Astronomy:Student Nitric Oxide Explorer

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Student Nitric Oxide Explorer
SNOE satellite
NamesExplorer 72, STEDI 1
Mission typeAtmospheric research
OperatorCU Boulder (LASP) / NASA[1]
COSPAR ID1998-012A
SATCAT no.25223
Mission durationFinal: 5 years, 9 months, 17 days
Spacecraft properties
ManufacturerCU Boulder (LASP)[1]
Launch mass115 kg (254 lb)[2]
Dimensions1.0 × 0.9 m (3.2 × 3.1 ft)[3]
Power37 watts
Start of mission
Launch dateFebruary 26, 1998, 07:07 (1998-02-26UTC07:07) UTC[5]
RocketPegasus XL HAPS F20
Launch siteVandenberg Air Force Base (Stargazer)
ContractorOrbital Sciences
Entered serviceMarch 11, 1998[4]
End of mission
DisposalAtmospheric reentry
Decay date≈December 13, 2003, 09:34 (2003-12-13UTC09:35) UTC[1]
Orbital parameters
Reference systemGeocentric
Perigee altitude535 km (332 mi)
Apogee altitude580 km (360 mi)
Period95.80 minutes
EpochFebruary 26, 1998, 02:07 UTC[5]
Explorers program

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).[3][6] 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.[7]


SNOE was equipped with three scientific instruments:[8]

  • An Ultraviolet Spectrometer, which performs a vertical profile of the concentration of nitric oxide.
  • A two-channel Auroral Photometer, which performs measurements of auroral emissions beneath the satellite.
  • A five-channel Solar X-ray Photometer, which measures the soft X-ray emissions by the Sun.

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:

  • Detailing how the variations of X-ray radiation from the sun affects the density of nitric oxide in the lower layer of the thermosphere.
  • How auroral activity increases the amount of nitric oxide in the polar regions.

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.[5]

Selected science results

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.[9] SNOE also helped to map the effect of global X-rays on the atmosphere.[4]

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.[4]


  1. 1.0 1.1 1.2 Wade, Mark. "SNOE". Encyclopedia Astronautica. Retrieved March 26, 2017. 
  2. Solomon, Stanley C.; Bailey, Scott M.; Barth, Charles A.; Davis, Randal L.; Donnelly, John A. (1998). "The SNOE Spacecraft: Integration, Test, Launch, Operation, and On-orbit Performance". 12th AIAA/USU Conference on Small Satellites. 1998. Logan, Utah.. 
  3. 3.0 3.1 "Launch vehicle dynamic envelope diagram". University of Colorado Boulder. Retrieved March 26, 2017. 
  4. 4.0 4.1 4.2 Bailey, Scott M.; Woods, T. N.; Barth, C. A. et al. (December 2000). "Measurements of the solar soft X-ray irradiance by the Student Nitric Oxide Explorer: First analysis and underflight calibrations". Journal of Geophysical Research 105 (A12): 27179-27194. doi:10.1029/2000JA000188. Bibcode2000JGR...10527179B. 
  5. 5.0 5.1 5.2 "SNOE - Trajectory Details". National Space Science Data Center. NASA. Retrieved June 28, 2016. 
  6. "Spacecraft Structure". University of Colorado Boulder. Retrieved March 26, 2017. 
  7. Solomon, Stanley C. et al. (October 1996). "The Student Nitric Oxide Explorer". Proceedings of the SPIE: Space Sciencecraft Control and Tracking in the New Millennium 2810: 121-132. doi:10.1117/12.255131. Bibcode1996SPIE.2810..121S. Archived from the original on 11 June 2010. 
  8. "Spacecraft Specs: Instruments". University of Colorado Boulder. Retrieved March 26, 2017. 
  9. Bailey, Scott M.; Merkel, Aimee W.; Thomas, Gary E. et al. (July 2005). "Observations of polar mesospheric clouds by the Student Nitric Oxide Explorer". Journal of Geophysical Research: Atmospheres 110 (D13). doi:10.1029/2004JD005422. D13203. Bibcode2005JGRD..11013203B. 

External links

  1. REDIRECT Template:Explorers Program