ISS Orbital Posture?

[wkitty42]

<p>we've been having a "discussion" around here for a long while, and i've finally decided to inquire of others who are more in "tune" with the ISS and its operation...&nbsp;</p><p>this question pertains to the "posture" of ISS and how it relates to the Earth. The question is actually a two-parter, though...&nbsp;</p><p>Q1. does the ISS "rotate" itself around the center of the Earth so as to keep its "belly" always looking at the Earth?</p><p>A1. yes, as shown by the animation that mouseonmars links to in his reply, below.</p><p>Q2. does the ISS "spin" after the shuttle has docked so that it is "leading" the shuttle instead of "trailing"?</p><p>A2. yes, as indicated by the below quoted paragraph from a link provided by kennyr's reply, below .</p><p>the above second part is the main crux of the "discussions" we've been having around here... it is based on the videos from NASA that appear to place the shuttle in <em>front</em> of the ISS for docking and departure procedures... videos seen during the docked part of the mission appear to indicate that the shuttle is apparently <em>behind</em> the ISS... the position of the shuttle in relation to the ISS is based on which way the Earth's image travels in the videos...</p><p>quoted paragraph answer to Q2: "Micrometeorite hits are a significant threat to loss of the shuttle and crew, and shortly after docking, the station was reoriented as planned to minimize the risk of micrometeoroid/debris impacts upon the shuttle. The new attitude with the shuttle docked essentially points the belly off line of the velocity vector to reduce hits by incoming particles and places more station structure between the belly of the orbiter and open space."</p> <div class="Discussion_UserSignature"> </div>

 

[Testing]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>we've been having a "discussion" around here for a long while, and i've finally decided to inquire of others who are more in "tune" with the ISS and its operation...&nbsp;this question pertains to the "posture" of ISS and how it relates to the Earth. The question is actually a two-parter, though...&nbsp;1. does the ISS "rotate" itself around the center of the Earth so as to keep its "belly" always looking at the Earth?2. does the ISS "spin" after the shuttle has docked so that it is "leading" the shuttle instead of "trailing"?the above second part is the main crux of the "discussions" we've been having around here... it is based on the videos from NASA that appear to place the shuttle in front of the ISS for docking and departure procedures... videos seen during the docked part of the mission appear to indicate that the shuttle is apparently behind the ISS... the position of the shuttle in relation to the ISS is based on which way the Earth's image travels in the videos... <br />Posted by wkitty42</DIV></p><p>I'll just throw out a few points.&nbsp; No sense in SARJ if the whole station retates. No sense in obsevation ports if they only point at Earth once in a while. ISS is also an observation post. If the radiators do not face away from the Sun what purpose do they serve? Perhaps an in depth search of the NASA ISS site would be of benifit.</p> <div class="Discussion_UserSignature"> </div>

 

[mouseonmars]

