The effect of moving the return-to-launch-site (RTLS) range-velocity (R-V) line closer to the landing site was studied. Results are presented which show that a five nautical mile shift in R-V line causes the last RTLS abort to occur approximately one second earlier and that the excess range capability to terminal-area-energy-management interface can be dissipated without an excessive roll angle history

Bown, R. L.

English

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https://ntrs.nasa.gov/search.jsp?R=19760026149 2020-03-22T13:49:38+00:00Z
MCDONNELL DOUGLAS TECHNICAL SERVICES CO.	 Lim- ^'^ G ^^
HOUSTON ASTRONAUTICS DIVISION
SPACE SHUTTLE ENGINEERING AND OPERATIONS SUPPORT
DESIGN NOTE NO. 1.4-4-19
RETURN-TC-LAUNCH-SITE VARIABLE RANGE-VELOCITY LINE
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M	 MISSION PLANNING, MISSION ANAL YSIS AND SOFTWARE FORMULATION
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This Design Note is Submitted to NASA Under Task Order
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Senior Engineer	 • iask Manager
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APPROVED BY:oc^o	 /3 ^
W. W. Hintcn, Jr. ^^	 W. E. Hayes
FPB Work Package Manager	 Project Manager
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RECEDED	
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DN No. 1.4-4-19
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1.0 SUMMARY
This document presents the results of a study to show the effect of
moving the Return-to-Launch-Site (RTLS) Range-Velocity (R-V) line
closer to the landing site. Results are presented which show that
a five nautical mile shift in R-V line causes the last RTLS abort
to occur approximately one second earlier and that the excess range
capability to Terminal-Area-Energy-Management .(TAEM) interface can
be dissipated without an excessive roll angle history.
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DN No.: 1.4-4-19
Page: 2
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i 2.0 INTRODUCTION
Preliminary RTLS guidance and targeting software for the Space
Shuttle is documented in Reference (A). This note documents
another in a series of performance verification studies planned
to verify the adequacy of that software.
This study -was conducted to determine the effect of moving the
RTLS Main Engine Cutoff Range-V--•locity (MECO R-V) target line
closer to TAEM interface. The R-V line is positioned such that
the Space Shuttle will have the._capability to reach the maximum
allowable TAEM interface range of 35 nautical miles for a three
sigma.(3cr) dispersed minimum range entry flight. This location
then determines the last abort time for the RTLS mode boundary
and the required time for an Abort Once Around (AOA). The use
of this R-V line does not take advantage of the additional powered
RTLS flyback range capability available for an earlier abort. It
has been proposed to use an R-V line targeted to the center of
the allowable TAEM range limit until the RTLS abort time increases
to the value that causes the flyback trajectory throttle setting
to exceed 100 percent. The targeting criteria could then be
changed to the mode boundary R-V line.
DN No.: 1.4-4-19
Page: 3
3.0 DISCUSSION
This study used a three degree of freedom simulation contained on
a modified Space Vehicle Dynamic Simulation (SVDS) 3.0 milestone
file (Reference (B)) for a Base Reference Mission (BRM) 3A RTLS
abort. The modifications to SVDS were:
a) . Addition of the turnaround time prediction logic
(Reference (C)).
b) Addition of the thrust termination logic (Reference (C)).
c) Interim SVDS milestone 3.1 entry aerodynamics.
The target inputs to the Powered.Explicit Guidance (PEG) module
were biased to the MECO minus ten seconds (MECO-10) conditions of
310,000 pounds of total weight, 230,0036 feet aititude, and a 33'
degree relative flight path angle. The biased desired flight
path angle results in an angle near zero at External Tank (ET)
'i	 separation. The mode boundary R-V target for MECO-10 was
R = .069VE - 104.1
For thrust termination the target line for MECO was
R = .068VE - 165.5
All ranges are in nautical miles measured from an aim point located
at 34°34' North Geodetic Latituue and 120°28' West Longitude. The
I
k	 aim point is located on a 3.6 nautical mile extension of the tangent
line from the space shuttle at MECO to the heading alignment circle
I
on a 18.5° earth relative true heading (Figure 1). The extension
is required to include the distance that must be flown around the
.. 
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Scale: N.M.
