10 state vector data provided by telemetry and tracking services should be sufficient to predict impact locations of staging and components at a 3-sigma level in order to account for systematic dispersions such as velocity errors and environmental dispersions such as wind.
7.3 Availability of Tracking Methods.
The following is a discussion of current tracking methods. An operator may propose new methods or a combination of new and current methods to meet § 450.167.
7.3.1 Telemetered Inertial Guidance.
The telemetered inertial guidance (TMIG) method of tracking is widely used as a primary independent source of real-time and/or post-operation tracking data. These systems receive, record, and relay signals from launch vehicles, satellites, and other aeronautical vehicles to determine position and performance. Signal data is collected and processed by a central telemetry hub and then forwarded to operators. This method relies upon a transmitter from the launch vehicle and a telemetry ground receiver geographically dispersed around the launch site. Coverage, number of antennas, track limits, and other restrictions are entirely dependent upon which launch site is being utilized. However, timing, modulation, formats, and rates are all Inter-Range Instrumentation Group (IRIG) compatible at each federal range. The IRIG is the standards body of the Range Commanders Council (RCC). It is generally recommended at federal ranges to validate inertial guidance against another accepted source, unless the inertial guidance solution has already been qualified under RCC 324. Federal ranges have published locations and antenna characteristics in user or instrumentation guides.
Mobile solutions are generally available for use at commercial spaceports but should be funded and have schedules de-conflicted prior to committing to their use for a commercial mission.
7.3.2 Radar Beacon Tracking.
Ranges typically support beacon tracking of coherent or non-coherent C-band transponders. These transponders provide metric data in real time and post-flight in the form of time, range, azimuth, elevation, and coordinates. Transponders are tracking aids for radars and extend the range and accuracy of in-place radars by replying to coded pulse interrogations from ground radars with a single return pulse in the same band.
These transponders operate in the C (G)-band and X (I)-band as non-coherent, pulse-type transponder equipment. The transponder return pulses allow differentiation of stages of the vehicle or payload when in close proximity, overcoming the natural inaccuracy of skin track radars downrange. Guidance for radar transponder usage and standards at federal ranges can be found within RCC 262-14. RCC 324 is an acceptable means of compliance for the airborne tracking sources such as C-Band transponders used with ground based command systems and for GPS receivers and inertial measurement units used as airborne tracking data sources.2
2 RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
7.3.3 Radar Skin Tracking.
Radar Skin Tracking is a method that is generally available at Federal launch facilities, though radar availability is unique to each range. Generally, these are very long-range radars operating in the C-band spectrum that can provide line of sight coverage to hundreds or thousands of miles. Characteristics such as antenna size, gain, beam width, polarization, and other technical classifiers should be discussed with the individual ranges. On both Eastern and Western ranges, the radars are geographically distributed throughout the coast, but the data are processed centrally at the range. Mobile solutions such as radars are available but have a high cost with movement and setup. Each range radar has advantages and disadvantages associated with it and users are encouraged to become familiar with the peculiarities, locations, and design of range instrumentation through user handbooks and instrumentation guides before designing a mission-tracking plan to comply with § 450.167. A downfall of utilizing radar skin tracking as the only tracking source is that when the vehicle being tracked is at a great distance from the radar, it is difficult to differentiate the deployed objects in close proximity such as payload, first stage, fairings, etc. due to weak signal strength. This difficulty is overcome by utilizing beacons as stated in paragraph 7.3.2 of this AC, but it is still recommended not to utilize radar skin tracking as the sole source of flight tracking as it is more likely to lose tracking data needed to ensure compliance with § 450.167(a).
7.3.3.1 Sensitivity Guidelines.
Users should be cautioned that natural dispersions in radio waves as well as beam length characteristics can cause unavoidable uncertainty built into position and velocity data received at a range ground processing station.
The particular uncertainties with a radar at a range should be built into the assumed flight safety rules of the vehicle and mission. A tracking margin of 6 dB above noise is recommended for quality data.
7.3.3.2 Ceiling Guidelines.
Users of skin-tracking radars should ensure that an alternate source is available until the radar can provide quality data. Coverage limitations and minimum beam travel distance often prevent tracking in initial stages of flight or in certain geographic locations due to blockage zones.
