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Abstract: In previous papers, the authors developed an active control scheme based on the linear quadratic regulator (LQR) to maintain the separation distance constraints of the NASA benchmark tetrahedron constellation. Two different active control schemes were used to maintain the separation distance constraints, but one control scheme applied to every eccentricity of the NASA benchmark problem. Through this paper, the digital LQR strategy will be developed with this active control scheme to maintain the separation distance conditions of the tetrahedron constellation. The motion of a pair of satellites in an elliptical orbit about the Earth is defined by the linearized Tschauner–Hempel (TH) equations. These equations will be defined discretely in the true anomaly angle for the development of the digital control scheme. In summary, the digital LQR approach will be implemented and studied to determine how this active control scheme maintains the separation distance constraints for different specific sizes of the NASA benchmark tetrahedron constellation. [Copyright &y& Elsevier]

Abstract: This paper summarizes results from two postmission disposal (PMD) parametric analyses based on the high fidelity NASA orbital debris evolutionary model LEGEND. The first analysis includes a non-mitigation reference scenario and four test scenarios, where the mission lifetimes of spacecraft are set to 5, 10, 20, and 30years, respectively, before they are moved to the 25-year decay orbits. The comparison among the five scenarios quantifies how a prolonged spacecraft mission lifetime decreases the effectiveness of the 25-year decay rule in the low Earth orbit region (LEO). The second analysis includes three 25-year decay PMD scenarios where the mission lifetimes of spacecraft are set to 5years but with disposal success rates set to 50%, 70%, and 90%, respectively. It illustrates how the PMD success rate impacts the long-term debris environment. The conclusion of this paper is that a prolonged spacecraft mission lifetime and a lower PMD success rate can have noticeable negative impact on the debris environment in the long run. [Copyright &y& Elsevier]

The global political structure has changed dramatically since the breakup of the former Soviet Union, and world changes have caused the United States to reprioritize its national hypersonic needs. The US Government has looked at the needs of the future, and the hypersonic aerospace plane is one of the systems included in alternative force structures. One hypersonic aerospace plane concept would involve magnetohydrodynamic (MHD) technology (i.e., the AJAX hypersonic flight vehicle concept) originally proposed by Russian scientist Vladimir Fraishtadt.This paper reports on the current progress and findings of an air-breathing horizontal takeoff and landing design concept using an MHD energy bypass injector ramjet engine being studied at MSE Technology Applications, Inc., HyperTech Concepts, and several universities for the National Aeronautics and Space Administration Langley Research Center under a Phase II Small Business Innovation Research project. The areas that are addressed in this paper include: (1) ionization required to achieve the required energy bypass, (2) utilization of a nonequilibrium model to calculate nonequilibrium engine ionization conditions, (3) hydrocarbon fuel reforming, and (4) vehicle performance and sizing. A quasi-onedimensional electromagnetic code combined with a new scramjet model, as well as other tools, were used to examine total system performance. [Copyright &y& Elsevier]

Abstract: The International Space Station (ISS) is rapidly approaching the long-awaited completion of assembly. All United States (US) core elements have been integrated and tested on-orbit and the principle elements of the European and Japanese laboratories were successfully deployed in 2008. The fully envisioned configuration is on schedule to be completed as planned by the end of US government fiscal year 2010. Section 507 of the NASA Authorization Act of 2005 designated the US segment of the ISS as a “national laboratory”, thereby opening up its use to other US government agencies, US private firms and US non-profit institutions. This paper reports on progress toward identifying and entering into agreements with entities outside of NASA that plan to use the ISS in the post-assembly timeframe. The original 1984 vision of a robust, multi-mission space station serving as a platform for the advancement of US science, technology and industry will soon be achieved. [Copyright &y& Elsevier]

Abstract: Nearly six years after the launch of the first International Space Station element, and four years after its initial occupation, the United States and our 6 international partners have made great strides in operating this impressive Earth orbiting research facility. This past year we have done so in the face of the adversity of operating without the benefit of the Space Shuttle. In his January 14, 2004, speech announcing a new vision for America''s space program, President Bush affirmed the United States’ commitment to completing construction of the International Space Station by 2010. The President also stated that we would focus our future research aboard the Station on the long-term effects of space travel on human biology. This research will help enable human crews to venture through the vast voids of space for months at a time. In addition, ISS affords a unique opportunity to serve as an engineering test bed for hardware and operations critical to the exploration tasks. NASA looks forward to working with our partners on International Space Station research that will help open up new pathways for future exploration and discovery beyond low Earth orbit. This paper provides an overview of the International Space Station Program focusing on a review of the events of the past year, as well as plans for next year and the future. [Copyright &y& Elsevier]

Abstract: Small satellite systems appear to be antithetical to human spaceflight systems and flagship robotic satellite systems: Small satellite missions have more focused scientific objectives, lower cost, far less complexity, and shorter development and deployment schedules. The shorter schedules offer an opportunity for injecting new technology into their design as a means for keeping costs and schedule under control, for enabling cost-effective operations, and for taking advantage of innovative ideas. It is often the case that small satellite missions benefit from technologies specifically targeted for their application, but benefits may also be realized by adopting or injecting technologies originally developed for human spaceflight systems, especially if these technologies were conceived using multi-use and multi-disciplinary development principles. In this paper, the authors discuss the precedent of injecting new technology developed for human spaceflight systems into small satellite missions. More importantly, the authors will present five new technologies recently proposed for making the NASA Space Shuttle safer to fly, all of which are directly applicable to small satellite mission design and operations. The technologies, when matured, will provide a means to create new generations of ultra-reliable flight hardware and software. The technologies are all currently at the developmental phase and require modest investment to achieve operational status. [Copyright &y& Elsevier]

