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Elrod, B. D.

Publications and source records attributed to Elrod, B. D..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

TDRSS Onboard Navigation System (TONS) experiment for the Explorer Platform (EP)

A TDRSS Onboard Navigation System (TONS) is currently being developed by NASA to provide a high-accuracy autonomous spacecraft navigation capability for users of TDRSS and its successor, the Advanced TDRSS. A TONS experiment will be performed in conjunction with the Explorer Platform (EP)/EUV Explorer mission to flight-qualify TONS Block I. This paper presents an overview of TDRSS on-board navigation goals and plans and the technical objectives of the TONS experiment. The operations concept of the experiment is described, including the characteristics of the ultrastable oscillator, the Doppler extractor, the signal-acquisition process, the TONS ground-support system, and the navigation flight software. A description of the on-board navigation algorithms and the rationale for their selection is also presented.

Gramling, C. J.↗
NASA NTRS1990

One-way return-link Doppler navigation with the Tracking and Data Satellite System (TDRSS) - The ultrastable oscillator (USO) experiment on the Cosmic Background Explorer (COBE)

The principal objectives of the USO experiment on the COBE spacecraft are defined, and results of space qualification studies for the COBE USO experiment are summarized. The principal objectives of the experiment are: (1) to determine flight performance of the USO coupled to the second-generation TDRSS transponder; (2) space qualify TDRSS noncoherent one-way return-link Doppler tracking; and (3) analyze algorithms for one-way navigation with real data. The three objectives of the experiment have been met in the first stage of the experiment analysis.

Dunham, J. B.↗
NASA NTRS1984

Low earth orbit navigation in the TDAS era

It is pointed out that by the 1990s projected increases in scientific data volume and spacecraft engineering data will require an extension of the Tracking and Data Relay Satellite System (TDRSS). There will also be requirements with respect to improvements related to navigation. The Tracking Data Acquisition System (TDAS) is defined as the heir to TDRSS for the 1990s and beyond. A pre-Phase A TDAS concept definition study has recently been completed. The study covers a 15 year planning period extending from 1990 to 2005. The present investigation is concerned with TDAS-based alternatives, taking into account aspects of orbit and time determination. Attention is given an overview of TDRSS capabilities, pertiment TDAS architecture options, potential user navigation accuracy requirements, and some results of preliminary navigation performance evaluations.

Elrod, B. D.↗
NASA NTRS1983

Tracking Data Acquisition System (TDAS) for the 1990's. Volume 6: TDAS navigation system architecture

One-way range and Doppler methods for providing user orbit and time determination are examined. Forward link beacon tracking, with on-board processing of independent navigation signals broadcast continuously by TDAS spacecraft; forward link scheduled tracking; with on-board processing of navigation data received during scheduled TDAS forward link service intervals; and return link scheduled tracking; with ground-based processing of user generated navigation data during scheduled TDAS return link service intervals are discussed. A system level definition and requirements assessment for each alternative, an evaluation of potential navigation performance and comparison with TDAS mission model requirements is included. TDAS satellite tracking is also addressed for two alternatives: BRTS and VLBI tracking.

Elrod, B. D.↗
NASA NTRS1983

Tracking and data acquisition system for the 1990's. Volume 8: TDAS frequency planning

Current planning calls for the TDAS to support new user and crosslink services, in addition to TDRSS-compatible services. TDRSS-compatible services would operate in current S-band and K-band channels used by TDRSS. New services, however, can take advantage of technology advances at microwave and optical frequencies. For augmented space-to-space services, 60 GHz and GaAs laser systems offer technical advantages, relative freedom from RFI, and a benign regulatory environment (i.e., minimal congestion and, in the case of 60 GHz, maximum regulatory support for TDAS-type services). For TDAS Earth-to-space and space-to-Earth services, the 30/20 GHz band offers the best mix of technical and regulatory advantages. But use of these bands would have to be coordinated with the U.S. military.

Heppe, S. B.↗
NASA NTRS1972

A quasi-inertial attitude mode for orbiting spacecraft.

A method is presented for achieving quasi-inertial orientation of an orbiting spacecraft with minimal control effort. Spacecraft motion is a small-amplitude oscillation about the orbit normal with one principal axis held in the orbital plane. The nominal orientation of this axis is arbitrary, so that any spacecraft axis normal to it may be pointed arbitrarily on the celestial sphere and remain within a small neighborhood of the nominal orientation. Oscillation amplitude can be chosen to minimize control requirements for maintaining the mode and may range up to 18.8 deg depending on spacecraft inertia. The quasi-inertial mode would be an efficient means for maintaining a nominal solar orientation for NASA's Skylab configuration if the control-moment-gyros fail in the primary attitude control system. This approach, which utilizes the backup reaction thrust system, affords a substantial reduction in propellant requirements compared to that for a true solar inertial attitude hold.

Elrod, B. D.↗
NASA NTRS1972

Equilibrium properties of the Skylab CMG rotation law

The equilibrium properties of the control moment gyroscopes of the Skylab are discussed. A rotation law is developed to produce gimbal rates which distribute the angular momentum contributions among the control moment gyroscopes to avoid gimbal stop encounters. The implications for gimbal angle management under various angular momentum situations are described. Conditions were obtained for the existence of equilibria and corresponding stability properties.

Elrod, B. D.↗
NASA NTRS1971

The quasi-inertial and wide-deadband modes as backup attitude options for the Skylab mission

The quasi-inertial (QI) and wide deadband (WDB) modes were investigated as alternatives to the solar inertial (SI) mode in case two control moment gyros fail during the Skylab mission. Both modes provide a substantial reduction in propellant requirements from the solar interial hold requirement with either the orbital assembly/thruster attitude control system or service module reaction control system. Spacecraft motion in the QI mode is produced by a command rate and results in a small amplitude oscillation (17 deg, maximum) about the SI orientation. In the WDB mode a somewhat similar, but larger amplitude motion (35 deg maximum) about the SI orientation is developed by appropriate choice of controller deadbands and switch line slopes.

Elrod, B. D.↗