designs, semi-empirical engineering tools are sufficient. For explosions in a tank with a common internal bulkhead and internal feed pipe, assume the explosion occurs inside the tank. If liquid propellants are housed in separate tanks without a common bulkhead, the center of explosion is considered to be external to the tanks in the inter-tank region.
7. For solid rocket motors that breakup with the vehicle, apply a physics-based algorithm or first principle high fidelity numerical method such as a finite element code to generate a list of motor case fragments and residual solid propellant fragments. Special consideration should be given to the aft motor segment and forward dome. The hazardous debris list and imparted speeds of the hazardous debris will depend on the net internal pressure and the remaining thickness of propellant grain. If using a finite element type code, the analysis should demonstrate that it can properly account for the variation in material strength properties with temperature, strain rate, pressure, and age of the propellant.
8. Use the vehicle drawings and descriptions to compute the surface area of one face of skin and panel type components. These will usually be associated with interstages, payload adapters, motor skirts, interior honeycomb or aluminum panels used to mount or isolate components, and trays to mount electronics (which may double as actively cooled heat sinks in some cases). For each type of skin or panel element, an operator should compute the mass per unit area. If hazardous debris fragment lists are to be applied to atmospheric reentry or hypersonic breakup where aerodynamic heating is a concern, material types should also be noted and may require additional final classifications of similar hazardous debris shapes and sizes by material type.
9. Estimate the number of fragments to assign to each skin and panel type assembly.
This is recognized to entail significant uncertainty, since loading and fracture or failure mechanical analysis is rarely performed or available. Several guiding principles should be applied:
a. The sum of the surface areas of the fragments should match the total un-fragmented surface area.
b. The mass of each fragment should be computed as the surface area of the fragment times the mass per unit area, plus any prorated distributed mass to be added to these types of fragments (e.g., paints, adhesives, small fasteners, stiffening ribs, insulation, sound suppression foam, or other items that are deemed to be spread over large areas of other components).
c. Assume that a range of fragment sizes are likely to be produced somewhat randomly from a statistical distribution. Historical events of large pressure vessels and combustion events of launch vehicles have suggested a log-normal distribution. The mean fragment length scale should be based on the length that would result in an ultimate strength exceedance from a 1D bending moment using the average tank skin thickness and the expected pressure on the material at break-up. The mode fragment length should be based on the average thickness, including stringer or support sections. Data has also suggested about a 1:1 to 1:5 variation in ratio of length to width. The skin or panel drawings may suggest some intuitive breakdown for fragment shapes or sizes if there are holes 31
cut in the structure or regions of relatively thin wall or weaker construction separated by stronger structural rings, plates, or frame elements. An example would be hemispherical domes, which tend to be built stronger and are of a shape that results in less stress concentrations. These shapes tend to stay intact and fail along weld lines. Careful consideration should be given to capture the smallest credible fragment size, particularly down to a ballistic coefficient of approximately one pound per square foot (psf), and/or mass greater than 0.4g, as those fragments create a hazard for aircraft and suspend in the atmosphere for significant fall-times. Characterizing fragments down to a ballistic coefficient of
3.0 psf is generally considered of high importance, as those have historically been in the range of hazards to persons exposed on the ground.
d. For panel and skin components close to the center of an explosion, assign relatively more small fragments and fewer large fragments. For panel or skin components farthest from the center of explosion only a relatively few large fragments should be considered unless the structure is very fragile.
e. Real fragments will have irregular shapes, but for risk analysis purposes simple shapes such as flat or curved plates, or rectangular cubes with uncertainties around drag, size and mass parameters, will serve as a reasonable approximation. If a more complicated shape is certain to survive, then parameters should be derived accordingly. When selecting fragment sizes, the geometry of the main assembly should constrain maximum fragment dimensions
(e.g., a fragment dimension should not be greater than the height, width, or circumference of the parent piece).
10. Identify strut and frame pieces from vendor drawings and photos. These items may be somewhat integrated into the skin and panel structures as stiffening ribs and rings. Generally, both the top and bottom of stages, interstages, and payload adapters will terminate in a structural ring that provides stiffness, load transfer capability, sufficient material for fasteners to mount skin panels, and lift points.
