On Orbit Refueling Repositioning

Welcome to the 3OORR - On Orbit Refueling and Repositioning technology roadmap page.

Our designator 3OORR denotes this is a "level 3" technology decomposition, providing analysis to the on-orbit refueling and repositioning subsystem level. This product is intended to be an iterative document that will be updated when new data becomes available.

Roadmap Overview

On-orbit refueling and repositioning (OOR) is rooted in the need to alter spacecraft and their orbital parameters after launch. Dating back to applications for the Russian Mir Space Station and early uses for the International Space Station (ISS), OOR has taken many forms during the space age. Recent interest in the need to refuel and reposition satellites for reasons ranging from adhering to deorbit laws to wanting to extend functional satellite lifetimes has increased the need to understand OOR and predict its maturation. To this end, this technology roadmap (TRM) focuses on the capability to refuel and reposition satellite systems in orbit. This roadmap considers both traditional systems (e.g. space station resupply missions including astronaut support) as well as modernized methods (e.g. autonomous/robotic refueling operations). To carry out this analysis, a level 1 roadmap of the OOR global marketplace is captured, allowing a level 2 analysis of specific OOR products and services, which is complemented by a level 3 decomposition of OOR subsystems and components.

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DSM Allocation (Interdependencies With Others Roadmaps)

When attempting to roadmap any technology, it is highly beneficial to map interdependencies of other roadmaps and related technologies. This approach educates the architects on the system and subsystem components while also informing viewers of strong dependencies, technology pushers and pullers, and items that may have the strongest benefit to performance if improved. To this end, a DSM of OOR satellite systems is shown to the right. Items noted on the rows are denoted as providing an output (fulfilling a dependency), while items in the vertical columns receive an input from the associated row (requiring a dependency). This approach to graphically representing their dependencies and relationships within the system allows an easier understanding of regions of high overlap as well as technologies that are isolated. The tiers of this analysis are broken down into the following categories:

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Tier 1: OOR System

Tier 2: OOR Subsystem Components

Tier 3: OOR Corresponding Subcomponents of All Tier 2 Items

Upon viewing the results shown in the DSM diagram, there are multiple notable insights gained:

Client Satellite Needs Can Highlight Key Stakeholder Needs

Client satellites are one of the largest technology “pullers” in the DSM, highlighting their representation of stakeholder's needs and potential impact in advancing the receptivity and compatibility of client systems

Command & Control is a Technology Pusher & Puller

Command and control (C2) of systems, for both launch vehicle and satellite systems, are a dominant reliance within the system (red boxes). C2 serves as both a strong technology pusher as well as a puller, highlighting the potential impact on OOR capabilities if advancements are seen in C2 capabilities/technologies

Client-Servicer Satellite Compatibility is a Key Characteristic

The compatibility of refueler/servicer and client satellite systems (yellow box) is a strong dependency that will likely require coordination and standardization to sustain improved technology development and maturation

Human vs. Robotic Functions Both Have Pros & Cons

The transition from astronauts to autonomous/robotic systems transfers dependencies, further increasing C2 needs while reducing the risk of life/limb, and likely reducing overall mission cost

Using the knowledge gained from generating this DSM, the authors believe advancements in the following related technologies will have great benefit to the maturation of OOR systems:

• Launch Vehicle Technology

• C2 Capabilities

• Satellite Autonomous Functions

• Space Robotics

• Remote Proximity Operations (RPO)

• Standardized Docking Interfaces

Harnessing the knowledge gained from this DSM and the above technological areas of potential high impact, this information can be used to inform our search for patents, prototypes, designs, and competition in the OOR tradespace. This honed research will aid in informing later steps of this technology roadmap. Next and more directly, the results of this DSM are modeled in OPM to create an OPM diagram of OOR, allowing us to relate dependencies to the form, function, flow, and make-up of OOR systems.

