Concepts
Cross-cutting material: a subject that is not one machine, one component, one facility or one destination, and that would otherwise be restated on every page it bears on. Two subjects are covered so far, the environment definitions hardware is designed against and the tether as a mechanical, electrical and data element.
Environment references
Section titled “Environment references”Environment references collects the documents hardware is designed against rather than measured by. The Cross-Program Design Specification for Natural Environments converts environment models into the design values a US deep space program’s requirements inherit [1]. Its 2017 revision leaves the lunar surface chapter reserved, so surface values come from a later revision or from the Lunar Sourcebook, the Apollo-derived synthesis of regolith, geology and surface conditions written for engineers [1][2]. The page also lists the Global Reference Atmospheric Model series for Mars, Venus, Titan and the giant planets, and the galactic cosmic ray and orbital debris models behind shielding mass. The destinations as measured are under Environments.
Tethers
Section titled “Tethers”Tethers is here because a tether belongs to no single vehicle class. The families on the page differ in what the tether has to do.
- Rappelling and tethered rovers use the line to carry the vehicle’s weight, power and data at once. Surveys of tethered robots for extreme planetary terrain cover pit walls, ice deposits, tether-deployed antennas and descending probes [3]. Tether management for a rappelling rover has been bench-tested with a series elastic capstan [4], and a shape-sensing fiber has been built into a rover tether to read tension and curvature [5]. These are laboratory and field-test results; none has flown.
- Surface power tethers move kilowatts over kilometers. A high voltage architecture for the lunar surface set the requirements [6], and the qualification of one such tether recorded a breaking force of 7219 N over a gentle bend at -190 C and 990 N over a 78 degree knife edge at +200 C, page 6 [7]. The test was ground-based, on single specimens.
- Orbital tethers carry momentum or a captured object. A 1985 guidebook gives the first-order tools for orbit mechanics, dynamics and strength-to-mass tradeoffs [8]. Later work covers tether tension for attitude control of a tumbling captured target [9] and the contact mechanics of debris removal [10]. Air-bearing simulators in a ground laboratory stand in for the orbital case [11].
What governs the surface tethers is breaking force at the bend and temperature actually encountered rather than a single rating, and the design tool that predicted strength overestimated it while the vendor’s bend radius was conservative [7].
What is not established
Section titled “What is not established”No orbital tether result is held here from flight; the orbital entries are analysis or laboratory simulation [8][9][11]. Surface tether strength rests on one design and single pulls, and vacuum, dust adhesion and thermal cycling were not tested together [7]. The environment page inherits the gaps of its sources: the lunar surface chapter of the 2017 specification is empty and the Lunar Sourcebook predates polar volatiles work [1][2].
Where other pages belong
Section titled “Where other pages belong”A page belongs here when its subject spans destinations and vehicle classes. A part with a published flight or qualification result belongs on Avionics, something that runs on a processor on Software, a laboratory on test facilities, and a destination’s own properties on Environments.
