The Mars Science Laboratory Organic Check Material
- First Online:
- Cite this article as:
- Conrad, P.G., Eigenbrode, J.L., Von der Heydt, M.O. et al. Space Sci Rev (2012) 170: 479. doi:10.1007/s11214-012-9893-1
- 1.2k Downloads
Mars Science Laboratory’s Curiosity rover carries a set of five external verification standards in hermetically sealed containers that can be sampled as would be a Martian rock, by drilling and then portioning into the solid sample inlet of the Sample Analysis at Mars (SAM) suite. Each organic check material (OCM) canister contains a porous ceramic solid, which has been doped with a fluorinated hydrocarbon marker that can be detected by SAM. The purpose of the OCM is to serve as a verification tool for the organic cleanliness of those parts of the sample chain that cannot be cleaned other than by dilution, i.e., repeated sampling of Martian rock. SAM possesses internal calibrants for verification of both its performance and its internal cleanliness, and the OCM is not used for that purpose. Each OCM unit is designed for one use only, and the choice to do so will be made by the project science group (PSG).
KeywordsMarsMars science laboratoryMSLSAMOrganic check materialOCMContaminationSample chain
The Mars Science Laboratory (MSL) mission will investigate the habitability potential of Gale Crater, a location near the martian equator at 4∘36′0″ S, 137∘12′0″ E (Grotzinger et al. 2012). This location has been advanced as a potential target of astrobiological significance (Cabrol et al. 1999; Pelkey and Jakosky 2002; Pelkey et al. 2004). To contemplate the daunting task of evaluating whether the planet is presently or was formerly capable of supporting life, assumptions must be made regarding the requirements for habitable environments based upon what we find associated with life on Earth. Factors such as water, a source of energy and organic (hydrocarbon) compounds are well-accepted evidence of an environment’s potential to allow the sustenance of life on Earth, and they will be important criteria for the evaluation of habitability potential at Gale crater through time as interpreted in the investigation of Gale’s deep stratigraphic record. The nature and distribution of organic material on Mars is of particular interest because while there are tantalizing clues (e.g., Mumma et al. 2009) of methane in the martian atmosphere, and a presumed in-fall of organic material by meteorite to the surface, we do not presently know whether the conditions on the martian surface or shallow subsurface will allow organic chemical reactions that would be necessary for life to take place. We do know that the surface of Mars appears to be an extremely oxidizing environment, so an important first order question to be answered is whether there is or was enough range in the redox potential of martian surface environments to allow for the preservation of reduced carbon phases somewhere in the stratigraphic record that is available to us at Gale Crater.
Mars Science Laboratory is equipped with instruments that can make a variety of chemical measurements, including sensitive detections of organic chemicals and the ratios of key isotopes with astrobiological significance. The payload is described in detail in the other articles in this issue. The investigation that will conduct a detailed molecular inventory of the solid samples that Curiosity is directed to acquire is The Sample Analysis at Mars (SAM) experiment. SAM is a trio of instruments—quadrupole mass spectrometer (QMS), gas chromatograph (GC) and tunable laser spectrometer (TLS) that are supported by a multiple sample manipulation system and a flexible gas processing system with two high temperature (1000 °C) pyrolysis ovens (Mahaffy et al. 2012). The SAM suite is also equipped with chemical extraction capability for a limited number of samples (nine) so that organic molecules not readily detected by pyrolysis might be derivatized and thus detectable by SAM, e.g. amino acids and nucleobases. The performance of SAM is such that it is capable of detecting very trace quantities of hydrocarbons, thus if there were organic contaminants either within the instrument system or elsewhere in the sample chain, they could mask potentially detectable analytes. So it is important to maintain a very high level of organic cleanliness (better than 40 ppbv) along the sample chain. While the SAM suite can bake itself out, the external parts of the sample chain cannot (drill, portioner, scoop and the SAM solid sample inlet tubes (SSIT) or their covers), hence their cleanliness must be periodically evaluated in some way in order to understand SAM’s findings with respect to organic materials on Mars.
In the Viking GCMS analyses, trace chloro-hydrocarbons were detected but originally thought to be products of solvents used to clean the hardware (Biemann et al. 1977). Now others have argued they could be products of perchlorate/organic matter chemistry in martian regolith (Navarro-Gonzalez et al. 2010). It is important to avoid such a situation with SAM/MSL. Note that Viking only had one oven to check GCMS background and no organic check material to understand sample path contamination.
