| 1971-093A | X-3 |
| 1974-013A | X-4 |
| 2010-015A | X-37B OTV-1 |
| 2011-010A | X-37B OTV-2 |
| 1997-058D | X-Mir Inspektor |
| 2011-015C | X-Sat |
| 2003-031J | XI-4 |
| 2005-043F | XI-5 |
| 2000-033B | Xinhua 1 |
| 1998-044A | Xin Nuo 1 |
| 2006-048A | Xin Nuo 2 |
| 2007-021A | Xin Nuo 3 |
| 2011-026A | Xin Nuo 5 |
| 2010-042A | Xin Nuo 6 |
| 2009-072B | Xiwang-1 |
| 2001-018A | XM-1 |
| 2001-012A | XM-2 |
| 2005-008A | XM-3 |
| 2006-049A | XM-4 |
| 1999-066A | XMM-Newton |
| 1998-044A | XN-1 |
| 2006-048A | XN-2 |
| 2007-021A | XN-3 |
| 2011-026A | XN-5 |
| 2010-042A | XN-6 |
| 2011-015C | XSat |
| 2003-005B | XSS-10 |
| 2005-011A | XSS-11 |
| 2005-005A | XTAR-EUR |
| 1995-074A | XTE |
| 2009-072B | XW-1 |