{"id":263324,"date":"2021-11-30T17:07:23","date_gmt":"2021-11-30T22:07:23","guid":{"rendered":"https:\/\/www.nasa.gov\/?migration=converted-node-475642"},"modified":"2023-09-29T16:22:53","modified_gmt":"2023-09-29T20:22:53","slug":"step-1-conjunction-event-prediction","status":"publish","type":"topic","link":"https:\/\/www.nasa.gov\/cara\/step-1-conjunction-event-prediction\/","title":{"rendered":"Step 1 Conjunction Event Prediction"},"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 1: Conjunction Event Prediction\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>The first step in collision avoidance orbital safety is to determine, under present practice about a week into the future, which space objects will come within proximity of a protected space asset, such as one of NASA\u2019s scientific missions.  To identify these close approaches, it is necessary to know the future predicted positions of both the protected asset (called the \u201cprimary\u201d object) and all of the other known objects in space.  In general, the protected asset is an operational payload, and such satellites produce predicted ephemerides that indicate their \u201cstate\u201d (position and velocity) and \u201ccovariance\u201d (expected uncertainty about that state) at regular time-points (in Low Earth Orbit (LEO) usually one-minute time steps) out several days into the future.  For the other known objects, statements of their position are either ephemerides that they produce and share (if they are active satellites) or ephemerides generated from a space catalogue maintained with tracking data collected by space surveillance sensors. The US DoD space catalogue is the source of this data used by NASA, although other nations and some commercial companies maintain space catalogues as well. <\/p>\n\n\n\n<p>Conjunction Assessment (CA) screenings are typically conducted by constructing a volumetric region about the primary object\u2019s position, then moving that volume along the predicted ephemeris, and determining whether any of the other catalogued objects penetrate this volume.  Any objects thus identified represent potential conjunction threats and are thus called conjunctors and also \u201csecondary\u201d objects in a conjunction (in contrast to the primary object, which is the protected asset).  In the diagram at right, the screening volume is shown by the green rectangular prism and is centered on the primary object, represented by the yellow dot.  The blue dot, representing a secondary object, is within the box during this screening and thus has been identified as a conjunctor.  For the CA screenings run by the US Space Force\u2019s 18th Space Defense Squadron, which at present is the principal provider of screening information for the space community, each screening volume penetration generates a Conjunction Data Message (CDM).  This message includes conjunction summary parameters, the states and covariances at the two objects\u2019 time of closest approach (TCA), and amplifying information about the orbit determination used to generate these states and covariances. <\/p>\n\n\n\n<p>It is important to recognize that CDMs are not collision warnings\u2014no actual assessment of collision risk has been performed in generating them.  Rather, they are proximity alerts, pointing out situations in which a serious close approach is possible.  It is rather like the back-up radar in luxury cars:  when the radar starts beeping, it does not mean that the driver is going to hit something; instead, it points out a situation in which is collision is possible and enjoins the driver to exercise some additional care.  This is why the next step in the CA process is to subject any received CDMs to a collision risk assessment process.<\/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\/conjunction_event_prediction_image1.png\"><img loading=\"lazy\" decoding=\"async\" width=\"972\" height=\"1354\" src=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?w=972\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Conjunction Event Prediction graphic 1\" 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\/conjunction_event_prediction_image1.png 972w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=215,300 215w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=768,1070 768w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=735,1024 735w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=287,400 287w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=431,600 431w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=646,900 646w, https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?resize=861,1200 861w\" sizes=\"(max-width: 972px) 100vw, 972px\" \/><\/a><\/figure><\/div><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>The first step in collision avoidance orbital safety is to determine, under present practice about a week into the future, which space objects will come within proximity of a protected space asset, such as one of NASA\u2019s scientific missions.  To identify these close approaches, it is necessary to know the future predicted positions of both [...]<\/p>\n","protected":false},"author":93,"featured_media":266794,"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":[10636],"coauthors":[9510,3854],"parsely":{"version":"1.1.0","meta":{"@context":"https:\/\/schema.org","@type":"WebPage","headline":"Step 1 Conjunction Event Prediction","url":"https:\/\/www.nasa.gov\/cara\/step-1-conjunction-event-prediction\/","mainEntityOfPage":{"@type":"WebPage","@id":"https:\/\/www.nasa.gov\/cara\/step-1-conjunction-event-prediction\/"},"thumbnailUrl":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?w=150&h=150&crop=1","image":{"@type":"ImageObject","url":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png"},"articleSection":"Organizations","author":[{"@type":"Person","name":"Garrett Shea"},{"@type":"Person","name":"NASA"}],"creator":["Garrett Shea","NASA"],"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":"2021-11-30T22:07:23Z","datePublished":"2021-11-30T22:07:23Z","dateModified":"2023-09-29T20:22:53Z"},"rendered":"<meta name=\"parsely-title\" content=\"Step 1 Conjunction Event Prediction\" \/>\n<meta name=\"parsely-link\" content=\"https:\/\/www.nasa.gov\/cara\/step-1-conjunction-event-prediction\/\" \/>\n<meta name=\"parsely-type\" content=\"index\" \/>\n<meta name=\"parsely-image-url\" content=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png?w=150&h=150&crop=1\" \/>\n<meta name=\"parsely-pub-date\" content=\"2021-11-30T22:07:23Z\" \/>\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=\"Garrett Shea\" \/>\n<meta name=\"parsely-author\" content=\"NASA\" \/>","tracker_url":"https:\/\/cdn.parsely.com\/keys\/nasa.gov\/p.js"},"read_time":3,"time_ago":"3 years","featured_image":{"id":266794,"file":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2021\/11\/conjunction_event_prediction_image1.png","title":"conjunction_event_prediction_image1","alt":"Conjunction Event Prediction graphic 1","caption":""},"_links":{"self":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263324"}],"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":4,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263324\/revisions"}],"predecessor-version":[{"id":464764,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/topic\/263324\/revisions\/464764"}],"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\/266794"}],"wp:attachment":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/media?parent=263324"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/categories?post=263324"},{"taxonomy":"news-tags","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/news-tags?post=263324"},{"taxonomy":"internal-terms","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/internal-terms?post=263324"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/coauthors?post=263324"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}