"Euphemisms are not, as many young people think, useless verbiage for that which can and should be said bluntly; they are like secret agents on a delicate mission, they must airily pass by a stinking mess with barely so much as a nod of the head. Euphemisms are unpleasant truths wearing diplomatic cologne."
(Quentin Crisp, Manners from Heaven)
Spacecraft clusters, or formations, are an emerging trend in space mission design. Proposed concepts utilize swarms of small micro- or nanosatellites acting in collaboration. For many applications, the vehicles within the swarm must maintain accurate position with respect to others in the group. To achieve relative position control, some type of formation-keeping propulsion is required on each vehicle. While the propulsive forces necessary are small (10's to 100's of microNewtons), precise application and control of these forces is difficult in practice. Also, continuous application of formation-keeping forces would quickly exhaust the propellant supply of traditional micro-rocket engines. In 2001, the Isp Lab was the first to propose the use of inter-vehicle Coulomb forces for use in spacecraft formation control. This concept relies on electrically charging spacecraft by expelling charged beams. The vehicles then experience electrostatic attraction or repulsion from the other vehicles in the swarm. The entire formation exhibits coupled, collective motion that can be exploited to maintain relative position. Since Coulomb propulsion requires no fuel, the concept can essentially maintain a formation for an indefinite period of time. The power required to affect Coulomb propulsion has been shown to be on the order of milli-Watts up to a few Watts. The required on-board mass of the system has been shown to be very small. Research continues on charging mechanisms, charge sensing/serving techniques, spacecraft/plasma interaction, and distributed control.
StefanR wrote:I must fully agree with you Osmosis and Junglelord.
StefanR wrote:But to get to the subject, I was wondering what the effective distance would be between the satellites for using such Coulomb Thrusting?
MGmirkin wrote:Anyone else want to join the Coulomb propulsion groupie train?
1.1 Virtual Coulomb Structure
Spacecraft formation or general proximity flying is increasingly gaining interest in the aerospace
community. The benefits of a spacecraft formation include lower life cycle cost, reconfigurability
of the formation shape and size, as well as adaptability of the formation in
case of a malfunctioning satellite.1–4 Applications such as synthetic aperture radar, space
interferometry and sensor web formation are more feasible using spacecraft formation flying,
rather than large monolithic structures.1, 2
For small spacecraft separation distances on the order of 100 meters or less, thruster exhaust
plume impingement issue with neighboring satellites is a major technological hurdle.
Further, conventional chemical thrusting concepts are not effective in generating the small
micro-Newton level forces required to maintain a cluster dozens of meters in size. Coulomb
thrusting provides an attractive and novel solution to these technological hurdles arising
from the control of a spacecraft in a tight formation.
The concept of Coulomb propulsion is based on the principles of electrostatic forces, which
arise due to the interaction between two charged bodies. Spacecraft in the formation are
charged to a certain potential. In the concept of static Coulomb formations the constant
Coulomb forces are used to cancel out the relative motion dynamics and maintain a fixed formation
with respect to the rotating formation chief Local Vertical/Local Horizontal(LVLH)
frame. The electrostatic forces acting on the spacecraft are internal forces, and thus cannot
change the total inertial angular momentum of the spacecraft.
Coulomb thrusting is considered an attractive solution as compared to electric propulsion for
control of a spacecraft in a tight cluster of less than 100 meters. Electric propulsion is a fuel
efficient method to control the spacecraft in a formation compared to traditional chemical
thrusting concepts. The usefulness of electric propulsion is diminished for small separation
Harsh A. Vasavada Chapter 1. Introduction 2
distances between spacecraft, as the ionic exhaust plume could potentially damage near-by
spacecraft. Coulomb propulsion has the advantage of being essentially propellant-less and
offers mass savings up to 98%.5, 6 Coulomb propulsion is a highly efficient propulsion system
achieving Isp to the order of 1013s. The power required to charge the spacecraft is in the
order of watts (W).6 In addition to being a highly efficient system, Coulomb propulsion is
also based on a renewable source, increasing the mission lifetime as compared to electric
The concept of static Coulomb formation is similar to a virtual Coulomb structure. In a
virtual Coulomb structure the truss and beam structural members are replaced with electrostatic
force fields. In the presence of external disturbances, the force fields are only able
to provide tension and compression to maintain the structural shape of a spacecraft cluster.
The force fields maintain static virtual structures as seen by the rotating LVLH frame. Figure
1.1 shows a Coulomb virtual structure in space. Here the connections between spacecraft
represent the electrostatic force fields acting on the spacecraft.
Coulomb Formation Flying
Plasma: cloud of positively and
negatively charged particles
➡ Debye Length ( ):
Characteristic length over
which charged particles in a
plasma influence each other -
an exponential effect.
➡ Beyond a few Debye lengths, a
charged particle appears to
have no charge and thus no
Max charge sphere
separation for practical
Coulomb thrusting is
about 2 Debye lengths
Spacecraft Collision Avoidance Using Coulomb Forces
with Separation Distance and Rate Feedback
COLLISION avoidance is a general concern in a tightly flying
cluster of spacecraft with separation distances ranging from
dozens to hundreds of meters. Such mission concepts include small
satellite swarms flying scenarios where a smaller spacecraft is
circumnavigating and inspecting a secondary craft. (Do I sense an asteroid?)
