Thursday, November 13, 2014

Rosetta Mission and Noodle Bridges

A couple of unrelated engineering feats occurred yesterday, and I'd like to address them.

First off, the European Space Agency (ESA) succeeded in landing a probe (Philae) on a comet (67P) for the first time in history.  The level of difficulty of accomplishing such a thing is truly off the scale.

A comet is tiny, 'celestially speaking'.  The mass of 67P is about 10^13 kg.  That's a one with 13 zeros attached to it.  But that makes its mass about 100,000,000,000 times lower than that of a typical planet.  Another aspect that makes docking with such a body tricky is its irregular, peanut-like shape.  It is far from a sphere (largest dimension about 5 km, and smallest about 2 km).  Still, regardless of where you land on this comet, the surface gravity is on the order of 0.001 m/s/s (about one ten-thousandth that of the Earth).  So, if you want to dock, you'd better hang on, because escape velocity is only about 1 m/s (jump, and you now orbit the Sun).

As a result of the tiny gravitational field near a comet, docking with it is like docking with a ridiculously large spacecraft.  But some months ago, Rosetta actually managed to fall into an orbit around 67P at an altitude of about 30 km (no probe had ever entered into a true orbit around a comet before this event).  It needed to have a relative speed less than 1 m/s in order to do so.  However, its actual speed (and that of 67P) around the Sun at the time was a mind-boggling 15 km/s.

If that were not enough, Rosetta was launched a decade ago.  The date, location, and velocity of its rendez-vous with 67P was predicted with high accuracy thanks to some precise computer models (67P sneaks into and out of our solar system in an elliptical orbit around the Sun once every 6.5 years).  Rosetta then entered into a ten year long journey that would see it arrive at the right place at the right time moving with the right velocity.  And this was some journey - it involved three slingshots around planets (Earth then Mars then Earth) in order to work up to this amazingly high speed.

The task of entering into this orbit was further complicated by the fact that all of the control was automated (no manual control from Earth); it had to be, because feedback to Earth comes with a more than 20 minute delay (owing to the 400 million km that separate it from Earth).  The delicate orbit entry was all done via a pre-programmed code based on machine-vision feedback.

After months of orbiting, we now have confirmation that Philae, a 100 kg lander deployed from Rosetta, has docked onto the surface of 67P.  It will send back information about this comet, which will certainly advance our knowledge base in the realm of astrophysics.

As for the other engineering feat that occurred yesterday...

On a slightly smaller scale, there was a bridge-building competition at my college.  Thirty seven teams competed to build bridges made of pasta and glue only, which span 40 cm and could support a maximum load at its center.  The winning team set the all-time record for Vanier College: 23.5 kg.  Amazingly, this spaghetti bridge could have supported my five-year-old - with pasta!  Imagine what they could do with steel!  Someone ought to commission these kids to replace Montreal's Champlain Bridge.

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