IPB

Welcome Guest ( Log In | Register )

67 Pages V  « < 63 64 65 66 67 >  
Reply to this topicStart new topic
Extricating Spirit, Digging out from Troy
djellison
post Apr 11 2010, 03:05 PM
Post #961


Administrator
****

Group: Chairman
Posts: 13744
Joined: 8-February 04
Member No.: 1



It's a see-how-we-go situation.

If the thing gets cleaned to 800Whr+ come spring, can you really imagine them sitting still and not trying to get out?
Go to the top of the page
 
+Quote Post
elakdawalla
post Apr 11 2010, 03:59 PM
Post #962


Bloggette par Excellence
****

Group: Admin
Posts: 4415
Joined: 4-August 05
From: Pasadena, CA, USA, Earth
Member No.: 454



Scott told me that they can actually move some centimeters without affecting the radio science campaign, so they can continue working on extrication efforts up to a point even while they are considered "stationary." In the event that they find they are successful and could move so much that they would ruin the radio science experiment, my impression is that the radio science experiment would be completed first, but obviously that's a decision that would be made if and when they actually face that situation.


--------------------
My blog - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
Go to the top of the page
 
+Quote Post
centsworth_II
post Apr 11 2010, 06:52 PM
Post #963


Senior Member
****

Group: Members
Posts: 2045
Joined: 28-December 04
Member No.: 132



In view of all the signage going up on Meridiani, I thought Spirit could use one.

Attached Image

Using Stu's "Stuck" image.
Go to the top of the page
 
+Quote Post
Guest_Bobby_*
post Apr 11 2010, 11:14 PM
Post #964





Guests






Does anyone have an image of the area taken by Spirit where she is stuck now? I would like
to see a ground level shot of where she is now and what direction she is going from that spot.
There is probably an image somewhere in an earlier thread. I just want to know if she has
to go up hill from where she is now to escape the sand trap???

Thanks
Go to the top of the page
 
+Quote Post
djellison
post Apr 11 2010, 11:23 PM
Post #965


Administrator
****

Group: Chairman
Posts: 13744
Joined: 8-February 04
Member No.: 1



QUOTE (Bobby @ Apr 12 2010, 12:14 AM) *
Does anyone have an image of the area taken by Spirit where she is stuck now?


The post previous to yours - with added rover for scale and perspective - is EXACTLY that.
Go to the top of the page
 
+Quote Post
Guest_Bobby_*
post Apr 12 2010, 01:28 AM
Post #966





Guests






Thanks Doug.
Go to the top of the page
 
+Quote Post
tanjent
post Apr 13 2010, 03:39 AM
Post #967


Member
***

Group: Members
Posts: 123
Joined: 30-December 05
Member No.: 628



QUOTE (elakdawalla @ Apr 11 2010, 11:59 PM) *
Scott told me that they can actually move some centimeters without affecting the radio science campaign, so they can continue working on extrication efforts up to a point even while they are considered "stationary."


Sols 1406 to 1782 (=386 sols) saw only small movements down the slope at Winter Haven 3. Tesh's maps are not quite accurate enough to estimate the minimum number of centimeters moved over a six month span, but whatever it may be, isn't that an upper bound for the amount of permissible movement during the core composition experiment? IIRC Spirit was able to call home during the previous winter, and yet the stationary observations that could have been done then were apparently not accurate enough. Anyway, it seems to me that if we are going to perform such a sensitive and difficult-to-repeat experiment, the observation error ought to be reduced as small as we can possibly make it by just keeping the rover stationary. I don't understand how some error can be permissible and more error can be impermissible.
Go to the top of the page
 
+Quote Post
stevesliva
post Apr 13 2010, 05:07 AM
Post #968


Senior Member
****

Group: Members
Posts: 1164
Joined: 14-October 05
From: Seattle
Member No.: 530



QUOTE (tanjent @ Apr 12 2010, 11:39 PM) *
I don't understand how some error can be permissible and more error can be impermissible.


I can speculate. The wavelengths are 2-4 cm and the frequencies are 12-8 GHz. A few cm movement of the rover isn't a big deal... it's still in the same place as far as the experiment's accuracy is concerned.
Go to the top of the page
 
+Quote Post
ElkGroveDan
post Apr 13 2010, 05:10 AM
Post #969


Senior Member
****

Group: Admin
Posts: 4657
Joined: 15-March 05
From: Sloughhouse, CA
Member No.: 197



There was an entire press conference on this topic and they went round and round on the issue of small movement. Ultimately, what Scott told Emily was described as within the tolerances of the experiment. I don't see why that is difficult to understand. Have you ever used a measuring tape to find the length of something? Did you stop to worry that the molecules at the end of the tape are vibrating back and forth the entire time? It doesn't affect your measurement though because that movement is within the tolerance you have accepted for that datum.


