To make your travel between worlds more enjoyable and safer, the ITA's TDRS has put together a set of rating and advisory codes to make it easier to identify the kind of world you may be visiting. The ITA does not publish the twitch coords for any world rated Class E or less. To get the twitch coords for a class F, you have to apply to the ITA Board of Governors. There will be a hearing, and you'll have to present your reasons for going to that world, and the ITA's ISS will speak out why not. Only 12% of Class F applications are granted.
Class A's range from A-1: Luxury worlds, to A-5: Motel 8 worlds. For those of you not native to the USA, think of a motel 8 world as Fawlty Towers without the charm. On this scale, Earth Prime rates a qualified A-2. It should really be a A-3, but there are enough hotels, spas, retreats, and parks of A-1 quality, that it gets an A-2 rating.
A Class B advisory indicates that while cultural differences may exist, travelers will not come to serious harm as long as they obey local regulations.
A Class C advisory indicates a lack of information or contradictory information on a particular world, or situations that might be dangerous, but not overtly so.
Class D advisories indicate conditions which potentially pose an immediate and personal danger to travelers. Many insurance companies will not insure a trip to a Class D area, and the others will charge considerably more than the standard policy.
A Class E area is an area where visitors stand a significant chance (in some cases better than 50-50) of not coming back. Class E advisories mirror the Class D categories, but indicate more dangerous conditions. For instance, a conventional regional war might be Class D-2, while the same war using chemical or biological weapons would be E-2. (A genocidal conflict would also be E-2.)
Class E Advisories are more etreme versions of Class D ones. Examples would include:
Class F, is an interdiction rather than an advisory. A Class F rating simply means that no travel is allowed under normal circumstances, and even scientific or diplomatic missions must obtain clearance prior to traveling. Class F doesn't mean danger, it means that the ITA has marked this world as off limits to contact and trade. In addition Class F interdictions are applied to areas where danger is extreme, such as lethal biological contaminants (Famine- Earth is one such world), radioactive wastelands, or areas where strangers are killed on sight. Pol Pot's Cambodia may be the closest OTL has ever come to a Class F area.
Class X worlds are those to which access is not denied, but of little use except as a source of resources. Access to X-3 through X-5 and X-7, X-8 are rountinely handed out, X-1 or X-2 are being held until it can be confirmed if sentient life exists on these worlds or not. X-6 worlds are not acknowledged to exist.
X-1: Methane Earth alternate
X-2: Chlorine Earth alternate
X-3: Vacuum
X-4: No sentient life
X-5: No life, reducing atmosphere.
X-6: Classified. The ITA has found something on this world, that it has been deemed so dangerous that they will not say who or what they have found. The coords are on recorded, encrypted, and the key is in five parts: the Governor of the ITA has one, the heads of the three main branches of the ITA, and the fifth Key is held in an escrow account on Marketplace Earth's Swiss bank. Even admitting that a world is rated X-6, is classified.
X-7: climate inhospitable to human life (above 120 F or below -50 C).
X-8: No dry land