This addon adds the spent upper stages called the Centaur-D booster, which were in active service from 1962 to 1989. As of November 2022, a total of 21 objects were available below, more will be added in the near future:
1963-047A = AC-2
1966-084B = AC-7 (Surveyor 2), later rediscovered as 2020 SO
1968-110B = AC-16 (OAO 2)
1969-069B = AC-18 (ATS 5)
1971-006B = AC-25 (Intelsat 402)
1971-116B = AC-26 (Intelsat 403)
1972-003B = AC-28 (Intelsat 404)
1972-041B = AC-29 (Intelsat 405)
1972-065B = AC-22 (OAO 3)
1973-058B = AC-31 (Intelsat 407)
1974-093B = AC-32 (Intelsat 408)
1975-042B = AC-35 (Intelsat 401)
1975-091B = AC-36 (Intelsat 4A-1)
1976-010B = AC-37 (Intelsat 4A-2)
1976-042B = AC-38 (Comstar 1A)
1976-073B = AC-40 (Comstar 1B)
1978-035B = AC-48 (Intelsat 4A-6)
1978-068B = AC-41 (Comstar 1C)
1981-018B = AC-42 (Comstar 1D)
1985-055B = AC-64 (Intelsat 5A-11)
1985-087B = AC-65 (Intelsat 5A-12)
2020 SO, the spent Centaur-D stage of Surveyor 2, on its closest approach to Earth on 2020-Dec-1