Liquid fueled alternatives to the Ares I solids.

[exoscientist]

This Astronautix page gives the old Saturn F-1 engine a vacuum thrust of 1,740,134 lbf at a weight of only 18,498 lb for a thrust to weight ratio of nearly 100 to 1:

F-1.
http://www.astronautix.com/engines/f1.htm

The Astronautix page on the Ares I solids give it vacuum thrust of 3,480,122 lbf but an empty weight of 221,230 lb (!) for a thrust to weight ratio of only 16 to 1 (!):

Ares.
http://www.astronautix.com/lvs/ares.htm

The tank mass for a kerosene-LOX engine is only about 1/100th that of the propellant mass. So even if you used the same propellant mass as the Ares I solids of about 1,400,000 lb that would only add 14,000 lb to the lower stage empty mass. But actually the propellant mass would probably be less since the F-1 had a better Isp at 304 s compared to 265 s for the Ares I solids.
Given this, how much larger payload could we launch to LEO using the 2 F-1 engines in place of the Ares I solids as the 1st stage?
How much could we launch to LEO using just 1 F-1 engine as the 1st stage?


Bob Clark

 

[exoscientist]

The Russian RD-171 and RD-180 are high thrust, liquid-fueled engines still in active operation. Here's the Astronautix pages on the RD-171 and RD-180:

RD-171
http://www.astronautix.com/engines/rd171.htm

RD-180
http://www.astronautix.com/engines/rd180.htm

You would need 2 to 3 of these to match the thrust of the Ares I first stage solids. But the thrust to weight is so much better you might be able to match the payload to orbit just using one of these engines. (You would have 200,000 lbs less dry mass at launch.)


Bob Clark

 

[exoscientist]

This page gives altitude and velocity of the Ares I at first stage separation as 59 km and 2024 m/s:

Space Launch Report - Ares I.
http://www.spacelaunchreport.com/ares1.html

Then we can estimate how much fuel it would take to reach this delta-v, including the gravity drag for that altitude, based on the Isp of the liquid fuel engines and the mass of
the Ares upper stage.

A preliminary calculation shows the RD-180 wouldn't have enough thrust for the fuel load required. However, the RD-171 should be able to do it using the specifications given here:

RD-171
http://www.astronautix.com/engines/rd171.htm

The second stage of the Ares I is about 175,000 kg, when you include payload. The RD-171 weighs 9,500 kg. Even if you used as much fuel mass as the SRB of 1,400,000 lb, a tankage mass ratio of 1/100th the propellant mass for kerosene/LOX engines would only add 7,000 kg. So call the the upper stage plus the empty weight of the lower stage 200,000 kg.
You want to reach the same velocity of 2,000 m/s and altitude of 50 km reached by the SRB. The delta-v required for the altitude can be found from the equation v^2 = 2gh. So for h = 50,000 m, v = 990 m/s.
Air drag losses it turns out are relatively small for large cylindrical rockets that get rapidly out of the atmosphere, about 150 m/s for medium sized launchers by this page:

Flight Mechanics of Manned Sub-Orbital Reusable Launch Vehicles with Recommendations for Launch and Recovery.
http://www.spacefuture.com/archive/flig ... very.shtml

So let's call the total delta-v 3,000 m/s. The Isp of the RD-171 is given on the Astronautix page as 309 s at sea level and 337 s in vacuum. Let's give it an average Isp of 320 s. Then the mass ratio is exp(3,000/3200) = 2.554. So for a mass at first stage burnout of 200,000 kg, the mass at launch would be 2.554x200,000 = 510718 kg. Of this 510,718-200,000 kg = 310,718 kg would be fuel, less than half of the fuel load of the SRB for Ares I.
The launch mass of 510,718 kg = 1,123,580 lb is well within the thrust capabilities of the RD-171 to lift, with its sea level thrust of 1,697,300 lb.


