1、Designation: E2900 12Standard Practice forSpacecraft Hardware Thermal Vacuum Bakeout1This standard is issued under the fixed designation E2900; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice establishes methods for thermal vacuumbakeout of spacecraft and spacecraft components.1.2 This practice defines the equipment, envi
3、ronment, andcertification criteria for each type of bakeout.1.3 The methods defined in this practice are intended toreduce component outgassing rates to levels necessary to meetmission performance requirements of the contamination sensi-tive hardware. Times, temperatures, and configurations con-tain
4、ed in this document have been found to provide satisfactoryresults. Experienced operators may find that other, similartimes, temperatures and configurations have provided satisfac-tory results. If deviations from these criteria are deemedappropriate, they should be detailed in the bakeout report.1.4
5、 This practice describes three bakeout methods: MethodA, using prescribed time and pressure criteria; Method B, usingprescribed QCM stabilization rate criteria; and Method C,which measures the QCM deposition rate.1.5 Determination of the acceptable molecular outgassing,selection of the bakeout metho
6、d, and determination of thespecific test completion criteria are the responsibility of theuser organization.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety
7、and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E1546 Guide for Development of Fire-Hazard-AssessmentStandardsE296 Practice for Ionization Gage Application to SpaceSimulatorsE834 Practice for Determining Vacuum C
8、hamber GaseousEnvironment Using a Cold FingerE1234 Practice for Handling, Transporting, and InstallingNonvolatile Residue (NVR) Sample Plates Used in Envi-ronmentally Controlled Areas for SpacecraftE1235 Test Method for Gravimetric Determination of Non-volatile Residue (NVR) in Environmentally Contr
9、olledAreas for SpacecraftE1549 Specification for ESD Controlled Garments Requiredin Cleanrooms and Controlled Environments for Space-craft for Non-Hazardous and Hazardous OperationsE1559 Test Method for Contamination Outgassing Charac-teristics of Spacecraft MaterialsE1560 Test Method for Gravimetri
10、c Determination of Non-volatile Residue From Cleanroom WipersE1731 Test Method for Gravimetric Determination of Non-volatile Residue from Cleanroom GlovesE2311 Practice for QCM Measurement of Spacecraft Mo-lecular Contamination in Space2.2 Other Standards:IEST-STD-CC1246 Product Cleanliness Levels a
11、nd Con-tamination Control Program3MIL-STD-1246 Product Cleanliness Levels and Contamina-tion Control Program4,5MIL-P-27401 Propellant Pressurizing Agent, Nitrogen5ISO-14644 Cleanrooms and associated clean environments3FED-STD-209 Federal Standard, Airborne ParticulateCleanliness Classes in Cleanroom
12、s and Clean Zones5,63. Terminology3.1 Definitions:3.1.1 ambient conditions, nroom temperature and pres-sure.3.1.2 pre-bakeout, nto clean or condition, or both, avacuum chamber prior to its use for flight hardware.1This test method is under the jurisdiction of ASTM Committee E21 on SpaceSimulation an
13、d Applications of Space Technology and is the direct responsibility ofSubcommittee E21.05 on Contamination.Current edition approved Nov. 1, 2012. Published December 2012. DOI:10.1520/E2900-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
14、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Institute of Environmental Sciences and Technology (IEST),Arlington Place One, 2340 S. Arlington Heights Rd., Suite 100, Arlington Heights,IL 60005-4516,
15、 http:/www.iest.org.4MIL-STD-1246 may be used in lieu of IEST-STD-CC1246 by mutual agree-ment of the parties in the contract.5Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,Philadelphia, PA 19111-5094, https:/assist.daps.dla.mil/quicksearch/6FED-STD-209 may be used in lieu of I
16、SO-14644 by mutual agreement of theparties in the contract.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.3 bakeout, na process by which volatile molecularcontaminants are removed from a spacecraft component orarticle by exposing
17、 it to vacuum and elevated temperature”.When the intent is to describe an action, this should be twowords: to “bake out”.3.1.4 cold finger, nthe device that is used in collecting thesample of the residual gases in an evacuated vacuum chamber.3.1.5 cold plate, na vacuum stable metal plate filled with
18、liquid nitrogen used to condense the volatile molecular (oroutgassing) contamination generated by the space componentundergoing the bakeout.3.1.6 cold shroud, nthe metal lining of the vacuumchamber (usually black painted or black anodized) used as aheating device or when filled with liquid nitrogen,