References
- Roberts, B. C. (2017). SLS-SPEC-159 Cross-Program Design Specification for Natural Environments (DSNE) Revision E
. NASA Marshall Space Flight Center. Source
BibTeX
@techreport{nasa2017sls, title = {SLS-SPEC-159 Cross-Program Design Specification for Natural Environments (DSNE) Revision E}, author = {Roberts, Barry C.}, institution = {NASA Marshall Space Flight Center}, year = {2017}, url = {https://ntrs.nasa.gov/citations/20170008140}, abstract = {The DSNE completes environment-related specifications for architecture, system-level, and lower-tier documents by specifying the ranges of environmental conditions that must be accounted for by NASA ESD Programs. To assure clarity and consistency, and to prevent requirements documents from becoming cluttered with extensive amounts of technical material, natural environment specifications have been compiled into this document. The intent is to keep a unified specification for natural environments that each Program calls out for appropriate application. This document defines the natural environments parameter limits (maximum and minimum values, energy spectra, or precise model inputs, assumptions, model options, etc.), for all ESD Programs. These environments are developed by the NASA Marshall Space Flight Center (MSFC) Natural Environments Branch (MSFC organization code: EV44). Many of the parameter limits are based on experience with previous programs, such as the Space Shuttle Program. The parameter limits contain no margin and are meant to be evaluated individually to ensure they are reasonable (i.e., do not apply unrealistic extreme-on-extreme conditions). The natural environments specifications in this document should be accounted for by robust design of the flight vehicle and support systems. However, it is understood that in some cases the Programs will find it more effective to account for portions of the environment ranges by operational mitigation or acceptance of risk in accordance with an appropriate program risk management plan and/or hazard analysis process. The DSNE is not intended as a definition of operational models or operational constraints, nor is it adequate, alone, for ground facilities which may have additional requirements (for example, building codes and local environmental constraints). "Natural environments," as the term is used here, refers to the environments that are not the result of intended human activity or intervention. It consists of a variety of external environmental factors (most of natural origin and a few of human origin) which impose restrictions or otherwise impact the development or operation of flight vehicles and destination surface systems.} } - Heiken, G. H., Vaniman, D. T. and French, B. M. (1991). Lunar Sourcebook: A User's Guide to the Moon
. Endeavour. Source
BibTeX
@book{heiken1991lunar, title = {Lunar Sourcebook: A User's Guide to the Moon}, author = {Heiken, Grant H. and Vaniman, David T. and French, Bevan M.}, journal = {Endeavour}, volume = {16}, pages = {96}, publisher = {Cambridge University Press}, year = {1991}, doi = {10.1016/0160-9327(92)90014-g} } - McGarey, P. (2021). Fit to be Tied: Embracing Tethered Robots for Exploring Extreme Planetary Environments
. International Conference on Environmental Systems. Source
BibTeX
@inproceedings{mcgarey2021fit, title = {Fit to be Tied: Embracing Tethered Robots for Exploring Extreme Planetary Environments}, author = {McGarey, Patrick}, booktitle = {International Conference on Environmental Systems}, publisher = {JPL Open Repository}, year = {2021}, url = {https://dataverse.jpl.nasa.gov/dataset.xhtml?persistentId=hdl:2014/55957} } - Brown, T., Stefanini, A., Georgiev, N., Sawoniewicz, J. and Nesnas, I. (2018). Series Elastic Tether Management for Rappelling Rovers
. IEEE/RSJ International Conference on Intelligent Robots and Systems. Source
BibTeX
@inproceedings{brown2018series, title = {Series Elastic Tether Management for Rappelling Rovers}, author = {Brown, Travis and Stefanini, Alessandro and Georgiev, Nikola and Sawoniewicz, Jacek and Nesnas, Issa}, booktitle = {IEEE/RSJ International Conference on Intelligent Robots and Systems}, pages = {2893-2900}, publisher = {IEEE}, year = {2018}, doi = {10.1109/iros.2018.8594134}, abstract = {The Axel rappelling rover was designed to enable access to intriguing and important science sites that lie in difficult terrains that are inaccessible to conventional rovers. Extended autonomous rappelling calls for careful control of tether tension, precise management of tether spooling, and some measure of shock tolerance. This paper covers the design and testing of a first-generation tether management system (TMS) for Axel. The system uses a double bull-wheel capstan driven