Using Space as a Giant Laboratory

One of the mission objectives of the strategy is 'to develop a strategy that ensures valuable scientific results and better answers to fundamental questions.' There is a wealth of information on the scientific objectives of visiting certain destinations in the solar system already published, and it is not our intention to review this here. What is proposed is to push beyond the limit of what is feasible today. The idea is to anticipate the future of space science.

Nowadays, space physics, aside from a few exceptions, is based on observation. Then, the new step will be to perform experiments in space and with space. In this sense, space will be used as a giant laboratory. Instead of looking at the clues of planetary creation and trying to piece together the past using traditional methods, we want to test modern hypotheses by active experimentation.

In space research, the development of ideas is often a "brain attack" when people are most motivated, i.e. it gives the highest probability of solving the problem(s). That will obviously force the apparition of new technologies, for example small nuclear reactors were originally developed for long life satellites and are now used to generate electricity in geographically remote areas. New scientific experiments in space may lead to the creation of new technologies of use to human exploration of space.

In the following we develop two innovative physics experiments ('baby magnetosphere' and 'space billiards') which are examples of the kinds of projects that may be achievable in the future, which have scientific, technological and human benefits. We will also discuss in less detail a number of future experiments covering a range of scientific fields. It is fair to say that based on current estimates, our experiments would be prohibitively expensive, although cost analysis of these experiments has not been performed. This is because all of our ideas need significant technological advancement in order to realize them, rendering present day cost analysis meaningless.

Baby Magnetospheres

The Earth's magnetosphere has been the subject of intense study ever since the start of the space age. Apart from pure scientific curiosity, as we rely more and more on satellites we need to gain a better understanding of the harsh environment in which they reside. The field of space weather is now developing too, as people become aware that explosions on the sun can have a direct impact on our civilisation on earth. Our knowledge is improving by means of scientific probes flying through the earth's magnetosphere as well as other magnetospheres such Jupiter's, which is much larger and has significant differences, but can lead us to a greater understanding of magnetospheric physics in general.

But what if we could create our own magnetosphere, using our physical constraints on size, shape, etc? This short discussion describes an initial attempt to assess the feasibility and benefits of creating a mini magnetosphere around a spacecraft for scientific study, and it's potential use in radiation shielding for human space flight.

The smaller we make a magnetosphere, the smaller the size of a magnetic field we need to create, and the less power we need. But what are the limiting factors to how small we can go? In order to maintain the same physical characteristics, we need a magnetosphere which is much larger than the debye lengths of the particles which it contains and which it will interact with. The debye lengths of particles in the solar wind are typically tens of meters, and magnetospheric particles can have debye lengths of hundreds of meters [Kivelson 1998]. So to be three orders of magnitude bigger than these lengths, lets suggest that the size of our magnetosphere needs to be of the scale of a sphere of one hundred kilometers radius.

To know the intensity of the magnetic dipole moment required to obtain such a magnetosphere, we can use the equation standing for the balance between the solar wind pressure and the magnetospheric pressure

where B0 is the equatorial surface field of the Earth, a is a compression factor, rsw is the solar wind density, usw is the velocity of the solar wind, mo is the permeability of free space, and K is a measurement of the solar wind flow divergence at the magnetopause. For a dipole, this equation becomes

where M is the magnetic dipole moment, and Lmp is the distance from the dipole axis to the magnetopause in the magnetic equatorial plane. The latter equation yields the relation

Given a Lmp of 100 kilometers, i.e. 1/600th of the Lmp for the earth's magnetosphere, we can conclude that we need a magnetic dipole moment M = 4x10-9 M_earth. As the earth's magnetic dipole moment is 8 x 10E15 Tm2 [Kivelson 1998], the corresponding figure for our mini magnetosphere is of the order of 4x10E7 Tm2.

In order to achieve this, a conventional electromagnet would need to have ten million turns with one ampere current flowing, enclosing a one meter squared area. Apart from the problems of constructing such an apparatus, issues such as heat production would need to be addressed. Possible solutions may lie in the development of superconducting coils, or further research into the origin of the earth's magnetic field leading to new ways of creating large magnetic fields using some kind of magnetic fluid rotation.

Starting with such a magnetic field, we have the possibility of changing many parameters such as the orientation of the dipole axis relative to the direction of the solar wind or the intensity of the magnetic field. We can also use a plasma generator to create an ionosphere around the spacecraft or inject some plasma in different locations of the mini-magnetosphere.

Once we have created this mini-magnetosphere, we need to devise ways of measuring the plasma environment created. Unfortunately, the lack of a large body at the center of our mini magnetosphere means that scientific micro-satellites necessary to gather scientific information will not naturally orbit our spacecraft.

