It's gettin' near that time.

Please post all comments regarding the last portion of Curiosity's voyage to Gale Crater here; thanks!

With all respect, nprev, isn't it a bit premature to close "MSL Aproach Phase" thread and leave just MSL EDL open?
MSL is still in the Final Approach phase, with one or maybe two TCMs still scheduled before EDL which starts by reaching the top of the Martian atmosphere....

ADMIN NOTE: After some discussion on the matter, the thread is open again. However, even MSL is in EDL-mode now

We can always begin a new thread and call it the 132 hours of terror ;-)

Paolo

Good solution, Paolo
... but, can someone withstand so many hours of terror?

Technically we are in that fuzzy zone where late cruise (approach phase) and EDL overlap. We MAY be in a place where we are done targeting and done with the cruise propulsion. We will see. It is looking pretty good.

We are now focussed on getting our security access badges.

The clock is ticking.

-Rob

Somehow, "132 hours of growing apprehension" doesn't really sing, does it?

132 hours of galloping ADD?

131 hours of finger-tapping impatience, 53 minutes of hair-pulling clock-watching, 7 minutes of terror and 2 years of fun!

Is there going to be another press conference before landing ?

See Emily Lakdawalla's summary of the planned press conferences:

http://www.planetary.org/blogs/emily-lakda...s-schedule.html

DG

I suspect nprev is in the pockets of the peanut grower's lobby... ;-)

Perhaps someone could use this point to summarize for everyone what communication signals will be possible from MSL, as it moves into EDL before blackout etc... so everyone will know the sequence and timing to expect (or hope for).


Also, as to whether it is too early or not for this thread, I just saw the following tweet from Curiosity:

Curiosity Rover ‏@MarsCuriosity

Timeline activated. Bleep-bop. I'm running entry, descent & landing flight software all on my own. Countdown to Mars: 5 days

Question: is it critical that the peanuts be Planters? Do they need to be in a sealed amerstat envelope? Is there a throughput range of peanuts/hour that needs to be maintained? Is 10% margin enough?
I only have a 124.75 hours left for V&V!

Paolo

I strongly urge all to run out and purchase many kilograms of "nprev" brand peanuts.

Yes, Nprev Brand EDL Peanuts!!! The shiny metal treat that TELLS you to bite it!!!

Seriously, though, as Burmese pointed out, we're definitely in the endgame now. Buckle up; it's gonna be quite a ride!!!

I bought mine from the TJ's in La Canada, next to JPL, they have a painting of MER (and Phoenix I think) on their walls. I guess their stuff is flight-qualified.

Paolo

Just to confirm: it is still a go for HiRISE to snap a pic? I didn't hear anything recently, so I'm assuming its not cancelled.

I heard there's 60% probability of successfully capturing MSL during (E)DL.

Paolo

Mars as seen from the spacecraft is now about half the size of our Moon as seen from Earth.

Thanks for that very telling factoid climber: good for visualizing the speed and distance involved.

Yes, it's what I like to imagine since Mariner 9 a long long time ago! Kms or miles to go mean a lot more if you can see with your own eyes what they represent. This is very different when a spacecraft nears (no pun intended) Jupiter or Vesta.

During the final stage of descent, can a gust of wind start MSL spinning and get the Skycrane cables all twisted up? Would that create a problem with releasing MSL upon landing?

Without knowing the details, the fact that we've succesfully landed six spacecraft on Mars using AFAIK pretty much the same sort of parachute schema (the terminal phases of EDL obviously differ for each spacecraft type & method) strongly implies that this problem has been solved.

Even a very high speed gust of wind produces a very small force in the low density Mars atmosphere. Remember the force of wind or the dynamic pressure per unit area = 1/2 rho v^2 where rho is the density of the atmosphere and v is the velocity. Mars' density is about 1/100th of earth so in order to "feel" the same force you would get on Earth with a 10 mph breeze, on Mars you would need the velocity of the wind to be 10 times faster (10^2 = 100) on Mars than on Earth. So a 100 mph wind on Mars "feels" like a 10 mph breeze on earth (not counting the sting of entrained dust slamming into your skin at 100 mpg .

In addition we simulated what would happen with a very high speed wind gust while in the skycrane phase and we found that the controller on the descent stage is very responsive. Much as you would be if you were to hold a suspended weight by your fingers. Try this: hang a weight and from a 2 foot string with your hand. Have someone swing it. Now see how fast you can damp the motion by moving your hand with the swinging motion. You will be amazing at how quickly you can stop the swinging. Now do in with your eyes shut. Same.

-Rob Manning
MSL Chief Engineer

PS I am totally focussed on surface now. We are looking really good for Sunday night! ( Knock on wood and pass the peanuts .. then the tums.)
I will be doing a little talking on NASA TV just before landing. If I say anything silly or in error, sorry! You all seem to know more about MSL than normal humans and perhaps even me! (although I try to keep up with you all.) This will be my 5th Mars landing. It never seems to get old.

