Table of contents
- The low Earth orbit environment
- Spacecraft/plasma interactions
- Evaluation of in-orbit spacecraft/plasma interactions
- Spacecraft wake effects
- Spacecraft contamination effects
- Spacecraft power system effects
- Spacecraft electromagnetic effects
- Evaluation of in-orbit spacecraft charging
- Spacecraft charging effects
- Conditions required for spacecraft charging
- Summary of previous work
- The ESPIRE computer codes
- Description of the ESPIRE codes
- The DICTAT computer code
The problems caused by interactions between a spacecraft and the environment in
low Earth orbits and polar orbits (see Fig. 1 for a schematic representation of
the polar orbit environment) are manifold ( , 199). Five broad areas of
spacecraft/plasma interactions cause effects of concern for future space
- effects caused by the supersonic spacecraft motion through the background
ions in the plasma;
- effects caused by exposure to high energy auroral electron fluxes in the
- effects on solar arrays operating in the relatively dense plasmas in low
- effects of contamination, both of the spacecraft itself, and by the
spacecraft on the ambient neutral and plasma environment;
- effects leading to the generation and emission of plasma waves and
Many of these phenomena will be affected by the move to large, active
structures, which will be accompanied in their orbits by a self-generated cloud
of contamination. The trends to larger size, longer lifetimes, higher power
requirement and frequent thruster firings and water and other waste dumps will
pose a series of important problems for the space system designer and operator.
|Figure 1. Plasma interactions with a spacecraft in polar
The low Earth orbit environment
The plasma environment in low Earth orbit (LEO) usually is relatively benign
compared to the environment commonly found in geostationary Earth orbit (GEO).
There is a large reservoir of high density cold plasma which tends to mitigate
any spacecraft charging effects by providing a large source of charged
particles from which neutralising currents may be drawn. The spacecraft is
closely coupled to the plasma environment under most conditions.
However, since Debye lengths (plasma charge shielding distances) in the
ionosphere are of the order of centimetres, as compared to metres or tens of
metres at geostationary altitudes, the effective current collecting area of a
spacecraft in LEO will be much smaller than that in GEO.
In addition, the spacecraft will create a large volume of disturbed plasma as
it moves through the ionosphere. The spacecraft orbital velocity is hypersonic
with respect to the plasma ions, and so phenomena such as bow shocks, ion
voids, trailing wakes and density enhancements and depletions will occur. These
aspects of the spacecraft/plasma interaction in LEO will not only cause a
complicated, disturbed environment local to the spacecraft, but significant
wake effects could introduce problems with differential charging.
This is liable to be a problem of some importance in the auroral precipitation
zones at high magnetic latitudes. Here, energetic electrons, with energies
typically in the range of 5-10 keV, precipitate down magnetic field lines in
sufficient intensity to have the potential of greatly modifying the spacecraft
Thus, in auroral regions a spacecraft moving along its orbit could suddenly
experience a transition from a situation with a spacecraft charging voltage no
more than a volt or two negative, to the case where it is intercepting a high
energy stream of electrons. If this occurs in darkness, where photoemission is
suppressed, and the electrons impinge on wake surfaces where ions are excluded
by the spacecraft motion, then the potential for charging is high.
The main spacecraft/environment interactions are summarised in Table I,
together with the effects they produce, and comments relating to their impact
on large spacecraft systems (typical of the elements being developed as part of
the International Space Station programme).
