ASEN Aerospace Environment -- Orbital Debris 1 Coronal holes and Solar wind speed and density The interplay between the inward pointing gravity and outward pointing pressure gradient force results in a rapid outward expansion of the coronal plasma along the open magnetic field lines. At low latitudes the direction of the coronal magnetic field is far from radial. Therefore the plasma cannot leave the vicinity of the Sun along magnetic field lines. At the base of low- latitude coronal holes, however, the magnetic field direction is not far from radial, and the expansion of the hot plamsa can take place along open magnetic field lines without much resistence  fast solar wind.

ASEN Aerospace Environment -- Orbital Debris 2 Coronal Holes One of the major discoveries of the Skylab mission was the observation of extended dark coronal region in X-ray solar images. These coronal holes are characterized by low density cold plasma (about half a million degrees colder than in the bright coronal regions) and unipolar magnetic fields (connected to the magnetic field lines extending to the distant interplanetary space, or open field lines). The figure on the right is from recent Yohkoh s/c. Near solar minimum coronal holes cover about 20% of the solar surface. The polar coronal holes are essentially permanent features, whereas the lower latitude holes only last for several solar rotations.

ASEN Aerospace Environment -- Orbital Debris 3 The first x-ray images > 30 keV have been obtained with the hard X-ray Telescope on the Yohkoh satellite. The relationship between the nonthermal (accelerated) electrons and the hottest thermal electrons can be studied by observing the time evolution of both components during a flare. Likewise, the relationship between these energetic components and somewhat cooler thermal plasma can be studied by comparing the hard x-ray observations with the evolution of the soft x-ray emission.

ASEN Aerospace Environment -- Orbital Debris 4 Solar Cycle Our ever changing Sun over its 11 year cycle - seen here in X-rays

ASEN Aerospace Environment -- Orbital Debris 5 The wavelengths most significant for the space environment are X-rays, EUV and radio waves. Although these wavelengths contribute only about 1% of the total energy radiated, energy at these wavelengths is most variable

ASEN Aerospace Environment -- Orbital Debris 6 SOME CONTRIBUTIONS OF HELIOSEISMOLOGY Convection zone deeper (R=0.71) than previously thought. Limits set on the abundance of Helium in convection zone. Rotation rate of the convection zone is similar to that of surface. Near the convection zone base, rotation rate near the equator decreases with depth, and rotation rate at high latitudes increases with depth, so that the outer radiation zone is rotating at a constant intermediate rate.

ASEN Aerospace Environment -- Orbital Debris 7

8 “Halo CME”

ASEN Aerospace Environment -- Orbital Debris 9 Electron density 7.1 cm -3 Proton density6.6 cm -3 He 2+ density0.25 cm -3 Flow speed 425 kms -1 Magnetic field 6.0 nTProton temperature 1.2 x10 5 K Electron temperature1.4 x10 5 K Observed Properties of the Solar Wind at 1 AU The pressure in an ionized gas with equal proton and electron densities is P gas = nk (T p + T e ) where k is the Boltzmann constant, x JK -1, and T p and T e are proton and electron temperatures. Thus, P gas = 2.5 x dyn cm -2 = 25 pico pascals (pPa) Similarly, a number of other solar wind properties can be derived (see following table) Derived Properties of the Solar Wind

ASEN Aerospace Environment -- Orbital Debris 10 THE INTERPLANETARY MEDIUM AND IMF Intermixed with the streaming solar wind is a weak magnetic field, the IMF. The solar wind is a “high-  ” plasma, so the IMF is "frozen in”; the IMF goes where the plasma goes. Consequently, the "spiral" pattern formed by particles spewing from a rotating sun is also manifested in the IMF. The field winds up because of the rotation of the sun. Fields in a low speed wind will be more wound up than those in high speed wind.

ASEN Aerospace Environment -- Orbital Debris 11 Loci of a succession of fluid particles emitted at constant speed from a source fixed on the rotating Sun. Loci of a succession of fluid parcels (eight of them in this sketch) emitted at a constant speed from a source fixed on the rotating Sun.

