History and current status of SISNAV: a brief report
Fausto O. Ramos∗
Independence to design and develop is crucial to technological progress. Inertial sensors
are essential elements for the operation of aerospace vehicles and systems and thus, strongly
subject to international embargo. In this work, the history of the Project SISNAV (Sistema
de Navegação Inercial ) is presented briefly. Firstly, it is introduced the roots of SISNAV
in the Program SIA (Inertial Systems for Aerospace Application), a joint initiative of
the Brazilian government to foster development, synergy and innovation in technological
areas related to inertial systems. Then, one by one the elements of SISNAV (Fiber Optic
Gyrometers, accelerometers interface and Platform Computer) are presented regarding
origin and development. The main milestones linked to ground and flight tests are also
included. Finally, a perspective of the next steps are presented, associated with new flight
tests and qualification tests, towards system certification.
I.
Introduction
In 2007, the Brazilian Government established a partnership between its Defence (MD) and Science &
Technology (MCT) Ministries1,a , in order to foster development, synergy and innovation in technological
areas. According to the MCT plan of action3 , this nationwide program aimed to ally defence needs with
industrial growth, being composed of the following activities:
1. infrastructure support for scientific and technological institutions by establishing laboratory networks
towards certification;
2. education reinforcement by human resource qualification and local aggregation in strategic areas;
3. financial resources allocation through sectoral funds;
4. partnership stimulus between military organizations, civilian institutes and universities, and excellence
centres of the industry.
The confluence of these activities formed, among other initiatives, the Project SIA (Inertial Systems for
Aerospace Applicationb ), with a budget of R$ 40,64 million4 (around US$20 million in 2007). The main
objective of the Project SIA is to develop and integrate prototypes of Inertial Navigation Systems (INS) for
aerospace applications, with participation of national industry. Some of the targeted applications were: the
launcher vehicle VLS-1c , suborbital platforms and aircrafts (Ministry of Defence / DCTAd ) and satellites
(Ministry of Science & Technology / INPEe ).
Actually, according to Dr. Waldemar de Castro (former DCTA researcher, now retired), the embryo of
SIA arose6 in 2002, with the Project SISNAVf (a synonym for INS). SISNAV aimed to provide an inertial
system to the VLS-1 launch vehicle. However, at that time there was no enough resources to advance the
initiative. Then, in 2004, Brigadier Thiago Ribeiro (another supporter of SISNAV) made a proposal to
∗ Head of the Control Group at DCTA/IAE: Praça Marechal Eduardo Gomes, 50, 12228-904, São José dos Campos, São
Paulo, Brazil. Email: [email protected]. Tel.: +55 (0)12 3947-5129.
a The decree no 750 was recently substituted by the decree no 8192 .
b From the Portuguese acronym Sistemas Inerciais de Aplicação Aeroespacial.
c From the Portuguese acronym Veículo Lançador de Satélite.
d From the Portuguese acronym Departamento de Ciência e Tecnologia Aeroespacial. DCTA was formerly CTA (before
2009), with two denominations5 : up to 2006, Centro Técnico Aeroespacial, then Comando Geral de Tecnologia Aeroespacial.
DCTA website: http://www.cta.br .
e From the Portuguese acronym Instituto Nacional de Pesquisas Espaciais. INPE website: http://www.inpe.br .
f From the Portuguese acronym Sistema de Navegação Inercial.
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DEPEDg (today known as DCTA5 ), regarding a financial support to inertial systems development, which
was achieved in 2005 through defence sectoral funds. The process continued in 2006, with a consultation
with MD about priority themes for subventions (aiming private companies of the defence segment). Finally,
SIA was formally born in 2007, benefiting not only SISNAV, but many other projects related to inertial
systems, developed byh governmental institutions (MD / DCTA / IAE, ITA and IEAv, and MCT / INPE)i
and private companies (OPTSENSYS, NAVCON and MECTRON, to name a fewj ).
II.
Birth and conceptions of SISNAV
In 2002, the purpose of SISNAV was to replace the VLS-1 inertial system, provided by Russia, composed
of a gimballed inertial platform, DTGs (Dinamically Tuned Gyros) and a computer, for a Brazilian INS,
designed and developed by DCTA/ IAE. The objective was clear: to update sensor technology (strapdown
platform, FOGs - Fiber Optic Gyros, accelerometers and a modern computer) and to avoid trade embargo.
Regarding the FOG, its research started in DCTA / IEAv in the 80s9 . The main difficulties faced by
the design team were related to the reduction of the long term drift, the linearization and stabilization of
the scale factor, the increase of the dynamic bandwidth, and the reduction of the detection noise. Besides,
other difficulties were also present when dealing with the constraints for applications (e.g., sounding rockets):
dynamic environment, flight time, electrical consumption, thermal dissipation, mass and volume, dynamic
bandwidth and resolutionk .
