SAGE III is a payload on the International Space Station that conducts measurements of ozone and other atmospheric constituents through the use of a moderate resolution spectrometer with an operating wavelength range of 290 nm to 1550 nm. Because of the optically sensitive nature of the payload, a suite of eight Thermoelectric Quartz Crystal Microbalances (TQCMs) were included to monitor the operating environment. During the rst year of operation, the SAGE III TQCMs were instrumental in detecting several periods of higher contamination and localizing their sources. A clear window made from quartz crystal covers the instrument assembly's aperture. Under nominal operating conditions, this window is only open during science gathering activities. However, if the rates of contamination accumulation are detected to be above the background rate, the window will be kept closed during science gathering to protect the optically sensitive instrument mirror. An analysis of the signal transmissions through the window for the wavelengths of 290 nm to 1550 nm has been conducted to determine any possible degradation of the window and potential in uence on science data collected to date, and established a baseline for future analysis

Bangert, Joshua

Flittner, David

Liles, Kaitlin

Porter, Samual

Seasly, Elaine

Stanley, Ryan

Thompson, Michael P.

English

NASA Technical Reports Server

Analysis of observed contamination through SAGE III’s first
year on orbit
Michael P. Thompsona, Joshua Bangerta, Samual Portera, David Flittnerb, Kaitlin Lilesb,
Ryan Stanleya, and Elaine Seaslyb
aScience Systems and Applications, Inc., 1 Enterprise Pkwy, Hampton, VA, USA 23666
bNASA Langley Research Center, 11 Langley Blvd, Hampton, VA, USA 23681
ABSTRACT
SAGE III is a payload on the International Space Station that conducts measurements of ozone and other atmo-
spheric constituents through the use of a moderate resolution spectrometer with an operating wavelength range
of 290 nm to 1550 nm. Because of the optically sensitive nature of the payload, a suite of eight Thermoelectric
Quartz Crystal Microbalances(TQCMs) were included to monitor the operating environment. During the first
year of operation, the SAGE III TQCMs were instrumental in detecting several periods of higher contamination
and localizing their sources. A clear window made from quartz crystal covers the instrument assembly’s aperture.
Under nominal operating conditions, this window is only open during science gathering activities. However, if
the rates of contamination accumulation are detected to be above the background rate, the window will be kept
closed during science gathering to protect the optically sensitive instrument mirror. An analysis of the signal
transmissions through the window for the wavelengths of 290 nm to 1550 nm has been conducted to determine
any possible degradation of the window and potential influence on science data collected to date, and established
a baseline for future analysis.
Keywords: SAGE III, Thermoelectric Quartz Crystal Microbalance, Optical Transmission, Dragon, Soyuz,
Progress, International Space Station
1. INTRODUCTION
The SAGE III instrument is a moderate resolution spectrometer capable of capturing spectra in the wavelength
range or 290 nm to 1550 nm.1,2 SAGE IIIs objective is to measure concentrations of ozone, aerosols, water vapor,
nitrogen dioxide, and other trace gases. Due to the nature of the instrument and the desire to acquire science
data ,especially at the lower wavelengths for as long as possible, the effect of contamination on the payload was
of high concern. As a result a suite of eight thermoelectric quartz crystal microbalances(TQCMS) was included
on the payload. These TQCMs were divided into two sensor arrays called contamination monitoring packages
(CMP). CMP 1 consists of five sensors one each pointing in Ram, Starboard, Nadir directions, and two ,one
with a reduced field of view, pointing in the direction of Node 2. Figure 1 shows a layout of the sensor locations
on the payload. This architecture provides 360◦ coverage in azimuth and nadir. The TQCMs used were QCM
research Mark 24 models with 15 MHz crystals and a mass sensitivity of 1.965 x 10−9 gHz∗cm2 .
3
The TQCMs output the difference in resonant frequencies between one crystal that is kept clean and one
who’s gold coated surface is exposed to the environment this is called the beat frequency. The beat frequency is
linearly correlated to the mass adsorbed on to the sensor through the sensitivity coefficient. SAGE IIIs TQCM
