LASER GUIDE STAR FOR LARGE APERTURE SEGMENTED SPACE TELESCOPES O LARGE APERTURE OF TARGETS SUCH AS EXOPLANETS. THE 10-10 CONTRAST NECESSARY TO DETECT AND CHARACTERIZE EARTH-LIKE PLANETS TRANSLATES TO ACHIEVING<10 PICOMETERS (RMS) ERROR PER WAVEFRONT SENSING AND CONTROL UPDATE (AN ONBOARD DEFORMABLE MIRROR IS USED FOR THE CORRECTION). USING NATURAL GUIDE STARS OF OPPORTUNITY DOES NOT PROVIDE ENOUGH SIGNAL TO CLOSE THE WAVEFRONT CONTROL LOOP FAST ENOUGH TO OVERCOME THERMAL INSTABILITIES JITTER OR OTHER DRIFTS IN THE SYSTEM. WITHOUT STRONG GUIDESTARS FOR FAST WAVEFRONT CONTROL WE WOULD NEED TO DESIGN AND BUILD TELESCOPES STABLE TO PICOMETERS OVER THE INTEGRATION TIME (MINUTES TO HOURS). WE PROPOSE A NEW SPACE TELESCOPE ARCHITECTURE THAT IS ANALOGOUS TO A LASER GUIDE STAR SYSTEM FOR GROUND TELESCOPES WHERE ONE OR MORE EXTERNAL SMALL SATELLITE LASER GUIDE STARS (OPTICAL BEACONS) ARE PAIRED WITH A LARGE APERTURE SPACE TELESCOPE. THE SATELLITE LASER GUIDE STAR WILL BE BRIGHT ENOUGH TO SUPPORT FASTER UPDATES (HZ TO KHZ) AND ABLE MOVE IN AND OUT OF THE FIELD OF VIEW OF THE TELESCOPE. SOME IMPORTANT ADVANTAGES TO THIS APPROACH INCLUDE: NEARLY COMMON PATH TO THE TARGET BEING IMAGED AND MORE PHOTONS WHICH ALLOW THE WAVEFRONT CONTROL LOOP TO RUN FASTER. THIS COULD GREATLY RELAX THE DESIGN REQUIREMENTS ON THE TELESCOPE AND INTRODUCE A WHOLE NEW PARADIGM FOR HIGH CONTRAST TELESCOPES IN SPACE. WHILE THIS APPROACH COULD BE APPLIED TO ANY HIGH CONTRAST SPACE TELESCOPE OUR ANALYSIS WILL FOCUS ON ITS APPLICABILITY FOR THE LARGE APERTURE ULTRAVIOLET OPTICAL INFRARED (LUVOIR) MISSIONS 12-M TELESCOPE. TO ENABLE NEW AND AFFORDABLE ARCHITECTURES WE PROPOSE USING CUBESATS AS THE SATELLITE LASER GUIDE STARS. THE CUBESATS WILL BE EQUIPPED WITH ONE OR MORE PRECISELY-POINTED POWER-EFFICIENT NARROW BEAMWIDTH LASER BEACONS AT WAVELENGTHS SELECTED FOR OPTIMAL WAVEFRONT SENSING AND CONTROL CAPABILITY WITH NO OR MINIMAL IMPACT TO THE SCIENCE. THE CUBESAT IS EQUIPPED WITH AN AGILE PROPULSION SYSTEM AND FLIES INDEPENDENTLY AT A SAFE DISTANCE FROM THE LARGE TELESCOPE. THE NARROW LASER BEAM FROM THE CUBESAT IS A MUCH BRIGHTER SOURCE THAN NATURAL GUIDE STARS OF OPPORTUNITY NEAR THE TARGET. THIS WOULD ALLOW THE WAVEFRONT SENSING AND CONTROL SYSTEM ONBOARD THE LARGE TELESCOPE TO OPERATE IN A CLOSED-LOOP MODE OVER A WIDE RANGE OF BANDWIDTHS SUCH AS FROM 0.1 HZ (SLOW BUT FAST ENOUGH TO REMOVE DRIFT) TO MORE THAN 400 HZ (FAST ENOUGH TO REMOVE JITTER). IF THE WAVEFRONT SENSING AND CONTROL LOOP CAN RUN FAST ENOUGH WHILE IN A CLOSED LOOP CONFIGURATION IT SHOULD BE POSSIBLE TO RELAX THE STABILITY REQUIREMENT ON THE LARGE TELESCOPE PERHAPS EVEN TO THE POINT OF ONLY NEEDING TO BE DIFFRACTION-LIMITED AT VISIBLE WAVELENGTHS. THIS WOULD GREATLY REDUCE THE COST AND COMPLEXITY OF LARGE APERTURE SEGMENTED SPACE TELESCOPES. WE WILL PERFORM A DETAILED ANALYSIS OF THIS CUBESAT LASER GUIDE STAR APPROACH ASSESSING ARCHITECTURES USING QUANTITATIVE METRICS SUCH AS STREHL THROUGHPUT REQUIRED SEGMENT SURFACE QUALITY THERMAL STABILITY SEGMENT ALIGNMENT AND COST. WE WILL STUDY THE ORBITS AND SEPARATION BETWEEN THE CUBESAT AND THE LARGE TELESCOPE CONSIDER DIFFERENT TYPES OF LASER TRANSMITTERS REFINE DETAILED RADIOMETRIC LINK BUDGETS POWER LEVELS AND BEAMWIDTHS FROM THE CUBESAT LASER TO THE LARGE TELESCOPS WAVEFRONT-SENSING DETECTOR AND ALSO CONSIDER THE USE OF MULTIPLE WAVELENGTHS FOR PHOTOMETRIC CALIBRATION. WE WILL DEVELOP A CONCEPT OF OPERATIONS INCLUDING ORBITAL MECHANICS PROPULSION TECHNOLOGIES AND TELESCOPE REPOSITIONING TOWARD MULTI-YEAR OPERATION OF THE CUBESAT. WE WILL SIMULATE AND PROTOTYPE PERFORMANCE TOWARD THE DESIGN OF A FLIGHT-DEMONSTRATION CUBESAT LASER GUIDE STAR PAYLOAD THAT WOULD RELAX REQUIREMENTS ON A LARGE APERTURE SEGMENTED SPACE TELESCOPE.