Jul 272017

There is a brand new video on YouTube today, explaining the concept of the Solar Gravitational Telescope concept:

It really is very well done. Based in part on our paper with Slava Turyshev, it coherently explains how this concept would work and what the challenges are. Thank you, Jimiticus.

But the biggest challenge… this would be truly a generational effort. I am 54 this year. Assuming the project is greenlighted today and the spacecraft is ready for launch in ten years’ time… the earliest for useful data to be collected would be more than 40 years from now, when, unless I am exceptionally lucky with my health, I am either long dead already, or senile in my mid-90s.

 Posted by at 11:27 pm
Dec 242016

Once again, I feel compelled to use the same image and same words that I have been using for many years, to wish all my family, all my friends, indeed everyone on the good Earth a very merry Christmas: the words of the astronauts of Apollo 8.

I know, I know, it’s the same thing every year. But there really aren’t any better words. Just imagine: three human beings, for the first time in human history, far from the Earth, in orbit around another celestial body. And back on Earth, one of the most troubled years in recent history: 1968. So on Christmas Eve, with about a billion people listening—a full one quarter of the Earth’s population at the time—they greeted us Earthlings with the opening passages from the Book of Genesis, the common creation mythology of several major religions.

And then Frank Borman ended the broadcast with words that are as appropriate today as we are heading towards more troubled times as they were back then: “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.”

 Posted by at 9:10 am
Apr 092016

This beautiful image is a frame capture of the latest SpaceX first stage rocket, moments after its successful landing on the drone ship Of Course I Still Love You (yes, that really is the drone ship’s name) last night:

The landing was a little sloppy. I mean, look how far off-center the rocket happens to stand.

Still… I am seriously beginning to believe that Elon Musk may accomplish his ultimate goal within my lifetime: the beginning of the human colonization of Mars.

To live long enough to see the first human set foot on Mars… now that’s a dream worth living for.

 Posted by at 10:21 am
Mar 292016

Until recently, this used to be one of my favorite deep space images:

It is a frozen lake in the Ruach Planitia region of Neptune’s Moon Triton: an incredibly distant, dark and desolate world.

OK, the image is still one of my favorites, but on my list of favorites, it’s just been taken over by this one:

That, ladies and gentlemen, is a large (about 30 km) frozen lake (most likely frozen nitrogen), in the Sputnik Planum region of the planet Pluto.

Who would have thought that Pluto, the recently demoted ex-planet, a frozen world at the edge of the solar system, would have such complex climate and such a fascinating geological history?


 Posted by at 9:35 am
Jan 292016

Eons ago, back when dinosaurs still roamed the Earth, George W. Bush was still a first-term president, there were only five Star Wars films and Java applets were still cool, I created an applet that showed what Mars would look like if its surface was covered by oceans.

I liked what I did so I added the capability to use other data sets, including data sets for the Earth.

The applet is worthless now, or almost so. Java applets are no longer supported in Google’s Chrome browser. They were never really supported on mobile platforms. Even in browsers that do still support Java, the user has to go through hoops and add my domain as a security exception (not recommended) to allow my unsigned applet to run; all this a result of vain attempts to address the security risks inherent in Java and its implementations.

Anyhow, the applet still works if you can run it. And this is what the Earth looks like today:

Someone recently asked what our planet would look like if it was devoid of oceans. If sea levels were 5000 meters below the present value, the planet would still have a shallow ocean in place of the Pacific. Otherwise, though, it would be mostly dry land with only some inland seas where the Atlantic and the Indian oceans used to be.  It would be possible to walk from pole to pole without wetting your feet; however, you might get a tad thirsty along the way, and there’d not be much rain either.

Decrease ocean levels by another 1000 meters to 6000 below present sea levels, and the last remaining ocean is gone:

Finally, at 7000 meters, the only open water that remains would be in places of the deepest ocean trenches. (Mind you, even then, some of these seas would still be up to four kilometers deep.)

