Performance Evaluation of Hinge Driving Separation Nut-type

Paper
Int’l J. of Aeronautical & Space Sci. 16(4), 602–613 (2015)
DOI: http://dx.doi.org/10.5139/IJASS.2015.16.4.602
Performance Evaluation of Hinge Driving Separation Nut-type Holding
and Releasing Mechanism Triggered by Nichrome Burn Wire
Myeong-Jae LEE*
Space Technology Synthesis Laboratory, Department of Aerospace Engineering, Chosun University, Gwangju 61452, Republic of
Korea
Yong-Keun LEE**
Optronics System Group, Hanwha Thales, Gyeonggi-do 13494, Republic of Korea
Hyun-Ung OH***
Space Technology Synthesis Laboratory, Department of Aerospace Engineering, Chosun University, Gwangju 61452, Republic of
Korea
Abstract
As one of the mission payloads to be verified through the cube satellite mission of Cube Laboratory for Space Technology
Experimental Project (STEP Cube Lab), we developed a hinge driving separation nut-type holding and releasing mechanism.
The mechanism offers advantages, such as a large holding capacity and negligible induced shock, although its activation
principle is based on a nylon cable cutting mechanism triggered by a nichrome burn wire generally used for cube satellite
applications for the purpose of holding and releasing onboard appendages owing to its simplicity and low cost. The basic
characteristics of the mechanism have been measured through a release function test, static load test under qualification
temperature limits, and shock measurement test. In addition, the structural safety and operational functionality of the
mechanism module under launch and on-orbit environments have been successfully demonstrated through a vibration test
and thermal vacuum test.
Key words: Non-explosive holding and release mechanism, Nichrome burn wire, Cube satellite
1. Introduction
The cube satellite program is an international, educational,
and practical project proposed by Professor Robert Twiggs,
of Stanford University. The cube satellite is a type of cubeshaped pico-class miniaturized satellite and is considerably
smaller than typical commercial satellites. This type of
satellite usually has a volume of 10 cm3 for a standard size of
one unit (1U), a mass of less than 1.33 kg, and typically uses
commercial off-the-shelf components [1]. Recently, cube
satellites have been used for increasingly complex missions
[2-5], and their functionality, in an extremely small package
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: September 9, 2015 Revised: December 18, 2015 Accepted: December 22, 2015
Copyright ⓒ The Korean Society for Aeronautical & Space Sciences
(602~613)15-141.indd 602
gives rise to numerous mechanisms and deployable structures
that are necessary for achieving challenging mission-related
functions. The cube satellite architecture also requires that
deployable structures such as solar arrays, antennas, and other
appendages, are stowed for launch, released, and deployed
in orbit for operation. The appendages require holding and
release mechanisms that can provide adequate strength
and stiffness to survive under the launch environment, as
well as release functions to allow the deployment of these
appendages in orbit.
Recently, various holding and release mechanisms have
been developed for the separation of the appendages.
* Master’s Course Student
Chief Engineer
**
*** Professor, Corresponding author: ohu129@chosun.ac.kr
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Myeong-Jae LEE Performance Evaluation of Hinge Driving Separation Nut-type Holding and Releasing Mechanism Triggered ...
under air conditions. The turnstile antenna developed by
Gomspace [14] consists of four monopole antennas with
nearly omni-directional coverage. All four antenna elements
are individually fixed by a nylon cable and released by the
activation of burn resistors.
Generally, these devices meet many of the basic
requirements for appendage separation on cube satellites.
However, system complexity is unavoidable when it
is applied to cube satellites with multiple deployable
structures. In some cases, where more than one heated
nichrome burn wire is used, synchronous release is an
important factor for mission success. A smaller constraint
force is also one of the disadvantages of the mechanism.
These drawbacks mentioned above are compelling motives
for the investigation and development of new approaches
for a holding and release mechanism for cube satellite
applications. To overcome the drawbacks mentioned above,
Oh et al. [15] developed a segmented nut-type holding and
release mechanism for cube satellite applications with the
advantages of a high load capacity and negligible shock.
The nut segment, which is built up by winding nylon cable
around it, is released by cutting the nylon cable using the
nichrome burn wire. The effectiveness of the design was
verified through a functionality test and a static load test
under qualification temperature limits on a demonstration
model of the mechanism.
