An analysis was performed to investigate whether or not the obstruction caused by boom-mounted probes forward of the Orbiter nose could cause Microwave Scan Beam Landing System (MSBLS) data dropout during the autoland flight phase of the Approach and Landing Test (ALT). The results indicate that there will be no interference from the nose boom to cause MSBLS data dropout for the flight conditions under which the ALT is to be performed. Additional analysis considering approach trajectories in more extreme wind conditions than anticipated for the ALT also indicates that the nose boom creates no interference

Tate, J. M.

English

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https://ntrs.nasa.gov/search.jsp?R=19760026273 2020-03-22T13:44:27+00:00Z
IKCDOYN-E L DOUGLAS TECHNICAL SERVICES CO.
HOUSTON ASTRC::AUTICS DIVISION
t
1
1.3411-60203-007
Page 1 of 27
SPACE SHUTTLE 0XIN'ERING AND OPERATIONS SUPPORT
DESIGN NOTE NO. 1.3-DN-CO203-007
AN EVALUATION OF Tfi MSBLS/NOSE BOOM
BgTERF=;CE FOR THE APFR04CH AND LANDING TEST
AVIDNICS ST=1 ENGINEERING
28 FEBRUARY 1975
This Design Note is Submitted to NASA Under Task Order
No. CO203, NAS 9-13970.
Prepared bP m	 :y
J. i. Tate
Design Engineer
488-;660-ext. 263
Approved by: r1r
W. H. Geissler
Technical Manager
488-5660-ext. 257
Z"l
	
Approved by:
R. F. Pannett
Project Manager
488-5660-ext. 258
kt'^E^VED.., ^^
(%- VS A-CP-151C1 5)	 AN EVALUATION OF THE
	 N7e-33361
MSBLS/NOSE ECOM TNTEEFERENCE FOR THE
A-'PFOACH ).NE LANLING TEST (McDonnell-Doug_ la=
Technical Services , 	27 p HC $4.GC CSCL 17G	 Unclas
r,3/32 C5738
1.3-Di'I-0O203-007
Page 2 of 27
1.0 SLTM^'_4RY
The backup air data subsystem of Orbiter 101 utilizes probes mounted
on a boom which extends approximately 17 feet forward of the Orbiter
nose. Concern that this obstruction could cause Microwave Scan Beam
Landing System (I!SBLS) data dropout during the Autoland flight phase
of the Approach and Landing Test (ALA') .led to the analysis described
herein. The results of the analysis indicate that there will be no
interference from the nose boom to cause MSBLS data dropout for the
flight conditions under which the ALT is to be performed. Additional
analysis considering approach trajectories in more extreme wind
conditions than anticipated for the ALT also indicates that the nose
boom creates no interference.
2.0 INTP.ODUCTION
The baselined radio frequency airborne Navigation Aid (NAVAID) for
the Shuttle approach and landing is the MSBLS. The function of the
MSBLS is to provide navigation information in the form of range,
elevation, and azimuth data relative to t yro ,ground transmitters adjacent
to the runway at the landing site (Figure 1).
_	 For ALT a Backup Air Data System, which utilizes a 17 foot nose boom,
will be used to calibrate the primary air data systems and supply
information to the Backup Flight Control System (BFCS) and Displays.
It is the nose boom and it's proximity to the N.SBLS onboard antennas
that has caused concern relative to MSBLS data dropout during the
Autoland flight phase of the ALT.
It is the purpose of this design note to exhibit the results of an
analysis performed to evaluate the possibility of MSBLS/nose boom
: ,NAI; PAGE IS
POOR QUALITY
1
	
