Chapter 7: Conclusion

7.1 General Remarks

As a whole, this project has been very successful indeed. In spite of the lack of any previous work studying catastrophic hypervelocity impact experiments in this way (that is, using a high-speed camera in an open outdoor arena, and analysing the resulting films using a computer), we have successfully carried out an almost complete experimental analysis of the ejected fragment field from the experiments carried out in 1989 and begun analysis of those carried out in 1992. The resulting computer system and software represents a unique facility for (in the case of HV-2) single-camera or (in the case of HV-3) full three-dimensional analysis of fragmentation experiments of this type. Not only will the HV-2 program be useful "as is" in future, but it will provide, together with HV-3, a solid software base upon which to build further. In the process of developing and using this software, the other members of the group and I have built up a good understanding of the problems involved in the computerised study of disruption experiments such as these. This experience which will no doubt prove invaluable in any future studies of this kind.

7.2 Confirmation of Previous Results

As with any experimental study such as this, it is important to consider the ways in which our results agree with and differ from those of other researchers. It has been very satisfactory to find that our results have agreed well, when comparison has been possible, with the (often limited) results of previous researchers in this field - particularly in the case of the less widely studied aspects of the ejecta field such as fragment rotation and energy partitioning (see Section 4.9).

7.3 Publications etc. Arising from this Research

Five publications bearing my name have resulted directly from this research programme. These are as follows, with references indicated in square brackets:

• A presentation, given by myself, to the XVI General Assembly of the European Geophysical Society, (abstracts published in proceedings) [Giblin et al., 1991];
• A refereed article based upon a presentation, entitled "Jets of Fragments from Catastrophic Break-Up and the Astrophysical Implications", given by Dr. Mario Di Martino to IAU Colloquium 126, Origin and Evolution of Interplanetary Dust (paper published in full) [Martelli et al., 1991];
• A refereed paper entitled "Fragment Jets from Catastrophic Break-Up Events and the Formation of Asteroid Binaries and Families", published in Astronomy and Astrophysics 271 [Martelli et al., 1993];
• A refereed paper entitled "Field Fragmentation of Macroscopic Targets Simulating Asteroidal Catastrophic Collisions", pending publication in Icarus [Giblin et al., 1994a];
• An refereed article based upon a presentation, entitled "Hypervelocity Impact Experiments Using a Contact Charge", given by myself to The 4th International Conference on Catastrophic Disruption of Solar System Bodies (published in full in a special issue of Planetary and Space Science) [Giblin et al., 1994b];

As a result of the high level of recognition given to the work of the Sussex/Turin collaborative group, two other main review papers, of which I am co-author, have been requested:

• A review, entitled "Catastrophic Disruption Experiments: Recent Results", given by Professor Giuseppe Martelli to The 4th International Conference on Catastrophic Disruption of Solar System Bodies (papers from this conference are published in full in a special issue of Planetary and Space Science) [Martelli et al., 1994];
• Another review, entitled "High Velocity and Hypervelocity Impact Experiments: A Tool to Simulate Asteroidal Catastrophic Collisions", given by myself to the XIX General Assembly of the European Geophysical Society (this paper to be published in Annales Geophysicae) [Giblin and Martelli, 1994].

7.4 Some Suggestions for Future Work

The study of catastrophic disruptions and fragmentation is a fairly new field - most of the significant work has been carried out within the past 15 years - and as such offers a host of possible avenues for future research. I limit myself here to those within the capability and direction of our research group. The most significant of these possibilities are:

• The dependence of fragment velocities upon target size - this would require the target size to be varied and other parameters, such as impact specific energy, to be held constant. Of interest would be both the general form of the velocity distribution and the specific velocities of standard reference points such as the antipodal cap;
• Further analysis of possible fragment jetting and its presence or absence depending upon the internal structure of the target - this could be studied in tandem with the previous point by conducting each experiment with and without a core;
• Systematic study of the velocity and rotation field for a variety of simple target shapes, for example ellipsoidal, conical and flat targets would be of interest;

The possibility exists for our group to carry out, in the near future, a range of experiments upon relatively low-cost spherical targets. This possibility is a direct result of the collaboration between the Sussex group, the Astronomical Observatory of Turin, and the Istituto di Astrofisica Spaziale del CNR, Rome, Italy.