A dedicated vessel for conducting habitable world and other planetary surveys
The Planetary Survey Craft is the vessel type that I've put the most time and thought into that also rates detailed discussion.
There are some key requirements unique to habitable world surveys that encourage the development of specialized survey craft (both from R3.02.1).
Habitable world surveys cannot be completed without the use of small craft
Large units are not effective habitable world surveyors without either (AC) capability or small craft onboard
However, WP surveys need neither small craft nor (AC). Could WP survey craft have either? Sure, and they might even be free — FT-hulled survey craft have (AC) at no cost, and 16+ HS craft have a free gig, but there's also the question of opportunity cost. Is it worth taking a WP survey flotilla off-task for a while to check out some real estate?
There is strong incentive to separate WP and habitable world surveys, then, in order to build the most cost-effective and time-effectiev units for each mission. "WP" and "habitable world", though, isn't a complete description of all possible survey types. Instead, we separate the missions into WP surveys and system body surveys.
A particular quirk of Solar Starfire, under the current rules revision, is that the basic shuttle (st) is far and away the most cost-effective system body surveyor in the game. At half the cost of the basic Xa science sensor (and with no maintenance payment), it generates twice the survey points (SPs) of that Xa sensor. One needs only get st to their destination and then turn them loose. The most cost-effective way to do this is with a single fast-hull unit.
Some quick math suggests how large a carrier is necessary. Habitable world, survivable bodies, and asteroid belt surveys all require 50 SP for standard (T or ST homeworld) races, so 50 SP is our benchmark. Let's target a one-month survey length. As st are Maximum Survey Speed (MSS) 3, the PSC needs to generate 17 SP per StMP spent surveying. As st generate 2 SP per StMP surveying, 9 st are required — however, the PSC must mount an X system to use st for surveying, and we can also consider the contributions of that X system to the total. Xp is the cheapest option, but its very slow survey speed (MSS 1) means that it will frequently not contribute any SP in time to reduce the st requirement below 9. Xa is more expensive, but it shares the st MSS of 3. One Xa plus 8 st generate 17 SP per StMP with an MSS of 3: precisely our target for the survey. The reduction of st from 9 to 8 more than justifies the additional cost of the Xa system (plus, in a pinch, the PSC will be capable of participating in a WP survey).
Xa + (Bsa)×8 makes for 9 HS of payload. That is barely within the allowances of an ES hull (add (Ica) and Qa to reach the maximum 12 HS), but a CT hull will allow some extra options. A CTf needs 5 HS of engines to reach full speed (5 StMP) plus 1 HS of life support; this total of 15 HS allows for one more system. I prefer Ya combat sensors to H, reasoning that system body surveys will only be conducted where I expect to have a good supply line from the CFN, but I can also see the argument that that assumption of rear-area security obviates the need for the combat sensors, too. One could also drop some speed in order to add (MNE) so that operations in hostile systems become viable.
Planetary Survey-class CTf 16 HS / 10 TS
[2] (Bsa)×8 Xa Ya Qa (ic) (Ic) (Ic) [5/5]
Trg: 1 Def: 0 Cost: 249.2 / 37.4 SL 1
14 HTK
Note that discussion on the SDS forums indicates that this class may become obsolete, or at least less capable, in a future rules revision due to an adjustment to small craft SP gathering rates.