It takes 12.4 houris Srts for Comet 67P to complete one rotation, but controllers of mission Rosetta have noticed that the icy dirt ball rotation is extending by about a second per day.
“The gas jets coming out of the comet, are acting like thrusters and are slowing down the comet,” said flight director Andrea Accomazzo.
The European Space Agency official spoke this week at the Royal Aeronautical Society in London, describing how his team has learned how to fly Rosetta around the 10-billion-ton, 4km-wide astral body with remarkable precision.
Navigators are using a landmarks system on the comet to understand how it is rotating and hurling through space thru information fed into a model which aid in the projection of the trajectory of the satellite.
It was during the running this model that the ESA team realized that the landmarks were not quite turning up in the right place at the expected time.
Determined in September last year, the rotation period has extended by 33 milliseconds per day. Now, with the comet moving closer to the Sun and throwing out much larger volumes of gas and dust, this spin-down effect is approaching a second a day.
Accomazzo said, “OK, it’s not going to slow down completely, but this gives you an order of magnitude for the accuracy we’re now achieving with the navigation of the spacecraft around the comet.”
In December and January, Rosetta was able to move within 30 km of Comet 67P and drive into a gravitationally bound orbit. This is no longer possible and Rosetta has retreated.
The ESA flight director told BBC News “The aerodynamic effects are now more and more important. The jets are getting stronger and stronger.”
“To give you an idea, these gases come out of the comet for a few kilometers and are moving at 800 meters per second. We definitely have to take this into account. We are a big spacecraft with 64 square meters of solar panels. We’re like a big sail.”
The trackers thought the dust particles were stars, in recent weeks. This came about, as the dust in the atmosphere around the comet had star trackers confused as Rosetta uses to work out its orientation.
Currently, Rosetta is flying hyperbolic orbits around 67P, using its propulsion system, coming generally no closer than 60km or 70km.
However, the scientific team is preparing some closer flybys.
One of these flights could go to as close as 20 km, and is used to picture the surface to try to find Rosetta’s lost landing probe, Philae. The robot has been unresponsive since November 12, having lost battery power a couple of days after touching down.
Esa believes the impending opportunity may be an opportune chance for a search. Lighting conditions will be much improved at its suspected resting place, compared to the previous campaigns.
Andrea Accomazzo said mission controllers are using Rosetta to make radio “shout outs” to the sleeping Philae, with hopes that enough solar energy will soon fall on the lander’s solar panels to awaken. “The problem is that even if Philae hears Rosetta, it has to have enough charge to turn on its radio transmitter.”
The flight director though is a somewhat doubtful that Philae will get enough energy to come back to life. “I put it at 50-50, but I will be the happiest person in the world if it happens.”