And so will I - but much earlier than Rob. I'll be on at about 8.50pm local time during the educational pre-show to talk about Eyes on the Solar System and the AR App. Infact, my colleague Jon and I will be sat about 6 feet behind Gay, the presenter of the EDL broadcast, on Sunday night. Rob - I promise not to heckle. :-)

And - tomorrow morning ( at 10am and 11am local ) there is a Science, and an Engineering pre-landing conference. Both should be worth watching.... usual links apply - www.nasa.gov/ntv or www.ustream.tv/nasajpl or /nasajpl2

According to the publish book: MSLanding, Mars at Glance, the Surface winds at the surface would be between 0 to 32kph, with gust of about 144kph. However the Sky crane will be deselarating and lowering very slow starting from 1.6km from the surface and continue descending at 2.7 kph (walking very slow) and it will release the Curiosity when Sky Crane is hovering at about 20 meters from surface. Besides, at this height, Sky crane must have a very good control of stability before releasing the Curiosity. Its descending will take about 27 seconds (0.75 m/sec). On the other hand, if at this moment there is wind, its wind is so light (1/100 density of Earth's) and the Curiosity is weighing about 341 kg at Martian gravity, then the wind push on Curiosity will be very small. I hope that the lowering controls have greater advantages to control against the spinning and twisting.

Rob Manning suggested:



I tried this, with my cat as the "someone" to swing it. You're right! It even works with my eyes shut!

edit: the 'spin' factor was not helped by my steadying hand, just the swinging back and forth, to and fro. I hope there aren't any giant cats waiting in Gale Crater!

I'm pretty sure DAN will show us very soon here what a Catcrane manoeuver would look like

To give a rought idea of what is coming up and when (mind, time is approximate and all PST)


Date : August 5th 07h30 am PST / August 4th 16h30 PST / August 3rd 10h30 am PST
Distance to Mars (km) : 192 000 / 384 000 / 768 000
Mars diameter (°) : 2 / 1 / 0,5
Equivalent : Earth seen from the Moon** / Earth-Moon distance / Moon seen from Earth


**: for the happy few that have seen with their own eyes what that really means

Been following your landings since Pathfinder/Sojourner... You've come a long way! - I presume the tension is still almost unbearable, but has the emotional experience changed in any way? More cerebral? Better able to "observe yourself"? Enjoying the moment more?

You have got multitudes rooting for you and backing you all over this good Earth!

Did this thread go through another delete / restore cycle again today? I had it loaded up on my mobile device yesterday, to start monitoring for the weekend's approach, but when I went to reload it this morning to get the latest, it 404'd on me. I navigated upside down and sideways and the thread simply did not exist anymore. Now it's back. Huh?

Anyway, glad to have it. Thanks, and back to lurking!

As far as I understand it, the spin of the S/C under parachute (so-called "wrist mode") is actively damped by thrusters.

ChrisC: There were a few hours' downtime today that shouldn't be repeated due to an IP address swap or something or other.

Almost certainly maintenance. It's in the extremely talented hands of one of our Admins.

Yes, that is correct. It's described in a section of this (rather hard to find) paper by Steltzner et al:

Mars Science Laboratory Entry, Descent, and Landing System Overview
http://www.google.com/url?sa=t&rct=j&a...cpdnJsZGq91vK3w

P.8: Wrist Mode Damping
Estimating the oscillatory behavior of an entry capsule suspended underneath a parachute is an extremely dynamic and complex problem. Initial conditions at parachute deployment can pump large energies into the capsule wrist mode (rotation underneath the parachute about the capsule center of gravity) which will decay with time. Historical attempts to bound the wrist mode behavior and its time evolution following parachute deployment have failed to bound the behavior observed during flight (e.g. MER-B ).
While the MSL team believes we have attained a deeper understanding of wrist mode dynamics and the energies involved, the sensitivity of subsequent EDL events to high wrist mode energies led to the inclusion of an active wrist mode damping mechanism using the RCS thrusters. In cases where the capsule wrist mode frequency violates the “safe” flight envelope, RCS thrusters will fire to reduce the wrist mode frequency to acceptable levels.
Wrist mode damping is active throughout parachute descent and ensures a safe heatshield separation, good TDS surface acquisition, and a safe backshell separation.

Click to view attachment

It's happening again in the run up to MSL... journalists pontificating about the percentage of Mars probe failures.

http://www.theverge.com/2012/8/2/3215863/m...missions-failed

http://www.wired.com/wiredscience/2012/08/...-to-reach-mars/



I thought a look at the data might help. I listed missions by country of origin and success or failure, allowing a partial success category as well. But even doing this gets complicated. I have listed Mars Express and Beagle 2 as separate because it seems unfair to categorize Mars Express as a partial success. I put Mars Polar Lander and Deep Space 2 as separate, for no very good reason. So should all the components of Mars 96 be listed separately? Is Viking two successes or four? And to be more realistic Mars 2 should be counted as a total failure.

