China will launch its first Mars spacecraft in 2020, which aiming is to orbit, land and deploy a rover on Mars and carry out scientific exploration activities. Precision orbit determination is the key technology of Mars exploration. In this paper, based on the experience of Mars exploration abroad and the actual results of lunar exploration orbit measurement in China, ground-based orbit measurement and determination system is designed. It is proposed that Chinese Deep Space Network and VLBI(Very Long Baseline Interferometry) network should be mainly used to realize the precision orbit measurement of Mars spacecraft, and the precision analysis of ranging, velocity measurement and VLBI data should be carried out. The result shows that it can meet the needs of China's Mars exploration activities.

Retrieval algorithms have been produced within the context of the prototype development of a dual-channel microwave radiometer by Omnisys Instruments, Gothenburg, Sweden.

Input data to describe the atmospheric properties are taken from ERA-Interim via its web interface. The quantities used are: surface pressure, temperature profile, geopotential altitude, humidity profile, liquid water content profile, and low cloud fraction. Data were downloaded for the years 2001–2014, for UT 00, 06, 12 and 18 at the highest available resolution. The position was selected to match the location of the Onsala Space Observatory. This atmospheric database contains about 20 000 cases.

The following assumptions were made about the radiometer: The antenna pattern was assumed to be sufficiently narrow that a pencil beam calculation represents the complete antenna temperature. The instrument channels were assumed to be sufficiently narrow that a monochromatic calculation represents the complete channel brightness temperature. The instrument was assumed to have two channels, with centre frequencies on and off the water vapour emission line at 22 GHz. The magnitude of uncorrelated (thermal) noise was assumed to be 0.6 K, for both channels (including noise added by the atmosphere and the calibration process). Errors fully correlated between the two channels were assumed to be between 0.37 K and 0.47 K. All instrument errors are assumed to be independent of the observed air mass.

The observation database produced by the ARTS forward model covers 15 GHz to 52 GHz, in steps of 200 MHz, and holds data for different viewing angles matching air mass factors between 1 and 6. The following quantities were calculated: brightness temperature, transmission, zenith hydrostatic delay, slant total delay, slant wet delay, geometric delay due to bending, water vapour path, and liquid water path.

Polynomial regression models are presented. The Onsala site is used for testing and demonstration of the retrieval performance, but the retrievals can easily be adopted to the conditions at other sites as the atmospheric data used to determine the regression coefficients are taken from a global atmospheric model (e.g. the ERA-Interim).

The errors found should be acceptable and match what is achieved by existing radiometers. The requirement for the transmission retrieval is met. In fact, this requirement is met with some marginal and the instrument performance could be poorer than estimated without violating the requirement.

