Low-G environmental tests

I’m reading a book on space colonization.  I’ve been making this point for many years now and this author mentions it but then sort of goes on with business as usual. 

The issue is the more we learn about living under weightless conditions, the more unhealthy it appears. It is just not responsible policy to plan missions to other planets under zero G. We know a fair amount about 1-G living and now quite a bit about 0-G living.  We know nothing whatever, however, about extended living and working under a fractional G.  We don’t have any idea whether we can stay healthy for months or years under lunar gravitation for instance. We don’t know if people can reproduce on Mars. If we can’t survive at least Martian gravity of about 37% earth normal, our long-term presence in space will be in rotating habitats orbiting various planetary bodies or the sun itself. Still people keep clamoring to go to Mars and politicians trumpet about going to the moon to stay!

My purpose here isn’t to scuttle human space exploration but we’re missing a very important step. We should be doing a long-term centrifugal experiment in near earth orbit to test first our ability to live under 1/6th G. Then it would probably be a good idea to try out Martian gravity. When this gets mentioned, people start talking about large rotating wheels or toroids, but all we need are two small, comfy habitats spinning about a common center, probably on a 300 meter tether.

A habitat vaguely football shaped seventeen feet in diameter and maybe twenty-four long would allow for two levels, providing quite a bit of living room for perhaps three persons.  Since there’d be two of them we could have six people all told.  Leave them up in orbit for a year and do exhaustive in-mission medical tests. Give them something cool to do like fabbing miniature devices designed for moon operations.

If it turns out that people do okay with a little bit of gravity then we can be confident we can make a lunar base work. We can be sure of being able to build a Martian colony someday.  If Lunar gravity hurts us nearly as much as living in free fall, then we need to seriously reexamine our goals in space.  One avenue might be genetic research to see if mammalian life can be adjusted to deal with low gravity.

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If Power-Sats are to be built part 3

The rocket projectile.

Methane is a propellant with an IsP in the 400 Seconds neighborhood and with a reasonable density, 422.62 grams per mol compared 1.141 G/mol for LOX.  A stoichiometric  mix of methane and oxygen is 4 grams of oxygen to one of methane.

If shaped into a test tube-like volume, hemispherical on one end, melding into a cylinder of radius 1 meter, two metric tons of methane would be 3.35 meters in length.  Eight tons of liquid oxygen in a cylinder one meter radius would be 4.46 meters in length. About 26 feet total.  If 5 tons of silica were shaped into a hollow test tube shape around this volume of fuel and oxidizer with the back end open, the wall would be a bit under 3 inches thick.  While this is sort of a non-conventional way to design a rocket it serves to show proportionality and rough feasibility.

We’ll need an engine of probably a million newtons or more, at least 220,000 pounds, so all of the rocket can’t be payload so the shell will be a bit thinner.  If our engine were mounted on a disc two meters in diameter fitting with fair snugness within the rocket shell, the force of the engine itself could compress oxidizer and fuel perhaps within deformable bladders and minimize and amount of pumping needed to drive both into the combustion chamber.   Our silica rocket shell/payload could be formed by isostatic pressing or some other means and sintered to give it significant strength.

Once in orbit we’d have something in the neighborhood of  1,200 kilos of pure silica once an orbital factory of minimal size has processed and cracked silicon from oxygen.  The oxygen we’ll find useful not only for crew life support but also propellant for solar or laser-powered plasma rockets used for towing our material from one orbit to another.

Having sketched a means for getting silicon into orbit, we need to comment on exactly where should the power-sat be located?  Conventional wisdom assumes geosynchronous altitude but satellites situated that high do nothing to shade the earth and actually add more heat to the earth environment than we had before.  Any other alternative though gives us a power0sat transiting the sky, describing a path about the earth.  A chain of small power-sats, perhaps in an equatorial common path, could keep a number of ground stations energized by aiming their beams away from the vertical which would require more intense beams than those under which cattle can graze.  The main point of the present exercise is to set forth some of the political and strategic issues we must face if orbital solar stations are to impact our global energy economy.

If a Power-sat is to be built… Part 2

Sizing the Catapult

 

Last time I discussed three strategies for placing silica in Earth orbit and tentatively concluded that to catapult small cargo rockets for orbital insertion might be the most direct and for the foreseeable future, most economical means of doing this.  There is the question of how much work should be done by the catapult and how large the cargo rockets should be.  We’d like to minimize track length, power expenditure and sizeof rocket so a strategy was devised to find an optimum mix of catapult assist and booster rocket.

