Dawn at Ceres Thread

[Frida Space]

Ceres is a lie

[Kryten]

Venting gaseous water doesn't mean there's neccessarily a hole through which it wents it. I'd expect the whole surface to vent it, like a giant comet.

What? Comets emit jets through vents, what he's expecting is exactly like a giant comet.

[Frozen_Heart]

If its unlikely to be ice, could it just be more lightly coloured rocks where they've been exposed?

I'm secretly hoping that its some alien structure. That would finally motive humanity to start funding space travel.

(Yes I know its not)

Any idea when we're likely to get more pictures though?

[Kryten]

Since Dawn entered orbit, it's now moving further away from Ceres. We won't be getting better images until some time in April.

[Frida Space]

Since Dawn entered orbit, it's now moving further away from Ceres. We won't be getting better images until some time in April.

Actually I think that the reason we won't be getting images until April is because Dawn will fly over the night side of Ceres, not because it will move further away.

[PB666]

Ceres is a lie

A cerius lie

[wasmic]

The thing is bathed in sunlight for half a day. Water ice is unstable this close to the Sun.

You sure about that? I'm pretty sure that the frost point is somewhere in the asteroid belt, but whether that's closer to the sun than Ceres of further away, I can't remember.

[lajoswinkler]

What? Comets emit jets through vents, what he's expecting is exactly like a giant comet.

Comets emit gaseous ices from their surface and vents. At least now with 67P we can see almost on daily basis that you don't need any holes to vent gases.

You sure about that? I'm pretty sure that the frost point is somewhere in the asteroid belt, but whether that's closer to the sun than Ceres of further away, I can't remember.

http://forum.kerbalspaceprogram.com/threads/107824-New-images-of-Ceres-by-Dawn?p=1763919&viewfull=1#post1763919

[PB666]

You sure about that? I'm pretty sure that the frost point is somewhere in the asteroid belt, but whether that's closer to the sun than Ceres of further away, I can't remember.

The increased gravity of Ceres would reduce its effect, if it simply subliming off the surface ice it might not have enough velocity to escape orbit before the dark cycle. Yeah sure eventually it will reach space, but if lingers long enough it can really slow the rate of sublimation. We also have to consider the fact that these could be liquids of higher melting or boiling point.

I really don't like it when people try to lead the science with conclusion, just wait, they will answer the question.

[Otherwise i might propose they will find negative energy between the monolith and two alien spaceship testing their warp drives in crater]

[Newt]

Actually I think that the reason we won't be getting images until April is because Dawn will fly over the night side of Ceres, not because it will move further away.

Actually we are moving further away. There was something that adjusted the flight path, and they needed to change the orbital entry path.

[EzinX]

Why is their final orbit so high? Surely they'd get better pictures if they were just a couple kilometers from the surface, right?

[gmpd2000]

Why is their final orbit so high? Surely they'd get better pictures if they were just a couple kilometers from the surface, right?

My guess would be the thrust of the ion engine and the fuel left.

A lower orbit would require a more costly transfer.

[vger]

My guess would be the thrust of the ion engine and the fuel left.

A lower orbit would require a more costly transfer.

They don't have enough fuel to transfer to a lower orbit?

I wonder how much of an impact that thrust problem from a few months back has on this.

[Kryten]

Why is their final orbit so high? Surely they'd get better pictures if they were just a couple kilometers from the surface, right?

At that kind of distance, the relative velocity would be high enough that it'd be difficult to get more than a blur from any of the instruments. Even if that wasn't the case, it'd make it extremely difficult to image all of Ceres at the required resolution before the end of the nominal mission-and with the reaction wheel issues, there's unfortunately very little chance of Dawn remaining operational for more than a few months after the nominal mission.

[tater]

Remember, ion engines will spiral in, the same way they would spiral out.

I seem to recall a gyro failure as well, so they are using fuel to point the antenna I think.

[Frida Space]

Actually we are moving further away. There was something that adjusted the flight path, and they needed to change the orbital entry path.

http://i.kinja-img.com/gawker-media/image/upload/s--T0gXNvMD--/c_fit,fl_progressive,q_80,w_636/hcjlzzh1hfasnpksf0ip.jpg

Yes, I know that. What I wanted to say is that that's not the reason as to why Dawn won't be snapping pictures until April. The reason is it will be flying over the night side of Ceres.

[Streetwind]

Oh, are we actually talking about Dawn and Ceres again? Awesome. I had almost given up hope.

