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MSC-03763
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
MSC INTERNAL NOTE NO. 70-FM-198
December 22, 1 970
SKYLAB LAUNCH WINDOW PROCESSOR
Program Development Branch
MISSION PLANNING AND ANALYSIS DIVISION.
m
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MANNED SPACECRAFT CENTER
HOUSTON,TEXAS
MSC-03763
MSC INTERNAL NOTE NO. 70-FM-198
SKYLAB PROGRAM
SKYLAB LAUNCH WINDOW PROCESSOR
By Jerome W. Kahanek
Program Development Branch
December 22, 1970
MISSION PLANNING AND ANALYSIS DIVISION
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
MANNED SPACECRAFT CENTER
HOUSTON,TEXAS
Approved
proved IC~yJU
„ , cting Chief
r Program Development Branch
Jo . cting?hf^f
Program Development Branch
SKYLAB LAUNCH WINDOW PROCESSOR
By Jerome W. Kahanek
1.0 SUMMARY AND INTRODUCTION
The Skylab launch window is the overlay of two separate windows: the
plane window and the phase window. The plane window is centered on the
lift-off time, which will provide an inplane launch with minimum payload
loss by the booster. This minimum payload loss lift-off time does not
coincide with the analytical inplane lift-off time but occurs some time
earlier. The reason for this is that the booster does not begin steering
toward the desired launch plane immediately. Therefore, if lift-off
occurs at the analytical point, the booster will be drifting out of plane
because of the rotational velocity of the earth; and, when steering starts,
the out-of-plane movement will have to be steered out. If the booster
lifts off before the analytical inplane lift-off point, then the earth's
rotational velocity component that the booster has during the early part
of launch before steering actually will be moving the booster toward the
final desired plane. This results in a lower payload loss caused by steer¬
ing into the desired launch orbit. The plane window opens and closes when
the booster fuel necessary to get in plane is 700 pounds.
2.0 DIS.CUSSION
Subroutine LWT is used to find the analytical inplane lift-off time.
This time is adjusted by an input value to determine the optimum launch
lift-off time. The opening and closing of the plane window corresponding
to fuel cost of 700 pounds is computed from this optimum lift-off time by
adding and subtracting an input delta time. The delta times to find the
optimum and 700-pound opening and closing will be determined before the
mission.
The phasing window for Skylab is a function of the delta velocities
of the NCI and NCC maneuvers. The nominal Skylab rendezvous sequence is
composed of four maneuvers plus terminal phase. These four maneuvers are
NCI, NC2, NCC, and NSR. The phase window opening for a given M rendezvous
number is defined as the lift-off time that corresponds to an NCC maneuver
of 30 fps. The closing of the phase window is defined as the lift-off time
2
corresponding to an NCI maneuver of 30 fps. Because the phase window is
a direct function of the maneuver plan, it is necessary to simulate or
compute the maneuver plan for different lift-off times to find the lift¬
off time corresponding to the opening and closing of the phase window.
The Skylab rendezvous plan is computed using the DKI processor by
means of the four-maneuver special route. To compute the lift-off time
for the opening and closing of the phase window, the DKI must be called
twice, for two lift-off times, to give two sets of data. These data are
used to define a slope of lift-off time as a function of maneuver delta
velocity. Using this slope, a linear extrapolation is used to estimate
the lift-off for the opening and closing of the phase window.
The first guess at the lift-off time for the launch window is com¬
puted by first finding the inplane lift-off time using subroutine LWT.
This time can be biased by an input value ATb to give a lift-off time
to be used as the starting point to find the lift-off time corresponding
to zero phase angle at insertion using subroutine GMTLOS. This zero
phase angle at insertion lift-off time is then biased by an input value
"BIAS" in subroutine RLOT to give the lift-off time corresponding to a
desired phase angle at insertion for the planned rendezvous. After com¬
puting the Skylab rendezvous plan for this lift-off time, the lift-off
time is increased by 1 minute and a new plan is generated. These two
plans are then used in the linear extrapolation to determine the opening
and closing of the phase window. After generation of the insertion vector
in subroutine RLOT, the separation maneuver is applied to the vector at
some input delta time from insertion before the DKI plan is computed.
If the phase window for more than two rendezvous numbers (M-lines)
are to be computed, the launch window processor (flow chart l) will com¬
pute only the phase windows for the first and last rendezvous numbers
specified. The intermediate M-lines will be determined by linear extrap¬
olation for display purposes. If an intermediate M-line is chosen for
the rendezvous plan, the launch window should be rerun using this M-line
as the first or only M-line desired.
