{"id":263323,"date":"2021-11-30T19:23:12","date_gmt":"2021-12-01T00:23:12","guid":{"rendered":"https:\/\/www.nasa.gov\/?migration=converted-node-475651"},"modified":"2023-09-29T16:22:50","modified_gmt":"2023-09-29T20:22:50","slug":"step-3-close-approach-risk-mitigation","status":"publish","type":"topic","link":"https:\/\/www.nasa.gov\/cara\/step-3-close-approach-risk-mitigation\/","title":{"rendered":"Step 3 Close Approach Risk Mitigation"},"content":{"rendered":"<div id=\"\" class=\" hds-module hds-module-full wp-block-nasa-blocks-secondary-navigation\"><div class=\"hds-secondary-navigation-wrapper z-top width-100 padding-0\"><div id=\"\" class=\"hds-secondary-navigation width-full border-bottom-1px text-center hds-color-mode-light hds-module hds-module-full wp-block-nasa-blocks-hdsnav\"><button type=\"button\" class=\"hds-secondary-nav-mobile-button display-flex tablet:display-flex desktop:display-none width-full flex-align-center bg-carbon-90 border-color-carbon-80 color-spacesuit-white\" aria-expanded=\"false\" aria-controls=\"hds-secondary-nav-track\"><span>CARA<\/span><svg width=\"16\" height=\"16\" alt=\"\" enable-background=\"new 0 0 400 400\" viewBox=\"0 0 400 400\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"m4.2 122.2 195.1 195.1 196.5-196.6-37.9-38-157.8 157.8-156.8-156.8z\" \/><\/svg><\/button><div class=\"hds-secondary-nav-track grid-container grid-container-extrawide padding-0 tablet:padding-x-3 desktop:padding-x-2 \"><div class=\"hds-secondary-navigation-menu-items\"><nav><ul class=\"usa-nav__primary usa-accordion flex-justify-center margin-0\"><li class=\"usa-nav__primary-item \"><a class=\"usa-nav__link\" href=\"https:\/\/www.nasa.gov\/cara\/\">CA Home<\/a><\/li><li class=\"usa-nav__primary-item \"><a class=\"usa-nav__link\" href=\"https:\/\/www.nasa.gov\/conjunction-assessment\/\">NASA CARA<\/a><\/li><li class=\"usa-nav__primary-item\"><button type=\"button\" class=\"usa-accordion__button usa-nav__link\" aria-expanded=\"false\" aria-controls=\"basic-nav-section-one\"><span>Conjunction Event Prediction<\/span><svg class=\"hds-desktop-submenu-toggle-icon display-none tablet:display-none desktop:display-block\" width=\"16\" height=\"16\" alt=\"\" enable-background=\"new 0 0 400 400\" viewBox=\"0 0 400 400\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"m4.2 122.2 195.1 195.1 196.5-196.6-37.9-38-157.8 157.8-156.8-156.8z\" \/><\/svg><svg class=\"hds-mobile-submenu-toggle-icon display-block tablet:display-block desktop:display-none\" width=\"16\" height=\"16\" viewBox=\"0 0 16 16\" fill=\"none\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><circle cx=\"8\" cy=\"8\" r=\"7.5\" fill=\"#0B3D91\" stroke=\"white\"\/><rect x=\"4\" y=\"7.6001\" width=\"8\" height=\"0.8\" fill=\"white\"\/><rect class=\"hds-mobile-submenu-toggle-icon-line-vertical\" x=\"7.59998\" y=\"12\" width=\"8\" height=\"0.8\" transform=\"rotate(-90 7.59998 12)\" fill=\"white\"\/><\/svg><\/button><ul id=\"basic-nav-section-one\" class=\"usa-nav__submenu\" hidden><li class=\"usa-nav__submenu-item \"><a class=\"usa-nav__link\" target=\"_self\" href=\"https:\/\/www.nasa.gov\/cara\/step-1-conjunction-event-prediction\/\">Step 1<\/a><\/li><li class=\"usa-nav__submenu-item \"><a class=\"usa-nav__link\" target=\"_self\" href=\"https:\/\/www.nasa.gov\/cara\/step-2-close-approach-risk-assessment\/\">Step 2 <\/a><\/li><li class=\"usa-nav__submenu-item \"><a class=\"usa-nav__link\" target=\"_self\" href=\"https:\/\/www.nasa.gov\/cara\/step-3-close-approach-risk-mitigation\/\">Step 3<\/a><\/li><\/ul><\/li><li class=\"usa-nav__primary-item \"><a class=\"usa-nav__link\" href=\"https:\/\/www.nasa.gov\/cara\/unique-conjunction-events\/\">Unique Conjunction Events<\/a><\/li><li class=\"usa-nav__primary-item\"><button type=\"button\" class=\"usa-accordion__button usa-nav__link\" aria-expanded=\"false\" aria-controls=\"basic-nav-section-one\"><span>More<\/span><svg class=\"hds-desktop-submenu-toggle-icon display-none tablet:display-none