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djellison
Rob Manning and I swopped emails last night - and we think it might make sense to pool all the questions people have about MSL (and specifically MSL's EDL ) into one thread - and then answer as many as make sense either via a Q'n'A in the style of the previous ones I've done with Steve and Jim - or via Rob's typing fingers.

It'll be a few weeks till we sort this out - but submit-away until then smile.gif

Doug
elakdawalla
Doug and I had the same idea -- he got to Rob first! -- but hopefully you'll also see Rob's responses in the future as a guest blogger.

Anyway, I'll start with one: in this post, Rob, you said:
QUOTE
(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.)
Please share!

Emily
Juramike
My Big list 'o Questions:

1) How scalable is this? How big (mass) a package could it deliver?
(Could you put down a future habitation module on Mars, deep drilling rigs, other cool stuff?)

2) Could you use it to put down multiple instruments in different (but fairly close, locations?)
[OK, you’d need to upgrade to more propellant, brains in the platform, and deal with COG issues]

3) Could you use it to move an instrument already on the surface to a new location?
[lotsa propellant, more brains in the platform, getting the rendezvous and “hook up” – but heck, the stability, lowering problems will already have been solved] (Imagine if we could send a Skycrane pick up Oppy and move her to another location within a 200 km radius – this would really change the post-Victoria discussion!)

4) Could it be used to deliver other packages down on other (airless) planetary surfaces?
[no chute, but using much, much more retro]? (Europa, for example).


5) Will it be possible to (exhaustively) test the Marscrane system on Earth before the big test on Mars?

-Mike
akuo
Ok, here is my question:

MSL is not limited by electrical power as much as previous rovers. The RTG will provide a constant current, though AFAIU batteries are still needed when power needs are higher.

Taking this into account, for how long time could MSL rove during a sol? Is it possible to move even during the night?
Jim from NSF.com
QUOTE (akuo @ Jun 1 2007, 03:43 PM) *
Ok, here is my question:

MSL is not limited by electrical power as much as previous rovers. The RTG will provide a constant current, though AFAIU batteries are still needed when power needs are higher.

Taking this into account, for how long time could MSL rove during a sol? Is it possible to move even during the night?


MSL operates off the batteries and the MMRTG recharges them. It will operate about 7 hours per sol
Stu
Apart from the obvious question that springs to mind after watching that new animation... "What were you guys smoking when you came up with the idea of the Skycrane?!?!?!?"... tongue.gif ... here are a couple, and apologies in advance if these have been answered elsewhere, but I can't remember reading the answers, and anyway, new people join UMSF all the time so these questions will be new to someone out there...

Will we be getting "video clips" from MSL?

In the light of the success of the "purely scenic" images taken during the NH Jupiter flyby, will MSL be programmed to take any similar images ("pretty pictures" as someone calls them... wink.gif ) purely for Outreach value and media appeal? Maybe dedicated imagery of Earth-in-the-sky scenes? We (and by "we" I mean we frontline Outreach troops who spread the word) really need a classic, colour, "Earth in Mars'sky" image please, thank you... smile.gif

How much more advanced will MSL's imaging instruments be than MER's?

Ta.
djellison
QUOTE (djellison @ Jun 1 2007, 04:11 PM) *
(and specifically MSL's EDL )


unsure.gif

Although hopefully we could find someone to do those other questions.
nprev
Okay, I got two:

1. How exactly is the MSL/crane separation sequence initiated? Does MSL have something like aircraft "weight-on-wheel" switches that tell the computer it's down, and therefore safe to cut the cords?

2. Is the crane in fact commanded immediately at separation to do a tilt & escape maneuver as shown in the animation? (In other words, since I gather it has no brains of its own, how is it told to vamoose instead of possibly hovering right over MSL until it runs out of fuel...?)
dvandorn
And here's a few more to add to nprev's:

3) What happens if the rover touches down before the belaying lanyards have been fully extended? Especially what happens if one wheel of the rover hits a decent-sized rock before the lanyards have been fully extended?

