So, if the exhaust pressure is below the ambient pressure, you end up with a negative term in your thrust equation. i.e. (Pe - P0)*Ae < 0. And ergo, a reduction in thrust.
Intrigued by the LANTR-concept, I tried to replicate the different Isps for different mixture ratios by using the formula Ve^2=2k/(k-1)*R*T/M, which I've found here and simplified a bit by removing the part with different pressures, as that factor would most likely be rather close to 1.However, I always get results that are way off, e.g., if I go for pure hydrogen & T=2900, according to the 1st linkI should get an Isp of around 940, so a Ve of around 9000. But what I actually get is: Ve=sqrt(2*1.666/0.666*8.314*2900/1)=347.311m/s, which is off by a factor of 30(!).Could anybody tell me what exactly I'm missing here?
What are the reasons for using hydrogen in a first stage? Ever? This is a genuine question.Ok, Shuttle did it, H-II does it, Ariane V does it. But all with (comparitively poor) Isp boosters.Hydrogen is _great_ for an an upper stage, but surely a royal pain in the rear in the volumes required (and the necessary insulation for that immense volume) in the warm lower atmosphere for a (necessarily large) first stage.Never mind embrittlement of alloys et al.Saturn used H2, but _only_ when high and fast in upper stages, Centaur ditto. No hydrogen low and slow.Looking back, hydrolox in first (boosted) stages looks like a fad. Methalox _now_ looks like a fad, but perhaps a much better one, though that is to be proven.I wonder as a mere software engineer if there ever was, or is, a good reason for a rocket engine to ever be burning hydrogen at close to sea level.
Quote from: nicp on 01/04/2018 11:51 pmWhat are the reasons for using hydrogen in a first stage? Ever? This is a genuine question.Ok, Shuttle did it, H-II does it, Ariane V does it. But all with (comparitively poor) Isp boosters.Hydrogen is _great_ for an an upper stage, but surely a royal pain in the rear in the volumes required (and the necessary insulation for that immense volume) in the warm lower atmosphere for a (necessarily large) first stage.Never mind embrittlement of alloys et al.Saturn used H2, but _only_ when high and fast in upper stages, Centaur ditto. No hydrogen low and slow.Looking back, hydrolox in first (boosted) stages looks like a fad. Methalox _now_ looks like a fad, but perhaps a much better one, though that is to be proven.I wonder as a mere software engineer if there ever was, or is, a good reason for a rocket engine to ever be burning hydrogen at close to sea level.All three of your examples use large SRBs. For example, Ariane 5 gets 90% of its takeoff thrust from the solids. So, one way of looking at it is the SRBs are the first stage while the hydrolox booster is the second stage. No matter what you call it, when the SRBs are very large, a hydrolox booster makes sense.
What are the reasons for using hydrogen in a first stage? Ever? This is a genuine question.Ok, Shuttle did it, H-II does it, Ariane V does it. But all with (comparitively poor) Isp boosters.
Hydrogen is _great_ for an an upper stage, but surely a royal pain in the rear in the volumes required (and the necessary insulation for that immense volume) in the warm lower atmosphere for a (necessarily large) first stage.Never mind embrittlement of alloys et al.
Saturn used H2, but _only_ when high and fast in upper stages, Centaur ditto. No hydrogen low and slow.
Looking back, hydrolox in first (boosted) stages looks like a fad.
Methalox _now_ looks like a fad, but perhaps a much better one, though that is to be proven.
With LH2, you get pretty good thrust....
Hi,please, how can I calculate needed amount of oxygen in gaseous state versus liquid. If you need 1 unit of liquid oxygen, how many units of gaseous it will be? Under atmospheric pressure, or under 200 bar?Thank you
Does anyone know how many rocket engine nozzles have been damaged in flight?I know STS-93 experienced a frightening event just after liftoff that I understand involved the regen nozzle being punctured through, but are there any other known instances of such problems elsewhere?-MG.
Maybe the Merlin 1C that failed on an early Falcon 9 flight? (I seem to recall that involved implosion of the nozzle, but I'm not sure).
...When considering the Pa term during the low altitude segment of the flight, is that very strictly the general atmospheric pressure at the rocket's altitude? I believe the forward travel of the rocket and backward travel of the high velocity exhaust gasses creates a localized low pressure at the base of the rocket (this causes the plume recirculation seen on some launches, right?). Does this area's lowered pressure need to be taken into account for a higher accuracy calculation of the thrust?
On CRS-1, a Merlin 1C engine had a fuel dome (a structure above the thrust chamber) rupture and lose pressure. Nothing to do with the nozzle.