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  NASA's Dawn to asteroids: Questions, comments

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Author Topic:   NASA's Dawn to asteroids: Questions, comments
Robert Pearlman
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posted 01-20-2015 10:19 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA's Dawn to asteroids: questions, comments

This topic is for comments and questions in response to the updates under: NASA's Dawn mission to asteroids Vesta and Ceres.

Dawn is the ninth mission in NASA's Discovery Program. The probe will be the first to orbit two planetary bodies, asteroid Vesta and dwarf planet Ceres, during a single mission. Vesta and Ceres lie in the asteroid belt between Mars and Jupiter.

Blackarrow
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posted 01-20-2015 10:22 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
As NASA's Dawn spacecraft closes in on Ceres, new images show the dwarf planet at 27 pixels across, about three times better than the calibration images taken in early December.
It is always exciting to see a new world getting clearer and clearer as a spacecraft approaches. I wonder what that bright spot is. We'll soon know!

Blackarrow
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posted 02-21-2015 10:10 AM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
These "latest" images of Ceres were taken on 12th February and made available to the public on 17th February. As of today, 21st February, there are no more recent images of Ceres on the JPL Dawn website.

Are images not being taken on at least a daily basis? Why does it take so long to release them? It seems like the public is being "drip-fed" a few images per week, in spite of the fact that entry into Ceres orbit is only about 2 weeks away. Why?

One of the most fascinating aspects of a new world, never seen in close-up before, literally opening up before our eyes, is the steady increase in resolution, day by day, as new pictures come in. Why are we being deprived of that experience?

I'm not an American taxpayer, but should those of you who do pay for NASA not be lifting the phone, tweeting and emailing to press for a more rapid release of Ceres images?

Robert Pearlman
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posted 02-21-2015 10:18 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
The images being returned are used to navigate Dawn into orbit around Ceres, a process called OpNav, as Marc Rayman, Dawn's chief engineer and mission director, explains:
The positions of the spacecraft and dwarf planet are already determined well enough with the conventional navigation methods that controllers know which particular stars are near Ceres from Dawn’s perspective. It is the analysis of precisely where Ceres appears relative to those stars that will yield the necessary navigational refinement. Later, when Dawn is so close that the colossus occupies most of the camera’s view, stars will no longer be visible in the pictures. Then the optical navigation will be based on determining the location of the spacecraft with respect to specific surface features that have been charted in previous images.

To execute an OpNav, Dawn suspends ion thrusting and turns to point its camera at Ceres. It usually spends one or two hours taking photos (and bonus measurements with its visible and infrared mapping spectrometer). Then it turns to point its main antenna to Earth and transmits its findings across the solar system to the Deep Space Network.

...Dawn turned to observe Vesta during that approach phase more often than it does on approach to Ceres, and the reason is simple. It has lost two of its four reaction wheels, devices used to help turn or stabilize the craft in the zero-gravity, frictionless conditions of spaceflight. (In full disclosure, the units aren’t actually lost. We know precisely where they are. But given that they stopped functioning, they might as well be elsewhere in the universe; they don’t do Dawn any good.)

Blackarrow
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posted 02-21-2015 01:04 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Thanks, Robert, that at least partly answers my questions. I now understand that Dawn cannot take continuous, or even daily, images of Ceres because it has to suspend ion thrusting in order to turn its cameras to point at Ceres. This isn't like (for example) Mariner 10's approach to Mercury in 1974. I also now know that we won't see ANY new images in March as Dawn enters its first orbit. That's disappointing, but at least I understand the reason.

However, this still doesn't explain why it took 5 days for the images taken on February 12th to be released, or why we still haven't seen the images which I assume were taken on February 19th. Surely in this day and age we can expect instantaneous release of images? Is there any explanation for the delay?

Robert Pearlman
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posted 02-21-2015 01:22 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
The images were taken on Feb. 12, but that doesn't mean they were transmitted back to Earth the same day. Dawn has to jockey for time using the Deep Space Network, so it can take a few days for the images to be received.

"This mission isn't for people who want instant gratification," Rayman said.

(You can see in real time which probes and spacecraft DSN is supporting here.)

Blackarrow
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posted 02-21-2015 04:30 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
I don't think that's the answer. Marc Rayman's 29th Jan. blog states: "To execute an OpNav, Dawn suspends ion thrusting and turns to point its cameras at Ceres. It usually spends one or two hours taking photos... Then it turns to point its main antenna to Earth and transmits its findings across the Solar System to the Deep Space Network. While it is turning once again to resume ion thrusting, navigators are already starting to extract information from the images to calculate where the probe is relative to its destination."

This sequence of events clearly shows that the images are ALREADY "in the can" as Dawn is resuming its attitude for ion thrusting.

