Brochure

Changing the economics of space
Antenna Pointing Mechanism (APM)
Sales Brochure
Ref: ST#0159689-005, March 2013
Introduction
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The APM is low-cost mechanism designed to
complete the payload downlink chain. Currently
the downlink chain utilises X-band.
The X-APM currently employs a narrow-angle
horn antenna to focus the X-band RF energy into
a high-gain spot-beam.
The 2-axis mechanism steers the horn antenna
to track the position of the Ground Station during
a pass to relay satellite payload data to the
ground.
The agile mechanism is able to track the Ground
Station even if the satellite performs high-slew
rate manoeuvres.
Two X-APM variants are currently available:
18dBi (Carbon Fibre horn) and 15dBi (Aluminium
horn).
Two 15dBi X-APMs are used on NigeriaSat2
(SSTL-300, 2.5m resolution imager), launched in
August 2011, and operating perfectly.
The 15dBi X-APM is baseline on 3 other SSTL
current projects: KAZ-MRES (SSTL-150),
NovaSAR, and the DMC-3 constellation (SSTL300-S1).
The 18dBi X-APM is flying for the first time on
TechDemoSat-1 (TDS-1, SSTL-150 structure),
expected to launch in 2013
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18dBi (left) &
15dBi (right)
X-APMs
TDS-1 with
2 APM
18dBi
Space Downlink Solution and Features
The APM enables low
transmitter power consumption
and reduced ground-station
dish size for comparable data
rates as conventional antenna
X-APM Features:
– Cost effective and versatile
– Low mass and small volume
– Flight heritage (NigeriaSat-2
launched Aug ‘2011)
– ITAR-free design
– CAN or RS422 interface
– Detailed feedback, including
position, temperature, current
X-Band Transmitter
(XTX) and X-APM
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System Benefits
• The use of SSTL's +18dBi APM is expected to yield an
improvement to the downlink Effective Isotropic
Radiated Power (EIRP) in the order of 13 to 17 dB,
compared to a common Isoflux antenna configuration.
• These figures take the APM's insertion losses into
account and assume a nadir pointing spacecraft.
• The exact improvement will depend on the required offnadir angle relative to the Ground Station during
operation.
• The increase in EIRP can be traded off against other
link budget parameters such as data rate, RF output
power, ground-station performance and link margin.
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Architecture
• The APM is modular, which
provides a highly versatile design
baseline
• The APM comprises the following
elements:
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X-Band antenna & RF Harness
Elevation drive module
Azimuth drive module
Electronics module
Associated brackets
joining the modules together
• The APM has 2 electrical interfaces:
– 50 Ohm RF SMA connector
– 15 way D-Type harness connector
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Architecture (cont)
• Each axis of rotation is an
independent module, each of
which comprises:
Elevation
Axis
– Hybrid stepper motor with integral
planetary gearbox (actuator)
– Spur gear transmission (with antibacklash pinion)
– Precision angular contact bearings
– Magnetic encoder (datum and pulse)
• Mechanical and electrical end
stops are present
• A spiral wrap DC harness passes
motor and telemetry channels
through the Azimuth axis to the
Elevation axis
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Azimuth
Axis
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Architecture (cont)
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The RF connection is completed from the
mechanism interface to the X-band
antenna, through 2 axes of rotation, via
non-contact RF rotary joints
The X-band horn antenna is mounted on a
Septum which sets the circular polarisation
of the RF signal (RH or LH), prior to the
horn focussing the energy
S/C interface can be altered easily by using
a different interface plate between
mechanism and S/C
S/C mounting plane
The APM design includes novel geometrical
placement and the use of counterweights to
balance it about both axis. There is no
resultant out of balance force, and hence no
launch locks are needed, and the APM
does not move during launch: improving
cost and reliability. This means that the
APM can be mounted off-axis too
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The SSTL Approach and the X-APM
