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nprev
We're now 45 days from landing, so as of 23 Jun please post all comments related to the end of the transit to Mars here.

Go Curiosity!!!!
Stu
Approach Phase.

Blimey.

blink.gif

Buckle up, people.

imipak
...and extinguish all cigarettes? Doesn't time fly in retrospect, but crawl when looking forwards...
Oersted
Good write-up by elakdawalla here:
http://www.planetary.org/blogs/emily-lakda...and-part-1.html
-Looking very much forward to the upcoming parts!

Just have a question, though. It says the "nose will tip upwards by about 20 degrees" when the first set of mass balances are thrown. I thought the nose would tip downwards, to enable a bit of lift by the airshell and heat shield? I.e. that the "plate" of the spacecraft would "lie more flat", in stead of "standing more on its edge", with respect to the Mars gravity field.
mcaplinger
QUOTE (Oersted @ Jun 25 2012, 04:54 AM) *
Just have a question, though. It says the "nose will tip upwards by about 20 degrees" when the first set of mass balances are thrown. I thought the nose would tip downwards, to enable a bit of lift by the airshell and heat shield?

The lift vector/bank angle is steered during entry in whatever direction is needed to hit the aim point. See http://trs-new.jpl.nasa.gov/dspace/bitstre...8/1/08-0255.pdf -- section 4.
Lightning
A third (and short) TCM occured yesterday. The spacecraft gained 50 mm/s, shifting as planned the landing site to about 7km toward Sharp Moutain.
Oersted
Ok, I found the answer to which way the entry configuration is influenced by the shedding of the cruise balance masses. As I thought, the "nose" of the spacecraft does indeed tip downwards by twenty degrees, to enable a guided lifting entry:

Described on p. 2 of
"Mars Science Laboratory. Entry, Descent, and Landing System Overview"
http://trs-new.jpl.nasa.gov/dspace/bitstre...9/1/10-1775.pdf

Click to view attachment

mcaplinger, yes, the spacecraft doers indeed maneuver around during entry, but the jettison of the CBMs gives it a new stable configuration, with the nose pointing downwards so the lift vector points slighty forwards.

- Another interesting fact, new to me, is that the thrusters may actually fire after parachute deploy, to dampen any unwanted rotation of the capsule under the chute. That's never been done before. "Wrist mode damping is active throughout parachute descent and ensures a safe heatshield separation, good TDS surface acquisition, and a safe backshell separation" (p. 8).

brellis
A question I had for Emily's *very entertaining and fear-reducing* Google-hang, still can't find an answer: how much more than .75m/sec vertical drop can the rover take, for example if the crane lets go too soon? Can it take the drop the Vikings withstood?

Edit: pospa's post in the Cruise thread provides the basis for my question.
PDP8E
I assume the cruise stages 'burn-up' (no heat shield).
Is there any evidence that there are pieces laying about in 'new craters' beyond or before the landing ellipses?
(i.e. Pathfinder, MER-A/B, Phoenix, others, and now MSL)
djellison
I've had a look downrange for Opportunity in whatever MOC and HiRISE images I could - but found nothing.

Most would burn up - a few small components might make it thru - but I doubt a thorough analysis has been done.

As for touchdown rates - this is interesting reading
http://trs-new.jpl.nasa.gov/dspace/bitstre...7/1/06-1785.pdf
brellis
Thanks Doug. So, on flat terrain, MSL can handle as much as 1.25m/sec vertical velocity whereas the Vikings landed at 2.5m/sec. I'm not nervous -- I'm perfectly calm! unsure.gif
djellison
And we have 30+ years of improvements in radar, IMU's, software etc etc.

Moreover - it's not like 1.26m/sec will result in complete and utter devastation - a dinged wheel, a slightly bent suspension strut etc etc - the rover would still be able to carry on.

I'l wager the actual touchdown vertical velocity will be < 0.8m/sec
ElkGroveDan
I'd also wager that those are spec tolerances. I'd be willing to bet it could take a bigger thump than that with no appreciable damage.
MarsEngineer
Hi again,

Doug is correct (he seems to have the knack, me on the other hand...). There is margin well above 0.8 m/s (I forget the number but it depends a lot on surface characteristics if my memory serves). With these sorts of multi-DOF control systems, either it is coming down well within the spec or ... it won't and something is wildly wrong.