beat frequency is sampled at 1 Hz. The data here is one minute averages of this data. On orbit TQCMs are known
to be susceptible to the effects of incident solar flux.4 This is visible in the SAGE III TQCM beat frequency
as an orbital variation in the beat frequency. In order to account for this any adsorption totals were calculated
by using the difference between orbital maximum frequencies. Each TQCM has its temperature controlled via
a thermoelectic cooler (TEC) with an operation range of −20◦C to 80◦C. Through the first seven months on
Further author information: (Send correspondence to Michael P. Thompson)
Michael P. Thompson: E-mail: michael.thompson@nasa.gov, Telephone: 757-864-7383
https://ntrs.nasa.gov/search.jsp?R=20200002575 2020-05-24T04:48:53+00:00Z
Figure 1. SAGE III TQCM pointing configuration
orbit all eight TECs were set to −10◦C. In October 2017 in order to better understand the amount of adsorption
onto the SAGE III sensitive surface the TEC for the Node 2 Focused TQCM was changed to 24.9◦C which is
an approximate average of the temperatures of the sensitive surfaces based on their correlation to the nearest
temperature sensors.
2. CONTAMINATION OBSERVATIONS
When SAGE III first reached orbit the CMPs and their respective TQCMs were used to asses the contamination
environment surrounding the payload. Once it was determined that environment was benign the contamination
window was enabled for nominal operations and began opening before each science event. The team continued
to monitor the TQCMS for unexpected or large increases in the beat frequency. These observations were crucial
to alerting the SAGE III team to the elevated rate of contamination during the berthing of CRS-11’s Dragon
capsule in June 2017. As well as characterizing the contamination signatures of visiting vehicles
The starboard facing TQCM faces outboard along the truss of station. There is little station structure in
this direction the largest portion of which is solar panels. This direction was chosen as the stow direction for our
instrument as it provided the best compromise between thermal constraints and having our sensitive surfaces
face a direction with the least potential for contamination. Figure 2 the beat frequency of the starboard TQCM
has displayed an small but steady increase in adsorbed material over the first year on orbit
The ram TQCM faces the direction that approximately half of our science events occur in. Figure 3 is the beat
frequency for this TQCM. Through the first 2 months on orbit material desorbed from the. Beginning in May
2017 material began to adsorb onto the sensor. There were three notable large contamination event observed by
this sensor. These were the visits of SpaceX CRS vehicles 11,12 and 13. There is an obvious correlation between
the beta angle and the amount of material adsorbed onto the sensors during each visit.
The Node 2 facing TQCMs field of view contains a large amount of stations structure. There are two of
these TQCMs the first has a 70◦ half angle field of view centered on node 2, the second is also centered on
node 2 wish a 50◦ half angle field of view. These sensors have adsorbed the most material while on orbit due to
completely encompassing the dragon capsules of CRS-11,12, and 13. Figure4 is the beat frequency of the node
2 focused tqcm. This TQCM has been noisy since SAGE III reached orbit. When the noise was not present
the material adsorption is less than the node 2 sensor but is proportional to that TQCM. Figure 5 is the beat
frequency of the node 2 facing sensor. This sensor has adsorbed the most material while on orbit. Both TQCMs
have observed three periods of elevated absorption rates that correlate to the visits of CRS-11,12, and 13. CRS
related absorption remains on the TQCMs despite multiple attempts to burn off the material by raising the
TEC setpoint to80◦C. The amount of material absorbed during each CRS visit had a positive correlation to
Figure 2. SAGE III Starboard facing TQCM beat frequency
Figure 3. SAGE III Ram facing TQCM beat frequency
how negative the solar beta angle. The more negative the solar beta angle the more material absorbed by the
TQCMs
The nadir facing TQCM has a field of view of empty space. It occasionally will adsorb material coming off
of approaching vehicles. Figure 6 shows the beat frequency of this TQCM. Through one year on orbit this is the
on of two TQCMs a net desorption of material during the first year on orbit.
The wake facing TQCM has a field of view of the rear of station and is the direction that the other half of
