surrey space centre capabilities, facilities and...

EPIC Lecture Series 2018

Surrey Space Centre Capabilities, Facilities and Technologies

A. Lucca Fabris

Surrey Space Centre, UK


Outline

1. Surrey Space Centre

2. SSC Electric Propulsion

3. Case Study I – Technology Development: Halo Thruster

4. Case Study II – Plasma Diagnostics: Laser-Induced Fluorescence

2


Surrey Space Centre

𝑷𝒆𝒍 =𝟏

𝟐η𝑰𝒔𝒑𝑻

Andrea • The Surrey Space Centre (SSC) at the University of Surrey is a world leading Centre of Excellence in Space

Engineering, and has multiple spacecraft design facilities, satellite assembly labs and propulsion test facilities • 10 academics, more than 50 graduate researchers and a dedicated space engineering team

Picture taken from

the Alsat Nano

cubesat designed

and built at the

Surrey Space Centre

(2016). The image

was taken by the

Open University

wide field camera.

Surrey Space Centre electric

propulsion laboratory.

RemoveDEBRIS

spacecraft was

released on

20/06/2018 from the

international space

station.


Electric Propulsion @ SSC

𝑷𝒆𝒍 =𝟏


1. Research Group • 1 Lecturer • 2 Postdoc Researchers • 3 PhD students • 1 Research Assistant

2. Facilities

• Daedalus chamber. Turbomolecular and cryogenic pumping. EP testing.

• Pegasus chamber. Cryogenic pumping. EP testing.

• Hermes chamber. Diffusion pump. Disruptive technologies testing.

• Icarus chamber. Turbomolecular pumping. Atomic oxygen exposure studies, EP testing.

• Dinko chamber. Turbomolecular pumping. Hollow Cathodes testing.

Andrea


TRL < 5 TRL 5 - 8 TRL 9

Hall Effect Thruster (Stanford Univ.)

Cusped Field Thruster (Stanford Univ.)

QCT (SSC/SSTL)

Areas of Expertise

Halo Thruster (SSC/SSTL)

Time-resolved LIF in a Hall Thruster (Stanford Univ.)

Satellite Electric propulsion • Hall Thruster • Quad Confinement Thruster • Cusped Field Thruster • RF Plasma Thruster • Pulsed Traveling Magnetic Field Accelerator • Pulsed Deflagration Thruster • Electron sources: conventional hollow cathodes

and alternative concepts

Low temperature plasma physics and simulation • Other plasma sources: inductive plasma sources

at atmospheric pressure, magnetrons, AC discharges, microwave cavities

• Plasma diagnostic systems • Plasma physics and simulation • Measurement systems

PIC simulations (Padova)


Emerging Technologies and Applications Research Drivers

∆𝑽 = 𝑰𝒔𝒑𝒈𝟎𝒍𝒏𝒎𝒇𝒖𝒆𝒍 + 𝒎𝒑𝒂𝒚𝒍𝒐𝒂𝒅

𝒎𝒑𝒂𝒚𝒍𝒐𝒂𝒅

𝑷𝒆𝒍 =𝟏


1. Development of disruptive technologies to fill performance/operational gaps in the EP worldwide

portfolio • Lack of EP devices for CubeSats/small satellites (emerging opportunity for low power EP systems) • Use of unconventional propellants • Lifetime, beam steerability, cost reduction

2. Development of experimental platforms to characterize EP technologies both in terms of performance and

underlying physics

3. Addressing unsolved research questions on established EP technologies

• Aspects of the underlying plasma physics of EP devices are not fully understood and solved (bottleneck for achieving reliable simulations)

EPIC Lecture Series 2018 7

Case Study: Technology Development


New Technologies Development Roadmap: the QCT example

2010

2014

2016

2018

First laboratory prototype

Advanced Engineering Model

Flight Model

Space Demo (SSTL NovaSAR, launched on 16/09/2018 )

Typical Development Roadmap Milestones

• First stage: new idea conceived within university research – proof of concept – preliminary experimental assessment

• Second stage: TRL rise in partnership with industrial partners • Third stage: industrial partners lead industrialization and

commercialization activities


Halo Thruster • Promising novel concept able to compete with

established technologies in the low power range • DC magnetised plasma propulsion device,

based on an E x B closed electron drift • Peculiar magnetic field topology characterised

by a null magnetic field annular region in front of the anode and a null point in front of the exit plane


Halo Development • Different laboratory models have been manufactured and tested with different channel

geometries (5 and 3 cm channel diameter) and different magnetic arrangements (permanent magnets and electromagnets)

• Current Halo thruster development activities are carried out by a collaboration between the

Surrey Space Centre, Imperial College London, SSTL and Airbus DS aiming to increasing the TRL of the system

• The development activities are supported by the UK Space Agency and Airbus DS

• In the current framework, we target an anode power of 150 W, a reference T/P ratio of 35-