These satellites carrying various instruments to analyze electric and magnetic fields as well as particle detectors, will need to regularly update their trajectories to ensure they pass frequently through our mini magnetosphere.

Another solution is to place the spacecraft on one of the two stable Lagrangian points of the Sun/Earth system, L4 and L5. The advantage of that location is that you can put satellites into a halo orbit around the spacecraft so that the measuring of the physical parameters of the magnetosphere becomes easier. Moreover we choose those two particular points because they are free of any permanent interference with the Earth's magnetosphere, and they are not as close to the Sun as L1 (which would require a stronger magnetic field as the solar wind pressure is greater there).

We can of course consider other places thereafter. For example, if we put the mini magnetosphere further away from the Sun, the solar wind pressure will be less and then the magnetosphere will expand. Or we can also try to look at the interaction of our magnetosphere with the plasma sheet in the tail of the earth's magnetosphere.

Producing such a mini magnetosphere will enhance our knowledge of how magnetospheres work. This will be a vital contribution to the new discipline of space weather, where scientists are trying to study the complete process of events on our sun travelling through the solar wind, interacting with the magnetosphere and impacting the earth and its inhabitants.

But there is a further exciting direction for this work, directly linked to human exploration of space. The technology which would be developed for this experiment may prove vitally useful for the magnetic shielding of spacecrafts against radiation as has already been suggested in previous studies [ISS SSP 1998]. By shielding a spacecraft magnetically rather than with physical structures, you can avoid the problems of secondary radiation effects.

Space Billiards

Asteroids may be like a snapshot of the first stages in planetary evolution. We are in the midst of en epoch of discovery in which we are just beginning to see what asteroids look like and to understand how they got to be the way they are.

In July 1994, The comet Levy-Schoemaker's fateful impact into Jupiter was broadcast on news channels worldwide. Not only did it provoke immense public interest, but it also produced fascinating data which was eagerly studied by the scientific community, see for example Sekanina 1995, Spencer 1995.

'Space Billiards' is an experiment which basically proposes to control the trajectory of small asteroids in order to be able to collide them with each other. The technological developments needed to control the trajectories of asteroids have already been discussed in section 2.6.2, and this experiment provides a test bed for developing such technologies.

The scientific interests are multiple. It will help to better understand impact cratering, catastrophic disruption of asteroids and related phenomena essential to the evolution of planetary geology and biospheres and to the accretion of solar systems. As the role of impacts in solar system creation becomes more widely considered, the field of crater studies has become a scientific discipline in its own right, complete with conferences and textbooks [Taylor, 1992; Melosh,1988]. Impacts may explain such phenomena as the retrograde motion of Venus, the 970 inclined rotation of Uranus, and the earth-moon connection. This experiment would allow scientists to test competing theories and answer some of the fundamental questions of solar system evolution. It will also provide calibration to the scaling laws used during laboratory research, improving current mathematical models of crater formation.

We will also be able to improve our knowledge of the composition of the target body and to get information from the seismic waves generated by the impact, by installing detectors on the target before impact. Ejecta velocities can be studyed, and the creation of dust and plasma on impact will interact with the vacuum of space in unexplored ways.

The chosen bodies dedicated for colliding experiment can be diverse in function of what would be specifically studied but the evolution of the technology to perform it has to be taken into account. As the average size of the asteroids ranges from 30 m to 3 km, the logical first experiment will be to deviate a small asteroid into a big one (in respect with the given dimensions). Knowing that some asteroids have their own moon, one could even think of smashing it into the asteroid and then gain in terms of energy needed thanks to the proximity of the two bodies. An analysis of collisions between asteroids may help explaining the structure and evolution of these small planetary bodies and help us understand the formation of planetesimals by accretion at the early time of the solar system.

To obtain the best scientific return, various asteroid collisions would need to be performed, although the shape and density of asteriods are so diverse that comparative studies will be difficult. Indeed, the outcome of such impacts depends on the degree to which the asteroid has been fractured and made porous by early collisions. Three different internal structures are cataloged: solid rocks, a pair of solid rocks in close contact, and a rubble pile with pore space accounting for 50 percent of its volume (see the gray box). The velocity is a significant factor, and impact energy will also be dependent on the angle of impact. The typical speed for collisions in the asteroid belt is 5 km/s.

Additional studies may explain many of the key processes involved in the evolution of the planets. In this way, whether other targets would follow, and which ones, would be subject to debate. Potential targets could be the dark side of the moon (not realistic due to public concern over its proximity to Earth ), the moons of Mars, Jupiter, Saturn and Neptune and the planet Venus. It must be stressed however that the emphasis of these impacts would not be to change the current state of the solar system, or the orbit of any planets, considering that asteroids of relatively small size would be used.

