2017 AMOS Technical Conference, 19-22 September, 2017, Maui, Hawaii, USA
THE ROLE OF IMPACTS AND MOMENTUM TRANSFER FOR THE EVOLUTION OF ENVISAT’S ATTITUDE STATE
Thomas Schildknecht, Jiri Silha, Astronomical Institute, University of Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland
Holger Krag Space Debris Office, ESA/ESOC, Germany
ABSTRACT
The currently proposed space debris remediation measures include the active removal of large objects and “just in time” collision avoidance by deviating the objects using, e.g., ground-based lasers. These techniques require precise knowledge of the attitude state and state changes of the target objects. In the former case, e.g. to devise methods to cap-ture the target with a tug spacecraft, in the latter, to precisely propagate the orbits of potential collision partners, as dis-turbing forces like air drag and solar radiation pressure depend on the attitude of the objects.
The long-term evolution of the attitude motion is, among many other causes, depending on the effects of possible im-pacts of debris and meteoroid, while momentum transfer from reaction wheels or other moving internal components may contribute to the root cause of the initial attitude motion. Impacts of small particles like meteoroids and space de-bris pieces on compact space objects are unavoidable events, which were already observed several times, e.g., on Inter-national Space Station, or rather recently on the Sentinel-1A on August 23, 2016.
This paper will discuss a detailed analysis of the effects of momentum transfer from the reaction wheels and of debris and meteoroid impacts for the particular case of Envisat. Based on the physical model of Envisat and the MASTER environment model, the likelihood to have an impact-related attitude rate increase in ten years larger than selected threshold rates was determined.
1. INTRODUCTION
Recently the determination of attitude states, and in particular rotation rates, of space objects became a topic of interest in the space debris community. This is to be seen in the context of the multitude of techniques which are currently pro-posed to remove space debris from orbit or to re-orbit them into disposal orbits. The majority of the techniques to re-move large objects, which are driving the evolution of the space debris population on the long term, require capturing the target with a robotic arm, a net, a harpoon, or another mechanism. The attitude motion is in all these cases a critical parameter and the maximum tolerable target rotation rate is limited.
The attitude motion of an inactive Earth orbiting object may change either due to dissipation of stored internal energy or internal momentum transfer, or because of external forces. Internal energy may be released, e.g., in form of leaking atti-tude control systems or pressurizes tanks, any type of breakup events, and momentum can be transferred from reaction wheels. External torques may results from the interaction with the gravity field gradients and the magnetic field of the Earth or from impulse transfer when colliding with other objects. The aim of this study is to assess the maximum angu-lar momentum change to be expected for the defunct Envisat spacecraft, on one hand due to angular momentum transfer from its reaction wheels, and, on the other hand, from impacts with space debris objects or micrometeorites. The latter was analyzed once for a single impact event and for a statistical particle flux over a then year period. The study was in particular triggered by the sudden acceleration of Envisat’s rotation observed about two months after its failure when Envisat’s attitude changed from an almost stable NADIR fixed attitude to a rotation with 0.547 rpm [1], [2], [3] (inertial rotation period ~ 110s; see Figure 1).
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Fi
The interactiparticles likeobserved mabody is not cmentum of thsudden chanchange will stion and impEnvisat satelthin plate withe momentalisted in the T
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22 September
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ANALYSIS
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[kg.m2]
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tellite bus) and
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as been generaenerated particangular momein period P. Twere analyzedn points defineround the priass interval whe resulting p
3]).
bit, and smalland has been
that the targete angular mo-ther effects, aar momentum, i.e. the loca-model for thesolar panel (a
we determinedof inertia are
d a thin plate
in the intervalatellite modelated by usingcle which wasentum , and
Three differentd. These casesed by positionincipal axis
were generatedprobability for
l n t -a
m -e a d e
l l g s d t s n
d r
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different angThe correspo
Figure 2: Visulting angul
These resultschange of thee.g., only a 0would changa mass of ~1the angular man event is pperiod of twspin rate charemote sensin
Figure 3: Proing a perfec(blue) and
and impact v
Technical Co
gular momentuonding angula
isualization oflar velocity ch
s clearly showe angular mom
0.9% probabilige the angular 100 g is requirmomentum chpredicted witho months. As
ange of Envisang observation
obability of coct inelastic col̂ (green). The
velocity distrib
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um changes ar velocities ar
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in the positio
w that there imentum and tity that the buvelocity by 0
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22 September
around the thrre provided in
nt collision scearget after a coon marked by
is an very smthus in a substus would be hi0.15 deg/s, corp Envisat fromd two months
y of 0.24% ovn we may cleaon with an obidence of any
g ten years of eee different caw the result of rated by the M
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enarios to deteollision. The ithe green poin
mall probabilittantial changeit by a particlerresponding to
m a stable attits after the conver a time spaarly excludedbject of this mdamage on E
exposure (verases causing mf 1,000 simula
MASTER prog
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axes over a pe
ermine the traimpactor is shnt and blue po
ty for an impe of the spin rae of 6.31 g who spin period otude to about
ntact with the san of 10 yearsd an impact evmass would haEnvisat.
