Advanced Telemetry Tracking System for High Dynamic Targets

Advaced Telemetry Trackig System for High Dyamic Targets Item Type text; Proceedigs Authors Mischwaer, Natha; Leide, Nelso Paiva Oliveira Publisher Iteratioal Foudatio for Telemeterig Joural Iteratioal Telemeterig Coferece Proceedigs Rights Copyright held by the author; distributio rights Iteratioal Foudatio for Telemeterig Dowload date 01/07/2018 12:05:37 Lik to Item http://hdl.hadle.et/10150/596448

ADVANCED TELEMETRY TRACKING SYSTEM FOR HIGH DYNAMIC TARGETS Natha Mischwaer ViaSat, Ic. Duluth, GA Dr. Nelso Paiva Oliveira Leite IPEV-EPD São José dos Campos, SP, Brazil ABSTRACT A ew advaced 2.4 meter telemetry trackig atea system allows for successful autotrackig of high dyamic targets. The system is desiged to work at C, S, ad L bads. Oe of these systems at L/S-bad was recetly implemeted ad tested i the field. The testig icluded trackig aircraft durig maeuvers such as rolls, spis, ad atea tower fly-by at high rates of speed. This paper examies test results ad some of the features of the ew system that allow for cotiuous trackig. KEY WORDS Flight Test; Telemetry Lik; ESCAN; Dyamic Test; L/S-bad. INTRODUCTION A ew telemetry trackig atea system was developed by ViaSat i partership with Orbital Systems i order to meet icreasig demads i the telemetry field. This system utilizes a 2.4 meter reflector above a Elevatio over Azimuth positioer. The system examied i this paper curretly uses a ESCAN L/S-bad prime focus feed. However, with the shift to the C-bad spectrum o the horizo, the system was desiged to easily add a cassegrai C-bad feed ad dowcoverter for operatio at C-bad. Features of the ew system will be examied, followed by the review of tests performed o the system, which iclude dyamics testig prior to ay aircraft missio ad trackig results from test flight campaigs. 1

SYSTEM OVERVIEW The outdoor equipmet (Figure 1) cosists of a L/S-bad feed, spars, 2.4 meter reflector, camera, ad a Elevatio over Azimuth positioer (which houses the trackig receivers, atea cotroller, servo amplifiers, motors, ad associated electroics). The idoor equipmet icludes a computer for cotrollig the system ad accessig the camera, a Lumistar receiver, a dehydrator, ad a video recorder. A sigle fiber cable is coected betwee the idoor ad outdoor equipmet for commuicatio, alog with RF cables for the telemetry data. Figure 1 - Telemetry Trackig System Outdoor Equipmet SYSTEM FEATURES The system operates i the traditioal L/S-bad betwee 1.4-2.4 GHz, ad is desiged to work i the ew C-bad telemetry bad betwee 4.4-5.25 GHz. A prime focus feed is used for L/S-bad operatio. ViaSat has bee providig S-bad autotrackig atea systems for over 50 years, ad utilized a previous feed desig to facilitate autotrackig for this ew system. The positioer for the ew system (Figure 2) was developed i partership with Orbital Systems. This ew desig has improved performace characteristics for both axes i order to autotrack high dyamic 2

targets. A sliprig is used i the azimuth axis (Figure 3) to allow for cotiuous rotatio so that autotrack is ot iterrupted. The etire positioer is pressurized (alog with the rest of the outdoor equipmet) via a dehydrator located idoors, allowig for operatio of the system i harsh eviromets for may years. Figure 2 - Telemetry Trackig System Positioer Figure 3 - Azimuth Axis Sliprig The idoor computer is used primarily to cotrol the system ad access the video stream from the camera. Users cotrol the system by accessig the outdoor atea cotroller through a Graphical User Iterface (GUI - Figure 4). The computer ca also be used to check the status of the outdoor trackig receivers via web iterface, as well as check the temperature ad humidity withi the outdoor positioer. SYSTEM DYNAMICS TESTING Prior to ay tests ivolvig the trackig of targets, automated tests were performed via the cotroller GUI to esure that the system could hadle trackig high dyamic targets. The system was desiged to have performace characteristics of ±60 /s velocity i the azimuth axis, ±45 /s 2 acceleratio i the azimuth axis, ±30 /s velocity i the elevatio axis, ad ±30 /s 2 acceleratio i the elevatio axis. Alog with the results of the automated tests displayed o the cotroller GUI, servo cotrol data from the system itself was recorded durig the tests to further aalyze the system s performace. 3

Figure 4 - Atea Cotroller Graphical User Iterface The results displayed o the cotroller GUI after the automated velocity testig are show i Figures 5 ad 6. The measured absolute velocities i azimuth ad elevatio were respectively 59.98 /s ad 30.02 /s. Figure 5 - Automated Azimuth Velocity Test Results 4