The concept of aspacecraft formation involves multiple satellites that work
together in a group to accomplish the objective of a larger, usually more
expensive, satellite. The spacecraft swarm concept envisions a large
number of satellites flying in space with loose position-keeping
requirements, while the swarm members provide a highly distributed
and redundant sensor platform. Collisions can occur when spacecraft
within the cluster have control or sensor failures, or lack a guidance
strategy to guarantee collision avoidance among a large number of
cluster members. Preventing collisions has many challenges. First,
the collision onset must be sensed with sufficient accuracy to warrant
a corrective maneuver. Second, a control strategy must be developed
to provide the required small corrective forces without causing
plume-impingement issues on neighboring satellites. This paper
focuses on a mission scenario in which loosely clustered satellites are
flying in deep space in a bounded configuration. The satellites are
assumed to have a low approach speed with respect to each other.
This strategy is not designed to repel high-velocity bodies.
To perform efficient collision avoidance maneuvers in a dense
spacecraft cluster, this paper presents a new approach that uses only
electrostatic (coulomb) forces. For tight clusters with spacecraft less
than 100 m apart, this approach stands out because the coulombforce
generation is essentially propellantless. Further, it will not
generate any propellant plume-impingement issues which could
threaten neighboring spacecraft. The use of coulomb thrusting in
spacecraft cluster flying has been studied frequently since King et al.
originally discussed coulomb formation flying (CFF) in .
The concept of CFF uses coulomb forces to achieve the desired
relative motion. Spacecraft will naturally charge to nonzero
potentials in a space plasma environment. With CFF, the spacecraft
charge level is actively controlled through the continuous emission
of electrons or ions. Coulomb-force control is 3–5 orders of
magnitude more fuel-efficient than electric propulsion (EP) methods,
and typically requires only a few watts of electrical power to operate
. Whereas conventional thrusters can produce a thrust vector
pointing in any direction, coulomb forces always lie along the lineof-
sight directions between the craft. Further, in space, the spacecraft
are not flying in a vacuum, but rather a sparse plasma environment
which can shield electrostatic charges. The plasma debye length
characterizes the amount of shielding [6,7].
Europe all set for lunar mission Chandrayaan-1
25 September 2008
Europe is participating in a big way in the Indian Space Agency’s Chandrayaan-1 mission to the Moon, by contributing three instruments. All these instruments have now been delivered, tested and integrated with the spacecraft.
SIR-2, a near-infrared spectrometer was delivered in the first week of November last year. SARA, Sub-kilo electron volt Atom Reflecting Analyser, was delivered on 8 April 2008. Europe’s contribution is now complete as the Chandrayaan-1 X-ray Spectrometer (C1XS), the third instrument, was tested and integrated with the spacecraft on 22 August.
SIR-2 will survey the Moon’s geological composition and the effect of space weathering on its surface. Data from the instrument will be used to study the formation of the structures that exist on the Moon. SIR-2 is led by the Max-Planck Institute for Solar System science.
Erd added, “SARA follows up on instruments used on board Mars and Venus Express and will be the first instrument to study plasma-surface interactions, while SIR-2 and C1XS build upon the legacy of SMART-1. The lessons we have learnt through experience will be put to good use with Chandrayaan-1.
Mysterious "dark matter" could lurk near Earth, according to a new theory to explain a puzzle that has baffled space flight engineers.
The suggestion that clumps of the enigmatic matter lie in our cosmic back yard, between the Earth and the Moon, has been put forward to explain a strange phenomenon called the "fly-by anomaly."
Almost every spacecraft that has swung around the Earth to speed it on its journey has recorded a velocity change that, according to the well-understood laws of gravity, should not have happened.
Some think the fly-by anomaly hints that something is wrong with the laws of physics and our best law of gravity, Einstein's general relativity, is due for an overhaul, which is a radical suggestion.
However, theorist Dr Stephen Adler of the Institute for Advanced Study, Princeton, has an alternative suggestion, which is based on an invisible stuff, the existence of which can only be inferred.
A US astronaut and a Russian cosmonaut completed a 5.5-hour spacewalk outside the International Space Station on Tuesday to install a device that monitors conditions around the orbital outpost.
Engineers believe electrical charges triggered glitches that caused Russian space capsules returning from the station to land hard and off-course during two consecutive homecomings in October 2007 and April 2008.
Flight controllers staged a spacewalk in July to disconnect suspect equipment on the last Soyuz capsule, circumventing the problem for its landing in October.
In search of more data, Russian flight controllers late on Monday dispatched station commander Michael Fincke, a veteran of four previous spacewalks, and flight engineer Yury Lonchakov, who made his first spacewalk, to install a probe to monitor electrical fields near where Soyuz capsules park.
"The space station is this big, old huge chunk of metal flying through a magnetic field," deputy program manager Kirk Shireman told reporters last week. "There's an electron cloud flowing around the station at all times. And then the station itself generates electricity."
Fincke and Lonchakov quickly completed the primary task of their spacewalk, then installed two science experiments to the outside of the station's module.
But when it came time to test new gear, flight controllers could not get any data to the ground.
With time running out, flight directors told the men to retrieve one of the experiments and head back to the airlock. "We've done everything we could," Finke, speaking Russian, said through a translator.
The station, a $100 billion project of 16 nations, is nearing completion after more than a decade of construction. Next year, NASA and its partners plan to expand the station's live-aboard crew size from three members to six.
NASA's next mission to the station is scheduled for February.
Users browsing this forum: No registered users and 1 guest