An ablation article, such as a conical heat shield, having an ablating surface is provided with at least one discrete area of at least one seed material, such as aluminum. When subjected to ablation conditions, the seed material is ablated. Radiation emanating from the ablated seed material is detected to analyze ablation effects without disturbing the ablation surface. By providing different seed materials having different radiation characteristics, the ablating effects on various areas of the ablating surface can be analyzed under any prevailing ablation conditions. The ablating article can be provided with means for detecting the radiation characteristics of the ablated seed material to provide a self-contained analysis unit

Erickson, W. D.

Sullivan, E. M.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
- 1043 9-1) ABLATION ABTICLE N73-27796
AND METHOD Patent (NASA) 5 p CSCL 20M
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U.S. patent No. ;• JJ^T 5| lT/(?
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NASA Patent Case No. ; L A A. ) °/ V31 -/
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Copy of patent cited above
https://ntrs.nasa.gov/search.jsp?R=19730019064 2020-03-17T08:53:58+00:00Z
PATENTED J«t 171973 3.745,816
INVENTORS
WAYNE D. ERICKSON
EDWARD M. SULLIVAN
ATTORNEYS
United States Patent [19]
Erickson et al.
mi 3,745,816
[45] July 17, 1973
[54] ABLATION ARTICLE AND METHOD
[75] Inventors: Wayne D. Erickson, Hampton;
Edward M. Sullivan, Newport News,
both of Va.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, O.C.
[22] Filed: Sept. 20, 1971
[21] Appl. No.: 182,033
.[52] U.S. Cl 73/86, 73/339, 73/432 R,
356/72
[51] Int. Cl GOln 17/00, GOln 19/06
[58] Field of Search 73/7, 15.4, 86;
356/72
[56] References Cited
UNITED STATES PATENTS
3,513,692 5/1970 Slone 73/86
3,566,670 3/1971 Ridle : 73/86
3,315,076 4/1967 Jordan 250/10 GT
Primary Examiner—S. Clement Swisher
Attorney— Howard J. Osborn, Wallace J. Nelson and
John R. Manning
[57] ABSTRACT
An ablation article, such as a conical heat shield, hav-
ing an ablating surface is provided with at least one dis-
crete area of at least one seed material, such as alumi-
num. When subjected to ablation conditions, the seed
material is ablated. Radiation emanating from the ab-
lated seed material is detected to analyze ablation ef-
fects without disturbing the ablation surface. By pro-
viding different seed materials having different radia-
tion characteristics, the ablating effects on various
areas of the ablating surface can be analyzed under any
prevailing ablation conditions. The ablating article can
be provided with means for detecting the radiation
characteristics of the ablated seed material to provide
a self-contained analysis unit.
10 Claims, 1 Drawing Figure
3,745,816
.S 1
^ ABLATION ARTICLE AND METHOD
ORIGIN OF THE INVENTION ^
 fo|towg a detai,e(J description of a preferred
The invention described herein was made by employ- embodiment of the invention, together with accompa-
ees of the United States Government and may be man- 5 nying drawings. However, it is to be understood that
ufactured and used by or for the Government for gov- the detailed description and accompanying drawing are
ernmental purposes without the payment of any royal- provided solely for the purpose of illustrating a pre-
ties thereon or therefor. ferred embodiment and that the invention is capable of
BACKGROUND OF THF INVFNTION numerous modifications and variations apparent toBACKGROUND OF THE INVENTION ,0 those skiUed jn ^  ^ Wlthout departmg froltl the spirit
The present invention relates to ablation articles hav- and scope of the invention.
ing an ablating surface useful in analyzing ablation of The single FIGURE of the drawing is a diagrammatic
that surface and to methods of analyzing the ablation side elevation, partly in section, of an ablative nose
thereof. In one aspect, the invention relates to such an cone and radiation detection system according to the
article useful in detecting transition between laminar IS present invention.
and turbulent flow in the boundary layer over the sur- With reference to the drawing, there is shown a coni-
face and to methods of detecting that transition. cal ablating heat shield generally designated by refer-
While it is important to be able to predict boundary ence numeral 1 and having synthetic resin ablation sur-
layer transition on non-ablative surfaces, such as the face 2 thereon. Ablation surface 2 is conventional and
surfaces of spacecraft nose cones, it is even more im- 20 is fabricated from forty parts by weight polyamide, 25
portant to be able to predict this transition on ablative parts by weight phenolic resin and 35 parts by weight
surfaces in order to define the amount of ablation ma- of phenolic microballoons. To a separate portion of the
terial required, since most ablation materials perform resin formulation is added a small amount of finely dt-
differently in laminar and turbulent flow. The problem vided aluminum particles in an amount of 0.1 atomic
of defining boundary layer flow transition is more diffi- 25 weight percent. To other separate portions of the resin
cult on an ablative surface, such as a spacecraft nose are added, respectively, 0.1 atomic weight percent of
cone, because conventional devices such as calorime- finely divided particles of the metals bismuth, gold,
ters and thermocouples are not designed for ablative lead, silver and tin. The resin formulation portions in-
surfaces and the test results may be questionable. A eluding these seed metal particles are located in the fin-
calorimeter surface will, in general, move relative to an 30 ished heat shield at discrete areas 3-8 of the ablating
ablative surface, resulting in projections or cavities on surface, each area being spaced longitudinally of the
the surface. Thermocouples present difficulties in ob- cone axis of the conical heat shield and each containing
taining reliable measurements because the material a different metal. In this example, the metals are dis-
surrounding the thermocouple is an inhomogeneous posed as follows: area 3 — aluminum; area 4 — bis-
gas-solid system with continuously changing properties. 35 muth; area 5 — gold; area 6 — lead; area 7 — silver;
Other experimental techniques for defining flow area 8 — tin. Each of seed areas 3-8 extend completely
transition on an ablating surface have been proposed around heat shield 1 and through the full depth of abla-
and are being investigated. They include sound pres- tion surface 2.