19、 used tosimulate deep space.3.1.7 cold wall test, na test configuration used to simulatedeep space, requiring analytical view factors for the calculationof outgassing rates.3.1.8 hot wall test, na test configuration, in which thehardware is isothermal with the surrounding environment. Itassumes homo
20、genous mixing for calculating outgassing rates.3.1.9 outgassing, nthe evolution of a gas from a material,usually in a vacuum.3.1.10 outgassing rate (g/s), nthe net rate of mass lossfrom a material sample as a result of outgassing. Outgassingrate can be normalized per unit sample surface area andexpr
21、essed as gcm-2s-1or it can be normalized per unit initialsample mass and expressed as gg-1s-1.3.1.11 QCM deposition rate stabilization (Hz/hr/hr), ntheacceleration of the QCM deposition rate.3.1.12 quartz crystal microbalance or QCM, na device formeasuring small quantities of mass using the properti
22、es of aquartz crystal oscillator.3.1.13 QCM deposition rate, nthe QCM output (or beat)frequency change per unit time caused by the mass of amolecular species condensing on the QCM crystal. The QCMdeposition rate units may be converted to g/cm2/s by multiply-ing by the mass loading constant (m) provi
23、ded by the vendorfor the crystal used (i.e., for a 10 Mhz crystal, m=4.42E-9g/cm2Hz).3.1.14 QCM thermogravimetric analysis or QTGA, natechnique in which a QCM is heated at a constant rate toremove a collected deposit.3.1.15 temperature stabilization, ntemperature stabiliza-tion has been reached when
24、 the unit temperature is within 2Cof the specified temperature and the rate of change is less than3C per hour as measured with the unit control thermocouple.This rate can be extrapolated over a 20 min sample time. Forexample, stabilization has been achieved if two temperaturemeasurements taken 20 mi
25、n apart are within 1C of each other.3.1.16 total collection area, nthe sum of the surface areain the vacuum chamber that is equal to or colder than the QCMcrystal temperature.3.1.17 visibly clean highly sensitive, VCHS, nvisual in-spection conducted at a distance of 1550 cm (618 in.) withwhite light
26、 of at least 1076 lumens/m2(100 fc) intensity. It maybe accompanied by ultraviolet (UV) inspection as well.3.2 Acronyms:3.2.1 GN2Gaseous Nitrogen3.2.2 LN2Liquid Nitrogen3.2.3 MLIMulti-Layer Insulation3.2.4 NVRNonvolatile Residue3.2.5 RGAResidual Gas Analyzer3.2.6 QCMQuartz Crystal Microbalance3.2.7
27、QTGAQCM Thermogravimetric Analysis3.2.8 TQCMTemperature controlled Quartz Crystal Mi-crobalance3.2.9 VCHSVisibly Clean Highly Sensitive4. Summary of Practice4.1 A vacuum chamber is configured in the same manner itwould be configured for the hardware bakeout, except that thetest article is omitted.4.
28、2 The empty chamber and its support equipment iscleaned and inspected to VCHS. Then, the chamber is evacu-ated and pre-baked at a temperature 10C above the hardwarebakeout temperature, using the same procedure used for thecomponent hardware.4.2.1 For Method A, the chamber is ready for installation o
29、fflight hardware after 24 h under vacuum and temperature anda visual inspection.4.2.2 For Methods B and C, the chamber is ready when themeasured QCM deposition rate, witness sample data and visualinspection results are acceptable.4.3 The spacecraft component to be thermal vacuum bakedis exposed to a
30、n elevated temperature and a vacuum of 5.0E-5torr or less for a specified amount of time or until the desiredoutgassing rate is reached.4.3.1 Method AThe bakeout is terminated at a specifiedtime limit and stabilized chamber pressure.4.3.2 Method BThe bakeout is terminated when the QCMdeposition rate
31、 stabilizes to a specified level.4.3.3 Method CThere is a bakeout phase and a certifica-tion phase. The hardware is exposed to the program specificqualification temperature (usually 10oC above maximum pre-dicted on-orbit operating temperatures) or the maximum toler-able temperature of the component
32、in accordance with MethodB. In the certification phase, the temperature is lowered to thepredicted maximum on-orbit operating temperatures and therate is measured. This provides realistic information that can beused to obtain outgassing rates in on-orbit conditions and alsoprovides information about
33、 the dependency of the componentoutgassing rates on temperature. The bakeout is terminatedwhen the QCM deposition rate reaches a specified level.4.3.4 At the end of the bakeout, witness plates are removedand NVR wipe samples are taken of the cold plate.E2900 1225. Apparatus5.1 DescriptionThe bakeout
34、 apparatus consists of threemain subsystems: a vacuum chamber (including ground sup-port equipment), a temperature control system, and a dataacquisition system. Methods B and C require a QCM.5.1.1 Vacuum ChamberThe principle components of thevacuum chamber are the pump, the chamber shrouds and thecr
