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Professor, Department of Aerospace Engineering, University of Pisa, Italy Chairman, Alta S.p.A, Via A. Gherardesca 5, 56121 Ospedaletto, Pisa, Italy
e-mail: [email protected]
IEPC-2005-187
Francesco Battista and Pietro Piliero
Mariano Andrenucci
Hall Thruster Scaling Methodology
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Introduction
• Expansion of human activities in space will certainly pose the need to develop high power propulsion systems
• HETs will certainly play a major role in that scenario• But power range of devices developed so far relatively narrow
• limited power levels affordable in laboratory experiments• modest power levels typical of past and current space systems
• At the opposite end of the power gamut, growing case emerging for the application of HET technology to very low power levels (less than 200 W)
• This would grant access to the mini/micro-satellite market, a potentially large market already expressing a significant demand for thrusters in the performance range suitable for Mini-HETs
• Issue:How to extrapolate sizing criteria worked out for thrusters developed to date to different scales, or different operating conditions
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Introduction
• sequel to previous paper
• mainly focussing on methodology
• more refined modelling of processes involved
4
Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
General approach
• We are concerned with the way in which the different parameters characterizing a device of a given family will vary as a result of a change of size (defined by the value of any suitable parameter)
• This will result from the interplay of different physical processes, which will generally obey different scaling laws
• Each scaling law will consist of a simple power-law relation between the involved parameters
• Other physical magnitudes resulting from the combination of different processes will be calculated as a function of those pertaining to each of the costituent processes
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Scaling Model
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Scaling modes
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Scaling mode algebra
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Calculation of scaling parameters
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
HET scaling Model: efficiency
• Standard description adopted
VA =VD −ΔV ηV =VA
VD
ID =I j + Ie i =Ie
ID
ηi =I j
ID
= 1− i
&m j =I j
M i
e &m = &mj + &mn =
&mj
ηm ηm =
&m j
&mtot
ηε =
ui2
v* 2 =v j
2
v* 2 =VA
VD
= 1−ΔV
VD v* =
2e
M i
VD
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
HET scaling Model: efficiency
• Loss factor
• Exhaust velocity from discharge voltage and loss factor
• and therefore
ηε =1 − ε L εL =ΔV
VD
= εW + ε a + ε i
vj
2 = 1−εL( )v*2 = 1−εL( )2eM i
VD =ηε2eM i
VD
T = &mjvj = &mj
2eVA
mi ve =
T&m
=&m jv j
&m j ηm=ηmvj =ηm
2eVA
mi
ηT = T 2
2 &mtot PD
= η mη j η ε
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
HET scaling Model: efficiency
• Other effects considered
• plume divergence
• spread of ion velocities
• Overall thrust efficiency
• usually assumed
η β ≈ cosβ 2 ≈uiz
2
ui2
η v ≈ui
2
ui2
ηT = η ε η J η m η β ηv
η β ≥0.9 η v ≥0.9η i ≈ 0.7 ÷ 0.8 η m≥ 0.98
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
HET scaling Model: other factors
• ionization
• diffusion length
• wall losses
• anode and ionization losses
• lifetime, heat loads, etc. (see paper)
λi =Li
L=
uaz
σ i ue n L~
uaz
n LT −3 2
λdiff =
LAD
L:
1
L
Te
32
n B
εw ~n Te
3 2d L
n uaz d bVD
=Te
3 2
uaz VD
L
b
εa =Pa
PD
~ nTe3 2 d b
PD
=Te
3 2
uaz VD εi =
Pi
PD
=Ei
e
I j
IDVD
:η j
VD
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Scaling Exponent Matrix
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
• Reference thruster: SPT-100
• Suppose we want to design a thruster with• 50 kw power• 369 mm average diameter• 88 mm channel width
• With respect to the reference thruster this meansP’/P=37.037 dm’/dm=4.341 b’/b=5.867
orln(P’/P)=3.612 ln(dm’/dm)=1.468 ln(b’/b)=1.769
• We need to use three independent transformations; we choose to use a combination of SL, L, R.
(1)Use of the model
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Use of the model
• From the general exponent matrix we extract
which means that
so that by matrix inversion we find
SL L R
P 3 1 1
dm
1 1 0
b 1 0 1
ln P '/ P( )
ln(dm'/ dm)
ln(b'/ b)
⎡
⎣
⎢⎢⎢⎢
⎤
⎦
⎥⎥⎥⎥
=3 1 11 1 01 0 1
⎡
⎣
⎢⎢⎢
⎤
⎦
⎥⎥⎥
lnςSL lnς L lnςR⎡⎣ ⎤⎦
lnςSL
lnς L
lnςR
⎡
⎣
⎢⎢⎢
⎤
⎦
⎥⎥⎥=
1 −1 −1−1 2 1−1 1 2
⎡
⎣
⎢⎢⎢
⎤
⎦
⎥⎥⎥
ln P'/ P( ) ln(dm'/ dm) ln(b'/ b)⎡⎣ ⎤⎦
(2)
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Use of the model
• We thus obtain
• so that the values of the scaling factors for the involved transformations are
• We can hence determine the equivalent overall scaling factor
and the relative weights of the component transformations
lnςSL =0.374 lnς L =1.094 lnςR1.395
ςSL =1.454 ς L =2.985 ςR =4.034
lnξ = lnς j =2.863
j∑ ⇒ ξ = ς j
j∏ =17.513
pj=
lnς j
lnς jj∑
⇒ pSL =0.131 pL =0.382 pR =0.487
(3)
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Use of the model
• We can thus generate the exponent vector for the equivalent transformation, where
and accordingly determine all other parameterssuch as
γi = α i jj
∑ p j
Isp =2398 s &m=127.145 mg/s T =2.991N ηT =0.622
VD =436 V VA =379V ID =114 A IA =92.85 A
etc.
