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Posted by: Seryddwr Apr 21 2012, 10:08 AM

I know nothing about either the technological constraints or the funding possibilities, but I was wondering if anyone knew what might happen to the probe once the extended mission at Mercury comes to an end. Is it definitely going to be decommissioned? Or is there a chance of sending it somewhere else? Is there sufficient propellant to allow it to break orbit using the LVA, and (say) conduct a flyby of an Aten or Apollo asteroid? I do not know how much delta-v would be required to do this, or even if there are any targets in favourable positions, but it would (to my untrained eye) be an excellent reuse of what has proven itself to be a very capable spacecraft.

Posted by: Paolo Apr 21 2012, 10:57 AM

with all the oxidizer used during the latest orbit lowering maneuver, the remaining delta-v must be quite small. I guess the only realistic end of mission is a series of Sun-perturbed lower and lower orbits and a final impact on the surface of Mercury

Posted by: Paolo Apr 21 2012, 11:07 AM

I have checked the biography of spaceflight mechanics guru Robert Farquhar, who worked on MESSENGER orbit design, and he does not discuss any end-of-mission scenario.
I remember reading somewhere that an option would be to lower the periapsis down to 25 km for close-up observations before crashing on the surface

Posted by: Phil Stooke Apr 21 2012, 12:28 PM

Impact on Mercury is the final act of Messenger's life. there's so much to see there, and only limited coverage at high resolution, that it would be very counter-productive to leave Mercury for a (say) 12 month cruise to an asteroid (even if it were possible, which it would not be with minimal fuel left).

Phil

Posted by: Seryddwr Apr 21 2012, 12:50 PM

Thanks both for your replies. It's sad in one way, but good in another - can't wait to see those very high-res images!

Posted by: Bill Harris Apr 21 2012, 09:19 PM

I imagine that having perfected the Skeet Shooting Technique at Enceladus very nice hi-res low-altitude imagery of selected Mercurian targets are very do-able.

--Bill

Posted by: brellis Apr 22 2012, 01:56 AM

Just for curiosity's sake, how far away from the sun could MESSENGER end up if it uses its last bit of fuel towards such a goal? It sure took a lot of gas to get it into Mercurial orbit. Could it be placed in some kind of safe solar orbit for the sake of future planetary historians?

Posted by: Phil Stooke Apr 22 2012, 03:17 AM

Most likely it could do no more than limp into a solar orbit close to Mercury's, which would be inherently unstable and end up with an impact anyway. Better to target it and get a few close-ups.

Phil

Posted by: Paolo Apr 22 2012, 09:54 AM

digging in my library I have found this, from Aviation Week (26 July 2004, p59)

I have also checked the special issue of Space Science Review dedicated to MESSENGER, but I have found nothing on end-of-mission plans.

Posted by: stevesliva Apr 24 2012, 12:12 AM

Any proposals they have for end of mission likely depended on remaining fuel and analysis of how well their solar-sailing techniques work. And because there are no planetary protection requirements at Mercury, no one has forced their hand yet.

That said, there seems to be little other mention out there other than what Paolo dug up.

Posted by: jasedm Apr 24 2012, 08:33 PM

No chance of Messenger spiralling sunwards I suppose, and snapping some solar limb movies on the way in ???

Posted by: djellison Apr 24 2012, 10:38 PM

Given that it took a very large MOI burn to get IN to Mercury orbit - I would have thought it's fairly obvious that they're not getting out again.

Posted by: JRehling Apr 24 2012, 10:56 PM

Moving into a gravity well is just as hard as getting out.

You've all seen those spiral wishing wells for coins:

http://farm4.static.flickr.com/3449/3283658810_1e235f0e17_o.jpg

Moving in or out of a gravity well requires propulsion in proportion to the local slope, which gets steepest at the center. A minimum-energy trajectory from Uranus to Neptune would require little impulse. Going from Mercury to the Sun would require more propulsion than any other two-body cruise in the solar system. Going from Earth to the Sun would require more energy than from the Earth to any other object in the universe. (Of course, a cruise from Earth to another galaxy would take a long TIME, but not as much energy as a cruise to the Sun.)

This is a key reason why it took so long to follow up on Mariner 10 and why Messenger utilized so many gravity assists.

Moreover, there's nothing much that Messenger could do in solar observation that a much bigger earthbound telescope can't do better from three times further away.

Finally, the planet itself has a nontrivial escape velocity. It's only slightly less than Mars's.

