Rocket Engine Q&A

[JosephB]

I'm curious to know how far the RS-84 program got. Did it end at the power point presentation stage or was there serious design work?
I can't help but envisage the Ares V using expendable kerolox engines with 5 seg boosters. Thanks.

[JosephB]

Never mind, after a little digging I see they did a PDR and tested a subscale preburner. Talk about a project worthy of finishing. Especially with shuttle retirement on the horizon.

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

[JosephB]

Anyone?

[Jim]

Never mind, after a little digging I see they did a PDR and tested a subscale preburner. Talk about a project worthy of finishing. Especially with shuttle retirement on the horizon.

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

Because RS-68 and SSME already exist

[JosephB]

Wow, that's a fast response. Thanks.
From what I read on the web isn't a modern kerolox supposed to be more reliable & less complex than LH2? For instance wouldn't 3 or 4 RS84's be better than 6 RS-68's? Not to mention less expensive (development costs aside)?

Or is the consensus that is room for improvement down the road?
The reason I ask is the extra RS68 & 1/2 segment on each side on the latest A5 could be remedied by the RS84 it seems.

[Antares]

Development costs and expertise.  Too much and too little.

[TrueGrit]

Merits of LO2/Kero over LO2/LH2 aside do how long it would take to develop a new engine?  Or cost?  Just as an example...  The RS-68/EELV inital contract was awarded in 1995 and first flight wasn't until 2002.  7 yrs with a price tag well under $1bil...  But that was a commerical structured development.  History has shown a NASA directed activity would take much longer and cost much more.  Heck the J-2X is costing more and taking long than the built from scratch RS-68...  7 yrs and $1.2bil.  My guess extraplotaed off this experience is that RS-84 would take ~10yrs to develop and cost ~$3bil.  Compare that to ~$200mil and ~2yrs to modify RS-68.

[JosephB]

Good points. I have to say I keep becoming more and more impressed with the designers & engineers from the 60's & 70's. What they accomplished with the tools, money & materials available in comparison to today...

As far as expertise goes, it seemed like the MSFC/Rocketdyne team had a pretty good handle on the project before it was shut down. Or is there more to it?Although it does sound like development is a BIT on the spendy side, it would be such an incredible 1st stage engine it seems worth it to swallow the up front costs to get on with moon/mars down the road. But as Jim said, if you can put enough 68's on it and get the job done...

With Goverment the way it is cost is relative. For the price of a couple B2 bombers we could have an engine to push us to the planets! I'd check a box on my 1040 to donate $3 to Ares V instead of presidential candidates.
Does anyone know how much shuttle engines cost to develop?

[Patchouli]

Merits of LO2/Kero over LO2/LH2 aside do how long it would take to develop a new engine?  Or cost?  Just as an example...  The RS-68/EELV inital contract was awarded in 1995 and first flight wasn't until 2002.  7 yrs with a price tag well under $1bil...  But that was a commerical structured development.  History has shown a NASA directed activity would take much longer and cost much more.  Heck the J-2X is costing more and taking long than the built from scratch RS-68...  7 yrs and $1.2bil.  My guess extraplotaed off this experience is that RS-84 would take ~10yrs to develop and cost ~$3bil.  Compare that to ~$200mil and ~2yrs to modify RS-68.

Instead of building the J2X in house they should have just handed a set of performance requirements to various engine manufactures and held a competition.

[William Barton]

Merits of LO2/Kero over LO2/LH2 aside do how long it would take to develop a new engine?  Or cost?  Just as an example...  The RS-68/EELV inital contract was awarded in 1995 and first flight wasn't until 2002.  7 yrs with a price tag well under $1bil...  But that was a commerical structured development.  History has shown a NASA directed activity would take much longer and cost much more.  Heck the J-2X is costing more and taking long than the built from scratch RS-68...  7 yrs and $1.2bil.  My guess extraplotaed off this experience is that RS-84 would take ~10yrs to develop and cost ~$3bil.  Compare that to ~$200mil and ~2yrs to modify RS-68.

Instead of building the J2X in house they should have just handed a set of performance requirements to various engine manufactures and held a competition.

In order for that to work there would have to be "various" engine manufacturers working in the technology and size class (in the US, for LH2/LOX there's PWR and who else?), and those various engine manufacturers would have to have and be willing to invest their own capital. Otherewise, if you hand out taxpayer money to various engine manufacturers in order to see who comes up with an engine first, it's not a competition, it's corporate welfare. Give me a billion dollars up front and I'll join any competition you want.