In laboratory experiments, it is standard practice to first analyze a blank sample (that is, one free of detectable analytes), followed by a standard calibrant (Skoog et al. 2004).
The SAM investigation is able to detect trace levels of organic molecules, so the investigation must be able to distinguish between organic chemicals that might be found on Mars and contamination that traveled there with the spacecraft. The SAM investigation does carry internal calibrants (spiked blanks) against which to compare the internal parts of SAM that can be cleaned, excepting the SAM solid sample inlet tubes (SSIT). Without an external calibrant that can be contacted and processed by the rover’s sampling system (SA-SPaH) and the SAM SSITs, there is no way to check for contamination associated with those parts of the sample chain.
If SAM were to detect organic molecules on Mars, this would be an important milestone in solar system exploration. Cleanliness of the spacecraft must be proven in order to determine that we are not detecting Earth-origin chemistry. So the sampling chain must be checked on Mars, because we must assume the possibility that the spacecraft materials could have undergone changes after launch and landing. Also, the martian environment is not identical to the conditions under which our pre-launch contamination testing was done, so it must be verified again in situ. The primary role of the MSL OCM is to clearly differentiate between terrestrial contamination and indigenous or meteoric martian materials. We must unambiguously verify the assumption that both SAM and the SA-SPaH are clean.
Six to ten organic check material samples are required to accurately assess levels of terrestrial contamination a few times during the baseline mission of one martian year. If only one OCM sample were to be flown, it could be used early in the mission if organic material is detected in a martian sample. This would leave MSL in a compromised position should the need for another OCM standard arise later in the mission, such as a suspected release of volatile contaminants or analysis of a solid sample containing new (as yet unobserved) organic compounds.
2 Scientific Objective and Requirements
The Organic Check Material is a verification tool for the organic cleanliness of those parts of the sample chain that cannot be cleaned other than by dilution with martian samples. By sample chain, we refer to everything that touches the sample before it arrives in a SAM sample cup, including SAM’s solid sample inlet tubes (SSITs). In order to accomplish the verification, the OCM must be processed through the entire sample chain from drilling and portioning to delivery into SAM through its solid sample inlet tubes. The SAM instrument suite (Mahaffy et al. 2012, this issue) is capable of cleaning itself by heating, and then verifying its cleanliness by running evolved gas blanks from empty sample cups. However the SSITs and the external sample processing components, e.g., drill, sample-portioner and scoop cannot be baked out; they can only be cleaned by dilution—repeated processing of martian material with the assumption that this process will dilute any contamination in the external sample chain (including SSITs). The dilution process can only be verified with a SAM solid sample experiment, so a sample of unknown (or not yet verified) cleanliness would have to be ingested by SAM. Without having knowledge of the native inventory of possible organics in the martian samples, it would be difficult to know whether detected hydrocarbons are coming from the hardware or indigenous to the rock unless the putative contaminant were known to be produced only by non-naturally occurring processes. Evaluating the cleanliness of a sample with a known initial cleanliness is the way out of the ambiguity, and the OCM serves that purpose.
2.1 Usage Concept
The OCM is a very limited resource on MSL, so to invoke its use requires agreement by the project science group (PSG). If SAM were to make a detection of organic compounds in a martian sample, certainly that experiment would be repeated, and then confirmation that the detection is not some sort of terrestrial contamination would be required. On Earth, the convention is to run a standard in advance of the unknown to verify the condition of the analytical tool, however on Mars, each use of an instrument (and of the SA-SPaH) has some risk associated with it, so it becomes important to interrogate martian samples as a high priority. The SAM solid sample experiments include background scans of the QMS before introduction of solids (Mahaffy et al. 2012, this issue), so there are procedural “blanks” built into the SAM experiment, and when needed, its internal calibration standards can be analyzed. The OCM not employed as a verification tool for SAM performance, but only to determine that the external sample chain has not contaminated a martian sample that tests positive for organic compounds.
In that regard, if there is reason to suspect that the initial state of cleanliness of the external sample chain is poor, one might argue that it not be used until repeated dilution cleaning cycles are executed, and in that case, the OCM would be needed to verify the efficacy of the dilution cleaning (Anderson et al. 2012, this issue).
With respect to management of resources for the duration of the nominal mission, if organic compounds are found early in the mission or become commonly associated with a particular rock facies or mineral phase, the strategic plan for preserving one or two OCM units for late in the mission or perhaps an extended mission (if deemed likely) would have to be considered.
