Our ability to use space in the long term is not guaranteed:
- Multiplication of government and private space operators:8 nations operate launch systems;
- More than 50 nations and regional organizations operate satellites in Earth orbit.
- A rapidly increasing number of (large and small) private companies operate commercial satellite systems.
- More than 4500 launches have taken place since 1957, about 900 satellites are operational today but 12500 identified debris larger than 10 cm are tracked by the US Space Surveillance Network. The space debris situation is becoming a real concern.

On the long term, this trend will require more discipline in managing frequency resources, orbital positions and space operations. Fortunately, deployment of weapons in space is not taking place (so far) but ground-based weapons can be used against low Earth orbit spacecraft. If they were activated during a conflict, they would jeopardize the secure use of near-Earth outer space. In other word, Space Security is fragile, particularly if one takes a long term view.

The "space debris" work of the IADC and the subsequent COPUOS adoption of UN Space Debris Mitigation Guidelines in 2007 is a good of how the international community can make some progress towards a regime of sustainable space operations. In June 2007, I proposed to the UN COPUOS delegations that they should tackle the issue of long term sustainability of space activities with a bottom-up approach comparable to the "UN space debris mitigations guidelines". In line with this proposal, a first implementation step took place on February 7 & 8, 2008 when France hosted in Paris an informal working meeting of space faring nations on the topic of "Long term sustainability of space activities". The purpose of this informal meeting was to discuss the possibility of setting up an ad hoc working group to develop information exchange mechanisms and consensus-based rules of behaviour which will contribute to a safer and more secure space environment. The conclusions of this meeting and of the second meeting held recently in Glasgow will be presented and the way forward described.

This presentation describes the United States approach to monitoring, predicting and applying space environmental data with an emphasis on application of this information to the operation of space systems, and to the services those systems are intended to provide. It will describe the components required to support SSA, specifically the sensors, types of data, models, and example applications currently used operationally and reveal areas of potential US/European collaboration.

Considering the geophysical characteristics of the medium, the ionosphere can be seen as consisting of three regions: low latitudes (between -20° to 20°), mid – latitudes (from 20° to 60°) and high latitudes (> 60°). Depending on the space weather, the medium may significantly be modified and this will affect the signals characteristics of transionospheric links. Those modifications are essentially: the scintillations (low and high latitudes), the magnetic storms (high and mid latitudes), the travelling disturbances (mid latitudes) and the auroral precipitations (high latitudes).

A ground radar aiming to track debris inside and above the ionosphere will be affected by such space weather modifications. The major effects will be the biases, the scintillations and the coherence properties of the medium, e.g. the scattering function. Small debris will have a low radar cross section (RCS) and will require a coherent signal processing.

This paper will present a review of the errors for different ionosphere conditions related to the three regions here above defined and conclusions will be drawn regarding possible requirements for space surveillance radars.

Keeping track of satellites requires accurate models of thermospheric density and dynamics. This has been an iterative process in the past with models of average conditions such as the Jacchia model being itself based on observations of satellite orbits. The HWM (Hedin Wind Model) is based largely on ground-based FPI and radar data. These models will be useful for prediction of average conditions but tracking has shown there to be smaller scale and short-period variations which are not so easy to predict or explain. Satellites such as CHAMP are revealing thermospheric structure that was not suspected before and first-principles models are having to be adjusted to find explanations for these. We will look at what is needed in the way of measurements to improve empirical and numerical models of the thermosphere and examine how important the dynamics are to understanding satellite orbits.

As defined by ESA, Space Situational Awareness (SSA) is the understanding and maintained awareness of the Earth orbital population, the space environment and possible threats to space assets. At the moment, European SSA is relatively poor and many studies are performed in that domain to propose an autonomous European system.

The SSA programme is envisaged as a common framework for addressing space weather and space surveillance user needs and this paper will present the possible correlations between these domains which appear when proposing cost-efficient solutions for the future system.

First, we will recall the space weather and space surveillance services required by potential future users of the European SSA system. Then, we will derive the mandatory assets to provide these services. Three levels are necessary: a generic structure for data whatever their type (space weather or space surveillance), sensors and non-sensor assets. For sensors, both types and locations will be analysed in order to derive possible correlations between domains. These correlations will be used for proposing candidate architectural options for the SSA system.

It is concluded that combining space weather and space surveillance functions in a common system offers several advantages. First, sharing space-based assets appear possible and to be a cost-effective approach for the deployment of an SSA space segment. Second, there are many mutual benefits as some tracking and surveying functions are subject to space weather effects, and conversely space weather products may be derived from tracking and surveying measurements.