Ironically the Phoenix and Viking landers could not afford to land slower due to dynamics issues with slower velocity (need for leg stroke for touchdown detection, surface-plume interaction, fuel cost, etc). However the velocity knowledge and control accuracy for Viking and Phoenix was fantastic and about the same as MSL's (in fact MSL and Phoenix both use the same inertial measurement unit (IMU) design). Because of the skycrane architecture, MSL is simply able to capitalize on the IMU and on the fact that the decent engines are a long way from the surface and wheels, that the engines are dynamically uncoupled with the rover touchdown event to allow a much slower terminal descent velocity. If we were willing to use more fuel we could probably have reduced the velocity even more, but we did not need to. The big benefit of a slower touchdown is that the rover's wheels (aka "legs") can be used as landing gear plus that slow velocity really broadens the spectrum of Mars surfaces that are considered "safe". (Of course I am wildly biased - opinions expressed are those of the co-co-co-co-inventer and do not reflect NASA/JPL/Caltech).

With "somewhat controlled velocity" landing systems like MER (6 solid rockets) or "nearly controlled velocity" landing systems like Pathfinder (3 solid rockets) the landing system obviously has to be robust to a much wider range of impact velocities (let alone surface characteristics).

You know I can't tell you how much fun it is to come by here (I wish I had more time!!!). I get a huge kick from the thoughtful discussions of risk, and the fun walks through memory lane (like the link that SFJCody left on Post#169 to a 1997 bulletin board about the weirdness of Pathfinder's landing system and even a discussion about my old web page on EDL I created back then - what a hoot!)

In my opinion, all of these missions (especially the ones that have to land safely on Mars) are experimental vehicles and have a rather substantial element of risk. For all of the Mars lander missions I have worked on (MPF, MER, PHX and MSL) like everyone else, I am initially daunted by the vast array of all the "things that must go right". The mountain ahead seems insurmountable. But then I (we) look down at my (our) feet and move myself one step at a time, one minute detail at a time, oftentimes with insufferable pauses as we ruminate, test and argue over the safety of each tiny step, sometimes having to go backwards and find another path or add new paths that we thought would never be there. Slowly, ever so slowly and with infinite patience we gain altitude, only vaguely aware of the progress we have made. The really hard part is knowing when the mountain has been scaled. Too often it appears that the summit is ahead and we can relax, only to discover that the top is further ahead than it appears, and yet another push must be mustered. Of course the top really can NOT be seen and no one knows for certain, until it is over.

I do find though that there is a feeling I get that tells me the top is there in front of me (if only I could see it). It is really a feeling that we have run out of places to put our feet. No more tests left to ponder, no more problem reports to close, no more reviews to hold, only a far away machine waiting for Mars to arrive. I think we have nearly run out of places to put our feet. Could it be that we are there? Almost, I see a couple of more places to step. Next couple of week perhaps?

-Rob Manning
MSL Chief Engineer and faux climber

Opinions expressed are indeed those of the author and do not reflect the opinion of NASA/JPL/Caltech

nprev
Rob, and we are absolutely delighted when you do have a chance to visit, believe me! smile.gif

Great post.
Tesheiner
Click to view attachment
Pertinax
Hi Rob,

Thank you for you post, particularly for your wonderfully visual description of methodically working through a seemingly impossible problem.

-- Pertinax
Oersted
I wonder whether the planning and programming for non-nominal landing scenarios includes alternative thrusting profiles in case the bridles snag or are blocked as they spool out. Say, if the rover only descended half a meter on the bridle, would the descent stage then be able to recognise the situation and descend accordingly? It would of course mean a higher risk of plume damage, but better a dinged rover than no rover.
MarsEngineer
QUOTE (Oersted @ Jun 29 2012, 07:33 AM) *
I wonder whether the planning and programming for non-nominal landing scenarios includes alternative thrusting profiles in case the bridles snag or are blocked as they spool out. Say, if the rover only descended half a meter on the bridle, would the descent stage then be able to recognise the situation and descend accordingly? It would of course mean a higher risk of plume damage, but better a dinged rover than no rover.


