As the complexity of nanosatellite missions have increased over time, the data generated on-board nanosatellites have increased multiple folds. As a result, there is a need to downlink large amounts of data. Multiple nanosatellite missions have started using spectral efficient modulation schemes recommended in DVB.S2 and DVB.S2X to make the best use of the available spectrum. One of the main challenges in adopting higher order modulation schemes is to power-efficiently upconvert and amplify the baseband signals. All the lost efficiency in converting the DC power to the RF output is dissipated as heat and the relatively small thermal mass of nanosatellites poses thermal management challenges. As a first step to addressing the challenge of improving the power efficiency of the communication module, optimization techniques to improve the Peak to Average Power Ratio (PAPR) of the modulation schemes (16/32-APSK) are discussed in this paper. The PAPR of 16-APSK reduces by ~2 dB by incorporating filtering techniques discussed in this paper. Further, a well-known efficiency and linearity enhancement technique; Out-phasing/LINC (Linear Amplification using Non-linear Components) is discussed. As a variant of the out-phasing architecture, a novel approach is proposed using two circularly polarized antenna to transmit the constant envelope signals in opposite polarizations and signal combining is performed at the receiver. Simulations results are used to demonstrate how higher efficiencies can be achieved using the proposed architecture.@en

Nano-satellite IoT/M2M missions are gaining popularity in recent time. Various companies have launched their pilot missions last year in 2018 and all these companies intend to place a constellation in (V)LEO that can communicate with low power sensors on the ground (sometimes remote locations) and relay it back to the end-user who is monitoring these sensors. This paper discusses two possible architectures of using nano-satellites for low latency IoT/M2M, by presenting information such as, number of satellites needed, number of orbital planes needed and communication strategy. The first proposed architecture will comprise of a self-sustaining network of nano-satellites that communicate with low power, low data-rate sensors on the ground and relay the data to rest of the nano-satellites in the network using inter-satellite links, which is downlinked by a nano-satellite that is in the view of a ground station that is connected to IMT. The second proposed architecture will use nano-satellites to communicate with low power, low data-rate sensors on the ground and relay it to satellites that intend to provide internet from space (Mega-constellation). The internet constellations considered in this study for the second architecture are: Telesat’s constellation, SpaceX’s Starlink, OneWeb’s constellation, Astrome’s SpaceNet constellation and Audacy’s constellation. Using both these architectures, it can be seen that the latency can be reduced considerably. @en

This paper presents a software-defined testbed to perform hardware-in-The-loop test of miniaturized coherent transponders. Such a setup has been designed to minimize the access threshold for future users, heavily relying on available open source applications and commercial hardware, targeting future coherent transponders for interplanetary CubeSats. The paper presents the overall architecture of the testbed, a tradeoff to select the most suited development framework and the detailed design of the different blocks. Upcoming interplanetary CubeSat missions that would require a coherent transponder are also presented to highlight the need sof such a system. Software qualification, given the use of third-party software with multiple developers, was also addressed to guarantee performances can be consistent and reliable.

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This paper presents the design of a multi-frequency deployable antenna system for femto-satellites as part of the Delfi-PQ project, a PocketQube with a size of 50x50x178 mm which is being developed by the Delft University of Technology. This new form factor brings its own challenges on every subsystem and it is seen as a stepping stone towards even more miniaturised satellites. In this paper we present the design trade-offs, the analysis and the and measurements on the antenna system. The system is designed to operate in 4 different bands to guarantee communications and payload operations. Due to the very limited available space on the external faces of the spacecraft, it was decided to deploy all the antennas and multiplex the different bands on the available antenna elements. VHF and UHF are used for satellite telemetry and commanding while a dual-frequency GPS receiver is intended as payload. The satellite design is presented, together with design drivers for such a system to justify the design choices. Three RF configurations are analysed and compared for omni-directional coverage and peak gain. RF measurements on one of the configurations is also presented to validate the simulations. The deployment system is also presented, giving details on the design and expected tests to complete the qualifications.@en

