Sevain said:
Operating in a gas giant is difficult due to the heavy gravity. If you look at the expanded movement section of High Guard you notice that you need to expend up to 2,5 points of Thrust to keep yourself from falling into the giant. That would leave a military ship with 6 Thrust only 3 Thrust for manoeuvring and dodging. We do know that even Thrust 1 ships can refuel at a gas giant, but that requires a pilot check which implies a specific orbit that is probably quite predictable. While you are refuelling your ability to disengage or manoeuvre is limited.
There is an expanded space combat section, and an alternate movement section. So just to be clear you are referring to the alternate movement section right? The alternate rules take into account vector movement, and in the case you are using (and using the example given in the book), a ships vector would be altered slightly closer to the gas giant based on straight-line maneuving. Any ship in the atmosphere of a gas giant pays the exact same penalty, so in many instances the issue would offset itself. Plus unless the SDB is configured for atmosphere work it's not necessarily going to be more maneuverable than the ship refueling.
If you are talking about a decently sized, and armed ship, it would use barrage tactics against SDB's attacking. And even though they are armored, they have no screen protections and would be decimated by meson, nuclear and particle-accelerator damage that their armor can't help them with. Firing nuclear weapons in return might not be as effective, as larger ships tend to be the ones with expensive screens.
Where SDB's might excel is attacking tankers, or freighters. While the JTAS article acknowledged that, it also stated that much of the initial damage to a fleet taken by an attacker is the result of their ships being attacked while attempting to refuel. Which implies NOT auxillary ships being attacked, but mainline warships.
Sevain said:
Why would you limit yourself to a 400 ton SDB? Build a 5 000 ton craft, give it airfins, high thrust, fuel scoop and say 6 month's supplies. Your defender now lie in wait for quite a long time. Then give it a stealth hull and long range meson weapons to maximize the odds of it surprising the enemy tankers. Build a second ship of similar design, but have that ship climb up on the other side of the giant to cut off any tankers attempting to flee upwards. You have committed 10 000 tons of ship to the gas giant's defence, but your enemy probably has to commit 20 000 tons of warship to match your firepower. Even then you can still give battle, since you do have a place to retreat to.
You aren't limited. The Dragon class SDB is supposedly the most popular one out there, and it's 400tons. You could build larger ships, no doubt about it. Bigger non-jump capable ships are getting into the battle-rider configuration too.
The issue with that is the money spent on a 5,000 ton SDB might be better spent on a dozen 400 ton SDB's. A single ship can only be in a single place. A dozen ships can be in port, under repair, patrolling around your primary planet, patrolling the system, or lurking deep in a gas giant waiting. And all that done simultaneously. The 5,000 ton ship cannot - it must choose which action it's going to be in and abandon the others.
The other thing is that gas giants are H-U-G-E. Trying to zip around the planet to cut off a fleeing ship is kind of improbable, if not impossible. It still takes time to circumnavigate, and the fleeing ships gets to go 'up' in a straight line. And, depending on just how 'deep' the SDB is in the atmosphere, it has to follow in-atmosphere flight rules rather than vacuum space ones. Speeds are reduced because of atmospheric pressure. If the ship comes up it may be vulnerable to High-guard fire, and thus lose the protection of lurking.
Sevain said:
Even if the system falls your presence still forces the enemy to commit a significant force to guard any refuelling operations at the gas giant. Even if you have been destroyed your enemy will want to commit that force, since it is very difficult to know if all the boats in the gas giant have been eliminated.
Yes, that's one of the reasons that SDB's are worrisome to an attacker. They are meant to be able to stooge around for long periods after an attacker may have seized the primary world, performing recon, raiding and even some strike missions. Hidden bases in the outer system, Oort cloud or asteroids allow them to refuel and re-supply. The one problem that ones hanging in a gas giant would be that they'd need to leave for supplies (fuel's there for the taking). I suppose it's quite possible to build grav supply platforms that could be accessed that carry supplies and are hidden as deep down as their design allows to prevent being crushed by pressure.