I would also like to think that a major NASA exploratory mission like Dawn can pre-book time on the DSN for a time-critical data transfer the timing of which must have been calculated weeks or months in advance.

What explanation does that leave? Might it be the case that commercial interests are in play here? In the same way that images from Rosetta and Philae have been delayed for weeks to let researchers have a "first look" at sensitive information, are the Dawn images being deliberately held back for commercial or proprietorial reasons?

Robert Pearlman
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posted 02-21-2015 08:40 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
I checked with Emily Lakdawalla with The Planetary Society, who follows robotic missions like Dawn much more closely than I do, and it turns out that it is a similar situation to the other European missions.

Dawn's framing camera is Germany's contribution to the mission, managed by the Max Planck Institute for Solar System Research. According to Emily, they hold up releasing data, and then there is the additional bureaucracy passing it through NASA and JPL. The camera team is also apparently resizing the images, stretching thin the actual pixel data.

Blackarrow
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posted 02-22-2015 04:19 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Yes, I thought it might be something like that. These European scientists who withhold scientific data from the international public are doing science a disservice and giving themselves a bad name. They may have designed the camera, but was it not paid for by European tax-payers? This kind of nonsense has already caused (and continues to cause) controversy in Europe with the outrageously slow release of Rosetta/Philae data. I don't believe we have yet seen properly enhanced pictures by Philae on the surface of the comet. Now here we go again with Dawn. It's time something was done about this.

BA002
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posted 02-23-2015 02:24 PM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
I am not sure that the release of pictures from Ceres is foremost in the minds of the European public.

SpaceAholic
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posted 02-26-2015 08:25 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
The latest image is astonishing... the bright spots have a natural illumination angle from far off (guessing about 20 degrees) above the horizon.

Blackarrow
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posted 02-26-2015 03:55 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
It's tempting to think that those must be two ice deposits lying in a crater (or two areas of "clean" ice exposed by meteorite collisions) but I'm aware that sun spots look misleadingly dark against the much brighter face of the sun.

I can magnify the image to 500% on my screen. Is that a large groove or furrow extending "upwards" from the larger bright spot, and apparently through the rim of the crater? Or is that what Percival Lowell might have suggested?

Robert Pearlman
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posted 03-06-2015 08:09 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
If everything went as planned, then Dawn is now in orbit around Ceres. The probe was scheduled to start circling the dwarf planet at 7:39 a.m. ET (1239 GMT) this morning (March 6).

Confirmation that Dawn is in orbit though, won't come until later. Mission managers tweeted at 8:45 a.m. EST:

Downlink has begun! We're analyzing the signal to confirm that the spacecraft is healthy and in orbit at Ceres.
Given Dawn's approach, under the steady thrust of its three solar electric ion engines, there is little doubt that it was captured by Ceres.

While confirmation of capture will come later today, there won't be any images from orbit until April 10, when Dawn emerges from Ceres's shadow.

Robert Pearlman
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posted 03-06-2015 08:44 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Dawn over Ceres:
Confirmed: I am in orbit around Ceres.

p51
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posted 03-06-2015 12:30 PM     Click Here to See the Profile for p51   Click Here to Email p51     Edit/Delete Message   Reply w/Quote
I know someone in the DoD who for several years has been convinced there's a large asteroid heading for earth and NASA knows about it long in advance.

While I don't buy into conspiracy theories at all, I do wonder why of a sudden NASA has taken such a big interest in landing on asteroids and how to move them around.

Robert Pearlman
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posted 03-06-2015 01:05 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by p51:
...why of a sudden
There's nothing really sudden about it. For example, Dawn was first proposed in 2003, and launched in 2007.

And there are no NASA missions in the planning (or in the works) to deflect an asteroid. The Asteroid Redirect Mission (ARM) as part of NASA's Orion program is not applicable to protecting Earth from a potential impact (the technique ARM is advancing is more applicable to moving cargo to Mars).

Robert Pearlman
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posted 05-14-2015 03:59 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
From user ZLD on UnmannedSpaceflight.com, a close-up flyover of the bright spots on Ceres.
For anyone wanting/needing a more focused look at the spot, I cropped and resampled this image.

Blackarrow
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posted 05-14-2015 04:11 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Fascinating... but I think I'm going to throw up!

Blackarrow
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posted 07-13-2015 04:05 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
While we have been watching the approach of New Horizons to Pluto, has anyone noticed that the Dawn website has been very quiet?

I now understand that Dawn actually suffered a computer glitch on 30th June and remains in its second mapping orbit, instead of preparing to drop into a lower orbit. It looks like communications have been restored, but I haven't seen actual confirmation that Dawn is completely out of the woods.

All times are CT (US)

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