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Reports of workshops on Probe Measurements of Particles and Radiation in the Atmosphere of Titan

The planned 1995 joint ESA-NASA Cassini mission to the Saturnian system will include an atmospheric probe to be dropped into the atmosphere of Titan for in situ measurements during descent. Because of the unique properties of the Titan atmosphere it is necessary to consider the peculiar requirements for such measurements and applicable techniques. The proceedings of two workshops dealing with the measurement of particles and radiation in the atmosphere of Titan are presented in two parts. The first part dealt with the measurement of particulate matter in the atmosphere of Titan. The second part dealt with the measurement of radiation in the atmosphere of Titan. The proceedings were first published and distributed informally, and are presented with only minor editorial changes. In the report of the particulate matter workshop, discussions of the mission background, the importance of the measurements, and descriptions of the desired information are followed by a description of appropriate measurement techniques and conclusions and recommendations. The proceeding for the workshop on radiation measurement and imaging contains a discussion of the importance of radiation measurements and imaging, and presents a summary of participants' experience with such measurements made from entry probes. This is followed by a description of appropriate measurement techniques and conclusions and recommendations.

Ragent, Boris↗

Titan aerosol and gas experiment for the Huygens Probe

The Cassini Mission is a joint undertaking of NASA and the European Space Agency (ESA) to explore the Saturnian System with a Saturn Orbiter and a Titan Probe. The launch vehicle and the Saturn Orbiter are the responsibility of NASA while the Huygens Probe (detachable Titan Probe) is the responsibility of ESA. The spacecraft will be launched in 1996 and the Huygens Probe will arrive at Titan in 2003. The Cassini Mission-Huygens Probe provides a unique opportunity to obtain detailed information about the atmosphere and, possibly, the surface of Titan. Titan possesses a substantial nitrogen atmosphere containing methane and many other organic compounds. Aerosols play an important role in the atmospheric processes on Titan. The Huygens Probe offers an opportunity to determine how organic particles are formed and grow which will clarify their role on Earth. A powerful analytical instrument, capable of addressing the above technology and other science questions, was recently proposed for the Huygens Probe. It is comprised of an aerosol and gas sampler and processor, and a gas chromatograph-ion mobility spectrometer. The instrument will be able to measure complex organics that make up the collected aerosols to the approximate 1 ppm level. Gases will be measured to approximately 10 ppb. Because the Titan atmosphere is expected to be quite complex, a gas chromatograph-ion mobility spectrometer is used to provide unequivocal identification of the components of the analytes. Further details of the science question to be investigated and the proposed instrument are described. The expected results and their implications are also addressed.

Carle, G. C.↗

Mass Spectrometers in Space!

Exploration of our solar system over several decades has benefitted greatly from the sensitive chemical analyses offered by spaceflight mass spectrometers. When dealing with an unknown environment, the broadband detection capabilities of mass analyzers have proven extremely valuable in determining the composition and thereby the basic nature of space environments, including the outer reaches of Earth s atmosphere, interplanetary space, the Moon, and the planets and their satellites. Numerous mass analyzer types, including quadrupole, monopole, sector, ion trap, and time-of-flight have been incorporated in flight instruments and delivered robotically to a variety of planetary environments. All such instruments went through a rigorous process of application-specific development, often including significant miniaturization, testing, and qualification for the space environment. Upcoming missions to Mars and opportunities for missions to Venus, Europa, Saturn, Titan, asteroids, and comets provide new challenges for flight mass spectrometers that push to state of the art in fundamental analytical technique. The Sample Analysis at Mars (SAM) investigation on the recently-launch Mars Science Laboratory (MSL) rover mission incorporates a quadrupole analyzer to support direct evolved gas as well as gas chromatograph-based analysis of martian rocks and atmosphere, seeking signs of a past or present habitable environment. A next-generation linear ion trap mass spectrometer, using both electron impact and laser ionization, is being incorporated into the Mars Organic Molecule Analyzer (MOMA) instrument, which will be flown to Mars in 2018. These and other mass spectrometers and mission concepts at various stages of development will be described.

