The Entry Systems Panel was chaired by Don Rummler, LaRC and Dan Rasky, ARC. As requested, each panel participant prior to the workshop prepared and delivered presentations to: (1) identify technology needs; (2) assess current programs; (3) identify technology gaps; and (4) identify highest payoff areas R&D. Participants presented background on the entry systems R&D efforts and operations experiences for the Space Shuttle Orbiter. These participants represented NASA Centers involved in research (Ames Research Center), development (Johnson Space Center) and operations (Kennedy Space Center) and the Shuttle Orbiter prime contractor. The presentations lead to the discovery of several lessons learned

Bersch, Charlie

Dixon, Sidney C.

Rasky, Daniel J.

Rummler, Donald R.

English

NASA Technical Reports Server

N93-22105
10.0 ENTRY SYSTEMS PANEL
DELIBERATIONS
The Entry Systems Panel was chaired by Don
Rummler, LaRC and Dan Rasky, ARC. As
requested, each panel participant prior to the
workshop prepared and delivered presentations
to:
1) Identify technology needs
2) Assess current programs
3) Identifytechnology gaps
4) Identify highest payoff areas R&D
Participantspresented background on the entry
systems R&D effortsand operationsexperiences
for the Space Shuttle Orbiter. These
participants represented NASA Centers
involved in research (Ames Research Center),
development (Johnson Space Center), and
operations (Kennedy Space Center) and the
Shuttle Orbiter prime contractor. The
presentations lead to the discovery of several
lessonslearned.
10.1 Technology Needs
Three key technology drivers for all anticipated
vehicles and missions were identified:
• Improved TPS performance for
safety/reliability
• Lower operating costs
• Increased vehicle capability and
supportability
These technology drivers lead to the
identification of fourteen high-payoff technology
needs as discussed in the following sections.
Metallic TPS Concepts
Metallic concepts offer the potential for more
flexibility in adverse weather environments
(moisture, impact, and lightning strikes), are
mechanically attached to the structure, and are
weight-compatible with ceramic, ceramic matrix
composite, and carbon-carbon TPS concepts.
However, metallics lack the certification testing
and flight experience of other TPS systems.
Also, little R&D has been conducted in the U.S.
in the last decade on this class of TPS. Coatings
having high temperature resistance and
emissivity, moisture resistance, and aerody-
namic/vibroacoustic stability should be
improved. High-temperature, flexible adhesives
that take advantage of warm (high-temperature
composite) structures should be developed.
Finally, all improvements should be
demonstrated through appropriate tests of
integrated TPS/structural systems.
Research to provide improvements in high-
temperature properties, coatings for low
catalytic and high emissivity, and oxidation and
corrosion resistance should be pursued. To
supplement this technology base, tests should be
conducted to verify thermal performance,
effectiveness of preventing hot gas flow to the
interior, and tolerance to acoustic loads.
Flexible Ceramic TPS Concepts
Flexible insulations such as felts, quilts, and
woven blankets offer excellent benefits such as
low weight, minimum certification investment
required for improved concepts due to flight
experience on the Shuttle Orbiter, and
potentially lower life cycle costs. However,
these concepts are currently temperature lim-
ited (FRSI - 700°F, AFRSI - 1500°F). Available
high-temperature fibers can significantly
increase the temperature capability for this
class of TPS.
Inorganic/organic yarns, fabrics, felts and blends
should be developed and evaluated using the
existing high-temperature fibers. Fabrication
methods to achieve lower cost, develop flexible
coatings having high temperature resistance
and emissivity, moisture resistance, and
aerodynamic/vibroacoustic stability should be
improved. High-temperature, flexible adhesives
to take advantage of warm (high-temperature
composites) structures should be developed.
Finally, all improvements should be demon-
strated through appropriate tests of integrated
TPS/structural systems.
Toughened Ceramic TPS Concepts
A strong motivation exists to continue with the
current RSI-type TPS, if its durability and
strength and temperature capabilities can be
improved, because of the extensive certification
data and flight experience available. Higher-
strength RSI could lead to direct-bond
applications, which would eliminate the need for
a strain isolation pad (SIP). Advanced fibers
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suggest the possibility of developing more
refractory RSI materials.