[William Barton]

Merits of LO2/Kero over LO2/LH2 aside do how long it would take to develop a new engine?  Or cost?  Just as an example...  The RS-68/EELV inital contract was awarded in 1995 and first flight wasn't until 2002.  7 yrs with a price tag well under $1bil...  But that was a commerical structured development.  History has shown a NASA directed activity would take much longer and cost much more.  Heck the J-2X is costing more and taking long than the built from scratch RS-68...  7 yrs and $1.2bil.  My guess extraplotaed off this experience is that RS-84 would take ~10yrs to develop and cost ~$3bil.  Compare that to ~$200mil and ~2yrs to modify RS-68.

One of the commonplace ideas that gets put forward from time to time is to allow taxpayers to designate how their taxes are spent, at the federal level. Put a form in with the 1040 that allows you to mark government agencies with a percentage of your tax outlay, is one version of it. You like welfare, pay for welfare. You like the Navy, pay for the Navy. You like art or basic science, your taxes turn to grant money. All the objections to it are trivial, along the lines of, what if nobody wanted to pay for defense (or whatever the objector thinks is important)? But the real reason it gets no traction is because the government already gets to take our money at gunpoint, and we get no real say in how it's spent. Voting only gives you a very tiny input. My favorite line from "Charlie Wilson's War" is too chauvinist to quote in full here, but it begins, "Honey, I'm not elected by voters..."

[JosephB]

It's frustrating to see all these vehicle & technology development programs never leaving the laboratory to get practically applied in space. It's unfortunate the Nasa paradigm is captive to each successive administration like it is & left chasing the next big thing without finishing the last every few years or so.

Welcome to the real world I guess.

We should be thankful to have shuttle & station.
And here I was all pumped to be be "taking the next step"....
Silly man.

[edkyle99]

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

It wouldn't work as a straight replacement for RS-68 engines on a long core. 

Although four RS-84 engines would produce roughly the same total liftoff thrust as six RS-68 engines, the substantial specific impulse advantage of the RS-68 LH2 engines provide much more payload.  The RS-84 powered core boosted by two five-segment boosters topped by a J-2X powered Earth Departure Stage would only boost about 3/4ths as much payload to TLI as the RS-68 powered core version.

An RS-84 engine would work better on a different launch vehicle design - probably something more like Saturn V with no solid boosters at all, a kerosene first stage, a big hydrogen second stage, and a smaller, optimized TLI third stage.  Or, alternatively, a hydrogen core lifted by RS-84 powered liquid boosters. 

 - Ed Kyle

[Jorge]

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

It wouldn't work as a straight replacement for RS-68 engines on a long core. 

Although four RS-84 engines would produce roughly the same total liftoff thrust as six RS-68 engines, the substantial specific impulse advantage of the RS-68 LH2 engines provide much more payload.  The RS-84 powered core boosted by two five-segment boosters topped by a J-2X powered Earth Departure Stage would only boost about 3/4ths as much payload to TLI as the RS-68 powered core version.

Since the mixture ratios are different, the tanks would have to be resized as well.

[edkyle99]

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

It wouldn't work as a straight replacement for RS-68 engines on a long core. 

Although four RS-84 engines would produce roughly the same total liftoff thrust as six RS-68 engines, the substantial specific impulse advantage of the RS-68 LH2 engines provide much more payload.  The RS-84 powered core boosted by two five-segment boosters topped by a J-2X powered Earth Departure Stage would only boost about 3/4ths as much payload to TLI as the RS-68 powered core version.

Since the mixture ratios are different, the tanks would have to be resized as well.

Right.  And they would be much smaller in overall length than the current core, which would complicate  the booster attachment design (it currently uses a thrust beam running through the core inter-tank).

 - Ed Kyle

[kraisee]

Good points. I have to say I keep becoming more and more impressed with the designers & engineers from the 60's & 70's. What they accomplished with the tools, money & materials available in comparison to today...

They did have one big advantage.   They managed to do pretty-much all of their designs before they lost their first crew. The loss of the Apollo-1 crew changed a lot of things. *Everything* had to be scrutinized a lot more after that, from initial designs to prototype hardware, to production processes and everything else all the way to launch -- and even after. Congress forced an enormous amount of additional oversight at every level in order to prevent such another international embarrassment from occurring again.