Bob Clark

 

[exoscientist]

There had been some suggestions to use the Atlas V Heavy as an alternative to the Ares I. According to this article NASA rejected the Atlas V Heavy for human missions because of the payload mass requirements:

Lockheed and Bigelow Human-Rated EELV deal.
Man Rating the Atlas V
September 21st, 2006 by Chris Bergin
"NASA considered and rejected the use of Atlas V as a Space Shuttle replacement for human space flight during their Exploration Systems Architecture Study (ESAS) last year. The ESAS stated that it deemed both Boeing Delta IV and Atlas V development options as ‘high risk’ for an on-time 2011 operational capability to meet CEV mass requirements."
...
"The reason for the NASA ESAS man-rating concerns was due to the 25mT CEV mass requirement, which ESAS maintained could not safely even be met by the massive Atlas V Heavy variant. According to a Lockheed Martin paper unveiled this week at the Space 2006 conference, the basic Atlas V 401 can meet FAA and NASA man-rating requirements with little modification with a much smaller capsule mass of 20,000 lbs."
http://www.nasaspaceflight.com/2006/09/ ... eelv-deal/

However, the reason the Atlas V Heavy wouldn't be able to lift the same payload as the Ares I is because it uses a much smaller engine for the upper stage, the RL-10A:

RL-10.
http://www.astronautix.com/engines/rl10.htm

The J-2X engine planned for the Ares I upper stage has 10 times the thrust of the RL-10A:

J-2.
http://www.astronautix.com/engines/j2.htm

Using two RD-180's, cheaper than the three for the Atlas V, to replace the Ares I first stage, while also keeping the J-2X for the upper stage, would actually allow you to increase the payload to orbit.

The same would be true of the RS-84 engine if development were restarted. This engine was also planned to be reusable:

July 21st, 2003
Kerosene Engine Passes Design Milestone.
Written by Fraser Cain.
http://www.universetoday.com/2003/07/21 ... milestone/

This article from 2003 stated a full scale model would have been ready for testing four years after that in 2007. The program was cancelled in 2004 however. If you suppose there was an additional year of development before it was cancelled in 2004, then conceivably a full scale model could be ready for testing by 2012 if development were restarted this year.


Bob Clark

 

[exoscientist]

The Atlas V 401 definitely could not make the 25 mT payload requirements to match the Ares I performance. This is an already existing booster so was suggested as an alternative to the Ares I to save cost.
The Atlas V HLV is only a proposed booster and has not been built or authorized. But its suggested payload to orbit would exceed that of the Ares I. It uses 3 RD-180's in its lower stage with a thrust of about 3,000,000 lb which is about comparable to the Ares I solids, but with a lower dry mass so should indeed be able to exceed the Ares I in payload to orbit. NASA's claim that it could not "safely" reach the 25 mT payload goal is puzzling, unless it means "man rating" of the engines but that should be true regardless of the payload mass.

So there are several options if the Ares I solids are to be replaced with liquid fueled engines for manned missions. All of these could surpass the Ares I in payload to orbit:

1.)Replace the solids with a single RD-171. This engine has been used many times, but is a Russian engine. It would be cheaper. But I consider it unlikely that the U.S. would want to be dependent on a Russian engine for all manned flights for a long period.

2.)Replace the solids with two RD-180's and keep the J-2X engine now proposed for the Ares I upper stage. The RD-180 has been contracted at least to be made by an American manufacturer, Pratt & Whitney, but I'm informed none have actually been made in the U.S.
This would be more palatable to be used for all near term manned missions if the ones used are made in the U.S. The fact there are two needed would increase the cost as well as the fact they would be made by an American company.

3.)Use the Atlas V HLV with 3 RD-180's for the lower stage, with the RL-10A, perhaps two of them, for the upper stage. Using 3 RD-180's would be more expensive but you might save on the cheaper RL-10A's for the upper stage compared to the J-2X.

4.)Restart development of the RS-84. Two of these would give comparable performance to using 2 RD-180's with a J-2X powered upper stage. This would be reusable so it gives you some more options for saving money if a flyback booster capability is developed. Main disadvantage is that it's still not completed. You would then have to figure also development costs.

Cheapest option is undoubtedly #1. But I consider it politically impossible.
My personal preferred option is #4 because it would be an American engine and also because it would be reusable, though very likely more expensive than the others.


Bob Clark

 

[ThereIWas2]

You left out another option: Reduce the 25mT requirement. I think part of the reason for that particular number is to force the choice of Ares as the solution. An old military procurement trick.

 

[docm]

Or use Falcon 9 Heavy if it works out: 29.6 mT, or more with the LH2 second stage they're already announced for F9. Since F9's designed to be man rated one would think that gives them a leg up doing the same with F9H.

Yeah, yeah...speculation, but so is using a so far non-man rated Atlas V.

Of course there is the argument that F9 hasn't flown yet, but if it does and well over the next several months IMO that option deserves looking at.

