LASP/CU Rocket Experiment Overview

Overview Picture

LASP/CU Rocket Science Objectives for 1992-1997

  1. Study and model the solar extreme ultraviolet (EUV) and soft X-ray (XUV) spectral irradiance and its variability
  2. Study and model the solar-terrestrial relationships involving absorption of the solar radiation, ionization, generation of photoelectrons, and airglow emissions
  3. Provide underflight calibrations for satellite instruments such as on San Marco, Voyager, EUVE, Galileo, SOHO
  4. Flight testing of the TIMED Solar EUV Experiment (SEE) satellite instrument

Additional Objective for 2002-2004

  1. Provide underflight calibration for TIMED SEE satellite instrument

Additional Objective for 2006

  1. Flight testing of the SDO EUV Variability Experiment (EVE) satellite instrument

LASP/CU Rocket Observations

Timeline for Observations
The payload is separated from the rocket motors at T+67 sec, and the attitude control system (ACS) maneuvers the payload to point the solar instruments toward the Sun and the airglow instrument toward the west horizon. The science data is taken for approximately 6 minutes while the payload goes from about 120 km up to its apogee of near 300 km and back down to 90 km. Then the instruments are turned off for re-entry into the atmosphere. The launch and recovery site is the White Sands Missile Range in New Mexico.

Solar Extreme Ultraviolet (EUV) Irradiance Measurements
The solar EUV radiation, below 120 nm, is highly variable with changes as much as a factor of 2 for solar chromospheric emissions and a factor of 10 to 1,000 common for the solar coronal emissions. This variability is over the 11-year magnetic cycle, and slightly lower rates of variability is also seen for the 27-day rotational period and for flares lasting a few minutes. This radiation is completely absorbed in the atmosphere, mostly above 80 km. This absorbed solar radiation creates the ionosphere, drives the thermospheric temperature up and down as the solar radiation varies, and is the catalysis for many chemical reactions in the upper atmosphere. However, the solar EUV irradiance is not well understood due to the lack of daily measurements with well-calibrated instrumentation. While this rocket experiment can not acquire daily measurements, it does address the absolute value of the irradiances as these instruments are accurately calibrated using Beam Line 2 of the Synchrotron Ultraviolet Radiation Facility (SURF-II) at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. These rocket instruments have also been developed for use on the NASA Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) mission, so daily measurements of the solar EUV irradiance, which can then adequately study the relative variability of the solar EUV output, are expected to begin in 2000.

Far Ultraviolet (FUV) Airglow Measurements (1992-2004)
The FUV airglow provides a means to monitor the structure of the upper atmosphere and how the solar radiation has affected it. The FUV airglow is dominated by two types of emissions, (1) solar fluorescence which is used to derive atmospheric density and composition and (2) electron impact excitation which is used to derive photoelectron flux in addition to the atmospheric density and composition.

Solar Soft X-Ray (XUV) Images (1992-2004)
The XUV radiation, that is at wavelengths below 30 nm, originates entirely within the chromosphere, transition region, and corona layers of the solar atmosphere. So the solar XUV images provide a map of the sources of variability on the Sun which can then be used in developing models of the solar EUV variability. In addition, off-disk images of the He and H emissions are obtained to study the He and H abundances in the hot corona.

LASP/CU Rocket Instrumentation

Payload Subsystems
Multiple EUV Grating Spectrograph (MEGS) (2006)
The MEGS is a set of two grating spectrographs packaged into single housing and designed for the SDO EUV Variability Experiment (EVE). It includes a grazing incidence spectrograph for the 5-37 nm range and uses a cooled backside illuminated CCD built by MIT Lincoln Lab. It also includes a two-pass grating spectrograph for the 35-105 nm range and uses the same type CCD. Both MEGS-A and MEGS-B spectrographs have a spectral resolution of 0.1 nm and measurement cadence of 10 seconds.

EUV SpectroPhotometer (ESP) (2006)
The ESP is transmission grating spectrograph with 4 EUV bands in the 17-36 nm range with 2 nm spectral resolution and a quad diode at zeroth order for the 0.1-7 nm range. It too is designed for the SDO EUV Variability Experiment (EVE).

XUV Photometer System (XPS)
A set of silicon photodiodes with metallic thin films deposited directly on the diodes is used to measure the solar soft X-ray (XUV) irradiance. The XPS spectral range is from 0.1 to 40 nm with each photometer having a spectral bandpass of 5 to 10 nm. The original XPs have flown in 1992, 1993, and 1994, and they were lost also on the failed METEOR satellite launch. The new XPS, the TIMED SEE prototype, has 12 silicon photodiodes: 8 XUV photometers, 1 Lyman-alpha phototmer, and 3 visible light photodiodes for measuring filter transmission. The new XPS has the same spectral range as the original XPS.

