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Posted by: vikingmars May 28 2008, 05:27 PM

With a little image processing, one can easily see the final descent trajectory of the Phoenix Lander with its plumes disturbing the top layer of the Martian surface. After the release of the lander from the backshell, the effect is barely seen first, but is becoming more obvious, until the final strong pulses before landing. Any better estimates ? Enjoy !

Posted by: bgarlick May 28 2008, 05:38 PM

Is it possible that what you are seeing is wind dispersal of kicked up dust? The parachute landed to the south of the backshell so presumably the wind was blowing from the north at the time of landing.

Posted by: fredk May 28 2008, 05:49 PM

I'm not convinced - there are comparable dark areas elsewhere in your middle plot. Also, we've heard that the final horizontal velocity was apparently very small. Anyone know its direction? Since the parachute drifted south, perhaps the lander was also moving south before it zeroed the horizontal velocity? In that case any direct effect of exhaust on the ground should trail off to the north.

Posted by: bcory May 28 2008, 05:55 PM

Also one must consider at what swing angle the decending package was at when the heat shield was jettisoned.

Posted by: kenny May 28 2008, 06:02 PM

Phoenix was of course programmed to thrust away from the parachute after being released, to avoid it being blanketed by the chute after it landed. So it may well have been travelling in a direction unrelated to the wind which governed the chute's descent.

Posted by: MahFL May 28 2008, 06:05 PM

Yes Phoenix was programmed to fly away. Mind you I am still surprised how close all the hardware landed together.

Posted by: vikingmars May 28 2008, 06:17 PM

OK, good points. Maybe I'm wrong then : let's wait for the final EDL trajectory release by the engineers...

Posted by: ugordan May 28 2008, 06:19 PM

Indeed. I was also surprised how close to the heatshield Phoenix landed. Keep in mind that the heatshield was jettisoned some 12-ish km and the velocity was supposed to be about 45 degrees to vertical/horizontal. Several minutes later the lander lands less than 200 meters of it.

Vikingmars, your plot would make sense if Phoenix descended slowly and had a large horizontal sliding velocity. What we know of is it basically came straight down.

Posted by: MahFL May 28 2008, 06:25 PM

Then again the atmosphere is very very thin and all the objects would not be blown much by any wind.

Posted by: kwan3217 May 28 2008, 06:30 PM

Actually this is about what I expect. The powered descent is not random. The lander specifically looked at its radar to see which way it was travelling across the surface. From how the parachute is blown, I would say that it is basically from due north. Having measured that, after it separated, it purposely flew upwind (to the north) a ways as parachute avoidance, then tipped back over the other way to slow down its horizontal velocity and land. It flew straight upwind because it was supposed to.

There is a PDF slide presentation posted here which shows the details of this "backshell avoidance maneuver".

I guess what I'm saying is that I think your interpretation is plausible.

Posted by: dmuller May 29 2008, 03:18 AM

As a non-engineer, I just love the engineering English [engenglish???] (from above document):
Mmm yeah, recontact

I was actually hoping to include more of these events (BAM. gravity turn, alignment etc) into my real-time simulation but could not get the necessary information. Maybe next time.

Posted by: AndyG May 29 2008, 09:09 AM

engenglish???

...Eng2lish?

Andy

Posted by: mhall May 29 2008, 11:57 AM

Engl-ish ?

Posted by: Greg Hullender May 29 2008, 04:16 PM

As an engineer and a linguist, I'd call that jargon, and what I find cool is that it follows its own domain-dependent rules. Consider how NASA uses the word "nominal." I like this one because I'm still puzzling over how they got "nominal" to mean "good," when it usually means "in name only." So if I said, "the orbiter is nominally functioning," that means that despite appearances to the contrary, I don't think it's working correctly, BUT, if I say "the orbiter is functioning nominally," that means there are no known problems, and I think it's working fine. Only the second is the "correct" way to use "nominal" when talking about space probes, and if you misuse it, you identify yourself as an outsider.

As for "recontact," I'd guess that arises from the fact that you can't say "contact," since these things are in contact to begin with. It crisply captures the idea of "to collide with, at any speed, but after separation." Standard English lacks such a term, since the circumstance is uncommon in daily life. (We'll ignore the fact that lots of people still think it's a solecism to use "contact" as a verb.) :-)

--Greg

Posted by: Adonis May 29 2008, 06:58 PM

I got also surprised. I remember the same happened with both MERs: their heatshields got very close to the landers. There must be some reason for these so many cases. MER's heatshield and parachute design closely matches that of Phoenix. Perhaps the dynamic flight behavior of these heatshield when they're free from their landers are close to that of the parachute when hanging the lander.

Posted by: dmuller May 29 2008, 08:46 PM

No doubt it is very precise language. Just imagine the press conference if the backshell did actually "recontact" with the lander on the ground!
Official: Ahm we've had an anomaly during landing as the backshell deviated from its nominal trajectory and recontacted the lander on the ground. We're currently working on the issue
Bewildered reporter: Huh, you mean the backshell crashed into the lander on the ground?
Official: It seems that an unplanned recontact was made and we're working the problem. We will update you during the next press conference (which I hope I wont have to attend ...)

Posted by: dmuller May 30 2008, 09:06 AM

Building on VikingMars' work, assumed wind (straight line from lander to backshell-impact to backshell) and having Phoenix fly into the wind, heatshield impact and heatshield, and assuming that North is NOT straight up in the pic, the ground track could look like this:

(Sorry for the quality of the drawing ... I dont have any decent software, still using Windows Paint )

EDIT: image reworked ... ignore this one and see post further below

Posted by: ugordan May 30 2008, 10:34 AM

Dmuller, doesn't that north vector contradict with the observed orientation of the solar panels?

Posted by: djellison May 30 2008, 10:39 AM

The vehicle intentionally rotated during terminal descent to put the arrays left right.

Posted by: ugordan May 30 2008, 10:46 AM

Quite. If anything, I'd say north is about 12 degrees clockwise from up judging by solar panel orientation.

Posted by: dmuller May 30 2008, 11:16 AM

Yes of course, overlooked that piece of evidence Yellow line up is North.

Assuming that the heatshield went straight into the ground (i.e. was not blown to the South by the wind), it would have about followed the blue line (as the landing ellipse went from NW to SE). So Phoenix would not have steered much to the North (into the wind), and the parachute made quite a trip South even though the atmosphere and hence the wind effect wasn't quite a hurricane as we know from Earth So the dark bulge to the SE of Phoenix would be windblown, and the bulge to the SW caused by the thrusters. It also looks like the backshell did hit the ground with quite some horizontal (N to S) speed judging from the ejectile and distance between first impact and backshell. The heatshield came in more vertical but bounced off to one side.

Even though all the debris is close to Phoenix, the landing design worked out very smart with all the relative movements and deviations. Great stuff

Posted by: dilo May 30 2008, 09:12 PM

Agree, Daniel. I reached same conclusions looking to pictures...
Anyway, I made this wallpaper from HiRes picture (eliminating pixelization from enlarged insets). North is almost up...

Posted by: Adonis May 31 2008, 04:05 PM

Is anywhere information about the final landing chronology, specially the retro-phase ... I mean high versus time data?

Thanks

Posted by: MahFL May 31 2008, 04:19 PM

The project manager said it would take several months to put the edl sequence together from the data.

Posted by: ahecht Jun 13 2008, 05:00 PM

There is an updated version of the EDL movie that was uploaded a couple days ago. While it doesn't appear to have ALL the EDL info in it (such as the creation of Holy Cow), it does show the partially-deployed parachute state as it was captured by HiRISE. I would've loved to see Heimdal in the background, but I guess a video like that will come once they have all the EDL numbers crunched.

http://www.jpl.nasa.gov/news/phoenix/phx-20080611.php

Posted by: cndwrld Jul 9 2008, 12:46 PM

MEX Failed To Image The Descent

I'm not sure it was in this thread, but I read that people did not know if Mar Express managed to image anything during the descent. And the answer is No, unfortunately. The information was posted, but it was in a place that many people did not see it. If you are interested, it is at:

http://www.esa.int/SPECIALS/Mars_Express/SEMAWQ1YUFF_0.html

Old news, but just for those who were curious.