This view of making science in space can be controversial, but collisions are something natural in space and provoking them has just the effect of speeding up the process in order to observe those fantastic phenomena under controlled conditions. Nevertheless, before starting such an experiment, legal and public issues would have to be addressed first. It should be mentioned here that NASA has recently approved a mission called Deep Impact which plans to fire a 500 kg projectile into a comet, so these types of questions are already being raised.

The feasibility and the assets of such kind of experiment have to be closely studied. Although there are numerous aspects to develop, they can be separated into two groups. The first one concerning the asteroids themselves, and the other one, the geological characteristics of the impact.

• For the asteroids, whatever the target, the general argument remains the same. The first phase is to improve the identification of the asteroids. Indeed, even if the endeavor to catalogue asteroids in the solar system has increased during the last 10 years, there is still a lot of time and work to be done to improve the database, due to the current difficulties in detecting small near earth objects (<< 1 km radius). The technology allowing us to advance in this way is the additional charge-coupled device (CCD) detection systems that were recently installed at dedicated search telescopes in the United States and abroad.

This detection phase is critical in selecting the most appropriate candidate asteroid. This latter has to fill some conditions such as having at least one node, or near to that ideal case, between its orbit and the one of the target body. Its mass has to be compatible with the maximum deltaV that the trajectory control system allows.

 

The asteroids are presumably representative of the small bodies that eventually grew into planets by accumulating additional matter. This accretion process must have involved numerous collisions between smaller bodies, and the main issue today is trying to find out what factors in a collision favor the accumulation of mass (allowing for the growth of planets) rather than disruption and loss of mass.

With regard to the complexity of the process dedicated to attaching the propulsion system to the asteroid, humans will play an important role. It means that the "space billiard" experiment will take place after the human exploration of NEOs or at least in parallel.

The simulation code in this fields begin to be well developed. To give an example, 4769 Castalia is a near Earth asteroid (NEA) whose shape, however unusual to us, may in fact be representative of many small planetary bodies. This impact simulation begins with a 16 meter (50 foot) diameter projectile (the white dot in the first frame) impacting at 5 kilometers per second (11,000 miles per hour), a typical encounter speed for objects such as these in the asteroid belt. The impactor weighs 6000 tons, compared with over 1 billion tons for Castalia. This impact speed, squared, times the mass of the impactor equals the impact energy: 17 kilotons, the same as the Hiroshima explosion.

 

 

Simulations rendered by Shigeru Suzuki and Eric M. De Jong of the Digital Image Animation Laboratory (DIAL) at NASA Jet Propulsion Laboratory (JPL).

• About geological characteristics for a controlled impact between an asteroid and its moon or between two asteroids, the observation and analysis of the impact by a flyby spacecraft must be coupled with human exploration after the event. Indeed, it would provide considerable improvement in understanding because of the ability to make intensive geological observations and take carefully chosen samples. This understanding concerns the nature of the rock revealed underneath the surface thanks to the impact (using spectrometry), the mechanism of the collision, accretion and separation. In long term view, the experiment should be repeated as much as possible to obtain a large range of initial conditions.

The recognition of the importance of meteorite impacts on Earth has come largely from the study of other planets. Exploration of the Moon and the solar system by astronauts and robotic spacecraft in the 1960s and 1970s, demonstrated that impact cratering has been, and still is, a major process in the origin and evolution of all the solid bodies of the solar system, from Mercury to the moons of Neptune. Observing the collision in real time will provide more information about formation of widespread ejecta deposits, the lava-like bodies of impact melt and the cliffs and terraces formed during crater development than merely studying the remains of these phenomena at old impact sites. In this context also Human exploration is justified after the experiment in order to perform unique geological observation. Indeed, even though most of the terrestrial impact structures have been removed by erosion, many fundamental concepts of cratering mechanics - crater modification, central uplifts, impact melt formation and emplacement - have been established on terrestrial structures and then applied to craters elsewhere in the solar system [French, 1998]. The proposed experiment will change this trend and provide the opportunity to get away from earth primordial information about the colliding mechanism.

The relevancy of such kind of experiment is the fact that the formation of a crater is an impact event and the formation of the resulting crater is virtually instantaneous. At the instant of impact, the object's kinetic energy is converted into intense high-pressure shock waves, which radiate rapidly outward from the impact point through the target rocks at velocities of a few kilometers per second, as well as back through the projectile body. Large volumes of target rock are shattered, deformed, melted, and even vaporized in a few seconds, and even large impact structures form in only minutes. A 1 km diameter crater forms in a few seconds.

The analysis of collisions between asteroids apart the scientific interest raises concerns about the feasibility of disrupting or deflecting an asteroid in the event that one is discovered going through space towards Earth. So, as with the Jupiter comet collision, we anticipate large public interest in this experiment and the possibilities of discovering an asteroid on a collision course with the Earth highlights an extra benefit of this work. The development of propulsion techniques for asteroids could then be used to prevent the asteroid colliding (see section 2.6.2).

