RENTRY21.BAS

In my ROCKET49.BAS program I developed a rudimentary simulation of a
multistage rocket flight into Space.  Having gotten you into orbit it
would seem reasonable to provide a way back down.  Caxton Foster's
publication of "The Orrery" has inspired me to complete my reentry
program.  Rentry2.1 is a basic program that simulates the reentry of a
spacecraft into the earth's atmosphere.  This is the second version and
it has two different options so that's why it's Re-entry v2.1.  It will
simulate a blunt heatshield cannon ball type of capsule or your high
altitude glide return type vehicle.

The program presents engineering data only, but I have included a
simple xy plotting program.  You will have to insert the file
instructions in the remarks into the rentry21 program and start the
plotting program without leaving Basic.  Your improvements are of
course welcome.

Some notes about spacecraft reentry.

Weight of course is in pounds.

Square foot area is the blunt end for capsules, and the bottom for
glide return.  I added 10% for frontal drag on the glide return, and
you can add drag devices also.  The Space Shuttle uses "S" turns to
lower itself into the atmosphere thereby increasing it's drag and you
can do "S" turns during reentry by typing an "S".  You will see a jump
in the Vertical Velocity whenever the program catches the keyboard
input.

The CD (Coefficient of Drag) is the shape factor of the capsule.  0.5
for slender, 0.8 for blunt.

The glide return section varies the angle of incidence to try to
maintain a zero sink rate.  This of course is only applicable for high
altitudes.  The numbers will not make sense below about 100,000 ft
because the program does not use aerodynamic lift/drag parameters.
Maybe the next version will roll it to a stop at the end of the runway.

The heat/sqft indicator has no units, I got the formula from an Air
Force Officers training manual (AU-18 Space Handbook, Air University)
which did not go into great detail, probably best for officers.

For some historical input;
Mercury - 2460#, 30.17 sqft, CD 0.8, Drogue 28 @ 21000ft, Main 3115 @ 9800ft.
Gemini - 5952#, 46.54 sqft, CD 0.8, Drogue 54 @ 50000ft, Main 5565 @ 9800ft.
Apollo - 11700#, 128.6 sqft, CD 0.8, Drogue 427 @ 22966ft, Main 15147@ 9843ft.
Soyuz-TM - 6600#, 40.69 sqft, CD 0.8, ????(need info on Soyuz parachutes)
Shuttle - 160000#, 3902 sqft.

The program is set up to do a reentry from Earth orbit, of course if
you really want to have fun, change the HV and VV at the CHANGE
VARIABLES stop, remember that the program subtracts 500 ft/sec on
startup so add 500 to your HV.  VV=0 and HV=501 is great fun.

Freeware: May be freely distributed as long as the heading remarks are intact.

Mark Goll
19785 Marbach Lane
San Antonio, Texas
78266
markgoll@wt.net
http://web.wt.net/~markgoll
