reusable and nonexplosive actuator for hold …reusable and non-explosive actuator for hold down and...
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REUSABLE AND NON-EXPLOSIVE ACTUATOR FOR HOLD DOWN AND RELEASE
MECHANISMS
Carlos Perestrelo (1)
, Vasco Pimenta (1)
, Luís Pina (2)
, Tiago Rodrigues (2)
, Jhonny Sá Rodrigues (2)
(1)
Spin.Works, S.A., Rua de Fundões n.º151, 3700-121 S. João Madeira, Portugal, [email protected]
(2) INEGI, Campus da FEUP, 4200-465 Porto, Portugal, luis.pina @inegi.pt
ABSTRACT
This paper presents the development of a fast-acting,
fully Re-Usable, Non-Explosive (RUNE), ultra-low
shock actuator for hold-down and release mechanisms
(HDRM), with a nominal preload capacity of 10 kN.
Assembly, Integration and test (AIT) procedures require
multiple HDRM releases, and are greatly simplified
when re-usable HDRM are employed. The re-usability
of an HDRM is thus a key feature with respect to its
implementation in space systems. RUNE is fully
reusable (i.e., resettable). The mechanism reset
operation is performed without disassembly, by one
operator in less than a minute.
The RUNE mechanism is a discrete point separation
device of generic type, i.e. independent from any
specific application. Its design is scalable in order to
widen as much as possible the range of potential
applications and preloads.
RUNE’s actuation is based on a high temperature NiTi
Shape-Memory Alloy (SMA), and it accepts standard
pyrotechnic electric actuation signals (26V-40V, 4.1A,
and 30ms pulse nominal).
DEVELOPMENT OBJECTIVES
A Qualification model /Engineering Model (QM/EM)
HDRM has been designed, manufactured with
representative materials and processes and tested in
representative conditions, corresponding to Technology
Readiness Level (TRL) 5/6. The HDRM is developed as
a qualification model (QM) up to Detailed Design
Review (DDR), and the production, assembly and
testing are carried on an engineering model (EM).
An EM has been built with representative materials and
processes, and tested in representative conditions
(TRL5/6).
An implementation plan was defined, describing forth
the future activities required for:
1. Successful qualification testing of a QM
2. Development of a COTS Flight Model (FM)
BACKGROUND INFORMATION
The level of re-usability of each HDRM is a key feature
with respect to their implementation in space systems.
Assembly, Integration and test (AIT) procedures require
multiple HDRM release, which are greatly simplified
when re-usable HDRM are employed.
Table 1. HDRM Reusability
Reusability AIT Procedures
Non-Reusable Replacement
Partially-
Reusable Refurbishment
Reusable Manual Reset
Self-Reset
HDRM can be are usually characterized with respect to
their Shock Response Spectrum (SRS) peak upon
operation, as presented in Tab. 2.
Table 2. Generated shock HDRM category
Shock
Category
Generated Shock at Release Max. SRS (5Hz to 10kHz)
Q=10
High Shock >3000g
Medium Shock Between 1000g and 3000g
Low Shock Between 300g and 1000g
Ultra-low Shock <300g
No-Shock Barely measurable
Time-critical releases, and Multi Hold Down Point
simultaneous releases require reliable and repeatable
release times (from electrical command to zeroing of the
preload and release actuator mobile elements secured),
with minimal scattering (dispersion) of individual
release times. This allows simultaneous operation of
several points, such as used in payload separations,
large solar arrays, synthetic aperture radar arrays and
antenna dishes.
The reliability of Hold Down and Release Mechanism
products needs to be very high and clearly established,
since confidence in the products is a key buying factor.
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
This is achieved through:
• Simplified (highly integrated) design,
• Redundancy for critical components (initiators)
MECHANISM DESIGN
The force reduction characteristic of the mechanism is
based in Euler friction provided by a cable which wraps
around a cylindrical body while constraining the
coupling elements. In conjunction with the used
coupling elements, this provides the required load
uncoupling and provides a very effective preload relief
function.