I was also asked what things would look like if the seas rose. There is a surprising amount of change to coast lines by an increase of a mere 50 meters:

Florida is gone; Western Europe looks noticeably different. Increase the sea level rise to 200 meters, and now the change is rather more dramatic:


India is now an island or almost so (there may be some land bridges connecting it to the Asian continent that are too narrow to be visible at this map’s resolution). Much of Europe, Russia, Australia, South America, and the eastern parts of North America, gone.

Finally, at 1000 meters, only mountain ranges remain:

With this little dry land left, there is not much in the way of storms; like Jupiter with its Great Red Spot, the Earth might also develop long-lived storms that circumnavigate the planet many times before dissipating.

 Posted by at 3:30 pm
Jan 282016

This is NASA’s week of tragedy.

Today is the 30th anniversary of the loss of the space shuttle Challenger with seven souls on board. One of my notable memories of this event is that it was the first time that I recall that the national broadcaster in then still communist Hungary didn’t dub a speech of Ronald Reagan. I think the speech was actually carried live (it took place at 5 PM EST, which would have been 11 o’clock at night in Hungary; late, but not too late) and it may have been subtitled, or perhaps not translated at all, I cannot remember. For me, it was also the first disaster that I was able to record on my VCR; for days afterwards, my friends and I replayed and replayed the broadcasts, trying to make sense of what we saw. (Sadly, those tapes are long lost. My VCR was a Grundig 2000 unit using a long-forgotten standard. After I left Hungary, I believe my parents used it for a while, but what ultimately happened to it and my cassettes, I do not know.)

Yesterday marked the 49th anniversary of the Apollo 1 fire that claimed the lives of three astronauts who were hoping to be the first to travel to the Moon. Instead, they ended up burned to a crisp in the capsule’s pure oxygen atmosphere, with no chance of escape. Arguably though, their tragedy resulted in much needed changes to the Apollo program that made it possible for Apollo 11 to complete its historic journey successfully.

And finally, in four days it will be exactly 13 years since the tragedy of Columbia, which disintegrated in the upper atmosphere at the conclusion of a successful 16-day mission. I remember that Saturday all too well. I was working, but I also had CNN running on one of my monitors. “Columbia, Houston, comm check” I heard many times and I knew something already that those in the mission center didn’t: CNN was already showing the multiple contrails over Texas, which could only mean one thing: a disintegrating vehicle. And then came the words, “Lock the doors”, and we knew for sure that it was all over.

Of course the US space program was not the only one with losses. The Soviet program had its own share of tragedies, including the loss of Vladimir Komarov (Soyuz 1 crash, April 24, 1967), three astronauts on boar Soyuz 11 (depressurization after undocking while in space, June 30, 1971), and several deaths on ground during training. But unlike the American cases, these Soviet deaths were not all clustered around the same date.

 Posted by at 3:35 pm
Dec 302015

It is nice to have a paper accepted on the penultimate day of the year by Physical Review D.

Our paper in question, General relativistic observables for the ACES experiment, is about the Atomic Clock Ensemble in Space (ACES) experiment that will be installed on board the International Space Station (ISS) next year. This experiment places highly accurate atomic clocks in the microgravity environment of the ISS.

How accurate these clocks can be depends, in part, on knowledge of the general relativistic environment in which these clocks will live. This will be determined by the trajectory of the ISS as it travels through the complex gravitational field of the Earth, while being also subject to non-gravitational forces, most notably atmospheric drag and solar radiation pressure.

What complicates the analysis is that the ACES clocks will not be located at the ISS center-of-mass; therefore, as the ISS is quite a large object subject to tidal accelerations, the trajectory of the ACES clocks is non-inertial.

To analyze the problem, we looked at coordinate transformation rules between the various coordinate systems involved: geocentric and terrestrial coordinates, coordinates centered on the ISS center-of-mass, and coordinates centered on ACES.