Brinckerhoff, William B.↗

Theoretical Calculations on Sediment Transport on Titan, and the Possible Production of Streamlined Forms

The Cassini Imaging Science System (ISS) has been returning images of Titan, along with other Saturnian satellites. Images taken through the 938 nm methane window see down to Titan's surface. One of the purposes of the Cassini mission is to investigate possible fluid cycling on Titan. Lemniscate features shown recently and radar evidence of surface flow prompted us to consider theoretically the creation by methane fluid flow of streamlined forms on Titan. This follows work by other groups in theoretical consideration of fluid motion on Titan's surface.

Burr, D. M.↗

Analysis of aerothermodynamic environment of a Titan aerocapture vehicle

The feasibility of an aerocapture vehicle mission has been emphasized recently for inner and outer planetary missions. Aerocapture involves a system concept which utilizes aerodynamic drag to acquire the velocity reduction necessary to obtain a closed planetary orbit from a hyperbolic flyby trajectory. It has been proposed to use the atmosphere of Titan for braking into a Saturn orbit. This approach for a Saturn orbital mission is expected to cut the interplanetary cruise travel time to Saturn from 8 to 3.5 years. In connection with the preparation of such a mission, it will be necessary to provide a complete analysis of the aerodynamic environment of the Titan aerocapture vehicle. The main objective of the present investigation is, therefore, to determine the extent of convective and radiative heating for the aerocapture vehicle under different entry conditions. This can be essentially accomplished by assessing the heating rates in the stagnation and windward regions of an equivalent body.

Tiwari, S. N.↗

Titan Probe navigation analysis

In the proposed Cassini mission, a combined Saturn Orbiter/Titan Probe spacecraft will be launched from the Space Shuttle to arrive at Saturn around 2002, by means of a delta-VEGA trajectory. After Saturn-orbit insertion and a pericrone raise maneuver, the probe will be released to enter the Titan atmosphere and impact onto its surface. During its descent phase and impact onto Titan, the probe will maintain radio contact with the orbiter. Since the Titan-probe experimental phase lasts for only about four hours, probe-orbiter geometry and probe-delivery accuracy are critical to successful completion of this part of the mission. From a preliminary navigation analysis for probe delivery accuracy, it seems feasible to deliver the probe within 50 km (1-sigma value) of the desired aim-point in the Titan B-plane. The covariance study, however, clearly indicates the need for optical data, in addition to radio metric data. A Monte Carlo study indicates that a Delta-V capability of 98 m/sec for trajectory correction maneuvers will be sufficient to cover 99 percent of all contingencies during the segment from Saturn-orbit insertion to Titan-probe release.

Vijayaraghavan, A.↗

Cryogenic Propulsion for the Titan Orbiter Polar Surveyor

Liquid hydrogen (LH2) and liquid oxygen (LO2) cryogenic propellants can dramatically enhance NASA sability to explore the solar system due to their superior specific impulse (Isp) capability. Although these cryogenic propellants can be challenging to manage and store, they allow significant mass advantages over traditional hypergolic propulsion systems and are therefore enabling for many planetary science missions. New cryogenic storage techniques such as sub-cooling and the use of advanced insulation and low thermal conductivity support structures will allow for the long term storage and use of cryogenic propellants for solar system exploration and hence allow NASA to deliver more payloads to targets of interest, launch on smaller and less expensive launch vehicles, or both. These new cryogenic storage technologies were implemented in a design study for the Titan Orbiter Polar Surveyor (TOPS) mission, with LH2 and LO2 as propellants, and the resulting spacecraft design was able to achieve a 43 launch mass reduction over a TOPS mission, that utilized a traditional hypergolic propulsion system with monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) propellants. This paper describes the cryogenic propellant storage design for the TOPS mission and demonstrates how these cryogenic propellants are stored passively for a decade-long Titan mission that requires the cryogenics propellants to be stored for 8.5 years.

