TNO report Trajectory Simulation Model for a Side- PML 1998-A80 Thruster Guided MLRS-Type Vehicle TNO Prins Maurits Laboratory DISTRIBUTION STATEMENT A Approved for Public Release Distribution Unlimited 19990907 029 * TNO report Trajectory Simulation Model for a Side- PML 1998-A80 Thruster Guided MLRS-Type Vehicle TNO Prins Maurits Laboratory Lange Kleiweg 137 Date P.O. Box 45 May 1999 2280 AA Rijswijk The Netherlands Author(s) Phone +31 15 284 28 42 Dr. G.M.H.J.L. Gadiot Fax +31 15 284 39 58 Classification Classified by Major J. Kerkvliet Classification date 6 April 1999 (after 10 years this classification is no longer valid) Title Ongerubriceerd Managementuittreksel : Ongerubriceerd Abstract Ongerubriceerd Report text Ongerubriceerd All rights reserved. No part of this publication may be reproduced and/or published by print, photoprint, microfilm or any other means 13 without the previous written consent of Copy no. TNO. 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The classification designation Ongerubriceerd is equivalent to Unclassified. 0 1999 TNO 4 DTc Q IJLM IgIpECTED N T TNO Prins Maurits Laboratory is part of TNO Defence Research which further consists of: / TNO Physics and Electronics Laboratory Netherlands Organization for TNO Human Factors Research Institute Applied Scientific Research (TNO) TNO report PML 1998-A80 2 Managementuittreksel Titel Trajectory Simulation Model for a Side-Thruster Guided MLRS- Type Vehicle Auteur(s) Dr. ir. G.M.H.J.L. Gadiot Datum mei 1999 Opdrachtnr. A95KL410 Rapportnr. PML 1998-A80 FiguurM .I.- Lancering van een M26-raket vanaf een MLRS 'launcher'. De Koninklijke Nederlandse Landmacht (KL) heeft het 'Multiple Launcher Rocket System' (MLRS) in gebruik. Met de huidige uitrusting kan men een dracht van 30+ km halen. Voor de toekomst heeft men behoefte aan een dracht van ongeveer 60 km. Het is de doelstelling van opdracht A95KL410 om kennis en inzicht te verzamelen over MLRS-achtige systemen met een dracht van 60 km. Ten gevolge van de grotere dracht zullen de fouten in de baan van de ongeleide raket sterker doorwerken, waardoor bij het doel grotere afwijkingen in de nauw- keurigheid optreden. De fouten worden onder andere veroorzaakt door de launcher: "* ten gevolge van zogenaamde 'tip-off' (richtingsafwijking van de raket door het contact met het lanceerplatform); "* ten gevolge van het functioneren van de voortstuwing ('thrust misalignment'); "* door de invloed van de atmosfeer, onder andere de wind. Het is mogelijk om met behulp van 'side-thrusters' de koers van de raket aan te passen en zo de raket dichter bij het doel te krijgen. In eerste instantie is onderzocht of het gebruik van side-thrusters in het zwaartepunt van de raket mogelijk is. Uit TNO report PML 1998-A80 3 deze studie kwam naar voren dat het mogelijk is om met behulp van 'side- thrusters' de fouten bij een range van 60 km terug te brengen naar fouten van dezelfde orde die nu optreden bij 30 km [1]. Daarna is gekeken naar de invloed van 'side-thrusters' die niet aangrijpen in het zwaartepunt van de raket. Wanneer de 'side-thrusters' aangrijpen v66r het zwaar- tepunt wordt het effect van de 'side-thruster'-puls versterkt. Om dit met het be- staande computermodel te evalueren is het model aangepast en is er een gedetail- leerde parameterstudie uitgevoerd. De voorbereidingen en de resultaten van deze studie worden in het onderliggende rapport beschreven. De resultaten van de studie onderschrijven de eerdere bevindingen [1] en geven aan dat ongeveer tweederde van de pulsenergie kan worden bespaard door de 'side- thrusters' zo ver mogelijk voor het zwaartepunt te plaatsen. Dit betekent dat er in principe grotere correcties mogelijk zijn of dat er met een kleinere 'thruster'module kan worden gewerkt. [1] Gadiot, G.M.H.J.L.; Marde, A.G.M. en Keus, L.J., 'Limited sensitivity study on side-thruster guidance for an extended range MLRS-type vehicle', TNO-rapport PML 1997-A36, augustus 1997. TNO report PML 1998-A80 4 Contents M anagementuittreksel ........................................................................................... 2 1 Introduction ........................................................................................... 5 2 The M LRS missile ............................................................................... 8 3 MLRS side-thruster guidance model (thrusters through c.o.g.) ....... 10 4 MLRS side-thruster guidance model (thrusters not through c.o.g.) ........ 14 4.1 M odification of the impulse formula ................................... 