7.3.4 Tracking and Data Relay Satellite System.
The Tracking and Data Relay Satellite System (TDRSS) is a network of geosynchronous satellites managed by National Aeronautics and Space Administration’s (NASA) Goddard Space Flight Center (GSFC). Of the total number of satellites, only several are active at any time. Each active satellite provides coverage over either the Atlantic Ocean, Pacific Ocean, or Indian Ocean region. Each satellite has one S-band single access antenna available for tracking purposes and needs to be de-conflicted well in advance with national tracking priorities in order to be utilized for commercial launches. This network system has multiple uses for data, voice, and navigational system relay, but can also provide nearly 100 percent coverage of telemetry data receipt from space vehicles during launch. Data are relayed either to White Sands Complex (WSC) or Guam Remote Ground Terminal (GRGT) and are then
12 forwarded to the end user. End user Mission Operation Control Centers (MOCCs) are already established at Eastern and Western Ranges. To use this system at a commercial spaceport or remote location, an end user would need to establish a data and crypto logical agreement with GSFC’s Network Integration Management Office (NIMO).
Users seeking to utilize this system to augment tracking data receipt must obtain a NASA Space Network compatible transmitter and coordinate with NIMO.
Specifications for transmitter characteristics, usage and network interfaces can be found in the Space Network User’s Guide published by GSFC.
7.3.5 GPS Metric Tracking via S-band Telemetry Downlink.
The GPS metric tracking method via S-band telemetry downlink utilizes existing GPS satellite base navigation system capability to significantly reduce the test range’s operations and maintenance costs. The exception to the S-band telemetry downlink is if an Autonomous Flight Safety System (AFSS) is utilized because the termination decision is made aboard the vehicle. For many vehicle systems, the tracking capabilities are currently operational from pre-launch activities until when flight abort is no longer necessary. The system onboard the vehicle consists of GPS L-band receiver antennas, a GPS tracking unit, and S-band transmitters and antennas. A benefit of this system is the availability of a precise GPS time base onboard the vehicle to provide tighter time correlation with external instrumentation and video, along with the opportunity to better time-synchronize vehicle dynamic and thermal analog data. Overall, the system provides position, velocity, and timing information to the end user. Federal range standards for configuration of the GPS metric tracking standards for testing, and guidance as tailored for Expendable Launch Vehicles (ELV) are found in RCC 324.3 For vehicles whose GPS metric tracking systems do not meet the Federal range standards, system qualification tests should be performed to ensure compatibility with the GPS network.
7.3.6 Optical Tracking.
Optical systems provide two-dimensional position-versus-time data. Optical systems include both fixed and mobile trackers. Optical systems are useful for rapid evaluation of launch vehicle attitude and integrity during early times of flight while other systems have tracking blockage zones. Optical systems are also useful for post mission analysis of data integrity from onboard tracking systems. Inherent limitations with line of sight and focal limits prevent these solutions from being utilized for the entire length of a mission, but for suborbital flights or open ocean captive carry type missions, optical tracking may be a suitable solution to demonstrate compliance with § 450.167.
3 RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
13 8 TRACKING AND RECORDING DATA.
During the flight of a launch or reentry vehicle, an operator must measure and record in real time the position and velocity of the vehicle, in accordance with § 450.167. A real-time system is one that adheres to functional (behavior) and temporal (timing constraints, deadlines) requirements. Real-time systems involve and affect hardware, software, communication, and human-in-the-loop contributions from tracking systems, GPS, data processing systems, display systems, command control systems, and flight safety systems. A real-time system requires results to be produced within a specified time period. Real-time does not mean zero lag time. Tracking must be sufficient to meet the requirements in § 450.167(a) to predict the expected impact locations and obtain vehicle performance data for comparison with pre-flight predictions.
8.1 Data to be Tracked in Real Time.
The primary types of data that an operator should provide for real-time tracking by the Flight Safety System (FSS) to aid in monitoring for off-nominal behavior are listed below. When monitoring behavior of the vehicle, the data should be defined in a coordinate system for position and velocity. Many types of coordinate systems are utilized and recognized by Federal ranges. These may include geodetic, polar, or Cartesian coordinate systems, among others. For example, to show a location about Earth using an earth-centered inertial system, Cartesian coordinates are used when tracking a vehicle.
