Captain Patton commanded PARGO (SSN650) and is now President of Submarine Tactics and Technology of North Stoning ton, CT.
Background
With the recent awarding of Increment One to the Submarine Comms at Speed and Depth (CSD) program, three devices are now being developed, built and fielded. These are:
- A three-inch fiber optic-tethered expendable that will provide two-way UHF/SA TCOM (line-of-sight) comms for submarines.
- A three-inch fiber optic-tethered expendable that will provide two-way IRIDIUM satellite comms for submarines.
- An expendable Acoustics to Radio Frequency (A2RF) buoy deplorable from submarines or Maritime Patrol Air- craft (MPA) that serves to modulate acoustic to radio communications (and vice versa) to enable connectivity between the two platforms while the submarine is below periscope depth. Conceptually, this could also be deployed by surface ships.
Because there is some time before these devices are in the fleet, it is appropriate that some thought be given early as to not only the capabilities they will provide, but also their limitations. Although it is a near certainty that such matters are currently being provided the necessary intellectual entrepreneurial ism of organizations such as Submarine Development Squadron TWELVE, it still seems appropriate that the large body of corporate submarine expertise embodied in such as the Naval Submarine League feel free to offer hopefully redundant (at the risk of perhaps being even erroneous) opinions as to the Concept of Operations (CONOPS) for the employment of these devices. Also, it is clear to everyone that CSD Increment One is not the ultimate answer to submarine connectivity, and that subsequent increments over the next decade or more could likely include such as the air or space-based blue-green laser option unsuccessfully attempted during the late 80s with SLCSA T (Submarine Laser Communications Satellite). Increment One is what will be available in the near term, however, and it is imperative that it be employed to maximum effect.
Discussion
One of the first realities of either the three-inch comms buoys or the A2RF buoys is that for both fiscal and physical storage reasons, there will not be an infinite number of such devices available for use, and some degree of circuit discipline will have to be ingrained in any OPCON- particularly concerning unrealistic connectivity expectations by non-submariners. In the continuing quest for the silver bullet that will provide submarines persistent, high data rate connectivity at operationally significant depth and speed, these devices are not it – but are a valuable addition to the ever expanding CSD toolbox of partial solutions, if their particular capabilities and limitations are understood and exploited by all concerned. Another critical property sought after in submarine comms is latency – best envisioned by the difference in the time domain of when a particular idea or information set is established, and when it clears the initiating entity and arrives at the intended recipient.
UHF/SATCOM Buoy
The period of connectivity that this buoy will provide is, of course, dependent upon the amount of fiber optic contained within, and thus varies as a function of ship’s speed. Not so intuitive is the fact that the rise rate of the buoy is a finite value, and although capable of being used from very deep depths, it must be kept in mind that fiber will be consumed as the device rises and the ship moves away from the launch point that will not be available for connectivity once the buoy breaks the surface. This will be in addition to the extra fiber just attributable to the deeper depth per se. Persistence will be poor in that each buoy will provide connectivity for only tens of minutes, and latency will be fair to good in that information could be loaded into a buoy standing by in a 3-inch ejector, and connectivity established in a few minutes- an order of magnitude more quickly than if the submarine came to periscope depth (P/D) for transmission with a hull-mounted antenna. As an entering tactical CONOP assumption then, if length of connectivity is important, more time will be provided if the buoy is deployed at shallower or moderate depths.
Since connectivity to a geosynchronous UHF satellite involves an information transit path of nearly 25,000 miles – unlike what is commonly called “Line Of Sight” (LOS) connectivity with nearby manned or unmanned platoons tens of miles for ships, 100-300 miles for aircraft at altitude) – transmit power requirements are much greater than for shorter range applications. Because of the large electrical demands when supporting high power transmissions, the effective period of connectivity for these buoys could be controlled by battery capacity rather than tether length when using a high active (transmitting) duty cycle at low submarine speeds. Also, since the UHF transmissions are intercept able and OF-able (susceptible to direction finding equipment), it must be kept in mind that if an accurate buoy position is established by an opponent, that position is conceptually exploitable as an aim point for homing weapons. As entering tactical CONOP assumptions then, if length of connectivity is important, more time will be provided if the active (transmitting) mode of the buoy is minimized in favor of a passive (listen on/)~ mode, and care must be exercised as regards the length of time transmissions are conducted and how long one remains in the vicinity of a transmission.
IRIDIUM Buoy
The Iridium buoy has three significant advantages. Having to reach a satellite constellation at only some 500 miles altitude versus nearly 25,000 for the UHF satellite, it will do so with far Jess instantaneous power, which translates into significantly longer battery life. Also, since the 66 satellites of the Iridium constellation are in polar orbit, performance of the system is virtually independent of ship’s latitude – dramatically different than UHF satellite connectivity, which is very poor at the high latitudes at which submarines frequently operate. The third consideration is that Iridium is a commercial service, and as such, its presence is not primacy evidence of the presence of a warship or submarine. Persistence and latency will be essentially the same as the UHF buoy. As an entering tactical CONOP assumption then, if operations at high latitudes are envisioned, per-deployment loadonts of 3-inch devices should probably be skewed towards Iridium versus UHF buoys.
