This paper describes the conceptual design of a soft X-ray telescope, Super-X, which we will propose for the Japan/US/UK Solar-B mission. Super-X will break new ground in both angular resolution and solar coronal temperature discrimination. The telescope design is based upon the successful Transition Region and Coronal Explorer instrument. It features four XUV spectral channels spanning the 0.3 to 20 MK temperature range with an angular resoluton of approximately 0.27 seconds of are. We will describe considerations affecting spectral line selection and some details of the characteristics of the instrument.

The Naval Research Laboratory (NRL) Skylab SO82A slitless spectrograph provided solar flare observations that have never been equaled in diagnostic capabilities for interpreting thermal flare physics. Improvements in detector technology, optics and optical coating technology, and almost two decades of analysis of SO82A data can be combined with the basic concept of an EW objective grating spectrograph to build an instrument to address many of the remaining mysteries of solar flares. This next generation instrument incorporates two sets of two identical, orthogonally mounted slitless spectrographic Cassegrain telescopes. Each telescope consists of a multilayer coated, Wadsworth mount objective grating and multilayer coated spherical secondary mirror; a backside illuminated CCD detector is installed at the focal plane. The orthogonal mounting changes the dispersion direction by 90 degrees on the disk image; processing on the two resulting images allows recovery of the undispersed disk image and spectral line profiles. The resulting instrument will obtain high time cadence, spectrally-dispersed images with improved spatial resolution, dynamic range, signal-to-noise ratio, and velocity discrimination.

The TransitionRegionand CoronalExplorerinstrument(TRACE) willuse narrow-bandinterferencefilters togetherwithotherappropriate bandlimiting elementstomake highresolution imagesofthe Sun intheC IV linesat 154.8and 155.0nm. Filter observations ofsolarC IV emissionarecomplicated by thepresenceofUV Continuum and nearbychromospheric linesbecauseoftherelatively widebandpasses ofthenarrowestcurrentlyavailable interference filters. TRACE willuse a seriesoffilters toestimatethe effects ofthe UV continuum and the long-wavelength "leaks"in the blockingfilters which we show are themost importantcontaminantsin theC IV images.Furtherimprovementsinfiltcrgrapherformance may be realized throughtheuse oftunableFabry-Perotctalons, which have been under developmentat Lockheed-Martin.We presentestdatafroma cultured quartzetalondesignedfor155nm, and willdiscuss theprospectsforetalonsoperatingatsubstantially shorterwavelengths.

The purpose of this paper is to survey some of the recent advances in the state of the art of soft X-ray spectrometers, particularly as they might be applied to Solar Observations. The discussions will center on the windowless region from roughly 1 to 100 A, and will cover both grating and crystal instruments. During the interval that has elapsed since the launches of the Solar Maximum Mission and P 78-1 satellites in the early 1980's, there have been a number of significant technological developments. Among these, are multi-layer mirrors, large format CCD detectors sensitive to X-rays, position sensitive photon counting detectors, new kinds of X-ray films, and the discovery of a number of ingenious new optical systems based on gratings with non-uniform ruling spacings. There have also been a number of improvements in the extent and accuracy of the atomic physics data sets on which the analysis of spectroscopic observations depend. Finally, the analysis of the data from the two missions mentioned above, from the earlier Skylab mission, and from recent sounding rocket flights, have raised a number of interesting questions that will greatly benefit from a new generation of instruments and the observations that they will produce. I will begin with a short discussion of the solar soft X-ray spectrum and its interpretation, followed by a few general comments on problems peculiar to soft X-ray instruments. The main portion of the paper will be devoted to a review of recent developments in spectrometer optical design, which has been a lively field during the last dozen years. This is particularly true in the case of grating spectrometers, because of the development of diffraction gratings with variable groove spacings or with curved rulings. The availability of multi-layer mirror coatings means that designs are not necessarily restricted to the glancing incidence region, giving additional design flexibility. The paper will conclude with a short section on telescope considerations, and some hopeful remarks on future flight opportunities.