New Mars Forums

Hi Soph!

    I think the Martian regolith is rich in sodium chloride, not to mention other salts and minerals.
    I'm no expert by any means, but my understanding is that any future Martian oceans will probably be salty, like Earth's, and no good for direct irrigation.

    If there is a high water-table, though, it may be possible to obtain bore-water in some places which might be pure enough for crops. But I'm just guessing.

Hi again, Josh!

    I was just re-reading Dr. Zubrin's "At Home in a Dome" section in his book, The Case For Mars. (It starts on page 177.)
    He describes a few different ways of tackling dome construction on Mars - and all but one involve the use of closed 'bubbles' of plastic. The odd one out is essentially a hemisphere of clear plastic with a skirt which is buried in the regolith, and possibly 'pegged' as well. This latter type is still presumed to be airtight, even though there is no floor in it except undisturbed Martian dirt! The trick is simply to hold the damned thing down by either burying the skirt and pegging (as Bob Zubrin suggests) or maybe by creating massive reinforced concrete footings, as we have discussed in other threads here over the past year.

    One of Bob's ideas is to dig a hemispherical hole, say, 50 metres across (25 metres deep), place a spherical 'balloon' of reinforced clear plastic in the hole, and then bring all the tailings in through the airlock and fill the sphere up to ground level again! The trouble with this idea is the enormous amount of material you have to dig out and push back in.
    A modification of this concept involves a hemisphere of clear plastic, again with a radius of curvature of 25 metres, attached to a section of a sphere with a radius twice as great. The section with twice the radius of curvature forms the bottom of the 'bubble' and is much shallower, requiring a correspondingly shallow excavation with a central depth of only 3.35 metres (instead of 25 metres). This way, the amount of soil moved is reduced from 260,000 tonnes to just 6,500 tonnes ... a hugely more manageable task!!

    If you could find an obliging crater of shallow depth and about the right diameter, you could perhaps save yourself some of the excavation work, and maybe use the crater walls as 'backfill' inside the dome. I think this is the kind of thing Byron is suggesting (? ) and it seems like a good idea.

    I was wondering about that first type of dome, though - the one which is simply a half buried sphere. I know there's a lot of soil to dig out (a hemispherical hole 25 metres deep), but what if you didn't put all that soil back inside at all? What if you made 6 or 7 floors of living area with a 10-metre-diameter central vertical shaft for elevators and for natural light. The roof of the topmost floor could be made level with the ground outside the dome, by covering it with a metre or two of soil for agriculture and radiation protection.
    This would make maximum use of the volume of the sphere for radiation-free living space, while also maximising the free and open space in the top half of the dome for farming and leisure purposes.
    I just haven't figured out what to do with the 260,000 tonnes of dirt outside the dome yet!!

                                          ???

Hi Josh!
    I've been thinking about your idea that a dome could be made to sit on the surface like a water droplet. I understand your concept, and it's a potentially elegant one, but I'm afraid a few 'back of the envelope' calculations show it won't work.

    Let's assume we want a modest-sized dome of 100 metres diameter. Since weight is important in holding this dome down, let's maximise the amount of dome material by making its shape hemispherical. The area of this hemisphere (from 2 pi r^2) is 15,710 sq.m.

    The area of ground under the dome (from pi r^2) is 7,855 sq.m.
    The area of bare ground, in from the 'sleeve', is 4/5ths of that area, i.e. 6,284 sq.m.  This is the area over which there is no force opposing the internal air pressure of the dome, except the weight of the dome materials themselves.

    Having assumed a modest dome, lets assume a relatively low pressure (high oxygen concentration) atmosphere inside the dome of only 350 millibars. Such an atmosphere will exert a pressure equal to 3.57 tonnes per sq.m.
    Therefore, the unopposed upward force on the dome is equal to 6,284 sq.m. multiplied by 3.57 tonnes per sq.m., or 22,434 tonnes - all of which must be resisted by the weight of the dome materials.

    We know the total area of dome materials is 17,281 sq.m. (the area of the hemisphere plus the area of the 'sleeve' which is 1,571 sq.m.) Hence, each square metre must weigh 22,434/17,281 or 1.3 tonnes. (Excluding the weight of the high tension wires, which I assumed to be negligible.)

    To get this figure of 1.3 tonnes for each square metre into perspective, we have only to consider the density of steel, which is about 7.85 tonnes/cubic metre.
    To oppose the upward force of 22,434 tonnes, even if you made your dome out of steel, it would have to be 16.5 cms thick ... that's 6.5 inches!!
                                         

    I think the only way to make your idea work is if you could produce an absolutely rigid and airtight floor for the dome. Then it would sit like a water droplet on the surface, with no net upward force.
    But the tendency for the edge of the floor to curl upward would be enormous, and I don't know of any material strong enough to remain flat over an area of 7,855 sq.m. under those circumstances.
                                   ???

There may be new hope for a big leap forward with photovoltaics.

    I found this interesting article about a new type of multi-junction cell based on layers of Indium Gallium Nitride with differing concentrations of Gallium.

    Apparently it has the potential (sorry !    ) to utilise photons from most of the visible spectrum, and a little beyond at each end. Thus possibly approaching theoretical limits for efficiency of 70%+ !!
    And it promises to be durable and not-too-expensive as well!

    The prospects for green energy production on Earth and for electricity generation in space could be vastly improved if this thing can be shown to work as advertised.

    Exciting stuff!!                 