A program should be initiated to identify and
develop toughened coatings and advanced fibers.
These new materials would require
characterization and thermal response tests in
arc-jets. The best candidates would then be
subjected to systems tests that demonstrate
acceptable performance for use on future space
transportation vehicles.
Advanced Carbon-Carbon TPS
Reinforced carbon-carbon (RCC) leading edges
and nose caps on the Shuttle Orbiter have no
flight anomalies. The advanced carbon-carbon
(ACC) materials have demonstrated up to five
times the strength of RCC, and fabrication of a
large, built-up structure of ACC has been
demonstrated. Thin, structural, oxidation-
resistant carbon-carbon (ORCC) composites for
both TPS and structural applications offer the
potential of low weight, durability, low main-
tenance and repair, and can be tailored for
Various service environments. The major
deficiency is iong-iife Oxidation protection. To
eliminate this deficiency, improved methods for
oxidation protection, including coatings,
inhibitors, sealants, and glazes should be devel-
oped. Critical, life-limiting tests should be
conducted to demonstrate advanced ORCC
materials. Continued efforts to improve
mechanical properties and to develop "one-side"
NDE techniques (see technology item 9) will be
very beneficial. The process and design
allowables should be well documented, and full-
scale components should be fabricated and
tested.
Low-Weight Ablators
Ablative TPS has been successfully used for
manned vehicles. Performance of an ablative
system is predictable, and unexpected thermal
excursions are not critical. However, no
development Work has been conducted for this
class of material since the Apollo and Viking
projects. Aeroassist and direct entry for lunar
and planetary missions require high-
temperature materials. Also, low weight is
required to maximize payload weight and/or
decrease cost.
New advanced low density ablation materials
should be developed and characterized. Using
these materials, subscale TPS should be built
and tested in arc-jets to verify performance.
Also, analytical models must be updated, then
verified. Arc-jet facilities to test large TPS
panels (see technology item 13) for certification
should be modified.
Special TPS Components
Special TPS components such as joints,
fasteners, and seams have had cost and
schedule impacts on the Space Shuttle Orbiter.
Such components, as well as TPS for moving
surfaces, are critical interfaces in all TPS
designs. Also, very high heating regions such as
nose tips and leading edges require special
design considerations including the possible use
of heat pipes or mass addition cooling
techniques. Research programs tend to address
acreage applications at the expense of such
"generic" details as gaps and fasteners, leaving
the solution of these problems to the more costly
development phases of hardware programs.
Advanced special TPS components must be
designed, fabricated and tested. Their efforts
should be coordinated with concept design
efforts under technology items one through five.
Design studies of proposed vehicles/missions to
determine potential need for and/or benefits of
heat pipe/mass addition cooling techniques for
regions of local, intense heating should be
conducted. Components for most promising
applications should be developed and
demonstrated. Modify facilities for testing of
these TPS components (see technology item 13)
should be modified.
TPS / Structural Integration
Better integration of TPS and structure offers
the potential of damage tolerant, oxidation-
resistant, lightweight systems with lower
acquisition and operational costs. One concept
consists of continuous fiber-re_inforc_ed cem_a_mic
matrix composite (CMC) face sheets bonded to a
RSI core that is hard bonded to a load-bearing
structure of CMC or graphite/polymide. This
combination combines the oxidation resistance,
durability, and strength of CMC materials with
the low weight and good insulation capabilities
of RSI. Other concepts utilizing other material
combinations also offer potential benefits.
Promising materials, concepts, and applications
must be identii%d. Material ch_-a-c-t_iz_on
tests for new materials will need to be
performed, and appropriate analysis codes
should be developed and identified. Processing/
fabrication methods should be developed and
330
radiant heating and arc-jet screening tests to
determine concept feasibility should be
performed.
Water-Based Composite TPS and Structures
Highly-innovative concepts may be needed to
meet the weight and cost goals of SEI-type
missions. The synergistic use of on-board
resources minimizes weight to orbit. For
example, water-based polymer or ice matrix
composites, which are non-toxic systems, could
