How did we land Rosetta on the Philae comet?

[CrutyRammers]

Just play Kerbal Space Program for a couple of weeks OP. Everything will become clear.



Or explode.



Mostly explode.

[MartG]

CrutyRammers said:

Mostly explode.

[Einion Yrth]

CrutyRammers said:

Just play Kerbal Space Program for a couple of weeks OP. Everything will become clear.



Or explode.



Mostly explode.

It will certainly teach the awful tyranny of the rocket equation.

[htrowsoc]

Max_Torque said:

All is revealed here:


rosetta_trajectory_animation


Pretty clever stuff!

Wow, incredibly complex but fascinating. Still can't understand how they achieved a safe enough and close enough speed to approach an object that is moving at 40,000 mph

[CrutyRammers]

htrowsoc said:

Wow, incredibly complex but fascinating. Still can't understand how they achieved a safe enough and close enough speed to approach an object that is moving at 40,000 mph

Because the probe was moving at 40,001 mph. It's all relative in space. When they dock with the ISS it's doing somewhere in the region of 17,000 mph

[Eric Mc]

htrowsoc said:

Max_Torque said:

All is revealed here:


rosetta_trajectory_animation


Pretty clever stuff!

Wow, incredibly complex but fascinating. Still can't understand how they achieved a safe enough and close enough speed to approach an object that is moving at 40,000 mph

Why are people fixated about the speed of the comet?

ALL rendezvous with planets, moons (even other spacecraft) occur at similar type speeds. A Soyuz docking with the ISS has to match the ISS's orbital speed of 17,500 mph.

A spacecraft heading for Mars (or any other planet) has to match its speed to that of the planets speed around the sun in order that it can go into orbit around the planet.

The major difficulty with a comet is not the speed the comet is travelling at but the fact that its orbit may be "eccentric", inclined to the plane of the ecliptic or even "retrograde".

An eccentric orbit is an orbit that is very out of circular.

An inclined orbit is an orbit that does not lie along the same plane on which the planets, moons etc of the solar system lie.

A retrograde orbit is an orbit which runs opposite in direction to that of the planets and most other objects circling the sun.

Quite a few comets' orbits are "odd" in some or all of these attributes.

[anonymous-user]

htrowsoc said:

Max_Torque said:

All is revealed here:


rosetta_trajectory_animation


Pretty clever stuff!

Wow, incredibly complex but fascinating. Still can't understand how they achieved a safe enough and close enough speed to approach an object that is moving at 40,000 mph

The other day, i managed to reverse my car into my garage, which is only about 6" wider than the car, whist we were doing 67,108mph! #parkingskills



(speed, of course, being relative)

[outnumbered]

Surely the OP is trolling...

[Eric Mc]

htrowsoc said:

outnumbered said:

Are you saying you find it unbelievable in a tinfoil-hat, "the moon landings were faked" way ?

Otherwise, it's just Newtonian physics, pretty much, but I guess they needed a decent amount of computing power to work out the trajectory needed to get the required accelerations from gravity slingshots, and end up in the right place after 10 years.

I just find it hard to believe that we could safely approach an object moving at 40,000 mph when you consider an escape velocity of 25,000 mph, with these kind of speed differentials I can't see how this is even remotely possible as the margin for error would be enormous.

A spacecraft leaving earth at 25,000 mph will go into orbit around the sun. To match the orbital velocity of this comet all that needed to be done was point the spacecraft in the right direction and fire its engines until it was travelling ion the right direction at the right speed.

If the rocket motors weren't powerful enough to get the draft up the required speed or the right trajectory, then gravitational assistance using another planet (or two) can be used - as has been done many times now over the past 40 years.,

Edited by Eric Mc on Monday 17th November 14:51

[Ayahuasca]

Was Rosetta's complete trajectory to rendezvous established at lift-off (like an artillery shell) or by means of continual corrections (like a guided missile)?

[Einion Yrth]

Ayahuasca said:

Was Rosetta's complete trajectory to rendezvous established at lift-off (like an artillery shell) or by means of continual corrections (like a guided missile)?

4 slingshots (Earth, Mars, Earth Earth) small delta V trajectory adjustments in preparation for each of these, plus some jiggery pokery to match 67P's orbit towards the end.

[Tiggsy]

htrowsoc said:

Max_Torque said:

All is revealed here:


rosetta_trajectory_animation


Pretty clever stuff!

Wow, incredibly complex but fascinating. Still can't understand how they achieved a safe enough and close enough speed to approach an object that is moving at 40,000 mph

Pretty cool.....I assumed they just sort of headed towards where they thought it would be and sped after it when it flew by.....sort of a "cut it off and the pass" style.....haha! Clearly not.

[Eric Mc]

No different to aiming and reaching any object in the solar system - which they have done many times.

[Ayahuasca]

Eric Mc said:

No different to aiming and reaching any object in the solar system - which they have done many times.

In principle yes, but the comet is a lot smaller than anything else and has less gravity to work with so the precision of the approach must have been incredible.

Separate question - how do they describe (say) a comet's speed and course? For an aircraft you could describe its speed and course as say 300 knots, 160 degrees true. What do you say for a comet?

[Einion Yrth]

Ayahuasca said:

In principle yes, but the comet is a lot smaller than anything else and has less gravity to work with so the precision of the approach must have been incredible.

Separate question - how do they describe (say) a comet's speed and course? For an aircraft you could describe its speed and course as say 300 knots, 160 degrees true. What do you say for a comet?

This.

[Eric Mc]

Ayahuasca said:

Eric Mc said:

No different to aiming and reaching any object in the solar system - which they have done many times.

In principle yes, but the comet is a lot smaller than anything else and has less gravity to work with so the precision of the approach must have been incredible.

Separate question - how do they describe (say) a comet's speed and course? For an aircraft you could describe its speed and course as say 300 knots, 160 degrees true. What do you say for a comet?

Every target chosen for a particular space mission has its own specific difficulties but the general methods used to send a spacecraft on a course to meet up with such a target is more or less the same - in principle.

People seem to be fixated with the speed of the comet and the perceived difficulty in getting the probe to match that speed. That aspect is not particularly different to rendezvousing with ANY target. The specific difficulties with this mission were -

sending the probe on a [path which matches the eccentric orbit of the comet

the fact that the comet may not be orbiting on the Plane of the Ecliptic

getting the probe into an orbit around an irregular shaped small object with a low gravity

Matching the speed was part of what all planetary/cometary probes need to do if the want to go into orbit around the object.

[Ayahuasca]

Einion Yrth said:

Ayahuasca said:

In principle yes, but the comet is a lot smaller than anything else and has less gravity to work with so the precision of the approach must have been incredible.

Separate question - how do they describe (say) a comet's speed and course? For an aircraft you could describe its speed and course as say 300 knots, 160 degrees true. What do you say for a comet?

This.

Cheers.

[Cmann]

Max Torque, thanks for sharing that animation. Helped me very poorly explain this whole thing to my nephew!