I created a series of calculations showing the combined energy required of the catapult and that contained in the fueled expended for various combinations.  Selecting a Specific Impulse for our fuel of 400 Seconds (4,000) meters/sec. E.V.)

I started with a rocket taking off from earth and going into near-earth orbit, using fairly ideal figures.

I then graduated in thousands of miles per hour combinations from zero contribution from catapult all the way to total catapult contribution and no fuel expenditure.

I calculated mass ratios for rocket in each instance.

The data are shown in the table below with entries occurring as follows, contribution of catapult, contribution of rocket, mess ration of orbit and energy unit expenditure total.

Since the numbers were big, I divided each by 1,000,000 in case anyone wished to graph them.

Table

0-18,000      7.467       51.8

1-17             6.68         46.17

2-16             5.99         42.29

3-15             5.37         39.72

4-14             4.78         37.9

5-13             4.275       36.77

6-12             3.823       36.33

7-11             3.42         36.09

8-10             3.06         36.03

9-9               2.74         36.05

10-8             2.445       35.99

11.7             2.186       35.92

12-6             1.956       35.79

13.5              1.749      35.52

14-4             1.564       35.14

15-3             1.398       34.62

16-2             1.25         33.98

17-1             1.118       33.24

18-0              0              32.375

 

Though it’s clear that from an energetic standpoint, catapulting a given mass is ideally the must energy efficient means of proceeding at 32.75 million joules per kilo.  But we don’t do too badly from about 5-13 onward.  A rocket with a mass ratio of around 3. Which we recall, actually means two kilos of fuel for each kills of rocket, seems a fairly handy way to proceed and this ratio occurs at about 8-10, meaning the catapult delivers 8,000 MPH (3,576 M/sec) and the rocket does the rest.  With an exit velocity of 8,000 MPH our catapult if operating at 30 G.s need only be 13.33 miles long.  It’s power consumption would average about 7.993 gigawatts per 15 metric ton load.  If a large city contributed a brief period of it’s power output say five minutes around midnight, we could put a good deal into orbit each day.

Next time we’ll look at the logistics of the rocket output would be.

 

If Power-Sats are to be built… Part 1.

Options:

For earth-orbiting power satellites to make a significant impact in the energy economy and the overall Earth environment, we’re looking at square kilometers in orbit. A rectangular photo voltaic array a thousand meters on a side we generate on the order of 100 megawatts of electric power. If we figure a kilo of mass per meter of collector area we’re looking at 500 tons of material in orbit, probably most of it silicon. How’s that going to get there?

After many years of thought on the topic it appears to me that there are basically three options.

1. Send material from the moon via catapult into nearer earth orbit. This was popularized by Arthur C. Clarke around 1962, more as a means of refueling interplanetary spaceships but other uses were implied. If a lunar catapult operates at 100 G.s it will need to be a bit over three Kilometers in length to toss loads at lunar escape velocity toward the Earth. If each load weighs only 50 KG, it will require at least 100 megawatts of power which will in turn require a square kilometer of photo voltaic cells (on the moon.) We’ll eventually need to learn to fab large numbers of solar cells on the moon but I suspect this is the hard way to start up a power-sat for Earth.

2. A small asteroid could be boarded and turned into a self-propelled rock barge. A huge solar collector, probably a balloon silvered on one hemisphere, could focus sunlight on one end of a huge heat engine while the asteroid itself functioned as the engine’s radiator. Such an arrangement could spew electrically-charged oxygen extracted from asteroid rock or bits of the rock itself to propel the asteroid toward an orbit around Earth. I confess I like this idea best but we would need to transport the engine, the collapsed collector and a good deal of mining and extraction equipment to the asteroid, which will require either an atomic rocket or one powered by laser from earth, Moon or an orbital position. Again a great deal of start-up technology before we can start building the power-sat.

3. Lifting stuff up from earth is the most direct and may well turn out to be the easiest way to proceed, especially once we get comfortable with the idea that we’re not talking about reusable cargo rockets but projectiles made of raw material delivered by small rockets getting an assist from a catapult launcher cited in a mountain location near Earth’s equator. In this manner we can minimize the size of both our catapult and the rockets we’ll need to provide final kick into orbit.

Free e-book on Venus and how to Terraform it — Explaining Science

Merry Christmas! With Christmas coming up I’d like to give a free gift to all my readers. My e-book ‘Venus and how to Terraform it’ will be available free in the Kindle bookstore for five days from today (19 December 2019). To get your FREE copy please click on the link below . Get free […]

via Free e-book on Venus and how to Terraform it — Explaining Science

Thoughts on Star Flight

The Star Trek phenomenon started when I was in Seventh Grade (which dates me as I never skipped or repeated any years) and ushered in something significantly new about space in the minds of most of us.

