Operational performance of falling sphere systems for measuring meteorological parameters of upper atmospher

Daniel, O. H.

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OPERATIONAL EXPERIENCE WITH PASSIVE FALLING
SPHERES ON THE AFETR*
By O. H. Daniel
Pan American World Airways, Inc.
Aerospace Services Division
Patrick AFB, Fla.
The use of small rockets to measure meteorological parameters above the altitude
limits of the balloon rawinsonde systems began on the Air Force Eastern Test Range
(AFETR) in 1957. The Range at that time was known as the Atlantic Missile Range and
the first meteorological rockets used were of the Loki II type with radar-reflective-chaff
payloads. The Army Ballistic Missile Agency at Huntsville, Alabama, the range user,
conducted their own launch operations during the early part of their program. The high-
altitude data were needed at that time to assess the environmental conditions affecting the
R & D testing of the Jupiter and Redstone rocket systems.
In 1959, the Air Force Cambridge Research Laboratories (AFCRL) implemented a
development program to try and improve the performance of the Loki II meteorological
rocket. Their version of this system was called the Overrange Wind Logging system
(OWL) and also used a radar-reflective-chaff payload. Data for altitudes as high as
250 000 ft were required in 1959 and 1960 for programs such as testing of the Atlas and
Titan missile systems. This was somewhat above the altitude capability of the Loki II
system when launched from sea level. The effort to improve the performance of the sys-
tem was not significantly successful and therefore was discontinued after a short flight-
test series.
During the same period the Office of Naval Research was engaged in a development
effort to develop the meteorological rocket system which became known as the Arcas.
This development effort was also supported by the Air Force and Army. The Air Force
Cambridge Research Laboratories developed the inflatable falling-sphere payload (Robin)
for use with the Arcas rocket, while at approximately the same time, the Army was
developing various configurations of parachute-borne sonde payloads, also for use with
the Arcas.
The first flight tests of the Arcas/Robin system were conducted on the AFETR in
1959. This series consisted of 25 systems, 13 of which properly deployed the Robin
sphere at or near apogee. The average apogee altitude reached by these 13 systems was
over 200 000 ft. A number of the remaining 12 systems ejected the sphere successfully,
*Activities reported upon in this paper were performed under contract to the Air
Force Eastern Test Range, Air Force Systems Command.
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althoughvarious malfunctions occurred with the payload, suchas rupture andpartial
inflation. During the period 1960through 1961the Arcas rocket system was usedinter-
spersed with Loki II chaff systems. The payloadsusedwith the Arcas at that time were
mainly Delta, Gamma,andAN/DMQ-6 sondesdevelopedby the Army andfurnished to the
AFETR to support the early Meteorological RocketNetwork (MRN) effort. Concurrently,
other series of flight tests of the Arcas/Robin system were conductedat Eglin AFB,
Holloman AFB, and NASAWallops Station.
To provide some idea of the Arcas/Robin performance of the system during the
1960-61period, the 104systems launchedat Eglin AFB producedusable density data in
40 cases. The averageapogeealtitude of the 104systems launchedwas 226 000feet. Of
the systems which producedusabledensity data, the average layer thickness of the density
datawas 69 000feet. The average lower altitude limit of the density data for the 40 suc-
cessful systems was 142000feet. The Arcas/Robins launchedat Holloman andWallops
Station resulted in somewhatlower performance for the Robinsphere than that obtainedat
Eglin AFB during this period.
Beginning in late 1961,a number of Arcas/Robin systems were procured by the Air
Force and madeavailable for both missile test support and MRN activities. Fifty-six of
these systems were launchedin 1962of which 45producedusabledensity data. In 1963,
72 systems were launched,48of which producedusabledensity data. Thirty-four sys-
tems were launchedon the AFETR in 1964,31of which were completely successful. The
averageapogeealtitude for these three years of operation with the Arcas/Robin system
wasapproximately 212 000feet. Theaverage lower limit for the usabledensity data
obtainedwas about 145000feet. In 1965,101Arcas/Robins were launched,89of which
producedusabledensity data for an 88-percent success rate. The averageapogeealti-
tude reachedby these 101launcheswas 210000feet, and the lower limit for the usable
density data still averagednear 145000feet.
During the period 1962through 1965,the Arcas/Robin systems were used primarily
for MRN support. Several of the missile test programs on the Rangeduring that period
had stringent requirements for wind, density, temperature, andpressure data from the
surface to about250 000feet. The Arcas/Robin system wasperforming well and pro-
ducingwhatappearedto be gooddensity andwind data in the region of from 145000to
200000feet. However, a severe gapin the density dataexisted betweenthe upper limit
of the rawinsondeobservations at about 105000 feet andthe averageRobinballoon col-
lapse altitude near 145000feet. The acquisition of density andtemperature data in the
intervening 40000-foot layer was significantly more important than the acquisition of the
data to altitudes above200000 feet. This is becauseof the obviously greater effects of
the atmosphereon missile system performance at the lower altitudes.
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From the early daysof the developmentof the Robinsphere payloadfor the Arcas
