It also doesn't help that all off the maneuvering to reorient the craft from the belly-flop attitude to the tail-first landing attitude is going to slosh the fuel around, which could lead to ullage and fuel and/or oxidizer flow problems. Basically, the proellant pumps are sucking in gas or foam rather than liquid, thus moving a smaller mass of propellant per second. The big green flame coming out of the engine right before the crash could be an indicator of copper-containing elements of the engine burning away in an oxidizer rich environment (as Scott Manley puts it, it was "engine-rich exhaust").
That's why they have dedicated, smaller "header" tanks for the landing burn, which are full at the time of ignition. The engines relit properly, but then had some kind of subsequent pressure problem.
That's why they have dedicated, smaller "header" tanks for the landing burn, which are full at the time of ignition. The engines relit properly, but then had some kind of subsequent pressure problem.
Yeah, I read up on the header tanks after Mjolnir's reply. In this case, it sounds like the low fuel header pressure may have been a result of the tank being inadequately filled.
On the topic of Starship and its fuel system, since it's intended to act as a interplanetary vehicle, I have to wonder about the choice of cryogenic fuels for something like a Mars trip. Liquid oxygen is a pain in the rear to store for long periods of time because it tends to boil off and need to be vented (liquid hydrogen is even worse). This is why less efficient but easier to store propellants are often used on long duration missions (hypergolics and monopropellants are preferred because the don't require an ignition system to fire the engines). It'll be interesting to see the workaround SpaceX comes up with for Starship and its cryogenic MethaLox propellants.
That's why they have dedicated, smaller "header" tanks for the landing burn, which are full at the time of ignition. The engines relit properly, but then had some kind of subsequent pressure problem.
Yeah, I read up on the header tanks after Mjolnir's reply. In this case, it sounds like the low fuel header pressure may have been a result of the tank being inadequately filled.
On the topic of Starship and its fuel system, since it's intended to act as a interplanetary vehicle, I have to wonder about the choice of cryogenic fuels for something like a Mars trip. Liquid oxygen is a pain in the rear to store for long periods of time because it tends to boil off and need to be vented (liquid hydrogen is even worse). This is why less efficient but easier to store propellants are often used on long duration missions (hypergolics and monopropellants are preferred because the don't require an ignition system to fire the engines). It'll be interesting to see the workaround SpaceX comes up with for Starship and its cryogenic MethaLox propellants.
Fuel quantity would have almost no effect on fuel pressure.
It uses cryogenic propellants because it has to produce propellant on Mars in order to come back, and producing hypergolic propellants requires a substantial industrial base. LOX/LCH4 can be produced from water and CO2 fairly simply. The atmosphere of Mars is mostly CO2, and they're targeting areas that have large water ice deposits.
Re: The "Real Aerospace" Thread
Posted: Mon Dec 14, 2020 10:44 pm
by Arioch
While oxygen and methane are a lot easier to keep liquid than hydrogen, I presume they will need to use some sort of active cooling system.
While oxygen and methane are a lot easier to keep liquid than hydrogen, I presume they will need to use some sort of active cooling system.
That's my assumption as well. I've seen people arguing that the vented tanks would act as a vacuum flask, but that only works in atmosphere, with the vacuum gap limiting heat transfer from the surrounding atmosphere to radiation. In space, you're already limited to radiation, and the outer tank walls are much hotter than the empty sky they're obstructing, especially when exposed to sunlight...they themselves will radiate, and they'll reflect what's radiated from other parts of the tank interior.
Re: The "Real Aerospace" Thread
Posted: Fri Jan 01, 2021 8:12 pm
by White
I came across this video, It's a very insightful show of different welding techniques, as well as of some technologies, like electron beam welding, which seem set to driving an industrial golden age in orbit.
I also wanted to show you guys this channel, which has a lot of good videos about space technology in general, and Starship in particular.
And then unfortunately later exploded while sitting on the pad. I think the hard landing ruptured something.
Progress!
My father and I were chatting after lunch and I happened to notice the stream was on, and we watched it live. And there was much rejoicing.
Yeah, there was a largish fire under the skirt that didn't go out, and probably a fair bit of methane in the fuelLOX tank above it boiling faster than relief valves could handle. Well, that simplifies the problem of making the vehicle safe...
Ah well, it wasn't likely to fly again even if it made a softer landing. SN11 will probably do better with just some software tweaks, and from what I've heard, SN15 has major improvements in the thrust dome area. It's possible it already has a fix for whatever broke when SN10 landed.
Re: The "Real Aerospace" Thread
Posted: Fri Mar 19, 2021 12:28 am
by Mjolnir
SN10's engine was producing lower-than-commanded thrust, thought to be due to helium ingestion. Ironically, it's thought to have been a quirk of how the propellant was flowing around the anti-slosh baffles that are intended to prevent that, Musk described it as the baffles acting like a straw. So, some things to tweak there, and probably a return to autogenous pressurization. (The cold propellant would quickly condense and collapse bubbles of gaseous propellant.)
The landing legs were also not latching into position, but it hit hard enough it would have just flattened them anyway. Workers were seen giving some extra attention to SN11's legs when it moved to the stand.