4) Is the cable/lanyard separation accomplished via a signal in the lander (i.e., a contact sensor of some kind), or in the crane (a slack cable signal)? If it's a slack cable signal, can we be certain that any unexpected buffetting encountered by the rover won't accidentally set it off?

5) Are we certain there won't be enough engine blowback from the surface to set the rover into motion, perhaps so much motion it will tip over at wheels-down? Has the landing-on-a-slope case been considered in this regard, where a given slope (or even badly placed rock) could reflect engine exhaust in such a way as to destabilize the rover?

6) Has the general issue of slopes been addressed? What happens if the rover has a small but significant sideways motion at touchdown (due to substantial winds, I would guess) and that direction just happens to be downslope -- of a significant slope (like 20 degrees or more)?

7) Will MSL's obstacle avoidance capability be able to recognize slopes (hills and craters) as well as blocks?

OK -- I think that's enough for now -- smile.gif . Thanks for being willing to address some of these questions, Rob!

-the other Doug
Stu
QUOTE (djellison @ Jun 1 2007, 10:45 PM) *
unsure.gif

Although hopefully we could find someone to do those other questions.



Okay, okay, I didn't read the brief properly. Please file my questions until a more appropriate opportunity.
Toma B
Thanks Doug!
Here are my questions:

a ) Tests of Skycrane on Earth:
1 ) Is there a plan to do at least one full scale test of the descent stage using as close as possible to flight hardware?

2 ) When and where will these tests be undertaken?

3 ) Is there an almost finished Skycrane NOW somewhere in labs? (I don't intend to steel it :-))


b ) How long can it work once it is released from backshell?
1 ) How much fuel does it carry?

2 ) What is Skycranes thrust to weight ratio at full throttle?

3 ) At what height is Skycrane released from the backshell?


c ) How far away will Skycrane crash after releasing MSL-lander? (I know this cannot be answered precisely)
1 ) Is it possible that Skycrane will (almost) soft land?

2 ) Is there a plan to visit it after or is that for any reason dangerous?


Thanks again for the opportunity to do this? Sorry for my English.....

P.S.
I love this place....
Eluchil
Here are a few Rob might know the answers to:

1) When is the MARDI descent movie expected to be downlinked?

2) What on-orbit assests are expected to relay telemetry during EDL; can others be substituted if they are unavailible?

3) Are the testing facilities for the parachutes and whole EDL systems adequate or would full on upper atmospheric tests be useful?

Eluchil
djellison
There's a few questions that I think I can do a bit of an answer about for now:

Lots of the same question - full scale test of the whole thing. That's not even possible on Earth - that's what makes landing on Mars so hard - you can't practice. You can try and do a chute deployment on Earth using low wind speed at 1000 mbar - similar dynamic pressure to deploying on Mars - but it's not exactly the same. There was a RFP for a large rig to simulate the decent stage from which they would hang a mobility model to test software and the physical process ot touchdown - including slopes. You can test fire engines - you can simulate sloshing or other harmonic issues with pressurised water - but there's no way to simulate the whole thing...you just test systems as best you can - the simulate the system of systems virtually. VKG, MPF, MPL, MER, PHX - none had a full up system test of everything - because you just can't do it here.

MARDI movie will be downlinked.....after landing. Product downlink priorities for data to be taken in three years time - that's a bit premature isn't it smile.gif I'm sure it will be something of a priority from a EPO perspective - but it'll be a big data product so it may take some time.

EDL comms will be to MRO and - if it's still around - Odyssey as well I would have thought - the same as Phoenix.

And here's the great thing about UHF, MRO and MSL ( and I'm hoping a DESCANO report on this - and the Phoenix one - will happen )

MER2Ody is 128k - or 256k if it's a good pass - typically 10-15 minutes - 50 to 150 Mbits in a pass.