One of our main conclusions is that in order for the clock to be fully utilized, the orbit of the ISS must be known at an accuracy of 2 meters or less. This requirement arises if we assume that the orbits are known a priori, and that the clock data are used for science investigations only. If instead, the clock data are used to refine the station orbit, the accuracy requirement is less stringent, but the value of the clock data for scientific analysis is also potentially compromised.

It was an enjoyable paper to work on, and it is nice to end the year on a high note. As we received the acceptance notice earlier today, we were able to put the accepted version on arXiv just in time for it to appear on the very last day of the year, bearing the date December 31, 2015.

Happy New Year!

 Posted by at 8:57 pm
Dec 242015

It has become a habit of mine. On Christmas Eve Day, I like to offer my best wishes to all my friends, members of my extended family, and indeed to all good people on this Earth with the words of the first three human beings in history who left our planet and entered orbit around another celestial body: The astronauts of Apollo 8, who accomplished their historic mission at the end of one of the most tumultuous years since World War 2, 1968.

And as they emerged from the dark side of the Moon and reestablished radio contact with the Earth, they greeted their fellow humans by quoting from the Book of Genesis. They then finished their broadcast with these unforgettable words: “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.

 Posted by at 5:00 pm
Dec 162015

The reason for my trip to China was to participate in the 3rd workshop on the TianQin mission.

TianQin is a proposed space-borne gravitational wave detector. It is described in our paper, which was recently accepted for publication in Classical and Quantum Gravity. The name, as typical for China, is poetic: it means a zither or harp in space or perhaps (sounds much nicer in English) a celestial harp. A harp that resonates in response to continuous gravitational waves that come from binary pulsars.

Gravitational waves are notoriously hard to detect because they are extremely weak. To date, we only have indirect confirmation of gravitational waves: closely orbiting binary pulsars are known to exhibit orbital decay that is consistent with the predictions of Einstein’s gravity.

Gravitational radiation is quadrupole radiation. It means basically that it simultaneously squeezes spacetime in one direction and stretches it in a perpendicular direction. This leads to the preferred method of detection: two perpendicular laser beams set to interfere with each other. As a gravitational wave passes through, a phase shift occurs as one beam travels a slightly longer, the other a slightly shorter distance. This phase shift manifests itself as an interference pattern, which can be detected.

But detection is much harder in practice than it sounds. Gravitational waves are not only very weak, they are also typically very low in frequency. Strong gravitational waves (relatively speaking) are produced by binaries such as HM Cancri (aka. RX J0806.3+1527) but even such an extreme binary system has an orbital period of several minutes. The corresponding gravitational wave frequency is measured in millihertz, and the wavelength, in tens or hundreds of millions of kilometers.

There is one exception: inspiraling neutron star or black hole binary systems at the very end of their lives. These could produce detectable gravitational waves with frequencies up to even a kilohertz or so, but these are random, transient events. Nonetheless, there are terrestrial detectors such as LIGO (Laser Interferometer Gravitational-wave Observatory) that are designed to detect such events, and the rumor I heard is that it may have already happened. Or not… let’s wait for the announcement.

But the continuous waves from close binaries require a detector comparable in size to the wavelength of their gravitational radiation. In short, an interferometer in which the laser beams can travel at least a few hundred thousand kilometers, preferably more. Which means that the interferometer must be in space.

This is the idea behind LISA, the Laser Interferometer Space Antenna project. Its current incarnation is eLISA (the “e” stands for “evolved”), a proposed European Space Agency mission, a precursor of which, LISA Pathfinder, was launched just a few days ago. Nonetheless, eLISA’s future remains uncertain.

Enter the Chinese, with TianQin. Whereas eLISA’s configuration of three spacecraft is designed to be in deep space orbiting one of the Earth-Sun Lagrange points with inteferometer arm lengths as long as 1.5 million kilometers, TianQin’s more modest proposal calls for a geocentric configuration, with arm lengths of 150,000 km or so. This means reduced sensitivity, of course, and the geocentric orbit introduces unique challenges. Nonetheless, our colleagues believe that it is fundamentally feasible for TianQin to detect gravitational waves from a known source with sufficient certainty. In other words, the primary mission objective of TianQin is to serve as a gravitational wave detector, confirming the existence of continuous waves emitted by a known binary system, as opposed to being an observatory, usable to find previously unknown sources of gravitational radiation. Detection is always easier: in radio technology, for instance, a lock-in amplifier can be used to detect the presence of a carrier wave even when it is far too weak to carry any useful information.

