286 research outputs found
An investigation of some effects of mach number and air temperature on the hypersonic flow over a blunt body
Mach number and air temperature effect on hypersonic flow over blunt bodie
Future exploration of Venus (post-Pioneer Venus 1978)
A comprehensive study was performed to determine the major scientific unknowns about the planet Venus to be expected in the post-Pioneer Venus 1978 time frame. Based on those results the desirability of future orbiters, atmospheric entry probes, balloons, and landers as vehicles to address the remaining scientific questions were studied. The recommended mission scenario includes a high resolution surface mapping radar orbiter mission for the 1981 launch opportunity, a multiple-lander mission for 1985 and either an atmospheric entry probe or balloon mission in 1988. All the proposed missions can be performed using proposed space shuttle upper stage boosters. Significant amounts of long-lead time supporting research and technology developments are required to be initiated in the near future to permit the recommended launch dates
Pioneer Venus 12.5 km Anomaly Workshop Report, volume 1
A workshop was convened at Ames Research Center on September 28 and 29, 1993, to address the unexplained electrical anomalies experienced in December 1978 by the four Pioneer Venus probes below a Venus altitude of 12.5 km. These anomalies caused the loss of valuable data in the deep atmosphere, and, if their cause were to remain unexplained, could reoccur on future Venus missions. The workshop participants reviewed the evidence and studied all identified mechanisms that could consistently account for all observed anomalies. Both hardware problems and atmospheric interactions were considered. Based on a workshop recommendation, subsequent testing identified the cause as being an insulation failure of the external harness. All anomalous events are now explained
Thermal structure in the Venus middle cloud layer
Thermal structure measurements obtained by the two Vega balloons show the Venus atmosphere in the middle cloud layer to be near-adiabatic, on the whole; but discrete air masses are present that differ slightly from one another in potential temperature and entropy. The Vega 1 temperatures are 6.5 K warmer than measured by Vega 2 at given pressures. Measurements taken by the Vega 2 lander on descent through these levels agree with the Vega 2 balloon data
Dayside thermal structure of Venus' upper atmosphere characterized by a global model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94843/1/jgre3057.pd
Implications of Preliminary VEGA Balloon Results for the Venus Atmosphere Dynamics
The typical 1-2 m/sec vertical winds encountered by the Vega balloons probably result from thermal
convection. The consistent 6.5-kelvin differential between the Vega 1 and Vega 2 temperatures is attributable
to disturbances of synoptic or planetary scale. According to the Doppler tracking the winds were stronger
than on earlier missions, perhaps because of solar thermal tides. The motions of Vega 2 may have been
affected by waves from mountainous terrain
Meteorological Data Along the VEGA-1 and VEGA-2 Float Paths
During their flight through the Venus atmosphere
the Vega 1 and Vega 2 balloon craft measured
the pressure and temperature of the ambient
medium, the vertical wind-velocity component (relative
to the gondola), the cloud-layer backscatter
coefficient, the mean illumination level, and the number
and time of possible lightning flashes. In addition, the ground radio telescope network measured
the balloon positions and drift velocities by the differential
VLBI technique; these data are now being
processed
Significance Tests for Periodogram Peaks
We discuss methods currently in use for determining the significance of peaks
in the periodograms of time series. We discuss some general methods for
constructing significance tests, false alarm probability functions, and the
role played in these by independent random variables and by empirical and
theoretical cumulative distribution functions. We also discuss the concept of
"independent frequencies" in periodogram analysis. We propose a practical
method for estimating the significance of periodogram peaks, applicable to all
time series irrespective of the spacing of the data. This method, based on
Monte Carlo simulations, produces significance tests that are tailor-made for
any given astronomical time series.Comment: 22 pages, 11 Encapsulated Postscript figures, AAS LaTeX v5.2
Submitted to Ap
Computations of Viking Lander Capsule Hypersonic Aerodynamics with Comparisons to Ground and Flight Data
Comparisons are made between the LAURA Navier-Stokes code and Viking Lander Capsule hypersonic aerodynamics data from ground and flight measurements. Wind tunnel data are available for a 3.48 percent scale model at Mach 6 and a 2.75 percent scale model at Mach 10.35, both under perfect gas air conditions. Viking Lander 1 aerodynamics flight data also exist from on-board instrumentation for velocities between 2900 and 4400 m/sec (Mach 14 to 23.3). LAURA flowfield solutions are obtained for the geometry as tested or flown, including sting effects at tunnel conditions and finite-rate chemistry effects in flight. Using the flight vehicle center-of-gravity location (trim angle approx. equals -11.1 deg), the computed trim angle at tunnel conditions is within 0.31 degrees of the angle derived from Mach 6 data and 0.13 degrees from the Mach 10.35 trim angle. LAURA Mach 6 trim lift and drag force coefficients are within 2 percent of measured data, and computed trim lift-to-drag ratio is within 4 percent of the data. Computed trim lift and drag force coefficients at Mach 10.35 are within 5 percent and 3 percent, respectively, of wind tunnel data. Computed trim lift-to-drag ratio is within 2 percent of the Mach 10.35 data. Using the nominal density profile and center-of-gravity location, LAURA trim angle at flight conditions is within 0.5 degrees of the total angle measured from on-board instrumentation. LAURA trim lift and drag force coefficients at flight conditions are within 7 and 5 percent, respectively, of the flight data. Computed trim lift-to-drag ratio is within 4 percent of the data. Computed aerodynamics sensitivities to center-of-gravity location, atmospheric density, and grid refinement are generally small. The results will enable a better estimate of aerodynamics uncertainties for future Mars entry vehicles where non-zero angle-of-attack is required
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