High-Data-Rate Communication Techniques for Small Satellites

Modulation and coding techniques that are both power and bandwidth-efficient are examined at the system level in this paper. Such techniques include convolutional encoding with QPSK modulation and the relatively new trellis-coded modulation. Power and bandwidth trade-offs are discussed, a sample link calculation is given, and hardware implementation is considered

Tone-Based Command of Deep Space Probes using Ground Antennas

A document discusses a technique for enabling the reception of spacecraft commands at received signal levels as much as three orders of magnitude below those of current deep space systems. Tone-based commanding deals with the reception of commands that are sent in the form of precise frequency offsets using an open-loop receiver. The key elements of this technique are an ultrastable oscillator and open-loop receiver onboard the spacecraft, both of which are part of the existing New Horizons (Pluto flyby) communications system design. This enables possible flight experimentation for tone-based commanding during the long cruise of the spacecraft to Pluto. In this technique, it is also necessary to accurately remove Doppler shift from the uplink signal presented to the spacecraft. A signal processor in the spacecraft performs a discrete Fourier transform on the received signal to determine the frequency of the received signal. Due to the long-term drift in the oscillators and orbit prediction model, the system is likely to be implemented differentially, where changes in the uplink frequency convey the command information

Tone based command system for reception of very weak signals

This disclosure presents a communication receiver system for spacecraft that includes an open loop receiver adapted to receive a communication signal. An ultrastable oscillator (USO) and a tone detector are connected to the open loop receiver. The open loop receiver translates the communication signal to an intermediate frequency signal using a highly stable reference frequency from the USO. The tone detector extracts commands from the communication signal by evaluating the difference between tones of the communication signal

MARKETING ASPECTS IN THE OPERATIONS OF THE VELEBIT NATURE PARK

The application of marketing in tourism involves marketing activities undertaken by all producers that are in any way connected to selling their products on the tourist market, as a means of earning revenue. Tourism marketing calls for a marketing concept to be implemented in companies in the tourism sector and other tourism-supply providers. Upon the adoption of the Management Plan of the Velebit Nature Park, a marketing concept, as an element of efficient park management, must be employed to help ensure the prosperity of Park operations in all areas and across all levels

IAEA methodology for on-site end-to-end IMRT/VMAT audits : an international pilot study

The IAEA has developed and tested an on-site, end-to-end IMRT/VMAT dosimetry audit methodology for head and neck cases using an anthropomorphic phantom. The audit methodology is described, and the results of the international pilot testing are presented. The audit utilizes a specially designed, commercially available anthropomorphic phantom capable of accommodating a small volume ion chamber (IC) in four locations (three in planning target volumes (PTVs) and one in an organ at risk (OAR)) and a Gafchromic film in a coronal plane for the absorbed dose to water and two-dimensional dose distribution measurements, respectively. The audit consists of a pre-visit and on-site phases. The pre-visit phase is carried out remotely and includes a treatment planning task and a set of computational exercises. The on-site phase aims at comparing the treatment planning system (TPS) calculations with measurements in the anthropomorphic phantom following an end-to-end approach. Two main aspects were tested in the pilot study: feasibility of the planning constraints and the accuracy of IC and film results in comparison with TPS calculations. Treatment plan quality was scored from 0 to 100. Results: Forty-two treatment plans were submitted by 14 institutions from 10 countries, with 79% of them having a plan quality score over 90. Seventeen sets of IC measurement results were collected, and the average measured to calculated dose ratio was 0.988 ± 0.016 for PTVs and 1.020 ± 0.029 for OAR. For 13 film measurement results, the average gamma passing rate was 94.1% using criteria of 3%/3 mm, 20% threshold and global gamma. The audit methodology was proved to be feasible and ready to be adopted by national dosimetry audit networks for local implementation

SIGNAL-TO-NOISE RATIO PERFORMANCE OF THE SAWTOOTH PHASE DETECTOR WHEN DEMODULATING PM SUBCARRIERS

International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, NevadaThe noise performance of the sawtooth phase detector when demodulating a sinusoidal subcarrier plus direct data modulation is studied. At predetection signal-to-noise ratio (SNR) levels of about 10 dB or more, significant improvements in the postdetection SNR of the subcarrier can be obtained using the sawtooth detector rather than a linear multiplier. Below predetection SNR levels of about 10 dB, significant improvements can still be obtained; however, a threshold occurs and the performance degrades until leveling off at 3.2 dB worse than that of a linear multiplier. The predetection SNR level where the sawtooth detector performance becomes worse than that of a linear multiplier depends upon the subcarrier and direct data modulation indices. Performance curves are given between predetection SNR levels of -20 dB and +20 dB for various values of subcarrier modulation index and direct data modulation index.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

Statistical analysis of the gamma evaluation acceptance criteria : A simulation study of 2D dose distributions under error free conditions

Purpose: To investigate the statistical distribution of the gamma value under error-free conditions, in order to study the relation between the gamma evaluation failure rate and statistically significant deviations in the general situation. Methods: The 2D absorbed dose distribution for 30 clinical head-and-neck IMRT fields were calculated in a QC phantom. For the same fields, dose measurements were simulated by assuming that the calculated value represented the expectation value, and by adding a random spatial uncertainty of 1–9 mm (1SD) and a random dose uncertainty of 1%–3% (1SD). The simulated measurements were then compared to the calculated dose using the gamma evaluation, and the distribution of the failure rate (i.e. the probability of gamma values above unity) was analysed. Results: For a wide range of the random measurement uncertainty, a distinct peak in the failure rate distribution was observed. The presence of higher failure rates was associated with large values of the second order derivative of the dose distribution. For spatial uncertainties larger than or equal to the resolution of the dose matrix, and for reasonable dose uncertainties, the median value of the failure rate distribution was fairly constant. Conclusions: Simulations showed, in the general case, that the probability of having a gamma value above unity under error-free conditions was not spatially uniform. We believe that this shortcoming may be partly responsible for the limited ability of the gamma evaluation method to detect errors in clinically relevant situations

The Near Spacecraft Telecommunications System

The Near Earth Asteroid Rendezvous (NEAR) mission, first in NASA\u27s Discovery series, is designed to gather scientific data about the near-Earth asteroid 433 Eros. Due to launch in February 1996, the spacecraft will rendezvous with and eventually orbit the asteroid. The telecommunications system is centered about two redundant X-band transponder systems that provide the command, telemetry, and tracking functions. Although the mission has a very tight development schedule, a significant amount of new technology has been used in the telecommunications system. Included in the design are the most recent developments in transponder hardware, an X-band solid state power amplifier (a deep space first ), and several microstrip patch antennas. During spacecraft emergencies, a microstrip array antenna becomes an integral part of a unique acquisition algorithm used to find the earth, similar to a search radar concept. To complement the flight hardware development, a comprehensive set of RF ground support equipment (RF GSE) has been developed. Also discussed are areas for potential technology improvements for future missions