The Organic Blank Working Group initially recommended that the OCM be crushed and somehow accessible to the soil scoop so that its cleanliness could also be verified, however this is not possible given the architecture of SA-SPaH. Curiosity’s rotary-percussive drill powders the rock as it penetrates the target and it conducts the powders directly into the portioner. The scoop and drill are arranged on the end of the rover arm in such a way that it is not possible to sample the OCM with the drill and somehow place the powdered OCM into the scoop. Should the scooped samples repeatedly yield results suspected to be self-induced contamination, the only path to verification would be elimination of other verifiable components in the sample chain and then an attempted mitigation by dilution cleaning.
thermal stability over the range of temperatures expected in cruise and on Mars both diurnally and seasonally
resistance to attack by ionizing radiation over the nominal mission life time, including background galactic cosmic rays, solar energetic particles and UV radiation
chemical compatibility with the inorganic matrix, e.g., non reactive and easily dispersed throughout the matrix compositional simplicity—avoids functional groups that could mask analytical targets of interest
organically clean as verified by levels <5 ppb of detectable hydrocarbon upon pyrolysis to 900 °C in SAM
the material must release no more than 0.1 % of its mass in non-hydrocarbon volatiles upon pyrolysis to 900 °C
the material must have a compressive strength <230 MPa in order to avoid excessive wear on the SA-SPaH drill bits
the material must have interconnected pore space in order to distribute the dopant throughout the material.
The material must not present a hazard to the SA-SPaH hardware by splintering into shards that could damage the drill, seals or portioner
In summary, the OCM material had to be clean, possess a marker that could ensure its detectability by SAM, not interfere with the scientific targets of interest on Mars, and it had to last in its pristine state throughout the duration of the nominal mission, one martian year.
3 Inorganic Matrix
Ceramics considered for the inorganic matrix material
Compressive strength [MPa]
Max T [°C]
0 (for glaze)
HP technical ceramics
1500 but softens over 1000
Data sheet FS120 fused silica
SiO2 and <0.5 % NaO
Amorphous, although during sintering, trace amounts of cristobalite can be formed at 1100 °C
Silica granules ranging from 10–500 microns and sintered
10 m2/g (estimated)
10–15 MPa (estimated)
Stable to 1500 °C, although above 1000 °C, cristobalite may form
3.1 FS-120 Testing
This is meaningful because the SA-SPaH portioning apparatus sieves the samples delivered to SAM and CheMin to exclude grains >150 μm, and the FS-120 will produce enough grains of sufficient size to deliver more than enough <150 μm sample portions. At the time this manuscript was in preparation, optimization of the MSL testbed model of the CHIMRA is ongoing and the behavior of in the OCM material during drilling and portioning will be better characterized.
4 Organic Dopant
Candidate fluorocarbon marker compounds
Boiling point (°C)
Vapor pressure (Torr)
Vapor pressure (Pa)
Poor interaction,* too volatile
2, 3(a), 3(b)
Poor interaction,* too volatile
Poor interaction,* too volatile
Poor interaction,* too volatile
Poor interaction,* too volatile
Poor interaction,* excessive carryover
2, 3(a), 3(b)
Poorly retained, too volatile
Well retained, too volatile
2, 3(a), 3(b)
In general, polycyclic aromatics adsorbed on surfaces are photo reactive in the presence of reactive oxidizing gases. However, the OCM material is hermetically sealed in a metal can until it is sampled, and minimal environmental exposure. During acquisition of the OCM sample, hardware presents a tortuous path which is likewise not going to expose the OCM sample to light. The radiation stability of polycyclic aromatics is quite robust, and every other moiety on the polycyclic aromatic hydrocarbon, e.g., hydrogen, is more likely to be emitted from the molecule before the fluorine, based upon the 70 eV beta radiation used to ionize the species in a mass spectrometer. Other inelastic collisions due to particle radiation will have similar results in the gas phase, and energy transfer to the surfaces to which the molecules are adhered will dominate the energetic decay of the radiation interactions in the aromatic hydrocarbons, like the relaxation of excited state toluene in air and low vacuum, which is dependent only upon intermolecular collision rates. These are strong reasons for selection of fluorinated polycyclic aromatics for the OCM application: their radiation stability, their unique ionization properties, their long-term molecular stability and chromatographic properties. The radiation dose at the surface of Mars is below the level that degradation of the material to any significant extent can be expected.
