InSight Cruise Phase, Events during Mars transit prior to EDL |
InSight Cruise Phase, Events during Mars transit prior to EDL |
May 8 2018, 05:35 AM
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#1
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Hey again, everyone. This thread will be for discussion of anything that happens between now & landing day, currently 26 Nov US Pacific time (UTC-8 hrs during that part of the year).
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Nov 18 2018, 12:24 AM
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#2
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
Attached is a text file with 1-minute sampling from the SPK file https://naif.jpl.nasa.gov/pub/naif/INSIGHT/...e09o_edl_v1.bsp -- items are J2000 time, distance from Mars center in km, and XYZ position and velocity in km from Mars center and km/sec, both in Mars body-fixed (iau_mars) reference frame.
Most of the SPK files on NAIF don't appear to have the landing portion modeled in them, they fly past Mars (atmosphere unmodeled, maybe.) edl.txt ( 34.22K ) Number of downloads: 833 -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Guest_mcmcmc_* |
Nov 18 2018, 07:36 PM
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#3
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Guests |
Most of the SPK files on NAIF don't appear to have the landing portion modeled in them, they fly past Mars (atmosphere unmodeled, maybe.) Too many variables and randoms factor to predict anything during EDL: each major event (parachute, heatshield, backshield) spans in a range of 20 seconds, i.e. "who knows when it will happen"? No luck also with Horizons data. Anyway what I am actually trying to build is a Phoenix simulator... which can be used, with a little of imagination and manually starting/restarting each event when NASA announces it has been confirmed, to "visualize" what is (approximately) happening in Mars sky during those 6 minutes of terror on 26/11. :-) And it will also be useful to analyze actual data after landing. |
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Nov 18 2018, 08:06 PM
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#4
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
Too many variables and randoms factor to predict anything during EDL: each major event (parachute, heatshield, backshield) spans in a range of 20 seconds, i.e. "who knows when it will happen"? Well, the way this works for the team (and I was pretty involved in this for MPL, PHX, and MSL) is that hundreds of Monte Carlo runs are done and the probability distribution of when major events could happen is calculated. Some parts of the descent are pretty locked down (for example, powered descent duration can't vary by much because you run out of fuel if it goes too long and you crash if it goes too short) whereas some parts are highly variable (time spent on parachute, for example). BTW, I can't download the attachment from my last message and maybe you can't either (some forum issue?), but I guess you're not interested anyway. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Guest_mcmcmc_* |
Nov 19 2018, 03:21 PM
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#5
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Guests |
(for example, powered descent duration can't vary by much because you run out of fuel if it goes too long and you crash if it goes too short this remembers me of something... how do Phoenix and Insight prevent Schiaparelli final event from happening? And by the way, recorded data on Phoenix show and incredibly wrong modelization of Pitch, Roll and Yaw for Phoenix: https://ntrs.nasa.gov/archive/nasa/casi.ntr...20080034645.pdf (fig. 6, 7, 8). By the way, is anything similar to Phoenix raw data available for unfortunate Schiaparelli mission? Or was it supposed to upload them once landed? |
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Nov 19 2018, 03:48 PM
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#6
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
And by the way, recorded data on Phoenix show and incredibly wrong modelization of Pitch, Roll and Yaw for Phoenix: By the way, is anything similar to Phoenix raw data available for unfortunate Schiaparelli mission? Or was it supposed to upload them once landed? Has it occurred to you that maybe the problem is your interpretation of the data, not that they are "incredibly wrong"? There was some realtime downlink of Schiaparelli data, I think it's described in the failure report. I'd be very surprised if it was online in raw form. Here's the Insight dump with 1-second intervals. edl.zip ( 2.37MB ) Number of downloads: 366 -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Guest_mcmcmc_* |
Nov 19 2018, 09:17 PM
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#7
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Guests |
Has it occurred to you that maybe the problem is your interpretation of the data, not that they are "incredibly wrong"? Suggestions? I just see two heavily different curves named "predicted" amd "reconstructed". No way to download this file, still gives an error, anyway never mind, I tried setting up the simulator with data I have: http://win98.altervista.org/space/explorat...-simulator.html It has yet to be cleaned up and I'll try to also add some fancy graphical instrument like I did here, if I have time, but time is short, only one week remains. |
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Nov 20 2018, 12:38 AM
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#8
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Junior Member Group: Members Posts: 48 Joined: 8-August 12 Member No.: 6507 |
Latest status. We did TCM5 yesterday (could not mention until official announcement came out Official InSight Twitter Page). So far looks like very good maneuver (well than 1 sigma error) and just waiting for Nav results to see if we are setup for entry as expected. Hoping to skip TCM6 this weekend, but ready if we have to do it. Things looking good for EDL.