A2RF Buoy
This device is significantly larger than the 3 inch devices, and is deployed from the submarine by using the Trash Disposal Unit (TDU) – a vertical 12 inch diameter, up to two-stories tall torpedo tube-like device whose primary purpose is to eject weighted garbage bags. From MPA, the unit is deployed from the same internal launch tube used to eject certain special sonorous from within the air frame. After deployment, the device floats, subject to winds and current, and will operate as a connectivity gateway for at least three days. With its significantly longer lifetime, the A2RF buoy provides more of the desired persistence per unit than its two 3-inch CSD cousins. However, the downside is the very constraining data rate limitations of acoustic-based connectivity, which also drops markedly with range between the buoy and the submarine. In practice, meaningful data rates can be maintained within a few hundred square miles of the buoy’s location – a limitation acceptable in some instances, but not in many others. There is also the consideration that acoustic energy injected into the ocean environment is the bane of submarine operations whenever the possibility exists of the presence of an opponent’s submarines or other passive acoustic listening devices. Further- more, there are very significant limitations on MPA being able to safely operate in contested littoral areas where such a persistent connectivity pipe would be very useful. As entering tactical CONOP assumptions, if acoustic stealth is appropriate, usage of A2RF buoys must be carefully weighed against other means of connectivity, and tire safety of any manned aircraft must be considered when operated in contested areas.
A positive consideration of A2RF buoys as compared to the 3- inch CSD devices is that it is unique in initiating connectivity by other than the submarine, although it does require the MPA to have reasonably accurate knowledge of the submarine’s present or predictable future location. Also, for the submarine-deployed case, it is unlikely that an A2RF would be kept loaded in the TDU, and its deployment from a dead start might easily take 30-60 minutes – resulting in poor latency. A conceivable operational construct would involve the MPA to establish connectivity as described above, then, if a high data rate exchange of limited duration is desired, direct the submarine to launch an expendable 3-inch UHF or Iridium device. As an entering tactical CONOP assumption, the A2RF buoy is more likely to be deployed from aircraft than by submarines if the tactical situation permits the safe operation of aircraft in the airspace above the submarine. If not, than the submarine may have to be the platform which deploys the buoy to provide a link to the Iridium constellation or to an aircraft operating at a safer standoff distance.
Future CSD Developments
Several recent and not so recent submarine incidents, including collisions, highlight the need for above air-water interface situational awareness – particularly when in shallow waters or when coming to periscope depth. In many cases, entirely doable derivatives of the 3-inch CSD devices could offer this through optronics, Automatic informational System (AIS), Electronic Support Measures (ESM), Global Positioning System (GPS) and other payloads. In fact, the extent to which modem electronics have reduced size and expense of such capabilities would permit more than one of these features to affordably be incorporated in a single device.
Also, a concept worth further CONOP investigation is a feature on 3-inch CSD buoys to load a preset message, use the tether link only to assure connectivity with the intended recipient of the information package, then cut the tether and leave the buoy datum; the buoy going active and transmitting the package after some preset time delay.
Since persistence and latency are such important characters tics of any FORCEnet submarine solution, both of these features need to be continuously improved upon. With the two recent disappointing failures of the much anticipated joint US-UK Recoverable Towed Optical Fiber (RTOF) buoy, it is perhaps time to reconsider the towed buoy option – reminiscent of the underemployed AN/BSQ-5 installed on two 637-class SSNs in the mid-70s whose electable mast provided two way HFNHF/UHF connectivity at speeds of up to 15 knots. Of course, it is only fair to add that in the mid-70s, the ability to chat with one’s shore side bosses was not a highly sought after capability by submariners.
Conclusions
The present CSD program is a first and vital step towards more flexible, persistent and short latency submarine connectivity. It is, however, only a first step – the ” … quick 75% solution for current problems” type referred to by Secretary of Defense Robert M. Gates at a National Defense University speech in September 2008. The submarine’s CSD “toolbox” has been virtually empty, and these three devices of Increment One will be much appreciated, once their optimum modes of employment are established. Much more remains to be accomplished, however – the ” … 99% solution for future problems” also referred to in the same SECDEF speech especially with the new missions SSNs, and particularly SSGNs are being tasked.
Expendables are a fertile and relatively unexploited field, and will provide not only situation ally appropriate tactical options, but will probably also contribute to safety of ship issues through such as a photonics capable fiber optic tethered 3-inch buoy launched immediately prior to a quarterly test of the Emergency Main Ballast Tank blow system to check for range clear of surface traffic, or an AIS-equipped buoy launched if circumstances require coming to P/D while transiting a crowded international strait.
There is a compelling argument that due to both fiscal and onboard stowage limitations, that submarine CSD expendables will never be able to provide the aggregate time-bandwidth product required to fully support a nominal deployment comprising of several different types of missions with widely variant persistence and latency requirements. If this is the case, which it almost certainly is, then these expendables would best be complemented with a towed, retrievable buoy of some sort which featured an antenna and other sensor-studded electable mast which, as directed, could penetrate the air water interface. When this feature was not needed, the buoy could be at several tens of feet depth to provide persistent, passive VLF connectivity – much as the SSBN community has relied upon for a half century, or be completely stowed to permit very high speed transits. In any case, the series of submarine CSD increments will remain a dynamic endeavor for the foreseeable future and could eventually achieve high persistence, low latency and high data rate connectivity through such as space-based blue-green lasers.