Posted by: 1101001 Jul 9 2008, 10:05 PM

The MRO team has given the Phoenix-on-parachute pixels another whack, and they might have spotted the falling heat shield:

http://hirise.lpl.arizona.edu/phoenix-descent-color.php

Posted by: Pertinax Jul 9 2008, 10:58 PM

Kudos again to the MRO team and a Mars bar to T-Man et.al ( http://www.unmannedspaceflight.com/index.php?s=&showtopic=5176&view=findpost&p=116143 )

-- Pertinax

Posted by: jmknapp Jul 9 2008, 11:18 PM

With the imaging by HIRISE, is there a definitive location (latitude, longitude) for Phoenix, to several decimal places?

Posted by: Pertinax Jul 9 2008, 11:59 PM

And altitude?

-- Pertinax

Posted by: Juramike Jul 10 2008, 03:44 AM

I'm pretty sure it's touching the surface.

Posted by: jmknapp Jul 10 2008, 10:13 AM

Although the present "altitude" reported by the PDS NAIF spice kernel (not sure how accurate) is -2.4 km! That may be correct, insofar as the zero-altitude reference is an idealized tri-axial ellipsoid, which no planet actually fits. So that would place the Phoenix landing site elevation somewhat below mean sea level, so to speak.

If I recall correctly, in one of the early press conferences Peter Smith mentioned that liquid water is actually stable in the landing area, due to the low elevation.

The lat and lon reported by the spice kernel is 66.217N 243.692E, but how accurate that is I don't know (predicted, actual, tentative?).

Posted by: akuo Jul 10 2008, 10:26 AM

The position was already reported http://www.unmannedspaceflight.com/index.php?showtopic=5171&st=90&p=115817&#entry115817 on this forum

Posted by: edstrick Jul 10 2008, 10:59 AM

At approximately 0 km elevation, the average pressure corresponds to the triple point of water (approximately, and not including seasonal atmosphere pressure variations). So at -100 meters (if this were exact and my arm waving numbers were exact), water 1/2 degree above freezing would not boil. It would evaporate damn fast, though, under most plausible conditions. At lower elevations, water some 5 to 10 deg F <half that for C> above freezing would not boil.

Regardless, it's REAL hard for plausible normal <not impact, for example> processes to supply enough energy to ice at the martian surface to melt it any faster than the water would likely evaporate.

Posted by: jmknapp Jul 10 2008, 11:00 AM

Thanks--is that link correct? The original reference doesn't seem to be there.

Posted by: akuo Jul 10 2008, 11:08 AM

Works for me. I guess this is another way to put it:
http://www.unmannedspaceflight.com/index.php?s=&showtopic=5171&view=findpost&p=115817

Posted by: jmknapp Jul 10 2008, 01:33 PM

Hmmm... still don't see it. Anyway, the location you quoted is very plausible based on NAIF spice kernels having MRO pointing squarely at that point at 26MAY2008 22:04:30. The published photo that MRO took of the lander on the ground is stated to have been taken 22 hours after landing (25MAY2008 23:46), so that fits.

Here's a simulation of the view from MRO at that instant, with the HIRISE look direction marked with crosshairs (MGS 200m mosaic, equalized):



HIRISE had moved pretty far off-nadir to take that shot.

I still wonder if part of that mosaic was taken when there were significant clouds over the Phoenix site, and another part when it was clear.

Posted by: Pertinax Jul 10 2008, 06:09 PM

Thank you Juramike!

I think I might have misunderstood the initial question, thinking that is was asking if the Lat/Lon (and altitude) of Phoenix in flight at the instant MRO captured it was pin-pointed yet.

-- Pertinax

Posted by: kwan3217 Jul 30 2008, 04:02 PM

I just did my hourly check of the spice kernels at NAIF and found that the EDL reconstruction is posted!

http://naif.jpl.nasa.gov/naif/data_mars.html, phoenix/ck/phx_edl_rec_att.bc, phoenix/spk/phx_edl_rec_traj.bsp

Now all we need is an exact time for the entry parachute photograph and we can tell everything about it.

Posted by: dmuller Jul 31 2008, 12:02 AM

I havent had a look at it nor do I know what these files show (too busy at the moment), but parachute deploy should show a big spike in deceleration

Posted by: jmknapp Jul 31 2008, 01:24 AM

Good thought. Here's a graph of the speed and acceleration:



But where along there did MRO take the picture? Anybody know the lat/lon of Heimdal Crater?

Posted by: gallen_53 Jul 31 2008, 02:15 AM

I also downloaded the files "phx_edl_rec_att.bc" and "phx_edl_rec_traj.bsp". They're binary files. What code did you use to get them into a readable form?

Posted by: gallen_53 Jul 31 2008, 02:22 AM

Hold on, I just found the NAIF website at http://naif.jpl.nasa.gov/naif/toolkit_C_PC_Linux_GCC_32bit.html . I'm downloading the SPICE toolkit tarball while writing this post.

I just got the SPICE tool kit package up and running but it's not friendly. I want the tool kit to translate the Phoenix binary data files into text files describing the vehicle's trajectory in the inertial frame. How do I do that? Does the SPICE database only model the trajectory as a 3-DoF point mass or does it include 6-DoF information from the vehicle's IMU? Thanks!

Posted by: kwan3217 Jul 31 2008, 04:07 AM

I use the NAIF spice toolkit and IDL, but the one for C works fine too. the .bsp file includes the position and speed (and Spice will convert it to any coordinate system you feel like) while the .bc file contains orientation. Together it is 6DoF.

Look up examples on the NAIF site for spkezr_c for the position stuff.

Posted by: gallen_53 Jul 31 2008, 06:35 AM

Thank you. I'll try it in the morning. Do you know where to find the Phoenix mass model, i.e. moments and products of inertia, center of gravity, etc.? Is there an aerodynamic model specific to the Phoenix 70 deg. aeroshell including Cm, Cmq, etc. accessible on the web? This information would be in the Lockheed-Martin databook for Phoenix but they're probably keeping it close to their vest. Thanks again.

Posted by: djellison Jul 31 2008, 07:51 AM

If someone can convert these into CSV's or something - that would be usefull for all I'm sure.

Doug

Posted by: jmknapp Jul 31 2008, 11:07 AM

Here's a CSV:

http://wikiputer.org/mro/phxedl.csv

The fields are:

1. UTC date & time
2. spacecraft ephemeris time
3. PHX subpoint longitude
4. PHX subpoint latitude
5. PHX altitude (km)
6. PHX speed (km/s)
7. PHX acceleration (g)
8. X coordinate (IAU_MARS)
9. Y coordinate (IAU_MARS)
10. Z coordinate (IAU_MARS)
11. X velocity (km/s)
12. Y velocity (km/s)
13. Z velocity (km/s)

Note that the altitude is relative to the idealized tri-axial ellipsoid model of Mars, & since the northern plains are below that model, Phoenix lands at "altitude" -2.74 km!

Posted by: djellison Jul 31 2008, 11:58 AM

Awesome - I'll have fun with that. Is this all DSN tracking-reconstructed do we think? If you plot Altitude-time, it's a bit \_ if you know what I mean.

Doug

Posted by: jmknapp Jul 31 2008, 03:01 PM

I see what you mean--after the parachute deployed, Phoenix only traveled horizontally the length of the red line below:



The black line shows the approximate MRO/HIRISE line of sight.