Overcoming such difficulties, in 1998 a FOG prototype (Fig. 1) was successfully tested9 during the flight
of a VS-30 sounding rocket (provided by MD / DCTA). Further flight tests were conducted, now with the
company OPTSENSYSl having the duty to produce the FOGs:
1. SDVm experiment, composed of 2 FOGs aboard VS-30 sounding rocket11 (2007; see Fig. 2 - Operation
Cumã II12 , DCTA and OPTSENSYS);
2. tri-axial FOG unit aboard MAR-113,n missile (2008; DCTA, OPTSENSYS and MECTRON).
Accelerometers. SISNAV team opted to develop only the electronic interface of the accelerometerso .
Therefore, asked by DCTA/IAE, in 2002 the company NAVCON sent a proposal to design, produce and
test a digitalization unit, based on V/F (Voltage-to-Frequency) converters. The electronics was packed in a
PC-104 form factor board.
Regarding the SISNAV platform computer, the brand PC-104 is also important to mention. Being offthe-shelf, it was a natural choice to easily and quickly build and integrate processor, V/F card (accelerometer
interface), serial channels (to FOGs), additional A/D and I/O interfaces and so on. The system aboard the
VS-30 vehicle for Operation Cumã II was built with that architecture.
III.
Integration and tests
Since the beginning of SISNAV, its individual components had been developed and tested individually.
Then, in 2008, an integrated configuration of SISNAV (named CSM)p was conceived by DCTA/IAE. CSM
was proposed as an experiment of Mission Maracati II14 (2010) , being composed of:
g From
the Portuguese acronym Departamento de Pesquisas e Desenvolvimento.
the following cited entities are located at São José dos Campos, the same city of the main headquarter of EMBRAER
(a Brazilian aerospace conglomerate that produces commercial, military, executive and agricultural aircraft)7 . EMBRAER
website: http://www.embraer.com .
i From the Portuguese acronyms: Instituto de Aeronáutica e Espaço, Instituto de Estudos Avançados and Instituto Tecnológico de Aeronáutica . Websites: IAE = http://www.iae.cta.br, IEAV = http://portal.ieav.cta.br and ITA =
http://www.ita.br .
j For a detailed list, see the study released by CGEE8 - Centro de Gestão e Estudos Estratégicos.
k Additional constraints apply for on-board equipments, regarding robustness against qualification tests under environmental
conditions: vibration (sinusoidal, random and shock), temperature, humidity, electromagnetic compatibility and electro static
discharge, vacuum and acceleration.
l The company OPTSENSYS was formed with former employees of the DCTA / IEAv Sensors Subdivision9 . OPTSENSYS
website: http://www.optsensys.com.br .
m From the Portuguese acronym Sistema Dinâmico de Vôo. The Fig. 2 is a translated photo10 .
n From the Portuguese acronym Míssil Anti Radar .
o Years later, an MCT group of strategic studies stressed the need of designing and developing Brazilian accelerometers8 .
p From the Portuguese acronym Conjunto Sensor de Movimento.
h All
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Figure 1: First FOG prototype developed by IEAv and tested during a VS-30 flight9 (1998).
Figure 2: Cumã II experiment, SDV (Sistema Dinâmico de Vôo), composed of 2 FOGs. (2007) .
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1. a platform computer (PC-104 card);
2. an accelerometer digitalization interface (PC-104 V/F card);
3. three accelerometers;
4. fourq Brazilian FOGs, with part of their electronics housed separatelyr ;
5. a physical support to which are attached the sensors;
6. ground control lines and telemetry communication channels;
7. a dedicated battery.
The participation of CSM in Maracati II was later cancelled, but its conceived architecture was adapted
and produced by the same DCTA / IAE team, for two ground tests16 , named Operation Parque I (2010, Fig.
3a) and Operation Parque II (2011, Fig. 3b). A roller coaster was employed for performance evaluations .
Some remarks for these tests:
1. the FOGs used in both tests were off-the-shelf (international supplier), since it would be easier to check
SISNAV concept and algorithms independently of the FOG development;
2. the tetrahedral FOG configuration of the Parque I was replaced by a trihedral one in Parque II ;
3. a second system was added to the Operation Parque II, in addition to the original SISNAV system; this
new system was built around an off-the-shelf INS, GPS-aided, whose measurements could be compared
to those of SISNAV.
A parallel development of a dedicated platform computer was also started at that time. In 2010,
DCTA/IAE specified the requirements for ProcSISNAV (SISNAV Processor), which resulted in a contract
with the company MECTRON. This processor would aggregate the main functions of the previous PC-104
architecture, with improved robustness. Reason: compliance with the harsh environment of a launch vehicle
(VLS-1) and other correlated aerospace applications.
