Density of gases in space for in-space collection and refueling of spacecraft

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Density of gases in space

The solar wind is a stream of plasma released from the upper atmosphere of the Sun. It consists of mostly electrons and protons with energies usually between 1.5 and 10 keV.- wp

The sun loses about 10⁹ kg/s. This loss occurs unevenly over the this gas radiates outward (below)

[TABLE=width: 500]

[TR]

[TD=align: center]___Planet____[/TD]

[TD=align: right]Sun Distance (~r; m)[/TD]

[TD=align: right]4pi*r² (m²)[/TD]

[TD=align: right]kg / m²s[/TD]

[/TR]

[TR]

[TD]Mercury[/TD]

[TD=align: right]0.58 x 10¹¹[/TD]

[TD=align: right]0.42 x 10²³[/TD]

[TD=align: right]2.3 x 10^-14[/TD]

[/TR]

[TR]

[TD]Venus[/TD]

[TD=align: right]1.08 x 10¹¹[/TD]

[TD=align: right]1.46 x 10²³[/TD]

[TD=align: right]6.8 x 10^-15[/TD]

[/TR]

[TR]

[TD]Earth[/TD]

[TD=align: right]1.50 x 10¹¹[/TD]

[TD=align: right]2.82 x 10²³[/TD]

[TD=align: right]3.5 x 10^-15[/TD]

[/TR]

[TR]

[TD]Mars[/TD]

[TD=align: right]2.28 x 10¹¹[/TD]

[TD=align: right]6.53 x 10²³[/TD]

[TD=align: right]1.5 x 10^-15[/TD]

[/TR]

[/TABLE]

The final column shows the mass of gas that passes any point at a given equitorial radius from the sun.

There are discussions which involve the in-space refueling based on gas scavenging from space. The problem as we see above is that you would have to find a means of evacuating large volumes of space, but in actuality one could not evacuate space in the same way one might evacuate a chamber. In a chamber the molecules do not travel far before they strike another particle, and this constant richochet of particles push the gas from highest pressure to lowest pressure. In space particles travel a large distance before the strike another particle.

But around the sun the particles move a way as a consequence of ionization, high-frequency excitation, and strong magnetic fields impart on that plasma a tremedous amount of kinetic energy. The wind travels between 0.3 - 0.8 Mm/s. Using a value of 0.4 Mm/Second.

The plasma density is basically 1kg spread out over 400 sun-centered radial kilometer of square areas specified (1 / '4th column') and so basically the density is much lower or or spread around around 10²⁰ m³ or 5 times the volume of the moon. Therefore non-directional evacuation will not work.

The next table shows how much hydrogen one could ideally extract from a collector of 1 sq meter, point in the incoming direction of the solar wind in one calender year (31557600s)

collected (kg/yr). It assumes that every bit of wind that crosses a section of a spherical surface at the given radius (specified by the planets orbital radius) will be collected.

[TABLE=width: 500]

[TR]

[TD]Ship near orbit[/TD]

[TD]Collection rate (kg / m²yr)[/TD]

[/TR]

[TR]

[TD]Mercury[/TD]

[TD]0.00000072[/TD]

[/TR]

[TR]

[TD]Venus[/TD]

[TD]0.00000021[/TD]

[/TR]

[TR]

[TD]Earth[/TD]

[TD]0.00000011[/TD]

[/TR]

[TR]

[TD]Mars[/TD]

[TD]0.00000005[/TD]

[/TR]

[/TABLE]

So lets say one need 1000 kg of hydrogen for a rocket being returned from mars to earth, the mission will be for 2 years after which it needs the fuel to return. How large should the collection plate of the collector be?

So for any given meter of collector at Mars radius collects 0.0000001 kg/2yr and since you need 1000 kg, this translates to a collector of surface area 10¹⁰. Lets argue that the collector in its simplest form is 0.1mm of D=1 plastic. Then 1 cubic meter of 0.1mm can cover 10000 m2, thus for 10¹⁰ square meters would be require 10⁶ m³, the weight of 10⁹ kg plastic. The amount of material to create the collector far exceeds any benefit one would get from collecting the gas. In fact if we assume it take 49 units of fuel to get 1 unit of plastic to mars, then we would argue that break even point for the Mars for an in space hydrogen collector would take 1 billion years. However, on the bright side at about the same time, and expansion phase sun will bring the hydrogen to mars.

There are other proposed methods. Use EMF to coerce protons to a central site thereby increasing density. The problem however if one does the calculations it requires a massive amount of amperage at extremely high voltages to cover the size of area that would collect 1kg of protons traveling 400,000 m/s