It sound like you are looking for a "mobile mine". In WWll mines were delivered by German forces by aircraft (in Traveller see B.A.R.D. for a small craft called a Hornet UCAV) this is a 2 D Ton remote flown craft with 14,000 kg ordinance capacity.
Mines were also developed by S-boat that used speed to drop a handful of mines. Again the UCAV comes to mind, except maybe a piloted version?
Mines were also dropped by raiders to very good effect. In Traveller this would be the old standby, the J-Hawk. The raiders go away with mining operations because they looked like they belonged in the shipping lanes--Guile.
Mines were also dropped by submarine, by either launching out of a torpedo tube. In FF+S it states that a missile tube has to be two times the size of a missile it launches, but it does not say that the missile/ mine has to be half the size of the missile tube.
A second way that mines were dropped by sub was by dedicated mine laying submarine. These subs had tubes that contained a number of mines, I think about four or five mines per tube for a total of 40 or so mines. The sub would move along in a strait line dropping mines that would become active some time after deployment. In Traveller terms you would design a "missile Tube and reloader" for your 0.5 D Ton mines.
As an alternative to the 0.5 D Ton mine tube, can a sandcaster launch 0.5 D Ton mines instead of sand canisters. I use sand casters to soften up targets on the ground by dropping bombs from orbit.
It sound to me like you are looking for a mobile mine. These are launched from contemporary subs via a torpedo tube, the mine uses an old torpedo body for propulsion. The mine/torpedo is launched as a standard torpedo would be, is probably guided by wire or pre- programmed and runs out to its target location and stops. When the mine/torpedo hears its target a smaller torpedo is "launched" from the propulsion part of the mine and hunts its target as a torpedo. In Traveller I found the HokHok missile in B.A.R.D. in the Vera file. This is a missile armed with a TL-12 500kt warhead and two 100kt warheads in magnetic slings (grapples?). You could come out of jump behind a moon, launch your HokHok missiles and mine an enemy planet and only the missiles would be at risk. As an alternative to this I would use a mine with a small ion drive and launch them via sand caster, missile tube or dedicated mine tube.
Fair warning mines can be used offensively too. As a counter to hiding behind a small moon, the locals could place a few mines on the moons surface if airless or in orbit if not and place a small 4-6 man warning station with a passive sensor on the moons surface and BOOM. Personally I would go with the guile approach---Hi I'm the innocent little J-Hawk from the next system over come to do some trading. "As you closed with the planet you could deploy 6 mines per 30 minutes from each mine tube. But remember your mines would have the same velocity as your ship so you would have to stop (not very clandestine) or have a small retro thruster to counter the launch velocity.