Hi Oersted,

In our "stress and robustness" simulations (which we have been doing a lot of in the last few months), we try to think up cases like this to see where the system "breaks" using one of our software simulations (we have a couple of variants of simulation for different purposes - plus the testbed with all of the electronics in it too). We have tried cases like: slower (sticky) engine throttle responses, lower or asymmetric throttle engine performance, super slow bridle deployment. I don't think we tried the case where the bridle does not fully deploy (I will ask), but I am pretty sure it would work to a point - the architecture does not depend on the bridle length being "just right". The software doesn't "recognize the situation" per se, the software really does not monitor nor really care about the position nor orientation of the rover with respect to the descent stage, it simply waits for he ground to show up and "off load" the descent stage. The software "knows" that the rover is on the ground when it notices that the throttle settings have cut in half (as it must in order to maintain the descent rate of around 0.7 m/s even after the rover is on the ground - at least for a couple of seconds). And for that reason, a half meter bridle would mean that the descent stage would come down and make contact with the rover in those 2-ish seconds that it take for the software to notice that the rover has been off-loaded (remember there are uptake reels on both ends of the bridles to take up the slack). Plus there would be a lot more plume issues being that close to the ground.

I have personally witnessed the BUD (bridle/umbilical device) testing as well as the system level separation tests and I know the design pretty well. John, Tom and the gang put a lot of thought put into it as well as incorporating lessons from MPF and MER (which used centripetal friction brakes instead of an electro-magnetic brake). You might recall that on Spirit landing, the bridle's brake was a tad "too good" (too much friction) and the lander with Spirit inside took "much" (a few seconds) longer than we expected to deploy the bridle to full length (over the coming 3 weeks before Opportunity arrived, we frantically re-re-tested the brake in the expensive 25 ft space simulator). This new design avoids this possibility. It is a nice clean and elegant design they came up with. This does not keep me up at night.

If and when we find stress cases that do not work, we decide whether or not to do anything about them depending on our best judgement of the probability of occurrence vs level of difficulty in mitigating the threat. More often than not we find that that system muscles through the problem (for example a very short data outage on the bridle) , however when we consider "hard failures" (such as a failure to cut a bridle) we already know the outcome will not be good and we have known that from the beginning. In those cases we count on the reliability and simplicity of he design ... and of course we test it like crazy to "prove" it (we often misuse the word "proof" which implies deductive reasoning, rather we should say "demonstrate" for the inductive reasoning behind the bulk of our reliability arguments).

(I am really procrastinating today. I love to talk about this stuff.)

-Rob

Opinions expressed are those of the author and do not necessarily represent the views of JPL/Caltech/NASA.
nprev
Rob, if you have the time & feel like it, I'd love to hear the history/thinking that led to the descent stage flyaway parameters.

When I first heard about it I figured the easy way would be to tilt it about 5 deg after bridle separation in any direction & let it rip full throttle until it smashed into something or ran out of fuel & crashed. Understand that the flight path is a bit more "elegant" now.
Oersted
QUOTE (MarsEngineer @ Jun 29 2012, 09:04 PM) *
......

(I am really procrastinating today. I love to talk about this stuff.)

-Rob


Rob, thanks for your informative and very interesting reply. We're fortunate to have caught you during those few extra moments when the preparations for the party are done, the rehearsals are all over, and the guests and relatives are just standing around, chomping peanuts and having a drink while awaiting the bridal, sorry, bridle arrival... ;-)

We know that you are of course actually very busy, but that just makes it an even bigger privilege to get these insights.
DavidVicari

Rob,

Thanks for the great replies!!

You said the bridle doesn't keep you up at night... I have to ask, is there anything about the landing that is keeping you up??

From an outsider the thing that worries me the most is the parachute deployment. It seems like the least controllable and most chaotic of all the events. My second biggest concern is the number of pyros that must work. I know that they are extremely reliable but it still scares me a little.

mchan
Another thanks to MarsEngineer. Your perspective on the engineering challenges give outsiders a view of the work on the inside, and are always informative and a pleasure to read.

