Keep in mind also that that camera is going to get seriously sandblasted as it plows through the central regions of the coma -- I wouldn't count on its photos being much better than those from the main spacecraft's HRI.

The images will be sub-frame towards the end.

Note that Tempel 1 is a much less active comet than 1P/Halley, and seems to be less active this orbit than on its last orbit. Deep Space 1 flew by Borelley without ever recording an impact that registered on the attitude control system. However, 20 km is a lot closer than either Giotto or DS1 got.

If memory serves, Giotto got hit on the camera steering mirror that was sticking out around the edge of the Whipple shield. A probe can either be safe and blind, or stick its "neck" out, get the data, and take the risk. The same goes for the fly-by.

There is also a very big difference in encounter velocity. Stardust was 6.1km/s, Deep Impact 11km/s vs Giotto 70?km/s That equates to an almost 50X kinetic energy content of similar sized dust particle that struck Giotto compared to DI.

Giotto *LOST* the periscope during the flyby.
During post-encounter testing, the camera saw approximately no illumination, though the CCD and detector system were working, Also, the spacecraft <spin stabilized> balance behaved abnormally while they attempted to point the periscope. Inference was that most of the periscope and mirror were destroyed and debris blocked the light path between CCD and inboard optics and the mirror.

(this is from memory, I can't be more precise)

I'd ***LOVE*** some millennium to see what Giotto ended up looking like after the encounter.

Anyone have a handle on the distribution of dust sizes? As I recall, the Halley dust was made of very tiny - almost smoke - particles. A couple of lumps of sand or ice could really impart a kick!

Comet dust seems to be made of stuff that's cigarette smoke sized. Look at the SUBSTRUCTURE of the dust-bunny clumps of cosmic dust we collect from the stratosphere. But this stuff does clump into clods, and even if a clod of comet dust has a density of 0.1 or maybe even 0.05 <like aerogel>... at 70 something km/sec, a 1 centimeter clod packs a whallop. Like the foam at 300 miles/hr and a shuttle wing, but with far far more bounce-per-ounce kinetic energy.

a 1 gramme clod at 11000 m/s is like a car hitting something at 30 mph or a Mach 1.5 golf ball

Doug

Just to put the problem of "cometary dust" in perspective.

0.05 grammes @ 70km/sec == kinetic energy of 1Kg at 1800kph.

Or about 60% of the KE of 1 round from the GAU-8, the gattling gun that the A-10 was basically built around (360 grammes @ 988m/sec). 6 of those is reckoned to be enough to take out a main battle tank, more or less.

50milligrams sounds small but it's about the mass of small piece of gravel, 5-6mm or so in diameter. Hopefully there's none of those.

The online material seems to indicate that nanometer to fractions of a micron in diameter particles are the order of the day at densities lower than the best vacuums on earth. I'd guess that it will be very nasty but much more like running into the top of a planetary atmosphere than hitting a shower of shotgun pellets.

Don't know why I was rabbitting on about 70km/sec. 10.2km/sec is what's up on the info page.

Yep ~30mph car it is, the idea of a Mach 1.5 golfball is too much to handle.

JoeM

So, there we are, on our bicycle...

Both Giotto and Stardust got clouted by several particles a sizable fraction of the mass of bullets, but travelling MUCH faster -- two such impacts knocked Giotto into a wobble that caused it to temporarily lose contact with Earth during its flyby, and Stardust got hit by four or five big enough to pierce the outer layer of its Whipple shields. (Its attitude-control system had been switched to an emergency high-thrust mode, so that even getting periodically shot -- there's no other word for it -- failed to shake its attitude stability.)

Presumably these are indeed fragile, easily crumbling clods, or they would have done a lot more damage. In fact, the local, high-density cloud of small particles that Stardust unexpectedly plowed through at one point when it was hundreds of km from Wild 2 seems to have been the result of a jet of such larger particles ejected from one of the comet nucleus' geysers -- which then evaporated their ice and exploded into puffs of their tinier component grains after they had traveled some distance from the comet, exactly like a fireworks display. (This model of explosively ejected fragile clods which then fragment further also seems to best explain the behavior of comets when they break up.) But, fragile or not, they are a real hazard for comet exploration spacecraft, and must be taken very seriously.

The 70 km/sec bit was the very rough figure for Giotto relative to Halley.

