Aerospace and Electronic Systems Magazine May 2018 - 58

Flexible CubeSat-Based System for Data Broadcasting
to remote areas such as North and South poles that are not covered
by geosynchronous satellite's footprints. In addition, the resilience
of satellite technology with respect to terrestrial infrastructure is
the value proposition of the proposed solution. The adoption of
CubeSat and therefore of CubeSat constellations represents a good
opportunity and an innovative solution for the delivery of broadcast messages in different application contexts. This is enhanced
by the CubeSat standardization, low cost of COTS electronics, and
new launch opportunities. Finally, it is worth underlining that, to
the best of our knowledge, the proposed CubeSat-based system
and the D-SAT mission are the first application of these concepts
and strategies to the data broadcasting in emergency scenarios: the
results of the mission demonstrate that this original approach is
effective in terms of performance, coverage, and costs [13], [14];
moreover the specific context of emergency and the need of delivering alert messages to the population over a large area led to the
adoption of satellite technology that may represent the only solution to reach the intended audience in time.

SYSTEM MODEL
The high-level architecture of the proposed flexible CubeSatbased system for data broadcasting is depicted in Figure 1. To better analyse the functioning of the whole transmission and reception
chain, following the information flow from the source (left side) to
the destination (right side), three macrofunctional components are
identified and detailed. These are:
C
C

Data gathering, processing, and message upload.
CubeSat message reception, on-board processing, and
broadcasting.
Broadcast message reception and interpretation.

DATA GATHERING, PROCESSING, AND MESSAGE UPLOAD
The Data Source can be represented by sensors distributed over
a monitored area or by other sensing/monitoring systems. It is responsible for gathering raw data and transmitting them to a collector for a preliminary processing.
The collector, named the Data Processing and Formatting
Unit (Figure 1), is in charge of processing the raw data coming
from the Data Source and generating an opportunely formatted
message that includes all the needed information extracted from
the received data. Different transport protocols and formats can
be implemented by the Data Processing and Formatting Unit,
depending on the specific application context. An example is reported later in this article.
The message is then received by the Satellite Earth Station-
Mission Control Center (MCC), which proceeds with the upload of
it to the CubeSat for the consecutive broadcasting.
As highlighted in Figure 1, the interfaces between the Data
Source and the Data Processing and Formatting Unit (Interface I1)
and the one between the Data Processing and Formatting Unit and
the Satellite MCC need to be defined to allow the proper information exchange among the involved entities. Details on a possible
implementation of such interfaces are reported later.
58

C ube S at MESSAGE RECEPTION, ON-BOARD PROCESSING
AND BROADCASTING
The space component is represented by a CubeSat, whose main
functions are: i) the reception of the messages uploaded by the Satellite MCC; ii) the processing of the received messages and consecutive storage of them, if needed; iii) the messages broadcasting.
Without losing in generality, in this section, the implementation of a CubeSat (named D-SAT) is described. D-SAT, that is
shown in Figure 2, despite of its compact dimension [(30 × 10 ×
10) cm3] and its mass lower than 4.5 kg, includes all the typical satellite subsystems. The On-Board Computer (OBC) comprises Attitude and Orbit Control System (AOCS) sensors (magnetometers,
sun sensors, gyroscope) and the drivers for AOCS magnetorquers.
The core of the OBC is a flight proven High-performance ARM7
Central Processing Unit.
The OBC has an on-board timer which is synchronized with
Coordinated Universal Time by means of a Global Positioning
System receiver within the satellite. The communication subsystem consists of an Ultra High Frequency (UHF) radio module and
a turnstile antenna. The Electric Power System includes batteries
and solar arrays and the D-Orbit Decommissioning device that has
been conceived to dispose the satellite.
In details, the communication subsystem includes an omnidirectional antenna and an UHF transceiver that uses a Gaussian
Minimum Shift Keying (GMSK) modulation over Frequency
Modulation signal at a baud rate of 4,800 bps. The bandwidth
of the signal is 14.6 kHz. For further information, the CubeSat
GMSK bandwidth is 4,800 Hz and frequency deviation is 2.5 kHz.
The data are coded with a Reed-Solomon (223, 255) coding and
randomized according to the Consultative Committee for Space
Data Systems (CCSDS) standard to reduce the probability of error and therefore increasing the reliability of the communication
link. The choice of UHF band is the result of a trade-off between
different bands: very high frequency (VHF), UHF, L-BAND, SBAND, and X-BAND. Technical and Programmatic criteria such
as Complexity of on-board and ground radio equipment, antenna
dimension, antenna gain, path-loss, atmospheric attenuation, Doppler effect, radio frequency license, and development cost were

Figure 2.

D-SAT flight and qualification models in D-Orbit clean room facility-
courtesy of D-Orbit.

IEEE A&E SYSTEMS MAGAZINE

MAY - JUNE 2018

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine May 2018