Posted by: kwan3217 Jul 31 2008, 04:26 PM

Except for reference area, the 70deg aeroshell is exactly the same as Pathfinder, which is reasonably well documented at ntrs.nasa.gov . It's the same shell all US missions have used since Viking. I remember readng presentations comparing all of them, and like I said, aerodynamically they all act identically when using the proper reference area. Unfortunately, the best curve I saw for Pathfinder was of actual Cd (only) as a function of mach number, but only along the entry corridor it actually experienced. Cd really is the most important thing. As far as Cm and such go, the center of pressure at hypersonic speeds is always a bit behind the center of mass, so it is stable.


Search for these on ntrs.nasa.gov

2007 Mars Phoenix Entry Descent and Landing Simulation and Modeling Analysis
Mars Pathfinder Atmospheric Entry Trajectory Design (Contains accel vs time curve, Cd vs mach curve, and mass, cg, and inertia tensor for Pathfinder, among other things)
Mars 2007 Scout Phoenix Parachute Decelerator System Program Overview (For aerodynamics of parachute)
Mars Exploration Entry Descent and Landing Challenges

Also, the reconstruction is incredible in its detail. The comments attached to the spice kernels claim 5ms resolution, and from what I see I believe it. At this resolution, the accelerometers act like microphones, so you can see loud events in the acceleration curves.

Posted by: Juramike Jul 31 2008, 04:56 PM

Thank you. That graph is so cool...

I think I just got myself seasick imagining being at the end of a tether yo-yoing back and forth from the yank of parachute deployment.

Posted by: djellison Jul 31 2008, 05:14 PM

Oh wow - that IS good stuff....

For excel-monkeys like me - keep CSV's coming

Doug

Posted by: kwan3217 Jul 31 2008, 05:26 PM

Is there a good way to get the actual orientation and pixel scale of the color Phoenix on the ground MRO image? If there is, it becomes possible to plot the final latitudes and longitudes of the last bit of the landing and answer the question posed by the first picture in this thread.

Posted by: gallen_53 Jul 31 2008, 05:43 PM

I can do the conversion myself but it might already be out there on the web. Is there a table of the above trajectory in the following coordinates:

altitude above a stated reference (MOLA)
free stream velocity (state if inertial or relative)
velocity angle with respect to the local horizon (state if inertial or relative)
azimuth angle (state if inertial or relative)
latitude (state if areocentric or areographic)
longitude

kwan3217 said:

"Except for reference area, the 70deg aeroshell is exactly the same as Pathfinder, which is reasonably well documented at ntrs.nasa.gov . It's the same shell all US missions have used since Viking. I remember readng presentations comparing all of them, and like I said, aerodynamically they all act identically when using the proper reference area. Unfortunately, the best curve I saw for Pathfinder was of actual Cd (only) as a function of mach number, but only along the entry corridor it actually experienced. Cd really is the most important thing. As far as Cm and such go, the center of pressure at hypersonic speeds is always a bit behind the center of mass, so it is stable."

The problem with the 70 deg. aeroshell is there are too many aerodynamic models. Martin-Marietta developed an extensive model for Viking but unfortunately that model was based upon wind tunnel results in air and NOT carbon dioxide (real gas effects were bogus). The aerodynamic model has evolved considerably since Viking. NASA Langley has the best model based upon CFD work. However there were several published variations of the NASA Langley model. There must be a canonical model that JPL believes in.

The aeroshell center-of-pressure doesn't change much when Mach > 6 [hypersonic limit] but begins to move forward as Mach number drops below Mach = 6. By the time Mach = 1.8, the center-of-pressure is almost of top of the center-of-mass and the vehicle is dynamically unstable (you need to pop the parachute before then). When Mach < 1.8, a 70 deg. sphere-cone will become statically unstable. This phenomena almost caused the Viking aeroshell to tumble. The Viking RCS was blowing lots of propellant prior to parachute deployment because the aeroshell was dynamically unstable.

The Phoenix EDL is extremely interesting in the context of trajectory software and aerodynamic model validation. Please correct me if I'm wrong but it's my understanding the Phoenix was despun prior to hitting the atmosphere and flew a lifting trajectory without RCS. MER and Pathfinder were both spin stabilized and flew ballistic entries. Viking flew a lifting entry and was 3-axis controlled but constantly banging its RCS. Phoenix should have a perfect trajectory for code and model validation. I'm sure there are lots of interesting real gas aerodynamic effects that can be extracted from the flight data.

Posted by: jmknapp Jul 31 2008, 05:48 PM

Here's one with 5msec resolution (warning: 90,000-line CSV file):

http://cboh.org/~jmk/phxedl5msec.zip

Posted by: djellison Jul 31 2008, 05:49 PM

Sweet.

Posted by: elakdawalla Jul 31 2008, 06:17 PM

Goody goody goody....keep the awesome graphs coming...I love that you can see the three individual leg deployments!!

--Emily

Posted by: kwan3217 Jul 31 2008, 06:27 PM

On the CSVs with velocity, make sure you specify the coordinate system, particularly whether it is inertial (J2000 or MME) or rotates with Mars (IAU_MARS). This is the difference between inertial velocity and airspeed (discounting wind). To get geodetic latitude, longitude and altitude, use IAU_MARS coordinates and run it through the code described here (fortran, but short and easy to translate) http://www.astro.uni.torun.pl/~kb/Papers/geod/Geod-BG.htm . The ellipsoid used with this spice kernel is a=3396.19km, b=3376.20km, centered on Mars center of mass, b axis=polar axis

Once you have the geodetic latitude and longitude, you can set up a local vertical coordinate system at each point and convert airspeed into north, east, up coordinates. Also, from the inertial velocity, you can do a numerical differentiation (acceleration=change in velocity/change in time) which is what I did to get the parachute graph above. You know the distance to the center of Mars and can therefore subtract off gravity and you are then left with non-gravitational accelerations generated by such things as drag, lift, engines, and resting on the ground. This non-gravitational acceleration is what the accelerometers feel. Also since you know the inertial velocity it is possible to set up a lift/drag local coordinate frame at each point to get lift and drag acceleration. With the inertial attitude provided by the attitude kernel, you can get angle of attack in both directions (and confirm that the entry vehicle is not spinning) and with the mass of the vehicle, you can get lift and drag force as a function of velocity and angle of attack along the entry corridor. You still need a Mars model atmosphere to get all the way to Cd and Cl, and this cannot be derived solely from the kernels.

So yeah, this data is enough to do some interesting aero models.

Event times, based on acceleration transients in most cases

Edit: Entry interface is 125km above a spherical Mars reference surface, or 3522.2km from the center of Mars. I originally had entry interface 125km above ellipsoidal surface. It turns out that the spice kernel starts within 5ms of entry interface as properly defined. It is obvious that the kernel is intended to start exactly at entry interface.

Posted by: Juramike Jul 31 2008, 06:42 PM

From the parachute deployment, the tether seems to have a natural 0.7 sec oscillation wavelength. Looking at the leg deployment on the acceleration graph above, it almost seems that the leg deployment sequence timing might've augmented the oscillation and caused more of a yo-yoing than necessary.

Kinda like when you pump your legs on a swing set to go higher.

Probably not a big deal, but a future landing might could be made smoother with a different leg deployment delay to dampen the oscillation - like 0.3 sec.

-Mike

Posted by: fredk Jul 31 2008, 07:25 PM

Who would ever want to translate code from such a wonderful language as fortran?

Thanks for your work on this, guys!

Posted by: CosmicRocker Aug 1 2008, 05:48 AM

I'm a bit out of my element in this thread, but when I saw the .csv data series files I couldn't help but dive in and see if I could do anything with such easily accessible data. I'm hoping I can take the lat/long/alt data at face value. I started out trying to make a 3D plot of the descent, but settled for this anaglyph rendition of the trajectory.

Does this even appear to be close to what you folks would expect? If it is, I'd like to find a way to plot this above a rendering of the Martian globe. With the white background, it's a bit stark as anaglyphs go. It might appear more clearly to to those of you who can double-up on the density of your red/cyan filters.

