OGO 1 reentered the atmosphere over Tahiti on Saturday, August 29th, a daytime event that was captured by PYF Spotters and posted to their Facebook page. (See video below). Also, check out this great old video of the launch of OGO 1 from way back in 1964. (Thanks to @ItsAstroKota and @_starbase_ on Twitter for the amazing find!)

An artist's impression of Orbiting Geophysical Observatory 1 in orbit.

A 56-year-old NASA spacecraft is about to burn up in Earth’s atmosphere. Known as Orbiting Geophysical Observatory 1 (OGO 1), it was the first in a series of six observatories launched by NASA in the 1960s — and the last one to drop from orbit.

OGO 1's imminent demise has come to light via the Minor Planet Mailing List (MPML) online message board. Initial postings described a mysterious object listed as C1979M1, spotted by the Catalina Sky Survey (CSS) on the night of August 25–26, that was heading toward Earth. Discussion on the board soon revealed the object’s true identity as OGO 1, which had been expected to reenter in August or September.

Astronomers at the University of Arizona's Catalina Sky Survey captured this image sequence revealing the OGO 1 spacecraft (circled) on the night of August 25–26.
Catalina Sky Survey / University of Arizona / NASA
OGO 1, imaged
Goran Gašparović shares his observations of OGO 1 taken on the morning of August 28th.
Goran Gašparović / iTelescope.net

OGO 1 is listed on Chris Peat’s Heavens-Above as COSPAR object 1964-054A and NORAD catalog number 00879. According to spacecraft expert Jonathan McDowell, at the moment the spacecraft's wide-ranging orbit, inclined 55° to Earth's equator, carries it from a distant apogee of 83,425 miles (134,260 km) to an unsustainable perigee of just 73 miles (117 km).

The spacecraft passed through its perigee earlier today while over Bolivia, at 15:05 Universal Time (1:05 p.m. EDT). Although its low altitude would ordinarily make it easily visible among the stars, OGO 1 currently swings through perigee over Earth's daytime hemisphere, rendering it invisible in a sunlit sky.

The wide-ranging orbit of OGO 1.
Chris Peat/Heavens-Above

Dynamicist Bill Gray (Project Pluto) uses observer sightings to create orbital elements for asteroids, comets, and satellites. Now, armed with the new OGO 1 positions found by CSS, Gray predicts an atmospheric reentry at perigee over the central Pacific Ocean near French Polynesian on August 29th around 21:00 UT (11 a.m. in Tahiti).

"The perigee being on the day side put the apogee out on the night side, where we could see it," Gray explains. "If it hadn't been for that, we might have had to go with just the last data we had — which were good enough to say it'd reenter in late August, but not much more than that."

The U.S. Defense Department’s Combined Space Operations Center (also a clearinghouse for reentry predictions) has yet to list OGO 1 on its Space-Track reentry forecast. This omission is not uncommon, however, for objects in higher orbits.

Gray notes that OGO 1's orbit has changed quite a bit since its launch on September 5, 1964. "This object has been observed a lot by asteroid hunters," he says, who've reported about 500 observations of it over the last five years alone. He adds that observations made after today's perigee should cinch whether reentry is probable on the upcoming August 29th daytime brush with Earth over the Pacific.

A Groundbreaking Mission

Launched September 4, 1964, from Cape Canaveral atop an Agena B rocket, OGO 1 was designed to study Earth's magnetosphere and its interaction with the Sun-Earth space-weather environment. Weighing in at 1,074 pounds (487 kilograms), OGO 1 is one of the largest artificial objects to reenter since the Chinese space station Tiangong 2 in July 2019. OGO 1 also made one of the first orbital observations of a comet, observing Comet 2P/Encke in the ultraviolet in 1970. Two booms on OGO 1 failed to deploy fully after launch, blocking a horizon sensor and limiting attitude control for the spacecraft. OGO 1 was placed in standby status in 1969 and formally deactivated in 1971.

An Orbiting Geophysical Observatory satellite getting prepped for launch.

OGO 1 represents an era of the early Space Age, but even-older satellites are still orbiting Earth. For example, the first Canadian satellite, Alloutte 1 (ID 1962-049A/424), was launched from Vandenberg AFB in California in 1962. It's still worth tracking down with binoculars on a clear night. And the oldest satellite still in orbit? That title goes to Vanguard 1, launched from Cape Canaveral on March 17, 1958. Definitely an oldie, it's only the fifth object to orbit Earth and boasts the incredibly low NORAD catalog number of 00005! Vanguard 1 is expected to remain in orbit for another 180 years, through the end of the next century. Obviously, they built 'em to last back in the day — when mission designers didn’t think much about space debris or planning for a controlled deorbit at the end of a satellite’s useful life-span.

Amateur satellite-tracking is as old as the Space Age. Early volunteers for Project Moonwatch tracked and verified the very first artificial satellite (including Sputnik 1) beginning in the late 1950s. Today, satwatchers still track missions in orbit, hunt for classified satellites such as the U.S. Air Force’s X-37B, and confirm (or dispute) claims of satellite launches by North Korea, Iran, and Israel. Today much of the online discussion concerning satellite tracking revolves around the SeeSat-L message board.

This bit of satellite-sleuthing by volunteer observers online and in the field for the recovery and reentry of OGO 1 shows that sky-watchers still provide a valuable service when it coming to following what’s up there in orbit.


Image of PGT


August 27, 2020 at 4:47 pm

Burning up on re-entry, or landing on someone's house?

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