The lack of a win for either team would have come as a huge blow. If neither mission had been selected, many would have perceived the decision as absurd, perhaps even insulting. The spacecraft designs were the best they could be. The momentum of the community was impossible to ignore. And now it had phosphine in its corner.
In other words, the tantalizing discovery of these lateral motions is a rare piece of tangible evidence that Venus is geologically active, or that it is, at the very least, on a transitional continuum from an active to inert state. Though its tectonic motion is nowhere near as expansive as Earth, these movements still make Venus an outlier compared to most other worlds in the solar system, such as Mars, Mercury, and the Moon.
Magellan Inert Momentum
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To see how this might work, consider a toy example: a car in which the wheels drive a pump that expels an inert reaction mass backwards at variable speed. The speed is adjusted so that, in the reference frame where the ground is stationary, the expelled propellant is also stationary. Ignoring friction, this system accelerates the car (thrust from the expelled propellant > drag from the pump on the wheels), because all the kinetic energy remains in the vehicle, and the mass of the vehicle is decreasing.
The approach to achieve this was to use the momentum and energy of a plasma stream flowing past the ship and using that energy to transfer momentum to an onboard propellant to drive the ship. That plasma stream would be the solar wind inside the solar system (or another star system), and an ionized interstellar medium once beyond the heliosphere.
Box 1 shows that net momentum (and force) can be attained when the energy of the drag medium and propellant thrust are equal. However this simple momentum exchange would not be feasible as a drive as the ejection mass would have to be greater than the intercepted medium resulting in very high mass ratios. In contrast, the Q-Drive, achieves a net thrust with a propellant mass flow far less than the medium passing by the craft, resulting in a low mass ratio yet high performance in terms of velocity increase.
In summary, the Q-Drive offers an interesting path to high velocity missions both intra-system and interstellar, with much larger payloads than the Breakthrough Starshot missions, but with anticipated engineering challenges comparable with other exotic drives such as antimatter engines. The elegance of the Q-Drive is the capability of drawing the propulsion energy from the medium, so that the propellant can be common inert material such as water or hydrogen.
Top-level leaders of companies are often not in a position to give direction to others, to get them excited about something, or to encourage them, simply because they themselves have not engaged their personal willpower. Managers who are distracted or disengaged, as well as those who procrastinate or take purposeful action only occasionally, are not good leaders. Moreover, they know that they are not good leaders. They feel overwhelmed by the expectations of their people. The subjective feeling of unease in their leadership role is neither an exception nor a surprise. How could they stimulate others when they themselves lack energy, i.e. they feel detached, exhausted or even burnt out? How could they provide orientation and meaning when they lack focus and thus are carried along by momentum of what is happening and much of their capacities is absorbed in firefighting? How could they create a context that encourages others to take the initiative when they themselves are insecure about the right way to go?
Many executives have experienced the decisive difference between the productivity and momentum of highly energetic companies and their inactive or inert counterparts. They have seen the symptoms of a lack of organizational energy: Apathy and inertia, tiredness, inflexibility, and cynicism. And they know that highly energetic organizations can be ineffective if their energy turns corrosive: Their force is invested in selfish or destructive actions. By contrast, some have experienced the momentum of positively energized organizations which have fully activated their potential in the pursuit of their business goals. But only few executives have a real understanding of the different energy states and the strategies that they can use to unleash the action potential of their companies.
An area where numerical modeling can be particularly effective is atmospheric dynamics (Sanchez-Lavega et al. 2017, this issue). Recent General Circulation Model (GCM) advances (e.g., Lebonnois et al. 2016) are capable of reproducing important features such as temperature structure, static stability and zonal winds. However, work is needed to understand the dynamics of key features (e.g., cold collar, large stationary gravity waves) and how they couple or not to the super-rotation. In addition, the role of eddy processes is crucial, but likely involves the complex interaction of a variety of different types of eddy, either forced directly by radiative heating and mechanical interactions with the surface or through various forms of instability. There is also a need for improved numerical models that are capable of spatially resolving the polar vortex morphology and accurately reproducing its dynamics, and the role of subgrid-scale processes in the angular momentum budget, especially small-scale gravity waves. Finally, the robustness of existing GCMs should be confirmed through inter-comparison between several models, with particular focus on the conservation of angular momentum.
Photochemical studies can also benefit greatly from new modeling work (Marcq et al. 2018, this issue). Detailed dynamical and photochemical studies of the Venus middle atmosphere (\(\sim70\mbox--110\mboxkm\)) can be used to understand the photochemistry, dynamics, heating, and microphysics that drive the atmosphere at these altitudes. Existing validated models with updated photochemical schemes can be used for this type of study. Models can also be used to address major questions regarding dynamical exchange between the lower and upper atmosphere. Understanding of aerosols can be improved through new microphysical models of sulfuric acid aerosol formation, growth and decomposition (Titov et al. 2018, this issue). In addition, such studies need to be expanded to other species (e.g., elemental sulfur) that may be consistent with observations of unknown absorbers in the UV and other wavelengths. Incorporation of new microphysical models into regional scale and global scale circulation models can then be used to study feedbacks between microphysics, chemistry, and the momentum and energy balance.
