REUSABLE AND NONEXPLOSIVE ACTUATOR FOR HOLD …REUSABLE AND NON-EXPLOSIVE ACTUATOR FOR HOLD DOWN AND RELEASE MECHANISMS . Carlos Perestrelo (1), Vasco Pimenta (1), Luís Pina (2),

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


MINIMUM CURRENT:


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


@ 26V, 3.5A, 40ms

MAXIMUM CURRENT:


Ambient Maximum current

Initiation

Current

Initiation

Voltage

Initiation

Duration Release

Maximum:

5.2A

Nominal:

26V

15 ms No effect

20 ms Released


@ 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


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


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


-Z IMPOSED SHOCK, QUAL. (12.5KN) PRELOAD:

Figure 12. Imposed Shock and Preload (-Z)


Figure 13. Imposed Shock SRS (-Z)


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.


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.


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.


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 25. “5min No-Actuation current” at +85C:

[email protected] + [email protected] & release @0.07A




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.


Documents

REUSABLE AND NONEXPLOSIVE ACTUATOR FOR HOLD …REUSABLE AND NON-EXPLOSIVE ACTUATOR FOR HOLD DOWN AND RELEASE MECHANISMS . Carlos Perestrelo (1), Vasco Pimenta (1), Luís Pina (2),