Posted by: djellison Aug 1 2008, 09:36 AM

The joys of 'plot' - a freeware app for OSX..

Posted by: Ant103 Aug 1 2008, 09:46 AM

I have made a KMZ file to see what it look in 3D by using alt, long and alt datas.
http://www.db-prods.net/blog/?p=362
(a direct link to the KMZ at the bottom of the GG Maps visualizator).

But, there are data bellow the reference level and in Google Earth, we can't see the last piece of EDL.

Posted by: djellison Aug 1 2008, 09:50 AM

What about cheating - just add 2.5k to every alt value.

Posted by: Ant103 Aug 1 2008, 10:01 AM

Yes, but how? There are a huge quantity of numbers.

Posted by: jmknapp Aug 1 2008, 12:17 PM

FYI, the values are planetocentric coordinates of the "near point" on Mars from Phoenix. The SPICE library calls:

subpt_c("near point","MARS",et,"LT+S","PHX",scsubpt,&alt) ; // get Phoenix subpoint, IAU_MARS rectangular coords
reclat_c(scsubpt,&subrad,&sublon,&sublat) ; // convert to rectangular to latitudinal (radius, longtitude, latitude)

For Mars there's not a big difference between planetocentric and planetographic.

Posted by: djellison Aug 1 2008, 12:18 PM

Last 55s or so of landing.

Altitude on black line, left axis.

X = blue, Y = red, Z = Green - velocity on right axis in km/sec

Note the brief -Z increase at seperation, then the gradual drop until the constant velocity phase at about 2.3m/sec

Posted by: jmknapp Aug 1 2008, 12:40 PM

Love the link to the Google Earth view!

Here's another version of the CSV with the altitudes offset to be zero at touchdown:

http://cboh.org/~jmk/phxedl_alt0.zip

Posted by: djellison Aug 1 2008, 01:41 PM

FWIW , Excel '08 on my Mac can open the CSV In full - but asking it to plot anything is a death-sentence. So I just use Excel to generate a CSV containing the time I want and the fields I want, and use Plot to then..er..plot it

Doug

Posted by: nprev Aug 1 2008, 01:50 PM

I was kind of curious about that altitude data. Is the offset due to the reference geoid (forgive the term!) used, a delta in the IMU data, a combination of both, or something else entirely? I'd have expected the rad alt data to trump this in any case.

Posted by: mcaplinger Aug 1 2008, 02:12 PM

Remind me not to let you navigate my spacecraft.

Posted by: Ant103 Aug 1 2008, 03:01 PM

jmknapp : thanks.
Your updated file is great, but, a little big
Can you make a version without so many lines? (about the same numbers of the first version, because Google Earth can't view a KML file with so many point)

Posted by: jmknapp Aug 1 2008, 04:35 PM

OK, here's one at one second intervals, so only ~500 lines:

http://cboh.org/~jmk/phxedl_1sec.zip

Posted by: jmknapp Aug 1 2008, 04:50 PM

Not sure, but I'd bet it's just the difference between the actual altitude and the reference geoid. According to the man page for subpt_c():



In an early press conference someone mentioned that the plains Phoenix is on are quite low, such that liquid water can even exist, so it might make sense that it would be 2.7km below the geoid.

Posted by: jmknapp Aug 1 2008, 05:05 PM

Just going by this http://www.daviddarling.info/encyclopedia/P/planetocentric_coordinates.html:

Posted by: dmuller Aug 1 2008, 05:08 PM

Again without having looked at the files, I recall from my pre-landing research for the countdown script that there was a regular mention of the landing site being at -2.5km to -3.5km MSL ... I always reckoned that it meant "mean surface level". Might reference to that. The simulator assumed a landing site altitude of MSL -3km, hence started entry interface at altitude 128 km (vertical above landing site).

Ooo how I would have loved having all these numbers PRIOR to the landing :-)

Posted by: mcaplinger Aug 1 2008, 09:02 PM

I'd have to say that reference is a little questionable. For Mars an areocentric latitude can be almost 0.4 degrees different from an areographic one, which corresponds to a distance of over 20 km. It may not matter for what this thread is talking about, but there are plenty of times when it does.

Posted by: djellison Aug 3 2008, 07:47 PM

A few close-ups of the accel during deployments etc.

Chute deploy, leg deploy, lander seperation, and touchdown.

Posted by: jmknapp Aug 3 2008, 08:39 PM

Weird how the acceleration pulses during the rocket-assisted descent--swinging from positive to negative, ten times a second.



Sure enough--difference of about 0.25 degree at the Phoenix landing site.

Posted by: djellison Aug 3 2008, 09:31 PM

That's what pulse-throttling will do for you

Doug

Posted by: dmuller Aug 4 2008, 04:24 AM

I notice one last peak of deceleration 0.35 seconds after landing ... did Phoenix bounce (a tiny little bit) on "impact"? To me the spike at L+0.35s does not seem to be part of a declining oscillations from the spacecraft vibrations

Posted by: Oersted Aug 4 2008, 09:03 AM

Would those small wobbles in g after landing be connected to the venting?

Posted by: Skyrunner Aug 4 2008, 10:15 AM

Or damping of the legs? Is it a spring-damper system? In a sort of way the answer is that any real system is, so I suppose the landing legs should have some oscillatory decay as response to this impulse.

Posted by: Ant103 Aug 4 2008, 10:24 AM

Many thanks! It works fine .

http://www.db-prods.net/blog/?p=362

Now, I can add informations like where the heatshield was released, where the parachute and the leg were deployed, etc. .

Posted by: djellison Aug 4 2008, 10:54 AM

Now that would be interesting. Ditto the exact moment that HiRISE image swathed past Phoenix. From that, we can see how long between heatshield-sep and the image, thus how far the heatshield was away from the lander tells us how much more quickly is was falling.

If we just presume a flat surface - we can then surely extrapolate between these and figure out a rough trajectory for the heatshield. We have a trajectory for the lander, and we know the mass of the lander comapred to the backshell and chute, so we can thus estimate the speed at which the backshell landed - and extrapolat a trajectory for it as well


And bingo - we have all three, animated.

I've got a balloon to fly this w'end, and animations of a different sort to do - but if someone can do large images that show, to scale, the above-projection of these trajectories, the side projection of them, and the times - I could knock something quite simple up rather quickly - with the HiRISE image as a back-drop


Although " http://www.unmannedspaceflight.com/index.php?showtopic=5174&st=60," isn't quite right. UMSF est un forum Britannique

Doug

Posted by: dmuller Aug 4 2008, 11:14 AM

If anybody is creating a very detailed timeline of EDL events, including possibly things like MRO MEX ODY activities, then I would be very grateful if you could share it ... I'd like to put it on my website where the realtime simulation used to be. I guess that'd be a fitting way to end the realtime simulation which incidentially still receives quite a number of hits.

If all else fails, I'll ultimately try and do it as well but that will be in the not-so-near future due to other commitments.

Posted by: climber Aug 4 2008, 12:33 PM

Not sure to understand what it has been said after this post but, does it means that the "0.35 seconds after landing peak" could be the heatshield impact?

Posted by: ilbasso Aug 4 2008, 12:44 PM

I think the heatshield would have impacted well before the lander touched down, since it was free-falling.

Posted by: djellison Aug 4 2008, 01:27 PM

Yeah - the heatshield would have been quite a lot earlier, and I doubt it would have been felt by the lander.

Maybe something to do with the prop system - not the He vent, but blow down of whatever was left in the engines perhaps.

I don't think it's a bounce - as that would have registered as the free-fall accel for a moment, which would be at a negative g number, as seen in-between the engine throttle pattern

Posted by: jmknapp Aug 4 2008, 01:33 PM

Well, the three legs didn't touch down at the same instant--could that be it?

