| Vela 3A | |
| Operator: | USAF |
| Cospar Id: | 1965-058A[1] |
| Satcat: | 1458 |
| Manufacturer: | TRW |
| Launch Mass: | 150kg (330lb) |
| Launch Date: | UTC |
| Launch Rocket: | Atlas Agena D 2A |
| Launch Site: | Cape Canaveral LC-13 |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Highly Elliptical |
| Orbit Periapsis: | 84534km (52,527miles) |
| Orbit Apoapsis: | 96238km (59,800miles) |
| Orbit Inclination: | 35.2° |
| Orbit Period: | 5,148.16 minutes |
| Apsis: | gee |
| Programme: | Vela |
| Previous Mission: | Vela 2B |
| Next Mission: | Vela 3B |
Vela 3A (also known Vela 5, Vela Hotel 5 and OPS 6577[2]) was a U.S. reconnaissance satellite to detect explosions and nuclear tests on land and in space; the first of the third pair of Vela series satellites; taken together with Vela 3B and ERS 17 satellites.
The secondary task of the ship was space research (X-rays, gamma rays, neutrons, magnetic field and charged particles). Sister Vela 3B was in a similar orbit, but 180 degrees from it, i.e. on the opposite side of the globe.
The satellite was rotationally stabilized (2 rps). The ship could work in real time mode (one data frame per second) or in data recording mode (one frame every 256 seconds). The first mode was used for the first 40% of the mission's duration. About 1 transmission was received every 4 hours. The second mode was used until the next pair of Vela satellites were launched.
The ship remains in orbit around Earth.