In this study, a new version of the separation nuttype holding and release mechanism is proposed and
investigated, which is simpler than the one proposed by
Oh et al. [15]. It does not require an outer housing with
Velcro fasteners to avoid interference between the released
nut and the constraint bolt immediately after separation.
This mechanism will be one of the main payloads to be
verified through the Cube Laboratory for Space Technology
Experimental Project (STEP Cube Lab) mission [16].
This is the first pico-class satellite to be developed at the
Space Technology Synthesis Laboratory (STSL) at Chosun
University and is scheduled to be launched in 2015. To
measure the basic characteristics of the newly proposed
mechanism, we performed a function test, static test, and
shock measurement test on the mechanism level. In this
study, the mechanism module design, considering the onorbit verification of the safety function of the mechanism
through the STEP Cube Lab mission was proposed and
investigated. The structural safety and normal operation of
the mechanism under launch and on-orbit environments
were verified through vibration test and thermal vacuum
test under the qualification level. These qualification test
results indicated that the proposed mechanism functions as
intended in the design.
Pyrotechnic devices are widely used in the aerospace
engineering field, especially for commercial satellite
separation, holding, and release of appendages, owing to
their high strength, stiffness, and successful deployments in
space missions. However, these devices often induce a highlevel of dynamic responses owing to the sudden transient
release of strain energy. This high-frequency pyroshock
sometimes causes malfunctions of electrical components
or critical damage to the brittle components of a launch
vehicle or satellite, resulting in mission failure [6]. The issue
of the large shock generated by the pyrotechnic device
becomes even more critical for pico-class satellites. The use
of pyrotechnic devices as a separation mechanism for picosatellites may easily cause problems because the external
and internal parts are in closer physical proximity to the
source of shock in pico-satellites than in larger satellites,
owing to the extremely small size and volume of picosatellites. Additionally, the cube satellite requirements do
not allow the use of explosive pyro devices.
To reduce the shock caused by pyrotechnic devices,
several types of non-explosive separation devices using a
shape memory alloy (SMA) [7-9] have been developed and
used in actual space missions [10, 11]. The advantages of the
non-explosive actuators are their lower shock, higher load
capability, and reusability for additional cycles after a simple
reset. However, even though the shock level is small, the
use of these devices may still have some limitations in cube
satellites because of their high cost and the fact that they do
not meet typical pico-satellite requirements of low weight,
small size, and generating relatively small shocks. The high
cost of these devices makes them impractical to use on cube
satellites that have development cost limitations.
A nylon cable has been widely used as a mechanical
constraint on the deployable appendages for cube satellite
applications owing to its simplicity and low cost. This
mechanical constraint is released by cutting the nylon
cable using a nichrome burn wire. Nakaya et al. [12]
developed a cable-cutting separation mechanism for
cube satellite separation from the launcher. The four jaws
of the mechanism that holds the cube satellite during
launch are tightened by the nylon cable, which is then cut
by heating a nichrome wire. Thurn et al. [13] developed a
burn wire release mechanism to release two carpenter tape
deployments and a stacer and tether deployment system.
It utilizes a compression spring system to apply a force
and a stroke to the nichrome burn wire for safer release.
They conducted functional performance tests in vacuum
conditions with the qualification temperature range of from
-50°C to 70°C. The test results show a shorter cut time of the
burn release mechanism under vacuum conditions than
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Int’l J. of Aeronautical & Space Sci. 16(4), 602–613 (2015)
2. Hinge Driving Separation Nut-type Holding and Releasing Mechanism
screwed into the nut through the housing, which constrained
the deployed appendages to which the housing is attached,
as shown in Fig. 1(a). The nichrome burn wire was used as
an actuator to release the mechanical constraint between
the segmented nut and the constraint bolt. The segments
of the nut, which were released by triggering the nichrome
burn wire, moved radially outwards and were attached to the
outer housing with Velcro strips by the restoration force of
the separation springs compressed inside the nut, as shown
in Fig. 1(b). The effectiveness of the mechanism design was
verified under qualification temperature limits through a
function test and a static load test of a demonstration model
of the mechanism.
Figure 3 shows the holding and released configurations
of the new version of the hinge driving separation nut-type
holding and releasing mechanism investigated in this study.
