An evaluation of the tactical instrument landing systems (TILS) for use in the orbiter autoland system was made. It was found that with certain modifications, the TILS can satisfy orbiter autoland requirements. These modifications, include (1) addition of DME equipment, (2) expansion of elevation coverage from 0-10 deg to 0-30 deg, and (3) expansion to redundant systems with associated ground monitors. Additional modifications that are not necessary to meet the orbiter requirements, but that can enhance performance margin are (1) tightening of elevation antenna beam width from 1.3 deg to 0.5 deg and (2) split site configuration to provide azimuth and range coverage through rollout

Tate, J. M.

English

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https://ntrs.nasa.gov/search.jsp?R=19760018248 2020-03-22T14:22:16+00:00Z
41^	 ..	 f
1.3-DN-COIC3-002
NASA C -
1-,,I- 7_7
Space Shuttle
Flight Control Integration Support
Nas 9-13970
Task Order No. C0103
Design Note
	
(NASA-CR-147773) EVALUATION OF TILS FOR USE
	
N76-25336
AS THE ORBITER LANDING NAVAID
(MCDONNELL-DOUGLAS CORP.) 18 P HC $3.50
	
CSCL 126	 UNCL AS
G3/18 43524
Evaluation Of T1 1S For Use As The Orbiter
Landing NAVAID
23 October 1974
Approved by: ` %/ p^^•2
W. H. Geissler
Project Engineer
Prepared by: Qs" - YK , J,&
J M. Tate
A ociate Engineer
Guidance and Control
Mechanics
Approved by:
H. W. Stegall
Senior Engineer
Guidance and Control
Mechanics
J±
JUN 19':
RECEIVED	 r
NAM'g
ls% INPUT BRANCH
MCOONNELL OOtIOLA
oowrow^^son
1.3-DN-COW -002
Page 1 of l/
Subject: Evaluation of TILS for Use as the Orbiter Landing NAVAID
1.0 Summary
An evaluation of the Tactical Instrument Landing System (TILS)
for use in the Orbiter Autoland System has been mEde. It has
been found that with certain modifications, the TILS can satisfy
Orbiter Autoland requirements. These modifications, include (1)
addition of DME equipment, (2) expansion of elevation coverage
from 0-10° to 0-30°, and (3) expansion to redundant systems with
associated qround monitors. Additional modifications that are not
necessary to meet the Orbiter requirements, but that can enhance
performance margin are (1) tightening of elevation antenna
beam width from 1.3° to 0.5° and (2) Split site configuration to
provide azimuth and range coverage through rollout.
2.0 Introduction
The baselined radio frequency ground-based navaid for the Shuttle
approach and landing  i s the Microwave  Scanning Beam Landing
System (MSBLS). The function of the MSBLS is to provide the
onboard receivers navigation information in the form of range,
elevation, and azimuth data relative to the ground transmitter.
The data is used to update the vehicle state vector which is in turn
used to compute vehicle energy and position.
The presently accepted baseline MSBLS ground system is scheduled
for delivery in December 1976, to support the Orbiter Aavroach and
Landing Test (ALT). The present delivery re q uirement for MSBLS ground
1.3-DN-CO103-002
Page 2 of 17
equipment to support the Shuttle Training Aircraft (STA) is
December 1975. In the interest of commonality between the Orbiter
and STA, and the delivery schedule conflict, it has become
necessary to investigate the availability of other microwave
scanning beam equipment that could satisfy the STA delivery date
requirement and still be acceptable for use with Orbiter airborne
MSBLS receivers. Of the available scanning beam systems, the most
promising is the TILS.
It is the purpose of this memorandum to compare the performance
of the TILS, a currently available production scanning beam sys-
tem,to the baseline MSBLS.
3.0 Discussion
As previously stated, the basic requirement of the MSBLS ground
system is to provide navigation information to the Orbiter during
approach and landing. The autoland system touchdown requirements
(Ref 1), are shown in Figure 1 which depicts the approach end
of the runway, the nominal touchdown point ie., 2700 feet from
threshold, the 3 0 Glideslope Intercept Point, and the 3 Q'
k
touchdown requirements footprint.
A pictorial description of the baseline MSBLS ground station is
shown in Figure 2. This configuration is capable of providing an
azimuth signal of ±20° relative to the runway centerline and an
elevation angle from 0° to 30°. The DME function will provide range
1.3-DN 0103-002
Page 3 of 11
from 12,000 feet altitude through touchdown and rollout. In the
practical application, the elevation angle signal is not useable
lower than one signal beam width to preclude masking and ground
clutter. Thus, the baseline elevation signal is available down
to 0.50 . The Level II requirement for autoland states that the
automatic system shall be capable of executing fully automatic
landings in "0-0" weather conditions with an all-up system (Cate-
gory IIIC Requirement). The baseline design reflects an inter-
pretation of these requirements to mean full MSBLS coverage through
autoland and rollout. To provide this type covers^	 P	 YP	 a it was d,-Pmed9
necessary to split the scanner sites as shown in Figure 2. The
elevation scanner is 200 feet normal to the centerline and 4000 feet
down the runway from the approach end to provide unrestricted
elevation coverage through touchdown. The azimuth scanner and DME
antennas are located on the centerline beyond the stop end of the
runway, approximately 12,000 feet from the elevation scanner, and
provide coverage through rollout. In the split site configuration
it is necessary to physically connect the two sites with a cable
to provide a synchronizing link between the two antennas.
TILS at the Baseline Position - The standard TILS provides elevation
and azimuth functions to airborne vehicles during final phases of
landing and touchdown. A pictorial de:,cription of the TILS ground,
station, at the baseline position, is shown in Figure 3. The con-
kv as A...00
1.3-DN-00103-002
Page 4 of 17
figuration is capable of providing an azimuth signal of +150 relative