Alternatively, some struts and frame items may be part of open structural support systems that do not directly incorporate skin panels. Some pressurization tanks are mounted with support struts between tanks.
11. Identify discrete components from drawings and photos. These are items such as avionics boxes, tanks, small thruster assemblies, or other items that appear to be compact and of relatively robust construction. Typically, these types of components are predominantly individual avionics items grouped together on side walls of the vehicle or avionics trays. The assumption that avionics boxes and batteries survive a vehicle explosion intact may underestimate the number of small pieces that could result if the boxes break up. Tanks used to store pressurized gases and liquid propellants are also included in the discrete component’s hazardous debris group.
Discrete components that are securely attached to skin or panel constructed items may break loose and retain the attached panel segment as part of a discrete component.
12. Identify piping and wiring harness items from drawings and photos. Estimate the total length of tubing and wiring used in various diameter categories and a mass per unit length for each category.
13. Identify components that can best be described as small irregular shaped pieces that do not fit into any of the previous categories. These tend to be items like heavier duty mounting brackets, housings for springs that are part of stage separation hardware, and small compressed gas orbital maneuvering thrusters. Fragment shapes assigned to such pieces tend to be “boxes” or “cylinders,” even though some bracket assemblies have numerous openings and are more like a small 3-dimensional frame structure than a solid 3-dimensional structure.
14. Identify materials that are to be treated as distributed mass over other previously defined fragments. To conserve total vehicle mass within the fragment list and to recognize that actual fragments will be combinations of items represented as separate items in a parts list, items that cannot be identified with a specific discrete component should have their masses distributed among the other defined fragments.
Items such as paint, insulation, and sound suppressing foam are typically applied to the skin and panel fragments and can be prorated to such fragments based on surface area calculations.
8.5.2 Aerothermal Breakups.
Unlike an explosive event, aerothermal breakup will typically begin at a high altitude
(e.g., 95km) and progressively shed an increasing number of fragments down to an altitude as low as 50km. This means fragments are shed from the body over time and space. If the reentry body is falling at a flight path angle that is nearly vertical, then the uncertainty in the hazardous debris impact location due to the shedding process is minimized, and the effect is mainly in the time differences of when hazardous debris pieces impact. This will be more important to predicting aircraft risk than ground risk.
One approach that has been used with object oriented reentry breakup models is to estimate all reentry breakup hazardous debris to be generated at one time at an altitude of 78km. This is based on empirical observations that many different types of reentering satellites all seem to experience a major breakup event near the 78km altitude. Some reentry bodies contain propellant tanks that may have residual liquid propellant.
Aerothermal heating may rupture these tanks due to heat transfer into the liquid and over pressurization of the tanks. In the case where a reentry explosion is predicted, the hazardous debris list development steps defined in paragraph 8.5.1 of this AC may be applied.
8.5.3 Small Hazardous Debris Hazardous to Aircraft.
Some hazardous debris may only be hazardous to aircraft and people on an aircraft, but not to people on the ground, whether in open areas, or sheltered in buildings, vehicles, or ships. This is mainly due to the closing speed between the aircraft and fragments.
Due to the high closing speeds, fragments can impart significant collision impact energy to an aircraft. Hazardous debris that damages an engine, penetrates the fuselage to produce a loss of cabin pressure, or causes a fuel leak can lead to a plane crash killing all persons on board. The fragment list should contain all fragments capable of causing 33
a casualty-producing event. Some aircraft vulnerability models consider dense fragments as small as 0.4g to be hazardous (see paragraph 12.8 of this AC). The closing speed is the relative velocity between the aircraft and the hazardous debris at impact.
This is much higher than the impact speed of the same hazardous debris impacting a ground target for two reasons: (1) due to low air density at aircraft altitudes, terminal speed of hazardous debris is greater at aircraft cruise altitude than sea level, and (2) aircraft fly much faster than most debris terminal velocities, especially low ballistic coefficient debris.
