Prof. Sir Robert Wilson
Developer of the International Ultraviolet Explorer satellite
Obituary published in The Independent on Tuesday, 24 September 2002
Robert Wilson was one of Britain's leading scientists in the second half of the 20th century; he will be most widely remembered for his role in the development of the International Ultraviolet Explorer satellite, but the much broader span of his scientific interests is reflected in the title of his 1996 Festschrift, Astrophysical and Laboratory Plasmas.
Wilson was born in South Shields, Co Durham, in 1927. After completing his first degree, in Physics, at King's College, Durham (now Newcastle University), he worked for his PhD at Edinburgh, in 1952 joining the staff at the Royal Observatory. During that time he performed a series of meticulous observations of the hottest, most massive stars known, and was the first to show that they lose a substantial fraction of their birth mass through highly supersonic outflows – subsequently recognised as a crucial factor in understanding in the life cycles of stars and galaxies.
However, the work from this period of which he was fondest (and which led to his first major publication, in the prestigious Monthly Notices of the Royal Astronomical Society) involved observations of a "Blue Sun", seen throughout Edinburgh on 26 September 1950. While most of the observatory staff (including his PhD supervisor) were dealing with the rash of enquiries from the public prompted by this phenomenon, Wilson was busy taking spectra in order to obtain a understanding of the physics involved. He was able to turn a meteorological curiosity into an opportunity to obtain direct experimental verification of a fundamental characteristic of "scattering theory", which describes the interaction of light with dust particles (in this case, originating from forest fires raging in Alberta, Canada).
After a short spell as a Research Fellow at the Dominion Astrophysical Observatory, in Vancouver, British Columbia, Wilson's career took a new turn when, at the age of only 32, he accepted an invitation from the Nobel Laureate Sir John Cockcroft to lead the new Plasma Spectroscopy Group at Harwell. During the 1940s and 1950s, British physicists had been working on Harwell's experimental large-scale fusion device, dubbed Zeta, the "Zero Energy Toroidal Assembly". Cockcroft declared that he was "90 per cent certain" that the machine, which remained cloaked in secrecy until the temporary thawing of the Cold War in the late 1950s, had produced hydrogen fusion, and it fell to Wilson to provide the evidence.
Using the expertise in spectroscopic analysis that he had developed in astrophysics, Wilson and his team showed that Zeta was in fact generating temperatures 10 times lower than had been believed, and that consequently fusion was not taking place. He realised that Zeta none the less provided a marvellous laboratory analogue of remote astrophysical plasmas, and in particular that many previously unidentified features in the ultraviolet spectrum of the Sun could be successfully interpreted using the same physics that he brought to bear on the Zeta project.
Ultraviolet radiation, though blocked by the Earth's atmosphere, is exceptionally rich in diagnostics of the chemical and physical properties of celestial sources. Recognising this, Wilson went on to lead a programme of development of rocket-borne ultraviolet spectrographs, primarily for the study of solar physics, with parallel work building the theoretical tools necessary for the analysis of the observations. First as Head of the Plasma Spectroscopy Division at Culham, which he created, and subsequently as Director of the Science Research Council's Astrophysics Research Unit, he thereby founded the continuing tradition of UK involvement in ultraviolet astrophysics.
With this background, it was inevitable that he should lead the British participation in the European Space Research Organisation's first astronomy satellite, and its most ambitious project to that time, the TD-1 mission (a name which Wilson considered lacked imagination, simply reflecting the Thor Delta launch vehicle). The satellite included an outstandingly successful Anglo-Belgian experiment, the equally prosaically named S2/68, which, starting in 1972, conducted the first survey of the entire sky in ultraviolet radiation; as one of the first all-sky surveys at any wavelength, it predated the current trend towards "wide field astronomy" by a quarter of a century.
At the behest of Sir Harrie Massey, who chaired the British National Committee for Space Research, and in response to a 1964 call for proposals from ESRO (forerunner of today's European Space Agency, ESA), Wilson had meanwhile been working on another major ultraviolet-astronomy mission, building a team drawn initially from Culham, Aldermaston, and University College London. Against strong international competition, Wilson's proposal was at first accepted for development by ESRO, only to be later abandoned as a result of financial strictures. A major redesign of the mission also ultimately went unapproved, in spite of exceptionally strong support from an independent science review team.
Undaunted, Wilson thereupon effectively donated the design and development work, without strings, to Nasa, through the agency of Leo Goldberg, chair of their Astronomy Missions Board. They supported the project, eventually leading to the launch of the International Ultraviolet Explorer satellite, IUE, on 26 January 1978 – by then a joint mission between Nasa, ESA, and the UK's Science Research Council, and a direct result of Wilson's creativity and persistence. His contribution was recognised by a Presidential Award for Design Excellence from Ronald Reagan; Wilson, who accepted on behalf of the UK project team, was the first recipient of such an award who was not a US citizen.
Although Wilson considered his period at Culham to be his most productive scientifically, IUE is his most widely recognised achievement. It was a landmark in space science: arguably the first true space observatory, and in many respects the direct predecessor of the more publicised Hubble Space Telescope, it was the first satellite to be accessible to the entire international astronomical community, without the requirement of specialised knowledge of the spacecraft systems.
With a notional mission lifetime of three years, in practice it continued operations almost without interruption for more than 18 years, with no significant hardware failures or reductions in performance; its record as the longest-lived, most productive astronomical space observatory is unlikely to be challenged for many years. Used by thousands of astronomers during its lifetime, its universally accessible data archive (another IUE first, and now a key factor for all satellite science missions) continues to provide an invaluable resource to researchers.
In 1972 Wilson accepted an appointment to the Perren Chair of Astronomy at University College London, where he built up a major group working on S2/68 data, on the development of IUE, and on the exploitation of its results. He was involved in many of the group's research projects, including detailed studies of the hot-star outflows which he had discovered a third of a century previously (and for which the ultraviolet region provides the most sensitive diagnostics), but, ever the physicist at heart, the studies he most enjoyed were of the so-called double quasar – a single distant object, magnified and distorted by an intervening "gravitational lens", whose characteristics were predicted by, and therefore provide a test of, General Relativity.
Robert Wilson – Bob to many colleagues and friends – was a gifted speaker, both as a communicator of science and as an entertaining raconteur. His ability to convey complex scientific principles clearly is demonstrated in his popular-level book Astronomy through the Ages (1998), and it ensured the success of his lectures at UCL, in particular to non-scientists.
While Wilson was an epicurean who enjoyed good food, good wine, and good company, he was absolutely without pretension, perhaps in part because of his working-class origins (the dedication in his book was to "a Durham miner" – his father, Robert Graham Wilson). He was a warm and sociable man, who, in spite of an unceasing burden of administrative responsibilities, always found time for those around him.
Prof. Ian Howarth
