Comet-Chasing Probe Wakes Up On Monday 67
Hugh Pickens DOT Com writes "Jason Major reports that after nearly a decade of soaring through the inner solar system, flying past Mars and Earth several times and even briefly visiting a couple of asteroids for a gravity assist, the European Space Agency's comet-chasing spacecraft, Rosetta, is due to 'wake up' on January 20 after 957 days of hibernation. The probe is awakening to prepare for its upcoming and highly-anticipated rendezvous with comet 67P/Churyumov-Gerasimenko in August. The spacecraft was designed to be put in hibernation for the coldest part of the journey that took it close to the orbit of Jupiter, because even with massive solar panels the size of a basketball court, Rosetta would not have enough power to complete its mission without this energy-saving strategy. Once Rosetta enters orbit around the comet — the first time a spacecraft has ever done so — it will map its surface and, three months later in November, deploy the 220-lb (100-kg) Philae lander that will intimately investigate the surface of the nucleus using a suite of advanced science instruments. 'It's the first time we've made a rendezvous with a comet — that's never been done before — and it's going to be the first time we've escorted a comet past its closest approach to the Sun,' says ESA project scientist Matt Taylor."
The 12-year Journey (Score:5, Informative)
For the curious, here's a video showing Rosetta's path: Rosetta's Twelve-Year Journey to Land on a Comet - ESA Space Science HD Video [youtube.com]
Re:units (Score:4, Informative)
The page on the ESA website [esa.int] says there are two panels, each 32 m^2.
I'm not familiar with basketball courts, but I assume they're quite a lot bigger than that.
Re:RTG? (Score:5, Informative)
I presume because a large solar array with some battery backup meets their power needs over the mission for less money than an RTG, and they only need to operate for a short period out near the outer limits of what is feasible for photovoltaics (roughly the orbit of Jupiter).
The solar panels will produce 850 watts at the rendezvous point -- roughly the same as the Cassini probe's RTG at launch. Those panels will produce prodigious amounts of power at the spacecraft's action-packed perihelion, which may be useful. For example a huge power budget would allow faster transmission of data [wikipedia.org].
The drawback I see is reliability. The spacecraft's systems have to be kept dormant for a long time when it's out near its aphelion.
Re:Amazing Picture from Rosetta of Asteroid Luteti (Score:5, Informative)
Wow, I don't remember seeing that pic before (must be from the 2010 flyby) but it's just about to become my desktop wallpaper. Thanks!
On a side note, for anyone who's not looked at the night sky before through a telescope, you can see Saturn somewhat like it is in that image, with an entry level (ish) telescope from your back yard. I first saw Saturn through an old TAL-1 newtonian that can be bought for as little as £100 here in the UK and on a good night you'll get a sharper view of Saturn than shown in that image. Or you could pop along to your local astro meet (there's bound to be one near you) and have a look at some of these objects through varying sizes and designs of telescopes.
Seeing Saturn for the first time through a telescope is, in my experience and from what others frequently say too, jaw dropping amazing. Then take a look at Jupiter with the same telescope and you should be able to make out Jupiter's bands and some of its moons, maybe even the great red spot if you time it right. We've all seen them in photos but there's nothing quite like the knowledge that your eye is at the receiving end of actual photons being reflected by the planets, or being emitted from galaxies.
orbital parameters (Score:5, Informative)
I dug around ESA's pages and finally found details on the orbital parameters: on Comet Rendezvous [esa.int], under "Comet mapping and characterisation (August 2014)" (halfway down) it says: "...the spacecraft is inserted into orbit around the nucleus at a distance of about 25 kilometres. Their [sic] relative speed is now down to a few centimetres per second. "
That slow orbital speed (OK, slow compared to what we're used to dealing with) is due to the small mass of the comet (again, compared to things like the Earth or Moon), which Wikipedia [wikipedia.org] gives as about 3e12 kg. Checking the math, the equation for circular orbital velocity v[circ] = sqrt(GM/R) ~= sqrt( (7e-11)(3e12) / 25e3 ) = 0.09 m/s = 9 cm/s, cool. (Even if the quoted 25 km is to the surface rather than the centre, using that figure for R is OK since the comet's radius is only about 2 km.)
FWIW, at the surface, escape velocity sqrt(2)*v[circ] = sqrt( 2(7e-11)(3e12) / 2e3 ) = 0.5 m/s. You could easily jump off of that comet!