utilizeresources now considered expendable.
Deployment and rigidizationof such a system
would minimize manpower and energy for on-
orbitfabricationofaerobrake structures.
Studies of water-based polymer/ice matrix
composites must be performed to determine
properties, processes, and fabrication techniques
for such materials. Representative concepts
should be fabricated and tested. Deployment
and rigidization on orbit should be demon-
strated on Shuttle or Space Station Freedom.
Inspection, NDE and Smart Materials
Current technology is typified by an inability to
determine the amount of oxidation/damage in
RCC as installed on the Orbiter; suspect RSI
bond conditions require removal and
replacement; current NDE/bond verification is
limited by schedule and funding (and this limi-
tation in turn adversely affects program
schedule and cost); on-orbit inspection is
impractical. The desired technology level calls
for designs that allow for self-analysis of the
material using NDT/NDE or smart
instrumentation within (or attached to) the
material.
NDT/NDE should be developed during original
design and manufacture of hardware. Failure
indicators should be designed into the material.
Tests will be necessary to verify that NDE/NDT
indicators performance is acceptable.
Simplified Certification/Recertification
Procedures
The present method of certification and
recertification is complex, costly and time
consuming. The OEX program provided a
means to certify without extensive certification
effort. Certification by similarity is not used as
extensively as it could be. The existing
certification policy was a major contributor to
the decision to not use advanced TPS concepts
on the last orbiter built despite their many
offered benefits indicated by all research efforts.
OEX development techniques should be
extended for certifying new materials, and
modeling/analytical methods for structural
changes/modifications should be used.
Documentation requirements should be changed
so that changes at sub-levels are allowed rather
than "treeing _ into total package. Recertifi-
cation requirements as affected by changes in
mission requirements should be standardized.
In non-critical areas, certification by familiarity
is recommended.
Environmental Compatibility
A need to improve weatherproofing of TPS
against terrestrial environments exists as
evidenced by the following:
Rain and tap water absorption increases
launch weight and causes freeze damage to
TPS.
• Hail and ice impacts erode TPS, causing loss
of TPS integrity.
• Some fuels, vapors, etc. are incompatible
with TPS materials.
Seals and flow paths to preclude absorption of
moisture in internal insulation (see technology
item 6) are needed. Coatings or outer face
sheets resistant to impact damage, impermeable
to water intrusion, and capable of surviving the
entry thermal environment should be developed.
Design studies of new or modified facilities to
protect space transportation vehicles for the
environment may be required.
The knowledge based on long-term space
environmental durability is small, although it is
increasing as results are obtained from analyses
of the Long Duration Exposure Facility. Atomic
oxygen attacks polymer materials and coatings,
radiation may degrade materials including
coatings and films, and particle impacts can
damage TPS. This item could be an enabling
technology for planetary missions.
The long term effects of vacuum, atomic oxygen,
debris/dust impact, and radiation on materials
must be determined. The compatibility of
proposed TPS materials with other spacecraft
system materials and fuels should be deter-
mined. Protective systems (improved materials,
shields, coatings, films, etc.) should be developed
331
and TPS performance in appropriate
environmentsand for appropriate duration to
provide acceptable design margins need to be
evaluated.
On-Orbit Activities
The Entry Systems panel expects that TPS
structures for planetary missions will have to be
deployed/erected and serviced on orbit due to
the size of the vehicles for planetary missions
and the size of constraints of Earth-to-orbit
launch vehicles. Virtually no experiments have
been performed in space to date. Thus, this
item is an enabling technology for planetary
missions.
A technology program similar to the program
developed for large space structures, including
Space Station, needs to be developed and
implemented. Ground simulations of deploy-
ing/erecting and servicing TPS for vehicles for
planetary missions must be devised and used to
evaluate various concepts and techniques. The
ground testing program must be followed by
flight experiments similar to the MAST
experiment on the Shuttle Orbiter conducted in
the mid 1980's, but with a focus on assembly of
