Here's the first of what will hopefully be many posts on running Eclipse Phase. Advice here is based on our experience running our own EP campaigns and shouldn't be taken as a canonical interpretation of the rules. Hopefully it will be helpful to GMs feeling their way around situations that the rules don't yet cover in detail.
This post started as a reply to a discussion in the forums about the role of spacecraft in covert operations. As my reply got more detailed, I decided it might merit a blog entry.
The problem posed, broadly, was whether it's possible to sneak up on a ship or hab in space. How would a Firewall team go about boarding and infiltrating a habitat or spaceship if egocasting in and getting resleeved weren't an option? And if their target were an asteroid or moon, would it be possible to do an orbital insertion undetected? I'll save discussion of how one boards a habitat or ship for another time and concentrate here on the issue of sneaking up on things over the vast distances of space.
Radar and infrared detection remain the primary means of detecting ships in space in the Eclipse Phase universe, so reducing the RCS (radar cross section) and IR signature of your ship are the two best ways to not be seen. From there, other factors come into play, like the visibility of a craft to the naked eye or lidar, but dealing with these challenges is trivial compared to avoiding electronic detection.
Stealthing a spacecraft or vac suit against radar is not difficult with the level of technology in the game. For vac suits, hard suits, and small vehicles, raising the cost by one category to reflect non-metallic construction, smaller form factor, and radar absorbing materials is about right. Stealthing something large like a GEV should be more expensive, and stealth construction on really large vehicles should not be possible (unless your plot really needs it). For any vehicle, anti-radar stealth should involve a reduction in cargo capacity (and probably fuel and life support range, as well). Since we don't list costs for ships, we leave it to GMs what sort of hoops PCs will have to jump through to get a ride. Just keep in mind that stealthing large vehicles is a design challenge, and therefore not cheap.
A ship stealthed against radar won't show up on radar screens. If a character actively monitoring radar has reason to believe something is there, they can try to use Interfacing (probably with a big negative modifier) to look for pings that the device AI discarded as ghost signals.
Foiling Visual Spotting & Lidar
Coating a vac suit, vehicle, or ship with a non-reflective coating to foil lidar and visual should be cheap, from Trivial for something small up to Moderate for a ship. Lidar won't bounce off a non-reflective coating. Characters in vac suits should receive an Infiltration test against visual spotters. For small vehicles, Pilot [Aerospace] with Infiltration as a complementary skill works well.
Avoiding infrared detection is the big challenge for both sneaking up on a hab and orbital insertions. EVA Sleds and Thruster Packs have no appreciable IR signature. Rocket Packs and ships do; firing rockets will light up the IR sensors on a habitat's tactical network like a Christmas tree.
How hard it is to do a stealthy orbital insertion depends upon how good the target's network of sensors is. A surface installation on a large body with only ground-based sensors is easier to sneak up on than an installation on a small body with a network of satellites or ground-based sensors covering the whole surface. A ship entering a planetary atmosphere will always generate a bright IR signature at the point of re-entry, but once in the atmosphere, it can stay hidden if it doesn't use rockets and isn't already locked on radar.
We have ships that can re-enter a planetary atmosphere and land without thrusters already. The most familiar are American space shuttles. (And here shall be one of the rare instances where I defense said sorry piece of technology!) On re-entry, a space shuttle uses the planetary atmosphere to brake, then performs a series of S-turn maneuvers to further slow itself. It then lands like a glider. The space shuttle requires a long runway, but if you build a ship that can do a gliding re-entry and is stealthed against radar, then firing rockets to brake when you're either very close to the ground or on the other side of the planetary body from the target's sensors becomes a viable option for stealth insertions.
The bad news is that this still relies on there being an atmosphere. The good news is that even a very thin atmosphere, such as Titan's, was sufficient for a combination of atmospheric braking and parachutes to bring the Huygens probe safely to ground. We don't describe ships that can glide in the rules, but GMs are welcome to introduce them. Bringing a ship in on a glide approach should require some tricky Pilot [Aerospace] rolls, along with Navigation rolls to land close to the objective. Groundside monitors watching sensors that could detect the spacecraft should receive Interfacing checks to spot the IR flare of a ship on reentry. From there, they may attempt to get a radar lock. Generous GMs might make this an opposed test.
Stealth Approach in Space
Sneaking up on a habitat or ship in space is the most difficult task described here, and in some cases might not be possible at all. The best option is to use RCS reduction and visual camoflauge in concert with cold gas thrusters like we have on present-day EVA suits. This mostly eliminates the IR signature and is really the only way to sneak up on a space habitat in a ship or EVA suit. The problem here is that the delta-V from a cold gas thruster is pathetic compared to a rocket, so the approach has to be really slow. If the target is a wide-open region of space with no cover than can occlude the incoming ship from sensors, the amount of time to cover the distance might be so long that the characters need to consider other options. Characters with Navigation or appropriate professional skills should be able to figure out whether such an approach is feasible very easily.
If the target is situated in an asteroid field, a character who's a stone player with orbital mechanics can probably figure out how to use rockets while hidden behind another object to decelerate to a speed where the ship or EVA suit can drift toward the target and then use thrusters to stop. This should require some very difficult Pilot [Aerospace] and Navigation tests with detection by the target or missing it completely likely consequences of failure. If the characters succeed and avoid visual detection, though, sneaking right up to the target and then decelerating with thrusters is possible. Due to the huge distances involved (even within an asteroid belt), this should be a very slow method of approach, possibly taking days of game time.
For a good description of the logistics of sneaking up on a spacecraft undetected, Stephenson's description in Anathem of the Avout boarding the Daban Urnud is pretty good stuff.
And what if they get spotted?
Well, then your PCs are in space combat. And as they should know by now, that's bad. Make the risks clear before they try this at home.