Table I. Summary of spacecraft/plasma interactions and their
|Interaction||Effects||Impact on large spacecraft systems|
|Supersonic motion through plasma||Density enhancement at ram;
density depletion in wake.||Disturbances will be large in spatial
extent; many body dimensions.|
|Collection of energetic auroral electrons||Negative charging in
wake; differential charging at surface.||Absolute voltage levels will be
much higher than for small or medium size bodies.|
|Dual spacecraft manoeuvres||Charging of spacecraft in wake, if
subject to energetic electron flux||Absolute voltage levels on second
body will be very high.|
|Neutral (natural and artificial atmosphere||Contamination of
spacecraft surfaces; contamination of space environment.||Greater levels
of contaminant emission, and increased possibility of disturbance.|
|Ion attraction by surfaces at negative potential||Sputtering of
surface materials||Life-limiting factor for surfaces and solar array
|Magnetic field||Modification of charging levels by suppressions
of electron escape||Absolute voltage levels will be much higher than for
small or medium size bodies.|
|Motion in magnetic field||Generation of electric field
gradients||Absolute field values will be greater than for small or
medium size bodies.|
|Current collection by solar arrays||Power loss drain through
plasma; arcing damage to surfaces.||Power losses may become
|Aspects of motion, spacecraft power leakage,
contamination||Generation of a range of plasma waves, at a range of
frequencies||A wider range of generation mechanisms, with more power,
and increased possibility of disturbance|
|Emitted particle beams in a plasma||Beam-plasma discharges,
excitation of plasma waves, spacecraft charging, optical
emissions||Increased possibility of disturbance and enhancement of
|Coupling of electromagnetic waves||Localised heating of plasma
at critical frequencies||Increased possibility of disturbance and
enhancement of effects|
There are five broad areas where spacecraft/plasma interactions cause effects
which may be of great concern for future missions.
It must be appreciated, however, that the interactions and effects referred to
above are not to be looked at in isolation from one another. Many of the
interactions not only produce primary effects, but are also responsible for
secondary effects, acting in synergism with other interactons. As an example, a
large structure with a large ion-free wake zone in a flux of energetic
electrons could experience high negative charging levels. These in turn could
attract contaminant ions to sensitive surfaces and modify the local plasma
environment, causing plasma wave emissions which could disrupt sensors and
monitors, or even in extreme cases on-board computers and communications.
- Effects caused by the supersonic spacecraft motion through the background
ions in the plasma. Large density and space potential disturbances will be set
up in the wake of bodies, and density enhancement will occur in the ram. These
disturbances will be many body dimensions in spatial extent, and could lead to
the shadowing of surfaces, disruption to instrumentation, enhanced particle
fluxes to other parts of the spacecraft, and many other related effects. The
motion across magnetic field lines will also introduce electric fields, and the
effects of these will be greater for large structures.
- Solar arrays operating in the relatively dense plasmas in low Earth orbit
will experience a current drain on the power system, as a result of losses
through coupling to the plasma. This will become more severe as systems are
enlarged and operating voltages are raised. Arcing of solar arrays in plasmas
could lead to damage and electrical noise. Arcing becomes likely when the array
is in a contaminated envrionment. Attraction of the ambient ions by negatively
charged areas of the array could lead to sputtering and mass loss rates that
may limit the lifetime of components, especially those designed for long
- Contamination will be a critical issue in future missions, and this can be
divided into two areas of concern. The first is that of spacecraft
contamination, where material properties may be changed, thermal contral
systems affected, delicate sensing equipment damaged, etc. The relatively dense
atmospheric pressure in LEO is important here. The second aspect is that of
modification of the ambient atmosphere by outgassing from the spacecraft
structure, thruster firings, water dumps, etc.
- There will be large scope for the generation and emission of plasma waves,
not just by active beam emissions experiments, but also by other spacecraft
interactions. Plasma wakes, spacecraft power leakage and contaminant ions all
provide a source of radiofrequency emissons. As spacecraft become larger and
produce more contamination, the possibilities of disturbance, and of a wider
range of generation mechanisms, frequencies and power levels, will all
- Exposure to high energy auroral electron fluxes in the polar regions can
lead to high levels of charging on spacecraft, particularl if the current
collectoin occurs in the ion-depleted wake zones. The orientation of the
magnetic field will complicate the interaction mechanisms, with fields parallel
to the collection surface inhibiting the escape of secondary emitted electrons
and enhancing charging. Again, these effects will be more important for large
structures, where voltages well in excess of the kilovolt level have been
predicted to occur. A related problem is that of the charging of one body
immersed in the wake of another. The dynamic nature of the charging mechanisms
will materials dependent and differential charging between adjacent surfaces
could be of concern, especially for large structures.