MSL2MRO can be up to 2048k - shorter on average than MER passes with Odyssey - but still potentially up to 1000 Mbits or more in a pass.

Doug
helvick
I presume you mean MSL2MRO there.
djellison
Yeah - that what I said.

laugh.gif

Cough ahem oops well spotted. smile.gif


Doug
DEChengst
Looking at it from an artistic point of view:

Is there any chance of MastCam tracking and making a movie as the Skycrane flies away, although the mast probably will still be stowed on the rover's deck ?
ElkGroveDan
Once science is well on the way, are there any plans for examination and study of the EDL hardware?
djellison
QUOTE (DEChengst @ Jun 2 2007, 03:07 PM) *
Is there any chance of MastCam tracking and making a movie as the Skycrane flies away, although the mast probably will still be stowed on the rover's deck ?


I would hope that the optics would be orientated so that they would be well out of the way of any rocket exhaust at fly-away.

Doug
nprev
QUOTE (DEChengst @ Jun 2 2007, 07:07 AM) *
Is there any chance of MastCam tracking and making a movie as the Skycrane flies away, although the mast probably will still be stowed on the rover's deck ?


In addition to Doug's observation about protecting the optics, from a risk mitigation standpoint it would be unwise to burden the flight software with a non-essential requirement so quickly after one of the most critical events of the entire mission. MSL's got to get its act together afterwards, we don't need to take a chance on incurring the equivalent of a 'blue screen of death' . (Don't get me wrong, though, DE; I'd really love to see that myself! sad.gif )
djellison
This skycrane/decent stage debate is ending. Now. We've had it before. We're going in circles. Stop. Now. This is a thread for questions about MSL's EDL - not the semantics of naming.

Multiple posts deleted.

Doug
mcaplinger
QUOTE (Stu @ Jun 1 2007, 02:17 PM) *
Will we be getting "video clips" from MSL?

That's a downlinked data volume question; the hardware can certainly do it at up to 10 fps. Of course, nothing much is moving at rates that would justify a frame rate that high; the team is still considering this. (And no, we can't see the descent stage fly away; Mastcam and MAHLI are still turned off and stowed, and MARDI is pointed down.)
QUOTE
Maybe dedicated imagery of Earth-in-the-sky scenes?

I'm certain we'll try this, but we only have 100 mm focal length, so I'm not sure the disk will even be resolved; it'll still just be a blue dot.
QUOTE
How much more advanced will MSL's imaging instruments be than MER's?

I'm not sure how to quantify "more advanced." They're about 100x faster with about the same noise performance. The MER cameras were all fixed-focus. Mastcam has a 10:1 zoom lens with autofocus. MAHLI (the MI equivalent) has adjustable focus with autofocus. All the instruments are capable of realtime image compression and other internal image processing and have 8 GB flash buffers for data storage. They can all take Bayer-pattern color images with one frame (some might call that less advanced than multiple exposures through color filters, but Mastcam can do that too.) On the other hand, they weigh more and are a lot more mechanically complex, which I can assure you is a development challenge.
Sunspot
Malin Space Science Systems has information on some of the cameras they are building:

http://www.msss.com/msl/mastcam/index.html
http://www.msss.com/msl/mahli/index.html
http://www.msss.com/msl/mardi/index.html

# Each Mast Camera has a 10x telephoto/zoom capability; the field of view (FOV) can be from 6°(zoomed) to 60° (not zoomed).

