| Date: | 2007-12-26 12:22:00 | |
| Sender: | Mark Davis, NRL <slrmail@dgfi.badw.de> | |
| Subject: | [SLR-Mail] No. 1634: URGENT | |
| Author: | Mark Davis, NRL | |
| Content: | ******************************************************************************** SLR Electronic Mail 2007-12-26 12:22:00 UTC Message No. 1634 ******************************************************************************** Author: Mark Davis, NRL Subject: URGENT Atmospheric Neutral Density Experiment MAA Spacecraft Re-Enters The Atmospheric Neutral Density Experiment (ANDE) Risk Reduction flight was launched on Dec. 9, 2006 and deployed into orbit by the Space Shuttle Discovery on Dec. 21, 2006. On Dec. 25, 2007 the MAA (ANDERRA) spacecraft re-entered the atmosphere; the FCal (ANDERRP) spacecraft is not expected to decay until April 2008. Thanks to the international laser ranging service (ILRS) and amateur HAM radio enthusiasts the ANDERR data set is extensive. The Naval Research Laboratory would like to that all of the sites that participated in data collection on the ANDERR MAA satellite and encourage continued efforts for the remainder of the ANDERR FCAL orbital lifetime (~April 2008). The primary mission objective is to test the deployment mechanism from the Shuttle for the ANDE flight in mid 2009 The follow-on ANDE mission scheduled for launch in 2009 will consist of two spherical spacecraft also fitted with retro-reflectors for SLR. One of these spacecraft will also carry instrumentation to measure the in-situ atmospheric density, composition and winds. Scientific objectives of the ANDE risk reduction flight include; monitor total neutral density along the orbit for improved orbit determination of resident space objects, monitor the spin rate and orientation of the spacecraft, provide a test object for the space surveillance network (SSN) sensors, both radar and optical. Each of the two ANDE missions consists of two spherical spacecraft fitted with retro-reflectors for satellite laser ranging (SLR). The constant and well-determined cross section and surface properties of the ANDERR spacecraft provide an ideal set of objects for monitoring atmospheric drag and the calibration of SSN assets. The ANDE risk reduction mission spacecraft each contain a small lightweight payload designed to determine the spin rate and orientation of the spacecraft from on-orbit measurements and from ground based observations. The 20th Space Control Squadron, USAF in Dahlgren, VA, processes US Space Surveillance Network (SSN) radar observation data of the two ANDERR spacecraft. The product is a set of vectors that is provided to NRL, along with the radar observations, up to three times a day. These state vectors merged with the SLR data and processed by NRL’s OCEAN orbit determination software to produce a set of ephemeredes. As a backup the radar data are processed at NLR using Special-K orbit determination software. These ephemeris files are reformatted into the consolidated prediction format used by the ILRS tracking stations. This format consists of minute satellite state vector (x, y, and z positions and velocities at a given time plus other parameters) over the several day prediction period. These predictions are distributed via the NASA CDDIS data center and the European Data Center. Onboard sun sensor data and thermal data are telemetered to the ground via HAM radio frequencies. These data are collected worldwide by amateur HAM radio enthusiast and stored in a database at NRL. The spin rate of the MAA spacecraft was estimated by several different methods; video from the STS-116 deployment, on-board telemetry from the MAA spacecraft, observations from the AEOS telescope on Maui, and satellite laser ranging (SLR) observations. The four independent measures of the MAA spin rate were plotted versus mission elapsed time in days and fit with an exponential function. The results is a decay constant of -0.189. It is clear that the ANDERR spacecraft are useful calibration targets due to their well-characterized size and shape. The SLR observations performed by the members of the ILRS have been used to augment the radar data to constrain the accuracy and stability of the estimated ballistic coefficient and to assess the accuracy of the predictions with absolute confidence. The data show a consistent over estimation of the density by the atmospheric models, NRLMSISE 2000 as well as J70. The average in-track time bias at the 24-hour mark improved by 15.2% with a 39.9% improvement in standard deviation. While the average fitted CD for J70 was closer to the analytic value, the MSIS CD values have considerably less variation. The over specification of total density is in agreement with the findings of Emmert and Picone (JGR, 2004), who have shown a consistent decrease in thermospheric density of the past three decades. The models are having a difficult time properly capturing the effect of geomagnetic forcing (especially at low end of the solar/geomagnetic forcing range), as correlations are evident in the fitted CD values with the geomagnetic ap index. The data set from the ANDERR mission will aide researchers in improving the current atmospheric density an wind models. Best Regards, Andrew Nicholas ANDE PI: Andrew Nicholas, NRL 7669, andrew.nicholas@nrl.navy.mil SLR POC: Mark Davis, NRL 8123, mark.davis@nr.navy.mil HAM POC: Bob Bruninga, USNA, bruninga@usna.edu From: slrmail@dgfi.badw.de ******************************************************************************** |