Development of a Cold Gas Propulsion System for the ... - SSL - MIT

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7 Ongoing and Future Work There are three main thrusts of ongoing and future work for the TALARIS CGSE. The first is validation testing of the CGSE, which couples further hardware testing with tests of GNC algorithms. The second is more complete characterization of the existing CGSE system’s capabilities as well as the development of best practices for its operation. The third is making changes to improve the TALARIS spacecraft emulator propulsion system. This work could range in scope from relatively small changes, like swapping out parts in the CGSE, to a full redesign of the system to utilize hydrogen peroxide as a monopropellant. 7.1 Validation Testing The single-stream component tests as well as the static characterization tests of the CGSE flight system had all been performed for verification; that is, to ensure that the CGSE met the derived technical performance requirements laid out in section 3.1.4. The next step was to check that these requirements added up to a system that performed the original top-level goals for which it was designed, and the way to accomplish this was through validation testing. As the NASA Systems Engineering Handbook says, “Validation testing is conducted under realistic conditions (or simulated conditions) on any end product to determine the effectiveness and suitability of the product for use in mission operations by typical users and to evaluate the results of such tests” [60]. For the TALARIS CGSE, validation means proving that it can propel and control the vehicle through all phases of a hover hop. However, it would be a very large leap to go directly from static characterization testing to unrestrained free flight, and due to its limited budget and rigorous safety constraints, the TALARIS project cannot tolerate a crash or other destructive failure. Thus, an incremental validation testing program was developed. It was planned that in the first few tests, the hopper would have some of its degrees of freedom (DOFs) restricted so that it could only move in certain ways. Closed-loop CGSE control could progressively be applied to more and more degrees of freedom, with a greater chance of catching any major problems early in a more controlled environment, until enough confidence had been developed in both the hardware and the software to permit 6-DOF free flight hopping. The execution of this plan is in progress at the time of writing this thesis. 7.1.1 Horizontal Traverse and Roll Testing When validation testing for the TALARIS CGSE began, the EDF weight-relief propulsion system was being upgraded and was not available for flight. Thus, the first CGSE validation tests focused on the horizontal 106
traverse phase of a hop and involved only the horizontal thrusters. For the very earliest tests, the two parts of the static test stand shown in Figure 6-7 were separated from the load cell, and wheels were bolted onto the bottom of the cradle. This formed a sort of cart into which the TALARIS hopper could be locked for 1-DOF horizontal testing, as shown in Figure 7-1. Figure 7-1. CGSE 1-DOF horizontal traverse testing on wheels. By firing its horizontal thrusters, the TALARIS hopper was free to roll back and forth across the floor parallel to the hopper’s Z axis, but it could not move in any other dimensions. However, it was soon found that there was a great deal of friction in the wheels, so the cart was not providing an accurate simulation of the transit phase of a hop. To reduce friction with the floor, the wheels were replaced with an air bearing of the sort used to help move vending machines or large pieces of furniture. This improved apparatus is pictured in Figure 7-2. 107
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Development of a Cold Gas Propulsio
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Abstract The TALARIS (Terrestrial A
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Table of Contents List of Figures .
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7 Ongoing and Future Work .........
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Figure 6-6. Identification of thrus
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Notation Acronyms and Abbreviations
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N newton Pa pascal psi pounds per s
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1 Introduction The TALARIS (Terrest
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the idea of hopping was born, and i
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However, as stated before, this doe
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Figure 2-3. Diagram of ACAT lander
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An alternate approach to resolving
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accurate conditions for testing GNC
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Ballistic hops tend to use less pro
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2.3.2 Comparison of Cold Gas and Mo
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Handling propellant There are sever
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and if the cold gas system was foun
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3 TALARIS CGSE Design Framework Aft
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Figure 3-1. Scaling of TALARIS terr
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(3) Providing attitude control Ther
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Figure 3-2 also shows the body coor
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4 Modeling and Flow Control Compone
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4.1.2 Rocket Propulsion Equations L
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variables in equation (4-8) deal wi
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equations. Equation (4-10) was then
Page 57 and 58: that of helium (0.227 MPa = 32.9 ps
Page 59 and 60: thruster solenoid valve, and chambe
Page 61 and 62: where
Page 63 and 64: discussed later in section 6.3.4, t
Page 65 and 66: The flight profile begins with maxi
Page 67 and 68: hop, any given valve or regulator o
Page 69 and 70: esponse time was an important perfo
Page 71 and 72: directly opens and closes the main
Page 73 and 74: If 1D isentropic flow is assumed, t
Page 75 and 76: 5 Single-Stream Component Testing A
Page 77 and 78: the solenoid valve, and a pressure
Page 79 and 80: As indicated in Figure 5-3, initial
Page 81 and 82: Figure 5-5. CGSE high side as const
Page 83 and 84: Figure 5-7 illustrates several aspe
Page 85 and 86: 6 Full Eight-Thruster Flight System
Page 87 and 88: Figure 6-2. TALARIS CGSE assembled
Page 89 and 90: stream tests revealed that changes
Page 91 and 92: Figure 6-5. Original CGSE control c
Page 93 and 94: other constraints. This was difficu
Page 95 and 96: variables (such as number of thrust
Page 97 and 98: One solution to this problem would
Page 99 and 100: One of the characterization tests w
Page 101 and 102: or more thrusters were firing toget
Page 103 and 104: Table 6-3. Valve timing metrics dur
Page 105 and 106: Figure 6-11. Redesigned CGSE contro
Page 107: The imaginary simplified thruster c
Page 111 and 112: Figure 7-3. GNC data from 3-DOF tes
Page 113 and 114: Tests on this vertical stand demons
Page 115 and 116: control the belay line can be put u
Page 117 and 118: accounting for changes in thrust le
Page 119 and 120: development under the supervision o
Page 121 and 122: documenting progress takes time whi
Page 123 and 124: were encountered, it was harder to
Page 125 and 126: [10] Bryant, K. M., Knight, C. J.,
Page 127 and 128: [31] Canadian Centre for Occupation
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[50] ISA - The Instrumentation, Sys
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