METEOROID AND ORBITAL DEBRIS FLIGHT EXPERIMENT DTO 1118
Darrell Winfield, & Russell GravesMeteoroid and Orbital Debris SubsystemBoeing Space and Missile Systems Sector
International Space Station Program, Houston, TX
andDr. Jeffrey R. Theall
NASA Johnson Space Center, Space and Life Sciences, Houston, TX
1.0 Abstract
The potential for spacecraft damage frommeteoroids has existed since the early days ofspaceflight. As man has increased activity in Earthorbit, a potentially more severe problem has beenintroduced in our wake in the form of orbital debris.These particles have collided with MIR, and startingin June 1998 the International Space Station (ISS), atrelative velocities that average 10 km/s for orbitaldebris and 20 km/s for meteoroids. Withoutappropriate design measures, hypervelocity impactscan penetrate spacecraft habitable modules, degradesolar arrays, or impact other exterior hardwarecausing a significant amount of damage. This paperwill give a short overview of the Russian MIR SpaceProgram, examine damage to the Russian spacestation MIR including the recent damage incurredbecause of the progress collision, and explain howthis damage assessment will help in planning and riskreduction for the ISS mission. The ISS program issponsoring this photography and damage assessmentof the Russian spacecraft MIR.
This paper is declared a work of the U.S. Government and is notsubject to copyright protection in the United States.
Space Shuttle Detailed Test Objective (DTO) 1118 is aphotographic and video survey of the exterior of MIR toassess damage to the craft from the Low Earth Orbit(LEO) environment. The primary concern is with thedamage associated with Meteoroid and Orbital Debris(M/OD) impacts. The ISS program developed anapproach to mitigate risk from M/OD. Management ofthese risks involve three principles: 1) Design to preventM/OD impacts from penetrating critical hardware by useof state-of-the-art shielding techniques, 2) use radartracking to complete collision avoidance maneuvers, and3) minimize residual risk by implementing risk controland abatement procedures. This damage assessment ofMIR is part of the overall strategic plan to identify riskand mitigate that risk to the best ability of the program.
2.0 Introduction
Spacecraft damage from meteoroids has existed since theearly days of spaceflight. As we increased activity inEarth orbit, a potentially more severe problem wasintroduced in our wake in the form of orbital debris.These particles will collide with MIR and theInternational Space Station (ISS) at relative velocities thataverage @ 10 km/s for orbital debris and 20 km/s formeteoroids. Without appropriate design measures,hypervelocity impacts can penetrate spacecraft habitablemodules, damage and degrade solar arrays, or impactother exterior hardware causing a significant amount ofdamage. This paper presents a overview the Russian MIRSpace Program, examines damage to the Russian space
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station MIR, and explains how this damageassessment will help in planning and risk reductionfor the ISS mission. The ISS program is sponsoringthe assessment of the Russian spacecraft MIR. SpaceShuttle Detailed Test Objective (DTO) 1118 is aphotographic and video survey of the exterior of MIRto assess damage to the craft from the Low EarthOrbit (LEO) environment. The main concern is withthe damage associated with Meteoroid and OrbitalDebris (M/OD) impacts. The ISS program hasdeveloped an approach to mitigate risk from M/OD.Management of these risks involves multipleprinciples and are grouped into 5 sections that areinter-related : 1) The environment, 2) Modeling, 3)Testing, 4) Hardware development and design, and5) Operations. The damage assessment of MIR is partof the overall strategic plan to identify risk andmitigate that risk to the best ability of the program.
DTO 1118 is a series of experiments completed onSTS 63, 71, 74,76, 79, 81, 84 and STS 86. The MIRstation has been photographed during approach,docking, while docked, then on the fly around as theshuttle is leaving. M/OD damage was seen to variousdegrees on all the hardware. Minor pits are evidentall over the structure and several large damage areaswere identified on the solar arrays. The mostsignificant damage is to the Spektr module that washit by Progress M-34 in June. While this was not ahypervelocity impact it did cause a penetration of themodule due to it's impact.
As the damage is being assessed and we learn moreabout the results of impacts to hardware, the ISShardware is being built to sustain operations withm/od impact events occurring. Crew and vehiclesafety are of utmost importance to the ISS program.Vehicle reliability and the ability to do maintenanceon damaged hardware is also of concern.Experiments on MIR will help us determine theneeded levels of maintenance and also what type ofrepairs may be needed. ISS will be a highly dynamicspace vehicle operating in what is predicted to be amore severe debris environment due to the amount ofOrbital Debris growth predicted by NASA and theRussian Space Agency. Mission planning and riskidentification and mitigation are necessary in order toachieve all the goals of the program.
