450 research outputs found

    Research on gravitational mass sensors Research contract status report, 15 Sep. - 15 Oct. 1965

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    Gravitational mass sensor - piezoresistive and barium titanate transducers, and torsional stress sensor

    Light levitated geostationary cylindrical orbits are feasible

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    This paper discusses a new family of non-Keplerian orbits for solar sail spacecraft displaced above or below the Earth's equatorial plane. The work aims to prove the assertion in the literature that displaced geostationary orbits exist, possibly to increase the number of available slots for geostationary communications satellites. The existence of displaced non-Keplerian periodic orbits is ÂŻrst shown analytically by linearization of the solar sail dynamics around a geostationary point. The full displaced periodic solution of the non-linear equations of motion is then obtained using a Hermite-Simpson collocation method with inequality path constraints. The initial guess to the collocation method is given by the linearized solution and the inequality path constraints are enforced as a box around the linearized solution. The linear and nonlinear displaced periodic orbits are also obtained for the worst-case Sun-sail orientation at the solstices. Near-term and high-performance sails can be displaced between 10 km and 25 km above the Earth's equatorial plane during the summer solstice, while a perforated sail can be displaced above the usual station-keeping box (75 ÂŁ 75 km) of nominal geostationary satellites. Light-levitated orbit applications to Space Solar Power are also considered

    Research on gravitational mass sensors Quarterly progress report no. 1, 15 Oct. 1964 - 14 Jan. 1965

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    Lunar orbiter and deep space probe gravitational sensor for determining mass distribution of moon and asteroid

    Research on gravitational mass sensors quarterly progress report no. 2, 15 jan. - 14 apr. 1965

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    Cruciform sensor head, phase shift tuned amplifier, and air bearing support for sensor for detecting presence of small moving mass through gravitational interaction

    Rotating gravity gradiometer study

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    Two rotating gravity gradiometer (RGG) sensors, along with all the external electronics needed to operate them, and the fixtures and special test equipment needed to fill and align the bearings, were assembled in a laboratory, and inspected. The thermal noise threshold of the RGG can be lowered by replacing a damping resistor in the first stage electronics by an active artificial resistor that generates less random voltage noise per unit bandwidth than the Johnson noise from the resistor it replaces. The artificial resistor circuit consists of an operational amplifier, three resistors, and a small DC to DC floating power supply. These are small enough to be retrofitted to the present circuit boards inside the RGG rotor in place of the 3 Megohm resistor. Using the artificial resistor, the thermal noise of the RGG-2 sensor can be lowered from 0.3 Eotvos to 0.15 Eotvos for a 10 sec integration time

    Advanced propulsion concepts study: Comparative study of solar electric propulsion and laser electric propulsion

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    Solar electric propulsion (SEP) and laser electric propulsion (LEP) was compared. The LEP system configuration consists of an 80 kW visible laser source on earth, transmitting via an 8 m diameter adaptively controlled phased array through the atmosphere to a 4 m diameter synchronous relay mirror that tracks the LEP spacecraft. The only significant change in the SEP spacecraft for an LEP mission is the replacement of the two 3.7 m by 33.5 m solar cell arrays with a single 8 m diameter laser photovoltaic array. The solar cell array weight is decreased from 320 kg to 120 kg for an increase in payload of 200 kg and a decrease in specific mass of the power system from 20.5 kg/kW to 7.8 kg/kW

    Interference of parallel cylindrical Langmuir probes

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    Current to a cylindrical probe of arbitrary cross section is discussed. Previous results for circular cylinders at the high bias and moderate radius R of interest for electrodynamic bare tethers, for which space charge may be ignored over a large neighborhood of the probe, depend in separate ways on both R and perimeter p. These results are extended to a general convex cross section by introducing certain equivalent radius Req. For any concave cross section, results use a proper equivalent perimeter peq , in addition to Req. Finally, for the joint cross section of separate parallel probes, certain effective perimeter peff replaces peq. Rules to determine Req. peq. and peff are used to discuss collection interference among two or more parallel cylinders when brought from far away to contac

    Development of a rotating gravity gradiometer for earth orbit applications (AAFE)

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    Some preliminary mission studies are described along with the design, fabrication, and test of a breadboard model of an earth orbital, rotating gravity gradiometer with a design goal of 10 to the minus 11th power/sec sq (0.01 EU) in a 35-sec integration time. The proposed mission uses a Scout vehicle to launch one (or two orthogonally oriented) spin-stabilized satellites into a 330-km circular polar orbit some 20 days before an equinox. During the short orbital lifetime, the experiment would obtain two complete maps of the gravity gradient field with a resolution approaching 270 km (degree 75). The breadboard model of the gradiometer demonstrated a combined thermal and electronic noise threshold of 0.015 EU per data channel. The design changes needed to reduce the noise to less than 0.01 EU were identified. Variations of the sensor output signal with temperature were experimentally determined and a suitable method of temperature compensation was developed and tested. Other possible error sources, such as sensor interaction with satellite dynamics and magnetic fields, were studied analytically and shown to be small

    A novel interplanetary communications relay

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    A case study of a potential Earth-Mars interplanetary communications relay, designed to ensure continuous communications, is detailed. The relay makes use of orbits based on artificial equilibrium points via the application of continuous low thrust, which allows a spacecraft to hover above the orbital plane of Mars and thus ensure communications when the planet is occulted with respect to the Earth. The artificial equilibria of two different low-thrust propulsion technologies are considered: solar electric propulsion, and a solar sail/solar electric propulsion hybrid. In the latter case it is shown that the combination of sail and solar electric propulsion may prove advantageous, but only under specific circumstances of the relay architecture suggested. The study takes into account factors such as the spacecraft's power requirements and communications band utilized to determine the mission and system architecture. A detailed contingency analysis is considered for recovering the relay after increasing periods of spacecraft motor failure, and combined with a consideration for how best to deploy the relay spacecraft to maximise propellant reserves and mission duration