The Artemis 1 mission’s Orion spacecraft has successfully entered and exited a distant retrograde orbit about Moon. DRO is a stable and easily accessible orbit requiring a low velocity change \Delta V. In DRO, Earth‘s non-negligible gravity contributes to a 3-body problem that makes the inertial space orbit non-Keplerian: an ellipse centered — not focussed — on Earth.
The attached animation, which I generated by numerically integrating the 3-body motion equations, displays a DRO in reference frames fixed relative to distant stars [left pane] and rotating with Moon about Earth [right pane]. From the north celestial hemisphere, Orion [red] orbits anti-clockwise relative to Earth [cyan], like our solar system’s planets, but clockwise (and hence retrograde) relative to Moon [white].
For Artemis 1, Orion spent almost a week in DRO, completing a half revolution about Moon (and a quarter revolution about Earth), and is currently returning to Earth. The crewed Artemis 2 will use a free return trajectory for safety, and future Artemis missions will use Near Rectilinear Halo Orbits to avoid Moon periodically eclipsing Earth.
Far from Earth [cyan], the Orion spacecraft [red] entered a distant retrograde orbit about Moon [white]. Relative to Earth [left pane] Orion orbits one way, but relative to Moon [right pane] Orion orbits the opposite way. (You may need to click to start the animation.)From a distant retrograde orbit, a camera at the tip of an Orion solar panel photographs Earth and Moon, 2022 November 28.
I stayed up late last night and early this morning to watch the successful uncrewed launch of Artemis 1. In Greek tradition, Artemis was the twin sister of Apollo, and the Artemis program hopes to return humans — including the first woman — to Moon as preparation for sending them onward to Mars.
As a child of the Apollo program, I am convinced that a future with humans living and working in space, on Moon and Mars, is much more exciting than one with humans confined to Earth, and in this regard the half-century gap between Apollo and Artemis has been deeply disappointing.
Today real hope exists for realizing Apollo’s promise to permanently extend the bounds of human experience beyond low-Earth orbit. Later this decade, the crewed Artemis 2 should circumnavigate Moon and the crewed Artemis 3 & 4 should land on Moon’s unexplored South Pole. I hope these and subsequent increasingly ambitious missions and their diverse explorers will excite and inspire a new generation, the Artemis generation; I know they will excite and inspire me.
As currently planned, Artemis 3 & 4 will require the development of a brand-new revolutionary launch vehicle — a true 21st century super-heavy liftrocket, which I have highlighted before and expect to soon discuss again.
A camera attached to the tip of the Orion capsule’s service module photographed Artemis 1 departing Earth orbit on 2022 November 16
When Crew 5 rocketed to orbit last week aboard the SpaceX Dragon “Endurance” bound for the International Space Station, I was curious to see their zero-gravity indicator. A tradition SpaceX crews have adopted from Russian cosmonauts, the zero-g indicator is usually a stuffed animal whose first float announces the free-fall of Earth orbit. Was that a plush Einstein doll?
On orbit, Crew 5 pilot and physicist Josh Cassada explained that the doll demonstrated Einstein’s happiest thought, that people falling can not feel their own weight. This insight, essentially the equivalence of inertial mass and gravitational charge, permits gravity to be interpreted as geometry in the theory of general relativity, still our best description of gravity. Crew 5 is experiencing Einstein’s happiest thought not merely momentarily but continuously!
Einstein doll zero-g indicator floats (top right) aboard the SpaceX Crew Dragon “Endurance” illustrating Einstein’s happiest thought. (NASA TV)
The dinosaurs didn’t have a space program, but we do.
I just watched live the first kinetic-impactasteroid-redirection test as NASA’s Double Asteroid Redirection Test spacecraft collided with the asteroid-moon Dimorphos of the asteroid Didymos. Below is the last image DART transmitted, truncated by the impact itself!
