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It is 16 MB large, better don't include it here directly.
A structure in the smaller spot! Very nice.
A structure in the smaller spot! Very nice.
[1]OmCheeto said:...
Marc Rayman...
(YAY! My newest pen pal, and bff. )
Om said:Hi Marc,
That, is simply incomprehensible. In a metro area with over 18 million people, only 2000 showed up.
I’m glad you agree that it wouldn’t have been worth my time, as I calculated that the $500 to fly down and stay the weekend would have come out to $1000/hr for your 30 minute talk.
Though, meeting you, and all the rest, would have made it worth it.
...
marcus said:there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif
Orbit dates altitude(km) pixelsize(m) res/HST period soccerball at
RC3 April 23–May 9 (13,500) (1,300) 24 15 days (3.0 meters)
Survey June 6-30 (4,400) (410) 72 3.1 days (1.0 meters)
HAMO Aug 4–Oct 15 (1,450) (140) 215 19 hours (33 cm)
LAMO Dec 8–end of mission (375) (35) 850 5.5 hours (8.5 cm)
I hope we can. I was interested in some of the things people had to say about getting stuff into orbit from Ceres and Mars.mfb said:Can we discuss Mars and space elevators in a different thread, please?
marcus said:there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif
newjerseyrunner said:I have a theory. The bright spot is supposedly highly reflective and it's nearly white in this image. Is it possible that the sun is directly behind the spacecraft and that is the probe's shadow?
Orbit dates altitude(km) pixelsize(m) res/HST period soccerball at
RC3 April 23–May 9 (13,500) (1,300) 24 15 days (3.0 meters)
Survey June 6-30 (4,400) (410) 72 3.1 days (1.0 meters)
HAMO Aug 4–Oct 15 (1,450) (140) 215 19 hours (33 cm)
LAMO Dec 8–end of mission (375) (35) 850 5.5 hours (8.5 cm)
I'm guessing dust on the camera lens.marcus said:Dotini, thanks for picking out those frames with the curious spots. I don't even have a guess as to what they could be. Hopefully someone else can offer a suggestion.
Ceres rotates once every 9 hours, if you track something on the surface (e.g. the bright spots) you can calculate it for this specific animation.Jimster41 said:Do we know the frame frequency?
Besides which, at 13,000 km, the probe would only have an angular size of 0.298 seconds of arc, while the Sun still has an angular size of ~11 minutes of arc. Thus the probe would not cast a discernible shadow of any size.marcus said:The pixel size is currently between 410 meters and 1300 meters per pixel. Those pictures were taken 4 May at altitude of 13,600 km.
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547
Code:Orbit dates altitude(km) pixelsize(m) res/HST period soccerball at RC3 April 23–May 9 (13,500) (1,300) 24 15 days (3.0 meters) Survey June 6-30 (4,400) (410) 72 3.1 days (1.0 meters) HAMO Aug 4–Oct 15 (1,450) (140) 215 19 hours (33 cm) LAMO Dec 8–end of mission (375) (35) 850 5.5 hours (8.5 cm)
Very roughly the 4 May pictures were taken at 1300 meters per pixel. The dark spots would be several kilometers wide. Too wide to be the shadows of the probe.
Jimster41 said:Do we know the frame frequency? And does the different angular relationship to the ice fort coincide with possible rotation of the camera? I have a hard time picturing loose dust, inside the instrument. Are those the only frames that show it?
The Camera System – Dawn's Eyes (MPS)
The Cameras in Numbers
Exposure times: 1 millisecond to 3.5 hours
Field of vision: 5.5 dregrees times 5.5 degrees
Memory: 8 GBit dRAM
CCD-sensor: 1024 pixel times 1024 pixel
Filter wheel: seven narrow-band filters and one clear filter
Quantum efficiency
This article deals with the term as a measurement of a device's electrical sensitivity to light. In a charge-coupled device (CCD) it is the percentage of photons hitting the device's photoreactive surface that produce charge carriers. It is measured in electrons per photon or amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. The QE for photons with energy below the band gap is zero. Photographic film typically has a QE of much less than 10%[2], while CCDs can have a QE of well over 90% at some wavelengths.
...
Springer Handbook of Lasers and Optics
...
Speed (page 604)
The speed of photographic films can be characterized
assuming that the grain must absorb a certain number
of photons to become developable [9.64]. The referred
number of photons depends on the grain size. Thus,
there is a correlation between the speed and the grain
size. For bare silver halide emulsions (which are sen-
sitive below 500 nm), the whole volume of the grain
absorbs and the speed of the film is the grain vol-
ume times the absorption coefficient.