HDRM are characterized with respect to their self-
generated Shock Response Spectrum (SRS) peak:
RUNE generates ultra-low shock (<50g SRS) during its
operation.
The high force reduction achieved enables the use of
low mass and volume SMA initiator, while maintaining
the electrical requirements of existing pyro lines
(current, voltage and pulse times). RUNE uses standard
pyrotechnic electric signals.
Dissimilar coatings and/or materials, as well as a
minimum hardness of 500 HV is selected for the
contacting surfaces; at least one of the separating
surfaces subject to relative motion is firstly ground to
the required surface roughness, then is coated with hard
coating (Physical Vapour Deposition (PVD) TiN)
followed by a low friction coating (PVD MoS2).
Aging processes are not specified for any of the springs
used in the mechanism; Instead, the dimensioning of the
springs’ motorization is derived considering worst-case
conditions, and the maximum uncertainty factor of 0.8
is used for spring motorization.
TEST RESULTS
1.1. PHYSICAL MEASUREMENTS
Table 3. Initiator resistance
Measured
Resistance
Requirement
RUNE-REQ-INTERFACE-01
1.25 Ω
(incl. leading
wires)
Pyro-Like Interface Bridge wire
resistance: from 0.95 to 1.15 Ohms
Table 4. Grounding resistance
Measured
Point
Measured
Resistance
Requirement
RUNE-REQ-
INTERFACE-03
Cover Side 2.3 mΩ
< 5 mΩ.
Cover Mid
2.9 mΩ
Cover Top 4.5 mΩ
MGSE
Ground
Reference
8.9 mΩ < 10 mΩ.
1.2. INITIATION THRESHOLD
In order to determine the minimum initiation signal
duration, the initiation signal duration is increased until
a positive release is registered. A 5 minute SMA cooling
time is maintained between consecutive repeats.
Note regarding the initiation signal measured “spikes”:
Shortly after starting generating the release signal, the
EGSE starts controlling the voltage in real time (under a
<5 ms EGSE response time), in order to control and
maintain the required fixed (maximum) current.
Table 5. Initiation threshold determination
Ambient, Nominal current
Initiation
Current
Initiation
Voltage
Initiation
Duration Release
Nominal:
4.1A
Nominal:
26V
20 ms No effect
25 ms No effect
30 ms Released
Figure 1. Initiation Threshold (IT) determination
@ 26V, 4.1A, 30ms
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
MINIMUM CURRENT:
Table 6. Initiation threshold determination
Ambient, Minimum current
Initiation
Current
Initiation
Voltage
Initiation
Duration Release
Minimum:
3.5A
Nominal:
26V
30 ms No effect
35 ms No effect
40 ms Released
Figure 2. Initiation Threshold (IT) determination
@ 26V, 3.5A, 40ms
MAXIMUM CURRENT:
Table 7. Initiation threshold determination
Ambient Maximum current
Initiation
Current
Initiation
Voltage
Initiation
Duration Release
Maximum:
5.2A
Nominal:
26V
15 ms No effect
20 ms Released
Figure 3. Initiation Threshold (IT) determination
@ 26V, 5.2A, 20ms
1.3. PRELOAD LOSS
A 48h preload-loss test is performed. After preload
application, the mechanism is left unactuated for 48h,
while the preload data is acquired.
Figure 4. Preload loss, during >48h
Preload variation is small, (< 0.5%), thus within the
required (RUNE-REQ-FUNCTIONAL-09).
Table 8. 48h Preload loss
Measured
% loss
Requirement
RUNE-REQ-FUNCTIONAL-09
<0.5%
Nominal Preload shall be guaranteed with +/-
5% after being exposed to:
a. Vibrations
b. Shock
c. 48-hour storage under nominal preload.
d. Thermal vacuum
1.4. GENERATED SHOCK
Generated shock measurement during nominal current
release, with nominal (10kN) preload, are presented in
Fig. 5 and 6.