to the runway centerline, and an elevation angle from 0 to 100.
In the practical application, the elevation angle signal is not useable
below 1.30.
Baseline MSBLS/TILS Elevation Coverage - Figurer 4 & 5
graphically depict both MSBLS and TILS elevation coverage from
the baseline position for the final and initial flare ranges
respectively. The basic MSBLS elevation co verage is from 0.5° to
30° as opposed to the TILS elevation coverage of 1.3° to 10°.
The three orbiter trajectories shown in Figure 5 were obtained from
Ref 1 and represent trajectories with headwind, no wind, and
tailwind conditions. As shown in Figures 4&5, the present TILS
configuration located at the baseline position will not provide
full elevation coverage during the steep glide slope approach and
prior to the final flare for the headwind trajectory. Figure 6
shows the planview of both elevation coverages in the baseline
position. It is apparent that elevation coverage is not provided
to touchdown in all cases described by the touchdown requirements.
In order that TILS satisfies the elevation requirements, the
elevation coverage must be raised from 10° to 30° and the eleva-
tion scanner must be located 2500 feet from the approach end
and 200 feet normal to the centerline of the runway as shown in
Figure 1. This move is made necessary by the 1.3° elevation
4Ulm-i
1.3-DN-00103-002
Page 5 of 17
restriction imposed by the standard TILS elevation scan. Figure 8
shows the planview coverage of the modified TILS at 2500 feet from
threshold and indicates that 15 0 width of the elevation scan
causes loss of signal in most cases described by the touchdown
requirements ellipse. However, for the headwind, nominal, and tail-
wind trajectories described in Figure 7, the data dropout
occured at 3, 4, and 5 seconds prior to touchdown. These
times-to-go correspond to 25, 32.5 ,and 40 feet in altitude
respectively and elevation coverage below these altitudes would
not be provided. However, elevation to touchdown is not a
necessity since altitude information from 400 to 100 feet
altitude is a blend of MSBLS and Radar Altimeter data and below
100 feet altitude, the information is provided entirely
by the Radar Altimeter. Furthermore, the IN could provide the
necessary azimuth and altitude information required for final
flare, touchdown, and rollout.
The other change that must be implemented, is the addition of the
DME function to the TILS. This is necessary in order that range
measuring capability accurate enough to meet the autoland
requirements is available for state 'vector u pdate. The
only other navaid which provides range information is the TACAN,
which has an accuracy of + 400 feet. The ± 400 ft accuracy
provided by the TACAN is equivalent to the 1 Q" tolerance of the
autoland requirements which is the tolerance for the total GN&C
system. Thus it is obvious that a more accurate DME than is
^+'`^^	 ^• #. ill s...«	 :Il ` ^	 ^ i	 —
1.3-DN-00103-002
Page 6 of 17
provided by TACAN is necessary (Ref 3). With the above mentioned
changes, and the addition of DME, the modified TILS will be able
1
to satisfy the basic Orbiter ground navaid requirements with 	 +
only a small amount of system degradation.
Rollout Coverage - As noted in Figure 3, the TILS is a colocated
scanning beam system. Given that the elevation scanning beam must
be located 2500 feet from threshold, a colocated system provides
azimuth and DME coverage to the Orbiter down to approximately
0-5 seconds prior to touchdown. The tradeoff implied is that
of cost savings of a colocated site versus the necessity of
azimuth and DME data during touchdown and rollout. Analysis
indicates that rollout guidance can be provided by using inertial
data from the IMU.
Figure 9 shows a comparison of the touchdown and rollout accuracies
of the baseline MSBLS and modified TILS.
The touchdown errors are shown both with and without Radar Alti-
meter to indicate the difference between the all-up system and
the failed Radar Altimeter case, which requires altitude to
be derived from MSBLS range and elevation angle.
The inertial contributions represent a 0.5 ft/sec velocity
error in each axis. This is based on a previously performed analysis
(Ref 4).
1.3-DN-CO103-002
Page 7 of 17
The final set of errors shown in Figure 9, represents the
total error at full stop in the basellne MSBLS due to MSBLS
system accuracy, and the TILS which includes both system
accuracy and the error contirbutions from the inertial
system during touchdown and rollout.
S
4.0 Conclusion
From the described analysis, it can be concluded that the TILS
can satisfy Orbiter Autoland system requirements with the following
requirements:
1. Addition of DME equipment.
2. Expansion of the elevation coverage
3. Expansion to redundant systems with
Additional modifications that would
the Orbiter requirements, but would
of performance are tightening the e
width from 1.30 to o.50 and a split
from 0-100 to 0-300.
associated monitors.
not be necessary to meet
contribute to the margin
levation antenna beam
site configuration to
provide azimuth and range information coverage through
completion of rollout.
5.0 References
1. Space Shuttle Automatic Landing Support Program PDRL No. UA 01
DTO Dune 1974; Sperry Flight Systems.
2. Microwave Scanning Beam Landing System (MSBLS) Navigation
Set for Space Shuttle Orbiter Vehicle; Presentation Handout,
H. Erwin, Aug. 1974.
AA
1.3-DN-00103-002
Page 8 of 17	 ►
t
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3. Space Shuttle Guidance, Navigation and Flight Control
Accuracy Control Document, DTD June 1974; Rockwell International.
4. Kriegsman, B., Mahar, K, "Entry and Landing Navigation System
Performance with Nsw Navaid Error Models", CSDL Shuttle Memo
10E-74-49, 10 September 1974.
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Evaluation of TILS for use as the orbiter landing NAVAID

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