8.6 Hazardous Debris Containing Toxic Material.
Upon impact, a liquid tank may not explode but instead break open and leak, or may explode but only partially consume the liquid propellants. Some liquid propellants used for rocket propulsion or spacecraft maneuvering, such as hypergolic propellants, are toxic to people. The possibility for this type of event should be evaluated to determine if there is a potential toxic hazard to people on the ground. If this hazard is considered credible, a flight safety analysis should evaluate the probability of the spill occurring over locations in the affected region, and the amount of liquid that could spill in accordance with § 450.139(c). This topic is covered in AC 450.139-1 Toxic Hazards Analysis and Thresholds.
9 AERODYNAMIC AND HARMFUL DEBRIS CHARACTERISTICS.
9.1 Ballistic Coefficients.
The equations of motion that propagate a fragment through the atmosphere apply force due to drag through the ballistic coefficient, 𝛽𝛽. This parameter indicates the relative importance of inertial and aerodynamic forces on a body in free fall. It is defined as:
𝑊𝑊 𝛽𝛽 = 𝐶𝐶𝐷𝐷𝐴𝐴𝑟𝑟𝑟𝑟𝑟𝑟 where 𝑊𝑊 is the fragment mass,2 𝐶𝐶𝐷𝐷 is the drag coefficient, and 𝐴𝐴𝑟𝑟𝑟𝑟𝑟𝑟 is the associated aerodynamic reference area. Values of 𝐶𝐶𝐷𝐷 and 𝐴𝐴𝑟𝑟𝑟𝑟𝑟𝑟 are obtained experimentally. The value of 𝐶𝐶𝐷𝐷 varies as a function of speed 𝑣𝑣, usually given in terms of the Mach number 𝑀𝑀 = 𝑣𝑣/𝑐𝑐 where 𝑐𝑐 is the speed of sound. The ballistic coefficient is nearly constant at low speeds (𝑀𝑀 ≤ 0.3), and this is called the subsonic ballistic coefficient, 𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠.
9.1.1 Flow Regimes.
The earth’s atmosphere contains three aerodynamic regimes: continuum flow at low altitudes, free molecular flow (FMF) at high altitudes, and a transitional regime. These are identified through the Knudsen number 𝐾𝐾𝐾𝐾 = 𝜆𝜆 ⁄ 𝐿𝐿 where 𝜆𝜆 is the molecular mean free path and L is the characteristic body length. Applying a constant ballistic coefficient derived for continuum flow (CF) to regions where free molecular conditions exist tends to underestimate the drag force. Therefore, accounting for drag force changes between the continuum and free molecular flow regimes typically reduces the size of the estimated impact dispersion areas. For larger debris, using a ballistic coefficient assuming continuum flow is usually an adequate model (except if the debris is traveling close to horizontally in the upper thermosphere or exosphere). However, for small debris, such as may be hazardous to aircraft, the effects of the flow regime can become important, especially if the debris spends significant time in the thermosphere or exosphere. The continuum flow regime is applicable where Kn ≤ 0.01, the transitional regime 0.01 < Kn < 10, and the FMF regime where Kn ≥ 10.
9.2 Drag Coefficient Estimates for Continuum Flow.
The content of this section has been removed. The replacement information is planned for the next revision.
2 The ballistic coefficient is sometimes represented using weight instead of mass. This affects its usage in equations of motion, as the conversion factor is gravity. However, in English units, g = 1.0 lbf / lbm at sea level, so numerically, this factor may drop out.
9.3 Drag in Transitional and Free Molecular Flow Regimes.
9.3.1 Reynolds Number.
A key parameter in these regimes is the Reynolds number, 𝜌𝜌𝑣𝑣𝐿𝐿 𝑅𝑅𝑅𝑅 = µ where µ is the absolute viscosity of the fluid. The Reynolds number is a dimensionless parameter that characterizes the ratio of inertial force and viscous drag force. There are two flow regimes: supercritical for Re >1 x 106, which corresponds to a smooth surface, and subcritical for Re <1 x 106 for a rough surface.