8.1.1 If an operator intends to launch from a Federal range, these coordinate systems should be defined and discussed with local flight safety organizations to ensure compatibility with local tracking and recording systems. Coordinate systems should be defined for position and velocity, and implemented in a fashion in which the operator can communicate impact predictions to the FAA and range provider if necessary. The FAA does not prescribe the use of any particular coordinate system; however, as described in paragraph 9 below, pursuant to § 450.167(b), operators must identify and describe in their application any coordinate system used to satisfy § 450.167(a). In order to determine vehicle position and velocity as a function of time in accordance with § 450.167(a), operators should record the following parameters as a function of time:
• Instantaneous Impact Point
• Orientation
• Orientation change rates
• Occurrence of discrete events such as staging, fairing jettison, engine cut off, etc.
8.2 Methods of Recording.
To compare vehicle pre-flight performance predictions and actual performance, an operator should propose methods of recording the tracking data that will allow the operator to identify any discrepancy or non-nominal activity occurring during the launch countdown and flight, as well as any deviation from any term of the license, or any other event posing a material risk to public safety. Recording tracking data also allows operators and the FAA to identify corrective actions for future flights.
8.2.1.1 Operators should be able to identify any flight environment that is not consistent with maximum predictions, identify any measured wind profiles not consistent with predictions used for launch, and should enable the prediction of impact location of any staging and components.
8.2.1.2 For any data that cannot be collected in real time due to line of sight limitations (e.g. while achieving orbit), operators may propose the use of alternative methods for recording and storing such data as an equivalent level of safety to § 450.167(a).
8.3 Data Fidelity.
In accordance with § 450.167(a), during the flight of a launch or reentry vehicle, an operator must measure and record in real time the position and velocity of the vehicle.
The following tracking fidelity guidelines are derived from AFSPCI 91-701 and RCC 324-11, which operators may find helpful in meeting the requirements of § 450.167(a). The FAA has adapted their descriptions for performance-based utilization. Further guidance specific to Federal ranges can be found in these manuals, and the metrics are as follows:
8.3.1 Sample Rate (S) 4 The specified sample rate(s) of the Range Tracking System (RTS), including Telemetry/Any Band downlink and ground processing, should ensure that the data delivered to ground processing systems is sufficient to allow evaluation of the flight abort rules and the prediction of expected impact locations of all stages and components. An operator may propose a lower data rate—at various points or all of the trajectory—based on vehicle performance, reliability and a limited impact to public safety. The specified sample rate(s) should be maintained throughout the flight period.5 Each sample should be a unique measurement and not a repeat or extrapolation of the previous value. Typically, a 10 Hz sample rate is recommended for FSS action. An operator may propose a lower data rate at various times in the trajectory such as coast after powered flight, or other times based on vehicle performance, reliability, and a limited impact to public safety such as remoteness to populated areas, ships, and aircraft. The use of an AFSS will ease this requirement.
8.3.2 System Delay Time (L) 6 State vector timeliness should enable an operator to terminate the vehicle’s motion or flight in accordance with mission parameters or, if an AFSS is utilized, in time to meet safety and analysis requirements. The total system delay time, including delays in RTS, Flight Termination System, and Range Safety Officer reaction time (where applicable),
4 See RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011. See paragraph 2.1.3.
5 See paragraph A.2.1.3 of RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
6 See Air Force Space Command Instruction AFSPCI 91-701, Launch and Range Safety Program Policy and Requirements, February 1, 2019. See definition of “adequate,” and paragraphs 6.1.2, 6.1.3, 6.4, and 6.9.6.
15 should allow evaluation of flight abort rules and prediction of the expected impact locations of all stages and components. The delay (data latency) introduced by each component or subsystem of the RTS should support the total system delay requirement.
This system delay time calculation should be measured from airborne sensor or radio frequency reception through the Range Safety display including any data buffering, transfer, processing, or smoothing. In general, a latency of less than 250 ms will meet most vehicle applications. The combination of all sources of delay from transmission of data to evaluation of parameters for off-nominal indications and operator corrective termination action should not exceed 5 seconds, although each Federal range will have different requirements. These latencies must be accounted for in generation of flight safety limits in accordance with § 450.108(d)(4).
