Heavy Lift an unnecessary impediment?

[jimoutofthebox]

If we want to get back to the moon I think we are going to have to use what has already been developed. One idea would be build a launcher that can deliver 50 tons to low earth orbit using current technology. One example would be a three stage rocket using four Falcon 9 first stage boosters in a cluster like the old Russian R7. The 2nd stage would be the Saturn IVB which is the 3rd stage of the Saturn 5 booster. The 3rd stage would be a twin engine Centaur. This booster would have a lift off weight of approximately 3.4 million pounds.
At launch all four Falcon booster engine clusters would be fed by two of the booster fuel tanks. When the fuel was used up in the two tanks the empty boosters would separate and the two remaining boosters would start drawing from their full tanks and continue firing until the fuel was exhausted. The S-IVB would then take over and boost the third stage into orbit.
The third stage would be a modified Centaur that had 80,000 lb fuel capacity. The third stage booster would come in three different versions. One version would be designed to land on the moon with a cargo of 15,000 lbs. The 2nd version would be designed to land on the moon with a manned lunar assent stage. The 3rd version would carry a smaller fuel load and be designed to boost a command module like the Dragon with an attached service module towards the moon.
The lunar mission in this scenario would require 3 launches. The first launch would deliver the cargo to the moon. The 2nd and 3rd launch would have to be coordinated to deliver the lunar lander and command module to lunar orbit at the same time. The astronauts would transfer to the lunar lander and descend to the surface where the cargo module had been prepositioned. At the end of the stay on the moon the astronauts would launch back into orbit and transfer back to the command module and return home just as Apollo astronauts did.
Most of the technology for the above has been developed already. For example, the Centaur uses the same engine as was used on the DC-X back in the 90s. We only need to dig out the data and designs from that project to help with the new design. The S-IVB design has been man-rated and has a reliable history. I would recommend using as much of the Apollo hardware as possible for the lunar assent stage including the engine system. I’m very concerned with the safety of using a H2 engine as proposed by NASA for their design for a new lunar assent stage. The Apollo design would have to be redesigned to carry 4 astronauts and not much else. Due to the severe limits of the weight that can be landed on the moon, all the supplies would have to be delivered by a separate cargo module.
The advantage of this proposal is that we wouldn’t have to re-invent the wheel. Also we would gain economies of scale since all three launches would use the same 1st and 2nd stages as well as common launch facilities.

 

[rockett]

three stage rocket using four Falcon 9 first stage boosters in a cluster like the old Russian R7.

They will have to be man-rated first...

At launch all four Falcon booster engine clusters would be fed by two of the booster fuel tanks. When the fuel was used up in the two tanks the empty boosters would separate and the two remaining boosters would start drawing from their full tanks and continue firing until the fuel was exhausted.

Fuel cutover might be an issue, remember we are dealing with volatiles here...

I would recommend using as much of the Apollo hardware as possible for the lunar assent stage including the engine system.

Problem is, it's all gone. We couldn't build a Saturn V or any of the Apollo hardware if we had to. Plans gone, specs gone, people gone, tooling gone, and data stored in an obsolete format that they don't have the equipment to decode anymore. The only thing they could reconstruct for Constellation was the J-2 engine design. Everything else would have to be all new.

 

[_110501_]

Every single aspect of the shuttle should and ought to be bought by a private-consortium, on charge. With bail-out money to make jobs. Continously expanded in volume and make and keep American presence in space, securely safe. As the commerical market boldly goes where not anyone has gone before. Only a fool would not recognize the greatness of that which is truly Great. It does appear that there are fools around. An Honest Ballot and an Honest Vote will stop them.

