Elon Musk ✔ @elonmuskStarship & Super Heavy will press tanks autogenously even in version 1. Very important, as helium costs more than oxygen on Falcon, even though liquid oxygen is 2/3 vehicle mass & helium weighs basically nothing.12:14 AM - Feb 13, 2019https://twitter.com/elonmusk/status/1095551826668138496
On Mars: run filtered, ambient air through the same hoses that were used on Earth. It costs a bit of energy and you need a backup in case your compressor dies. But really, you need to be able to compress Mars atmosphere for fuel production anyway.
On Mars, take the 1.6% argon left over from liquefying the atmosphere for fuel production and run it through the transpiration system. That would both keep dust out and keep CO2 from freezing in the channels as you fill the tanks with LOX/LCH4. It might keep dry ice from freezing on the vehicle entirely.
Nitrogen ISRU is a by-product of atmospheric compression for the production of Methane. At the rate of 250 tonnes per ship, that's about 2.5 tonnes of methane per 100 transported colonist for Starship type vehicles. Supposing another 4 ships as cargos that's 10 tonnes of methane per traveller. The production of this methane requires 4 times as much mass of CO2 as the mass of the methane. So the CO2 production rate will be 40 tonnes of CO2 per traveller.At 2,7% nitrogen in the atmosphere you get about 1000 kg of methane per colonist. With a density of about 1 kg/m3 for atmosphere, that's enough methane for 1300 m3 of space when you add in the oxygen. Although this seems large, a typical suburban home in the US has about 780 m3 of volume, or 1000 m3 if you include roof spaces and wall volume. If you add in the volume required for food production, then all the nitrogen is used to fill the colony volume with [air], and it might be just a little short. ...So nitrogen production from propellant production is just sufficient for colony development, but might be a limiting factor, or require compressing the atmosphere for nitrogen production exclusively, or using the argon that comes along as well with the compression.There might also be some nitrogen from methane production as industrial feedstock.
Quote from: docmordrid on 02/12/2019 08:48 pmQuote from: JonathanD on 02/12/2019 07:35 pmI get the re-entry cooling concept for the main body of Starship, what in the world are the fins and canards are going to be made out of? They are going to be subject to some pretty rough re-entry temps.If the fins and canards are stainless 310 and folded up (dihedral) ISTM they'd be 1) more heat resistant and 2) largely protected within the trailing methane envelope, but they may use TUFROC on hot spots. They have an SAA to work on TUFROC at Ames. https://www.teslarati.com/spacex-new-bfr-heat-shield-advancements-nasa-assistance/No reason they can't use same active cooling as rest of vehicle.
Quote from: JonathanD on 02/12/2019 07:35 pmI get the re-entry cooling concept for the main body of Starship, what in the world are the fins and canards are going to be made out of? They are going to be subject to some pretty rough re-entry temps.If the fins and canards are stainless 310 and folded up (dihedral) ISTM they'd be 1) more heat resistant and 2) largely protected within the trailing methane envelope, but they may use TUFROC on hot spots. They have an SAA to work on TUFROC at Ames. https://www.teslarati.com/spacex-new-bfr-heat-shield-advancements-nasa-assistance/
I get the re-entry cooling concept for the main body of Starship, what in the world are the fins and canards are going to be made out of? They are going to be subject to some pretty rough re-entry temps.
Quote from: livingjw on 02/12/2019 09:50 pmQuote from: docmordrid on 02/12/2019 08:48 pmQuote from: JonathanD on 02/12/2019 07:35 pmI get the re-entry cooling concept for the main body of Starship, what in the world are the fins and canards are going to be made out of? They are going to be subject to some pretty rough re-entry temps.If the fins and canards are stainless 310 and folded up (dihedral) ISTM they'd be 1) more heat resistant and 2) largely protected within the trailing methane envelope, but they may use TUFROC on hot spots. They have an SAA to work on TUFROC at Ames. https://www.teslarati.com/spacex-new-bfr-heat-shield-advancements-nasa-assistance/No reason they can't use same active cooling as rest of vehicle.Are the fins still supposed to be actuated during entry? If so, then the cooling fluid must go through the actuated joints somehow. Moreover, the actuation must work, while the whole structure becomes quite hot. Does not seem to be easy. We had worried a lot about actuation even before we learned about the actively cooled hot metal thing.
Their Titanium grid fins are the largest single piece cast & cut. The wings / legs(2) are another magnitude larger, more complex but I wonder how their titanium experience can scale to this effort?
Quote from: rcoppola on 02/13/2019 07:23 pmTheir Titanium grid fins are the largest single piece cast & cut. The wings / legs(2) are another magnitude larger, more complex but I wonder how their titanium experience can scale to this effort? How did Shuttle flap joints survive repeated reentries without needing replacement?
Are the fins still supposed to be actuated during entry? If so, then the cooling fluid must go through the actuated joints somehow. Moreover, the actuation must work, while the whole structure becomes quite hot. Does not seem to be easy. We had worried a lot about actuation even before we learned about the actively cooled hot metal thing.
Quote from: geza on 02/13/2019 06:33 pmAre the fins still supposed to be actuated during entry? If so, then the cooling fluid must go through the actuated joints somehow. Moreover, the actuation must work, while the whole structure becomes quite hot. Does not seem to be easy. We had worried a lot about actuation even before we learned about the actively cooled hot metal thing.If they use (vane rotary type) hydraulic actuators with liquid methane as the working fluid that cooling problem would be much easier.
<snip>https://twitter.com/elonmusk/status/1091147092016254977Tweet Content Yes, ship needs pitch/roll/yaw control across wide Mach regime & angle of attack
As I understand the past BFR/Starship control surfaces and actuators discussion, methane makes for a very poor hydraulic working fluid. Probably going to be electric, IMO.
Consider that Falcon 9 uses hydraulics for gimballing and grid fins - they could have used electric. Modern aircraft are still mostly all hydraulic too with power by wire only making some inroads.
IMHO hydraulic pump will be driven by gasseous CH4 pneumatic motor from the autogenous pressurisation pipeline. That hydraulic pump will drive aerospace grade "plain" hydraulic system with synthetic oil and hydraulic accumulator as seen in that Raptor render from IAC2016.
Quote from: DusanC on 02/14/2019 02:11 pmIMHO hydraulic pump will be driven by gasseous CH4 pneumatic motor from the autogenous pressurisation pipeline. That hydraulic pump will drive aerospace grade "plain" hydraulic system with synthetic oil and hydraulic accumulator as seen in that Raptor render from IAC2016.- Autogenous pressurant is not available unless engines are firing. Engines are not firing during reentry when actuators are needed. - Will probably use RCS high pressure tanks to run a small turboshaft burner. They probably will match this to an electric generator, and use electro-hydraulics for the actuators.- I agree with: ....That hydraulic pump will drive aerospace grade .... hydraulic system....