Something else: I wil try to take a look what happens with my C8. Could someone tell me what will be the exact time (corrected for one way light-time) of the impact ?

Take a look at the Griffith Observatory page:

"The collision between the Deep Impact impactor and the nucleus of Tempel 1 is to be within a few minutes of 10:52 p.m. PDT on July 3 (allowing for the seven-minute light time delay between the actual collision and when its effects are seen here)."

Tempel 1 may be difficult in a C8. I had a gander in it a couple of weeks ago in my 12.5" dob and it took some some work to see. It's fairly diffuse and my skies are only so-so as far as light pollution goes. You'll probably need some really dark skies.

Good luck!

Can someone tell me why all images taken so far are taken with Medium res camera?
They said that HRI is fixed...
HRI has 10x resolution of MRI...so why not HRI???

The accurate velocity was actually 68 km/s

Because of the focus issue with the HRI, images taken by it have to be mathematically deconvoluted to give them proper focus. That deconvolution process is time-consuming. So, I imagine they are taking pictures with the HRI -- it is just taking some time for those pictures to be processed such that they are in focus.

-the other Doug

Hi,

Image contrast will suffer from the deconvolution.
Spatial resolution will be recovered, and I think that the images of the comet nucleous will be fine, but to image the coma, jets, and other large tenuous features around it you need contrast.

So my guess is that the MRI, even with lower resolution, might record this structures much better.
Also, there isn't much detail in the latest images, so in my opinion the HRI wouldn't give better results at the present time.

Hope this isn't a repost (I skimmed the topic but couldn't find it):

Dan Maas, of the awesome MER animations fame, has turned his rendering attentions towards Deep Impact.



Encounter Animation

(Requires QuickTime)

I sure hope there aren't any bright jets positioned so that the impactor ends up aiming off into empty space...

If you look at the JPL website, you see that the MRI has a focal length of 2100cm and a diameter of 12. That makes it F/17.5. The HRI has a focal length of 10500cm and a diameter of 30. That makes it F/35 or twice as "slow" as the MRI. "Speed" helps in photographing dim things like the coma, which favors the MRI.

Thanks ! But....impact will be 6:50 in the morning at my place. Sun rises 1 hour and 23 minutes before: it wil be daylight then !

I'm shut out too, Tempel 1 will be below my horizon at impact time

From what I've read, the change in brightness from the impact is expected to be
too faint to be observed visually, but it could show up in CCD images.

Let's hope our more westerly friends have their cameras rolling!

Gas jets shoot from Deep Impact’s target

Plumes of dust and gas shooting from Comet Tempel 1, captured in a Hubble Space Telescope image, have given a preview of what may be seen on 4 July when NASA's Deep Impact spacecraft smashes into the comet.

Hubble captured the brief spurt of activity on the icy body while performing a practice run for its observations on 4 July. The jet of gas and dust was seen in several images snapped over the course of eight hours on 14 June

http://www.newscientistspace.com/article/d...cts-target.html

I didn't know about that till last week. I just assumed that it would be like Huygens, Deep Impact would aim itself at the nucleus, then it would release the impactor, and finally DI would aim itself safely away. This ability to auto-navigate is a worry, not just for you and me, particularly in light of the new jet.

Yeah, it is a worry -- they had a lot of trouble, even without the jet factor, in designing the Impactor's targeting software, since it must aim the Impactor not just for the center of the illuminated part of the nucleus, but for an area which isn't in any local shadow caused by terrain features. (Which helps explain why they couldn't just release the Impactor when the main craft was far away from the nucleus and let it fly -- although the distance at which the Impactor must be released is so far from the nucleus that it would be impossible to aim a passive Impactor for an impact with the tiny nucleus at that range anyway.)

This thing is a real gamble and always has been, even without the HRI problem. Its selection as a Discovery mission was something of a surprise, and I suspect that that choice was yet another of Dan Goldin's harebrained PR brainstorms -- big fireworks display on the 4th of July and all that.

What is the phase angle on the approach to the comet. The simulatoins show a "gibbous" phase, maybe 70 degrees phase angle.

The dust plumes, as Giotto saw, (compared with the soviet VEGA images of Halley, and compared with Borelly and Stardust data at Wildt), are much brighter at high phase when backlit.