# Near the rover, Mastcam images have a spatial resolution of about 150 micrometers per pixel. With the telephoto system, objects at 1 kilometer distance can be resolved at 10 centimeters per pixel.
djellison
Here's one for you Mike - I get bayer filters - and I get the normal way of doing filtered obs. How do you set up a CCD to do single shot colour but ALSO do filtered obs as well? Is it like a hybrid bayer filter that has an R, a B but only one G with what would be the 'other' G as a clear for use with filters? (That's a complete and utter guess)

Doug
nprev
Nice, you guys; sounds like some exciting pics are pending! smile.gif smile.gif smile.gif

Truly off-the-wall Skycrane question here: How much hydrazine is expected to remain in its propellant tanks after a nominal descent? Reason I ask is that if (a big if, admittedly) the tank(s) rupture after impact, it might be interesting for MSL to cautiously approach the wreckage at a safe distance a few sols later in order to take a few spectra of any obviously NH4-'splashed' soil to see what sort of reaction compounds may have formed... a unique opportunity for understanding local minerology if it presents itself and is safe to pursue.
Jim from NSF.com
The amount of fuel in the DESCENT STAGE should be only vapors if the fly away manuver is "successful"
nprev
Ah. So, then, the descent stage is expected to stay airborne until it runs out of fuel, Jim? That seems to place some topographical constraints on the landing site; maybe the landing site slope question is moot.
Jim from NSF.com
Not really, the flyout is independent of landing site slope. Anyways the slope is going to be minor, if any
nprev
I see; thanks! I was wondering about some of the candidate clay-bearing sites in canyons, which apparently have fallen off the target list; wouldn't do for the descent stage to bash into a canyon wall & blow up too close to MSL...
mcaplinger
QUOTE (djellison @ Jun 2 2007, 12:18 PM) *
Here's one for you Mike - I get bayer filters - and I get the normal way of doing filtered obs. How do you set up a CCD to do single shot colour but ALSO do filtered obs as well? Is it like a hybrid bayer filter that has an R, a B but only one G with what would be the 'other' G as a clear for use with filters? (That's a complete and utter guess)

That might work well, but we use an off-the-shelf sensor so we can't have a custom filter. No, the narrowband filters work because the Bayer filters are transparent in the near-IR, where the narrowband color can be used to look for iron-bearing minerals. In the visible, there is always some overlap between the narrowband filter and at least one of the three Bayer filters, often two. In those cases we just adjust the interpolation appropriately to use only the pixels that have usable signal after light has passed through both the Bayer and narrowband filters.
djellison
Ahh - suddenly it all becomes clear(er) - cheers Mike

Doug
climber
Question for both Phoenix and MSL : what kind of colour-target / sundial will we have ?

As it's gona be the most targeted target.... tongue.gif
mcaplinger
QUOTE (climber @ Jun 2 2007, 02:21 PM) *
Question for both Phoenix and MSL : what kind of colour-target / sundial will we have ?

Phoenix cal target: http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1149.pdf

MSL cal target is still being designed.
monitorlizard
Given the power output of MSL's RTG and the best model you have of rate of power output decline due to plutonium decay, how long could the RTG provide enough power to keep MSL roving (assuming nothing else failed)? Thanks.
Thu
I have some questions:

1. What is the ratio of final mass delivered (the rover) and entry mass at Martian atmosphere for the two methods: SkyCrane and airbag delivery method on Mars?
I'm expecting SkyCrane to have better efficiency than using airbag but could anybody give me some specific numbers for comparison?

2. I remember reading somewhere that MSL will be equipped with a flashlight that will allow it to move or perform some science observations at night. Is this true and what's the advantages for observing in the dark on Mars?

3. Another question, maybe a stupid one: Did engineers find out what went wrong with Spirit's right front wheel and come up with an upgrade for MSL's wheels? Or should we let it happens because who knows a dragging wheel may lead to an unexpected discovery tongue.gif

4. Thinking of the 3rd question, I come up with this last one: if something bad forces MSL to move backward just as Spirit is doing now, I think it'll be more difficult for MSL's computer to navigate because her camera mast is not at the center as her sister's. How do you think about this?