Regarding the parachute, there is a great series of videos on the design and tests of the parachute and of the folks doing the design / test. You can see how early tests resulted in shredded chutes. One video featured a great practical joke where the data acquistion appeared to be bad in a full-scale wind tunnel test. This aspect of EDL appears to be well tested.
Oersted
"JPLnews" Youtube channel:

Martian Series: Testing Curiosity's Parachute Part 1:
http://www.youtube.com/watch?v=O7vf2HUMMdo

Martian Series: Testing Curiosity's Parachute Part 2:
http://www.youtube.com/watch?v=JRRcbZlofOk

Martian Series: Testing Curiosity's Parachute Part 3:
http://www.youtube.com/watch?v=-NJamPhtRjA

Martian Series: Testing Curiosity's Parachute Part 3:
http://www.youtube.com/watch?v=J6TceTZq1L0
claurel
I noticed that there's a relatively recent SPICE kernel available for MRO that covers the time window around MSL's entry, descent, and landing. I was curious what view MRO would have of Gale Crater, so I created a short visualization of the two spacecraft's trajectories near the time of the landing.

http://youtu.be/-f0BDnJNW-8

MRO's trajectory is plotted in a Mars-centered inertial frame, while MSL's is depicted in a Mars-fixed frame. Of course, the actual EDL trajectory of MSL is likely to vary somewhat from the predicted one in the SPICE kernel.

--Chris


fredk
Sorry if this has been discussed, but I noticed Scott Maxwell say in a recent interview:
QUOTE
With MSL about to land and join his older sister on the red planet...
We've always referred to the MERs as "she's". Is the team referring to MSL as "he"? Oppy's younger (but bigger!) brother?
elakdawalla
Scott insists that the rover is a "he" and affectionately calls him "George." I'm not sure of the origin of that name -- I'm sure he'd tell me if I asked him! -- but I always imagine the Looney Tunes yeti whenever I hear the name, which may itself be a reference to Of Mice and Men. (Of course the yeti's name wasn't George, that was the yeti's name for his pet bunny rabbit, but still...)

I, however, think Curiosity is a girl. So there.

I've heard "he," "she," and "it" from various people involved in the mission. Gender is, I guess, in the imagination of the speaker. You'll never see an official JPL press release refer to the rover as anything but "it."
stevesliva
^ Curious George
djellison
I call the testbed rover George - but I'm still getting used to Curiosity for the rover - and vessels of exploration are always she's - that's something Scott and I just have to disagree on smile.gif
RoverDriver
Since curiosity in italian is LA curiosita' (femminine), MSL is definitely a she.
climber
QUOTE (RoverDriver @ Jul 2 2012, 07:55 PM) *
Since curiosity in italian is LA curiosita' (femminine), MSL is definitely a she.

Works the same way in French...
pospa
QUOTE (climber @ Jul 2 2012, 09:40 PM) *
Works the same way in French...

As well as in Czech & Slovak. rolleyes.gif
But in Russian its "it", I gues .
CryptoEngineer
QUOTE (pospa @ Jul 3 2012, 03:06 AM) *
As well as in Czech & Slovak. rolleyes.gif
But in Russian its "it", I gues .



We're invading Mars with a one-ton atomic robot, armed with a laser capable of vaporizing solid rock. Phobos-Grunt was a misdirection ploy.

Sounds like a male to me smile.gif

pt
SteveM
Since English has almost no gendered nouns and Curiosity's drivers are in the county of Los Angeles, it seems that the Spanish gender of la curiosidad (feminine) should govern here.

Steve M
ElkGroveDan
QUOTE (elakdawalla @ Jul 2 2012, 10:08 AM) *
Scott insists that the rover is a "he" and affectionately calls him "George." I'm not sure of the origin of that name


It may be a bit arcane, but in one of the Looney Tunes Marvin Martian cartoons, Marvin takes Bugs Bunny to Mars as a pet for "Hugo" the Abominable Snowman (from a previous Bugs Bunny episode) that Marvin has captured and brought to Mars. Hugo grabs Bugs and declares, "I will hug him, and stroke him, and sing to him, and cuddle him, and call him George," Bugs then tells Hugo he doesn't want a rabbit, he wants a robot and tells him, " 'George' is a perfect name for a robot."