5 OCM Containment System
The requirements for the OCM could not be met without some type of containment to protect its cleanliness and prevent potential loss of the marker. Several engineering constraints were placed upon the containment system to avoid risk to the SA-SPaH as well. One such constraint was to avoid adding more actuators and associated heaters as would be needed for a motorized cover. Another was to avoid having the drill pierce through metal, either by drilling or puncturing, although this latter constraint was ultimately relaxed after testing demonstrated minimal risk. Other requirements for containment included individually sealed OCM canisters (to maintain cleanliness). Individual, single-use canisters minimize the potential for contamination from use to use. The hermetic seals had to be maintained with a leak rate no greater than 10−9 atm-cm3 s−1 He with canister pressure lower than Mars atmosphere shown by test and analysis, and there needed to be some means of verifying the seal integrity on ground. Access ports for doping the bricks with the fluorocarbon markers were required as well, and these would also be verifiably sealed.
The dimensions of the OCM bricks (and hence the containment canisters) were driven by (a) a need to accommodate the depth to which martian rocks were to be drilled—4 cm plus some margin to avoid drilling through the entire brick and hitting the bottom of the can, and (b) the lateral accommodation of up to 13 mm radial two degree angular drill misalignment. The reason for the depth requirement to match the sampling depth of the martian samples was to ensure that the entire length of the drill bit that touches rock be verified for cleanliness.
Canister components and assembly procedures were required to be sufficiently clean to guarantee that the collected sample be free from organic contamination greater than 36 PPB and this number had to be verifiable.
The OCM bricks had to be immobilized within the cans so that they would not rotate along with the drill, and the canister units had to be secured and protected against all loads, including preloading and drilling, and they had to be accessible to the drill, so the front panel of the rover was selected as the mounting site for the OCM assembly. There was insufficient space to accommodate more than five canisters, so the original recommendation of six to eight units could not be met.
Various containment strategies were considered. A single large box with motorized cover holding several OCM samples was dismissed because (a) after first use, all subsequent samples would have successively been exposed to more opportunities for contaminations, (b) the use of a motorized lid would not only have required yet another actuator and heater, but the requirements for its use might have limited accessibility of the OCM for thermal considerations, and (c) the single lid is, of course, a single point of failure risk. We also investigated the use of non-porous ceramic glazing with which to encapsulate each brick. This strategy also offered more risks than solutions: the physical properties of such glazes make them brittle and there is significant cracking under preload and drilling, and they also would have presented a challenge for providing access ports to the porous brick for doping with the marker compounds.
The five canisters are held in place on the front of Curiosity by a mounting plate, also constructed of the 6Al–4V Ti (Fig. 4). The foil surfaces of the can lids are flush with the surface of the mounting plate, and the cans are mounted by screwing them to the rear of the plate with the mounting flanges on the cans as shown in Fig. 6b. The front surface of the plate also includes prong contact pads for the drill sensors against which the preload is applied for puncture of the lid and for drilling (Fig. 4b).
6 Preparation of Flight Units
6.1 FS-120 Bricks
The OCM cylinders were verified to be within size tolerances at the time of manufacture at HP Technical Ceramics, Ltd in Sheffield (65+0.5/−0 mm×57+0.1/−0.2 mm). At JPL, the bricks were subsequently machined so that the top rim was chamfered and an alignment slot created in the base into which the coupling plate would secure the brick against rotation (Fig. 2).
The bricks were baked at 550 °C for four hours under gentle flow of Earth atmospheric gas to combust any residual material. While fused silica will tolerate a higher temperature bakeout to 1000 °C without risking the formation of cristobalite (high temperature SiO2 crystals), it is important not to dehydrate the silica too much, which diminishes its capability to adsorb the dopant fluorocarbon markers. Cleaned bricks were then wrapped in double sheets of baked ultra high vacuum foil until installation into the containment canisters.
6.2 Encapsulation Hardware
All hardware components were precision cleaned by a multi-step procedure. Note that all solvents were HPLC grade to minimize the potential for contamination by traces of other compounds. First the parts were immersed in a clean beaker of HPLC grade acetone and sonicated for 2 to 5 minutes. Then they were immersed in HPLC grade hexanes under sonication for another 2 to 5 minutes. A third sonication in HPLC grade isopropyl alcohol (IPA) for 2 to 5 minutes followed this step. A final rinse was then performed on a class 100 laminar flow bench using HPLC grade hexanes, wetting all hardware surfaces. The rinse solvent was collected in a cleaned vessel and labeled for later verification analysis. The cleaning procedure was completed by forcing the hardware dry with ultra high purity N2 gas.
