Student Nitric Oxide Explorer
Names | Explorer 72 STEDI-1 UNEX-1 |
---|---|
Mission type | Space physics |
Operator | Laboratory for Atmospheric and Space Physics |
COSPAR ID | 1998-012A |
SATCAT no. | 25223 |
Website | lasp |
Mission duration | 5 years, 9 months, 17 days (achieved) |
Spacecraft properties | |
Spacecraft | Explorer LXXII |
Spacecraft type | Student Nitric Oxide Explorer |
Bus | SNOE |
Manufacturer | University of Colorado Boulder (Laboratory for Atmospheric and Space Physics) |
Launch mass | 120 kg (260 lb) [1] |
Dimensions | 0.9 × 1.0 m (2 ft 11 in × 3 ft 3 in) |
Power | 37 watts |
Start of mission | |
Launch date | 26 February 1998, 07:07 Pegasus XL HAPS (F20) |
Launch site | Vandenberg, (Stargazer) |
Contractor | Orbital Sciences Corporation |
Entered service | 11 March 1998 [2] |
End of mission | |
Last contact | 13 December 2003 |
Decay date | 13 December 2003, 09:34 UTC [3] |
Orbital parameters | |
Reference system | Geocentric orbit[4] |
Regime | Sun-synchronous orbit |
Perigee altitude | 535 km (332 mi) |
Apogee altitude | 580 km (360 mi) |
Inclination | 97.70° |
Period | 95.80 minutes |
Instruments | |
Auroral Photometer (AP) Solar X-ray Photometer (SXP) Ultraviolet Spectrometer (UVS) | |
Student Nitric Oxide Explorer mission patch Explorer program |
Student Nitric Oxide Explorer (SNOE ("snowy"), also known as Explorer 72, STEDI-1 and UNEX-1), was a
Overview
SNOE was the 72nd mission of the Explorer program by NASA dedicated to the scientific investigation of the space environment of the
Mission
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:[5]
- 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 of Earth
Spacecraft
SNOE was a compact hexagonal structure, approximately 0.9 m (2 ft 11 in) high and 1 m (3 ft 3 in) across it widest dimension, weighing a maximum of 120 kg (260 lb).
Launch
It was launched, on 26 February 1998 at 07:07
Instruments
SNOE was equipped with three scientific instruments:[8]
- 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
- An Ultraviolet Spectrometer, which performs a vertical profile of the concentration of nitric oxide
Auroral Photometer (AP)
The auroral photometer (AP) is a two-channel broad-band instrument that is used to determine the energy deposited in the upper atmosphere by energetic auroral electrons. It is similar to airglow photometers developed by LASP and flown on OGO-5 and OGO-6 in the late 1960s. Each channel consists of a Hamamatsu phototube detectors, a UV filter, and a field of view limiter (circular, 11° full-cone). The combination of a Caesium iodide (CsI) photocathode and a Calcium fluoride (CaF2) filter produces a bandpass from 125 to 180 nm for channel A, allowing a combined measurement of the LBH bands, the OI doublet at 135.6 nm, and the OI triplet at 130.4 nm. For channel B a barium fluoride (BaF2) filter is used producing a 135 to 180 nm bandpass and providing a measurement of the LBH bands and the OI doublet at 135.6 nm with the exclusion of the OI triplet at 130.4 nm. The sensitivity of channel A at 130.4 nm is 23 counts/second/Rayleigh and the sensitivity of channel B at 135.6 nm is 26 counts/second/Rayleigh. The AP is mounted with its optical axis perpendicular to the spacecraft spin axis. The AP produces continuous data with an integration time of 183 ms, but only the downward-looking part of each spin will be stored.[9]
Solar X-ray Photometer (SXP)
