测距(ΔDOR)是一种高精度测角技术, 在深空探测任务的高精度测定轨方案中得到广泛应用. 介绍了ΔDOR测量的基本原理及CCSDS (国际空间数据系统委员会)关于ΔDOR测量的相关标准. 针对中国探月工程月面软着陆任务提出的高精度测定轨要求, 分析了ΔDOR测量的信号形式、工作模式以及测量精度, 推导了解模糊过程. 研究表明,ΔDOR测角精度达到25nrad, 对应到月球上的距离约为10m.

Interplanetary navigation along the low-thrust trajectory of BepiColombo

For BepiColombo's five-year journey into the inner solar system, a combination of low-thrust arcs and six flybys (one at Moon and Earth, two at Venus and two at Mercury) will be used to reach Mercury with low relative velocity. At arrival a gravitational capture approach is foreseen, in which the Sun perturbation is exploited to get weakly captured around Mercury for a number of orbits. This trajectory imposes severe constraints from a navigational point of view. Very precise navigation is required due to the low flyby altitudes planned for Venus (300 km) and Mercury (200 km) and the level of accuracy needed for the final arrival through the vicinity of the Sun–Mercury L1 point. Besides that, the solar plasma effect severely degrades the quality of the radiometric measurements near superior solar conjunctions, which are more frequent for missions to the inner solar system. Moreover, perturbations, as the ones introduced by momentum wheel desaturation burns, entry into safe modes or solar radiation pressure, must also be taken into account. Delta-differential one-way range measurements are found to be required in periods of poor orbit determination prior to some gravity assists. Nevertheless, if a safe mode is triggered at a critical moment that produces a change in velocity in an unfavourable direction, the mission could be jeopardised. To avoid that risk, an increase in the flyby altitude and possibly a partial or total redesign of the trajectory to avoid flybys near solar conjunctions are considered.

2001 Mars Odyssey Orbit Determination During Interplanetary Cruise

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Using delta differential one-way range to determine highly elliptical earth orbits

Acquisition strategies for delta differential one-way range measurements are designed for determining highly elliptical Earth orbits. The mission orbit for the U.S. Charged Composition Explorer spacecraft of the international Active Magnetospheric Particle Tracer Explorers serves to illustrate these acquisition techniques. The study assumes intercontinental baselines formed by Deep Space Network antennas at Goldstone, Canberra, and Madrid. The best performing strategy employs data spanning baseline view periods covering both inbound and outbound legs near the same orbit periapse. Rapidly changing viewing geometry yields both angular position and velocity information but frequently imposes the need for a different reference quasar for each observation. Although limited by an S-band transponder and a small bandwidth, the addition of delta differential one-way range to coherent Doppler and range improves apogee position accuracy by more than an order of magnitude. The measurement noise, highly dependent on acquisition geometry, varies several orders of magnitude across the baseline view periods primarily due to parallax. Careful selection of observation times minimizes the geometric influence on data noise. Additional measurement accuracy improvements, possible with dual frequency calibration, increased spanned bandwidth, and water vapor radiometry, are presented for comparison. Quasar position uncertainties then dominate the measurement noise.