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.
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
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
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
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!
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
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?
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
digging in my library I have found this, from Aviation Week (26 July 2004, p59)
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.
No chance of Messenger spiralling sunwards I suppose, and snapping some solar limb movies on the way in ???
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.
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.
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).
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).
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.
...and if we could find a wardrobe big enough, it could fly to Narnia...
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?
There's no soft way of doing it. Indeed, a more eccentric 'lobbed' orbit will involve higher speeds at perigee.
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
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.
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
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
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
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