Algorithms for Improved, Heading Assisted, Maneuver Tracking

The evolution of the SSR mode S system makes it possible to receive airborne measurements at the ground station. The possibility of using data-linked heading measurements to assist present trackers to track maneuvering aircraft is investigated. The quality to be expected from heading measurements is investigated from available on-board recordings. Maneuver detection and false measurement rejection schemes are developed, and finally suitable maneuver tracking filters are constructed and evaluated.     

Precision orbit determination for TOPEX/Poseidon using TDRSS doppler tracking data

Precision orbit determination on the TOPEX/Poseidon (T/P) altimeter satellite is now being routinely achieved with sub-5cm radial and sub-15 cm total positioning accuracy using state-of-the-art modeling with precision tracking provided by a combination of: (a) global Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), or (b) the Global Positioning System (GPS) Constellation which provides pseudo-range and carrier phase observations. The geostationary Tracking and Data Relay Satellite System (TDRSS) satellites are providing the operational tracking and communication support for this mission. The TDRSS Doppler data are of high precision (0.3 mm/s nominal noise levels). Unlike other satellite missions supported operationally by TDRSS, T/P has high quality independent tracking which enables absolute orbit accuracy assessments. In addition, the T/P satellite provides extensive geometry for positioning a satellite at geostationary altitude, and thus the TDRSS-T/P data provides an excellent means for determining the TDRS orbits. Arc lengths of 7 and 10 days with varying degrees of T/P spacecraft attitude complexity are studied. Sub-meter T/P total positioning error is achieved when using the TDRSS range-rate data, with radial orbit errors of 10.6 cm and 15.5 cm RMS for the two arcs studied. Current limitations in the TDRSS precision orbit determination capability include mismodeling of numerous TDRSS satellite-specific dynamic and electronic effects, and in the inadequate treatment of the propagation delay and bending arising from the wet troposphere and ionosphere.     

Modelling mesoscale processes in the global geospace system

Intermediate or mesoscale processes mediate the transfer of mass, momentum, and energy across the dynamic solar wind-magnetosphere interface, and the propagation of this input through the system to the ionosphere and atmosphere. The Dartmouth-Berkeley-Minnesota theory team has identified a number of mesoscale phenomena to be investigated as part of the GGS program, including: (1) effects of upstream density fluctuations on magnetopause dynamics, (2) three-dimensional reconnection, (3) magnetopause depletion layer studies, (4) ring current interaction with Pc 1 and Pc 5 waves, (5) generation of ion Larmor-scale current layers in the near Earth plasmasheet, (6) test particle studies in the magnetotail, (7) simulation of magnetosphere- ionosphere coupling including effects of kinetic Alfvén waves and (8) auroral acceleration region studies of the effects of kinetic Alfvén waves on particle distribution functions. A broad range of techniques will be implemented including ideal and reduced MHD, two fluid, hybrid, particle-in-cell and test particle simulations. Detailed comparison of simulation results with GGS satellite and ground based data will be undertaken.     

Thermal and nonthermal flare emission observed with the Nobeyama Radio Heliograph

The early phases of three flares, observed by the Nobeyama Radio Heliograph, are studied. Nonthermal and thermal radio sources are identified by comparison with soft X-ray images taken by the Soft X-ray Telescope onboard the Yohkoh satellite. Two of the flares are mainly of nonthermal origin and their location coincides with one of the footpoints of soft X-ray loops. Another flare has both thermal and nonthermal components which start to brighten simultaneously. This suggests that particle acceleration and plasma compression develop simultaneously.     

Cloud profiling radar for the CloudSat mission

The Cloud Profiling Radar (CPR) for the upcoming CloudSat Mission is a spaceborne 94-GHz nadir-looking radar that measures the power backscattered by clouds as a function of distance from the radar. This sensor is expected to provide cloud measurements at a 500-m vertical resolution and a 1.5 km horizontal resolution. CPR will operate in a short-pulse mode and will yield measurements at a minimum detectable sensitivity of -28 dBZ.     

Rocket observation of the ultraviolet spectrum of comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on 26 February 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 × 10²⁹ s⁻¹ and the volume mixing ratio of CO to H₂O is 21%. The predicted brightness distribution from a radial outflow model with H₂O and CO as parent molecules are in accordance with the measured spatial profiles of OI and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker CI emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3% of the water production rate is included in the model.     

The time delay of a solar grazing photon

Moving clocks and clocks in a gravitational field slow down, not due to the effects of special relativity nor to the space-time curvature of general relativity, but due only to the principle of equivalence and the conservation of energy. However, some might argue that there has been a further “test” of the effect of gravity on time, namely, the measurement of the time-delay of a round-trip, solar-grazing radar beacon performed by Shapiro in the 1960s. In this test, Shapiro bounced a radar pulse off Mars at superior conjunction (a feat in itself for the time), and compared the measured round-trip travel time of this pulse with the expected round-trip time of a signal traveling at c for the entire trip, as determined from highly accurate planetary ephemerides. Shapiro had predicted this time-delay long before being technologically able to make such a measurement. While general relativity can be used to correctly obtain the magnitude of this delay, it is not the only explanation. As earlier with the analysis of clocks in motion and of clocks in a gravitational field, this paper derives the same result without invoking the space-time curvature of general relativity     

Pioneer Venus observations during comet Halley''s inferior conjunction

On February 4, 1986 Halley passed through inferior conjunction with Venus but was at high latitudes. Not all data for this time period have been received. However, the data that are available suggest that at most only weak effects associated with Halley were seen at Pioneer Venus. The data during this time, however, are useful for correlating with the behavior of the plasma tail.     

Psychological countermeasures for extended manned spaceflights

The authors examine psychological issues and countermeasures in extended space flight. Individual-oriented pre-flight countermeasures include basic psychological selection and training of astronaut candidates. Crew-oriented pre-flight countermeasures include crew composition based on psychological compatibility and psychological mission preparation. Psychological inflight support measures include those that address the emotional state and well-being of astronauts, performance efficiency, and prevention of task overload. Suggestions for an integrated approach to psychological countermeasures for extended flights are presented. Case reports examine psychological selection and training of German astronauts in preparation for the STS-55 mission.     

Preparing EMU for Space Station

In today's fiscally constrained environment, it can be expected that systems designed for one space program will increasingly be used to support other programs. The example of the U.S. extravehicular mobility unit (EMU), designed for use with the Space Shuttle, and now part of the baseline for the International Space Station (ISS) program, illustrates the adaption process. Certifying the Shuttle's EMU for use aboard ISS requires addressing three fundamental issues: Identifying new ISS requirements to be imposed on the EMU. Extending Shuttle's EMU on-orbit service interval to meet ISS's longer missions. Certifying Shuttle's EMU to meet new environments unique to ISS. Upon completion of the certification process, Shuttle's EMU will meet all requirements for supporting both the Shuttle and ISS program. This paper discusses the processes for addressing these issues and progress to date in achieving resolution.