ASEN Aerospace Environment -- Orbital Debris 12 IMF as a function of the distance  The following equations shows the IMF as a function of r. The radial and azimuthal component of the IMF behave quite differently.  The radial component decreases with r -2, whereas the azimuthal component decreases only as r -1. Thus as going outward, the magnetic field becomes more and more azimuthal (it “wraps around”) in the equatorial plane.  At the same time the field behaves quite differently over the solar polar regions.

ASEN Aerospace Environment -- Orbital Debris 13 Heliosphere, a schematic view Note that IMF is dominated by the azimuthal component at large distance, while the solar wind flow is always dominated by the radial component.

ASEN Aerospace Environment -- Orbital Debris 14 Coronal holes and Solar wind speed and density The interplay between the inward pointing gravity and outward pointing pressure gradient force results in a rapid outward expansion of the coronal plasma along the open magnetic field lines. At low latitudes the direction of the coronal magnetic field is far from radial. Therefore the plasma cannot leave the vicinity of the Sun along magnetic field lines. At the base of low- latitude coronal holes, however, the magnetic field direction is not far from radial, and the expansion of the hot plamsa can take place along open magnetic field lines without much resistence  fast solar wind.

ASEN Aerospace Environment -- Orbital Debris 15

ASEN Aerospace Environment -- Orbital Debris 16 > 700 keV ions and > 500 keV electrons

ASEN Aerospace Environment -- Orbital Debris 17

ASEN Aerospace Environment -- Orbital Debris 18 > 20 MeV Ions (most protons)

ASEN Aerospace Environment -- Orbital Debris 19 SAMPEX measured Anomalous Cosmic Ray Particles (Oxygen Nuclei, >200 keV/nucl)

ASEN Aerospace Environment -- Orbital Debris 20 As the magnetized solar wind flows past the Earth, the plasma interacts with Earth’s magnetic field and confines the field to a cavity, the magnetosphere.

ASEN Aerospace Environment -- Orbital Debris 21 (Temerin and Li, 2002) Prediction efficiency=91% Linear correlation coeff.=0.95

ASEN Aerospace Environment -- Orbital Debris 22

ASEN Aerospace Environment -- Orbital Debris 23 Review of Charged Particle Motions Gyromotion motion:  =p 2  /2mB (1st), T_g~10 -3 sec Bounce Motion: J=  p || ds (2nd), T_b~10 0 sec Drift motion:  =  BdA (3th), T_d~10 3 sec

ASEN Aerospace Environment -- Orbital Debris 24 Loss Cone and Pitch Angle Distribution Obviously this will happen if  eq is too small, because that then requires a relatively large B M (|B| at the mirror point). The equatorial pitch angles that will be lost to the atmosphere at the next bounce define the loss cone, which will be seen as a depletion within the pitch angle distribution. B loss cone Particles will be lost if they encounter the atmosphere before the mirror point.

ASEN Aerospace Environment -- Orbital Debris 25 The core motions are induced and controlled by convection and rotation (Coriolis force). However, the relative importance of the various possible driving forces for the convection remains unknown: heating by decay of radioactive elements latent heat release as the core solidifies loss of gravitational energy as metals solidify and migrate inward and lighter materials migrate to outer reaches of liquid core. Venus does not have a significant magnetic field although its core iron content is thought to be similar to that of the Earth. Venus's rotation period of 243 Earth days is just too slow to produce the dynamo effect. Mars may once have had a dynamo field, but now its most prominent magnetic characteristic centers around the magnetic anomalies in Its Southern Hemisphere (see following slides).

ASEN Aerospace Environment -- Orbital Debris 26 Aerospace Environment ASEN-5335 Instructor: Prof. Xinlin Li (pronounce: Shinlyn Lee) Contact info: phone: , or , fax: , website: TA’s office hours: 9-11 am and 3:15-5:15 pm Wed at ECAE 166 for this and next week. Guest Lectures next week: Terry Onsager on 4/8 and David Klaus on 4/10. Quiz-6, 4/15 (Tue), about radiation and other effects on s/c and human beings; and space Debris. HW5 due 4/3 (Thu) and HW6 due 4/17 (Thu)

