Comet-Chaser Rosetta Ready For Launch

Karl Kennedy writes "Europe's Rosetta space mission, which aims to chase and then land on a comet, is standing by for lift-off in French Guiana. Once up in space, Rosetta will be placed in orbit around Earth before departing for the outer Solar System. In 2014, Rosetta will reach the comet and deliver a lander to its surface. The probe will perform three close fly-bys of the Earth and one of Mars in "slingshot" manoeuvres that will use the planets' gravity to help the probe build up speed."

Comments

Orbit a comet?

[lgbarker]

The article states that the probe "will enter orbit around the comet".
A comet has enough gravity to orbit? I would have expected that the probe would have to match the comet's speed & course - more like docking.
This is an impressive long-term mission.

Re:Orbit a comet?

[Baron_Yam]

Any two objects can orbit. Distance, speed, and outside gravitional effect must be taken into consideration, and one assumes the comet outmasses the probe (otherwise the comet would likely be described as orbiting the probe!), but there is no reason the probe couldn't enter into an orbit of the comet.

Orbit animation here...

[snake_dad]

IMHO this is ESA's biggest challenge thusfar. 10 years is a very long time to wait for results of your mission... This flash animation shows Rosetta's long journey. This mission is even more awe inspiring than Stardust or Deep Impact.

Re:Slingshots and speed

[philbert26]

It works because the planet you slingshot around is moving. NASA has a page talking about it in quite some detail.

Energy and momentum are conserved. A slingshot slows down the planet by a tiny bit (just like you move the Earth when you jump in the air). The speed at which you leave the planet isn't any faster relative to the planet, but since the planet itself is moving, your speed relative to what you're aiming at can be increased.

Been done before, or close

[Tau Zero]

The NEAR spacecraft landed on the asteroid Eros over 3 years ago. Eros is rather eccentric, spinning, and small by our usual standards.

Re:Been done before, or close

[cobbaut]

Eros is an asteroid, not a comet.
Asteroids circle the sun more or less like planets,
comets go much further, come back a lot faster and sometimes get much closer to the sun.
NEAR was a great mission, but much simpler than Rosetta.

Re:Been done before, or close

[hubie]

However, don't forget that NEAR was not designed for landing, so it didn't have landing gear, contact sensors, etc.

Both the asteroid and the comet are both going around in elliptical orbits, where the comet orbit has a larger eccentricity, but getting to each one is basically the same. Getting to the comet will have a more complicated trajectory, but the orbital guys have that problem pretty well licked. If you can do ISEE-3/ICE you can do just about anything.

Launch is postponed

[rpiquepa]

It's just been announced. Because of high winds above Kourou, the launch of Ariane 5 carrying Rosetta is being postponed until (at least) tomorrow.

Re:speed?

[snake_dad]

I don't know the numbers, and am too busy at work to look them up (:-)), but the comet's speed is indeed very high with respect to the Sun. That is why Rosetta does 3 Earth flyby's, and one Mars flyby. Each slingshot adds speed to Rosetta until it matches the comet's speed. Rosetta's speed will be very slow wrt the comet, they want to stay in orbit around it.

The surface temperature? I couldn't find any meaningful information in a quick google, but since the comet stays outside Earth's orbit it receives less energy from the Sun than Earth does. So I wouldn't imagine the comet as a red hot glowing piece of molten rock that might melt the spacecraft.