ABSTRACT The aim of this work is to summarize and to describe the present results of the research of influences of Martian ionosphere on satellite navigation system. This research work includes the description and analysis of the first steps within the experimental calculation. In this work are included new information and research results. The research described in this work is focused on analysis of ionospheric influences on radio signal transmission through the ionosphere of Mars and on calculation of the deviation and range error with use of experimental frequencies. The final analysis answers the question which orbits are most suitable for proposing of the GNSS1 for Mars. This research is a part of more complex research work with name “Theoretical Concept of Satellite Navigation System for Mars” (GNSS FATIMA2 ) of author Jozef Kozar, PhD. Please note that the results in this research may vary from the current research results as this continuously evolves.
KEYWORDS GNSS for Mars, GNSS FATIMA, Ionosphere of Mars, Ionospheric profiles of Mars, Navigation.
Satellite navigation system for planet Mars (GNSS FATIMA) is a proposed complete solution for provisioning of precise navigation and resulting navigation services. It also provides an accurate time service covering a whole planet Mars. Therefore it is essential to focus on each specific stage of the scientific research. This includes the experimental calculation of the accuracy of the positioning on Martian surface and the ionosphere and troposphere impact on the accuracy. Ionosphere, troposphere and meteorological influences make the highest share of the exact operation of the system. In the following research work we will take a look on influences of Martian ionosphere.
2 Material and methods
Experimental analysis and calculation using simulated conditions and real data from ionosphere of Mars.
3 Definition of research targets
A design of the theoretical concept of a small satellite navigation system for planet Mars must be based on real natural conditions, planetary parameters and the results of simulations and calculations of individual condition. The basic objectives and targets of the calculation should be defined respectively to the different stages of calculations, which define the individual tolerances, and accuracy of the theoretical system in real conditions. Individual calculations must focus on the following areas:
1. Influences of ionosphere of Mars
2. Influences of magnetic fields around Mars
3. Tropospheric influences
4. Gravitational influences of near celestial bodies
In this research work we were focused on influences of ionosphere of Mars on distribution and transmission of signal of GNSS FATIMA. So during the research and study we were trying to find out the average deflections (errors) in precision of positioning on surface of Mars in dependence of evolution of local and global weather, troposphere and its layers. Also we were focused on research and study of ionosphere and it layers and its evolution according to solar activity in solar cycle. The input data into this experimental calculation in this research are the ionospheric data measured by NASA’s Mars Global Surveyor and ESA’s Mars Express. In this research work we have not studied the influence of surrounding magnetic fields and gravitational effects of the close planetary bodies.
4 Ionosphere of Mars
The ionosphere of Mars is the most important factor which has influence on correct functionality of potential global navigation satellite system. It is because of the interaction of ions and ionized gases with the broadcasted signal in high altitudes. This interaction can cause a huge degeneration of the quality of precise positioning on the surface. The ionosphere of Mars is different on every side of the planet. According to measurements and research using the data of Mars Express is the dayside ionosphere different than the night side ionosphere. This phenomenon is caused by the extreme ultraviolet radiation by which the Sun ionizes the neutral gases in upper layers of the atmosphere. This effect results in a radical increase of density of electrons in these layers. The experiment “Radio Science Experiment” of Mars Express orbiter has provided us around 500 vertical ionospheric profiles. The ionosphere of the planet causes the delay in radio transmission from satellite in orbit to receiver on the surface. The result is the range of errors in precise positioning.
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Figure 1: Profiles of electron density in Mars ionosphere. The upper row and the first two charts in lower row from the left display the dayside ionosphere. The last chart in lower row displays the contrast between dayside and night side ionosphere. Source: ESA/AOES Medialab.
The errors caused by the ionosphere can vary of course. These can be in tens of centimeters but also in meters which can have a huge impact on effectivity of use of a whole global navigation satellite system. These errors can be eventually corrected by application of corrections broadcasted by a local differential positioning system station in the desired area. There are also verified solutions which can be applied as well. For example the use of the best suitable frequency for a given system or use of the most suitable altitudes of orbits of space segment of GNSS. Therefore when designing a global navigation satellite system it is useful to count with the most suitable frequency and suitable orbital parameters of navigation satellites. By this way, it is possible to minimize the influences of the ionosphere. The following use of the local reference station broadcasting the positioning corrections would be a secondary proposed solution. This solution would be suitable for example for very precise geodetic measurements on Mars or for future proposed flying exploration systems (in atmosphere of Mars, i.e. Martian airplanes/drones). The flying devices in case of Mars are at present only in phases of concepts or ideas. Therefore it is primarily suitable to focus on classic use of the navigation services by surface probes, rovers, orbiters on low Mars orbits or by planned future manned mission in the first half of the 21st Century.
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Figure 2: Illustration of ionosphere of Mars on its dayside and night side. The radius of Mars is 3389.50 km. The ionosphere begins at 100 km and reaches 700 km on dayside and 3000 km on night side of Mars. Source: ESA/AOES Medialab.
The average value of total electron content is in each altitude different. It depends on a position on the planet. The total electron content (TEC3 ) on Mars is a primary function of the solar zenith angle (SZA4 ) with the highest value 1 TECU5 (10 electrons/m2) in the point of solar zenith. The global average of values is according the MARSIS6 experiment (ESA Mars Express) following:
- Day conditions (SZA<75°): electron content is ~6 TECU (1016 el./m )
- Night conditions (SZA>105°): electron content is ~0.3 TECU (1016 el./m )
The day values of TEC are increased in regions with 0-30° latitudes. The night values are increased in regions with stronger magnetism. The entire variability of changes of TEC values in ionosphere of Mars can reach the ranges ~±5% during the day and ~±20% during night. In experimental calculation (simulation) in the project of the concept of satellite navigation system for Mars (GNSS FATIMA) we used the real TEC values measured by ESA probe Mars Express. In this place it is necessary to mention, that as the TEC values for GNSS research and application should be used only the average values. The extreme values can have a huge influence on functionality of GNSS and other orbital devices, but these extreme values are very sporadic and can occur only when there is increased solar activity during the solar cycle. It is recommended to count with these extreme values in the calculation as a part of predicted random errors of individual distance measurements of the system.
1 GNSS - Global Navigation Satellite System
2 FATIMA - Fix And TIme provisioning system for MArs. Concept of GNSS for Mars. Author of the concept: Jozef Kozar, PhD.
3 TEC - Total Electron Content
4 SZA - Solar Zenith Angle
5 TECU - Total Electron Content Unit
6 MARSIS - Mars Advanced Radar for Subsurface and Ionosphere Sounding
- Quote paper
- Jozef Kozar (Author), 2016, Experimental analysis of precision of Mars GNSS FATIMA according to ionosphere of Mars, Munich, GRIN Verlag, https://www.grin.com/document/336217