Posted by: kwan3217 Aug 4 2008, 02:49 PM

More CSV goodness, this time rotation matrices

As it says in the header, this includes position, velocity, rotation matrix from reference frame to lander cruise frame, and vector from Mars to Sun. Rate is exactly 24 frames per second. Perfect for all your animation needs, and in fact I am working on one, but I don't know if I will ever publish it, it's not yet Maas quality and I have high standards. But if I did want to post it, how would I?

This one is in the inertial MME frame (Like J2000, but aligned along the Mars polar axis). All distance units are meters (not km!) and all time units are seconds.

Posted by: kwan3217 Aug 4 2008, 02:53 PM

This one is in IAU Mars, which rotates with the surface of Mars.

Interesting things to notice:

1) The lander really swings under its parachute a lot, maybe ~20deg or so by my eye.
2) Wind is significant, especially towards the end of the parachute part. Wind backcast: From the north at 6m/s gusting to 14m/s
3) It seems that Phoenix oriented itself facing north almost perfectly. I can't see even a degree of difference between the sides of the spacecraft and local true north.

Posted by: Ant103 Aug 4 2008, 03:34 PM

It's hard to find it and deduce it by seeing graphs and numbers in CSV, but, where can I find the exact time of EDL events and the time of MRO shot?

Posted by: dmuller Aug 4 2008, 03:35 PM

I agree with earlier suggestions that the heatshield would have impacted before the lander touchdown and probably didnt quite trigger an impact that Phoenix would have registered.

I am also not sure if it's the 3rd leg touching down late. Vertical speed was 2.4 m/s, and that spike was .35 secs after landing, so one side of Phoenix would have tilted up 2.4 x .35 = 84cm which would be a tilt of 10% or so (assumes a Phoenix diameter of 5 meters)

Posted by: kwan3217 Aug 4 2008, 03:50 PM

I had a post earlier which has a timeline of all events visible from velocity or acceleration plots, relative to a certain UTC SCET time. I still don't know the time of the MRO shot, but now that we know the location history of the lander and MRO, maybe someone can reconstruct the image and back out the time.

Posted by: Ant103 Aug 4 2008, 04:01 PM

Yes, I've seen it. But, the timeline is show as a duration from EDL begining. I need simple hours (hh:mm:ss) .

Posted by: jamescanvin Aug 4 2008, 04:16 PM

Ant, http://www.unmannedspaceflight.com/index.php?s=&showtopic=5174&view=findpost&p=121870 the x-axis is given in time past a given UTC, you should be able to get some accurate times off that.

Posted by: jmknapp Aug 4 2008, 04:53 PM

Ant103's Google Earth trajectory seems to show some wind effects, the trajectory wandering a bit towards the end:

Posted by: kwan3217 Aug 4 2008, 05:00 PM

All the times in the timeline I posted are in seconds after that same UTC, 2008 May 25 23:30:57.920

Posted by: jamescanvin Aug 4 2008, 05:09 PM

Looking along the final decent path.

Posted by: Ant103 Aug 4 2008, 05:28 PM

I have updated my GG Earth kmz of Phoenix EDL. Now, there are the principle events along the path. I enjoy a lot to put in some information and picture into the "bubbles" .
http://www.db-prods.net/blog/?p=362

Posted by: ilbasso Aug 4 2008, 08:32 PM

Now I'm wondering, would the backshell and parachute have hit the dirt just after Phoenix landed? Would that have been detectable?

Posted by: djellison Aug 4 2008, 09:24 PM

They've have landed quite some time afterwards, a minute or so ( only 40 seconds to land by Phoenix, and with Phoenix off the backshell, the parachute and backshell have a lot of drag for not a lot of mass ) - and with a comparatively gentle touchdown - certainly not that second peak.

Doug

Posted by: Oersted Aug 4 2008, 11:00 PM

But the oscillations do not diminish, so no dampening seems to be going on...

Posted by: djellison Aug 4 2008, 11:09 PM

I think those wibbley wobbles that persist after landing are a symptom of whatever did these measurements - that's its noise floor.

Doug

Posted by: nprev Aug 5 2008, 12:00 AM

Generally, IMUs are pretty stable...unless the frame that they're mounted to isn't. Is it possible that the vehicle was oscillating a bit on the landing legs immediately after landing from any transverse component of the landing vector?

Posted by: kwan3217 Aug 5 2008, 02:26 AM

http://video.google.com/videoplay?docid=-8983810920439147166&hl=en

Quality is poor but at least you can see the spacecraft swinging around during the parachute drop.

Any suggestions on how to host a 42MB video with better quality than this? Also any suggestions on cinematography?

As far as terminal velocity of just the backshell goes, I get the following:

drag force=gravity force
(1/2)(Cd)(A)(rho)(v^2)=(mu)(m)/(r^2)

mu=mars gravity parameter=42828.314e9m^3/s^2
A=parachute effective area=109.36m^2
Cd=Parachute drag coefficient=0.63
r=Distance from center of Mars=3380000m
rho=Atmospheric density=0.018kg/m^3
m=backshell mass=110kg

Plugging these all in and solving for v

v^2=2(mu)(m)/(r^2(Cd)(A)(rho))
v=sqrt(2(mu)(m)/(r^2(Cd)(A)(rho)))

The calculation for the fully gassed up system minus heatshield only (m=587kg) gives a terminal velocity of 59.57m/s, which compares well with the observed downward velocity of 55.09. By adjusting rho to 0.021kg/m^3, we get a match for the lander+parachute+backshell system. Now taking these same parameters and putting in the mass of the backshell and parachute only we get a mass of 110kg and a terminal velocity of 23.85m/s

Parachute detatch happened at 948.14m above the landing site. With this vertical velocity, the backshell hits the ground in 39.76s, just before touchdown, which happened 41.065s after separation. Does this make sense? Sure. The lander drops at 55m/s and gaining once it separates, but uses its rockets to slow down almost immediately. It starts with twice the speed of the parachute but slows to 2.5m/s after 30s.

Posted by: CosmicRocker Aug 5 2008, 04:53 AM

That was really quite nice. I'm humbled to see even a simple animation replaying the actual telemetry like that. I think I can guess which vectors some of the colored arrows were portraying, but would you mind posting them? Very nice. I can't wait to see more.

Posted by: kwan3217 Aug 5 2008, 05:57 AM

The white bar has one end at the spacecraft position 1/24 second ago, and the other 1/24 in the future. The orange arrow is non-gravitational acceleration, each meter length is 1m/s^2 of acceleration. The blue, yellow, and magenta arrows describe the local drag frame. The cyan one points in the direction of motion, the magenta one is horizontal and perpendicular to the first, and the yellow one is perpendicular to both and points up as much as possible.

Posted by: dvandorn Aug 5 2008, 06:03 AM

Truly outstanding presentation, Kwan.

I do find myself wishing I could see an image post-'chute-deploy that centers on the chute and not the aeroshell/lander. From the motions of the aeroshell, it's obvious that it's swinging pretty fast under that 'chute. I'd love to watch that dynamic.

-the other Doug

Posted by: djellison Aug 5 2008, 07:34 AM

Kwan - Hosting, I can sort for you, no problem. (drop me an email - djellison@mac.com ) It's an AMAZING video...just bloody amazing! What was it rendered in - and where did the models come from -they're very good indeed!

I can imagine tying that into the sort of rendering I did for the those HiRISE DEM animations for a stunning end result!

Doug

Posted by: dmuller Aug 5 2008, 08:00 AM

Wow ... genius! And the background music gives a nice comparison with the planned sequence of events (those of us who have disected that animation sec by sec or frame by frame would be very well versed in the meaning of the background music )


I should be able to host it for you at the Space Outreach Library. That would be an impressive first file for the library (which is coming soon, I promise ... it is well enough to host files at this moment)

Posted by: kwan3217 Aug 5 2008, 08:42 AM

Thanks! I've already got the next two versions in the pipe. One is audio, with the music tweaked to hit the actual events as opposed to planned, and with JPL audio. The next is with a HUD.



