Advanced Concepts Studies

Adaptive Large Optics
Technology (ALOT) Program

During the last decade the Department of Defense’s Strategic Defense Initiative Organization (SDIO) actively sponsored development of the technology needed to make spacebased large optical systems feasible. As part of this program SDIO developed many of the components for an ultralight-weight 4 m aperture space telescope, equipped with an advanced active optics system. When the program was cancelled for budgetary and redirection reasons many of the component development continued under the socalled Advanced Technology Demonstrator (ATD) program of the Ballistic Missile Defense Organization. Very sophisticated hardware is now available from this program, including the superlight weight primary mirror cell and metering structure, the center segment and several large segments of the active optics primary mirror and the mirror actuator system and controls.

The basic features of the Advanced Technology Demonstrator are:

• A 4 meter aperture, 17 mm thick, primary mirror equipped with 260+ actuators for on-orbit refitting.
• Afocal Optics with an image stabilization mirror located at an image of the entrance pupil to adjust the image within a 5.7 arc min region without moving the spacecraft
• Graphite polycyanate structure for the entire telescope assembly
• Use of on-board inertial reference to maintain pointing stability over a bandwidth from 1 to 300 Hz
• Ability to track stars as faint as 19th magnitude through the full aperture of the telescope to maintain stability against disturbances a frequencies of less than ~ 10 Hz.

Evaluation of the systems capabilities of the ATD for scientific applications indicates that the ATD has major advantages in the following areas:

• In the near infrared ( 2-4 microns), where the sky back ground is reduced by several orders of magnitude
• In the far red ( > 0.7 microns) where the sky background is reduced by 1 order of magnitude
• For programs that depend on high contrast between a point source and it neighborhood, or those that require sub-arcsecond spatial resolution.

The major accomplishment of the ATD system development, however is the proof of concept for development of such a large telescope within the current state of technology. The implication to a next generation space telescope of this size class are obvious.