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At least 163 records · Page 9

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NASA NTRS1983

Dust particles in the anomalous tail of Comet Kohoutek (1973 XII)

Intermediate results from theoretical models of the anomalous spikelike dust distribution observed in the tail of Comet Kohoutek using the Skylab white-light coronograph on December 28.996, 1973, are reported. The time evolution is studied using the model of Finson and Probstein (1968) and assuming power-law variation of the dust-production rate and the particle-size distribution. Brightness profiles are calculated and presented graphically for comparison with those derived from the observation photograph: the model predicts a longer duration of the spike phenomenon than was observed. It is shown qualitatively that this discrepancy can be removed by introducing a finite dust-emission velocity (e.g., 1 m/s) into the model.

Keller, H. U.↗

NASA NTRS1985

Space Station Spartan study

The required extension, enhancement, and upgrading of the present Spartan concept are described to conduct operations from the space station using the station's unique facilities and operational features. The space station Spartan (3S), the free flyer will be deployed from and returned to the space station and will conduct scientific missions of much longer duration than possible with the current Spartan. The potential benefits of a space station Spartan are enumerated. The objectives of the study are: (1) to develop a credible concept for a space station Spartan; and (2) to determine the associated requirements and interfaces with the space station to help ensure that the 3S can be properly accommodated.

Lane, J. H.↗

NASA NTRS1983

The isotopic composition of helium at high rigidities

The isotopic abundance distribution of the cosmic radiation at energies beyond 1 GeV/AMU can at the present time be determined only with the geomagnetic method. A balloon-borne instrument was flown for 12 hours near the geomagnetic equator to measure the relative abundance of the helium isotopes He-3 and He-4 around 12 GV rigidity. The sharp rigidity cut-off at equatorial latitudes permitted separation of the two isotopes using a high-resolution-gas Cerenkov counter. The experiment thus confirms the predicted sharp cut-off at those latitudes and demonstrates the potential for isotopic separation of other elements, once flights of longer duration can be made.

Jordan, S. P.↗

NASA NTRS1986

Nucleation experiments in a microgravity environment

A simple experimental apparatus is described in which a wide variety of vapor phase nucleation studies of refractory materials could be performed aboard NASA's KC-135 Research Aircraft. The chief advantage of a microgravity environment for these studies is the expected absence of thermally driven convective motions in the gas. The absence of convection leads to much more accurate knowledge of both the temperature distribution in the system and the time evolution of the refractory vapor concentration as a function of distance from the crucible.The evolution of the apparatus will be described as more experience is gained with the microgravity environment. Such experiments will be used to prepare for similar ones carried out aboard either the shuttle or Space Station where considerably longer duration experiments are possible.

Nuth, J. A.↗

NASA NTRS1986

Acoustic penetration and impact detector for micrometeoroid and space debris application

The Two-Stage Acoustic Penetration and Impact Detector is a simple device for measuring the impact event time, the projectile velocity, the flight path direction and the momentum. The results of laboratory tests have shown that this detector can be used in a wide range of projectile size and velocity. According to measurement purposes the size of the detection area, the distance between the front foil and the target plate and the number of microphones as well as the evaluation procedure can easily be adjusted. The target plate area can also be replaced by another foil detector, if two penetration stages are preferred. This active detector is suitable for a variety of applications in meteoroid and space debris exploration. It can also be supplied with capture cell properties for chemical analysis of inside-deposits. Therefore, this measurement principal has been taken into consideration as a possible flight experiment for instance for a later Longer Duration Exposure Facility (LDEF) flight or future space station activities.