FIGURE 1 - Definition of RTLS Aim
Point for Mission 3A
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EDN No.. 1.4-4-19
Page: 5
heading alignment circle to the runway azimuth. The BRM 3A
Rockwell International (RI) aim point (Reference (D)) was used	
yy^
in previous studies. The aim point used in this study results
in an approximate one nautical mile decrease in range from the
MECO conditions used in the previous studies. The RI R-V lines
were modified by one nautical mile so that the range at-the
start of entry would be consistent with previous simulations.
The relative velocity ( VE ) is in feet per second.
At MECO-10 a powered pitch down is initiated at an average rate
of six degrees per second and terminates at minus four degrees
angle of attack required for ET separation. A thrust termination
and coast sequence ends at ET Senaratinh . Tho ci pw ilatinn rnntinsioc
with a AZ translation, RTLS load relief, and entry sequence
which terminates at TAEM interface. TAEM interface is at 30
nautical miles from the aim point at a relative velocity of 1500
feet per second.
The Analytical Drag Control (ADC) entry guidance has been modified
for RTLS load relief. The load relief angle of attack is 35.0
degrees and the load factor limit is 2.2. The abort conditions
used in this study were 140, 230, 241, and 248 seconds from lift-
off. The 140 and 230 second aborts simulate early and late aborts
after Solid Rocket Booster (SRB) separation. The 241 second
abort simulates the last abort at which an immediate turnaround
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DN No.: 1.4-4-19
Page: 6
yields an initial 100 percent flyback throttle setting. The RTLS/
AOA mode. - boundary abort is simulated by the 248 second abort. The
powered portion of the trajectories was shaped in the inertial
velocity-altitude plane to be similar to the imode boundary abort
as presented in Reference (E).
The modified RI R-V line was used for all cases with nominal entry
aerodynamics to establish reference trajectories. A 3a dispersed
Lift over Drag ( L/D) uncertainty envelope is exhibited in Figure 2
which has been reproduced from Reference (F). The L/D•copdition
at test point seven resulted in minimum range capability. Maximum
range. occurred for the L/D condition at test point five. The
minimum range L/D condition was used to test the applicability of
the RI R-V line in the simulation used in this study.
The R-V line was moved ten nautical miles closer to the aim point
for 140 and 230 second abort cases to determine the effects on
turnaround time, MECO conditions, and nominal entry range. ADC
guidance dissipates excess range capability of the orbiter by
commanding successive reversal roll connnands. -The MECO conditions
on the minus ten nautical mile R-V line provide the orbiter with
additional excess range capability-with respect to TAEM interface
for nominal entry conditions. The change of nominal range capa-
bility between the two R-V lines a:as m-2asured by executing the
entries with zero roll angle.
k
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FIGURE 2
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DN No.: 1.4-4-19
" Page: 7
_MAXIMUM RANGE	 _ 
MINIMUM
.	 -1^ANGE-- =	 • —lid
Figure 3.1-11
POSSICLC Cl. ;diU C r ; "1C%' TAT';TY [%': ELCPE
Repoduced from "RILS Entry L0,1d Relief Parancter
Optimization", MDTSC0 DN 1.4-4-9, 27 Jute 1975
3I11ITT OF THS
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tDN No.: 1.4-4-19
Page: 8
The magnitude of the R-V line shift toward the aim point is con-	 :
r
strained by the requirement that ADC guidance absorb a plus 3a
dispersed excess range capability. This constraint was tested by
4
executing the minus ten nautical mile R-V line entry trajectories
with the test point five maximum range L/D.value of Figure 2.
The change in the mode boundary abort time caused by moving the
R-V line was determined by executing successive aborts until an
immediate turnaround yielded a 109 percent initial flyback throttle
setting. The last abort for a 100 percent flyback throttle was
determined in a similar manner.
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DN No.: 1.4-4-19
Page: 9
4.0 RESULTS
Selected powered RTLS trajectory conditions are presented in Table I
for the abort times and R-V lines used in this study. For a minus
ten mile shift in the R-V line, the change in turnaround time was
minus 1.8 to 1.9 seconds. The MECO arrival point moved 4.3 to 4.4
I nautical miles closer to the aim pint Oth an associated 82 to
84 feet per second increase in relative velocity. The change in
MECO R-V arrival points is shown in Figure 3 for the two R-V lines.
