1. PLANETARY PROBE LASER PROPULSION CONCEPT 7 TH INTERNATIONAL PLANETARY PROBE WORKSHOP 13-19 JUNE 2009, BARCELONA LE, T. (1), MOBILIA, S. (2), PAPADOPOULOS, P. (3) GRADY, J. (3) (1) San Jose State University, One Washington Square, San Jose, CA 95192, USA, Email:Le.Tina@Yahoo.com (2) Global Enterprise Initiative, Space Portal, MS 555-3, Moffett Field, CA 94305, USA, Email:smobilia@globalenterpriseinitiative.com (3) San Jose State University, One Washington Square, San Jose, CA 95192, USA, Email:periklis.papadopoulos@sjsu.edu (4) SGEEI, Ames Research Center, MS 555-3, Moffett Field, CA 94035, USA, Email: james.r.grady@nasa.gov ABSTRACT The objective of this paper is to study a moon-based laser propulsion system to reduce spacecraft fuel consumption and travel time. The study considers a small satellite demonstration in lunar orbit and the proposed system would ultimately be expanded for missions across the solar system. A design tool was written in Microsoft Excel to simulate a laser-assisted interplanetary probe system, either using laser-sail or ion engine propulsion. This design tool calculated that a 1000 W laser with a 75 cm diameter mirror would result in a change of velocity of 1.92×10 -1 m/s after 100 days of operation for a probe using laser-assisted solar sails. Using the same laser, a laser-assisted ion engine would result in a change of velocity of 529 m/s after 100 days of operation. The change in velocity when using a laser-assisted ion engine is enough to significantly reduce travel time. This particular application can help expand interplanetary travel by providing infrastructure to reduce travel time while decreasing the mass of the spacecraft. INTRODUCTION The scope of interplanetary travel has been limited by the amount of fuel that a probe can be designed to hold. With the concept of laser propulsion: Probes can be designed to go deeper into the solar system Maintain reasonable payload requirements On higher end laser propulsion systems, travel time can also be significantly reduced This paper is studying two concepts for a laser propulsion system demonstration: Using either laser sail propulsion Laser beam to power an ion engine. Lunar Prospector Mission Trajectory The Lunar Prospector was chosen as a benchmark because it was a recent mission of the size typical for interplanetary probes. MISSION OBJECTIVE The mission objective for this paper is to study two concepts for a possible laser propulsion demonstration in low Earth orbit to reduce spacecraft fuel and travel time. The demonstration would involve beaming the laser to a small probe over short distances in order to measure the boost provided by the additional power. A more permanent system could be built in lunar orbit or at one of the LaGrange points around Earth to assist probes travelling throughout the solar system. METHODOLOGY A simple design tool was created in Microsoft excel to study the two laser propulsion systems. The program was sectioned into four parts, Power Beam Sizing, Laser Sail Acceleration, Ion Engine Acceleration, and Power Beam Optics. This design tool can be seen below. The Power Beam Sizing portion of the design tool calculates: The size of the array necessary to beam a set amount of power to propel a planetary probe. This set amount of power can be input into the design tool and will depend on the design parameters. The Laser Sail Acceleration portion of the design tool calculates: The acceleration that the power beam could provide to a probe utilizing laser sail propulsion. The Ion Engine Acceleration portion of the design tool calculates the acceleration that an ion engine could provide if powered by the laser beam. The defaults for the total efficiency of the ion engine and specific impulse were based on the HiPEP engine. These can be changed with inputs to the design tool. The Power Beam Optics portion of the design tool calculates: The diameter of the receiver necessary for the probe to receive power from a laser using given optical specifications. It will also calculate the optics necessary to beam power to a given receiver. RESULTS AND DISCUSSION With