Why space missions?
ESA has performed a number of activities to date to support the characterisation and monitoring of NEO's.
A phased approach is necessary so as to assess the threat, to make a credible forecasting of impacts and to make a catalogue of the dangerous objects. This would include all the 1km or bigger objects –deemed to be able to trigger a global catastrophe-, but ideally the survey limit should be pushed down towards the 100m objects (which are still capable of causing enormous local damage) as far as practical. First-hand information of the physical characteristics of these bodies is also mandatory.
Why going to space?
For certain types of investigations, space missions offer significant advantages over groud-based facilities. In the case of the NEOs, the results of the studies commisioned by ESA provide a very strong support for this view. In this activity two broad types of space missions have been addressed:
Observatory-type missions, performing tasks such as detection, tracking (i.e. orbit determination) and remote characterisation (e.g. taxonomic type, albedo). For these functions the space option enables an improved access to certain types of objects i.e. IEOs and Atens, access to a broader range of wavelengths and an improved duty cycle. These favourable conditions can also result in efficient and extensive surveys in which smaller objects down to a few hundred meters in size may also be considered.
In-situ characterisation-type missions, seeking precise mass, volume, and internal structure determination, among other physical properties of the objects. Space borne instruments are clearly the best and often only option to obtain these data, which are essential for the assessment of the consequences of an impact and the countermeasures that can be adopted to prevent it.
Both types of space missions would complement ground-based programmes, to extend the surveys, complete the catalogues and to provide "ground truth" and fundamental physical data that cannot be obtained any other way.
Last update: 9 May 2012