3.0 Russian Space Station MIR overview
The MIR program was started to replace Salyut 7with the launch of the MIR core module in February
1986. See Table #1 for technical details for each module.The MIR is made up of 6 primary modules and severalsecondary attachments. The MIR core module is forhabitation, life support, thermal control system (TCS),power, and provides docking ports. The Kvant 1 modulefunctions are astronomy, life support, and Progress andSoyuz docking. The Kvant 2 module added the ability ofremote sensing to the MIR and provides the EVA airlockfor MIR. The Kristall module was added to providematerials production, remote sensing, and an APASdocking node. The spherical node on the Kristall moduleprovides the APAS ports the Shuttle docked to on STS 71and subsequent missions. The Spektr and Priroda moduleswere additions primarily for use as science laboratoriesfor the ISS Phase I program.
See Figure #1 for an overview of the MIR configurationsince the STS 74 flight.
The three newest modules added to MIR are the Spektr,Priroda, and Docking Module. The Spektr module waslaunched on a Russian Proton rocket from the Baikonurlaunch center in central Asia on May 20, 1995. Themodule was berthed at the radial port opposite Kvant 2after Kristall was moved out of the way. Spektr carriedfour solar arrays and scientific equipment (including morethan 1600 pounds of U.S. equipment). The focus ofscientific study for this module is Earth observation,specifically natural resources and atmosphere. Theequipment onboard was supplied by both Russian and theUnited States. This is the module that was damagedduring the progress collision this summer. Repairs are stillunderway.
The Priroda (Nature) module was launched on a Protonlauncher for rendezvous and docking with the spacestation on April 26, 1996. The module carried more thana ton of U.S. cargo for astronaut Shannon Lucid aboardthe space station. When docked, the new modulecompleted the MIR construction complex started tenyears earlier. Unlike previous modules Priroda has nosolar power arrays but must rely on its on-board batteriesas long as it is not docked to MIR.
The Docking Module was launched in the payload bay ofAtlantis and berthed at Kristall's androgynous dockingport during the STS-74 mission. The Docking Modulewill provide clearance for future Shuttle dockings withMIR and will carry two solar arrays. One array is Russianand one was jointly developed by the U.S. and Russia toaugment MIR's power supply.
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DTO 1118 is being done under the ISS Phase I officeat JSC. This experiment is part of the joint Russianand NASA participation in space program. Thephotographic survey of MIR has been carried out byJSC Space and Life Sciences Earth Science branch.All imagery data is being reviewed by both NASAand Russian technical experts. STS 63 was the first ofthese photographic survey's. During the approachand fly around of the MIR by the Shuttle, video andphotographs were taken to examine the overall MIRstation on all the flights to date.
Damage can be seen to various degrees on all thehardware. Minor impact damage is evident all overthe structure and several large damage areas havebeen identified on the solar arrays (Ref. 1,3,4). Aftereach flight, the photo's and video are examined andthe information is published in a DTO 1118 missionreport.
5.0 Damage Assessment of MIR
The newest and most visible damage to MIR is due tothe Progress collision that occurred on June 25th whenProgress M-34 crashed into the Spektr module duringa TORU guidance system test. While this was not ahypervelocity impact event it did cause a penetrationof the pressurized vehicle. The pressure dropped from750 mm Hg to 675 mm Hg in the main vehicle andthen to space vacuum in the Spektr after the hatchwas closed. Photographs of the MIR damage can beseen at the web site in reference #6. MIR power wasdegraded close to 50% because of this event. MIRrepairs continue to recover this loss and look for thehole in the module.
M/OD impacts have been observed on all the MIRsurfaces. These impacts are visible on all smoothsides exposed to space and on various solar arraypanels. One such impact was visible fromphotography taken during STS-74 (Ref. 1).Significant damage was found on the port side solararray panel of the MIR Base Block. This damageillustrates an orbital debris strike where an object hasapparently traveled completely through a panel. Thearea of damage was measured to be 27 cm2. At leastsix adjacent cells appear to have suffered ancillarydamage. In addition, the port side solar array panel ofthe Kristall module has a 9 cm2 damaged area. This
damage may have been caused by an external impactor electrical damage. There are multiple impactdamage sites all over all the arrays.
The Kvant -2 Solar array SP#2 continues to be one ofthe arrays that has the most M/OD damage. Two newimpacts were found during STS 81. Six to eight cellswere damaged on one impact site and a through holewas located at another site on SP #2 (ref 8).
Multiple items have had to be replaced and externaldamage is very evident but only one systems failurehas been attributed to a M/OD penetration The MIRTCS system had to be repaired due to a smallpuncture prior to the NASA/MIR program started.The amount of damage seen to date matches with thesafety assessments NASA has done to prepare forShuttle / MIR missions during phase I.
Smaller impacts are seen in damaged areas all overthe vehicle. See Table #2 for general damage andReference #1, #3, #4, #7 and #8 for details of allimpacts and damaged areas located to date.