desktop:display-block\" width=\"16\" height=\"16\" alt=\"\" enable-background=\"new 0 0 400 400\" viewBox=\"0 0 400 400\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"m4.2 122.2 195.1 195.1 196.5-196.6-37.9-38-157.8 157.8-156.8-156.8z\" \/><\/svg><svg class=\"hds-mobile-submenu-toggle-icon display-block tablet:display-block desktop:display-none\" width=\"16\" height=\"16\" viewBox=\"0 0 16 16\" fill=\"none\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><circle cx=\"8\" cy=\"8\" r=\"7.5\" fill=\"#0B3D91\" stroke=\"white\"\/><rect x=\"4\" y=\"7.6001\" width=\"8\" height=\"0.8\" fill=\"white\"\/><rect class=\"hds-mobile-submenu-toggle-icon-line-vertical\" x=\"7.59998\" y=\"12\" width=\"8\" height=\"0.8\" transform=\"rotate(-90 7.59998 12)\" fill=\"white\"\/><\/svg><\/button><ul id=\"basic-nav-section-one\" class=\"usa-nav__submenu\" hidden><li class=\"usa-nav__submenu-item \"><a class=\"usa-nav__link\" target=\"_self\" href=\"https:\/\/www.nasa.gov\/cara\/cara-services\/\">CARA Overview<\/a><\/li><\/ul><\/ul><\/nav><\/div><\/div><\/div><\/div><\/div>\n\n<div id=\"\" class=\"nasa-gb-align-full maxw-full width-full padding-0 hds-module hds-module-full wp-block-nasa-blocks-page-intro\">\n\t<div class=\"padding-0 bg-spacesuit-white wp-block-nasa-blocks-page-intro\">\n\t\t\t<div class=\"hds-page-intro hds-page-intro-banner width-full maxw-full padding-0 hds-cover-wrapper minh-tablet\">\n\t\t<div class=\"hds-foreground-wrapper display-flex\">\n\t\t\t<div class=\"grid-row grid-container grid-container-block margin-top-auto margin-bottom-auto width-full maxw-desktop-lg padding-top-9 padding-x-3 z-400\">\n\t\t\t\t<div class=\"grid-col-12 desktop:grid-col-6 desktop:padding-right-4 margin-bottom-3 desktop:margin-bottom-0\">\n\t\t\t\t\t<div class=\"margin-bottom-2\">\n\t\t\t\t\t\t<h1 class=\"page-heading-md line-height-sm color-spacesuit-white-important\">\n\t\t\t\t\t\t\tStep 3: Close Approach Risk Mitigation\t\t\t\t\t\t<\/h1>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<p class=\"p-lg color-carbon-30-important\">\n\t\t\t\t\t\tConjunction Risk Assessment\t\t\t\t\t<\/p>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"grid-col-12 desktop:grid-col-6 desktop:padding-right-4 margin-bottom-3 desktop:margin-bottom-0\">\n\t\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t<\/div>\n\t\t<div class=\"skrim-overlay skrim-left mobile-skrim-top z-200\"><\/div>\n\t\t<figure class=\"hds-media-background  \"><img fetchpriority=\"high\" decoding=\"async\" width=\"1200\" height=\"630\" src=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?w=1200\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Conjunction Risk Assessment\" style=\"transform: scale(1); transform-origin: 50% 50%; object-position: 50% 50%; object-fit: cover;\" block_context=\"nasa-block\" srcset=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg 1200w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=300,158 300w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=768,403 768w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=1024,538 1024w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=400,210 400w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=600,315 600w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/07\/cara-web-banner-wp-jul23.jpg?resize=900,473 900w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" loading=\"eager\" \/><\/figure>\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\n<p>For close approaches that manifest a high level of collision risk and thus can be expected to require mitigation, mitigation planning begins about three days prior to the time of closest approach (TCA).  Planning at this point includes beginning to discuss mitigation options.  The great majority of protected assets have active propulsion systems and thus will mitigate high-risk conjunctions with a propulsive maneuver to change their trajectory so as to avoid the secondary object.  