The early ’60 series Fireball XL-5 had to do primarily with flights from earth, returning fairly soon on completion of some mission.  The flight of the Jupiter II in Lost In Space was supposed to have been a one-way journey to colonize another planet and most of the action was ground side.

Most of the science fiction movies I’d seen were about journeys from here to there and an intention to return home.  I’d read a story in Boys’ Life from about 1963 about  a Generation Ship and featuring a Tenderfoot Space Scout who’d never known any other life than that aboard a ship.  Still for most of us, an intentional community aboard a starship which would be out there for five years, was something rather new for most of us.

Certainly a preponderance of the Trekian action happened on some alien planet or other but the only home we generally saw was aboard the good old Enterprise.  Next Generation was more of the same with resort-quality accommodations and even kids aboard and Voyager was in some ways even more so.

Still from the perspective of the late ‘60s and early ‘70s however, I read a novel called Worlds for the Taking by the mid-20th century author Kenneth Bulmer when I was 15 or 16.  In this novel a significant portion of the human race lived aboard City Ships which were en route to someplace, doing something or other, though it wasn’t always apparent as to what.  They seemed to be basically essentially huge space stations on interstellar trajectories. A lot of things about this book made it quite memorable although I’ve never heard anyone else talk about it.

In a book I hurried to complete prior to an heart operation in 1998, I discussed the subject of living in space rather than on a planetary surface.  I came to a conclusion satisfactory to me at least, that in general and over the next millennium or so, there would not be any point in sending out starships from our solar system if we didn’t intend making landfall. If we planned to just live in orbit or some trajectory between planets or stars, there was plenty of space a lot nearer.  I’ve also written elsewhere about the following but an interesting issue arises when we ponder the energetics of building and deploying starships capable of making the crossing to a nearer star within the lifespan of a human being.

To send out a ship of 10,000 tons, able to make a journey to Alpha Centauri within an half century, if powered by matter beams from Luna or elsewhere, would require an amount of energy equal to that delivered by an area on the moon the size of Nevada, covered with solar cells.  If we had such a capability however we’d need to ask ourselves some crucial questions.  Is it really so important to deliver one colonizing party to it’s destination within a generation, or could we take longer and plant several?  The same energy supply could send out 10 ships each massing 100,000 metric tons and though the crossing time would be in centuries rather than decades, life aboard the larger ships would be much like that in Babylon 5 or Heinlein’s Luna City.

There remains the question of why?  I guess today we’re not really supposed to talk about Manifest Destiny, it not being PC or something, but if there was some sort of imperative to obtain, hold, garrison or develop a lot of extrasolar real estate, this would appear to be the way to do it.  It may be that even though the various colonization ships have been conceived to deliver settlers to frontier planets, it wouldn’t mean that all residents of the ships  need necessarily disembark any more than all Polynesians need emigrate to the mainland once discovered by Captain Cook!

We might have therefore, city ships, traveling not at faster-than-light or even 0.1-C velocities but perhaps a leisurely 6 or 7 megamiles per hour.  The propulsion and shielding issues would be greatly simplified and by now they’d continue to exist because it’d be a way of life that seemingly has always been and needs no more justification than we feel obligated to offer for living on the outside of an inner solar planet!

 

Interplanetary Intuition

 

My recent novel Entanglement, available as a paperback or a download, is in large part an outgrowth of my lifelong fascination with the possible convergences between physics/engineering and mental science.

In this case I don’t mean so much psychophysics or human factors engineering, but what sorts of hitherto unexpected things might the mind/brain be able to accomplish in conjunction  with advanced technology and visa versa.  SF literature is of course full of examples of virtual realities which become real and persons dreaming dreams which turn out to be real as well as realities which turn out to be dreams. What about something, which given a reasonable degree of development in robotics and computer-brain interface, is almost certain to be possible?  I’m speaking of direct experiencing, by a human participant, of artificial sensory data from a land rover on Mars or other extraterrestrial surface.

Time lags between Earth and the other planets are suitably long that any direct remote control interaction between here and any place much further than the moon is impractical.  Still, if mealtime information from a rover (visual, tactile, audio, possibly even chemical translated to taste and smell) could be fed continuously to an operator here on Terra, via a direct brain feed, it may be possible that what our brain is able to do with the information, i.e. what our intuition does to the information, and how it operates to glean insight, might add a new dimension to the impressions received.