Figure 5. Release and Generated Shock
Nom. (10kN) preload
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
Figure 6. Generated Shock SRS
Nom. (10kN) preload
Generated shock measurement during nominal release,
after qualification (12.5kN) preload, are presented in
Fig. 7 and 8.
Figure 7. Release and Generated Shock
Qual. (12.5kN) preload
Figure 8. Generated Shock SRS
Qual. (12.5kN) preload
1.5. SHOCK SUSCEPTIBILITY
The mechanism and MGSE are mounted on the
pendulum shock test (Fig. 9), for each of the six
directions and the pendulum mass is released on the
preloaded mechanism. A functional test release is
performed after each individual shock event, and after
this, the mechanism is repositioned, reset and preloaded
in preparation for the next shock direction.
Figure 9. Mechanism + MGSE and accelerometer
mounted on the pendulum shock table
+X IMPOSED SHOCK, NOM. (10KN) PRELOAD:
Figure 10. Imposed Shock and Preload (+X)
Nom. (10kN) preload
Figure 11. Imposed Shock SRS (+X)
Nom. (10kN) preload
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
-Z IMPOSED SHOCK, QUAL. (12.5KN) PRELOAD:
Figure 12. Imposed Shock and Preload (-Z)
Qual. (12.5kN) preload
Figure 13. Imposed Shock SRS (-Z)
Qual. (12.5kN) preload
1.6. SINE & RANDOM VIBRATION
All axes are excited separately, with an independent
actuation cycle (reset, preload, release) set between each
axis excitation (six actuations/ full-level excitations;
corresponding to three axes, sine and random).
SINE VIBRATION
The measured input and output accelerations for the
three sine vibration runs are presented in Fig. 15.
Figure 14. Shaker table and data acquisition system –
Mechanism mounted in +/-X direction
Figure 15. Sine Vibration – Input and responses
X, Y and Z axes
The differences in the measured modal response, before
and after the three qualification sine vibration tests (in
each X, Y and Z axes) are presented in Fig. 16.
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
Figure 16. Resonance search comparison (pre/post sine
qual.) –With ECSS +/-5% freq. & +/-20% ampl. Δ
RANDOM VIBRATION
The measured input and output accelerations for the
three random vibration runs are presented in Fig. 17.
Figure 17. Random Vibration– Input and responses
X, Y and Z axes
The differences in the measured modal response, during
the resonance searches, before and after the three
qualification random vibration tests (in each X, Y and Z
axis) are presented in Fig. 18.
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
Figure 18. Resonance search comparison (pre/post
random qual.) –With ECSS +/-5% freq. & +/-20%
ampl. Δ
Although the mechanism functional testing is performed
successfully after each six vibration tests (3 axis Sine, 3
axis Random), the variation of the resonance modes
between the pre- and post- vibration test is higher than
the success criteria for the resonance search:
1. Less than 5 % in frequency shift, for modes
with an effective mass greater than 10 %;
2. Less than 20 % in amplitude shift, for modes
with an effective mass greater than 10 %.
The mechanism is not actuated, nor the preload or any
other mechanism configuration is otherwise modified,
between the PRE- and POST resonance searches. While
it is believed that the main reason for the resonance
search variation should be related to preload
accommodation, the reasons for the resonance
variations are not yet fully understood at the moment.
1.7. AMBIENT NO-ACTUATION CURRENT
The maximum no-actuation current in ambient
temperature & pressure, for 5min, is determined to be
0.6A, as demonstrated with a sequence of signals of
duration 5min, and progressively increasing current
until release.
Figure 19. “5min No-Actuation current” at ambient
temperature & pressure - @0.6A: No Release at 5min
1.8. SELF-RELEASE TEMPERATURE, IN AIR
The mechanism self-release temperature is determined
using a controlled ambient chamber, set to gradually
ramp the temperature until +100C.
