Monday, October 22, 2018

Interstellar Missions a 21st Century Possibility

I was at the 2nd Montreal Space Symposium this past Friday, held this year at Concordia University.  I could only attend one of the days, and was again impressed by the level of professionalism the student-organized two-day conference was run with.  I appreciated the format this year, where more than 50 talks (mostly around 15 minutes with 5 minutes of questions) were run, usually two concurrently.

The one talk I took in at the conference that I will never forget was given by Professor Andrew Higgins (Mechanical Engineering Department of McGill University).  He and I have not crossed paths much since the last time I was a student in one of his courses (Fluids II in 2003, I believe).  The talk, entitled, "Bringing Interstellar Down to Earth," was delivered with his usual sense of humour and flair for the dramatic.

Higgins began the talk by explaining the typical reservations he holds for very futuristic project proposals (personally, having spent most of my adult life exploring the dynamics of space elevators, I hold few such reservations).  But, current breakthroughs in some key technological areas have him believing that he may live to see a fraction of light-speed transit to an exoplanet.

Today, we can detect the presence of exoplanets (planets orbiting stars other than the Sun) and even get a sense for their habitability (temperature, and whether it may have an atmosphere).  There is, however, no reason to believe that telescopes near Earth will enable us to learn any more than this about such planets, which are located at minimum around five light years away.  The only way we can hope to learn if life did or currently does exist on such a planet would be to go to it and take a picture, and send the image back to Earth.

While such a mission was laughable even five years ago, it is conceivable that we are now as little as two or three decades away from sending such probes to far off lands.  The challenge is to get a tiny satellite (a few inch diameter thin disk on the order of grams) to move at some fraction of the speed of light.  The number envisaged in the talk was 0.3c.

The 'TinySat' would be propelled to such a mind-boggling speed by a concentrated collection of coherent photons striking its surface... Basically, we would focus sunlight in a fancy way up to the satellite, where it would strike it (each photon carries a tiny amount of momentum, which it can transfer upon colliding with a surface).  The idea is to focus these streaming photons onto the satellite for a matter of minutes, accelerating the disk to, perhaps 0.3c.  If this were accomplished, TinySat would reach an exoplanet that is, say, 6 light years away, in about 20 years.  Then, it could snap some pictures, and send the images back to Earth, where it would arrive exactly 6 years later.  So, in total, in this scenario, pictures of the exoplanet arrive 26 years after the mission launches.  "Launches" ... This mission gives new meaning to the term launch.

What makes this plan reasonable to even discuss is threefold: (1) the emergence of the field of photonics, (2) advances in reflective materials (the surface of the satellite disk could reflect 99.9995% of the photons, and avoid melting during the photonic barrage), and of course, (3) the miniaturization of electronics, which means a useful satellite could be on the order of grams.

The project is known as "Breakthrough Starshot".  Some of the major challenges were outlined by Higgins.  He seemed most interested in how space dust might collide with a TinySat moving at 0.3c.  Would it destroy it?  In my mind, the most exciting challenge is those few minutes of acceleration.  At such high speeds, even the smallest non-zero torque would cause a rotation and a TinySat that moves very fast, but not in the direction that was intended.  Keeping the satellite pointed correctly during this acceleration is a monumental control challenge.  But, while we are on the subject of 'minutes', why not add a few more minutes of acceleration and get to 0.5c?  I mean, it would save us years of waiting for the probe to reach its destination.

Here is another challenge: can we even take a useful picture while moving at some fraction of the speed of light?  Maybe yes, if we account for the Doppler shift - I honestly do not know.  But that is what made the talk so exhilarating.  The numerous challenges posed by this mission are new, and many of them solvable and even testable in a lab here on Earth.  If I were looking for graduate work in engineering or physics, I would surely consider tackling some aspect of this project.

At the end of his 15 minute talk, Higgins was surrounded by eager young students with questions and novel ideas.  The enthusiasm in the room was palpable.  What I can say with confidence is that although the Breakthrough Starshot is a long shot (in every sense of the word), a lot of kids are going to have a lot of fun trying to make it. 

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