Kuzcera, H.↗

NASA NTRS1985

Mars missions and bases - A recent look

This paper discusses some of the key options for Mars programs, missions, bases, elements, and systems. Program and mission options include Mars flyby, orbiting, and landing missions; they include near-term 'sortie' missions, and later, longer-duration Mars-base missions. Key program and mission parameters include the mix of manned/unmanned elements, the number and types of space vehicles used, types of science done, trajectory options and implications launch timing and schedules, etc. The key mission parameters strongly affect the nature, sizing, and quantity of earth-to-orbit (ETO) vehicles. On-orbit assembly of space vehicles (SVs) is also an important related consideration. The potential degree of utilization of the Space Station (SS) and other then-existing elements is a key question, and several possibilities are discussed in this paper. Several configurations of SVs are provided. Several options are identified for the Mars base infra-structure, and parametric data is shown for buildup of bases as a function of mission and vehicle type. Technologies required for the missions are also discussed.

Butler, J. M., Jr.↗

NASA NTRS1986

Comparison of stratospheric air parcel trajectories calculated from SSU and LIMS satellite data

Midstratospheric trajectories for February and March 1979 are calculated using geopotential analyses derived from limb infrared monitor of the stratosphere data. These trajectories are compared with the corresponding results using stratospheric sounding unit data. The trajectories are quasi-isentropic in that a radiation scheme is used to simply cross-isentrope flow. The results show that in disturbed conditions, quantitative agreement the trajectories, that is, within 25 great circle degrees (GCD) (one GCD about 110 km) may be valid for only 3 or 4 days, whereas during quiescent periods, quantitative agreement may last up to 10 days. By comparing trajectories calculated with different data some insight can be gained as to errors due to vertical resolution and horizontal resolution (due to infrequent sampling) in the analyzed geopotential height fields. For the disturbed trajectories described in this paper the horizontal resolution of the data was more important than vertical resolution; however, for the quiescent trajectories, which could be calculated accurately for a longer duration because of the absence of appreciable transients, the vertical resolution of the data was found to be more important than the horizontal resolution. It is speculated that these characteristics are also applicable to trajectories calculated during disturbed and quiescent periods in general. A review of some recently published trajectories shows that the qualitative conclusions of such works remains unaffected when the calculations are repeated using different data.

Austin, J.↗

NASA NTRS1986

A manned Mars mission concept with artificial gravity

A series of simulated manned Mars missions was analyzed by a computer model. Numerous mission opportunities and mission modes were investigated. Sensitivity trade studies were performed of the vehicle all-up mass and propulsion stage sizes as a function of various levels of conservatism in mission velocity increment margins, payload mass and propulsive stage characteristics. The longer duration but less energetic type of conjunction class mission is emphasized. The specific mission opportunity reviewed was for a 1997 departure. From the trade study results, a three and one-half stage vehicle concept evolved, utilizing a Trans-Mars Injection (TMI) first stage derived from the Space Shuttle External Tank (ET).

Hubert P Davis↗

NASA NTRS1986

Model for the 5 March 1979 gamma-ray transient

A model is proposed for the March 5, 1979 gamma-ray transient. A small lump of strange matter, previously ejected from a supernova explosion, struck a slowly rotating strange star. This resulted in a high-intensity flash of radiation from a hot spot produced by the impact. The high-intensity radiation blew open a crater in the crust; the energy released as this crater refilled was responsible for the longer-duration, lower-intensity phase. The 8-s modulation is due to the rotation of the star. A plausible scenario for the production of this event is discussed.

Alcock, Charles↗

NASA NTRS1987

The determination of nutritional requirements for Safe Haven Food Supply System (emergency/survival foods)

The Space Station Safe Haven Food System must sustain 8 crew members under emergency conditions for 45 days. Emergency Survival Foods are defined as a nutritionally balanced collection of high density food and beverages selected to provide for the survival of Space Station flight crews in contingency situations. Since storage volume is limited, the foods should be highly concentrated. A careful study of different research findings regarding starvation and calorie restricted diets indicates that a minimum nutritional need close to RDA is an important factor for sustaining an individual's life in a stressful environment. Fat, protein, and carbohydrates are 3 energy producing nutrients which play a vital role in the growth and maintenance process of human life. A lower intake of protein can minimize the water intake, but it causes a negative nitrogen balance and a lower performance level. Other macro and micro nutrients are also required for nutritional interrelationships to metabolize the other 3 nutrients to their optimum level. The various options for longer duration than 45 days are under investigation.

