Tuesday, September 27, 2016

Mars: Dust Particles, part 1

Dr. Robert Duncan-Enzmann

Image of Earth dust from: http://entropymag.org/on-dust/

Dust enters the atmosphere of Mars from outside the planet as meteorite debris and from the surface of Mars due to atmospheric forces. In the lower 10,000 feet of the atmosphere the suspended dust is almost exclusively of surface origin. Dust is subtracted from the atmosphere of Mars by gravitational forces. The removal of suspended matter from the atmosphere to form surface deposits is accelerated by: 1) surface friction; 2) coagulation of dust particles; 3) vapor condensation on dust; and 4) adhesion of dust to ice (H20?) crystals.

The spread of suspended dust through the atmosphere of Mars is limited to several factors: 1) the balance of forces tending to add and subtract dust described in the above paragraph; 2) vertical extent and size of turbulences in the immediate ground environment; 3) vertical extent and size of turbulences above the immediate ground environment; 4) mean wind velocities; 5) adherence of particles to the surface at contact and as a function of time. Turbulence, which may be measured by the size of eddies or vortices, dominates transport and mixing of dust in an atmosphere. Instead of molecular kinetics, as expressed by molecular viscosity, conductivity, and diffusivity, the spread of particles is described on the basis of eddy viscosity, eddy conductivity, and eddy diffusivity.

To estimate the amount of dust in the atmosphere, it is necessary to know the factors outlined above and also something about the surface. For strong mixing to occur between the immediate ground level and higher levels it is necessary to have major turbulence, as introduced by topographic interference. Source and sink areas should also be considered. In the Earth environment sources are land areas and sinks are oceans. In the Mars environment there seems to be nothing like standing bodies of water. Adherence of particles to the surface may be enhanced by polar cap materials; adherence of particles may be enhanced by dark areas which could represent moisture. Generally conditions seem to be those of a cold, relatively flat desert with little interstitial water at the surface. Such an environment would parallel the worst desert conditions of Earth, with little tendency for particles to adhere to each other over relatively vast areas.

Using the Kaplan atmosphere and estimates made by Vaucouleurs, dust per unit volume of atmosphere in the immediate surface environment and also through the troposphere should be within one order of magnitude of terrestrial conditions.

In conclusion, although total dust content per unit volume of the Mars atmosphere may approximate or even exceed that of the Earth’s atmosphere, it should not cause any difficulties in communications or erosion. The average wind velocity is low, perhaps 20 mph average in the Trade Wind Belt, precluding significant wind erosion in anything but geological times. The low wind velocity also suggests a low frequency for static noise due to dust impacting on uninsulated antenna.

(Stay tuned for Mars Dust Particles, part 2: Effects of Suspended Dust)

Thursday, September 8, 2016

Notes Concerning the Atmosphere of Mars

Notes concerning the atmosphere of mars by Dr. Robert Duncan-Enzmann:

Wind profiles and velocities
Dust particles
Topographic considerations
Introduction to interactions with lithosphere and hydrosphere

Vertical Wind Profiles 

During the last 3 to 5 km of descent the capsul will be in the stratosphere and troposphere. It is possible that at certain times and locations – as is sometimes the case in terrestrial Polar locations – that the stratosphere of mares will be in direct contact with its surface, resulting in the local absence of a troposphere.
The following layers, which could strongly perturb descent, will be present in the last 3 to 5 km of descent regardless of whether the general zoning is tropospheric, stratospheric, or both:
1. horizontal cross winds with shearing as expressed by Helmholtz interference
2. surface turbulent channel extending from the surface to a minimum of 10 meters to a minimum of 300 meters above the surface
3. the so-called logarithmic layer a few centimeters above the surface
4. the major eddies associated with the topography
5. ground effect when the vehicle is a distance above surface on the order of its horizontal extent.

It is recommended that these features be examined for the amount of perturbance associated with each feather be studied. This can be done on the basis of maximum and minimum values. Sufficient information is available to yield such values, which in turn will indicate the maximum and minimum parameters for which the system will have to be built. 

