I’ll be giving a virtual talk tonight, courtesy of a Texas astronomy club:
I hope it will be well received.
I’ll be giving a virtual talk tonight, courtesy of a Texas astronomy club:
I hope it will be well received.
This morning, a drone took flight. It successfully took off from the ground, hovered for a few seconds, and then landed safely.
What, you ask? How is this supposed to be a big deal? There are millions of drones out there, kids playing with them and whatnot.
Oh, but this drone is special, and not only because it carries a small piece of fabric from the Wright brothers’ very first airplane.
It is special because it flew on Mars.
The next in our series of papers describing the extended gravitational lens (extended, that is, in that we are no longer treating the lensing object as a gravitational monopole) is now out, on arXiv.
Here’s one of my favorite images from the paper, which superimposes the boundary of the quadrupole caustic (an astroid curve) onto a 3D plot showing the amplitude of the gravitational lens’s point-spread function.
I was having lots of fun working on this paper. It was, needless to say, a lot of work.
I really cannot tell which impresses me more: The incredibly complex landing or the fact that there is now a de facto infrastructure in orbit around Mars, in the form of earlier spacecraft that provide communications relay capabilities for real-time tracking of the landing.
Or perhaps the fact that Perseverance also carries the Ingenuity helicopter. If successful, it will be the first drone to fly in the atmosphere of another planet.
The children of future settlers on Mars will be learning about these moments in school.
I was recently interviewed by a Hungarian podcaster, mostly about my participation in the early days of game development in Hungary, but also about my more recent work, including my scientific contributions.
I just listened to the interview and thankfully, I didn’t say anything colossally stupid.
Tonight, Slava Turyshev sent me a link to an article that was actually published three months ago on medium.com but until now, escaped our attention.
It is a very nice summary of the work that we have been doing on the Solar Gravitational Lens to date.
It really captures the essence of our work and the challenges that we have been looking at.
And there is so much more to do! Countless more things to tackle: image reconstruction of a moving target, imperfections of the solar gravitational field, precision of navigation… not to mention the simple, basic challenge of attempting a deep space mission to a distance four times greater than anything to date, lasting several decades.
Yes, it can be done. No it’s not easy. But it’s a worthy challenge.
A few weeks ago, Christian Ready published a beautiful video on his YouTube channel, Launch Pad Astronomy. In this episode, he described in detail how the Solar Gravitational Lens (SGL) works, and also our efforts so far.
I like this video very much. Especially the part that begins at 10:28, where Christian describes how the SGL can be used for image acquisition. The entire video is well worth seeing, but this segment in particular does a better job than we were ever able to do with words alone, explaining how the Sun projects an image of a distant planet to a square kilometer sized area, and how this image is scanned, one imaginary pixel at a time, by measuring the brightness of the Einstein-ring around the Sun as seen from each pixel location.
We now understand this process well, but many more challenges remain. These include, in no particular order, deviations of the Sun from spherical symmetry, minor variations in the brightness of the solar corona, the relative motion of the observing probe, Sun, exosolar system and target planet therein, changing illumination of the target, rotation of the target, changing surface features (weather, perhaps vegetation) of the target, and the devil knows what else.
Even so, lately I have become reasonably confident, based on my own simulation work and our signal-to-noise estimates, as well as a deconvolution approach under development that takes some of the aforementioned issues into consideration, that a high-resolution image of a distant planet is, in fact, obtainable using the SGL.
A lot more work remains. The fun only just began. But I am immensely proud to be able to contribute to of this effort.
I just saw the news: Alexei Leonov died.
Leonov was a Soviet cosmonaut. The first man to ever take a spacewalk (which, incidentally, nearly killed him, as did his atmospheric re-entry, which didn’t exactly go as planned either.)
Leonov was also an accomplished artist. Many of his paintings featured space travel. Here is a beautiful picture, from a blog entry by Larry McGlynn, showing Leonov with one of his paintings, in 2004 in Los Angeles.
So Leonov now joins that ever growing list of brave souls from the dawn of the space age who are no longer with us. Rest in peace, Major General Leonov.