rocket, there were several reservations in the minds of meteorologists at the AFETR
regarding the reliability of the density data beingobtained. These reservations stemmed
from our experiencewith numerouschaff payloadlaunches,which on manyoccasions
seemedto indicate the presenceof significant vertical componentsto the high-altitude
wind field. This, in our opinion at that time, causeduncertainties in the meanlayer den-
sities computedfrom the Robindata. We suspectedother uncertainties in the data caused
by the questionablereliability of drag information available at that time for use in the
data-reduction routine. Several times during the developmentof the Robindata-reduction
process, changesin drag datawere madeas a result of additional data analysesand study.
This hadthe effect of changingdensity values previously computedby several percentage
points and, in onecase, by a range of from 10 to 15percent.
Someof the AFETR test programs required temperature data for use in evaluation
of heat-transfer processesin the developmenttesting of ablative materials and reentry
vehicles. A particular program having important needsfor density andtemperature data
in the critical region from 100000 to 200 000feet was the aerothermodynamic structural
systems environmental test (ASSET)program. Sincethese data requirements were not
being met by the Arcas/Robin system, the launch sites that were activated at Eleuthera,
SanSalvador, GrandTurk, andAntigua to support this program usedthe Arcas rockets
with sonde-typepayloads.
During the mid-1960's, a sondepayloadwas developedfor the Loki II meteorological
rocket system. There was also a Robinpayloadadaptedto the Loki system but this was
never employedon the AFETR. With the adventof the sondepayloadfor the low-cost
Loki system and its marked advantageover the Robin in the measurementregion between
100000and 150000feet, nearly all test support data since 1965havebeenprovided on the
AFETR by sonde-typepayloadswith either the Arcas or Loki II rockets. The exception
to this hasbeenthe use of the Viper-Dart-Robin system to acquire dataabove200000ft.
Someof our MRN requirements have beenpartially met by the use of Arcas rockets with
outdatedRobin payloadswhich were not expectedto inflate properly for density determina-
tions but were usedonly for wind measurements.
The Viper-Dart rocket system with Robinpayloadbecameavailable for useon the
ETR in the fall of 1968in time to support the high-altitude data requirements of the
Apollo 7 launch from CapeKennedy. The Viper systems usedon the ETR during the past
year have beena combinationof developmentalflight-test models launchedin support of
anAFCRL developmentproject and a quantity of preproduction models purchasedby the
ETR for Apollo launchsupport.
For the Apollo support, density andwind data to 295 000feet are required. At the
present time, the Viper-Dart vehicle with a Robin payloadis the only near-operational
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system capableof supplyingthese data to this altitude. Of 20 similarly configured Viper-
Dart systems with Robin payloads,12producedthe required wind anddensity data to
295 000feet. The averageapogeealtitude achievedby these 12systems was 430000feet,
and the average lower limit of usabledensity datawas about 170000 feet. The average
thickness of the layer through which density datawere obtainedwas therefore 125000 ft.
Wind data were generally usablebeginningat about 20000 feet abovethe altitude for the
usabledensity data, andof course, the wind datawere obtainedwell below the minimum
altitude for the density databy continuingto track the partially collapsed sphere.
Of the eight systems which failed to produce the required data, three failed because
of no inflation of the sphere; one,becauseof a motor malfunction; one,becauseof nopay-
load separation; andthree, becauseof late radar acquisition of the payload.
We plan to continuethe use of the Viper-Dart system with the standard Robin pay-
load during the immediate future to obtain density and wind data abovethe altitude of the
Loki-Dartsonde system. By using Rawinsonde,Loki-Dartsonde andViper-Dart-Robin
systems, completeprofiles of winds and densities are obtainedto approximately
295 000feet, with additional parameters suchas temperature and pressure beingobtained
from the surface to the top of the Loki-Dartsonde profile at about 200 000feet.
The data from the three different observations, Rawinsonde,Dartsonde,and Robin,
display remarkable agreementin the overlap regions. Onearea presently causingsome
difficulty is in the transonic-fall-rate region of the high-altitude Robin system where
someunusualoscillation in the density profile is evident. Recentinvestigations of this
problem by AFCRL andthe University of DaytonResearch Institute have resulted in the
experimental useof somerevised drag data which, in most cases, seems to improve the
consistencyof the computeddensity in the area of concern. Thefall rate of the Robin
sphere whendeployedat above400 000feet with the Viper-Dart rocket system is tran-
sonic at approximately 233 000feet. The layer of questionabledensity datausually
extendsover several thousandfeet on either side of this point, thoughpredominantly on
the subsonicside. In general, density data computedthroughout the altitudes where the
sphere is falling supersonically appearquite consistent, which seems to suggestsome-
what more reliable data than those obtainedin the subsonic-fall-rate region.
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Operational experience with passive falling spheres on the AFETR

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