CERTIFICATE OF RE-ENTRYOrbital Register™ · by Orbital Radar™
Entry no.
1978-0499
EXPLORER 51 (AE-C)
EXPLORER 51 (AE-C) (NORAD 6977) re-entered Earth’s atmosphere on 12 December 1978, after 4 years, 11 months in orbit.
Official date
NORAD number
6977
International designator
1973-101A
Object type
Spacecraft
Country
United States
Launched
16 Dec 1973Vandenberg
Re-entered (UTC)
12 Dec 1978UTC calendar day
Time in orbit
4 years, 11 months1,822 days
How it ended
Re-entered (natural decay)
Latitude range
67.9°N to 67.9°SFinal inclination 67.9°
Mass
668 kg
Operator
GSFC
Built by
RCA/East Windsor
Bus
AE-C
Programme
Explorer AE
Where it came down
Latitude band its orbit allowedExact position not recorded
No position was recorded for this re-entry. Its final orbit, inclined at 67.9°, allowed a re-entry anywhere between 67.9°N and 67.9°S.
Life in orbit
4 years, 11 monthsEXPLORER 51 (AE-C)’s lowest and highest points above Earth, week by week, from its tracking history.
Also ended on 12 Dec 1978
6 entriesFrom the same launch
1973-101
Entered in the Orbital Register™, founding volume, September 2026.
Record version 1 · No corrections · orbitalradar.com/register/1978-0499
© 2026 Orbital Radar. Cite this entry by its number; the register itself may not be copied.
Record version 1 · No corrections · orbitalradar.com/register/1978-0499
© 2026 Orbital Radar. Cite this entry by its number; the register itself may not be copied.