Yesterday, we posted our latest paper on arXiv. Again, it is a paper about the solar gravitational lens.
This time around, our focus was on imaging an extended object, which of course can be trivially modeled as a multitude of point sources.
However, it is a multitude of point sources at a finite distance from the Sun.
This adds a twist. Previously, we modeled light from sources located at infinity: Incident light was in the form of plane waves.
But when the point source is at a finite distance, light from it comes in the form of spherical waves.
Now it is true that at a very large distance from the source, considering only a narrow beam of light, we can approximate those spherical waves as plane waves (paraxial approximation). But it still leaves us with the altered geometry.
But this is where a second observation becomes significant: As we can intuit, and as it is made evident through the use of the eikonal approximation, most of the time we can restrict our focus onto a single ray of light. A ray that, when deflected by the Sun, defines a plane. And the investigation can proceed in this plane.
The image above depicts two such planes, corresponding to the red and the green ray of light.
These rays do meet, however, at the axis of symmetry of the problem, which we call the optical axis. However, in the vicinity of this axis the symmetry of the problem is recovered, and the result no longer depends on the azimuthal angle that defines the plane in question.
To make a long story short, this allows us to reuse our previous results, by introducing the additional angle β, which determines, among other things, the additional distance (compared to parallel rays of light coming from infinity) that these light rays travel before meeting at the optical axis.
This is what our latest paper describes, in full detail.
The world is celebrating the 50th anniversary of one of the most momentous events in human history: the first time a human being set foot on another celestial body.
It is also a triumph of American ingenuity. Just as Jules Verne predicted a century earlier, it was America’s can-do spirit that made the Moon landing, Armstrong’s “one small step” possible.
And today, just like 50 years ago, their success was celebrated around the world, by people of all nationality, religion, gender or ethnicity.
But that’s not good enough for some New York Times columnists.
Instead of celebrating the Moon landing, Mary Robinette Kowal complains about the gender bias that still exists in the space program. Because, as we learn from her article, this evil male chauvinistic space program was “designed by men, for men”. Because, you know, men sweat in different areas of their body and all. Even in the office, temperatures are set for men, which leaves women carrying sweaters.
Sophie Pinkham goes further. Instead of celebrating America’s success on July 20, 1969, Pinkham goes on to praise the Soviet space program in a tone that might have been rejected even by the editors of Pravda in 1969 as too over-the-top. Because unlike America, the Soviets put the first woman in space! Their commitment to equality did not stop there: They also sent the first Asian man and the first black man into orbit. Because, we are told, “under socialism, a person of even the humblest origins could make it all the way up.”
Just to be clear, I am not blind to gender bias. We may have come a long way since the 1960s, but full gender equality has not yet been achieved anywhere: not in the US, not in Canada, not even in places like Iceland. And racism in America remains a palpable, everyday reality. Back in 1969, things were a lot worse.
But to pick the 50th anniversary of an event that, even back in the turbulent 1960s, had the power to unify humanity, to launch such petty rants? That is simply disgraceful. Or, as the New York Post described it, obscene.
The New York Post also makes mention of one of the female pioneers of the US space program, Margaret Hamilton, whose work was instrumental in making the Apollo landings possible. Yet somehow, neither Pinkham nor Kowal found it in their hearts to mention her name.
I have to wonder: Are columnists like Pinkham or Kowal secretly rooting for Donald Trump? Because they certainly seem to be doing their darnedest best to alienate as many voters as possible, from what appears to be an increasingly bitter, intolerant, ideological agenda on the American political left.
Fifty years ago today, fifty years ago this very hour in fact, at 9:32 AM EDT on July 16, 2019, Apollo 11 was launched.
And thus began a journey that, arguably, remains the greatest adventure in human history to date.
I was six years old in 1969, hooked on the novels of Jules Verne. With Apollo 11, Verne’s bold imagination became the reality of the day.