40 mN/kW, a thrust of 5-6 mN, a Isp of about 1600 s and an anode efficiency in the 25% interval

• A reference operating point would be (250-300 V, 0.4-0.6 A) with a Xe flow rate of 3-4 sccm


Halo Development • Performance characterisation (Surrey Space Centre)

• Plasma physics experimental characterisation (Surrey Space Centre, Imperial College

London)

• Numerical modelling (Imperial College London)

• Hollow Cathode Neutraliser development (modelling: Surrey Space Centre, hardware: SSTL)

• Engineering Model development – TRL increase (SSTL)


Hollow Cathode Neutraliser Development

HCN model: • Conservation of mass for orifice and

insert regions

• Conservation of energy for orifice and insert regions

• Conservation of current at the insert surface

• Poiseuille law for neutral flow

• Thermionic emission data for BaO

• Excitation and ionization cross sections for Xenon


Hollow Cathode Neutraliser Development • The HCN plasma model has been coupled with a finite

element thermal solver to estimate the insert temperature originating from the predicted plasma flows to the walls

• Hollow cathode modelling has allowed to size the geometry in terms of orifice and insert regions length and diameter

• SSTL is responsible for the mechanical design and a more detailed thermal design of the cathode

• Thermal design is a fundamental task and is iterated with numerical modelling to update the cathode design

SSTL HCN developed for the Quad Confinement Thruster flight model on board of the NovaSAR spacecraft


Laboratory Model Testing

HALO


Laboratory Model Testing – 5cm Halo

• Measurements show an average thrust-to-power ratio of about 29 mN/kW (or 35 W/mN)

• Anode specific impulse is 1450s and 1550s at 5 sccm and 10 sccm, respectively, with anode efficiency of

about 23-24%


Laboratory Model Testing – 3cm Halo

• The thrust-to-power ratio ranges within the interval 20-32 mN/kW for Xe flow in the 4-6 sccm range • Specific impulse of 1400s and 1500s has been recorded for the 4sccm and 6sccm cases. Maximum resulting

anode efficiency is about 15-17%.


Plasma Physics – 5cm Halo

• Langmuir probe measurements have mapped the plasma properties within the discharge channel of the

thruster • The null magnetic field appears to form a path of low resistance for electron axial transport to the anode; in

this region the plasma potential is close to the anode voltage • Electron temperature ought to be greatest where potential drops are observed, as the presence of a sustained

electric field induces a closed-loop E x B electron drift and associated Joule heating


Halo Upcoming Activities

• Future activities at SSC will continue to focus on understanding the fundamental plasma

physics using different plasma diagnostic tools (OES, analysis of the possible presence of multiple charge ions)

• Optimization activities will explore the impact of new magnetic field topologies on the thruster performance

• An advanced Engineering Model will be manufactured by SSTL and tested at SSC facilities

• The EM model will incorporate a HCN tailored to this thruster class; the HCN will be tested as a stand-alone system first, and then integrated with the thruster

• Further activities will be performed on unconventional configurations (centrally located cathode, permanent magnet arrangement)


Case Study: Plasma Diagnostics Development


Hall Effect Thruster

∆𝑽 = 𝑽𝒆𝒙𝒍𝒏𝒎𝒇𝒖𝒆𝒍 + 𝒎𝒑𝒂𝒚𝒍𝒐𝒂𝒅


n n n

n n n

n n n + –

–

–

– – –

– – n –

+ +

+

+

+

+

+

• The propellant (neutral xenon) is injected at the anode plate, located at the closed end of the discharge channel • An external hollow cathode neutralizer provides primary electrons for triggering the ionization process and neutralizing the

ejected ion beam • Electrons are trapped by the radial magnetic by the generation of a Hall current (E x B azimuthal electron drift) • The reduced electron mobility due the radial magnetic field establishes a potential drop nearby the thruster exit plane

producing ion acceleration


• Under certain operating conditions, Hall thrusters present strong current fluctuations due to ionization oscillations (“breathing mode”)

• Some aspects of the plasma fundamental physics are not fully understood

• The lack of understanding of some aspects of the fundamental physics is a bottleneck to achieving reliable

simulation and further optimization of the device

Hall Effect Thruster: breathing mode

Hall thruster operating on xenon


Laser-Induced Fluorescence Velocimetry

Moving ions see a Doppler shift in the incoming light!