<p>There's a flash animation on the NASA site that covers some of the different attitudes.</p><p>Don Pettite mentioned this in one of his Science experiments. Depending on the attitude, water behaves differently in various flow experiments. </p> <div class="Discussion_UserSignature"> "I am your God. I am all knowing." Baal, Stargate SG-1 </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'll just throw out a few points.</DIV></p><p>the more the merrier &nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>No sense in SARJ if the whole station retates.</DIV></p><p>well, we've talked about that, too... it would seem that the ARJs (SARJ being on the Starboard side and PARJ being the Port side) would still be desirable if the station does rotate... why? to keep the panels facing the sun </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>No sense in obsevation ports if they only point at Earth once in a while. ISS is also an observation post.</DIV></p><p>yes, the last one is true... but i hesitate on the first... why? surely there are observation ports in other places other than just on the Earth facing side we're also pretty sure that they are used for more than just observing Earth... but this is also where the video cameras come into play... at least those that they point at the Earth which make up a majority of the video stuffs seen from NASA on the NASA TV channel... </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If the radiators do not face away from the Sun what purpose do they serve?</DIV></p><p>this has been another aspect of our discussions, as well... obviously the trusses that the radiators are mounted on do not rotate around the truss axis (is that the X, Y or Z axis?) like the ARJs but they do, IIRC, "spin" parallel to the station's main body... could be wrong on that, though... </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Perhaps an in depth search of the NASA ISS site would be of benifit. <br /> Posted by Testing</DIV></p><p>believe it or not, we've attempted that but that site is not very easy to get around on and there's a huge mess of information that, if it is located there, is extremely hard to locate :?&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>There's a flash animation on the NASA site that covers some of the different attitudes.Don Pettite mentioned this in one of his Science experiments. Depending on the attitude, water behaves differently in various flow experiments. <br /> Posted by mouseonmars</DIV></p><p>Excellent! thank you muchly!</p><p>i would also say that, according to that animation, since the main solar arrays are in position, that the station is flying in what they term as XVV (X-axis in the Velocity Vector) mode... since the velocity vector, unless i'm mistaken, is circular so as to travel around the Earth, would this not indicate that the station <em>does</em> "rotate" to keep its "belly" toward the Earth?</p><p>yeah, i may have asked that question a tad early as i've just started that animation and am only on the second "slide" </p><p>[edit] yeah, a minor correction... it is the Angular Velocity Vector that is "circular" but this animation DOES show that the station always keeps its "nose" pointed to the "front" (X+ axis?) and that it does "keep its belly toward the Earth"... at least when it is flying without the shuttle docked, anyway... [/edit]</p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If the radiators do not face away from the Sun what purpose do they serve? <br /> Posted by Testing</DIV></p><p>i wanted to touch back on this... which radiators are/were you thinking of? there are several sets... the large ones attached to the P1 and S1 trusses and then smaller ones attached with the solar arrays which appear to rotate with the solar arrays and which do appear to "remain in the shade" (somewhat) for maximum cooling effect...these smaller ones look to be mounted on the P4, P6, S4 and S6 trusses... of course, S6 is not yet in place, IIRC... </p> <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Excellent! thank you muchly!i would also say that, according to that animation, since the main solar arrays are in position, that the station is flying in what they term as XVV (X-axis in the Velocity Vector) mode... since the velocity vector, unless i'm mistaken, is circular so as to travel around the Earth, would this not indicate that the station does "rotate" to keep its "belly" toward the Earth?yeah, i may have asked that question a tad early as i've just started that animation and am only on the second "slide" [edit] yeah, a minor correction... it is the Angular Velocity Vector that is "circular" but this animation DOES show that the station always keeps its "nose" pointed to the "front" (X+ axis?) and that it does "keep its belly toward the Earth"... at least when it is flying without the shuttle docked, anyway... [/edit] <br /> Posted by wkitty42</DIV></p><p>Yes, the ISS generally "flies" with its nadir pointing at the Earth and the Harmony node in front.&nbsp; It has large gyroscopes which it uses to maintain this attitude.&nbsp; When they break down, it uses thrusters aboard the Zvezda module to accomplish the same purpose.&nbsp; (Exception: I believe that there are times during docked operations when the Shuttle is put in charge of attitude control.)</p><p>The main viewing windows on the ISS are actually facing downwards for the sake of Earth observation.&nbsp; I believe there are smaller windows elsewhere on the station, mainly to assist in rendezvous operations, since they're not really useful for observing the stars or things like that. </p><p>Incidentally, the Shuttle normally flies "upside down and backwards" -- tail first, payload bay pointing at Earth.&nbsp; The only exception is when there's some particular reason to fly some other attitude (like when docking with the ISS).&nbsp; This often has the radiators inside the payload bay sunlit, but they still work okay.&nbsp; The reason in this case is partly Earth observation, partly a better line-of-sight for communication with ground station, and partly micrometeoroid protection -- put the toughest parts of the vehicle in the most hazardous positions. </p> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Slava33]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>we've been having a "discussion" around here for a long while, and i've finally decided to inquire of others who are more in "tune" with the ISS and its operation...&nbsp;this question pertains to the "posture" of ISS and how it relates to the Earth. The question is actually a two-parter, though...&nbsp;Q1. does the ISS "rotate" itself around the center of the Earth so as to keep its "belly" always looking at the Earth?A1. yes as shown by the animation that mouseonmars links to in his reply below.&nbsp;Q2. does the ISS "spin" after the shuttle has docked so that it is "leading" the shuttle instead of "trailing"?A2. unknown at this time&nbsp;the above second part is the main crux of the "discussions" we've been having around here... it is based on the videos from NASA that appear to place the shuttle in front of the ISS for docking and departure procedures... videos seen during the docked part of the mission appear to indicate that the shuttle is apparently behind the ISS... the position of the shuttle in relation to the ISS is based on which way the Earth's image travels in the videos... <br /> Posted by wkitty42</DIV></p><p>I don't have a definitive answer to whether the station rotates 180deg with the shuttle. &nbsp;However, I would be surprised if it did since it would be a major attitude reorientation, a high risk event. &nbsp;Normally, the station flies in a "torque equilibrium attitude", which is a few degrees off XVV to balance out its two primary sources of torque disturbances: J2 gravity gradient and aerodynamic drag, as described in the attitude control section of ISS familiarization.&nbsp;</p><p>I'm also highly doubtful shuttle is ever used in attitude control (maybe in emergencies in a manual mode) since I don't think it is tied into the closed-loop ISS controller. &nbsp;However, Progress and ATV do perform attitude control in different modes with the Service Module, namely Progress thrusters are used for roll control since it has a good moment arm in Z.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[kennyr]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>... it would seem that the ARJs (SARJ being on the Starboard side and PARJ being the Port side) would still be desirable... <br /> Posted by wkitty42</DIV></p><p>Just to clear up a point:&nbsp; "SARJ" stands for "Solar Alpha Rotary Joint."&nbsp; There is both a Port SARJ and a Starboard SARJ.&nbsp; </p><p>The Alpha designation refers to the reference frame about which that joint rotates.&nbsp; The Alpha joint rotates the arrays like a paddle wheel. &nbsp; This can be compared to the "Beta Gimbals," which allow each array wing to "twist" about their own axes </p>

