{"id":15922,"date":"2015-11-19T00:14:12","date_gmt":"2015-11-18T16:14:12","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/explained-why-atlas-5-will-have-longer-windows-for-station-flights\/"},"modified":"2015-11-19T00:14:12","modified_gmt":"2015-11-18T16:14:12","slug":"explained-why-atlas-5-will-have-longer-windows-for-station-flights","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/explained-why-atlas-5-will-have-longer-windows-for-station-flights\/","title":{"rendered":"Explained: Why Atlas 5 will have longer windows for station flights"},"content":{"rendered":"
\"Atlas
Atlas 5 launch. Credit: ULA<\/figcaption><\/figure>\n

CAPE CANAVERAL \u2014 Expanding a single instant in time to 30 minutes, the upcoming United Launch Alliance Atlas 5 rockets with Cygnus cargo-delivery freighters bound for the International Space Station will have an unprecedented opportunity available to launch each day.<\/p>\n

The first of two such launches in a 100-day span from Cape Canaveral, known as the OA-4 mission for Orbital ATK, is scheduled for Dec. 3. The pair of flights will deliver over 15,000 pounds of supplies to the outpost.<\/p>\n

The timing for a launch to the station, flying 250 miles above the Earth, is dictated by getting into the orbital plane of the complex for a rendezvous.<\/p>\n

\u201cInstantaneous launch windows are the standard way to accomplish a rendezvous mission with a low-earth object like the ISS, and this approach can significantly limit the probability of an on-time launch,\u201d said Jim Sponnick, ULA\u2019s vice president for Atlas and Delta programs.<\/p>\n

\u201cA mission like this needs to be delivered to the right orbit, including precise timing relative to the ISS, to enable a timely rendezvous between the Cygnus and the ISS.\u201d<\/p>\n

The SpaceX Falcon 9, Russian Soyuz, European Ariane 5 and Japanese H-2B rockets all have instantaneous launch windows for space station missions, giving them a split second each day to fly or else scrub.<\/p>\n

The now-retired space shuttle had 10 minutes and the Orbital ATK Antares rocket has had between five and 10 minutes.<\/p>\n

That leaves little time to wait for a stray rain shower to pass by, a technical gremlin to be resolved or a boat in restricted waters to be chased away.<\/p>\n

But it will be a bit different for the Dec. 3 flight of the Atlas 5 from Cape Canaveral and another cargo mission for the rocket coming up March 10.<\/p>\n

The performance of the Atlas 5 will produce a 30-minute launch window each day.<\/p>\n

\u201cIt is all about available energy to steer you to the right place,\u201d said Dan Tani, a former astronaut who spent 120 days living and working aboard the station on Expedition 16 and now Orbital ATK\u2019s manager of mission and cargo operations.<\/p>\n

\u201cThere is an ideal launch moment, and that\u2019s what SpaceX targets. A lot of other launch vehicles use excess performance to not have to hit a moment and use that energy to steer to the right place.<\/p>\n

\u201cAtlas has so much available energy that they can accommodate what I consider a very large, off-nominal time of launch \u2014 15 minutes early, 15 minutes late. That is a lot of steering, but they have that capability and they are the ones that came to us and asked if they could have that margin. And it gives them a lot of flexibility around weather, around the unknowns.\u201d<\/p>\n

Sponnick added: \u201cThe ULA team always strives to implement longer launch windows in our mission designs, to maximize the probability of a first-day launch for our customers. We have been enhancing our mission design capabilities and operational processes for years in order to make good use of the launch vehicle performance to provide the flexibility to accomplish launch window objectives.<\/p>\n

\u201cThese enhancements include the development of steering algorithms to compensate for the rotation of the Earth relative to the orbital target.\u201d<\/p>\n

The launch window on Dec. 3, based on current projections, opens at approximately 5:55:41 p.m. EST (2255:41 GMT). That will be updated based on radar tracking of the International Space Station and determination of its precise orbit.<\/p>\n