Actually we are moving further away. There was something that adjusted the flight path, and they needed to change the orbital entry path.

http://i.kinja-img.com/gawker-media/image/upload/s--T0gXNvMD--/c_fit,fl_progressive,q_80,w_636/hcjlzzh1hfasnpksf0ip.jpg

The "something" was a cosmic ray strike event that scrambled Dawn's ion drive somewhere on the trip between Vesta and Ceres. They brought it back online just fine, but the procedure cost them several days worth of thrusting. And with the miniscule thrust that these electric engines put out, that lost time nearly resulted in them missing Ceres altogether.

The adjusted approach orbit you see here, half barreling past the target on the wrong side before barely clinging on to the SoI, is a result of this.

Why is their final orbit so high? Surely they'd get better pictures if they were just a couple kilometers from the surface, right?

Dawn will actually go through a series of different orbits over the course of its primary science mission. Some of them come a lot closer to the surface than pictured here (at one point, down below 250km even if I recall correctly).

There's also room for additional, unplanned maneuvers after the end of the primary science mission. Dawn isn't exactly in the most peachy shape, having lost reaction wheel control, running very low on RCS fuel and having suffered multiple ion engine and/or electronics outages over its lifetime... but as for the ion engines themselves, they still have excess dV to use. It's just a question whether they can maintain control of the probe for long enough to make use of it.

You can be pretty sure that if the primary science mission doesn't bring a conclusive answer to what the shiny mystery spots are, they will make every effort in the extended mission phase to get the best possible orbit to examine them. It's literally the most interesting object(s) on Ceres, and the mission scientists are just as giddy about it as we are

[Frozen_Heart]

Oh, are we actually talking about Dawn and Ceres again? Awesome. I had almost given up hope.

The "something" was a cosmic ray strike event that scrambled Dawn's ion drive somewhere on the trip between Vesta and Ceres. They brought it back online just fine, but the procedure cost them several days worth of thrusting. And with the miniscule thrust that these electric engines put out, that lost time nearly resulted in them missing Ceres altogether.

The adjusted approach orbit you see here, half barreling past the target on the wrong side before barely clinging on to the SoI, is a result of this.

Dawn will actually go through a series of different orbits over the course of its primary science mission. Some of them come a lot closer to the surface than pictured here (at one point, down below 250km even if I recall correctly).

There's also room for additional, unplanned maneuvers after the end of the primary science mission. Dawn isn't exactly in the most peachy shape, having lost reaction wheel control, running very low on RCS fuel and having suffered multiple ion engine and/or electronics outages over its lifetime... but as for the ion engines themselves, they still have excess dV to use. It's just a question whether they can maintain control of the probe for long enough to make use of it.

You can be pretty sure that if the primary science mission doesn't bring a conclusive answer to what the shiny mystery spots are, they will make every effort in the extended mission phase to get the best possible orbit to examine them. It's literally the most interesting object(s) on Ceres, and the mission scientists are just as giddy about it as we are

I will be so cross if they end up losing the probe before getting any useful info from Ceres. I doubt another mission there will be launched in my lifetime.

[Streetwind]

Oh, they're pretty confident it'll last the entire planned science phase at Ceres (into 2016). It's the potential for an extended science mission after that that's in question.

Wikipedia says:

"It was initially hoped that after the primary mission, a flyby of the remaining protoplanet in the asteroid belt, Pallas, might be possible when it crosses the ecliptic in 2018. (...) However, with two of Dawn's reaction wheels out of commission, the remainder of Dawn's hydrazine fuel will need to be expended to orient the craft in low Cererian orbit. (...) it will not be possible for Dawn to leave Ceres. Dawn will become a long-term satellite of Ceres when the hydrazine fuel is exhausted, with orbital stability on a time scale of centuries."

So basically, once it's scheduled work is complete, it'll be running on fumes. The ion drive can do more, but that won't help if there's no attitude control to direct the antenna towards Earth for command and data transfer.

On the other hand, our ancestors might be able to pick it up and put it in a museum once they have settled the solar system a few hundred years from now

[smjjames]

That's descendants, not ancestors, ancestors is in the past.

They may may also decide that it's best to leave it in orbit, who knows.

[Streetwind]

Yeah, you're right. Total brainfart there.

(I blame copious amounts of delicious lunch)

[-ctn-]

So who else is counting down the days?!

[Darnok]

So where are those high quality photos?

[Streetwind]

Dawn's not been bothering to take any, since it spent most of its time on Ceres' night side. Its on a highly eccentric orbit which just happens to have its apoapsis in the worst possible spot for photography.

Also, ion engines are slooow. Scientists estimated they'd need at least six weeks after orbit insertion in order to tweak Dawn's orbit into something useful. Those six weeks are not yet over.

Here's a recent update on the situation: http://www.space.com/29043-dawn-spacecraft-one-month-ceres.html

[-ctn-]

One of the OpNav events was today, as well as on the 14th. I was hoping they'd have released the navigation photos!