Fu­ture tech sus­tain­able space travel

How we'll be mak­ing oxy­gen and wa­ter in space to travel among the stars

All About Space - - Contents -

Anew study, re­cently pub­lished in Na­ture

Com­mu­ni­ca­tions, has pro­posed a new way to man­u­fac­ture oxy­gen (to breathe) and hy­dro­gen (for space­craft fuel) while in space. The idea in­volves trans­port­ing large amounts of wa­ter (H2O) on board the space­craft, a semi­con­duc­tor ma­te­rial and the ever-present re­source that is sun­light. The idea be­hind the process is to split mol­e­cules of wa­ter into their con­stituent atoms us­ing an elec­tric cur­rent.

There are two ways of sep­a­rat­ing wa­ter mol­e­cules. One way is through a process known as elec­trol­y­sis, which in­volves pass­ing an elec­tric cur­rent through a wa­ter sam­ple con­tain­ing some sol­u­ble elec­trolyte. This will break down wa­ter into hy­dro­gen and oxy­gen and they are col­lected at dif­fer­ent elec­trodes. Al­though this is the­o­ret­i­cally pos­si­ble, the equip­ment is not read­ily avail­able and ap­pro­pri­ate for space­flight as of yet.

The method proven more ap­pro­pri­ate for space­flight is a process called ‘pho­to­cat­alytic wa­ter split­ting’. In this sce­nario, a semi­con­duc­tor is in­serted into the wa­ter and ab­sorbs pho­tons, which gives enough en­ergy to an elec­tron on the semi­con­duc­tor to jump and leave a hole. This free elec­tron can then in­ter­act with pro­tons to form hy­dro­gen, whereas the hole ab­sorbs elec­trons from the wa­ter to form pro­tons and oxy­gen.

This process can also be re­versed, and the mol­e­cules can be ‘re­com­bined’ in or­der to cre­ate wa­ter in a fuel cell, which re­turns so­lar en­ergy. The idea that three vi­tal el­e­ments for long-term space travel – wa­ter, hy­dro­gen and oxy­gen – can be used and cre­ated in a sus­tain­able way is tan­ta­lis­ing. The only is­sue with this is what to do with the bub­bles.

The re­searchers wanted to test the vi­a­bil­ity of the pho­to­catal­y­sis in space by set­ting up an ex­per­i­ment down a 120-me­tre (394-foot) drop tower. With an ob­ject in freefall, grav­ity is es­sen­tially nonex­is­tent, cre­at­ing the per­fect en­vi­ron­ment to test ex­per­i­ments with­out ac­tu­ally go­ing to space. Dur­ing the drop the re­searchers showed it is pos­si­ble to split the wa­ter, but there is a prob­lem with the bub­bles that are cre­ated.

When bub­bles are cre­ated on Earth, grav­ity au­to­mat­i­cally makes sure the bub­bles rise to the top and dis­si­pate. In space the bub­bles do not know where to go and per­me­ate the wa­ter. If the bub­bles were to stick on the cat­a­lyst, there would be no free room for the next bub­ble to form. The re­searchers com­bated this prob­lem by cre­at­ing pyra­mid-shaped zones where the bub­bles could eas­ily be re­leased from the cat­a­lyst. How­ever, there was still a prob­lem with the evac­u­a­tion of bub­bles from the liq­uid. To prove vi­able there needs to be artificial grav­ity, as it will pro­vide the force needed to evac­u­ate the bub­bles from the wa­ter.

Space fuel Hav­ing a fuel tank that can be re­filled provides new op­por­tu­ni­ties for a new des­ti­na­tion once Mars has been colonised, or even are­turn trip back to Earth.Sun­light Sun­light is ever-present through­out the So­lar Sys­tem and is eas­ily har­nessed into a valu­able re­source. In this case it is vi­tal toen­er­gis­ing the semi­con­duc­tor. Wa­terWa­ter will be in abun­dance in any space­flight as it is a ne­ces­sity for life. Re­cent news of sub­sur­face wa­ter at Mars makes the space­craft’s wa­ter tanks re­fill­able.

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