ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
454   Conclu ding Remarks  

This paper describes  how complex  the nozzle design was for something that overall is rather simple. It’s  typical that designs quickly become boxed in by competing requirements and practicality. But t he added  dependency of full system test to feedback the next design iteration made this more difficult and schedule  critical. The original project plan included four (4) granite table “flying” prototypes  (Free -Flyer Level  prototypes) . The prototype (iterative) philosophy was a good choice for this development. However,  because the centralized fan wasn’t the original propulsion system choice, it wasn’t until Pr ototype 4 (P4)  that it could be fully tested and provide valuable data for the next iteration.  

The centralized fan propulsion system has proven itself capable and a high-performance  option for intravehicular  robots. Future centralized fan propulsion designs can be scaled and optimized. The Astrobee  Free-Flyers serve both as a feasibility demonstration and reference design for future mission- critical intravehicular robot systems.  

References  

[1] website https://www.nasa.gov/astrobee   [2] website https://www.nasa.gov/spheres   [3] Malloy, Robert A., Plastic Part Design for Injection Molding, Hanser/Gardner Publications, C incinnati ,  OH (1994).
455 Major Design Choices and Challenges that Enabled the Success of the Ejectable  Data Recorder System  

Jeff Hagen* , Michael Burlone* and Kristina Rojdev* 

Abstract 

The Ejectable Data Recorder (EDR) subsystem was added to the Crew Module (CM) of the Ascent Abort  2 (AA- 2) test flight due to a risk that the communications architecture would be insufficient to downlink all  the data to the ground during the test flight. S ince the EDR subsystem was a secondary system for data  collection, AA -2 management enabled the team to take a different approach to hardware development that  was more agile- like. This paper discusses key design decisions , technical challenges, and lessons learned  that enabled the success of the EDR system during its flight on July 2, 2019 . 

Background  

The successful Ascent Abort 2 (AA -2) test flight on July 2, 2019 demonstrated the Orion Launch Abort  System (LAS) performance during the maximum dynamic pres sure phase of the launch ( Figure 1). In order  to reduce costs, the test used an aerodynamically and structurally representative boilerplate substitute for  the Orion spacecraft Crew Module (CM), which was not equipped with a parachute recovery system.  Rather, the CM was discarded several miles off shore at the conclusion of the test. Although data from the  developmental flight instrumentation (DFI) system was returned via high data rate telemetry link, the risk of  interruption in the telemetry justified the development of a backup data recording system. T he CM splashed  down into the ocean after the launch and was not intended to be recovered. Thus , the data recorders were  ejected after completion of the LAS test phase of the flight , but prior to water impact of the CM . Then,  the  data recorders were independently retrieved via water recovery operations .  

Figure 1. AA-2 launch.  

The Ejectable Data Recorder (EDR) subsystem had three major functions: record the data, eject the  payloads and provide the location of the payloads so that they could be retrieved. These functions were  implemented through a dual string redundant system that consisted of a US Air Force AN/ALE -47 flare and  chaff dispenser system, a breakout box that contained the computer for the recordi ng capability and routed  power and data, and a payload ( Figure 2) with a memory device and a beacon. The details of this design 

* NASA Johnson Space Center, Houston, TX;  jeffrey.d.hagen@nasa.gov  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA J ohnson Space Center, 2020
457 Ejection System Concept 

In the ALE -47 system, the payloads were packaged into cartridges that function similar to a mortar tube  (Figure 3). Crimping of the open end of the aluminum cartridge case restrains an aluminum closeout plate  (cap) that retains the payload in the cartridge until ejection. A specially designed machine performs the  crimping operation, which guarantees that the payload has no residual gap and cannot move within the  cartridge. An electrically initiated pyrotechnic squib installed in the base of the cartridge provides the  propelling gas that forces the payload and closeout plate through the restraining crimps and out of the  cartridge. A plastic piston assembly installed in the bottom end of the cartridge ensures that the combustion  gasses from the squib do not leak past the payload and negate the propelling force, analogous to the  function of the wadding in a shot gun shell.  

Figure 3. The figure on the left shows the components for assembling the payload into the cartridge and  the figur e on the right shows the pass thru plugs installed into the payload interface.  

The cartridges were packaged into a magazine that constituted the operational load element of the system,  and were installed on the vehicle by sliding into the muzzle of the ALE -47 dispenser after installation of the  pyrotechnic squibs ( Figure 4). The modularity of the dispenser and magazine system enables installation  of as many as 30 cartridges of varying sizes with payload cross sections ranging from 1” x 1” up to 2” x  2.5”. Only six of the largest size cartridges required for the AA -2 EDR payload can fit in each dispenser,  which leaves 24 of the electrical squib contacts in the dispenser breech plate unused and dead faced  against the cartridge bases.  

