TRANSFER TO PHOBOS

In this Transx tutorial you are in a fairly low Mars orbit within a couple degrees of alignment with Phobos. The mission goal will be to do a single burn that adjusts both Prograde and Inclination as well as the time of the burn to transfer to Phobos.

It is set up to be used in conjunction with this scenario. Extract it into your Orbiter folder and run a Window version of Orbiter so you can follow the tutorial doing what it does in your running Orbiter application.


START CLICKING:
Bring up Transx in both MFD's (LeftShift-J and RightShift-J).

TARGET.
In the left MFD,...
click "VW" to get "Setup".
click the "++" as needed to make the target Phobos.
You will now notice a couple of yellow radius lines which shows where your deltaglider and Phobos will be when they are closest to one another.

MANOEUVRE MODE
In the left MFD...
click "VW" until "Manoeuvre Mode" is shown.
click "++" to turn it "On".
The following image shows what you have so far.

ADD PROGRADE.
In the left MFD,...
click "VAR" as needed to get "Prograde vel"
click the "++" as needed to expand the yellow ellipse to exceed the orbit of Phobos a bit as shown in the next image. Note that a dashed radius line is now showing near the green radius line. This is the location of the burn you have started setting up. You have not adjusted the "Man. date" (manoeuvre date) yet so it's actually behind you right now.

MANOEUVRE DATE
In the left MFD...
click the "VAR" until "Man. date" appears.
click "ADJ" to toggle to "Ultra"
click the "++" to scroll the yellow ellipse close together.
There is a closest approach number "Cl. App. (rough)" which happens to be 256.5K in the image below.

INCLINATION
in the Left MFD, Click the "VAR" as needed to show the plane change variable "Ch. Plane vel." Click the "++" a few times to swing that white line that's crossing the orbits. You might want to reduce the increment to medium or finer as you get closer. Note that the white line is where your orbit intersects the orbit of Phobos so try to get the white line to lay across the two yellow dashed radius lines. See the next image.

FINE TUNE the amounts. Now go back and forth a few times between "VAR" prograde and change plane each time reducing the "Cl App" distance. Make the adjustments finer as you go until you are using "Ultra" or "Super" with each one. The image below shows the closest approach as 1.499K meters. The variable values used to get this if you are having trouble are prograde 396.1, Man date 53750.5619, Outward vel 0, and Ch plane 180.9. I purposely left it fairly wide. You might be able to get it to under 100 meters with a bit of pecking of the prograde date and plane change variables. Note that as you get closer in the "Cl App" distance the"Man. date" (manoeuvre date) adjustment becomes too sensitive even on "Ultra". Once that happens just adjust the other 2 variables. Also, you could adjust the "Outward vel" if you like but there's no need to as all you really need are the other variables. But feel free to try it to see what it does.

VIEW THE ENCOUNTER
In the right MFD...
click "FWD"
click "VW" as needed to get "Encounter".
The green line is your pathway across or by Phobos (the white circle). This view also gives the actual closest pass by the center of gravity of Phobos as well as inclination and if you missing the rock, it gives the distance from the surface.

DO THE BURN.
In the left MFD...
click the "VW" to get the attitude target.
use ROT RCS to center the green "x".
Hint: Start the burn at about 15 to 20 seconds before T=0 and bring the "Rel V." to zero.

Turn OFF Manoeuvre Mode.
In the left MFD...
click "VW" as needed to get "View:Manoeuvre"
click "VAR" as needed to get "Manoeuvre Mode"
click "++" to turn the Manoeuvre Mode "OFF".
Now the distance of "Cl. App." changes from the planned distance of the manoeuvre to what you are actually getting after your burn. In this next image it shows the closest approach to Phobos as being 1.579K meters, with an approach speed of 495.6 m/s and the time of arrival will be when the MJD clock is 53750.6477.

BURN ON THE FLY
Advance the clock and watch the left MFD to watch the positions of your ship and Phobos in their orbit around Mars. When you are getting closer but still perhaps 10 or 20 degrees of orbit before they intersect (as shown in the next image) slow the clock to real time. Bring the ship Level to the surface of Phobos by clicking "L", and also bring up the SURFACE MFD in the left MFD (LeftShift-S) to be sure you are actually referencing Phobos and that you are leveling to the surface. (It references to whichever object is closest to you). Once you are level with Phobos, kill the rotation "5" and then use LIN RCS in side to side to bring your trajectory distance from the center of Phobos "Focus PeD" as seen in the right MFD. Burn alternately the side to side "1" and "3" and the forward and aft "6" and "9" each time minimizing the distance. You are getting so that your actual direction will be directly through the center of mass of Phobos. In the image below it shows the actual trajectory of the ship to be only 2.678 meters from dead center of Phobos.

Hover to a STOP.
All that's left now is to be aware of your distance from the surface and your closing rate. I use the general and conservative approximation to start the hover when a distance above the surface by squaring the approach speed taking it as multiples of 100 m/s and that's the Km above the surface to start full hover engine. Since in this example you are arriving at a bit under 500 m/s, square 5 to get 25 and so when 25 Km above, the surface be sure you are exactly level ["L" key] and turn on the hover engine. Watch your altitude in SURFACE and your rate of descent. Turn the hover engine on and off as needed to hover to your desired height. Feel free to touch the LIN RCS 1,3, 6 and 9 buttons to keep your trajectory still toward the center of Phobos. Once you are hovering go to external camera for a fun view of Phobos. If you get too close the ship may be below the virtual graphic surface so you might want to stop a few hundred meters or more above the surface.