Podcaster: Richard Drumm
Title: Space Scoop: Achievement Unlocked: Landing on a Comet
Organization: Astrosphere New Media
Link : astrosphere.org ; http://unawe.org/kids/unawe1443/
Description: Space scoop, news for children.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
Achievement Unlocked: Landing on a Comet
Touchdown! For the first time in human history we have landed a spacecraft on the surface of a comet.
After a 10-year journey, Rosetta and Philae finally reached their destination at Comet 67P/Churyumov-Gerasimenko. Since then, Rosetta has been steering closer and closer to the comet, preparing for the mission’s next challenge – dropping Philae onto the surface.
The closer Rosetta got to this strange world, the more wonderful it became. We discovered it’s littered with craters, towering cliffs and boulders the size of houses. There are even jets of gas and dust streaming from the surface.
After many weeks studying the surface of the comet, experts eventually chose the best spot for Philae to land. With this decision made, the next task was to pick the best path around the comet so that Philae would land in the right place.
Finally, it was time for Philae to bid Rosetta farewell. Early on the morning of November 12th, Philae began the long descent onto the comet. For seven nail-biting hours, we sat waiting helplessly as Philae drifted through space; with no way of steering if it went off course.
With a huge sigh of relief and a round of applause, we received word from Philae that it had arrived safely and this extraordinary feat had been achieved!
Well, sort of.
Here’s a timeline, courtesy of Emily Lakdawalla of the Planetary Society who was there for several days at the ESA Space Operations Center in Darmstadt, Germany:
– The cold-gas thrusters were not operable. We knew this a day before the lander separated from Rosetta on the morning of November 12th.
– The harpoons that were to secure Philae to the comet did not fire.
– Philae bounced back at about 1/3 of it’s 1 meter/second impact velocity, and without the harpoons to hold it down it went slowly back into space.
– It was tumbling at the same time due to the internal flywheel that was being slowed down. For every action there’s an equal and opposite reaction you know. So the stabilizing flywheel now had an un-stabilizing effect that its controllers surely didn’t want.
– The tumbling stopped after 2 hours, possibly as a result of bouncing a second time (spending only 7 minutes off the surface this time) and then finally touching down.
– Rosetta orbited past Philae’s horizon after only 30 minutes and the radio link was lost.
– The link was re-established the next morning, November 13th.
– Telemetry data was uploaded from Philae after the link had stabilized.
– Philae uploaded a 6 image panorama of it’s final resting spot. This took 2 tries, but it eventually worked.
– This showed that the lander was on its side with at least 1 leg sticking up into space. So the screws on the legs probably didn’t do much.
– The lander appears to be at the base of a boulder or cliff partly in shadow. Due to this:
– The solar panels on Philae only get 1.5 hours of less than 1 watt charging and 20 minutes of 3 or 4 watts charging, not enough to charge the lander’s battery.
– There is only 1 communication window per day that Rosetta has with Philae which should have lasted 6 hours, but because of the location of the lander, the window only lasts about 4 hours instead.
– The operators commanded the MUPUS soil penetrator to deploy but Rosetta’s link was lost without knowing if the deployment was successful.
– The next day, November 14th, saw the team take more risks to get the lander upright. There is power only for this day and not much more.
– The operators did get about 80% of the data they expected to get from the first sequence of science measurements.
– The team determined that MUPUS deployment had worked and they operated the SD2 drill in the hope that they could get data regarding the internal composition of the comet. They did not get any composition data, though, but did determine that there was a very hard crust on the surface, which is something that the orbiter Rosetta could not have done.
– Rosetta orbited past the horizon before they knew if the drill operation was a success. It also was before the command to enter “low power mode” was sent. Ouch!
– Then on the next day, November 15th the team regained contact with Philae late in the evening, at 11:23PM local time or 10:23 Universal time.
– The lander sent data from its COSAC instrument to Rosetta & Earth.
– The team then sent a command for Philae to move by extending its landing legs 4 centimeters and rotating the top of the lander 35° to hopefully put the largest solar panel in a better position for charging the battery.
– Telemetry data from the lander indicated that the move was successful.
– But night had fallen at the lander’s site. Ouch again!
– Executing the move command drained most of the lander’s remaining battery power.
– Even with the low power that was left, the lander sent a new series of ROLIS images of its location.
– The lander also performed a last CONSERT radar ranging experiment.
– By 1:30am, now November 16th, the lander went into standby mode due to low power, and shut down its instruments. At 1:44am the radio link broke and Philae was asleep.
– At this point ESA still doesn’t know exactly where the lander landed, but Rosetta will search the comet at high resolution for signs of Philae.
– If the comet gets significantly more sunlight as it passes closer to the sun it may be enough to revive Philae, but this is not expected. The comet only gets 1 au from the Sun at its closest, or just outside Earth’s orbit.
– So Philae has gone into a deep sleep like Sleeping Beauty, but maybe a handsome prince will come and wake her!
Again, a big thank you goes out to Emily Lakdawalla of the Planetary Society for her tireless reporting from Germany!
Cool Fact
Comet 67P/Churyumov-Gerasimenko is currently zooming towards the Sun at 60,000 km per hour, that’s more than twice as fast as the Space Shuttle!
Thank you for listening to 365 Days of Astronomy!
End of podcast:
365 Days of Astronomy
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