Evaluation of in-orbit spacecraft/plasma interactions
A spacecraft moving through the space plasma at LEO orbital speeds of the order
of 8 km/s produces changes in the lcoal environment, and the local environment
induces changes in the properties and performance of the spacecraft. These
interactions result in significant changes in the local environment properties
and include enhancement of neutral and ionised particle densities in the ram
direction and rarefaction in the wake behind the spacecraft.
While ions and electrons will be constrained by the magnetic field of the
Earth, neutral particles generated by the spacecraft will be free to travel
with the vehicle until disturbed by collisional processes. This will be
especially of concern for large structures carrying out active emissions of
neutral particles, e.g. water and waste dumps, thruster firings, atmospheric
venting, etc. In one sense, a spacecraft carries its own atmosphere along with
it in orbit.
Space power systems will have to operate in a plasma environment. For solar
arrays, with exposed solar cell interconnects, the ionised plasma may be a
cause of current leakage and power loss from the array. Operation of the array
at high voltage, to reduce cabling losses and array mass, may experience
problems with plasma induced breakdowns and arcing, and with anomalous current
collection phenomena. Biasing of interconnects at negative voltages in excess
of sputter thresholds could lead to ion-induced erosion of the interconnects
and destruction of the integrity of the array.
The environment will be turbulent, not only as a result of plasma disturbances
caused by spacecraft passage and perturbation of the ambient density, but also
because of such activities as thruster firings and water dumps. The turbulence
could lead to the generation of electromagnetic emissions with a wide range of
frequencies, leading in turn to possible problems with sensors,
instrumentation, communications and control systems.
All these effects will have an impact upon future programmes in LEO and polar
orbits. The possible phenomena that could occur, the possible consequences of
the interactions with the spacecraft, and ways of monitoring and alleviating
the effects require detailed study and analysis.
Spacecraft wake effects
The hypersonic motion of a spacecraft through the ionospheric plasma creates a
shock wave in front and to the side of the body, and a large region behind the
body which is depleted in ions. When the body size becomes large compared to
the Debye length, then the interaction effects relative to the filling in of
the wake become more severe. Typical wake lengths are many times the spacecraft
The filling of the wake behind a large body moving supersonically or the
expansion of a plasma into a rarefied area has been studied. Multiple charged
particle populations result in polarisation electric fields which control
particle motion along with flow expansion in the collisionless case and
diffusion in cases where collisions must be considered. From these processes
the wake region becomes a source of electron heating and ion acceleration,
preferentially of lighter ions and of minor constituents. Other processes
involve plasma oscillations and instabilities, strong jump discontinuities in
plasma parameters at the expansion front, and rarefaction wave propagation into
the ambient plasma. These phenomena all depend on the ionic constituents and
concentrations, ambient electron temperature and density gradients, and the
size of the body relative to the Debye length.
Spacecraft contamination effects
Early observations indicated that the Shuttle's local environment was
controlled by the movement of the Shuttle through the ambient medium and by
contaminant sources on the Shuttle. These sources, in the form of particulates
and gases, are generated by Reaction Control System (RCS) and Orbital
Manoeuvring System (OMS) engine firings, cabin gas leaks, water releases and
outgassing of materials. Initial operational concerns over contamination
focused on particulates scattering light into Shuttle based optical detectors
to produce false signals, and on gaseous contaminants condensing on thermal
control and optical sensing surfaces to degrade their performance.
Observations suggest that the Shuttle may be immersed in a large gas cloud,
made of atoms and molecules from various outgassing sources, whose shape is
governed by the Shuttle's interaction with the ambient neutral atmosphere and
space plasma environment. Ionisation of contaminants and charge exchange
ionisation processes lead to the formation of pick-up ions, tailing behind the
spacecraft. Engine firings enhance the contaminant cloud and may produce their
own characteristic contaminant cloud or plume that has an associated engine
firing light flash which illuminates the Shuttle and enhances the surface glow
phenomena. Particulate contamination is also enhanced when RCS engine exhaust
plumes impinge directly on Shuttle surfaces. All of these observations suggest
a close coupling between the various contaminant sources which contribute to
the formation of a multispecious gas cloud surrounding the Shuttle.
