Editing GPIS 5: Dancing In The Dark

Jump to navigation Jump to search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

Latest revision Your text
Line 39: Line 39:
 
[[File:GPIS_5_3.png|alt=Orbits]]
 
[[File:GPIS_5_3.png|alt=Orbits]]
  
It’s clear that with the same orbital period , T(A)=T(B)=90 minutes, the two ships will never “catch up” with each other. Something has to change. If your ship A makes a small prograde burn at P (figure 2), this burn point becomes its periapsis, and its orbital period is increased by (say) one minute. The other figures show what happens as a result on the next two orbits. By “speeding up” with a prograde burn, you now have a bigger elliptical orbit that takes one minute longer to complete than the target’s (B) still- original orbit. So on each orbit you “fall back” by one minute. After two orbits, you have fallen back by two minutes and now reach the point P at the same time as the target ship B (figure 4). To prevent falling back further, you would need to make a small retro burn at P to return to the original smaller circular orbit (velocity as well as position matched or “synced” with the target, figure 5).
+
It’s clear that with the same orbital period , T(A)=T(B)=90 minutes, the two ships will never “catch up” witheachother.Somethinghastochange. IfyourshipAmakesasmallprogradeburnatP(figure2), this burn point becomes its periapsis, and its orbital period is increased by (say) one minute. The other figures show what happens as a result on the next two orbits. By “speeding up” with a prograde burn, you now have a bigger elliptical orbit that takes one minute longer to complete than the target’s (B) still- original orbit. So on each orbit you “fall back” by one minute. After two orbits, you have fallen back by two minutes and now reach the point P at the same time as the target ship B (figure 4). To prevent falling back further, you would need to make a small retro burn at P to return to the original smaller circular orbit (velocity as well as position matched or “synced” with the target, figure 5).
 
In general, it won’t be quite this simple. Both orbits would probably be elliptical, the difference in arrival time won’t be a simple number like 2 minutes, and the adjustment burn to match orbits with the target when you get near it won’t be a simple retro burn. But the Sync MFD handles the numbers to allow you to line up the times pretty easily for the general case.
 
In general, it won’t be quite this simple. Both orbits would probably be elliptical, the difference in arrival time won’t be a simple number like 2 minutes, and the adjustment burn to match orbits with the target when you get near it won’t be a simple retro burn. But the Sync MFD handles the numbers to allow you to line up the times pretty easily for the general case.
  
 
== Docking Notes ==
 
== Docking Notes ==
  
Rendezvous or orbit synchronization can get you close to your target (within a few kilometers or even closer), and then the docking HUD and Docking MFD will help you with the rest. The first job once you are close in position is to also get yourself close in speed, adjusting your relative velocity to make your orbit closely match that of the target. Symbols projected on the docking HUD show your relative velocity as well as position information, giving you visual cues on where to point and thrust to reduce your relative velocity, and on where you are heading relative to the target. Unless your orbit is almost exactly the same as the target’s when you get close to the target, you will find that it can take several cycles of reducing relative velocity, pointing and thrusting toward the target, adjusting alignment, and again fixing up the velocity. Although the HUD and MFD give you good feedback, “keeping everything happy” can seem like a juggling act at first. The details are easier to explain with an actual example, coming up shortly. It can also help to watch the flight recording, which realistically shows how this can all work. An expert could probably make a faster, more efficient, and more accurate approach than what is shown in this recording, but this way you can learn from those mistakes as well!
+
Rendezvous or orbit synchronization can get you close to your target (within a few kilometers or even closer), and then the docking HUD and Docking MFD will help you with the rest. The first job once you are close in position is to also get yourself close in speed, adjusting your relative velocity to make your orbit closely match that of the target . Symbols projected on the docking HUD show you relative velocity as well as position information, giving you visual cues on where to point and thrust to reduce your relative velocity, and on where you are heading relative to the target. Unless your orbit is almost exactly the same as the target’s when you get close to the target, you will find that it can take several cycles of reducing relative velocity, pointing and thrusting toward the target, adjusting alignment, and again fixing up the velocity. Although the HUD and MFD give you good feedback, “keeping everything happy” can seem like a juggling act at first. The details are easier to explain with an actual example, coming up shortly. It can also help to watch the flight recording, which realistically shows how this can all work. An expert could probably make a faster, more efficient, and more accurate approach than what is shown in this recording, but this way you can learn from those mistakes as well!
  
 
== Setting Up ==
 
== Setting Up ==
  
In the case of the Space Shuttle docking with the ISS, available delta-V is very limited and orbital plane alignment with the target and preparing for a close intersection are done mainly by choosing the right launch window and flying a precise ascent. Using the Delta Glider, you have plenty of delta-V, and you could start with nearly any LEO situation and make the necessary burns to align orbits, rendezvous, and dock with the ISS. But in this case we will show you a different setup method that’s possible only in Orbiter – the Scenario Editor.
+
In the case of the Space Shuttle docking with the ISS, available delta-V is very limited and orbital plane alignment with the target and preparing for a close intersection are done mainly by choosing the right launch window and flying a precise ascent. Using the Delta Glider, you have plenty of delta-V, and you could start with nearly any LEO situation and make the necessary burns to align orbits, rendezvous, and dockwiththeISS. Butinthiscasewewillshowyouadifferentsetupmethodthat’spossibleonlyin Orbiter – the Scenario Editor.
  
 
The Scenario Editor has many capabilities and is explained in more detail in Appendix B and in its own PDF manual installed in the Orbiter /Doc folder. In this case you will use its ability to directly change the orbital elements of any spacecraft in the currently running scenario, starting with a scenario where you are already docked and modifying it to put the DG in a different starting orbit. We will give the basic steps here without explaining too much about the orbital elements or the Scenario Editor.
 
The Scenario Editor has many capabilities and is explained in more detail in Appendix B and in its own PDF manual installed in the Orbiter /Doc folder. In this case you will use its ability to directly change the orbital elements of any spacecraft in the currently running scenario, starting with a scenario where you are already docked and modifying it to put the DG in a different starting orbit. We will give the basic steps here without explaining too much about the orbital elements or the Scenario Editor.
Line 331: Line 331:
 
|style="text-align:right" width="33%" |[[GPIS_6:_Reentry|Chapter 6: Reentry]]
 
|style="text-align:right" width="33%" |[[GPIS_6:_Reentry|Chapter 6: Reentry]]
 
|}
 
|}
 
[[Category: Articles|Go Play In Space 06]]
 
[[Category:Tutorials|Go Play In Space 06]]
 
 
{{HasPrecis}}
 

Please note that all contributions to OrbiterWiki are considered to be released under the GNU Free Documentation License 1.2 (see OrbiterWiki:Copyrights for details). If you do not want your writing to be edited mercilessly and redistributed at will, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource. Do not submit copyrighted work without permission!

To protect the wiki against automated edit spam, we kindly ask you to solve the following hCaptcha:

Cancel Editing help (opens in new window)