System must be "impervious" to attacks, be "extensible... in a flat and/or decreasing budget environment"

The National Aeronautics and Space Administration's (NASA) Goddard Space Flight Centers (GSFC) have put out their feelers via a Request For Information (RFI), soliciting contractors to help it build a "Space-Based Relay Architecture" by 2022.  NASA wants an affordable and reliable solution that can deal with the idiosyncrasies of space and serve as an "interplanetary internet" of source.

I. NASA: Build an "Impervious", Robust System on a Shoestring Budget

While the will and feasibility to send a manned mission back to the Moon or to Mars remains an open debate in the U.S., the RFI discusses using the system for communications with such missions, or robotic alternatives.  It writes:

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.

NASA elaborates that the system could be used in "aircraft, small science satellites, clusters of small sats, robotic and human exploration vehicles, long duration balloons, airships and unmanned aerial vehicles."

Dawn probe
The new system would be used for both manned and unnmanned missions
[Image Source: NASA/JPL-Caltech/UCLA/McREL]

The space agency also has lofting goals for the system's security, writing:

The resultant architecture should take into consideration the need for security and be protective of these national assets and impervious to system breach.

That requests sounds pretty worrisome considering NASA's assertion regarding funding:

Architectures should be cost effective, extensible and sustainable in a flat and/or decreasing budget environment.

It appears amid all the talk of fiscal sequestration that NASA is anticipating it may bear the brunt of more cuts.  NASA funding has long been on the decline.  When President John F. Kennedy proposed to send a human to the Moon in 1961, the budget was $13.878B USD -- around $101B USD in 2010 purchasing power [source].  Today the budget is expected to dip to less than a fifth of that, at $17.77B USD (2012 dollars).

II. Old System is Aging Quickly

The GSFC currently ferry data for near-Earth missions via the cruder Space Communications and Navigation (SCaN) Program.  Signals include requests for data (position, timing, images, audio, and other messages) and commands.  Security is a major concern for the GSFC after it was revealed that attackers (reportedly in China) successfully tampered with communications with two NASA satellites in 2007 and 2008.

The backbone of SCaN is the so-called Space Network, made up of the Tracking and Data Relay Satellite System (TDRSS) and ground-based control stations.  Currently there are seven low-Earth orbit (LEO) TDRS satellites that form the backbone of the system.  The satellites operate in the so-called S-, Ku-, and Ka-Band frequencies.

Other links in the TDRSS include the International Space Station (ISS), scientific aircraft and balloons and launch vehicles (Russia's Soyuz, SpaceX's Dragon).  The system services civilian and government satellites alike.

While the TDRS satellites have performed admirably, they are aging badly; many are long past their planned retirement age.  NASA has plans to launch three new third-generation TDRS satellites, but it's already contemplating a much bigger overhaul to its space network.

TDRS wide
NASA's first (left) and second (right) generation TDRS satellites need to be retired by 2020.

The new system will like utilize NASA's Disruption Tolerant Networking (DTN) protocol, an data protocol that NASA's been testing.  Last year NASA used the protocol to successfully remote control a robot in Germany from the ISS.

Terrestrial internet uses the transmission control protocol (TCP).  TCP is easy and effective, but relies on low bit-error rates (BER) and low latency.  By contrast space communications are high latency, high BER.  A message to Mars can take up to 8 minutes to reach a lander.  To make matters worse, cosmic radiation leads to signal corruption (BER), raising the need for redundancy and other forms of error correction.  Line-of-sight is another major challenge -- celestial bodies can block the path of transmissions.

These difficulties have made current space protocols more cryptic.  But DTN is more analogous to TCP, while retaining fault resistance.  NASA describes:

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. 

The remaining TDRS satellites will need to be retired by 2020, so the clock is ticking to cook up a replacement.  Despite its severe budget cuts, NASA is hanging on thanks in part to a new wave of private space contractors, such as SpaceX.  NASA is surely hopeful that it can tap some of that mojo for its new interplanetary communications network.

Source: RFI

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