Figure 4. SAGE III Node 2 facing focused TQCM beat frequency
Figure 5. SAGE III Node 2 facing TQCM beat frequency
SAGE III science events occur in. The field of view includes several docking locations for Soyuz and Progress
vehicles. Figure 7 shows the beat frequency of the wake TQCM. This sensors beat frequency displays several
temporary increase that correlate to the arrival of either Soyuz of Progress vehicles to station. The amount of
adsorption is correlated with the more negative beta angles after a period of time the material associated with
these vehicles always desorbs from the TQCM. This TQCM also displayed a net desorbtion of material during
SAGE IIIs first year on orbit
Figure 6. SAGE III Nadir facing TQCM beat frequency
Figure 7. SAGE III Wake facing TQCM beat frequency
The PMM facing TQCM has a field of view directly port of the payload centered on the Permanent Multi-
purpose Module. This includes the majority of the stations structure as well the berthing locations of Dragon,
Cygnus and docking locations for Soyuz and Progress vehicles Figure8 is beat frequency of this TQCM. The beat
frequency has visible in it the permanent adsorption associated with Dragon vehicles . As well as the temporary
adsorption characteristic of Soyuz and Progress vehicles
The MLM facing TQCM has an inboard field of view from SAGE IIIs site on ELC 4. This field of view
Figure 8. SAGE III PMM facing TQCM beat frequency
contains docking locations for Soyuz and Progress vehicles and is centered on the site that the Multipurpose
Laboratory module will be added to station. Figure 9 is the beat frequncy of the MLM TQCM. This TQCM
just has the best observations of just Soyuz and Progress vehicles with their characteristic signal of material
absorbing onto the TQCM then desorbing off of the TQCM
Figure 9. SAGE III MLM facing TQCM beat frequency
Though sunwise TQCMs were used these sensors are still affected by incident solar light causing an orbital
dependent noise in the beat frequency. It was observed that this noise grew and shrunk in magnitude dependent
on the solar beta angle. Solar beta affects the amount of illumination the sensor saw leading to a noisier
period when the sensor saw more illumination and a quieter period when the sensor was shadowed by station
architecture.
Adsorption estimates for the SAGE III Instrument sensitive surfaces as well as totals for each TQCM are
listed in Table 1. Adsorption on the sensitive surface were estimated by using a script to create a virtual CMP
on top of the scan head. This virtual CMP rotates with the scan head so that the sensors are always pointing
in the same direction relative to the scan head. The beat frequency signal of the virtual CMP is generated by
combining the changes in beat frequency signals of the other real TQCMS that it shared a field of view with
for each time step. The virtual beat frequency was the result of taking the average change in frequencies of all
TQCMs with a field of view around the virtual sensor for each time step. The resulting delta value was used as
the delta value for the virtual beat frequency for the time step in which it occurred. The adsorption totals for
each TQCM were the differences between the last orbital max frequency value and the first orbital max frequency
value for the first year on orbit.
Table 1. Adsorption estimates for SAGE III sensitive surfaces and adsorption totals for SAGE III TQCMs .
Adsorption Surface Total Beat Frequency Change Total Adsorption A˚ Total Adsorption ngcm2
Contamination Window 137 27.41 269.3
Scan Head Radiator 881.3 176.26 1731.8
Starboard TQCM 117 23.4 229.9
Ram TQCM 86.2 17.2 169.3
Node 2 Focused TQCM 1631.5 326.3 3205.9
Node 2 TQCM 1642.6 328.5 3227.6
Nadir TQCM -117.2 -23.4 -230.3
Wake TQCM -65.4 -13.1 -128.5
PMM TQCM 492.8 98.6 968.3
MLM TQCM 79.5 15.9 156.2
Optical transmission through the contamination window decreases during periods of increased material ad-
sorption. Figure 10 is the contamination window transmission for light wavelengths critical to SAGE III science.
The most notable events have occurred during the visits of of CRS vehicles; where elevated levels of material ad-
sorption have been noticed on the Node 2 TQCMs. The use of the Node 2 TQCMs in determining possible affects
from contamination on window transmission analysis is due to its optimal location well within the viewing pane of
the CRS berth location. Following the CRS-11, CRS-12, CRS-13, and CRS-14 unberthings, the decreased optical
