• Author: Roascio Danilo PhD
  • Description:

    This research activity develops in the rapidly and constantly growing field of
    avionics for small satellites. The relatively widespread availability of low-cost piggyback
    launch opportunities recently provided to an heterogeneous set of entities
    the access to orbit. Universities, industries, local governments and even amateurs,
    all became interested in space and the rather unique opportunities offered by its
    This led to the development of a large number of nano and pico-satellite missions,
    respectively with spacecrafts of mass lower than 10 kg and 1 kg orbiting in Low Earth
    Orbits (LEO) under 700 km of altitude. Such tiny satellites are usually built with
    commercially available electronic components not qualified for the space environment,
    allowing for savings along the whole development cycle in recurring and non recurring
    costs. Design re-use extends the cost reduction to the system level, with an aggressive
    exploitation of existing technologies and, possibly, of space-flown architectures.
    Communication subsystems, a small but critical set of elements common to every
    mission, are not exempt from such a philosophy. On-board networks, on-board
    transceivers, antennas, ground stations, and the protocols in between them are all
    critical elements for a spacecraft mission and, at the same time, some of the most
    specialized and complex ones. Design re-use is then sought at every level, to the point
    of favoring “old and trusted” technologies in spite of lower performances and reduced
    While this was acceptable for pioneer pico-satellite missions, with the growth
    of the scientific goals the traditional trade-offs are not appropriate anymore. Even
    further, the stream of innovations coming from the ground mobile market is not being
    adequately exploited and today outdated communication architectures set — rather
    than match — mission capabilities and achievable goals.
    This research aims at finding new solutions to common problems becoming prevalent
    in this field. Better trade-offs are needed in the ground and flight communication
    segments and in the elements linking them. Better performances are achievable with
    an increase in system complexity, always taking into account energy, mass and cost
    In chapter 1 we will start from the communication systems of the ground segment,
    the moving antennas that track and provide communication with LEO satellites as
    they fly by over them. A typical pass of a LEO satellite over a ground station, from
    rise to set, lasts about 10-15 minutes on average. For a single ground station and an
    high-inclination orbit, the number of passes/day can be as low as 2. This limits the
    contact time with the spacecraft with understandable restrictions on the spacecraft
    control and data retrieval capabilities of the mission. At the same time, the ground
    station itself is heavily underused and a networking effort with other universities and
    individuals, the GENSO network, will be able to provide relevant improvements.
    During the design and developement of the GENSO network other limitations
    of the current, typical, pico-satellite architecture became apparent. The concern for
    security of transmitted data and, thus, of the mission itself, demonstrated that the
    lack of confidence in the network may hinder the adoption rate of leading missions.
    While all the communications within the network are kept secure by industry-standard
    public-key encryption protocols, the signals at a certain remote station will
    leave the network to be transmitted to space. The current paradigm of pico-satellite
    missions relies on security through obscurity and, at the very least, this can be easily
    undermined by statistical analysis of the outgoing data. Chapter 2 investigates the
    security problems and proposes a strategy based on peer reviewed standards to solve
    them. The choices are shown to be compatible with the requirements of nano and
    pico-satellite missions.
    Nonetheless, for a proper and permanent solution based on asymmetric, public-key
    protocols, the need for on-board programmable logic becomes apparent. The current
    approach, relying on simpler and lower power microcontrollers, is quickly becoming
    dictated more by convenience than by energy savings. This point, along with many
    others, will be addressed later in chapters 4 and 5.
    Chapter 3 focuses instead on attitude determination systems and a gap in the
    capabilities of the available sensors. While this topic may sound unrelated to communication
    systems, it will be shown how an all-analog phase-tracking receiver is
    potentially able to provide an accurate attitude reading in a less structurally-invasive
    manner compared to existing solution.
    Even though this solution may better fit micro than nano-satellites, during its
    implementation it quickly became apparent that the reliability and power savings
    offered by analog components come with a relevant board area penalty. At a given
    complexity level, the fast evolution of digital architectures is becoming a much more
    flexible approach.
    As will be envisioned in chapter 4 and shown later in chapter 5, the commercially
    available digital solutions are becoming compatible with the tiny resources available
    on-board pico-satellites. But, more importantly, they are being demanded by the
    growing needs of missions.
    More work is needed to make an all-digital pico-satellite transceiver a reality, but
    this will be discussed with some closing remarks in chapter 6.

  • Year: 2013
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