Quote from: nadreck on 01/31/2016 04:04 pmWhich argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.An orbital depot is probably a requirement just because it would be very inefficient for BFS and/or the tankers to have to lug around the cryocooling equipment.
Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.
In regards to the MCT Depot, I think we are in the early planning stages where general issues can be discussed before any commitments will be made. I am trying to devise a few tools to help the discussion. Attached is an simple Excel spreadsheet that calculates some data for this purpose. The inputs are the number of berths (Line 2), the assumed diameter of MCT (line3), and the minimum acceptable gravity force at the tank location closest to the depot center (line15). Some of the data of interest to me are depot diameter, the highest gravity force that will be recorded at the outermost edge of each tank, and the rotational acceleration required to achieve these gravity forces. These are just a few of the factors to be considered. Please check it out.
It will have to cryocool propellant on Mars, which is more difficult than cryocooling in heliocentric orbit.
PSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.Thank you.
Quote from: Robotbeat on 01/31/2016 05:53 pmPSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.Thank you.No but they do in transfer operations and to avoid the need for cryocooling to achieve zero boil off in orbit you need a attitude control and reflective shielding and radiative surface area that does not get that radiation reflected back at it.
Quote from: nadreck on 01/31/2016 05:59 pmQuote from: Robotbeat on 01/31/2016 05:53 pmPSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.Thank you.No but they do in transfer operations and to avoid the need for cryocooling to achieve zero boil off in orbit you need a attitude control and reflective shielding and radiative surface area that does not get that radiation reflected back at it.They don't if both tanks are cool, which can be done passively and without a big sunshield.
Pressure. Seriously, they already have to worry about hydrazine freezing in tanks. Just paint your spacecraft white and keep it out of the Sun except the skinny way. It'll naturally get that cold.
If the receiving tank is below boiling point, it'd have a lower pressure and could actually condense the propellant. No venting required.Also remember that the figures you're using are at STP. Higher boiling point at 100psi ullage pressure.Anyway, it's well understood that methane/LOx are "space storable" as XCOR advertises. Sick of arguing with people thinking that because boiloff s big for hydrogen that it must also be for methane and oxygen.
If the receiving tank is below boiling point, it'd have a lower pressure and could actually condense the propellant. No venting required.
Also remember that the figures you're using are at STP. Higher boiling point at 100psi ullage pressure.
Anyway, it's well understood that methane/LOx are "space storable" as XCOR advertises. Sick of arguing with people thinking that because boiloff s big for hydrogen that it must also be for methane and oxygen.
Quote from: BSenna on 01/31/2016 03:23 pmMaybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS. You're offering 25 tons for 100 people.
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?
Quote from: Burninate on 01/31/2016 04:29 pmQuote from: BSenna on 01/31/2016 03:23 pmMaybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS. You're offering 25 tons for 100 people.How do the rest of you account for this?
Why has LOX/RP-1 (or even LOX/methane) historically not been used for delayed burn operations, which have almost always, if not always, used hydrazine?
Quote from: Burninate on 01/31/2016 08:30 pmQuote from: Burninate on 01/31/2016 04:29 pmQuote from: BSenna on 01/31/2016 03:23 pmMaybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS. You're offering 25 tons for 100 people.How do the rest of you account for this?Depends on your assumptions for "closed loop".3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).