Ahmed, Selina↗

NASA NTRS1988

Cardiovascular effects of weightlessness and ground-based simulation

A large number of animal and human flight and ground-based studies were conducted to uncover the cardiovascular effects of weightlessness. Findings indicate changes in cardiovascular function during simulations and with spaceflight that lead to compromised function on reambulation and/or return to earth. This altered state termed cardiovascular deconditioning is most clearly manifest when in an erect body state. Hemodynamic parameters inidicate the presence of excessive tachnycardia, hypotension (leading to presyncope in one-third of the subjects), decreased heart volume, decreased plasma and circulating blood volumes and loss of skeletal muscle mass, particularly in the lower limbs. No clinically harmful effects were observed to date, but in-depth follow-ups were limited, as was available physiologic information. Available data concerning the causes for the observed changes indicate significant roles for mechanisms involved with body fluid-volume regulation, altered cardiac function, and the neurohumoral control of the control of the peripheral circulation. Satisfactory measures are not found. Return to preflight state was variable and only slightly dependent on flight duration. Future progress awaits availability of flight durations longer than several weeks.

Sandler, Harold↗

NASA NTRS1988

The heating environment during Martian atmospheric descent

It has been shown that a vehicle with a lift/drag ratio of 2.3 entering the Martian atmosphere at parabolic speed of 5 km/sec, or from a low orbit at 3.5 km/sec, has a very large landing footprint. At the 5-km/sec entry speed, the trajectory exhibits large skipping motions; however, a lateral range of up to 3300 km is attainable. The entries from low satellite orbit yield a gliding lateral range of 2500 km. The distances correspond to latitude changes of 57 and 42 deg, respectively. The high-speed, skipping entries were accompanied by the most intense heating. The peak stagnation point convective rates varied from 59 W/sq cm to 88 W/sq cm for partially and fully catalytic walls, respectively; the corresponding equilibrium wall temperatures were 1900 K and 2100 K. The peak heating at a wing leading-edge point reached 50 W/sq cm because of the presence of a transitional boundary layer. The lower-speed, gliding entries experienced much milder heating with a peak stagnation point rate of about 14 W/sq cm, resulting in a wall temperature near 1300 K. However, the longer duration of the gliding entries resulted in comparable heat loads for both entry speeds. The highest heat loads approached values experienced by the Shuttle orbiter stagnation point during a typical entry.

Tauber, Michael E.↗

NASA NTRS1988

Nuclear propulsion: A vital technology for the exploration of Mars and the planets beyond

The physics and technology issues and performance potential of various direct thrust fission and fusion propulsion concepts are examined. Next to chemical propulsion the solid core fission thermal rocket (SCR) is the olny other concept to be experimentally tested at the power (approx 1.5 to 5.0 GW) and thrust levels (approx 0.33 to 1.11 MN) required for manned Mars missions. With a specific impulse of approx 850 s, the SCR can perform various near-Earth, cislunar and interplanetary missions with lower mass and cost requirements than its chemical counterpart. The gas core fission thermal rocket, with a specific power and impulse of approx 50 kW/kg and 5000 s offers the potential for quick courier trips to Mars (of about 80 days) or longer duration exploration cargo missions (lasting about 280 days) with starting masses of about 1000 m tons. Convenient transportation to the outer Solar System will require the development of magnetic and inertial fusion rockets (IFRs). Possessing specific powers and impulses of approx 100 kW/kg and 200-300 kilosecs, IFRs will usher in the era of the true Solar System class speceship. Even Pluto will be accessible with roundtrip times of less than 2 years and starting masses of about 1500 m tons.

