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Unmanned Spaceflight.com > Mars & Missions > Past and Future > Phoenix
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vikingmars
smile.gif 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 ! rolleyes.gif
Click to view attachment
bgarlick
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.
fredk
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.
bcory
Also one must consider at what swing angle the decending package was at when the heat shield was jettisoned.
kenny
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.
MahFL
Yes Phoenix was programmed to fly away. Mind you I am still surprised how close all the hardware landed together.
vikingmars
OK, good points. Maybe I'm wrong then : let's wait for the final EDL trajectory release by the engineers... smile.gif
ugordan
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.
MahFL
Then again the atmosphere is very very thin and all the objects would not be blown much by any wind.
kwan3217
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.
dmuller
QUOTE (kwan3217 @ May 29 2008, 04:30 AM) *
There is a PDF slide presentation posted here which shows the details of this "backshell avoidance maneuver".

As a non-engineer, I just love the engineering English [engenglish???] (from above document):
QUOTE
... there is an increased probability the backshell/parachute will recontact the lander ...
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.
AndyG
engenglish???

...Eng2lish? laugh.gif

Andy
mhall

Engl-ish ?
Greg Hullender
QUOTE (dmuller @ May 28 2008, 08:18 PM) *
As a non-engineer, I just love the engineering English [engenglish???]


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
Adonis
QUOTE (ugordan @ May 28 2008, 08:19 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.


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.
dmuller
QUOTE (Greg Hullender @ May 30 2008, 02:16 AM) *
As for "recontact," ... It crisply captures the idea of "to collide with, at any speed, but after separation."

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 ...)
dmuller
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:
Click to view attachment
(Sorry for the quality of the drawing ... I dont have any decent software, still using Windows Paint ph34r.gif )

EDIT: image reworked ... ignore this one and see post further below
ugordan
Dmuller, doesn't that north vector contradict with the observed orientation of the solar panels?
djellison
The vehicle intentionally rotated during terminal descent to put the arrays left right.
ugordan
Quite. If anything, I'd say north is about 12 degrees clockwise from up judging by solar panel orientation.
dmuller
QUOTE (ugordan @ May 30 2008, 08:34 PM) *
Dmuller, doesn't that north vector contradict with the observed orientation of the solar panels?

Yes of course, overlooked that piece of evidence blink.gif Yellow line up is North.
Click to view attachment
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 rolleyes.gif 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
dilo
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...
Adonis

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

Thanks
MahFL
The project manager said it would take several months to put the edl sequence together from the data.
ahecht
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
cndwrld
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.
01101001
The MRO team has given the Phoenix-on-parachute pixels another whack, and they might have spotted the falling heat shield:

Phoenix Descent with Color and the Heat Shield in Free-Fall
Pertinax
Kudos again to the MRO team and a Mars bar to T-Man et.al ( http://www.unmannedspaceflight.com/index.p...st&p=116143 )

-- Pertinax
jmknapp
With the imaging by HIRISE, is there a definitive location (latitude, longitude) for Phoenix, to several decimal places?
Pertinax
QUOTE (jmknapp @ Jul 9 2008, 07:18 PM) *
With the imaging by HIRISE, is there a definitive location (latitude, longitude) for Phoenix, to several decimal places?


And altitude?

-- Pertinax
Juramike
QUOTE (Pertinax @ Jul 9 2008, 07:59 PM) *
And altitude?

-- Pertinax


I'm pretty sure it's touching the surface. smile.gif
jmknapp
QUOTE (Juramike @ Jul 9 2008, 11:44 PM) *
I'm pretty sure it's touching the surface. smile.gif


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?).
akuo
The position was already reported in an earlier post on this forum smile.gif
QUOTE
68.218830N 234.250778E, IAU 2000 Areocentric
edstrick
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.
jmknapp
QUOTE (akuo @ Jul 10 2008, 06:26 AM) *
The position was already reported in an earlier post on this forum smile.gif


Thanks--is that link correct? The original reference doesn't seem to be there.
akuo
Works for me. I guess this is another way to put it:
http://www.unmannedspaceflight.com/index.p...st&p=115817
jmknapp
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.
Pertinax
QUOTE (Juramike @ Jul 9 2008, 11:44 PM) *
I'm pretty sure it's touching the surface. smile.gif


laugh.gif Thank you Juramike! rolleyes.gif

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

kwan3217
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.
dmuller
QUOTE (kwan3217 @ Jul 31 2008, 02:02 AM) *
Now all we need is an exact time for the entry parachute photograph and we can tell everything about it.

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
jmknapp
QUOTE (dmuller @ Jul 30 2008, 08:02 PM) *
parachute deploy should show a big spike in deceleration


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?
gallen_53
QUOTE (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.


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?
gallen_53
Hold on, I just found the NAIF website at http://naif.jpl.nasa.gov/naif/toolkit_C_PC..._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!
kwan3217
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.
gallen_53
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.
djellison
If someone can convert these into CSV's or something - that would be usefull for all I'm sure.

Doug
jmknapp
QUOTE (djellison @ Jul 31 2008, 02:51 AM) *
If someone can convert these into CSV's or something - that would be usefull for all I'm sure.


Here's a CSV:

PHX EDL 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!
djellison
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
jmknapp
QUOTE (djellison @ Jul 31 2008, 07:58 AM) *
If you plot Altitude-time, it's a bit \_ if you know what I mean.


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.
kwan3217
QUOTE (gallen_53 @ Jul 31 2008, 12:35 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.


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.



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