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Patricia A. Hansen 
NASA, Goddard Space Flight Center 

David W. Hughes, Kristina M. Montt, and Jack J. Triolo 
Swales Aerospace 


Maintaining contamination certification of multi-mission flight hardware is an innovative 
approach to controlling mission costs. Methods for assessing ground induced degradation 
between missions have been employed by the Hubble Space Telescope (HST) Project for the 
multi-mission (servicing) hardware. By maintaining the cleanliness of the hardware between 
missions, and by controlling the materials added to the hardware during modification and 
refurbishment both project flinding for contamination recertification and schedule have been 
significantly reduced. These methods will be discussed and HST hardware data will be 


The Hubble Space Telescope (HST) was designed to be periodically serviced on-orbit during 
its 15 year mission. The Space Transportation System (STS) serves as the platform from which 
the HST is serviced and servicing carriers provide an interface from the Orbiter to the scientific 
instruments and orbital replacement units. While the servicing carriers are configured for each 
mission to accommodate mission unique orbital replacement units, the basic carrier (structure 
and support airborne flight equipment) remains unchanged. The HST servicing carriers were 
flown during the HST Servicing Mission 1 (SMI), STS-61 (December 1993) and the HST SM2, 
STS-82 (February 1997). Currently, the servicing carriers are being reconfigured for the HST 
SMS (May 2000). 

Due to the extreme sensitivity of the HST, scientific instrument, orbital replacement unit 
optics to molecular and particulate contamination, all aspects of a servicing mission are assessed 
for subsequent contamination effects to these optical elements. The assessment begins with the 
basic requirements for the telescope and extends to each mission component. Because of the 
large surface area of the servicing carriers, both outgassing levels and surface cleanliness levels 
are controlled during all aspects of integration, test, launch activities, and on-orbit operations. 

By maintaining the cleanliness of the hardware between niissions, and by controlling the 
materials added to the hardware during modification and refurbishment both project funding for 
contamination recertification and schedule have been significantly reduced. These methods will 
be discussed and HST hardware data will be presented. 


The HST servicing carriers include: the Solar Array Carrier (SAC), the Orbital Replacement 
Unit Carrier (ORUC), the Flight Support System (FSS), the Rigid Array Carrier (RAC), the 
Second Axial Carrier (SAC), and the Multi-Use Lightweight Experiment (MULE). The carriers 
are shown in Figures 1-6 and the servicing mission manifest is illustrated in Table I. The 15' 
long X 15' wide x 15' high Solar Array Carrier functioned as a load isolation system for the Solar 
Array 2 during the First Servicing Mission. For the Second Servicing Mission, the Solar Array 
Carrier was reconfigured, renamed the Second Axial Carrier, and provided a load isolation 
system for the Axial Scientific Instrument Protective Enclosure which in turn provided a 
contamination and thermally controlled environment for the Near Infrared Cosmic Origins 
Spectrograph (NICMOS). 

Table 1. Carrier Mission Manifest 


Flight Support System 
Multi-Use Lightweight Explorer 
Orbital Replacement Unit Carrier 
Rigid Array Carrier 
Second Axial Carrier 
Solar Array Carrier 
Unidentified Carrier(s) 














For the Third Servicing Mission, the Rigid Array Carrier, Orbital Replacement Unit Carrier, 
Flight Support System, and Multi-Use Lightweight Explorer have been manifested and are 
shown in the flight configuration in Figure 7. The Rigid Array Carrier and Orbital Replacement 
Unit Carrier are Spacehab pallets that have been modified to provide scientific instrument and 
orbital replacement unit stowage for the sen/icing mission. The 12' long x 15' wide x 15' high 
Rigid Array carrier functions as a load isolations system for the Solar Array 3 and will be used to 
stow the replaced Solar Array 2 during two extravehicular activity (EVA) days. The most 
contamination sensitive carrier is the 12' long x 15' wide x 15' high ORUC. The Orbital 

