Technology Development for an Ultraviolet Imaging Spectrograph for Solar Physics, 15-9443

Principal Investigator
Donald M. Hassler

Inclusive Dates:  12/01/03 – 11/31/04

Background - This project was intended to support development of technology needed for an ultraviolet (UV) imaging spectrograph for solar physics research, to assist with the development of a sounding rocket instrument payload funded by NASA. Our proposal to NASA was selected for funding contingent upon receiving internal support for the difference in proposed and funded cost.

Because of NASA budget cuts in the sounding rocket program for this year, it was unlikely that the full budget amount could be obtained for the first year, even though SwRI's proposal received high ratings. By doing this technology development portion of the work under this project, we enabled NASA to select this proposal within its current budget and be fully funded at the original proposed cost for the second and third years of the project. Developing this technology and building this sounding rocket instrument also improve SwRI's chances for future satellite experiments through the Explorer program.

Approach - The optical design of RAISE is based on a new class of UV/EUV imaging spectrographs, which use only two reflections to provide quasi-stigmatic performance simultaneously over multiple wavelengths and spatial fields. Previous instruments based on this concept include EUNIS and EIS, to be flown on sounding rockets and on the Solar-B mission, respectively. The design uses an off-axis parabolic telescope mirror to form a real image of the sun on the spectrometer entrance aperture. A slit then selects a portion of the solar image, passing its light onto a near-normal incidence toroidal grating, which re-images the spectrally dispersed radiation onto an array detector. Two full spectral bandpasses over the same one-dimensional spatial field are recorded instantaneously with no scanning of the detector or grating. The two different spectral bands [1st-order 1,205 – 1,243 angstroms (Å) and 1,526 - 1,564Å] are imaged onto two intensified APS detectors whose focal planes are individually adjusted for optimized performance.

The single grating in the baseline RAISE design has a toroidal surface (Sagittal Radius = 1042.2 mm, Tangential Radius = 1034.0 mm), but with varied line space (VLS) rulings of the type developed originally for spherical substrates by Kita, Harada, and collaborators (1983, 1995). By combining this VLS concept with toroidal surfaces, a new class of spectrometers is potentially possible with truly remarkable imaging properties, as described by Thomas (2003). RAISE will be one of the first to take advantage of this new optical technology approach. The purpose of this project is to complete the detailed design for this new technology grating, obtain quotes from possible vendors and manufacturers, select and place an order with one of them with the intent to test and characterize the performance of the new grating and evaluate its suitability and performance for the RAISE sounding rocket program.

Accomplishments - The RAISE sounding rocket program is on schedule and in budget, with a launch scheduled for June 2006. We have a rocket number assigned (36.219) for our summer 2006 launch, and we had our Mission Initiation Conference (MIC) at Wallops Flight Facility on September 30. The MIC was successful, with much interest in the flight, and no identified problems. We then had our Requirements Definition Meeting (RDM) on November 10. We have completed top-level design of the rocket payload, with total mass estimates coming in at 242 pounds, in excellent agreement with our proposal estimate of 250 pounds (± 20 percent). We are currently on schedule for the Design Review scheduled for the week of May 16.

Procurement activities are on schedule, and we have ordered all our long-lead items (TVLS gratings, Intensified APS cameras, Primary Telescope Mirror), and have developed a schedule that shows instrument fabrication beginning in February, unit level testing beginning in March, and integration and assembly beginning in September. End-to-end testing is scheduled to begin in January 2006, with a launch date scheduled for June 2006.

We have ordered our diffraction grating with an estimated delivery time of six to eight months. We have chosen the approach of mechanically ruling the grating. This procedure is much better from a grating efficiency point of view and is less expensive to produce. However, it has potentially higher stray light, which we will characterize as soon as possible. We have found collaborator support at the Max Planck Institut fur Aeronomie in Lindau, Germany (collaborators from previous projects) to assist in our detector procurement, fabrication, and testing. They will provide part-time labor for 1 researcher and 1 technician to support the rocket effort.

Thus based on this project effort and the progress shown in this report, NASA has released next year's (Year 2) award funds. Figure 2 shows the RAISE sounding rocket design maturity during the fourth quarter of this internal research project.

2005 Program Home