The separation nut was constrained by winding the nylon
cable around it, and the constraint was released by triggering
the nichrome burn wire, similar to the conventional
mechanism shown in Fig. 1. Separation springs were
compressed inside the separation nut. When the nichrome
burn wire was heated, the nylon cable wound around the
integrated nut is cut and the nut is subsequently separated
by the restoration force of the two separation springs. The
separation springs allow the release of the constraint bolt
when the segments of the separated nut rotate away from the
bolt around the hinge on the bottom side of the mechanism.
This makes it possible to avoid interference between the
released nut and the constraint bolt immediately after
separation, as shown in Fig. 3(b). The operating principle of
2.1 Operating Principle of Mechanism
Figure 1 shows both the stowed and released configurations
of the segmented nut-type holding and release mechanism
developed in the previous study [15] for cube satellite
applications, with the corresponding demonstration model
is shown in Fig. 2. The mechanism was made out of Al-6061
and composed of a segmented nut, an M6 constraint bolt,
a nylon cable, a nichrome burn wire, a separation spring,
and a housing with Velcro fasteners. The segmented nut was
mechanically constrained by winding the nylon cable around
it, and the Velcro strips were attached to the surface of the
integrated nut and the inside the housing, as shown in Fig.
2. To facilitate wrapping the nylon cable, V-shaped grooves
are carved in the surface of the nut. The constraint bolt was
(a)
(b)
(a)
Fig. 1. Configuration of aof
segmented
nut-type holding andnut-type
release mechanism
[15]
Fig. 1. Configuration
a segmented
holding
and release
((a): Holding state, (b): Release state)
mechanism [15] ((a): Holding state, (b): Release state)
(a)
23
(a)
(a)
(b)
(b)
(b)
Fig. 2. Demonstration model of a segmented nut-type holding and release mechanism [15] ((a): Fig. 3. Configuration of the separation nut-type holding and release mechanism proposed in this
study ((a): Holding state, (b): Release state)
Integrated nut, (b): Inside of housing)
Fig. 2. Demonstration model of a segmented nut-type holding and
release mechanism [15] ((a): Integrated nut, (b): Inside of housing)
Fig. 3. Configuration of the separation nut-type holding and release
mechanism proposed in this study ((a): Holding state, (b): Release state)
24
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604
25
(b)
Fig. 2. Demonstration model of a segmented nut-type holding and release mechanism [15] ((a):
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Integrated nut, (b): Inside of housing)
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Myeong-Jae LEE Performance Evaluation of Hinge Driving Separation Nut-type Holding and Releasing Mechanism Triggered ...
Mechanical System (MEMS) based solid propellant thruster,
a Concentrating Photovoltaic (CPV) power system, and
the novel non-explosive holding and release mechanism
triggered by nichrome burn wire heating proposed in this
study.
The variable emittance radiator and CPV system were
located on the +z panel and side solar panels, respectively, as
shown in Fig. 4(a). In the satellite configuration shown in Fig.
4 (b), +z panel and side panels are intentionally blanked for
an easier understanding of the mechanism implementation.
The holding and release mechanism and PCM were located
on the payload panel, and the MEMS thruster module was
implemented on the –z panel, although it is not clearly
shown in the figure.
The current design of the satellite configuration shown in
Fig. 4, is different from the preliminary design of the STEP
Cube Lab configuration proposed in the previous study
[15]. In the preliminary design, a single mechanism was
proposed for the synchronous release of the four turnstile
communication antennas, as opposed to the four activation
mechanisms required for the burn wires in the conventional
method. For this, the cube satellite was composed of upper
and lower cube modules, and the mechanism constrained
the motion of the upper cube module in the out-of-plane
direction to ensure the structural safety of the satellite during
lift-off. A constraint in the in-plane direction was provided
by a longeron interface with an in-plane mechanical
displacement limitation. When current was sent through
the nichrome burn wire, the upper cube module with the
antenna-holding brackets is deployed by the restoration force
of the preloaded springs compressed inside the longeron
beams. Subsequently, the antennas are released and are
automatically deployed. However, if unexpected problems
occurred in activating the newly developed mechanism
on-orbit, execution of main missions to verify the normal
operation of payloads cannot be expected. Therefore, to
minimize the risks leading to mission failure, we decided
to follow the conventional heritage for communication
antenna deployments. Therefore, the final design of the
STEP Cube Lab has been changed, as shown in Fig. 4, and the
mechanism was not used for the communication antenna
deployment, but the verification of normal operation of the
mechanism on-orbit.