Replacement Unit Carrier provides a load isolation system for an Axial Scientific Instrument 
Protective Enclosure (SIPE) and the Fine Guidance Sensor SIPE. These SIPEs, collectively 
known as the BISIPE, provide a contamination and thermally controlled environment for a 
stowed scientific instrument and Fine Guidance Sensor. Because of the optical sensitivity of the 
NICMOS, scientific instruments, and Fine Guidance Sensors, the Second Axial Carrier and the 
Orbital Replacement Unit Carrier are the most contamination sensitive carriers. The 5' long x 
15' wide X 15' high Flight Support System is used as the maintenance platform to berth the HST 
to the Orbiter during the EVAs. The 5' long x 15' wide x 15' high Multi-Use Lightweight 
Explorer provides stowage for orbital replacement units and is shown with the Aft Shroud 
Cooling System radiators mounted. 

The SIPEs provide a thermal environment equivalent to that inside the HST. The warm 
thermal environment not only ensures that the scientific instruments and Fine Guidance Sensors 
will remain within their temperature limits during the EVA. This also ensures that any 
outgassing inside the SIPEs, which would otherwise affect the optical performance, will not 
condense on the scientific instruments or Fine Guidance Sensors. The SIPEs also provide a 
purge interface, which allows the scientific instruments and Fine Guidance Sensors to be purged 
until launch (T-0). Vent restrictor plates (37 ^m mesh) inhibit particulate contamination of the 
scientific instruments or Fine Guidance Sensors during all ground and launch activities. 

Due to the diversity of the orbital replacement units and scientific instruments manifested for 
each flight, the carriers provide the most flexible stowage capability for the servicing mission 
hardware. Because of this flexibility, two carriers will be flown for all planned servicing 
missions - the Orbital Replacement Unit Carrier and the Flight Support System. Because of the 
planned multiple missions of the Orbital Replacement Unit Carrier and Flight Support System 
over a decade, the HST contamination control program looked at the "big picture" to determine 
the most cost effective contamination control approach that both provides the needed 
contamination controlled environment for the scientific instruments and Fine Guidance Sensors 
while controlling cost. Because of the excessive cost and schedule required to recertify the 
molecular outgassing levels of the individual carriers for each servicing mission, the HST 
contamination control program looked at innovative methods to alleviate the recertification of 
the carriers for each mission. Controlling the material added to the carriers and individually 
certifying new hardware prior to integration onto the carrier accomplished this. The storage, 
integration and test environment is also controlled, with the carriers spending the majority of 
these activities in a Class 10,000 (M 5.5) cleanroom. When not in the cleanroom, the carriers are 
double bagged. During storage, the carriers are cleaned periodically to maintain the surface 
cleanliness levels. 


The servicing missions are complex and require that the telescope be exposed to the Orbiter 
(including carriers) environment during the installation of the scientific instruments and Fine 
Guidance Sensors into the HST Aft Shroud. This exposure is typically from one to seven hours. 
During the scientific instrument installation, one EVA crewmember (i.e., an astronaut) enters the 
Aft Shroud to guide both the old instrument out of the telescope and the new instrument into the 
telescope. Because of this exposure and to maintain the Ultraviolet (UV) capabilities of the 

telescope, the contamination requirements placed on both the Orbiter and carriers are quite 
stringent. While one might argue that the scientific instrument is the most contamination 
sensitive element, in reality, maintaining the low contamination flux in the telescope's optical 
path is the primary contamination requirement. 

Neither the Orbiter nor the extravehicular mobility unit (space suit) contamination levels can 
be verified by methods other than by visual examination. Outgassing levels are not measured, 
and by the nature of Orbiter, many materials generally not used around sensitive hardware are 
used for performance. Where possible, materials which are verified to be high outgassing, which 
would not impact the Orbiter performance have been removed for the HST servicing missions. 
In addition, a best effort is made to control contamination during Orbiter processing activities. 