transmission of the contamination window clears-up approximately within one month. With SAGE III/ISS just
recently surpassing one-year on-orbit, it should be noted that the contamination window transmission change
has been minimal, and the impact to SAGE III/ISS science collection is negligible. Currently the internal in-
strument system response has not changed. Indicating that the observed material adsorption has not degraded
the instruments optics and currently SAGE III/ISS has detected no significant long-term optical degradation of
the contamination window
3. CONCLUSION
Through their first year on orbit the SAGE III CMPs and their TQCMs have been instrumental in detecting
periods of increased contamination too the payload. The Node 2 facing TQCMs were pivotal in detecting a large
amount of material being out gassed from CRS vehicles. As a result SAGE III was able to close its contamination
window in a timely fashion during the visit of CRS-11 when elevated material adsorption levels were first detected
and now keeps its contamination window closed during Dragon capsule visits. This has played a large part in
Figure 10. Optical transmission through the contamination door for wavelengths of 290, 320, 350, 450, 520, 850 nm.
The beat frequency for the Node 2 TQCM has been included for ease of correlation of drops in window transmission to
material adsorption
preventing degradation to the optics train. Due to the contamination control efforts prior to launch and knowing
when to inhibit the contamination window while on orbit, SAGE III/ISS has seen no significant degradation in
any of the critical wavelengths for the SAGE III science product. The SAGE III TQCMs have also been able
to observe characteristic adsorption signals for the most common vehicles to visit station. Soyuz and Progress
vehicles will result in a short period of increased material adsorption on the TQCMs the amount of which
correlates to the solar beta angle, this material then desorbs within a month after material adsorption ends. The
characteristic signal observed for Dragon vehicles is that of elevated material adsorption with the rate correlated
again to how negative the solar beta angle is. Unlike Soyuz and Progress the material adsorbed from Dragon
vehicles does not desorb even when the TECs control the TQCM temperature to 80◦C. No meaningful material
adsorption has been observed during the visit of Cygnus vehicles. Analysis of light transmission through the
contamination window has revealed that during the periods that the window is kept closed due to elevated rates
of adsorption on the TQCMs a decrease in signal through the contamination window was observed. However
after the rate of adsorption has returned to normal with in a month the transmission through the window has
returned to normal levels.
ACKNOWLEDGMENTS
The SAGE III Project would like to acknowledge and thank Mr. Carl Maag of T&M Engineering for his
outstanding vision and contributions that made the SAGE III Contamination Monitoring Package possible. Carl
is an internationally recognized expert in contamination control, planetary protection, material and processes,
and space environment and effects and was the contamination control and materials and process lead during
SAGE III development and commissioning.
Carl has previous experience as a principal investigator, co-investigator, and consultant for spaceflight pay-
loads investigating space environmental effects and astrophysics including work with sixteen NASA Space Shuttle
payloads and leadership of an ESA sponsored payload assessing the contamination environment/micrometeoroid
environment of the Russian MIR Space Station. Carls outstanding background made him the right person to
lead development of the CMP concept, provide essential and critical design advise, and devise a measurement
strategy that has made the CMP a useful tool supporting SAGE III on-orbit operations while expanding our
knowledge of the space environment. Thank you Carl the SAGE III CMPs are working great and are providing
data to help all of us advance the state of the art well done!
The SAGE III Project would like to acknowledge and thank the Boeing ISS Space Environments team for
their support in assessing the impacts of Dragon contamination as well as reviewing this paper.
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Analysis of Observed Contamination Through SAGE III's First Year on Orbit

Analysis of Observed Contamination Through SAGE III's First Year on Orbit

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