Theoretical sensitivity curve of the proposed TianQin mission.
Theoretical sensitivity curve of the proposed TianQin mission.

The challenges of TianQin are numerous, but here are a few main ones:

  • First, precisely controlling the orbits of shielded, drag-free test masses such that their acceleration due to nongravitational forces is less than \(10^{-15}~{\rm m}/{\rm s}^2\).
  • Second, precisely controlling the optical path such that no unmodeled effects (e.g., thermal expansion due to solar heating) contribute unmodeled changes more than a picometer in length.
  • Third, implementing time-delay interferometry (TDI), which is necessary in order to be able to compare the phases of laser signals that traveled different lengths, and do so with sufficient timing accuracy to minimize the contributions due to fluctuations in laser frequency.

Indeed, some of the accuracy requirements of TianQin exceed those of eLISA. This is a tall order for any space organization, and China is no exception. Still, as they say, where there is a will…

Unequal-arm Michelson interferometer
Unequal-arm Michelson interferometer.

One thing that complicates matters is that there are legal barriers when it comes to cooperation with China. In the United States there are strong legal restrictions preventing NASA and researchers at NASA from cooperating with Chinese citizens and Chinese enterprises. (Thankfully, Canada is a little more open-minded in this regard.) Then there is the export control regime: Technologies that can be utilized to navigate ballistic missiles, to offer satellite-based navigation on the ground, and to perform remote sensing may be categorized as munitions and fall under export control restrictions in North America, with China specifically listed as a proscribed country.

The know-how (and software) that would be used to navigate the TianQin constellation is arguably subject to such restrictions at least on the first two counts, but possibly even the third: a precision interferometer in orbit can be used for gravitiational remote sensing, as it has been amply demonstrated by GRACE (Gravity Recovery And Climate Experiment), which was orbiting the Earth, and GRAIL (Gravity Recovery And Interior Laboratory) in lunar orbit. Then there is the Chinese side of things: precision navigation requires detailed information about the capabilities of tracking stations in China, which may be, for all I know, state secrets.

While these issues make things a little tricky for Western researchers, TianQin nonetheless has a chance of becoming a milestone experiment. I sincerely hope that they succeed. And I certainly feel honored, having been invited to take part in this workshop.

 Posted by at 5:32 pm
Nov 122015

I almost forgot: The International Space Station just celebrated fifteen years of continuous occupation.

Continuous occupation by humans, that is. I wonder if they’ve had the same ship’s cat all this time.

 Posted by at 10:01 pm
Oct 282015

So here I am, listening to, not really watching CBC NewsWorld, when they briefly cut to a live picture from the International Space Station where a spacewalk is underway, and I hear this:


Yup, that’s what the anchorwoman said: Scott Kelly has two pair [sic!] of legs.

You’d think that such a scary, dramatic mutation would have received more coverage already. But what do we know? Must be another liberal mainstream media conspiracy, hiding the facts from people.

 Posted by at 8:28 am
Sep 292015

In Douglas Adams’s immortal Hitchiker’s Guide to the Galaxy, someone builds a device called the Total Perspective Vortex. This device invariably drives people insane by simply showing them exactly how insignificant they are with respect to this humongous universe.

The Total Perspective Vortex may not exist in reality, but here is the next best thing: A model of the solar system, drawn to scale.


The scale of this page is set so that the Moon occupies one screen pixel. As a result, we have an image that is almost a thousand times wider than my HD computer monitor. It takes a while to scroll through it.

Thankfully, there is an animation option that not only scrolls through the image automatically, but does so at the fastest speed possible, the speed of light.