The loss of Challenger and Columbia both also forced considerable increases in the work needed behind the scenes too.

One example:   Take the re-design work which had to go into the foam Ice Frost Ramps on the External Tank, or the removal of the Pal Ramps.   When you look at them, the changes are pretty simple jobs to accomplish physically -- essentially just shave some 'excess' foam off the tank -- but the process required to quantify the aerodynamic effects of those changes took *years* of effort to allow the Shuttle Program to actually certify the changes.

Back in the early days, such a change as that might very well have been decided in a two hour long meeting and a pad rat would be sent out to the Pad to shave the offending article off the vehicle within a few hours of that!   That sort of 'fix' did happen from time to time back then.

The agency today is a world apart from its younger self in terms of being risk averse.   Some say that's a good thing. Others say its gone too far.   As is so often the case, the truth is probably somewhere in between the two extremes.

But regardless, the effects are very tangible:   Human rated hardware for NASA is a lot more expensive and takes a lot more time to prepare than hardware for almost any other human endeavour.   Because when someone screws up, people die in an extraordinarily visible way and these days all the world watches the USA screw-up live on CNN.

That's the biggest difference between then and now.

Ross.

[gospacex]

Any thoughts as to why a kerolox RS-84 would/wouldn't work with the 10m Ares V and 5 seg boosters?

It wouldn't work as a straight replacement for RS-68 engines on a long core. 

Although four RS-84 engines would produce roughly the same total liftoff thrust as six RS-68 engines, the substantial specific impulse advantage of the RS-68 LH2 engines provide much more payload.  The RS-84 powered core boosted by two five-segment boosters topped by a J-2X powered Earth Departure Stage would only boost about 3/4ths as much payload to TLI as the RS-68 powered core version.

Well, "the same total liftoff thrust" means that your core stage is much smaller, because RP-1 is so much more dense. If you retain general dimensions of tankage, LOX/RP-1 based booster would weigh much more, need more engines, but also would have much bigger performance.

Anyway, as resident gurus say, "rockets aren't lego blocks", swapping LH engines for RP-1 ones cannot be done like that, serious redesign of the stage is inevitable.

[gospacex]

The agency today is a world apart from its younger self in terms of being risk averse.   Some say that's a good thing. Others say its gone too far.   As is so often the case, the truth is probably somewhere in between the two extremes.

But regardless, the effects are very tangible:   Human rated hardware for NASA is a lot more expensive and takes a lot more time to prepare than hardware for almost any other human endeavour.   Because when someone screws up, people die in an extraordinarily visible way and these days all the world watches the USA screw-up live on CNN.

That's the biggest difference between then and now.

Ross.

Do you have an explanation why "risk-averse" NASA's designs are complex and work-intensive? This doesn't look logical.

[MKremer]

Do you have an explanation why "risk-averse" NASA's designs are complex and work-intensive? This doesn't look logical.

Imagine, starting tomorrow, everything you do once you wake up must be documented - not only on paper (with details and samples tested) but with photographs during and after, including your morning ablutions, dressing, travel, workday, lunch, and going home, etc., etc.

Things you use must have extensive documents as well - for example, your toothbrush must have documents detailing how it was made, the materials (sources and processing), how it was inspected and packaged (with its own documented evidence), when and how it was purchased, and when it was opened and additional inspections at that time as well.
(and that's just for one item!)

That's what's meant by "complex and work-intensive". Everything dealing with manned spaceflight hardware, down to individual components, must have a documentation and testing trail that follows it through creation, assembly, and testing. Doesn't matter if it's part of the spacecraft, the booster, or anything else being 'flown' (including crew items), it has to have extensive and expensive testing and documentation, which costs lots and lots of extra $$$.

[JosephB]

Man you guys are good! Thanks for all the detailed info and thanks for taking the time to explain. Reading the more technical members posts is the main reason I joined L2. What appears to make sense to an interested observer is very deceiving. It IS rocket science after all! Also, very interesting commentary on the old/new Nasa.

I have a bit of a moon/Mars bias so reading about heavy lift becoming a reality raises an eyebrow or two. What likelihood would you guys give Ares V actually seeing a launch pad?