Figure 6 - Automated Elevatio Velocity Test Results For idepedet verificatio of the true system performace, the servo cotrol data was examied from all 10 time slices (s 1 through s 10 of Figure 5) at steady speed (i.e. ±60 /s ad ±30 /s respectively for the azimuth ad elevatio axes). The measured mea speed (V m ) of each slice was the computed as: V m = Where: t k t ff V(t k) t k t ss m=[1:10] (eq. 1) m is the slice umber (m = [1:10]); V m is the mea speed of the m th slice; t sm, t fm are respectively the startig ad fiishig time of the m th slice (S i ); ad is the umber of samples of each slice The, i coformace with EA-4/02 Stadard (EA, 2002), the axis speed error ( V j ) of each j th stabilized measuremet, the associated ucertaity (σ v) withi 1σ cofidece level ad the mea speed of the etire test (V t ) were computed usig: V j = V(t k ) tss t k t ee VV m=[1:10] (eq. 2) j=1 2 σ v = ± V j 1 2 j=1 V j V t = 10 m=1 [( 1)m+1. V m ] ± σ m v (eq. 3) (eq. 4) 5

The usig acquired data show i Figures 7a ad 7b, the resultig computed absolute speed measuremets were 59.99 /s ± 0.18 /s @ 1σ ad 30.00 /s ± 0.04 /s @ 1σ respectively for the azimuth ad elevatio axes. Figure 7 - Measured Absolute Speed Results Durig Velocity Testig, (a) Azimuth; (b) Elevatio. The results of the automated acceleratio testig displayed o the cotroller GUI are show i Figure 8, yieldig 44.91 /s 2 ad 29.68 /s 2 respectively for the azimuth ad elevatio axes. Figure 8 - Automated Acceleratio Test Results, (a) Azimuth; (b) Elevatio. For idepedet evaluatio of the pedestal acceleratio usig the measured servo cotrol data, it was ecessary to compute the first derivative of the actual pedestal speed ad select the slices where the pedestal acceleratio was costat (i.e. ±45 /s 2 ad ±30 /s 2 respectively for the azimuth ad elevatio axes). This procedure was required due to the lack of direct acceleratio measuremet i the servo cotrol data set. Therefore: A(t) = dd(t) (eq. 5) dd With data provided from equatio 5 the measured mea acceleratio (A m ) of all 10 time slices (Figure 9) was computed usig: 6

t k t ee A m = A(t k) t k t ff m=[1:10] (eq. 6) Figure 9 - Acceleratio Test Slices, (a) Azimuth; (b) Elevatio The, the axis acceleratio error ( A j ) of each j th stabilized measuremet, the associated ucertaity (σ A) withi 1σ cofidece level ad the mea acceleratio of the etire test (A t ) were computed usig: A j = A(t k ) tss t k t ee AA m=[1:10] (eq. 7) j=1 2 σ a = ± A j 1 2 j=1 A j (eq. 8) A t = 10 m=1 [( 1)m+1. A m ] (eq. 9) ± σ m a Usig acquired data show i Figure 10, the resultig computed acceleratios are 45.04 /s 2 ± 2.01 /s 2 @ 1σ ad 29.94 /s 2 ± 2.92 /s 2 @ 1σ respectively for the azimuth ad elevatio axes. Figure 10 - Measured Absolute Acceleratio Durig Acceleratio Testig, (a) Azimuth; (b) Elevatio Comparig the results of the automated tests to the desired characteristics of the system, it was cofirmed the system could move quickly eough ad had eough acceleratio to keep up with iteded targets. Lookig over the velocity ad acceleratio errors, the acceleratio errors do appear high, but this should ot affect the iteded system performace, ad the velocity errors were cosidered satisfactory. 7

PRELIMINARY TRACKING ERROR ESTIMATION After the automated tests were performed, it was ecessary to verify the system trackig capabilities uder high dyamics. The pedestal was slaved to computer geerated trajectory that simulates the aircraft path i order to exercise the pedestal dyamics uder maximum acceleratio regime for both axes. The the trackig error was computed as the differece of pedestal actual positio ad the required positio (i.e. computer-geerated commad). The test results that iclude the pedestal commad ad positio respose, its speed ad estimated trackig error are preseted i Figures 11, 12 ad 13. Figure 11 - Pedestal Azimuth Positio at Dyamic Trackig Test, (a) Azimuth; (b) Elevatio. Figure 12 - Pedestal Speed at Dyamic Trackig Test, (a) Azimuth; (b) Elevatio. Figure 13 - Estimated Trackig Error at Dyamic Trackig Test, (a) Azimuth; (b) Elevatio. The measured trackig error was 0.01 ±0.70 @2σ ad 0.03 ±0.85 @2σ respectively for the azimuth ad elevatio axes (Figures 13a ad 13b). This trackig error was compared to the 3 db beamwidth of the system i order to verify the system dyamics would allow for successful aircraft trackig uder high 8

