Author Topic: ISS/Shuttle ground track question  (Read 13753 times)

Offline Tahii

  • Fetch me a fix of anesthetic
  • Full Member
  • ***
  • Posts: 382
  • Lurking around the Awarua Space Tracking Station
  • Invercargill, New Zealand
  • Liked: 1
  • Likes Given: 10
ISS/Shuttle ground track question
« on: 08/02/2005 10:12 AM »
As asked in the Flight day 7 thread.

Normally, the orbit of the ISS takes it all over the world - its ground track moves around a lot. Lately, the ground track seems to have been solidly over Australia, South America, Europe and China, and NZ. Its ground track seems to have been in this one place for a long time.

Has the ISS changed orbit, to accomodate the orbiters landing? Does anyone understand my post at all?

Offline Flightstar

  • Lurking around OPF High Bay 2
  • Full Member
  • ****
  • Posts: 1871
  • KSC, Florida
  • Liked: 11
  • Likes Given: 5
RE: ISS/Shuttle ground track question
« Reply #1 on: 08/02/2005 11:14 AM »
I do, but I think that's more a question for NASA Twix.

Offline rhwinger

  • Searching for a place in space
  • Member
  • Posts: 62
  • Liked: 0
  • Likes Given: 0
RE: ISS/Shuttle ground track question
« Reply #2 on: 08/02/2005 11:21 AM »
I'm not an orbital mechanics expert, but the ISS ground track in reference to a fixed point on the surface of the earth does change over time.  If you go to the NASA website, you can see a program that predicts when you will be able to see ISS at your location. http://spaceflight1.nasa.gov/realdata/sightings/  Those viewing opportunity times change, so by observing that fact, I think you could see that the ground track shifts.  Also, an interesting presentation of a satellite orbit:  http://spaceflight1.nasa.gov/realdata/elements/graphs.html


I seem to recall reading that they recently made an adjustment to the ISS orbit in preparing for the expected orbiter docking, but I don't know if it was just an altitude adjustment or not.

Hope this helps.

Offline Tahii

  • Fetch me a fix of anesthetic
  • Full Member
  • ***
  • Posts: 382
  • Lurking around the Awarua Space Tracking Station
  • Invercargill, New Zealand
  • Liked: 1
  • Likes Given: 10
RE: ISS/Shuttle ground track question
« Reply #3 on: 08/02/2005 11:34 AM »
Cheers, that helps. I thought it was just an altitude change they did for the shuttle, but it may have been more. To me it seems as if its changed its inclination compared to the equator, but hey, I'm just a farm boy from NZ, I don't know these things :D

Offline FransonUK

  • Don't ya wish your spaceship was hot like me...don't ya
  • Full Member
  • ****
  • Posts: 867
  • Liked: 3
  • Likes Given: 1
RE: ISS/Shuttle ground track question
« Reply #4 on: 08/02/2005 12:31 PM »
How does the ISS 'swing'? Does it actually turn, or what?
Don't ya wish your spaceship was hot like me

Offline rhwinger

  • Searching for a place in space
  • Member
  • Posts: 62
  • Liked: 0
  • Likes Given: 0
RE: ISS/Shuttle ground track question
« Reply #5 on: 08/02/2005 03:35 PM »
If by "swing", are you referring to the curved ground track or are you asking does the ISS swing around in orbit?

If you are asking about the ground track:  The plane of the ISS orbit is tilted something like 51 degrees in relation to the earth's equator.  So if there were a rope with a piece of chaulk dangling straight down from the ISS as it orbits the Earth, and if the Earth did not spin around on the north/south axis, the line drawn by the chaulk would be a simple straight line tilted at 51 degrees as the ISS goes above and below the equator.  But, the Earth rotates below the ISS, so the line produced by the chaulk would look line a sine wave as the ISS crossed above, and then below, the equator.  God, I hope this makes sense?

Uh, I'm getting dizzy.

If you are asking if the ISS swings around in orbit, I have an opinion.  But before we go there, I'd like to know if I answered your question first?

Offline FransonUK

  • Don't ya wish your spaceship was hot like me...don't ya
  • Full Member
  • ****
  • Posts: 867
  • Liked: 3
  • Likes Given: 1
RE: ISS/Shuttle ground track question
« Reply #6 on: 08/02/2005 05:06 PM »
Great answer, thank you.
Don't ya wish your spaceship was hot like me

Offline NASA_Twix_JSC

  • Supporting FDOs since 1999
  • Full Member
  • ****
  • Posts: 690
  • Liked: 2
  • Likes Given: 1
RE: ISS/Shuttle ground track question
« Reply #7 on: 08/02/2005 06:23 PM »
Good answers. What is left to answer?

Offline rhwinger

  • Searching for a place in space
  • Member
  • Posts: 62
  • Liked: 0
  • Likes Given: 0
RE: ISS/Shuttle ground track question
« Reply #8 on: 08/02/2005 07:02 PM »
Well, I wasn't sure if the "swing" in question was with regard to the development of the sinusoidal ground track, or the orientation (x,y,z directions) of the ISS as a whole structure as it traveled around the earth during an orbit.

I'm finding it difficult to put this into words, without sounding like a total dweeb.  I used to wonder if the orbiter was over, say, Florida with the wings "parallel" to the ground - one tip into the velocity vector, (nose pointed to the north pole) - by the time it moved to, say, Russia, would one wing be pointed at the ground and the other be pointed out into space?  Then would the orbiter be upside down with the wings parallel to the ground by the time it got to, say Asia?  Back over Florida, the wings would be situated as before?  

But then I read about gravity gradient stabilization and this helped me realize that the vehicle would tend to maintain it's orientation relative to the earth, not the solar system.  Or, I'm just a babbling idiot, totally out of my field here?  No formal education in orbital mechanics.

Offline Tahii

  • Fetch me a fix of anesthetic
  • Full Member
  • ***
  • Posts: 382
  • Lurking around the Awarua Space Tracking Station
  • Invercargill, New Zealand
  • Liked: 1
  • Likes Given: 10
RE: ISS/Shuttle ground track question
« Reply #9 on: 08/03/2005 05:51 AM »
I had a thought about this today at work, and if I remember correctly, the ISS is pretty low in altitude at the moment isn't it? That would mean it would orbit slightly faster around the Earth, and the Earth wouldn't have as much time to move under it, meaning the ground track takes longer to move.

...I think

Offline rhwinger

  • Searching for a place in space
  • Member
  • Posts: 62
  • Liked: 0
  • Likes Given: 0
RE: ISS/Shuttle ground track question
« Reply #10 on: 08/03/2005 01:00 PM »
I think you are correct.

If you consider a geosyncronous satellite, it's orbit is way out there, but the ground track is a stationary dot on the surface of the earth.  Conversely, the closer you get to earth's surface, then the ground track would "speed up"?

Tags: