Should launch providers switch to common methalox engines?

[Robotbeat]

That's not a better source.

A better source than what? You have not even given one.

but you're quite close if you just use a factor of 2.

"quite close" is not good enough.

Ive explained my reasoning in sufficient detail and provided a link to supporting analysis (if you want, I can point to the pressure vessel equation, but it just says vessel dry mass is proportional to volume). You haven't supplied a link or explained reasoning in any detail. The ball is in your court.

[TrevorMonty]

A point of trivia the Vulcan ACES PF is 96%

No way.

 Centuar is 90% with IVF expected to increase that to low 90s. So 96% for ACES may not be far off the mark.

[Oli]

Ive explained my reasoning in sufficient detail and provided a link to supporting analysis (if you want, I can point to the pressure vessel equation, but it just says vessel dry mass is proportional to volume). You haven't supplied a link or explained reasoning in any detail. The ball is in your court.

First, my numbers come from this post, which is a methalox rocket design from actual Russian engineers. The upper stage has a pmf of 92%, but I was nice and picked the pmf of the first stage which is 93% (both rounded).

Your "source" does a rather unsophisticated calculation of payload for a constant-volume SSTO. They say the model should be used to compare fuels with roughly similar density/isp. More useful formulas for dry mass calculation can be found here. In-space stages are less volume-limited than SSTO (no drag, TPS).

Centuar is 90% with IVF expected to increase that to low 90s. So 96% for ACES may not be far off the mark.

In terms of actual mass savings its a huge step.

Centaur has the best pmf of any hydrolox upper stage to date. Of course there's always better stuff out there, e.g. the Ariane 5 core, but I tried to make a fair comparison.
 
If you look at NASA designs for in-space stages, they usually have far worse pmfs than upper stages.

[Robotbeat]

Ive explained my reasoning in sufficient detail and provided a link to supporting analysis (if you want, I can point to the pressure vessel equation, but it just says vessel dry mass is proportional to volume). You haven't supplied a link or explained reasoning in any detail. The ball is in your court.

First, my numbers come from this post, which is a methalox rocket design from actual Russian engineers. The upper stage has a pmf of 92%, but I was nice and picked the pmf of the first stage which is 93% (both rounded).
...

Russians generally build their rocket stages like tanks. You can see people walk on top of Soyuz boosters as they're being built. In contrast, the American hydrolox stages like Centaur that can achieve 90% PMF are built with balloon tanks, with metal so thin it can't even support its own weight under gravity and must be pressurized at all times. You're using a false comparison.

(This isn't a dig at Russian engineering. Building their rockets like that has served them well.)

[Pipcard]

What they [Arianespace] don't have is the culture of a SpaceX, which allows them to change the ways to adapt quickly with what might be heretical approaches that challenge technology base and heritage - because evolving a hydrolox propulsion system to a less expensive, modular launch architecture (possibly reusable) requires addressing massive changes of esoteric nature with a KISS approach that can be replicated with lowest labor costs, in an environment that is motived by entirely the opposite mindset.

Kerolox and methalox launchers with a single engine type make for the most economical LV - this simply won't go away. Forget for the moment the reusability aspect - just from the standpoint of supporting reliable production through the smallest footprint, approaches like this win at the budget level, but compromise at the launch vehicle performance level. If you can't accept the performance compromise(including flying multiple launch missions) then one must accept the burden of 10x budget (or more) for what it takes for optimal propulsion.

If a launch vehicle manufacturer had already made investments into developing "high-energy" hydrolox stages, should they abandon that, or should they retain that knowledge and capability?

[jongoff]

This is the thinking behind Mars direct, but it is also applicable to the lunar poles since LCROSS found out that the ice in dark lunar craters contains more CO than H2O.

This actually may not be correct, based on a conversation I had with Paul Spudis at a conference this last week that I summarized in this post:

http://forum.nasaspaceflight.com/index.php?topic=39559.msg1612453#msg1612453

tl;dr version is that he says of the two sensors that measured concentrations, the one that they have much more confidence in was saying 90-95% water. The sensor that was revised down to show less water was one that we don't have a lot of confidence in our ability to interpret.

~Jon