NASA Technical Reports Server (NTRS) 19940026832: Investigation of sonic boom for the Space Shuttle: Low cross-range orbiter

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by  NASA Technical Reports Server (NTRS)

,_ASA-TM-]O8237
INVESTIGATION OF SONIC BOOM FOR THE SPACE
SHUTTLE : LOW CROSS-RANGE ORBITER
By
Lionel L° Levy, Jr., Raymond M. Hicks,
_and ,_____]J°elP. Mendoza _
It is desired that the space-shuttle orbiter be capable of landing
at airports equipped to handle present-day jet transports. Since the
majority of such airports are located near heavily populated areas, an
investigation has been undertaken to determine whether or not the
I
sonic boom generated during reentry of space-shuttle orbiters is poten-
tially a serious problem. The investigation was concerned with the
low cross-range orbiter and reentry concept proposed by Faget (ref. i)
of the Manned Spacecraft Center (MSC). This report describes the
approach used and presents the results obtained to date.
f_
NO_fl_NCLATURE*
,-I _n
_n m o
I _" u_
U 0
C 0 h flight altitude
Z _ 0
LID lift-drag ratio
1 length of body
M Mach number
U-
C_ 01
LU
Z..J , P wind-tunnel free-stream static pressure
Ob=-_
r distance bel_ model in wind tunnel
b-_ 0 S total wing area
I--LU _-4
W,_W
S ray-path along which pressure signal propagates
Z (.__-_I_
W orbiter weight
_COC
f_ w_J
*All units given in mks and English systems unless otherwise noted.
_y0 Z -C;
COU._ U
i c) (.n ¢)
_tJL)
ZO_
-2-
angle of attack
Y flight-path angle, negative below the horizontal
Ap sonic-boom overp ress ure
-i
Mach angle, sin I/M
Subs crip ts
e effective
m model
p payload
i, 2 relative values of
APPROACH
Sonic-boom overpressures are normally estimated using Whitham's
theory (ref. 2). His theory is based on the linearized-flow small
perturbation potential equation and therefore is limited in its appli-
cation to slender vehicles at small angles of attack, _. The near-
field pressure signature is estimated using the vehicle "F-function"
which, for slender vehicles at small _, may be obtained analytically
as indicated in reference 2 or semiemperically as demonstrated in
reference 3. The near-field signature is then extrapolated to far-
field conditions for straight and level flight at constant velocity
in a uniform atmosphere. The ground-level overpressures so estimated
are subsequently corrected for propagation of th>g pressure signals
through the actual (nonuniform) atmosphere.
In the case of the space shuttle, the orbiter reenters the atmos-
phere on a predetermined trajectory while flying at a high angle of attack
(a = 60o). The orbiter flow field is characteristic of a blunt-like
vehicle with a strong detached bow wave; see, for example, figure i. This
type of flow field cannot be calculated with linearized-flow theory and
the analytical treatment of Whitham is not valid, particularly the
analytical determination of the vehicle F-function. Therefore, an alter-
nate approach was taken in the hope that the semiemperical technique
-3-
developed by Hicks andMendoza(ref. 3) for evaluating the F-function
for slender vehicles at small _ might also be valid for blunt-like
vehicles at large _. If so, the semiemperically deducedF-functions
could be used to extrapolate experimentally determined near-field
pressure signatures of the shuttle orbiter to flight conditions. In
addition to corrections for a nonuniform atmosphere, corrections for
variations in deceleration and flight-path angle along the trajectory
could be included.
To investigate the validity of applying the Hicks-Mendoza technique
to the MSClow cross-range orbiter, the Whithamnear-field theory was
used (as described in ref. 3) to deducean F-function from an experi-
mental pressure signature measuredat one distance, r I, below a model
in a wind tunnel. The deducedF-function was used to predict the
signature at a greater distance, r2, from the model. Comparisons
between the predicted andsubsequently measuredsignature at r2 showed
very good agreement. A typical result is shownin figure 2 for tests
at a Machnumber, M, of 2.7 and _ = 60°•
At r2 = 1.216 m (47.88 in.) only half of the signature could be
measureddue to the limited travel of the survey mechanism. However,
the agreement shownbetween predicted and measuredsignatures demonstrates
that the semiemperical technique of reference 3 is valid for blunt
vehicles at large = and provides somemeasureof confidence that
extrapolations of the wind-tunnel data to flight conditions will be
valid.
