Dock with ISS - a tutorial

[Gary Shaw]

     For the absolute beginner: Load up a scenerio with the shuttle in orbit and begin a spacewalk
with (MMU) by pressing the "E" key.  You need to learn how to use the thrusters which will work
the same if you are manuevering the spacewalker or trying to manuever the shuttle to dock.  

    When manuevering with thrusters, the most important key is the slash bar key above the
numeric keypad.  Tapping this key toggles the thrusters between rotational and linear movement.  
Tapping the F1 key toggles between external view of the vessel (spacewalker, shuttle, ISS,
whatever) and internal view.  Tap F1 until you are inside the spacewalkers helmet looking straight
ahead.  Note that in the upper left area of your screen, there are two bars that either form an "X"
or they are parallel.  (The numeric slash bar toggles between parallel and "X").  When the bars
form an "X" then the  thruster keys on the numeric keypad rotate you on an axis.  When the bars
are parallel then the keys on the numeric keypad move you up, down, left, right, forward or back
without rotating you on an axis.  With your spacewalker out spacewalking, play with these keys a
LOT.  You need to be very efficient with these vessel movements or you will never be able to dock
or spacewalk.  REMEMBER that fuel is GOLD in space.  Do not waste it.  If you aim toward a target
then a short burn toward it will eventually get you there because you will continue in that direction
until you give a counter-burn to stop.  Be patient.  Do not continue to burn toward the target.  Just
a short burn and then wait until you get there and you will use very little fuel.  If you are in the
rotational thruster mode (by toggling the slash bar key) then you can automatically STOP
ROTATION by pressing the 5 key on the numeric keypad (this is handy and you will use it
constantly to aim your vessel (or spacewalker)).  MOVE SLOWLY.  If you want to dock the
spacewalker, note that he docks CHEST FIRST (not feet first).

     BURNING TOWARD ISS:  As you prepare to make the final burn toward the ISS, (You will need to
have HUD in dock mode and set NAV 1 to 108.10 ).   When you get within 100km of ISS then you
will see  a square drawn around it on your HUD you will also be able to see a triangle on your HUD  
with ISS in parenthesis.  This triangle is pointing toward the vector that you want to burn toward.  
(You do not yet burn directly at the ISS because it will be long gone when you get there.  You burn
toward the vector that I describe here).  Find this vector by using rotational thrusters (numeric
slash bar to toggle between rotational and linear).  The vector that you are looking for is a circle
with a cross-hair inside it.  Use the thrusters and the kill rotation key to lock on this vector (Hit the
Slash bar to switch from ROTATIONAL to LINEAR thrusters) and then  fire main engine in linear
mode to burn toward this vector as the number below it decreases toward zero.  You want to get
this number as close to zero as possible.  You may have to switch to rotational thrusters and re-
center on this vector and then fire linear again.  It will move around as you fire toward it and I
have found tapping or holding down 2 key on the numeric keypad will reduce the vector movement
as I burn toward it.  I can get this vector to a decimal less than 1.  

     When you get this vector to near zero then you are no longer closing on the ISS and it is no
longer closing on you.  Next, you will see a green triangle that is marked ISS but there is no
parenthesis around the ISS on this triangle.  This triangle is pointing you toward the ISS itself.  Aim
the nose of your ship directly at the ISS using Rotational thrusters.  When you are pointing directly
at the ISS then switch to linear thrusters (numeric slash bar) and burn toward the ISS by pressing
the numeric + key.  A cross-hair (not enclosed in a circle) will appear on the screen and as you
burn, the number below it will increase, telling you how fast you are closing on the ISS.  Stop
pressing the fire key when you reach the closing speed that you desire.

     How fast I close on ISS depends on how far away I am.  (If I am not within at least 30km of ISS
(Preferebly less than 20)  then I go back to orbtal adjustments to get closer before I start this
process)  Start with a closing speed of at least 10 unless you are already within 5 or 6 km (then
use 5 or less closing speed).  Any time that you want to stop closing on the ISS then simply find
the vector with the circle around it and fire LINEAR until its number is near zero ; you will then stop
moving near or away from ISS.

     As you  close on the ISS, your approach will "fizzle out" and you will quit closing.  You will then
have to repeat the process by finding the circle cross-hair, fire it to zero again and then aim at ISS
and once more fire closing thrusters.  I have often had to go through this process more than
several times to get within the 200m  (that´s meters, NOT kilometers - in other words, VERY close)
that I like to be.