Spacecraft power system effects
Exposed voltages on any part of a spacecraft cause current to flow between the
element and the ambient low energy plasma environment. As an example, current
flow to a solar array terminal could result in unacceptable power losses. At
present, most spacecraft power systems use voltages less than 50 V. In future,
it is planned to use much higher voltages. Although actual flight experience in
space is limited, initial experiments have shown that leakage currents increase
non-linearly with high positive voltages and that arcing occurs for high
negative voltages. In addition, there are a number of other environmental
effects on solar arrays in LEO that contribute to degradation and cause
Spacecraft electromagnetic effects
Any AC and DC electric and magnetic fields on or near a spacecraft will be
driven by two sources:
In the case of the Space Shuttle, the environment was found to be dominated not
by Orbiter generated noise but by plasma interaction noise.
- spacecraft electromagnetic interference (EMI) associated with the hardware
- fields associated with the interaction of the spacecraft and its
Analyses of the wave environment aboard the Space Shuttle have led to the
emerging picture that the broadband noise environment is dominated not by the
induced environment associated with the large body interaction (although these
effects certainly have a role to plasy), byt by the production of waves by the
neutral gas cloud as it expands and undergoes chemical interactions, such as
charge exchange which results in an ion tail, and creates plasma waves presumed
to be driven by the ion currents. If this is the case, then it should be
possible to correlate the level of background noise with the density of the
neutral cloud, and indeed this has been done in the case of water releases from
Evaluation of in-orbit spacecraft charging
Spacecraft charging effects
The buildup of large potentials on spacecraft relative to the ambient plasma is
not, of itself, a serious electrostatic discharge (ESD) design concern.
However, such charging enhances surface contamination, which degrades thermal
properties. It also compromises scientific missions seeking to measure
properties of the space environment. Spacecraft systems referenced to structure
ground are not affected by a uniformly charged spacecraft. However, spacecraft
surfaces are not uniform in their material properties, surfaces will be either
shaded or sunlit, and the ambient fluxes may be anisotropic. These and other
charging effects can produce potential differences between spacecraft surfaces
or between spacecraft surfaces and spacecraft ground. When a breakdown
threshold is exceeded, an electrostatic discharge can occur. The transient
generated by this discharge can couple into the spacecraft electronics and
cause upsets ranging from logic switching to complete system failure.
Discharges can also cause long term degradation of exterior surface coatings
and enhance contamination of surfaces. Vehicle torquing or wobble can also be
produced when multiple discharges occur. The ultimate results are disruptions
in spacecraft operation.
Surface charging could disrupt environmental measurements on scientific
spacecraft. For this application and others where control of electrostatic
fields is required, meterial selection to minimise differential charging is
mandatory. For operational spacecraft, surface charging can also cause
problems. The hallmark of the spaceraft charging phenomena is the occurrence of
electronic switching anomalies. These anomalies are believed to result from
transients caused differential charging induced discharges. These anomalous
events even seem to occur in systems that are supposedly immune to noise. The
discharge induced transients, under very severe environmental conditions, can
cause system failures.
Conditions required for spacecraft charging
Work with the Defence Meteorological Satellite Program (DMSP) allows the
required conditions for spacecraft charging (spacecraft surface potentials at
least 100 V different from the potential of the surrounding plasma) to be
defined. These conditions are:
- The spacecraft must encounter an auroral electron plasma which imposes on
it a sufficiently large ratio of high energy electron ambient flux to total ion
(ambient or ram flux).
- The ambient electron plasma has a relativel large fraction of its total
flux at energies well above the secondary yield maximum of the spacecraft
surface material, in order to suppress secondary emission effects which would
tend to discharge the spacecraft.
- The spacecraft must be in darkness in order to suppress photoemission
effects, which would tend to discharge the spacecraft.
In addition, theoretical work suggests that:
- Charging is more likely for larger spacecraft because electron collection
increases more rapidly with spacecraft size than ion collection does.