That's right.
    The great man died on Dec. 20th 1996 at the way-too-young age of 62.

    Pathfinder became The Carl Sagan Memorial Station as a mark of respect.

I know this is going to sound suspiciously like bragging, but, as a long standing member of The Planetary Society, my name has been sitting in The Carl Sagan Memorial Station on the floodplains of Ares Vallis since 1997.

    YEAH, YOU'RE RIGHT!!! It is bragging!! I can't help it ... it's something I'm very proud of!
    I've been a financial member of TPS since I first heard of their existence and have responded to most of their letters begging for donations over the years. I did all this because I think if you really believe in something, it's not good enough to just talk ... you have to actually DO SOMETHING about it!

    I sometimes imagine future natives of Mars putting up a large plaque, rather in the style of the American Vietnam War Memorial, with all the 100,000 names of The Planetary Society members of 1997 inscribed on it.
    If there is an afterlife, I'd be smiling from ear to ear to think that my small contribution was actually recognised by the people of the New World I'd always wanted to see but never could.

Hi Phobos!
    Yes, you're right about Germany having done a lot to research on 'solar chimneys'.

    An Australian company called Enviromission has exclusive rights to the technology here in Australia, and plans to start building the first tower near Mildura, which is on the border between New South Wales and Victoria.

    They call it a solar thermal power station and it will generate 200MW of electricity - enough to power about 200,000 homes. The actual tower will be the tallest structure ever built, at a height of 1 kilometre.
    They plan to build several more over the following 5 to 10 years, which will provide a substantial proportion of Australia's power needs, but with no greenhouse emissions and no chance of running out of fuel (fossil or otherwise) !!

    I think it's just about the best thing since processed cheese (! ) and have serious plans to buy shares in the company.
                                         

Point taken, Dicktice!

    If a space elevator on Mars can only be achieved by destroying one or both Martian moons, I would be very reluctant to proceed without exceptionally good reasons.

    I realise that the raw materials for fuel and air that Phobos and Deimos almost certainly carry in abundance are an absolute treasure trove!
    Until the "Podkletnov Drive" is in common use, you're right that we can't afford to be too hasty about these things!!

Phobos writes:-

    I thank you sincerely for your much appreciated support. The hat will be passed around shortly. A few coins would be most welcome!

My apologies, Josh!
    Here I am, the first person to complain about acronyms with no explanation, the first person to whinge about IT posts with no explanation, and off I go with numerical claims I fail to explain myself!!
                                Sorry!

    Earth's atmospheric pressure at sea-level has been measured in various units as:-
              1000 millibars
               760mm Hg (Mercury)
               14.7lbs/sq.in.
               1013.25 hectopascals

    For all my praise and glorification of the metric system, I still find the 14.7lbs/sq.in. measurement the easiest to remember and the most evocative of the weight of Earth's atmosphere! To me, it's a measurement you can almost feel!! Anyway ... enough of the BS !

    A 500 millibar atmosphere under your canyon tent on Mars (i.e. half an Earth atmosphere), must exert an upward pressure on the material of the tent of 7.35lbs/sq.in.
    There are almost exactly 1550 square inches in a square metre. So each sq.m of the tent must hold down a force of 11,392.5lbs ... or 5,169kgs ... which is 5.17 tonnes (to two decimal places).

    [I confess I have assumed the Martian atmosphere to be negligible, which is not strictly true. In fact, it will push downwards with a force of about 62kgs for every square metre of tent.
    So my figure of 5.17 tonnes per sq.m should really be 5.11 tonnes (to two dec. places again). This doesn't materially affect the outcome, though.]

    I plucked the dimensions of the tent out of thin air! I could imagine a vast tent, many kilometres long and spanning a canyon 2 or 3 kilometres wide. But I thought I'd be conservative and choose a quite modest little canyon to illustrate my point.
    50 metres by 500 metres (ignoring the sealing material at each end) gives us an area of 25,000sq.m
    25,000sq.m multiplied by 5.17 tonnes/sq.m gives us 129,250 tonnes of upward force.
    If we allow for the Martian atmosphere's weight, we still get a net upward pressure of 127,750 tonnes. All I was trying to do was to point out that such forces will require enormously strong footings for the tent.
                                       

Welcome, Tim!

   The idea of a one-way trip to Mars has been suggested before but I don't think I've ever come across a plan to send an all-female crew with men replaced by semen samples.
    I suppose one of the problems we might face is finding women prepared to leave Earth forever, renounce their chance of a normal relationship with a man, live a very spartan existence on a strange world, and act as baby-making machines! You, yourself, have referred to possible difficulties in finding such people.

    If I were a woman, I don't think I'd be interested in going to Mars in circumstances like that, but who knows what drives different individuals.

    I'm hoping that when we finally get off our butts and go to Mars, it won't be on such a shoe-string budget that your suggestion becomes necessary. It doesn't really fit in with my vision of Martian exploration and colonisation, but then you never know what the future might bring.

The 'star system' is not, of itself, important.

    What is important is the quality of the posts and whether they further people's appreciation of the many facets of planetary exploration, especially Martian exploration. In addition, posts in the appropriate places are worthwhile if they serve to forge cyber-friendships between people with similar interests.

    A long series of pointless 3-word posts, made for the sole purpose of increasing the number of little gold stars next to your name, is not what the system was designed for.
    Such behaviour could be misconstrued as infantile, as could a well-thought-out argument like: "Just shut up, dumbass."