There's one intriguing science target left for Messenger, and that's Mercury itself.

Posted by: Eutectic May 5 2012, 05:42 PM

Even if Messenger were not orbiting Mercury, because of the planet's high orbital velocity around the Sun, getting much closer to the star would take significant energy. Mercury's orbital velocity is about sixty percent higher than the Earth's. At the other end of the speed scale, Neptune orbits at less than twenty percent of Earth's velocity. So if you wanted to drop straight into the Sun, it would be almost nine times easier to do so from Neptune than from Mercury, which is pretty counter-intuitive. The way to spiral in from Mercury would be to use the solar wind for drag...

Posted by: Explorer1 May 6 2012, 05:24 AM

I doubt the camera is even designed to image the sun without being wrecked.
Though sunrise from Mercury orbit would be quite a sight (and without protection, one's last).

Posted by: nprev May 6 2012, 05:26 PM

A 15 nm orbit sounds fascinating, but I wonder if the cameras would be able to capture any imagery that wasn't hopelessly smeared. Sounds as if they'd have to use a high-speed version of Cassini's 'skeet-shoot' technique on preselected targets, and presumably that would require considerable ACS activity (and fuel).

Posted by: ugordan May 6 2012, 05:30 PM

Keep in mind MESSENGER's orbital velocity is about an order of magnitude lower than what Cassini was whizzing by Enceladus with and the cameras are also lower resolution.

Posted by: djellison May 6 2012, 05:41 PM

The whole spacecraft isn't designed to point that way - it would cook. The thermal blanket covering one side of the spacecraft is sun pointed at all times to avoid damage to the spacecraft.

Posted by: antoniseb May 8 2012, 09:04 PM

Not to quibble, and take a seriously off topic tangent, but wouldn't it take a huge amount of energy to escape our galactic orbit? I think we'd need to change velocity about 200 miles/second to get to Sgr A*, which is way more than the mere 19 miles a second for the Earth-Sun trip.

Posted by: Stu May 8 2012, 09:35 PM

...and if we could find a wardrobe big enough, it could fly to Narnia...

Posted by: brellis May 9 2012, 01:19 AM

It's a bit disappointing to characterize the end of this fantastic mission as more of a skid than a crash, in terms of the photo opportunities. Isn't it possible to lob it into a softer trajectory as the fuel runs out?

Posted by: djellison May 9 2012, 01:29 AM

There's no soft way of doing it. Indeed, a more eccentric 'lobbed' orbit will involve higher speeds at perigee.

Posted by: Phil Stooke May 9 2012, 03:41 AM

If you come in slower there should be more time to transmit a few last images during the descent, and they'll be sharper - so I'd say it's better to skid than crash. Except it's a crash either way! The one thing I had wondered about was whether the end was expected to be controlled and trackable.

Phil

Posted by: Gsnorgathon May 10 2012, 12:49 AM

Does anyone know if any provision is being made to choose the impact site in co-ordination with the BepiColombo mission? They might be able to excavate some compositionally interesting material for BepiColombo to look at.

Posted by: Phil Stooke May 10 2012, 01:58 AM

One point about this - there's no fuel left to change the shape of the orbit, and the low point is near the north pole. There might be a small amount of orbital evolution under solar tidal influences, but the chances are the low point will still be very close to the north pole. So that's the only place an impact can occur. It may not be right at the pole, but close to it.

Phil

Posted by: Paolo Oct 11 2012, 07:23 AM

I have received a copy of this paper http://www.iafastro.net/iac/paper/id/13288/summary.lite/ which I cannot share.
I have not had the time to read it in detail yet, but there are a couple of things in it that I wanted to share: in November 2013 comet Encke will pass just 3.7 million km from Mercury and MESSENGER could be used to observe it.
the paper also confirms that surface impact is planned for the end of mission. provided budget is available until then, impact could occur in March or April 2015

Posted by: TheAnt Oct 11 2012, 05:15 PM

Too bad that there hardly will be a chance to study any ejecta plume from that impact due to the distance involved. Since Messenger itself have added further information supporting the hypothesis that there http://www.lpi.usra.edu/meetings/lpsc2012/pdf/1476.pdf at the poles of Mercury.

Posted by: Paolo Oct 11 2012, 05:48 PM

by the time of impact, solar perturbations will have brought the periapsis latitude back to somewhere around 60°N. so that is where the impact will take place