Roadmap Model Using OPM (ISO 19450)

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The next step in the TRM process is to build a better understanding of the functional flow, form, relationships, and interactions between the critical components of an OOR system. To achieve this, an OPM diagram of On-Orbit Refueling was generated using OPCloud. Again, through the use of a pictorial representation of our system, we can more easily see some of the defining characteristics of our system:

Limited Physical Items in the System

One fundamental takeaway from this diagram is that there are limited physical aspects within the system, including the two satellites, operational ground stations, and the launch vehicle (which is outside the boundary of the system but still affects it). The complexity of the servicing and client satellite systems is emphasized here.

FOMs are Ommitted but Tied to Functions (Blue Circles)

Notably, the Figures of Merit (FOMs) were not included in this diagram and instead are covered in the next section of this webpage. That said, the intent behind the FOMs is captured through the functionality provided by the blue circles in the OPM diagram.

Client-Servicer Compatibility is a Key Consideration

The traceability of key functions in this OPM diagram draws attention to the docking, interfacing, and overall compatibility of the servicer and client satellite systems.

The functional takeaway from this figure is that refueling is the action being completed, which transits and transfers fuel from the servicer satellite to the client satellite. This fulfills the need to refuel/reposition the client satellite so that it may maneuver for a longer period of time (fixing the problem of not being able to maneuver without additional fuel). Items that are in dashed boxes still impact the system under consideration but are considered outside the scope/boundary of the system itself. It is powerful to provide traceability between the DSM and OPM diagram approaches, as we see in this technology. The combined importance of servicer and client compatibility, seen in both the dependencies of the DSM and the operational flow of the OPM diagram, further emphasizes the importance of mating, docking, and satellite compatibility as an enabler for broader OOR advancement. The exclusion of "developing & manufacturing", "launch vehicle", and "launching", from the system boundary was made to ensure that the technological considerations are rooted in OOR advancements. That considered, the authors also note that advancements in launch technology directly impact the potential benefits and capability space of OOR, and should be closely tracked to determine cost and performance implications.

Figures of Merit (FOM)

To qualitatively track the technological progression of OOR, it is necessary to select metrics that can capture the progression rate of specific technological characteristics. Looking at the figures of merit selected for OOS, figures were chosen to track the technology's progression over time that captured stakeholder needs, used quantifiable engineering metrics, and were derived from available data. The table below displays the selected FOMs for OOR and descriptions of each figure, with more detailed descriptions and intent of each provided after the table.

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FOM Generation Background/Intent

(Refueling Cost / KG Fuel Delivered)

The selection of this metric is considered a fundamental quantitive metric for tracking the cost associated with the potential benefits of refueling satellites on orbit. "Cost" in this context includes two potentially different values depending upon the type of program being considered. For commercial services, the price charged/advertised to customers per kg of fuel delivered is directly used for the value. For Research & Development (R&D) missions, the total mission cost was used as the monetary value, divided by the toal mass of fuel transferred to customer satellites. This figure aids in determining the market interest in services as well as the advancement in manufacturing and providing refueling, where lower values assume companies are able to provide the service at a profit by harnessing advancements in technology.

(% Customer Lifetime Extension)

This metric is a notable deviation from other approaches to capturing OOR value, which commonly harness fuel transferred (in KG). Although a KG of fuel metric can be beneficial and should still be tracked, the authors elected to harness a more holistic value to capture differences in fuel types and thrusters (e.g. chemical vs. electric propulsion), satellite sizes, and intended lifecycle use. By capturing the percentage that a customer's satellite lifetime is extended, the total mass transferred to customer satellites can be captured in a more informative manner. Lifetime extension percentages can grow well over 100% if a satellite is refueled or repositioned multiple times, with that value being captured via the percentage and not simply a kg value of fuel.

