ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
481 wire to a ring terminal which is connected to two flying leads and provides the electrical connection to the  release mechanism. The nichrome wire is secured between the ring terminal and the underside of the head of the #0-80 screw (See Figure 2). The ring terminals which can be purchased cheaply with tin plating will need to be stripped by a plating manufacturer for a small cost, approximately $1 per ring terminal. The #0-80 screw is secured into the tapped hole of the dowel pin using 3M Scotch-Weld™ 2216 B/A on the threads of the screw to prevent the screw from backing out and losing the secure connection of the nichrome wire. Figure 3 shows CAD models of the nichrome burn wire release mechanism in the deployed and stowed states.  

Figure 2. Nichrome wire secured between the button head screw and ring terminal 

Figure 3. Nichrome burn wire release mechanisms in the deployed and stowed configurations. 

The mechanism was designed to thermally cut through two different deniers of Vectran cable. Both Vectran cables were 12 strand tubular braids with either 200 or 400 denier strands and were
482 manufactured without an oil finish for low outgassing. The 200 denier Vectran cable has a tensile  breaking strength of 300 N and the 400 denier Vectran has a tensile breaking strength of 600 N. Vectran cable was selected as the primary tie down cable due to its low creep over time, its relative strength to other materials, and its resistance against self-abrasion.   The entire burn wire release mechanism once assembled has dimensions of approximately 32-mm (1.25”) long by 16.5-mm (0.65”) wide by 11.5-mm (0.45”) tall. Figure 4 shows two, redundant burn wire release mechanisms stowed on the TEPCE tether deployment system. Due to the small size, assembly and workmanship, inspection is best done with the aid of magnification such as a stereo microscope.  

Figure 4. Release mechanisms on Vectran tie down cable for TEPCE tether deployment system 

Testing 

The goals established for a generic CubeSat class release mechanism were: 1.) to be simple enough to replicate the build and assembly by all CubeSat users (including Universities), 2.) be inexpensive, 3.) reliably release in a few seconds but rugged enough to survive for a 30 second timer for each actuation, 4.) have a design life at least 50 actuations, 5.) work at the same power draw in both air and vacuum and 6.) fit into as small a volume as possible. A burn wire based release device was selected based on a trade study between numerous miniature actuators including bolt releases, pin pullers, and linear and rotary actuators. Then the parameters associated with the burn wire, the compression springs and the tie down cable were investigated. Since a large number of parameters needed to be tested in order to find the optimal design of a nichrome wire system, a design of experiments (DOE) approach was taken in order to test multivariable changes in the minimum number of experiments. The parameters chosen to test were the nichrome spring stroke and force applied, the nichrome wire diameter, the free length of the nichrome wire and its corresponding resistance, the tie down cable, the tension on the tie down cable, the current supplied to the nichrome wire, the number of actuations (life) for each nichrome wire, the performance in air and vacuum and the effect of the environmental temperature. Additionally, minimizing the cut time of the Vectran tie down cable was a goal. Using the JMP Statistical Discovery software a DOE test matrix was designed and tests were conducted and important factors in the design were determined.
483 Through the DOE analysis in JMP, it was found that the most important factor for successful cut times in  both air and vacuum was the supplied current to the nichrome wire. As long as the compression springs supplied spring stroke all the way through the Vectran tie down cable and the nichrome wire had enough current to thermally cut through the tie down cable then the release mechanism would successfully release. The diameter of the nichrome wire was then based on that which provided a large enough electrical current margin to reliably release in air balanced against not failing in vacuum due to  overheating the nichrome wire . An electrical circuit was designed to supply a constant current to the  nichrome wire independent of the resistance of the wire and the voltage available from the spacecraft. As  long as the minimum required power (0.9 W) was available from the spacecraft then the electrical circuit would supply a constant current to the nichrome wire.   It was found that the 30 AWG nichrome wire provided an acceptable margin relative to overheating in vacuum versus failing to thermally cut in air. Since the design envelope for the two failure modes was not large, the constant current source was kept to tight tolerances. The minimum amount of current needed to reliably cut through the tie down cable in air (worst case) was 1.40 amps. The supplied current to the nichrome wire that would cause a failure due to overheating in vacuum (worst case) was 1.90 Amps. Therefore a constant current requirement of 1.60 ± 0.05 amps was selected to provide margin on either side of the failure modes and was used to design the electrical circuit. This allowed the mechanism to successfully operate in both air and in vacuum without having to change any circuitry or software. It is critical to note that the critical operating window – in vacuum/space where it must work – is larger than the  worst case window that includes operation in air for ground testability. Additionally, in all tests to date where the nichrome wire has been overheated to failure, it has first cut through the Vectran cable for a successful release prior to the nichrome wire failing such that this has not actually resulted in a failure to deploy but rather ended the reusable life of the nichrome wire filament. This shows that the nichrome burn wire release mechanism has a much larger margin to work successfully in vacuum where it counts. The schematic for the constant current circuit design used on the nichrome burn wire release mechanism is given in Figure 5.   