     During this phase, I have found it helpful to bring up the docking MFD (Shift D) and as long as
there is yellow in the right bar then I am closing on the ISS.  When the yellow goes away then I
take another bite at it.

DOCKING:  Having practiced with the spacewalker, I used to dock with the ISS using external
view.  This would require slowly moving toward the docking bay looking from many different angles
but I got so that I could do it.  One day I started playing with the docking MFD and once I learned
how to use it, I found it to be many, many times easier than trying to dock with external view.  

     Load up the "Atlantis ISS resupply" scenerio.  Press F4 and select ship (make sure you are in
shuttle and not in ISS control).  Un-dock from the ISS by pressing  ctrl D.   Set your NAV 1 radio
frequency to 108.10 (Shift C) and select docking HUD mode (press "H" key to toggle HUD to Dock
mode and it should show the 108.10 NAV frequency).

Bring up the dock MFD (Shift D) and play with the dock MFD to learn to use it.  Some tips:

1. Set thrusters to rotational and play with the 2,4,6 and 8 keys.  You will find that you can move a
large red cross-hair around.  When you move this cross-hair to the center with the 2,4,6 and 8
keys then the large red cross hair will turn white.  This will indicate that the plane of your dock  
tube is aligned with the plane of the ISS docking tube.  In other words, if you put a large sheet of
cardboard over your dock tube and a different large square of cardboard over ISS dock tube, the
two pieces of cardboard will be parallel to each other (This is good).  This does not mean that the
two tubes are aligned.  It simply means that the two tube rims are parallel to each other.
2. You will next direct your attention to a bright red triangle that you can move clockwise or
counter-clockwise around a circle by having thrusters in rotational and pressing the 1 or 3 key.  
Move this triangle to the 12:00 O´clock position (straight up).  This will indicate that the shuttle
nose is pointed in the correct direction for docking at this particular
bay.                                                                                                                                      
3. Once you have steps 1 and 2 done then you can switch thrusters to linear (as opposed to
rotational) and leave the thrusters in linear until docked.
4. Next, direct your attention to the large green cross-hair.  Place your thrusters in the LINEAR
mode and you can move this crosshair left or right with the 1 or 3 keys and you can move it
forward or back toward you with the 6 or 9 keys  (these keys move the shuttle just like these keys
moved your spacewalker when you were practicing with the MMU earlier).  Some of these burns
are longer burns because you must now manuever the shuttle with reference to the ISS to actually
align the two docking tubes and you are probably a long way out of alignment.  When this green
square is centered then your docking tube is perfectly aligned with the ISS docking tube. You have
to get the two tubes fairly aligned before the green cross-hair begins to move and the stop
rotation key (key 5) will NOT stop the movement that you have started.  You will have to fire
counter thrusters to stop a movement direction when thrusters are in the linear mode.  When this
green cross-hair is centered then the two tubes are aligned.  If the cross-hair is too near to you
(below the center of the circle) then the ISS is too far ahead of you and you need to press the 6
key to move your shuttle forward.  This will eventually move the cross-hair away from you (up on
your screen) and toward the centerline of the circle.  Be ready to quickly press the 9 key to fire
counter thrusters to stop the forward movement of the shuttle.  You can adjust the cross-hair up
and down on your screen (shuttle forward or backward) to finally center it using the 6 and 9 keys
(forward and reverse).  You do the same thing with the 1 and 3 keys but these keys move the
green cross-hair left and right as opposed to forward  and reverse.  If the cross-hair is left of the  
center of the circle then press the 1 key and it will eventually move the cross hair to the right.  If
the cross-hair is to the right of center then press the 3 key and it will eventually move the cross-
hair to the left. Again, you must fire counter thrusters to stop any movement that you started ( for
example, if you press the 1 key and the cross-hair starts to move to the right  then it will continue
to move to the right until you press the 3 key to stop it)  When you get these adjustments near to
the center then they become more sensitive to thrusters and it takes a bit of practice to center
AND STOP this green cross-hair but it can easily be done after some practice.  You would think that
I am playing some kind of musical instrument if you were looking at my fingers as they play over
the numeric keyboard during this crucial final alignment.
5. After completing steps 1 through 4 above, you will be STOPPED and directly under the docking
tube, you will be faced in the correct direction and your  docking tube rim will be parallel with the
ISS docking rim.  Your next move is to press the 2 key and begin to raise you shuttle toward the
ISS.  The yellow bar on the right side of the docking MFD should show some yellow as you close
with the ISS.  Be prepared to make some minor adjustments to the green cross-hair as you rise.  
You will slowly move up and DOCK>  
6. I do not pay much attention to the yellow arrow that jumps around the circle of the dock MFD as
I fire different thrusters.  This arrow points to the direction of your movement in relation to the
green cross-hair.  If you are moving in the correct direction with your thrusters then this arrow will
point toward the green cross-hair but I do not find this particular info to be very helpful.
7. A FINAL NOTE:  As you approach ISS with the NAV 1 set to 108.10 and the HUD in dock mode,
you will see a string of green squares that are supposed to guide you to the correct dock bay.  
These would be great if you are docking a vehicle with the dock bay in the nose of the craft but I
find these green approach squares to be as confusing as helpful when trying to blindly approach
from below the ISS.  I slowly  use linear thrusters to approach to within 200 or so meters of the
ISS and then I stop.  I look the station over and can easily spot my docking bay from that
distance.  I next use rotational and linear thrusters to slowly position myself a bit below,
somewhat aligned with a reasonable approach and a bit backed-off from the ISS dock bay of
choice (In this case, 108.10).  I am now in what I call "the docking ball park" and I can do this
without ever resorting to an external view.  I adjust my posture (with thrusters) so that the ISS is
level and not moving in any direction with respect to my shuttle.  At this time, I then begin to use
the docking MFD as described in steps 1 through 5 above
This docking MFD works and is worth the time to learn to use.

