| Code | Description | Explanation | Implementation caveats |
|---|---|---|---|
| D-SO | Down/SO Targeted | One good way of avoiding leaving a large empty
rocket stage in orbit is to make the large stage just marginally suborbital
(perigee less than 80 km), so that it
crashes back to Earth at a predictable, targeted place and time on the other side of the world,
and you can issue warnings to keep ships and aircraft out of the area. Then the job
of performing the last little bit of orbit insertion with a much smaller rocket engine,
often part of the payload.
Examples include the Shuttle External Tank, the Tsiklon-2/US-P, and the Ariane 5G core stage. | The reentry catalog includes cases with perigees between -1000 and +80 km. Cases with perigees less than -1000 km are not included (and are considered fully suborbital, rather than marginally suborbital ones that could have been orbital with a slightly different design). |
| D-DO | Down/Deorbited | Restart an upper stage rocket engine, or fire a payload rocket engine, to lower orbital perigee into the atmosphere and cause destructive reentry within less than one orbit at a targeted place and time. | |
| D-LAND | Down/Landed | As deorbit, but the vehicle is designed to survive entry and reach the surface intact. | |
| D-LEO25 | Down/LEO Reentry <25yr | A low Earth orbit (LEO) object which made an uncontrolled reentry into the atmosphere and burned up within 25 years of the end of active life; | |
| D-NL25 | Down/LEO-crossing <25yr | Uncontrolled reentry within 25 years of end of active life for an object which starts in an orbit whose perigee is in the LEO zone and whose apogee is at a higher altitude. | |
| U-LEO25 | Up/LEO <25yr expected | Object still in LEO, but expected to reenter within 25 years of end of active life. | Based on analysis of the historical data, I use the simple (but highly approximate) rule that objects left at an orbital height of 600 km or more will take more than 25 years to reenter. |
| U-NL25 | Up/LEO-crossing <25yr expected | Object still in orbit, with initial apogee above LEO, but expected to reenter within 25 years of end of active life. | |
| U-MEO-E | MEO Graveyard (ell.) | Object left at end of mission life in medium Earth orbit (MEO). Sub-case: Elliptical orbit in which the orbit spends less than 25 years every 200 years in the MEO protected zone. | For this and other MEO cases, instead of doing the proper calculation for a 200 year propagation, I simply use an extra 100 km padding: the initial disposal orbit is more than 400 km either side of the 20183 km MEO value. |
| U-MEO-C | MEO Graveyard (circ) | Object left at end of mission life in medium Earth orbit (MEO). Sub-case, circular orbit avoiding the MEO protected zone; the orbit spends less than 25 years every 200 years in the MEO protected zone. | |
| U-GGYD | GEO Graveyard | Object left at end of mission life in GEO graveyard orbit, avoiding crossing the GEO protected zone for 100 years. | Instead of doing the proper calculation for a 100 year propagation, I use the initial disposal orbit and add a 100 km padding to the GEO protected zone. |
| D-LUN | Down/Lunar | Object left at end of mission life on the lunar surface (either intact landing or destructive impact). | I note that this is not included as an option in the US ODMSP, but is a reasonably harmless method of disposal. |
| U-HEL | Heliocentric | Object departed the Earth-Moon system and left in heliocentric orbit or in the vicinity of another world. | |
| D-LEO | Down/LEO Reentry | Object was left in LEO and made an uncontrolled reentry more than 25 years after end of mission life | |
| D-NL | Down/LEO-crossing Reentry | Object was left in orbit with perigee in LEO but higher apogee, and made an uncontrolled reentry more than 25 years after end of mission life | |
| U-LEO+ | Up/LEO | Object was left in LEO and is still in orbit more than 25 years after end of mission life | |
| U-LEO | Up/LEO | Object was left in LEO and is still in orbit; it is expected to still be in orbit 25 years after end of mission life | Implemented using the criterion of a 600 km or greater disposal orbit altitude. |
| U-NL+ | Up/LEO-crossing | Object was left in orbit with perigee in LEO but higher apogee, and is still in orbit more than 25 years after end of mission life | |
| U-NL | Up/LEO-crossing | Object was left in orbit with perigee in LEO but higher apogee, and is expected to be still in orbit more than 25 years after end of mission life | |
| U-DEST | Destroyed | Object was destroyed in orbit and reduced to debris | |
| U-GTO | Crosses LEO and GEO | Object was left in an orbit crossing both the LEO and GEO zones | |
| U-XMEO | Violates MEO rule | Object was left in an orbit crossing the MEO protected zone for more than 25 of the next 200 years | Currently using the laughably inadequate approximation of no orbit perturbations but a 100 km additional padding. |
| U-XGEO | Crosses GEO | Object was left in an orbit that crosses the GEO zone. | |
| U-GEO | In GEO | Object was left in an orbit in the GEO zone | |
| U-CISL | Cislunar | Object was left in a distant Earth orbit beyond 150,000 km. Such orbits can be chaotic due to lunisolar perturbations, and result in hard to predict outcomes which can include Earth reentry, lunar impact and heliocentric escape. |