Thanks,
mcaplinger
QUOTE (Thu @ Jun 3 2007, 06:18 PM) *
2. I remember reading somewhere that MSL will be equipped with a flashlight that will allow it to move or perform some science observations at night. Is this true and what's the advantages for observing in the dark on Mars?

http://www.msss.com/msl/mahli/MAHLI_description.html

"MAHLI has a suite of white light LEDs and a suite of ultraviolet LEDs to provide illumination of the targets it is imaging. The white light LEDs permit the instrument to operate at night and allows the science team to avoid problems of shadowing during daytime imaging. The ultraviolet LEDs provide an opportunity to look for minerals that fluoresce."
remcook
If you've got an RTG you might as well do nighttime observations. So, I guess science of MSL is limited by data rates, not power?
centsworth_II
QUOTE (Jim from NSF.com @ Jun 1 2007, 05:16 PM) *
MSL operates off the batteries and the MMRTG recharges them. It will operate about 7 hours per sol


How fixed is this seven hour figure? Is it a maximum? An average? And what does "operate" mean?
The MERs routinely "operate" their spectrometers for 12, 24 or more hours at a time.
elakdawalla
Here's a few that I've received by email. The first two are variations on a theme:

What kind of AI, if any, is built into the descent stage in terms of selecting an exact point to set the rover down? In other words, does the sky crane "look around" for a suitable spot as it descends, or does it just go straight down regardless?

Is it the rover or the descent stage that decides when the rover is safe on the ground? I'm guessing they both need to know when touch-down occurs because, from the video, it looks like the rover releases the cables and the descent stage flies clear of the rover. So do they both detect it? Or does one detect it and communicate to the other? How is detection done? Radar? Touch sensor?

Why is the "skycrane" concept better than just lowering the rover to the ground with retrorockets (as if using zero-length cables)? Are the cables used for cushioning? Wouldn't it be better for the "skycrane" to hover in one place and lower the rover by unwinding the cables very slowly till the rover touches down, rather than descending with the cables fully extended, as in the video?
Jim from NSF.com
QUOTE (centsworth_II @ Jun 4 2007, 10:45 AM) *
How fixed is this seven hour figure? Is it a maximum? An average? And what does "operate" mean?
The MERs routinely "operate" their spectrometers for 12, 24 or more hours at a time.


Operate = rove

QUOTE (remcook @ Jun 4 2007, 04:44 AM) *
If you've got an RTG you might as well do nighttime observations. So, I guess science of MSL is limited by data rates, not power?


limited by power
Jim from NSF.com
QUOTE (elakdawalla @ Jun 4 2007, 01:22 PM) *
1. Why is the "skycrane" concept better than just lowering the rover to the ground with retrorockets (as if using zero-length cables)? Are the cables used for cushioning? Wouldn't it be better for the "skycrane" to hover in one place and lower the rover by unwinding the cables very slowly till the rover touches down, rather than descending with the cables fully extended, as in the video?


Skycrane concept eliminates thruster plumes and dust on the rover

The mobility system (wheels etc) absorb the shock

no, extended hover is harder to maintain
Alex Chapman
I know it’s a little off topic but I have a quick question about something I saw on the animation post EDL. The animation shows a sample being loaded into, what I asume is, one of the sample holders in the Chemistry & Mineralogy X-Ray Diffraction (Chemin) instrument. From what I can see it looks like there is 24 or so separate sample holders and I was wondering if each holder only be used once and so limiting the number of samples analysed by Chemin.

Do the instruments within the Sample Analysis at Mars Instrument Suite (SAM) have similar limitations on the number of samples that can be studied? Just one last thing, why does Sam have two sample entry ports on the rover’s deck?

Thanks
Jim from NSF.com
SAM is being redesigned at the moment
Cugel
QUOTE (Jim from NSF.com @ Jun 4 2007, 10:30 PM) *
Skycrane concept eliminates thruster plumes and dust on the rover


Would that be a problem when there is no solar panel up there?
I believe the big advantage of the skycrane is that it minimizes the mass that actually lands.
And by doing so it reduces the stress and loads caused by touchdown.