Figure 4. The fi gure on the left shows the payload packaged inside the cartridge and the cartridge being  installed in the magazine. The first on the right shows the assembled dispenser next to the breakout box  installed in the forward bay area of the CM.
458 Two independent ejection systems were mounted in the forward bay parachute compartment of the AA -2  CM, pointing in opposite directions ( Figure 5).  

Figure 5. EDR ejections. Figure on the left is an artist rendering and the first on the right is an image from  the actual f light.  

Risk Definition  

Risks were based on perceived probability and consequences, but also ranked according to the expediency  or difficulty of accomplishing closure. Tests that could be conducted rapidly and efficiently received  schedule preference in order to identify pitfalls  as soon as possible. T he principle risks identified were as  follows:   • Functionality of the COTS ejection system and EDR unique payload   • Adequate separation performance of the ejection system in the poorly characterized post -test flight  environment   • Mechanica l survival of the payload during flight, ejection, and impact environments   • Recording of the data stream and storage of the data in the payloads   • Separation of the power and data connections of the payload through the ejection system  • Packaging of the payload elements   • Buoyancy and stability of the payload   • Location and recovery of the payloads   • Survival of the system in the flight vibration and shock environment   • Payload battery performance and survivability   • Beacon activation  

Critical Developmental and Risk Redu ction Testing  

Project resource limitations drove testing concepts to prioritize low -cost approaches using existing or readily  available, and often non- traditional, assets to the fullest possible extent. One of the earliest tests was  performed using an air craft and recovery boat to drop and recover inert simulated payload shapes into open  water. The simulated payload shapes were constructed from a prototype syntactic foam mixture and were  dropped from an altitude well in excess of that necessary for the pay loads to reach terminal velocity. This  testing proved that syntactic foam provided sufficient protection to the payload. This test was followed by  an ejection from the ALE -47 dispenser using inert simulated payloads . With the data from this initial testing   and multiple iterations of design and 3D printing, the team began to close on a payload design that  encompassed the volumetric, buoyancy, and structural constraints.
459 The next payload prototype included a n early generation,  functioning locator beacon and recording  computer, contained within a 3D printed plastic payload shell ( Figure 6),  as opposed to an alumi num shell  used in the initial design. Ultimately, this shell printing process proved vital to the frequent and rapid iteration  of the payload design,  the extremely low production costs and quick fabrication times . 3D printing also  enabled the project to construct the numerous development and replacement  payload units  needed to work  through many test failures , as well as  the large number of flight units for redundancy  purposes . The ejection  performance test was repeated with this enhanced payload, and showed that the ejection system could  adequately eject a  functionally complete payload wit h sufficient velocity, and that the payload could survive  the ejec tion forces.  

Figure 6. The image on the left is a set of 3D printed payload shells and scaffold. The image on the right  is an assembled payload that is prepared for foam pouring.  

Collaborative use of a NASA- owned Gulfstream III aircraft equipped with an instrument package  deployment capability allowed for early demonstration of water impact survivability and recoverability of  prototype active payloads. Five payload prototypes of varying configuration were dropped from  approximately 5000 f eet (1.5 km)  above sea level and approximately 50 miles  (80 km)  off shore from  Galveston, Texas. Beacon signals were received from all units, although two units failed to send proper  GPS coordinates . These discrepancies were thought to be due to unsuitable antenna configurations or  assembly defects. The other three units were recovered and their simulated data retrieved  (Figure 7) .  

Figure 7. Early drop testing and retrieval operations.  

Following were data writing tests, initial demonstrations of payload power and data harness separation,  vibration testing of the ejection system elements, tests of data writing during vibration, increasingly complex  payload recovery operations, thermal exposure followed by ejections  (Figure 8),  ejection system  performance with fully active payloads, payload beacon battery failure margin testing and recovery beacon  activation tests.
460   Figure 8. Ejection testing of a data recorder mass simulator.  

Dispenser Vibroacoustic Mitigation  

The expected vibroacoustic environment during the abort sequence of the AA -2 mission greatly exceeded  the rated capabilities of the ALE -47 dispenser  (Figure 9). The system specifications of the off -the-shelf  dispenser accommodated a lower amplitude vibroacoustic environment, but for a much longer duration than  the abort sequence (3 hours for the benign rated environment, as opposed to 5 seconds of the AA -2 abort  environment).  

Figure 9. Dispenser rating compared with the AA -2 abort environment.  