(4)
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
50 kW Thruster50 kW Thruster ---------------------------------------------------------- Scaling modes: SL,L,R ---------------------------------------------------------- Power scaling factors ---------------------------------------------------------- P(SL)= 3.0755 P(GL)= 1 P(L)= 2.9852 P(R)= 4.0342 ---------------------------------------------------------- Geometry ---------------------------------------------------------- L(mm)= 31.993 d_m(mm)= 369 b(mm)= 88 thickness_BN(mm)= 58.667 d_inner (mm)= 163.67 ---------------------------------------------------------- INPUT ---------------------------------------------------------- B_max(G)= 200 V_D(V)= 436.27 mdot (mg/s)= 127.09 ---------------------------------------------------------- Parameters ---------------------------------------------------------- lambda_i= 0.12378 lambda_diff = 0.42634 epsilon_w = 0.033813 epsilon_i = 0.068866 epsilon_anode = 0.028932 ---------------------------------------------------------- Performance ---------------------------------------------------------- V_A(V)= 378.85 v_e(m/s)= 23588 J_d(A)= 114.61 I_sp(s)= 2404.4 T(mN)= 2997.7 ETA_TOT = 0.62537 t_{life}[hr] = 23467 Th_l_{anode}(W/cm^2)= 4.4549 Th_l_{w} (W/cm^2)= 18.843
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
5kW variants
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
5 kW Thruster5 kW Thruster ---------------------------------------------------------- Scaling modes SL,GL ---------------------------------------------------------- Power scaling factors ---------------------------------------------------------- P(SL)= 3.1852 P(GL)= 1.1628 ---------------------------------------------------------- Geometry ---------------------------------------------------------- L(mm)= 37.639 d_m(mm)= 145.42 b(mm)= 25.663 thickness_BN(mm)= 17.109 d_inner(mm)= 85.543 ---------------------------------------------------------- INPUT ---------------------------------------------------------- B_max(G)= 172 V_D(V)= 441.4 mdot(mg/s)= 12.561 ---------------------------------------------------------- Parameters ---------------------------------------------------------- lambda_i= 0.12234 lambda_diff = 0.42139 epsilon_w = 0.13482 epsilon_i = 0.068066 epsilon_anode = 0.028596 --------------------------------------------------------- Prestazioni ---------------------------------------------------------- V_A(V)= 339.22 v_e(m/s)= 22320 J_d(A)= 11.328 I_sp(s)= 2275.2 T(mN)= 280.36 ETA_TOT = 0.55345 t_{life}[hr] = 7957.5 Th_l_{anode}(W/cm^2)= 3.8312 Th_l_{w} (W/cm^2)= 16.205
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Alta’s 5 kW HET
Operating power: nominal 5 kW, maximum efficiency 7 kW. Axially symmetric magnetic coil arrangement, three separate
windings Maximum recorded efficiency: 49% at 4.1 kW, including cathode
and magnetic circuit Thrust: 200 mN, Isp: 1850 s.
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
100 W variants
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
100 W Thruster
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100 W Thruster ---------------------------------------------------------- Scaling criteria GL,SL,A ---------------------------------------------------------- Power scaling factors ---------------------------------------------------------- P(SL)= 0.024444 P(GL)= 0.87945 P(A)= 3.4457 ---------------------------------------------------------- Geometry ---------------------------------------------------------- L(mm)= 19.348 d_m(mm)= 21.695 b(mm)= 5.1114 thickness_BN(mm)= 3.3592 d_inner(mm)= 9.8652 ---------------------------------------------------------- INPUT ---------------------------------------------------------- B_max(G)= 227.41 V_D(V)= 300 mdot(mg/s)= 0.36963 ---------------------------------------------------------- Parameters ---------------------------------------------------------- lambda_i= 0.18 lambda_acc = 0.2 epsilon_w = 0.68352 epsilon_i = 0.10015 epsilon_anode = 0.042074 --------------------------------------------------------- Performance ---------------------------------------------------------- V_A(V)= 52.278 v_e(m/s)= 8762 J_d(A)= 0.33333 I_sp(s)= 893.17 T(mN)= 3.2387 ETA_TOT = 0.12549 t_{life}[hr] = 1777.2 Th_l_{anode}(W/cm^2)= 5.0655 Th_l_{w} (W/cm^2)= 21.426
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Alta’s HT-100 Mini-HET
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Comparison with data
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Power levels > 5 kW
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Comparison with data
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Power levels > 5 kW
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Comparison with data
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Power levels > 5 kW
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Comparison with data
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Power levels < 500 W
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Comparison with data
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Different operating points
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Hall Thruster Scaling Methodology
29th International electric propulsion Conference - Princeton University, October 31 - November 4, 2005
Conclusions
• Despite simplicity of model adopted, fairly good approximation of the scaling behaviour of experimental devices easily obtained by careful combination of a few basic scaling modes
• Useful preliminary design tool, allows quick evaluation
of impact of design choices or operating conditions
• Possibility to improve predictive capability by more refined modelling of involved processes
• Intrinsic interest of methodology