i
1.3-M-0203-007
Page 3 of 27
interference. Figures 2a and b show representations of the airborne
RDP relative to ground station geometry and the airborne to ground station
IL MS look angle geo::etry respectively. These fiZ:res will lend clarity to
the nose boom interference problem.
3.0 DISCUSSIM
The primary purpose of this analysis is to determine if the nose beam inter-
feres with the 1.5BU signal reception during the Autoland flight phase of
the ALT. Interference can result from two sources. (1) A physical obstruc-
tion to signal reception such as could be the case with the nose boom, and
(2) Rate of change of power received. The Automatic Gain Control (AGC) has
the ability to track changes in power received of +3 to -2 decibels/second
(db/sec). Therefore changes which exceed these rates would cause the
MSBIS to drop signal lock and result in data dropout.
Figure 3, a Radiation Distribution Pattern (RDP), is a Ku Band antenna
pattern obtained from Rockwell and is representative of the antenna to
be used on the Orbiter. The numbers on the RDP represent the normalized
_ antenna gain as a function of pitch and yaw antenna look angles. The
interference created by the nose boom is clearly defined in the lower
portion of the RDP. Rapid motion in either pitch or yaw antenna look
_	 angles while in this region, (approximately +12 0 in pitch) would consti-
tute '__ ELS/nose boom interference and could cause data dropout by exceeding
the AGC tracking rate (Reference 1).
The technique used in this analysis is as follows: Obtain the time
histories of both pitch and yaw antenna look angles from the ALT
approach trajectory utilizing various wind conditions and the Space
ORIODIAD P.
^	 f
1.3-Dil-0O203-007
Page 4 of 27
Shuttle Functional Simulator (SSFSY. This was done to ascertain if the
antenna look angles fall in the lower portion of the RDP and create
interference due to the inability of the AGC to track the signal in that
portion of the RDP.
In addition, the following procedure was used to check the gain margin
to ensure that it is within limits. Read a corresponding normalized
gain value of the airborne antenna ( Gr) from the RDP Figure 3, as a function
of pitch and yaw look angles. Subtract the RDP gain value from 5, (the
assumed maximum gain). Calculate slant range to the ground antenna,
(applying the root sum squared technique) using the altitude of the
airborne antenna and the ground range to the ground antenna. Inserting
the value calculated above, along with the known values into the power
received equation,
2
Pr - Pt + Gt + Gr + 10 loglo X R
the total power received can be calculated.
Where:
Pr
 = poM!' received (dbM)
Pt
 = transmitted power (+60 db)
Gt
 = ground antenna gain
+31 db for the elevation antenna
+27 db for the azimuth antenna
Gr n of the airborne antenna
Za—ssumed 5 db maximum)
X= wave length (assumed .02 meters)
R = slant range
The power received calculation was made assuming a clear day, (no rain
losses) and no airborne waveguide and miscellaneous losses were used.
The receiver threshold for power received for elevation and azimuth signals
, pAOE IS
ORIGINAL
OF ppOR Quaw
^	 C	 I	 i	 t
.3-DII-0O203-007
Page 5 of 27
is -74dbM and -77 dbM for the Distance Measuring Equipment (DME).
The DME signal emanates from the same location as the azimuth
signal. Therefore, any signal which falls below -74 or -77 dbM
respectively would constitute loss of signal.
4.0 RESULTS
The simulations evaluated were, (1) nominal trajectory with no winds,
(2) nominal trajectory with headwinds and gusts, (3) nominal
trajectory with crosswinds (left to right, which causes the vehicle
to yaw away from the ground station)_and gusts.
Figures 4,6,8, and 10 show the time history of pitch (THETA) and
yaw (PSI) antenna look angles in degrees as a function of time in
seconds for the elevation station. These figures represent trajectories
1,2,3, and 4 respectively. In none of the cases evaluated, do the pitch
antenna look angles exceed +10° prior to threshold. Only after
threshold passage do both pitch and yaw angles began to diverge which
is as expected in as much as the vehicle is approaching ground station
fly-by and loss of signal from the elevation station would occur.
No nose boom interference is seen in the trajectories
analyzed for the elevation station.
The ability of the MSBLS air borne unit to respond to changes in power
received is of concern. The airborne AGC can track changes in power
received in the range of +3 to -2 db/sec. As a result of this analysis,
the rate of change seen in all trajectories analyzed, ( +2.45 to -1.72 db/
eec) did not exceed these rates for the elevation station. Therefore
ACC tracking is not a problem.
^i	 r
	