Figure 5 (a) and (b) show the stowed and deployed
configuration of the flight model of the mechanism
module to verify its normal operation under launch and
on-orbit environments through STEP Cube Lab mission,
respectively. The mechanism module was located on the
payload panel and composed of the hinge driving separation
nut-type holding and release mechanism shown in Fig.
the mechanism is simpler than that of the conventional one,
and it does not require an outer housing with Velcro fasteners
to catch the separated nut to avoid interference between the
released nut and the constraint bolt after separation.
The nichrome wire was positioned on the V-shaped
interface, far away from the mechanism’s heat sinks to
avoid heat loss and ensure a successful cut. In addition, the
nichrome wire was reciprocally woven in a zigzag line through
the nylon cable, as shown in Fig. 3(a). The effectiveness of the
implementation method has already been verified through
separation function tests under qualification temperatures
[15]. This guarantees a reliable cut through the cable by
avoiding inferior contact between the nichrome burn wire
and the cables, which can be caused by a decrease in the
cable tension due to a partial cut of the cable.
2.2 Mechanism Module for On-orbit Verification
Figure 4 shows the STEP Cube Lab configuration and
location of payloads. It is based on a 1U cube satellite design,
and it will fly a number of payloads for on-orbit verification
of technology for future missions. The payloads [16] to be
verified through the STEP mission are a variable emittance
radiator, a Phase Change Material (PCM), a Micro-electro
(a)
(b)
Fig. 4. Configuration
the STEP
Cube Lab
location
of payloads
Fig. 4. Configuration
of theofSTEP
Cube
Labandand
location
of payloads
((a): with +z panel,
(b):
w/o
+z
and
side
panels)
((a): with +z panel, (b): w/o +z and side panels)
26
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and the mechanism was not used for the communication antenna deployment, but the verification of
normal operation of the mechanism on-orbit.
Figure 5 (a) and (b) show the stowed and deployed configuration of the flight model of the
mechanism module to verify its normal operation under launch and on-orbit environments through
STEP
Lab mission,
respectively.
The mechanism
module was located on the payload panel and
Int’l
J. ofCube
Aeronautical
& Space
Sci. 16(4), 602–613
(2015)
composed of the hinge driving separation nut-type holding and release mechanism shown in Fig. 5, a
The basic functional performances of the hinge driving5, a deployment status switch (Honeywell, S&C-111SM2)
deployment status switch (Honeywell, S&C-111SM2) to judge a successful release status of the
type holding and release mechanism, such as successful
to judge a successful release status of the mechanism onqualification
orbit
and two
compressed
springs to springs
imposetoaimpose
preload
of
mechanism
on-orbit
and two compressed
a preload
ofrelease
60 N inunder
the axial
direction ontemperature limits and holding
capability under preload condition and measured shock
60 N in the axial direction on the mechanism. The roles of
the mechanism. The roles of the guide beam structures on the mechanism module are to guide the
level, were verified and measured at the mechanism level.
the guide beam structures on the mechanism module are
The
structural
safety andand
functionality of the mechanism
to
guide the
movement
of spring
the compressed
spring in
thea release
movement
of the
compressed
in the axial direction
after
action
of the mechanism
under the launch vibration environment and on-orbit
axial direction after a release action of the mechanism and
impose aamechanical
constraint
in the
in-plane
direction
of theof
mechanism
under launch
environment,
thermal
vacuum
environment were verified at the
impose
mechanical
constraint
in the
in-plane
direction
mechanism
module
level, which is the flight configuration.
the
mechanism
under
launch
environment,
which
occurs
at
which occurs at the interfaces between the holes in the circular brackets and the beam structures.
the interfaces between the holes in the circular brackets and
selectstructures.