Ground processing activities, Orbiter integration and the overall mission activities are 
assessed for subsequent contamination effects to the HST and the scientific instruments and Fine 
Guidance Sensors for each servicing mission. This assessment begins with the basic 
requirements for the HST and extended to each mission component. An overall contamination 
budget is developed which allocates acceptable degradation among mission phases. The 
servicing mission cleanliness requirements and budgets are set with respect to hardware line-of- 
sight views of sensitive surfaces, purging of the scientific instruments for sustaining critical 
element functional lifetime, Orbiter and EVA effects, Orbiter cleanliness, cleanroom protocol, 
and Kennedy Space Center integration activities. 

Prior to each servicing mission, the HST contamination control philosophy is reviewed to 
determine it applicability to reflown carrier hardware, new scientific instruments, new orbital 
replacement units, and HST optical performance. The current contamination control program 
evolved from both the SMI and SM2 program and has been updated for SMS based on post- 
mission results (1, 2). The servicing carriers met stringent outgassing requirements prior to 
SMI, and the integrity of the outgassing certification of the carriers have been maintained for 
both SM2 and SMS. Only new carriers, and significantly reworked contamination sensitive 
hardware, such as the SEPEs, are certified to the required outgassing rate prior to a servicing 

Telescope and Scientific Instrument Requirements 

To maintain the UV performance of the telescope and therefore, the scientific instruments, 
the telescope contamination requirements address both the surface level cleanliness of the 
Primary and Secondary mirror and the allowable outgassing flux rate for the telescope's optical 
path (known as the hub area). The scientific instrument requirements are based on the optical 
sensitivity of the scientific instrument. 

Primary and Secondary Mirrors 

The particulate contamination requirements are less than a 5 percent maximum area coverage 
for the summation of the Primary and Secondary Mirrors. This was determined pre-launch by 
measuring the obscuration ratio of optical witness mirrors. To date, no scientific instrument data 
has indicated that this requirement has been violated. 

The molecular contamination requirement is less than a 10 percent decrease in reflectance at 
Lyman- Alpha (1216 Angstrom) wavelengths on the Primary and Secondary Mirrors after 5 years 
on-orbit. This was determined pre-launch by measuring optical witness mirrors. Neither 
integrated nor periodic measurements indicated that this requirement had been violated: The 
initial outgassing criteria was 4.33 x 10"" g/cm^-s flux as measured with the mirrors at nominal 
operating temperatures and the collector at -20°C. The optical witness mirror reflectance 
degradation also needed to be less than 3 percent at Lyman-Alpha wavelengths. 

Hub Area 

The light path of the telescope is referred to as the hub area. The four axial and one radial 
scientific instrument apertures, the three Fine Guidance Sensor apertures and the back of the 
primary mirror define this area. To control the amount of contamination entering this area and to 
prevent cross contamination, contamination requirements are flowed down to the scientific 
instruments and Fine Guidance Sensors. The outgassing rate from an instrument aperture or a 
Fine Guidance Sensor aperture into the hub area cannot exceed 1.32 x 10' g/sec. The Fine 
Guidance Sensor's outgassing rate is measured with the instrument at worse case hot operational 
temperatures (approximately 25°C) and the collector at -65°C. Similariy, the surface level 
contamination requirements for any item entering the telescope are Level 400B per MIL-STD 

Aft Shroud 

Four axial scientific instruments are installed in the Aft Shroud. To control the amount of 
contamination entering this area and to prevent cross contamination, the scientific instruments 
must meet minimum surface level cleanliness and outgassing requirements. The scientific 
instrument exterior surface cleanliness level shall not exceed 400B per MIL-STD 1246. The 
outgassing requirement measured at the scientific instruments aft vent cannot exceed an 
equivalent rate of 1.56 x 10"' g/hr-cm^ based on the exterior surface area of the instrument. This 
outgassing rate is measured with the scientific instrument ten degrees above the worse case hot 
operational temperatures and the collector at -20°C. While the largest percentage of the 
outgassed produrts is vented through the telescope's aft vents, there is a small probability that an 
instrument could increase the flux in the hub area, affecting the telescope's performance. 