 

[jimoutofthebox]

I’ve seen the canard repeated several times that it would be easier to design from new than copy from the past. As an engineer for 27 years I can guarantee that I would rather use a proven design than re-invent the wheel. Even if I had to send a team of technicians to crawl all over a museum piece with the goal of reverse engineering. While it’s true that I would not reuse the electronic components, most of the hardware such as valves, pipes, and structures could be used as designed. Would the reversed engineered hardware have to be validated? Absolutely. As for the designs being stored on obsolete formats, I used to work with engineers that designed the Apollo hardware and the format they used were hand drawings on paper. I’m not saying that the drawings weren’t destroyed long ago. But if they do exist they would be very easy to work from and give us a big leg up on returning to the moon. There are two main things I have learned as an engineer, first keep-it-simple, and 2nd its lot easier lurching into the unknown if aren’t stumbling from the unknown.

 

[edkyle99]

I would count STS as a large launch system. It places more than 100 tonnes into orbit during each flight, and has done so 130 times in 131 attempts, making it one of the world's most reliable launch systems. Delta 2 has flown only a few more times (147) than STS. I see no reason that a large launch system can't be as reliable as a smaller system, as long as the propulsion is also scaled so as to keep the number of engines or motors reasonable. (SRB, which produces 6.6-ish million pounds of thrust using just two big motors, has been key, IMO, to Shuttle's reliability results - but this is all history now.)

Well generally less experience leads to less reliability. Yes the Shuttle has flown 131 times, put that pales in comparison to the number of launches made by Delta II class vehicles. Also when talking about super heavy lift like the Ares V these vehicles are in a whole class of their own.

The idea that smaller is more reliable sounds good when first presented, but does not hold up under statistical examination. Consider, for example, that Shuttle, Soyuz U, and Delta 2 lead the world in reliability with roughly the same results (essentially 2-3% predicted failure rate). Shuttle puts up 100 tonnes, Soyuz 7.5 tonnes, and Delta 2 about 5-6 tonnes to LEO. Meanwhile, smallsat launcher Pegasus ( 0.4 tonnes to LEO) has a 12% failure rate, Taurus (up to 1.4 tonnes to LEO) has failed in one-quarter of its attempts, and Falcon 1 - well, never mind about the Falcon 1 record.

It seems clear to me that size is not closely correlated to launch vehicle reliability. Something else dominates the results. Experience with the flight system is clearly part of the equation, but there is more to it than just experience. Diligence is the word that comes to mind. Diligence, when institutionalized in systems engineering, can cost big bucks, so funding can play a role in determining reliability. Good old-fashioned solid engineering, either work done well from the start or work done well by learning from early failures, is clearly a critical factor too.

- Ed Kyle

 

[rockett]

I’ve seen the canard repeated several times that it would be easier to design from new than copy from the past. As an engineer for 27 years I can guarantee that I would rather use a proven design than re-invent the wheel. Even if I had to send a team of technicians to crawl all over a museum piece with the goal of reverse engineering. While it’s true that I would not reuse the electronic components, most of the hardware such as valves, pipes, and structures could be used as designed. Would the reversed engineered hardware have to be validated? Absolutely. As for the designs being stored on obsolete formats, I used to work with engineers that designed the Apollo hardware and the format they used were hand drawings on paper. I’m not saying that the drawings weren’t destroyed long ago. But if they do exist they would be very easy to work from and give us a big leg up on returning to the moon. There are two main things I have learned as an engineer, first keep-it-simple, and 2nd its lot easier lurching into the unknown if aren’t stumbling from the unknown.

I don't disagree with you. It's really a shame, if not downright criminal that the designs were not saved. NASA went through this exercise to do exactly what you suggest, designing Constellation. But as I said before, the J-2 was all they came up with reborn as the J-2X, after crawling around cellars, prowling museums, and checking closets.

Another point though, is "man-rating" back in the Apollo days doesn't mean anywhere close to what it does today. The astronauts of the Mercury, Gemini, and Apollo programs were military test pilots, not teachers, scientists, and so on. The mortality for test pilots in the 1950s was about one a week, which is the world they came from, before becoming astronauts. No, they didn't have a death wish, but the acid test of any aviation design back then was having and exceptional pilot who was also an aeronautical engineer flying it. Those guys were the best we had, and they knew the risks. But they were willing to accept a greater level of risk than either the media or any politicians would allow today. Truth be told, there was a lot the media didn't know, and has only become public in the last few years. If we could rebuild the Apollo hardware, bolt for bolt, I seriously doubt much, if any, would pass man-rating today. One piece I'm pretty sure wouldn't, would be the LEM.

