|Names||Explorer 72, STEDI 1|
|Mission type||Atmospheric research|
|Operator||CU Boulder (LASP) / NASA|
|Mission duration||Final: 5 years, 9 months, 17 days|
|Manufacturer||CU Boulder (LASP)|
|Launch mass||115 kg (254 lb)|
|Dimensions||1.0 × 0.9 m (3.2 × 3.1 ft)|
|Start of mission|
|Launch date||February 26, 1998, 07:07UTC|
|Rocket||Pegasus XL HAPS F20|
|Launch site||Vandenberg (Stargazer)|
|Entered service||March 11, 1998|
|End of mission|
|Decay date||≈December 13, 2003, 09:34UTC|
|Perigee altitude||535 km (332 mi)|
|Apogee altitude||580 km (360 mi)|
|Epoch||February 26, 1998, 02:07 UTC|
The Student Nitric Oxide Explorer (SNOE), also known as Explorer 72 and STEDI 1, was a small scientific satellite which studied the concentration of nitric oxide in the thermosphere. It was launched in 1998 as part of NASA's Explorers program. The satellite was the first of three missions developed within the Student Explorer Demonstration Initiative (STEDI) funded by NASA. The satellite was developed by the University of Colorado Boulder's Laboratory for Atmospheric and Space Physics (LASP) and had met its goals by the time its mission ended with reentry on December 13, 2003.
SNOE had a compact hexagonal structure 0.99 m (3.23 ft) high and 0.94 m (3.08 ft) wide with a mass of 115 kg (254 lb). It was spin-stabilized at five revolutions per minute, and its axis of rotation was perpendicular to the orbital plane. The exterior of the satellite was covered with solar cells that provide 37 watts.
SNOE was equipped with three scientific instruments:
The satellite features a GPS receiver to accurately determine its orbit and orientation.
SNOE was the 72nd mission of the Explorer program by NASA dedicated to the scientific investigation of the space environment of the Earth. SNOE was the first of three projects developed within the university satellite program (STEDI) whose objective is to reach students in the development of satellites with limited means in the context of the strategy of "faster, better, cheaper" promoted by then-NASA administrator Daniel Goldin. The program was funded by NASA and managed by the Universities Space Research Association. The mission, developed by the University of Colorado Boulder in 1994, was selected among 66 proposals to be one of the six pre-selected satellites of the program. In February 1995 the satellite was selected along with TERRIERS of Boston University and CATSAT of the University of Leicester in the United Kingdom. SNOE was built and operated entirely by the Laboratory for Atmospheric and Space Physics of the university.
The objective of the mission was the detailed study of variations in the concentration of nitrogen monoxide in the thermosphere. Nitric oxide, though a minor component of this region of space, has a significant impact on the composition of ions in the ionosphere and in the heat of the thermosphere. The detailed objectives are:
SNOE was launched on 26 February 1998 at 07:07 UTC by a Pegasus-XL rocket, along with the Teledesic T1 satellite. The rocket was lofted by Orbital Sciences' Stargazer L-1011 aircraft based out of Vandenberg Air Force Base. SNOE was placed into a Sun-synchronous orbit of 535 by 580 km (332 by 360 mi) with an inclination of 97.7 degrees. The spacecraft functioned normally until its orbit degraded and it reentered the atmosphere on 13 December 2003.
The limb-scanning Ultraviolet Spectrometer on SNOE observed polar mesospheric clouds, finding that PMCs occur more frequently in the northern latitudes than in the southern, but that they otherwise conform well to the standard model of cloud formation. SNOE also helped to map the effect of global X-rays on the atmosphere.
Enhanced fluxes of solar soft X-rays were detected by SNOE. Solar soft X-ray irradiance was measured by the spacecraft's Solar X-ray Photometer (SXP) between 2 and 20 nm, and covered irradiance levels outside of solar minimum and maximum conditions. In the 2 to 7 nm interval the irradiance levels ranged from 0.3 to 2.5 mW/m2, while in the 6 to 19 nm interval the range was observed to be 0.5 to 3.5 mW/m2. These values were a factor of four times higher than those predicted by the Hinteregger, et al. (1981) empirical model.
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