3.0 DESCRIPTION OF SUBROUTINES USED
BY SKYLAB LAUNCH WINDOW PROCESSOR
3.1 LWT
Purpose: To find the analytical inplane northerly or southerly
launch time (flow chart 2)
3
Input: Target vector and time; X Lg , launch site longitude; <f> Lg ,
launch site latitude; NS, flag for north or south launch; DAY, day of
launch; ATh, time bias to be added to inplane launch time
Output: TIP, time of inplane launch plus ATb
3.2 RLOT
Purpose: Compute insertion elements at insertion for input lift¬
off time or to find lift-off time corresponding to a desired phase angle
or time bias past zero phase angle at insertion (flow chart 3)
Input: Target vector and time; X Lg , 4> LS , R^ g - landing site radius
TLO, lift-off time; I is a flag, use to input TLO or compute a TLO; BIAS
delta time to bias lift-off for zero insertion phase angle; TPF, PFA,
VF, y, RINS, YS
Output: Vectors at insertion, time of insertion
3.3 GMTLOS
Purpose: Compute lift-off time corresponding to zero phase angle
at insertion (flow chart *0
Input: Target vector and time; TLO, lift-off time to start search¬
ing from; RINS, VF, y, TPF, PFA, X Lg > 4> Lg , R Lg , MV - maneuvering vehicle
Output: TLO, lift-off time for zero phase at insertion
U.O DEFINITIONS OF INPUT FOR THE
SKYLAB LAUNCH WINDOW PROCESSOR
BIAS time bias added to lift-off time corresponding to zero phase
angle at insertion
COSR phase angle desired at TPI (if input)
DAY day of launch; 0 = day of time reference
DET time tolerance
It
DHNCC
delta height desired at NCC
DHNSR
delta height desired at TPI
DHT
delta height tolerance
DOS
phase angle tolerance
DTSR
minimum delta time required between NSR and TPI
DVWOjDVWC delta velocity for phase window opening and closing
ICOMBO
central flag to force the phase adjustment maneuver to
set up a common node 90° from KC1
IDKI
flag used in subroutine TIMA to identify DKI run
I HALF
counter line or period option
= 0 counter line option
- 1 period option
IPC
vehicle number for plane change
IPUTNA
flag that determines how the maneuver line is defined e
computed
IR
flag
= 0 compute launch window
= 1 compute DKI plan for input lift-off time TLO for
display on launch window display
lit
flag for Skylab four-maneuver route
= 0 regular DKI
= 1 Skylab rendezvous route
KCOSR
control flag for phase angle at TPI
KOP
optimize maneuver line control flag
KRAP
control for initial phase angle wrapping
Klt6
control flag for TPI time computation
5
LNH flag to relocate NH if minimum height is violated
= 0 no
= 1 yes
MF final M-line or rendezvous number
MI initial M-line or rendezvous number
MNH flag to determine where to place NH in multiple plans
= 0 same point
= 1 relative to NSR
MV maneuvering vehicle
NCC maneuver line point for the NCC Skylab maneuver
NCI maneuver line point for the NCI Skylab maneuver
NEGTIV flag that determines whether initial phase angle is
negative or positive
NH maneuver line point for the NC2 Skylab maneuver
NPC maneuver line for the plane change maneuver
NS flag for northerly or southerly launch opportunity
NSR maneuver line point for the NSR Skylab maneuver
PFA powered flight arc
PMIN minimum height allowed in DKI plan
PUTNA value of the initial maneuver line
PUTTNA time of initial maneuver line
RINS insertion radius
R^g launch site radius
TIMLIT delta time of lighting condition for TPI
6
TLO lift-off time
TPF time of powered flight
TTPF time of TPF
TTPI time of TPI
VF insertion velocity
WHTI weight of target vehicle
WHTM weight of maneuvering vehicle
YS yaw steering capability
y flight-path angle
ATb time bias added to inplane launch time to give first guess
at lift-off
ATOP delta time from optimum inplane launch time to analytical
inplane launch time
ATSEP delta time from insertion to separation
AT700 delta time from optimum inplane launch time to 700-pound
opening and closing
AVSEP delta velocity of separation
e elevation angle
longitude of launch site
<(> L g latitude of launch site
LfiU/vc.H HH/uPiw p ROG-RPiM
Flow chart 1.- Launch window program.
8
Flow chart 1.- Continued.
9
I ?fiC- £
| 3 -+ 4 '
Flow chart 1.- Continued.
10
Flow chart 1.- Concluded.
11
C LWT ^
cortir utes tw5 \m?l*/je lift ofr time /^crthE tuy
oP s<-' T i)[ KI,7 lAUivlH,
Flow chart 2.- LWT.
PflS-E
1 .-f 2
12
(Tfi77~
I X A 1
Flow chart 2.-Concluded.