Scientific Instruments and Fine Guidance Sensors 

The scientific instruments and Fine Guidance Sensors have individual contamination 
requirements based on their optical sensitivity. For example, scientific instruments viewing in 
the UV wavelength regions would have the most sensitivity to molecular contamination. While 
those scientific instruments viewing in the infi-ared wavelength regions would have the greatest 
sensitivity to particulate contamination. The scientific instruments and Fine Guidance Sensors 
are delivered to NASA with verification of internal contamination levels. These levels are 
maintained throughout the integration, test and launch activities through contamination controls 
such as a gaseous Nitrogen purge. 

Orbiter and EVA Effects 

In addition to many hardware cleanliness requirements, numerous analyses were performed 
for the Orbiter environment and EVA contamination impacts. These analyses provided critical 
assessments for controlling on-orbit contamination generating activities and provided the 
necessary quantitative details for imposing ground processing requirements for the Orbiter. The 
major analyses include plume impingement, waste/water dumps, SIPE, extravehicular mobility 
unit (EMU), Orbiter reboost, and HST configuration changes including deployed solar arrays. 
These analyses represent the core of the cleanliness concerns associated with the shuttle and 
EVAs. In addition to the analysis for the Orbiter, cleaning requirements were assessed and 
levied on the Orbiter payload bay. To quantify the effects of the crew compartment on 
subsequent EVAs relative to the particulate environment, two witness plates were flown on STS- 
51. These results were used to determine crew cabin and EMU (space suit) cleanliness 
requirements (4). 

The analysis of the Orbiter plume impingement assessed the degradation of the HST surfaces 
due to gaseous and liquid droplet impingement from thruster firings during maneuvers and 
station keeping operations. Byproducts from the incomplete combustion, such as monomethyl 
hydrazine (MMH)-nitrate, can have detrimental effects on contamination sensitive and thermal 
control surfaces. The station keeping and attitude adjustments considered were low-Z and norm- 
Z modes. Because the byproduct mass flux in the Norm-Z thruster firing case was significant, 
limitations were imposed for Orbiter operations. 

Significant droplets are formed during Orbiter waste/water exhaust. These droplets may pose 
a potential threat to the HST during EVA operations when the telescope's Aft Shroud doors are 
open. The estimation of the maximum effluent released during these dumps is approximately 
320-lbm for each dump. Since this represents a significant amount of released material during 
the HST servicing operations, restrictions were set in both the First Servicing Mission and 
Second Servicing Mission flight rules. All dumps were constrained 120 minutes prior to and 
during EVA to preclude potential impingement on critical area of the HST. 

Because the SIPEs provided cleanliness protection during launch, ascent, and on-orbit 
operations for the scientific instruments, a separate analysis was performed to assess 
contamination impacts. The primary objective was to examine impacts due to the particle 
control redistribution within the SIPEs, molecular flow, and moisture control within the SIPEs. 
All of the elements of this analysis accounted for any degradation to the scientific instruments 
during these phases. 

During an EVA, the amount and type of contamination emitted by the astronaut was 
considered a threat to optical surfaces on the HST. In addition, the astronaut was in close 
proximity (e.g., line of sight) to the scientific instruments and Afl Shroud. The main concern 
was contamination contributions from the EMU (i.e., space suit). The EMU exhaust was 
analyzed and assessed for molecular and particulate contributions. The main byproduct of the 
EMU exhaust was estimated to be 1 to 1.5 Ib/hr of water vapor/ice. Because the sensitive HST 
surface temperatures were above the water condensation temperature for a low pressure 
environment, no contaminant depositions from the EMUs were expected. 

