Reduction of Aircrew Workload Through the Use of INSGPS While Employing Standoff Weapons

Captain Earl W. Stolz, USAF Captain Keith J. Kosan, USAF 40th Flight Test Squadmn/DOOB 505 W ChoctawhatcheeAve Ste 1 Eglin AFB FL 32542.5722 USA

SUMMARY Subjective assessmentsof the value of the MCG modification Modem tighter aircraft are capable of unprecedentedattack were made using aircrew questionnaires and a modified Cooper- accuracy. However, the risk associatedwith close-in delivery Harper Scale. against well-defended targets is often high. As a result, current tactics call for delivery of precision-guided munitions from LIST OF SYMBOLS increased standoff ranges. The AGM-130 was designed to till AFB Air Force Base this need. AGL above ground level AGM air-to-ground The AGM-I30 evolved from the GBU-IS family of glide bombs BLU bomb live unit and is equipped with a rocket motor to increase standoff range. CCF Centralized Control Facility With the increase in launch ranges came an increased workload C/A coarse/acquisition due to difficulty locating targets within the seeker’s field of FOM figure of merit view (FOV). A launch heading offset or crosswind could FOV tield of view require the weapon systems officer (WSO) to scan a large GBU guided bomb unit area to locate both the target itself and any required waypoints. GPS global positioning system The midcourse guidance (MCG) program is an enhancement lMIRS improved modular infrared sensor designed to address this difficulty by decreasing workload with IMU inertial measurement unit an autonomous guidance capability in the midcourse portion of IMV instrumented mockup vehicle the flight and the ability to point the seeker at the target. INS inertial navigation system LOS MCG midcourse guidance The objective of the ACM-130 MCG test program is to evaluate MITL man-in-the-loop the benefits associated with reductmn of aircrew workload with nmi nautical miles the mtroduchon of an inertial navigation system (INS) that is PDOP position dilution of precision position- and velocity-aided by the global positioning system SWAT subjective workload assessmenttechnique (GPS). This paper will discuss flight test techniques and results TM telemetry obtamed from the Phase I test program, which focused on initial TSPI time-space-position information integration efforts using profiles to attack vertical targets. Phase TVGS television guidance seeker II will address the capability to attack horizontal targets and is USAF United States Air Force currently being tested. A secondary objective of demonstrating WAGE wide area GPS enhancement the advantagesof guidance using wide area GPS enhancement WGIJ weapon guidance unit (WAGE) corrections was also accomplished, wso weapon systems officer

Testing involved a series of ground functional tests. captive 1. INTRODUCTION carries in which the aircraft flew the weapon’s profile. and three The AGM-130, like many standoff man-in-the-loop (MITL) live launches. munitions, is a demanding system to employ. Most of the demands placed upon the WSO occur when trying to locate the The stated goal of the MCG program is to ensure that the target target area through the small seekerFOV in the midcourse appears in the seeker’s wadeFOV at 15 secondstime-to-go 95% phase of flight. of the time. In all cases this criteria was met. Additionally, the target was within the narrow FOV 100% of the time. To assist the WSO in target acquisition, a closely coupled INS driven by GPS position and velocity updates has been added. Using the subjective workload assewnent technique (SWAT) in This system guides the weapon during the midcourse phase and a head-to-head comparison with a non-MCG-guided AGM-130. can pant the seeker at the target. This modified weapon is a 25% reduction of WSO workload was demonstrated. referred to as AGM-I30 MCG.