the design tool we created, we examined the acceleration created by potential laser propulsion systems. These results are displayed Acceleration generated with laser sail propulsion system and DeltaV after 100 days of Operation. Acceleration generated with ion engine propulsion system and DeltaV after 100 days of Operation.. Figures show that using the laser to power the ion engine would be much more effective. Using the 1000 W laser, the demonstration, would provide an acceleration boost of 6.13*10 -5 m/s 2, to a 300 kg probe using ion engine propulsion, but would only provide an acceleration boost of 2.22*10 -8 m/s 2 for a 300 kg probe using laser sail propulsion. After 100 days of operation, the laser demonstration could provide a change in velocity of 529 m/s to the 300 kg probe using ion engine propulsion. After 100 days of operation, the laser demonstration could provide a change in velocity of 0.192 m/s. The ion engine would be the preferable laser propulsion design option in all but the most extreme cases. CONCLUSIONS After studying the two laser propulsion design systems, the laser powered ion engine appears to be the more useful of the two options. If this system is expanded and implemented, it can help significantly reduce travel time and increase the range for interplanetary probe missions. www.GlobalEnterpriseInitiative.com Power Beam Sizing P_laser = (1400/R_sl,au^2)*ε_las*π*R_array^2 Power-beam LaserP_laser1000 W Solar array radiusR_array 3.0315227m Efficiency of sunlight conversion to a collimated EM radiation beamε_las 0.075 Separation between the Sun and the solar-pumped laser power stationR_sl,au 1Au Laser Sail Acceleration ACC_laser-sail = [(1+REF_sail)/M_s*c]*P_laser Acceleration of the solar sailACC_laser-sail 2.224E-08m/s^2 Sail reflectivity to the laser beamREF_sail 1 Ship massM_s300 kg speed of lightc 299792458m/s Thrust of the Laser Sail, ACC_laser-sail*M_s=T_laser-sailT_laser-sail 6.671E-06N Ion Engine Acceleration T_ion-engine = (2* η _t*P_laser)/(g*Isp) Thrust of the Ion EngineT_ion-engine 0.0184N Total Efficiency of the Ion Engineη_t 0.5413464 Specific Impulse of Engine PropellantIsp 6000s Ship massM_s300 kg Acceleration of Gravityg 9.807m/s^2 Acceleration of the Ion Engine, T_ion-engine/M_s=ACC_ion-engineACC_ion-engine 6.133E-05m/s^2 Power Beam Optics 2.44*λ_laser/D_las-tran = D_sail/D_las-ship,max Laser wavelengthλ_laser 1.07E-06m Diameter of the Laser-transmitting opticsD_las-tran 0.75m Separation between the laser power station and the starshipD_las-ship, max2000000 m Sail diameterD_sail 6.9621333m LASER SAIL Beam Power (W) Vehicle Size (kg) Acceleration (m/s^2) deltaV after 100 days (m/sec) 10003002.22376E-080.192132919 10002003.33564E-080.288199378 10001006.67128E-080.576398757 1000501.33426E-071.152797513 1000252.66851E-072.305595026 100003002.22376E-071.921329188 100002003.33564E-072.881993783 100001006.67128E-075.763987565 10000501.33426E-0611.52797513 10000252.66851E-0623.05595026 1000003002.22376E-0619.21329188 1000002003.33564E-0628.81993783 1000001006.67128E-0657.63987565 100000501.33426E-05115.2797513 100000252.66851E-05230.5595026 10000003002.22376E-05192.1329188 10000002003.33564E-05288.1993783 10000001006.67128E-05576.3987565 1000000500.0001334261152.797513 1000000250.0002668512305.595026 100000003000.0002223761921.329188 100000002000.0003335642881.993783 100000001000.0006671285763.987565 10000000500.00133425611527.97513 10000000250.00266851323055.95026 ION ENGINE Beam Power (W) Vehicle Size (kg) Acceleration (m/s^2) deltaV after 100 days (m/sec) 10003006.13333E-05529.92 10002000.000092794.88 10001000.0001841589.76 1000500.0003683179.52 1000250.0007366359.04 100003000.0006133335299.2 100002000.000927948.8 100001000.0018415897.6 10000500.0036831795.2 10000250.0073663590.4 1000003000.00613333352992 1000002000.009279488 1000001000.0184158976 100000500.0368317952 100000250.0736635904 10000003000.061333333529920 10000002000.092794880 10000001000.1841589760 1000000500.3683179520 1000000250.7366359040 100000003000.6133333335299200 100000002000.927948800 100000001001.8415897600 10000000503.6831795200 10000000257.3663590400