Not invented here isn't a valid reply.

 

[MarkStanaway]

A cheap and nasty way to overcome any performance shortfall with Ares 1 would be to strap a few GEM's (Graphite Epoxy Motors) to the base. These have the advantage of being able to be fired in sequence to limit G forces and tuned for maximum performance at altitude.
They have been doing this to enhance Delta 1 and 2 performance for decades.

 

[exoscientist]

Glad to see the Augustine commision is at least considering the development of a new heavy thrust kerosene engine:

Loss of Ares I work wouldn't end world.
Sunday, August 16, 2009 By Shelby G. SpiresTimes Aerospace Writer
"For example, the commission reviewed proposals that would ask contractors to build an engine that would use liquid oxygen and kerosene, also known as rocket fuel RP-1, to power a "rocket that might not look like the Saturn V, but would be similar," said Ed Crawley, a panel member.
"This is the same type of engine as the F-1 engine that was used on the first-stage booster of the Saturn V and got the rocket 38 miles high in the Earth's atmosphere on its trip to the moon. Flying at more than 17,000 miles per hour, the space shuttle rockets can only take humans and cargo into low Earth orbit, but a Saturn V-type rocket can zoom to more than 22,000 miles per hour - fast enough to escape the tug of Earth's gravity - and put astronauts on a course to the moon."
...
"Panel members pointed out that developing an F-1 type engine would move American rocket companies away from relying on Russian technology, which creates complex legal and trade issues because Russia does business with Iran and North Korea.
"There are some negatives to developing a new engine like the F-1, Augustine panel members said, because America has not developed this type of engine for almost 50 years.
"Dennis Wingo, a Hunts-ville space entrepreneur who has worked for NASA and the University of Alabama in Huntsville, said starting a new engine design could become another half-finished program, just like the Ares I might become.
"Developing an F-1 class engine would be a marvelous idea as the (commercial rocket) program needs it. However, for a heavy lifter for the exploration program, it has the same problem that all the other heavy lift ideas have - lack of money,' Wingo said last week."
http://www.al.com/news/huntsvilletimes/ ... thispage=2

The development costs wouldn't need to be exorbitant however, if the construction was of engines that already had significant development work already done. I mentioned the Boeing/RocketDyne RS-84 that conceivably could have a prototype model by 2012 if restarted this year.

Another was the Northrup Grumman TR107:

TR107 Engine Component Technologies.
http://www.nasa.gov/centers/marshall/pd ... _tr107.pdf

This article from 2002 stated the development costs for two heavy thrust liquid fueled prototyoes would cost $1.3 billion:

TICKET TO RIDE.
"Potential replacements for the Space Shuttle
are taking shape as NASA struggles to finalise
the requirements for a second-generation
reusable launch vehicle."
GRAHAM WARWICK / WASHINGTON DC
8-14 OCTOBER 2002 FLIGHT INTERNATIONAL
"Engine development"
"The success of our architecture depends
on the success of NASA's engine development
programme," says Young. The space
agency is funding work on four main
engine candidates, two hydrogen fuelled
and two kerosene-fuelled. Pratt &
Whitney and Aerojet are developing
the Cobra, a 600,0001b-thrust (2,670kN)
hydrogen-fuelled, staged-combustion, firstand
second-stage engine, while Boeing's
Rocketdyne division is working on the
650,0001b thrust-class RS-83. Rocketdyne
is also pursuing the RS-84, a kerosene fuelled,
staged-combustion, first-stage
engine generating 1,100,0001b thrust,
while TRW is developing the 1,000,0001b
thrust-class TR107.
The plan is to test two prototype
engines at a cost of $1.3 billion. "NASA will
go for prototype engines that bracket the
requirements of the three contractors,"
says Ford. He suggests the emphasis has
shifted towards the kerosene-fuelled
engines. "NASA wants to address kerosene
first to reduce risk," he says. The USA has
little experience with kerosene-burning
rocket motors, having focused for decades
on cryogenic engines."
http://www.flightglobal.com/pdfarchive/ ... 02996.html

Note that the original development cost for the Ares I lower stage was slated as $1.8 billion, though the development fixes likely have increased that value.
SpaceShipOne showed that a flyback booster could be developed at low cost as long as the velocity could be kept in the Mach 3-4 range so that the reentry heating is much less.
This speed range is one of the possibilities the Air Force is considering for their flyback booster program. Then the development costs of the engine as well as the flyback airframe could be shared by NASA and the Air Force.
Actually considering how Scaled Composites was able to get SpaceShipOne done at such low cost it might be better to let them handle the design of the airframe rather than assigning it to the usual big aerospace companies with their usual accompanying, ballooning cost overruns.