Paper presented at the AGARD FVP Symposium on “Advances in Flight Tesfing”. held in Lisbon, Portugal, 23-26 Seprember 1996, and published in CP-593. 2. WEAPON SYSTEM DESCRIF”IJON The secondary mode of operation is MANUAL. This mode The AGM-130 (Figure I) was developed from the GBU-15 mdicates that the INS is not using the GPS navigation solution family of glide bombs. The primary difference between the due to figure of merits (FOM) not meeting the appropriate GBU-IS and the AGM-130 is the addition of a rocket motor. criteria. If the weapon is launched with MANUAL displayed, radar altimeter, and digital autopilot. Both weapons are the autopilot would not use the INS for navigation (it would use modular systems and can use either a Z,COO-lbgeneral purpose a heading hold mode) nor would it point the seeker to a set of bomb (MK-84) or a penetrator warhead (BLU-109). The target coordinates. If the weapon is launched in MANUAL and weapons are controlled via a radio frequency datalink with the GPS signal improves, a launch point re-initialization may either an RT-lZIO/AN/AXQ-I4 datalink pod. Both the current occur and the weapon will upgrade to GOOD. If the weapon fielded versions of the GBU-15 and the AGM-130 “se ather a degradesto MANUAL after being launched with GOOD DSU-27 electro-optical or a WGU-33 imaging infrared seeker. displayed, the autopilot would still use the INS navigation Recent testing has certified two new. more advanced seekers. solution and fly to a set of coordinates. When the system Both the WGU-40 television guidance seeker (TVGS) and the degradesto MANUAL after loss of GPS, seeker pointing would WGU-42/B improved modular infrared sensor (IMIRS) will also still be available. However, the navigation solution would soon be fielded. be based strictly on the INS solution with no GPS updates (degraded accuracy). The weapon has three phasesof flight: midcourse, transition. and terminal. During the midcourse phase, the seeker is slewed The worst case is for the weapon to be in a mode with FAIL independently of the weapon platform, The only way the WSO displayed, This indicates a shutdown of the IMU, resulting in a can adjust the flightpath of the weapon in this phase is with totally inoperative weapon. discrete heading or altitude commands. In the transition phase of flight, the WSO has dmxt yaw control of the weapon via A NO KEY messageindicates that a GPS cryptokey has not slew commands. In this phase, the WSO still has no direct been loaded. and a NO SAT messageindicates that the GPS control over pitch. The final phase is the terminal phase in receiver has not yet started to track satellites. Figure 4 shows which the weapon platform steers, in both pitch and yaw, in the FOMs required for a GOOD to he displayed at different response to seeker slew inputs. See Figure 2 for a typical low- times-to-go. altitude launch profile.

The MCG kit includes a GPS antenna. a GPS receiver, an INS, The MCG upgrade provides the WSO with the existing basic and an autopilot. weapon capabilities and a significant increased capability for target acquisition, especially under adverse weather conditions. The MCG upgrade will also support the attack of horizontal The GPS receiver sent accurate position and velocity to the INS. targets - a capability not currently available in the fielded This receiver used only the LI frequency, which provided time, system. position, and ephemeris data for each satellite being tracked.

During preflight, the weapon will be loaded with the GPS The INS provided a navigation solution to the autopilot. The cryptokeys. The cryptokey comes on a tape that is read by a Kalman filter imbedded in the INS used inputs from both the KOI-I8 tape reader. The KOI-18 will then transfer the key to a GPS receiver set (positions and velocities) and the inertial KYK-13 or CYZ-IO for loading the weapon. A position update measurementunit (position/attitudes, velocities/rates, and may be initiated using an AN/PSN-I 1 precision lightweight accelerations) to provide the best navigation solution to the GPS receiver to speed up the inertial measurement umt’s (IMU) autopilot. alignment. Target coordmates, approximate launch coordinates, alignment data, and desired nnpact angle are loaded by slewmg The autopilot calculated both a guidance solution and a stability the target designator control (Figure 3). This obviates the need solution based on inputs from the INS, IMU. and radar for developing an expensive capability for loading this data altimeter. During the midcourse and transition phases of flight. using the aircraft’s 1760 Bus. Using the same method, targets the autopilot relied on the INS and radar altimeter to provide a may he reprogrammed inflight. guidance solution based on zeroing the line of sight (LOS) angles/ratesto the target and maintaining a programmed/ In captive or free-flight with the weapon operating normally, the commanded altitude. During terminal flight, the autopilot used WSO would see one of five messages: GOOD, MANUAL, proportional navigation to guide to the target by zeroing the FAIL, NO KEY, or NO SAT. The primary mode of operation is LOS rate to a given target coordinate, guiding the seeker lock- with GOOD displayed. In this mode, the weapon would on designation, or guiding to a manually selected seeker navigate to the target coordinates and point the seeker at the crosshair location. The autopilot used information directly from target. When GOOD is displayed, the weapon could the inertial measurement unit during all phasesof flight to autonomously (no WSO inputs) navigate to and impact the provide a stability solution to maintain a level weapon platform. target with GPS/INS accuracies. to-3