...
marcus said:https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
That means I'm going from altitude 7,600 to 8,200 km with respect to #Ceres today #orbitalmechanics
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
My planned trajectory is temporarily increasing in altitude b/c my orbit is slightly elliptical...
marcus said:Dawn has reached the apoapsis (far point) of its quasi-elliptical loop and will start closing in again this evening, according to this tweet of about 2PM pacific on 19 May
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 4h4 hours ago
Today I am orbiting #Ceres between ... (8,200 and 8,400 km) in altitude. Tonight I will resume descending.
These tweets originate from Marc Rayman, we are told. He is providing update info and someone else relays it.
...
bolding and bracketed items mine.May 19, 2015 12:45 PM
Hi [Om],
In addition to a new image every day, I now post a mission status update one or a few times a week, as I did at Vesta. I don’t tweet, but I provide information to someone else who tweets for Dawn every day.
[The one and only] Marc [Rayman, JPL, Om's hero]
May 19, 2015 12:42 PM
Hi [Om],
I don’t have time now to look at the forum (I have only ever visited it very briefly), but the images do have artifacts. Some are the result of dust that occasionally separates from the spacecraft and, being small and out of focus, can look larger than it really is. We have observed this throughout the mission, but the flux of dust is very low and it does not compromise the scientific value of the images. There are also electronic artifacts from the CCD. Most spacecraft experience both, and image processing removes them. We are releasing images that have not yet gone through the (time-consuming) full processing, although ultimately all the data, both uncorrected and fully corrected, calibrated, will be released. Of course, all images are scrutinized for moons and other real phenomena, but we know with 100% confidence that none of the stuff we see is anything other than an artifact.
We post a new image every (work) day.
Regards,
marc
Well, Ceres is a bit smaller, so it would be only about 8.22 minutes of arc wide compared to 30 for the Moon. That and it being ~33% less reflective would drop a full Ceres-lit night to ~1/20 as bright as a full moon-lit night.OmCheeto said:Just posted a new question via twitter:
@OmCheeto · 53 seconds ago
@NASA_Dawn Any idea what Ceres would look like, from Earth, if we replaced our moon, with her? The albedos are quit different.
Albedos (per wiki)
Luna: 0.136
Ceres: 0.090
hmmm...
Not really that different.
And I don't know how to spell.
hmm...
Janus said:Well, Ceres is a bit smaller, so it would be only about 8.22 minutes of arc wide compared to 30 for the Moon. That and it being ~33% less reflective would drop a full Ceres-lit night to ~1/20 as bright as a full moon-lit night.
However, if you brought Ceres in so that it looked as large as the Moon does, it would be 33% dimmer. This would also decrease the time between full Cereres(sp?) to 3 days 23 hrs, 5 min and 43 sec.
That's a great observation!OmCheeto said:
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May 20, 9:17 PM
Hi [Om],
I’m glad to know you follow the tweets. I don’t, so I don’t usually know which of the facts I send to our tweeter each day actually get tweeted, but it’s good to know they’re of interest. Only when she feeds questions back to me do I find out what has been tweeted. Don’t worry about not delving into Facebook. I believe most of the posts there are only taken from my Dawn Journals, mission status reports, and tweets.
The trajectory design is very complex and results in entirely counterintuitive solutions. (Well, after years of actually working on missions like this backed up by a lifetime of devotion to physics, they start to become somewhat intuitive.) We have many complicating considerations, including even that we (sometimes) thrust when thrusting isn’t mathematically optimal because it allows us to use less hydrazine. (We did this extensively on DS1, where we thrust at a low throttle level to allow thrust vector control with the ion engine. I called it thrusting at impulse power.) We also have to accommodate periods of coast for the two optical navigation sessions. I have attached a plot I made for you. (I know you and your friends are technical, so I take advantage of that in my responses.) It shows that the orbit energy (as expressed in the orbit period) decreases the whole time (except when we coast for opnavs) even when the orbit radius (distance from the center of Ceres to the spacecraft ) increases. This covers only the first part of the transfer from RC3 to survey orbit because that was most convenient for me to plot quickly, but I am sure the second part will have the same character
To keep the fun at a (local) maximum, I’ll accede to your point and not give any further detail.
Marc