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The Early History of IUE

IUE in the Clean Room Before Launch

The beginning of IUE goes back to the late 1960's and the success of the early astronomical satellites such as OAO-2 and Copernicus (OAO-3) in the US and TD-1 in Europe. Various studies were being pursued at NASA and within the European Space Research Organization (ESRO, the predecessor of ESA) for new astronomy satellites. One such study, for an Ultraviolet Astronomical Satellite (UVAS), was proposed by a team from the UK. This became the basis for a joint project among NASA, ESRO, and the UK's Science Research Council (SRC).

The approval process was especially challenging, since it involved three different agencies. But approval for the International Ultraviolet Explorer was won in 1971. Under the interagency agreement, NASA was reponsible for the overall system design, design and construction of the telescope, spectrograph, and spacecraft, the launch, and the US spacecraft control station at Goddard Space Flight Center (GSFC). The UK was responsible for the design and construction of the cameras and contributed to the optical design and the sunshade. ESA provided the solar arrays and the European spacecraft control station near Madrid, Spain.

Several unique design elements were part of the planned IUE mission.

First, the spacecraft was to be placed into geosynchronous orbit. This would allow it to be controlled in real time and thus be operated much like a ground-based observatory. Weight was therefore a major consideration. One compromise was to place the spacecraft into an eccentric orbit. In this orbit, the spacecraft dipped into the Van Allen belts at perigee. This became the "US2" high radiation shift, during which observers took shorter exposures because of the radiation background affecting the cameras.

Second, the goal of a long scientific mission was incorporated into the project design. The scientists pushed hard for a five-year mission. But the engineers would agree only to a three-year design lifetime, with a five-year "goal" as a compromise. Ironically IUE lasted much longer than five years!

Finally, control of the satellite would be passed between two control stations on two different continents. This concept caused some concern, since a clear chain of command is required for safe, successful spacecraft operations. Various steps were taken to insure well-coordinated operations. A standard protocol was used for "handover" of command between the two stations. The Goddard control center stayed online during VILSPA shifts to monitor and backup the European operations. Both stations used essentially identical command computers, software, and Flight Operations Directives.

Concerns about the radiation enviroment resulted in the last-minute installation of a radiation monitor. As it turned out, the radiation environment was not as bad as feared, but the radiation monitor was very useful in helping the observers better estimate exposure times during the high radiation shift.

IUE was launched on January 26, 1978, on a Delta rocket from Cape Canaveral, Florida. It was placed initially in an eccentric transfer orbit, then the apogee boost motor was used to circularize the orbit. After this IUE was so close to its nominal station (i.e. longitude) that it was not neccesary to use the jets move the spacecraft orbit. Initial check-out of the hardware went smoothly. The first spectrum, of the calibration star Eta Ursae Majoris, was obtained on the third day.

The spacecraft was then operated for 60 days under a Commissioning Period. Various high priority calibration and science observations were performed. For each spectrograph, there were prime and redundant cameras. It was quickly learned that the Short-Wavelength Redundant (SWR) camera was not functioning properly, and it was not used after the Commissioning Period. The SWP camera experienced significant microphonic noise, a major concern, until the source of the noise was found (the Panoramic Attitude Sensor, used for attitude determination after launch) and turned off. The LWP camera, in some ways better than the LWR, experienced sporadic scan errors, so the LWR was chosen as the default long-wavelength camera.

Routine operations began on April 1, 1978... and continued until October 30, 1996, an amazing 18 years and 9 months!

More information?

Please see "The History of IUE" (Boggess, A., Wilson, R., Barker, P. J., and Meredith, L. M. 1987, in Scientific Accomplishments of the IUE, Reidel: Dordrecht, ed. Y. Kondo, pg. 3). Most of the information above is condensed from this excellent article.

In addition, please see the series of articles written about IUE published in Nature , beginning with Boggess, A., et al. , 1978, Nature , 275 , 372. The first paper describes IUE, while the others describe the results of the Commissioning Period observations of various types of astronomical objects.