The goal is to measurably change the speed of Dimorphos as it orbits Didymos to test asteroid planetary defense. Ground-based telescopes cannot resolve the system, which is only a few hundred meters across. (To DART Dimorphos looked like a spheroidal rubble pile). However, the system undergoes mutual eclipses as seen from Earth and its brightness dips periodically when one asteroid blocks or shadows the other. The head-on collision should have slowed Dimorphos, lowering its orbit and reducing its orbital period by several minutes, which should be noticeable over the next few weeks. Confounding variables include momentum exchanged with ejecta and the consequent gravity change due to their reshaping.
(In 2005, NASA’s Deep Impact space probe released an impactor into comet Tempel 1 not to redirect it but to excavate the interior for remote analysis, like taking a core sample from a tree.)
Final image transmission from DART cut-off by its impact with the asteroid Dimorphos
Last month I drove across the United States, coast-to-coast back-and-and forth diagonally, 8000 miles through 18 states, as in the animation below. Amazing was driving through the Great Plains of the North American flatland with uninterrupted 360° horizons as the sun slowly set and civil, nautical, and astronomicaltwilight seemed impossibly long. The explanation was the nearness of the summer solstice, when Earth’s tilt extends the sunset by spinning an Earth-bound observer diagonally across the day-night terminator, which is blurred by atmospheric refraction, as illustrated in the diagrams below.
My 2022 July road trip, back-and-forth across the continental US, 8000 miles across 18 states. (You may need to click to start the animation.)At the equinoxes Earth is not tilted to (or from) Sun and its spin sweeps earthlings rapidly through twilight (short thick black line segment at left). But at solstices, Earth is tilted to (or from) Sun and its spin takes longer to sweep earthlings through twilight (long thick black line segment at right).
Nearly a quarter century in the making, I was tremendously excited and relieved last week by the release of the first images from the JamesWebbSpaceTelescope. I remember the trials, tribulations, and triumph of the HubbleSpaceTelescope and am now confident that Webb’s gallery of images and spectra will meet or exceed Hubble’s and begin a new chapter in astronomy.
To distinguish Hubble and Webb images, look for their signature diffraction spikes: Due to their primary mirror shapes and secondary mirror support strut configurations, bright stars in Hubble and Web space telescopes images display distinctive 4 and 6 + 2 = 8 diffraction spikes.
Hubble and Webb images of the galaxy cluster SMACS 0723 with signature diffraction spikes around the bright foreground star
In Alfonso Cuarón‘s Oscar-winning 2013 movie GRAVITY, actress Sandra Bullock‘s Dr. Ryan Stone makes an emergency entrance into an abruptly abandoned International Space Station. This month, European Space Agency astronaut Samantha Cristoforetti recreated this scene onboard the space station, as in the photograph below, with the movie playing on the ISS Viewscreen.
In GRAVITY, “gravity” refers to both the Newtonian force that causes the astronauts and their spacecraft to endlessly free-fall around Earth and to the grave nature of their situation, a brilliant and stunning drama of adversity, courage, persistence, and triumph.
Astronaut Samantha Cristoforetti (bottom) enters a module of the real International Space Station as actress Sandra Bullock’s Dr. Ryan Stone enters the fictional station in the movie GRAVITY (top)
As part of my science history project, the article “Science, serendipity, coincidence, and the Oregonator at the University of Oregon, 1969–1974” has been published in Chaos: An Interdisciplinary Journal of Nonlinear Science.
It’s especially exciting because it’s the Feature article in the Focus Issue, From Chemical Oscillations to Applications of Nonlinear Dynamics: Dedicated to Richard J. Field on the Occasion of his 80th Birthday.