Figure 5. Schematic for the constant current circuit design.
484 Results 

The design and optimization of the burn wire release mechanism revolved primarily around understanding the performance of the nichrome wire. The failure current of the nichrome wire under only the tension of its own weight was first investigated and the results for the 30 AWG nichrome wire is given in Table 1. This data shows that the upper bound of the nichrome wire failure current is established at 1.90 amps. 

Table 1. Failure currents of the 30 AWG nichrome wire under only the tension of its own weight. 

Nichrome Wire  Resistive  Length (mm/in) Resistance ( ) –   as measured from  screw to screw Failure  Current  (amps) Failure Time  (sec)  13 / 0.50 0.8 2.15 7  19 / 0.75 1.1 2.05 7  25 / 1.0 1.5 1.95 7  32 / 1.25 1.3 1.95 9  38 / 1.50 1.5 1.9 10  45 / 1.75 1.6 1.95 14  51 / 2.0 1.8 1.9 20  57 / 2.25 2 1.9 17  64 / 2.5 2.1 1.975 30  70 / 2.75 2.2 1.975 19  76 / 3 2.2 1.975 13  83 / 3.25 2.4 1.9 15  89 / 3.5 2.6 1.9 19  Avg. Failure Current 1.960     Using the tight tolerance constant current circuit, 419 successful tests of the release mechanisms have been conducted without a failure. Of the 419 tests, 242 were conducted in air at room temperature and 177 were conducted in vacuum at various temperatures. Tests were also conducted to intentionally overheat the nichrome wire and cause it to fail but even in these cases; the nichrome wire always first cut through the tie down cable ensuring a successful release and then the nichrome wire would fail after the successful cut from overheating. Figure 6 shows test data taken for the air and vacuum operation of the burn wire release mechanisms cutting through 200 and 400 denier Vectran cables.
485     Figure 6. Release mechanism deployment times for varying currents of both Vectran cables in air  and vacuum environments. 

Using the constant current circuit which supplied the nichrome wire with 1.60 amps with a 30 second powered timer, the cut times for the burn wire release device in air and vacuum and using both Vectran cables ranged from 2.4 to 7.2 seconds. For the critical operating window in vacuum this gives approximately a 10X margin on the cut time versus the 30 second powered timer limit. Table 2 gives a summary of the average cut times for the operating conditions. 

Table 2. Average cut times of the burn release mechanisms. 

 Average Cut Time  (sec)  200 Denier Vectran in Air 5.3  200 Denier Vectran in Vacuum 2.6  400 Denier Vectran in Air 6.2  400 Denier Vectran in Vacuum 3   The burn wire release device was also tested down to -50°C and up to 70°C without any noticeable effect on the performance. This is likely due to the nichrome wire heating up to over 750°C and having negligible thermal mass, such that the difference in initial temperature has a negligible effect. It was also
486 demonstrated that when using the tight tolerance constant current circuit the burn wire release  mechanism can be actuated at least 50 times without having to change out the nichrome wire. Many of the burn wire release mechanisms were used past the 50 actuations, up to 80 actuations, and still performed nominally Figure 7 shows the release mechanism immediately following a successful cut through the Vectran cable in vacuum with the nichrome wire still glowing hot.     

Figure 7. Burn wire release mechanism immediately following   a successful cut through Vectran cable.   To be useful to all CubeSat users, including Universities the burn wire release mechanism needed to be simple to manufacture and assemble and to be cost effective. For the NRL TEPCE CubeSat program headed by NRL, the cost for all hardware associated with building 10 of the burn wire release mechanisms was $1600 making the cost per mechanism $160. This cost included having a local machine shop manufacture both the upper and lower saddles and the dowel pins. However, a student with reasonably proficient machining skills could make the mechanism components themselves and eliminate all but the anodizing costs which could drop the price for 10 mechanisms to approximately $200. Table 3 gives a price breakdown of the hardware associated with machining and building up the burn wire release mechanisms for use on a small satellite.   The nichrome wire release device has been through component level testing in different configurations ranging from carpenter tape deployments to a stacer and tether deployment to the deployment of 3U solar array panels on a CubeSat. The release device has also undergone system level testing on the TEPCE CubeSat program.
488 the screw to hold the nichrome wire. While properly securing the nichrome wire and verification of this  connection has proven successful in testing to date, the concern still exists that the nichrome wire could slip out from under the screw head and increase the nichrome wire free length which would in turn allow the compression springs to relax and spring preload could be lost.   Conclusions   The burn wire release mechanism was designed in order to be used by a broad range of small satellite users in a manner that was simple, reliable, and inexpensive. Using a nichrome burn wire design the release device is capable of cutting through various tie down cable materials and providing successful satellite mechanism deployments. The burn wire release mechanism specifications were chosen in order to be user friendly in both air and vacuum environments and to give the user the ability to implement a release mechanism which has been previously tested and will work in a number of applications.  Drawings and assembly procedures have been produced in order to allow any small satellite user to conveniently reproduce the nichrome burn wire release mechanism for their specific application. The nichrome burn wire release mechanism will hopefully allow for a more universal release mechanism which can be reliably used in a wide array of applications for CubeSat and other small satellite users. By giving the engineer a mechanism which has proven reliability, the hope is that the cost and complexity of smaller satellite programs can be kept at a minimum.    References 

