scholarly journals Impact of Attitude Model, Phase Wind-Up and Phase Center Variation on Precise Orbit and Clock Offset Determination of GRACE-FO and CentiSpace-1

2021 ◽  
Vol 13 (13) ◽  
pp. 2636
Author(s):  
Junjun Yuan ◽  
Shanshi Zhou ◽  
Xiaogong Hu ◽  
Long Yang ◽  
Jianfeng Cao ◽  
...  
Keyword(s):  
Data Quality ◽  
Three Dimensional ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Dual Frequency ◽  
Phase Center ◽  
Phase Center Variation ◽  
The Impact ◽  
Clock Offset ◽  
Attitude Model

Currently, low Earth orbit (LEO) satellites are attracting great attention in the navigation enhancement field because of their stronger navigation signal and faster elevation variation than medium Earth orbit (MEO) satellites. To meet the need for real-time and precise positioning, navigation and timing (PNT) services, the first and most difficult task is correcting errors in the process of precise LEO orbit and clock offset determination as much as possible. Launched in 29 September 2018, the CentiSpace-1 (CS01) satellite is the first experimental satellite of LEO-based navigation enhancement system constellations developed by Beijing Future Navigation Technology Co. Ltd. To analyze the impact of the attitude model, carrier phase wind-up (PWU) and phase center variation (PCV) on precise LEO orbit and clock offset in an LEO-based navigation system that needs extremely high precision, we not only select the CS01 satellite as a testing spacecraft, but also the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). First, the dual-frequency global positioning system (GPS) data are collected and the data quality is assessed by analyzing the performance of tracking GPS satellites, multipath errors and signal to noise ratio (SNR) variation. The analysis results show that the data quality of GRACE-FO is slightly better than CS01. With residual analysis and overlapping comparison, a further orbit quality improvement is possible when we further correct the errors of the attitude model, PWU and PCV in this paper. The final three-dimensional (3D) root mean square (RMS) of the overlapping orbit for GRACE-FO and CS01 is 2.08 cm and 1.72 cm, respectively. Meanwhile, errors of the attitude model, PWU and PCV can be absorbed partly in the clock offset and these errors can generate one nonnegligible effect, which can reach 0.02~0.05 ns. The experiment results indicate that processing the errors of the attitude model, PWU and PCV carefully can improve the consistency of precise LEO orbit and clock offset and raise the performance of an LEO-based navigation enhancement system.

Altitude dependent empirical modeling of the topside ionosphere and plasmasphere using GPS- TEC from Swarm, GRACE-FO and the Sentinel satellites.

2020 ◽  
Author(s):  
Lucas Schreiter ◽  
Claudia Stolle ◽  
Daniel Arnold ◽  
Adrian Jäggi
Keyword(s):  
Three Dimensional ◽  
Empirical Modeling ◽  
Topside Ionosphere ◽  
Electron Content ◽  
Dual Frequency ◽  
Three Dimensional Model ◽  
Total Electron ◽  
Leo Satellites ◽  
Phase Center Variation ◽  
The Impact

<p>Slant Total Electron Content (sTEC) measurements can be obtained by dual-frequency GPS<br>onboard Low Earth Orbiting (LEO) satellites. Within the last few years, a fleet of LEO Satellites at<br>altitudes ranging from 450 km (Swarm A/C) to 815 km (Sentinel 3) became operational. With<br>Swarm B, the recently launched GRACE-FO, and the Sentinel 1 and 2 satellites orbiting at<br>intermediate altitudes, we gain insight into the altitude dependent profile of the topside ionosphere<br>and plasmasphere.<br>We make use of this constellation to estimate a global three dimensional model of the electron<br>density distribution and will also carefully asses the impact of different profile functions, geometry-<br>free phase center variation maps and the P1-P2 receiver biases. Since the absolute value of the P1-<br>P2 biases are generally unknown, we focus on a consistent estimation for the whole LEO<br>constellation.<br>We will present first results for selected months in 2019 and investigate the day to day variability of<br>the topside ionosphere and plasmasphere. We also intend to make use of COSMIC-2 data to<br>improve local time coverage in equatorial regions.</p>

