Satellite Gravimetry: A Review of Its Realization

Since Kepler, Newton and Huygens in the seventeenth century, geodesy has been concerned with determining the figure, orientation and gravitational field of the Earth. With the beginning of the space age in 1957, a new branch of geodesy was created, satellite geodesy. Only with satellites did geodesy become truly global. Oceans were no longer obstacles and the Earth as a whole could be observed and measured in consistent series of measurements. Of particular interest is the determination of the spatial structures and finally the temporal changes of the Earth's gravitational field. The knowledge of the gravitational field represents the natural bridge to the study of the physics of the Earth's interior, the circulation of our oceans and, more recently, the climate. Today, key findings on climate change are derived from the temporal changes in the gravitational field: on ice mass loss in Greenland and Antarctica, sea level rise and generally on changes in the global water cycle. This has only become possible with dedicated gravity satellite missions opening a method known as satellite gravimetry. In the first forty years of space age, satellite gravimetry was based on the analysis of the orbital motion of satellites. Due to the uneven distribution of observatories over the globe, the initially inaccurate measuring methods and the inadequacies of the evaluation models, the reconstruction of global models of the Earth's gravitational field was a great challenge. The transition from passive satellites for gravity field determination to satellites equipped with special sensor technology, which was initiated in the last decade of the twentieth century, brought decisive progress. In the chronological sequence of the launch of such new satellites, the history, mission objectives and measuring principles of the missions CHAMP, GRACE and GOCE flown since 2000 are outlined and essential scientific results of the individual missions are highlighted. The special features of the GRACE Follow-On Mission, which was launched in 2018, and the plans for a next generation of gravity field missions are also discussed.

Experimental Reflection Evaluation for Attitude Monitoring of Space Orbiting Systems with NRL Arch Method

The increasing number of satellites orbiting around Earth has led to an uncontrolled increase in objects within the orbital environment. Since the beginning of the space age on 4 October 1957 (launch of Sputnik I), there have been more than 4900 space launches, leading to over 18,000 satellites and ground-trackable objects currently orbiting the Earth. For each satellite launched, several other objects are also sent into orbit, including rocket upper stages, instrument covers, and so on. Having a reliable system for tracking objects and satellites and monitoring their attitude is at present a mandatory challenge in order to prevent dangerous collisions and an increase in space debris. In this paper, the evaluation of the reflection coefficient of different shaped objects has been carried out by means of the bi-static reflection method, also known as NRL arch measurement, in order to evaluate their visibility and attitude in a wide range of frequencies (12–18 GHz). The test campaign aims to correlate the experimental measures with the hypothetical reflection properties of orbiting systems.

(Un)earthly governance: beyond functional frameworks to flourishing spacescapes

Purpose Humanity has a weakness in how we approach the “challenge” of using outer space. This paper aims to show how the global and national frameworks that address our planetary activities and crises are inadequate for the opportunities and challenges of life in outer space. Design/methodology/approach The authors draw on multidisciplinary perspectives to refine an organising governance framework that better showcases the challenges and pathways needed for living and thriving in space-age. The authors prioritise two key pillars and overview the practical and social implications that space-age humanity must address. Findings Social sciences and humanities are vital to problematising post-war colonial legacies of governance by distinguishing the unique and overlooked challenges for thriving and working offworld and identifying progressive research agendas. Research limitations/implications The highlighted agenda has implications for collaborative research institutes and project design. As the vital basis for continuous learning, university-based research institutes span bodies of knowledge, experience, convention and imagination that can support vibrant and overdue debate on good governance that is out of this world. Practical implications This expansive approach has practical implications for the decision-making processes and subjects of spacescape, from reconciling the space commons with prospecting and human occupation to potential governance regimes that capitalise on the zeal for moving beyond merely “existing” off-world. Social implications Examining the governance deficit as we pursue developing spacescape frontiers is an enriching (not reductionist) agenda that deliberately troubles the existing and emerging regime for governing our scientific and imagined off-world society. Originality/value This framework appeals to humanity’s highest evolution in co-producing a fair and flourishing off-world governance framework (beyond replicating planetary regimes).