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<H2><A ID="SECTION00072000000000000000">
Navigation Equations</A>
</H2>
For the distance <I>d</I> travelled with initial acceleration
<I>a</I><SUB>1</SUB> and final deceleration <I>a</I><SUB>2</SUB> the values of interest for the journey
are the maximum velocity at the turning point (where we change from
acceleration to deceleration) <I>v</I><SUB>u</SUB>, the distance <I>d</I><SUB>2</SUB> of the turning
point from the target and the time <I>t</I><SUB>d</SUB> that is needed for travelling the
distance <I>d</I>.
<P>
We assume that forces other than those produced by our own engines can be
neglected and that we start and reach the target with zero velocity.
Furthermore we assume that the engines are used all the time at full power.
<P>
If the main engine is used for acceleration <#179#><EM>and</EM><#179#> deceleration the
equations are very simple:
<P></P><DIV ALIGN="CENTER">
<tex2html_verbatim_mark>#math158#
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD></TD><TD ALIGN="CENTER" NOWRAP>
<TABLE>
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER"><I>v</I><SUB>u</SUB> = <tex2html_image_mark>#tex2html_wrap_indisplay2056#</TD>
</TR>
</TABLE>, *1<I>cm</I><tex2html_image_mark>#tex2html_wrap_indisplay2057#, *1<I>cm</I><tex2html_image_mark>#tex2html_wrap_indisplay2058#
</TD>
<TD WIDTH=10 ALIGN="RIGHT">
(2)</TD></TR>
</TABLE>
</DIV>
<P>
This fastest mode of flight is used to accelerate up to the turning point
velocity at the distance <I>d</I><SUB>2</SUB>, turn the ship and decelerate until the
target is reached.
<P>
If the autopilot is used instead, it will use the main engine for
acceleration and the secondary thrusters (retro thrusters) for deceleration.
In this case we get the equations:
<P></P><DIV ALIGN="CENTER">
<tex2html_verbatim_mark>#math159#
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD></TD><TD ALIGN="CENTER" NOWRAP>
<TABLE>
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER"><I>v</I><SUB>u</SUB> = <tex2html_image_mark>#tex2html_wrap_indisplay2062#</TD>
</TR>
</TABLE>, *1<I>cm</I><tex2html_image_mark>#tex2html_wrap_indisplay2063#, *1<I>cm</I><tex2html_image_mark>#tex2html_wrap_indisplay2064#
</TD>
<TD WIDTH=10 ALIGN="RIGHT">
(3)</TD></TR>
</TABLE>
</DIV>
<P>
The time <I>t</I><SUB>d</SUB> is always a lower bound for the really used time because the
autopilot doesn't use the engines at full power all the time.
<P>
I approximated the real time consumption of autopilot flight with a least
mean square fit of data from 20 undisturbed flights with a Cobra MK III.
Measuring the distance in astronomical units [<I>AU</I>] and the acceleration in
units of earth gravitational acceleration [<I>g</I>], I got for the time [<I>d</I>]:
<P>
<P></P><DIV ALIGN="CENTER">
<A ID="time"><tex2html_anchor_mark></A><tex2html_verbatim_mark>#math160#
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD></TD><TD ALIGN="CENTER" NOWRAP>
<I>t</I><SUB>d</SUB><SUP>A</SUP> = <tex2html_image_mark>#tex2html_wrap_indisplay2070# <tex2html_image_mark>#tex2html_wrap_indisplay2071# - 0.001
</TD>
<TD WIDTH=10 ALIGN="RIGHT">
(4)</TD></TR>
</TABLE>
</DIV>
<P>