Orbiter Payload Bay Cleanliness Requirements 

The Orbiter payload bay liner and thermal control blankets (forward and aft bulkheads, Bays 
12 and 13) provides thermal control to the payload and may be flown on many mission. A 
reflown liner sertion or thermal control blankets may provide a large outgassing source to a 
payload if contaminated by a previous payload on another mission. As this potential outgassing 
source could not be quantified or outgassing specified identified, a new, unflown payload bay 
liner was requested for the entire payload bay. The thermal blankets could not be replaced due to 
excessive cost; however, they were cleaned with an isopropyl alcohol (IPA)/deionized (DI) water 
mixture and verified to have no significant fluorescing molecular contamination. Small amounts 
of molecular contamination could be tolerated, but were evaluated on a case-by-case basis and 
were dependent on location within the payload bay. 

Based on the hardware cleanliness requirements, for both the First and Second Servicing 
Mission a new payload bay liner was cleaned to visibly clean highly sensitive (VCHS), per 
Johnson Space Center Document Number SNC-0005C, with an IPA/DI water mixture. During 
the Orbiter servicing in the Orbiter Processing Facility (OFF), the payload bay liner and thermal 
blankets including bilge area and wire trays were vacuumed every three days. Both the Goddard 
Space Flight Center and Kennedy Space Center contamination teams were success orientated, 
and as such, cleaned the payload bay to VCHS at the Pad Payload Changeout Room (PCR). 
Vertical cleaning at the Pad provided both the best access to all levels, but also provided a top 
down cleaning approach so that any particles cleaned from the level above, but not captured, 
would fall to a level which would be subsequently cleaned. Again, the thermal blankets were 
verified to have no significant fluorescing molecular contamination. 

Cleanroom Protocol 

The biggest contamination threat to the servicing carriers is the personnel working on or 
around them. To control this threat, the servicing carriers spend the majority of their time in a 
Class 10,000 (M 5.5) cleanroom. The cleanroom protocol, detailed in Reference 1, was derived 
from the hardware requirements, contamination control practices, and data from previous 
missions. Personnel constraints, cleanroom operating procedures, and site management issues 
are addressed for each facility in which the servicing mission hardware is assembled, integrated 
or tested. Activities, which have the potential to contaminate the hardware, were identified and 
controlled by procedure. These activities include crew familiarizations, alignment and 
envelopment measurements with the High Fidelity Mechanical Simulator and scientific 
instrument to SIPE fit checks and integration. 

Launch site integration activities are also a challenge to maintaining the servicing carriers 
contamination levels. Because of their size, the servicing carriers must be integrated in Class 
100,000 (M 6.5) facilities. However, the Class 10,000 (M 5.5) cleanroom protocols are used 
which typically results in a significantly lower operating level - Class 10,000 to Class 20,000 
during typical integration activities. During the scientific instrument insertion into the SIPE, the 
cleanroom is run as a Class 10,000 (M 5.5) cleanroom with strict personnel limits (5). For both 
the First and Second Servicing Missions, these cleanroom protocols have resulted in hardware 
contamination levels significantly below the required limit. 


The post-mission surface cleanliness results are similar for both SMI and SM2. These levels 
were measured while the carriers were in the payload bay at the Orbiter Processing Facility 
within hours of the payload bay door opening. For both SMI and SM2, the particle levels 
ranged from Level 200 to Level 2000, per MIL-STD 1246. Those samples, which measured 
Level 2000, typically included clothing fibers. Two swab samples were taken from each carrier, 
one along the centerline and one from either the starboard or port sides of the carrier depending 
on personnel access. These samples measured less than 1.0 mg/m^. As the carriers were 
nominally 2.0 mg/m^ just prior to launch and no suspicious species were identified, it was 
concluded that neither the telescope nor the Orbiter had contaminated the carriers. 

It should be noted that after the Second Servicing Mission, prior to the payload bay door 
opening, work was performed on the Orbiter Thermal Protection System located on the payload 
bay doors. When the carriers were inspected, debris was found on the carriers along the 
centerline of the Orbiter. The debris was later identified through chemical analyses to be RTV 
560, the adhesive used to bond the Thermal Protection System to the Orbiter. The payload bay 
doors do not form a tight seal and the RTV fell into the payload bay and onto the carriers while 
the Thermal Protection System work was performed. The cleanliness levels above do not 
include this debris in the particle level results. 