Nominal aerodynamics provide sufficinet range capability to reach
THEM interface from both R-V lines for all of the abort cases
(29.5 to 31.2 nautical miles). The range capability of the two
R-V lines was determined by executing the entries with zero roll.
angle. The entries were terminated at the'TAEM interface velocity
of 1500 feet per second. The ranges from the aim point are shown
in Table II. The range for the modified RI R-V line is 26.4 to
26.8 nautical miles. The range for the shifted R-V line is 14.9
to 16.3 nautical miles. This substantiates that the MECO R-V line
is a line of equal opportunity. Also the ratio of the change in
entry range capability per range change in R-V line is approximately
one to one (10.5 to 11.5 nautical miles/10 nautical mile change in
R-V line).
M I
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DN No.: 1.4-4-19
Page: 10
TABLE I
POWERED RTLS TRAJECTORY CONDITIONS
FOR A VARIABLE R-V LINE
ABORT TIME
SEC
MECO
LINE
TURNAROUND
SEC
MECO CONDITIO4
R-n.mi.
	 VE-fps
140 (1)* 301.3 311,	 1 7007
140 (2)* 299.2 306.8 7091
230 (1) 248.5 293.8 6354
230 (2) 246.7 289.4 6836
239** (2) 239 285.7 6782
241** (1) 241 290.0 6696
246*** (2) 246 285.8 67£3
248*** (1) 248 291.4 6718
* (1) R = .068VE
 - 165.5
* (2) R = .068VE
 - 115.5 (10 N.+. closer to aim point)
** Last at 100 10' flyback throttle
*** Last at 109% flyback throttle
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Page: 12
TABLE. II
TAEM INTERFACE RANGE FOR VARIABLE R-V LINSS
USING NOMINAL AND 3a DISPERSED L/D
RTLS ABORT
TIME - SEC
4ECO
R-V LINE
ENTRY CONDITIONS RANGE AT
TAEM - N.M.
140 (1) Nominal 30.1
140 (1) Nominal - Zero Roll 25.4
140 (1) - 3a L/D 39.4
140 (2) Nominal 29.5
140 (2) Nominal	 - Zero Roil -14.9
1 (2)
- 3a L/b 32.4
!40 (2) - 3a L/D - Zero Roll 28.8
140 (2) + 3a L/D 28.5 .
140 (2) + 3a L/D - Zero Roll 9.0
230 (1) IN0,-.^ i na 1. .0
230 (1) Nominal - Zero Roll 26.3
230 (1) - 3a L/D 39.5
230 (2) Mominal 29.8
230 (2) Nominal	 - Zero Roll 16-3
230 (2) - 3a L/D 33.3
230 (2) - 3o L/D - Zero Roll E. 3 
230 (2) + 3a L/D 28.3
230 (2) + 3(-, L/D - Zero Roll 7.0
239 '?) Nominal 29.7
241 (1) Nominal 31.2
246 ( 2) Nonni na1 29.7
248 (1) Nominal 30.6
(1) R n .068V E - 165.5
(2) R = .060V E - 1'5.5 (10 N.M. clo , er to aim point)
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DN No.: 1.4-4-19
Page: 13
The RI R-V line does not provide enough range capability for the
simulation used in this study. As shown in Table II, the 3a
minimum range L/D entries terminated at 39.4 to 39.5 nautical
miles.. This is 4.4 to 4.5 miles short of the maximum TAEM range
of 35 nautical miles. This indicates that the R-V line must be
moved approximately five nautical miles closer to the aim point
for the simulation used in this study. Another five mile shift
is required to target the R-V line to the nominal TAEM interface
range of 30 nautical miles.
Entr; trajectories were executed from the shifted R-V line using
the maximum and minimum entry range L/D conditions. The minimum
range L/D simulations terminated at 32.4 to 33.3 nautical miles.
The maximum range L/D simulations terminated at 28.3 to 28.5
nautical miles when ADC ranging was used. The zero roll angle
terminal ranges for-these cases are 7.0 to 9.0 nautical miles.
