InSight Cruise Phase, Events during Mars transit prior to EDL Options

[nprev]

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).

[Guest_mcmcmc_*]

Insight will have same EDL profile of Phoenix, so while we wait for november 26th we can imagine how it will be: this video mixes real mission control audio+video with video simulation to show what happened 10 years ago and what will happen 3 weeks from now:
https://www.youtube.com/watch?v=hH5pNFROlYU


Note: for some reasons, the "freefall phase" after parachute jettisoning is not called like that for Insight, but instead called "gravity turn"; then engines are started ("Powered descent phase"), and after 3 seconds of freefall+deceleration Insight will enter the "Constant velocity phase"; once Insight slows down to 30 km/h (around 50m from ground) it turns on ground contact sensors on legs; at 8 km/h engines are turned off, to prevent too much regolite from being blown around, and a final free-fall (few centimeters) starts, and we are on Mars.

This document analyses actual Phoenix EDL recorded data:
https://ntrs.nasa.gov/archive/nasa/casi.ntr...20080034645.pdf

Reconstructed Insight timeline (from multiple inconsistent sources):



Text version:

CODE

n    t    alt m    v m/s    v mph    v kmh    Event
1    -420                    cruise stage detachment
2    -390                    Entry turn starts
3    -300                    Entry turns end
4    0     128000      75301      13000      17017     atmosphere entry
5    100                    7.4g
6    223     12000     415    928    1494    Parachute
7    238     10300     132    295    475.2    heat shield jettisoned
8    248.0                    leg1
9    248.5                    leg2
10    249.0                    leg3
11    249.5                    legs ready
12    300     5500                 Radar on
13    333     2300                 Radar acquires ground
14    351     1100     61    136    220    Parachute/Lander separation
15    354     900                 Gravity turn start (free fall)
16    378     51     8    17    28    Constant velocity start (powered descent)
17    393.75        2.2    5    8    Engine off
18    394    0    0    0    0    Touchdown

Status monitor:
http://win98.altervista.org/space/exploration/



Phoenix EDL analysis:



Sources:
https://www.seis-insight.eu/en/public-2/the...mission/landing
https://mars.nasa.gov/insight/timeline/land...escent-landing/
https://www.jpl.nasa.gov/news/press_kits/in...ion/Layer-2.jpg

[propguy]

Note: for some reasons, the "freefall phase" after parachute jettisoning is not called like that for Insight, but instead called "gravity turn"; then engines are started ("Powered descent phase"), and after 3 seconds of freefall+deceleration Insight will enter the "Constant velocity phase"; once Insight slows down to 30 km/h (around 50m from ground) it turns on ground contact sensors on legs; at 8 km/h engines are turned off, to prevent too much regolite from being blown around, and a final free-fall (few centimeters) starts, and we are on Mars.

Actually gravity turn is not a freefall. There is a very short freefall once we separate from the backshell and parachute (~0.5 second) and then we begin the tip-up portion of powered descent. That lasts ~2.5 seconds (the tip-up is the align the lander with the velocity vector, which should still have some appreciable horizontal velocity, whereas when we drop out of the backshell we will mostly be dropping down). Then we begin gravity turn which is the main portion of powered descent where we are eliminating the horizontal velocity and reducing vertical velocity down to 2.5 m/sec or so. After we hit that vertical velocity limit we enter the final phase of powered descent called constant velocity. Constant velocity is where we descend at the 2.5 m/sec rate until one of the three legs achieves contact with the surface and the descent engines are then turned off. This is one of the keys to powered descent. The main goal is to achieve constant velocity not too close to the surface (or you risk hitting at too high a speed) or too high (or you end up using too much fuel since you have a very long time at this slow descent rate). As shown in the above Phoenix diagram we spend a third of powered descent in constant velocity while only descending the last 50 meters or so (luckily also at a lower thrust since at this point we only have to thrust at a value equal to the Mars gravity of the lander, so fuel usage is lower). So to summarize, the freefall begins at separation from the backshell and parachute, followed by tip-up, then gravity turn, and then constant velocity, and then landing (Whoohoo!).

Here is a little InSight summary too (without providing any true details, which I am not allowed to provide, that must come from official sources). We are as you know nearing Mars. S/C is performing beautifully. We have 3 potential maneuvers left (TCM4, 5, and 6) set on the next 3 Sundays (11/11, 18, and 25). These are only required to fine tune the entry location and time (i.e. TCM3 pointed us at the correct location, these are used to adjust for errors in final arrival location). This is the same plan that Phoenix had and they only performed the middle one (TCM5). If I were to guess I think that may be or path to entry too, but that is simply a guess. Also today I am reviewing the final EDL sequence for upload (one of the many reviewers who have to approve) and that should go up in the next week (same sequence we have had for a while, we just rerun one final time with the latest vehicle state and entry parameters for timing). Starting to get very real and will be quite busy in 2 weeks as we get ready for entry.

P.S. My company has put out a website about InSight EDL and it has lots of facts plus a podcast I am in with one of our system engineers. You can even see what I look like (I am the guy in the dark shirt on the right in the photo). I hope you find the website interesting.

Go InSight and Go Marco! (so hopefully we get real time EDL data just like we did on Phoenix).

https://www.lockheedmartin.com/en-us/news/f...ng-to-mars.html

[Guest_mcmcmc_*]

so hopefully we get real time EDL data just like we did on Phoenix

Thanks, very interesting. NASA site has a lot of pictures but very few science/engineering data!

I really would like to setup a simulator for Insight like I did for OSIRIS-Rex, but specifically for Insight EDL, with multiple countdowns for each phase. I was thinking about synching it with youtube animation of EDL. Synching it also to realtime telemetries would be great! I don't know if it is feasible in just 12 days, but I want to try.

Planned development phases:
1) Setup multicounter page - quick & easy once I have the timeline... which I posted above.
2) Synch to youtube - I need to study youtube API and find the most suitable video/animation of Insight; looks quite feasible in time.
3) Synch to realtime telemetries - Possible only if:
a) fast network available
B) official json data available
c) anonymous CORS access to data allowed
d) only main events shown (at least 10 seconds one from the other)

Do you think you could setup in such a short time a json URL with realtime telemetries?

[mcaplinger]

Do you think you could setup in such a short time a json URL with realtime telemetries?

Not to rain on your parade, but this is extremely unlikely to happen. For past missions the EDL data were released to PDS years after the landing. Even the MSL landing simulation on Eyes wasn't based on realtime data AFAIK.

[Guest_mcmcmc_*]

Not to rain on your parade, but this is extremely unlikely to happen. For past missions the EDL data were released to PDS years after the landing. Even the MSL landing simulation on Eyes wasn't based on realtime data AFAIK.

He said "so hopefully we get real time EDL data just like we did on Phoenix"; assuming that people officially involved in the uploading EDL firmware will receive realtime telemetry by sure, I deduced he was talking abouth something like publishing realtime telemetries. Did it happen for Phenix?
Anyway, telemetries of "just" surface operations like initially happened for Philae would be good too. :-) (I followed in realtime the depletion of the battery... until DLR cut the feed :-( )

[mcaplinger]

...like publishing realtime telemetries. Did it happen for Phenix?

No.