Cryogenic Propellant Storage↗

Titan In-situ Resource Utilization (ISRU) Sample Return (TISR)

Titan is unique in the outer solar system in that it is the only moon with a thick atmosphere, and the only body in the solar system outside the Earth with liquid seas on its surface. The Titanian oceans, however, are seas of liquid hydrocarbons, and the rocks on the surface are solid water ice. Like other icy Moons of the outer solar system, beneath the ice crust, Titan also has a subsurface ocean. Rodriguez et al. refer to it as the “world with two oceans”, an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. [1] Titan is scientifically fascinating in many ways [2], [3], [4]. The Compass Team will emphasize just one here: Titan is a high priority target for astrobiology [4] [5] [6] [7] [8] [9] [10] [11]. It is a world with a surface and atmosphere rich in the complex organic compounds known as tholins. A detailed understanding of the nature of these complex compounds will require an analysis using a full laboratory on Earth. Because of its value to understanding the organic compounds of the outer solar system which may be the primordial building-blocks of life, return of samples from Titan to laboratories on Earth will be the primary goal of this mission. While this would give unprecedented science return, returning even a small sample from Titan using conventional technology would be tremendously difficult. Saturn is almost a billion miles from the Earth, about thirteen times farther than Mars. A return mission to Saturn requires such a large total-mission ∆V that, with conventional technology, the mass ratios required are prohibitive. Such a sample return would truly be “mission incredible.” But to date, a sample return mission from so distant a target has been assumed to be, not merely incredible, but mission impossible. The Compass Team has proposed [2] [12] that by manufacturing the propellant for the return to Earth using the resources available on Titan, such a mission becomes possible. The task of this report is to show that it is reasonable with credible space technology.

Titan↗

Detection Opportunity for Aromatic Signature in Titan's Aerosols in the 4.1-5.3 μm Range

The Cassini/Huygens mission provided new insights on the chemistry of the upper atmosphere of Titan. The presence of large molecules and ions (>100's of amu) detected by Cassini at high altitude was not expected, and questions the original assumptions regarding the aerosol formation pathways. From recent laboratory studies, it has been shown that the inclusion of trace amounts of aromatic species drastically impacts the chemistry of aerosol formation and induces observable changes in the properties of the aerosols. In this Letter we focus on the effect of one of the simplest nitrogenous aromatics, pyridine (C5H5N), on the infrared signature of Titan's aerosol analogs. We introduce initial gas mixtures of (i) N2–C5H5N (100%/250 ppm), (ii) N2–CH4–C5H5N (99%/1%/250 ppm), and (iii) N2–CH4 (99%/1%) in a cold plasma discharge. The material produced, herein called tholins, is then analyzed by mid-infrared spectroscopy. When adding pyridine in the discharge, the tholins produced present an aromatic signature in the 4.1–5.3 μm (1850–2450 cm−1) spectral region, attributed to overtones of aromatic C–H out-of-plane bending vibrations. We also observe a spectral shift of the nitrile and iso-nitrile absorption band with the inclusion of pyridine in the gas mixture. These results could help to investigate the data obtained at Titan by the Cassini/Visual and Infrared Mapping Spectrometer (VIMS) instrument in the 1–5 μm infrared window.

Mathé, Christophe↗

Optimal orbit transfer for out-of-ecliptic mission using a solar electric spacecraft

This paper analyzes the performance capability of a Titan IIIE/Centaur/SEP (15 kw) for out-of-ecliptic missions. Two classes of orbital transfer modes are considered; circular-to-circular and circular-to-elliptic. The results presented compare the achievable heliographic inclination using these different transfer modes and also show the degradations in performance due to constrained launch azimuth and thruster life. It is observed that the latter transfer mode could deliver a spacecraft to a much higher inclination than the former, but the final orbit is very eccentric and could come very close to the sun. In view of the existence of many trajectories by which this mission can be performed, it is suggested that a trajectory other than IAU circular out-of-ecliptic type be used to explore more scientifically rewarding missions.

