JSTARS and the P8 Poseidon


Just as the USAF may be accepting that their JSTARS replacement might look a lot like the RAF’s Sentinel, the mood music seems to be indicating that the Sentinel can be sacrificed on the altar of getting the JSTAR’s size P8 in service.

OK, so I am taking some rather large liberties here but Raytheon, Lockheed Martin and Bombardier are offering this;


Which to my untrained eye looks very similar to this;

RAF Sentinel

Northrop Grumman, General Dynamics, Gulfstream, and L-3 are also partnering, obviously with a Gulfstream business jet platform.

Boeing, the third competitor, will be offering a 737-700 Boeing Business Jet (BBJ) derivative, not a version of the larger 737-800 based Poseidon.

There seems to be an almost casual assumption in a great deal of online chatter that the capabilities of the Sentinel can be replaced as part of a possible P-8 Poseidon purchase, either taking a Boing JSTAR’s recap win (artist impression below), or by adding an external sensor pod to the P-8 and using the same aircraft for both.


The external sensor pod in question is called the AN/APS-154 Advanced Airborne Sensor (AAS), a US Navy programme that is a derivative of the Littoral Surveillance Radar System (LSRS). It is currently on track for Increment 2 of the P-8A Poseidon programme.

Naval Air Systems Command describes the AAS as;

The APS-154 radar represents the next generation of maritime patrol and reconnaissance radars which will provide military commanders highly accurate battle-space situational awareness as an integrated Maritime Intelligence, Surveillance, Reconnaissance and Targeting (ISR&T) asset.

In January this year Boeing were awarded a $60.7 million contract for AAS integration kits for Low Rate Initial Production Lot IV (13 aircraft) and Full Rate Production Lot I (16 aircraft). The AAS is said to be a very advanced system, superior to the E8 JSTARS but the million dollar question is, is it as good as the ASTOR, especially given ASTOR and AAS ar Raytheon products and ASTOR is being modified to incorporate maritime and littoral surveillance capabilities.

The sensor is only one part of the equation, the platform is just as important. One of the key selling points of the Bombardier Global Express platform used for Sentinel is its high service ceiling and long endurance. Both are reduced by the weight and drag imposed by the mission equipment but they are still impressive. Altitude is important, the higher you go the further you can see although someone much cleverer than I once explained it was all to to do with graze angles. Long endurance also has obvious benefits, as does its high speed. The P8 is a bit lardy in comparison, much shorter range than the Sentinel. The Sentinel cruises at the top speed of a P-8A and can fly about five or six thousand feet higher. Unless an RAF P-8 is modified with a refuelling probe or Voyagers fitted with a boom, range may be ‘a bit of a problem’

It is also not clear whether the Boeing proposal for the JSTARS recap utilises the AAS or some other system. Interestingly, Boeing are not offering a P8 plus pod for the JSTARS programme and reading between the lines there is more than a fair share of inter-service shenanigans between the USAF and USN.

This poses a few interesting dilemmas for the UK.

Sentinel currently has a reprieve until 2018 but no funding beyond that, the final decision coming out of SDSR 2015 and the ISTAR Optimisation Study completed by the RAF.

We cannot know the performance differences between ASTOR and AAS but we can reasonably estimate the flight performance differences between the P8 and a Sentinel, and not forgetting the range figures given for a P8 are without the hefty podded sensor attached.

Costs are equally an unknown but the problem for using an RAF P-8 in the Sentinel role is as much about politics as anything else, if we can have British Poseidons off doing the Sentinel mission then obviously the glaring gaps and massive risks used to justify a P-8 suddenly look a bit hollow. Go for a larger fleet of P-8’s to cover both missions and you are lugging around all that maritime patrol kit (and having to support more than you would for a pure MPA role) so the overall costs rise.

As ever, trade-offs to the fore, but personally, I see using Sentinel replacement as part of the business case for P-8 as rather weak.

We also don’t know whether the US Navy would let us have the AAS and at what cost it would be.

I would rather see us expanding the role of the Sentinel by the use of a range of software and sensor upgrades such as adding an electro-optical turret or the DB-110 sensor from RAPTOR pods as GR.4 goes out of service. With advances in computing technology some of the weight of the ASTOR systems may be possible to be reduced. Certainly, as its role has evolved and connectivity improved, the field deployable ground station component would seem to be of less value so some cost savings, particularly in squadron manning, may be found there.

Any purchase of the P-8 would then be right sized for the maritime patrol mission, optimised for such and personnel dedicated to this very important mission.

So, a developed Sentinel plus a minimum sized fleet of P-8’s (or equvialent, including combinations of unmanned aircraft) instead of an overiszed P-8 fleet trying to do everything.

The flip side is to go with the 737-700 based Boeing JSTARS and use the same aircraft platform for a future AWACS replacement, thus having very high levels of commonality across the three large missions.



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