| Primary satellite | Secondary satellite |
| Name | Transit 4A | Cosmos 1861 |
| Spacetrack catalog number | 116 | 18129 |
| Radar cross section | medium | large |
| Epoch of two-line elements (UTC) | 2021 Jan 22 17:16 | 2021 Jan 22 20:50 |
| Time of closest approach (UTC) | 2020 Dec 01 13:27:33.754 |
| Minimum distance | 7.313 km |
| Height difference | 6.550 km |
| Relative speed | 13.312 km/s |
| Angle between velocity vectors | 130° |
| Geographic position | 51.3°N, 81.0°W |
| Height | 985 km |
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