Several mitigation strategies were necessary to produce a design that could reliably withstand the extreme  environments induced by the abort motor . These strategies included using additional structural attachment  points to the dispenser and mounting the dispenser on cup- style elastomeric isolators ( Figure 10) . Notably,  the dispenser with its custom mounting interface was tested to the extreme abort environments while  mounted on hard mounts (i.e. solid aluminum stand- ins for the isolators) and survived. However, with the  dispenser in the hard- mounted conf iguration, data transfer to the data recorders loaded inside was  unsuccessful.
461 The off -the-shelf dispenser provides four attachment points near the muzzle of the dispenser to attach to  vehicle structure (Figure 10 ). The center of mass of the dispenser is not in plane with these attach points,  resulting in a cantilevered arrangement. To avoid this cantilevered arrangement, the AA -2 custom design  made use of the subassembly fasteners near the breech of the dispenser to affix plates and brackets such  that the custom dispenser mounting interface was nearly coplanar with its center of mass.  

Figure 10. The image on the left shows the four attachment points. The image on the right shows the  suite of dispenser modifications.  

These additional brackets were located in such a way that when mounted on isolators, the center of mass  of the dispenser was near the centroid of the isolators . This design eliminated rotational coupling (i.e.  swaying motion) of the dispenser when exposed to vibrational environments, keeping the resulting motion  almost entirely translational .  

The isolators themselves were selected such that the natural frequency of the isolated mass would be  approximately 32 Hz, providing vibroacoustic attenuation for frequenci es above 45 Hz . Figure 11 shows  the frequency response of the isolated dispenser based on the theoretical transmissibility of the selected  isolators.   

Figure 11. Theoretical Frequency response of isolated dispenser.
462 Even with the isolators, the dispenser experienced a vibroacoustic environment above its rated values for  frequencies below 200 Hz . However, with the customized mounting arrangement of the dispenser and brief  exposure to the abort loads, the system design passed qualification testing and was ultimately successful  in the AA -2 Mission.  

Lessons Learned During Vibroacoustic Testing  

Cartridge Crimp Failure   An early vibration test had a failure of the crimped cartridge to contain the ejectable data recorders . Ideally,  the contents of the cartridge would be preloaded in a manner that resulted in no backlash or motion of the  contents of the cartridge. However, an error in the crimping procedure resulted in a free displacement of  the recorder between .007 in (0.18 mm)  and .044 in (1.1 mm)  within the c artridge. Even this small motion  was enough to produce significant impact loads on the crimp feature, which was defeated. During the test,  the lids came off the cartridges, and due to the asymmetric friction resistance of the piston seal (i.e. higher  force needed to push seal in than to pull out), the vibration motion “ratcheted” the piston and data recorder  out of the enclosed cartridge. Recalibration of the crimping machine at the cartridge loading vendor’s facility,  along with inclusion of a felt spacer and a bead of RTV sealant as used in the standard cartridge  configurations, resolved the loose fit issue such that this failure did not reoccur ( Figure 12).  

Figure 12. Cartridge crimp failure during vibration testing.  

Dispenser Isolator Failure   Another  test failure occurred on the dispenser when an erroneously entered test profile was programmed  to the shaker table, which resulted in the destruction of the isolators . After the failure occurred, it was  determined that the erroneous profile differed from the intended profile as shown in Figure 13. The 32 Hz  frequency is notable since that is the system’s natural frequency based on dispenser mass and isolator  stiffness.
463   Figure 13. Figure on the left shows the erroneously tested vibration profile. The images on the right show  the resultant cup isolator following the test.  

Curiously, the g rms value of the erroneous profile that destroyed the isolators was 17% lower  than the g rms  value of the intended profile (29 g rms vs. 35 g rms), even though the isolators were proven to survive the  intended profile when tested on a later date.  

In this case, the erroneous profile exceeded the intended profile in the most crucial frequency range, the  low frequency domain, which included the system’s natural frequency of 32 Hz  (Figure 14). Applying the  isolators’ transmissibility to calculate the frequency response of the isolated dispenser creates a clearer  picture of why the erroneous profile was an over -test. 

Figure 14. Dispenser frequency response to er roneously tested vibration profile.  

As before, the g rms value does not tell the full story . The frequency response of the isolated mass shows  only a slight increase in g rms when comparing the erroneous profile to the intended one (12.1 g rms and  10.9 grms, respectively) . The true significance of the exceedance in the low frequency is not apparent until  examining the rms displacement, instead of the rms acceleration.  

Acceleration values resulting from oscillating motion are linearly proportional to displac ement amplitude  and proportional to the square of the oscillation frequency . This means, for example, that for a body
464 experiencing a given rms acceleration from sinusoidal motion at 400 Hz, the peak -to-peak displacement  when experiencing the same rms accel eration at 40 Hz is 100 times greater . Thus, given the two  acceleration profiles, with similar g rms values, shown above, it is expected that the profile with a higher  acceleration spectral density in the low frequency domain, namely the erroneously tested profile, will have  a greater rms displacement.  