I WANT AT LEAST 20% FUEL LEFT WHEN I AM FINALLY DOCKED.  IT WILL ONLY TAKE ABOUT 15%  
TO DE-ORBIT BURN.  I USUALLY WIND UP WITH CLOSER TO 40% (AFTER LAUNCH AND DOCKING
MANUEVERS)  BUT SOMETIMES I HAVE TROUBLE AND WIND UP WITH UNDER 30%.  (Once you get
close to ISS then it does not take much fuel to thruster into the dock)  I easily dock every time with
very little effort but  I am embarrassed to tell you how much time I have had to practice to do so.
(Of course, If I worked at NASA then I would practice all day, every day for months - this is not for
the feign of heart).

[ChristopherT]

   Great Work, Gary!  Now if you can teach me Synch Orbit I'll be psyched!    I can use
the align plane MFD, but the Synch Orbit still drives me nuts!  

     Christopher

[Gary Shaw]

ChristopherT

   If you and the ISS are in the same plane with same PeD and ApD then your T (or time of orbit)
will be the same and you will never rendevous.  In the Orbit MFD with the ISS as target, the brown
line (the ISS) will rotate either ahead or behind the green line which is your ship.  There are two
ways to rendevous:  Method 1 - slow down to let the ISS slowly pull up behind you (or, conversely,
speed up to slowly pull up behind the ISS.  Method 2 - Lift yourself high into orbit and then swoop
down on the ISS as it passes under you.  

    Method 1.  To slow down your shuttle, simply fire PROGRADE to lift your orbit and increase your T
(time of orbit on Orbit MFD). (Then sit and watch as the brown line closes on your green line each
orbit) If you and the ISS are a long ways apart then fire (looking at the T data line in Orbit MFD and
100 difference would be used but be careful at this large number or you and the ISS will fly past
each other at great speed.  When the two lines get close to each other, turn and fire RETROGRADE
while looking at the T data line and decrease it from 100 to a lesser number to slow down the
approach.  Conversely, to speed up your shuttle, fire RETROGRADE to lower your orbit and
decrease your T time, allowing you to pull up behind the ISS.  Its simple, If you are ahead of the
ISS and it is traveling faster (a smaller T data line in orbit MFD) then it will catch up.   Because of
the shuttles or the ISS eccentricity, the ISS  might seem to be getting farther from the shuttle  
during part of its orbit but overall, it will catch up.  (I always try to fire near PeD or ApD consistently
the keep from getting too far out of kilter with the ISS orbit.  Sometimes I have to touch up orbits,
align plane again and make a more suttle approach to the ISS.