--------------------
If Occam had heard my theory, things would be very different now.
Go to the top of the page
 
+Quote Post
Stu
post Apr 13 2010, 05:48 AM
Post #970


The Poet Dude
****

Group: Moderator
Posts: 5548
Joined: 15-March 04
From: Kendal, Cumbria, UK
Member No.: 60



QUOTE (ElkGroveDan @ Apr 13 2010, 06:10 AM) *
Have you ever used a measuring tape to find the length of something? Did you stop to worry that the molecules at the end of the tape are vibrating back and forth the entire time?


Doug and I measured out the whole solar system with a tape measure last year, and I can honestly say that by the time we got down that long hill to Pluto, the state of the molecules at the end of the ******** tape were not foremost in our thoughts...! laugh.gif


--------------------
Go to the top of the page
 
+Quote Post
tanjent
post Apr 13 2010, 03:26 PM
Post #971


Member
***

Group: Members
Posts: 123
Joined: 30-December 05
Member No.: 628



Is there a transcript of the above mentioned press conference available somewhere? I am interested in this experiment and I want to understand it better.

Meanwhile, limping along on what I have read and heard, I am reasoning as follows:
To build on the tape measure analogy, measurement error can usually be discounted when the question at issue is binary.
Like: "Will this bookcase fit through the door of my den?" Even with just a centimeter to spare, it's a done deal, unless I have a very badly frayed tape measure or I confuse centimeters with inches or something like that.
If I thought the center of Mars was either wholly liquid or wholly solid, (whatever that means when applied to metals) it would still be a binary call and measurement errors less than a certain size would probably not affect whether the hypothesis is to be rejected or sustained.
But in this case there are a number of continuous variables to be estimated - coefficients of plasticity, or the diameter of whatever "liquid" core may exist.
If I take your photo, your face may be recognizable even if my hand trembles or you blink your eyes. But photographers usually try to minimize that noise to get the best picture possible.
BTW, if we are going to sacrifice some measurement accuracy to perform an extrication maneuver essential to Spirit's survival, I am OK with that, but it is not the same argument as saying that movements of less than n centimeters do not have consequences and movements of more than n centimeters do have consequences.
Go to the top of the page
 
+Quote Post
Phil Stooke
post Apr 13 2010, 03:54 PM
Post #972


Senior Member
****

Group: Members
Posts: 5631
Joined: 5-April 05
From: Canada
Member No.: 227



I think you'll find that it is not centimeters that are being measured, but doppler shifts and times.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
fredk
post Apr 13 2010, 04:13 PM
Post #973


Senior Member
****

Group: Members
Posts: 3162
Joined: 17-January 05
Member No.: 152



What matters is that the movement of the rover is small compared to the relevant scale. No doubt the rover shifts a bit each time the wind changes direction, but probably by only a very small fraction of a millimetre. Surely such movements would be unimportant for the core studies, but those same movements could be critical for the seismology experiments.

In the case of the core studies, there is some relevant scale, but I don't know what it is. As mentioned above the signal wavelength sets an absolute lower limit to movement that you'd care about, in the cm range. There could be many factors that make that lower limit larger. If it was several metres, then movements of tens of cm would be unimportant. The errors induced by the rover movement would be swamped by other errors.

Another point is that it might be that the movements could be corrected for in the core studies. Remember that the driven rover movements aren't random noise - the distances and directions and orientations are known with high precision.

Edit - definitely you're right, Phil, that cm are not measured directly. But still the relevant timing errors correspond to some position errors, since the signals travel at a fixed speed, 300 000 km/s.
Go to the top of the page
 
+Quote Post
centsworth_II
post Apr 13 2010, 04:46 PM
Post #974


Senior Member
****

Group: Members
Posts: 2045
Joined: 28-December 04
Member No.: 132



So as I see it, they measure the effect of Mars' wobble on Spirit's radio signal in real time. Spirit can move between measurements without the overall study being effected. It seems to me that a much bigger problem would be motions due to thermal changes or a stiff breeze during the measurement.

NASA - Spirit's Journey to the Center of Mars
"Mars wobbles, or precesses, as it spins," says Bruce Banerdt of NASA's Jet Propulsion Laboratory. "We'll measure that wobble by looking at the Doppler shift of Spirit's radio signal."
Go to the top of the page
 
+Quote Post
stevesliva
post Apr 13 2010, 05:24 PM
Post #975


Senior Member
****

Group: Members
Posts: 1164
Joined: 14-October 05
From: Seattle
Member No.: 530



Well, since it is the doppler shift they're interested in, the distance of the Spirit from the center of Mars affects its radial velocity, so that movement upslope...

...is going to be a probably immeasurable difference. ph34r.gif

Actually, compared to the frequency variability implicit in the temperature of the oscillator on the rover... yeah, it would be very lost in the wash.
Go to the top of the page
 
+Quote Post

67 Pages V  « < 63 64 65 66 67 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 2nd September 2014 - 04:46 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.