Intuition has been hypothetically described as rational thought at high speed. This may be true.  Whatever it is however, it involves living within the situation and being part of what is going on.  Though the lag between idea at home and execution of suggested action Out There, may be minutes or hours in duration, the insights rendered by the interacting human brain may well enhance the process of exploration by remote control.

 

Considering the Bombardier Beetle

Bombardier Beetle and Sunrise.png

After discussing the concept of the space chicken in the last post, and it’s chemical propulsion system based upon Pheropsophus Verticalis’s thermo-chemical defensive organ, I decided to look at the propulsive potential  of a protein-based organism using the Bombardiers native reaction.

Hydrogen peroxide, which can be generated in a variety of living organisms including humans, is reacted with  Hydroquinone, a solid, aromatic hydrocarbon, basically a benzene derivative.  The hydrogen peroxide oxidizes the H.Q. to generate hot gas and an evidently noxious byproduct called Benzoquinone which is the bug’s actual spewing agent, emitted at high-temperature via a muscle-derived nozzle.

Both the peroxide and the wax basically, can be synthesized using whatever the beetle ingests.  Since we are dealing with a beetle made up of protein and chitin and other local organics, the blast of the bug though impressive is somewhat less hot than boiling water and though H2O2 has an I-Sp of about 300 seconds, our brave beetle won’t achieve more than a fraction of this if it decided to use it’s defensive apparatus instead for propulsion

Though it is in theory, possible to manufacture hydrogen peroxide from H2 and O2 or even by combining O2 and water at high pressures, it’s a little hard to see how this could come about biologically.  If we could make silicon analogs for some of the processes contributing to the operation of fairly simple life forms, we might be able to use a reaction of either H2O2 or N2O (Nitrous oxide) with ammonia or hydrocarbons found in the atmosphere of Jovian moons.  N2O can act at about 1,100 Degrees F as a monopropellant with a specific impulse of about 180 Sec.s but it can also be combusted with something like methane to yield it’s own stored energy plus that obtained in burning the methane with the oxygen N2O liberates in decomposition.

Nitrous Oxide is most often derived from the decomposition of Ammonium-nitrate but it can be made through the partial oxidation of Ammonia gas or generated through mixtures of nitrate and sulphate salts.  It looks as if either way the Space Chicken will need water or some other source of oxygen, and could use either ammonia or methane to complete a powerful propulsive mix making it able to do some serious rocketry from a moon’s surface or in orbit from body to body!

Musings on Synthetic Biology

chemistry-2938901_640

 

I’ve always found it fascinating to think about why I did things the way I did, how things could have been different and what outcomes I wanted then or still want now.

From the perspective of my summer after graduating high school I think an ultimate goal was the development of a self-reproducing solar array which used biological molecules to photo-synthetically generate hydrogen or other fuels.  I had no idea how this might be done nor even what pathway a person must take to attempt the doing.  I had originally intended to take an undergraduate degree in engineering physics, a sort of combination of physics, mechanical and electrical engineering, then available at Texas Tech University.  I’d follow that I supposed, with a Master’s in some branch of bioengineering then a doctorate in biophysics.  My life intention was to use what I learned in space and somewhat incidentally, to better conditions here on earth.

I ended up at the University of Washington and that’s another story.  They didn’t offer engineering physics and I was advised that since I hadn’t yet taken calculus I shouldn’t jump immediately into physics classes.  In those days undergraduate degrees in biophysics and bioengineering were scarce on the ground.  I was inspired by R. J. Bollard, the Director of the Department of aeronautics and astronautics at the time.  He convinced me that the degree his (later my) department offered could take me into rocketry, bioengineering, even biophysics if that’s where I wanted to go.  The energy crisis struck around 1973 and I got interested in biomass energy and graduated in A. and A. with a strong interest in alternate energy technology.

Around 25 years ago I first read about the Space Chicken, a truly fascinating engineering dream of Dr. Freeman Dyson of Princeton.  Melding photocell technology, microcomputing and the thermochemistry of the bombardier beetle, Dr. Dyson envisioned a part creature, part machine which could be propelled by laser launcher to the moons of Jupiter.  I wondered at the time what would a person study in order to someday design and build a space chicken or a self-replicating silicon solar tree.

The engineering discipline of synthetic biology might offer a pathway for those persons wishing to realize dreams of this kind and scope.  Synthetic biology is involved with taking apart and putting back together various building blocks of life to achieve things totally novel and exotic. Most of the work is involved with our carbon-based protein system common to most lifeforms currently known but the more abstruse branches of chemistry have yielded some self-replicating systems not based on carbon.