The solar X-ray photometer (SXP), measures the solar irradiance at wavelengths from 2 to 35 nm. Each of the five photometer channels contains a silicon photodiode; wavelength selection is accomplished by thin metallic films deposited onto the diode surface. Coatings are selected so that overlapping bandpasses can be used to isolate key parts of the spectrum at low resolution: Tin (Sn): 2-8 nm; Titanium (Ti): 2-16 nm; Zirconium/Titanium (Zr/Ti): 5-20 nm; Aluminum/Carbon (Al/C): 15-35 nm. The field of view is 70° full cone. The SXP takes 12 measurements per spin, centered on the zenith, with a 63 seconds integration time. Thus, it obtains an integrated solar measurement once per orbit, when the Sun is near the zenith.[10]
Ultraviolet Spectrometer (UVS)
The objective of the ultraviolet spectrometer (UVS) is to measure the density of nitric oxide in the terrestrial upper atmosphere (thermosphere) by observing the (1,0) and (0,1) gamma bands. The UVS design is similar to instruments flown on the Solar Mesosphere Explorer (SME), Pioneer Venus Orbiter, and several launch vehicles. It consists of an Ebert-Fastie spectrometer, an off-axis telescope, and two Hamamatsu phototube detectors. The combination of the spectrometer and the detectors produces a spacing of 22 nm between the two channels and the exit slits are sized to give each detector a 3.7 nm bandpass. The grating in the spectrometer is set to place the (1,0) gamma band (215 nm) on one detector and the (0,1) gamma band (237 nm) on the other detector. Both channels have a sensitivity of 450 counts/second/kiloRayleigh. The UVS is mounted with its optical axis perpendicular to the spin axis of the spacecraft. Its telescope images the entrance slit of the spectrometer on the limb with the long axis of the slit parallel to the horizon. The image of the slit on the limb is 3.5 km (2.2 mi) high, which determines the fundamental altitude resolution of the instrument. The integration time is 27 ms.[11]
Selected science results
The limb-scanning
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
Atmospheric entry
SNOE re-entered the atmosphere on 13 December 2003 at 09:34 UTC (± 6 minutes), descending over 2.9° South, 273.8° East, on orbit 32248, after 5 years and 290 days.[5]
See also
- Explorer program
References
- ^ Solomon, Stanley C.; Bailey, Scott M.; Barth, Charles A.; Davis, Randal L.; Donnelly, John A.; et al. (1998). The SNOE Spacecraft: Integration, Test, Launch, Operation, and On-orbit Performance (PDF). 12th AIAA/USU Conference on Small Satellites 1998 Logan, Utah.
- ^ S2CID 121207264.
- ^ "SNOE". Encyclopedia Astronautica. Archived from the original on 28 December 2016. Retrieved 26 March 2017.
- ^ a b "Trajectory: SNOE (Explorer 72) 1998-012A". NASA. 28 October 2021. Retrieved 29 November 2021. This article incorporates text from this source, which is in the public domain.
- ^ a b c d e "Display: SNOE (Explorer 72) 1998-012A". NASA. 28 October 2021. Retrieved 29 November 2021. This article incorporates text from this source, which is in the public domain.
- ^ "Spacecraft Structure". University of Colorado Boulder. Laboratory for Atmospheric and Space Physics. Retrieved 26 March 2017.
- S2CID 17583117. Archived from the original(PDF) on 11 June 2010.
- ^ "Instruments". University of Colorado Boulder. Laboratory for Atmospheric and Space Physics. Retrieved 26 March 2017.
- ^ "Experiment: Auroral Photometer (AP)". NASA. 28 October 2021. Retrieved 29 November 2021. This article incorporates text from this source, which is in the public domain.
- ^ "Experiment: Solar X-ray Photometer (SXP)". NASA. 28 October 2021. Retrieved 29 November 2021. This article incorporates text from this source, which is in the public domain.
- ^ "Experiment: Ultraviolet Spectrometer (UVS)". NASA. 28 October 2021. Retrieved 29 November 2021. This article incorporates text from this source, which is in the public domain.
- . D13203.
External links
- SNOE website by the University of Colorado Boulder
- SNOE entry at ESA's eoPortal