Yen, C.-W. L.↗

Fuel-Cell Power Source Based on Onboard Rocket Propellants

The use of onboard rocket propellants (dense liquids at room temperature) in place of conventional cryogenic fuel-cell reactants (hydrogen and oxygen) eliminates the mass penalties associated with cryocooling and boil-off. The high energy content and density of the rocket propellants will also require no additional chemical processing. For a 30-day mission on the Moon that requires a continuous 100 watts of power, the reactant mass and volume would be reduced by 15 and 50 percent, respectively, even without accounting for boiloff losses. The savings increase further with increasing transit times. A high-temperature, solid oxide, electrolyte-based fuel-cell configuration, that can rapidly combine rocket propellants - both monopropellant system with hydrazine and bi-propellant systems such as monomethyl hydrazine/ unsymmetrical dimethyl hydrazine (MMH/UDMH) and nitrogen tetroxide (NTO) to produce electrical energy - overcomes the severe drawbacks of earlier attempts in 1963-1967 of using fuel reforming and aqueous media. The electrical energy available from such a fuel cell operating at 60-percent efficiency is estimated to be 1,500 Wh/kg of reactants. The proposed use of zirconia-based oxide electrolyte at 800-1,000 C will permit continuous operation, very high power densities, and substantially increased efficiency of conversion over any of the earlier attempts. The solid oxide fuel cell is also tolerant to a wide range of environmental temperatures. Such a system is built for easy refueling for exploration missions and for the ability to turn on after several years of transit. Specific examples of future missions are in-situ landers on Europa and Titan that will face extreme radiation and temperature environments, flyby missions to Saturn, and landed missions on the Moon with 14 day/night cycles.

Ganapathi, Gani↗

Titan atmospheric composition by hypervelocity shock layer analysis

The Cassini Mission, a NASA/ESA cooperative project which includes a deployment of probe into the atmosphere of Titan, is described, with particular attention given to the shock radiometer experiment planned for the Titan probe for the analysis of Titan's atmosphere. Results from a shock layer analysis are presented, demonstrating that the mole fractions of the major species (N2, CH4, and, possibly Ar) in the Titan atmosphere can be successfully determined by the Titan-probe radiometer, by measuring the intensity of the CN(violet) radiation emitted in the shock layer during the high velocity portion of the probe entry between 200 and 400 km altitude. It is shown that the sensitivity of the CN(violet) radiation makes it possible to determine the mole fractions of N2, CH4, and Ar to about 0.015, 0.003, and 0.01, respectively, i.e., much better than the present uncertainties in the composition of Titan atmosphere.

Nelson, H. F.↗

Laboratory Studies of Low Temperature Rate Coefficients: The Atmospheric Chemistry of the Outer Planets and Titan

Laboratory measurements have been carried out to determine low temperature chemical rate coefficients of ethynyl radical (C2H) for the atmospheres of the outer planets and their satellites. This effort is directly related to the Cassini mission which will explore Saturn and Titan. A laser-based photolysis/infrared laser probe setup was used to measure the temperature dependence of kinetic rate coefficients from approx. equal to 150 to 350 K for C2H radicals with H2, C2H2, CH4, CD4, C2H4, C2H6, C3H8, n-C4H10, i-C4H10, neo-C5H12, C3H4 (methylacetylene and allene), HCN, and CH3CN. The results revealed discrepancies of an order of magnitude or more compared with the low temperature rate coefficients used in present models. A new Laval nozzle, low Mach number supersonic expansion kinetics apparatus has been constructed, resulting in the first measurements of neutral C2H radical kinetics at 90 K and permitting studies on condensable gases with insufficient vapor pressure at low temperatures. New studies of C 2H with acetylene have been completed.