 

[rockett]

The idea that smaller is more reliable sounds good when first presented, but does not hold up under statistical examination. Consider, for example, that Shuttle, Soyuz U, and Delta 2 lead the world in reliability with roughly the same results (essentially 2-3% predicted failure rate). Shuttle puts up 100 tonnes, Soyuz 7.5 tonnes, and Delta 2 about 5-6 tonnes to LEO. Meanwhile, smallsat launcher Pegasus ( 0.4 tonnes to LEO) has a 12% failure rate, Taurus (up to 1.4 tonnes to LEO) has failed in one-quarter of its attempts, and Falcon 1 - well, never mind about the Falcon 1 record.

It seems clear to me that size is not closely correlated to launch vehicle reliability. Something else dominates the results. Experience with the flight system is clearly part of the equation, but there is more to it than just experience. Diligence is the word that comes to mind. Diligence, when institutionalized in systems engineering, can cost big bucks, so funding can play a role in determining reliability. Good old-fashioned solid engineering, either work done well from the start or work done well by learning from early failures, is clearly a critical factor too.

- Ed Kyle

Too true, Ed. Checking, testing, and rechecking through each stage of design and build takes time, which costs money, lots of it. People seem to think that launch vehicles are made on assembly lines like Chevrolets, but they are not. Each one is essentially hand crafted for the most part, more like a Lamborghini.

One other problem with smaller, more frequent launches that nobody seems to be commenting on is total upmass. Smaller more frequent launches run it up real fast, because each small unit is a complete launch stack. That doesn't even include mission personnel and launch infrastructure. All told for the same overall mass, dollars per pound are naturally going to be higher for smaller, more frequent launches.

 

[pathfinder_01]

Too true, Ed. Checking, testing, and rechecking through each stage of design and build takes time, which costs money, lots of it. People seem to think that launch vehicles are made on assembly lines like Chevrolets, but they are not. Each one is essentially hand crafted for the most part, more like a Lamborghini.

Cars were once built that way and they remained expensive so long as they were hand made. The goal is to provide an incentive to automate the process. By using existing rockets it might be possible to increase demand to the point where automation can pay off. By using separate heavy lift systems this process is not nurtured.

One other problem with smaller, more frequent launches that nobody seems to be commenting on is total upmass. Smaller more frequent launches run it up real fast, because each small unit is a complete launch stack. That doesn't even include mission personnel and launch infrastructure. All told for the same overall mass, dollars per pound are naturally going to be higher for smaller, more frequent launches.

Perhaps but you save on developing HLV and you might save on keeping separate infrastructure for it if it needs separate launch facilities, separate assembly lines ect.

 

[edkyle99]

One other problem with smaller, more frequent launches that nobody seems to be commenting on is total upmass. Smaller more frequent launches run it up real fast, because each small unit is a complete launch stack. That doesn't even include mission personnel and launch infrastructure. All told for the same overall mass, dollars per pound are naturally going to be higher for smaller, more frequent launches.

Perhaps but you save on developing HLV and you might save on keeping separate infrastructure for it if it needs separate launch facilities, separate assembly lines ect.

One nice thing about a "commercial" LEO propellant depot approach is that existing launch vehicles could fly from Day One, but market forces would drive vehicle choice after that. Gradual upgrades to existing vehicles might result. All-new, more capable vehicles could appear too, but only if market forces made it pay.

- Ed Kyle

 

[DarkenedOne]

Well generally less experience leads to less reliability. Yes the Shuttle has flown 131 times, put that pales in comparison to the number of launches made by Delta II class vehicles. Also when talking about super heavy lift like the Ares V these vehicles are in a whole class of their own.