sure devices which sense changes in acoustic energy When subjected to ablating conditions, such as by ex-
level in the boundary layer and vibration detectors 40 posure to a rapidly moving gas stream either in test ap-
which sense the response of either the ablator or the paratus or in passing through space, a boundary layer
basic structure. Background noise level is a major prob- 9 develops adjacent the ablation surface 2 of the heat
lem with these devices. shield. When surface 2 ablates, seed material from
It is an object of the present invention to provide ab- areas 3-8 of surface 2 will also ablate and, in accor-
lation articles having ablation surfaces useful in analyz- 45 dance with the present invention, radiation from the
ing ablation of those surfaces and to methods of analyz- ablated seed material is detected to analyze ablation
ing ablation thereof which do not disturb the surface effects without disturbing the ablating surface,
being ablated and which are therefore free of the disad- A suitable radiation detection system is shown in the
vantages noted above. It is a further object of the inven- drawing and generally designated by reference numeral
tion to provide such articles and methods useful in the 20. In this instance, the radiation detection mounted
detection of transitions between laminar and turbulent within is heat shield 1 thus providing a self-contained
flow in the boundary layer over an ablating surface. unit useful in space applications. It will be clear that the
BRIFF SUMMARY OF THF INVFNTION detection system can be mounted elsewhere and, in test
BRIEF SUMMARY OF THE INVENTION devices, it would ordinarily be preferable to mount the
The foregoing and other objects which will be appar- system separate from the article being tested. Detec-
ent to those having ordinary skill in the an are achieved tion system 20 includes a lens 21 for focussing an ob-
according to the present invention by providing in an served volume 22 of the boundary layer 9 in the wake
ablating surface of an ablation article, at least one dis- of the heat shield and adjacent the rear edge thereof,
crete area of a seed material. The seed material cm- Volume 22 will include radiating products of ablation
ployed is one which has one or more spectral lines of including seed metals from each of areas 3-8 which are
sufficient intensity to permit positive detection upon undergoing ablation. The focussed radiation is directed
ablation of said surface and which has a spectral line through aperture 23 and lens 24 onto transmission grat-
signarure distinct from that of said ablating surface dur- ing 25 by means of mirror 26. Grating 25 splits the inci-
ing ablation thereof. Ablation of the surface is analyzed
 65 dent beam into its component frequencies and the por-
according to the invention by subjecting the surface to tions of the beam associated with the characteristic
ablating conditions, and detecting radiation emanating spectral lines are then focussed on individual photo-
from the seed material ablated from said surface. multiplier detectors 27-32, one specific for each seed
3,745,816
3 4 .
element. The output of each photomultiplier will be can vary widely within the foregoing criteria for a given
proportional to the intensity of radiation from the cor- ablation material and a few metals useful with the ny-
responding seed element. Each photomultiplier output Ion-phenolic ablator mentioned above are as follows:
then gives a measurement which is proportional to the
heating rate at the location of the associated seeded 5 Melting Boiling
,„ Point Point . Vaporization Point
area J-».
 («c) (=c) CO
The system as shown in the drawing can be readily Element
packaged inside a spacecraft in a fixed position to mon- BtanuSr"1 27? ?560 1520
itor the flow in one region of the base of the heat shield. Gold 1063 2970 2620
The number of detector systems could be increased 10 ad " "
. . . . . . _ . . . auvcr y o i v
and the entire base region monitored continuously dur- Tin 232 2270 2070
ing the entire flight. An alternate scheme for increasing .
the coverage of radiation detection could be achieved The amount of seed material can also vary widely and
by continuous rotation of mirror 26 and lens 21. This will in general be present in an amount sufficient to
scheme would give a full 360° coverage of radiation 15 provide a readily detectable radiation signature under
and can be utilized to distinguish between various dis- ablating conditions. This minimum amount will itself
crete areas of the ablating surface. The rotating mirror vary depending upon the ablating conditions. For ex-
and lens would be covered by an optical grade quartz ample, in one system, radiation from an amount of 0. 1
cap which would serve as a window and thermal pro- atomic weight percent aluminum is not readily discern-
tective system. 20 ible at a heating rate of 268 Btu/ft^sec. whereas it is
While the system just described can be used, inter readily discernible at a higher heating rate of 736 Btu/f-
alia, to determine the existence of ablation at a specific t*~sec. In general, it is considered that a minimum
area of surface 2 or to provide a measure of the rate of amount of 0.01 atomic weight percent will be suitable.
