tailieunhanh - MEMS and Microstructures in Aerospace Applications - Robert Osiander et al (Eds) Part 11

Tham khảo tài liệu 'mems and microstructures in aerospace applications - robert osiander et al (eds) part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 246 MEMS and Microstructures in Aerospace Applications The exhaust velocity is in turn defined via the relationship seen in Equation VE QCm 11 18 where Q is the absorbed input energy of laser light per mass unit of ablated material. It is obvious that in order to convert a certain amount of tape into a plasma a fixed energy is necessary. This threshold intensity can be described by the empirical formula as a function of the laser pulse duration t 0th 2 36 X 104 t 0-45 11 19 Operation above this value leads to the production of higher charge states and increasing light absorption within the plasma which limits the amount of energy available to ablate material. System Requirement and Comments While at first glance the laser ablation thruster seems to be an extremely powerful device it has to be noted that it includes some overheads. Apart from using a fairly powerful diode laser a motor has to be used to move the fuel tape. Efficiency losses due to these items have to be taken into account. The total system mass may approach 1 kg using commercially available parts not including the electronics that will be needed to adjust the tape speed and laser output. However once these control mechanisms are in place the Isp can be adjusted by controlling laser output parameters like intensity and pulse lengths which makes this thruster very versatile. The tape drive acts as a propellant feed mechanism suitable for long missions. The plasma output is quasineutral and non-metallic although carbon might be produced with some propellants which will minimize problems associated with contamination. Due to the lack of high voltage and the laser-produced plasma EMI problems should be minimal. Integration into a MEMS system might be possible with additional development. With shrinking laser size the output power will be reduced which in turn will reduce the spot size to submicron ranges and very small thrust levels. It is debatable if at this point the system losses like