The Telltale Experiment for the Mars Phoenix Lander
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Mars Simulation Laboratory
c/o Haraldur Páll Gunnlaugsson
Aarhus University
DK-8000 Århus C
Denmark
UV test
Prepared by:
Jon Merrison
Haraldur Páll Gunnlaugsson
Log:
27/3 2006: Final
9/3 2007: Some typos and formatting made.
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1 Content
1
2
3
Content ......................................................................................................................................... 2
Introduction .................................................................................................................................. 2
Description of the experiment ...................................................................................................... 2
3.1
UV lamp characteristics ....................................................................................................... 2
3.2
Sample and experimental ..................................................................................................... 2
3.3
Characterisation ................................................................................................................... 3
4
Results .......................................................................................................................................... 3
5
Conclusions .................................................................................................................................. 4
2 Introduction
In the CCC review, it was required that the UV resistance of the Kevlar fibres would be tested
(therein actually called Teflon part, but this was a typo). The purpose of this test is to demonstrate
that Telltales are unaffected by UV irradiation, especially the Kevlar fibres, that can be expected for
the first three months of the mission. Apart from direct UV induced damage to the Telltales, there is
the possibility that UV irradiation changes the damping characteristics of the Kevlar fibres.
3 Description of the experiment
3.1 UV lamp characteristics
Simulation of Martian UV conditions is achieved with a 150 W mercury-xenon lamp (Hamamatsu
Photonics L2482). It is typically run at around 100 W with a water cooling system and focusing
mirror. Calibration of the lamp has been performed using a photo-chemical process called
actinometry in which a photo sensitive solution can record the absolute UV photon flux {Bunce,
N.J., Handbook of Organic Photochemistry, (1987), 241-244}. Measurement was performed using
band pass filters (10 nm width) at wavelengths of 239 nm, 281 nm and 350 nm. Values of
2.06×1017, 2.26×1017 and 8.02×1017 photons s-1 nm-1 m-2 were obtained respectively. Care was taken
in this calibration and during operation to avoid the focal point of the lamp such that a reasonably
uniform illumination was achieved.
For comparison to Martian conditions the average flux at surface of Mars is required. Direct
measurement of this parameter has not been made and is dependent upon atmospheric conditions
(primarily dust loading). Based on an in-depth study of solar UV flux at the surface of Mars an
expected value of 6×10-3 W m-2 nm-1 has been obtained in which averaging has been performed
over the Martian year and the Martian day at a latitude of 11.6°N and for a wavelength of 239 nm.
Based on this intensity the lamp produces (at 239nm) around 35 times the averaged UV flux
experienced at the Martian surface.
The spectrum of the lamp can be found on the producers website (www.hamamatsu.co.uk) and
compared to the solar spectrum on Mars {e.g. Patel et al., Icarus 168, (2004), 93-115 }
3.2 Sample and experimental
The Telltale (UAP-PHX-630-b) with serial number TTFmb1#4m0 was used for the experiment.
The Kevlar fibres of this Telltale were found to be rather unevenly attached to the Kapton foil,
resulting in it not being considered as flight unit. This unit has negligible differences from the flight
units
The Telltale Experiment for the Mars Phoenix Lander
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It was decided to run the experiment without coating the Telltale with gold, as the gold may
present some protection and this allows us to study the worst case scenario.
The Table below shows the UV doses applied:
Table 1: List over UV experiments and their corresponding Martian exposure.
Test
label
Exposure time
Conditions
UV1
47 hours
UV2
47+93 hours
UV3
47+93+71
hours
Room temperature,
P < 10-2 mbar
Room temperature,
P < 10-2 mbar
Room temperature,
air 1 bar.
240 nm
correspondence on
Mars
1622 hrs
280 nm correspondence
on Mars
4830 hrs
1512 hrs
7280 hrs
2279 hrs
508 hrs
3.3 Characterisation
Before the experiment the Telltale was characterised using drop and tilt measurements. After each
UV dose, the telltale was inspected to see whether any visible damage had taken place, any colour
changes or visible changes in the material.
4 Results
Table 2 shows the results of Tilt measurements. For description of the nomenclature see the
calibration report or the CCC document(s) within Calibration Data Inputs.
Table 2: Results of tilt measurements on UV irradiated Telltale.
Telltale
Treatment
ATILT
Lb/LK
Hyst (o)
0 (o)a
0 (o)a
TTFmb1#4m0 None
0.141(2) 0.66(1) 22(2)
55(3)
0.3(2)
dob
UV1
0.126(9) n.d.c
n.d.
n.d.
0.3(2)
dod
UV2
0.12(1) n.d.c
~24
n.d.
0.3(2)
d
e
do
UV3
All very similar
a
Maximum intensity 0 at observation angle 0. bOnly 90o and 135o data useful.
c
Not determined. dOnly 90o and 135o data used. eDetails not determined
Table 3 shows the results from drop measurements
Table 3: Results of drop measurements on UV irradiated telltale.
Telltale
Treatment
TTFmb1#4m0
None
after UV3
ADROP
(s-2)
362(6)
CDROP
(s-2)
0.87(3)
Comments
Only 45o and 90o successful.
Offset data in good
agreement with tilt data
Similar, details not
determined.
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5 Conclusions
No significant changes were observed in Telltale characteristics for exposure at 240 nm
corresponding to 297 sols on Mars and at 280 nm corresponding to 93 sols on Mars, allowing the
conclusion that no changes are expected to take place during the Phoenix mission.