The geographic distribution of winds, horizontal wind patterns, and the vertical profiles of winds should be considered in designating landing sites, and in designing landing mechanisms. Winds over the surface of Mars and to approximately 10,000 feet above the surface are estimated to move at relatively low velocities. The estimates have been made by observation of moving cloud patterns, observation of yellow dust cloud movements, computation from thermal gradients as a function of latitude, computations treating the planet as a black body, estimate of time necessary to transfer supposed water from the cold trap at one pole to the cold trap at the other pole. (13 Vaucouleurs) Observations and estimate indicate a rather low average wind velocity  perhaps 20 mph. Locally wind velocities may exceed this value.
Conditions indicating winds in excess of 20 mph are to be expected in association with the following features, which are listed in order of importance, the feature with the strongest winds first.

1. Sub-polar Spot: (Capricorn and Cancer) The heat capacity of the atmosphere about Mars is relatively low. Much heat is stored in the rocks of the surface, however, this is released quickly, therefore winds about the sub-polar spot may be expected to be strong. The writer estimates up to 80 mph.
2. Trade Wind Belt: Expected to be a zone of prevailing winds moving from east to west; these winds are positioned somewhat to the south of the geographic equator.
3. Westerly Belts: Zones of northern and southern westerlies seem to show more rapid movements of clouds and fronts than over an average area of the planet
4. Polar Easterlies: Zones in which winds moving from east to west may be expected to exceed average values.
5. Atmospheric Channels: Winds seem to be stronger over the dry hemisphere from long. 270˚ to long. 90˚ and on a lesser scale through the Pandorae-Fretum / Hellespontus structure.
6. Surface Thermal Anomalies: The areas of Noachis seems to show abnormal temperatures. It may be the reason for localization of cyclonic circulation and development of darkening in the Pandorae Fretum. It is located at long 350˚ and 360˚. The writer estimates on the basis of terrestrial differences between ambient winds and winds beneath such cloud structure, that winds could reach velocities of 300% above average in temporary gusts. 

Wind Profile Charts:

Stay tuned for the next section on Dust Particles

Monday, October 19, 2015

The Enzmann Starship: History and Engineering Appraisal

JBIS, Vol. 65, pp.xxx-xxx, 2012

Icarus Interstellar, 20 Downlands Place, Boondall, QLD 4034, Australia.
Email: acrowl@icarusinterstellar.org1, 2. kelvin.long@tesco.net2 and robousy@icarusinterstellar.org3

This paper was presented at the British Interplanetary Society
symposium “World Ships - The Long Journey to the Stars”, 17
August 2011.

During his student days Robert Duncan-Enzmann imagined a space vehicle design which he depicted in a watercolour painting and apparently dated 1949. In the 1960s he was heavily involved in space-mission design and introduced the concept of a fusion powered interstellar spacecraft design which utilised a 305 m diameter sphere of frozen Deuterium and a long cylindrical habitat/propulsion section joined onto it by a connecting structural column. The spacecraft was to be manned by a small community of people setting out to colonise nearby stars and the entire vessel would have a launch mass of between 3-12 million tons, most of which would be the propellant. Long time space advocate G. Harry Stine, presented the concept to
a wider audience via “Analog Science Fact & Science Fiction” magazine in 1973. Stine envisioned the Starship to be part of a wider programme of interstellar exploration, beginning in the 1990s. Although the Enzmann Starship is relatively well known in science fiction circles, it is not well known within the interstellar research community and indeed just as little is known about its creator, Robert Enzmann. Very little has been written about the concept in the academic literature and no modern assessment of its engineering credibility exists. This paper sets out to reliably describe what is known about the Enzmann Starship design and also how the idea originated, based upon what is known to date. In this paper the engineering configuration is described, and a performance assessment is given in the context of modern scientific knowledge. Further information on the history and design of the Enzmann Starship is invited so that this concept can take its rightful place in the history of interstellar spacecraft design proposals.

A review of modern textbooks on interstellar travel will find little mention of the Enzmann Starship design, a surprise to the authors of this paper given its ingenuity. However, a review of
science fiction internet sources will reveal more about this wonderful concept, which was first proposed by the American Dr Robert Duncan-Enzmann. Little is known about Enzmann except that he was an MIT Professor and an employee of Raytheon Corporation. He is the fourth pioneering Robert in the field of interstellar research, the other three being Robert Bussard, Robert Forward and Robert Frisbee and he deserves as much credit for his idea. In realising the dearth of information on this concept it was decided to perform a literature research and to then write up a summary of the results, describing the engineering design and the history behind its development. This paper is the result of this effort which took over a year. It is the intention of this paper to provide greater awareness of the idea, within the technical science community, and if other authors have information of relevance this is invited.