The idea that smaller is more reliable sounds good when first presented, but does not hold up under statistical examination. Consider, for example, that Shuttle, Soyuz U, and Delta 2 lead the world in reliability with roughly the same results (essentially 2-3% predicted failure rate). Shuttle puts up 100 tonnes, Soyuz 7.5 tonnes, and Delta 2 about 5-6 tonnes to LEO. Meanwhile, smallsat launcher Pegasus ( 0.4 tonnes to LEO) has a 12% failure rate, Taurus (up to 1.4 tonnes to LEO) has failed in one-quarter of its attempts, and Falcon 1 - well, never mind about the Falcon 1 record.

It seems clear to me that size is not closely correlated to launch vehicle reliability. Something else dominates the results. Experience with the flight system is clearly part of the equation, but there is more to it than just experience. Diligence is the word that comes to mind. Diligence, when institutionalized in systems engineering, can cost big bucks, so funding can play a role in determining reliability. Good old-fashioned solid engineering, either work done well from the start or work done well by learning from early failures, is clearly a critical factor too.

- Ed Kyle

Your right Ed. There are other considerations.

One such consideration is the level of testing. The size of your rocket and of your budget determines the amount of testing a vehicle can undergo. The cheaper the test the more tests can be done. A rocket like the Falcon 9 can be tested much more thoroughly than a rocket like the Ares V before it is ever used to transport humans. Rockets that cost billions of dollars per launch are simply too expensive to do many test flights even for NASA.


These include things like redundancy, fault protection, higher design tolerances, extra inspection, more component testing, higher quality materials, and abort capability to manned launches. However just as in practically every other industry increasing safety and reliability means increasing price.

That is one of the best things aspects of ideas like fuel depots. Rockets and spacecraft used to transport fuel would not have to be nearly as reliable or safe as the rocket transporting humans and other high value payloads.

 

[DarkenedOne]

Too true, Ed. Checking, testing, and rechecking through each stage of design and build takes time, which costs money, lots of it. People seem to think that launch vehicles are made on assembly lines like Chevrolets, but they are not. Each one is essentially hand crafted for the most part, more like a Lamborghini.

Manufacturing processes are dictated by the amount of the product to be produced. This fact is definitely in favor of smaller launch vehicles and a fuel depot infrastructure and is a big problem for large, sparely launched rockets.

Everywhere you look in industry you find economies of scale in manufacturing. This fact applies to rockets as well.

One other problem with smaller, more frequent launches that nobody seems to be commenting on is total upmass. Smaller more frequent launches run it up real fast, because each small unit is a complete launch stack. That doesn't even include mission personnel and launch infrastructure. All told for the same overall mass, dollars per pound are naturally going to be higher for smaller, more frequent launches.

That is true, however up mass is not the largest nor most expensive aspect of spaceflight. The ISS weighs approximately 344,000 kg. Assuming the $10,000/kg that the commercial rocket industry usually provides that comes out to $3.44 billion. That is 3.4% of its $100 billion dollar price tag. However instead of using commercial launch vehicles 50% or 50 billion dollars went into the shuttle, which brings up the one great point for the argument of abandoning these super heavy lift in favor of fuel depots and commercial payloads. The expense.

1. Super Heavy Lift Rockets are expensive to develop and take many years to develop. The Saturn V took 5 years to develop and $43.5 billion in todays currency to develop. The Shuttle took about 35 billion in todays dollars and about 5 years to develop. I know Ares V was going to take about 5-6 years to build once development started and a yet to be determined cost.
Assuming 2 of each of the HLV at our desposal, the Delta IVH, the Atlas VH, and the Falcon 9 Heavy, were used year we could put a comparable amount of mass into space.

2. Once you get the rocket it is expensive to maintain even when you are not using it. The space shuttle for example cost $200 million a month totaling up to $2.4 billion a year in fixed expenses.