9.3.2 Drag in Free Molecular Flow Regime.
The drag coefficient depends on the wall temperature and the accommodation coefficient for the surface. With the conservative assumptions provided in reference [15] of paragraph 3.4 of this AC, the drag coefficient for a sphere in FMF can be computed as a function of Reynolds number:
𝐶𝐶𝐷𝐷 (𝐾𝐾𝐾𝐾 ≥ 10) = 0.92 + 1.7𝑅𝑅𝑒𝑒𝑒𝑒(−0.1𝑅𝑅𝑅𝑅) 𝑆𝑆𝑒𝑒ℎ𝑅𝑅𝑒𝑒𝑅𝑅 and that for a stable thin plate by:
𝐶𝐶𝐷𝐷 (𝐾𝐾𝐾𝐾 ≥ 10) = 1.83 + 1.12𝑅𝑅𝑒𝑒𝑒𝑒(−0.3𝑅𝑅𝑅𝑅) 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑅𝑅 𝑇𝑇ℎ𝑖𝑖𝐾𝐾 𝑃𝑃𝑆𝑆𝑆𝑆𝑆𝑆𝑅𝑅 while a tumbling thin plate is obtained by applying a factor 1.56.
9.3.3 Drag in Transitional Regime.
Values of CD in the transitional regime at a given altitude h, are computed using Gaussian interpolation between the CF and FMF regimes:
1 1 ℎ − ℎ 𝐶𝐶𝐷𝐷 (0.01 < 𝐾𝐾𝐾𝐾 < 10) = + � �2 2 √2𝜎𝜎ℎ where ℎ is the midpoint altitude between the upper CF and lower FMF altitude bounds.
The standard deviation 𝜎𝜎ℎ is 1/6th the distance between the two altitude bounds (treating the bounds as a 6-σ spread).
9.4 Lift Uncertainty.
Lift uncertainty accounts for changes in the orientation of the body while on a free-fall trajectory. Lift force is always orthogonal to the drag force vector. Fragments generally tumble for at least a portion of flight during which the lift direction changes momentby-moment. The effect of lift, like drag, is modeled with a coefficient 𝐶𝐶𝐿𝐿 . Values of this coefficient should reflect the net effect of the tumbling and stable portions of flight.
Because lift is uncertain, the ratio of the lift to drag is characterized as a one-sigma uncertainty, (𝐶𝐶𝐿𝐿 /𝐶𝐶𝐷𝐷 )𝜎𝜎. Example values are given in Table 1 for different shapes.
Table 1 – Example Values for Lift Uncertainty Shape (𝑪𝑪𝑳𝑳/𝑪𝑪𝑫𝑫)𝝈𝝈 Spherical 0.00 Blunt 0.01 Intermediate 0.03 Flat plate or similar 0.05
9.5 Required Information in the Hazardous Debris Model.
In accordance with § 450.121(d)(5), a quantitative description of the physical, aerodynamic, and harmful characteristics of hazardous debris must be submitted.
9.5.1 For any given time of the flight, for any foreseeable nominal or malfunction trajectory, there should be a stochastic hazardous debris model from which flight safety analysis can extract a realization of a set of hazardous debris from the breakup event. It is customary to separate classes of hazardous debris models by breakup mode for all major vehicle systems associated with phases of flight (i.e., stages, boosters, and payload) and combine them as necessary depending on vehicle configuration. These hazardous debris models should capture the changes to the vehicle (including current mass of propellants, chamber pressure, temperature, velocity, angle of attack) and the breakup environment (altitude, ambient air pressure, temperature). It is common to define different hazardous debris lists that apply to different time ranges. Each such hazardous debris list represents a constant set of fragments that is unvaried during that time range. For example, one may generate ten hazardous debris lists for FTS breakups for the duration of active burning of a SRM.