ASEN Aerospace Environment -- Orbital Debris 27 Earth’s Orbital Debris Environment Over 9,000 objects in Earth orbit are currently tracked An unknown number of undetectable objects of various sizes are known to exist Earth’s atmosphere is bombarded by tons of meteoric material daily What are the hazards ? LEO GEO

ASEN Aerospace Environment -- Orbital Debris 28

ASEN Aerospace Environment -- Orbital Debris 29

ASEN Aerospace Environment -- Orbital Debris 30  This is the impact crater on the number 5 window of the Space Shuttle Challenger. Occurred June, 1983, on the STS 7 mission. Affected area is about 0.5 cm diameter. Impacting particle was a 0.2 mm fleck of white paint of the same type used to paint Delta upper stages. Models suggest relative speed of 3-6 km/s at impact. A Debris Example (Courtesy of Prof. R. Culp of ASEN)

ASEN Aerospace Environment -- Orbital Debris 31 Space Junk: What is the Potential Damage? Size of ObjectDamage Less than 1/250 inchsurface erosion Less than 1/25 inchpossible serious damage 1/8 inch ball traveling atLike a bowling ball 22, mph; (bad) 1/2 inch aluminum ballLike a 400-lb safe traveling at 22, mph; (nasty)

ASEN Aerospace Environment -- Orbital Debris 32 References Johnson, N.L., and D.S. McKnight, Artificial Space Debris, Orbit Book Co., Malabar, Florida, History of on-orbit satellite fragmentations, Orbital debris program office, N. Johnson et al., NASA Johnson Space Center, JSC 29517, LMSEAT33746, July, The new NASA orbital debris engineering model ORDEM2002, J-C Liou et al., NASA/TP , May,

ASEN Aerospace Environment -- Orbital Debris 33 Orbit Categorizations LEOGEO

ASEN Aerospace Environment -- Orbital Debris 34 Space Debris Overview Originate from comets, asteroids 200 kg of mass within 2000 km Largest flux below size of 0.5 mm Low densities & mass; ( g cm -3 ) High velocity - avg 19 km s -1 Flux steady with time Affected slightly by solar cycle Quasi-isotropic flux (some Earth shielding factor) > 9000 large enough to be tracked x 10 6 kg within 2000 km Largest flux above size of 1 mm Higher densities & mass; (2-9 g cm -3 ) Lower velocity – km s -1 Flux increasing with time Affected by launch rate, launch operations, solar cycle Majority in high-use orbits Natural Debris Artificial Debris

ASEN Aerospace Environment -- Orbital Debris 35 Factors Affecting Satellite Population Satellite Population Launch and Operations Activity Satellite Deteriorations Satellite Fragmentations Retrieval and Deorbits Orbital Decay SINKS SOURCES Atmospheric Drag Solar-Lunar Perturbations Radiation Pressure Launch rate Rocket Stages Loose Hardware Atomic oxygen Solar Radiation Deliberate Accidental/Propulsion Collision Unknown

ASEN Aerospace Environment -- Orbital Debris 36 Overview of Artificial Debris Population Primary factors affecting satellite population launch rate satellite fragmentations solar activity Projection primarily based on traffic

ASEN Aerospace Environment -- Orbital Debris 37 Ten of more than 4150 space missions flown since 1957 account for 21% of all catalogued satellites in orbit as of May 2001 All but one are discarded rocket bodies The majority of detectable fragmentation debris have already fallen out of orbit The effects of 45% of all fragmentations have disappeared

ASEN Aerospace Environment -- Orbital Debris 38 Satellite Fragmentations Fragmentation Debris -- destructive disassociation of an orbital payload, rocket body or structure -- wide range of ejecta velocities Anomalous Debris -- result from unplanned separation of object(s) from a satellite which remains intact, i.e., deterioration of thermal blankets, protective shields, solar panels -- low relative velocities Operational (Mission-Related) Debris -- ejected during deployment, activiation, de-orbit of payloads, manned operations, etc. Relative segments of the catalogued in-orbit satellite population

ASEN Aerospace Environment -- Orbital Debris 39 Debris Type vs. Orbit Accounting, 30 May 2001

ASEN Aerospace Environment -- Orbital Debris 40 Debris Source vs. Type Accounting, 30 May 2001

ASEN Aerospace Environment -- Orbital Debris 41 Debris Source vs. Orbit Accounting, 30 May 2001

ASEN Aerospace Environment -- Orbital Debris 42 U.S. Space Surveillance Network Dedicated -- USSPACECOM primary spacetrack mission Collateral -- USSPACECOM other primary mission Contributing -- controlled by non- USSPACECOM NE -- near Earth DS -- deep space What are the data sources ?