1. Vectran Technical Data Brochure. Kuraray America, Inc. Vectran Division. 2008 2. General Considerations for the Processing of Vectran Yarns. Kuraray America, Inc. Vectran  Division. 2007  3. Fette, R.B., M.F Sovinski. Vectran Fiber Time-Dependent Behavior and Additional Static Loading  Properties. NASA/TM-2001-212773. December 2004  4. ASTM B344-01. Standard Specification for Drawn or Rolled Nickel-Chromium and NickelChromium-Iron Alloys for Electrical Heating Elements. American Society for Testing and Materials. August 2010.  5. JMP 9 Statistical Discovery software. SAS. 2010
489 Antenna Deployment Mechanism for the Cubesat Xatcobeo.   Lessons, Evolution and Final Design 

José Antonio Vilán Vilán*, Miguel López Estévez* and Fernando Aguado Agelet* 

Abstract 

This paper aims to explain the whole development process that has been undertaken over the past few  years including the problems encountered and the solutions adopted in what was to become the final design of an antenna deployment system for the Xatcobeo picosatellite. This mechanism was first presented at the 40 th Aerospace Mechanism Symposia. At that time, we presented an evolved version of  our antenna deployment mechanism, with many conclusions and lesson learned. However, only now can we present the final version of this mechanism with all the development problems, solutions and conclusions reached as well as the lessons learned over 3 years of work. 

Introduction 

In the paper published for the 40 th AMS we explained the mechanism's general operation. This included  how the antenna retention system, the burning system, and the opening detection all worked. Although, in general terms, none of these features has been changed to any great extent, they are all different in some way from what we described then. This is due to the many problems we came across and the way their solutions have led to changes in all the device's parts.  Modifications  This article will analyze in detail all the changes the design has undergone throughout the development period. Namely:   The dimensions of some of the parts on the main piece (sub-chassis)   The sub-chassis design   New attachments   The materials used   The retention wire burning circuit. Two resistance types   Retention wire tying   Power Voltage   Thermo-vacuum test   Also, totally new features will be explained that have been developed since the first article, such as:   Electrical interface   Mechanical interface   Design of the RBF. PEM nut   New part for resistance support   Thermal interface between the sub-chassis, the new support part, the resistance and the  shielding panel   Calculations for avoiding the appearance of ESD following ECSS standards   Compliance with the standard for outgassing values   Final integration process and envelopes. Problems with dimensions and assembly.   Modification of the margin with the enveloping film   Qualification Tests 

                                                     * University of Vigo, Vigo, Spain
490 Mechanism Background 

This deployment mechanism is based on one main part, called the sub-chassis, which is designed to be  built from a polymer using fast prototyping. All the elements needed for the mechanism's operation are installed onto this piece. This includes the antenna enveloping film, the burning resistance, and the opening detection switch. The sub-chassis can itself be installed in the shielding panel on one side of the Cubesat, which means that everything is easily inserted in a modular way.   Operation is very simple. The retention film is attached to the sub-chassis and allows the antennas to be folded and retained against the edge of the sub-chassis. Once the assembly is closed, a nylon wire passes through both the film and the antennas, and it is this that keeps everything folded away until the time for burning. At that moment, the burning resistance will cut the retention wire and the antennas will be deployed, leaving the retention film joined to the sub-chassis unable to detach itself.  

Figure 1.  Final Deployment Mechanism  

General view of the Mechanism   General operation is, as mentioned above, basically the same as before. The main difference lies in the fact that the enveloping film, instead of being fixed to the sub-chassis together with one of the antennas with which it was in direct contact, is now attached independently onto the sub-chassis. This way avoids problems related to the noise that could be produced on the antenna, but which requires a new nut and bolt to be included.  Furthermore, the enveloping film attachment moves from point S on the sub-chassis to point E. This is due to the fact that if it were attached at point S, the end of the antenna attached at point E would end beyond the retention point. The pressure from the retention wire would thus lead to this unpressed end opening towards the outside in such a way that it would exceed the limit given by the available envelope. In compensation, the film is roughly 80 mm longer. It needs to be perforated twice for the retention wire to pass through, which means its capacity for retention is much greater precisely because it passes twice over the retention point and none of the antenna's parts are left with no pressure against the sub-chassis. 

