ESA Call For Student Papers

In order to stimulate some innovative research and encourage European research students to participate in the Planetary Defence Conference the Advanced Concepts Team (ACT) at the European Space Agency is releasing a few interesting ideas that young researchers may wish to develop in a scientific paper.   The ideas are explained below, giving an outline of the general concept and suggesting possible, non-exhaustive paths that may be investigated. 

To be part of the ESA Call for Student Papers the paper must be based on one of the ACT suggested topics and thus the ACT reserve the right to contribute and be co-authors on the final paper if significant collaboration should arise.

The research topics

TOPIC:Deflecting Binary asteroid systems
POSSIBLE RESEARCH AREAS: Space systems engineering, orbital mechanics

Binary asteroid systems are common; around 15% of all near Earth asteroids are thought to binaries. The dynamics of such a system is very different from that of a single-body. This raises many questions:

• How effective are existing mitigation concepts on binary systems?
• What modifications and considerations to existing deflection conepts would be needed in such cases?
• What new deflection techniques could be conceived for binary systems?
• How does the impact prediction differ from the non-binary case?

TOPIC:Deflection during close approach
POSSIBLE RESEARCH AREAS: Space debris, Space law, space systems engineering, astrodynamics

 So that orbital debris is minimized and popular orbits don't become too congested, satellites that have reached the end of their mission are commonly sent into the Earth's atmosphere to burn up or put into 'Graveyard orbits'. Much effort is put into the design of modern satellites to ensure this, and extra fuel is carried on-board to guarantee these manoeuvres. So many satellites are already out there with some residual fuel available. These 'expired' satellites could be transferred into orbit in due collision with an asteroid performing a close Earth approach and predicted to have a resonant return. This technique, similar to the kinetic impactor method but acting in reverse, is capable of achieving high relative velocities at impact.

Several issues can be addressed:

• Can we design effectively a satellite constellation able to actively shield the Earth from reonant returns?
• For a given asteroid such as Apophis, what are the favourable satellite orbits to implement this concept? Are there satellites already out there that can be used?
• How effective would the technique be in deflecting a given, Apophis-like asteroid?
• How does this concept compare with other mitigation techniques?

TOPIC: Maximum charge of a satellite
POSSIBLE RESEARCH AREAS: Electrostatics, plasma physics, mission analysis,  space systems engineering

 In the Electrostatic Tractor deflection concept [1] a satellite and the asteroid are charged, either pulling or pushing the NEO so that it does not impact with the Earth. One limitation behind the effectiveness of this concept is the amount of charge that a satellite is able to hold. The primary interest for space engineers has always been to obtain a neutrally charged satellite, as a consequence little is known about situations in which high potentials are desirable on board the satellite. Authors could consider the following:

• What technologies could help a satellite withstand a greater charge when using standard designs?
• How could a spacecraft be redesigned so that the charge does not affect the sub-systems?
• Are there any novel ways to prevent electrostatic arc on spacecraft?
• What would the impact of such modifications be on the Electrostatic Tractor concept?

[1] Murdoch, N., Izzo, D., Bombardelli, C., Hilgers, A., Rodgers, D., Carnelli, I.: Electrostatic tractor for near Earth object deflection, Proceeding of the 59th International Astronautics Conference, Glasgow, UK, 2008.

TOPIC: Deflection strategies using multiple spacecraft
POSSIBLE RESEARCH AREAS: Artificial intelligence, space systems engineering, robotics
Deflection strategies consider often one single spacecraft and of course sending many satellites of the same size would require many more resources. Instead, it would be interesting investigate how the existing single satellite concepts could be broken down into several smaller spacecrafts, or even numerous miniature ones.
Authors should base their study on at least one of the known deflection concept (such as the gravitational or electrostatic tractor, kinetic impactors…). A comparison between the multiple and single spacecraft mission should be done, including effectiveness, resources required, reliability and so on.
Other ideas that may inspire research include:

• Is it possible to utilise many smaller satellites and still achieve or improve upon the current possible performance levels of a given technique?
• Dynamics of the multi-body system.
• The use of swarm intelligence in such a strategy.

