Success criteria and risk management for the new millennium program

The National Aeronautics and Space Administration (NASA) New Millennium Program (NMP) is a technology development and validation program that will flight-validate advanced, new technologies with space flight applications. NMP's purpose is twofold. First, it will develop technologies that will enable future spacecraft to be smaller, more capable and reliable, and to be launched more frequently. Second, it will validate the technologies in flight to reduce the risks to future science missions that fly these technologies for the first time. To measure the program's success, NMP has devised a set of criteria that stresses the relevance of technologies selected for flight validation to NASA's 21st-century science mission needs. Also, NMP has instituted a ‘risk management’ policy, where, through a combination of adequate resources and early risk assessment and risk mitigation plans for the technologies, the overall risk of the NMP flights can be rendered acceptable.     

Ensuring equal access to the benefits of space technologies for all countries

There is a concern in the developing world that industrialized countries have not done all they might under Article 1 of the Outer Space Treaty to make the benefits of space technology available to all countries; some are now seeking codification of rights and responsibilities in this sphere. This article discusses recent debate on the issues by COPUOS and its Legal Subcommittee on whether an additional legal framework is necessary to ensure a fairer distribution of benefits. G77 countries were strongly in favour of some form of technology and information transfer, while industrialized countries favoured the existing practice of developing international cooperative space projects. The author believes that a new set of principles will be formulated in the next few years and that organizations like Intelsat and Inmarsat can provide valuable models for ensuring access through cooperative programmes.     

Thermal resistance in satellite mounting plates due to conductive heat transfer

The thermal resistance due to conductive heat transfer between two heat generating boxes mounted symmetrically on a thin mounting plate, one side of which is subjected to a constant heat flux and the opposite side is convectively cooled, is considered. The other two sides are maintained at constant temperature. A numerical solution for the temperature field is obtained and the heat transfer between the boxes is found by integrating between the critical heat flow lines. Various nondimensional parameters are identified and their influence on the thermal resistance is studied.     

Orbital and relative motion of a tethered satellite system

A simplified model for the orbital and relative motion of a tethered satellite system is presented. The tether acts as a light elastic string with small structural damping but without bending stiffness. Its mass is taken into account in the calculation of the total kinetic and potential energies of the tethered system. This formulation allows the inclusion of the complete gravity gradient influence on the dynamics of the system. The resulting three-dimensional motion is separated in the centre of mass orbital motion on the one hand and the relative motion of the end-bodies on the other. No restrictions on length of the tether or on mass ratio of the end-masses are imposed. It is found that the frequencies and amplitudes of the longitudinal tether oscillations are realistic as long as the tether mass is less than that of the subsatellite.     

Aeroshell design techniques for aerocapture entry vehicles

A major goal of NASA's In-Space Propulsion Program is to shorten trip times for scientific planetary missions. To meet this challenge arrival speeds will increase, requiring significant braking for orbit insertion, and thus increased deceleration propellant mass that may exceed launch lift capabilities. A technology called aerocapture has been developed to expand the mission potential of exploratory probes destined for planets with suitable atmospheres. Aerocapture inserts a probe into planetary orbit via a single pass through the atmosphere using the probe's aeroshell drag to reduce velocity. The benefit of an aerocapture maneuver is a large reduction in propellant mass that may result in smaller, less costly missions and reduced mission cruise times. The methodology used to design rigid aerocapture aeroshells will be presented with an emphasis on a new systems tool under development. Current methods for fast, efficient evaluations of structural systems for exploratory vehicles to planets and moons within our solar system have been under development within NASA having limited success. Many systems tools that have been attempted applied structural mass estimation techniques based on historical data and curve fitting techniques that are difficult and cumbersome to apply to new vehicle concepts and missions. The resulting vehicle aeroshell mass may be incorrectly estimated or have high margins included to account for uncertainty. This new tool will reduce the guesswork previously found in conceptual aeroshell mass estimations.     

Advantages and disadvantages of prizes in a portfolio of financial incentives for space activities

The National Aeronautics and Space Administration (NASA) has proposed to use financial prizes to encourage innovation in space technology. Public debate about the use of prizes questions their effectiveness, the role of government compared with the private sector in administering prizes—for example, the Ansari X-Prize for human suborbital flight was privately funded and administered—and other issues that are likely to influence the success of this approach.     

n-Body problem: Selective effects of triple close approaches

In Celestial Mechanics the triple close approach is a highly unstable phenomenon that leads very often to the formation of a very small binary escaping with a large velocity in the direction opposite to the escape of the third body.That third escaping body is generally either the smallest mass or the second smallest and it implies a very selective effect in star clusters: the lightest stars are statistically the first to be ejected.     

Benefits to world agriculture through remote sensing

Remote sensing of agricultural land permits crop classification and mensuration which can lead to improved forecasts of production. This technique is particularly important for nations which do not already have an accurate agricultural reporting system. Better forecasts have important economic effects. International grain traders can make better decisions about when to store, buy and sell. Farmers can make better planting decisions by taking advantage of production estimates for areas out of phase with their own agricultural calendar. World economic benefits will accrue to both buyers and sellers because of increased food supply and price stabilization.

This paper reviews the econometric models used to establish this scenario and estimates the dollar value of benefits for world wheat as 200 million dollars annually for the United States and 300–400 million dollars anually for the rest of the world.     

Flow of a water jet into vacuum

At certain intervals excess water has to be dumped into space overboard of the Spacelab cabin. For the development of a useful nozzle the behaviour of a water jet flowing into vacuum was investigated experimentally and theoretical interpretations of the flow phenomena which were found are given. The influence of parameters like the shape of the nozzle, the temperature and the gas content of water were studied. At certain test conditions, the jet leaves the nozzle exit in bundled form and ends abruptly bursting into droplets and ice-particles. The “bursting”-mechanism is explained by a sudden boiling of the water in the jet causing the growth of vapor bubbles decomposing the jet. The formation of vapor bubbles is initiated by a superheating of the water of the jet caused by a sudden pressure drop and a cooling at the surface of the jet. The expansion of vapor bubbles in the jet is retarded by surface tension forces which results in a relaxation time for the bursting of the jet. The vapor flow in radial directions of the jet is approximately described by a plane radial source flow. The measurement of the pitot-pressure radially to the jet proves that the vapor flow is supersonic.     

Interaction onde de choc-couche limite laminaire sur un corps de revolution en rotation

(Shock Wave-Laminar Boundary Layer Interaction on a Spinning Axisymmetric Body)—A method is developed to predict the shock wave-laminar boundary layer interaction on an axisymmetric body spinning in axial flow. The integral scheme of Lees, Reeves and Klineberg is used. The Falkner Skan “type” equations is then established for the boundary layer on spinning cylinder and used to construct the polynomial representation of the integral quantities. The independence of the polynomials with respect to the spinning rate is demonstrated. A cylinder of 200 mm diameter with a flare is built and tested up to 5000 rmp in wind tunnel at M = 2.21. The pressure measurements are in good agreement with the theoretical results. The rotation induces the decreasing of the pressure level and boundary layer separation inside the interaction region.