A contamination control program has been developed for multi-mission flight hardware, 
which must meet stringent contamination requirements. The HST servicing carriers are integral 
to the HST servicing missions, but cannot be a potential contamination source to the telescope 
during EVA activities. Post-mission results from two servicing missions indicate that the 
servicing carriers do not contaminate the telescope and conversely, the HST and the Orbiter do 
not contaminate the servicing carriers. The main points of the HST servicing carrier 
contamination control program that are applicable to any multi-mission hardware are listed 

1. Store, integrate, and test multi-mission hardware in stringently controlled 
environments, preferably a cleanroom. When not in a cleanroom, double bag 
hardware with approved bagging material. 

2. Control the type and amount of all added materials to the multi-mission hardware so 
that outgassing limits are not violated. Verify, by test, that the batch of material 
used will not be a significant contamination source. 

3. Certify outgassing levels of added (new) hardware at the sub-assembly level prior 
to integration onto the multi-mission hardware. 

4. Maintain surface cleanliness levels during storage or low work periods. Periodic 
cleaning is required for multi-mission hardware that is not bagged. 


The authors would like to thank the many people whose collaborative effort ensures the HST 
Servicing Mission successes. The NSI Contamination Control Group who maintains the 
hardware cleanliness levels: Wayne Geer, John Di Bartolo, Leon Bailey, Jeff Mobley, Joe 
Hammerbacher, Scott Lange, Joe Colony, and Barry. Greenberg. The NASA team who verifies 
all our surface levels: Alex Montoya, Mary Ayers-Treusdell, Doris Jallice, Neil Walter (Unisys), 
John Scialdone, Ben Reed (Unisys), and Fred Gross (Unisys). The modeling team who 
determines our cleanliness requirements: Shaun Thomson (NASA), Glenn Rosecrans (SA), 
Aleck Lee (LMMS), Mike Fong (LMMS), and Cliff Gee (LMMS). The Orbiter contamination 
team: Sally Hill (USA), Chris Webber (USA), Dave Baska (Boeing), Wayne Batungbacal 
(USA), Chuck Calin (USA), Jean Abernathy (NASA), Martin Mc Clellan (USA), Carol Nguyen 
(Boeing), and Gene Borson (SA). The purge team who provided a continuous purge to the 
carriers for five launch site facilities: Craig Chivatero (LMMS), Schonda Rodriguez (NASA), 
Max Swanko (NSI), and Larry Dell (LMTO). 


1. R.J. Hedgeland, P. A. Hansen, and D.W. Hughes, "An Integrated Approach for 
Contamination Control and Verification for the Hubble Space Telescope First Servicing 
Mission", SPIE 2216: 10-21, July 1994. 

2. P. A. Hansen, et. al., "Hubble Space Telescope Second Servicing Mission Contamination 
Control Program", SPIE 2864: 27-35, August 1996. 

3. P. A. Hansen and C.R. Maag, "Contamination Control Program for the Hubble Space 
Telescope Second Servicing Mission", Proceedings of the 7^ International Symposium on 
'Materials in Space Environment', SP-399: 135-142, June 1997. 

4. P. A. Hansen, R.J. Hedgeland, C.R. Maag, and C.H. Seaman, "Results of STS-51 Orbiter 
Crew Compartment Contamination Generation and EVA Payload Bay Transfer Experiment", 
SPIE 2261: 2-9, July 1994. 

5. D.W. Hughes, R.J. Hedgeland, W.C. Geer, and B.N. Greenberg, "Maintaining a Class M 5.5 
Environment in a Class M 6.5 Cleanroom", SPIE 2261: 46-57, July 1994. 


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Figure 7. The HST SMS Carrier Configuration 

The servicing carriers are shown integrated with the Orbiter. From the Aft (tail) forward are the 

MULE, FSS, ORUC and RAC. The Orbiter external airlock is shown forward of the RAC. 


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