Sub-chassis 

The sub-chassis, as stated above is the cornerstone of this mechanism. Its special features allow it to be extremely light and act as the piece that enables the installation of all the other mechanism elements. This means it is of vital importance for endowing the assembly with modularity and simplicity.   EW N S
491 Material and Manufacture  One of the main changes in this piece involves the material chosen to make it. In the previous article we  had chosen polyamide 6 as the material and Selective Laser Sintering as the manufacturing method. During the development of this piece research into the properties of various polyamides led us to opt for polyamide 12 with fiberglass reinforcement. There were several reasons for this:   The first reason is that PA12 is lighter than PA6 by about 10%, and absorbs less water. This was  a step in the right direction which was to reduce the weight of the whole assembly as much as possible.   The second is that the prototypes manufactured using SLS on PA12 with Fiberglass  reinforcement were more precise than those made from PA6 with Fiberglass. This favored the correlation between the CAD model and the actual model. Bearing in mind that the attachment of the various parts onto the sub-chassis was based on a tight fit, it was very important to suitably meet this correlation. Moreover, this was also a way of improving repeated similarity between the different prototypes that were commissioned. 

Figure 2. Sub-chassis detail. E point Figure 3. Burning receptacle. W point  Design and Dimensions  The changes made in the sub-chassis were aimed at solving problems arising during the development stage. Below we outline both the problems and the solutions in the design:   Burning receptacle (resistance, switch, wire, tying system, increase of material in the area in  order to insulate the resistance as much as possible and make the parts that are heat sensitive as massive as possible).   New attachment for the film (equilibrium of the part, improvement in retention)   Modification of the tabs (longer at the corners and narrower)   The piece was reduced in width from 6.5 mm to 6.3 mm 

Retention and Burning System   The previously published version of the system for burning and cutting the retention wire explained that a 0.125-W 9- Ω resistance had been chosen. The parameters used for dimensioning this resistance were  early ones and the voltage for the power was later modified to 3.3 V. Once this value was accepted as the one which would produce the burn, a re-dimensioning of the resistance was begun to maintain the dimensions and nominal value of the power, i.e., the sought after resistance would be 0.125 W.   Test  In order to select the correct resistance from those available commercially, thermo-vacuum and room-temperature tests were carried out. The thermo-vacuum tests were redesigned until pressures even lower than those used earlier were achieved; a new vacuum pump was installed; the vacuum chamber and the
492 electrical connections were modified. This was all with the intention of achieving lower pressures, gaining  greater control of temperature and eliminating losses in the vacuum chamber electrical connectors.   To reach the desired low temperatures, liquid nitrogen was used. To apply the liquid nitrogen indirectly, a system was designed comprising a bath of the liquid in a container within the vacuum chamber into which an oval-shaped piece of copper was dipped. While the lower part of the copper was submerged in the nitrogen, the upper part had the deployment mechanism bolted to it. The copper acted as a thermal conductor and the device's temperature was quickly reduced. Finally, a probe was installed in contact with the sub-chassis, as this is the part with the lowest heat conductivity and therefore the one that would be the slowest at changing temperature. The probe would thus provide the most reliable temperature reading for the parts that have a thermal balance inside the assembly. This is the atmosphere in which the device was enclosed and connected up in order to be fed power for the deployment to take place.   Figure 4. Thermo-vacuum chamber Figure 5. Thermal image of the resistance (ºF)  Besides this device, various tests were carried out on the wire burning at room temperature using a thermal camera for observation. With the combined results from thermal-vacuum and room-temperature tests, in which the same potential was burned and the same resistance used, the temperature value was found that the resistance must reach at room temperature in order to burn the retention wire in the thermal-vacuum atmosphere. This temperature is directly linked to an electrical power value needed, and it is thus simpler to select a resistance from commercially available values.  Thanks to these tests we detected that the resistances, on being subjected to much greater powers than the nominal ones, underwent deterioration and variation in their properties when the current was passed through them. This was helpful when determining the point at which the resistance was capable of burning the wire in the coldest environment and not destroy itself at room temperature. For this, the deterioration was related to the variation in the current flow by maintaining the power voltage constant over time. This fact can only be due to the variation in the resistance value over time due to the deterioration through overload. The graph in Figure 6 shows the results from observation of the resistance in a thermal-vacuum test at 3.3 V over more than a minute of burning, with two seconds of stop before the opening of the antennas