Some late afternoon, when the sun is maybe 20 degrees above the horizon, take a handfull of dusty dirt and throw it in the air between you and the sun. The dust is pretty bright. Now turn so the sun is behind you and repeat the experiment. Contrast between dust and the ground will be much lower.

Charcoal-black rough surfaces like a comet's nucleus show very strong phase angle effects. Looking upsun, you see mostly black shadows and surfaces that are on the average tilted away from the sun and not well illuminated. And since the surface is black, both macroscopic shadows, and the non-illuminated side of even microscropic dust grains will be nearly black, without bounce light adding much indirect illumination.

Having the impactor aim for a dust jet is possible, but it's probably less likely than some really unanticipated software or hardware glitch.

It now seems that fdeep Impact's second destination is likely to be Comet Boethin:
http://www.space.com/businesstechnology/05...act_beyond.html

This is a change from what I was told by A'Hearn two years ago, which was
that the leading second destination was Comet Finlay.

Also note the latest conveniently vague comment on how well deconvolution
may correct the HRI problem: "[Ball Aerospace official] Henderson said
through this process, Deep Impact's picture taking can be 'massaged and
tweake' on the ground to greatly overcome the out-of-focus problem."

"Greatly overcome" it? Still nothing said lately on what kind of resolution
they're actually hoping for.

MRI gallery of last week images:

And a false color version to enhance both nucleus and faint coma (based on images I suspect a spacecraft orientation change after Jun,29):

Comet Boethin was also considered as a target for a CONTOUR extended mission. Is there any word yet on the possibility of retargeting Stardust after 2006?

Unfortunately, I was told a couple of years ago by Don Brownlee that there is no chance of an extended mission for Stardust, because it simply won't have enough attitude-control and maneuvering fuel to make it worthwhile.

That's a pity. Do we know the targets of opportunity for Dawn yet?

JPL and the Deep Impact site have a link for viewing "near realtime mages" They're only thumbnails though

I continue to be somewhat astonished by Stardust not having enough "consumables" for an extended mission.

I keep wondering if they used propellants at a higher than expected rate during the mission, or during design cut the supply margin too close for real comfort...?

Well - the difference between having a sensible margin, and having enough for an extended mission - is not inconsiderable

Doug

We've lost missions, recent example being DART, which had a "reasonable" excess of propellant, and used it all up and failed.

Deep Impact's going to have <I think> do it all on it's own to retarget to an extended mission target.

Stardust releases the return capsule and then can do a deflection maneuver to do a range of earth swingby's, rather like Contour was going to do, giving a gravity assist magnified delta-V capability to retarget for an extended mission.

I'd like details I don't have on Stardust's performance.

Brownlee told me they had taken into account the possibilities of an Earth gravity-assist flyby to retarget Stardust -- there was simply no way, even then, to maintain its maneuvering and attitude fuel supply long enough for another target.

I'm wondering what the magnitude of the burn to deflect from the earth-impacting capsule release trajectory to a flyby trajectory is. While atmosphere entry doesn't have the same G limits Apollo astronauts had, it's not a vertical descent. But it could still be a very considerable deflection maneuver that would use almost the entire remaining propellant supply. Potentially considerably larger than Deep Impact's deflection burn.

Not every mission can get extended. Mariner 2 fried and died some 10 days or 2 weeks after Venus flyby.

Mariner 4 made it once around and got back into radio contact for some months of interplanetary weather study before attitude control gas ran out. Mariner 5 was flying at the same time, but when it came around and back into antenna range, it wasn't there. They FINALLY found it, way off frequency and wandering in frequency, carrier wave only, varying in amplitude with a slow spacecraft roll. They got it eventually to lock on to an uplink, but it was a "mindless reflex". Signal strength and behavior provided no indication it ever responded to any uplinked command. Nowdays, I'd call it a Persistant Vegetative State. They wanted simultaneous deep space solar wind observations with Mariner 4 but never got it.

Mariner 6 and 7 had brief extended missions as they flew out into the inner fringe of the asteroid belt. They'd been launched on fast-trajectory Mars flybys and had extra encounter speed and got a mild gravity assist from Mars during the flyby. The did engineering tests, post encounter and fired the midcourse engines a second time and watched the exhaust cloud's spectra with the short wave channel on the infrared spectrometers. No interplanetary science instruments onboard, so they couldn't do much else.