There are two aspects of the charging phenomena that should be kept in mind
when assessing the impact upon future spacecraft systems:
- Recorded charging levels were for spacecraft with typical dimensions of one
metre. As noted above, the charging levels are expected to increase in relation
to an increase in the spacecraft dimension. Thus, while maximum charging levels
of the order of -0.5 kV have been observed on polar transiting spacecraft to
date, levels of charging in excess of -1 kV are anticipated for larger
spacecraft. This must be considered during the design of such systems.
- Presumably, the charging levels recorded by the spacecraft instrumentation
represented absolute charging levels, with the whole vehicle assuming the
potential with respect to the plasma. Possible more serious in the context of
future systems is the question of differential charging. Ion density depletion
levels in the wake of a spacecraft, or components of a spacecraft, can be very
large and very high levels of charge could accumulate upoon surfaces or
equipment, if subject to high energy precipitating electrons. Again, this is an
area that must be considered during the design of the systems.
Summary of previous work
The integrated study, and understanding, of a wide range of spacecraft/plasma
interactions and their effect in low Earth and polar orbits must be an
important component of efforts directed to the design, construction, and
successful and safe operation of future spacecraft and large space systems.
Several of these problem areas have been investigated in laboratory
experiments. However, it is important to appreciate that the simulation of a
complex environment, such as the low Earth orbit ionosphere, in the laboratory
is a difficult task. In general, there are five areas to which close attention
should be paid:
- the scaling laws that must be applied to reproduce large scale phenomena in
- the need to avoid significant backgrounds of slow, charge exchange
generated ions in test facilities;
- the production in the laboratory of monoenergetic ion streams, rather thatn
ones with thermal velocity component;
- the need to minimise ion stream divergence and axial density variations;
- the simulation of the on-orbit magnetic field, and an understanding of its
influence (or otherwise) on plasma interactions.
A comprehensive review of test facilities used in experimental simulation
studies led to the following conclusions:
- In plasma wake studies, slow background ions can be controlled in a
satisfactory manner, and resonable values of divergence can be achieved.
However, these have not always been reproduced at the same time, and data from
many facilities must be treated with caution. Little work has been reported on
plasma wakes created by large bodies.
- In solar array studies, most facilities have not adequately simulated the
correct ambient pressure. Operating pressures are often in the 10-5
torr range and above, and this can lead to anomalous plasma conditions near
solar array samples, distorting experimental results. In addition, most
facilities have produced Debye lengths (plasma screening distances) of the same
order as the solar cells. Only recently have Debye lengths of the same
dimension as array interconnects been produced.
- In spaccraft charging studies, initial experiments relevant to conditions
in low Earth and polar orbit have only recently begun, and information is
limited. Again the presence of slow facility ions has caused distortion of the
The problems have also been studied using numerical and computational
simulation methods. There are essentially two different philosophies that can
be applied when writing computer codes to simulate the spacecraft/plasma
interaction in low Earth orbit:
- the use of analytical fluid equations to represent the plasma;
- the use of numerical methods to compute the trajectories of particles by
solving their equations of motion.
It is a feature of analytical codes that they describe only macro-processes
(i.e. above the scale of individual particles) that are explicitly included by
the author. Hence, in a sense, they tell the user only what he/she already
knows and will not surprise him/her with unexpected behaviour.
There are generally less approximations in particle tracking codes than in
analytical ones. Where approximations appear, they are, for example, in the
form of the secondary electron emission spectrum and not in the particle
In additon to this ground based work, account must be taken of space based
experience. Over the past years, an ever increasing number of publications have
appeared on the plasma modifications around a vehicle orbiting in the low Earth
plasma. The mid-latitude, low Earth orbit region has been investigated fairly
extensively by a series of satellites plus a few sounding rockets. In polar
regions on the other hand, very few satellites have yet been flown which
carried adequate instrumentation to monitor plasma modifications. However, many
rocket payloads have been launched into the auroral zones.
|Figure 2. Spacecraft interactions with ambient plasma|
The current status of affairs can be summarised as follows:
- Of a wide range of spacecraft/plasma interactions and their effects (see
Fig. 2), many hold serious implications for future large, long lived, active
structures in space, and in some cases information is limited. Again, the
presence of slow facility ions has caused distortion of the experimental
- Laboratory experiments can adequately simulate the space environment and
its interaction with spacecraft, but attention must be paid to the validity of
the simulation. Plasma wake studies have generally only coverd small to medium
vehicles. A reasonable data base on solar array interactions exists. Spacecraft
charging studies in polar orbit conditions are in their infancy.