by a low-stiffness series elastic actuator (SEA) to provide tension control and decouple internal spooling tension from external tether tension. A series elastic actuator was chosen for this application to permit closed-loop tether tension control and to provide shock/drop tolerance of the rappelling system both while moving and when the system is inactive with the motors locked. Experiments on the new TMS show that this design performs well in keeping nearly constant spooling tension while rejecting large dynamic disturbances at the output. While the SEA is very effective at maintaining a given tension contribution, the additional effects of friction and the unique mechanical properties of the tether result in substantial errors in the measured output tension. Upcoming field trials will be used to evaluate the effectiveness and sufficiency of this system when integrated in Axel.} } - Brown, T., Nesnas, I., Templeton, E. and Kominsky, D. (2018). A Novel Sensing Tether for Rovers
. AIAA Aerospace Sciences Meeting. Source
BibTeX
@inproceedings{brown2018novel, title = {A Novel Sensing Tether for Rovers}, author = {Brown, Travis and Nesnas, Issa and Templeton, Emily and Kominsky, Daniel}, booktitle = {AIAA Aerospace Sciences Meeting}, publisher = {American Institute of Aeronautics and Astronautics}, year = {2018}, doi = {10.2514/6.2018-1534} } - Barchowsky, A., Amirahmadi, A., Botteon, K., Carr, G., Jin, C., McGarey, P., Sposato, S. and Yang, S. (2022). A High Voltage Tethered Power System for Planetary Surface Applications
. IEEE Aerospace Conference. Source
BibTeX
@inproceedings{barchowsky2022high, title = {A High Voltage Tethered Power System for Planetary Surface Applications}, author = {Barchowsky, Ansel and Amirahmadi, Ahmadreza and Botteon, Kyle and Carr, Gregory and Jin, Curtis and McGarey, Patrick and Sposato, Shelly and Yang, Summer}, booktitle = {IEEE Aerospace Conference}, pages = {1-8}, publisher = {IEEE}, year = {2022}, doi = {10.1109/aero53065.2022.9843731}, abstract = {In the pursuit of human and robotic expansion of the Lunar surface and other planetary bodies, power conversion and transmission over long distances has emerged as a distinct need. The ability to transmit power over kilometers at high efficiency enables human settlement, in-situ resource utilization, and extreme terrain robotic exploration, through the ability to reach previously unreachable places. The critical building blocks of such a system are being developed by the Tethered Power System for Lunar Mobility and Power Transmission (TYMPO) project, a NASA project aimed at reaching flight readiness by 2024. This paper presents an architectural and requirements overview of the TYMPO project, along with technology discussions on the GaN-based multilevel DCX converters, dual fiber optics and power-line communications system, and high-voltage tether. Finally, a set of proposed future missions will be presented, mapping the capabilities of the TYMPO system to missions that may soon explore planetary surfaces throughout the solar system.} } - Goddu, A., Jin, C., Caballero, M., Botteon, K., Wright, M., Barchowsky, A. and Brown, T. (2024). TetherCAD: A Python library to aid in the design of Electromechanical Tethers and Tethered Systems for applications in Robotics and Spacecraft
. Mars Exploration Program Analysis Group. Source
BibTeX
@inproceedings{goddu2024tethercad, title = {TetherCAD: A Python library to aid in the design of Electromechanical Tethers and Tethered Systems for applications in Robotics and Spacecraft}, author = {Goddu, Austen and Jin, Curtis and Caballero, Matthew and Botteon, Kyle and Wright, M. and Barchowsky, Ansel and Brown, T.}, booktitle = {Mars Exploration Program Analysis Group}, publisher = {JPL Open Repository}, year = {2024}, doi = {10.48577/jpl.bfesih}, abstract = {Tethered robotics offer unique potential to access and operate in harsh terrain and provide power and communication for exploration and infrastructure on the Moon and Mars. The tether is the lifeline for these systems, allowing robots to access impassable terrain features, maintaining power and communication. Their criticality stipulates that they must be designed to survive the harsh environments, while enduring the mechanical and electrical constraints of the systems which deploy them. Designers must perform complex trades to create tethers for their missions, balancing system performance requirements against mass and volume to create viable tethered robotics systems. This paper discusses TetherCAD: a set of tools to aid in high-level design and performance analysis of tethers. TetherCAD helps users create tether solutions that meet their system's unique needs, incorporating length, voltage, losses, power transfer, communications, tensile strength and minimum bend radius to generate tethers that can be fabricated from standard products and are viable for the Lunar and Martian environments. It presents a tether designed using the tools, along with the results of tensile testing over various bend radii and abrasion testing in vacuum, both over a range of Lunar temperatures.} } - Carroll, J. A. (1985). Guidebook for Analysis of Tether Applications