It all depends on how far out it's done and that depends on the battery life of the entry capsule. Far enough out and a small burn will do it. The difficult part is getting it on to a trajectory that will make it intercept another target.

And you dont want to do it too early - because you have no control of the entry capsule after you deploy it, so you want to be attached to the thing that can adjust your trajectory essentially until the last possible moment

PS - I dont think it's worth making a deep impact forum on its own - but i'll start a new threads after the 1800UT press conf (3:15 from now)

Doug

It impacted! Hurray hurray! And happy july 4 for the USA guys in this forum.

Any idea of their final orbital parameters? I always assumed they were in classic Hohmann transfer orbits and *just* grazed Mars at their apogee - it never struck me before that they were in fast solar orbits. Still, maybe that explains the high energy Atlas-Centaur combo (rather than the Atlas-Agena for Mariner 4) despite still being relatively small spacecraft.

There's orbit info in the JPL TR series final mission technical report on Mariner 69, but I don't have those volumes. They got more or less out to the inner edge of the asteroid belt. They were the furthest from the sun on solar power till <maybe/probably> Near or certainly Stardust.

The spacecraft were too heavy for Atlas Agena and too light (in effect) for Atlas Centaur. Some, I think 900 lb vs 450 or so lb for Mariner 4 and nearly 1 ton for Mariner 9, which was almost the same spacecraft, but with fuel tanks and an orbit-insertion engine added.

Just threw this together to give myself a bit of a context shot of where the impactor most likely hit.
Hope we get some good shots of the crater from underneath that bright ejecta cone.

Teased some more detail from on the great image of the comet.
ImageShack isn't cooperating so have to upload it here

An animation made from an impactor image and a deconvolved hi resolution camera image:
Click to view attachment

I used a demo version of the "FocusFixer" filter for photoshop for the deconvolution, which is the reason for the watermarks on that image.

A mosaic of several impactor images.
It's a little big but this way you can see the context of the impact area.

This evening, I grabbed "tif" versions of press release images from the Planetary Photojournal site and did bandpass filtering enhancements on the images. I've spotted things that haven't been commented on and am posting 3 sets of images with some comments.

Note: A lot of the so-called TIF images on the photojournal apparently were initially generated as jpg's and were then turned into tifs, complete with jpg artifacts. Enhancing those tends to result in a mess with the jpg artifacts being strongly enhanced with other small low contrast details.

Pia02127 is a whole-comet image from the impactor, and is the best single-frame view of the nucleus I've seen. The nucleus is divided into at least 3 "regions" with well divided curving borders separating them. Region 1 is the top half of the visible nucleus, Region 3 is the bottom, lower left and lower right edges. Region 2 is sandwiched between 1 and 3, but the borders between 2 and 3 curves up and 2 pinches out in a triangular "cusp" between the borders of 1 and 3. 1 and 3 both give the impression of overlapping 2, with features and texture patterns in 2 stopping abruptly at the borders. In both the region 1 border and the lower right border of region 3 against 2 and against 1, there are features sub-parallel to the border behind the border, giving both borders a very substantial width of a couple hundred meters.

The whole impression is of plastically deformed bodies that were gently "smushed" <very technical geological term, there> together to form one body, which is now being "etched" as ices ablate and crust disintegrates and blows away into space, shownig internal traces of how it was assembled. This is not a "rubble pile", but I get the impression of an assembled object, put together with ultra-low-speed collissions.

The top half of region 1 is very irregular, above the "pitted plains" that are nearly at the center of this view of the nucleus. The large depression with strong shadows on its wall to the right seems floored with very irregular material, and the sharp edges on the right and bottom sides disappear on the upper left. Above it is a smooth plains unit with little texture above the noise and artifacts in the image, and to the depression's upper left is another depression, shallower, but also vaguely circular, filled or floored with extremely irregular material which may have a raised edge compared with the irregular textured material on the uppermost part of the nucleus. Some possible lobes of the smooth plains seem to extend up to a very obliquely viewed facet or depression at the top edge of the nucleus. The plains seem superimposed on the rough terrain with in places locally sharp boundaries.

Another plains unit is present on Region 2, with well defined escarpments as edges. There's faint textures within this feature, but it's surface is remarkably uniform and smooth in all images I've seen.

