Debris Field

http://uni2.ogame.de/game/img/galaxy/tf_a.gif Debris field in the galaxy menu

A debris field (often shortened to DF) consists of metal and/or crystal. The size of the DF is shown via a mouseover effect in the galaxy menu.

A debris field is created with every battle on a planet or moon. The size of the debris field depends on the number of destroyed units, with 30% of the build cost going into the debris field in normal universes.

The debris field forms at the planet position of the attacked planet. In the galaxy menu you see it as an image representing the debris, in the DF column. Hovering the mouse over the image shows the size of the debris field. Special case: an empty debris field is also created by an attack in which no ships are destroyed — that is, a unit doesn't necessarily have to be destroyed for a debris field to form; a battle simply taking place is enough.

Calculation

The costs are the sum of the individual ship costs.

For normal universes (30% into DF):

 DF metal = 'metal cost of the destroyed ships' * 0.3
 DF crystal = 'crystal cost of the destroyed ships' * 0.3

For "defense into DF" universes (30% into DF, a feature not used in pr0game's current universes):

 DF metal = 'metal cost of all destroyed units' * 0.3
 DF crystal = 'crystal cost of all destroyed units' * 0.3

In "defense into DF" universes, destroyed ships and defense both count. It doesn't matter whether or how much defense rebuilds itself.
The debris field from defense is halved if an engineer officer is used.
If a debris field already exists before the battle, the new resources are added to it.

Example

In a battle, 100 Light Fighters and 100 Rocket Launchers are destroyed, and 70 Rocket Launchers rebuild themselves after the battle:

Normal universe: debris field of 90,000 metal and 30,000 crystal
"Defense into DF" universe: debris field of 150,000 metal and 30,000 crystal

(Note: pr0game's current universes all use the 30%-ships-only calculation — the "defense into DF" and elevated-percentage variants above are documented here as they exist in the general OGame ruleset, see also the per-universe "% of destroyed defense goes into the debris field" settings on the universe overview page, which set this independently per universe.)

Harvesting

Debris fields can only be harvested by recyclers. When sending your fleet, "harvest" must be selected as the order. You can also send other ships along to a debris field, as long as at least one recycler is part of the fleet. This makes a debris field a good target to use for fleet saving as well.

In such a case, however, a recycler only fills its own cargo hold while harvesting, so it's not possible, for example, to harvest a debris field of 40,000 resources with only one recycler and one Large Cargo Ship. To compensate, resources can be sent along on the flight to a debris field without being lost, though this can in turn reduce the effective cargo capacity available for harvesting.

When a debris field is flown to, the owner of the corresponding planet is not notified about it. This means it's not easy to find out who harvested a debris field that may no longer be there.

Sending Recyclers

The "debris field" position can only be flown to if a debris field is registered in the database at that spot and the fleet contains at least one recycler. It doesn't matter whether a debris field is actually shown in the galaxy view or not, see also the "special debris fields" section below.

Once you've picked a debris field (e.g. via the galaxy menu), switch to the fleet menu, select the number of recyclers, enter the coordinates, and select "DF" instead of "planet" as the position. Finally, select "harvest" as the order and confirm.

If you have trouble remembering coordinates and don't want to write them down either, you can also send recyclers directly from the galaxy view as follows: hover the mouse over the planet next to the DF you want to harvest until the context menu appears. Select "attack" there, set the number of recyclers in the fleet menu -> [Continue]. The coordinates should already be filled in; now select DF instead of planet -> [Continue]. Finally, activate "harvest" instead of "attack" and off you go.

Commander holders can also harvest debris fields directly from the galaxy view, as long as recyclers are available on the active planet. Without a Commander, this button and a confirmation prompt take you to the officer menu instead.
If no debris field exists yet, but recyclers should be sent to collect the debris expected from a planned attack, a DF must first be created. This is usually done by attacking with an espionage probe.

Special Debris Fields

Besides the normal debris fields shown in the galaxy view, there are also a few special types of debris fields.

Invisible Debris Fields

Invisible debris fields are debris fields that contain fewer than 301 resources and are not shown in the galaxy view. Espionage probes are therefore well suited in normal universes for creating invisible debris fields, since they're the only unit whose destruction can create an invisible DF (of 300 crystal). If an invisible DF already exists, it becomes visible once (another) probe is destroyed there.

Invisible debris fields can be flown to and harvested normally.

Empty Debris Fields

Empty debris fields are debris fields that exist but contain no resources. They're created by any attack in which no ship is destroyed. Fully harvested debris fields also remain in the database as empty debris fields.

Empty debris fields are not shown in the galaxy view, but can still be flown to normally.

Ghost DFs

Ghost DFs are debris fields without a planet. These can occur when the planet belonging to a (visible) debris field is deleted — whether the planet disappeared due to abandoning the colony, account deletion, or inactivity deletion doesn't matter. They can be flown to and harvested like normal debris fields.

If a new planet forms at the position of a ghost DF (e.g. through colonization), it can happen that the debris field, along with its resources, becomes visible again.

Ghost DFs no longer exist in the current game version — DFs are visible even without a planet, as long as they contain more than 300 resources.

Cleanup Script

Invisible debris fields and empty debris fields are removed from the database every Monday at approximately 1:10 AM by a debris field cleanup script.

Cleanup Prevention

If fleets are en route to an invisible or empty debris field, or are still on their return trip, during the cleanup process, the DF is not deleted.

Moon Formation

If a debris field is large enough, a moon can form from it. For every (new) 100,000 resources in the debris field, the probability of moon formation is 1% (maximum 20%). The debris field remains intact even if a moon forms, and can still be harvested.

Resources already present in the debris field before the battle, or the timing of harvesting, do not influence moon formation, since this runs together with the battle script.

Combat Report

In a combat report, the resulting debris field is listed in the last lines, after the end of the battle. If it's large enough, the chance of moon formation is also shown, as well as documentation of a moon actually forming, if one did, as in the following example:

328,800 metal and 158,100 crystal now lie at these space coordinates.
The chance of moon formation is 4%.
The enormous amounts of free metal and crystal attract each other and form a satellite around the planet.

Trivia

In the past, all debris fields with at least one resource were visible.
The DF cleanup script was introduced, among other reasons, to relieve load on the database. Initially, however, only debris fields with fewer than three resources were deleted.

Adapted and cleaned up from owiki.de (GNU Free Documentation License 1.3), a general OGame community wiki — the conceptual explanation applies generally, but specific numbers/formulas may differ from the pr0game source code and are not verified.