. NASA, NASA-CR-178903. Source
BibTeX
@techreport{carroll1985guidebook, title = {Guidebook for Analysis of Tether Applications}, author = {Carroll, Joseph A.}, number = {NASA-CR-178903}, institution = {NASA}, year = {1985}, url = {https://ntrs.nasa.gov/citations/19860011337}, abstract = {Engine testing, ceramic component fabrication and evaluation, component performance rig testing, and producibility experiments at Pontiac comprised AGT 100 activities of this period, January to December 1984. Two experimental engines were available and allowed the evaluation of eight experimental assemblies. Operating time accumulated was 115 hr of burning and 156 hr total. Total cumulative engine operating time is now 225 hr. Build number 11 and 12 of engine S/N 1 totaled 28 burning hours and constituted a single assembly of the engine core--the compressor, both turbines, and the gearbox. Build number 11 of engine S/N 1 included a 1:07 hr continuous test at 100% gasifier speed (86,000 rpm). Build number 8 of engine S/N 2 was the first engine test with a ceramic turbine rotor. A mechanical loss test of an engine assembly revealed the actual losses to be near the original design allowance. Component development activity included rig testing of the compressor, combustor, and regenerator. Compressor testing was initiated on a rig modified to control the transfer of heat between flow path, lubricating oil, and structure. Results show successful thermal decoupling of the rig and lubricating/cooling oil. Rig evaluation of a reduced-friction compressor was initiated. Combustor testing covered qualification of ceramic parts for engine use, mapping of operating range limits, and evaluation of a relocated igniter plug. Several seal refinements were tested on the hot regenerator rig. An alternate regenerator disk, extruded MAS, was examined and found to be currently inadequate for the AGT 100 application. Also, a new technique for measuring leakage was explored on the regenerator rig. Ceramic component activity has focused on the development of state-of-the-art material strength characteristics in full-scale hardware. Injection-molded sintered alpha-SiC rotors were produced at Carborundum in an extensive process and tool optimization study.} } - Wang, D., Huang, P. and Meng, Z. (2015). Coordinated stabilization of tumbling targets using tethered space manipulators
. Journal of Raman Spectroscopy, 3. Source
BibTeX
@article{wang2015coordinated, title = {Coordinated stabilization of tumbling targets using tethered space manipulators}, author = {Wang, Dongke and Huang, Panfeng and Meng, Zhongjie}, journal = {Journal of Raman Spectroscopy}, volume = {51}, number = {3}, pages = {2420-2432}, publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, year = {2015}, doi = {10.1109/taes.2015.140530}, abstract = {Tethered space robots (TSR) have wide application prospects in future on-orbit missions such as debris removal. However, it's rather complex and difficult for TSR to realize stabilization of tumbling combinations after target capture. Therefore, this paper addresses a novel control scheme for achieving attitude stabilization by coordination of the tethered space manipulator (TSM), the tether itself, and thrusters accommodated on the base of the TSM. Simulation results validate the feasibility of the attitude control scheme in the postcapture phase.} } - Bigdeli, M., Srivastava, R. and Scaraggi, M. (2025). Mechanics of Space Debris Removal: A Review
. Aerospace, 4. Source
BibTeX
@article{bigdeli2025mechanics, title = {Mechanics of Space Debris Removal: A Review}, author = {Bigdeli, Mohammad and Srivastava, Rajat and Scaraggi, Michele}, journal = {Aerospace}, volume = {12}, number = {4}, pages = {277}, year = {2025}, doi = {10.3390/aerospace12040277}, abstract = {The growing population of space debris poses a critical risk to space operations, requiring urgent removal strategies. Numerous scientific investigations have focused on debris capture mechanisms in Earth’s orbits, including contact and contact-less capturing methods. However, the known debris population exhibits a multiscale distribution with broad statistics concerning size, shape, etc., making any general-purpose removal approach challenging. This review examines the mechanics of debris detection, capture, and mitigation, analyzing contact-based and contactless removal techniques. Special focus is given to net capturing methods and their mechanical limitations.We also aim to provide comprehensive discussion, beginning with an overview of current debris statistics followed by detection and removal methods, by analyzing key mechanical parameters relevant to removal. Therefore, we delve into the key parameters essential for the engineering of novel debris removal technologies. Finally, we discuss the preventive measures, regulative frameworks and future research directions.