A three-dimensional wake model for low earth orbit

1983 ◽  
Author(s):  
I. KATZ ◽  
D. COOKE ◽  
D. PARKS ◽  
M. MANDELL ◽  
A. RUBIN
Keyword(s):  
Three Dimensional ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Wake Model

scholarly journals Atmospheric drag effects on modelled low Earth orbit (LEO) satellites during the July 2000 Bastille Day event in contrast to an interval of geomagnetically quiet conditions

2021 ◽  
Vol 39 (3) ◽  
pp. 397-412
Author(s):  
Victor U. J. Nwankwo ◽  
William Denig ◽  
Sandip K. Chakrabarti ◽  
Muyiwa P. Ajakaiye ◽  
Johnson Fatokun ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Satellite Orbits ◽  
Percentage Increase ◽  
Atmospheric Drag ◽  
Drag Effect ◽  
Satellite Drag ◽  
Ballistic Coefficient ◽  
The Impact

Abstract. In this work, we simulated the atmospheric drag effect on two model SmallSats (small satellites) in low Earth orbit (LEO) with different ballistic coefficients during 1-month intervals of solar–geomagnetic quiet and perturbed conditions. The goal of this effort was to quantify how solar–geomagnetic activity influences atmospheric drag and perturbs satellite orbits, with particular emphasis on the Bastille Day event. Atmospheric drag compromises satellite operations due to increased ephemeris errors, attitude positional uncertainties and premature satellite re-entry. During a 1-month interval of generally quiescent solar–geomagnetic activity (July 2006), the decay in altitude (h) was a modest 0.53 km (0.66 km) for the satellite with the smaller (larger) ballistic coefficient of 2.2×10-3 m2 kg−1 (3.03×10-3 m2 kg−1). The associated orbital decay rates (ODRs) during this quiet interval ranged from 13 to 23 m per day (from 16 to 29 m per day). For the disturbed interval of July 2000 the significantly increased altitude loss and range of ODRs were 2.77 km (3.09 km) and 65 to 120 m per day (78 to 142 m per day), respectively. Within the two periods, more detailed analyses over 12 d intervals of extremely quiet and disturbed conditions revealed respective orbital decays of 0.16 km (0.20 km) and 1.14 km (1.27 km) for the satellite with the smaller (larger) ballistic coefficient. In essence, the model results show that there was a 6- to 7-fold increase in the deleterious impacts of satellite drag between the quiet and disturbed periods. We also estimated the enhanced atmospheric drag effect on the satellites' parameters caused by the July 2000 Bastille Day event (in contrast to the interval of geomagnetically quiet conditions). The additional percentage increase, due to the Bastille Day event, to the monthly mean values of h and ODR are 34.69 % and 50.13 % for Sat-A and 36.45 % and 68.95 % for Sat-B. These simulations confirmed (i) the dependence of atmospheric drag force on a satellite's ballistic coefficient, and (ii) that increased solar–geomagnetic activity substantially raises the degrading effect of satellite drag. In addition, the results indicate that the impact of short-duration geomagnetic transients (such as the Bastille Day storm) can have a further deleterious effect on normal satellite operations. Thus, this work increases the visibility and contributes to the scientific knowledge surrounding the Bastille Day event and also motivates the introduction of new indices used to describe and estimate the atmospheric drag effect when comparing regimes of varying solar–geomagnetic activity. We suggest that a model of satellite drag, when combined with a high-fidelity atmospheric specification as was done here, can lead to improved satellite ephemeris estimates.