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Invest in a focussed design phase,
designing with large margins, whilst still
being mass-economical
Some analysis is used to verify design
before committing to manufacture
Rapid design cycle allows Engineering
Models (EM) and thereafter Qualification
Models (QM) to be manufactured and
committed to thorough test campaigns
early, with rapid response to lessons
learnt
Focus is placed on product flexibility and
adapting to future uses within the market
place. As a result the APM is modular,
and has large margins on structural
brackets, bearings and actuation torque
Modularity is demonstrated by the lower
axis of the EM APM being altered into a
low-power (300W) SADM, completing a
60,000 cycle life test
ECSS directives are used as guidelines
through design rather than exclusively,
however, many aspects meet ECSS
specification through SSTL’s approach
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Finite element structural analysis
EM APMs
QM APM
SADM
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The SSTL Approach and the X-APM
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SSTL remains a pioneer in affordable small-satellite technologies, and one way this
is achieved is through employing Commercial Off The Shelf (COTS) components
where applicable, whilst also offering high performance
COTS suitability is assessed, to ensure high-reliability is retained
Where COTS components are not directly suitable, SSTL works with suppliers or
performs in-house modifications to COTS components to achieve space-suitability,
whilst retaining cost-effectiveness
APM examples of COTS technologies:
Commercial magnetic
sensors as position
encoders, and gears
as transmission
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Commercial vacuum
stepper motors (with
vibration modification)
Commercial bearings
lubricated in-house
Commercial electronic
components on
printed circuit boards
However, SSTL does also have experience with full ECSS-specification
developments and relationships with suitable suppliers, if there is requirement
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X-APM Qualification Model Testing History
Functional & RF testing (pre-EVT)
Thermal
vacuum
life test:
28,500
cycles
Vibration test
(missionspecific levels,
15grms X and
Y, 16.5grms Z,
see appendix)
Functional & RF testing (post-EVT)
Vibration test
to higher
generic levels
(21grms for
15dBi,
20grms for
18dBi, see
appendix)
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Extended life-test in
vacuum: additional
280,000cycles (no failure)
Ambient life test 74,000
cycles to date (18dBi)
Further vibration & life
test activities planned…
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Qualification Specification
Parameter
Achieved / Qualification
Notes
Pointing accuracy
<0.25 °
Step size / resolution
≤0.024 °
Slew range
Azimuth: ±270 °
Elevation: ±110 °
Measured during test.
(+/-110°Elevation range possible
for 18dBi axis depending upon S/C
accommodation)
Slew rate
≤ 20.0 °/s
SSTL missions typically drive at
1-2°/s, & 8°/s in extreme scenarios
Acceleration
<5 °/s 2
Both axes
First Modal Freq
>140 Hz
To avoid S/C mode coupling
Random Vibration
21.2grms 15dBi X-APM
20.0grms 18dBi X-APM
See ICD for exact profiles
Radiation
The TID requirement at the Control electronics shielded by
PCA is <5krads(Si)
mechanism and S/C panel. 3mm of
shielding provided by the
mechanism typically assumed
1mm from panel.
Encoder sensors above S/C
mounting plane qualified separately
– no degradation below 12.5krads
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Qualification Specification (cont)
Parameter
Achieved / Qualification
Notes
Life
7.5 years
Electrical life
No. Qual Cycles
>28,500 cycles (TVAC) +
further >280,000 cycles
(VAC only)
Large margin on SSTL mission
requirements (typical SSTL in-orbit
usage equates to 16,000 cycles)
Survival
Temperature
-50°to +70°C Mechanics
-30°to +60°C Electronics
Proven via thermal vacuum life test
on QM APM
Operational
Temperature
-40 °to +60 °C Mechanics
-20 °to +50 °C Electronics
Micro-vibration
Minimised – see following
slides
Total mass
3.0 kg +/-5% for 15dBi. 3.25kg +/-5% for 18dBi
Power
3.9 W dynamic operation
(28V and 5V powered)
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Through micro-stepping of stepper
motor driver and low speeds
1.3W static operation (5V powered
only), operating voltage 28+/-7V,
5+/-0.25V.