QUOTE (Jim from NSF.com @ Jun 4 2007, 10:30 PM) *
The mobility system (wheels etc) absorb the shock


I don't think a rocker-bogie system does much shock absorbing as it is completely rigid.
This simply means the vertical speed at touch down must be very small.

BTW, I'm much more concerned about horizontal speed at landing than about vertical speed, which is much more easy to control. I'm afraid the suspension system will not have much tolerance for horizontal speed at touchdown and any swinging motion of the rover must be dampened by the skycrane. Or does the rover have any reaction control system of its own? (I don't think so, as it doesn't carry any fuel tanks).
This will be a pretty tough control job in the windy Martian atmosphere and coming from a huge horizontal entry speed.
centsworth_II
Hold a Yo Yo by the string. With a few cm of string, the Yo Yo swings wildly
when the string is shaken back and forth. As the string is lengthened, the
swinging becomes less. When the string is sufficiently long, it can be moved
back and forth quite a bit with little or no motion of the Yo Yo.
tty
QUOTE (Cugel @ Jun 5 2007, 03:44 PM) *
Would that be a problem when there is no solar panel up there?


Rocket plumes are always a problem close to the ground and they start impinging on it. Not only do they raise dust, but if the ground is uneven you can get quite difficult control problems. Back in the forties they experimented a great deal with using retrorockets to airland loads without parachutes. It worked quite well right until the rockets started impinging on the ground. Then the load invariably turned over.
Jim from NSF.com
QUOTE (Cugel @ Jun 5 2007, 09:44 AM) *
Would that be a problem when there is no solar panel up there?
I believe the big advantage of the skycrane is that it minimizes the mass that actually lands.
And by doing so it reduces the stress and loads caused by touchdown.
I don't think a rocker-bogie system does much shock absorbing as it is completely rigid.
This simply means the vertical speed at touch down must be very small.

BTW, I'm much more concerned about horizontal speed at landing than about vertical speed, which is much more easy to control. I'm afraid the suspension system will not have much tolerance for horizontal speed at touchdown and any swinging motion of the rover must be dampened by the skycrane. Or does the rover have any reaction control system of its own? (I don't think so, as it doesn't carry any fuel tanks).
This will be a pretty tough control job in the windy Martian atmosphere and coming from a huge horizontal entry speed.



The dust and the effluents from the thrusters would contaminate the rover

there is no "huge" horizontal velocity, it is coming vertical by the time the rover is repelling
Cugel
QUOTE (Jim from NSF.com @ Jun 5 2007, 04:31 PM) *
there is no "huge" horizontal velocity, it is coming vertical by the time the rover is repelling


I stand corrected on that one.
Pertinax
QUOTE (mcaplinger @ Jun 3 2007, 10:53 PM) *
http://www.msss.com/msl/mahli/MAHLI_description.html

"MAHLI has a suite of white light LEDs ..."


I would presume that this would also be useful in further constraining 'true color' as we will be able to view an object under both under daylight conditions and under a fully understood source of illumination.

BTW, what is the spectrum of the white light LED' in MAHLI?


-- Pertinax
mcaplinger
QUOTE (Pertinax @ Jun 5 2007, 12:34 PM) *
I would presume that this would also be useful in further constraining 'true color' as we will be able to view an object under both under daylight conditions and under a fully understood source of illumination.

To an extent, but the LEDs are not intended to be calibrated light sources and there is likely to be some color shift as a function of current and temperature. White LEDs typically have a narrow peak in the blue where the LED actually emits, and then a broader peak centered in the yellow where the phosphor emits; see http://en.wikipedia.org/wiki/LED
Pertinax
Thank you.

I didn't know if there were any other kinds of white LED (the kind you describe being the only sort I was aware of, though I am far, far from being an LED expert wink.gif ).

-- Pertinax
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