Indeed, when comparing the dispenser’s frequency response displacement from the erroneous profile, with  its response displacement from the intended profile, it becomes clear that the erroneous profile was muc h  more severe. Figure 15 shows the comparison on a non- logarithmic plot.  

Figure 15. Dispenser frequency response displacements to erroneously tested vibration profile.  

The rms displacement of the intended profile is 0.107 cm, while the rms displacement  of the erroneous  profile is 0.299 cm. The test failure that occurred was a result of excessive displacement of the isolators . It  is notable that although the erroneous test profile indicated a 17% more benign acceleration value (g rms),  the resulting displacement that the isolators experienced was almost triple the intended value.  

Data and Charging Link Challenges  

The standard ALE -47 system dispenses only passive payloads and does not include any provision for data  or power interfaces betwe en the host vehicle and the payloads, as required by the AA -2 EDR application.  The power connection served only to charge the EDR batteries prior to launch and therefore did not function  during the flight environment, but the data connection had to maintai n integrity of the 20 Mbps real time  data stream between the local data controller and the USB solid state memory embedded in the EDR  throughout the full flight load, vibration and EMI environments. Additionally, these connections had to be  separated upon ejection in a manner that preserved the data connection for use after recovery. Each of the  two connections required four independent conductive paths. The field installation nature of the ejection  system pyrotechnic devices required that the payloads be i nstalled and thus these connections be made  for the final time only during the later stages of the launch preparation process, long after the EDR system  had been built and installed in the host vehicle.  

There were two concepts traded to sever the data and  power lines between the vehicle and the payload.  The first concept employed a blade in the cartridge that would cut the wires as the payload ejected, similar  to a guillotine. The other concept routed the power and data lines through connecting plugs between the  payloads and dispenser, oriented with their axis of separation aligned to the axis of payload ejection. After
465 several different tests and trade discussions, the concept that employed a connecting plug interface was  selected due to the ability to eas ily insert and remove the populated magazine from the dispenser multiple  times. Ejection of the payload pulled the plugs from their associated jacks. Routing of the cables to the  external interfaces took advantage of the excess pyrotechnic squib electrical  interface locations in the  dispenser breech plate not required for use in the six payload configuration, such that installation of the  loaded magazine into the dispenser accomplished engagement of the plug. Because the gas expansion  chamber formed by the piston and the base of the cartridge case fully encompassed the end face of the  payload perpendicular to the axis of ejection, the umbilical connections had to pass through both sides of  the gas expansion chamber without introducing an excessive leak path.  Due to the imprecise nature of the  EDR construction, the positioning of the connecting jacks within the payload were not tightly controlled. The  relative positioning of the payload connectors to the cartridge base, the cartridge base to the dispenser  breech plate, and the connector location to the piston seal constituted three independent alignment  challenges, each with six degrees of freedom,  that had to be accommodated by a separable umbilical  connection routing through the cartridge base and dispenser breech. The connection was required to  prevent separation or electrical chattering of the plugs under all conditions prior to payload ejection.  

The design solution employed four conductor, coaxial mini -phono connectors as the separable plugs due  to their axisymmetric nature in eliminating the need to accommodate rotational alignment constraints, self - alignment of plug insertion, robust connection strength, compact size with high conductor density per cross  section area, and low cost. The precise fit nature of these connectors required compliance for each plug to  follow the unique lateral, axial, and angular alignment of its corresponding jack. In order to simplify the  combined alignment challenges, each separable plug connection was split into two different plug and jack  pairs, with one pair constituting the mating interface for the loaded magazine installation function and the  other pair constituting the demating interface for the payload ejection function. Due to the nature of the  payload assembly within th e cartridge, it was necessary to have a separable connection at the payload to  cartridge interface, and another one in series at the cartridge to dispenser interface. The results was the  “pass through plug” ( Figure 16),  which consisted of a mini phono plug on the payload mating end linked to  a mini phono jack on the dispenser mating end.  

Figure 16. Pass through plug and floating plug installation.
468 channels of the breakout box noted during testing, but accepted d ue to the impracticality of repair and  protection of massive redundancy.  

Other than the noted issues with early versions of the payload beacon activation circuit and data writing  software, the programmatic and operational performance of the system fully validated the selected design  choices and development philosophy of the EDR subsystem.  

References  

1. Rojdev, K., Hagen J., Burlone, M., Petri, D., Jackowski, A., et al., “An Ejectable Data Recorder  Subsystem for the Ascent Abort -2 Test Flight of the O rion Launch Abort System,” Proceedings of  the IEEE Aerospace Conference, Big Sky, March 7- 14, 2020.