I
1.3-DN-CO203-001
	
3
Page 6 of 27
Figures 5 ,7,9 and 11 show a time history of power received in
decibel meters (dbll) as a function of time in seconds and slant range
in feet for the elevation station. The figures represent trajectories
1,2,3 and 4 respectively. As expected, the power received improves as
the distance between the airborne and ground antennas decreases.
Furthermore, the power received does not go below -74 dbM and there
is no loss of signal due to lack of power received. Therefore there is
no evidence of nose boom interference.
Figures 12,14,16 and 18 show the time history of pitch (THETA) and
yaw (PSI) antenna look angles in degrees as a function of time in
seconds for the azimuth/DME station. These figures represent
trajectories 112,3, and 4 respectively. In none of the cases evaluated
do the pitch antenna look angles exceed +8°. Therefore inasmuch as
the pitch antenna look angles did not move through the lower portion of
the RDP (Figure 3) the condition for nose boom interference is not
present.
Figures 13,15, 17, and 19 show the time history of power received in
=	 dbM as a function of ,time in seconds and slant range in feet for the
azimuth/EKE station. These figures represent trajectories 1,20, and 4
respectively. As was the case with the elevation antenna, the power
received improves as the slant range decreases between the airborne and
ground, and the power received does not go below -74 dbM for the
azimuth or -77 dbM :or the ME antennas.
There is a discontinuity which occurs in figures 15,17, and 19. The
discontinuity represents a limitation in the printer used to print
ORIGINAL PAGE IS
OF POOR QUALITY
P
I.age7fiof2703-007
Figure 3. The vehicle attitude during these discontinuities was one of
nose below the tail and would therefore improve signal reception.
Additionally the changes in power received, (+0.97 to - 0.79 db/sec)
do not exceed the AGC tracking rates. There was therefore, no data
dropout due to nose boom interference for the azimuth/DE ground antennas.
5.0 CCIICLi1SICN
The results of this analysis indicate that for the particular trajectories
and conditions analyzed, that the onboard MSBLS will be able to acquire
and retain lock. Except for the discontinuities noted in the results,
the system performed as expected. The vehicle pitch attitude did not
reach a position which would cause the nose boom to interfere with
HSBIS signal reception. Furthermore, the vehicle yaw did not attain yaw
rates which would cause the AGC to drop signal lock from either elevation
or azimuth/=E stations.
It can be concluded based on the conditions of this analysis that there
is no N.SBIS/nose boom interference.
It should be noted however, that should the conditions on which this
analysis was based be changed, it is recommended that an analysis based
on the new conditions be made.
ORrGIN4L P
OF pppR @UPS
e -sIIkniITU
135 00'
I
^,	 I
1.3-u;4-Cj2j3-007
Page a of 27 JMT
2-28-75
MSBLS GROUND STATION GEOMETRY
P PCIOR AGR LS
R QU^'Y
FIGURE I
#►
 "DING YAGF, B LANK NOT FIIMM
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2-28-75
1.3-D;N-^A203-=
Page 9 of 27
RDP / GROUND STATION GEOMETRY
FIGURE 2A
LOCAL HORIZONTAL
AryNLG
YAW* ci'1
KL00
ANGLE
GROUND
STATION
ORIGINAL PAGE IS
OF POOR QUAIIT)&
+ ANGLE ROTATION SEQUENCE IS PITCH , YAW
AIRBORNE TO GROUND STATION klSBLS LOOK ANGLE
FIGURE 2B
4
1.3-[):1 -0O203-007	 .
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page 15 of 27
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Page 17 of 27
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FIGURE 13
1.3-D+;-0O203-007
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FIGURE
	
15
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1.141'1 -0O203-007
Page24 of 27
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Pace 26 of 27
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mm
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FIGURE 19
0
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1.3-^'!-COZ03-00^
Page 27 Of 27
6.0 R"--EFEP'.CE'S
1. Err-i, };az rJ 0. Jr. and Johnson, Marvin L, "The Effect of YSBIS
Antenna Pattern gulls Caused By the Air-Data-Probe," JSC Internal
Note 09", 14 January 1975 •


An evaluation of the MSBLS/nose boom interference for the approach and landing test

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