Rosetta rendezvous

[PeterEde]

http://rosetta.esa.int/

[sn1987a]

Thanks Peter, awsome!

[elfinke]

This is the most grin inducing thing I've read in some time. The magnitude behind every part: conception, execution, forethought, sheer distance and speeds. I marvel at it.

[julianh72]

A simply stunning achievement!

[glend]

I was just looking at the photos, amazing detail and still 100kms to go. What an achievement, the most difficult mission in terms of getting to this point. Well done to the mission crew.:eyepop:

[PeterEde]

Images look like parts of the comet have been soft/liquified or melted to a point. Nice smooth areas

[geolindon]

i totally concur.....amazing exploration and science, plus? as far as i can discern a significant leap forward in man's ability to travel. i am having some difficulty finding out the maximum velocity the craft achieved or will achieve e.g. to calculate the hypothetical travel time to Proxima Centuri.

comet 67P G-C is travelling at as much as 135,000 km/h (from ESA www) = 375 km/sec = approximately 0.125% of speed of light, and Rosetta space craft is now orbiting it. As Rosetta approached 67P it did a series of burns to slow down to the comet's speed.

other space craft such as New Horizons, Voyager 1 and 2 seemed to all travel at about 16 km/sec and i was starting to wonder what was special about that speed?

is it correct to deduce there has just been a 20+ fold increase in our effective travel velocity/speed?

[pluto]

Rosetta is not orbiting the comet, it's orbiting the Sun in an almost identical orbit as the comet, though it will enter orbit around the comet in a few months. The comet will reach it's maximum speed of 135,000 km/h at perihelion and so will Rosetta. Both the comet and spacecraft are travelling much slower than that now.

135,000 km/h is faster than the maximum speed of the Voyagers (Voyager 1 max speed was 62,136 km/h but it's comparing apples with oranges. The Voyagers are technically not in orbit around the Sun, having exceeded escape velocity.

If the Voyagers were moving a bit slower, so that they were still orbiting the Sun, and if they had a similar perihelion to Rosetta then they would be travelling significantly faster than Rosetta when they reached perihelion.

Likewise to raise Rosetta's speed at perihelion to escape velocity would require adding many km/s to it's velocity.

So while Rosetta will achieve a faster top speed, relative to the Sun, the Voyagers/Pioneers/New Horizon have more orbital energy.
This spaceflight is amazing and full of "firsts" but it really relies on tried-and-tested propulsion technology and gravitational assists. :D

P.S. I think 135,000 km/h is 37.5 km/s which I get as 0.000125 %c, however maths was never my strong suit :)

[julianh72]

Today, Rosetta is just 100 km from the comet’s surface, but it will edge closer still. Over the next six weeks, it will describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then at 50 km.

At the same time, more of the suite of instruments will provide a detailed scientific study of the comet, scrutinising the surface for a target site for the Philae lander.

Eventually, Rosetta will attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer.

http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_arrives_at_comet_destinatio n

[pluto]

Yeah, that's what I said!
The "triangular-shaped trajectories" are movements relative to the comet while the spacecraft is in a heliocentric orbit. This is why they called it a rendezvous and not an orbital insertion. It's like when the Shuttle used to do the "fly arounds" of the ISS before docking, they were both in orbit around the Earth and the Shuttle was just changing it's orbit very slightly to move around the station.

The gravitational influence of the comet on Rosetta at 100km is quite small, even at 50km it's still pretty small. For Rosetta to achieve orbit around the comet it will need to be close enough that the comets gravitational influence is dominant over the gravitational influence of the Sun. There was a great video from ESA showing the triangular-shaped trajectories and the close orbits, I'll see if I can find it.
EDIT: here it is - https://www.youtube.com/watch?v=fNBUep7mPdI

[geolindon]

thanks Hugh,
that and the discussion with Julian does help me understand it better. 67P has so little gravity that even at 1 m/sec or walking speed they are anchoring Philea to the comet in case it bounces off.

any ideas on why most craft travel at that 16-17 km/sec.?
and with the propulsion and slingshot technology what is the best time we could do the Proxima C. run in?

and yes i embarrassingly missed a 0 in my /hour to /second conversion but then you forgot the "and x by 100 to get %" after the division by the speed of light. so it is .0125%. Just proves 2 heads are better than one . . . us north islanders have these problems!!