Bogan, Denis↗

The Saturn Orbiter Dual Probe mission concept

This paper presents the results of a mission design study for NASA of the next Saturn mission to follow Voyager. The Saturn Orbiter Dual Probe (SO2P) mission combines three spacecraft - a Saturn orbiter, a Saturn probe, and a Titan probe/lander - into a multipurpose Saturn exploration package. The mission is to conduct a survey from orbit around Saturn and to physically probe bodies in the Saturnian system, the first such mission to do so. The mission has many possible options including: combining solar electric propulsion with earth gravity assist, assembling of IUS stages in orbit, and aerocapture at Titan to insert into Saturn orbit.

Roberts, P. H., Jr.↗

Design of a Long Endurance Titan VTOL Vehicle

Saturn s moon Titan promises insight into many key scientific questions, many of which can be investigated only by in situ exploration of the surface and atmosphere of the moon. This research presents a vertical takeoff and landing (VTOL) vehicle designed to conduct a scientific investigation of Titan s atmosphere, clouds, haze, surface, and any possible oceans. In this investigation, multiple options for vertical takeoff and horizontal mobility were considered. A helicopter was baselined because of its many advantages over other types of vehicles, namely access to hazardous terrain and the ability to perform low speed aerial surveys. Using a nuclear power source and the atmosphere of Titan, a turbo expander cycle produces the 1.9 kW required by the vehicle for flight and operations, allowing it to sustain a long range, long duration mission that could traverse the majority of Titan. Such a power source could increase the lifespan and quality of science for planetary aerial flight to an extent that the limiting factor for the mission life is not available power but the life of the mechanical parts. Therefore, the mission could potentially last for years. This design is the first to investigate the implications of this potentially revolutionary technology on a Titan aerial vehicle.

Prakash, Ravi↗

Final Environmental Impact Statement for the Galileo Mission (Tier 2)

This Final Environmental Impact Statement (FEIS) addresses the proposed action of completing the preparation and operation of the Galileo spacecraft, including its planned launch on the Space Transportation System (STS) Shuttle in October 1989, and the alternative of canceling further work on the mission. The Tier 1 (program level) EIS (NASA 1988a) considered the Titan IV launch vehicle as an alternative booster stage for launch in May 1991 or later. The May 1991 Venus launch opportunity is considered a planetary back-up for the Magellan (Venus Radar Mapper) mission, the Galileo mission, and the Ulysses mission. Plans were underway to enable the use of a Titan IV launch vehicle for the planetary back-up. However, in November 1988, the U.S. Air Force, which procures the Titan IV for NASA, notified NASA that it could not provide a Titan IV vehicle for the May 1991 launch opportunity due to high priority Department of Defense requirements. Consequently, NASA terminated all mission planning for the Titan IV planetary back-up. A minimum of 3 years is required to implement mission-specific modifications to the basic Titan IV launch configuration; therefore, insufficient time is available to use a Titan IV vehicle in May 1991. Thus, the Titan IV launch vehicle is no longer a feasible alternative to the STS/Inertial Upper Stage (IUS) for the May 1991 launch opportunity.

Source record↗

CASSINI. Report on the Phase A study: Saturn Orbiter and Titan probe

An in-depth, second phase exploration of Saturn is proposed. The scientific objectives involving Titan, Saturn's rings, icy satellites, magnetosphere, Jupiter, asteroids, and cruise science are covered. Other topics presented include: (1) the model payloads; (2) project requirements; (3) mission; (4) launch vehicle; (5) the orbiter system; (6) the Titan probe system; (7) mission operations; (8) management; and (9) development plan.

Source record↗

Centaur D-1T propulsion and propellant systems

Modifications are described which have been introduced to the Centaur high-energy upper stage (which is being integrated with the Titan IIIC booster) to improve mission flexibility and reliability, and to provide three-burn synchronous orbit capability. The addition of a sidewall radiation shield significantly reduces heat transfer to the liquid hydrogen tank. This radiation field, in conjunction with a newly developed computer controlled propellant tank venting and pressurization system, permits the use of improved techniques for propellant management during orbital coast. Some minor changes in the propulsion and propellant systems which were necessary to adapt these systems for synchronous orbit trajectories are described, together with the redundancy incorporated to reduce the number of single failure points.-

Goette, W. E.↗