In World War I, Britain came up with a novel defense against German U-boats that preyed on shipping fleets. They would heavily arm some minority of merchant vessels and keep that armament hidden and even fill the cargo holds with cork or wooden caskets so that even if they were torpedoed, they could remain afloat.
U-Boats had limited numbers of torpedoes, so a lone, heavily damaged, or otherwise vulnerable target might encourage the U-boat captain to surface and finish a ship off with a deck gun. Once the U-boat was vulnerable, the Q-ship's panels would drop to reveal the deck guns, which would immediately open fire, hopefully sinking the U-boat.
In Aurora, missiles are valuable and a fleet of freighters or colony ships might be best engaged at close range to save ammunition.
I'm not sure if the AI thinks that way, but player vs. player, I definitely would try to close and destroy a freighter with beams unless I just had an unreasonable number of missiles.
The Doppelganger class Q-Ship below has identical tonnage, speed, and thermal signature to the Gemini class Cargo ship. It also has substantial passive sensor and an active sensor array that would generally stay off until needed to fire.
Its two CIWS emplacements and thick armor make it very survivable, without alerting enemy commanders that this is a military ship (like ECM and anti-missiles might).
The Q-ship will probably travel with regular formations of freighters but might instead travel alone.
When an enemy ship comes within 150,000km, the Doppelganger will launch a devastating barrage of 240 warhead strength-49 missiles split between as many as 10 targets and without enough time for enemy anti-missile systems to engage it.
Doppelganger class Q-Ship 47,650 tons 447 Crew 4648.3 BP TCS 953 TH 4000 EM 0
4197 km/s Armour 10-117 Shields 0-0 Sensors 70/70/0/0 Damage Control Rating 40 PPV 360
Maint Life 4 Years MSP 2469 AFR 448% IFR 6.2% 1YR 246 5YR 3696 Max Repair 125 MSP
Intended Deployment Time: 24 months Spare Berths 0
Magazine 2400
500 EP Commercial Internal Fusion Drive ( 8 ) Power 500 Fuel Use 4.42% Signature 500 Exp 5%
Fuel Capacity 1,000,000 Litres Range 85.5 billion km (235 days at full power)
CIWS-160-2 (2x8) Range 1000 km TS: 16000 km/s ROF 5 Base 50% To Hit
Size 10 Box Launcher (240) Missile Size 10 Hangar Reload 75 minutes MF Reload 12.5 hours
Missile Fire Control FC10-R80 (10) Range 10.5m km Resolution 80
Blunderbuss Mk 2 (240) Speed: 30,000 km/s End: 0.9m Range: 1.6m km WH: 49 Size: 10 TH: 180/108/54
Active Search Sensor MR54-R100 (1) GPS 3921 Range 54.9m km Resolution 100
Thermal Sensor TH5-70 (1) Sensitivity 70 Detect Sig Strength 1000: 70m km
EM Detection Sensor EM5-70 (1) Sensitivity 70 Detect Sig Strength 1000: 70m km
Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s
This design is classed as a Military Vessel for maintenance purposes
For reference:
Gemini class Cargo Ship 47,650 tons 249 Crew 1504 BP TCS 953 TH 4000 EM 0
4197 km/s Armour 1-117 Shields 0-0 Sensors 14/14/0/0 Damage Control Rating 1 PPV 0
MSP 20 Max Repair 125 MSP
Intended Deployment Time: 24 months Spare Berths 0
Cargo 25000 Cargo Handling Multiplier 30
500 EP Commercial Internal Fusion Drive ( 8 ) Power 500 Fuel Use 4.42% Signature 500 Exp 5%
Fuel Capacity 1,000,000 Litres Range 85.5 billion km (235 days at full power)
Thermal Sensor TH1-14 (1) Sensitivity 14 Detect Sig Strength 1000: 14m km
EM Detection Sensor EM1-14 (1) Sensitivity 14 Detect Sig Strength 1000: 14m km
This design is classed as a Commercial Vessel for maintenance purposes
The downside is that it's hard to dedicate a huge militarily shipyard to a project like this, particularly when it's unlikely you'll build more than one or two. Also frankly, it's expensive and not very versatile or something that could easily team up with other fleet assets. And a player is unlikely to fall for the trick twice.
*Another hat tip to GenJeFT for the short-range missile idea.