(Fuel-Mass-Ratio of Servicing Satellite)

To capture the advancements made in space refueling technology as well as the intent to "optimize" refueling satellite systems, the ratio of servicer satellite fuel (in KG) to the total servicer satellite mass (in KG) was tracked and compared. This ratio highlights missions that are experimental in nature or those that have multiple intended objectives for a single satellite. By highlighting these missions, they can be independently considered for inclusion or omission, allowing a honed focus on OOR missions with intentions of advancing the state-of-the-art in OOR or maximizing fuel transferred on orbit. This metric approach allows an engineering-backed filtering of OOR space missions, believed to be more accurate at tracking and predicting OOR technology maturation.

(Mean Fuel Transfer Rate)

By tracking the mean time to transfer fuel between a client and servicer satellite, real-world considerations can be captured in the use of OOR systems. With this time including docking and fuel transfer, systems that are incompatible can be highlighted as well as those with designed direct compatibility. This means of tracking also allows TRM architects to potentially track the progression rate of standardized adapter solutions in OOR, an item of active discussion in the community.

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Capturing Client & Servicer Needs

With this technology having a unique consideration of capturing both a product as well as a service that is needed (in the form of the technology), the authors elected to analyze and track the traceability of qualities needed, how the FOMs are informed, and which stakeholder needs are identified for the technology. This level of traceability allows us to ensure stakeholder requirements are met, that we properly capture the product-service relationship, and that the FOMs created harness executable and available data and metrics. The figure to the right displays these interactions and draws focus to some key considerations in the development of our FOMs for OOR:

• In a product-service-focused technology, client, servicer, and shared needs must be considered

• Metric traceability from client and servicer systems to FOMs (right side of figure) has the potential to concurrently root FOMs into two separate yet intertwined stakeholders

• Metric traceability from FOMs to identified stakeholder needs (left side of the figure) may increase confidence that stakeholder needs are captured, addressed, and tradable to quantifiable values

Applying this approach to OOR, we see that client-related items (blue), servicer-related items (green), and shared items (orange), can be easily tracked to determine the inputs and outputs of each FOM. Having identified the metrics necessary to comprise each FOM and traced them to stakeholder needs, it was possible to generate mathematical models for each FOM. With these metrics founded in direct measurements from operations, engineering designs, or requiring introductory orbital mechanics calculations, the need to generate complex models to gather critical data was limited. To further validate this approach, traditional-focused FOMs (e.g. total kg fuel transferred) will be tracked in parallel with the proposed FOMs to inform a comparative view of the results. Next, the development of mathematical models and bounding of input variables for FOM modeling was necessary.

Capturing FOMs Mathematically

The table below shows units and nominal values that the authors propose to track the technology progression over time using engineering-based data. Upon searching available literature for the required data and direct FOMs, some were easily located, while others were limited in availability. Sources used to generate nominal values and value ranges are noted in the citation column, drawing attention to real-world missions or near-term prototypes. Of the selected FOMs, the Fuel Mass Ratio was easiest to quantify, while the Mean Refuel Rate proved to be the most difficult, with total refueling time for historic missions difficult to locate for multiple satellites. Even with this being the case, the authors will continue to explore this metric and attempt to capture more data in this area.

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Example In-Depth Exploration of a FOM

To gather data, multiple online sources, including databases, news articles, FCC filings, and user manuals were used. Citations [5-43] were used to gather this data. The figure below (left) shows all unfiltered data found on satellite refuelers and related technology demonstrations for fuel-mass-ratios of refueling satellites. Mission dates range from 1978 to future missions in 2025. For satellites in the future, projected or advertised values were used to generate their fuel-mass-ratio values. It is also important to note that for three of the data points, calculations of fuel onboard were completed to gather the required data point. Due to the competitive landscape of on-orbit refueling, some companies limit the publicly available data to alternative metrics (e.g. lifetime extension time) that require calculation of fuel mass. These calculations were completed for the MEV-1 and MEP systems. For ease of viewing, a vertical dashed black line is included in the figures below to highlight the current day. Once the data was fully generated and plotted, a line-fit was applied to attempt to find a mathematical/quantitative rate of improvement. We see that in the left figure, a linear fit provided a mathematical prediction but is somewhat poor in overall fit with an R-squared value of 0.1 (with a third-order polynomial having an R-squared value of 0.4). To overcome this limitation, it was necessary to filter the data points to those that are most valid for the analysis.

