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10/02/2022 – Ephemeris Extra – NASA goes on the offensive

October 2, 2022 Comments off
Didymus and Dimorphos from DART

DART images of both Didymos, the big one, and Dimorphos, on approach. Credit NASA / JHAPL

This is a slightly revised version of my article in the Stellar Sentinel, the newsletter of the Grand Traverse Astronomical Society. Educators may receive a free PDF copy of this monthly publication via email, which covers astronomical topics and events visible from Northwest Lower Michigan. Send your request, stating your affiliation, to info@gtastro.org.

The score is: Asteroids-billions, NASA-1. It’s a bit unfair, since asteroids have been hitting the Earth for 4.567 billion years or so, and NASA has been around for 64 years before DART spacecraft collided with the asteroid Dimorphos. Hey, this was their first attempt at a small asteroid. As far as the 21st century destructive asteroid score is 1 to NASA’s 1, as far as I know.
That strike was in Chelyabinsk, Russia. That was February 15, 2013. We were all waiting on another asteroid making a close pass of the Earth, when the Chelyabinsk meteoroid exploded 14 miles above the city. Over a thousand people were injured by the blast wave. They saw the bright flash and rushed to the windows to see what it was. Then the blast wave hit, shattering the windows, causing glass cuts for over a thousand people. One building’s wall collapsed, and a fragment fell into a lake outside of town.
NASA’s record in attempting to hit a planetary object dates back to the early 1960s and the nine Pioneer missions to crash a probe on the Moon, sending back pictures all the way down. Back in the early 60s, just hitting a 2,100-mile (3380 kilometer) wide object a quarter of a million miles away was a dicey prospect. It’s one thing to miss the Moon on one side or the other, but to not have enough oomph to even make it all the way is downright embarrassing. NASA did much better by the end of the decade with the Apollo manned landings and bombarding the Moon with used space vehicles for seismic studies of its interior.
NASA actually collided a spacecraft into a comet. That was July 4, 2005, when the impactor part of the Deep Impact spacecraft hit Comet Tempel 1’s nucleus, attempting to study part of its subsurface. The non-impactor part was later renamed EPOXI and went on to fly by the dog-bone shaped Hartley 2 comet nucleus. Another reused comet explorer spacecraft Stardust after collecting cometary dust from Comet Wild 2 (pronounced Vilt 2), and possible interstellar dust penetrating the solar system, and after dropping the sample re-entry capsule back on Earth it ended in solar orbit. Later it was repurposed as the Stardust-NexT mission and flew by Tempel 1 six years later to study the crater the Deep Impact Impactor made in the comet.
To study the effect of a collision of a spacecraft from the Earth despite the fact that Dimorphos cannot be seen is a trick. However, the pair is an eclipsing binary from our point of view, so the brightness of the unresolved pair changes as they eclipse each other.
Before the collision, Dimorphos had an 11.9 hour orbit of Didymos. Dimorphos is a fifth the size of Didymos orbiting it at three times the primary’s radius. If the orbit is near circular, Dimorphos’ orbital velocity is only 0.39 mph (0.63 kph). It should be relatively easy to see a tiny change in Dimorphos’ orbital period.

Last frame Dimorphos fit in from DART

Last frame Dimorphos fit in from DART. Credit NASA / JHAPL.

Two images from the LiciaCube satellite

Two images from the LiciaCube satellite launched from the DART spacecraft 15 days before the impact, and trailing it to record the collision with its wide and narrow angle imagers. Dimorphos does appear to be a rubble pile asteroid from its appearance and the amount of ejecta caused by the impact. The ejecta adds to the effect of the spacecraft’s kinetic energy by pushing away from the asteroid by Newton’s third law of motion. Credit: Italian Space Agency.

Dimorphos ejecta from Atlas

A frame from a time-lapse video taken from the ATLAS Project’s South African observatory of the unresolved Didymos – Dimorphos pair and the expanding ejecta cloud. The asteroid pair developed a dust tail like a comet for a while.
ATLAS is an acronym for a rather apocalyptic title “Asteroid Terrestrial-impact Last Alert System”. Developed by the University of Hawai’i and funded by NASA. It has two telescopes in Hawai’i, one in Chile, and one in South Africa. Credit: NASA/UH.

Days later, Dimorphos was exhibiting a thin dust tail, like a comet.

Now we wait on Earth’s observatories to observe of the period of Dimorphos’ orbit. It should decrease the orbital time.

04/12/2021 – Ephemeris – Human space flight began 60 years ago today

April 12, 2021 Comments off

This is Bob Moler with Ephemeris for Monday, April 12th. Today the Sun will be up for 13 hours and 21 minutes, setting at 8:24, and it will rise tomorrow at 7:01. The Moon, 1 day past new, will set at 9:05 this evening.

60 years ago today Yuri Gagarin a Soviet Air Force pilot became the first cosmonaut and first person to orbit the Earth in his Vostok-1 spacecraft. The event has been celebrated around the world since 2001 as Yuri’s Night. Gagarin was strictly a passenger on his flight, but was given a key to override the automated functions of the spacecraft to take over manually if needed. He ejected from the capsule as planned to land by parachute. His flight came three weeks before the United States and NASA launched Alan Shepard on his sub-orbital flight in his Freedom 7 Mercury Capsule on May 5th 1961. It wasn’t until February 20th the next year that John Glenn made three orbits of the Earth in his Friendship 7 Capsule to match Gagarin’s feat.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Yuri Gagarin in space helmet
Yuri Gagarin in his space suit and helmet.
Vostok-1 rocket at launch
Vostok-1 rocket at launch carrying Yuri Gagarin on his single orbit of the Earth. The current Soyuz rocket is a direct descendant of the R-7 used for Yuri Gagarin’s flight and the Soviet’s first ICBM.
Vostok capsule upopn landing
The Vostok capsule upon landing. Gagarin was ejected from the capsule at 7 kilometers altitude to land with his own parachute rather than trying to survive a rough hard earth landing in the capsule.
Yuri's Night logo
Yuri’s Night logo