9.5.2 A hazardous debris model should be specified for a given flight time range, for a given stage and for a given breakup mode. Typical hazardous debris lists contain hundreds to thousands of debris pieces. It is possible to have a general model that can output a full realization of all the hazardous debris with all the required properties. However, it is common to define a hazardous debris list as a list of hazardous debris groups where statistical parameters needed to generate a realization of hazardous debris in this group are specified. All the hazardous debris in the generated hazardous debris list should have the following information defined:
• Description of the hazardous debris group,
• Mass properties,
• Aerodynamic properties sufficient to define trajectory from the point of breakup until it is no longer a hazard,
• Statistical distribution of breakup-induced imparted velocities,
• Properties needed for aerothermal heating and ablation, 37
• Energetic properties: sufficient to define secondary explosions at impact, and
• Toxic properties: sufficient to estimate toxic hazards to people and environment immediately or long term.
9.6 Consideration for Grouping Hazardous Debris to a Hazardous Debris Group.
All fragments within a class should have similar material composition and produce the same type of hazard (inert, explosive, toxic, etc.). Further, each class should be constrained in terms of the variations of parameters important to aerodynamics and hazard produced as follows.
• The hazardous debris group should have a representative fragment mass. The group should constrain the ratio the minimum and maximum fragment masses to Wmax/Wmin < 2.
• The hazardous debris group should have a representative mean projected area that is the extent of the fragment’s hazard to people. The group should constrain the ratio of the minimum and maximum fragment areas to Amax/Amin < 2.
• The hazardous debris group should have a representative ballistic coefficient, which is the geometric mean of the fragments in the group. The group should constrain the ratio of the minimum and maximum ballistic coefficients to max(𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠)/ min(𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠) < 1.7.3 Fragments with 𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠 less than or equal to 1.3 psf typically pose negligible public risks.
• The group should constrain the ratio of the maximum breakup-imparted velocity to minimum breakup-imparted velocity within the following bound:
𝛥𝛥𝛥𝛥𝑚𝑚𝑚𝑚𝑚𝑚/𝛥𝛥𝛥𝛥𝑚𝑚𝑚𝑚𝑚𝑚 = 5/(2 + log10 𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠)
9.7 Description of the Hazardous Debris Group.
For each hazardous debris group, the criteria used to include hazardous debris should be described.
9.7.1 Mass Properties.
For each hazardous debris group, a statistical model to describe the mass should be specified. The minimum level of information provided should include the mean plus and minus three-sigma, total mass, and the number of hazardous debris in the hazardous debris group.
9.7.2 Aerodynamic Properties.
Aerodynamic properties of the hazardous debris are needed to predict the propagation over the atmosphere until they become no longer hazardous. Minimum amount of properties that should be provided are described below.
• The group should have a representative nominal ballistic coefficient β, and plus and minus three-sigma uncertainty bounds that is represented by a lognormal distribution. Values should correspond to tumbling motion for an unstable fragment, 3 In logarithmic space, approximately log10 𝛽𝛽𝑚𝑚𝑚𝑚𝑚𝑚 − log10 𝛽𝛽𝑚𝑚𝑚𝑚𝑚𝑚 < 0.2 or ln 𝛽𝛽𝑚𝑚𝑚𝑚𝑚𝑚 − ln 𝛽𝛽𝑚𝑚𝑚𝑚𝑚𝑚 < 0.5.
and for controlled motion for any duration of time that a fragment stabilizes with respect to its angle of attack. The nominal value should represent median subsonic ballistic coefficient βsub the hazardous debris group.
• The group should have a common representative mean lift coefficient to characterize the lift force. The group should have three -sigma uncertainty bounds of the lift coefficient corresponding to a tumbling fragment.
• βsub should have one or more CD vs. Mach curves to convert to various Mach values that include supersonic flight. The CD vs. Mach curve accounts for the fragment shape. Curves should correspond to tumbling motion for an unstable fragment, and for controlled motion for any duration of time that a fragment stabilizes with respect to the angle of attack. If stability is due to lift, then there should be an associated coefficient of lift CL vs. Mach curve. A hazardous debris model should provide equations for the curves, or data points adequate for a piecewise linear description.