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When selecting which data points were valid, it was necessary to track which satellites were considered state-of-the-art while also having the sole intent of transferring maximal amounts of fuel. With some of the satellites developed as prototypes to prove specific aspects of refueling in orbit, they were not built with the intent of maximizing fuel transferred, as would be the case in a fully functioning system. To account for this, any satellite that was not focused on fuel transfer or advancing the state-of-the-art in refueling was removed from the analysis to provide a more accurate view of technology trending, as seen in the above right figure. Looking at the progression trend of the filtered data, we find that a third-order polynomial line fit is moderately effective at capturing the technology advancement, with an R-squared value of 0.78. This type of line fit also better informs where the technology is likely in its maturation phase. With the FOM stagnating from 1978 to the mid-2000’s, we see a notable increase in capability in the current day as well as the near-term projected future. Bounding this within the theoretical limit (discussed later), this leads us to believe that on-orbit refueling is in the innovators / early adopters phase of its lifecycle adoption, as covered in the class lecture (early lifecycle). Using a plot similar to those described in Lecture 7 (Technological Diffusion and Disruption), on the technology capability S-curve, we assert that on-orbit refueling is somewhere within the green box in the figure to the right.

File:OOR Picture8.png

The curve parameters are highlighted by a shallow increase in capability in its early lifecycle (during the first golden ages of space, later leading to MIR and the ISS), followed by a dramatic jump in capability that the authors believe current-day shows to be the initial stages of large capability jumps. Stagnation of the technology development occurs when vast improvements have been made in tertiary sciences (e.g. materials science), allowing subtle improvements to OOR satellite performance. With on-orbit refueling offering significant capabilities but also introducing significant risk to satellite systems, the authors believe there is a need to validate and test out OOR capabilities before they will be widely adopted. This phenomenon will likely result in a dramatic technological improvement that leads to an increased adoption rate of the technology. It is important to note that although this one FOM shows a steep increase in performance, other FOM preliminary results show somewhat similar advancement in trends.

The final aspect of the fuel-mass-ratio plots is the theoretical limit imposed by the system on the FOM. Considering that a higher fuel-mass ratio is better for the system, this value will likely continue to improve over time but is limited by the design of satellite systems. Advancements in material sciences can make satellite components smaller and/or lighter, but there will always be a need for satellite subsystems, including structures, fuel tanks, thrusters, communications systems, etc. These systems require a portion of the mass budget on a satellite system. To account for potential advancements in space systems and related materials sciences, this theoretical limit was placed at 95% of the satellite mass (meaning 95% of the satellite mass could be fuel). Any ratio beyond this is thought to be impossible due to the mass needs of the other satellite subsystems for a fully functioning refueling system.

References

[1] Orbit Fab | Spacecraft Refueling. (n.d.). Retrieved September 17, 2023, from https://www.orbitfab.com/

[2] Refuel in Orbit, 22,000 Miles Above Earth, with Orbit Fab Gas Stations. (n.d.). Retrieved September 17, 2023, from https://www.linkedin.com/pulse/refuel-orbit-22000-miles-above-earth-fab-gas-stations-christopher-u-

[3] GPS Block IIF – Spacecraft & Satellites. (n.d.). Retrieved September 17, 2023, from https://spaceflight101.com/spacecraft/gps-block-iif/

[4] Robotic Refueling Mission | NASA’s Exploration & In-space Services. (n.d.). Retrieved September 17, 2023, from https://nexis.gsfc.nasa.gov/robotic_refueling_mission.html

Citations [5] - [43] were used to gather the required data for the FOM trending plot