ASEN Aerospace Environment -- Orbital Debris 43 Measurements of near-Earth orbital debris is accomplished by conducting ground-based and space-based measurements of the orbital debris environment. Data is acquired using ground-based radars and telescopes, space-based telescopes, and analysis of spacecraft surfaces returned from space. The data provide validation of the environment models and identify the presence of new sources. ground-based radarstelescopesspace-based telescopesspacecraft surfaces Orbital Debris Measurements Optical MeasurementsRadar Measurements

ASEN Aerospace Environment -- Orbital Debris 44 Representative US SSN Coverage at 400 km altitude For fragmentations below about 400 km, much of the debris may reenter before detection, identification & cataloging can be completed Red: optical Blue: radar At low altitudes (<2000 km) cataloged debris are larger than ~10 cm in diameter At higher altitudes objects less than ~1m in diameter may be undetectable Need for detection of smaller debris (<10 cm) in most of space

ASEN Aerospace Environment -- Orbital Debris 45 The space object environment is usually described in terms of a spatial density [1/km 3 ] that represents an effective number of spacecraft and other objects as a function of altitude (i.e., an object in circular orbit represents much more of a collision hazard than one that occasionally traverses this region) The geosynchronous altitude population, 28 May 2001 GPS/Glonass Spacecraft Higher-altitude near-Earth and general deep-space populations

ASEN Aerospace Environment -- Orbital Debris 46 Near-Earth ( km) population, 28 May 2001 Linear scale Log scale ORBCOMM Constellation IRIDIUM Constellation OPS-4682 SNAPSHOT Spacecraft Note: fragmentation debris often dominate

ASEN Aerospace Environment -- Orbital Debris 47 Satellite Fragmentations during the 1990’s 1 Jan 2000 Areas of bubbles proportional to number of debris created by a specific event 55 explosions and the first recorded unintentional collision occurred during the 1990’s

ASEN Aerospace Environment -- Orbital Debris 48 Satellite Breakups Proportion of all cataloged satellite breakup debris Number of breakups by year since 1957 The most important category of on-orbit debris Account for 38% of the existing satellite population 170 satellites have broken up since 1961 Primary causes are deliberate actions & propulsion-related events

ASEN Aerospace Environment -- Orbital Debris 49 Aerospace Environment ASEN-5335 Instructor: Prof. Xinlin Li (pronounce: Shinlyn Lee) Contact info: phone: , or , fax: , website: TA’s office hours: 9-11 am and 3:15-5:15 pm Wed at ECAE 166 for next week. Guest Lectures next week: Terry Onsager on 4/8 and David Klaus on 4/10. Quiz-6, 4/15 (Tue), about radiation and other effects on s/c and human beings; and space Debris. HW5 due today and HW6 due 4/17 (Thu)

ASEN Aerospace Environment -- Orbital Debris 50 The space object environment is usually described in terms of a spatial density [1/km 3 ] that represents an effective number of spacecraft and other objects as a function of altitude (i.e., an object in circular orbit represents much more of a collision hazard than one that occasionally traverses this region) GPS/Glonass Spacecraft Higher-altitude near-Earth and general deep-space populations Anomalous Debris -- result from unplanned separation of object(s) from a satellite which remains intact, i.e., deterioration of thermal blankets, protective shields, solar panels -- low relative velocities

ASEN Aerospace Environment -- Orbital Debris 51 Overview of Debris Population Natural vs. Artificial Debris Debris Sources and Sinks Characterization of the Debris Environment –Detection, tracking, surveillance –Impact characterization (Gabbard diagrams) –Modeling the environment Long Duration Exposure Facility (LDEF) Future Trends/Mitigation Strategies Earth’s Orbital Debris Environment