MKWE4U.I W

Figure 1. AGM-130

Midcourse

Transitjon

Figure 2. Typical Low-Altitude AGM-130 MCG Profile

LAT: N5423.!323 LNG: E138:24231 CRS: RALT ELV: 00510 MSL

IAT: N54:2S.S23 VEL: 480 KTAS LNG: Et Z8zZ424231THDG: 067 DEG ALT: 30,cco MSL

Figure 3. AGM-130 MCG Figure 4. MCG GOOD/MANUAL Criteria Targeting Page The WAGE weapon modified the MCG kit with a different GPS Tbe captive-carry weapon was also equipped with a flight-test- receiver. It used a second frequency, L2, which provided the only modification to allow removal of the GPS signal. same information as the Ll frequency. By receiving satellite Launches would be made with the weapon in GOOD status. data over two frequencies, the GPS receiver software was better The GPS signal would then be removed. The degradation of the able to compensate for timing errors due to propagation through weapon’s ability to accurately guide itself was then monitored. the atmosphere. Additionally, the WAGE-specific GPS The next launch was made with the weapon in MANUAL message sent from the appropriate satellite included updated status. Immediately following launch, the GPS signal was GPS clock and ephemeris data. By incorporating a dual band restored. The improvement in the weapon’s ability to guide antenna and receiving the additional WAGE messages,the itself was then monitored. receiver set was able to calculate a near differential position and velocity solution for the INS. Immediately following each mission, the WSO tilled out an aircrew questionnaire with workload ratings from the modified The WAGE missions were only a demonstration and there Cooper-Harper Scale. With this and the aircrew’s flight test are no current plans to field an AGM-130 with WAGE report, a qualitative assessmentof aircrew workload and other modifications. human factors issues were made. The modified Cooper-Harper Scale used can be found in Figure 5. 3. FLIGHT TEST METHOD On seven of the captives, two passeswere flown against first- The AGM-130 MCG Phase I test program consisted of 3 ground look targets. These passeswere used in conjunction with function tests, 14 captive flights, and 3 live launches. The SWAT to determine a quantitative level of WSO workload AGM-130 MCG Phase II test program will evaluate the reduction. These tactical targets had never been seen by the system’s ability to attack horizontal targets and is scheduled to WSOs, except for photographs used in mission planning. The begin in fall 1996. first pass was flown with the weapon set to MANUAL, thus essentially providing an AGM-130 without a MCG guidance Eglin AFB was selected for this test program because of its capability. The second pass was flown using the full unique capabilities for standoff weapons testing. Eglin’s large capabilities of the MCG weapon. land and water ranges provide a realistic environment for testing weapons at significant standoff ranges. Eglin AFB also SWAT is a subIective technique used to gather quantitative data possessesa series of operationally realistic tactical targets, on workload. It evaluates workload using time, mental effort, including hardened aircraft shelters, bunkers. surface-to-air and psychological stressas the factors. Four WSOs participated missile sites. and buildings. Finally, Eglin was able to provide in the study. A group workload scale factor was used with a Centralized Control Facility (CCFl that was capable of psychological stressbeing the most important factor, followed receiving, processing, and displaying, m real-time, all aircraft, by mental effort and time, respectively. Psychological stress is weapon, and pod telemetry (TM). Additionally, the CCF defined as the anxiety level of the WSO while he is guiding the provided real-time positive control of the test aircraft for safety- weapon. Mental effort is defined as the amount of concentra- of-flight and would command the destruction of the weapon if tion required to guide the weapon. Time is defined as the necessary. The CCF also processeddifferential GPS signals, amount of time spent on the task of guiding the weapon. The thus providing real-time time-space-position information (TSPI) importance of each factor was determined from the WSO’s sort to the required accuracies. of the 21 SWAT cards prior to the testing. These cards representedall combmations of the three factors and each WSO Tbe ground functional tests evaluated system functionality with sorted them in the order of importance to them. Following each all possible configurations of seekers and datalinks. pass,the WSO would call out a rating for the three areas. Ratings went from I (easiest) to 3 (most difficult). Based on the card sorts, a numerical rating between I and 100 was calculated. The captive flights consisted of an F-ISE loaded with an One is the easiest and 100 is the hardest. AGM-130 MCG instrumented mockup vehicle (IMV) and an AXQ-14 datalink pod makmg repeatedpasses against selected tactical targets. The IMV exactly duplicated a live weapon in Following the mission. these numbers would be input into all respects except for actual separation from the aircraft. With software and developed by the USAF’s Armstrong Laboratories. an IMV. the aircrew could actually pickle the weapon and By comparing a WSO’s values for each pass with the card sort simulate free-flight of the munition. This was done by having numbers, one can obtain a quantitative assessmentof WSO the aircraft fly the weapon’s attack profile. Truth data was workload reduction. obtained through the use of differentially corrected GPS pods. Three of the captive carries were dress rehearsal missions prior A dedicated mission was flown to test the system’s ability to to launches. Tbe objective of these missions was to provide a operate usmg coarse/acquisition (C/A) code wth no cryptokeys. realistic practice for all members of the test team including the test aircrew, chase aircrew, safety engineers, and test engineers. Figure 5. Modified Cooper-Harper Scale