8.3.3 Accuracy.
The accuracy of the state vector7 delivered to the ground safety display systems should be sufficient to allow for the evaluation of the flight abort rules and the prediction of expected impact locations of all stages and components of a flight vehicle when using flight abort in accordance with § 450.145(d)(4). The accuracy of the airborne and applicable ground RTS should be specified to support development of flight safety limits.8 The range users’ RTS accuracy should be factored into any range supplied ground systems to ensure the overall accuracy meets Range Safety requirements. The required accuracy should be maintained throughout nominal vehicle flight. The RTS should not produce out-of-specification state vector accuracy during non-nominal flight.
The specified accuracy should include noise and systematic errors. In accordance with RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, for various flight trajectories, the following 3-sigma parameters may be necessary to ensure accurate tracking:9
• Launch area Instantaneous Impact Point (IIP) (IIP Range < 66,000 feet) uncertainties should not exceed 330 feet for cross-range or down-range. Present position uncertainties, expressed as the square root of the sum of the squares (RSS) of the errors in the 3 orthogonal axes, should not exceed 250 feet.10
• Midcourse IIP (IIP Range > 66,000 feet) cross-range uncertainties should not exceed 0.5 percent of the vacuum IIP range, and down-range uncertainties are recommended not to exceed 1.0 percent of the vacuum IIP range.
7 See paragraph 2.1.10, RCC Standard 324-11 Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
8 See AFSPCI 91-701, February 1, 2019, para. 6.10.2.3.
9 See Id., para. 6.4.2.1.2.
10 See paragraph A2.1.10 of RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
8.3.4 Reliability (R) 11 In accordance with paragraph 2.1.4 of RCC 324-1112, the RTS reliability for a nominal mission should ensure that the minimum number of required tracking sources (two in most cases) are available at least 97 percent of the time period when flight abort is required as a hazard control strategy. Each source should have no single point failure mode showing a non-nominal vehicle is nominal—these failure modes include but are not limited to forward prediction, Kalman filters, or indications of data loss.
8.3.5 Quality/Confidence Indicators (R)(Q) 13 The RTS should provide indications of system performance status. This data should allow real time evaluation of the critical performance parameters. Quality indicators (flags) should be made available for detectable events that result in out-of-specification state vector performance data.14 In general, GPS should include dilution of precision (DOP) and number of satellites tracked.
8.3.6 Independence (I) 15 All required tracking sources should be independent of each other to the extent necessary to ensure that a failure of one tracking source does not adversely affect any required performance parameter of the other. A source is considered independent if it is electrically, mechanically, and structurally separate from any other tracking source, so that one does not influence another tracking source.
11 See AFSPCI 91-701, para. 6.9.6.3.1.
12 See paragraph A2.1.4, RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
13 See RCC Standard 324-11, para. 2.1.11.
14 See paragraph 2.1.11 of RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
15 See paragraph. 2.1.9. of RCC Standard 324-11, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard, dated February 2011.
17 9 APPLICATION REQUIREMENTS.
Under § 450.167(b), an applicant must identify and describe each method or system used to meet the tracking requirements of § 450.167(a).
9.1 Methods.
An applicant must identify and describe in their application each tracking method used to meet § 450.167(a). An applicant may elect to use any of the methods listed in in Paragraph 7.3 of this AC it proposes to use, either alone or in combination, or any other tracking method. If the operator plans to use different tracking methods for different phases of flight, then the operator should identify which method will be used for each phase of flight. The FAA reviews the use of the proper method or combination of methods used during the application process for protection of the public.
9.2 Systems.
An applicant must describe each tracking system used to meet § 450.167(a). An applicant may use C-Band telemetry to download tracking data to the ground. An applicant should describe how vehicle data will be used to predict impact locations.
9.3 Range Commander’s Council (RCC) 324.
An applicant may use RCC 324, Global Positioning and Inertial Measurements Safety Tracking Systems Commonality Standard to demonstrate compliance with the requirements of § 450.167(b). Since RCC 324 is generally tailored to the particular operation, an applicant utilizing this standard to show compliance with § 450.167 should similarly provide a tailored RCC 324 at the time of application.
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