rtical axis) vermaximum rotatations using thgram assuming
A
eriod of ten y
nsferred anguhowed as a redosition vector.
act which woate around anyhich in the woof ~40 min. A0.4 rpm, whicspacecraft hass or with a provent for the exave damaged
rsus received ation around th
he MASTER Mg Envisat orbi
years are given
ular momentumd point collidin.
ould result inny axis of Envorst case (caseAn impact of ach would be cs been lost (Fiobability of 0xplanation ofthe spacecraf
angular momehe principal axMMOD populit and 10 years
n in Figure 3.
m and the re-ng with target
a substantialvisat. There is,e (a) Figure 2)an object withcomparable toigure 1). Such
0.004% over af the observedft severely but
entum assum-xes (red), lation (mass s of exposure.
.
t
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-
.
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For each impangular momlar velocity ((left vertical
Figure 4: Prohorizontal axcases causing
1,000 simu
To investigatESA MASTEare given in Fa 10 year pertion and assuangular mom(a), 12.2 kg given in Figuwith a mass 0.033 deg/s,
Figure 5: Cwas generate
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pact geometrymentum we can(lower horizonaxis).
obability of coxis) and resultg maximum roulations using
M
te the effect thER model MMFigure 5. Theriod. In total aume that all immentum receiv
m2s-1 for caseure 6.The resuequal to ~0.4and 0.042 de
Cumulative died by MASTE
2014 to 01-1
onference, 19-2
y (related also n calculate thental axis) and
ollision duringing spin periootation aroundthe MASTER
MASTER pro
4. S
hat would be MOD populati MASTER toabout 5 106 pampacts occurreved from this e (b), and 97.ults of these c45 g, ~0.45g eg/s for the thr
stributions forER for the Env11-2024 using
22 September
to given mome obtained rotresulting spin
g ten years of eod (upper horizd the principalR MMOD popogram assumin
STATISTICA
caused by a flion of particleol was then uarticles were ied at one of thflux of particl.6 kg m2s-1 focumulative mand ~0.55g, r
ree cases.
r the mass (onvisat orbit (refg the MASTER
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E FLUX IMPA
es impacting En 10-15 kg wat impacts of thvisat. We maya), (b), or (c) ears is relativespectively. Sonsfers are equresulting in a
size (on the ri02014). The spulation in the
A
Reference sol. In Figure 4 axis) as a func
) versus receivrfect inelastic ̂ (green). The
velocity distribrs of exposure
ACTS
Envisat durings used. The pr
his MMOD poy now again cdefined in Figely small, namome characteruivalent to an angular veloci
ight) of the Msimulation cove mass range 1
ource not foucan be seen re
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ved angular vecollision for te figures showbutions) genere.
g ten years of roperties of thopulation withconsider a wogure 2. The tomely 29.4 kg ristics of thesimpact of a s
ity changes of
MMOD particlevered 10 year10-15 g - 1 kg.
nd.) and totaleceived angu-bility of event
elocity (lowerthree differentw the result ofrated by the
exposure, thehis populationh Envisat overrst case situa-
otal amount ofm2s-1 for casee impacts are
single particlef 0.013 deg/s,
es. The flux s from 01-11-
l -t
r t f
e n r -f e e e ,
-
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2017 AMOS
Figure 6: Imcles. The f
years fro
There are in Figure 7. Ontem used in tare aligned a
Figure 7: D
Each of the fmum angula
= 8
For this analywere determi
[kg
17023.3
The maximube transferred
Technical Co
mpact velocityflux was generom 01-11-201
total five reane reaction whthis paper). Tw
along the
Distribution an
five reaction war momentum 0 N m s and f
ysis we used sined by ESA (
m2]
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onference, 19-2
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5. MOMEN
action wheels heel is alignedwo reaction w(along the a
nd direction ofand
wheels has a c which
for it is
slightly differ(Table 2).
ble 2: Moment
angular veloc, is given in T
22 September
(left) and impSTER for the E024 using the
NTUM TRAN
installed on d along the wheels are aligaxis)
f the reaction win the ESA sa
capacity of 40can be trans
= 40 N
rent values for
[kgm
124825.7
ta of inertia fo
ity for the thrable 3.