6.3 Fluorocarbon Marker Compounds
Variables used in calculations
Total brick volume minus pores
Total brick volume including pores
1 FN atomic mass
1 FN density
3 FP atomic mass
Calculations for determining the amount of dopants needed per brick
10 nmol/0.05 cm3 brick×10−9 mol/nmol×105.45 cm3 brick=
2.11×10−5 mol of each dopant per brick
(2.11×10−5 mol 1FN×146.17 g/mol×1000 μl/ml)/1.330 g/ml=
2.3 μl 1 FN per brick
2.11×10−5 mol 3 FP×196.1 g/mol×1000 mg/g=
4.14 mg 3 FP per brick
Ratio 1 FN/3 FP (μl/mg) =
Target verses actual amounts of dopants per brick
Number of bricks*
Amount of 3 FP in dopant solution
Amount of 1 FN in dopant solution***
Amount of 3 FP per brick
Amount of 1 FN per brick
Amount of 3 FP expected per 0.05 cm3 brick
8.65 nmol (5.50 nmol)
Amount of 1 FN expected per 0.05 cm3 brick
26.0 nmol (16.5 nmol)
6.4 Assembly and Doping of OCM Units
6.4.1 Hardware and Bricks
After the bricks, canisters, doping port/gland assemblies and brick retention hardware were cleaned, the OCM units were assembled in a class 1000 clean room at the Jet Propulsion Laboratory. All personnel donned full clean-room garb: “bunny suits”, masks and double gloves. Work surfaces were covered with clean sheets of ultra high vacuum (UHV) foil for each assembly.
The flow of canister assembly was designed to minimize the chance of contamination and units were fully assembled one at a time. First, the doping ports were installed and their leak-tight seal checked with a helium leak detector. Because the seals were tested prior to installation of the bricks and welded foil lids, a special leak-test cover and viton O-ring were used and the actual gland port assemblies closed off at the distal ends of the nickel tubes by the Swagelok valves. All hardware was handled with precision-cleaned tools (cleaned by the multi-step process described in Sect. 6.2). Following successful installation of the doping ports (two per can as shown in Fig. 6) The coupling plate was installed in the bottom of the can, then the brick, by peeling away one layer of foil and grasping the brick by the remaining layer whilst lowering it into the can and pressing it onto the coupling plate. The retaining hardware was then installed by pressing the conical face of a clamp ring over the chamfered edge of the brick and then a wave spring and spiral retaining ring. Shims were employed beneath the wave spring to maintain a consistent spring height, and shim thickness recorded for each unit.
The units were then ready for closure with the welded lid. The welding procedure included a custom fixture on a rotational stage. The foil disks were positioned using the welder operated by the laser-welding technician. Helium flow was established for five minutes prior to the welding operation, and then the welding was executed. Following the welding procedure, a helium leak test was conducted by using one of the Swagelok valves on the gland ports to establish test pressure on the leak tester, and then flowing helium at the weld site. If the leak rate was less than 1×10−9 atm-cm3 s−1 He, the weld was deemed successful, and the can gently purged with nitrogen and valves closed. A protective aluminum cover was installed over the foil lid.
Once the units were assembled, they were double-wrapped in baked UHV foil, enclosed in two dry nitrogen-purged Amerstat bags and labeled for shipment. Fifteen units (five for flight, five for the SAM testbed, two flight spares, two manufacturing contingency units and one qualification unit) were hand carried to NASA Goddard Space Flight Center for the doping operations.
The doping manifold was designed to not only enable a uniform injection process for each unit, but to minimize the potential for contamination and allow for verification of the cleanliness of the injection pathway as well as verification of the fluorocarbon marker compounds downstream of the injected canister.
Assemble a precision-cleaned injection adaptor into doping manifold.
Attach a bypass tube from canister input and output manifold lines and pump down the manifold with N2, then take a residual gas analysis (RGA) measurement of manifold background. Also collect a tenax trap sample to record manifold background. Then bypass the trap.
Connect the OCM unit into doping manifold (see Fig. 8) and open inlet valve.