- Numerical and computational studies can aid in interpretation of the
interaction phenomena and, to a lesser extent, in spacecraft design. The
assumptions inherent in sevral codes limit their application to design
activities, until a more fundamental understanding of the basics behind the
interactions has been achieved.
- There is a large literature concerned with space based experiences, but
interpretation is, at times, difficult and contradictory. Vehicle charging in
polar orbits has been indicated, and the adverse effect that active beam
emissions can have on vehicles are well established. Again, a reasonable data
base on solar array interactions exists, but it should be noted that this is in
conflict with ground data.
The ESPIRE computer codes
The Spacecraft/Plasma Interactions and Electromagnetic Effects Program Suite
ESPIRE was developed for ESA to be used as an aid to spacecraft design,
addressing some specific problem areas in spacecraft/plasma interactions. This
computer program suite was complemented by experimental work to aid the code
validation. This was carried out in two different plasma simulation facilities.
One had a large volume and a high gas pumping speed, and was capable of
creating conditions which enabled large spacecraft with dimensions of hundreds
of Debye lengths to be simulated. The second facility was smaller, but had the
ability to vary or to cancel the magnetic field present in the plasma.
Experimental work on plasma wake phenomena used simple metallic models in the
shape of a disc and a rectangular plate, placed in a streaming plasma. The wake
structure downstream of the model was studied as a function of the Debye length
or body size, model potential and Mach number. A valid simulation requires
control of the slow ion population, using high pumping speeds and low operating
pressures, and this was successfully achieved in both facilities.
Experimental studies in support of spacecraft charging used high energy (5-20
keV) electron guns to bombard the wake side of a model placed in a streaming
plasma. Isolated metal targets of different materials and isolated Kapton were
placed in the wake position. The charging levels were measured as a function of
such parameters as ambient ion density, background pressure, ion energy, and
The final outcome has been the development of a flexible software suite to
model important aspects of spacecraft/plasma interactions and spacecraft
charging. The emphasis has been upon experimentally validated engineering tools
for use in spacecraft design. The suite is constructed in such a way as to
facilitate future additions tot he programs as a result of the continuing
development of engineering software tools.
Description of the ESPIRE codes
The interaction of a space vehicle with its surroundings in low Earth orbit is
a complex phenomenon and no simple description will allow all the features to
be adequately quantified. The use of computer codes does, however, provide the
spacecraft designer with a powerful tool to analyse some of the effects since
many of the physical processes occurring may be included in such coded.
Nevertheless, despite the potential of computational methods, it is not
realistic, at present, to design a code which includes all the physical
processes that may be present in a rigorous and self-consistent manner. Indeed,
such a code might be too slow or cumbersome to use for simple calculations of
importance to the spacecraft designer.
The solution to this issue is the creation of a suite of computer programs each
capable of analysing a part of the spacecraft/plasma interaction problem on the
basis of a specific but restricted set of assumptions. While each code
individually will allow only part of the problem to be addressed, the entire
suite will allow a much more complete picture to be obtained. The ESPIRE
program suite structure is illustrated in Fig. 3.
|Figure 3. Structure of the Spacecraft/Plasma Interactions and
Electromagnetic Effects Program Suite ESPIRE|
LEOPOLD Is a simple menu driven
code whose function is the rapid determination
of the principal parameters that characterise the low Earth orbit environment.
The input to the code is the orbital altitude.
Using empirical and theoretical relationships and in-built data bases, the code
evaluates and outputs seventeen space environment parameters. The input menus
have been replaced by HTML forms in the
SPENVIS implementation of LEOPOLD.
SOLARC Is the first of two programs lying at Level 2 in the software suite and
as such is somewhat more complicated than LEOPOLD.