EUV Grating Spectrograph (EGS) (1992-2004)
The EGS is a Rowland-circle grating spectrograph that makes solar extreme ultraviolet (EUV) spectral irradiance measurements. The original EGS made measurements from 30 to 115 nm with 0.1 nm spectral resolution. This EGS version made measurements in 1988, 1989, 1992, 1993, and 1994, and it was lost during the failure of the Conestoga / METEOR satellite launch. The new EGS, the TIMED protoflight version, covers the spectral range from 20 to 200 nm with 0.2 nm spectral resolution.

Advanced X-ray Spectrometer (AXS)
A silicon avalanche photodiode (APD) is used in photon-counting mode to measure the energy of each detected photon via pulse height analysis (PHA). The solar XUV irradiance spectrum from 0.1 to 5 nm is measured by AXS with a spectral resolution of 10, that is 0.5 nm at 5 nm and 0.01 nm at 0.1 nm.

FUV Airglow Spectrograph (FAS) (1992-2004)
The FAS is a Wadsworth grating spectrograph that makes airglow measurements in the far ultraviolet (FUV) from 125 to 160 nm with 0.2 nm spectral resolution. The brightest airglow emissions in the FUV are from atomic oxygen and molecular nitrogen.

Multiple XUV Imager (MXUVI) (1995-1997)
The MXUVI consists of a two-dimensional detector, telescope mirrors with multi-layer coatings, and foil filters to obtain solar images at 17.5 nm (Fe XI/X), 30.4 nm (He II), and 121.6 nm (H I). The He and H emissions are measured off-disk while the Fe emission is obtained as a full-disk image.

Single XUV Imager (SXUVI) (1992-2004)
The SXUVI consists of a two-dimensional detector, telescope mirror, and Lyman-alpha filters to obtain solar full-disk images at 121.6 nm (H I). Rebuilt in 2003 with AIM intensified CCD and renamed CLASSIC.

Reference for More Instrument Information

Woods, T. N., G. J. Rottman, S. M. Bailey, and S. C. Solomon, Vacuum-ultraviolet instrumentation for solar irradiance and thermospheric airglow, Optical Engineering, 33, 438-444, 1994.

New Rocket Payload in 2006

New Payload Layout

The payload was rebuilt in 2006 to accommodate the SDO EVE MEGS and ESP channels. This rebuild included larger rocket skins (22 inch diameter instead of 17 inch diameter), movement of the solar imager into the CLASSIC section, and new control section. The XPS, CLASSIC, and AXS from previous rocket flights are included in this new payload. The NASA telemetry (TM) subsystem was updated to a 10 Mbps TM system to handle the higher volume of data from the CCDs on MEGS.

LASP/CU Model Developments

Airglow Model
Scott Bailey and Stan Solomon at CU/LASP have developed an airglow model to predict the FUV airglow brightness based on the measured solar EUV irradiance, laboratory cross sections, and atmospheric densities derived from the solar absorption profiles. This model first calculates the photoelectron flux throughout the atmosphere and then calculates the electron impact excitation rates for the molecular nitrogen Lyman-Birge-Hopfield (LBH) bands and the atomic oxygen line at 135.6 nm. Finally the brightness of each of these emissions are calculated by integrating along the line of sight for the airglow spectrograph.

Solar FUV Proxy Model
John Worden (NSO), Tom Woods, Dick White (HAO/NCAR) and Gary Rottman have developed a proxy model for the solar UV irradiance for times when solar irradiance measurements are not available. This model uses three components as the sources of variability: quiet sun, active network, and plage regions. The proxies are derived from NSO Ca II K images, NOAA Mg II core-to-wing ratios (C/W), and NSO He II 1083 nm equivalent widths (EW). The current solar proxy model is for the FUV range between 120 and 200 nm and will eventually be extended down into the EUV range.

Flare Irradiance Spectral Model (FISM)
Phil Chamberlin has developed a proxy model for the solar EUV and FUV irradiance based on the TIMED SEE satellite data taken from 2002 to 2006. This model uses five components as the sources of variability: solar minimum reference spectrum, long-term variations (108 days), short-term variations (day), flare impulsive phase (1-min), and flare gradual phase (1-min).

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Revised January 2007