As the in-space economy continues to expand, the demand for the mission extension of space vehicles and on-orbit repair technologies is growing. The key enablers to meeting these on-orbit demands are the successful execution of Rendezvous, Proximity Operations, and Docking (RPOD) missions and the connectivity and satellite networks that will power their operations.

According to Kevin Stadnyk, CEO of Obruta Space Solutions, RPOD capabilities provide a wide range of critical on-orbit activities that enhance the effectiveness, sustainability, versatility and enablement of space missions.

“The biggest benefit that RPOD brings to space missions is through the servicing and maintenance of satellites,” explained Stadnyk. “ROPD is the act of flying up to, operating around and docking with another space object. Once you have done this you can provide on-orbit services such as inspecting, refueling, repairing, and upgrading satellites. These services can significantly extend the operational life of satellites, reducing the need for new satellite launches and lowering their overall mission costs.”

Jon Beam, CEO of Rogue Space Systems Corporation, also pointed to the emerging need for on-orbit servicing as the primary driver for RPOD. “The largest need for RPOD capabilities will be for in-space logistics,” he explained. “In the near future, a ‘circular economy’ will exist where raw materials and finished goods flow to, from and within space. This will involve both human-habited, uncrewed persistent platforms and many robotic orbital transfer vehicles. In the future…RPOD will become as routine as a semi-truck backing into a loading dock.”

A key component of executing successful RPOD missions will be for satellites to be manufactured as on-orbit servicing-ready. “Starting now, satellites will be built with ‘servicing’ in mind,” explained Beam. “Fuel ports, fiducials, and docking and grappling fixtures will become part of standard satellite designs. Once these features are available, a wide variety of satellite servicing tasks will become much more cost-effective.”

Besides constructing satellites to be servicing-ready before launch, other satellite network requirements are needed, both in space and on the ground.

The Role of Satellite Networks in RPOD Missions

Every mission that is executed in space heavily relies on the communications and connectivity capabilities enabled by satellite and ground system networks. RPOD missions are no exception to this rule.

“Networks in space and on the ground will be critical to providing the communication backbone between space assets and ground control,” said Adam Harris, Chief Commercial Officer of Orbit Fab. “The challenge for RPOD will be to have robust and secure communications links during the operations.”

According to Stadnyk, satellite networks will facilitate navigation, space domain awareness, communication, data exchange for command and control, and coordination between spacecraft, ground stations, and mission control centers for RPOD missions.

“Well-developed networks are especially important during the most critical periods of a RPOD mission, such as the final approach and docking, as they lead to longer communication windows and more time for operators to perform the maneuvers,” explained Stadnyk. “Emerging space-based networks promise improved capabilities with their inter-satellite links, allowing for continuous communication with a satellite no matter its position in orbit.”

For RPOD missions to be effective, Beam also agreed that continuous communications is incredibly important, but some roadblocks are in the way. “Continuous communication paradigms are difficult to obtain due to the lack of a sufficient number of ground stations,” he explained. “Currently, RPOD missions take many days or weeks due to having to be broken up into hundreds of maneuvering control points, with dynamic maneuvers occurring over the three to 10-minute communication windows currently available. Such long RPOD operations could not sustain an economy.”

But Beam does see light at the end of the tunnel as it pertains to bridging this coverage gap. He pointed to Low Earth Orbit (LEO) communications constellations like Starlink, OneWeb, Kuiper and others that will greatly assist in establishing more continuous communications with ground controllers by providing more robust coverage, but they won’t eliminate all the comms roadblocks.

“Challenges will still exist with high-bandwidth communications due to the conflicting priorities of pointing the servicer toward the client and pointing the servicers’ antennas toward the transmitting and receiving antennas,” said Beam.

For Stadnyk, current network challenges for RPOD missions span bandwidth limitations, filling in gaps of coverage areas, overcoming signal interference and lost data in transmission, securing networks from cyber-attacks, and latency issues.

“As we venture farther away from the Earth, latency is an issue as RPOD missions require real-time communication when they’re in their most critical phases,” he said. “The large distances in space mean that real-time communications are not always possible, and an increase in autonomous RPOD capabilities is necessary to overcome this physical limitation.”

TT&C and Continuous Comms During RPOD

Telemetry, Tracking, and Command (TT&C) is also a fundamental component of effective RPOD missions that relies on the link between spacecraft and ground stations to ensure that mission operations are monitored by satellite operators.

“Due to the high-risk nature of operating spacecraft in proximity of one another, continuous monitoring of the spacecraft position, velocity, altitude, video feeds, systems overall health, and more is necessary for spacecraft operators who receive this data and make informed decisions on the maneuvers for the spacecraft to perform,” said Stadnyk.

According to Stadnyk, low-latency communication is important to ensure that telemetry and commands are sent and received as near real-time as possible to ensure there are no delays that could lead to “flying blind” scenarios.

“This is particularly important during higher-risk phases of RPOD missions such as the final approach and docking when the risk of a collision is heightened,” he said. “Additionally, the length of communication windows is carefully planned during these mission phases to ensure there is continuous communications and no times in which an operator cannot communicate with the satellite. High bandwidth connections are preferred to ensure the volume of data is transferred in near real-time, and communications are encrypted and checked for errors in the data transfer for safety.”

Though the requirements and capabilities are high and demanding for RPOD missions, the long-term benefits greatly outweigh the technological investments that are required to make them viable.

“Without RPOD, providing these services wouldn’t be possible and satellites would continue with their single-use nature,” explained Stadnyk. “We don’t throw away other infrastructure and assets like cars and airplanes when they malfunction or run out of fuel. We repair and refuel them. RPOD is what lets us navigate our environment and provide these services in space.”

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