The Student Nitric Oxide Explorer (SNOE) measured nitric oxide density in the Earth’s lower thermosphere (100-200 km altitude) and analyzed how the Sun and the Earth’s magnetosphere affect its abundance. SNOE carried three instruments: an ultraviolet spectrometer to measure nitric oxide altitude profiles, a two-channel auroral photometer to measure auroral emissions beneath the spacecraft, and a five-channel solar soft X-ray photometer. Under the supervision of LASP and industry mentors, University of Colorado students worked on the design study, built the spacecraft and instruments, wrote the flight software, integrated and tested the instruments and subsystems, and integrated with the launch vehicle.
Nitric oxide is an important minor constituent of the upper atmosphere that exhibits strong solar-terrestrial coupling. Nitric oxide directly affects the composition of the ionosphere, the thermal structure of the thermosphere, and may be transported downward into the mesosphere and stratosphere where it can react with ozone. However, significant unanswered questions about nitric oxide remain. The scientific objectives of the Student Nitric Oxide Explorer were:
- To determine how variations in the solar soft X-radiation produce changes in the density of nitric oxide in the lower thermosphere
- To determine how auroral activity produces increased nitric oxide in the polar regions
- Mission Principal Investigator, Charles Barth
- The ultraviolet spectrometer (UVS)
- A two-channel auroral photometer (AP)
- A five-channel solar soft X-ray photometer (SXP)
- Student-run mission operations
The primary function of the ultraviolet spectrometer (UVS) was to measure the density of nitric oxide between the altitudes of 100 and 200 km in the terrestrial upper atmosphere by observing the (1,0) and (0,1) gamma bands. The UVS design was similar to instruments flown on the Solar Mesospheric Explorer (SME), Pioneer Venus, and several rocket flights. It consists of an Ebert-Fastie spectrometer, an off-axis telescope, and two Hamamatsu phototube detectors.
The auroral photometer (AP) was a two-channel broad-band instrument that was used to determine the energy deposited in the upper atmosphere by energetic auroral electrons. It was similar to airglow photometers developed by LASP and flown on OGO-5 and -6 in the late 1960’s. The channels consisted of two Hamamatsu phototube detectors, a UV filter for each channel, and a field of view limiter for each channel. Both channels had circular fields of view, 11 degree full-cone.
The solar X-ray photometer (SXP) measures the solar irradiance at wavelengths from 2 to 35 nm in the soft X-ray to hard EUV (or “XUV”) portion of the solar spectrum. Each photometer channel consists of a silicon photodiode; wavelength selection is accomplished by thin metallic films deposited directly onto the diode surface. A door with a fused silica window covers the diodes. When it is open, the diodes measure solar X-rays plus some visible light contamination. When it is closed, the X-rays are blocked and only the visible light is measured. By subtracting the door-closed measurment from the door-open measurement, the X-ray fluxes are obtained.
For more information about the SNOE mission, see:
Launch date: February 25, 1998
Launch location: Vandenberg Air Force Base, California
Launch vehicle: Pegasus XL
Mission target: Earth orbit
Mission duration: 5 years
Other key dates:
- SNOE reentered Earth’s atmosphere: December 13, 2003
Other organizations involved:
- NASA’s Goddard Space Flight Center (GSFC)
- NASA’s Jet Propulsion Laboratory (JPL)