Magnetometer-Only Attitude and Rate Estimates for Spinning Spacecraft

3,l.Challa*, G.. Natat_son, and N. OttensteinComputer Sciences Corporation, 7700 Hubble Dri_'e, Lanham-Seabrook (MD 20706)ABSTRACTA deterministic algorithm and a Kalman filter forgyroless spacecraft are used independently to estimatethe three-axis attitude and rates of rapidly spinningspacecraft using only magnetometer data. In-flight datafrom the Wide-Field Infrared Explorer (WIRE) duringits tumble, and the Fast Auroral Snapshot Explorer(FAST) during its nominal mission rood8 are used toshow that the algorithms can successfully estimate theabove in spite of the high rates. Results using simulateddata are used to illustrate the importance of accurateand frequent data.INTRODUCTION AND OB_IECTIVEWe have demonstrated earlier that two algorithms -Deterministic Attitude Determination fromMagnetometer-Only Data (DARDMOD) 13 and the RealTime Sequential Filter (RTSF) 4"5-can successfully 6_1estimate the three-axis attitude and rates of spacecraftusing only three-axis magnetometer (TAM) data inspite of no a priori knowledge of the spacecraft state.Our past studies have included spacecraft such as theSolar, Anomalous, and Magnetospheric ParticleExplorer (SAMPEX), the Earth Radiation BudgetSatellite (ERBS), the Rossi X-ray Timing Explorer(RXTE). In particular, we have shown that: SAMPEXrequirements can be met 6"7'9in both nominal andsafehold modes if the Sun sensor fails, and that theERBS attitude and rates could be successfullyestimated t° during its 1987 control anomaly 1-"when [ttumbled at about 2 degreessecond (deJsec) resultingin the TAM being the only functional attitude sensor.The accuracies obtained in such work are 0.5 -2.0 degin attitude, and 0.002 -0.01 deffsec in rates. Thus wehad shown that a single TAM can be a surprising@effective low-cost attitude-and-rate sensor.A feature of our past studies has been the relatively lowspacecraft spin rate: 1 rotation per orbit (0.06 deJsec)during SAMPEX and ERBS nominal modes, and about2 deffsec during the ERBS tumble.The present study aims to evaluate the TAM-onlyperformance of the above algorithms in an importantalternate scenario: when the rates are high, of the orderof tens ofdeg/sec. A successful outcome would allowtwo important capabilities in spacecraft guidance forthree-axis stabilized and spin stabilized spacecraft:* an early warninJrecovery system forspacecraft tumbles• a magnetometer-only attitude determinationsystem for cheaper spacecraftThe present study uses high-rate in-flight data from thefollowing two scenarios:• The Wide-Field Infrared Explorer (WIRE) _3post-release tumble Z4.when the rates eventuallyreached 360 deffsec.• Nominal mode data from the Fast AuroralSnapshot Explorer (FAST) _swhich spins at 12rpm (72 deg/sec).The rest of this paper is organized into sections dealingwith the following topics: brief theoretical descriptionsof the DARDMOD and the RTSF, applications to theWIRE tumble, applications to the FAST, andconclusions.THEORYDeterministic Attitude and Rate DeterminationUsin R Magnetometer-Only Data (DARDMOD}The DARDMOD algorithm solves for the attitude andrates using a batch of T,%M measurements and controllaw data such as wheel angular momentum andmagnetic torquer dipole moments. The resultingmathematics can be complex _31_, involving the" This paper is declared a _vork of the U.S. Government and is not subject to copyright protection in the UnitedStates.' Senior Member -.-\IAA, Phone: 301.794..2321. E-mail: mchalla@csc.com, Fax: 301.79;.72081American Institute of Aeronautics and Astronauticshttps://ntrs.nasa.gov/search.jsp?R=20000084154 2020-04-25T22:35:02+00:00Z