Wrap the manifold with heating tape and thermocouples and heat to ∼75 °C±15 °C to encourage migration of the dopant toward the cooler brick
Inject dopant through the syringe adaptor into the cans.
Cool until manifold temperature is down to 40 °C and remove OCM can from manifold and place in tray for baking at 250 °C for four hours.
6.4.3 Pinch-off and Sealing of Dopant Ports
The brick canisters were always wrapped in a layer of UHV foil during doping and heating so that handling would be minimized.
6.5 Verification of Dopant Distribution
OCM bricks were sampled with a solvent cleaned steel ice pick and hammer and directly collected in UHV foil. About 250 milligrams of each OCM brick sample were placed in an ashed glass tube immediately upon removal from the brick. All samples were collected in duplicate. Blank material (unused FS120 brick ashed at 550 °C for 3 hours) placed in a glass tube at the same time as the other samples was interspersed in the analytical sequence.
Samples were analyzed via automated thermal desorption-gas chromatography mass spectrometry (TD-GCMS) using a Water Quattro Micro GC fitted with a Gerstel thermal desorption unit attached to a pressure-temperature volatilization (PTV) inlet (Gerstel CIS4). The Quattro Micro GC was tuned to optimize detection for 50–550 m/z scans (on MS2) at 5000 scans/second and enhance signal to noise. Samples were thermally desorbed at 300 °C for 3 minutes and condensed in the inlet at 50 °C before being transferred to the column at 300 °C. The analytes were separated on a RTX-5ms column (30 meter length, 250 micrometer i.d., 25 micrometer film thickness) that was held for 1 min at 50 °C then ramped at 6 °C/minute to 320 °C. Dopants were detected based on matching GC retention time and mass spectra of the original dopant solution.
FS-120 powder collected from the OCM verification brick
3-FP nmol/ 0.05cc*
1-FN nmol/ 0.05cc*
1σ standard deviation
1σ standard deviation
12.5 mm depth
17.5 mm depth
24.5 mm depth
34.5 mm depth
41 mm depth
48 mm depth
50 mm depth
The MSL Organic Check Material units are a limited resource on the Curiosity rover. The retention of five identical units at the SAM test bed provides an opportunity to investigate hypothetical interactions of martian materials or potential contaminants with the OCM in an analogue investigation. The accommodation of multiple units allows operational flexibility throughout the length of the mission. The approach to the fabrication and containment of this external standard is a new capability in extraterrestrial chemical characterization and will support the interpretation of such experiments as Curiosity enables our robotic exploration of Gale Crater.
The study group was convened in April 2007 and consisted of M. Anderson (JPL analytical chemist), D. Blake (CheMin PI), P. Conrad (SAM co-I & IS), J. Crisp (MSL Dep. Proj. Scientist), P. Mahaffy (SAM PI), D. Ming (CheMin & SAM Co-I), R. Morris (CheMin and SAM Co-I), A. Sessions (Caltech professor), R. Summons (MIT professor), R. Welch (MSL Dep. Proj. System Engineer). Ex-officio: E. Stolper (then MSL Proj. Scientist), M. Meyer (MSL Prog. Scientist).
At JPL: Thanks to William Abbey for technical assistance in evaluation of ceramic materials, and Andrew Etters for early conceptual work on the encapsulation. James Pura provided technical assistance during the machining of the bricks, and Mark Anderson conducted the cleanliness analysis. John Bousman provided patience and expertise in the precision cleaning and assembly of all containment hardware. Jerry Mulder executed the laser welding and Jim Okuno conducted the leak checks and Domenic Aldi conducted the mechanical tests. At GSFC: Many kudos to Chris Johnson and Ryan Wilkinson for fabrication of the doping manifold, and Wilkinson again for technical assistance during doping and executing the pinch-off operations. Marvin Noriega also assisted with pinch-off. Jeff Mobley did the final cleaning and packaging of the assembled flight units prior to delivery to JPL. Thanks also to Dennis Nehl for thermal monitoring during the doping procedure. Rob Taminelli provided a specialty configuration for the clean room operations at GSFC and provided an extra set of hands during the doping and pinch-off procedures. Amy McAdam assisted with XRD and XRF analysis of the verification brick. Melissa Floyd assisted with GCMS analysis of the verification brick. At HP Technical Ceramics: Tim Wang went beyond the call of duty for a vendor providing excellent technical advice and execution of extraordinary cleanliness measures during fabrication of the bricks.
This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.