So there you have it. According to Bugs Bunny the perfect name for a robot on Mars is "George."

The clip begins at about 6:20
brellis
The third chapter of Emily's excellent series of blog entries about EDL mentions "landing gear", with an image of Curiosity prior to "landing gear" release. Does ~he~ have shock absorbers? I know, I'm worrying too much! hehee

I'm going to the Planetfest thingie in Pasadena, bringing a BIG bag of pistachios!
Oersted
Just the suspension inherent in the rocker-bogie wheel configuration. It deploys from a folded-up state, but I am actually at a miss as to how it deploys. Just gravity drop? My guess is that there are some springs that are released with pyro firngs on deploy and which then serve as suspension afterwards.
RoverDriver
Yep, the suspension system is released with springs/pyros. The "spokes" on MSL wheels also can take quite a beating. The tread also is compliant.

Paolo
brellis
Reading this article about MSL and "fresh craters", I wonder if consideration was given to aiming the descent stage and creating a brand new crater nearby?
nprev
I think that the overriding concern is still residual hazmat for the descent stage; Curiosity's almost certainly never gonna go anywhere near the wreckage for that reason. Plus, I very much doubt that it'll hit hard enough to make a crater deep enough to excavate anything interesting from an orbital view.

Heck, come to that wouldn't be too surprised if it survives the crash in fairly good condition. The big variable is probably how much residual fuel (and therefore added velocity) it can burn off before it hits the dirt.
RoverDriver
I haven't heard anything about observing the descent stage. I think you are probably right, the lesson from Oppy observing the heat shield will be influencing decisions in that regard. It wouldn't surprise me if they would use the mastcam to take a few pictures tho.

Paolo
charborob
QUOTE (nprev @ Jul 8 2012, 04:13 PM) *
The big variable is probably how much residual fuel (and therefore added velocity) it can burn off before it hits the dirt.

According to Emily's blog post about MSL's landing, the original plan was to burn off all the remaining fuel in the descent stage, but she says it will now burn for a fixed time (she doesn't say how long) and crash at least 150 m away.
Explorer1
Spirit's trenches were that deep at least.
Speaking of which, can MSL do the same thing with its wheels?
centsworth_II
There was a reason to examine MER's heat shield that does not apply to the MSL descent stage. To see how well the materials weathered atmospheric entry. I wonder how far MSL's heat shield is likely to be from the rover after it lands.
djellison
QUOTE (brellis @ Jul 8 2012, 01:47 PM) *
I wonder if consideration was given to aiming the descent stage and creating a brand new crater nearby?


There will already be craters made by the heatshield, and the ballast masses ejected just before parachute deployment - they'll all be worth looking at and would, I'd have thought, be downrange ( east ) of the landing site by a km or 2.

The descent stage can't be aimed specifcially. It takes 4 engines to 100% and flies away at 45 degrees for 4 seconds of thrust and then falls ballistically, probably landing a very long way away. This was discussed, in length, in another MSL thread. Because it contains much organic chemistry and could potentially be and explosion risk - they will not be driving towards it for close study.
Phil Stooke
And we'll see it with HiRISE. Points on a map!

Phil

djellison
HiRISE will have...

Rover
Crashed Descent Stage
Backshell & Chute
Heatshield impact and debris
6 ballast mass impacts.

...to look at. It's going to be amazing smile.gif
B Bernatchez
I wonder if the first two ballast masses wouldn't burn up in Mars' atmosphere? Is there any expectation that they would survive enough to impact the surface? And if they did, would it be large enough for HiRISE to detect?
climber
Would be fun to look for the ballast. Total weight of the 6 is 125kg ... to be compared to Oppy's 185 kg. huh.gif
Oersted
QUOTE (djellison @ Jul 9 2012, 06:20 PM) *
HiRISE will have...

Rover
Crashed Descent Stage
Backshell & Chute
Heatshield impact and debris
6 ballast mass impacts.

...to look at. It's going to be amazing smile.gif


"Carpet bombing" comes to mind... blink.gif

And yes, Explorer1, MSL will definitely be able to excavate some monster trenches by dragging its wheels. I am certain that this essential capability, the supreme serendipitous discovery of the MER missions, will be brought to bear in Gale Crater.


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