After many months of email exchanges and virtual meetings, I met Bob Mazo for the first time in person this January (see blog entry ‘50 years later‘). Together with Dick Field, the sole living scientist of the Field-Kőrös-Noyes (FKN) mechanism, developed in the early 1970s we revisited the exciting start of a new field in physical chemistry. The FKN mechanism was the first complete reaction scheme to describe the behavior of the Belousov-Zhabotinsky (BZ) reaction, a nonlinear chemical reaction-diffusion system (more here). Shortly after, they developed a mathematical three-variable model to describe the BZ reaction’s nonlinear behavior – the Oregonator model. The name was a response to the Brusselator model, developed by Ilya Prigogine in Brussels in the 1950s and 1960s. For his work on non-equilibrium thermodynamics and dissipative structures, Ilya Prigogine was awarded the Nobel Prize in Chemistry in 1977.
Fun fact: The total author age is 225, the average author age is 75! This will be difficult to beat.
Not only can suns stand still in the sky, from some exoplanets their motion can apparently reverse! Wooster physics-math double majors Xinchen (Ariel) Xie ’21 and Hwan (Michelle) Bae ’19 and I just published an article elucidating these apparent solar reversals.
Michelle and I began studying the architecture of daylighting terrestrial buildings for energy efficiency as part of her senior thesis, but due to our mutual interests, we gravitated to extraterrestrial possibilities. After my return from a yearlong sabbatical, Ariel eagerly continued the work for her senior thesis. Despite a pandemic keeping us a planet apart and meeting via video conference at simultaneously very early and very late hours, we completed the project, one of the most beautiful in my 33 years at Wooster. During one of our early morning, late evening sessions, we mathematically derived the solar reversals condition for the important special case of zero obliquity or tilt.
In the first figure below, exoplanet spin-orbit ratio\rho increases rightward, orbital eccentricitye increases upward, and timet increases outward. Red rods represent planetary observers, and coils represent apparent position and angle of their suns for 8 orbits. Yellow and cyan indicate apparent clockwise and counterclockwise motion, which signify reversals in coils with both colors. Our own solar system’s Mercury (Me) is just inside the reversal region. Red-white-blue background colors represent the product of the differences of the planet’s spin angular speed and its extreme orbital angular speeds at apoapsis and periapsis; red means no apparent solar reversals, blue means reversals, and the saturation indicates the reversal magnitude.
On Mercury, one (solar) day lasts two years, and once a year an equatorial observer witnesses a brief solar reversal, as in the second figure below, surely a special day for any future inhabitants. For a civilization inhabiting such a planet, we expect “reversal day” to be culturally significant.
Apparent solar motion for different spin-orbit ratios and orbital eccentricities; red background means no apparent solar reversals, blue means reversals, and saturation indicates the reversal magnitude.
Solar strobe plots. (a) Earth-like planet whose sun appears to rise in the east and set in the west every day; rainbow hues code time. (b) Mercury-like exoplanet whose sun appears to reverse its motion once a year near periapsis where it appears largest.
When grocery shopping, I normally just glance at the newspapers in the newsstand. However, this morning, I was excited to see “above the fold” of the Wall Street Journal a large reproduction of the first image of the supermassive black hole Sagittarius A* at the center of our Milky Way galaxy!
The Event Horizon Telescope team combined signals from radio telescopes that span Earth to reconstruct the image using Very Long Baseline Interferometry. Famously, not even light can escape a black hole, but EHT can see the glow of compressed and ionized gas or plasma in its orbiting accretion disk and the “shadow” of its event horizon. A conventional false-color black-orange-white palette makes visible the averaged radio-wave data.
The Wall Street Journal in a newsstand at my local grocery story unveiling “above the fold” the first photo of the back hole at the center of the Milky Way
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Thanks, Mark! I enjoy reading your posts as well.
Nice post, John! Thanks for writing these. I always enjoy them.
![Far from Earth [cyan], the Orion spacecraft [red] entered a distant retrograde orbit about Moon [white]. Relative to Earth [left pane] Orion orbits one way, but relative to Moon [right pane] Orion orbits the opposite way. (You may need to click to start the animation.)](http://woosterphysicists.scotblogs.wooster.edu/files/2022/12/DRO8.gif)
Thanks, Mark! I enjoy reading your posts as well.