V = 0

V

V

λ = λ0

λ > λ0

λ < λ0

• Powerful laser-based non-intrusive technique applied to the measurement of the velocity field of propellant ions in plasma thrusters

• The fluorescence peak presents a wavelength shift in comparison with a stationary reference

• The laser wavelength is scanned small range around an atomic transition

• Fluorescence is collected

• Fluorescence signal intensity peaks when the laser wavelength hits the exact atomic transition

shift

Inte

nsi

ty

Flu

ore

scen

ce In

ten

sity



• Fabry-Perot interferometer for precise wavelength tuning reconstruction

• Optogalvanic xenon cell for stationary reference

0 1 2 3 4 5 6

x 104

−1

0

1

2

3

4

5

Index

Eta

lon

Sig

na

l

Fabry-Perot Etalon

Relative laser wavelength vs. time

15 20 25 30 35

0

20

40

60

80

100

120

140

160

Frequency (GHz)

Tru

e S

ign

al (m

V)

C

B

Optogalvanic Cell

Absolute wavelength reference



• Light noise: light emitted by the plasma other than the fluorescence induced by the laser

• Homodyne detection / Optical bandpass filtering:

used to reject plasma background light noise and scattered laser photons

• Xe ions Doppler shift: moving ions in plume absorb laser radiation at a different wavelength compared with a stationary reference

• Fluorescence peak location: most probable velocity • Fluorescence peak height: relative number of excited ions

present

Velocity or Frequency shift

Inte

nsi

ty

Fewer Ions

More Ions


LIF time-synchronization methods

∆𝑽 = 𝑽𝒆𝒙𝒍𝒏𝒎𝒇𝒖𝒆𝒍 + 𝒎𝒑𝒂𝒚𝒍𝒐𝒂𝒅


• Applicable to periodic or quasi-periodic plasma phenomena: pulsed plasmas, magnetized discharge instabilities, AC plasma sources, fluctuations in ICP discharges

• Applicable to time-resolved laser absorption or laser-induced fluorescence spectroscopy

• The methods have been demonstrated in a broad frequency range: 60 Hz – 50 kHz. They can be extended both at higher and lower

(a) Sample-Hold: Emission signal collected in each blue gate is averaged and held until the next gate at the same current phase. The induced fluorescence signal is extracted out of the bright background emission using homodyne detection with a lock-in amplifier (b) Fast Switching: Only signal collected in each blue gate is sent to the lock-in amplifier, which can still extract the fluorescence signal thanks to the high chopping rate. A higher chopping frequency may allow operation in a range with reduced spectral noise density


Hall Effect Thruster: Stanford 350 W Hall Thruster

0 20 40 60 80 100 120 140 160 180 2000

1

2

3

4

Time (ms)

Dis

cha

rge

Cu

rren

t (A

)

0 20 40 60 80 100 12010

−6

10−4

10−2

100

Frequency (kHz)

FF

T P

ow

er

(a.u

.)

0

2

4

Cu

rren

t (A

)

−80

−60

−40

−20

220

240

260

Vo

ltag

e (

V)

−40

−20

0

Pow

er

Spe

ctr

al D

en

sity (

dB

/Hz)

0 50 100 150 200 2500

0.5

1

Time (ms)

Pow

er

(kW

)

0 20 40 60 80 100

−20

0

20

Frequency (kHz)

0

2

4

Cu

rren

t (A

)

−80

−60

−40

−20

220

240

260

Vo

ltag

e (

V)

−40

−20

0

Pow

er

Spe

ctr

al D

en

sity (

dB

/Hz)

0 50 100 150 200 2500

0.5

1

Time (ms)

Pow

er

(kW

)

0 20 40 60 80 100

−20

0

20

Frequency (kHz)

Channel ID: 42 mm

Channel OD: 72 mm

Channel depth: 23 mm

Anode flow rate: 2 mg/s (Xe)

Cathode flow rate: 0.15 mg/s (Ar)

Anode voltage: 240 V

Anode current: 1.7 A

Anode power: 400 W

Chamber pressure 2e-5 mbar



A. Lucca Fabris, C. V. Young, M. A. Cappelli. Journal of Applied Physics 118, 233301 (2015).

Velo

city (

km

/s)

−5

0

5

10

15

20

25

0 200 400 600 800

−6

0

6

12

18

24

30

Fre

qu

en

cy (

GH

z)

0 20 40 60 80 100 120

1

2

3

Time (ms)

I D (

A)

1

2

3

AVG

0 5 10 15 200

0.2

0.4

0.6

0.8

1

Velocity (km/s)

LIF

in

ten

sity (

a.u

.)


Hall Effect Thruster: Stanford 350 W Hall Thruster • Higher ion velocity in the current trough between

consecutive discharge current peaks

• At z = 5 mm, the velocity doubles from 7.5 km/s to 15.4 km/s, indicating strong variations in the local accelerating potential structure over the breathing mode cycle


• Velocities at z = 15mm and z = 20mm fluctuate up to 38% and 34%, respectively, about their median values




• Time-resolved traces show how broad time-averaged feature is actually a single narrower ion population moving in time

• Time-averaged data only shows part of the story with a highly time-dependent process like the breathing mode



• Large swing in ion velocities at z = 5 mm due to moving acceleration zone characteristic of the breathing mode

+


Thank you for your attention

33

Acknowledgements: Airbus DS, SSTL, UK Space Agency, Stanford Plasma Physics Lab

surrey space centre capabilities, facilities and...

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