Ascension is a short period inactive comet with aphelion inside Urlum's (OPM) orbit. Kerbal Astronomical Society thinks landing on it would be a great idea, but certain members fear any thrusters would knock it into Kerbin one day. Despite those fears, majority of Kerbal scientific community doesn't care about it and even looks forward seeing such dreadful development as it would be a valid reason to visit it again and shove it around some more.
This is a modified part of Sentar Expansion mod made by Borisbee, which itself is a modernized Planet Factory by Kragrathea. Both of them did a massive great job.
My longstanding opinion is that KSP should get a body like Ascension (and Ablate, for that matter) for its unique qualities and mission opportunities, but years have passed and no development regarding the solar system was observed. For those reasons I've decided to do make this modification so that a stockalike comet reaches wider audience.
Some crucial parameters of the original comet have been tweaked after calculations and experimenting in order to make it behave more realistically for stock KSP solar system. All the original orbital parameters have been preserved as Kragrathea made them. Only the comet itself has been reduced in size and mass and its surface has been darkened. Sadly, there is no tail because I really don't know how to make one, but if/when circumstances allow it, it will get both coma and a tail full of poisonous goodies, preferably variable in size.
fuel requirements - Missions require loads of Δv and careful planning. This is way worse than trying to catch an asteroid about to hit Kerbin. Speed differences are enormous.
thermal protection - Be careful with timing your mission. If you stay on the comet during perihelion, whatever you landed there might cook.
surface mobility - I recommend Kerbal Attachment System mod to anchor your vessels firmly against the surface. Kerbals should use jetpacks as they can't walk. "Orbital mode" for the view could be used without any issues as "down" is barely applicable here. Rovers can't use wheels, but tiny landers with reaction wheels can happily hop around.
One must observe care when orbiting Ascension or moving on its surface. KSP experiences floating point errors at extreme values, being large or small . For example, gravitational constant gets wonky. Also, Ascension rotates at 66.6% of maximum (superfast rotator) speed, so if a Kerbal jumps from the equator, it's possible there is no coming back if the cliff is high enough. It's entirely safe to jump on poles, but make sure you pack propellant unless your Kerbal doesn't mind spending hours falling back.
Even though surface gravity is enough to keep them on the ground, the floating point problem gets even worse in the case of Kerbals just standing on the equator. They aren't held by the ground properly. That's KSP's problem, not something that I can solve.
home signal - Mind the aphelion distance because even the strongest stock relay antenna will lose signal near comet's aphelion.
tiny inactive comet, a crumpled rubble pile problems catching it and staying on it periapsis below Moho and apoapsis above Eeloo (or, if you use Outer Planets Mod, between Sarnus and Urlum) "biomes" gravity so low Gilly feels like your mom
coma and tail(s) active surface (gas jets) surface scatter
if you have "Sentar Expansion" mod installed, delete the Ascension folder from it, for obvious reasons
extract the "Realistic Ascension" folder into your GameData folder like this: Kerbal Space Program\GameData\RealisticAscension
install latest Kopernicus for your version of KSP