The docking module docking mechanism is still aparticular concern because the same mechanism willbe used on ISS. The mechanism shows some smalldamage to the seal surface. NASA experts areevaluating the damage to date but no issues havearisen with the shuttle during any Russian dockingmission. No leakage between the shuttle seal andMIR has been reported.
The damage assessment being done is becoming ofmore use as data is collected over time. Thephotographic record of damage from Mission toMission is being compared and new data fromimpacts can be analyzed and compared against theold damage.
6.0 Russian M/OD experience and ISS Planning
Russian MIR design philosophy was to preventmicrometeoroids from damaging systems. This wasaccomplished by use of thin aluminum andhoneycomb shields and by placing wiring and tubingunder the shields or under the thermal protection ofthe vehicle. Russian design also used the radiators toshield RCS tanks. The Russian MIR has experiencedno known penetrations of an inhabited pressurized
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volume due to M/OD in the eleven years of flight.This is consistent with both NASA and Russiandamage models because of the limited area exposedto M/OD over those eleven years. The MIR has beenflying in a low orbit with a relatively small exposedarea in a time of high solar activity. This flightexposure has worked out so the orbital debrisenvironment is much less than we expect to encounterduring ISS missions. The MIR station exposed areaof critical hardware has varied from 150 m2 toapproximately 500 m2 today. While this is asignificant area it is nowhere near the 2000 m2 ormore of exposed critical area planned for ISS. ForM/OD Probability of No Penetration (PNP) one ofthe critical factors in the calculation is the area-timeproduct. As area increases and exposure timeincreases, the PNP goes from 1.0 (no impacts) tolower probabilities based on the shielding designedinto the vehicle. The current MIR station wasdesigned to prevent meteoroids and small orbitaldebris particles from penetrating critical hardware.While the Russians have seen no penetrations ofmanned modules to date, the probability of an eventoccurring is high compared to NASA safetystandards. The philosophy used by the Russians hasbeen modified for the ISS program to achieveacceptable risk levels.
7.0 Risk Management Planning for ISS
The goal for ISS is to develop and deploy the safestpossible design for on orbit use. ISS is the firstNASA program to plan for the Orbital Debrisenvironment in the design and development of thehardware. A program strategic plan was developedby NASA and Boeing engineers working on OrbitalDebris definition, shielding, and collision avoidance.The most cost effective methods of protecting thevehicle and safety of the crew were identified and theprogram is working to implement these conceptsnow. The basic plan as seen in Figure #2 as createdby the ISS Meteoroid and Orbital Debris Team is: 1)Define the environment, 2) Model the design for PNPand PNCF assessments, 3) Test the hardware todetermine ballistic limits and failure criteria, 4) Buildthe hardware and finalize the development ofprotection, and 5) Implement operational proceduresto reduce risk to the crew and the vehicle.
As the damage to MIR is being assessed and we learnmore about the results of impacts to hardware, theISS hardware is being built to sustain operations withpotential hypervelocity impacts of all sizes occurring.Crew and vehicle safety are of utmost importance to
the ISS program. Vehicle reliability and the ability todo maintenance on damaged hardware is also ofconcern. These photographic survey's and otherexperiments will help determine the need to domaintenance on space structures and also what levelsof repairs to hardware may be needed.
ISS will be a highly dynamic space vehicle operatingin what is predicted to be a severe M/ODenvironment in LEO due to the Orbital Debrisgrowth predicted by NASA and the Russian SpaceAgency. Mission planning and risk identification andmitigation are necessary in order to achieve all thegoals of the program.
8.0 Summary
Protecting the ISS hardware and crew over a 15 yearperiod is a very challenging problem. The ISSprogram created a Meteoroid and Debris SubsystemTeam to work this area and the team has set forth aplan to meet requirements and set specific goals tominimize overall risk to the program. The RussianMIR photography DTO is an integral piece of theoverall risk mitigation effort. ISS will continue toevaluate what has happened on orbit to help usunderstand the type of damage expected with thefuture vehicle. Some significant impacts haveoccurred on the MIR arrays and although they hadlittle effect to the MIR, they would have been verydestructive had the impacts occurred on pressurizedmodules or propulsion units. A depress event similarto the Spektr depress would most likely occur. Thedamage assessment overview in this paper willcontinually be updated after each Shuttle /MIRrendezvous and our risk mitigation efforts will beadjusted as needed.
9.0 Contributing Analysis
Significant contributions were made by the ImageScience and Analysis group at JSC. Mr. Mark Holly,Mr. Mike Gaunce, and Mr. Robert Scharf did theprimary analysis in reviewing the majority of thephotographs and video taken during this DTO. Ifphotographs or video is needed, these individualsmay be contacted at JSC's Space and Life SciencesDirectorate.
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