\u201cFor the OA-4 mission, the ULA mission design team has worked very closely with the Orbital ATK team to provide a design approach that enables a longer launch window. The OA-4 launch design approach accounts for the fact that the ISS orbit can change shortly before the launch, if either an overall orbit adjustment or evasive debris mitigation maneuver is required,\u201d Sponnick explained.<\/p>\n

\u201cConsidering the capabilities inherent in the Atlas design, the late changes that can occur in the ISS orbit, and the close coordination with the Orbital ATK Cygnus rendezvous design, we have implemented a 30-minute long window, which will occur within a bounding 50-minute-long window that accounts for the potential late orbital changes for the ISS.\u201d<\/p>\n

Taking everything into account, the launch team will set five discrete launch opportunities \u2014 one at the opening of the launch window and four other shots spaced at 7.5 minute intervals.<\/p>\n

* 5:55:41 p.m. EST
\n* 6:03:11 p.m. EST
\n* 6:10:41 p.m. EST
\n* 6:18:11 p.m. EST
\n* 6:25:41 p.m. EST
\n*times are approximate<\/p>\n

\u201cWe target the first launch opportunity. We\u2019ve made that decision because there is no benefit in waiting for the middle of the window,\u201d Tani explained.<\/p>\n

\u201cSince they have the energy, we aren\u2019t losing anything, they don\u2019t drop us off lower (in altitude) at the edges of the window than at the middle of the window. They drop us off at the same place. So it\u2019s in our interest to get flying as soon as possible, so we\u2019re targeting the beginning of the window.\u201d<\/p>\n

And getting off the ground as soon as possible has other considerations, too.<\/p>\n

\u201cDecember is an extremely busy time for the space station. There\u2019s a lot of comings and goings with the Russian vehicles. So that restricts our ability to approach. Right now, launch dates of (Dec.) 3rd, 4th, 5th and 6th are fantastic. Anything after that we would really have to do some head-scratching and some desk-pounding to figure out when we would approach the space station,\u201d Tani said.<\/p>\n

December 3
\nLaunch: 5:55:41 p.m. EST
\nISS arrival: Dec. 6<\/p>\n

December 4
\nLaunch: 5:33 p.m. EST
\nISS arrival: Dec. 7 or 8<\/p>\n

December 5
\nLaunch: 5:10 p.m. EST
\nISS arrival: Dec. 9<\/p>\n

December 6
\nLaunch: 4:44 p.m. EST
\nISS arrival: Dec. 19<\/p>\n

One other scenario is, if the flight is delayed, the Cygnus could launch later and then hang around in orbit for a couple of weeks before the rendezvous.<\/p>\n

\u201cWe have a couple weeks of loiter capability, so that\u2019s in our box of tricks. But right now, if we miss the 6th, we would have to wait almost a month to get to the station,\u201d Tani said.<\/p>\n

One of the Russian Soyuz capsules at the station will relocate from one docking port to another on Dec. 11. Three new residents launch aboard another Soyuz on Dec. 15 and a Progress cargo ship goes up Dec. 21 and docks Dec. 23. Three station residents undock Dec. 21 for landing.<\/p>\n

There\u2019s also a solar-angle blackout period for the Cygnus to launch from Christmas Eve through Jan. 3.<\/p>\n

See earlier Cygnus OA-4 coverage.<\/p>\n

Our Atlas archive.<\/p>\n","protected":false},"excerpt":{"rendered":"

Atlas 5 launch. Credit: ULA CAPE CANAVERAL \u2014 Expanding a single instant in time to 30 minutes, the upcoming United Launch Alliance Atlas 5 rockets with Cygnus cargo-delivery freighters bound for the International Space Station will have an unprecedented opportunity available to launch each day. The first of two such launches in a 100-day span […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[724,3800,286,2304,639,717,3801,2899],"class_list":["post-15922","post","type-post","status-publish","format-standard","hentry","category-news","tag-atlas-5","tag-av-061","tag-cargo","tag-crs","tag-cygnus","tag-international-space-station","tag-oa-4","tag-orbital-atk"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/15922"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=15922"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/15922\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=15922"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=15922"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=15922"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}