Advanced technologies for
the development of an antenna reflector with lower mass and higher geometric
accuracy - ITAR
Funding agency: ROSA,
Project no. 135 /2017
Coordinator: National
Research and Development Institute for Gas Turbines COMOTI
Project Leader: Eng. Mihai
Dragos
Partners:
High Performance Structures Inovatie si Dezvoltare SRL
Partner project manager Eng. Astrid Mihaela Cojocaru Draguleanu
National Institute for Research and Development in Optoelectronics
- INOE2000
Partner project manager Dr. Viorel Braic
National R&D Institute for Cryogenics and Isotopic
Technologies
Partner project manager Dr. Eng. Mihail Culcer
Abstract
Objective
Reflector
performance on communication satellites is primarily determined by factors such
as the weight-to-stiffness ratio, thermo-elastic behavior, and the electrical
and thermo-optical properties of the surface coating.
Reflector
performance on communication satellites is primarily determined by factors such
as the weight-to-stiffness ratio, thermo-elastic behavior, and the electrical
and thermo-optical properties of the surface coating. Antennas are susceptible
to large temperature variations based on the spacecraft mission. The orbit
parameters, thermo-optical characteristics (solar absorptivity, IR emissivity,
transmissivity), sun incidence, and radiative and conductive couplings with the
surrounding spacecraft components all affect the temperatures that the
materials experience during thermal cycling. The reflector's material and
geometry should minimize thermomechanical deformations, and the application of
a low resistivity coating should maximize the electrical conductivity of the RF
reflecting area. Appropriate coatings with spectral filtering capabilities
could reduce the thermal optical effects of solar radiation.
The
challenge is to maintain the on-orbit thermal distortion surface accuracy as
low as possible (RMS<50µm) in order to create a low mass antenna reflector
that can withstand a wide temperature range. From a material standpoint,
titanium is one of the best options for guaranteeing the aforementioned
specifications for reflectors. The task at hand involves achieving a low mass
antenna reflector capable of withstanding a broad temperature range while
preserving the lowest possible on-orbit thermal distortion surface accuracy
(RMS<50µm). From a material standpoint, titanium is one of the best options
for guaranteeing the aforementioned specifications for reflectors. Controlling
the residual stress caused by the manufacturing process in the surface or close
to the surface of titanium reflectors is a challenging task because it can
impact the accuracy of the reflector surface and, in turn, the antenna
performance. Several manufacturing technologies will be examined in order to
enhance the physical properties of the reflector and control the residual
stresses induced. In addition, a reflective coating will be created to enhance
the reflector's capacity for radio frequency (RF) transmission.
Starting
with a titanium reflector concept made entirely of one part (a parabolic dish
with a back rib structure), the design activity will aim to obtain a minimum
thermo-elastic distortion of the reflector surface and structure in a high
temperature range.
After
formulating its concept, the reflector development begins at TRL 2 and seeks to
validate the demonstrator through TRL 5. The reflector's design will be
optimized using thermo-elastic finite element analysis to ensure that it meets
all requirements and has the lowest mass.
Following
the definition of the manufacturing technologies, two breadboards will be
produced using different machining techniques to assess how the induced
material stress affects the reflector geometry. A test campaign including
vibration testing, thermal vacuum cycling, and surface electrical conductivity
will be conducted on the breadboards. Prior to and following the testing
campaign, the manufactured breadboards will be inspected using a high accuracy
coordinate measuring machine.
To ascertain the impact of the
space environment on the reflector, a dedicated thermal-vacuum testing facility
will be created. The levels of expansion and contraction on the reflector can
be checked using thermal vacuum cycling, and the distortions that are found
will be assessed using a laser-based measurement device designed especially for
this test.
Using
the breadboard test results, an optimized design for the reflector demonstrator
shall be developed and the process engineering updated. Based on the improved
design and technology the reflector demonstrator will be manufactured and
validated up to TRL5 according to the previously defined test plan.
The
project's intended outcomes include a fully optimized manufacturing process
that was developed through testing and validation. This process will serve as a
model for future research and development of extremely light satellite antenna
reflectors with the best surface and in-orbit accuracy. It is anticipated that
the project consortium will be able to create metal antenna reflectors that
could satisfy every possible customer need for reflectivity and stability as a
result of optimized manufacturing technology and design.
The
most preferred option for satellite antennas is a reflector antenna due to its
lightweight, straightforward structure, and well-developed design. While
special reflector antennas are made for particular uses like meteorology,
cross-link, earth coverage, and auto tracking, communication reflector antennas
are primarily used for tracking, telemetry, and command operation throughout
the mission phases.
The
suggested work could benefit deep space mission and in-earth observation
programs in addition to future ESA missions in the area of integrated systems
and telecommunication.
The
primary goal of the ITAR project, which aims to secure Europe's future in the
global satellite communications market, is in line with the main objective of
the Advanced Research in Telecommunications Systems (ARTES) Program of ESA. The
project's output could be readily improved upon, qualified at the highest level
of design, and adapted to the best possible solution for the target market
within the framework of the ARTES program.
Specific objectives for INOE 2000:
v Competencies
in developing specialized thermal-vacuum testing capabilities in accordance
with mission requirements;
v Reflective
coating materials for the antenna and technological know-how;
v Test
capacities for vacuum-thermal cycling up to the limits set by the testing
chamber
Results:
- System
for space conditions thermal vacuum testing of satellite dish antennas
The
system for space conditions thermal vacuum testing of satellite dish antennas is aiming to
expose the coated satellite dish breadboards to representative space conditions
– a vacuum state combined with repeated cycling between high and low thermal
extremes, such as their likely flight performance to be assessed.
