Bryden Allen's Website

Building and Launching our Rockets


I naturally started this whole work by going to my local Ashfield library to see what books they had on this subject. The library only had one substantial book, which was called "Lost in Space". This book seemed quite reasonable and the author discussed the cost of getting material into space in great detail. He thought that this cost should drop to $100 per pound in the near future (to an ISS orbit like we are considering in this project). But then I read Wikipedia on this subject and the costs they gave were far higher than this.
            But the cost of getting material up into space is absolutely crucial to this project. So I am afraid we must study the differences between these possible costs very carefully indeed. This is not going to be an easy webpage – it can't be.


The one figure we can calculate reasonably accurately is the amount of money we can afford to spend on getting material into space. So let us do this job right now. We will work in terms of kilos.
            The weight of our proposed colony will be 50 tonnes per person (see next webpage). And there will be 500 people in the colony. So the weight we need to raise up into space is:
            50x500x1000          = 25,000,000 kilos
Our manpower per year on this project will be 50,000 people (as shown in my "The Free-Time our Communities will Generate" webpage). And we expect this construction to go on for 10 years. And one man-year is equivalent to $40,000. So we expect to spend:
            50,000x10x$40,000 = $20,000,000,000
on this task.
            So these two figures tell us that we have $800 to raise every kilo of material up into space. So roughly we can afford to spend four times as much on this project as this $100 estimate. But the Wikipedia were still higher than this (of the order of $1,000 per pound). However you should be able to see that this amount of money, which we can afford to pay, is in the correct ball-park. (And if we can't do the job at this price then we will just have to spend longer and get more people to do the job.)


However it is enormously important that we have some idea of the sort of rockets we will use and how difficult they will be to construct. So now we must go into the details.


First let us think about fuel. It is a fundamental that the best fuel will also be the most dangerous (because it will burn to give the highest temperature). But we must accept this. Going up into space can never be really safe.
So we will use oxygen and hydrogen, which will burn to make water (this reaction gives us the highest chemical energy density). Fortunately the cost of producing this fuel is relatively easy to calculate.
This fuel is made by electrically separating water into oxygen and hydrogen.
            Using the standard ½ mv2 formula, the energy needed to produce
1 kilo of this fuel will be ½ x 3600 x 3600 Joules (where 3600 m/sec is the velocity associated with this reaction).
            This gives 1.8 Kwh. So this is the minimum amount of energy we need.


Naturally we will produce this energy ourselves using PV panels. And these panels, over a 20 year period of use, will produce one Kwh for less than 10 cents, which is quite reasonable. The usual problem with this PV energy is that it is hard to store. But, in this case, this limitation doesn't matter because we only need to make the fuel when the sun is shining.
            So this gives us a price of 18 cents per kilo - or $180 per tonne. But with all the problems of storing the oxygen and hydrogen etc, I think a more practical value to consider is:
            $1.0 per kilo (i.e. $1,000 per tonne).


We now need to consider the nature of the rocket system we will use. And this becomes complex because these costs go up exponentially, when the required velocities are greater than the exhaust velocity of this fuel. Fortunately I will avoid this complexity because I can use a special case for this difficult problem. But the two following cases demonstrate how this exponential growth problem occurs.


            Now a rocket is made up of three parts: the payload, the rocket system (fuel containers and burners) and the fuel. Now a tonne of our fuel could theoretically accelerate one tonne of the payload and rocket to 3.6 km/sec. Now let us assume we are quite clever and we reduce the weight of the rocket part to a minimum. So then 1 tonne of fuel could accelerate just the payload to 3km/sec (and the rocket is discarded). Then my first method could look like:
Stage 1            1 tonne payload + 1 tonne fuel gives 3 km/sec
Stage 2            2 tonne payload + 2 tonne fuel + stage 1 gives 6 km/sec
Stage 3            4 tonne payload + 4 tonne fuel + stage 2 + stage 1 gives 9 km/sec
Stage 4            8 tonne payload + 8 tonne fuel + stage 3 + stage 2 + stage 1 gives 12 km/sec
So this method needs 15 tonnes of fuel to put a 1 tonne payload into full space.


A better more realistic method is probably:

Stage 1            1 tonne payload + 2 tonnes fuel gives 4 km/sec
Stage 2            3 tonne payload + 6 tonne fuel + stage 1 gives 8 km/sec
Stage 3            9 tonne payload + 18 tonne fuel + stage 2 + stage 1 gives 12 km/sec
So then this method needs 26 tonnes of fuel to put a 1 tonne payload into full space.