The frequency range below 30 MHz remains one of the last unexplored frequency ranges in radio astronomy However, Earth-based observations at these wavelengths are severely impeded, due to man-made radio frequency interference (RFI) and atmospheric opacity. To overcome this impediment, various space-based radio astronomy studies have been proposed in the past decade, notably the OLFAR (Orbiting low Frequency Antennas for Radio Astronomy) study, which proposed a satellite swarm for ultra-long wavelength observation. To realize this mission, various technological challenges of a satellite swarm are currently being addressed, particularly antenna design, navigation, communication, distributed processing, and overall system and mission design. Secondly, the RFI levels at various altitudes from Earth is currently unknown, which is a hindrance in general for radio astronomy. To this end, we propose the use of high-altitude ballooning experiments to validate OLFAR sub-systems in pseudo-representative conditions. Furthermore, these ballooning experiments will measure the RFI in the ultra-long wavelength spectrum at various altitudes from Earth. Our project is termed LOBE (Low-frequency observations using high-altitude Balloon Experiments), and in this paper, we present an overview of the science objectives, payload, and the technological and programmatic challenges of the LOBE project.

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The inter-satellite link (ISL) in swarm and constellation missions is a key enabler in the autonomy of the mission. OLFAR (Orbiting Low Frequency Array for Radio astronomy) is one such mission where 10 to 50+ nanosatellites are placed in the Lunar orbit and perform astronomical observations from the far-side of the moon. Each of the nanosatellite in the swarm would carry a receiver that performs observations between 0.3 - 30 MHz, which are the least explored frequency bands in radio astronomy, thus attracting a large scientific interest.
Observations in this frequency bands from Earth are highly challenging as the ionosphere is opaque to these frequency bands. Furthermore, RFI (Radio Frequency Interferences) generated on Earth makes it highly challenging to perform astronomical observations below 30MHz band. The impediments faced by Earth-based or near-Earth-based radio astronomy for these frequency bands is the motivation to perform measurements from the far-side of the moon.
The purpose of using a swarm of nanosatellites to perform low frequency observations is to enable the realization of long observation baselines and additionally, the effective aperture of observation increases with the number of satellites. For the swarm of nanosatellites to operate as a single aperture, it is very important to cross-correlate the information collected by each satellite and this is where the ISL becomes very crucial. Apart from exchanging data collected by the payload, other information such as attitude and timing information needs to be exchanged.
This work derived mission level requirements which would be used to define a suitable communication architecture for space-based radio astronomy missions such as OLFAR. The approach chosen for communication system for such a swarm mission will comprise of two types of ISL: High data-rate directional link that will be used to exchange payload date and low data-rate omni-directional link that will be used to exchange attitude, timing information and be used for localization, positioning and ranging of the nanosatellites in the swarm. This work will present link budgets to show the feasibility of the proposed communication architecture and derive the specs to further design the transceivers.@en

This paper discusses some of the solutions to the issue of data congestion in Nano-satellite missions. The complexity of Nano-satellite missions has increased over the years, generating more data than ever and this paradigm shift has in-turn resulted in the need for larger downlink bandwidth requirements. The larger bandwidth's necessity and limited availability of frequency spectrum in lower frequencies spectrum has resulted in the problem of data congestion and invoked the need to investigate the use of mmWave frequency bands for Nano-satellite missions. In this paper, three use cases are discussed to demonstrate the need for using frequency bands higher than X-band and the communication strategy discussed in the use-cases are not restricted to the specific application mentioned in the use-cases but can be extended to similar applications. Irrespective of the frequency bands, there is a need to adapt standards such as DVB.S2 and DVB.S2X (Satellite digital broadcasting standard) that provide spectral efficient modulation schemes. Although these well-established standards are already used in satellite communications, this work proposes further optimization on the modulation schemes that helps improve efficiency of the transmitter front-end. A comparison between 16/32-QAM, 16/32-APSK, 16/32-oAPSK and the proposed 16/32-pAPSK (Polar-filtered Amplitude Phase Shift Keying) modulation schemes are discussed. Some of the practical challenges in using mmWave communications for nano-satellite missions are addressed in this paper with a study on the state-of-the-art mmWave semiconductor technology that are suitable for SSPA (Solid State Power Amplifier) design specifically for nano-satellite missions.

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