They're stacking BN1 now: https://twitter.com/elonmusk/status/1372688191803768840
That's roughly twice as tall as Starship itself. It's just a pathfinder for working out manufacturing issues and ground handling, BN2 will fly. If things go well, BN3 will loft a Starship on an orbital attempt in July.
Re: The "Real Aerospace" Thread
Posted: Sun Apr 11, 2021 10:37 pm
by Arioch
Looks like the F-15EX is already being delivered to the Air Force for testing. This is just a Boeing marketing video, but it has some nice shots.
The F-15EX "Eagle II" is an updated version of the Strike Eagle with modern avionics and a digital cockpit. I think its main role is to be a missile bus, using its large payload capacity to launch weapons at targets designated by F-22's or F-35's. But, of course, it can do anything the current F-15C/D and F-15E Strike Eagles can do, so it's also a hedge against future stealth-penetrating technologies. I also like that it's a two-seater, because the complex modern electronic battlefield needs more human management, not less.
Here's hoping it doesn't have the usual Boeing software problems.
In the past, I was never a huge fan of the F-15. I mean, it's a big, expensive jet that performs just as well as a big expensive jet should. But lately, seeing even more expensive jets performing not really any better, I've got a bit more respect for it.
I wonder who came up with the idea to name it the F1-5EX though...
Re: The "Real Aerospace" Thread
Posted: Mon Apr 12, 2021 9:01 am
by Krulle
Hey, every marketer knows, 5-EX sells!
Re: The "Real Aerospace" Thread
Posted: Mon Apr 12, 2021 9:33 am
by Arioch
I don't know, but I would guess that the E is due to it being derived from the F-15E, and the X because of the main selling point of the platform being its extra ordnance capacity... and because every marketer loves X.
Re: The "Real Aerospace" Thread
Posted: Tue Apr 13, 2021 7:20 am
by QuakeIV
Originally it was just F-15X to reference the idea that its experimental afaik. I'm not sure the X or EX is staying long term.
Re: The "Real Aerospace" Thread
Posted: Sat Apr 17, 2021 7:39 am
by Arioch
The winner of NASA's Artemis contract is... SpaceX.
The winner of NASA's Artemis contract is... SpaceX.
As the sole award, too. Not surprising that Blue Origin wasn't chosen, they would have had to be a politically mandated choice...in the words of Lueders: "I do not have enough funding available to even attempt to negotiate a price from Blue Origin that could potentially enable a contract award." The Dynetics proposal was a surprise though. It somehow went from half the cost of the Blue Origin one to even higher cost, while ending up in the red on their mass budget and apparently becoming less capable. Not sure what happened there.
As the sole award, too. Not surprising that Blue Origin wasn't chosen, they would have had to be a politically mandated choice...in the words of Lueders: "I do not have enough funding available to even attempt to negotiate a price from Blue Origin that could potentially enable a contract award." The Dynetics proposal was a surprise though. It somehow went from half the cost of the Blue Origin one to even higher cost, while ending up in the red on their mass budget and apparently becoming less capable. Not sure what happened there.
I'm surprised and impressed that NASA didn't throw the Blue Origin team a bone, since it included Lockheed-Martin and Northrop-Grumman. Perhaps this is a sign of better days to come.
As the sole award, too. Not surprising that Blue Origin wasn't chosen, they would have had to be a politically mandated choice...in the words of Lueders: "I do not have enough funding available to even attempt to negotiate a price from Blue Origin that could potentially enable a contract award." The Dynetics proposal was a surprise though. It somehow went from half the cost of the Blue Origin one to even higher cost, while ending up in the red on their mass budget and apparently becoming less capable. Not sure what happened there.
I'm surprised and impressed that NASA didn't throw the Blue Origin team a bone, since it included Lockheed-Martin and Northrop-Grumman. Perhaps this is a sign of better days to come.
Yeah, their lineup of partnerships was clearly designed to get political support on their side, and the usual Congresscritters are already complaining about the award (Rep. Eddie Bernice Johnson complaining they didn't wait for "Ballast" Nelson to get in place as administrator first, as if it wasn't Lueders' job and responsibility to make the decision). Some of the other problems with Blue Origin's proposal, like asking for advance payments that were specifically not allowed and proposing more restrictive licensing and sharing of IP than the request required, make me wonder if they overestimated the political clout they had.
Yeah, their lineup of partnerships was clearly designed to get political support on their side, and the usual Congresscritters are already complaining about the award (Rep. Eddie Bernice Johnson complaining they didn't wait for "Ballast" Nelson to get in place as administrator first, as if it wasn't Lueders' job and responsibility to make the decision). Some of the other problems with Blue Origin's proposal, like asking for advance payments that were specifically not allowed and proposing more restrictive licensing and sharing of IP than the request required, make me wonder if they overestimated the political clout they had.
I watched Scott Manley's video on the subject, and apparently according to the internal documents it just boiled down to cost. Congress had limited the budget for Artemis to one-third of what NASA asked for, and SpaceX was the only one of the three that could deliver a proposal at that price, never mind that the system delivered at that cost has like ten times the capability of either competitor. Unless Congress is willing to fork over another ten billion dollars, I don't think complaining about it will do them any good.
From SpaceX's point of view, it's about as big a win as one can get... to have NASA pay you almost 3 billion dollars for something you were doing on your own anyway.
So... I'm wondering what NASA will do when Starship beats SLS/Orion to the Moon.