The different regions have distinctly different populations of surface features. The bottom half of region 1, above the thick border with regions 2 and 3, has multiple rimless crater-like pits, resembling those on Comet Wildt as seen by Stardust. In contrast, Region 2, other than the superimposed smooth plains, seems to have an abundance of dark rimmed features with light spots or patches in the centers. The most prominent is the thing everybody's seeing and saying "impact crater", and I think it probably is... but ... there are many other smaller dark spots with light centers you can see in the next pair of images I'll post. The dark "rims" indeed appear to be raised, both on the "crater" and the smaller spots, as though they're erosion resistant relative to the lighter material outside the spots. Perhaps these are indeed impact craters, with altered, maybe compressed or heated and sintered crater walls and near-wall material resisting erosion. Why these are so different from the flat floored rimless craters in region 1... go figure!

These images are press-released and enhanced versions of image PIA02135, from the impactor, showing most of region 2, it's border with region 3, and the smooth plains superimposed on region 2.

The smooth plains have weak textures converging into it's center from the upper right and lower right edges, but is remarkably smooth and flat. The escarpment at it's edge seems pretty uniform in height over much of it's length. Scattered bright spots are visible for a ways to the right and below the edge of the smooth plains. Some of these appear to be real albedo features, rather than sunward facing slopes.

Further to the right, region 2 seems smoother, but has the scattered dark spots, many/most with light centers, as described in the previous posting. Light patches seem decidedly less common.

The border of Region 3 and 2 forms a well defined topographic break on the surface of region 3, but seems to descend into a hummocky "badlands" as it transitions into region 2. Much of the border below and to the lower right of the topographic break is fairly smooth, but the rest of region 3 all the way down to the the limb is extremely rough and "hackly" Some vaguely elliptical features give the impression of obliquely viewed crater-form depressions in the rough terrain, but resolution is not good enough to clearly tell if this is so.

Pia02130 is a cleaned up but not deconvolved hirez camera image of the impact. The enhanced version clearly shows the defocused blur pattern of the high contrast sun-facing wall of the sharp depression at the terminator. The picture is badly out of focus, but at least this file does not have JPG artifacts introduced before it was turned into the TIF I downloaded.

The images is labled "Moment of Impact". The caption says, in part:

"When NASA's Deep Impact probe collided with Tempel 1, a bright, small flash was created, which rapidly expanded above the surface of the comet. This flash lasted for more than a second. Its overall brightness is close to that predicted by several models. After the initial flash, there was a pause before a bright plume quickly extended above the comet surface. The debris from the impact eventually cast a long shadow across the surface, indicating a narrow plume of ejected material, rather than a wide cone."

In the enhancement, the bright part of the flash is *NOT* saturated in the press release image, and has a very well defined sharp edge, beyond which there is diffuse glow which progressively gets fainter beyond the edge. I cannot tell if the edge is real, or an artifact of the imaging system or data processing, but if it's real, it's clearly an important feature of the expanding plasma and vapor cloud.

Low contrast mottled features are visible within the edge of the bright spot, in particular, there is a dark smudge at the bottom of the ejecta plume's shadow, apparently shadow visible through the bright "blob". The ejecta plume is not itself at all clearly visible or recognizable. Of particular interest, not otherwise noted yet that I've seen.. the shadow is *DOUBLE*.. with a darker portion on the right, and parallel to it a fainter portion on the left. This *might* suggest an irregular, maybe keyhole shaped hole punched in the surface layer of the comet with the high angle early ejecta emerging in a double plume.

I've tried enhancing later post-impact images. In the versions on the planetary photojournal, the brighter portions of the eject plume are saturated and contain no detail. Elswhere, there are strong vertical stripe and some horizontal stripe artifacts that have not been cleaned up from the totally raw data before the images were deconvolved, and they really degrade the enhancement. Image Pia02123 is the best of the 4 (2 of the 4 are the same data). The ejecta streamers are not perfectly radial to one point, but they do converge on a not-saturated part of the image just above a main saturated area and to the left of a smaller saturated bright spot. Texture is faintly visible in this area behind the strong vertical and several horizontal stripes from the camera artifacts, but no feature I'm inclined to interpret as a crater is evident above the noise and artifact level.