In
vacuum the heat transfer occurs only by radiation, as the convection is no
longer possible in the absence of air. In space, at the transition zone, the
parts facing the sun become hot while those facing deep space keep cool, the
resulting thermal gradients inducing thermal deformation and stress. The
thermal vacuum testing (TVAC) represents the closest possible
replication of space conditions being reproduced on the terrestrial surface,
with prolonged testing serving to identify otherwise unknown defects in
materials, processes and designs.
Thermal
vacuum testing chamber for TVAC developed in INOE 2000
Schematic
view of the TVAC comprising:
§ Vacuum
chamber: 60 cm diameter, 50 cm long, 2
sliding doors, water cooled walls.
§ Vacuum
pumping unit: 500 l/s turbopump, 12 mc/h mechanical pump.
§
Thermal envelope: Cu sheet with
brazed Cu pipes for liquid nitrogen circulation and SS thermal shield; 6 kW heating quartz lamps.
§ Controls: 1 PC data acquisition from 8 thermal sensors,
3 vacuum ,
gauges, 4 liquid nitrogen valves; 1 PC data acquisition from laser
optical module.
Thermic
excursion cycle of an antenna: starting temperature(+21
oC), lowest temperature(-170 oC), and final temperature (+23 oC) with limited gradient temperature
Satellite
dish antenna breadboard evaluation for mechanical deformation of the parabolic surface
during TVAC – performed through laser beam illumination of the surface and
image capturing by HD camera and subsequent image analysis.
- Thermal
vacuum cycling (TVAC) of satellite dish antenna breadboards
Simulated
space environment conditions:
ü
Vacuum < 5.10-6
mbar;
ü
Temperature range: -175 oC ¸ +175 oC;
ü
Temperature gradient < 2 oC/min;
ü
Number of cycles: 8 with 2 h
plateau at the 2 extreme points.
Vacuum test facility from INOE 2000 used for
thermal tests in relevant space conditions,
with a breadboard inside
Antenna
thermal testing over the course of temperature cycle
Unitary shear forces for carbides
brazed with Cu alloy
:
+26 oC → -170 oC
→
+170 oC → +38 oC
- Low resistivity
Copper-Carbon and silica-ZnO based coatings with
thermo-optical properties for antenna reflectors intended for space
communication
Antenna reflector performance on communication satellites is
primarily determined by factors such as weight-to-stiffness ratio,
thermo-elastic behavior, and electrical and thermo-optical properties of the
surface coating. In order to keep the system operating within a temperature
range that is safe, the antenna must present an electrically conductive
surface, have high reflectivity, low absorbance in the solar spectrum, and high
emittance in the infrared. We report on the deposition of thick ZnO-silicate composite thermal control coating, transparent
to microwaves, and low carbon Cu-C coatings by HiPIMS
on TiAlV.
The necessary thermo-optical properties for a space communication
antenna are low solar absorptance (α<0.2) and high IR thermal emittance
(ε> 0.9).
The manufactured system as a whole demonstrated the necessary thermo-optical
properties: α<0.139 and ε> 0.939.
Coated antenna reflector demonstrator
According to XRD analysis, the carbon content and coating grain
size have an impact on the electrical resistivity of Cu-C coatings. As per ASTM
D3359 method B, a better adhesion of the coatings to the Ti6Al4V substrate was
achieved. The ZnO-silicate composite thick thermal
control coating, which was transparent to microwaves, was sprayed on the Cu-C
coated samples. This allowed the system to exhibit the necessary thermo-optical
characteristics for a space communication antenna, including low solar
absorptance (α<0.2) and high IR thermal emittance (ε> 0.9).
Additionally, eight temperature cycles in the range of -170 0C
to +170 0C were applied to the coated antenna.
Thermo-optical characteristics of the coated space communication
antenna:
low solar absorptance (α<0.2) and high IR thermal
emittance (ε> 0.9).
Observed
standards – European Cooperation for Space Standardization
1. ECSS –
E – ST – 10 – 02C/6 March 2009 – Verification
2. ECSS – E – ST – 10 – 03C/1 June 2012 – Testing.
Papers
published and presented at international conferences
“ Design,
analysis and evaluation of titanium antenna reflector for deep space missions”,
D. Mihai, R. Mihalache, I.F. Popa, I.S. Vintila, D. Datcu, I. Ciocan, V. Braic,
I. Pana, A.E. Kiss, N.C. Zoita, P. Burlacu, Acta Astronautica
184 (2021) 101-118, doi:
10.1016/j.actaastro.2021.04.006
"System for space conditions
thermal vacuum testing of satellite dish antennas", V. Braic, D. Mihai,
N.C. Zoita, M. Braic, R. Mihalache, A.E. Kiss, 18th International
Balkan Workshop on Applied Physics, 11 – 13 July 2018, Constanta, Romania.
“Low resistivity Copper-Carbon
and silica-ZnO based coatings with thermo-optical
properties for antenna reflectors intended for space communication”, C.N.
Zoita, I. Pana, C. Vitelaru, D. Mihai, R. Mihalache, A.E. Kiss,V.
Braic, XXth
International Conference on Plasma Physics and Applications, 14th –
16th June, Iasi, Romania