The measured self-release temperature (in air) is +98C,
which has a +13C margin over the required +85C
maximum (operating and non-operating) temperature
for the mechanism. This margin is lower than the sum
of acceptance and qualification temperature margins
(+5C and +10C, respectively according to ECSS-E-ST-
33-01C Rev.2, 1 March 2019), which implies a non-
conformance to the design requirements.
The Mechanism self-release temperature is determined
to be +98C. The maximum design temperature is
[+98C-10C-5C] =+83C.
Considering uncertainties, the maximum operating and
non-operating temperature is demonstrated to be +80C.
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
Figure 20. Self-release temperature, in air: +98C
1.9. Thermal-Vacuum Chamber (TVC)
The test results from three representative TVC
actuations (out of ten total TVC actuations) are
presented in Fig. 21 to 28.
Figure 21. TVC Pressure (TVC_02)
Figure 22. TVC Temperature & Preload (TVC_02)
Figure 23. TVC Pressure (TVC_04)
Figure 24. TVC Temperature & Preload (TVC_04)
Figure 25. “5min No-Actuation current” at +85C:
[email protected] + [email protected] & release @0.07A
Figure 26. TVC Pressure (TVC_08)
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019
Figure 27. TVC Temperature & Preload (TVC_08)
Figure 28. 50ms Initiation pulse @ 4.1A (TVC_08)
1.10. SUMMARY OF THE TEST RESULTS
This section presents a summary of the most relevant
test results.
Grounding Resistance:
Cover Side: 2.3 mΩ
Cover Mid: 2.9 mΩ
Cover Top: 4.5 mΩ
MGSE Ground Reference: 8.9 mΩ
Initiator Resistance:
1.25 Ω (250µm SMA)
Mechanism mass:
208g
Minimum Actuation Signal:
60ms Initiation pulse @ 3.5A, -50C TVC
30ms Initiation pulse @ 4.1A, Ambient
temperature & pressure
10ms Initiation pulse @ 5.2A, +85C TVC
No-Actuation Current
TVC +85C (worst-case)
- 0.06 A for 5min, no-actuation
Ambient temperature & pressure:
- 0.6 A for 5min, no-actuation
Ultra-Low Shock release:
The Shock Response Spectrum (SRS) peaks
- < 40g (all axis), for 10 kN preload.
Total actuation time & scatter:
Total actuation time (from signal start up to
final bolt release), corresponding to the worst-
case combination of the temperature and input
power extremes:
- 55 ms and 180 ms.
At ambient temperature & pressure conditions,
the mechanism’s average total actuation time is
- 105 ms, with a measured scatter of
17 ms.
At minimum operating cold temperature: (-
50C) vacuum conditions, the mechanism’s
average total actuation time is
- 170 ms, with a measured scatter of
110 ms.
Maximum operating temperature:
Self-release: +98C.
Maximum operating (& non-operating)
temperature, including margins: +80C.
LESSONS LEARNT
The used TVC for imposes infeasible long test
cycles, because of heat transfer limitations
during TVC cooling. Further development
work should be done to reduce cooling time
and enable eight full temperature cycles for
each of the ten TVC actuations, as per ECSS
standards.
SMA phase change dependency on stress, (in
addition to temperature) must be
experimentally characterised in detail, in order
to optimize use of available actuation energy
and SMA temperature range.
Investigating novel initiation technologies is a
plus, but a careful trade-off must always take
serious consideration of development risk.
CONCLUSIONS
The project developed, built and tested a fully-reusable
non-explosive actuator for hold-down and release
mechanism, with a preload capacity of 10 kN.
An Engineering Model has been built with
representative materials and processes, and tested in
representative conditions (TRL5/6).
RUNE was demonstrated through testing to be a fast-
acting, simultaneous (low actuation time scatter), fully
re-usable, ultra-low shock and reliable HDRM.
_____________________________________________________________________________________________ Proc. 18. European Space Mechanisms and Tribology Symposium 2019, Munich, Germany, 18.-20. September 2019