TOPIC: Avoiding reaggregation by electrostatic charge
POSSIBLE RESEARCH AREAS: Electrostatics, plasma physics, dynamics, geology, nuclear physics, space systems engineering

 The asteroid deflection technique of using explosives is seriously undermined because of the recombination of the asteroid over time due to its own gravitational field. It is known that electrostatic fields develop at the surface of resistive asteroids exposed directly to solar radiation and the solar wind [1]. This process is expected to lead to the levitation and transport of charged grains. It has also been proposed to artificially charge an asteroid to kV potentials. Papers on this topic should address the possibility of disrupting an asteroid whilst electrostatically charged so as to avoid reaggregation. Questions raised:

• What level of charge would be required to overcome the gravitational reaggregation?
• What is the timescale for particles to be neutralised by the space plasma?
• Novel methods of artificially electrostatically charging asteroids
• Approaches to electrostatically charging and maintaining the charge on asteroids' diffuse material.

[1] Lee, P., Electrostatic Levitation of Fines on asteroids, Meteoritics, vol. 30, no. 5, page 535, 1995

TOPIC: The Magnetostatic Tractor
POSSIBLE RESEARCH AREAS: Material Science, magnetic physics, space systems engineering, asteroid composition

 The observation of the asteroid Gaspra by the Galileo spacecraft in 1990 showed that Gaspra has a magnetic moment, strong enough to disturb the interplanetary plasma flow. Some remnant magnetization from the formation of the asteroid could create a chaotic magnetic field. Gaspra's magnetic moment has been estimated around 1.5*10^{11} Gauss m^3, predicting a surface magnetic field around 0.5 Gauss at a radius of 7 km. [1] Very little is known for other asteroids. Could a natural or induced magnetic interaction between an asteroid and a spacecraft be exploited to produce a deflection force and hence produce a Magnetostatic Tractor? Areas of interest include:

• How strong could the natural magnetic interaction between asteroid and spacecraft be?
• How could an artificial magnetic field be generated around an asteroid?
• For what size and composition of asteroids could this be an attractive option?

[1] Jacques P. Vallée ,Observations of the Magnetic Fields Inside and Outside the Solar System: From Meteorites (~ 10 attoparsecs),Asteroids, Planets, Stars, Pulsars, Masers, To Protostellar Cloudlets (< 1 parsec),"Fundamentals of Cosmic Physics", Vol. 19, pp. 319-422, 1998.

TOPIC: Lorentz Deflection during an Earth fly-by
POSSIBLE RESEARCH AREAS: Electrostatics, tethers, magnetospheric physics

As an electrostatically charged satellite passes through the Earth's magnetic field it is subject to the Lorentz force. The physics involved in this interaction is well understood. Could the same force acting upon a passing asteroid be used to deviate its path? Research topics could include:

• The level of electrostatic charge that would have to be reached on the asteroid to produce a "Lorentz Deflection"
• The location and timescales of the asteroid encounter with the Earth's magnetic field for optimal deflection
• Could a resonant asteroid be deflected enough in order to avoid future impact scenarios?
• Could tethers or other systems be added to the asteroid to increase this force?

TOPIC: Observing Apophis with LISA
POSSIBLE RESEARCH AREAS: Gravitational physics, interferometry, asteroid geology

 LISA, the Laser Interferometer Space Antenna, could be launched between 2018 and 2020. It aims to detect gravitational waves in the low frequency range. It has been shown that its encounter with asteroids will produce detectable signals, depending on the relative velocity, the shortest distance between one of the LISA satellites and the asteroid, and on the mass of the asteroid.[1] Possible topics for further study include:

• Could LISA give us more insight into the internal structure of Apophis?
• Possible changes to LISA (engineering / mission) in order to improve our understanding of Apophis.
• Can LISA improve our trajectory estimation error for Apophis?
• Can LISA be used to infer any more information about Apophis?

[1] Vinet, J-Y, ''LISA and asteroids'', Classical and Quantum Gravity, Volume 23, Issue 15, pp. 4939-4944 (2006).

TOPIC: Changing the internal structure of asteroids
POSSIBLE RESEARCH AREAS: Impact physics, asteroid geology, chemical engineering

The potential threat posed by an asteroid does not just depend on its size or mass, but also on its internal structure. Asteroids are known to exist with densities ranging from <1g/cm3 to ~5g/cm3 and a wide range of porosities. Can we somehow alter the internal structure of an Earth threatening asteroid to reduce its threat to Earth?

Possible questions to be asked include:

• The optimal internal structure to minimise damage to Earth
• Possible methods for altering internal structure
• Could a chemical reaction affect an asteroids internal structure, albedo, temperature etc..

Dates and location :

27, 28, 29 and 30 April 2009. Granada, Spain.

For more information: See the conference web page at http://www.congrex.nl/09c04/