The ever growing demand for returning large data volume from space to earth has led to considering either higher radio frequency bands or optical wavelengths for near earth and deep space science missions.
Optical communications are promising for deep space communication links in this respect. Compared to radio-frequency satellite systems, free space optical (FSO) technology has a great variety of advantages like capability for higher throughput, reduced mass and low energy consumption among others. For deep space optical communications, the space agencies in CCSDS (Consultative Committee for Space Data Systems) recently concluded on a standard for High Photon Efficiency (HPE). The standard comprises a specification on the coding and synchronization layer [1] and one on the physical layer [2]. In order to assess the requirements and the performance of deep space links an accurate link budget analysis is necessary.
In this paper, a practical link budget tool based on the CCSDS HPE is presented. The main elements that must be taken into account in order to calculate the signal and the noise photon rates are accurately predicted are incorporated in the link budget tool. Among others, the transmitter/receiver aperture gains, the atmospheric losses, the miss pointing and scintillation losses, the system/detector efficiency and the detector blocking and jitter losses are factor in. Additionally, the background noise from planets, stars and sky in accordance with the detector’s dark current noise are taken into consideration. Outputs of the tool are the signal and noise photon rates, the data rate, the bit error rate and the capacity of the deep space optical link.
The main assumptions of this contribution involve an optical downlink operating under cloud free line of sight conditions (CFLOS) between an optical terminal on board a deep space spacecraft and an optical ground station. A Poisson channel model is representative of deep space optical links. Due to the power limited nature of these links intensity modulation (IM) and direct detection (DD) with photon counting detectors are considered for the transmitter and receiver architecture, respectively. Both single photon detectors and single photon detector arrays are studied. Under these conditions, the Pulse Position Modulation (PPM) signaling and a Serially Concatenated-Pulsed Position Modulation (SCPPM) are capacity achieving.
Additionally, a methodology for the selection of the optimum signaling parameters (modulation order, code rate, slot width) achieving the higher data rate depending on the signal and noise photon rates without resorting to lengthy coded Bit Error Rate (BER) evaluations that otherwise are needed, is presented and employed in this analysis. According to CCSDS HPE the proposed analysis includes the allowed values of PPM order (4, 8, 16, 32, 64, 128, 256), of the code rate (1/3, ½, 2/3) and of the slot widths (0.125ns, 0.25ns 0.5ns, 1ns, 2ns, 4ns, 8ns and 512ns).
Finally, various hypothetical deep space missions, like for Mars and Venus orbits and for distances from 0.3AU (Astronomic Unit) to 2 AU, are studied and valuable conclusions are extracted. A sensitivity analysis of the signal and noise photon rates are computed for different ranges and different system considerations, i.e. a variety of receiver/transmitter aperture diameters, either only one single photon counting detector or an array of single photon counting detectors and different background radiances among others, and the maximum achieved data rate is computed in each case.
This work is under the ESA’s project “DEEP SPACE OPTICAL LINK BUDGET SW TOOL”, ESA Contract Nr. 4000121821/17/NL/FE.
References
[1] CCSDS Red Book, Draft Recommendation for Space Data System Standards “Optical Communications Coding & Synchronization Sub layer.2017.
[2] CCSDS Red Book, Draft Recommendation for Space Data System Standards “Optical Communications Physical Layer”, CCDS 141.0-R-1, Nov. 2017.

The Proba-3 mission is the first mission dedicated to precision formation flying and its enabling technologies, with two satellites flying together in a fixed configuration. The scientific motivation is to study the Sun’s faint corona, where one satellite (CSC) hosts the coronagraph instrument and the other (OSC) carries a large occulting disk and has the objective of blocking the sun from the coronagraph instrument. Such a mission requires precision manoeuvring and the ability to maintain a constant relative position between both satellites, which is the perfect motivation to test precision formation flying. In Proba-3, the role of the ISL is critical. It must allow the two satellites to exchange information during the formation flying phases of the mission, in order to acquire and maintain their relative position. It must be considerate of the required data rates and must work up to the maximum distance that the satellites will be separated by. The proposed technical solution for the Proba-3 ISL is a state of the art SDR communications platform, operating in S-Band, between 2.40 and 2.45 GHz. The platform is capable of delivering up to 2 Mbit/s and of communicating up to a distance of 10 km, which is in line with the Proba-3 requirements. Together with communications, ranging algorithms can also be implemented in the ISL platform, which is an asset for formation flying technology demonstration.

On the other hand, the international Asteroid Impact & Deflection Assessment (AIDA) cooperation is the first demonstration of asteroid deflection. It consists of a kinetic impactor, NASA’s Double Asteroid Redirection Test (DART) and of ESA’s Hera inspector spacecraft that will rendezvous the target asteroid, the binary 65803 Didymos, in 2026, nominally 4 years after the DART impact. The early characterisation phase of Didymos will start from a moderate distance of around 30 km to determine the shape and the gravity field. The detailed characterisation phase will be conducted from about 10 km distance. During this phase CubeSats will also be released. Very close flybys of Didymoon are envisioned towards end of mission as part of the technology demonstration based on the so-called onboard landmark navigation.