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Qualification Specification (cont)
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Parameter
Achieved / Qualification
Notes
RF Frequency
8.0 – 8.5 GHz
RF Antenna Gain and
Beam-width
>15dBiC bore-sight (3dB
beam-width 26°full cone)
>18dBiC bore-sight (3dB
beam-width 18°full cone)
Measured at 8.2GHz
Antenna Axial Ratio
<3dB
At bore-sight
RF Path Return Loss
<-12dB
RF Path Insertion
Loss
<-2dB
Measured from S/C interface to
horn antenna interface
The 15dBi X-APM combined with the 6W XTX typically delivers
up to 160Mbps
The 18dBi X-APM combined with the 12W XTX typically delivers
up to 400Mbps
Enables ground station dish sizes to remain small and cost-effective
Agile enough to enable near-real time imaging and downlink (i.e.
payload operation and downlink simultaneously)
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15dBi and 18dBi X-APM Micro-Vibration
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Typical measurements, hard-mounted, both axes rotating at 1°/s
Key:
Red: 18dBi APM Green: 15dBi APM
APMs operating on NigeriaSat2 (2.5m resolution imager) show no
degradation to images (even at full speed)
Micro-vibration from the APM is not expected to be a problem on sub 1
metre resolution imager spacecraft either (testing will prove this)
Forces in X, Y, Z
Moments in X, Y, Z
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15dBi X-APM Interface Control Drawing
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X-APM Batch Build and Test (11 off)
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APM Options
• If required, SSTL will consider offering
the APM in a variety of configurations:
– Different antenna
– Separate control
electronics module box
– Without control
electronics
– Internal
redundancy (dualwound motors,
redundant encoders,
electronics etc)
– Single axis solutions
– Antenna only (without mechanism)
– Alternative bi-axis alignment (not 90°)
– Different feed and payload (e.g.
optical, C-band, S-band or L-band)
– Inter-satellite links
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Motor nominal voltage
28V DC
Motor nominal phase
current
0.15A
Motor phase resistance
48Ω
Motor phase inductance
24mH
Motor step resolution
200 steps/rev
(1.8°)
Az gear ratio (motor
shaft to output shaft)
94.12 : 1
El gear ratio (from motor
to output shaft)
75.29 : 1
PCA Electronic Microstepping
16 micro-steps /
full step
Encoder channels
2 pulse
channels 90°
out of phase, 1
datum channel
Encoder power supply /
output
5V DC
Encoder nominal current
20mA
Az Bearing Static Load
Capacity
13.4kN
El Bearing Static Load
Capacity
4.55kN
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Interface Data for current X-APM
Other Developments: Ka-Band
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SSTL is currently evolving its LEO X-APM into a LEO
Ka-band APM, to exploit the wider bandwidth for a
further increase in data throughput of up to 500Mbps
or even 1Gbps
Ka-band transmitter development underway
The Ka-APM product is likely to incorporate a lowloss high-power capacity waveguide feed (instead of
coaxial)
Rotary joint design and arrangement is currently
being reviewed
It is likely that a Cassegrain reflector designed inhouse will be used to achieve the gain necessary
The larger antenna and altered RF feed can be easily
incorporated into the existing mechanism, with minor
modification
RF Frequency Band
The proven fundamental mechanism
RF Antenna Gain
components remain identical to the firstgeneration X-APM, which is possible
RF Power Handling
through the design’s modular layout and
Channels
generous design-margins
Insertion Loss
The Ka-APM development has potential
Return Loss
for use as an inter-satellite link (uplink and
downlink) in addition to pure data downlink Mass
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25.5 – 27GHz
>30dBi
<110W
Single
<1.8dB
<-18dB
<5kg
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Other Developments
• GEO APM development also underway… watch this space!
– Targeting the low mass, compact and low cost sector
• Second batch of APMs (6 off) to be manufactured during 2013,
some for stock
– Perfect for small and agile satellites
– Indicative selling price for 15dBiC or 18dBiC X-APM: £165,000 per unit
(includes build, module test, thermal test (ambient pressure) and
vibration test)
SSTL-100
Commercial
in Confidence
SSTL-150
SSTL-300
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Changing the economics of space
Thank You
For further information,
please contact SSTL
© Surrey Satellite Technology Ltd.
Tycho House, 20 Stephenson Road, Surrey Research Park, Guildford, Surrey, GU27YE, United Kingdom
Tel: +44(0)1483803803 | Fax:+44(0)1483803804 | Email: [email protected] | Web:www.sstl.co.uk
Appendix
• Mission-Specific Vibration Levels (15dBi)
– X and Y Axes:
14.97grms
– Z-Axis:
16.48grms
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Appendix
• 15dBi Generic Vibration Levels
– 21.2grms all axes
• 18dBi Generic Vibration Levels
– 20.0grms all axes
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