ASEN Aerospace Environment -- Orbital Debris 52 IMPACT CHARACTERIZATION Brief review of orbital perturbations Gabbard Diagrams posigrade impulse original orbit final orbit Semi-major axis & period increase final orbit original orbit retrograde impulse Semi-major axis & period decrease At perigee: posigrade/retrograde will raise/lower apogee At apogee: posigrade/retrograde will raise/lower perigee Radial impulse apogee, perigee change semi-major axis & period almost unchanged Out-of-plane (  ) impulse little change

ASEN Aerospace Environment -- Orbital Debris 53 Gabbard Diagrams  +  + circular orbit elliptical orbit Single-satellite Gabbard diagrams Depict apogee, perigee, and period of orbiting objects Used to infer information about fragmentation events

ASEN Aerospace Environment -- Orbital Debris B  + Gabbard diagram for debris from breakup of satellite B same apogees different perigees These fragments received a net retrograde impulse from the breakup These fragments received a net posigrade impulse from the breakup different apogees same perigees initially circular orbit Note: retrograde pieces have apogee altitudes similar to the perigees of the posigrade pieces. This follows from the impulse maneuver analogies: An impulse at perigee (apogee) does not affect perigee (apogee) height, but only changes the apogee (perigee) height. For a circular orbit, apogees and perigees are defined once the impulse occurs

ASEN Aerospace Environment -- Orbital Debris A  + Gabbard diagram for breakup of a satellite in elliptical orbit mostly retrograde impulse Same perigee height; therefore, fragmentation occurred near perigee Range of apogees depends on magnitude of impulse fragmentation height = 587 km

ASEN Aerospace Environment -- Orbital Debris A  + mostly retrograde impulse Nearly same apogee height; therefore, fragmentation occurred near apogee Another example of satellite fragmentation in elliptical orbit fragmentation height = 2088 km

ASEN Aerospace Environment -- Orbital Debris B  + fragmentation height = 1450 km Fragmentation at a height other than apogee or perigee will exhibit some combination of the previous characteristics

ASEN Aerospace Environment -- Orbital Debris B  + nearly circular; breakup at 750 km A pure radial impulse alters both apogee and perigee while maintaining the same orbital period. A particular explosive event will produce points above and below the “arms” of the Gabbard diagram. Since they appear to surround the parent satellite, they are sometimes called “halo” debris

ASEN Aerospace Environment -- Orbital Debris C For low-altitude breakups, the left arm of the Gabbard diagram can collapse due to orbital decay

ASEN Aerospace Environment -- Orbital Debris pages Summarizing, some of the questions you can try to answer using Gabbard Diagrams include: Initial orbit type Breakup location wrt apogee/ perigee Distinct asymmetries in breakup Weighted Gabbard Diagrams include a 1,2,3,4,5 designation for each object, depending on radar cross-section (and therefore presumably mass) By comparing the distributions of fragments of various mass, it is usually possible to distinguish between collision- or explosion-induced fragmentations

ASEN Aerospace Environment -- Orbital Debris NASA Web Resources In-Situ Measurements

ASEN Aerospace Environment -- Orbital Debris 62 NASA's Long Duration Exposure Facility (LDEF) was designed to provide long-term data on the space environment and its effects on space systems and operations. LDEF had a nearly cylindrical structure 57 experiments were mounted in 86 trays about its periphery and on the two ends. The spacecraft measured 30 feet by 14 feet and weighed ~21,500 pounds with mounted experiments LDEF remains one of the largest Shuttle-deployed payloads LDEF was deployed in orbit on April 7, 1984 by the Shuttle Challenger. LDEF was retrieved on January 11, 1990 by the Shuttle Columbia.

ASEN Aerospace Environment -- Orbital Debris 63

ASEN Aerospace Environment -- Orbital Debris 64 Largest impact - side view Crater & Ejecta Thermal Blanket Penetration On-Orbit Thermal Blanket

ASEN Aerospace Environment -- Orbital Debris 65 Blanket penetration Typical Aluminum Impact Typical Aluminum penetration Metal Silica Oxide (MOS) detector Beta cloth penetration

ASEN Aerospace Environment -- Orbital Debris 66 Trapped Van Allen protons (E ~ Mev) in the South Atlantic Anomaly (SAA) account for most of the energetic particle exposure on LDEF

ASEN Aerospace Environment -- Orbital Debris 67 The LDEF observations revealed data on crater numbers (and fluxes) as a function of crater size, surface orientations relative to the spacecraft orbiting velocity vector, and surface materials, including metals, polymers, composites, ceramics and glasses, some with coatings and paints applied.