ADC guidance must dissipate the excess range capability that results
from the 35 maximum range L/D. The entr y roll history for the 140
second abort case that used the shifted R-V line and nominal aero-
dynamics is shown in Figure 4. The roll history for the 3c maximum
range L/D is shown in Figure 5. The roll histories with the same
entry conditions are displayed in Fi g ures 6 and 7 for the 230 second
abort case.
As shown in Figures 5 and 7, the excess range capability was
absorbed a;ithout exc:,ssive roll saturation. After load relief
terminates, AM co-;imands a ran ir,g roll at tho linit of 70 degrees for a
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duration of approximately 25 seconds. As the roll angle command
is decreasing the azimuth error build up causes a roll reversal.
The magnitude of the roll command continues to decrease after the
reversal as shown in Figures 4 to 7. In the nominal simulations
the roll command decreases to the minimum magnitude of ten degrees
Approximately twenty seconds later the roll command magnitude is
increased due to the requirements of ADC guidance. In the maximum
range L/D simulations the roll command magnitude starts the'same
increase prior to reaching the minimum angle. The roll histories
of Figures 5 and 7 represent a dissipation of 19.5 to 21.3 nautical
miles of excess range capability.
As stated earlier the modified RI R-V line did not provide an entry
capability to reach TAEM interface with minimum range L/D for the
simulation used in this study. The R-V line was moved ten nautical
miles to satisfy the minimum range requirement and to move the TAEM
target from 35 to 30 nautical miles. The overall effect was an
approximate two second decrease in the last RTLS abort time
(248 to 246 seconds shown in Table I). This indicates that a five
nautical shift of the R-w line would change the last RTLS abort
time by approximately one second. A R-V lire targeted to 30
nautical miles could be selected for those missions which contain
a RTLS/AOA mode boundary overlap that could absorb the loss of
approximately one second. The software necessary to change the
R-V line targeting criteria dur • 'ng flight consists of a logic test
r	
	
DN No.: 1.4-4-19
Page: 19
and two additional storage locations for the A(1) constants of the
MECO-10 and MECO lines where:
VE = A(1) + A(2)R
To eliminate this additional software the R-V line targeted to
35 nautical miles could be selected for RTLS critical missions.
DN No.: 1.4-4-19
Page: 20
5.0 C04CLUSIONS
The following conclusions can be made concerning a shifted R-V
line:
1. The zero roll angle TAEM arrival range decreases approximately
one nautical mile per nautical mile MECO R-V line shift towards
4	 the aim. point.
f	 2. The MECO R-V line is a line that provides equal capability to
reach a specified range at TAEM interface.
i	 3. The ADC guidance can dissipate the excess range capability
resulting from a five mile R-V line.shift towards the aim
point and a three sigma maximum range L/D dispersion.
4. An R-V line targeted to the TAEM interface range of 30 nautical
miles can be selected for missions which contain a RTLS/AOA
mode boundary overlap by giving up approximately one second of
RTLS abort capability.
5. An R-V line targeted to the limit TAEM interface range of 35
nautical miles should be selected for missions which do not
have a RTLS/AOA mode boundary overlap.
Dtl No.: 1.4-4-19
Page: 21
6.0 REFERENCES
(A) FM41 (75-32), Return-to-Launch-Site (RTLS) Preliminary Combined
Guidance and Targeting Formulation Presented to the Powered
Flight Working Group (April 2-3, 1975), April 28, 1975.
(B) User's Guide for the Space Vehicle Dynamics Simulation (SVDS)
Program Revision 2, JSC Internal Note No. 73-FM-67 November
14, 1974.
(C) "Powered Flight Guidance Ascent Supervisor", John P. Higgins,
December 18, 1974.
(D) Rockwell International (RI) Internal Letter SAS/NR&I-75-063
"Targeting Criteria for the Powered Phase of Mission 3A RTLS
Aborts", April 1, 1975.
(E) ,
 MDTSCO Design Note No. 1.4-4-14, "Return-to-Launch-Site
Trajectory Shaping", October 17, 1975.
(F) MDTSCO Design Note No. 1.4-4-9, "RTLS Entry Load Relief
Parameter Optimization", June 27 1975.
e
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Return-to-launch-site variable range-velocity line

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