13
^ fi LOT ^
K t c e ajo e p ,
'R veer#* reft.
\ Pfiic-t
| 1 -f 1
Flow chart 3.- RLOT.
iEF.0
lit
^C-/lltLO S ^
Con iPuTfS LIFTOFF TIME coA K £5 Pan viNb To
filUtCE AT \HSFKT\t>H
Flow chart 4.-GMTLOS.
14 klrai
r
CHANGE SHEET
FOR
: INTERNAL NOTE 70-FM-198 (MSC-03763) DATED DECEMBER 22, 1970
SKYLAB LAUNCH WINDOW PROCESSOR
By Jerome W. Kahanek
Change 1
August 15, 1972
rnpY
DO NOT REMOVE ’
cJL* n mi LL^ ?
. , Elric N. McHenry, Acting Chief
Software Development Branch
1 }}j.) J L \ 4 -<- _
\ < £ Johd P. Mayer, Chief
Mission Planning and Analysis Division
NOTE: A black bar in the margin indicates the area of change.
After the attached enclosures, which are replacements and additions,
have been inserted, insert this CHANGE SHEET between the cover and the
title pages and write on cover, "CHANGE 1 inserted".
1. Replace pages.
Change History for 70-FM-198
Change no.
Date
Description
8/15/72
The following changes have been
made.
Page Change
6 Input definition changes
7 Flow chart change
8 Flow chart change
10 Flow chart change
11 Flow chart change
12 Flow chart change
13 Flow chart change
1^ Flow chart change
NOTE: The detailed flow charts
have been replaced in full.
5
LNH
flag to relocate NH if minimum height is violated
= 0 no
MF
= 1 yes
final M-line or rendezvous number
MI
initial M-line or rendezvous number
MNH
flag to determine where to place NH in multiple plans
= 0 same point
= 1 relative to NSR
MV
maneuvering vehicle
NCC
maneuver line point for the NCC Skylab maneuver
NCI
maneuver line point for the NCI Skylab maneuver
NEGTIV
flag that determines whether initial phase angle is
negative or positive
NH
maneuver line point for the NC2 Skylab maneuver
NPC
maneuver line for the plane change maneuver
NS
flag for northerly or southerly launch opportunity
NSR
maneuver line point for the NSR Skylab maneuver
PFA
powered flight arc
PMIN
minimum height allowed in DKI plan
PUTNA
value of the initial maneuver line
PUTTNA
time of initial maneuver line
RINS
insertion radius
r ls
launch site radius
TIMLIT
delta time of lighting condition for TPI
6
TLO
lift-off time
TPF
time of powered flight
TTPF
time of TPF
TTPI
time of TPI
VF
insertion velocity
WHTI
weight of target vehicle
WHTM
weight of maneuvering vehicle
YS
yaw steering capability
flight-path angle
ATb
time bias added to inplane launch time to give first
guess at lift-off
ATOP
delta time from optimum inplane launch time to
analytical inplane launch time
ATSEP
delta time from insertion to separation
ATOPEN
delta time from optimum inplane launch time to opening
of window (depends on fuel reserves allowed for
steering)
ATCLOSE
delta time from optimum inplane launch time to closing
of window (depends on fuel reserves allowed for
steering)
AVSEP
(AX, AY,
delta velocity components of separation maneuver
AZ)
elevation angle
X LS
longitude of launch site
latitude of launch site
Change 1, August 15, 1972
7
Flow chart 1.- Launch window program.
Change 1, August 15, 1972
Tin t afi £'
Flow chart 1.- Continued.
Change 1, August 15, 1972
9
Flow chart 1.- Continued.
10
Flow chart 1.- Concluded.
Change 1, August 15, 1972
11
( L ^ T )
CortU’uTES TWf IfJFi-A/JC. LlfT off TI/WE fo/i As <. /< T>< £ ft. L y
cf S<'~" T rffitt'Y L A lJ /v c H ,
Flowchart 2.- LWT.
Change 1, August 15, 19T2
12
[7*71
I 1 .1 !
Flow chart 2.- Concluded.
Change 1, August 15, 1972
13
(flL0T )
Computes reco nmi m e p liftoff Ti<*'E i/use#Tu><u
MtcioK of I^iRRTle/V 1/EtTo?. foR JA'PoT LiFToff T I « t
I Pf'-E
| 1 4 1
Flow chart 3.- RLOT.
Change 1, August 15, 1972
11*
(E3
CortlPoTfS L.tloflr linE CoARES Pon VinlC- To IEH.0 fHAi£
AV!>^t AT \fj SCAT ION
Flow chart 4.- GMTLOS.
Change 1, August 15, 1972
Flow chart 4.- Concluded.