Elon Musk believes the second test tank could perform significantly better if pressurized with a cryogenic liquid. The steel will cryogenic harden when exposed to extremely cold temperatures which will make it stronger.
Starship 9 meter test tank made 7.5 bar at room temp. It had a small leak at a weld doubler. It will be repaired and retested at cryogenic temperatures.
SpaceX’s second Starship test tank has 125% safety margin.
Elon says SpaceX can immediately start building the first Starship for spaceflight.
Starship 9m test tank made 7.5 bar at room temp! Small leak at a weld doubler. Will be repaired & retested at cryo. pic.twitter.com/Bz3lrwkYRU
— Elon Musk (@elonmusk) January 27, 2020
Parent material strength roughly doubles, so weld strength is the only real question mark
— Elon Musk (@elonmusk) January 28, 2020
Liquid nitrogen cryogenic strength test underway ☃️ pic.twitter.com/qRPBLInqm0
— Elon Musk (@elonmusk) January 29, 2020
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I think Update was asking whether these are absolute or gauge values. Though throwing psi into the question is confusing.
That is, whether the 6.0 bar is 1.0 of normal atmospheric pressure, plus 5.0 bar of overpressure. Or if it’s just 6.0 bar of overpressure.
If 8.4 is 1.4 times 6, then they are using the full value of 6, not just the (6-1) which is what you would be multiplying by if it was absolute values.
So I think that, if the math is as given, that they are using gauge pressure, not absolute.
A “bar” is 100kpa, thousand newtons per square meter. Chosen because it’s metric, but is also almost identical to atmospheric pressure at sea level. So you can work with it as a metric number, but think of it as “times atmospheric pressure”.
Musks Twitter feed said the tank hit 8.5 bar at burst with LN2. 8.4 bar was needed for a 1.4x safety factor (for humans on board) with 6.0 bar being the operating pressure. I assume these are all psia values.