Repair Missions Research Articles

Model-Free High-Order Sliding Mode Controller for Station-Keeping of an Autonomous Underwater Vehicle in Manipulation Task: Simulations and Experimental Validation.

The use of autonomous underwater vehicles (AUVs) has expanded in recent years to include inspection, maintenance, and repair missions. For these tasks, the vehicle must maintain its position while inspections or manipulations are performed. Some station-keeping controllers for AUVs can be found in the literature that exhibits robust performance against external disturbances. However, they are either model-based or require an observer to deal with the disturbances. Moreover, most of them have been evaluated only by numerical simulations. In this paper, the feasibility of a model-free high-order sliding mode controller for the station-keeping problem is validated. The proposed controller was evaluated through numerical simulations and experiments in a semi-Olympic swimming pool, introducing external disturbances that remained unknown to the controller. Results have shown robust performance in terms of the root mean square error (RMSE) of the vehicle position. The simulation resulted in the outstanding station-keeping of the BlueROV2 vehicle, as the tracking errors were kept to zero throughout the simulation, even in the presence of strong ocean currents. The experimental results demonstrated the robustness of the controller, which was able to maintain the RMSE in the range of 1–4 cm for the depth of the vehicle, outperforming related work, even when the disturbance was large enough to produce thruster saturation.

Testing satellite control systems with drones

In space, it is usually not possible to repair equipment when things go wrong. While astronauts ventured into space aboard the Space Shuttle to repair the infamously flawed Hubble Space Telescope, these types of repair missions are extremely expensive and rare. Limited repair options make spacecraft engineers turn their attention to reliability in an attempt to avoid failures altogether. Building a reliable system starts with a robust design, incorporates proven parts, and—most importantly—involves a lot of testing.

An updated re-entry analysis of the Hubble Space Telescope

The Hubble Space Telescope (HST), launched in 1990, has without question given us a better understanding of the Universe [1]. The storied spacecraft has far exceeded its design life and, in spite of four repair missions, is nearing the end of its useful lifespan. Originally designed to be returned by the Space Shuttle, the HST has no on-board propulsion system. A 2012 study estimated that without intervention, the HST will re-enter the atmosphere in approximately 2027 with a 1:240 risk of fatality [2]. This study updates that analysis with more recent de-orbit technologies and updated trajectory information. We propose a design solution to safely perform a targeted de-orbit, assuming a worst-case scenario (a non-functional, tumbling spacecraft). Multiple de-orbit options are assessed to actively capture the satellite. Results frame an approach that could be accomplished with proven technologies at reasonable cost to improve the fatality risk as required by US Government regulation [3]. Moreover, delayed action would significantly increase mission cost and complexity so we recommend a project start in the near future.

Probabilistic Trajectory Optimization Under Uncertain Path Constraints for Close Proximity Operations

Rendezvous and docking operations have been an integral component of manned spaceflight from the beginning of the space age. However, there is now a growing interest in close proximity spacecraft operations in the new areas of orbital debris removal, on-orbit assembly, on-orbit refueling, and on-orbit servicing and repair missions. Current trajectory planning methods focus on performing rendezvous and docking to very well-known targets and in very well-known conditions. Inherent to these new mission types, however, is an increasing element of uncertainty to which new trajectory optimization architectures will need to be robust. There is an inherent tradeoff here between safety and performance. This paper attempts to address the uncertainties underlying path constraints while maintaining a probabilistically optimal level of performance. The goal is to find baseline trajectories with the best expected performance over large uncertainties in mission critical parameters, such as knowledge of an obstacle’s position or attitude of a target spacecraft while knowing that the trajectory is able to be replanned on board the spacecraft when higher-precision information is obtained. Results specific to this problem and the associated analysis motivate the use of this probabilistic planning framework in future space missions.

Using TRIZ to Improve the Procurement Process of Spare Parts in the Taiwan Navy

Abstract: The Naval Maintenance and Repair Command Acquisition Management Unit (NMRC-AMU) of the Taiwan Navy suffered from poor stock control of spare parts and inadequate modification of requested items and manufacturer/part codes during recent years. Therefore, the purpose of this study is to investigate core categorization, coordination, and procurement (CCP) problems, to formulate feasible solutions and then to improve the CCP performances of spare parts in NMRC-AMU. The Teoriya Resheniya Izobreatatelskih Zadatch (TRIZ) method was applied to solve this issue. A problem hierarchy analysis (PHA) was first used to identify the core problems. Then, the 40 principles were used to determine the ideal improvement solution and formulate a solution strategy that simultaneously simplified CCP processed and enhanced the correctness of procurement tasks, thereby elevating CCP efficiency, supporting the Taiwan Navy repair missions, and satisfying fleet maintenance and servicing demands. The results indicated that total 6925 requests for coordination and procurement were submitted. Of these requests, 4366 requests had been completed (with total 102 cases), and the CCP efficiency is 63.0%. After improvement by this study, a total of 4529 items were submitted and 3592 executed items were completed (with a total of 172 cases), and the CCP efficiency is 79.3%. The improvement percentage of the CCP efficiency and completed cases are 30.6% and 68.6%, respectively. The performances are good and the TRIZ could be applied for other military forces.