Numerical models of atmospheric dynamics have achieved significant success (Sanchez-Lavega et al. 2017, this issue) but many uncertainties remain, especially in the deep atmosphere. Precise wind field retrieval below the upper clouds (surface to 60 km) as a function of location (long/lat) and local time is an essential ingredient required to derive the vertical distribution of the angular momentum, momentum transfer and super-rotation origin. In addition, observations of waves (e.g., gravity, Kelvin, Rossby and tidal) below the clouds are needed to better understand their role in the inertial forces caused by super-rotation. While in situ measurements are generally the most direct approach to measuring these parameters, they are limited by short lifetimes (hours to days) and small spatial coverage inherent to current in situ approaches. As remote sensing techniques are improved and in situ lifetimes are extended, there is ultimately a need for more detailed observations of the deep atmosphere that can match the coverage obtained by missions such as Venus Express in the middle atmosphere.
Nuclear-Electric Propulsion (NEP), relies on a nuclear reactor to provide electricity to an ion engine using an inert gas (like xenon) to create thrust (rather than spewing a radiative exhaust). The resultant thrust is less than that of either NTP or chemical propulsion, but it has the advantage of being able to be maintained for far longer periods, potentially allowing a crewed vehicle to gently accelerate to the half-way point to Mars before trying around and using that same thrust to decelerate gently and achieve orbit around Mars. This could cut a 6-month journey to Mars in half.
A good on-line resource for information and images of Venus is NASA's Space Science Data Center Venus page.Thursday October 27Venus and Mars are an interesting pair of planets to compare with Earth, as they are both fairly close to the Earth's mass, and at close to the same distance from the Sun. However, they are enormously different both from Earthand from each other in their current properties.VENUSSome numerical points:The density of Venus is similar to that of Earth also, so we can infer that itsoverall elemental composition is about the same.We cannot see the surface of Venus in optical light. This is because Venus is shrouded in a thick, perpetually cloudy atmosphere. In fact, we can't even see much in the way of structure inthe atmosphere in visible light. Ultraviolet images reveal the flow patterns in the Venusian atmosphere in much more detail. And radar mapping, both Earth-based, and satellite-based, have given us a fairlydetailed view of the surface. We also have visible images of small patches of the Venusian surface from a series of Russian Venera landers from the 1970s and 80s.One really surprizing result of early (1960s) Earth-based radar mapping observations is that Venus actually rotates "backward". That is, the sense of Venus's rotation is opposite to the sense of its revolution around the Sun (such motion is called retrograde rotation). Also, the rotational period is very long, about 243 terrestrial days. (Note that because of this a Venus Solar day -- about117 Earth days -- is shorter than the Venus rotation period). The best current idea for why Venus rotates so slowly is that Venus suffered a very large impact, fairly late in the epoch of planet formation, and the angular momentum imparted by that impact essentially stopped the planet's rotation.Venusian AtmosphereVenus's atmosphere is very different than Earth's. For one thing, there's a LOT more of it. The surface pressure on Venus is about 90 times higher than it is on Earth. The composition is also quite different:96% CO23.5% N20.5% H2O, H2SO4, HCl, HF (nasty stuff)The cloud deck is mainly H2SO4 (sulfuric acid) in an aerosol. It is very thick down to about 33 km above the surface. The Venera landers found that, below this depth, the atmosphere was very clear (notethat the horizon is visible on the upper right in the linked image).The atmosphere of Venus rotates coherantly (leading to the structure we see inthe UV images, and very quickly. A probe dropped into the equatorial cloud deck would circle the planet in twelve hours or so. This is very different from thepatterns we see in the Earth's atmosphere. Even very large mid-latitude cyclones in our atmosphere are only a small fraction of the Earth's diameter. Current thinking is that this difference is due to the different rotation rates of the planets. Venus rotates so slowly that this introduces relatively little turbulence into the atmospheric rotation, thus allowing for the global-scale circulation. Recent mission (the ESA mission Venus Express and the Japanese satellite Akatsuki) have been directed at understanding the physics of the Venus atmosphere. As Venus Express was in a polar orbit, it was able to see things like the evolution of the south polar vortex on Venus over multi-hour timescales.I have already noted that the surface pressure on Venus is very high (about90 times what we experience on Earth). The surface temperature is also very high. It is roughly 750 K. This is several hundred degrees hotter than thesunlit side of Mercury, so something other than direct Solar heating is clearlyat work here.The condition of the Venus atmosphere is a result of a RunawayGreenhouse. It is thus a cautionary example to us of how bad things can get if the atmosphere can trap too much heat.Here is a summary of how we think the Venusian atmosphere evolved to itscurrent state: The early Venus atmosphere was much cooler than it