Slot Architecture for Separating Satellites in Sun-Synchronous Orbits

A slot architecture is developed for separating satellites in congested Sun-synchronous orbits that are a limited natural resource in low Earth orbit. A key feature of the slot architecture is a phasing rule that provides sufficient separation between slots in the vicinity of their orbital crossing points. Other features involve the discretization of orbital parameters such as semi-major axis and right ascension of the ascending node. The design parameters of the slot architecture were selected with detailed consideration of various operational aspects and orbital perturbations. A preliminary analysis indicates that slotmaintenance requirements are automatically satisfied by maneuvers that are routinely performed by current high-value Earth observation satellites to satisfy their existing mission objectives. A simulation analysis of satellites currently in Sun-synchronous orbit confirms that implementation of the proposed slot architecture would greatly reduce the frequency of close approaches between these satellites.Delft University of Technolog

The CloudSat mission and the A-train: a new dimension of space-based observations of clouds and precipitation

CloudSat is a satellite experiment designed to measure the vertical structure of clouds from space. The expected launch of CloudSat is planned for 2004, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA-CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL). A unique feature that CloudSat brings to this constellation is the ability to fly a precise orbit enabling the fields of view of the CloudSat radar to be overlapped with the CALIPSO lidar footprint and the other measurements of the constellation. The precision and near simultaneity of this overlap creates a unique multisatellite observing system for studying the atmospheric processes essential to the hydrological cycle.The vertical profiles of cloud properties provided by CloudSat on the global scale fill a critical gap in the investigation of feedback mechanisms linking clouds to climate. Measuring these profiles requires a combination of active and passive instruments, and this will be achieved by combining the radar data of CloudSat with data from other active and passive sensors of the constellation. This paper describes the underpinning science and general overview of the mission, provides some idea of the expected products and anticipated application of these products, and the potential capability of the A-Train for cloud observations. Notably, the CloudSat mission is expected to stimulate new areas of research on clouds. The mission also provides an important opportunity to demonstrate active sensor technology for future scientific and tactical applications. The CloudSat mission is a partnership between NASA's JPL, the Canadian Space Agency, Colorado State University, the U.S. Air Force, and the U.S. Department of Energy

Dedicated launch of small satellites using scramjets

Reduced scale and improved responsiveness will be the technical and economic drivers of future satellite systems. Based on decades of practical experience with rocket-only expendable launch vehicles, current technology is operated close to theoretical limits. Scramjets have an advantage over rocket propulsion in terms of a significantly higher specific impulse. Other benefits of airbreathing propulsion for access-to-space are increased launch flexibility and the possibility of reusable aircraft-like operations. This article describes the use of a three-stage rocket-scramjet-rocket system for transporting payloads of the order of 100 kg to a Sun Synchronous Orbit. The reusable second stage is based on a winged-cone vehicle and is powered by hydrogen fueled scramjets. Analysis of the complete three-stage system was performed based around a fully trimmed trajectory simulation of the second stage. The scramjet powered second stage accelerated from Mach 6.0 to Mach 9.3 with an average net specific impulse of 923 seconds. As a result, the overall system showed a payload mass fraction of 1.26% to Sun Synchronous orbit, which is significantly higher than expendable rocket based systems of this scale