the separation springs compressed inside the separation nut, the torque budget, based on
theTo
beam
3. Functional Performance Test Results at
To select the separation springs compressed inside the
the ECSS rule [17], was derived by
Mechanism Level
separation nut, the torque budget, based on the ECSS rule
[17], was derived by  = 2(1.25ℎ + 3 + 1.11 )
3.1 Release Function Test
(1)
(1)
Figure 6 shows the functional test configuration of the
mechanism to check the stable release function of the
mechanism to release the constraint bolt. To confirm the
release status of the mechanism, the constraint bolt was
connected to a tensioned bar to retract the bolt immediately
after the activation of the mechanism. Release function
tests were performed five times under the qualification
temperature limits of -20 °C and 50 °C, which were obtained
from (system-level) on-orbit thermal analysis of the STEP
Cube Lab. Although the details of the thermal analysis
were not dealt with in this study, according to the results
of thermal analysis, the temperatures of the mechanism in
the worst cold and worst hot cases were -4.7 °C and 31.0 °C,
respectively. Based on these values, temperature margins
for analysis (±5 °C) and qualifications (±10 °C)—a total of
where, TR is the required torque to guarantee the successful
release of the mechanism and the acquisition of the release
7
signal from the deployment status switch. Torque
budget
values are summarized in Table 1.
(a)
(b)
Fig. 5. Flight model of the holding and release mechanism module
Fig. 5. Flight model of the holding and release mechanism module ((a):
Holding state, (b):
state)
((a):Release
Holding state,
(b): Release state)
Table 1.Table
Summary
1. Summary
of Torque
of Budget
Torque of
Budget
the Separation
of the Separation
Spring Spring
Table 1. Summary of Torque Budget of the Separation Spring
TorqueTorque
ℎ ℎ
 
 
1

1

Values Values
(Nm) (Nm)
27
0.035 0.035
4.851 ×4.851
10−5× 10−5
2.742 ×2.742
10−4× 10−4
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Fig. 6. Test set-up for a release function test of the demonstration model of the separation nut-type
Fig. 6. Test set-up for a release function test of the demonstration
release mechanism
model of the separation nut-type release mechanism
0.088 0.088
606
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The measured release times when the input power was 6
W, were less than approximately 3.4 s and 5.5 s under high
and low qualification temperature conditions, respectively,
although there was little variation. The release time
measurement test results obtained at air temperature, when
the input power was 10 W, were also plotted in Fig. 8. The test
results indicate that the release time can be greatly reduced
by increasing the input power. The burn release mechanism
should be faster under vacuum than under air conditions
[13]. The release function test results indicate that the
current design of the mechanism can guarantee a reliable
cut through the cable without failure when 6 W is provided.
This can be provided by a Li-ion battery with a capability of
10 W, which can then be reduced using an electrical circuit to
supply a constant current to the nichrome wire independent
of the resistance of the wire and the voltage available from
the spacecraft. The release function test results indicate that
the mechanism functions as intended in the design under
the qualification temperature limits.
±15 °C—were applied to each of the values obtained from
the thermal analysis, hence the range became -20~50 °C.
The target temperature was measured at the temperature
reference point on the head of the constraint bolt for judging
the stabilized target temperature. The low and high target
temperatures were achieved using dry ice and an indirect
heater, respectively.
Figure 7 shows images captured by the high-speed camera
of a successful release of the mechanism triggered by the
nichrome burn wire at the lower limit of the qualification
temperature range, -20°C. The images indicate that the
separation was successful without any interference with the
constraint bolt during the release sequence.
Figure 8 shows the results of the release time measurement
test obtained at air temperature and the minimum and
maximum qualification temperature limits. In this test, five
release function tests were performed for each temperature
condition. The function tests were performed successfully.
3.2 Static Test
Figure 9 shows the static load test configuration for
measuring the characteristics of the mechanism in constantrate extension/compression tests using a universal testing
machine (REGER Co., MTS-810) under the low and high
qualification temperature limits of the mechanism. As before,
the temperature reference point used to judge stabilization at
the target temperature was on the bolt head. In this test, five
cycles of axial extension/compression loads were applied
repeatedly to the mechanism by moving the crosshead of
the load tester up and down at various temperatures. The
stiffness was measured to judge the structural safety of the
mechanism before and after exposure to the qualification
Fig. 7. Example of a successful release sequence of the mechanism
Fig. 7. Example of a successful release sequence of the mechanism
6
Input Power (6W)
Input Power (10W)
Release Time (s)
5
4
3
29
2
1
0
-40
-20
0
20
40
60
Temperature ( C)
Fig. 9. Test set-up for a static load test of the demonstration model of the separation nut-type release
Fig.