Linked to the ProcSISNAV development, the Brazilian FOG also was following its pace. The OPTSENSYS and DCTA/IAE teams redefined the sensor configuration, so that all the electronics needed was then
embedded in the FOG itself, reducing mass and electrical/optical connections. Not so good for performance
(as observed before), but just fine for an onboard system of an aerospace application.
One can see that two versions of SISNAV were coexisting: Parque I/II (for ground testing) and VLS-1
(for flight testing). Regarding this last one, the description given in the preceding two paragraphs can be
summarized in the Fig. 4, that particularly shows the FOG evolution. The remaining FOG electronics (low
profile box at right in the Fig. 4b) was only its power supply, which could even migrate to ProcSISNAV.
Tests. One can now devise another benefit of Project SIA to SISNAV: infrastructure. The inauguration,
in February 2011, of the Laboratory of Identification, Control and Simulation18 (LINCS, Fig. 5)t , expanded
considerably the former DCTA/IAE resources for testing and simulation of inertial sensors and systems. This
facility comprises several 3-axes and 2-axes tables for dynamic and environmental tests (thermal, vacuum and
acceleration). In addition, there are setups for actuator identification, accelerometer characterization and
testing of attitude control platforms (air bearing table). There is even a setup for structural identification
(bending, torsion and sloshing). Finally, with the LabView environment, one can range from simple sensor
characterization to complex real-time Hardware-In-The-Loop simulations.
A second DCTA/IAE laboratory was inaugurated in July 2013, named LabSIA19 (an obvious acronym)u .
This facility (Fig. 6) has double purpose:
• fiber-optic winding and FOG integration;
q Only 3 FOGs would be used for inertial measurement of angular rates, added by a spare FOG to tackle single sensor failure.
In other words, a redundant scheme.
r Though many FOG suppliers claim that the main reason for coil separation from electronics is versatility of implementation,
it has to do with performance as well15 .
s The roller coaster idea was borrowed from a master thesis of a Swedish university student17 .
t From the Portuguese acronym Laboratório de Identificação, Navegação, Controle e Simulação .
u From the Portuguese acronym, Laboratório de Sistemas Inerciais para Aplicação Aeroespacial.
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(a) Parque I
(b) Parque II
Figure 3: SISNAV setups for Operation Parque I and Operation Parque II
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(a) SISNAV, with FOG’s optic coil separated from electronics.
(b) SISNAV, with embedded electronics FOG.
Figure 4: VLS-1 SISNAV and the evolution of the FOG.
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Figure 5: Laboratório de Identificação, Navegação, Controle e Simulação 18 .
• an MCT/INPE development and testing environment for SISCAO (Attitude and Orbit Control System
for Orbital Platforms), integrating additional SIA projects: onboard computer (CBPO), tetrahedral
FOG unit (BGPO), control simulator (DVT) and software (SCPO, stellar sensor = SES), and support
equipment for testing and simulation (EAPO).
IV.
Current status and perspectives
Currently, there are two SISNAV offsprings being developed:
• the VLS-1 SISNAV (Fig. 4b), almost ready for qualification tests;
• the SISMIv (Inertial Measurement System, see Fig. 7), a more robust version of the PC-104 system
used in Parque I/II, although without the navigation algorithm.
For VLS-1 SISNAV, a flight test is planned aboard VSISNAV (a VLS-1 derivative). However, due to
VSISNAV program reconfiguration by DCTA/IAE, the launch mission schedule is not still available.
For SISMI, it is planned to fly aboard VS-40M vehicle21 , inside the SARA Suborbital I payload. The
flight is expected to the 2nd semester of this year. Despite the spinning dynamics of VS-40M, SISMI has its
longitudinal sensing FOG designed with a convenient measuring range.
Finally, certification is required from SISNAV in order to be aboard VLS-1 and other controlled vehicles,
as the main INS. The certification entity is IFI (Industrial Fostering and Coordination Institute)w and the
certification is to be acquired in medium-term, after validation by qualification tests and a full experimental
flight. Such flight will test hardware, software (mainly that related to INS algorithms) and system robustness
according to the aerospace environment. Also regarding certification, the standard ISO 17025 is being
implemented in LINCS laboratory.
Despite some “headwind” for the SISNAV successful achievement, regarding the nearby ending of the
Project SIA and some crescent deficit of human and material resources faced by DCTA22 and INPE23 , the
v From
w From
the Portuguese acronym Sistema de Medição Inercial.
the Portuguese acronym Instituto de Fomento à Indústria. IFI website: http://www.ifi.cta.br/en .
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(a) External view of LabSIA19 .
(b) Optic coil winding machine19 .
(c) SISCAO environment20 .
Figure 6: LabSIA facility.
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Figure 7: SISMI tests in LINCS 3-axes table. Bottom right: exploded internal view.
Brazilian society is anxiously waiting for a fruitful conclusion of such initiative, which will consolidate the
country position in the aerospace international scenario.
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