If the 1960s were the golden age of human space exploration, then the 1970s and 1980s was the golden age of interstellar Starship design. During this period many colourful and original concepts were generated including a number of fusion based propulsion designs such as Project Daedalus [1] and the Bussard interstellar ramjet [2]. It is in this context that the Enzmann Starship was also turned into a credible engineering concept, a period in history where scientists began to apply rigorous engineering methods to speculative proposals as a way of answering fundamental questions about our universe and the possibility of intelligent life.

In writing this paper the authors have attempted to assemble data on the Enzmann Starship wherever possible, including contacting individuals (Robert Enzmann, Don Davis, Rick 
Sternbach) involved with its early development. We first discuss what is known about the history of the idea. We then give an overview of the concept, its configuration layout and claimed
performance. We then discuss some follow up proposals to use the Enzmann Starship for a wide scale program of interstellar colonisation. Finally, we provide an engineering assessment of
the proposal in the context of four decades of subsequent research. It is the hope that this paper will reveal more about this unique idea and perhaps advance it to a more credible level.

In personal communications [3] to the authors of this paper Robert Enzmann says that he developed an interest in space flight during his very early school days, and he imagined the
distinctive configuration for the space vehicle on the 6th August 1945 during the WW2 bombing of Japan. He constructed paintings of the idea back then and one of which is shown in Fig. 1
dated 1949. These authors are unsure if this is meant to be “1969”.

Fig. 1 Enzmann Starship Painting (1949) by Robert Enzmann.

 It is claimed by several sources, in particular internet based, that a report was submitted to the New York Academy of Sciences as early as 1964 detailing the idea although an extensive literature research by these authors has revealed no such reports in existence. Subsequent authors have claimed that the Enzmann Starship was referenced in the book ‘Journey to Alpha Centauri’ by John McVey [4], however, searching this book and the later 1969 republished version has found no specific reference to Enzmann, although the book does discuss century long missions to Alpha Centauri. Enzmann also submitted several papers relating to ‘Mission Planning’ to the New York Academy of sciences in 1966 although these were not pertaining to Starships [5]. Although the article contains little technical information on the proposal, it is worth noting that in the 1960s America was in the full swing of Project Apollo and
indeed landed on the Moon in 1969. Enzmann says that he took inspiration from these events and was committed to humanity making its first steps towards the stars. It is the view of these
authors that it was during the mid-1960s that the idea for the Enzmann Starship probably began to crystallise in the mind of Robert Enzmann, although he had the idea much earlier.

During 1972 the original concept for the Starship was modified in collaboration with the space artists Don Davis and Rick Sternbach [6, 7]. In particular the original eight engine design was changed to a 24 engine design and the modular sections were made such that they could be split off from the main vehicle. The new design also depicted smaller spheres and the nested toroids at intervals along the hull, was to allow the ship to split up into as many as three separate ships once a primary destination had been reached. The torus became something of an all-around connecting shape, able to latch onto most any other module, along with the engines. This would require significant undocking and redockings of the component parts. The ability to rearrange modules would also afford the expedition an added degree of safety in the event of a problem that prevented a complete ship from completing the journey. Sternbach, Dixon and Enzmann initiated, in those 1972 discussions, the idea that parts from a disabled vehicle could be added
to a healthy one, and the trip could continue, albeit at some cost in time and velocity. These creators also discussed the possibility of a dedicated tanker ship, but it never went anywhere; due to the issue of having to push not only the fuel for itself, but for the other ships. At the same time Sternbach, Dixon and Enzmann worked to further develop the design and produce illustrations of the concept, which included spraying metallic plasma onto a balloon which mimicked the appearance of the Deuterium sphere. Sternbach experimented with a number of different shapes, volumes and masses to finally evolve the 24 engine configuration. Sternbach reports in personal correspondence [7] that the idea for the metal plasma fuel sphere fabrication
may have come from Richard Hoagland, who had been discussing the technique not only for big metal spheres, but also for enormous telescope mirrors.