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General Discussion => Q&A Section => Topic started by: Dalhousie on 07/13/2017 03:33 pm

Title: ITS Earth return propellant
Post by: Dalhousie on 07/13/2017 03:33 pm

Is there an authoritative reference for the estimated mass of propellant needed to return t the ITS from Mars surface to Earth?  I need it for a conference presentation. 

Otherwise some best attributable estimates would be appreciated.

Thanks

Dalhousie

Title: Re: ITS Earth return propellant
Post by: envy887 on 07/14/2017 12:33 pm

On May 2, 2017, Tom Mueller, propulsion CTO at SpaceX, conducted a speech/interview with some members of the New York University Astronomy Society.

Quote from: Tom Mueller

The Mars rocket is meant to be completely reusable. Both stages, ship and [inaudible] can lift hundreds of tons in a single flight; it can go all the way to Mars and back, and you’ll have to fuel it on Mars; we’ll need to make about 1000 tons of propellant on Mars over a two-year cycle; bring it back; and that’s a tall order. You need about half a megawatt of energy to [inaudible] that much propellant [inaudible]

https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription/

Title: Re: ITS Earth return propellant
Post by: Lar on 07/14/2017 03:27 pm

Quote from: envy887 on 07/14/2017 12:33 pm

On May 2, 2017, Tom Mueller, propulsion CTO at SpaceX, conducted a speech/interview with some members of the New York University Astronomy Society.

Quote from: Tom Mueller

The Mars rocket is meant to be completely reusable. Both stages, ship and [inaudible] can lift hundreds of tons in a single flight; it can go all the way to Mars and back, and you’ll have to fuel it on Mars; we’ll need to make about 1000 tons of propellant on Mars over a two-year cycle; bring it back; and that’s a tall order. You need about half a megawatt of energy to [inaudible] that much propellant [inaudible]

https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription/

1000 tons (or tonnes) of propellant can get you the water needed as follows

Assume stoich (a SWAG) and no other losses (again a SWAG) and integer atomic weights (a fair approximation at this accuracy level) so the atomic ratios are :

 1 CH4          + 202     ( -> 1 CO2 + 2 H20 )
    12 + 4*(1) + 4*16 or  80  of which the hydrogen is 4 or 1/20

So you need 50 tons (or tonnes) of hydrogen

The water is going to be (2+16)/2 more than that or 9x or about 450 ton(nes)

Check this, how much CO2 is needed

 12+2*16/80 = 44/80ths or 550 ton(nes) 

Yaay it balances.

Title: Re: ITS Earth return propellant
Post by: Dalhousie on 07/15/2017 03:44 pm

Excellent!