 

[kennyr]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't have a definitive answer to whether the station rotates 180deg with the shuttle. &nbsp;However, I would be surprised if it did since it would be a major attitude reorientation, a high risk event. &nbsp;Normally, the station flies in a "torque equilibrium attitude", which is a few degrees off XVV to balance out its two primary sources of torque disturbances: J2 gravity gradient and aerodynamic drag, as described in the attitude control section of ISS familiarization.&nbsp;I'm also highly doubtful shuttle is ever used in attitude control (maybe in emergencies in a manual mode) since I don't think it is tied into the closed-loop ISS controller. &nbsp;However, Progress and ATV do perform attitude control in different modes with the Service Module, namely Progress thrusters are used for roll control since it has a good moment arm in Z.&nbsp; <br /> Posted by Slava33</DIV></p><p>Actually, the station performs quite a few attitude maneuvers during shuttle missions.</p><p>1.&nbsp; During docking, the station flys with Destiny "forward", facing with the velocity.&nbsp; The shuttle approaches from below, up to a point directly in front of the station, and then "backs up" to dock.</p><p>2.&nbsp; Upon docking, the station and shuttle go to free drift, with no attitude control.&nbsp; This allows all movements to dampen out and everything to stabilize.&nbsp; During the last mission, this actually took over half an hour, and the station rotated nearly 60 degrees from its initial orientation.</p><p>3.&nbsp; Once the shuttle is hard mated, attitde control is restored.&nbsp; The orbiter takes control and the station is maneuvered to protect the heat shield of the orbiter from MMOD&nbsp; (see http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/DOCKS11178.xml, about 7 paragraphs down).</p><p>4.&nbsp; During the mission there are several other times that the attitude is readjusted.&nbsp; For example, when a water dump is performed by the orbiter, the station is re-oriented to minimize impingement of debris on the station surfaces.</p><p>And it is not at all unusual for the shuttle to have attitude authority.&nbsp; In fact, it is the norm.&nbsp; For large station attitude changes with the orbiter docked, the CMG's <em>could</em> re-orient the station, but they would most likely need to use station propellant to desaturate them.&nbsp; It is desireable to just use orbiter prop to do the orientation than to use precious ISS prop. </p>

 