[5] Hall, Rex D.; Shayler, David J. (2003). Soyuz: A Universal Spacecraft. Springer-Praxis. p. 272. ISBN 1-85233-657-9

[6] Progress 1 - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Progress_1

[7] 35 Years Ago: STS-41G – A Flight of Many Firsts - NASA. (n.d.). Retrieved October 6, 2023, from https://www.nasa.gov/history/35-years-ago-sts-41g-a-flight-of-many-firsts/

[8] Orbital Refueling System (ORS) - Google Books. (n.d.). Retrieved October 6, 2023, from https://books.google.com/books?id=DvV2Cghvkm8C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

[9] Landsat-4 and Landsat-5 - Earth Online. (n.d.). Retrieved October 6, 2023, from https://earth.esa.int/eogateway/missions/landsat-4-and-landsat-5#instruments-section

[10] Landsat-4 and 5 - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/satellite-missions/landsat-4-5#spacecraft

[11] Krebs, Gunter D. “Progress-M1 1 - 11 (11F615A55, 7K-TGM1)”. Gunter's Space Page. Retrieved October 07, 2023, from https://space.skyrocket.de/doc_sdat/progress-m1.htm

[12] Progress (spacecraft) - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Progress_(spacecraft)

[13] Krebs, Gunter D. “Progress-M 1M - 29M (11F615A60, 7KTGM)”. Gunter's Space Page. Retrieved October 07, 2023, from https://space.skyrocket.de/doc_sdat/progress-m-m.htm

[14] Progress (spacecraft) - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Progress_(spacecraft)

[15] STP-1 - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/satellite-missions/stp-1#astro-autonomous-space-transfer-and-robotic-orbiter-of-oe

[16] U.S. Air Force to End Orbital Express Mission | Space. (n.d.). Retrieved October 7, 2023, from https://www.space.com/4018-air-force-orbital-express-mission.html#

[17] ESA - Europe’s automated ship docks to the ISS. (n.d.). Retrieved October 6, 2023, from https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/ATV/Europe_s_automated_ship_docks_to_the_ISS

[18] Jules Verne ATV - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Jules_Verne_ATV#cite_note-ESA_Docking-17 Huge Cargo Ship Arrives at Space Station Ahead of Shuttle Discovery | Space. (n.d.). Retrieved October 6, 2023, from https://www.space.com/10939-cargo-ship-docks-space-station-discovery.html

[19] Johannes Kepler ATV - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Johannes_Kepler_ATV

[20] Europe’s New Space Rocket Is Incredibly Expensive | The Motley Fool. (n.d.). Retrieved October 7, 2023, from https://www.fool.com/investing/2020/11/10/europe-space-rocket-incredibly-expensive-airbus/

[21] Spaceflight Now | Breaking News | Space station partners assess logistics needs beyond 2015. (n.d.). Retrieved October 7, 2023, from https://spaceflightnow.com/news/n0912/01atvhtv/

[22] Robotic Refueling Mission | NASA’s Exploration & In-space Services. (n.d.). Retrieved October 6, 2023, from https://nexis.gsfc.nasa.gov/robotic_refueling_mission.html

[23] Krebs, Gunter D. “Progress-MS 01 – 40” Gunter's Space Page. Retrieved October 08, 2023, from https://space.skyrocket.de/doc_sdat/progress-ms.htm

[24] Progress (spacecraft) - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Progress_(spacecraft)

[25] ISS: RRM3 (Robotic Refueling Mission 3) - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/other-space-activities/iss-rrm3#mission-status

[26] Krenn, A., Stewart, M., Mitchell, D., Dixon, K., Mierzwa, M., & Breon, S. (n.d.). Flight servicing of Robotic Refueling Mission 3.