Bob Clark

 

[exoscientist]

Just saw this article that says Ares I is all but certain to get cancelled:

John Kelly: Is Ares I work all for nothing?
As milestone passes, billions wasted if rocket is canceled.
BY JOHN KELLY • FLORIDA TODAY • August 17, 2009
"...The evening before KSC workers finished putting the first Ares I together, a panel of President Barack Obama's space advisers all but canceled Ares I and maybe even scuttled the whole moon-Mars program.
"NASA nevertheless is under orders to press ahead with Ares until the president makes a decision. That work is costing you about $300 million a month."
...
"Whatever the future holds for NASA, folks in Washington are near a consensus that the Ares I rocket has no place in it. That shiny new test model stacked and almost ready to fly at KSC might never roll to the pad. NASA and the taxpayers will again see a multibillion-dollar bid to replace the shuttles felled by the budget ax."
http://www.floridatoday.com/article/200 ... or+nothing

The problems with Ares I stem largely from the solid rocket first stage. The money spent on the upper stage including the crew vehicle would not need to have been wasted if it is retained while replacing the first stage solids with reusable liquid-fueled engines.
Even the money already spent on the solids need not have been wasted if the decision is made to still use solid rocket boosters on Ares V.
I don't rule this out, but my view is that we need to move forward to having reusable flyback boosters, certainly at least for the Ares I replacement.


Bob Clark

 

[vulture4]

Glad to see all the interest in Dr. Goddard's invention. Liquid fueled launch vehicles have major advantages beyond just ISP. Large segmented solids are hazardous from the moment they arrive. Dropped and/or ignitied solid stages have already killed people around the world. With liquids the rocket is essentially nonhazardous until it is ready to launch. There is to this day no way for the servicing personnel in the VAB to escape death if a stage is accidentally dropped and ignited. There are times in space exploration when risk is unavoidable. This is a risk that is completely avoidable, but which was ignored.

Large solids are many times as massive as liquids during the assembly process, requiring much larger ground transport systems. Compare the gargantuan MLP and crawler needed for the Shuttle with the (by comparisn) simple rubber-tired Kamag transporter that carries the entire Delta IV Heavy. Assembly of segmented solids requires many hours of tedious and expensive hazardous operations, with people doing such things as putting their hands under the crane-suspended segment to align the o-rings, and all solids produce toxic exhaust.

The only thing more inexplicable than the decision to use SRBs on the shuttle was the decision, after over 20 years of experience, to use them again on the Ares. The only part of the Ares planned for reuse is the SRB, yet despite over 20 years of experience, there is not a single study providing a shred of evidence that it is cost-effective to do so! The SRBs must be totally dissassembled and stripped to the bare metal, then rebuilt. This was apparently a matter of raw politics. Small, monolithic solids are fine for military missiles. But there is no way a large segmented solid-fueled launch vehicle will ever be either safe for ground operations or practical in cost for human spaceflight. The shuttle was the first solid-fueled rocket to carry people, and it should be the last!

 

[radarredux]

Putting on my conspiracy hat:

You left out another option: Reduce the 25mT requirement. I think part of the reason for that particular number is to force the choice of Ares as the solution. An old military procurement trick.

I have heard this on more than one occasion regarding multiple projects. NASA will specifically define requirements to exclude existing solutions in order to justify building something new. I got the feeling NASA wanted to build rockets.

NASA nevertheless is under orders to press ahead with Ares until the president makes a decision. That work is costing you about $300 million a month.

Wow! Is that right? Is that just for the Ares I booster or the Ares I, J-2X, and Orion?

 

[docm]

Looks like collectively;

AP story....

While the review is being done, NASA will continue the Ares and Orion programs. The space agency is spending about $300 million a month on those plans, but Scolese said it doesn't make sense to put moon spending on hold in the meantime because that would mean an even longer gap between the end of the space shuttle and the first flight of a new spaceship.

That may have been true in May when this story was published, but in light of what's been coming out of Augustine suspending may not be such a bad idea.

Then again, with this bunch of spendthrifts, O may have a JFK moment justifying it as some sort of 'stimulus'. Let's not forget that 80% of TARP is unspent, along with much of the stimulus bill.