• An estimate of the axial, transverse, and mean tumbling areas of each fragment. If the fragment may stabilize under normal or malfunction conditions, the hazardous debris model should also provide the projected area normal to the drag force.
• An estimate of the ballistic coefficient corresponding to the axial, transverse, and tumble orientation for each fragment.
• The mean and plus and minus three-sigma axial, transverse, and tumbling areas for each fragment or fragment class.
9.7.3 Initial Velocity and Location.
Any additional velocity imparted on the hazardous debris due to any explosive effects should be specified. For instantaneous breakup of vehicles, all the hazardous debris can have the same initial state vector. However, for breakup cases that shed hazardous debris along the way, state vector for each hazardous debris group can be different.
9.7.3.1 The hazardous debris group should characterize the imparted speeds and directions relative to the pre-breakup center of mass motion. In-flight explosions or pressure vessel ruptures release energy with the potential to fracture the vehicle and disperse the resulting fragments.
9.7.3.2 The hazardous debris group should specify the magnitudes and directions of imparted velocity vectors and their associated uncertainty. For no preferred direction of the imparted speed, a Maxwellian distribution applies with speed defined as the maximum value equal to the 97th percentile. If there is uncertainty in the maximum value defined, then a statistical model for uncertainty of the maximum value should be specified. If velocity is not random, then a directed velocity model should be defined that specifies the distribution of directions and uncertainty in imparted velocity in those directions.
9.7.4 Aerothermal Heating Properties.
An aerothermal heating and demise model for the hazardous debris in each hazardous debris group should be defined for reentry or late ascent failure modes where falling hazardous debris can reach high enough velocity to cause melting in the hazardous debris. Aerothermal properties needed to support evaluation of component melting include: material type (to set melting temperature and heat of fusion), fragment stagnation radius, and heated surface area.
9.7.5 Energetic Properties.
9.7.5.1 Propellants.
Various types of propellant produce different hazards, so the amount and condition of loaded or residual propellants should be updated at the envisioned time of breakup.
9.7.5.1.1 Liquid propellants—such as Kerosene (“RP-1”) and Oxygen (“LOX”)—as individual constituents—may pose only a fire hazard, following an intact impact of a tank on the ground, with some additional hazardous debris hazard from the impact and rupture of the pressurized tank. Multiple constituents however, if landing as coupled or proximal items, may produce a combustive overpressure, and fragment speeds that are 1-2 orders of magnitude faster. Therefore, a hazardous debris catalog should account for the condition of these “hazardous debris items” (tanks) as they reach ground to perform the vehicle impact and breakup analysis of § 450.121(b).
9.7.5.1.2 Solid propellants can produce both explosive and toxic hazards, when impacting the ground and/or burning thereafter—while sometimes also modestly “burning back” as fragments fall (which reduces the amount reacting after contact with the ground). For these reasons, solid propellant hazardous debris catalogs are obligated in accordance with § 450.121(d)(5) to account for these predicted solid propellant fragment masses, counts, and mid-air burning conditions. For solid propellant hazardous debris, the following information should be provided:
• Mass of propellants
• Type of propellants
• Explosive energy in terms of TNT equivalent mass
• Burning status: burning now, can start burning during fall due to aeroheating, or contained (will not burn during fall)
• Equation and coefficients for burn rate at both motor pressure and ambient pressure; additional information is available in reference [16] in paragraph 3.4 of this AC.
• Snuff-out pressure 40
9.7.5.1.3 “Hypergolic” tanks, whether holding mono- or bi-propellants, may also survive a breakup and produce a several possible types of hazards on the ground (hazardous debris, overpressure, fire, and toxins). For these reasons, an operator should characterize any amounts of onboard hypergolic propellants in the hazardous debris catalog for their predicted condition (shielded tank in a stage, released tank as an individual hazardous debris item, a ruptured tank with mid-air dispersion).
9.7.5.2 Other Energetic and Hazardous Debris.
9.7.5.2.1 All remaining potential energies at time of ground contact (including batteries, intact propellant reservoirs, pressurized tanks, ordnance, compressed springs, elevated hardware temperatures, nuclear materials, toxins, chemicals, and any other potential hazard to humans or the environment) should be assessed.