In making the extrapolations to flight conditions, the F-functions
deducedfrom the measuredpressure signatures were used in conjunction
with Mach-number, altitude, deceleration, and flight-path-angle parameters
of a representative reentry trajectory as input to the computerprogram
developed in reference 4. This program calculates the ground-level
overpressure directly beneath a vehicle and includes corrections for
the effects of decelerating flight through a 1962standard atmosphere.
The atmospheric corections were fC_ther updated using the correction
factors more recently published in reference 5.
The corrections for the effects of flight-path angle,y, were
incorporated by using the computerprogram (ref. 4) to extrapolate the
input data to an effective flight altitude. The effective altitude,
he, was determined for propagation of a signal through a uniform
atmosphere andwas based on the geometric relationshi_ of the actual
flight altitude, h, y, and the Machangle _ (sin-_ I/M) shownin
figure 3. A pressure signal emitted from the nose of a body, described
-4-
relative to the ground by h and y, propagates normal to _ along
ray path s. The strength of the signal reaching the ground is con-
sidered to be that directly below the body (normal to the flight path)
at altitude h . Thus,
e
h = h cosu
e cos (_+_)
RESULTS
Experimental pressure signatures were measured in the Ames Unitary-
Plan Wind Tunnels for a O.178-meter (7 in.) model (body length) of the
MSC low cross-range orbiter at a = 60° and Mach numbers of 1.2, 1.68,
2.17, and 2.7. One signature was also measured at _ -- 16° and M = 1.2.
The flight conditions considered correspond to the altitude-, deceleration-,
flight-path-angle-Mach number histories shown in figure 4. These parameters
describe a portion of a representative reentry of a 1134 kg-payload
(25,000 lb.), 45.7 m-long (150 ft.), 81,600 kg (180,000 lb.) orbiter with
a total wing area of 180.3 m2 (1940 ft.2) flying a descent trajectory at
= 60° and a lift-drag ratio of 0.525.
The sonic-boom overpressures estimated by extrapolating the experi-
mental signatures, as described in the APPROACH section, to the above
flight conditions are shown in figure 5 as a function of Mach number.
"Acceptable" threshold levels of overpressure for supersonic flight over
populated areas have not yet heen established by the Federal Aviation
Agency. However, the goal of sonic-boom researchers in this country is
to design transport aircraft which create ground-level overpressures of
48 N/m 2 (i psf.) or less. Hence, the estimated &p for the MSC orbiter
of 98 N/m 2 (approx. 2 psf.) at M = 1.2 is potentially an objectionable
level. This is particularly true when one notes that the present data
do not include the effects of rate-of-change of flight-path angle.
Haefeli has shown (ref. 6) that corrections for the type of y maneuvers
shown in figure 4 result in increases in Ap, particularly at transonic
Mach numbers.
It is of interest to note one promising means of reducing &p; that is,
by the combined tailoring of the trajectory, the physical and aerodynamic
characteristics of the vehicle, and the attitude of the vehicle during
reentry. This was partially demonstrated by assuming the angle of attack
of the MSC orbiter varies during reentry in such a manner that it
negotiates M = 1.2 on the same trajector_ shown in figure 4, but at _ = 16°.
The result shown in figure 5 for _ = 16v at M = 1.2 indicates nearly a
50-percent reduction in Ap.
REFERENCES
i, Faget, M. A.: New Configuration Concept for Space Shuttle That
Provides Suitable Characteristics for Launch, Entry, and Landing.
Paper presented at AIAA 6th Annual Meeting and Technical Display,
Anaheim, California, Oct. 20-24, 1969.
c Whitham, G. B.: The Flow Pattern of a Supersonic Projectile.
Communications on Pure and Applied Mathematics, vol. V, no. 3,
Aug. 1952, pp. 301-348.
. Hicks, R. M. and Mendoza, J. P. : Prediction of Aircraft Sonic
Boom Characteristics from Experimental Near Field Results.
NASA TM X-1477, Nov. 1967.
4_ Friedman, M. P.: A Study of Atmospheric Effects on Sonic Booms.
Technical Report 89, Massachusetts Institute of Technology
Aerophysics Laboratory, Cambridge, Massachusetts, Dec. 1963.
De Pierce, A. D. and Thomas, C. L.: Atmospheric Correction Factor
for Sonic-Boom Pressure Attitudes. Journal of the Acoustical
Society of America, Vol. 46, no. 5, (Part 2), Nov. 1969.
e Haefeli, R. C." Effects of Atmosphere, Wind, and Aircraft Maneuvers
on Sonic Boom Signatures. NASA CR-66756, April 1969.
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