Besides the scientific goals of the mission, HERA will also allow for key technology demonstration activities. Particularly, in order to overcome computation capability limitations as well as complexity of fully independent GNC visual based navigation systems on-board CubeSats, establishing a network of space elements connected by inter-satellite link systems providing ranging capabilities could enhance the navigation system by providing relative positioning. This experiment shall demonstrate the capability of using ranging information from the inter-satellite link systems to enhance CubeSat autonomous position determination.

Additionally, in order to overcome communication with ground capability limitations on-board CubeSats in deep-space, establishing a relay network through a mother-ship spacecraft would be a simple and efficient mean to reduce resources needs to operate CubeSats in deep-space. A solution to this problem is to relay all communications between ground and the CubeSat through a mother-ship spacecraft with full communication capability with ground. This can be done using inter-satellite link systems. This experiment shall demonstrate the capability of using inter-satellite link systems to transfer housekeeping, telecommands and payload data between the Hera spacecraft and the CubeSat.

This paper focuses precisely on bringing an Earth-orbiting ISL system to the challenges of a deep space mission, with multiple platforms coordinating actions to perform a common goal. It goes over the overall system architecture and focuses on the major modifications and additional capabilities required by Hera, either in support of the main scientific mission and as demonstration of technological capabilities for the future.

STCAD Pro 2019 is the newest and upgraded release of the original STCAD, a successful tool developed under ESA Contract in 2016. The new version has been redesigned from scratch and includes numerous new features that makes it a powerful and practical tool for Engineers in the area of Satellite communication subsystems.
The new tool helps in the generation of architectural designs. It is intended to assist in the trade-offs and the definition of TT&C subsystem architectures for a variety of space missions. Several analyses are available to help in this design in an iterative process. The tool characteristics and features:
• Visual Design, user friendly with intuitive interaction. The graphical interface provides a layout with key areas to allow fast design and analysis and pre-configured components which help to setup a TT&C architecture in a quick and convenient way.
• Provides a complete palette (library) of components ready to use. The user can modify existing components or add new custom ones. The component behavior is implemented with source code modifiable by the user in real-time, thanks to real-time compilation. Components can be connected through Coaxial, Waveguide lines or a direct connection (ideal line).
• Tailored for TT&C subsystems
 Element library (typical models & parameters)
 Measured components (S-Parameter files) can be used
 Simulated parameters (supporting Link budget analysis)
• Cascade analysis
 Multi-frequency simultaneous analyses.
 Models are defined by their S-parameter matrix.
 Includes passive and active components non-linear performances
 Mismatch accounts for the whole chain
 Thermal noise accounts for different temperature of elements.
 Backward and forward propagation of energy through the cascade.
 Frequency dependent behavior of Waveguides, Amplifiers, Filters, Diplexers, Triplexer
 Antenna Coupling.
 Automatic identification of all possible signal paths found in the schematics.
 User defined Filter Masks, Amplifier models and Antenna Gain Patterns.
 Nominal, worst- and best-case analysis.
• Link Budget analysis
 Flexible computation of all most common link budget parameters for suppressed/residual carriers.
 CNES Propa ® tool based atmospheric losses calculation (using a runtime library).
 Multiple choices of user-provided, cascade-analysis derived or locally computed parameters (EIRP, G/T, atmospheric losses, C/No – bent pipe repeater)
 Static and dynamic simulations, based on custom-defined, imported or internally generated orbital trajectory (SGP4, based on Keplerian parameters).
 Adaptive application of most common link performance degradation contributions (Transmitter EVM & C/I3, spacecraft pointing losses, interferences).
 Uses Ephemerides (NASA JPL 405) for Sun and Moon Positions.
 Dynamic Noise from celestial bodies and background radiation.
 Antenna Gain Patterns and Filter Masks manually defined or imported from CSV files.
• A command console is available together with and API. This provides enormous opportunities for automation and for custom analysis. Command line use is possible using scripting language (C# code).
• Includes Designers for Orbits and Trajectories, Filter Masks, Amplifier Data and Antenna Gain Patterns. All results can be plotted comparatively, and everything can be printed out.