[pluto]

It really depends on the mission. Of course the speed is linked to the orbit the object is on. For example the Earth is travelling faster than Venus, relative to the Sun, but Mars is travelling faster than the Earth.
This page has a good comparison of the 5 spacecraft currently on escape trajectories: http://www.heavens-above.com/SolarEscape.aspx. You can see that the craft have very different velocities so they're not all around 16-17km/s.

How long it would take to Proxima Centauri depends on a lot of things. But just for the sake of discussion let's assume it's a small spacecraft that we can accelerate to 20km/s, which would be realistic using traditional chemical propellants. In this case it would take about 63000 years to reach our nearest neighbour system.

If you really wanted to do this though, and you were still happy to wait many generations you could employ existing ion propulsion with some kind of long term power generation (most likely nuclear fission or thermal for smaller stuff). then you could potentially accelerate to much higher speeds.

Then there are also solar sails which could get you moving even faster but these have only had small scale, short duration tests and, while very promising, are still in need of more research to make them viable.

[geolindon]

looking at the smooth patches in one of the photos i note that most of the smooth patches end in a cliff with many in the same orientation - in the picture's case to the right. to geo - lindon that is indicative of pressure moving from the left to right and building up until the cliff is formed by a piece being plucked out.

in earth-faults, a similar though much smaller feature forms by the relative movement of two slabs or rock and is called 'slickensides'. they indicate the direction of the most recent movement.

IF (and that's a BIG IF!!) the 67P features are slickensides they may have formed by pressure building up on a now removed layer of material that slid left to right over the layer we now see before being plucked away with the loosened material that was to the right of the now cliff.

if they are not slickensides n only resemble 'em then i dunno . . . but probably the stellar winds formed the features in a similar way with out the assistance of an over layer.

the features do seem to indicate a direction though. is that what we would expect when 67P has a 12.7 hour rotation period? is that fast enough so that it does not present a constant aspect to the pressure long enough to form fairly consistently rather than more randomly orientated features :question:

maybe the features preserve the direction of pressure in the last few hours before the pressure was sufficiently relieved at the end if its last perihelion.

oh what fun :D

[Matt Wastell]

How luck are we.
- Rosetta
- New Horizons (check out the latest long range image)
http://pluto.jhuapl.edu/
- Curiosity on MArs for 2 years
and lets not forget Venus Express (ending its gig)
http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Venus_Express_rises_again

[sn1987a]

and Dawn!

[pluto]

Let's not forget about Oppy, still sending back amazing data and images every day after 10 years. In fact I generally look forward more to Opportunity's images than I do Curiosity's at the moment with the incredible view she has of Endeavour crater.

And Cassini which just gets better with age. I can't wait for her "Grand Finally" where the periapsis of her final few orbits will take her between the innermost ring and Saturn's cloud tops. There are sure to be some stunning views during that portion of the flight :)

And just when our tour at Saturn finishes there'll be Juno arriving at Jupiter to do it all again!!

[PeterEde]

You guys aware the NRO donated three (I think) Hubble sized "spare" telescopes to NASA a few years back. Apparently they were just laying around the spy office. NASA struggles for funding but here's the NRO with 3 spare telescopes?

http://www.space.com/20955-nasa-spy-satellite-telescopes-missions.html

http://www.spacenews.com/article/civil-space/40010nasa-still-intends-to-use-donated-spy-telescope-for-dark-energy-mission

[pluto]

I read about that a couple of years ago so it's great to see they didn't just gather dust. Funny to think of how many 'Hubbles' there are in orbit looking down!

[Matt Wastell]

Check out the video down the page - interesting to say the least!
http://blogs.esa.int/rosetta/2014/08/21/landing-site-selection-the-race-is-on/

[Matt Wastell]

no, not that one - I cannot find it now - talking about electromagnetic planetary evolution rather than the disc theory - I will try to find it again

[Matt Wastell]

https://www.youtube.com/watch?v=qYIpU0DpZzM#t=61

[adman]

To my mind the bigger problem is how you slow down at the other end...