14 4.2 Sensitivity study ................................................................... 25 5 Evaluation ........................................................................................... 41 6 Conclusions and recomm endations ..................................................... 43 7 References ........................................................................................... 44 8 Authentication .................................................................................... 45 TNO report PML 1998-A80 5 1 Introduction This report describes the status of the work carried out by the TNO Prins Maurits Laboratory (TNO-PML) for the Royal Netherlands Army (RNIA) under project A95KL410, titled: 'Guidance concepts for indirect fire munitions' [2]. This work is related to the general interest within the military world in extending the range of artillery rocket systems. It is of particular interest to the Royal Netherlands Army who are considering upgrading their existing 30+ km range Multiple Launch Rocket System (MLRS) to a 60 km extended range version. When the range of such a bal- listic rocket is upgraded, the effectiveness of these weapons will degenerate if the accuracy in position at impact is not kept at the same level or, preferably, improved. To achieve an improved accuracy, the ballistic rocket must be guided to its target. Two basic forms of guidance can be identified; aerodynamic guidance and guidance using small side-thruster rockets. This report focuses on the latter guidance method. Within this framework, a study [1 has been performed to identify the order of the guidance effort required to realize the same target accuracy for an upgraded MLRS- like missile with a range twice as long (60 km) as currently available (30 km) and guided by side-thrusters. Furthermore, it is assumed that the guidance is performed with navigation updates sent from the ground. To prevent jamming of the signal, the guidance takes place only up to the time of apogee, for it is assumed that jamming will only occur when the missile is approaching the target, and after the missile is past its apogee. For the study, a simulation model (Direct Side Thrusting Guidance, DSTG) was developed which is able to simulate a ballistic trajectory in a standard atmosphere (US 76) of a missile from the moment the propulsion section bums out until the moment of impact. The model is based on aerodynamic data and the vehicle mass after bum-out of the propulsion section. Furthermore, a guidance algorithm is implemented with which the required side-thruster impulses can be calculated. This work is partly based on a study carried out in the US on an MLRS-type vehicle with aerodynamic guidance [3]. TNO report PML 1998-A80 6 guided trajectory disturbed trajectory ref. trajectory \ altitude (m) 15000 10000 5000 isturbed burn-out point 66oo0000000 ref. burn-out point 0 downrange (m) 0 10 20 30 40 50 60 70 80 crossrange (m) Figure 1.]: Typical reference, disturbed and side-thrusterg uided trajectory. In the study, the 30 km range of an MLRS-like missile has been improved to 60 km, by increasing the velocity at bum-out. To keep the error budgets at impact for the 60 km range at the same level as for the 30 km range, the upgraded missile is guided with side-thrusters during the first half of the trajectory after bum-out up to the time of apogee. To obtain a first impression of the required guidance effort (total impulse of all side-thruster firings combined), a disturbance case with errors in the bum-out state is used as a reference. A typical reference, disturbed and side-thruster corrected trajectory is given in Figure 1.1. For determining this case, a missile with a range of 30 km and an impact just inside an assumed accuracy range of ± 50 m in cross- and downrange around the nominal ballistic point of impact was taken. Using a linear-quadratic regulator, the upgraded MLRS-like missile could be guided such that the accuracy at impact was similar to that of the 30 km range reference vehicle. For achieving this, a total impulse of 300 -500 Ns side-thruster firings was required. A limited number of different guidance approaches were taken for the study, varying the total number of side-thruster firings and guidance time interval. All approaches were successful in guiding the extended range missile, but differed in the amount of total side-thruster power required. The study showed that the greatest control effort should be applied at the beginning of the guidance time-frame. It seems to be cost effective to apply guidance as early as possible in time after bum-out. After