Flight Question Rendezvous with ISS - Travelling in opposite direction

[NTpspE]

Hi There,

I apologize in advance if this has already been posted, but I couldn't find anything when I did a search (Possibly because I don't know the proper terminology).

So I set off from KSC runway with the XR5, and achieved orbit, matched it with the ISS, then got ready for plane alignment.

However, I looked on the map screen, and noticed that we're actually travelling in the opposite direction to the ISS (ISS is travelling from east to west, we're travelling west to east).

My first question, if I use sync MFD to sync the orbital (trajectory?) will we still be travelling in the opposite direction, or will it be a long process of getting the direction the same as well?

And my second question, if we're travelling at the opposite direction, is it still possible to rendezvous with the iss and dock successfully? or would it take an ungodly amount of fuel to slow down so that I don't pass it?

Obviously I know it seems like I may have to re-land and re-launch at the correct direction xD

Many Thanks,
NT

 

[jedidia]

However, I looked on the map screen, and noticed that we're actually travelling in the opposite direction to the ISS (ISS is travelling from east to west, we're travelling west to east).

You either interpreted something wrong, or you have your headings backward. The ISS does travel from west to east. Launching the station retrograde would have been that much more expensive, and absolute nonsense...

And my second question, if we're travelling at the opposite direction, is it still possible to rendezvous with the iss and dock successfully? or would it take an ungodly amount of fuel to slow down so that I don't pass it?

Yes and yes. Yes, it is still (theoretically) possible to dock with a trickshot in orbiter, if you manage to hit the docking port at a relative velocity of 14000 meters per second. If you pull that of, we'll be forced to make up some medal for you. In reality, it wouldn't be possible at all.

And yes, it does take an ungodly amount of propellant, which means that either you have to pull off the bad-ass stunt described above, or use unlimited fuel if you want to dock from this approach.

 

[Cras]

Abort. Dont even bother trying to rendezvous with a prograde traveling object when in a retrograde orbit.

Start over and try again. And always always always launch to the East. At least when launching from Earth anyway.

 

[mc_]

Hm, it should be better to say i didn't think about it. Opposite direction orbit - for why?

Even if you can meet the ISS, it will be impossible to dock normally - you'll need too much fuel to align speed vectors (8k-(-8k)=16k).

So, it's better to land, refuel the ship and start again.

 

[NTpspE]

Thanks guys,

@Jedidia sorry I wrote the directions back to front, the ISS is travelling west to east, and we're travelling east to west (Don't know how I got that wrong, since I was saying "Never Eat Shreadded Wheat" lmao)

I was attempting to go for realism on this flight, so I won't be planning on using any cheats for the fuel and such. I'll try land back at KSC and launch again with the right heading (I started this scen before I knew about working out launch heading).

Thanks a lot for your help guys, and I apologise for such a short thread!

Kind Regards,
NT

 

[dgatsoulis]

And yes, it does take an ungodly amount of propellant, which means that either you have to pull off the bad-ass stunt described above, or use unlimited fuel if you want to dock from this approach.

I'd hardly call ~3400 m/s of dV in an XR5 an "ungodly amount of propellant".

 

[Rtyh-12]

In the Align Planes MFD, check the RInc (relative inclination) value. It should be fairly small (20° should be enough to align, 10° is good, under 1° is excellent). If it's around 180° you are, indeed, travelling in the wrong direction. Too late, you already checked that, sorry.

Note that it's still possible to align, but only using some tricks. You can, for example, drop into the upper atmosphere and turn like you would during atmospheric flight (you still have to use some fuel to counteract the slowdown the atmosphere will cause). Or you could swing around the Moon. But don't even bother with these, at least before you learn interplanetary transfers

 

[garyw]

And my second question, if we're travelling at the opposite direction, is it still possible to rendezvous with the iss and dock successfully? or would it take an ungodly amount of fuel to slow down so that I don't pass it?

You'll have major issues docking as you are travelling at orbital velocity in the wrong direction. You'll make a hell of a missile though and there is some fun in seeing the ISS flypast at 0.1x timewarp still moving with some serious speed. :lol:

 

[N_Molson]

Actually, with the right (insane) engine and Isp settings, doing a sort of "cobra" at 0.1x time accel to reverse suddenly the direction of your revolution could be fun... :hmm:

But the crew will probably complain about the G-force involved :lol:

Then you watch it at x1 with playback mode and make a video of it.

 

[statickid]

It would be a good way to destroy the space station I suppose :hmm:

 

[NTpspE]

Haha all very good ideas, but I think I'll play it safe and just land
I like the idea of slingshotting around the moon though, might have to try that sometime. I've done LEO-Lunar transfer a few times, and I've docked with the ISS fine in the past, I just seem to have gotten left and right mixed up this time :facepalm:

Kind Regards,
NT

 

[george7378]

To change your direction and travel east, you'd need enough fuel to come to a complete stop in space, and then enter orbit from scratch in the other direction! Also, I'd love to see an attempt at docking in the opposite direction! I had an idea once to launch vertically from the ground, and ascend directly to the ISS when it passes overhead, so that I could dock without entering orbit! That would be cool too.

 

[garyw]

To change your direction and travel east, you'd need enough fuel to come to a complete stop in space, and then enter orbit from scratch in the other direction!

You could go around the moon then come back to Earth and enter an eastwards orbit..... I have no idea if the fuel expenditure for that is less than changing orbital direction - I think it might be but I'll leave it to someone who is better at maths to make that call!

 

[jedidia]

You could go around the moon then come back to Earth and enter an eastwards orbit..... I have no idea if the fuel expenditure for that is less than changing orbital direction - I think it might be but I'll leave it to someone who is better at maths to make that call!

I should think so. you're going somewhere towards 8000 m/s at that altitude, so required DV is towards 16000 m/s. For comparison, Hohman transfer to Mars takes somewhere about 6000 with a good launch window (including establishing orbit)... So you could probably get to Mars and insert yourself the other way around on the way back and have about the same DV expenditure. :lol:

 

[jangofett287]

Would Orbiter even allow you to dock at a relative velocity of 16km/s, regardless of the accuracy required?

 

[jedidia]

Would Orbiter even allow you to dock at a relative velocity of 16km/s, regardless of the accuracy required?

As far as I know, yes. Though it's never been actually tested, there is no mention of a speed limit for autodock.

 

[Enjo]

Oh yes there is. The manual says less that than 0.1 m/s is acceptable.

 

[jangofett287]

Docking a craft to a station at 16km/s relative velocity?

 

[dgatsoulis]

Assuming that you could get exactly aligned with a docking port, there has to be a limit for the speed that you can actually dock with it and it would have to do with the simulation time interval between frames.

In one frame you would be an x amount of meters "before" the docking port and in the next one an x amount of meters "after" it, so as far as Orbiter was concerned you were never in "capture" range.

A little bit of testing showed that this happens at a speed of ~8 m/s relative to the port but results could vary if you change the fixed time steps value. (Or even if running Orbiter on a different PC?)

 

[Rtyh-12]

Wouldn't it also depend on your framerate? There has to be a difference between when the sim is running at 20 FPS and when it's running at 120, right?