Small （〈100 kg） spacecrafts are being developed in many countries but their propulsion systems still have many challenges. Although there is demand for small spacecraft propulsion, the number of missions at present...Small （〈100 kg） spacecrafts are being developed in many countries but their propulsion systems still have many challenges. Although there is demand for small spacecraft propulsion, the number of missions at present is small due to several commercial and technical reasons. Poor performance of existing small spacecraft propulsion systems is one of the main reasons for the small number of missions. Several reasons are given for the poor performance of existing small spacecraft propulsion. Suggested improvements focus on small spacecraft and propulsion hardware mass optimization rather than on specific impulse enhancement. Propellantless propulsion systems are also recommended for small spacecraft interplanetary missions.展开更多
The United States is experiencing a renaissance in interest in space due to the advent of new lowercost small spacecraft. New launch entrants, such as Interorbital Systems, promise to lower launch cost levels. Many de...The United States is experiencing a renaissance in interest in space due to the advent of new lowercost small spacecraft. New launch entrants, such as Interorbital Systems, promise to lower launch cost levels. Many developers also benefit from free-to-developer launch services from NASA or the ESA. Unfortunately, existing commercial off the shelf (COTS) CubeSat hardware is priced based on amortization of design costs across low-sales volume. A lack of trained staff in any one of the numerous disciplines required for spacecraft design or other resources required for in-house development restricts entry into the small satellite industry to those who can afford expensive COTS hardware or pay for significant design expenses. With entry-level satellite hardware still priced in the six-figure range, limited market growth is expected even as the average CubeSat launch cost continues to decline. A new archetype could lower barriers to entry for building small satellites. A free, public-domain architecture for building a small satellite could allow low-cost, in-house satellite development. Under this paradigm, the expenses for initiating a small satellite program are limited to component and launch vehicle costs. The proposed framework allows for broad access to small satellite hardware, greatly increasing the size of the small satellite developer community. In the context of the small satellite market, freely offering plans to construct an entry-level satellite will court new non-traditional actors into building space hardware for launch on commercial and government small satellite launchers. The low-cost, high flight rate possible with the next generation of launch systems affords operators the freedom to experiment and innovate in a risktolerant environment. Successfully demonstrating products and services utilizing low-risk, publicdomain plans will stimulate demand for mature and more capable flight systems in the retail marketplace. If technical schools, community colleges, universities, small businesses and even amateurs can enter into the small satellite ecosystem, at an affordable entrance price, a positive spiral of increasing demand and decreasing cost may be created over time. A free, public domain satellite architecture may, thus, open the door to sustained growth and commercial opportunity for the small satellite industry.展开更多
The attitude control problem of a spacecraft underactuated by two single-gimbal control moment gyros （SGCMGs） is investigated. Small-time local controllability （STLC） of the attitude dynamics of the spacecraft-SGC...The attitude control problem of a spacecraft underactuated by two single-gimbal control moment gyros （SGCMGs） is investigated. Small-time local controllability （STLC） of the attitude dynamics of the spacecraft-SGCMGs system is analyzed via nonlinear controllability theory. The conditions that guarantee STLC of the spacecraft attitude by two non-coaxial SGCMGs are obtained with the momentum of the SGCMGs as inputs, implying that the spacecraft attitude is STLC when the total angular momentum of the whole system is zero. Moreover, our results indi- cate that under the zero-momentum restriction, full attitude stabilization is possible for a spacecraft using two non-coaxial SGCMGs. For the case of two coaxial SGCMGs, the STLC property of the spacecraft cannot be determined. In this case, an improvement to the previous full attitude stabilizing control law, which requires zero-momentum presumption, is proposed to account for the singu- larity of SGCMGs and enhance the steady state performance. Numerical simulation results demonstrate the effectiveness and advantages of the new control law.展开更多
文摘Small （〈100 kg） spacecrafts are being developed in many countries but their propulsion systems still have many challenges. Although there is demand for small spacecraft propulsion, the number of missions at present is small due to several commercial and technical reasons. Poor performance of existing small spacecraft propulsion systems is one of the main reasons for the small number of missions. Several reasons are given for the poor performance of existing small spacecraft propulsion. Suggested improvements focus on small spacecraft and propulsion hardware mass optimization rather than on specific impulse enhancement. Propellantless propulsion systems are also recommended for small spacecraft interplanetary missions.
文摘The United States is experiencing a renaissance in interest in space due to the advent of new lowercost small spacecraft. New launch entrants, such as Interorbital Systems, promise to lower launch cost levels. Many developers also benefit from free-to-developer launch services from NASA or the ESA. Unfortunately, existing commercial off the shelf (COTS) CubeSat hardware is priced based on amortization of design costs across low-sales volume. A lack of trained staff in any one of the numerous disciplines required for spacecraft design or other resources required for in-house development restricts entry into the small satellite industry to those who can afford expensive COTS hardware or pay for significant design expenses. With entry-level satellite hardware still priced in the six-figure range, limited market growth is expected even as the average CubeSat launch cost continues to decline. A new archetype could lower barriers to entry for building small satellites. A free, public-domain architecture for building a small satellite could allow low-cost, in-house satellite development. Under this paradigm, the expenses for initiating a small satellite program are limited to component and launch vehicle costs. The proposed framework allows for broad access to small satellite hardware, greatly increasing the size of the small satellite developer community. In the context of the small satellite market, freely offering plans to construct an entry-level satellite will court new non-traditional actors into building space hardware for launch on commercial and government small satellite launchers. The low-cost, high flight rate possible with the next generation of launch systems affords operators the freedom to experiment and innovate in a risktolerant environment. Successfully demonstrating products and services utilizing low-risk, publicdomain plans will stimulate demand for mature and more capable flight systems in the retail marketplace. If technical schools, community colleges, universities, small businesses and even amateurs can enter into the small satellite ecosystem, at an affordable entrance price, a positive spiral of increasing demand and decreasing cost may be created over time. A free, public domain satellite architecture may, thus, open the door to sustained growth and commercial opportunity for the small satellite industry.
基金supported by the National Natural Science Foundation of China (No.10902003)
文摘The attitude control problem of a spacecraft underactuated by two single-gimbal control moment gyros （SGCMGs） is investigated. Small-time local controllability （STLC） of the attitude dynamics of the spacecraft-SGCMGs system is analyzed via nonlinear controllability theory. The conditions that guarantee STLC of the spacecraft attitude by two non-coaxial SGCMGs are obtained with the momentum of the SGCMGs as inputs, implying that the spacecraft attitude is STLC when the total angular momentum of the whole system is zero. Moreover, our results indi- cate that under the zero-momentum restriction, full attitude stabilization is possible for a spacecraft using two non-coaxial SGCMGs. For the case of two coaxial SGCMGs, the STLC property of the spacecraft cannot be determined. In this case, an improvement to the previous full attitude stabilizing control law, which requires zero-momentum presumption, is proposed to account for the singu- larity of SGCMGs and enhance the steady state performance. Numerical simulation results demonstrate the effectiveness and advantages of the new control law.