Gynecologic Risk Mitigation Considerations for Long-Duration Spaceflight

2020 ◽  
Vol 91 (7) ◽  
pp. 543-564
Author(s):  
Jon G. Steller ◽  
Rebecca S. Blue ◽  
Roshan Burns ◽  
Tina M. Bayuse ◽  
Erik L. Antonsen ◽  
...  
Keyword(s):  
Risk Mitigation ◽  
Low Earth Orbit ◽  
Space Environment ◽  
Earth Orbit ◽  
Mineral Density ◽  
Management Options ◽  
Health Maintenance ◽  
Medical Risk ◽  
Long Duration ◽  
The Impact

INTRODUCTION: As NASA and its international partners, as well as the commercial spaceflight industry, prepare for missions of increasing duration and venturing outside of low-Earth orbit, mitigation of medical risk is of high priority. Gynecologic considerations constitute one facet of medical risk for female astronauts. This manuscript will review the preflight, in-flight, and postflight clinical evaluation, management, and prevention considerations for reducing gynecologic and reproductive risks in female astronauts.METHODS: Relevant gynecological articles from databases including Ovid, Medline, Web of Science, various medical libraries, and NASA archives were evaluated for this review. In particular, articles addressing preventive measures or management of conditions in resource-limited environments were evaluated for applicability to future long-duration exploration spaceflight.RESULTS: Topics including abnormal uterine bleeding, anemia, bone mineral density, ovarian cysts, venous thromboembolism, contraception, fertility, and health maintenance were reviewed. Prevention and treatment strategies are discussed with a focus on management options that consider limitations of onboard medical capabilities.DISCUSSION: Long-duration exploration spaceflight will introduce new challenges for maintenance of gynecological and reproductive health. The impact of the space environment outside of low-Earth orbit on gynecological concerns remains unknown, with factors such as increased particle radiation exposure adding complexity and potential risk. While the most effective means of minimizing the impact of gynecologic or reproductive pathology for female astronauts is screening and prevention, gynecological concerns can arise unpredictably as they do on Earth. Careful consideration of gynecological risks and potential adverse events during spaceflight is a critical component to risk analysis and preventive medicine for future exploration missions.Steller JG, Blue RS, Burns R, Bayuse TM, Antonsen EL, Jain V, Blackwell MM, Jennings RT. Gynecologic risk mitigation considerations for long-duration spaceflight. Aerosp Med Hum Perform. 2020; 91(7):543–564.

scholarly journals The Impact of Innovation in the Satellite Industry on the Telecommunications Services Market

2020 ◽  
Vol 73 ◽  
Author(s):  
Krasimir Terziev ◽  
Dimitar Karastoyanov
Keyword(s):  
Low Earth Orbit ◽  
Earth Orbit ◽  
Orbit Satellite ◽  
Leo Satellites ◽  
Different Types ◽  
Telecommunications Services ◽  
Global Communications ◽  
The Impact

The article analyses the role of the satellites in global communications. Different types of orbits and different types of satellites are described. The commercial start of low and medium orbit satellites is considered. The integration of some Low Earth Orbit (LEO) projects with Teleports is commented. Some significant LEO/MEO (Medium Earth Orbit) projects are cited. The impact of the satellite industry and the Teleport systems on the technological ecosystem is discussed. LEO satellites for monitoring the earth's surface are presented. Keywords: LEO, Orbit, Satellite, Teleport.

scholarly journals Precise Relative Orbit Determination for Chinese TH-2 Satellite Formation Using Onboard GPS and BDS2 Observations

2021 ◽  
Vol 13 (21) ◽  
pp. 4487
Author(s):  
Bin Yi ◽  
Defeng Gu ◽  
Kai Shao ◽  
Bing Ju ◽  
Houzhe Zhang ◽  
...  
Keyword(s):  
Orbit Determination ◽  
Low Earth Orbit ◽  
Asia Pacific ◽  
Earth Orbit ◽  
Reference Orbit ◽  
Satellite Formation ◽  
Relative Orbit ◽  
Comparison Results ◽  
Geo Satellites ◽  
The Impact

