MET - Lidar & Telltale Options

[antipode]

There seem to be a lot of frayed threads holding up that telltale, it would be embarassing if it blew off at some stage

P

[climber]

Telltale caugth in movement : http://phoenix.lpl.arizona.edu/images.php?...3206&cID=47

[elakdawalla]

I noticed the frayed thread too, it's really obvious in the sol 11 images, like this one


I wonder what could have caused that?

--Emily

[nprev]

Vibration, normally, presumably during launch. You see the same effects on aircraft flight control cables over time. Swaging the cable ends naturally weakens or even breaks individual strands, and eventually they start to fray. The temp extremes at the landing site will exacerbate the process.

[Stu]

Hasn't it always been frayed? This pic from Sol 5 suggests a lot of fraying even then...

[nprev]

Oh, yeah...it's just gonna get worse, though. Hopefully the MET team will take into account the increased surface area exposed to the wind when calculating wind velocities.

[Stu]

Here's a crop of a Sol 2 pic...



Maybe the much-reported corrosive nature of martian dust is fraying it even more? Stands to reason that if we've seen it blowing then dust is blowing past and through it... countless teeny tiny sharks teeth sawing away at it with each soft whisper of Barsoomian wind...

Edit: interesting pic here... maybe it's not that frayed at the end, after all... some damage up the length of the thread tho...

[Bill Harris]

>There seem to be a lot of frayed threads holding up that telltale...

What is the telltale thread made of? If it is a Kevlar/aramid tow, then that fraying is not abnormal nor is it serious.

--Bill

[Airbag]

What is the telltale thread made of?

Kevlar, according to a person in the know a few posts ago. It is not surprising that any damage was already visible right from the start; after all, the tell-tale was never locked in place so must have been thrown around quite a bit during launch and descent (and was tested for those conditions).

Airbag

[Airbag]

Guide to Martian weather conditions:



Airbag

[ugordan]

Guide to Martian weather conditions:

[Stu]

Genius!

[elakdawalla]

Classic. That went straight to the blog.

[Pando]

Haha!

(This draws some parallels with teh Wyoming wind sock )

[Guest_Oersted_*]

What most people don't realise is how extremely light the Tell-tale assembly is: only 20 grams (0.71 ounces). The active part of the Tell-tale, the kapton tube, weighs only an incredible ten-thousandth of a gramme! (0.0001 gramme equal to 0.0000035 ounce). This light weight is necessary to achieve a measurable deflection in the rarified Martian air of only 1 percent Earth sea-level atmospheric pressure.

The kevlar fibers from which the kapton tube is suspended also had to be incredibly light of course, but mainly they had to have some very particular properties. They had to deflect uniformly and steadily, so the wind pressure could be properly read in a single photo. It would be no good if the kevlar fibers just allowed the kapton tube to oscillate randomly.

The famous dust "storms" on Mars only exert a wind force on the back of your hand equal to the force from moving the hand through the air in a slow sweeping motion here on Earth. This was explained by Tell-tale's Islandic team leader Haraldur Páll Gunnlaugsson at the June 4 University of Arizona press briefing. Let's not go into what the Mars atmospheric pressure would do to your hand, if you were to expose it on Mars!

During the first vibration tests - exposing the Tell-tale to the forces of a rocket launch - the instrument failed completely. It took an involved redesign effort to make it comply with the two highly conflicting parameters: sufficiently sensitive to measure the winds on Mars and sufficiently sturdy to survive launch and EDL. But the team succeeded, as we can now see in daily pictures from the surface of the planet!

Tell-tale is the name for a piece of string suspended from the sail or stays of a sailing boat, to indicate the wind direction and -force. The University of Aarhus Tell-tale is a deceptively simple-looking instrument, which however took some very clever engineering for it to work properly in the Martian environment. It has already supplied important information about the winds at the Phoenix landing site: we now know that the winds go through 180 degrees from South to North during the Martian day. Important knowledge, because it can be taken into account during digging, so that various samples won't be contaminated by airborne dust from previous digs.

The University of Aarhus in Denmark is my alma mater, so I am very proud to see that it made the Tell-tale on Phoenix! (Aarhus is the second-largest city of Denmark with 250.000 inhabitants. The university is rather new, from the 1920's, and got its first Nobel prize (Jens Chr. Schou, Chemistry) in 1997). Until now it was mainly the Niels Bohr Institute in Copenhagen that made Danish contributions to JPL Mars expeditions, focusing on magnetism. As you may note from my user name, we have quite a tradition in that field (sic..) in Denmark.

The Tell-tale is described more in depth at the Aarhus University Mars Lab page: http://www.marslab.dk/ (sub-page for Tell-tale: http://www.marslab.dk/TelltaleProject.html).