Skycrane, Innovative landing technology Options

[mars_armer]

Be careful drawing conclusions from the MER landings. The lateral descent velocity was due to steady prevailing winds, and the change in direction occurred during RAD firing due to pendulum motion of the backshell/bridle. Neither of these will be a concern for Skycrane, because of the active control system starting at 1 km. There is plenty of control authority to null out the lateral velocity and develop a smooth, purely vertical descent, even under the influence of winds, since there is no parachute dragging the system around at that time.

The JPL engineers working on Skycrane are many of the same people who were responsible for implementing the Pathfinder/MER EDL system. Believe me, they are ecstatic about Skycrane (though of course it still has to be tested and proven). It promises to be a much more robust system, and much less susceptible to uncertainties about the Martian environment.

One non-obvious benefit of the tethered set-down is that it is very stable (i.e., zero rebound). On an uneven ground surface, one wheel will touch down and that corner's bridle goes slack, while the other corners are still taut (and still removing energy from the rover impact). The bridles aren't cut until the rover is firmly on the ground.

Also, the mobility system is already designed to survive driving off of rocks, so it doesn't need any (or at least not much) enhancement to survive the touchdown.

[RNeuhaus]

Be careful drawing conclusions from the MER landings.  ...

Mars_Armer
Thank you much to let us know about your good note. I love to know on how these problems will be solved. I didn't account about the promiment wind direction for the landing process.

How far and how long time can Skycrane fly during its searching for the best place to land the MSL Rover? Will Skycrane start to fly at 1 km above of the surface? What is RAD?

Rodolfo

[Gsnorgathon]

RAD = rocket-assisted deceleration. Those are the rockets in the backshell that fire from ~120m to ~12m above ground level, to slow the lander's decent velocity to ~zero when the bridle connecting the lander to the backshell/parachute is cut. As opposed to (or orthagonal to...) TIRS - transverse impulse rocket system, which is intended to cut the lander's horizontal velocity to zero.

Mars Exploration Rovers Entry, Descent, and Landing Trajectory Analysis has lots of details (except the expansion of the acronym 'TIRS', oddly enough).

[djellison]

Transverse Impulse Rocket System ( I think?)

and DIMES was Descent Imaging Motion Estimation System...

Ladies and Gentlemen - welcome to acronym heaven

Doug

[lyford]

AH?

[dvandorn]

And what does AH stand for? Altitude Horizon sensor?



-the other Doug

[djellison]

AH...acronym heaven

Doug

[dvandorn]

Ah - AH!

Makes perfect sense...



-the other Doug

[ljk4-1]

When the Skycrane has completed its purpose of depositing MSL safely on the
Martian surface - where is it going to go? And what will happen to it?

[djellison]

Basically the same as the MER/MPF backshell - it'll fly away and destroy itself. I think the trade was still under debate as to if the 'fly away' would be actively controlled onboard or if it would just seperate and throttle up until the fuel ran out, the statistics of the situation dictating that 'recontact' was very very unlikely.

Doug

[MarsEngineer]

Basically the same as the MER/MPF backshell - it'll fly away and destroy itself. I think the trade was still under debate as to if the 'fly away' would be actively controlled onboard or if it would just seperate and throttle up until the fuel ran out, the statistics of the situation dictating that 'recontact' was very very unlikely.

Doug

That's right Doug. You have done a wonderful job of explaining the skycrane concept, and yes we ARE excited about this new design.

(I have heard many a puzzled observer wonder why we are headed toward even more RubeGoldbergian designs. Rather than blame ever-cannonball polishing engineers like me, I would rather blame that frustrating Red planet that beckons us. Someday I will share the genesis of the Skycrane design concept - you might not be surprised that we conjured this - and other new designs in early 2000 in the wake of the MPL loss in late 1999.)

The latest baseline is that the Descent Stage will have a simple computer on it that will fly the descent stage away at either a fixed attitude or a profiled attitude until the descent stage has run out of fuel at which point it "lands" unceremoniously some 100's of meters away from the rover.

By the way, I have notcied that some folks get our terminology confused. We do not use the word "skycrane" to describe the descent stage. Instead we use the term "skycrane" for the landing maneuver ("skycrane maneuver") that the descent stage performs. These include rover separation and lowering the rover on the triple bridle at a fixed, slow vertical velocity until the rover wheels have off-loaded the weight of the rover under the bridle and the descent stage releases (cuts) the bridles and flys away (as you describe). The fly-away atttitude of the decent stage is such that the descent stage is assured not to re-contact the rover. (By the way, we may use an electric brake to slow the rover-descent stage separation rather then the centrifuge/drum brake design of MER and MPF.)

I see a lot of interesting comments in this thread from last year, too bad I was not a member then, I would have enjoyed clearing up a few questions.

-Rob

***********
Comments made here are the authors and do not represent the views of NASA, Caltech nor JPL.

[chris]

I see a lot of interesting comments in this thread from last year, too bad I was not a member then, I would have enjoyed clearing up a few questions.

Well if you find any that weren't answered, now's your chance

Chris

[climber]

Someday I will share the genesis of the Skycrane design concept - you might not be surprised that we conjured this - and other new designs in early 2000 in the wake of the MPL loss in late 1999.)
-Rob

And we, poor human, we thought that you just came back to Airbags system because you were sure it was working OK... I mean except yourself, Rob, since you nearly turned blue on Spirit landing day

By the way, I have notcied that some folks get our terminology confused
So, in the terminology, "Skycrane maneuver" will be part of the EDL?

I love this place! Sometimes I feel I work for JPL.

[djellison]

Skycrane is the manouver conducted by the decent stage to deploy the rover... I think that puts the three phrases into their proper context.

Doug

[centsworth_II]

By the way, I have notcied that some folks get our terminology confused. We do not use the word "skycrane" to describe the descent stage. Instead we use the term "skycrane" for the landing maneuver ("skycrane maneuver") that the descent stage performs.

In this case you might want to go with the flow and call the descent stage a skycrane. It's such a cool name for a levitating crane! I can see this piece of equipment developing a fan base which attributes a personality to it similar to what has happened with the MERs. Of course the MSL will be the real star but I think Skycrane will find a place in people's hearts. I can't imagine this happening with any previous decent system. Noone called the MER system Baggie, or the Phoenix system Footsie.