ASEN Aerospace Environment -- Orbital Debris 68 Some effects originated from preflight & postflight exposures, and Shuttle sources, as well as on-orbit material degradation. Some thin polymeric films and blanket materials were virtually destroyed and created on-orbit debris that were distributed over adjacent surfaces. A low-density particulate debris cloud in LDEF's wake was observed as the Shuttle approached for retrieval. Inorganic thermal-control paints, anodized aluminum and silverized Teflon thermal-control blankets maintained their optical properties, and thus, their thermal control function. Organic materials such as Mylar, Kapton, paint binders, and bare composites showed the expected severe erosion and degradation under atomic oxygen exposure. Coated composite materials survived and generally maintained their mechanical properties.

ASEN Aerospace Environment -- Orbital Debris 69 Typical List of LDEF Experiments (Systems)

ASEN Aerospace Environment -- Orbital Debris 70 Typical List of LDEF Accomplishments (Materials) Besides LDEF, A number of other missions provide data to the Space Environments and Technology Archive

ASEN Aerospace Environment -- Orbital Debris 71 The New NASA Orbital Debris Engineering Model ORDEM2000 LEO km Current version - windows 95/98/2000/NT computers & Unix Supercedes ORDEM96 Based on “finite element” concept, rather than curve-fitting Two modes:1. Orbiting spacecraft 2. Ground-based detection ProvidesUsers 1. Debris flux onto spacecraft designers Spacecraft surfacesand operators 2. Debris detection rateDebris observers Provides statistical debris environment as a function of altitude, inclination, & size distributions -- EVOLVE inputs used to extrapolate to 2003 Similar ESA model -- MASTER’99 For satellite breakup risk assessment --- use NASA SBRAM For more realistic long-term debris evolution --- use NASA EVOLVE

ASEN Aerospace Environment -- Orbital Debris 72 Data Sources Primary:SSN catalogto build the 1-m and 10-cm populations Haystack radar datato build the 1-cm population LDEF msmsts.to build the 10-  m and 100-  m populations Other sources used to verify and validate model predictions

ASEN Aerospace Environment -- Orbital Debris 73 Used theoretical & experimental equations and empirical fitting to relate crater depth and material density to particle density and impact speed. Extrapolated to non- LDEF altitudes

ASEN Aerospace Environment -- Orbital Debris 74 Analysis of some LDEF surfaces allowed estimates of the relative fluxes of artificial debris and micrometeoroids Fitted meteoroid crater distribution Craters due to meteoroids + unknowns Craters due to debris Cumulative number Fitted crater debris distribution Crater size (microns) CME gold surface

ASEN Aerospace Environment -- Orbital Debris 75 EVOLVE was used to extrapolate the current orbital debris environment into the future Number/km2

ASEN Aerospace Environment -- Orbital Debris 76 Sample ORDEM2000 Output: Debris Flux on ISS in 2005 No/m2/year Diameter (cm)

ASEN Aerospace Environment -- Orbital Debris 77 ORDEM2000 Comparisons with Observations

ASEN Aerospace Environment -- Orbital Debris 78 ORDEM2000 Comparisons with Observations

ASEN Aerospace Environment -- Orbital Debris 79 ORDEM2000 Comparisons with Observations Cumulative Number ORDEM 2000 STS

ASEN Aerospace Environment -- Orbital Debris 80 Mitigation is the Best Strategy for Diminishing Future Orbital Debris Impacts Debris mitigation techniques span all phases of a space system’s life Launch/ Deployment Mission Termination Operations Protect Assets by …. shielding active/passive avoidance redundancy avoid trackable objects Mitigation of spent rocket stages separation devices deployment mechanisms Mitigation of …. operational debris explosions/collisions secondary debris deterioration Removal by …. disposal orbit deorbit by design active deboost