[Slava33]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Actually, the station performs quite a few attitude maneuvers during shuttle missions.1.&nbsp; During docking, the station flys with Destiny "forward", facing with the velocity.&nbsp; The shuttle approaches from below, up to a point directly in front of the station, and then "backs up" to dock.2.&nbsp; Upon docking, the station and shuttle go to free drift, with no attitude control.&nbsp; This allows all movements to dampen out and everything to stabilize.&nbsp; During the last mission, this actually took over half an hour, and the station rotated nearly 60 degrees from its initial orientation.3.&nbsp; Once the shuttle is hard mated, attitde control is restored.&nbsp; The orbiter takes control and the station is maneuvered to protect the heat shield of the orbiter from MMOD&nbsp; (see http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/DOCKS11178.xml, about 7 paragraphs down).4.&nbsp; During the mission there are several other times that the attitude is readjusted.&nbsp; For example, when a water dump is performed by the orbiter, the station is re-oriented to minimize impingement of debris on the station surfaces.And it is not at all unusual for the shuttle to have attitude authority.&nbsp; In fact, it is the norm.&nbsp; For large station attitude changes with the orbiter docked, the CMG's could re-orient the station, but they would most likely need to use station propellant to desaturate them.&nbsp; It is desireable to just use orbiter prop to do the orientation than to use precious ISS prop. <br /><p> Posted by kennyr</DIV></p><p>I must plead ignorance on ISS operations with the shuttle docked. &nbsp;I guess the shuttle attitude control thrusters are not much diferent from the SM/Progress ones, and it is far removed from the CG to have a good amount of control torque. &nbsp;I stand corrected.</p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Just to clear up a point:&nbsp; "SARJ" stands for "Solar Alpha Rotary Joint."&nbsp; There is both a Port SARJ and a Starboard SARJ.&nbsp; The Alpha designation refers to the reference frame about which that joint rotates.&nbsp; The Alpha joint rotates the arrays like a paddle wheel. &nbsp; This can be compared to the "Beta Gimbals," which allow each array wing to "twist" about their own axes <br /> Posted by kennyr</DIV></p><p>ahh, my bad... we were under the impression, contrary to the terms used, that SARJ was the starboard rotary joint and that the port side one would be a/the PARJ... thanks for the correction &nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Actually, the station performs quite a few attitude maneuvers during shuttle missions.1.&nbsp; During docking, the station flys with Destiny "forward", facing with the velocity.&nbsp; The shuttle approaches from below, up to a point directly in front of the station, and then "backs up" to dock.2.&nbsp; Upon docking, the station and shuttle go to free drift, with no attitude control.&nbsp; This allows all movements to dampen out and everything to stabilize.&nbsp; During the last mission, this actually took over half an hour, and the station rotated nearly 60 degrees from its initial orientation.3.&nbsp; Once the shuttle is hard mated, attitde control is restored.&nbsp; The orbiter takes control and the station is maneuvered to protect the heat shield of the orbiter from MMOD&nbsp; (see http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/DOCKS11178.xml, about 7 paragraphs down).</p><p>[chomp remains]</p><p> Posted by kennyr</DIV></p><p>bingo! that would indicate that the station/shuttle complex DOES spin around the Z-axis/nadir to place the shuttle "behind" the station... yes, FWIW, we have discussed this possibility with regard to protecting the shuttle's heat shield tiles... this seems to answer Q2 of my original post in the <strong>affirmative</strong> but i will follow up on your link tosee what else i can find </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Micrometeorite hits are a significant threat to loss of the shuttle and crew, and shortly after docking, the station was reoriented as planned to minimize the risk of micrometeoroid/debris impacts upon the shuttle. The new attitude with the shuttle docked essentially points the belly off line of the velocity vector to reduce hits by incoming particles and places more station structure between the belly of the orbiter and open space.</DIV></p><p>and there is it... an excerpt from the link provided by kennyr... i'll update my original post in a bit...</p><p>&nbsp;</p><p>FWIW: most of those against either question being a "yes" answer were "only" looking at the effects of what would happen to the microgravity stuffs... my arguments, in particular, was to simply <strong><em>look</em></strong> at the videos on the NASA channel and look at which way the Earth was "flowing" during each stage of the mission...</p><p>it is quite obvious that the shuttle is "heads up" with nose pointing in direction of travel before the "gainer" (aka "backflip") and that it, after returning to the "heads up" attitude, simply pulls forward and up in front of the station so that the shuttle's belly is facing in the direction of travel so that it can "rise" (from the shuttle's POV) to dock with the station... later videos show that the Earth is not approaching from the shuttle's belly as it was during the docking phase but is, instead, receding which, according to Occum's Razor, must indicate that the complex has spun around the Z-axis to place the shuttle in a trailing position...