Rendered in a modified version of MegaPOV, itself a modified version of http://www.povray.org/. Took 14 hours on four cores in two boxes. Models are translated from an Orbiter model by http://orbithangar.com/searchid.php?ID=3452

Posted by: Oersted Aug 5 2008, 09:58 AM

I was thinking that as well, but when I then look at around 218 seconds before touchdown, there aren't such pronounced wiggles. Would the "noise floor" be different in flight? - I am thinking that it would more likely be some residual movement, but the strange thing is that it doesn't taper off...

On another note: Fantastic animation kwan! - Talk about contributing to the forum!

Posted by: djellison Aug 5 2008, 10:51 AM

If you can export to 3DS with animation - hint hint - let me know

Back shell gyro compared to lander gyro - assuming they're separate like MER?

Posted by: imipak Aug 5 2008, 12:40 PM

Thirded, fantastic stuff kwan! Regarding cinematography - would it be possible to show the vehicle from different distances, especially as the backward-pointing arrow disappears from the field of view? It's a great way to visualise the accelerations as physical lengths relative to the size of the lander. Also perhaps "cutting" to different camera angles around the time of key events (parachute deployment, backshell jettison etc) might be good? Integrating it with Doug's stuff with surface imagery and relieft would be just too awesome - the only reason I haven't started sending the link to people is the thought that an even better version could be in store...

Just 2c from the peanut gallery, from someone who can only admire the incredible talent around here

Posted by: Ant103 Aug 5 2008, 01:04 PM

Fantastic animation . It's a great work.

On my side, I continue to work on my KMZ file. I've added superimposition of picture to show the ellipse landing site, the MRO of landing site and a vertical projection made by NASA .
The respective scale of the image are a little approximative, but, I believe that it's pretty good.
You must know that you absolutely need the Google Earth software to see these superimposition .

http://www.db-prods.net/blog/wp-content/uploads/2008/08/phoenixedl-ech1.png
http://www.db-prods.net/blog/wp-content/uploads/2008/08/phoenixedl-ech2.png
Always here : http://www.db-prods.net/blog/?p=362

Posted by: kwan3217 Aug 5 2008, 01:53 PM

http://video.google.com/videoplay?docid=1679027418837385215&hl=en

Posted by: TheChemist Aug 5 2008, 02:11 PM

This is really fantastic, thank you kwan3217 !

May I humbly suggest, that after landing, it would be great if the video fade out to the real view from the deck of Phoenix, i.e a scroll through the Peter Pan panorama, keeping in sync the sounds of joy from the mission control ?

Many thanks once more for this great work of yours .

Posted by: jmknapp Aug 5 2008, 02:30 PM

So cool, particularly knowing that every wobble is true to life!

One thing--the ground controller at one point mentions that the parachute is "normally deployed at this time" but the animation shows the chute coming out a few seconds later. The animation may be more correct than the ground controller as for that timing, but maybe it takes several seconds after chute deployment for the "signal" to show up in the accelerometer?

In fact, the http://hirise.lpl.arizona.edu/phoenix-descent.php showing the Heimdall crater image notes that it was taken "just a few seconds after the parachute opened" and "about 13 km above the surface." In the SPICE data, there's nothing unusual happening around altitude 13km, and the first real tug from the chute is seen at around 10.5km altitude.

On the other hand, looking at the Heimdall image, it's hard to believe that the chute isn't already pulling pretty hard on Phoenix.

Posted by: djellison Aug 5 2008, 03:11 PM

Given that the heatshield is already some distance from the backshell, yeah - that altitude figure must be wrong.

OR

Perhaps that's when the image started being taken? HiRISE swoops out an image over time...but I don't think it's that long.

Doug

Posted by: Stu Aug 5 2008, 05:24 PM

Great animation, many congratulations! Did anyone else feel those Landing Night butterflies take wing in their stomachs again when they heard the soundtrack? Strange for such a gentle piece of music, but now whenever I hear it I really do feel very nervous again, as I have a flashback to watching the EDL animation projected on my living room wall in realtime on Landing Night...

Posted by: jamescanvin Aug 5 2008, 05:36 PM

Yes, I did. And the landing commentary still brings a tear to my eye.

Posted by: MahFL Aug 5 2008, 06:02 PM

I still marvel at the fact it worked, the shear number of things that had to go right in order to land perfectly.
I'd love to see the software flow charts on the EDL sequence.

Posted by: Oersted Aug 5 2008, 06:45 PM

..and it is amazing to see how rock-steady that powered descent is by the lander. Hardly hardly any wiggling, yawing, slewing, rolling, except for the planned yaw to align with the N-S axis. Just perfect smooth control!

Posted by: dmuller Aug 6 2008, 12:20 AM

Question about the wobbling when PHX hangs on the parachute: does it pivot around the center of the spacecraft gravity (which seems to be what is animated) or would it pivot around the point where the parachute is attached to the backshell?

Posted by: kwan3217 Aug 6 2008, 01:22 AM

I actually think it pivots at or near the center of pressure of the parachute. I am imagining a pendulum with a heavy bob. Even though the center of mass is near the bob, the whole system rotates around the pivot, which may have near no mass at all.

I put the orange arrow in the system for something like this purpose. I hypothesize that at all times while the chute is deployed, the parachute riser is parallel to the orange arrow, which represents the nongravitational acceleration. Nearly all of this is aero force on the chute, the remainder is aero force directly on the backshell. Since the center of pressure of the chute is near or on the chute axis, and since a rope can only support tension, the rope should be parallel to the force it exerts. What interests me is that this says that the wrist movement is actually very small. The orange arrow almost always emerges out of the top of the backshell, its origin is near the center of mass of the lander, much closer to the heatshield, so this is significant. If there was a large wrist movement, the orange arrow would emerge somewhere else, like it does at times during peak deceleration on the heatshield.

Posted by: nprev Aug 6 2008, 01:32 AM

Wow, Kwan, that was just great! Watched 1A & 1B, both were delights. Thank you!

Posted by: MarsEngineer Aug 6 2008, 02:16 AM

Wow wow Kwan. Very nice job.

Doug E. pointed this work out to me today and I have to say that I am very impressed with you and all of the gang. I was not aware that the NAIF data had been released. It is very cool that you can do this work.

As I told Doug, I wish the rules allowed people like me to borrow your skills to help us. I don't know how many times I wish I could post something here and have some of you do some engineering / rendering for me! (the price is right and you all have the"chops" to do this)

Reconstructing & studying how things work (when they do) is the fun part, I am glad that you and Doug and the other UMSF gang have been able to dive in.
Our (small) Phoenix EDL reconstruction team is running behind you (a little) as already they are getting busy on other jobs, but a couple are diving into this data and comparing our sims with this (and the radar) data. One of the aspects of having a bit of "truth" (for a change) is that we can see how far off we are in our ability to predict what can happen during EDL. We will certainly learn something from this, but so far we are collectively happy that it was pretty close to what we expected. (there was a lot of room for variation even in our models). What is especially exciting is that we can compare this "passive, unguided & non-spinning" entry vehicle with our ballistic range data and maybe confirm or update our aero models. Hopefully the team will publish in the coming months.

I sent a link to this thread to the Phoenix EDL gang. I think they are impressed too!

Have fun!

Now back to MSL for me ...

Your fan,
Rob Manning aka MarsEngineer


********
Comments are those of the author and do not represent the views of NASA, Caltech nor JPL.

Posted by: dmuller Aug 6 2008, 07:14 AM

Well Rob, none of us would be able to do anything if you folks didn't put in that much hard and brilliant work in the first place ...

Posted by: vikingmars Aug 6 2008, 12:49 PM

YES : 5 wheels to you, MarsEngineer, to ALL what you did since MPF and for all new landing techniques you found and for the technologies you developed and tested so well on Mars !!!!
Should there be a Nobel Prize for Planetary Exploration, you would be #1 on the list !