TH-2 is China’s first short-range satellite formation system used to realize interferometric synthetic aperture radar (InSAR) technology. In order to achieve the mission goal of InSAR processing, the relative orbit must be determined with high accuracy. In this study, the precise relative orbit determination (PROD) for TH-2 based on global positioning system (GPS), second-generation BeiDou navagation satellite system (BDS2), and GPS + BDS2 observations was performed. First, the performance of onboard GPS and BDS2 measurements were assessed by analyzing the available data, code multipath errors and noise levels of carrier phase observations. The differences between the National University of Defense Technology (NDT) and the Xi’an Research Institute of Surveying and Mapping (CHS) baseline solutions exhibited an RMS of 1.48 mm outside maneuver periods. The GPS-based orbit was used as a reference orbit to evaluate the BDS2-based orbit and the GPS + BDS2-based orbit. It is the first time BDS2 has been applied to the PROD of low Earth orbit (LEO) satellite formation. The results showed that the root mean square (RMS) of difference between the PROD results using GPS and BDS2 measurements in 3D components was 2.89 mm in the Asia-Pacific region. We assigned different weights to geostationary Earth orbit (GEO) satellites to illustrate the impact of GEO satellites on PROD, and the accuracy of PROD was improved to 7.08 mm with the GEO weighting strategy. Finally, relative orbits were derived from the combined GPS and BDS2 data. When BDS2 was added on the basis of GPS, the average number of visible navigation satellites from TH-2A and TH-2B improved from 7.5 to 9.5. The RMS of the difference between the GPS + BDS2-based orbit and the GPS-based orbit was about 1.2 mm in 3D. The overlap comparison results showed that the combined orbit consistencies were below 1 mm in the radial (R), along-track (T), and cross-track (N) directions. Furthermore, when BDS2 co-worked with GPS, the average of the ambiguity dilution of precision (ADOP) reduced from 0.160 cycle to 0.153 cycle, which was about a 4.4% reduction. The experimental results indicate that millimeter-level PROD results for TH-2 satellite formation can be obtained by using onboard GPS and BDS2 observations, and multi-GNSS can further improve the accuracy and reliability of PROD.

scholarly journals Evaluation of Precise Microwave Ranging Technology for Low Earth Orbit Formation Missions with Beidou Time-Synchronize Receiver

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4883
Author(s):  
Xiaoliang Wang ◽  
Shufan Wu ◽  
Deren Gong ◽  
Qiang Shen ◽  
Dengfeng Wang ◽  
...  
Keyword(s):  
Dynamic Models ◽  
Estimation Error ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Time Interval ◽  
Relative Navigation ◽  
Dual Frequency ◽  
Processing Scheme ◽  
Time Frequency ◽  
Range Rate

In this study, submillimeter level accuracy K-band microwave ranging (MWR) equipment is demonstrated, aiming to verify the detection of the Earth’s gravity field (EGF) and digital elevation models (DEM), through spacecraft formation flying (SFF) in low Earth orbit (LEO).In particular, this paper introduces in detail an integrated BeiDou III B1C/B2a dual frequency receiver we designed and developed, including signal processing scheme, gain allocation, and frequency planning. The receiver matched the 0.1 ns precise synchronize time-frequency benchmark for the MWR system, verified by a static and dynamic test, compared with a time interval counter synchronization solution. Moreover, MWR equipment ranging accuracy is explored in-depth by using different ranging techniques. The test results show that MWR achieved 40 μm and 1.6 μm/s accuracy for ranging and range rate during tests, using synchronous dual one-way ranging (DOWR) microwave phase accumulation frame, and 6 μm/s range rate accuracy obtained through a one-way ranging experiment. The ranging error sources of the whole MWR system in-orbit are analyzed, while the relative orbit dynamic models, for formation scenes, and adaptive Kalman filter algorithms, for SFF relative navigation designs, are introduced. The performance of SFF relative navigation using MWR are tested in a hardware in loop (HIL) simulation system within a high precision six degree of freedom (6-DOF) moving platform. The final estimation error from adaptive relative navigation system using MWR are about 0.42 mm (range/RMS) and 0.87 μm/s (range rate/RMS), which demonstrated the promising accuracy for future applications of EGF and DEM formation missions in space.

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