9.7.5.2.2 Batteries can contain hazards from residual electrical charges or the ingredients within the battery that are released at rupture—in addition to batteries themselves being relatively high ballistic coefficient hazardous debris items.
9.7.5.2.3 Even a “depleted” propellant tank typically holds some residuals (typically ~2-5 percent of its capacity) that cannot be reliably burned during normal operation. These amounts can be unusually reactive, as they are nearer to the vapor state required for combustion. Therefore, hazardous debris catalogs should account for hazards posed by remaining propellants in “empty” tanks.
9.7.5.2.4 Inert gases (like helium, such as used for ullage) produce no toxic hazard, but may be contained in tanks that are many times higher pressure than other tanks on board (e.g., 5,000 vs. 100 psig). Similarly, hydraulic fluids (often a synthetic hydrocarbon), may be contained in tanks or reservoirs pressurized to high pressures (e.g., 2,500 vs. 100 psig), and any toxic effect may be negligible in comparison to other hazards. For this reason, stored pressure energy (i.e., a tank, tire, pneumatic cylinder, or otherwise) should be characterized within the hazardous debris catalog, for the potential overpressure hazard on ground.
9.7.5.2.5 Vehicles can contain hundreds of “ordnance items” such as contained energetic devices (cartridges, igniters, shape charges) designed to separate stages, deploy payloads, break bolts, cut electrical or fluid lines, jettison items, or destroy the vehicle itself (i.e. Flight Termination ordnance).
When the vehicle—or its hazardous debris—reaches the ground, some of this ordnance may not have been rendered inert (fired and consumed), due to the stage at which the failure occurred, or due to the ordnance function being interrupted by the breakup itself. Unexploded ordnance can then remain as a hazard on ground, so the hazardous debris catalog should track 41
these potential energy items and their expected condition during the various nominal and malfunction scenarios.
9.7.5.2.6 Other sources that are expected to produce non-negligible amounts of energy should also be included. An example is compressed mechanical springs, which can be used to isolate or stabilize onboard hardware, jettison stages or payloads, or otherwise, and may retain a hazard on the ground after the hazardous debris has come to rest, including if the item’s retention hardware has been damaged. The size and pre-compression of these potential energy items should be tracked in the hazardous debris catalog, with their expected conditions during various nominal and malfunction scenarios.
9.7.5.2.7 Elevated temperatures of inert hardware (such as fractured nozzle components, hardware heated by plume radiation) can remain a burn hazard or an ignition source on ground after hazardous debris has come to rest. Residual temperatures above approximately 250°F have potential for igniting ambient ground brush or foliage, causing uncontrolled fires on the terrain around the hazardous debris footprint. Hardware temperatures above 130°F can cause burns to skin. For these reasons, any hazardous debris anticipated to retain elevated temperatures to ground should be tracked for that characteristic in the hazardous debris catalog.
9.7.6 Toxic Properties.
Any information that is needed for toxic effects of hazardous debris in accordance with § 450.139(c)(1) should be provided in the hazardous debris list. Toxins, chemicals, and heavy metals include a wide range of potential constituents on a vehicle. These can include residual hypergols, acids used for long-term reactions in payloads, lead used for ballast, or any other constituent that can pose a hazard to people or the environment— including if the hazardous debris is not recovered (such as chemicals or lead leaching into the soil or groundwater during the years following the mishap). Batteries have chemicals that affect long-term health of environment. If there are hazardous chemicals that can affect the impact area, then they should be identified. Some payloads may carry hazardous material, such as nuclear material, and any hazardous materials as defined in 49 CFR § 172.101 must be identified, in accordance with § 450.43(i)(1)(v), so that the Administrator can determine the need for any special analysis or safeguards.
9.7.7 Related to Hazard/Casualty Area of a Hazardous Debris.
An estimate of the mean area of each fragment that is the extent of a fragment’s hazard to people should also be included.