CubeSail: A low cost CubeSat based solar sail demonstration mission

CubeSail is a nano-solar sail mission based on the 3U CubeSat standard, which is currently being designed and built at the Surrey Space Centre, University of Surrey. CubeSail will have a total mass of around 3 kg and will deploy a 5 × 5 m sail in low Earth orbit. The primary aim of the mission is to demonstrate the concept of solar sailing and end-of-life de-orbiting using the sail membrane as a drag-sail. The spacecraft will have a compact 3-axis stabilised attitude control system, which uses three magnetic torquers aligned with the spacecraft principle axis as well as a novel two-dimensional translation stage separating the spacecraft bus from the sail. CubeSail’s deployment mechanism consists of four novel booms and four-quadrant sail membranes. The proposed booms are made from tape-spring blades and will deploy the sail membrane from a 2U CubeSat standard structure. This paper presents a systems level overview of the CubeSat mission, focusing on the mission orbit and de-orbiting, in addition to the deployment, attitude control and the satellite bus.     

Sumbandilasat—An operational technology demonstrator

Technology advances in sensor, digital technology and a standardised modular satellite bus are enabling a new generation of 80 kg micro-satellites with a better than 6.5 m GSD multi-spectral performance, to be specified, built and deployed with a dedicated launch within 12 months. The result of the standardised modular bus is lower cost, higher reliability and fast deployment. Operational remote sensing with a micro-satellite is thus within reach of individual organisations for dedicated missions. Sumbandilasat (pioneer in the Venda language) is a second generation satellite technology building on the expertise obtained in the Sunsat small satellite programme. The components used to build Sumbandilasat are the result of a technology development program of more than 3 years. Sumbandilasat is an operational technology demonstrator with more than 90% newly developed or improved subsystems and a compact refractive imager as a precursor to the MSMISat satellite with the same multi-spectral band set. The scalable, standardised modular satellite bus architecture enables satellites with a mass of 80–450 kg to be adapted to the specific mission requirements with minimum new engineering effort.     

Mission building blocks for outer solar system exploration

Summary A meaningful outer-planet exploration program can be conducted within expected economic constraints. The spacecraft needed can be developed in an evolutionary manner from the existing Pioneer and Mariner families. Advanced propulsion capability may reduce the costs associated with constrained weight margins and long trip times.This is one of the publications by the Science Advisory Group.     

Human exploration of near earth asteroids: Mission analysis for chemical and electric propulsion

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future.     

Air-Ground, Ground-Air Communications Using Pseudo-Noise Through a Satellite

An air-ground, ground-air communications system that utilizes a satellite and a central control facility is described. The double-hop pseudo-noise system advantages, including equal sharing of power, use of frequency translating repeaters, optimum multipath rejection, and acceptable power densities on the ground are discussed. The selection of code division is presented together with an analysis of signal-to-noise ratios with a varied input. Modulation schemes are discussed, pro and con, and the effective radiated power versus antenna sizes for several combinations are analyzed.     

Cubesat solar sail 3-axis stabilization using panel translation and magnetic torquing

A Cubesat mission with a deployable solar sail of 5 meter by 5 meter in a sun-synchronous low earth orbit is analyzed to demonstrate solar sailing using active attitude stabilization of the sail panel. The sail panel is kept parallel to the orbital plane to minimize aerodynamic drag and optimize the orbit inclination change caused by the solar pressure force normal to the sail surface. A practical control system is proposed, using a combination of small 2-dimensional translation of the sail panel and 3-axis magnetic torquing which is proved to have sufficient control authority over the gravity gradient and aerodynamic disturbance torques. Miniaturized CMOS cameras are used as sun and nadir vector attitude sensors and a robust Kalman filter is used to accurately estimate the inertially referenced body rates from only the sun vector measurements. It is shown through realistic simulation tests that the proposed control system, although inactive during eclipse, will be able to stabilize the sail panel to within ±2° in all attitude angles during the sunlit part of the orbit, when solar sailing is possible.     

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H₂SO₄ particles and of volcanic ash.     

An alternative approach to solar system exploration planning

Planning for the future exploration of the solar system has involved the structuring of a series of missions that address major scientific objectives at a minimum runout cost for the entire endeavor. In many cases, however, the optimal structuring of a program that would minimize the runout cost would entail an unacceptable high annual funding. Our actual planning must consider the planning wedge imposed on the National Aeronautics and Space Administration. It is vital that a plan be structured that copes with the annual restraint. If we do not recognize this, our plan will not be realized and a queing problem will result, thus negating all of our planning efforts.This paper presents ideas as to how planetary initiatives can be structured, wherein the peak annual funding is minimized. One vital aspect in the plan is to have a transportation capability that can launch a mission in any planetary opportunity. Solar electric propulsion can provide this capability. Another cost reduction approach would be to structure a mission set in a time sequenced fashion that could utilize essentially the same spacecraft for the implementation of several missions. This opportunity does exist. A third technique would be to fulfill a scientific objective in several sequential missions rather than attempt to accomplish all of the objectives with one mission. This approach might be applied to a mission currently in the planning stage designated the Saturn Orbiter Dual Probe mission. The current concept involves the delivery of a Saturn probe, a Titan probe, and a Saturn Orbiter by a one Shuttle launch. In this case, the orbiter must serve as a relay station for both probes; map the magnetosphere of Saturn; conduct a survey of Saturn's major satellites; and perform the planetological observation of Saturn itself. This mission entails the development of a complex spacecraft that would be required to have a fairly long life due to the extended mission operations at the benefit of accomplishing the mission with one launch. An alternate approach would be to break the mission into two separate elements. We could, for example, launch a Saturn orbiter carrying a Saturn entry probe. After serving as a communications relay system for the Saturn probe, the orbiter would then be specialized to map the magnetosphere of Saturn. A second launch would involve the delivery of a Titan probe by another orbiter where after delivery the orbiter would conduct the planetological observation of Saturn and its satellites. For the split-launch option, the runout cost for the two missions would be greater than the single launch option. However, optimum structuring of the two missions could materially reduce the peak annual funding.This paper presents data on the estimated cost on a year by year basis of a mission set structured to minimize the runout cost with no concern as to the peak annual funding as compared to a mission set that would yield the same scientific objectives in a slightly longer time span wherein the annual peak funding would be minimized. The consequences of this revised plan are analyzed.