Let's hope that if he does, and Congress goes along, they have sense to build Ares a new first stage or set on man-rating a commercial launcher (if LockMart isn't already well on the way for Orion Lite).

IMO the time/money spent on battling the issues with ATK's pet pork project could be better spent on something with more flexibility and a future beyond Ares I. What about using it on Ares V? IMO that's a pipe dream at best with the commission putting it at 2028 or beyond. Hell, ATK might not even be around by then.

Given the testimony in the last week or so there's also a possibility Augustine will recommend a commercial heavy lifter, a good project for another COTS style competition.

 

[exoscientist]

My opinion, NASA was not being foresightful when it cancelled some programs that could have prevented the Ares I mess:

NASA cancels technology development programs.
Posted: Fri, Mar 19, 2004, 7:42 AM ET (1242 GMT)
"NASA has started canceling technology development programs that don't fit the needs of the new space initiative, including a hypersonic flight program and a new reusable engine, a top NASA official said Thursday. Craig Steidle, the associate administrator for NASA's new Office of Exploration Systems, told members of the space subcommittee of the House Science Committee on Thursday that the agency has completed a review of all 140 technology development programs run by the agency. Under questioning by Rep. Nick Lampson (D-TX), Steidle said that the agency had cancelled both the X-43C and the RS-84 programs. The X-43C, a joint project with the Air Force Research Laboratory, was a hypersonic flight test program that was designed to follow on from the X-43A program currently in progress, while the RS-84 was a large reusable rocket engine being developed by Rocketdyne under a project that dated back to the Space Launch Initiative. Steidle said that neither program met the needs of the exploration program at this time. He did not specify when those programs were cancelled, but earlier in the week officials with the exploration office said that they had completed the review of all their technology programs at the end of last week. Steidle had previously stated that the agency planned to drop those technology programs that did not meet the agency's exploration needs, but that new programs would be started to fill in the gaps identified in the review."
http://www.spacetoday.net/Summary/2263

The Air Force is moving ahead with its hypersonic research with flight tests coming up in October. Successful ground tests give confidence in the success of the flight tests.
The Air Force is also recommending implementation of flyback boosters for its future launchers. For the heavy lift missions this will require heavy thrust, reusable engines. The RS-84 heavy thrust engine would have had protoypes available by 2007 if development had not been cancelled. And its active service could have commenced well before the 2015 proposed start date of Ares I, perhaps even before the 2010 planned ending of shuttle flights.
These systems are forward looking and certainly within the range of current technical understanding. Plus, they would have allowed the developmental costs to be shared by the Air Force. Yet the decision was made to go backwards and use solid rocket engines.
I believe this decision was largely due to this architecture being proposed by former administrator Mike Griffin. And with Griffin as the administrator this decision was perpetuated despite its numerous shortcomings. Moreover, this fact discouraged dissent because it was the understanding it was the agency's head boss's baby.

Bob Clark

 

[MeteorWayne]

My opinion, NASA was not being foresightful when it cancelled some programs that could have prevented the Ares I mess:


Bob Clark

NASA has a very limited budget, so needs to cancel programs that it can't afford. Yell at Congress, not NASA.

 

[exoscientist]

Here's another source suggesting the Augustine panel is recommending against Ares I:

Augustine Panel takes final options to White House staff.
posted by Robert Block on Aug 14, 2009 11:44:48 AM
"The Constellation program in all of its guises is presumed to have scored very low, a sign that NASA’s work for the last four years on the Ares I and Ares V rockets and the Orion crew capsule may be stillborn.
"According to panel insiders, until yesterday committee members were working hard to make option 5b -- the flexible deep space option to explore the solar system using an EELV -- fit more closely to the budget. This option would likely relay on a rocket with a liquid oxygen and kerosene engine that would be designed and operated by a commercial company and bought by NASA."
http://blogs.orlandosentinel.com/news_s ... staff.html

Interesting they seem to be saying the preferred option is an EELV using LOX/kero. That could mean the Atlas V, but that uses the RD-180, a Russian engine. The "designed and operated by a commercial company" part doesn't necessarily mean an American company but it certainly implies it.
Again this could mean restarting the RS-84. But if you use a RS-84 on an EELV that would be extremely wasteful because it was designed to be reusable.
The similarity of the design of SpaceShipeTwo compared to SpaceShipOne suggests the increased payload size, at least for a Mach 3 flyback vehicle, is merely a matter of scaling. On that basis the design of a flyback airframe to carry the RS-84 back to the launch site would be a trivial add-on cost compared to the cost of developing the engine (or compared to the cost of the Ares I solids) especially if designed by Scaled Composites.