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NSFER FRO
Envisat [1]. T axis (ESA
gned along the
wheels installatellite body c
0 N m s (40 ksferred from tN m s.
r moment of in
m2]
or the Envisat
ree axes, if the
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and elevation d(reference to 2MOD populat
OM REACTIO
The configurareference sys
e axis (al
ed on Envisatcoordinate sys
kg m-2/s) with the wheels to
nertia of the p
spacecraft de
e momentum
A
distribution (ri21102014). Thtion in the mas
ON WHEELS
ation of the restem) or alonglong the ̂ axi
in the satellitstem.
a torque rango the body am
principal axes
[kg.m2]
129112.2
termined by E
from fully loa
right) of the Mhe simulation ss range 10-15
S
eaction wheelg the axis (ris) and two re
te body coordi
ge of ±0.45 Nmounts thus t
of inertia of E
]
ESA.
aded reaction
MMOD parti-covered 10 g - 1 kg.
s is shown inreference sys-action wheels
inate system
m. The maxi-to =
Envisat which
n wheel would
n -s
-=
h
d
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Principal axis No.ofreactionwheelsaligned withaxis
Reactionwheel capaci‐ty
[kgm2s‐1]
ENVISAT
momentof
inertia
[kgm2]
Maximum
angularvelocitychange[degs‐1]
Correspondingrotational
period
[hour]
1 40 17023.3 0.1346 0.743
2 40 + 40 124825.7 0.0367 2.723
2 40 + 40 129112.2 0.0355 2.817
Table 3: The maximum angular velocities and corresponding rotational periods of Envisat which can be obtained from reaction wheel(s) assuming different principal axis of inertia.
These results show that a momentum transfer from the reaction wheels cannot explain the observed spin-up of Envisat as the maximum change in angular velocity from this transfer is almost two orders of magnitudes smaller than the ob-served one (period of ~120s).
6. SUMMARY
Effects of debris and meteoroid impacts and of momentum transfer from the reaction wheels for the particular case of Envisat were analyzed. Based on the physical model of Envisat and the MASTER environment model, the likelihood to have an impact-related spin rate change in ten years was determined.
There is an very small probability for a single impact which would result in a substantial change of the angular momen-tum and thus in a substantial change of the spin rate around any axis of Envisat over a ten year time period. A particle of ~100 g is required to spin up Envisat from a stable attitude to about 0.4 rpm, which would be comparable to the angular velocity change observed two months after the contact with the spacecraft has been lost. The probability for such an event is less than 0.25%. Simulations showed that the accumulated momentum transfer from the entire MASTER MMOD population is also minor and would in with worst case assumption result in angular velocity change of 0.04 deg/s.
The maximum momentum which could be transfer from the Envisat’s reaction wheels to its body, assuming that the wheels were fully loaded, would result in an angular velocity change of 0.14 deg/s, 0.037 deg/s, and 0.036 deg/s, re-spectively, for the three main axes of inertia. Again, this is by far not sufficient to explain the observed spin-up of Envi-sat after its failure.
7. ACKNOWLEDGEMENTS
This work was performed in the context of the ESA study “Debris Attitude Motion Measurements and Modelling”, (ESA/ESOC 4000112447/14/D/SR).
8. REFERENCES
[1] Sommer, S., Rosebrock, J., Cerutti-Maori, D., & Leushacke, L. (2017). Temporal analysis of ENVISAT’s rotation-al motion. In 7th European Conference on Space Debris, ESA/ESOC, Darmstadt/Germany, 2017.
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[3] Kirchner, G., Steindorfer, M., Wang, P., Koidl, F., Kucharski, D., Silha, J., Schildknecht, T., Krag, H. & Flohrer, T. Determination of Attitude and Attitude Motion of Space Debris, Using Laser Ranging and Single-Photon Light Curve Data. In 7th European Conference on Space Debris, ESA/ESOC, Darmstadt/Germany, 2017.
[4] Flegel, S., Gelhaus, J., Möckel, M., Wiedemann, C., Kempf, D., Krag, H. and Vörsmann, P. Maintenance of the
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2017 AMOS Technical Conference, 19-22 September, 2017, Maui, Hawaii, USA
ESA MASTER Model – Final Report. Technical Report ESA Contract Number: 21705/08/D/HK, Institute of Aero-space Systems (ILR), June 2011.
[5] Bargellini, P.; Garcia Matatoros, M. A.; Ventimiglia, L.; Suen, D., Envisat Attitude and Orbit Control In-Orbit Per-formance: AN Operational View, 6th International ESA Conference on Guidance, Navigation and Control Systems, held 17-20 October 2005 in Loutraki, Greece. Edited by D. Danesy. ESA SP-606. European Space Agency, 2006. Published on CDROM., id.52.1
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