SOLARC Is an O-D code which provides an assessment of the current collection
and the power loss that would be experienced by a solar array in LEO and polar
environments. For a given set of conditions, specified by the user, the code
creates current-voltage characteristics derived from two sets of empirical
formulae by finding the solar array voltage distribution that produces a zero
net collected current.
The first set of equations (model 1) were based upon the results of
ground-based solar array experiments undertaken at the NASA Lewis Research
Center. The second set of equations (model 2) were derived from space based
data obtained on the PIX-2 test flight.
The equations are fully integrated with the
SOLARC code. Any of the program
variables (such as solar array area, voltage relative to space plasma
potential, electron and ion current densities and temperatures) may be altered
independently within the code.
The second code residing at Level 2 is EQUIPOT.
EQUIPOT Is a flexible
menu-driven code which permits a rapid assessment of the likelihood of charging
for surface materials on a spacecraft. It utilises a simple geometry, a small
isolated patch of material on a spherical spacecraft, calculates the various
components of current to both the body (structure) and the patch, and estimates
the equilibrium potentials which will develop in order to achieve zero net
current. Approximate charging time is also computed. The user selects the
structure and patch materials, and also the plasma environment by defining
energy spectra for electron and ion fluxes. In the
SPENVIS implementation of EQUIPOT,
the menus have been replaced with HTML forms.
A number of options are available to cater for plasma regimes with Debye length
large (GEO) or small (LEO), solar illumination or shadow, spacecraft velocity
(ram and wake effects), and normal or isotropic incidence of particles. For
small Debye lengths, it is reasonable to assume that current collection is
sheath limited (plane probe assumption); for large Debye lengths, the geometry
becomes more important and a spherical probe assumption offers an alternative
SAPPHIRE Is the first of two programs lying at Level 3 in the software suite.
The programs at this level are specialised and require operator familiarity
with the codes in order to run them. Due to their complexity, the Level 3
programs are outside the scope of SPENVIS, and have not been implemented.
SAPPHIRE Is a two dimensional particle and potential code which calculates the
ion and electron densities and the electrostatic potential about a body or
bodies in the presence of a streaming plasma. It has the capability of
representing a variety of spacecraft geometries and allowing different
potentials to be specified. A number of ambient plasma conditions may be
modelled including monoenergetic plasmas and plasmas with a Maxwellian
PICCHARGE Is particle-in-cell code that requires few non-physical assumptions.
In the restricted situations to which it is limited, it produces accurate
simulations of object/plasma interactions. Complex shapes can be modelled, with
different materials making up their surfaces, and the charge buildup on
different surface areas can be monitored. The object can be placed anywhere
within the simulation space so that, with drifting plasmas, ram and wake
effects can be examined.
The DICTAT computer code
Electrical charging of dielectric materials in the magnetosphere is a major
cause of satellite anomalies. Where surface charging is concerned, there are a
number of software tools (e.g.
(NASA Charging Analyzer Program) and
enable satellite designers to model the extent of the problem and to make
satellites more resistant to this effect. For the internal charging problem a
useful scientific tool is provided by the ESA-DDC code [Soubeyran and
Floberhagen, 1994]. DICTAT
Was developed to provide a practical engineering tool to address problems of
internal dielectric charging.
DICTAT calculates the electron current that passes through a conductive shield
and becomes deposited inside a dielectric. From the deposited current, the
maximum electric field within the dielectric is found. This field is compared
with the breakdown field for that dielectric to see if the material is at risk
of an electrostatic discharge.
Martin, A. R., Spacecraft/Plasma Interactions and Electromagnetic Effects in
LEO and Polar Orbits, Final Report for ESA/ESTEC Contract No.
7989/88/NL/PB(SC), Vol. 3, 1991.
, , Final Report for ESA/ESTEC Contract No.
7989/88/NL/PB(SC), Vol. 1, 199
Soubeyran, A., and R. Floberhagen, ESA-DDC 1.1 User Manual, Matra Marconi
This text is based on Volume 3 of the Final Report for ESA/ESTEC Contract
No. 7989/88/NL/PB(SC) (Martin, 1991).
Last update: Mon, 01 Mar 2010