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Scientific Assessment of NASA's SMEX-MIDEX Space Physics Mission Selections (Chapter 4) Scientific Assessment of NASA's SMEX-MIDEX Space Physics Mission Selections 4 STEDI Missions: Models for the UNEX Explorer Line The Student Nitric Oxide Experiment (SNOE) SNOE, the STEDI mission at the University of Colorado scheduled for launch in December 1997, addresses the role nitric oxide (NO) plays as a major source of neutral cooling in the lower thermosphere. Understanding the distribution of NO is critical in deciphering the thermal structure of the atmosphere and its variations with solar and magnetic activity. The transport of thermospheric NO to mesospheric altitudes on the nightside also plays an important role in mesospheric ozone chemistry. This is a specific component of the much broader objective of understanding the causes of mesosphere/lower- thermosphere structure and variability, cited in "The Middle and Upper REPORT MENU Atmospheres and Their Coupling to Regions Above and Below," Chapter 4 in the NOTICE Science Strategy (SSB, 1995). MEMBERSHIP FOREWORD Past measurements have clearly indicated a variation in NO with solar EXECUTIVE SUMMARY CHAPTER 1 and magnetic activity. However, the exact nature of this relationship and the CHAPTER 2 relative importance of inputs associated with each of these types of variability are CHAPTER 3 not known. SNOE's prime scientific focus is to resolve this question by making CHAPTER 4 simultaneous observations of NO abundance, solar emissions, and magnetic CHAPTER 5 activity (as inferred from auroral imaging). REFERENCES APPENDIX TERRIERS TERRIERS is the Boston University–based STEDI mission with an ionospheric focus. Scheduled for launch in January 1998, it is intended to provide a global view of ionospheric structure and variability by using tomographic techniques to deconvolve the ionospheric profile down to an altitude as low as 100–120 km, depending on the strength of the signal. This is a new technique file:///C|/SSB_old_web/smexch4.html (1 of 3) [6/18/2004 1:43:47 PM]

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Scientific Assessment of NASA's SMEX-MIDEX Space Physics Mission Selections (Chapter 4) with the potential for further scientific applications. One focus is on the equatorial ionosphere, with major advances expected in understanding large-scale equatorial irregularities like spread-F and equatorial bubbles. The NRC Science Strategy report identifies the low-altitude ionosphere, which is highly structured, as an underexplored region with strong electrodynamic coupling between the atmosphere and the near-space environment. Further progress in understanding large-scale electrodynamic coupling to the magnetosphere requires a global survey of the ionospheric plasma distribution as it responds to changing conditions. Recent spacecraft could provide only point measurements at the satellite altitude, whereas ground-based facilities produce time sequences of ionospheric profiles but only over limited geographical areas. Tomographic imaging of the ionosphere on a global scale down to low altitudes would contribute critical information to the science objectives identified in the NRC Science Strategy report. Summary of STEDI Missions STEDI appears successful in providing hands-on educational opportunities for both undergraduate and graduate students in engineering and software development, which makes the students highly marketable after graduation. STEDI investigators are staunch advocates of the program in its current format. The final test of the technical, management, and scientific success of the STEDI missions awaits their launch, which is normally on Pegasus vehicles. file:///C|/SSB_old_web/smexch4.html (2 of 3) [6/18/2004 1:43:47 PM]