On launch missions. a minimum of three passes were executed, chase followed the AGM-130 after launch. The high-speed denoted alpha, bravo. and chadie. On the alpha pass, various impact cameras ran when the weapon entered the camera’s weapon functions were checked with TM and radio communi- FOV. cations were confirmed between the test aircrew, chase aircraft, and the test engineer at the CCF. Weather minimums were also 4. FLIGHT TEST RESULTS checked on this pass. 4.1 Subjective Workload Assessment Technique On the bravo pass, a power changeover from mrcraft to weapon Four WSOs participated in the SWAT study over seven battery power was made and a practice pass over the target was missions. Using the WSO’s card sort, a workload level performed. The safety engineer conducted a TM check of the of 58.57 was determined for the non-MCG AGM-130. flight termination system destruct signal and directed the range Similarly, a workload level of 33.93 was determined for the controller to ensure no personnel were within the weapon MCG ACM-130. This represents a workload reduction of profile. The radarTSP1 trackers and cinetheodohtes performed 24.64%--a significant reduction in WSO workload. system checks on the alpha and bravo passes and recorded data on the Charlie pass. 4.2 GPS Pointing Accuracy The GPS-cued seeker pointing perfommnce was critical to WSO The Charlie pass was the weapon release pass. The aircraft workload reduction by pointing the seeker at the target. GPS- controller in the CCF adjusted the standoff range based on cued seeker pointing performance was satisfactory. The target winds and vectored the aircraft onto the run-in heading. The was within the seeker’s wide FOV 100% of the tune. The axcwv launched the weapon. performed an egress manewer, seeker was pointed to within I degree (2 degrees overall) 80% and the WSO controlled the weapon to impact. The safety of the time. Figure 6 shows the maximum probability of the target being outside the seeker’s FOV at different confidence satisfactory. The target was within the seeker’s wide FOV on levels. The test results Indicate that there is a 95% probability all passes. The seeker was pointed to within I degree (2 degrees that the target wdl be in the FOV at the 95% confidence level. overall) 60% of the time. Figure 7 shows the maximum probability of the tqet being within the seeker’s FOV at different confidence levels. 4.3 GPS Pointing Accuracy with C/A Code The GPS-cued seeker pointing perfom~ance with CIA code was

