Some info about the upcoming prop transfer demo (2025):
According to a tweet on it:
According to this presentation, the turnaround between these two launches would be of three to four weeks. Refilling will be done through the existing quick disconnect which will sport a probe-and-drogue system for docking.
Sounds like they were happy with the internal prop transfer demonstration in IFT-3.
The big issue with propellent transfer is getting fluids to move and settle in microgravity. Have they finalized how exactly that’s going to work?
They’ll use their reaction control system–i.e., hot gas thrusters. It really doesn’t need much. Maybe they’ll have some device to keep the propellant blob in place via capillary action, but actually getting it to the output port is just a matter of applying a tiny amount of thrust.
“Ullage”
Ullage is the name for the empty space in a tank. Ullage motors, ullage thrusters, etc. are used to settle the fluid so the ullage is where you want it to be (usually opposite the fluid intake). Often the ullage motors are the same as the reaction control system.
I thought the term referred to boil off from the cryogenic tanks; which since the gas has to go somewhere was used to provide the settling thrust.
That would be the hot gas of the hot gas thrusters. But different rockets have different systems. The Saturn V had dedicated solid rocket motors. The Falcon 9 has nitrogen thrusters. Starship is using the ullage gas.
The major problem with Shuttle’s tiles is they were aft of the external tank’s shedding.
Starship’s are forward.
IFT-1 mishap report, courtesy of FOIA:
There is not much point in opening the report. It’s about 98% redacted! Some typical pages:
I read something about an electrical fire?
Yeah, not much detail though. Ship 31 (IIRC) was doing some cryo testing and there was a small… energetic event on the side. Didn’t destroy the ship and it looked more electrical than flamey. That ship is set for IFT-6, though, so it’s pretty far down the line. Plenty of time to repair it.
Musk said the other day that IFT-4 was likely 3-5 weeks away. So no May flight, unfortunately.
An image of the damage:
Looks like a short inside the raceway caused a small fire and bulged out the cover. Doesn’t seem like too difficult a repair, though obviously they want to figure out the root cause. Unless it was an intentional stress test of some kind.
It turns out this is possible. The FAA just made this announcement:
If the FAA agrees no public safety issues were involved in the mishap, the operator may return to flight while the mishap investigation remains open, provided all other license requirements are met.
I’m not sure if this is a new regulatory path or if SpaceX just hadn’t pursued it before. It does mean that we can’t necessarily expect a mishap report before the next launch.
IFT-1 obviously had the potential for a public safety impact given the pad damage and flight termination failures, and the IFT-2 stages failed in a way where they didn’t land in the nominal places. But IFT-3 had no issues in that respect. The booster stage hit the ocean harder than it would have otherwise, but it was always intended to crash into that part of the ocean. Same with the second stage, which broke apart in the intended place. There was no reasonable safety issue that needs to be fixed before the next flight.
Some deets on Flight 4:
Also a few details on Flight 3:
They seem to be having contamination issues of some kind:
The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps.
And:
The most likely root cause of the unplanned roll was determined to be clogging of the valves responsible for roll control.
They don’t say what the contaminants were. Water ice, CO2 ice, oxygen ice, metal particles, internal structural components, etc. are some possibilities (also, the main filters and the valve issues are probably different things).
They’re still shooting for early June for Flight 3. Should be exciting as always.
June 5th is penciled in pending regulatory approval and Mother Nature.
"Provided that paperwork comes through and no technical issues arise, Starship will launch June 5 from SpaceX’s Starbase site in South Texas, during a window that opens as early as 8 a.m. EDT (1200 GMT; 7 a.m. local Texas time)."SpaceX targeting June 5 for 4th test flight of Starship megarocket | Space
SpaceX has confirmed that a major issue in IFT-3 was solidification of combustion products in the LOX tank.
Starship uses the LOX turbopump preburner exhaust to pressurize the LOX tank. But because the exhaust contains CO2 and water vapor, those products turn into ice & dry ice when in contact with LOX.
The strainers that SpaceX installed in the LOX tank to catch the ice, were ineffective, and it clogged the LOX turbo pump inlet. So they will try new strainers and different ullage techniques in IFT-4.
Using exhaust for autogenous pressurization saves the weight & complexity of a helium pressurant, but introduces other issues. Other vehicles use a heat exchanger to drop out the ices before they get into the tank, but that too adds weight. SpaceX is trying to minimize the weight & complexity of the Raptor engines.
Speaking of Raptors, one exploded spectacularly on the test stand this week. No comment from SpaceX. Raptor test failures are common as they push the envelope.
Since the combustion products of methane and oxygen are carbon dioxide and water, how does the preburner produce anything that can pressurize at LO2 temperatures?
They’ve confirmed no such thing. They said there was a filter blockage. There are many possible things that could block the filter.
There is no evidence of this and plenty of evidence that it’s not the case. The autogenous pressurant is pure methane (or oxygen) which has passed through a heat exchanger. Any claim that they’ve deleted the heat exchanger is pure speculation since it would be internal to the Raptor and no one outside SpaceX has seen that.
There are a couple of people pushing this rumor (i.e., that the filter blockage is water ice originating from preburner exhaust) but it’s no more than a rumor and more like a conspiracy theory at this point.
I wouldn’t completely exclude the possibility that the blockage is water ice, though likely from a different source, such as water in the ambient air that maybe didn’t get purged or some kind of leak. Regardless, it’s currently unknown what the source is.
The preburner burns a small amount of methane in a large quantity of oxygen (or probably, burns it roughly stochiometrically and then mixes in more oxygen). So most of the gas in the LOX preburner is gaseous oxygen, with smaller amounts of H2O and CO2 from the combustion products. The theory is that they used this directly instead of running pure LOX through a heat exchanger to gasify it. But it’s pure speculation at this point.
June 5 is still looking pretty good.
The new flight is a simplification of IFT-3 in some ways. It’s clear that they’re almost entirely focused on the heat shield. So no propellant transfer demo, cargo door, etc., since those are all things that could impede the heat shield test. Everything else is “easy” in comparison. Though they will attempt a backflip (ocean) landing if they make it through reentry.
Musk is clearly worried about the heat shield. He said this on X:
This is a matter of execution, rather than ideas. Unless we make the heat shield relatively heavy, as is the case with our Dragon capsule, where reliability is paramount, we will only discover the weak points by flying. Right now, we are not resilient to loss of a single tile in most places, as the secondary containment material will probably not survive. I will explain the problem in more depth with @Erdayastronaut next week. This is a thorny issue indeed, given that vast resources have been applied to solve it, thus far to no avail.
It’s also clear from other statements that he considers the Space Shuttle solution to be a failure. It worked, but it wasn’t rapidly reusable. It took a minimum of a month to refurbish and more typically was several months. Starship needs a solution that requires no refurbishment (just inspection and regular maintenance).
Well, the Everyday Astronaut interview should be interesting. I’m not a huge fan of his style, but he asks good questions.