On a side note, I have been trying to come up with a good EDL song to play that day on the way into work. For launches there are lots of ones that work, but none that seem to cover landing. Best I could think of was Helter Skelter "Coming down fast from miles above you". Good line but the rest of the song does not fit my hopes for that day. Any good ideas? |
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Guest_mcmcmc_* |
Nov 20 2018, 10:02 AM
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#9
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Guests |
Latest status. We did TCM5 yesterday Good to hear that. I just found out a weird thing I did not know: during travel toward Mars, probes are not oriented as we see in all videos, but in such a way that solar panels are correctly oriented toward sun, then the "tip turn" (which I would call "Entry Attitude Setup Maneuver") is performed. I also read that only a short time before Phoenix arrival at atmosphere interface somebody thought that there was a possibility of recontact between cruise stage (or parts of it) and lander after lander deployment, as they're both on same ballistic trajectory, and cruise module is only slightly slowed down by the pyro devices during lander deployment: it was calculated a minimum distance of 6 meters between lander and cruise module during EDL! So, if I understand correctly, now the lander deployment is performed before EASM, so cruise module is not just slowed down by lander deployment, but it is also put on a different trajectory due to the transverse force impressed by pyro devices; is this interpretation correct? But if this "Cruise Module Avoidance Maneuver" was introduced only with Phoenix... how did it go for Pathfinder and MERs? And I wonder if cruise stage falling parts could have messed up Schiaparelli descent. During Phoenix EDL they also figured out through simulation that thrusters in the backshell can't be used as designed (i.e. during hypersonic phase), because simulations showed that due to "werid" aerodynamic effects and interactions at high speed they could result in a force being applied to the lander in the OPPOSITE direction w.r.t. what the thrusters were supposed to do! So they were not used at all during descent, unless an "emergency situation" was encountered. These are all interesting manuevers and "rocket science things" which I've never seen in any video, but they would look much more interesting in a video than in a PDF! |
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Nov 20 2018, 07:53 PM
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#10
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Junior Member Group: Members Posts: 48 Joined: 8-August 12 Member No.: 6507 |
Good to hear that. I just found out a weird thing I did not know: during travel toward Mars, probes are not oriented as we see in all videos, but in such a way that solar panels are correctly oriented toward sun, then the "tip turn" (which I would call "Entry Attitude Setup Maneuver") is performed. I also read that only a short time before Phoenix arrival at atmosphere interface somebody thought that there was a possibility of recontact between cruise stage (or parts of it) and lander after lander deployment, as they're both on same ballistic trajectory, and cruise module is only slightly slowed down by the pyro devices during lander deployment: it was calculated a minimum distance of 6 meters between lander and cruise module during EDL! So, if I understand correctly, now the lander deployment is performed before EASM, so cruise module is not just slowed down by lander deployment, but it is also put on a different trajectory due to the transverse force impressed by pyro devices; is this interpretation correct? But if this "Cruise Module Avoidance Maneuver" was introduced only with Phoenix... how did it go for Pathfinder and MERs? And I wonder if cruise stage falling parts could have messed up Schiaparelli descent. During Phoenix EDL they also figured out through simulation that thrusters in the backshell can't be used as designed (i.e. during hypersonic phase), because simulations showed that due to "werid" aerodynamic effects and interactions at high speed they could result in a force being applied to the lander in the OPPOSITE direction w.r.t. what the thrusters were supposed to do! So they were not used at all during descent, unless an "emergency situation" was encountered. These are all interesting maneuvers and "rocket science things" which I've never seen in any video, but they would look much more interesting in a video than in a PDF! We do jettison the cruise stage prior to the slew to entry attitude (what you call EASM). That event occurs roughly 30 seconds before the slew begins, which is about 6-7 minutes prior to the start of entry. I am not allowed by ITAR to discuss the why or how come we decided to do that (sorry). I can say that all the EDL monte carlo sims also look for cruise stage contract and flag those runs, so it is not something we have missed or have forgotten. From the limited info I know about the Schiaparelli failure this is an unrelated topic (the publicly available report EXOMARS 2016 - Schiaparelli Anomaly Inquiry shows their failure was due to high rates on the parachute swamping some fault protection values for rates and thus the IMU data was ignored and they miss estimated altitude and shut off the descent engines too early). I doubt any rate that could come from contact with the cruise stage prior to entry could result in rates that created an issue at parachute deployment while still allowing for a successful entry portion (where angles of attack are very narrow for survival). Regarding the roll reversal issue on the RCS thruster in hypersonic. That was a predict on Phoenix that came out of some a CFD analysis (see page 12 of this paper Analysis of effectiveness of phoenix entry reaction ... - NTRS - NASA). No one is sure if that is accurate or not, but to be safe Phoenix (and InSight) inhibit thruster usage after a certain time in the entry portion to avoid any potential issue. The only thing the RCS would be doing a that time anyway is roll control and as opposed to MSL we do not have a tight roll control requirement on entry (just don't spin up like a top). |
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Guest_mcmcmc_* |
Nov 20 2018, 10:07 PM
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#11
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Guests |
From the limited info I know about the Schiaparelli failure this is an unrelated topic (the publicly available report EXOMARS 2016 - Schiaparelli Anomaly Inquiry shows their failure was due to high rates on the parachute swamping some fault protection values[...] I imagine debris from cruise stage falling over the open parachute amd causing a mess. Anyway, in the meantime I slightly updated my simulator, now you can see something moving eventually! :-) http://win98.altervista.org/space/explorat...-simulator.html Unfortunately data at low altitude are quite low in precision. It's a pity I have no time to further study and process telemetry data to get a yaw/pitch/roll graphical representation, maybe I'll do on real Insight data once available; for now I can try adding acceleration, and possibly atmosphere data (temp, pressure and density), all contained in same PHXPROFILES.TAB file. I also see "attack angle" in PHXPROFILES.TAB, I wonder if I can turn it into an image of Phoenix/Insight rotating while going down in these remaining 4 days. |
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