ablation at that area, a particularly advantageous use of The maximum amount of seed material is that which
the invention is to detect transition between laminar 25 would substantially affect the ablation characteristics
and turbulent flow in boundary layer 9 and, even more of the ablator. In tests run with aluminum, no apprecia-
advantageously, to make that determination for various ble change in recession of an ablated nose cone can be
areas of the ablating surface. As mentioned above, detected with aluminum in amounts up to 1 .0 atomic
most ablation materials perform differently in laminar weight percent at various heating rates. In general, it is
and turbulent flow. It is therefore important to be able 30 preferable to use a minimum amount of material and,
to predict the transition on ablative materials in order therefore, it is preferred not to exceed about two
to be able to predict the amount of ablation material atomic weight percent.
required for a given application. This is particularly im- What is claimed is:
portant in space applications where weight is a critical 1. In an ablation article having an ablating surface,
factor. The transition from laminar to turbulent flow is 35 the improvement comprising providing in at least one
easily detected according to the present invention by discrete circumferentially disposed exterior area of said
an increase in characteristic radiation associated with surface, a seed material, said seed material being one
the transition. For example, the aluminum radiation which has one or more spectral lines of sufficient inten-
doublet at 3944 A and 3961 A is seen very distinctly sity to permit positive detection upon ablation of said
against faint CN tail bands in a spectrogram of a nylon- 40 surface and which has a spectral line signature distinct
phenolic model seeded with 0. 1 atomic weight present from that of said ablating surface during ablation
aluminum and exposed to a heating rate of 736 Btu/f- thereof.
t*~sec. 2. An improved ablation article according to claim 1
The nature of the seed material can vary widely. It including at least two of said seed materials, each of
must, however, have one or more spectral lines of suffi- said seed materials being located in a different area of
cient intensity to permit positive detection and it must said surface, and each having a spectral line signature
have a spectral line signature different from that of the different from each of the other seed materials.
ablating material. Where a plurality of seeding materi- 3. An improved ablation article according to claim 1
als are used in different areas of the ablating surface, wherein said article comprises a space vehicle heat
each preferably has a spectral signature different from shield.
that of all other seed materials and, where the individ- 4. An improved ablation article according to claim 3
ual positions of the individual seed material areas on wherein said heat shield includes means for detecting
the surface are not otherwise discernible, such as by a radiation emanating from said seed material ablated
rotating mirror and lens as described above, this differ- from said surface.
ence is required in order to distinguish between the dif- 5. An improved ablation article according to claim 2
ferent seeded areas. Preferably, the spectral signatures wherein said article comprises a space vehicle heat
of the seed materials are in the visible or near infrared shield, said heat shield being conical in shape, said dif-
fer simplicity of transmission and detection with con- ferent areas being spaced longitudinally of the cone
ventional optical devices. The seed materials should axis on the outer surface of said conical heat shield.
also be chemically inert with respect to the ablating 6. An improved ablation article according to claim 1
material and used in small enough quantities to mini- wherein said seed material comprises a metal selected
mize the likelihood of any change in the ablation per- from the group consisting of aluminum, bismuth, gold,
formance of the seeded portions of the ablator. The lead, silver and tin.
melting and vaporization temperatures of the seed ele- , , 7. A method of analyzing the ablation of an ablating
ments should also be compatible with the pyrolysis and surface comprising the steps of: providing an ablation
char removal temperatures of the ablation material. It article having an ablating surface, said surface includ-
will be apparent that the nature of the seed material ing a seed material in a discrete circumferentially dis-
3,745,816
ffosed exterior area thereof, said seed material being
one which has one or more spectral lines of sufficient
intensity to permit positive detection upon ablation of
said surface and which has a spectral line signature dis-
tinct from that of said ablating surface during ablation
thereof; subjecting said surface to ablating conditions;
and detecting radiation emanating from seed material
ablated from said surface.
8. A method according to claim 7 wherein said sur-
face is subjected to ablating conditions induced by
moving a gas relative to said surface, the temperature
and velocity of said gas being sufficient to ablate said
surface.
9. A method according to claim 7 for detecting a
transition between laminar and turbulent flow in the
boundary layer adjacent said ablating surface compris-
10
15
ing subjecting the surface to first ablating conditions,
detecting radiation emanating from seed material ab-
lated from said surface during said first ablating condi-
tions, subjecting the surface to second, different ablat-
ing conditions, detecting radiation emanating from said
seed material ablated from said surface during said sec-
ond ablating conditions, and comparing the radiation
detected under said first and second conditions to de-
tect a change between laminar and turbulent flow in
the boundary layer adjacent said ablating surface.
10. A method according to claim 7 wherein said radi-
ation is detected by focussing said radiation, splitting
said focussed radiation into its component frequencies,
and detecting said component frequencies.
20
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Ablation article and method

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