Assessment of the commercial viability of selected options for on-orbit servicing (OOS)

The aim of this paper is to determine the commercial viability of on-orbit servicing of communications satellites in geostationary orbit. Previous studies have shown the technical feasibility of servicing as well as the financial viability of some missions, in particular refuelling, therefore this paper analyses these repair missions and life extension missions. A simple parametric model for simulating communications satellite revenue streams is developed and the results are used to determine the maximum possible revenue for a servicing satellite operator. From this, the maximum cost of the servicing satellite as a proportion of the cost of the communications satellite is determined under three profit scenarios representing zero profit, acceptable profit to an operator in a mature industry and acceptable profit to an operator in an emerging industry. The results show that while servicing is financially viable (zero profit scenario), those missions which result in an increase in Comsat life which is a multiple of the mission duration are more likely to be commercially viable. Refuelling is therefore viable in all cases but life extension in most cases is only marginally viable. Repair missions to satellites which are partially operable are also unlikely to deliver sufficient value to justify carrying out servicing. Also the timing of a servicing mission in relation to the expected remaining life expectancy is a major factor in determining the mission׳s viability.

Neues Instandhaltungsfahrzeug für Oberleitungsanlagen

The distinct focus of this vehicle is fault intervention, in particular for carrying out rapid repair missions after contact wires and catenaries have been damaged. The four-axle bogie vehicle is powered by a diesel hydraulic drive and can reach a maximum velocity of 140 km/ h. It has two driver's cabs with two seats each. In addition, there is a well-insulated staff room with a fully equipped kitchenette and dining table, a wet room with toilet and hand basin and, most importantly, a generously laid out work and storage room. The approx. 20 m long roof is fully walkable. There is a working platform on both the left and right of the roof hatch, for access from the workshop area. These platforms enable work up to 21 m above and 9 m below head of rail. In addition, there are two hydraulic pushing devices for the messenger and catenary wire as well as a pantograph on.

The Hubble Wars by Eric Chaisson

TECHNOLOGY AND CULTURE Book Reviews 435 Similarly, Sagan makes some telling observations about the social reasons for the unique safety record of nuclear weapons technology. For instance, people in positions of power would be much more di­ rectly affected by accidental thermonuclear war than by other kinds of accidents. The chief executive officer of Exxon did not get tar in his house or on his person as a consequence of the Valdez accident. Quality of life for the president of the United States, however, would be severely affected by nuclear war. In the end, Sagan concludes that careful examination of these his­ torical examples has led him to find the normal accidents theory more convincing. While I find his research impressive and his ideas suggestive, as a historian I am deeply doubtful about the enterprise as a whole. Essentially, Sagan is using social science tools of predictive and prescriptive modeling to postulate a counterfactual past. As a political scientist using historical case studies, Sagan is caught between the demands of two disciplines. Arwen Mohun Dr. Mohun is an assistant professor in the Department of History at the University of Delaware. She was coorganizer, with Julie Johnson, of a conference at the Hagley Museum and Library on “Danger, Risk, and Safety: Ideas and Practices.” The Hubble Wars. By Eric Chaisson. New York: HarperCollins, 1994. Pp. xi + 386; illustrations, bibliography, index. $27.50. Eric Chaisson, former senior project scientist at the Space Tele­ scope Science Institute—the National Aeronautics and Space Admin­ istration (NASA)-funded body that interprets the Hubble’s data— has written a superb (though at times slightly rhetorical) account of the horrific labor pains astronomy’s most expensive instrument un­ derwent over the decade it took to place it in orbit. Although it is the Hubble Space Telescope (HST) that is studied here, no one can read this book and not feel somewhat depressed about the prospects for Big Science in general if the crushing political baggage and puerile internecine turf wars of the Hubble are any indication of project procedure. If the book has a central thesis, it is surely that securing funding for megascience in the United States requires the consensus of so many regions, interests, and institutions that the resulting struc­ ture is monstrous: a hydra of differing, insular, and noncommunicat­ ing cultures, disciplinary identities, and plain big egos. How should the public respond, for example, except with incredu­ lity, when learning that none of the Hubble’s principal investigators would allow press photos of objects from “their part” of the sky for fear someone in the astronomical community might scoop them? Or that most of the technical problems the HST experienced had long been solved by its own contractor, Lockheed, for the Department of Defense’s Keyhole spy satellite program (some would call the HST 436 Book Reviews TECHNOLOGY AND CULTURE just a Keyhole pointing the other way) but “national security” reasons were used for not sharing information with the HST designers? The Hubble’s flexible solar panels—donated by the European Space Agency and thus inviolate politically—actually flapped in space, im­ parting to the Hubble a periodic oscillation which then had to be removed electronically, at some cost to the instrument’s usefulness. Yet another installment for not-so-great-moments in engineering: the HST’s protective lid, when triggered, slams down like a kitchen gar­ bage pail so hard it disrupts the entire telescope. Perkin-Elmer, contractor for the Hubble’s main mirror, skipped the “thermal-vacuum” test, the preeminent final environmental thrashing all spacecraft typically undergo prior to launch, for “cost­ saving reasons.” Yet if one reads between the lines, one surmises that this decision meshes well with NASA’s desperate search for some­ thing to do with the space shuttle—use it for repair missions. After languishing in warehouses year after year, instruments were hope­ lessly out of date by launch time. “Second-generation” instruments, NASA claimed, would be installed on future shuttle flights, taking the heat off NASA for installing (among other things) the equivalent of a Commodore 64 as the Hubble’s central computer, and in the process giving the shuttle a reason to live. In fact, the...