So these two methods demonstrate how the amount of fuels increases exponentially as the required velocity increases.


But fortunately our particular case has a m

uch simpler solution. We will assume that we will only use one rocket to go to our orbit (i.e. just one stage). Then this solution only depends on the good old simple "Conservation of Energy Law". This is that:
The energy of the fuel = The energy gained by the rocket
            We will just use the usual E = ½ m v2 formula. We will call the mass of the fuel X and the mass of the rocket and payload 1.0 .
Then            ½ x X x (3600)2 = ½ x 1.0x(7100)2
So                                     X = 3.9
Naturally I will call the 3.9, to be 4.0 . This means that, if we build a rocket to go to our space colony, then 4/5 of it must consist of fuel and 1/5 can be rocket and payload.
            The size of rocket I would like to consider would weigh 100 tonnes (before its journey). So the rocket would have 80 tonnes of fuel and the empty rocket and payload would be 20 tonnes. I will divide this 20 tonnes into 5 tonnes for payload and 15 tonnes for the rocket structure. With modern materials I think 15 tonnes should be able to cope with making the fuel containment and the burner nozzles (which is what a rocket basically consists of). And, as far as I can make out, this looks like what the modern commercial Antares rocket seems to attain.
            Suppose we say that the material used in this rocket and payload costs $10 per kilo ($10,000 per tonne). And cost of our fuel, as described before, is $1 per kilo ($1,000 per tonne).
            Then the cost of materials for this rocket would be
                                    = 80,000x$1 + 20,000x$10
                                    = $280,000


Now let us consider what will actually happen every week with this type of rocket. Fortunately, over a 10-year period there are roughly 500 weeks. And there are 500 people who need to be sent up into space in this period. So, every week, one person must be sent up into space together with their 50 tonnes of material (which they will need to support themselves).


Now the huge advantage of this simple system is that whole rocket hardware arrives at the orbit spot as well. In the first couple of years of this long project, these empty rockets would be of no use at all. But, when the colony has plenty of energy and their furnaces are all working, then these old rockets can become very useful indeed. They can be remade into objects the colony really wants. (Also the rockets could be made out of the materials, which the colony particularly wants.)
            On average I will say that the 5 tonnes of payload is directly useful and 5 tonnes of the 15 tonnes of rocket is also useful. So this means that there must be 5 trips per week to deliver all this 50 tonnes materials. So every working day of every week, a 100 tonne rocket must go up into space.
            But, on the other hand, this simple regularity will make the whole job much easier. So, if this devoted colony makes this rocket every day, then this colony must soon become very, very skilled in making these rockets. And essentially a rocket is a very simple form of machine – it has very few moving parts. So I think that this colony will eventually be able to make these rockets without any problem at all.


So now let us check our sums. Each week we will send 5x $280,000 dollars of material up into space.
                                    = $1,400,000
But each week we will receive 50,000x$800 of "free" labour ($800=$40,000/50). So we can use

                                    = $40,000,000 to do this task.
So, strangely enough, our state should be able to do this huge task comparatively easily.
            In fact the colony may be able to put this material into space for less than $100 per pound. Also - remember - this rocket is a very well tried technology. We have been sending such rockets up into to space for more than 50 years now. Some day "scramjet" rockets may be able to do this job more efficiently (because they can carry less oxygen). But I don't want to make any such assumptions.


This then is my case that a colony of this size can in fact do this task. Of course nobody can predict all the problems we will meet. But we should give the task a proper go. We have nothing to lose because we will all be doing this task of our own free will. I, for one, would simply love to have a go at this glorious challenge.
            The costs of going up into space will not really be all that great. So eventually I think all people in our Town-State could spend a year in their Space Colony, if they wish to. This would provide these people a very special different year in their lives. This would be the year in their lives, which they would remember before all others. So in all possible ways this great task would be very worthwhile.


Naturally my next webpage is called "Initially Starting our Space Colony".

 

You might now also like to look back at:

either my "Home Page" (which introduces this whole website and lists all my webpages),

or "The Ultimate Ascent" (which introduces these webpages),

or "A Path to Create a Full Space Colony", (which introduces the coming webpages in more detail).

 

Updated on 11/11/2016.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

You can click on any of the following pictures and this will send you to the relevant webpage.