9. Test set-up for a static load test of the demonstration model of
mechanism
the separation nut-type release mechanism
Fig. 8. Release time of the mechanism under qualification temperatures under the input power of
Fig. 8. Release time of the mechanism under qualification tempera6W and 10W
tures under the input power of 6W and 10W
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Int’l J. of Aeronautical & Space Sci. 16(4), 602–613 (2015)
on the mechanism’s performance. A release function test
was also performed to check the functional performance
variation of the mechanism after the static load test, and the
mechanism was released successfully, without any failure, as
shown in Fig. 6.
Figure 11 shows a time history of the load on the
mechanism responding to the triggering of heating during
extension of the mechanism at a constant extension rate.
The test result indicates that the mechanism can guarantee
a successful release under a preloaded condition on the
mechanism and the mechanism is released about 3 s after
burn release activation of with an input power of 6 W, which
is almost the same amount of time measured from the static
tests under air conditions.
Figure 12 shows the fracture test results to measure the
allowable axial load on the mechanism. The mechanism is
capable of holding an axial load of approximately 3200 N. This
is much larger than the required allowable axial preload of
60 N for the current application. However, this also indicates
that the mechanism can be applied to various deployment
systems of small satellites where a high allowable axial load
capability is required.
temperatures.
Figure 10 shows the measured stiffness values under air and
qualification temperatures. The measured stiffness values
after the tests, at the low and high qualification temperature
limits, are also plotted in the figure for comparison with the
stiffness before exposure to the qualification temperatures.
The average axial stiffness of the mechanism is 4227 N/
mm. On the other hand, although variations in the axial
stiffness of the mechanism were observed in Fig. 10. in the
low- and high-temperature cases, due to an effect of the
nylon cable, which contracted and elongated with variations
in the temperature, the stiffness variation, before and after
exposure of the mechanism to the low and high qualification
temperatures, was within 4% and thus had a negligible effect
5500
Before Low Temperature Static Test (ambient)
Low Temperature Static Test
High Temperature Static Test
After High Temperature Static Test (ambient)
Stiffness (N/mm)
5000
4500
4000
3.3 Shock Level Measurement Test
Figure 13 indicates the SRS (Shock Response Spectrum,
1/6 Octave Band) obtained from the acceleration
release shock measurement test using an accelerometer
(PCM piezotronics Inc., 352C03). The maximum SRS is
approximately 65g when a Q factor of 10 is applied. The
separated nut hitting the base, owing to the restoration force
of the separation springs after the triggering of the burn wire,
is responsible for most of the shock. However, the shock level
3500
3000
1
2
3
4
No. of Test
Fig.
10.10. Measured
axial stiffness
values
before andvalues
after staticbefore
load cycling
tests after
at qualification
Fig.
Measured
axial
stiffness
and
static
load
temperature limits
cycling tests at qualification temperature limits
3500
3000
Force (N)
2500
2000
1500
32
1000
500
0
0
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10
20
30
40
50
Time (s)
Fig. 11.
Time
history
of loading
the mechanism
to the triggering
the nichrome to
Fig.
11. Time
history
ofonloading
on and
theresponse
mechanism
andof response
burn
during extension
the nichrome
mechanism at aburn
constantwire
extension
rate extension of
thewire
triggering
of of
the
during
the mechanism at a constant extension rate
12. Fracture
test results
of the mechanism
Fig. 12. Fracture testFig.
results
of the
mechanism
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low cost, high load capacity, and negligible shock.
is negligibly lower than the conventional frangibolt-type
SMA actuator (FC2 Model4)), which has a maximum SRS
value of 2000 g, even though the allowable axial load of the
mechanism described in this paper is almost same as that
of the conventional SMA actuator. The shock level can also
be reduced by using separation springs with lower stiffness.