} } - Jaynes, E., Inness, J., Garg, K., Lee, J. and Putman, A. (2024). Design and Applications of Tethered Spacecraft Simulators
. International Conference on Tethers in Space, 20240005792. Source
BibTeX
@inproceedings{jaynes2024design, title = {Design and Applications of Tethered Spacecraft Simulators}, author = {Jaynes, E. and Inness, J. and Garg, K. and Lee, J. and Putman, A.}, booktitle = {International Conference on Tethers in Space}, number = {20240005792}, institution = {NASA}, address = {Toronto}, year = {2024}, url = {https://ntrs.nasa.gov/citations/20240005792}, abstract = {Small, tethered spacecraft, or space tugs, are a promising space capability. They can be deployed on tethers and used for a wide variety of in-space activities; a large portion of which fall under in-space servicing, assembly, manufacturing (ISAM) functions. This includes functions such as structural mating and assembly, servicing, proximity operations, capture, docking, mating, and relocation. However, there is a great deal of work to be done to raise the Technology Readiness Level (TRL) of the capabilities needed to fully realize these capabilities. The Flat Floor Robotics Lab (FFRL) at NASA’s Marshall Spaceflight Center (MSFC) has been working on space tug development for several years. The eponymous floor is 44 by 86 feet, made from a self-leveling epoxy. This creates an extremely smooth surface that air bearings can float on with very little friction, creating a simulation of zero gravity in a two-dimensional plane. The lab has several platforms of various sizes that act as vehicle simulators for testing sensors, control algorithms, mechanisms, etc. One of these platforms is a small spacecraft simulator, which can be tethered to simulate a space tug. In the last several months, the FFRL team has been working with MSFC’s welding group to conduct a laser beam welding demonstration on air bearing platforms. This demo is utilizing a space tug simulator to fly up to a floating weld platform, where two parts are clamped together and laser welded. The space tug simulator has an air bearing to provide float, as well as several actuated air thrusters to provide propulsion and make the simulator maneuverable. Currently, flights of this simulator are completed by a human operator. An RF hand controller sends signals to both actuate and fire three sets of thrusters on the simulator. This makes any maneuvers of the space tug highly subject to human error, and operators must have dedicated practice time before being able to perform maneuvers with any sufficient reliability. For the current laser welding demonstration, human operated performance is sufficient, but future implementations of in-space welding and other ISAM efforts will require higher precision, reliability, and autonomy. MSFC has funded a project that will allow a small team in the FFRL to develop the next generation of space tug simulator, which will be automated. Closed loop control will allow a user to command a position, or set of positions, that the simulator will be able to “fly” to on its own. This Maneuverable Automated Tethered Spacecraft (MATS) simulator will have configurable design, to allow a variety of payloads and mission configurations to be demonstrated on the air bearing floor. This will be an invaluable test bed for low and mid TRL advancement for space tether mission subsystems, such as more advanced demonstrations of in-space welding. Once one MATSS is constructed and demonstrated effectively, several more can be built, enabling more advanced tether missions; Electric Sail test beds, sensor arrays, and other science-enabling missions. This paper will detail the design and test of the FFRL’s MATS simulator, including efforts to establish closed loop control and autonomous capabilities. It will also detail use cases for this technology, and how it will further develop both develop science and exploration missions} }
Further reading
- Mcgarey, P., Nguyen, T., Pailevanian, T. and Nensas, I. (2020). Design and Test of an Electromechanical Rover Tether for the Exploration of Vertical Lunar Pit . ASME Journal of Mechanisms and Robotics. Source