Borowski, Stanley K.↗

NASA NTRS1988

Variable polarization in X-ray binaries - HD 77581 (= 4U 0900-40)

Variable linear polarization has been observed from the X-ray binary system HD 77581 (= 4U 0900-40). These observations, together with observations of HD 153919 (= 4U 1700-37) and HD 152667, have been analyzed by the method of Brown et al. (1978). A polarimetric analysis should include only observations made over a time during which the scattering region producing the polarization does not change its structure. It is found that this time is typically on the order of 10 days for systems with OB supergiant primaries. An observation set compiled over a longer duration can introduce systematic errors into the derived parameters. The orbital and physical properties of HD 153919 and HD 152667 analyzed under these constraints are consistent with those derived from polarimetric observations taken 4 years earlier.

Dolan, J. F.↗

NASA NTRS1989

Recent results in the NASA research balloon program

The NASA Balloon Program has progressed from a total hiatus in the fall of 1985 to an unprecedented flight success rate in the fall of 1988. Using heavy-lift balloons being regularly supplied by two manufacturers, the program has provided a timely response for investigations of Supernova 1987A from Australia, low energy cosmic ray investigations from Canada during periods of near-solar-minimum, and routine domestic turnaround flights for a variety of investigations. Recent re-evaluation of balloon flight-safety have resulted in severe constraints on flights launched from the Palestine, Texas facility. The future program must rely heavily on the use of remote launch sites to meet the growing requirements for more frequent and longer duration flights being planned for the next 3 - 5 years.

Jones, W. Vernon↗

NASA NTRS1989

Analysis of an algae-based CELSS. II - Options and weight analysis

Life support components are evaluated for application to an idealized closed life support system which includes an algal reactor for food production. Weight-based trade studies are reported as 'break-even' time for replacing food stores with a regenerative bioreactor. It is concluded that closure of the life support gases (oxygen recovery) depends on the carbon dioxide reduction chemistry and that an algae-based food production can provide an attractive alternative to re-supply for longer duration missions.

Holtzapple, Mark T.↗

NASA NTRS1989

The Rapid Geodetic Survey System (RGSS)

The Rapid Geodetic Survey System (RGSS) is a system employing a high-accuracy gimbaled inertial platform. It provides a cost-effective capability for accurate direct measurement of the change in position, elevation, gravity intensity and deflection of the vertical from an initial point. The RGSS is an adaptation of the production version of the U.S. Army Position and Azimuth Determining System (PADS). Several hardware and software enhancements to improve the performance of the system, primarily for gravity vector survey, have occurred over the last few years. The basic principles for the control of error in the survey measurements due to noise and systematic error are discussed below. Actual acceptance test results for the RGSS which indicate an inherent capability of the system to measure change in the deflection of the vertical to a few-tenths of an arcsecond over survey periods of one to two hours using careful survey techniques are also presented. Finally a simple method to extend the capability of the system for longer duration surveys is indicated.

Huddle, J. R.↗

NASA NTRS1989

Nuclear propulsion - A vital technology for the exploration of Mars and the planets beyond

The physics and technology issues and performance potential of various direct thrust fission and fusion propulsion concepts are examined. Next to chemical propulsion the solid core fission thermal rocket (SCR) is the only other concept to be experimentally tested at the power (approx 1.5 to 5.0 GW) and thrust levels (approx 0.33 to 1.11 MN) required for manned Mars missions. With a specific impulse of approx 850 s, the SCR can perform various near-earth, cislunar and interplanetary missions with lower mass and cost requirements than its chemical counterpart. The gas core fission thermal rocket, with a specific power and impulse of approx 50 kW/kg and 5000 s offers the potential for quick courier trips to Mars (of about 80 days) or longer duration exploration cargo missions (lasting about 280 days) with starting masses of about 1000 m tons. Convenient transportation to the outer Solar System will require the development of magnetic and inertial fusion rockets (IFRs). Possessing specific powers and impulses of approx 100 kW/kg and 200-300 kilosecs, IFRs will usher in the era of the true Solar System class spaceship. Even Pluto will be accessible with roundtrip times of less than 2 years and starting masses of about 1500 m tons.

Borowski, Stanley K.↗