Table 2 summarizes the specification of the non-explosive
separation nut-type release mechanism and the results
obtained from the experimental investigations performed in
this study. The results shown in the table indicate that the
mechanism achieves the main development objectives of
4. Qualification Test Results at the Mechanism Module Level
4.1 Launch Environment Test
Figure 14 shows the vibration test configuration of
the mechanism module using a vibration shaker (LING
Electronics., 1216VH). In the test, sine burst, sine vibration,
and random vibration loads under qualification level are
applied to the mechanism module. The test level is based
on the QB50 test specifications18) summarized in Table
3. The objectives of the test were to verify structural safety
of the mechanism module under qualification vibration
Acceleration (G)
100
10
1
0.1
10
100
1000
10
4
Frequency (Hz)
Fig. 14. Test set-up
for a vibration test of the mechanism module
Fig. 14. Test set-up for a vibration test of the mechanism module
13. Shock
level measurement
results ofof
the the
mechanism
Fig. 13. ShockFig.
level
measurement
testtestresults
mechanism
Table 2. Specification of the demonstration model of the holding and release mechanism
Table 2. Specification of the demonstration model of the holding and release mechanism
Items
Specifications
Volume
φ20 mmⅹ27 mm
Mass
22 g
Allowable axial force
3200 N
Release time (Air)
<3.5 s (25°C), <5.5 s (at -20°C)
SRS Max.
65 g
Required min. power
6W
Qualification temperature
-20°C / 50°C
Constraint bolt
M6 (Al-6061)
Material
Nylon
36
Diameter
0.3 mm
Allowable tensile force
93 N
Number of turns
7
Material
Nickel Chromium
Diameter
0.2 mm
35
Nylon cable
Nichrome burn wire
Release principle
Nichrome burn wire triggering
Material
Al-6061
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test was also performed, and the mechanism was successfully
released as show in Fig. 15. The test result indicates that the
mechanism module can withstand the qualification level of
launch vibration loads.
loads when a preload of 60 N is applied to the mechanism,
and to achieve successful release signal acquisition from
the deployment status switch after vibration tests. An
accelerometer, used to apply the input test loads on the
mechanism, was located on the test fixture of the vibration
shaker. The structural safety of the mechanism was judged
by the accelerometer, installed on the bolt head, through the
comparison of the low-level sine sweep test results before
and after the full level vibration test. In the sine burst test, a
design load of 12 g is applied to the mechanism module in
each axis by the test method employing ramp up and down
for 7 cycles. In addition, random and sine vibration tests were
performed according to the qualification test specification in
Table 3.
Table 4 compares the 1st eigen frequencies obtained
from the low-level sine sweep test performed before and
after vibration tests. The maximum variation of the 1st eigen
frequency of the mechanism was within 2.2% for z-axis
excitation. After finishing the vibration tests, release function
4.2 On-orbit Environment Test
Figure 16 shows the thermal vacuum test configuration
of the mechanism module to confirm the stable release
function of the mechanism and measure the release time
under a space simulated thermal vacuum environment. The
thermal vacuum test was performed using a thermal vacuum
chamber (Thermotron Co., Thermotron 8200) under low and
high temperatures of -35 °C and 35 °C, in contrast with those
for the case of mechanism, -20~50 °C. This was because
of the thermal vacuum test conditions: all of the mission
payloads in the STEP Cube Lab simultaneously experienced
vacuum inside a single chamber. Therefore, the temperature
of the MEMS thruster was adopted as the reference
Table 3. Qualification level vibration test specifications based on the QB50
Table 3. Qualification level vibration test specifications based on the QB50
Sine Burst Test
Amplitude (g)
Sweep
12
Ramp up/down : 7cycles
Sine Vibration Test
Freq. (Hz)
Amplitude (g)
5
1.3
8
2.5
100
2.5
Sweep
2oct/min
Random Vibration Test
Freq. (Hz)
Amplitude (g2/Hz)
20
0.009
130
0.046
800
0.046
2000
0.015
g rms
Duration
8.03 g
120 sec
Table 4. Frequency differences of the mechanism module before and after vibration tests.
Table 4. Frequency differences of the mechanism module before and after vibration tests
Axis
x
y
z
DOI: http://dx.doi.org/10.5139/IJASS.2015.16.4.602
Status
1st Freq. (Hz)
Before
341
After
342
Before
703
After
696
Before
558
After
546
Difference (%)
0.3
0.28
2.2
610
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Myeong-Jae LEE Performance Evaluation of Hinge Driving Separation Nut-type Holding and Releasing Mechanism Triggered ...
