[X] My Assistant

[vikingmars]

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 !

[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.

[gallen_53]

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.

[kwan3217]

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.

Attached thumbnail(s)