I think were I to start as a Freshperson next Fall, I would study biophysics as an undergraduate, taking care to add foundation courses in engineering and would seek out a program in synthetic biology for graduate studies.   (In rereading my latest science fiction novel Entanglement, I had cause to revisit artificial life as well as the physics of social systems and some of the things which can happen to someone who tries to invent a science too Early!)

Space-sicles

Short of a moon based matter beam, there would seem to be no greater boon to inner system operations than a supply of hydrogen fuel with liquid oxidizer in Earth orbit.

This isn’t exactly rocket science.

Well, actually it is, but not real deep.  Any plans, however, to build and supply an orbital fuel dump is likely to start off on the wrong foot—or wing.

Creating liquid hydrogen and oxygen here on Earth and sending it up into orbit in bulky insulated cryogenic tanks is a difficult and expensive proposition.  Sending water from which both reagents can be made is much more compact and manageable.  8,000,000 pounds of water, a good deal more than it would take to refuel an Apollo V, can be contained in a tank 100 feet high and only 40 feet in diameter.  Ice is a little less dense, therefore bulkier but being rigid, could be sent with little or no tanking.

Twenty-five tons of ice could be formed into a cylindrical slug about 12 feet high and about 11 in diameter and could be formed  by filling a big plastic bag with water, contained in a shaped hood or lid.  Liquid oxygen or nitrogen would be pumped through a modest amount of piping contained within the bag and the water would be first frozen then super-chilled perhaps to 60 or so degrees below zero F.  The hood would then be removed and the ice slug would be placed upon a “space barge,” essentially a platform with engines and pumps mounted below.  The ice could either be formed on the barge or transferred later.

When the ice is formed and secured, fuel tanks sufficient to get the whole system into orbit could be loaded on top of the ice and connected to the engine pumps beneath the barge platform.   Staging could be accomplished by pressure-forcing fuel and oxidizer from top tanks into bottom ones and tossing aside the top tanks as they empty.  The barge with it’s load of ice and a set of empty tanks would arrive in orbit and the ice could then be melted and converted to fuel and oxidizer.

Of course in orbit there’s plenty of unfiltered solar energy to operate electrolytic cells for cracking water.  If we imagine a disc 50 meters in diameter and even in earth orbit where we’d be shaded from the sun half the time, we could expect to generate about 9,000 KWH of electricity per day. This is enough energy to crack about 1.6 metric tons of water per day.   A system like this would take about eight and a half years to refuel a Saturn but there are lots of jobs much smaller than what a Saturn V would carry out and nobody says we can’t build more than one orbital disc..  A ton and a two thirds per day of highly energetic fuel would be highly useful in launching deep space probes, asteroid missions, even supply runs to the moon.

The orbiting solar power disc could be made starting with a somewhat massive hub or sort of spool from which a number of cables would be unwound under centrifugal force, the cables being themselves big power cords would be weighted on the ends so they’d unreel easily from the spools holding them.  Once a sort of multi-armed wheel with cable arms is established, robotic spider bots would begin constructing a spiral array  of connecting power lines into which solar panels could be plugged.  Perhaps one bot carrying a spool of cable would propel itself by throwing cable backward, unwinding it’s spool as it goes, hopping from arm to arm and a follow-up spider, crawling along the spiral line could secure the cable together where they crossed.  Later bots would make there way in a spiral path from the hub outward, plugging solar panel modules into the insulated power strands.

If we made solar panel units weighing perhaps a kilogram per square meter, the panels would only weigh about seven and a half tons.  The operation could be done using automation and direct oversight and control from earth where necessary.  Nobody would need to leave the earth to build the array.  Panels would be connected in such a way as to give voltages on the order of 240-V and power would be fed toward the hub along the initial cable arms.  At the hub The DC power might be turned into AC using an inverter then the current lowered via transformer to 3 volts, all that is needed to electrolyze water, then rectified back to DC.  We’d experience a little power loss but not a great amount.  We’d lose more trying to send low-voltage current through fifty or more meters of cable.

Hydrogen and oxygen could be stored in large, silvered balloons until sufficient has been accumulated to warrant liquefaction and a small, solar-powered unit would accomplish this step, perhaps with super-chilled water cooled on the night side of the orbit about the Earth.  Liquefied gazes could be stored in the tanks brought up on the ice barge—or excess tankage could be used as fuel.  The barges themselves could be provided with heat shields and small retro packs and could be sent back to earth to splash down, be reloaded with more ice and tanks and sent aloft again.

I believe both the ice barge concept and the solar power disc is something a private company could well take on and whatever the price charged per kilo of liquid fuel in orbit, it’s likely to be less than bringing it up from the ground the old-fashioned way!

 

—Dave Plassman July 12, 2017.