Galileo is the world’s third global satellite navigation system, built by the European Union, operating in parallel with the American GPS system and Russia’s GLONASS. It has been partially operational since 2016, with a full constellation if satellites expected to enter service this year.
But as of early Monday, July 15, Galileo has been down for nearly four days, completely inoperative in fact:
As of the time of this writing, no explanation is being offered, other than one article mentioning an unspecified issue with Galileo’s ground-based infrastructure.
It really is difficult to comprehend how such a failure can occur.
It is even more difficult to comprehend the silence, the lack of updates, explanations, or any information about the expected recovery.
I almost forgot: a couple of months ago, I was interviewed over the telephone by a journalist who wanted to know my thoughts about one of my favorite moments in manned space exploration: The Apollo 8 “Genesis” moment, the reading of the opening verses of the Old Testament, on Christmas Day, 1968, by the astronauts of Apollo 8 as their spacecraft emerged from behind the Moon.
Today, something reminded me of this interview and I did a quick search. Lo and behold, there it is: My words, printed in The Boston Globe on December 23, 2018:
“It was a beautiful moment, and Genesis is part of our Western cultural heritage,” said Viktor Toth, an atheist and a senior research fellow at Carleton University in Ottawa, Canada, who played the lead role in the investigation of the Pioneer Anomaly, the mysterious acceleration of the Pioneer 10 and 11 spacecrafts in deep space. “This was an awe-inspiring thing: Human beings for the first time cut off from the Earth, and then they reemerged and saw the Earth again. The message was entirely appropriate.”
Though shortened, this pretty accurately reflects what I actually said during that roughly 10-minute conversation with the journalist.
Even as China was celebrating the first successful landing of a spacecraft on the far side of the Moon, NASA’s New Horizons continued to radio back data from its New Year’s Day encounter with Ultima Thule: a strange, “contact binary” asteroid in the Kuiper belt, far beyond Pluto.
Ultima Thule will remain, for the foreseeable future, the most distant celestial object visited by spacecraft. While there is the odd chance that New Horizons may find another target within range (as determined by the on-board fuel available, which limits trajectory corrections, and the aging of its nuclear power source that provides electricity on board), chances are it won’t happen, and it won’t be until another deep space probe is launched, quite possibly decades from now, before we get a chance to see a world as distant as Ultima Thule.
Another piece of news from the New Horizons project is that so far, the probe found no moon orbiting Ultima Thule. No Moon At All.
OK, the far side of the Moon is not really dark, but it is kind of hard to see. But now, from the department of unqualified good news: China successfully landed its spacecraft, Chang’e 4 (named after the Chinese Moon goddess), on the dark side of the Moon, and it has already sent us back some pictures.
This is big. Really big. To make it happen, China first had to launch a lunar orbiter, Queqiao (“Magpie bridge”), in order to maintain communication with the lander. And being on the far side of the Moon, the lander is completely shielded from radio signals from the Earth, which means an unprecedented opportunity to study radio signals of extrasolar origin.
Chang’e 4 also carried a rover, Yutu-2, which has since been deployed.
By any reasonable measure, this is a huge success for China’s space program, and for humanity overall. Hopefully, both lander and rover will remain operational and able to fulfill their scientific objectives.
A quote from 50 years ago is the most appropriate one tonight, considering that our world is just as troubled as the world of 1968:
“And from the crew of Apollo 8, we close with good night, good luck, a Merry Christmas – and God bless all of you, all of you on the good Earth.“
I spent several years working with Slava Turyshev and others on this. It was a lot of very hard, difficult work.
As part of my (both published and unpublished) contributions, I learned how to do precision modeling of satellite orbits in the solar system. I built a precision navigation application that was sufficiently accurate to reconstruct the Pioneer trajectories and observe the anomaly. I built a semi-analytical and later, a numerical (ray-tracing) model to estimate the directional thermal emissions of the two spacecraft.
But before all that, I built software to extract telemetry from the old raw data files, recorded as received by the Deep Space Network. These were the files that lay forgotten on magnetic tape for many years, eventually to be transferred to a now obsolete optical disc format and then, thanks to the efforts of Larry Kellogg, to modern media. My own efforts, to make sense of these telemetry files, is what got me involved with the Pioneer Anomaly project in the first place.