</p><p>that the station "rotates around the oribital center" is/was a bit harder to figure out due to numerous cameras on the station and their movability... however, this, too, is actually faily easy to see when one realizes that there's an antenna array in most of the shots... albeit this array may be different places with regard to the edges of the shots which are likely due to the reorientation of the camera to keep "the target" of the shot within the camera's view and harbour as clean and unobstructed a view as possible... </p><p>thanks again for the provided answers and i welcome any additional posting on this topic &nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[kennyr]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>ahh, my bad... we were under the impression, contrary to the terms used, that SARJ was the starboard rotary joint and that the port side one would be a/the PARJ... thanks for the correction &nbsp; <br /> Posted by wkitty42</DIV></p><p>No problem.</p><p>Another way to think about these orientations (and try to keep a mental picture in your head) is to think about the station in the XVV orientation, which is the normal flight configuration once the solar arrays were placed outboard the truss (after P6 was taken off the Z1 truss and placed in its final P6 position).&nbsp; With Destiny and Node 2 pointing forward (with the velocity vector), the port solar arrays are on the left, and the stbd arrays are on the right.&nbsp; That's where the naming convention for the arrays came from.&nbsp; As the station orbits, the same face always points nadir (towards the earth), node 2 always points forward, and the arrays stay left (port) and right (starboard).</p><p>Note that, although this is the "normal" orientation, many other requirements come into play to determine actual orientation. &nbsp; Solar beta angle, visiting spacecraft docking requirements, heat rejection from the radiators, communication antenna shadowing effects, thrusting orientation for debris avoidance, etc are all taken into account when engineers determine day-to-day station orientation.</p>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>as described in the attitude control section of ISS familiarization.<br /> Posted by Slava33</DIV></p><p>i wanted to come back and thank you for your link to the "ISS familiarization" pdf file... it is a nice source of information even though it is 10 years old </p><p>[i don't know why the link to it doesn't show up in my quote, though :?] </p> <div class="Discussion_UserSignature"> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>No problem.Another way to think about these orientations (and try to keep a mental picture in your head) is to think about the station in the XVV orientation, which is the normal flight configuration once the solar arrays were placed outboard the truss (after P6 was taken off the Z1 truss and placed in its final P6 position).&nbsp; With Destiny and Node 2 pointing forward (with the velocity vector), the port solar arrays are on the left, and the stbd arrays are on the right.&nbsp; That's where the naming convention for the arrays came from.&nbsp; As the station orbits, the same face always points nadir (towards the earth), node 2 always points forward, and the arrays stay left (port) and right (starboard).Note that, although this is the "normal" orientation, many other requirements come into play to determine actual orientation. &nbsp; Solar beta angle, visiting spacecraft docking requirements, heat rejection from the radiators, communication antenna shadowing effects, thrusting orientation for debris avoidance, etc are all taken into account when engineers determine day-to-day station orientation. <br /> Posted by kennyr</DIV><br /><br />yep, mouseonmars' posted link to the animation on NASA's site gives a lot of this info with graphical details... it is quite easy to see...</p><p>FWIW: we were thinking that the acronyms were "Starboard Array Rotary Joint" and "Port Array Rotary Joint"... we also knew about the gimbal joints but didn't really have or know of any names for them...</p><p>ya know? this whole discussion has also answered a couple of other questions regarding the station... the main one(s) being about the axis'... we now know that the X-axis is oriented centrally thru harmony and zarya... the y-axis is the main station truss line and the z-axis went thru the science and early power segment (P6) that was mounted "on top" (away from the earth) of the station... </p><p>all in all, the whole thread has been very revealing on numerous aspects and the answers to the questions asked were easily understood and forthcoming &nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>all in all, the whole thread has been very revealing on numerous aspects and the answers to the questions asked were easily understood and forthcoming &nbsp; <br />Posted by wkitty42</DIV><br /><br />Well, welcome to Space.com, and I hope you will hang around a bit and see what else makes this such a great place to learn and share!</p><p>&nbsp;</p><p>Wayne</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[wkitty42]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Well, welcome to Space.com, and I hope you will hang around a bit and see what else makes this such a great place to learn and share!&nbsp;Wayne <br /> Posted by MeteorWayne</DIV></p><p>thanks muchly, wayne...</p><p>truth be known, i've been "here" for a long long time but it seems that my account gets deleted after some period of inactivity :?</p><p>i started here when space.com first picked up the daily space activities newsletter that was sent out by another party some years back... that was back in the day just a few short months or so before space.com actually provided email addresses for its members which it then decided to remove due to all the spam and the decision that it was too much work/trouble to bitbucket and/or filter it :?</p><p>in any case, thanks for the welcome (back) </p> <div class="Discussion_UserSignature"> </div>