BTW according to canon any craft with chem thrusters has an ADF of 1 (no MR penalties). Fuel is the limitation as to how much acceleration you can perfrom at that rate, and sadly that isn't spelled out. But if you're equipping a ship with the thrusters for atmospheric use while incorporating any additional jump capable drives, it really is a moot point as once the ship is out of atmosphere it will resort to said jump capable drive system.

I know I read somewhere about fighter pilots needing extra shielding against the atomic engines... so I'm disinclined to just handwave away the thrust.  It sure would make some things easier admittedly.

Got ya, the penalty is for the extra system. 

The fighter pilot is not being exposed to the thrust, he's being exposed to the atomic drive mounted in the hull behind him.

Assault Scouts have those drives mounted outboard on their wings, and the crew needs to vacc-suit it to access them. Frigates (and larger) have them on struts that are hollowed out for airlocks & decontamination stations in order to service them (and you would still need to vacc-suit or workpod to access the bits beyond the strut housing). The simple fact is if you need all that protection while working on the drive, it goes without saying you shouldn't be cracking those panels open in an atmosphere.

I know I saw this somewhere, but honestly don't recall where. Like the ruling about "system ships up to HS:5 can land in atmospheres" versus "Scouts are the only starships that can land" rule, it's no doubt one I easily house ruled around.

Granted, under KH Vector rules it makes sense but under the canon table top gaming rules I didn't see a need for it. The fact that "powerful ion drives" and "(insert any less than splendid adjective) chemical drives" perform at the same paltry rate, I didn't see the need to further hamper those systems. More so when the rules also state you can make your full compliment of MR facing changes while stationary...acceleration rates obviously have no impact on maneuvering in this game.

Just my personal rambling on the matter...

Chemical: 1 ADF

Ion: 1 ADF (low speed but, long endurance)

Improved Ion: 1/2 listed ADF (faster)

Atomic: mormal

So PCs can take their HS 4 or 5 freighter planet-side but, they don't thumb their noses at the militia because that frigate can land right next to them with a 40 man crew! Plus it keeps the need for assault transports to need shuttles, etc.

I still use no Ion ships land on planet rule...don't like it but...maybe something will change.

TO -- I still am going to download your story pdf... had a minor issue last time and gave up to easily.

The Following is a C/P from the page 37 of the revised pdfs

It's the released energy from the reaction that is harnessed as thrust...not neccesarily the radioactive material itself. Electricity from a nuclear power plant goes to your home as a result of the same type of reaction.

The rest of that simply supports why you shouldn't be performing maintenance on them in an atmosphere.

We have no tech to directly convert the energy released in the fission reaction into electiricty.  It we did those power plants would produce probably a hundred fold more eletricity.  Modern nuclear power plants heat water with the fission raction which turns to steam that physically turns turbines.  That is why the water becomes contaminated... the nuclear waste isn't actual spent plutonium... it is radioactive water.

So... I'm still thinking for an atomic drive to land on a planet they need some kind of hybrid engine such as chemical... or... the tech in SF has to be advanced enought to directly convert the fission energy into SEU power.  I say SEU instead of electricty cause we don't know exactly what is in an SEU... just that it is alot of energy.

Don't they basically charge them from "energy" from a ship engine or something?  What powers a parabattery?  In Star Trek the whole thing with them using "Plasma" and not electiricy is a Sci-Fi way to assert it is way more powerful than electricty.  I'm guessing SEU's are something like that... like super electricity.

I agree with AB (?) [the little green moster guy] (sorry I can't see your username), the canon material sounds like they are using a controlled fission reaction to expel radioactive particles out the back of the atomic engines. Like a jet engine only using radioactive particles as a substitute for superheated air. That's not too different than the nuclear powered bomber proposal from the 50s.  In space it wouldn't be a hazard and explains why atomic engined ships are not permitted to land on habitable planets. 

Just for the sake of this discussion here is a drawing to help people visualize what an atomic engine looks like.

Heater Exchanger: This allows reactor coolant to be cooled and keeps the reactor from over heating.
Directional Thusters:  Allows the ship to make slight changes in directions.
Reactor:  The atomic reactor.
Turbine:  Super heated coolant creates steam which is then forced through a turbine to create electricity.
Electronics:  This is the equipment that monitors the reactor, it's output and turbines.
Thruster:  Whether it be a particle thrower or an electro-static drive this provides the ship with propulson.

The biggest fear of this type of drive system is damage to the reactor vessel (the vessel containing the reactor core).  As already stated, if the core is exposed to the atmosphere, melts down or breeched by weapons fire, large areas of the planet surface could be containinated for a long time.  If the reactor is destroyed on reentry you could have a globe event causing even a larger swath of the planet being containated.

In the case of the thruster being a particle thrower (ie Ion drive) depending on the type of particle being thrown and the intensity of the stream you could technically create a weapon by pointing the engine at something.  This type of weapon is known as a Particle Accelerator Weapon.  It has been used in several sci-fi stories.  Larry Niven used it in Man-Knintzi war (Total misspeling here) just to name one.  So governments might not like the idea of having an Ion engine near a major city due to fears that it might be used as a weapon.

Using a real world example, there have been major concerns over use of atomic batteries in space exploration.  The fear here is, if the rocket carrying the probe malfuctions in the atmosphere the battery could cause radiactive fallout.

So yes, I see why planets would limit the use of atomic engines...