is now. Cool enoughfor liquid H2O. But Venus is closer to the Sun than Earth is, so it was warmer than Earth. Because of this, less of the surface water was in liquid form, and theliquid H2O could dissolve less CO2 in it than the water on Earth (not just because there was less of liquid water, but also because CO2 dissolves better in cooler water than in warmer water). So there was more CO2 in the atmosphere, and this allowed the atmosphere to trap heat more efficiently. This lead to more evaporation of liquid H2O, and the introduction of even more CO2 and H2O to the atmosphere. From here the process diverged (hence the term "Runaway Greenhouse"),until all the surface water had evaporated, and all the CO2 was in theatmosphere.It is worth noting that if all the CO2 dissolved in Earth's oceans, in the soil, in biomass and locked up in carbonates (seashells, coral reefs, limestone, etc.) was put into Earth's atmosphere, we would be Venus. The pressure would be about as high as on Venus, and the heat capacity would be about as high.But what about the water? There is almost no water in the Venusatmosphere now. If the idea outlined above is correct, all the water on theearly Venus would have evaporated. The reason it is no longer in theatmosphere is that water molecules in the atmosphere are subject to photodissociation from Solar uv. This does not happen to the water inEarth's atmosphere because the water vapor is nearly all below the ozone layer(which absorbs the Solar uv). On Venus, no protective ozone existed, so thewater molecules were broken up into H and O. The H escaped quickly, and the O reacted with other things in the atmosphere and on the surface.Venusian SurfaceAlthough the atmosphere is opaque to optical light, radio waves can reach thesurface, and be reflected back. Since the 1960s, there have been numerousmissions to mapVenus with radar. The early observations were Earth-based, but since the1970s there have been several radar-mapping satellite missions. Thisculminated in The MagellanMission in the early 1990s.About two thirds of the surface are lowland rolling plains. The other thirdis highlands, with about 5% true mountains, all of which appear to be volcanic. The plains appear to be lava flows. But unlike Mercury or Mars, the crater density is about the same on both the highlands and the lowlands. Further, the crater density is fairly low, and all the craters look fresh.The implication of this is that the entire surface of Venus is relativelyyoung.This is probably connected to the strong active vulcanism we see on Venus.Unlike the volcanos we see on the Earth, there are no chain volcanos, eitherfrom plates moving over mantle hot-spots (like the Hawaiian islands), or fromextended subduction zones (like the Cascade Mountains). Instead we see shieldvolcanos, formed by mantle hot-spots over stationary crust. Thus Venusdoes not have plate tectonics - the crust is not moving with respect to themantle.There are a number of curious features associated with vulcanism on Venus.Among them are lavachannels, similar to Lunar rilles, but thousands of km long. Some of thelava-flow fields look quite fresh. There are also pancakedomes formed by subsidiery eruptions near the major shield caldera, andcoronaearound large volcanos. These appear to be due to crustal subsidence from themass of the volcanos pressing down on the crust.Evolution of Venus Differentiation. Much like on the Earth. One observation that impliesa profound subsequent difference is that Venus has no detected magnetic fielddown to 0.00004 that of the Earth. From the density of Venus, we know it musthave an iron core. And if the core is liquid and rotating there should be astrong magnetic field. The lack of a magnetic field could be the result ofVenus's slow rotation, but that is unlikely to be the whole story. The otherpossible explanation would be for Venus to have a solid core. But why shouldVenus have cooled so much more rapidly than the Earth has? Impact phase. It must have happened, but as there is no old surface onVenus, we have no record of it. Resurfacing. Based on crater counts, we think that the entire surface wasrepaved about 500 Myr ago. This may only have been the most recent event in arepeating series of global lava flooding. Slow evolution. Basically, this is due to vulcanism. There are fewerrecent impact craters than we see on the Earth, as Venus's atmosphere is sothick that all but the largest infalling objects burn up in the atmosphere.Why is there no tectonic activity on Venus? The crust is dry. This means the crustal rock on Venus is less dense thanit is on Earth, so the Venusian crust is more buoyant. As a result it is muchharder to get it to subduct. The crust is hot. This means the crustal rock on Venus is less brittlethan it is on the Earth. Thus, instead of breaking into independent plates, as the crust does on Earth, the Venusian crust simply bends (or "distorts plastically").This also suggests an explanation for the lack of a magnetic field on Venus.It could be that the crust is sufficiently plastic that it all "turns over" atonce every few hundred million years or so. Sort of like a very slow boil.If this happens (and recall this is pretty speculative), then this wouldprovide a very efficient means for the interior to cool. It would loose a lotof heat whenever the crust turned over. That could have allowed the interiorto cool sufficiently that it has now solidified, even though the interior ofthe Earth is molten and will remain so for several billion years. 2ff7e9595c
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