Extreme Ultraviolet Imaging Telescope - History

History

EIT was a difficult sell to the scientific funding agencies, as it was not clear in the early 1990s that simple imaging of the corona would be scientifically useful (most of the other instruments on board SOHO are spectrographs of various kinds). The EIT PI, Jean-Pierre Delaboudiniere, was forced to scrounge funding and resources from several locations to construct and launch the instrument. For example, EIT alone of the SOHO instruments does not have its own flight computer; it is connected to the LASCO instrument flight computer, and is treated operationally as an additional LASCO camera. No funding was available for a pointing adjustment mechanisms, so EIT is bolted directly to the spacecraft and hence forms the SOHO pointing reference: the other instruments all align themselves to the EIT images. Focus adjustment is achieved by thermal expansion: the internal survival heaters (found in most spaceborne instruments) are used to achieve microscopic changes in the size of the telescope structure and hence the mirror spacing. EIT was originally allocated only about 1 kbit/s of data -- about the same speed as a 110 baud teletype -- but after its utility became clear much more telemetry bandwidth was allocated to it.