Here's a SABRE brain teaser: will flying through heavy rain and/or ingesting spray kicked up from the nose gear be any cause for concern? In a generic turbojet the compressor blades have to deal with rain drops, but by the time you get to the back, high pressure stages I think the water has evaporated so you just pass humid air to the combustion chamber. But in Skylon the rain/water has to pass in-between the precooler tubes before it hits the compressor. Looking at that exploded diagram it's hard to tell what will happen. Will most of the rain (relatively dense) fly past the pre cooler into the bypass ducts? Or does it get sucked through the precooler? And if the operating pressures are high enough ahead of the compressor then perhaps it just evaporates before it's of any concern?This is the sort of thing they could test with their current precooler setup - if it wasn't too risky.
Can anyone discern any thirst vector control hardware for those nozzles? To the untrained eye they appear locked in place by the structure.
I'll attach it here, just in case that article ever blows up for whatever reason.
Quote from: john smith 19 on 01/05/2016 08:33 amQuote from: JCRM on 01/02/2016 08:25 amare people going to carry on accepting the necessity of falling COPVs?The COPV for the F9 stage was inside the tank most of the time.I was thinking of the hairy black space balls that farmers come across from time to time
Quote from: JCRM on 01/02/2016 08:25 amare people going to carry on accepting the necessity of falling COPVs?The COPV for the F9 stage was inside the tank most of the time.
are people going to carry on accepting the necessity of falling COPVs?
No boil off means no burn off.
Quote from: john smith 19 on 01/03/2016 09:52 pmNo boil off means no burn off. No such thing with hydrogen. There is always boil off.
Quote from: Jim on 01/25/2016 04:39 pmQuote from: john smith 19 on 01/03/2016 09:52 pmNo boil off means no burn off. No such thing with hydrogen. There is always boil off.AFAIK all LH2 work has been done at NBP. I'm also not sure how these systems are pre cooled, or wheather they have just flushed the system and let it flash boil to GH2 before venting.I think this has a lot to do with design decisions made in the 1960's. IIRC the SLS LH2 delivery system will cut the H2 waste by 50%. My instinct is the key issues are a)Precooling all the hardware down to be the precooled level b)Precooling the LH2.REL plan to operate around 16-18K, rather than 20K+what has been done is not the limit of what can be done.
Quote from: RanulfC on 01/25/2016 07:16 pmI think Jim's point was that "boil-off" isn't something you can prevent due to the nature of LH2. Doesn't matter what temps REL is planning on working with as long as it's lower than ambient the propellant WILL boil, the question is at what rate. REL "planning" on having zero-boil off is part of the reason folks don't accept they fully understand what they are talking about Wikipedia tells me Hydrogen won't boil off below 20K. But the manual doesn't claim zero boil off, it only has zero venting (minimising boil off would help with that)
I think Jim's point was that "boil-off" isn't something you can prevent due to the nature of LH2. Doesn't matter what temps REL is planning on working with as long as it's lower than ambient the propellant WILL boil, the question is at what rate. REL "planning" on having zero-boil off is part of the reason folks don't accept they fully understand what they are talking about
QuoteI'll admit that line struck me as odd as well:"However REL's COP is to load and launch within 2 hrs or recycle the propellants to long term storage. By pre cooling the hardware and the propellants they expect zero boiloff under normal operation."Load and launch in two hours is pretty strict timingFuel loading is 40 minutes, followed by 24 minutes of towing and final checks, followed by a hold time of up to two hours, during which time the temperature rises in the foam insulated tanks inside a nitrogen purged atmosphere inside layers of Mylar, inside the ceramic shell. If the temperature gets above 20K, then the pressure in the tank will start to rise - I don't know if that's accounted for in the concept design, but these people have spent decades working with the thermodynamic properties of hydrogen If it's not gone in that time it needs to be towed back
I'll admit that line struck me as odd as well:"However REL's COP is to load and launch within 2 hrs or recycle the propellants to long term storage. By pre cooling the hardware and the propellants they expect zero boiloff under normal operation."Load and launch in two hours is pretty strict timing
Quote and by "pre-cooling" the hardware they are in essence planning on flowing large amounts of LH2 THROUGH the system and a large percentage of it is going to be fully gaseous and either need to be recycled or dumped until the system is fully cooled and even THEN the on-board LH2 is going to be trying to boil unless they are constantly cycling propellant through the tanks. (And all that piping is NOT going to be as insulated as the tanks are btw)* Install pipes and run LN2 through* Connect to liquid Helium source and fill to cool. Drain and recover helium* Connect LH2 and LO2 pipes and fill. Fill to 95% then top offI'm assuming "Draw vacuum in filler tube [...] Tank chill down (H2 boils off until tank is cold)" refers to the storage tank where they sub-cool the hydrogen, otherwise cooling Skylon with helium seems like an unneeded step.
and by "pre-cooling" the hardware they are in essence planning on flowing large amounts of LH2 THROUGH the system and a large percentage of it is going to be fully gaseous and either need to be recycled or dumped until the system is fully cooled and even THEN the on-board LH2 is going to be trying to boil unless they are constantly cycling propellant through the tanks. (And all that piping is NOT going to be as insulated as the tanks are btw)
QuoteSimply put, until REL shows a zero-boil off storage tank made of flight-weight materials and shows no "boiling" for two full hours no one who has worked with LH2 on a consistent basis is going to take the assumption seriously.It's conceptual operations of a conceptual vehicle. If a top-up and vent hose had to be used, no one would have batted an eyelid - but these people who have spent decades working with the thermodynamic properties of hydrogen seem to think it wont be needed - if it turns out they're wrong they have egg on their face, ConOps needs revising, infrastructure costs go up, and some mass margin is lost - but the vehicle concept probably remains valid.I guess that's a step along from no-one taking the idea seriously because intake air would be too hot, or no-one taking the idea seriously because precoolers are too slow, or no-one taking the idea seriously because precoolers are too heavy, or no one taking the idea seriously because undercarriage would be too heavy.
Simply put, until REL shows a zero-boil off storage tank made of flight-weight materials and shows no "boiling" for two full hours no one who has worked with LH2 on a consistent basis is going to take the assumption seriously.
QuoteI for one have noted that REL seems to be confusing/conflating "pre-cool" with "sub-cool" of the LH2 which btw runs into "slush-hydrogen" operations which seems to be what they are talking about rather than "pre-cooling".REL or commentators?My understanding is they precool Skylon, before filling it with sub-cooled hydrogen, where sub-cooled means significantly below the boiling point of hydrogen, but above freezing.
I for one have noted that REL seems to be confusing/conflating "pre-cool" with "sub-cool" of the LH2 which btw runs into "slush-hydrogen" operations which seems to be what they are talking about rather than "pre-cooling".
"Below the boiling point but above freezing" is in fact the usual definition of "slush" hydrogen used in most cases hence my question.
I thought it referred to hydrogen at it's triple-point of 14.01 K