Posted by: kwan3217 Aug 6 2008, 04:42 PM

Who is speaking during the EDL commentary? Early through there is one american-sounding guy, then later most of the announcements are by a french-sounding guy. What are their names?

Posted by: nprev Aug 6 2008, 05:35 PM

The 'French-sounding' guy actually sounded more Middle Eastern to me (I'm an American, BTW)...but, I have no idea at all.

Posted by: MahFL Aug 6 2008, 06:13 PM

Google is your friend.

""Phoenix has landed! Phoenix has landed! Welcome to the northern plains of Mars!" mission commentator Richard Kornfeld exclaimed from the control center at the Jet Propulsion Laboratory. "

Posted by: MarsEngineer Aug 6 2008, 07:08 PM

MahFL is right, it was Richard Kornfeld (good guess - he comes from Switzerland originally). Richard was the lead engineer for orchestrating the "EDL Comm" for Phoenix. He sweated the all of the interfaces and details with Mars Express, Odyssey, MRO, Greenbank and the DSN. Had Phoenix has a failure during EDL, the data being sent and recorded from 3 different spacecraft as well as Earth would have allowed us to figure out what happened and why. Fortunately we did not have to. He did a great job! He is now spending a lot of time bopping over to Tucson to help in surface ops. He really loves Mars time! (not really ... no one does!)

The other voice is Robert Shotwell. Robert was the Phoenix "Project System Engineer" responsible for many things but most importantly he organized and ensured that the verification and validation program for Phoenix was comprehensive and complete. It is an exhaustingly detailed and technically impossible job. But he was outstanding at it.

Real people with real jobs. Each person bringing unique skills and personalities (there was no shortage of personalities on Phoenix). Amazing.

take care,

Rob M.

Posted by: ElkGroveDan Aug 6 2008, 07:21 PM

Richard was such a great narrator. Count me as one vote to have him call out MSL when the time comes, even if he's not part of that team. There's a certain amount of excitement in his voice, but its subtle enough to not be a distraction. That 9 minutes was one of the most exciting and enjoyable as any space related live event in my 47 years of following these events.

EDIT: admittedly I guess I didn't follow my first one too closely, Explorer 11 -- being an infant at the time.

Posted by: Oersted Aug 6 2008, 10:05 PM

Of course Rob Manning wouldn't be allowed to do that, but I don't see a problem with an anonymous UMSF member going by the user name MarsEngineer, whoever he would be, posting little tidbits from time to time...

Posted by: nprev Aug 7 2008, 01:32 AM

I gotta chime in & totally agree with this statement, Dan...it was really terrific, will never forget it!

Posted by: mcaplinger Aug 7 2008, 02:07 AM

Of course, one might wonder why JPL, which as far as I know has a team of several people to do nothing but "visualization", would need to do that in the first place.

Posted by: elakdawalla Aug 7 2008, 04:05 AM

Geez, Mike, can't you let a guy throw a bone to his fans?

--Emily

Posted by: Oersted Aug 7 2008, 07:58 AM

Maybe kwan will get a job offer from Maas Digital soon?

Posted by: djellison Aug 7 2008, 08:41 AM

Come on Mike - that's not exactly fair. Sometimes, even though the talent is there, the time or money to do something isn't. Surely you more than most here, should understand that.

DOug

Posted by: OWW Aug 7 2008, 09:03 AM

Correct me if I'm wrong, but did the lander legs deploy twice in the animation? The first time just after heatshield separation at 4:12? The second time at 5:36.

Posted by: dmuller Aug 7 2008, 09:04 AM

Well I think in "kwan vs JPL Visualization" (sorry for putting it that way) we are talking about two different things.

Kwan's animation is amazing because it is scientifically and engineering-wise "correct", which is of great excitement for those interested in the science and engineering of it all (i.e. the majority on this forum).

The JPL Visualization's task, I can imagine, is to sell "space" and "spaceflight" to the masses (and hence guarantee funding etc). So that stuff has to look good. I somehow doubt that the big masses do get any excitement out of the big wobbles prior to parachute deploy, the resonances of leg deploy, the steadiness at constant velocity

Posted by: Skyrunner Aug 7 2008, 09:15 AM

It would be neat if JPL could build a piece of SW in the lines of Meastro that let us do al kinds of imaging stuff. Give us a course we have to complete. Ensure the program documents all steps the user takes to alter the image, panorama or anaglyph. Unfortunately NASA would need another way to protect it's data. Now their researchers can just keep the calibration data to ensure they can work towards the results they have already invested years in. I guess it would not be very doable to let us all sign an NDA kind of document. It would be cool if we enthusiasts could all help with the 'simple' tasks (as far as simple tasks exist...let me rephrase that to relatively simple, repetitive tasks) to lighten the burden on the team but giving them al the credit were it is due (of course UMSF would be noticed in the image credits ).

Just daydreaming

Posted by: kwan3217 Aug 7 2008, 04:23 PM

In my animation, the legs deploy at 4:12-4:13 and stay down. The geometry is poor and most of the event is hidden by the backshell. However, the commentary doesn't mention the legs until 5:35. Either the telemetry for the legs took that long to come down (possible and understandable, mechanical one-time telemetry might run at a slow rate) or the commentator didn't notice until then (Also understandable, he seemed to be focused on the radar telemetry)

As for competing with JPL, nothing I have done is hard. It's about 250 lines of animation script, which is basically just read the table, orient the model, draw the frame, repeated 13152 times. I'd be precisely nowhere without the hard work of the guys at JPL who figured out the stuff that's in the tables (Not to mention getting a real spacecraft to Mars in the first place).

I'm also nowhere near Dan Maas and crew. I make animations to see what things "really look like" and I've been disappointed with a lot of my work because to be honest, space events are hard to film. The lighting is never right. It's hard to see critical events. Space is slow. As mentioned above, two minutes hanging on a parachute? From a fixed view point? Whoopee. Maas and crew, and the vis guys at JPL have the cinematography skills and tools to make these events look good and exciting. I am still practicing. I aspire to Maas-like quality, but I'm still a little ways away.

Posted by: gallen_53 Aug 7 2008, 06:35 PM

What I found particularly interesting in this animation was seeing the dynamic instability growing in the aeroshell's angle-of-attack just before parachute deployment. This phenomena was first seen with the Viking aeroshells and would have caused the aeroshells to tumble if Viking didn't have a reaction control system. The dynamic instability is triggered by shockwave separation due to reducing Mach Number but driven by vortices in the aeroshell's wake and real gas effects (very difficult to model).

Posted by: nprev Aug 8 2008, 01:26 AM

THAT is an interesting tidbit! So parachute deployment is as much about keeping the vehicle stable at low Mach as it is about deceleration...great dual-application solution.

Has anyone ever considered using a ribbon chute for stabilization & holding off on a main conventional chute for later? Seems like getting a single chute to work properly in supersonic conditions is a real challenge ("squidding"), don't know if its behavior is easier to simulate or predict at lower speeds, nor if it would provide enough deceleration if deployment were deferred.

Posted by: gallen_53 Aug 8 2008, 06:51 AM

Yes, the 70 deg. sphere-cone becomes dynamically unstable at around Mach = 1.8 . A 45 deg. sphere-cone such as used with Pioneer Venus or the Galileo Probe can be aerodynamically stable all the way to the ground provided the center-of-gravity is correctly located. However a 45 deg. sphere-cone has significantly less drag that the 70 deg. sphere-cone. Because the Martian atmosphere is so thin, you want the vehicle to decelerate as rapidly as possible (maximum bluntness is highly desireable).



Mars landers use a disk-gap-band parachute because that type parachute can safely deploy at supersonic speed. One would prefer to deploy the parachute subsonically but that's not really an option on Mars due to the thin atmosphere.

