MSL EDL Hardware, Its state & fate Options

[stevesliva]

They decided not to burn to depletion-- mentioned here before and after the event many times. I wonder if they figured they could learn something about skycrane performance by measuring the distance flown away and comparing it to the preprogammed burn time. Maybe they learned it didn't go quite as far as they expected, for instance.

[Kaputnik]

They decided not to burn to depletion-- mentioned here before and after the event many times. I wonder if they figured they could learn something about skycrane performance by measuring the distance flown away and comparing it to the preprogammed burn time. Maybe they learned it didn't go quite as far as they expected, for instance.

Probably going over old ground here, but my understanding is that the descent stage, once cut free, had no 'brain' as such and would only follow the pre-programmed set of commands to the engines. The safest option was to give it commands that would tilt it to the north, fire at full throttle for six seconds, and then shut off.
The longer the stage is thrusting, the more likely it is to risk adopting an undesirable attitude, e.g. tumbling, thus posing a potential risk to the rover.

[mcaplinger]

Probably going over old ground here, but my understanding is that the descent stage, once cut free, had no 'brain' as such...

[This discussion is in the wrong thread.]

See page 19 of http://trs-new.jpl.nasa.gov/dspace/bitstre...0/1/11-1328.pdf

Fly Away Segment.
After touchdown is declared, transition to flyaway begins. Flyaway is performed using the flyaway
controller executing on the descent stage processor (SPARC) in the Descent Motor Control Assembly
(DMCA) on the descent stage. The following events occur after touchdown is declared:

1. Descent stage slows down to 0 m/s.
2. Controlled [sic] transferred from Rover Compute Element (RCE) to DMCA.
3. Bridle and electrical umbilical are cut.

Once the bridle and electrical umbilical are cut, the flyaway controller exhibits three phases:

1. Hover – Used for the period of time required to cut the electrical umbilical between the rover and
the descent stage.
2. Ascent – To maintain MLE plume ground pressure below landing pressure, the descent stage trav-
els straight up.
3. Turn and Burn – Two of the MLE engines are brought to 100% while the other two engines are at
slightly less than 100%, causing the descent stage to pitch about the descent stage Y-axis to 45°.
Once the turn duration is complete, all four engines are brought to 100% with the controller mak-
ing adjustments for maintaining zero attitude rates. Constant thrust is applied for enough time to
ensure that the descent stage will impact the surface at least 150 m from the rover’s position.

[djellison]

No motion between +6 and +12 sols.

Attached thumbnail(s)

 

[djellison]

That paper is slightly outdated. I believe the throttle level ended up being 60% ( about twice what it was during the hover phase...which is actually a continual .75m/sec downward motion of the descent stage toward the ground ) And it ran for approx 6 seconds.

D

[john_s]

Constant thrust is applied for enough time to
ensure that the descent stage will impact the surface at least 150 m from the rover’s position.

Interesting number- "150 m" is about the size of the impact debris field, and that errant fragment to the south-west flew about a kilometer.

John

[eoincampbell]

That's a weird straight edge the (disappearing disc part) of the chute left behind ...

[marswiggle]

No HiRise anaglyphs of (all of) the hardware has yet been posted as far as I know, so here my versions, in 2 x the original size, moderately sharpened and/or color adjusted. The rover, the backshell and parachute, plus a special version of the rover, blown up 3 times from the original. (My first post in MSL threads.)

Attached thumbnail(s)

 

[marswiggle]

Continuing... the ds impact site and the heatshield.

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[ddeerrff]

No motion between +6 and +12 sols.

What is that dark area moving across the backshell (5 o'clock - 4 o'clock positions)? Almost looks like a very slow moving cloud.

[mcaplinger]

Interesting number- "150 m" is about the size of the impact debris field...

Right, but the debris is all in the forward scattering 180 degrees. The chance of something bouncing straight back would seem to be remote. Of course, I don't know how the descent stage engineers feel about the size of the debris field.

http://www.engr.utexas.edu/features/marsskycrane

After the landing, it was confirmed that the flight distance was about 650 meters (more than 2,000 feet), which was way beyond our minimum flight distance requirement.

[fredk]

What is that dark area moving across the backshell

Changing lighting (sun) direction between the frames.

[djellison]

What is that dark area moving across the backshell (5 o'clock - 4 o'clock positions)? Almost looks like a very slow moving cloud.

Just changing lighting conditions. It would have to be one heck of a cloud to move like that over a 12 day period.

[markril]

Here's another anaglyph of the sky crane impact site, this one animated before & after:



Mark

[elakdawalla]

Oh that is really cool. You can see how secondary impact spots made long dark disturbances when they occurred on flatter areas, but were confined to smaller impact dots where they crashed into slopes facing the impact site.