Lightweight Deployable UV/Visible/IR Telescopes

Frank Peri, Jr.Earth Science

Technology Office

NASA Goddard Space Flight Center

Michael HagopianEarth Sciences Directorate

NASA Goddard Space Flight Center

Mark LakeComposite Technology

Development, Inc.

Future remote sensing instruments may need to employ large numbers of frequency-agile instruments capable of multi-scene observations. Real-time, autonomous adaptive sensing and taskability will be critical. Advanced capabilities will include:

– Miniaturized observatories

– Robust, compact instrument architectures

– Large deployable apertures

– Aperture synthesis

– Miniaturized/programmable components

– Low cost manufacturability

Technology Enablers to the VisionKey Characteristics

MotivationProgrammatic Limiters to the Vision

• Length of time to plan, development and deploy space-based instruments for periodic focused measurements

The result: A decade may pass between the theoretical identification of a phenomenon and the deployment of a space-based asset limits measurement continuity and applicability

• Limited budgets preclude continually launching unique instruments targeted toward specific measurement needs

The result: Instrument designs are targeted to specific measurements and consequently once deployed cannot accommodate new scientific findings

Lightweight Deployable UV/Vis/IR TelescopesPathway to the Vision

Science Needs:• Lidar observations for high vertical resolution mapping of

tropospheric ozone, CO2, water vapor, NO2, aerosols, and for imaging, and

• High resolution imaging and spectroscopic observations from high orbits (GEO, LI, and L2)

Lightweight Deployable UV/Vis/IR TelescopesPathway to the Vision

Science Needs Resolution, m

Telescope Diameter,

m

Figure

Orbit km/orbit

Imaging spectro-radiometer

30-100 >2.5 λ/20GEO, L1,

L2

Lidar observation 100-500 >3.0 λ/2 500/polar

Lidar imager 30-300 >3.0 λ/20 500/polar

Lightweight Deployable UV/Vis/IR TelescopesProblems Unique to Earth Observing Measurements

Extensive on-going work associated with NGST in deployable telescopes. Unique problems associated with typical Earth observing missions:

• Thermal cycling effects due to variable solar loading, day/night transitions, thermal shock from going into and out of eclipse and pointing close to Sun line

• Pointing non inertial reference frame or scene reference complicates attitude control

• Doppler shifts (wavelength calibration)

• Orbit maintenance, thruster issues, contamination, control law issues

• Minimize structural mass with uniform and low CTE across structure with good optical surface

• Active/adaptive control on Earth scenes (wide dynamic range)

• Image registration (mapping, land-marking)

Lightweight Deployable UV/Vis/IR TelescopesProblems Unique to Earth Observing MeasurementsRecent advancements in mirror research have considered the

following materials:

• composite mirrors • carbon silicon carbide

• glass/composite • thin meniscus glass

• beryllium • light weighted glass

• membranes (powered and flat) • fresnel lens

The fundamental issues associated with these materials are their manufacturability and their subsequent integration into associated control actuators, reaction structures, and deployment systems. Other factors include filter coatings to reduce the heat load on the mirror and the ability to control the mirror in the dynamic thermal environments.

Lightweight Deployable UV/Vis/IR TelescopesProblems Unique to Earth Observing Measurements

Structures and mechanisms are also a significant challenge for deployable telescopes. The state of the art is currently:

• Mid-modulus CFRP, open truss design

• USAF/RL MISTI (solid hexagonal frame)

• Multifunctional structures

• Isogrid vs. solid tubular frame

Lightweight Deployable UV/Vis/IR TelescopesSummary of Technology Approaches

• Light-weight mirrors

– glass/composite– thin film (stretch membrane/replicated shells)

• Structures and latches

– deploy/redeploy capability– elastic memory composite materials

• Optical alignment techniques

– active vs. passive– deformable/correction optics– wavefront sensing/control

Now

Arr

ay A

rea (

m2)

20202010

10

ArealDensity(kg/m2)

1

100

100

1000

10000

10

.1

Adaptive Adaptive MembranMembrane Opticse Optics

50m High 50m High Resolution Resolution

ImagerImager

GEO HighGEO HighResolution Resolution

Thermal Thermal ImagerImager

Deployable Deployable Segmented Segmented TelescopesTelescopes

InflatableInflatableAntennasAntennas

Deployable UV/Vis/IR TelescopesVision-driven RoadmapKey Technologies– Deployable Structures– Multifunctional

Structures– Adaptive Control

Systems– Membrane Optics and

Large Deformable Mirrors

Payoff– Enables large

diameter instrument front ends

– Enables high spatial resolution science

Potential Partners– Department of

Defense/Energy– NOAA– Academia &

Industry– Other U.S. Gov’t

Labs

Lightweight Deployable UV/Vis/IR TelescopesNotional Validation Flight

In developing a validation test plan to determine what characteristics will be tested, the following elements must be considered:

• characterization of disturbance sources (e.g., sunshields, reaction wheels, fine-pointing and alignment systems)

• microdynamic response of mechanically deployable support structures and active control of microdynamics

• dimensional stability of thin-membrane mirrors and active wavefront correction

UV DIAL: 308/320 nm @ 10Hz; O3 vertical resolution 2.0-2.5 km in troposphere; horizontal resolution 100 km; IFOV < 100 m

FY 02 03 04 05 06 07 08 09 10 11 12

Composite Mirror Panels

NMP - flight validation

Technology Validation

Mission

Tropospheric Ozone Measurement

Capability

Salient requirements: 500mJ, 308/320 nm @ 10Hz

Salient requirement: 3m aperture

Salient requirements: repeatability reliability, one-time operation

Tropospheric Ozone Measurement (UV)Technology Roadmap

Precision Latch & HingeDeployment Mechanisms

Diode-pumped Laser Transmitter (UV)

Lightweight Deployable UV/Vis/IR TelescopesConcluding Remarks

The science needs established by the vision of NASA’s Earth Science Enterprise challenge the state of the art for instrument technologies.

A process by which technology requirements are developed begins by translating the science needs into notional measurement implementations and then defining the critical drivers for achieving the science needs. These drivers result in a set of technology requirements from which development plans can be established.

A nominal space validation experiment would include fabrication of a test article of a deployable telescope structure and mating it to a microgravity test platform on the ISS. Tests of micro and macrodynamic characteristics of the structure would be conducted in order to understand and characterize the dynamic responses and deployment of the structure in zero-g.

Partnerships between NASA and interagency, international, commercial and academic organizations will be essential to achieve this vision. The economic benefits will be shared across the globe.