TPS/structure for proposed vehicle concepts for
planetary missions such as an aerobrake. On-
orbit-assembled TPS hardware should be
returned to ground for inspection and arc-jet
testing to assure that the required thermal per-
formance was obtained for hardware that was
assembled on-orbit.
Test Facilities
No new arc-jet facilities have been activated in
the past 20 years. Some facilities, such as those
at Langley Research Center, have been
decommissioned. Existing operational arc-jet
facilities are inadequate for testing large TPS
arrays at representative conditions. Existing
arc-jet instrumentation is limited to intrusive
flow measurements. There are no facilities that
would provide the proper on-orbit simulation for
ground tests for assembly of various concepts
and techniques.
To adequately meet the experimental needs of
technology development and hardware
demonstration efforts, upgrades of existing arc-
jet facilities and associated instrumentation are
needed. Facilities should be improved to:
• Accommodate large size TPS arrays
• Provide uniform high quality flow
• Provide combined radiative and convective
heating
• Provide appropriate planetary gas
compositions (Mars, Venus, Titan)
Instrumentation should be developed to
measure:
• Tunnel flow conditions and intrusive flow
methodology
• Test article strain at elevated temperatures
• Surface temperature distribution
• Aero/acoustic environment
Facilities to adequately simulate conditions for
evaluation of the viability of various
TPS/structure concepts for on-orbit assembly
should be devised and built.
Interdisciplinary Modeling Codes
For advanced thermal protection materials and
concepts optimum TPS with adequate
performance considering all requirements can
best be obtained by use of interdisciplinary
codes with the capability to consider:
• Micro-level material effects
• Materials response
• Coupling to advanced CFD codes for
complete system response modeling
• TPS/structure thermal and structural
response
• Life predictions
• Aeroelastic response
• Design optimization
Such codes do not exist. Specific analysis codes,
such as ablative modeling codes, are 10-20 years
old, and other codes such as those required for
analyzing micro-level material effects are only
beginning to evolve.
332
The first essential step is to establish a working
relationship between the CFD, CSM,
computational materials, and structural
optimization communities. The next stop is to
build on the existing methodology for
interdisciplinary codes, such as those evolving
for aeroelastic and strength optimization and
integrated flow/thermal/structural analysis.
Significant computational resources must be
available to support code development. The
final necessary step is to generate the required
benchmark data for validation of the
multidisciplinary code.
10.2 RECOMMENDATIONS
In addition to identifying the fourteen tech-
nology items described above, which define in
essence "what we need to do," the Entry
Systems Panel discussed issues related to "how
we do it. _ The following items summarize this
discussion:
Technologists tend to overlook mundane
problem areas, which is why we still
struggle with problems such as accessibility
to equipment and structures for inspection
and servicing, weatherproofing of TPS, and
extensive checkout operations.
A gap between technology products and
program needs often exists. Advanced
development programs should be supported
(funded) to bridge this gap, or the
technologist should make his products
readily useable by the system developer and
the system user.
Cultural and programmatic barriers to
efficient technology transfer exist.
Responsible and dedicated NASA-wide
working groups are recommended for
various disciplined to plan specific
programs. A step in this direction was the
Ames-Johnson group effort on RSI and the
Langley-Johnson group effort on carbon-
carbon, but technology transfer can still be
improved, especially before NASA commits
to a project and the clock has started.
Entry Systems test facilities in the U.S. are
aging and must be upgraded. Flight test
"facilities" are also needed. SEI cannot
succeed without efficient, cost effective test
facilities with realistic test environments.
Certification for space-based]long duration
flight entry systems will be a major issue
and will need to augment our current
methodology to accommodate it.
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10.3 PRESENTATIONS
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10.3.1 Space Assembled Entry Systems Certification
by Donald M. Curry, NASA JSC
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Entry Systems Panel deliberations

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