these initial results, the DSTG computer program was modified to include the propelled part of the guided missile flight and the influence of the weather in the form of a wind profile. The former makes it easy to introduce different propulsion TNO report PML 1998-A80 7 concept, e.g. the standard rocket motor or an extended range motor, and allows for a study of variations due, for example, to temperature on range and performance (typical operational aspects). The inclusion of a wind profile is important as wind effects lead to considerable deviations in missile trajectory near the target area. In parallel, a study was carried out on the effect of side-thruster pulses that do not occur not through the centre of gravity. By taking advantage of the aerodynamic moment resulting from the side-thrust not aimed through the centre of gravity (c.o.g.), the required impulse can be diminished by up to 70%, and less total impulse is needed, or larger deviations may be corrected for. The MLRS missile description is presented in Chapter 2. The MLRS side-thruster guidance model results with side-thrusters through the c.o.g. and with the side- thrusters not through the c.o.g. are presented in Chapters 3 and 4, respectively. An evaluation of the results is presented in Chapter 5, followed by conclusions and recommendations in Chapter 6. TNO report PML 1998-A80 8 2 The MLRS missile General The Multiple Launch Rocket System (MLRS) is a free-flight, area-fire, artillery rocket system that supplements cannon artillery fire by delivering large volumes of firepower in a short time against critical, time-sensitive targets (enemy artillery, air defence systems, mechanized units, or personnel). The MLRS provides counterbat- tery fire and suppression of enemy air defences, light materiel, and personnel targets. MLRS units can use their shoot and scoot capability to survive while providing up- front fire support for attacking manoeuvre elements. See Reference 1 for more detail. The MLRS consists of a self-loading launcher with an onboard fire control system (Figure 2.1). This system is mounted on a mobile track vehicle that carries twelve rockets. Each of these rockets may be fired individually or simultaneously to cover a range beyond 30 km. The basic warhead carries improved conventional submunitions. The extended range MLRS (ER-MLRS) will provide longer range rockets with lower submunition dud rates than for the MLRS. The ER-MLRS is a free-flight, area-fire, artillery rocket designed to complement the capabilities of the MLRS. Its mission is to engage targets beyond the range of the existing MLRS, up to 50 km. WoadingB ooms Launcher-oLader Module -. (cage, Turret an~dB oseA ssemblies) Communications Elevation Actuator "Batery Antennas (2) CageA ssembly Fire ControlP anel (FCP)P anel \" Payload Interface Module (PIM) Power Distribution Improved Electronicese Short/No (NVToltage Unit (IEU) Ture Electronic Box Asseby Rocket Podn (2) Fire Control Unit Boom Controller/ Rocket Tubes (12) (FCU) Improved Stabilization Reference Package/ Position Determining System (ISRP/PDS) Figure 2.1: MLRS M270 missile launcher. TNO report PML 1998-A80 9 Performance in the Gulf War The MLRS proved itself in the Gulf War. This was the first time the MLRS has performed in combat. During the Gulf War, the MLRS served as the 'primary coun- terfire weapon' against Iraqi artillery. Some of its advantages are: "* MLRS was lethal and effective against a variety of targets; "* MLRS was very manoeuverable; "* MLRS was responsive and delivered large volumes of accurate fire. It also must be noted that the success of the MLRS is in part due to the weakness of Iraqi artillery. Nevertheless, the MLRS system proved that the future of artillery lies in a more mobile structure. Thus the MLRS has become the foundation of our future rocket launchers. Additionally, the MLRS also had its problems during the Gulf War. In spite of the poor performance of the Iraqi artillery in the war, it is significant to note that they had (missile systems) that could outrange the MLRS. Although the range of the ATACMS is farther, it is not used as a primary counterfire weapon like the MLRS. Additionally, the MLRS faced problems in providing current meteorological data due to the extreme weather conditions. Furthermore, although many of the batteries had access to the Global Positioning System (GPS), they failed to establish an accu- rate known direction for laying fire. These problems were overcome due to the good training of the MLRS crew and also in part to the poor execution of Iraqi artillery.