temperature for the thermal vacuum test. In fact, the results
of thermal analysis of the MEMS thruster in the worst cold
and hot cases were -16.8 °C and 20.9 °C, respectively. In these
conditions, the temperature limits (including qualification
margins) were -35 °C and 35 °C, respectively, which were
15 °C lower than those of the mechanism level. However,
these values of -35 °C and 35 °C were applied to the thermal
vacuum test, even though the low temperature of -35 °C was
relatively lower than that of the mechanism level, because
the allowable temperature of the deployment status switch,
-54~85 °C, has a sufficient margin. In addition, the nichrome
burn wire could approach a value of 85 °C, which is the
minimum temperature for releasing the mechanism, in the
low-temperature case of -35 °C [13]. The target temperature
was measured at the temperature reference point on the head
of the constraint bolt to judge the stabilized temperature. In
the test, three repeated cycles of thermal loads were applied
to the mechanism module, and the release function test was
performed at the coldest condition, -35°C, and at the last
cycle because this was the worst condition for nichrome
burn wire activation. The status of the deployment status
switch was checked before the release function test at the
last cycle.
Figure 17 indicates an example of the time profiles
obtained from the deployment status switch and input
voltage to the nichrome burn wire under the release function
test at the coldest condition, -35°C, and at the last cycle. In the
test, an input power of 10 W was applied to the mechanism,
which can be provided by the selected Li-ion battery with a
max power capability of 10 W. The test results indicated that
the mechanism can guarantee a reliable cut through the
constraint wire, without failure, under the worst conditions,
and the measured release time was approximately 0.71s.
Figure 18 compares the release times obtained from the air
and vacuum conditions under various temperature ranges
when the applied input power is 10W. The test results under
air condition were obtained before the qualification tests of
the mechanism. The response time of the mechanism under
(a)
(b)
Fig. 15. Successfully
releasedreleased
mechanism
vibration
test ((a) :
Fig. 15. Successfully
mechanism after
after thethe
vibration
test
Before release, (b) : After release)
((a) : Before release, (b) : After release)
37
(a)
4
Input Voltage (V)
3
Deployment Status Switch
Switch On State
2
1
Switch Off State
0
4
Burn Wire
3
Burn Wire
Triggering Start
2
1
0
36
38
40
42
44
Time (s)
(b)
Fig. 16. TestFig.
set-up
a thermal
the mechanism
mod16. Testfor
set-up
for a thermalvacuum
vacuum testtest
of theof
mechanism
module
ule ((a) : Thermal vacuum test set-up, (b) : Temperature sensor
((a) : Thermal vacuum test set-up, (b) : Temperature sensor location)
location)
Fig. 17.
Time
profiles
of the deployment
status switch andstatus
input voltage
obtained
the release
Fig.
17. Time
profiles
of the deployment
switch
andfrom
input
voltfunction test during the thermal vacuum test
age obtained from the release function test during the thermal vacuum test
38
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Int’l J. of Aeronautical & Space Sci. 16(4), 602–613 (2015)
mechanism proposed in a previous study, which requires
the catching of the separated nuts using Velcro strips. In
this study, the mechanism module design was proposed to
perform the on-orbit verification of the mechanism through
cube satellite missions. The reliable function and structure
safety of the mechanism module, under launch and on-orbit
environments, were verified through a sine burst test, sine
vibration test, random vibration test and thermal vacuum
test under the qualification test level. From the tests results,
we concluded that the mechanism can withstand the launch
loads and guarantee reliable release under severe launch
and on-orbit environments. In addition, the mechanism
combined with a ball-and-socket interface, as proposed in
this study, opens up the possibility of applying it to other
holding and release applications.
Fig. 18. Release time comparison under air and vacuum conditions when the input power was 10W
Fig.
18. Release time comparison under air and vacuum conditions
when the input power was 10W
Acknowledgement
the low temperature vacuum condition show a 7 times faster
response than that of the air condition although the test
temperature was 15°C lower than that of the air condition.
The minimum and maximum prediction temperatures of
the mechanism through on-orbit thermal analysis at system
level were -19.5°C to 9°C under the worst coldest and hottest
orbital conditions, respectively. The parameters used in the
on-orbit thermal analysis were
40 obtained from the thermal
model correlation with the thermal balance test results
although the details are not described in this paper. This
means that the test temperatures applied in this study can
cover the predicted operating temperature of the mechanism
with a margin of 10°C.
This research was supported by research fund (2015) from
Chosun University.
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A separation nut-type release mechanism developed for
use in cube satellites has been proposed and investigated as
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