Abstract: The United States space exploration goals expressed in January 2004 call for the retirement of the Space Transportation System (STS or Shuttle) following completion of International Space Station (ISS) construction. Since the Shuttle is instrumental in transporting large quantities of cargo to and from the ISS, this functional capability must be preserved to ensure ongoing station operations in a post-Shuttle era. Fulfilling ongoing cargo transport requirements to the ISS is a prime opportunity for NASA to reduce costs and preserve and repurpose the unique and limited Shuttle resource by acquiring cargo transportation services commercially. Further, implementing such a service prior to retirement of the Shuttle reduces risk to the vehicle and her crews by eliminating their use for routine cargo transport missions while accelerating the readiness for alternative ISS-support transportation. This paper examines ISS cargo traffic requirements, provides an assessment of current and proposed cargo vehicles envisioned for ISS cargo transport, and examines major cost drivers associated with development of cargo transport systems. Consideration of these factors, coupled with SPACEHAB''s extensive involvement in cargo transport to the Mir and ISS, has led to the development of a Commercial Payload Service (CPS). The CPS mission models, system description and performance, and structure of the commercial service model are presented. [Copyright &y& Elsevier]

Abstract: In order to verify that the International Space Station (ISS) payload facility racks do not disturb the microgravity environment of neighboring facility racks and that the facility science operations are not compromised, a testing and analytical verification process must be followed. Currently no facility racks have taken this process from start to finish. The authors are participants in implementing this process for the NASA Glenn Research Center (GRC) Fluids and Combustion Facility (FCF). To address the testing part of the verification process, the Microgravity Emissions Laboratory (MEL) was developed at GRC. The MEL is a 6 degree of freedom inertial measurement system capable of characterizing inertial response forces (emissions) of components, sub-rack payloads, or rack-level payloads down to ''s. The inertial force output data, generated from the steady state or transient operations of the test articles, are utilized in analytical simulations to predict the on-orbit vibratory environment at specific science or rack interface locations. Once the facility payload rack and disturbers are properly modeled an assessment can be made as to whether required microgravity levels are achieved. The modeling is utilized to develop microgravity predictions which lead to the development of microgravity sensitive ISS experiment operations once on-orbit. The on-orbit measurements will be verified by use of the NASA GRC Space Acceleration Measurement System (SAMS). The major topics to be addressed in this paper are: (1) Microgravity Requirements, (2) Microgravity Disturbers, (3) MEL Testing, (4) Disturbance Control, (5) Microgravity Control Process, and (6) On-Orbit Predictions and Verification. [Copyright &y& Elsevier]

Abstract: Students from the University of Michigan have developed a small satellite—dubbed Icarus—to serve as an active endmass for NASA''s ProSEDS (Propulsive Small Expendable Deployer System) electrodynamic-tether propulsion mission. The ProSEDS experiment will be launched in early 2004 as a secondary payload attached to the second stage of a Delta-II rocket. Following the completion of the Delta-II primary mission, the Icarus endmass satellite will be cast off from the Delta-II second stage, deploying a 12 km space tether. Throughout tether deployment, and for the duration of the ProSEDS mission, Icarus will collect and transmit data on tether deployment and dynamics. The endmass is responsible for providing tether–endbody location information (using a GPS receiver) and endbody attitude dynamics (using an aspect magnetometer). The data from these instruments will be stored and transmitted to ground telemetry stations. This paper details the Icarus satellite system and lessons learned from the project. [Copyright &y& Elsevier]

There is a belief that exists in the United States about public support for NASA''s activities. The belief is almost universally held that NASA and the cause of space exploration enjoyed outstanding public support and confidence in the 1960s during the era of Apollo and that public support waned in the post-Apollo era, only to sink to quite low depths in the decade of the 1990s. These beliefs are predicated on anecdotal evidence that should not be discounted, but empirical evidence gleaned from public opinion polling data suggest that some of these conceptions are totally incorrect and others are either incomplete or more nuanced than previously believed. This paper explores evolution of public support for space exploration since the 1960s. Using polling data from a variety of sources it presents trends over time and offers comments on the meaning of public perceptions for the evolution of space policy and the development of space exploration in the United States. [Copyright &y& Elsevier]

The Skybridge system is a worldwide ATM broadband communication system based on a 80 low Earth orbit satellite constellation. The minimization of space debris generation has been taken into account very early in the frame of this program.The objectives are, first to identify the contribution of Skybridge to the space debris generation and secondly to assess the risk due to space debris for the whole system. This paper summarizes the approach of the Skybridge program for debris assessment and mitigation.As no international regulation dealing with this subject exists, the analysis is based on the existing NASA 1740 Safety Standard. The methodology and the software presented in this document were applied to demonstrate the compliance of Skybridge with the requirements. In addition the new CNES standard was used to derive additional requirements.The first point deals with the production of space debris in the various mission phases: this concerns debris released during launch, constellation deployment and mission operations. Besides these normal operations, space debris can also be generated through material ageing or in case of accidents such as explosion due to on-board stored energy or collision with other orbiting objects.In the second part the collision risk is analyzed: the probability of collision with the large cataloged objects is determined. Concerning the smaller debris, the flux models give the probability of impact per surface unit: the analysis identifies components most vulnerable to debris impact together with their shielding and gives the associated probability of failure taking into account the architecture of the satellite.The problem of the post-mission disposal procedure is then discussed in the third part. [Copyright &y& Elsevier]