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Written by Szymon Ender |
| Thursday, 03 April 2008 |
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RSfD Lesson 5 : There's no place like Home
Time to head back to Brighton Beach, the spaceport on the Moon. Be sure
that you have activated Reentry MFD
in modules tab before starting the simulation.
You must download
This save state or its
EXE alternative.
Now we are set up to begin our descent into Brighton Beach - we are on
the right path and have reduced our altitude above the surface to as low as
is comfortable. The point in doing so was that we easily cancelled out some
of our orbital energy, which will make our actual descent easier then going
down from a more elliptical, thus higher in energy means orbit. The nav/com
radio is tuned to the VOR frequency at Brighton Beach, and also to the ILS
frequency for landing pad 1 respectively. We'll need these later, and we'll
be far too busy to tune them then...
 | Open ReentryMFD in left display, and select Brighton Beach with [left
shift B]. |
 | Open VOR/VTOL MFD in right display, and make sure nav 1 is selected -
use [right shift N] if it isn't. |
 | Point the craft prograde, engage the horizon level autopilot [L], and
switch the HUD to surface mode [H]. |
The most important displays on ReentryMFD are at the bottom -
Decel req is a constant deceleration that is needed to bring you to
a halt exactly over the targeted base. Decel act is your
actual deceleration created by your thrusters or by the atmosphere - It is
your job to keep these two numbers equal.
A green blob and a cross in the middle of the MFD show how off course you
are - the blob is very sensitive - try to keep the blob centred, and you'll
fly straight to the targeted base.
Also shown is your current altitude and ascent/descent rate.
Before we continue I highly recommend getting a grip on changing a
vector's direction described below.
I'll use VOR/VTOL MFD to illustrate what goes on during base approach. If
you were heading for Brighton without doing anything from now, below a
distance of 500 km your VOR/VTOL MFD would catch Brighton's radio signal and
would look like this:
If the horizontal speed vector and target direction marker don't coincide,
we will miss the target. To change our path we have to rotate our speed
vector to place it more or less on the direction marker. If we only want to
rotate the vector and not change its magnitude, we have to apply
acceleration 90° left or 90° right from our prograde direction. Here,
because our target is positioned right from our flight path, we have to
choose the 2nd option. Notice that when we start to accelerate 90° right,
thus changing the vector's direction, we will loose the proper orientation,
because we will be no longer oriented exactly 90° from the vector, causing
an increase of the vector's magnitude, which is exactly what we don't want
to do if we want to stop our ship. This is why you should set small to
medium engines' power and initiate a slight rotation which will keep up with
the vector's direction change:
Have you noticed a similarity with orbital inclination changes? There the
autopilot also had to rotate the ship while you were thrusting. When we
start the actual deceleration, you'll see that we need less power to turn
our ship at lower speeds, which also applies to inclination changes.
After roughly aligning the two lines it is time for fine tuning. Turn
prograde (using rotational thrusters - yaw, not the autopilot). You should
start decelerating with the auxiliary thrusters. If you see in the reentry
MFD, that the small green circle is offset (left/right) to the cross in the
middle, you'll have to rotate the vector further. As we already need to be
decelerating, we'll use a part of the deceleration vector to turn our
current speed vector. As we are using retro thrusters, the proper
orientation to turn the vector is inverse from the previous situation. In
the picture below I was moving too much to right this time, so I had to turn
a bit right from my prograde marker. The proper orientation will be easier
to understand if you imagine a deceleration vector coming from the centre of
VOR/VTOL MFD, directed down and think that the decel. vector and the current
speed vector are being added.

Let's continue.
 | Coast onwards until the required deceleration is around 3 m/s/s - use
[control S] to quick save the mission. It may take a few attempts before
you get a feel for this. |
 | Engage the auxiliary thrusters...change the power setting to match the
required deceleration. |
 | Use yaw to keep the blob centred. |
 | As you begin to slow, your descent rate will increase - use hover
thrusters to keep it under control |
 | Brighton Beach will come into view at around 70km out - you may want
to toggle the panel with [F8] to get a better view. Lower your gear with
[G]. |
 | Keep a close eye on the required deceleration, and use the hover
thrusters to place your velocity vector just above Brighton Beach. |
 | Once your distance to Brighton is below 25 km, it's time to begin you
final approach into Brighton Beach - switch Nav beacons with [right shift
N] to Pad-01. From now on forget about reentry MFD's green circle which
measures course w.r.t. the centre of the base and focus on VOR/VTOL MFD's
indicators |
 | You may want to switch engines to translation mode, and using [Num 1]
and [ Num 3] try to make velocity vector and base position indicator
coincide. |
 | Now it's time to see how good a virtual pilot you really
are...Constantly keep rotating the vector so that it's exactly on the
direction marker. You also should try to place the prograde marker a bit
above the pad (or above one of them if you don't have a visual) with hover
and translational thrusters. If you miss the target and are unable to
rotate the vector any more, stop the shuttle immediately, by using retro
thrusters in the direction of the prograde marker, rotate it to face
Pad-01 (thus the direction marker) and use translational and hover
thrusters to keep the prograde marker on the pad.
As you get closer, keep decelerating with aux thrusters or with [Num 9] if
you are already going slowly. Once you are very close to the pad, HoldAlt
autopilot will be very helpful. Enable Surface MFD in left display,
activate HoldAlt and let it stabilize the hover acceleration (wait for ~ 0
m/s/s VACC in the Surface MFD), then deactivate it. The reason behind this
is that now we are at hover above pad and we can set and adjust constant
vertical speed (VS in the Surface MFD) with translational [Num 8] and [Num
2]. After you got the direction indicator's cross inside the red -> green
cone (or better - in the very centre of the MFD), cancel out all
horizontal speed and start the final descent with [Num 8]. Set the VS
below -0.5 m/s for a soft touchdown. When grounded, turn off hover engines
and disable all autopilots, which you were using, eg. Hold-Level [L], to
allow refueling.
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Congratulations! You have (hopefully) landed in Brighton Beach,
concluding the first phase of this tutorial. If not, or if you want to
practice some more you can always load the quicksave. A thing to consider
before next landing is waiting for a different Decel. req. The later you
start decelerating, the more fuel you'll save because you'll need to counter
gravity with hovers for shorter time, plus you'll be quicker at the base.
You can even turn retrograde and use 3 times more powerful main engines to
maximize fuel efficiency. The problem is that Decel req. increases
exponentially, so it's easy to overshoot the mark. The choice is yours.
Remember that if you want to adjust your inclination and LAN to make your
trajectory pass over a base at bodies rotating faster than Moon , you'd best
use BaseSynchMFD. |
| Last Updated ( Wednesday, 21
May 2008 ) |
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