A smaller subset of missions perform trajectory modification through a process called <em>differential drag<\/em>, in which they reorient their satellite in order to change the frontal area in the velocity direction and thus the atmospheric drag and, by extension, the satellite trajectory.  An even smaller subset, which lacks any trajectory modification capability, can still reduce collision risk by reorienting their satellite so that its minimum projected area is facing the direction of the oncoming secondary object. <\/p>\n\n\n\n<p>For missions that mitigate through propulsive maneuvers, a <em>maneuver trade-space<\/em> plot is constructed that gives a high-level laydown of the propulsive mitigation possibilities; an example of such a plot is given below.  The x-axis is the burn intensity, the y-axis is the time of burn, and the color is the Pc of the conjunction as mitigated by the maneuver.  From such a plot, one can determine to what Pc level one wishes to mitigate the conjunction as well as the combination of burn size and time that will achieve this level of mitigation.  One can see that maneuvering earlier (higher up on the y-axis) can allow a given degree of mitigation with a smaller burn size, and this is one of the interesting tensions of conjunction mitigation:  mitigating can be accomplished with less fuel if done early; but because many events drop off in risk level as TCA is approached and uncertainty decreases, waiting to mitigate can often eliminate the need to mitigate altogether.  For reference, the NASA requirement for conjunction mitigation is to reduce the Pc one and one-half orders of magnitude below the mitigation requirement of 1E-04, or approximately 3E-06. <\/p>\n\n\n<div id=\"\" class=\"hds-media hds-module wp-block-image\"><div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\"><div class=\"hds-media-wrapper margin-left-auto margin-right-auto\"><figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-none \"><a href=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg\"><img loading=\"lazy\" decoding=\"async\" width=\"2000\" height=\"974\" src=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?w=2000\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Stage 3 MTS Example\" style=\"transform: scale(1); transform-origin: 50% 50%; object-position: 50% 50%; object-fit: cover;\" block_context=\"nasa-block\" srcset=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg 2000w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=300,146 300w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=768,374 768w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=1024,499 1024w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=1536,748 1536w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=400,195 400w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=600,292 600w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=900,438 900w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?resize=1200,584 1200w\" sizes=\"(max-width: 2000px) 100vw, 2000px\" \/><\/a><\/figure><\/div><\/div><\/div>\n\n\n<p>Based on a plot like the above, missions choose a maneuver that provides the needed mitigation and also aligns with their own fuel budgets and timeline constraints.  They then build an ephemeris that contains this maneuver and submit that ephemeris for screening against the catalogue.  If the ephemeris clears a screening interrogation without generating additional high-risk events, then the maneuver can be safely executed.  At the maneuver commitment point, which is typically 1 to 0.5 days to TCA, a final examination of the conjunction risk is made and a decision taken regarding whether to mitigate.  Many events drop off in risk after planning begins but before the maneuver commitment point, allowing the mitigation action to be dispensed.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>For close approaches that manifest a high level of collision risk and thus can be expected to require mitigation, mitigation planning begins about three days prior to the time of closest approach (TCA).  