[27] ISS: SpaceX CRS-16 (International Space Station: SpaceX Commercial Resupply Service -16 Mission) - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/satellite-missions/iss-crs-16#iss-spacex-crs-16-international-space-station-spacex-commercial-resupply-service--16-mission---iss-utilization

Total mass of satellite was derived from total payload minus other experiment masses

[28] MEV-1 & 2 (Mission Extension Vehicle-1 and -2) - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/satellite-missions/mev-1#spacecraft

[29] Anderson, J. (n.d.). Technical Appendix (MEV-2 FCC Application for Authority to Launch). FCC. https://fcc.report/IBFS/SAT-LOA-20191210-00144/2098823.pdf

[30] Another MEV Rescue Mission - BusinessCom Networks. (n.d.). Retrieved October 7, 2023, from https://www.bcsatellite.net/blog/another-mev-rescue-mission/#

Same mass ratio from MEV-2 was used for MEV-1

[31] MEV-1 & 2 (Mission Extension Vehicle-1 and -2) - eoPortal. (n.d.). Retrieved October 6, 2023, from https://www.eoportal.org/satellite-missions/mev-1#spacecraft

[32] Anderson, J. (n.d.). Technical Appendix (MEV-2 FCC Application for Authority to Launch). FCC. https://fcc.report/IBFS/SAT-LOA-20191210-00144/2098823.pdf

[33] China’s Tianzhou-2 cargo spacecraft docks with space station core module at record-breaking speed, delivers supply for upcoming crewed flight mission - Global Times. (n.d.). Retrieved October 6, 2023, from https://www.globaltimes.cn/page/202105/1224902.shtml

[34] ELSA-d CONOPS and Debris Mitigation Overview. (n.d.). Retrieved October 6, 2023, from https://sa.catapult.org.uk/. https://fcc.report/IBFS/SES-STA-INTR2020-00086/2166969.pdf

[35] Otter Pup Satellite Technical Description. (n.d.). https://apps.fcc.gov/els/GetAtt.html?id=311144&x=

[36] Orbit Fab to launch propellant tanker to fuel satellites in geostationary orbit - SpaceNews. (n.d.). Retrieved October 6, 2023, from https://spacenews.com/orbit-fab-to-launch-propellant-tanker-to-fuel-satellites-in-geostationary-orbit/

[37] SpaceLogistics Announces Launch Agreement with SpaceX and First Mission Extension Pod Contract with Optus | Northrop Grumman. (n.d.). Retrieved October 6, 2023, from https://news.northropgrumman.com/news/releases/spacelogistics-announces-launch-agreement-with-spacex-and-first-mission-extension-pod-contract-with-optus

[38] Orbital station-keeping - Wikipedia. (n.d.). Retrieved October 6, 2023, from https://en.wikipedia.org/wiki/Orbital_station-keeping

[39] End-of-Life Disposal of Satellites in Geosynchronous Altitude. (2010). https://apps.dtic.mil/sti/pdfs/ADA633333.pdf

Backing out fuel figure using 6 year mission extension in GEO for 2000kg satellite with ISP = 300 sec needing 45m/sec per year of station keeping

[40] OSAM-1 Decommissioning Orbit Design. (n.d.). Retrieved October 6, 2023, from https://www.researchgate.net/publication/343587900_OSAM-1_Decommissioning_Orbit_Design

[41] This Satellite Tow Truck Could Be the Start of a Multibillion-Dollar Business | Air & Space Magazine| Smithsonian Magazine. (n.d.). Retrieved October 6, 2023, from https://www.smithsonianmag.com/air-space-magazine/satellite-rescue-180975337/

[42] Fill ’er up - Aerospace America. (n.d.). Retrieved October 6, 2023, from https://aerospaceamerica.aiaa.org/features/filler-up/

[43] LEO Refueling of Electron/Photon for High-Performance Interplanetary Smallsat Missions. (n.d.). http://www.intersmallsatconference.com/past/2021/E.5%20-%20French/Rocket%20Lab%20-%20ISSC%20Presentation.pdf

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