These were fun days. And I’d be lying if I said that I have no tinge of regret that in the end, we found no anomalous acceleration. After all, confirmation that the trajectories of these two Pioneers are affected by an unmodeled force, likely indicating the need for new physics… that would have been tremendous. Instead, we found something mundane, relegated (at best) to the footnotes of science history.
Which is why I felt a sense of gratitude reading this article. It told me that our efforts have not been completely forgotten.
There is a very interesting concept in the works at NASA, to which I had a chance to contribute a bit: the Solar Gravitational Telescope.
The idea, explained in this brand new NASA video, is to use the bending of light by the Sun to form an image of distant objects.
The resolving power of such a telescope would be phenomenal. In principle, it is possible to use it to form a megapixel-resolution image of an exoplanet as far as 100 light years from the Earth.
The technical difficulties are, however, challenging. For starters, a probe would need to be placed at least 550 astronomical units (about four times the distance to Voyager 1) from the Sun, precisely located to be on the opposite side of the Sun relative to the exoplanet. The probe would then have to mimic the combined motion of our Sun (dragged about by the gravitational pull of planets in the solar system) and the exoplanet (orbiting its own sun). Light from the Sun will need to be carefully blocked to ensure that we capture light from the exoplanet with as little noise as possible. And each time the probe takes a picture of the ring of light (the Einstein ring) around the Sun, it will be the combined light of many adjacent pixels on the exoplanet. The probe will have traverse a region that is roughly a kilometer across, taking pictures one pixel at a time, which will need to be deconvoluted. The fact that the exoplanet itself is not constant in appearance (it will go through phases of illumination, it may have changing cloud cover, perhaps even changes in vegetation) further complicates matters. Still… it can be done, and it can be accomplished using technology we already have.
By its very nature, it would be a very long duration mission. If such a probe was launched today, it would take 25-30 years for it to reach the place where light rays passing on both sides of the Sun first meet and thus the focal line begins. It will probably take another few years to collect enough data for successful deconvolution and image reconstruction. Where will I be 30-35 years from now? An old man (or a dead man). And of course no probe will be launched today; even under optimal circumstances, I’d say we’re at least a decade away from launch. In other words, I have no chance of seeing that high-resolution exoplanet image unless I live to see (at least) my 100th birthday.
Still, it is fun to dream, and fun to participate in such things. Though now I better pay attention to other things as well, including things that, well, help my bank account, because this sure as heck doesn’t.
It’s the same, each and every Christmas. As Christmas Eve approaches, I remember that famous moment from 49 years ago. The astronauts of Apollo 8 just orbited the Moon. It was Christmastime. These three men were a thousand times farther from the Earth than any human being in history. It was an awe-inspiring moment. Once radio contact with the distant Earth was re-established, the three astronauts took turns reading the first ten verses of Genesis. Frank Borman then closed the broadcast with words that, in my mind, remain the most appropriate words for this evening: “good night, good luck, a Merry Christmas – and God bless all of you, all of you on the good Earth.”
NASA’s Cassini spacecraft is no more.
Launched 20 years ago, Cassini arrived at Saturn in 2004 and has been studying the ringed giant ever since. Cassini also carried the Huygens probe, which executed a successful descent into the dense atmosphere of Saturn’s moon Titan, and even transmitted data from its surface.
Its fuel nearly exhausted, Cassini was steered into a trajectory that led to its intentional demise: a fiery plunge into Saturn’s atmosphere earlier this morning. As planned, the spacecraft was able to transmit observations until the very end, when its thrusters were no longer able to maintain its attitude during the descent.
I feel sad that Cassini is gone, but I should also feel elated because it has been an incredibly successful mission. I just hope I live long enough to see another probe visiting Saturn, perhaps a probe or set of probes that are designed to land on Titan, maybe even sail its hydrocarbon seas, in search of possible life on that icy world.