Figure 7. GPS-Cued Seeker Pointing Accuracy (CIA Code) 4.4 MCG Navigation Accuracy altitude. This indicates that a consistent An autonomous MCG capability allowed the WSO to perform altitude error was not corrected. Figure IO shows the mean additional crew duties and still accurately guide to the target. navigation accuracy and standard deviation for each pass with The navigation performance was satisfactory. The weapon GPS the WAGE weapon. Figure 11 gives the overall mean receiver set rarely tracked the optimal combination of satellites navigation accuracy and standard deviation for the WAGE while being captive-carried. This was due to aircraft masking. W.%pO”. The weapon GPS receiver tracked the optimal combmation of satelbtes while in free-flight. The tracking state was It should be noted that postmission analysis demonstrated that satnfactory. The INS FOMs mdacate the quality of the weapon the implementation of WAGE was not optimal. This was INS esbmates was also consistently opbmal. Figure 8 shows the attributed to modifying an existing weapon design rather than mean navigation accuracy and standard deviation for each pass. designing a new weapon to take full advantage of the improved Figure 9 gives the overall mean navigation accuracy and accuracies available with WAGE corrections. standard deviation. 4.5 MCG Navigation Accuracy with CIA Code The WAGE navigation performance was satisfactory. In The navigation performance with CJA code was satisfactory. captive flights, the GPS antenna rarely tracked the optimal set of The weapon GPS receiver set consistently tracked the optimal satellites due to aircraft masking. The weapon GPS receiver set combmarion of satelbtes. The tracking state was consistently correctlv tracked the optimal combmatlon of satellites in free- optimal. The INS FOMs indicate the quality of the weapon INS flight, This combinatibn gave the lowest position dilution of &mates were also consistently optimal. Figure 12 shows the precwon (PDOP). The tracking state was optimal. The INS mean nawgation accuracy and standard deviation for each pass FOMs mdicate the quality of the weapon INS estimates was also with C/A code. Figure 13 gives the overall mean navigation optimal. Postmission data analysis shows that the weapon accuracy and standard deviation with C/A code. consistently estimated its position lower than its actual

Figure 8. Individual Pass Navigation Accuracy

Figure 12. Individual CIA Pass Navigation Accuracy Figure 13. Overall C/A Code Navigation Accuracy

4.6 Live Launches immedtafely after release. The WSO periodically slewed Table 1 lists the desired launch conditions for each of the live throughout the profile, then returned to GPS pointing. The launches. WSO-commanded transition and terminal occurred at I7 seconds time-to-impact. The WSO manually guided the weapon to impact. Table 1. Desired Launch Conditions

The guidance and navigation performance of the weapon was satisfactory. The weapon GPS receiver made no constellation changes and stayed in the State 5 track state. During free-fltght, the recetver processed the optimal number of 4 pseudorange and 4 pseudorange rate values. The INS FOMs were low, indicating that the quality of the weapon INS was optimal. An extrapola- tion of the weapon INS estimate from the time the WSO intervened to impact indicates that the position estimate was less than 20 ft (6.1 m) off at impact.

Weather for the launch was marginal with a cloud deck at 1,500 ft (457 m) AGL and a considerable amount of haze. Because of this, the WSO initially identified the wrong target. but corrected his emx when MCG pointed the seeker at the CoIreCt target.

