ESA’s Deep Space Network consists of three ground stations located in New Norcia in Western Australia (NNO-1, in use since June 2003), Cebreros Spain (CEB-1, in use since November, 2005), and Malargue in Argentina (MLG-1, in use since December 2012). The stations are multi-mission, however over the course of the ESTRACK DSN evolution, each new station was equipped with a slightly different combination of frequency bands.

The 35 meter beam waveguide antennas have the unique characteristic of supporting a number of feeds at different frequency bands to be installed in the base of the antenna. Each feed is able to transmit/receive via a system of mirrors that direct the RF signals to the main reflector, where they are radiated to the spacecraft.

In the context of the EUCLID mission, ESA identified the requirement for CEB-1 and MLG-1 to have the added capability of reception at K-Band (26 GHz) for high bandwidth downlink capabilities, whilst simultaneously maintaining its current X-Band transmit and receive functionality. The solution was to add a new X/K band feed in the base of the antenna, and to implement the necessary mirrors and mirror positioners that allow the beam waveguide to access this new feed. In the case of MLG-1, the original design had foreseen the need for the main mirror in the antenna base to be motorized, such that it could be positioned to select a number of feed positions. MLG-1 also had been conceived from the beginning with a larger feed enclosure area to accommodate up to three separate feed assemblies. This made the integration task in MLG-1 relatively simple.

By comparison, in the case of CEB-1, the main mirror at the base was fixed to one position and additional space was needed to accommodate the new X/X/K band feed. SED was tasked with the overall integration responsibility, which involved extensive preparation of the antenna base to incorporate a motorized mirror, as well as new feed positions for future expansion. Both sites were then fitted with new feeds, cryogenic LNAs, frequency conversion equipment and with the necessary adaptation to existing equipment and infrastructure.

This paper describes the implementation challenges, the design criteria and the performance of both Stations after the integration. In particular, it will address the scope of the modifications that had to be made to each station, and will contrast the operational impacts that were necessary during the installation phase at each station. The paper will also highlight some of the specific equipment that had to be developed for the project and the major technical advancements that have been made. Test results and performance outcomes will be presented and discussed. Emphasis is given to show how the existing beam waveguide 35m antennas have been given enhanced functionality that satisfies the multi-mission support capabilities, including simultaneous operation in X and K frequency bands. Efforts to harmonize the design and functionality between the two stations will be described.

A 2016 European Space Agency (ESA) General Support Technology Programme (GSTP) study showed the technical feasibility of converting a dual C and Ku band 32m (GHY-6) satcom antenna into a Deep Space Antenna. The study investigated whether the GHY-6 antenna, -located at Goonhilly Earth Station (GES) in Cornwall United Kingdom- could support the Orion spacecraft on the Space Launch System (SLS) Exploration Mission 1 (EM-1) lunar flight. Although a request for support was never formalised by NASA, the GSTP study produced several valuable technical outputs and the awareness that upgrading GHY-6 was indeed feasible and it could be of high benefit for supporting lunar missions and providing deep space services from the UK. The study concluded with a technical and financial proposal for the complete project.

The Cornwall and Isles of Scilly Local Enterprise Partnership - the body responsible for growth and development of the Cornish regions, recognised the project’s potential to rejuvenate and attract highly skilled jobs into the area. After extensive due-diligence from the UK Space Agency the programme was initiated through a third-party agreement with ESA through the team at European Space Operations Centre (ESOC).

This paper describes the implementation of the upgrade project, from the feed system through to the back-end systems required to enable the GHY-6 antenna to be included in ESA’s Augmented ESTRACK Network. The offered services, which includes S-band and X-band for near and deep space communications as well as ranging and Doppler tracking, are expected to be made available by mid-2020. The timescales are such that the system can be used in support of Cubesat missions delivered by the SLS EM1 mission, that will also deliver Orion to Lunar Orbit.