In the case we ever identify an asteroid or comet on a collision course, it would be best to know our enemy so that we can get it before it gets us.

Other Experiments

• Cell Exposure

On Earth, laws protect humans from environmental work hazards. Indeed, if a gas leak were detected, workers would be evacuated immediately from the area. Yet astronauts and cosmonauts regularly travel into space, where the hazards are still not fully understood. Our strategy will send humans beyond the relative safety of the Van Allen radiation belts. Experiments looking at the fundamental effects of radiation on living organisms need to be performed.

Initially yeast cells could be sent into low-Earth orbit (LEO) for two years, with a control population kept on Earth (similar to the 1994 'Exploring the Solar System' ISU design project). In space, the cells can be divided into a number of populations surrounded by various radiation shielding technologies while leaving one population to suffer the fate of no radiation shielding. The next step would be to repeat the experiments using mammalian cells. Yeast cells are eukaryotic organisms and easy to maintain, so they are ideal as the first test system to determine radiation effects.

At first, populations of mammalian cells could be tested in vitro. Eventually it would be interesting to test specific cells from specific organ systems like the gastrointestinal system, the neural system, and skin. The disadvantage today is that this does not allow us to study the effects of radiation at the individual cell level. In order to overcome this problem, it might be interesting to develop arrays to which single cells could be attached. For instance, neural cells could be attached to form a neural network. Then specific cells could be identified and studied. Interactions between the cells could also be studied, such as changes in cellular factor production or receptor expression. Different types of mammalian cells in isolation would be studied first, and then groups of mammalian cells. Only then will we be able to get a real idea of the effects that radiation may have on the human body at a cellular level.

• Where Are We?

Between 1990 and 1993, the Hipparcos satellite collected an incredible amount of data about the position and velocity of tens of thousands of stars, providing us with a new view of our Galaxy. It was the first satellite dedicated to that function, and even though we learned a lot from that mission, much still needs to be done.

To increase the precision of the distance measurements, we need to have a longer baseline for the parallax and to know its length very well. We need to choose a place where the orbit perturbations are minimized and station two satellites at these points as the ends of the baseline. The Earth-Sun system's L4 and L5 points seem to be the most appropriate places due to the fact that they are gravitationally neutral and provide a baseline 1.7 AU in diameter.

• Veggie Transmission

The means of growing vegetation on another planet (or a spacecraft) may need to be developed in the future. Growing vegetables in space will provide fresh produce and a less mundane type of food for humans. In addition to playing a role in future closed-loop life support systems, plants may help create a more relaxed environment for the crew.

One solution is to send seeds to our destination and grow the plants there. This would require more effort at the final destination, but would enable a variety of plants to be sent. In the future, this could be taken further. Instead of sending seeds, you could send individual cells of different plants and develop the plants from these cells. Experimental techniques to do this are currently being developed on Earth, as exemplified by the "Dolly" sheep cloning experiment (Telegraph, 1997).

In the far future, it may become possible to create a plant cell from the DNA code itself. Imagine the possibilities this could present. Bases on distant planets could request the DNA codes for particular plants, and this code could then be sent from Earth via radio transmission, alleviating the need for a spaceflight altogether.

• Hunting Gravity Waves

Gravitational waves have become an important research field for astronomers in the last few years, since the technology has improved enough to detect them. For instance, the Laser Interferometer Gravitational-Wave Observatory (LIGO) will be built as a facility dedicated to the detection and measurement of cosmic gravitational waves. It will consist of two widely separated installations within the United States, operated in unison as a single observatory.

Gravitational waves are ripples in the fabric of space-time produced by violent events in the distant Universe; the collision of two black holes or a supernova explosion, for example. These waves are emitted by accelerating masses much as electromagnetic waves are produced by accelerating charges. The ripples in space-time travel to Earth, bringing with them information about their violent origins and the nature of gravity.

The weak signal to noise ratio of these gravitational waves is an important obstacle for measurement on Earth. The idea is then to put a gravitational wave observatory similar to LIGO on the Moon, since it has a lower background vibrational noise than the Earth (less seismic and manmade vibrations). The experiment can be set up to run in an automated fashion. Humans would periodically be sent to perform maintenance and repair tasks beyond what the automated system can accomplish.

For the long-term view, there is a very interesting place at the extreme reaches of the solar system (further than 550 AU) where the gravitational field of the Sun focuses light and gravitational waves. Putting instruments at this location would result in the deep field view being magnified significantly. The gravitational lens telescope could only be pointed at the star field directly behind the Sun, so this limits the amount of sky watching that can be accomplished.

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