4.6.1 launch I The objective of the first launch was to demonstrate accurate 4.6.2 Launch 2 guidance, navtgation, and GPS-cued seeker pointing. The The second launch was intended to be an endpoint demonstra- weapon was successfully launched wthin tolerances and tion of the increased capability gamed in employing an satisfactorily impacted the target. The weapon was launched AGM-130 with MCG. The weapon was launched within under datalink control and GPS potnting was engaged tolerances and satisfactorily impacted the target. The launch profile was changed to add 4 decrements to get below a 1,X0-ft opbmal. The weapon hit the target above the target aimpoint (457-m) cloud ceding. The launch point was moved coordinates. Postmission data analysts shows that the weapon approximately I na&al mile (I.85 km) closer to the target to consistently navigated to a pomt higher than the target aimpoint. correct for a significant headwmd. The weapon was launched This indicates that a conswent guidance system altitude error under datalink control with a IO-degree heading offset and I1 was not corrected. degrees of bank. Immediately after launch, GPS pointing was commanded. The weapon automatically corrected its course. The WAGE guidance performance was satisfactory. The At 21 seconds time-to-impact the WSO locked onto the target. weapon gutdance error was less than 2 ft (0.61 m). Postmission The weapon went autoterminal at 15 seconds time-to-impact. analysis shows that the autopilot guided the weapon within 2 ft (0.61 m) of the INS estimate of the target aimpoint coordinates.

Impact occurred after 118.5 seconds bme-of-flight. An unusually large miss distance IS attributed to the seeker 5. CONCLUSIONS/LESSONS LEARNED correlation tracker drifting due to low contrast at approxunately The following are the unportant conclusions demonstrated by 4 seconds time-to-impact. the AGM-130 MCG Phase I test program:

The guidance and nawgat~on performance of the weapon was 1. The AGM-130 MCG weapon system significantly reduces satisfactory. The weapon GPS receiver made no constellation WSO workload and increases target acquisition capability. changes and stayed in the State 5 track state. During free-flight, the receiver processed the optimal number of 4 pseudorange and 2. The ACM- I30 MCG provides increased operational utility 4 pseudorange rate values The INS FOMs were low. indicating with the improved capability to strike in low vwbrlrty that the quahty of the weapon INS was optimal. An extrapoh- conditions and to accurately retarget while the aircraft is lion of the weapon INS estimate from the time the WSO airborne. intervened to impact indicates that the position estimate was less than 160 ft (48.8 m) off at impact. The large error, compared 3. The AGM-130 MCG, when used in conjunction with either with prewous sorbes. 1s the result of an unusally high PDOP for the TVGS or IMIRS seekers, provides for a significant increase the launch. in detection ranges (at day or night) and improves the ease of operation at increased aircraft launch distances. This launch was the most challenging ever attempted by an AGM-130. Not only was the ceiling low and the wslbday poor. 4. Standoff MITL weapons can benefit greatly with a MCG but there was conslderable precipitation the prevmus 24 hours. capability. This made for extremely poor Infrared conditions. Additionally, the selected target was a simulated SA-3 we hldden in a 5. MlTL weapons provide an added benefit of instant bomb wooded area. The adverse weather combined with the impact assessment and bomb damage assessment over challenging launch profile truly demonstrated the mcreased a”tO”OmO”S systems. capability of MCG for standoff weapons. The target actually broke out from the surrounding clutter at less than 25 seconds 6. REFERENCES AND ACKNOWLEDGMENTS tune-to-ullpact. For reference materials and acknowledgments, please contact your AGARD hatson. 4.63 Launch 3 The third launch, with the modified WAGE-capable weapon, was successfully launched within tolerances and satisfactorily impacted the target under Its own mtemal guidance. The launch profile was changed to 1,000 ft (305 m) AGL cruise due to a cloud deck at 1,500 ft (457 m) AGL. The weapon was launched under datahnk control with GPS pointing engaged. The WSO remained hands-off for the entire flight with the exception of a planned demonstration of manual seeker slewing and GPS pointing 20 seconds after launch. The autopilot commanded autoterminal at 15 seconds time-to-impact. The weapon unpacted the target 96 seconds tune-of-flight. It missed the Intended point of impact by 25.3 ft (7.71 m).

The WAGE nawgation performance was satisfactory. The weapon GPS recewer set correctly tracked the optimal combmation of satelbtes. Th,s combination gave the lowest PDOP. The tracking state was optimal. The INS FOMs Indicate the quality of the weapon INS esbmates were also