Furthermore, GHY-6 will be the first antenna of a Goonhilly funded activity to create a series of privately own Deep Space communications assets around the world. This global network, scheduled to be on-line by end of 2021, is positioning itself to offer around the clock communications and ranging services to the increasing institutional and commercial missions expectedon, or in orbit around, the Moon

Current commercial-off-the-Shelf Software Defined Radios (SDR) have sufficient capabilities to serve as a cost-effective solution for mission development and operation. Some of the benefits are faster development time and a much lower cost compared to what is typically required in a custom-design development. In this paper, we describe our experiences in using the commercial SDR in three different projects. The equipment - named Recorder/Playback Assembly (RPA) - offers a capability to record an RF/IF signal and to play back the recorded data at selectable frequency, from 10 MHz to 6 GHz range. In the first project, the RPA serves as a replica of the Exploration Mission 1 (EM-1) spacecraft flight radio. It is used for compatibility testing with the Japanese Aerospace Exploration Agency (JAXA) 34-m ground system at Uchinoura, Japan. In the second project, the RPA complement the testing of the 21-m ground station at the Morehead State University, Kentucky. The objective is to verify the receiver functionality and performance by using spacecraft signals normally tracked by the NASA Deep Space Network (DSN). This approach overcomes one main difficulty with lower signal power reception at Morehead, mainly due to smaller antenna aperture compared to the DSN. For the third project, the RPA helps to increase data return to the Voyager mission, using the Parkes Observatory’s 64-m antenna in Australia. Here, the RPA serves as a bridge across two continents. By joining the Parkes’ antenna front-end with the DSN back-end systems, it makes data received from Parkes seamlessly flown to the Voyager mission operation system as if it comes from the DSN antenna.
In the paper, we will discuss the benefits and constraints that the SDR approach offers. Performance observed with our particular selected SDR product, such as degradation to the signal to noise ratio (SNR) that is sensitive to telemetry data and frequency stability that affects Doppler measurements, will also be presented.

In principle, the performance of downlink reception for deep space missions can be improved by directly increasing the antenna size or by arraying several antennas. The most obvious advantage of a single large 70-m antenna is the fact that it would be a well-known approach in terms of antenna design. However, several factors, such as gravity, thermal and wind loads can impair its performance, Moreover, a single 70-m dish has normally very high maintenance costs and would be a single-point of failure.
The alternative is an array of antennas, capable of ensuring the same level of performance as that of a much larger single-dish antenna. An antenna array represents a more attractive solution, as it would allow for an operative system which can grow progressively. In addition, the array may be partitioned to simultaneously support more than one mission and is much more fail-safe against the failure of components, ensuring in all cases support with only partially degraded performance. This solution, on the other hand, requires a tool capable of combining the signals acquired at different Ground Stations.

This paper presents the realization of a prototype of off-line software correlator for up to four 35 m antenna array over long baselines, in the order of 10000 km. In general, the different replicas of the signal present differential delay and phase that must be known a-priori or estimated. Several error sources, such as deviation from the parabolic shape and errors induced from the troposphere, prevent the knowledge or estimation of the phase accurately. The troposphere is particularly important in combination algorithms that require the estimation of the phase through a cross-correlation of the signals, as the integration time scale for the fluctuations of the troposphere may not be optimum to reduce the thermal noise. The contribution of these errors increases with the spatial separation of the antennas, and its evaluation becomes crucial in this case. The design of the tool has been preceded by a thorough analysis of the most promising combination methods, correlation algorithms, computation of the combination losses and definition of the operating areas of the array in terms of symbol rate and power to noise density ratio.

The correlator implements the Full Spectrum Combining (FSC) and Symbol Stream Combining (SSC) combination methods. The former has better performances, since the signals are combined at IF level, resulting in a lower demodulation loss. Moreover, it is independent of the modulation scheme, and can be used at very low symbol energy per noise ratio. The latter, in which the signals are combined at soft-decision level after the demodulator, is simpler to implement, and can be used in cases in which the change of the differential phase between the signals is too rapid to be tracked with FSC (for example during solar superior conjunctions).
For FSC, the differential delay and phase are estimated through cross-correlation. The Sumple correlation algorithm was implemented. Instead of pair-wise cross-correlating the signals, each signal is correlated with the sum of the remaining ones. After the convergence of the system, the result is a floating reference signal, whose phase wanders due to thermal noise. Nevertheless, a master-antenna mode has been added, in which one signal is chosen as reference, allowing for a simpler way to generate two-way observables from the combined signal, to be used for navigation. Such correlation method presents larger correlation SNR, thus allowing to combine weaker signals. Moreover, being an off-line correlator, a non-real time version of the Sumple algorithm has been implemented, in order to get a better estimation of phase and delay for every cross-correlated chunk of data, resulting in lower combination losses.

The correlator implements a software demodulator, for PCM/BPSK/PM, PCM/SP-L and GMSK modulations, improved with off-line optimizations, such as forward-reverse PLL, with a 3-dB gain over the standard PLL, and side-band aiding, useful to recover the carrier phase using also the information coming from the subcarrier. Finally, the combined symbol stream is decoded, and the information bits reconstructed. The decoder works with the Reed-Solomon code concatenated with the convolutional code, and with Turbo Codes with rate 1/2, 1/4 and 1/6, which are some of the standardized solutions for telemetry links.