Even so, you can see that most failures are Soviet, most successes American. Most failures are early, most successes recent. Most journalist claims are literally true but misleading to make a good story. The worst point is the one about 30 percent of landers succeeding. Six out of seven US landers worked, so to get the 30 percent success rate you have to count every separate lander on every Soviet mission, including launch failures where the lander was never put to the test.


Phil

One thing they don't understand is that we have something nobody else has: ROB MANNING!!!

Paolo

From MSL, Mars is now 0.561° in angular diameter -- larger than the Moon from Earth (0.507° average).

Are we there yet?

Yes we are. Start packing your toys and stuff, we are almost home.

Paolo

Present your E-tickets tickets to the lady at the turnstile. Fasten your seat-belts and stand clear of the closing doors. It is important to secure all loose objects, and please keep hands and arms inside at all times.

So, no L-2 TCM, I'm assuming? (saw no news of it, but maybe I missed it)

You forgot the turret as well. Sorry, couldn't resist.



Apparently they are so dead on that they don't need to do any corrections.

Paolo

Blame is at least in part misdirected -- that narrative is coming out of NASA HQ. Reporters doing this, I can at least understand. And NASA making sure people understand there are risks, I can understand. Jim Green pushing the 40% story--that seems like a disservice. Christian Science Monitor was working on a story -- the reporter seemed to be calling BS on that narrative.

In the press conference going on right now, a reporter tried to pin the panel down on the estimate of the odds, but no one bit. Doug McCuistion, director of the Mars program, essentially said there were too many variables and no way to put a meaningful number on it, and Richard Cook, flight operations manager, said that they've done lots of Monte Carlo simulations of what might happen during EDL, but always assuming that the hardware works.

Since NASA was able to come up with risk assessments for the Shuttle (what was it, something like 1 in 100?), not sure why a ballpark number couldn't be put on this one.

IMHO, such figures for complex systems that aren't tested a statistically-meaningful number of times are essentially meaningless. IIRC estimates of shuttle reliability before Challenger varied by several orders of magnitude; the 1:100 was just the one that turned out to be right.

Also, consider that many failures could be caused by bad software.

Since software reliability is something I do know about...

Limiting reliability assessments to either 1 or 0 is absurd; in such a case, the reliability must be assumed 0. Complex software systems will not be defect-free. The appropriate questions are whether sufficient testing has been done, whether defects are encountered during a particular operation (EDL, for example), whether the defect causes significant problems, whether there is sufficient error detection and recovery in place, whether redundancies are in place, whether failover mechanisms are in place (and function correctly), whether a failure in one module can affect correct operation of other modules, etc.

I used to work on programming for public telephone switching systems. The watch-phrase was "belt and suspenders" - always have a backup system in place and ready to take over immediately.

I trust that the MSL software engineers have done their work well, and I look forward to great celebrations on Monday.

I'd like to think I do too; among other things I wrote most of the flight software in the science cameras for MSL (Mastcam/MAHLI/MARDI.)

The quote was from an article in the Communications of the ACM, a leading computer science journal.

At any rate, all I was suggesting is that quantifying the likelihood of encountering a software bug is potentially meaningless. Obviously we have had many successful runs of the EDL sequence and all known bugs have been dealt with.

From a layman, the main thing is it's designed to be successful, so barring a mistake, bad luck or hardware fault, it should all work just fine !

Writing flight software for any part of MSL sounds like an enormously fun and challenging job. I'm looking forward to seeing years of photos from your software!

As far as the CACM quote, it really felt like it was dodging the issue and taking a rather fatalistic attitude. (It's also from 1990; the same author might have an entirely different viewpoint today.) There are metrics, starting with code coverage, test cases run, etc. Part of the quality assessment is historical, from either operational use or from simulations, as you mention. Part of the assessment is qualitative, too, from activities such as code and test plan inspections, etc. Reducing it to "1 or 0" is like saying that either we'll all be happy after EDL, or not. It says nothing about the hard work, creativity, or ingenuity required to maximize the probability of success.

Some measures of quality have to be approached statistically. On the telephone system, I worked in billing; we had two requirements in particular: no more than 10,000 billing records lost in any outage, and no more than 1 record lost or in error out of every 100,000 records. Since billing records tend to be lost (or worse, duplicated) in blocks of 80 or so, and usually with multiple buffers or files involved, there's no real way to measure, and the statistical arguments then go to "over what time period", "across how many systems", etc. Given enough trials, the probability of error approaches certainty, but that says nothing at all about the probability of error in any single trial. Measures such as reliability, availability, and fault tolerance are really not "pass/fail" assessments.

Just to be safe, when I see the landing time listed as 10:31 pm (Pacific time) tomorrow, is that the time on Mars or when we see the signal here?

That's earth-received time, plus or minus a minute or so due to weather & other uncertainties, according to today's press conference.