Bob Clark

 

[radarredux]

Interesting they seem to be saying the preferred option is an EELV using LOX/kero.

I'm making a potentially unjustified leap here, but I think one reason the Augustine Panel wants to promote LOX/Kero is that it is easier to store in orbital fuel depot.

I recall in the past one of the criticism of such an approach is that hydrogen boils off too easily, so if you go with Kerosene you get rid of some of that problem.

The Panel also liked the idea that a fuel depot could be another avenue to support commercial companies providing launches of fuel. If the the rockets are less than human rated, thats OK if you blow up a rocket on launch. Just launch some more later.

Fuel depots would also alleviate the need for super super heavy boosters because you could launch the spacecraft dry, gas up in LEO, and then take off.

 

[MeteorWayne]

"Fuel depots would also alleviate the need for super super heavy boosters because you could launch the spacecraft dry, gas up in LEO, and then take off."

LOL, I don't understand the gain in efficiency here. The plan is to use one rocket to launch fuel to a depot (over multiple launches), then launch an empty booster so it can be resupplied by the propellant you've already had to boost in several launches to the depot?

Maybe I'm dense, but can you explain how 2 or 4 launches are better than one?

Sure you can use cheaper (I guess lower reliability, cheaper boosters to get the propellant up there) but I'm not sure that in the long run it's cheaper or more reliable.

 

[StrandedonEarthsince1970]

LOL, I don't understand the gain in efficiency here. The plan is to use one rocket to launch fuel to a depot (over multiple launches), then launch an empty booster so it can be resupplied by the propellant you've already had to boost in several launches to the depot?

Two advantages:
1. It saves development of a super-heavy-lifter if there isn't one in stock.
2. Even if there is, it could be used to launch a heavier probe farther and faster after refueling.

A fuel depot would also be very useful for an aerobraking lunar shuttle. Obviously that is far in the future with the current state of affairs.

 

[radarredux]

Maybe I'm dense, but can you explain how 2 or 4 launches are better than one?

One key to getting costs down is to increase launch frequency. The shuttle budget is pretty much the same whether they launch 1 mission per year or 6 missions per year because much of the cost is the labor cost. If NASA only launches 1 or 2 Ares V every 2 years, that is going to be a very expensive rocket.

Also, if you want to support commercial market, this is a good strategy. Pay them to fill the depot.

The negatives include:
(1) enhances mission complexity.
(2) As Bohdan Bejmuk, former manager at Boeing, points out, America does not have a lot of experience with hydrocarbon engines (SpaceX may beg to differ).

 

[MeteorWayne]

Both good answers, Thanx.

 

[docm]

SpaceX may beg to differ

Indeed. As many as they are making/testing, and soon using at 10 per Falcon 9, they're getting lots of experience, quickly.

 

[samkent]

LOL, I don't understand the gain in efficiency here.

It's like the old saying.

Yea I'll lose 10 million on each launch. But I'll make up for it in volume!


LOL I agree. It's a silly idea.

 

[docm]

Better not tell the Augustine commission that as they seemed to like the idea of fuel depots.

 

[radarredux]

[It's like the old saying.
Yea I'll lose 10 million on each launch. But I'll make up for it in volume!
LOL I agree. It's a silly idea.

But that is a true statement when you have a large upfront development cost. Think of making a factory to turn out cans of soup. It may cost several million dollars to build the factory, and if you are only going to sell a handful of cans, you need to either charge hundreds of thousands of dollars for each can, or you take a huge loss on each can. But if you can sell millions of cans of soup, you can amortize the cost of building the factory across all of those cans, so you can sell the cans at a low price.

Rockets are like that too. It costs a huge amount of money to initially develop a new rocket, and that development cost needs to be spread across all the rockets you launch. If you only plan to launch ~1 rocket per year (an estimate for Ares V), each launch is going to be hugely expensive. But if you can build a smaller rocket and launch it 15-20 times a year, the cost of each launch can be much smaller.

The advantage of the smaller rocket is that you can find many more customers who can use it (thus increasing your launch rates, thus reducing the cost for each launch). There will not be a lot of customers for an Ares V class rocket.