What kind of network can support future commercial and government space trips around Earth and support bigger distances to the moon and Mars?
NASA is in the process of exploring exactly what technology will be needed beyond 2022 in particular to support future space communication and navigation. The agency recently issued a Request for Information (RFI) to begin planning for such a new architecture.
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NASA's RFI includes some very broad stokes about what it wants this new network to support. For example, it states: "It shall also consider future science missions with greatly increased sensitivity of sensors that are capable of large data captures as well as future missions to the Moon and Mars where surface activities require supporting communications. The cost value proposition of the future architecture must be an integral part of its design.
The future architecture must be flexible to meet dynamically changing needs between investments in operations (e.g. to lower cost) and development. The architecture must be affordable as well as sustainable within a flat or decreasing budget environment. The architecture must be extensible to address new requirements from traditional (e.g. higher data rate or ultra-precise orbit determination missions) and non-traditional markets (e.g. human deep space missions).
The resultant architecture should take into consideration the need for security and be protective of these national assets and impervious to system breach. Responders should make assumptions about user needs and data volumes for the 2022 and beyond timeframes based on representative science missions and extensions. These objectives should not limit consideration of non-traditional concepts, models and/or designs," NASA stated.
The RFI comes from NASA's Goddard Space Flight Center (GSFC) which handles communications and navigation services for space flight missions in the vicinity of the Earth. This includes the Space Communications and Navigation (SCaN) Program which supports missions with communication services that may include transmitting data and/or commands to and from crewed and/or uncrewed space vehicles ; deriving information from transmitted signals for tracking, position determination, and timing, NASA stated..
GSFC also manages the Space Network, comprised of the Tracking and Data Relay Satellite System (TDRSS) and associated ground stations. TDRSS customers include Low Earth Orbiting scientific satellites, the International Space Station (ISS) and its servicing fleet, scientific aircraft and balloons and expendable launch vehicles. The SN consists of a constellation of seven TDRS geosynchronous satellites and associated ground systems. While the SCaN Program is in the process of launching three new third generation TDRSS satellites by the end of this decade the remaining on-orbit satellites are aging and expected to be retired within the next decade or so. Most of these satellites have exceeded their design life. With constellation capacity projected to fall below aggregate mission demand by the early 2020's, it is here that a need to begin planning for a future communication architecture is most important, NASA said.
NASA has other future networking systems in the pipeline. For example, last November it teamed with the European Space Agency to successfully test an experimental version of an "interplanetary Internet" to control a robot on the ground in Germany from a laptop onboard the ISS.
That test employed NASA's Disruption Tolerant Networking (DTN) protocol to transmit messages between the ISS and the robot. DTN technology is designed to allow Internet-like communications between space vehicles and habitats or infrastructure on another planets NASA said.
From NASA: "The core of the DTN suite is the Bundle Protocol (BP), which is roughly equivalent to the Internet Protocol (IP) that serves as the core of the Internet on Earth. While IP assumes a continuous end-to-end data path exists between the user and a remote space system, DTN accounts for disconnections and errors. In DTN, data move through the network "hop-by-hop." While waiting for the next link to become connected, bundles are temporarily stored and then forwarded to the next node when the link becomes available.
Low latency, coupled with low bit error rates (BER), allows TCP to reliably transmit and receive acknowledgements for messages traversing the terrestrial Internet. One of the best examples of high latency, high BER links, with intermittent connectivity is that of space communications. One-way trip times, at the speed of light, from the Earth to the moon incurs a delay of 1.7 seconds; while one-way trip times to Mars incur a minimum delay of 8 minutes. The problem of latency for interplanetary links is exasperated with increased BER due to solar radiation. In addition, the celestial bodies are in constant motion, which can block the required line-of-sight between transmit and receive antennas, resulting in links that at best are only intermittently connected. Intermittent link connectivity is commonplace terrestrially as well. "
NASA says DTN operates in two environments: low-propagation delay and high-propagation delay. "In a low-propagation environment such as may occur in near-planetary or planetary surface environments, DTN bundle agents can utilize underlying Internet protocols that negotiate connectivity in real-time. In high-propagation delay environments such as deep space, DTN bundle agents must use other methods, such as some form of scheduling, to enable connectivity between the two agents. The convergence layer protocols provide the standard methods for transferring the bundles over various communications paths. The bundle agent discovery protocols are the equivalent to dynamic routing protocols in IP networks. To date the location of bundle agents, DTN agents, has been managed, analogous to static routing in IP networks.
DTN is currently being studied in research environments for a number of applications including: sensor networks, mobile devices, use of data mules, military communications which involve stressed disconnected and disrupted networks, along with space-based store-and-forward networks. There is current work ongoing to extend the DTN architecture to smart mobile phone-based mobile ad-hoc networks, NASA says.
According to NASA, DTN technology is still under active development. In addition to network security, research goals for the DTN activity will focus on testing and evolving important network services including naming and addressing, time synchronization, routing, network management and class of service.
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