Planning at this point includes beginning to discuss mitigation options.  The great majority of protected assets have active propulsion systems and thus [...]<\/p>\n","protected":false},"author":93,"featured_media":266790,"parent":401428,"menu_order":0,"template":"","meta":{"nasa_hds_core_meta_l10n":"en-US","nasa_hds_core_meta_article_editor":"","nasa_hds_core_meta_article_contacts":[],"nasa_hds_core_meta_article_topic":"","nasa_hds_core_meta_linked_locations":[],"nasa_hds_core_meta_article_related_articles":[],"hds_migrate_meta_pr_release_id":"","hds_migrate_meta_pr_release_type":"","nasa_hds_core_meta_location_x":"","nasa_hds_core_meta_location_y":"","nasa_hds_core_meta_gallery_images":[]},"categories":[11813],"news-tags":[],"internal-terms":[],"coauthors":[3854,9510],"parsely":{"version":"1.1.0","meta":{"@context":"https:\/\/schema.org","@type":"WebPage","headline":"Step 3 Close Approach Risk Mitigation","url":"https:\/\/www.nasa.gov\/cara\/step-3-close-approach-risk-mitigation\/","mainEntityOfPage":{"@type":"WebPage","@id":"https:\/\/www.nasa.gov\/cara\/step-3-close-approach-risk-mitigation\/"},"thumbnailUrl":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?w=150&h=150&crop=1","image":{"@type":"ImageObject","url":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg"},"articleSection":"Organizations","author":[{"@type":"Person","name":"NASA"},{"@type":"Person","name":"Garrett Shea"}],"creator":["NASA","Garrett Shea"],"publisher":{"@type":"Organization","name":"NASA","logo":"https:\/\/www.nasa.gov\/wp-content\/themes\/nasa\/assets\/images\/nasa-logo.svg"},"keywords":["Organizations","Conjunction Assessment Risk Analysis Team (CARA)"],"dateCreated":"2021-12-01T00:23:12Z","datePublished":"2021-12-01T00:23:12Z","dateModified":"2023-09-29T20:22:50Z"},"rendered":"<meta name=\"parsely-title\" content=\"Step 3 Close Approach Risk Mitigation\" \/>\n<meta name=\"parsely-link\" content=\"https:\/\/www.nasa.gov\/cara\/step-3-close-approach-risk-mitigation\/\" \/>\n<meta name=\"parsely-type\" content=\"index\" \/>\n<meta name=\"parsely-image-url\" content=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg?w=150&h=150&crop=1\" \/>\n<meta name=\"parsely-pub-date\" content=\"2021-12-01T00:23:12Z\" \/>\n<meta name=\"parsely-section\" content=\"Organizations\" \/>\n<meta name=\"parsely-tags\" content=\"Organizations,Conjunction Assessment Risk Analysis Team (CARA)\" \/>\n<meta name=\"parsely-author\" content=\"NASA\" \/>\n<meta name=\"parsely-author\" content=\"Garrett Shea\" \/>","tracker_url":"https:\/\/cdn.parsely.com\/keys\/nasa.gov\/p.js"},"read_time":3,"time_ago":"3 years","featured_image":{"id":266790,"file":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/cara_mtsexample2022.jpg","title":"cara_mtsexample2022","alt":"Stage 3 MTS Example","caption":""},"_links":{"self":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263323"}],"collection":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic"}],"about":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/types\/topic"}],"author":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/users\/93"}],"version-history":[{"count":3,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263323\/revisions"}],"predecessor-version":[{"id":464782,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263323\/revisions\/464782"}],"up":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/401428"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/media\/266790"}],"wp:attachment":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/media?parent=263323"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/categories?post=263323"},{"taxonomy":"news-tags","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/news-tags?post=263323"},{"taxonomy":"internal-terms","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/internal-terms?post=263323"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/coauthors?post=263323"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}