The tool has been successfully tested with simulated data and static data generated in ESOC GSRF. Finally, tests with ESA missions Mars Express (PCM/SP-L with 524288 sps) and GAIA (GMSK with 3333333 sps) were performed. After the combination of the signals acquired in Cebreros and Malargue Ground Stations, proving the gain in SNR of the array, the combined signal has been demodulated and decoded. The information bits were compared to the data frame reported in the ICD of the missions and resulted to be in perfect agreement. The successful testing with actual data from flying spacecraft endorses the tool for offline use in the near future

Due to the atmospheric attenuation and the very long distance separating the ground station and the satellite, the deep space communication systems are often characterized by a very low signal-to-noise ratio (SNR). To overcome this problem, an antennas array can be used at the reception to maximize the signal power and the data return from the spacecraft by allowing higher data rate or to decrease mission cost. Nevertheless, to take advantage of the combination gain, the received signals must be synchronized prior to the combining stage. In addition, antenna arraying offers several benefits such as: more tolerance to antenna-pointing error, increase the system operability and flexibility, capex and opex cost saving …

With respect to its position in the demodulation system, two main categories of signals combining can be distinguished: Post-detection combining (or symbols stream combining) and Pre-detection combining. The first one consists to use two or more independent demodulation channels and coherently combine the soft symbols. Algorithms such as maximum ration combining (MRC) can be used to create more powerful symbols and enhance the SNR before processing the channel decoding. This method is relatively simple and very efficient provided that all previous demodulation stages (synchronization, equalization…) can ensure a good performance at low SNR, but the cost of simplicity is no gain in terms of the operating threshold of the overall demodulation system. This technique is interesting when the demodulator threshold is below the threshold with one antenna.

To overcome this drawback, pre-detection combination can be used. The signals received by the array elements are combined prior to the demodulation. In this case, the signals must be aligned in time and in phase using synchronization techniques such as phase locked loop (PLL) and cross-correlation based delay estimation. Thus, the system operating threshold can be decreased by the combination gain, for example a 3-dB gain can be obtained by combining two identical antennas.

In previous works, we presented a blind phase error detector for GMSK modulation derived from the maximum a posterior (MAP) criterion. Compared to the CORDIC based detector, the MAP phase detector has a much lower detection threshold and larger lock-in range which makes it more suitable for antennas arraying schemes, especially with post-detection schemes because the detector works at very low SNR (E_s/N_0≃ -8 dB).

In this paper, we present our work in baseband combining for satellite communication. In the first part, we consider the post-detection scenario. This technique has been tested a few years ago with two antennas array separated by 300 meters and a data rate of 300 Msps. The obtained result has shown a combination gain of 2.8 dB for the quadrature phase shift keying modulation (QPSK) and in PM/PCM. Nevertheless, the demodulator was still limited by the detection threshold of the CORDIC phase detector and the acquisition system. The gain has been mainly proved at the end of the pass in the LEO scenario. To have the combining gain at acquisition phase and have the same demodulator detector sensitivity, combining must be performed before demodulation.

A variety of pre-detection antenna arraying algorithms such as SIMPLE, SUMPLE and EIGEN have been used in deep space network (DSN) to enhance the data return from deep space missions. Unfortunately, due to the squaring loss generated by the cross-correlation based delay estimator, these algorithms cannot ensure a reliable response at very low SNR. This method has an operating threshold around -6 dB which is above the MAP carrier loop (at -8 dB). To minimize the squaring loss effect, a very long correlation duration is required and we need to store a big amount of data and remove Doppler effects. Thus, this method is an off-line solution and is not suitable for real time applications.


In this work, we propose a novel method for pre-detection antennas arraying which resolves the squaring loss problem and enhances the combiner performance (threshold around -12 dB). In addition, our solution is able to align and synchronize the received signals in real time. The main idea behind our algorithm is to detect the attached synchronization markers (ASM) positions in the received signals using a matched correlator and CA-CFAR detector. The CA-CFAR is very suitable for our system since it uses an adaptive threshold target detection and does not require a SNR estimation.

Using this method, we can combine the signals from the different receiving-antennas and generate an output SNR higher than the operating threshold of the MAP carrier loop which will allow us to properly demodulate the resulting signal. The simulation results of this method applied to a Turbo encoded GMSK modulation will be presented in this paper