Oh, did I mention that it still takes well over five hours to scroll all the way to Pluto?

By the way, the nearest star, our closest stellar neighbor is roughly 2,000 times as far from us as Pluto.

Or, once again in the words of Douglas Adams, “Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.”

 Posted by at 12:41 pm
Jul 152015

For the past ten years, I have been thinking about NASA’s New Horizons probe as the space probe that will eventually fly by Pluto if all goes well and its systems perform as expected.

Well, that historic flyby happened today, and New Horizons sent back pictures to prove it. Best of all, it successfully re-established contact after performing its flyby observations. Now we will have to wait many months (more than a year, as a matter of fact) before all the collected data is radioed back to the Earth.

But we already have amazing photos. A sight never seen by a human being up until just over a day ago.

 Posted by at 1:35 am
Apr 302015

OK, I have had some sad good-byes in my blog this month, so here is a bittersweet one.

Earlier this afternoon, NASA’s Messenger probe, the first planetary probe to orbit Mercury, crashed into Mercury’s surface.

Although this means the end of Messenger, it also means that this particular probe fulfilled all expectations and then some: it worked flawlessly until it ran out of fuel and could no longer maintain a stable orbit around Mercury. The information it provided about the Solar System’s innermost planet will no doubt be studied for many years to come.

Good-bye, Messenger, and thanks for all the good work.

 Posted by at 4:50 pm
Jan 162015

Beagle 2 has been found.

Beagle 2 was the British lander component of the European Space Agency’s Mars Express mission. It was supposed to land on Mars on Christmas Day, 2003; however, no radio signal was ever received from the spacecraft. Beagle 2 was considered lost, its fate unknown.

But now, it has been found. Beagle 2, together with its parachute and rear cover, have been spotted by the High Resolution Imaging Science Experiment (HiRISE) camera on board the Mars Reconnaissance Orbiter (MRO) spacecraft, which itself has been orbiting Mars since March 10, 2006.

Imagine: a spacecraft orbiting another planet was able to spot an object barely more than a square meter in size, on that planet’s surface.

We may not yet have humans walking on Mars, but nonetheless, we live in amazing times. Now if only we somehow managed to stop murdering and hating each other, I might even begin to believe that there is hope for us yet…

 Posted by at 11:27 pm
Dec 242014

Year after year, I can find no better way to wish Merry Christmas to all my family, my friends, and all good people on Earth, than with the immortal words of Apollo 8 astronaut Frank Borman from 46 years ago: “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.

 Posted by at 3:57 pm
Nov 122014

Judging by the enthusiastic reaction I just saw moments ago on CBC Newsworld, the lander Philae, part of the Rosetta mission to the comet 67P/Churyumov-Gerasimenko, has landed successfully.

This is big. This is the first time a man-made device landed on a comet. It is called “primary exploration”.

It is also big for the European Space Agency. Rosetta is a major deep space mission: the spacecraft spent ten years traveling to this comet.

All in all, wonderful news.

 Posted by at 11:12 am
Oct 302014

Spacecraft sometimes catch a glimpse of the Sun as it reflects off a sea or an ocean. Here is an example:

Except that this example was not captured by Earth-orbiting spacecraft. The sea here is not a terrestrial ocean. It is a hydrocarbon sea of Saturn’s largest moon, Titan.

Just to clarify, the reflection of the Sun is in the upper left of the image, where the outline of the sea is also clearly visible. The redder, arrow-shaped object closer to the center is a cloud formation.

 Posted by at 10:37 pm
May 312014

Yesterday, around 7:17 AM in the morning Eastern time, I took a look at the new NASA site that is streaming Earth-observing video live from the ISS.

While I looked, I noticed a strange plume. It was barely visible, but it was definitely there. As I watched, it was quickly fading away/disappearing behind the horizon, so I was barely able to get a screen capture.

An asteroid impact? A secret nuclear test? Alien invasion? Who knows.

 Posted by at 6:33 pm