dyamics regime. For L/S-bad operatio, the 3 db beamwidth at 2.4 GHz is 3.65 for this system, so trackig should ot be a issue. For future C-bad operatio, the 3 db beamwidth at 5.25 GHz is 1.67, so there should ot be ay trackig issues i this bad either due to system dyamics. DYNAMIC TARGET TESTING After successful o-site system istallatio, certai flight test profiles were chose to verify system trackig at the highest possible speed for the system. Oe of these trackig tests was a tower fly-by test poit used by the Brazilia Divisão de Formação em Esaios em Voo (Flight Test School - EFEV) for the air data system (ADS) calibratio flight test campaig. Therefore a particular test sceario was selected, where the elevatio of the system was almost costat, but the azimuth axis would eed to move ear maximum speed ad acceleratio. Test results for the XAT-29 (EMBRAER Super Tucao) aircraft flyig at 255 kts (Figure 14a) shows that the atea reached its maximum speed (i.e. +60 /s). Also at the same coditio the measured trackig error (Figure 14b) shows that the maximum error was withi the -3db beam width of L, S ad C Bads. Therefore the measured azimuth trackig error of -0.13 ± 1.06 @2σ ad the pedestal dyamic performace could be cosidered satisfactory. Figure 14 - Tower Fly-By Test Results, (a) Azimuth Speed; (b) Azimuth Trackig Error To evaluate both axes the EFEV 2014 class studets performed a over-head pass of the XAT-29 aircraft, where the test bed flies almost directly over the system. Such profile would require both axes to move close to their maximum speeds (Figures 15a ad 15b) ad acceleratios. 9

Figure 15 - Over-Head Pass Test Results, (a) Azimuth Speed; (b) Elevatio Speed Figure 16 - Over-Head Pass Test Results, (a) Azimuth Trackig Error; (b) Elevatio Trackig Error A detailed aalysis of the over-head test poit (Figures 16a ad 16b) shows that the azimuth axis trackig error exceeded the 2.4GHz -3db beamwidth. With this coditio we would expect to lose autotrack capability, however the atea cotrol system could maitai test bed trackig. Oe possible reaso for such behavior could be attributed to the high RF sigal stregth, so the e-sca trackig sigal could still be properly geerated. At the other side the elevatio trackig error was iside the 2.4GHz -3db beam width limits. After the high dyamic testig, the aircraft performed a 6-tur ormal ad iverted spis test to determie if the system could successfully track the aircraft i a real test sceario where the RF polarizatio is chagig fast due to the propagatio effects of such maeuver. Due to some limitatios, the system trackig error was ot recorded durig such tests; however the atea frot ed was able to properly hadle trackig ad received all data without ay oise ad/or dropouts as expected. 10

CONCLUSIONS The ew desig by ViaSat ad Orbital Systems for a advaced 2.4 meter telemetry trackig atea system ca successfully track high dyamic targets. Utilizig a sliprig, the system has cotiuous rotatio i the azimuth axis which allows for cotiuous trackig of a target throughout its missio. The dyamics testig showed the system could hadle trackig targets that required the system to move ad accelerate quickly. With the help of IPEV ad EFEV, flight profiles were executed to fully test the trackig capabilities of the system. Durig the tower-fly by test, the system ever lost track ad the trackig error was withi the -3dB beamwidth for L, S, ad C bads. Although the over-head pass had a azimuth test poit for trackig error that was outside the -3dB beamwidth for S-bad, the system did ot lose track, ad the rest of the data poits were iside the beamwidth. Furthermore, reviewig the data from the flight tests, the results idicate that trackig at C-bad should ot be a issue. Some of the trackig errors for the over-head pass were outside of the -3dB beamwidth, but with some trackig gradiet adjustmets for the trackig receivers, future C-bad trackig should be possible. ACKNOWLEDGEMENTS We wish to thak the ucoditioal support give by the Istituto de Pesquisas e Esaios em Voo (IPEV), specially the EFEV Flight Test Course 2015 Class Studets, for supportig the tower fly-by ad the spi flight tests campaigs. Also we like to thak Fiaciadora de Estudos e Projetos (FINEP) alog with Fudação de Ciêcia, Aplicações e Tecologia Especiais (FUNCATE) uder agreemet 01.12.0518.00 ad 01.12.0545.00 that fuded the developmet of this system ad the presetatio trip. REFERENCES [1] EA. EA-4/02: Expressio of the Ucertaity of Measuremet i Calibratio. Europea Co- Operatio for Accreditatio, 1999. Available: http://www.europea-accreditatio.org. 11