35、yogenic cold plate if needed.5.1.1.1 The pump should be capable of maintaining therequired pressure for a mean free path greater than the largestdimension of the chamber. Diffusion pumps use oil to capturegases and will increase deposition on the QCM. A cold trapbetween the diffusion pump and vacuum
36、 chamber is recom-mended to reduce backstreaming. Clean, oil-free pumps suchas cryogenic, sorption, and turbomolecular are preferred toavoid backstreaming.5.1.1.2 High Vacuum GaugeAn ion gauge or other gaugecapable of monitoring pressures below 1e-4 torr. See PracticeE296 for guidance in using ioniz
37、ation gauges.5.1.1.3 Chamber ShroudsThe chamber shall be equippedwith an inner lining or shroud that provides temperature controlwhich is maintained cold for “cold wall” testing and hot for“hot wall” testing. A bakeout box may be substituted for theshroud for hot wall testing.(1) Cold wall testing r
38、equires the hardware to be heatedwhile the chamber shroud is kept cold, typically at LN2temperatures.(2) Hot wall testing requires an environment that is isother-mal with the hardware, this is typically accomplished with abakeout box or the chamber shrouds. The bakeout box is anenclosed structure wh
39、ich surrounds the hardware and providesuniform heating of components. There are only holes in the boxto allow for a small planned vent and a view port for the QCM.The chamber shroud is normally heated with hot GN2and theheater plates operate using heater tapes or circulating hot fluid.Whichever heat
40、ing system is chosen, it should be sufficient toheat the item uniformly. Thermocouples should be placedappropriately to insure uniform heating of the hardware.5.1.1.4 Cold TrapsThere are three different types ofequipment that can be used to trap contaminants: a LN2filledcold wall of the shroud, an L
41、N2filled cold plate/cold finger, orthe cryopump/diffusion LN2trap. The cold trap is kept coldthroughout the test and may be analyzed afterward for con-taminant identification.5.1.2 Temperature Control SystemAll temperatures of thebakeout hardware and the QCM are maintained by indepen-dently controll
42、ed heaters to a precision of 62C.5.1.2.1 Heating EquipmentIn general, six different typesof equipment may be used to heat the component: a bakeoutbox, heat lamps, resistance bars, heater plates, heater tapes, orthe chamber shroud. Methods A and B are independent of themethod of creating the environm
43、ent temperature, whileMethod C requires either a hot wall or cold wall configuration.(1) Arrays of heat lamps or resistance bars are commonlyused for solar panels.(2) The chamber shroud or aluminum heater plates arecommonly used for electrical components. The chambershroud is normally heated with ho
44、t GN2and the heater platesoperate using heater tapes or circulating hot fluid.(3) Heater tapes can be used on the component directly, butheater tape adhesives can bias the results and possibly con-taminate the hardware.5.1.3 Data Acquisition SystemData acquisition, storageand manipulation can be acc
45、omplished by any method that iscapable of monitoring QCM frequencies, QCM temperatures,QCM heater/cooler voltages, hardware temperatures, chamberpressure, and data collection times at specified intervals. Thesystem should be able to store collected data for later retrievaland analysis. An automated,
46、 computer operated data collectionsystem is recommended.5.1.3.1 The QCM heater/cooler voltage is used as a diag-nostic tool. If there is significant variation in the QCMfrequency, it may be related to poor QCM heater/coolercontrol.5.1.3.2 Data storage intervals should be short enough tocollect inher
47、ent variability of the QCM collection device. It hasbeen found that 1 to 5 min between records is satisfactory.5.1.4 QCMThe placement of the QCM has a significanteffect on the measurement of outgassing rates. If the QCMviews hot chamber surfaces capable of re-emittingcontamination, such as it would
48、in a hot box, the readings maybe artificially high. If it views a cold shroud, the readings willbe too low.5.1.4.1 The QCM used for this test shall have a sensitivityof at least 1.0E-08 gcm-2Hz-1. 10 MHz or 15 MHz crystalsmeet this requirement and are typically used for this applica-tion.5.1.4.2 The
49、 QCM shall be thermally connected to a heatsink enabling the QCM to operate in its full temperature range.It may be necessary to cool the heat sink mounting bracket withfluid or gas to keep the temperature stable.(1) The sink for a TQCM must be maintained at no morethan 40C above the crystal operating temperature (see TQCMmanual for details). This ensures that the indium seals will notmelt due to internal heat generated by the TQCM. It may benecessary to heat a TQCM if the surrounding area is too coldfor its electronics. An alterna
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