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Comment by valarauca1 | Hacker News Reader

Not exactly. The "real" difference is if we cut down to a 4 cylinder at half the horse power, half the torque. While a "newer" engine does achieve higher thrust to weight nobody is building engines with anywhere close to the trust of the J-2.

NASA actually is attempting to rebuild the J-2, with the J-2X program. The problem is nobody knows how the J-2 works and part of the contract included NASA shipping several J-2's back for re-engineering.

I should also remind you that a year ago NASA didn't actually know "how" the j-2 worked. Their numbers said the bell should melt during flight. Eventually they realized that helium is injected on a outer ring of injectors to insulate the bell.

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My point was more that you don't need the raw thrust of the F-1 / J-2 so much these days because we've made up for the lack of single-launch capacity by advances in other areas. Look at the ISS - it could not have been launched with Apollo-era tech, because the Saturn V couldn't launch it in one hit, and they didn't know how to put things together on-orbit. +(see edit)

These days it becomes a cost/benefit analysis - is the extra cost of doing things in one big monolithic lift more or less than the extra cost incurred by having to break things into smaller components and assemble on orbit. Clearly heavy lift still has advantages - there's a reason everyone is excited about Falcon 9 Heavy, but rockets are tricky beasts, and multiple smaller launches helps mitigate against catastrophic failure (although it may increase the risk of partial failure).

Edit: Just to be clear, I'm talking about automatic on-orbit assembly, which means that you don't have to launch a pilot + life support each time you want to join two bits together.

Your argument is that orbital assembly didn't exist in the Apollo era, when Orbital Assembly WAS the runner up to the SaturnV single launch option [Source Original Posters Article].

This means logically some times its more cost efficient, or simpler to put 27 tons in orbit in one launch, then assembly 6 5 ton launches.

Actually it is far better to minimize the number of launches to complete any mission. For example, Elon Musk has repeatedly mentioned that he is not currently a fan of in-orbit assembly. So having a really powerful engine is of great utility. The problem is one of cost-benefit. Having a huge engine means a big rocket which needs to be launched multiple times to achieve economy. But there are not too many missions around which require such capacity. Just look at the proposed SLS cadence. So having a Falcon Heavy with 27 engines is a much better solution any way. I cant wait when Merlin 1Ds are replaced with Raptors on first stage on Falcon Heavy. That would be one monster of a rocket.

> Actually it is far better to minimize the number of launches to complete any mission.

Doubtful. To design a big rocket takes a lot of money - and big rocket doesn't get to be used as much as a smaller rocket sometimes, which makes it more expensive per flight.

The opinions of Elon Musk aren't always perfect either. Certain technical decisions are made not because they are best, but because they are available - like, SpaceX just knows how to do that, and considers it expensive to learn the alternatives. Which is quite justifiable on economical grounds.

> I should also remind you that a year ago NASA didn't actually know "how" the j-2 worked. Their numbers said the bell should melt during flight. Eventually they realized that helium is injected on a outer ring of injectors to insulate the bell.

I think this is remarkable, given that film cooling of the nozzle is a known aspect [0] of the first stage engines of Saturn V.

[0] Thrust Chamber Nozzle Extension section on page 3 http://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Eng...

That's wrong. Vulcain 2 on Ariane 5 flew four times in 2013. It's a 1340 kN thrust LOX-hydrogen engine. By contrast the J-2X will have 1307 kN.

Also the F-1 engine has been surpassed in thrust and efficiency by the Russian RD-170 family which flies today in the Zenit rocket.

I'm sure you could learn a lot from studying the J-2 and J-2S. No harm in that. But mystifying Apollo has done a lot of harm to sane space technology engineering and policy.

Sources: http://www.arianespace.com/news-launch-logs/2013-2014.asp http://www.sea-launch.com/missions-q1-past_launches.aspx http://www.spacelaunchreport.com/log2013.html

They (well, contractors) are re-engineering the F-1B as well: http://arstechnica.com/science/2013/04/new-f-1b-rocket-engin...

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