     Method 2 (The sync Orbit MFD)  is simple to use.  Just set the manual reference line of the Sync
Orbit MFD with this thought in mind "I want my shuttle and the ISS to arrive at this point at the
very same time".  Have your PeD, ApD and orbital plane the same as the ISS - Fire Prograde until
one of the numbers in the left column equals one of the numbers in the right column.  (Then wait
and when these two numbers work their way to the top of the list, the rendevous is near and will
occur at the next intersection with the reference line).If these matching numbers are 5 down from
the top then the rendevous will occur in 5 orbits.  Be prepared  (when near to rendevous) to fire
RETROGRADE at your new PeD to again set your PeD and ApD with the ISS.  Do not be alarmed if
the matching numbers are not side by side.  This will not matter.  
     If You are in a hurry and have plenty of fuel then you can keep firing PROGRADE and move the
matching numbers higher on the list to rendevous sooner (When the matching numbers get to the
top of the list then the rendevous will occur as your ship marker hits the manual reference line that
you set earlier).   If You are not in a hurry or don't have spare fuel then just fire until some of the
lower numbers are equal and then wait (orbit by orbit) for these numbers to work their way to the
top of the list and rendevous.
     I have found that even after using the Sync Orbit MFD, I more often then not, have to use
Method 1 to move me even closer to the ISS or I will waste a lot of fuel trying to burn to the ISS.  I
use Orbit tricks like this to move within 20km of ISS and then use the final assault approach that I
described earlier in this thread.

     I carefully plan my launch window and adjust RInc as I climb to keep it less than 1.  I launch to
an orbit ahead of ISS and my PeD is near enough to it to match it without a great burn.  I used to
use the Syn Orbit MFD but I never use it anymore.  I do not like to burn fuel to circle my orbit and
then turn around and burn fuel to extend my ApD (for the great swoop).  Then, turn around and
burn more fuel to circle my orbit again.

     I can not give you launch data because I have downloaded the 3.2 Atlantis and installed the
Carina Satellite with its cradle and added its mass (5000) to my weight so my launch data will be
of no value to you.

[Arkalius]

One thing to keep in mind about the shuttle is that it's OMS engines have about a 13 degree pitch
to them. This is because they are high up on the craft, and they need to point toward the shuttle's
center of gravity or they will induce rotation when firing. This also means that when firing your
OMS engines, you are actually accelerating in a direction about 13 degrees negative pitch from
your current heading. So, if you use the prograde or retrograde autopilot to keep yourself aimed
right during a burn, you will actually change your inclination a little bit.

To avoid this, I use a heads up attitude (wings level with respect to the horizon), make sure I'm
aimed in the prograde direction, and then use the surface HUD mode and manually hold about a
13 degree positive pitch while accelerating. This will ensure that I will not incur any plane changing
acceleration, and only orbit shape changing acceleration. You can also do a heads down attitude,
just make sure you remember you'll have to pitch "down" from the horizon in that case (even
though it's really still up, if you consider the fact that you're upside down).

[ChristopherT]

Thanks, Gary.  That's the best explanation of the Orbit Synch MFD I've seen.  You might consider
writing some tutorials for the new Orbiters.    
     

    Christopher

[Gary Shaw]

Arkalius:

    Thank you for the 13 degree tip.  This is a factor that I have overlooked in the past but shall not
in the future.  I have noticed that on large orbit adjustments that I often have to go back to align
MFD and set my RInc back to zero.  Probably because of my 13 degree oversight.  Thanks - Gary

[Gary Shaw]

I did not want to over-complicate the Sync Orbit explanation mentioned earlier so I add this
statement in this new message - If the ISS is slightly ahead of you in orbit (as opposed to behind
you) then you will have to fire a long, long, time  to  match numbers (lift your orbit way, way up
there).

In this case, it would be better to swoop UNDER the ISS (to pick up speed) and then swoop  up to
meet it as we pass under it (as opposed to swooping down on it as described earlier).  To do this,
simply fire RETROGRADE to start instead of PROGRADE and then when near to rendevous, fire
PROGRADE to rise back up to the ISS orbit level

[Arkalius]

Yeah it's all kind of counter-intuitive for the uninitiated. If the ISS is behind you, speed up, if it's in
front of you, slow down. Doesn't make sense by conventional thinking but that's how it works.