Designing parachutes is a black art. Correctly simulating a parachute with a computer model is hard to do. Also squidding can happen at subsonic speeds. The early MER parachute prototypes squidded in the NASA Ames 40 x 80 wind tunnel at subsonic speeds.

Posted by: Oersted Aug 8 2008, 10:23 PM

No, they also do the visualization of actual data that comes down. See for example the MER airbag bounce movie.

Posted by: djellison Aug 8 2008, 11:04 PM

Langley was responsible, at least partially, for the Spirit movie of 'chute descent and RAD/TIRS firing -the file name is something of a clue.

http://marsrovers.jpl.nasa.gov/gallery/video/movies/spirit/Langley_TIRS_Animation.avi

The AMA in another filename suggests Analytical Mechanics Associates.
http://www.ama-inc.com/ps/engineering/engineering.shtml


Doug

Posted by: dmuller Aug 9 2008, 02:57 AM

Glad to know!

Posted by: kwan3217 Aug 18 2008, 09:43 PM

This image is the best match I have found so far between the MRO image and the spice kernels. It happens 273 seconds after Spice kernel startup. The Phoenix model is scaled by a factor of 20, the actual location of Phoenix is at the center of the backshell. The point of view is at MRO and the field of view is 0.5deg horizontally. This uses the MGS MOLA 128/deg topography and Emily's map at http://planetary.org/blog/article/00001431/

I can't find a perfect match, I think that the image of the crater was distorted by the fact that the TDI and motion compensation was following Phoenix, not the ground.

227.825, parachute firing
228.935, first peak parachute deceleration, 82.962m/s^2
242.825, heat shield jettison
252.985, leg deploy
253.485, leg deploy
253.980, leg deploy
~273, MRO photo

This is ~45 seconds after parachute deploy, a bit later than I had heard before. Don't take my word as Gospel, it is certainly possible I made a mistake somewhere.

Posted by: kwan3217 Aug 22 2008, 01:53 PM

http://video.google.com/videoplay?docid=-7698299724281449208

Now I've got Emily's map and MOLA topography, and illegible HUDs instead of vectors attached to the spacecraft. Trust me, the HUDs are readable at their original resolution.

I'm not done yet.

Posted by: jmknapp Aug 22 2008, 02:25 PM

Terrific! Love the changing camera angles and attention to detail (the whoosh of helium, etc.).

Curious as to what the HUD polar display is showing.

Posted by: kwan3217 Aug 22 2008, 06:37 PM

Polar chart shows:
(Dist)ance and direction to actual touchdown point in m and degrees (all azimuths are in degrees, N=0, E=90, S=180, W=270)
(Hspd) Horizontal speed and azimuth in m/s
(FPA) Flight path angle in degrees, 0 is horizontal, +90 is straight down
(Alt)itude in meters
(Vspd) Vertical speed in m/s
(Vrel) Total ground-relative speed in m/s
(Acc) Non-gravitational acceleration (what's felt by accelerometers) in m/s^2

The vectors in the polar chart show the vector to the actual touchdown point (green) and the vector of current horizontal speed (yellow) in a logarithmic manner. Inner ring is 1m and 0.1m/s, and each next outer ring is 10x as much. Similarly the bars under altitude and vspd are logarithmic.

This is all modeled after the VTOL instrument in the Orbiter sim.

The vector ball in the upper right has bars every 45deg in latitude and longitude. It's polar axis is the local vertical. The red bar is true North. It shows the X, Y, and Z lander frame relative to the current viewpoint (red,green,blue). The local drag frame is shown with only vector arrowheads. The cyan arrowhead (mostly covered by the red vector) is the relative velocity. Assuming no wind, Drag is exerted opposite this direction. The yellow arrowhead is the "vertical" lift vector, perpendicular to the relative velocity vector and in the local vertical plane containing the relative velocity vector. The magenta arrowhead is the "horizontal" lift vector, perpendicular to both of these and as a consequence always in the horizontal plane. The orange arrow is the direction of acceleration as felt by the accelerometers (excluding gravity) and therefore registers 1 Mars G when sitting at the surface.

Upper left is a clock in UTC, spacecraft event time.

All the sound effects, as well as the music, come from the EDL HUD video published by NASA before landing. I can't take credit there. I just tweaked things to match the actual timeline, and am not done yet.

Posted by: jmknapp Aug 23 2008, 12:38 AM

Thanks... did you ever find a server to host the file? How big is it? Would love to see the hi-res version.

Posted by: CosmicRocker Aug 23 2008, 03:53 AM

Wow! It gets better and better. If you're not done yet, I can't wait to see the next version. That was amazing.

Posted by: djellison Aug 23 2008, 09:02 AM

UMSF is happy to host it.

Posted by: kwan3217 Aug 24 2008, 11:47 PM

Actually I have acquired some web space of my own for this -- http://astro.kwansystems.org/.

Posted by: dmuller Aug 25 2008, 01:55 AM

Kwan, I'd love to link from my (ex-) Phoenix realtime simulation to your movie. Let me know once all the UMSFers have downloaded it and your website has bandwidth available for more visitors :-)

Posted by: kwan3217 Aug 28 2008, 02:34 AM

OK, now I'm done, because it's time to move on to a new project. http://astro.kwansystems.org/ now has posted version 3C, version The Last.

Also, I am in the process of packing up and posting the source code for the education of anyone who cares.

Emily, djellison, dmuller, anyone else who wishes to: You may get and host any or all of the content of Kwan Astrodynamics. It will probably be gone in a few weeks.

Posted by: Astro0 Aug 28 2008, 03:47 AM

Just brilliant!
That turn to ride behind Phoenix as she heads in and seeing where she's going to land - FANTASTIC.

"If you need Visuals that are Dramatic, call Kwan Astrodynamics"

Astro0

Posted by: eoincampbell Aug 28 2008, 04:54 AM

... STUNNING ... thank you,
Eoin

Posted by: imipak Aug 29 2008, 01:15 PM

Fantastic Kwan! I wondered if you'd do plasma heating effects, a friend who does CG professionally once told me flames, smoke, vapour clouds etc are one of the hardest things to get right.

The words "Phoenix has landed! Phoenix has landed! Welcome to the north plains of Mars!" brings a lump to my throat once more, because the final reveal shot pulling back from the lander and target marker to the planetary context view is the perfect complement, illustrating the scale of the achievement. That's why those simple words mean so much to us all, and your work illustrates it magnificently.

I've mentioned work this as a work-in-progress to a couple of friends, but haven't shown them it yet because you promised further developments. It was a hard temptation to resist after the first version, because it was already so good, but I'm glad I did... I'm actually looking forward to getting back to the office after my break, now

I'll show them my local copy rather than sending the link, to spare your b/w, but I really hope someone can find the space for a permanent mirror - it's an all-time classic, IMHO. Many, many thanks.

Posted by: dmuller Aug 29 2008, 03:36 PM

I will put it on the Space Outreach Library in due course, when I am a bit less busy.

Just out of curiosity ... would there be a "demand" for such large files to be available offline, i.e. burnt on CD and sent my snail mail, for a nominal fee of say US$x for 1 to 2 CDs to cover for postage & stationary & a bit extra for the time involved? This could be a service that the Space Outreach Library could offer, of course only with the approval of the authors of the files in question (I dont want to appear to be "selling" other people's work)

Posted by: Oersted Aug 31 2008, 09:25 PM

holy mother, what an amazing development since the first already stunning video! - a great work of art and science to come home to after the summer vacation. Art because you really nailed the music score, nd because of various flourishes like the final zoom-out.

Only slight thing I can't get my non-engineer mind around is showing the swinging under the parachute with the viewpoint fixed to the backshell, and not to the shared c.o.g. of the backshell-parachute combo. In my "reality" the backshell should be not just wiggling - as it seems from the movie - but swinging quite violently around as well. Just a question of visualization, I know.

Thanks so much Kwan, you well deserve the kudos heaped on you. From the Phoenix team as well no less!