 

[vulture4]

DarkenedOne has hit the nail on the head. In fact, ULA has already advertised growth variants of the D-IV up to about 100MT to LEO. It's not clear why NASA would have to design any HLV, except to create jobs, even if we had a 100MT payload. It doesn't require any new technology, so it could just be purchased.

 

[rockett]

DarkenedOne has hit the nail on the head. In fact, ULA has already advertised growth variants of the D-IV up to about 100MT to LEO. It's not clear why NASA would have to design any HLV, except to create jobs, even if we had a 100MT payload. It doesn't require any new technology, so it could just be purchased.

Good information vulture4.

If the Delta IV is that capable, and from what I understand in the process of being man-rated, why is everyone debating the point anyway? Why do we even need a "new" HLV capability in the first place?

Smells of politics to me...

 

[DarkenedOne]

Good information vulture4.

If the Delta IV is that capable, and from what I understand in the process of being man-rated, why is everyone debating the point anyway? Why do we even need a "new" HLV capability in the first place?

Smells of politics to me...

Well I still endorse NASA decision to separate crew from cargo. Doing so will cut costs and development time by allowing NASA to simply buy proven crew to LEO transport rather than have to worry about man-rating a new rocket. This decreases costs because manned rated rockets have to meet much higher standards than unmanned ones. It will also ensure better safety and reliability as doing so will rely on old more proven vehicles rather than new untested vehicles. It will also be a redundant capability since the Russians and the Chinese already have such vehicles. The US, India, and maybe Japan and ESA should have them shortly.

As far as a heavy lift is concerned to me it is all about why you need a heavy lift. My problem is with the modus operandi that NASA was using for Constellation. It was the same for Apollo and that is to build one giant rocket with which you can launch the entire moon mission in one go. Develop new everything and use no commercial or existing infrastructure. The problem as I as well as others have pointed out is that it is extremely expensive and takes a huge amount of time to develop. All that for the capability to go to one destination.

The real benefits of fuel depot type infrastructure is not in the costs as many think it is but in the operational flexibility. Once you have a fuel depot in space there is nothing that says you are restricted to going to the moon like Constellation. Since the vast majority of the mass for a Mars mission is fuel the same infrastructure will help you get to Mars without needing super heavy launch vehicles. It is only a matter of increasing the amount of fuel you have stored in space. It is a single infrastructure for many destinations.

 

[neutrino78x]

If the Delta IV is that capable, and from what I understand in the process of being man-rated, why is everyone debating the point anyway? Why do we even need a "new" HLV capability in the first place?

Smells of politics to me...

Hey rockett, aren't you the guy who was complaining that Constellation, including the heavy lift aspect of it, was canceled? As opposed to the Obama Plan of stimulating the commercial space industry to get a Star Wars future where most rockets and most ships are merchants, instead of military/NASA? So why are you now saying that we don't need new heavy lift? If that's true, then the Constellation heavy lift isn't needed either.

--Brian

 

[neilsox]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel. Worse a wide variety of fuels are in use, and unmanned rendezvous are likely to remain unreliable = possibly destroying both the vehicle and the depot in a collision. Depots in orbit around the Sun are even worse IMHO. Considerable fuel and time is needed to rendezvous in most cases. Storage of hydrogen and oxygen is costly even on Earth. Neil

 

[neutrino78x]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel.

Yes, but, my argument against fuel depots is, unless you are using a technology to refill the depot that does not use fuel itself, it defeats the purpose. I can understand a fuel depot on the Moon, or on Phobos or something, anywhere you can locate the depot at the same place where the fuel is being generated. If you put the depot in low earth orbit, the fuel is presumably being sent from Earth, so you probably had to use a rocket to send it there, so, you might as well have sent a earth departure module with sufficient fuel to begin with.

I still haven't heard a good counter-argument to that.

--Brian

 

[EarthlingX]

You need a very big rocket, which you don't have, is one - and once (if) you have it, it must fly a lot to make sense - not once per year, let say 5 - 10 times (if that's enough), or you end up with fixed costs (wages, infrastructure) strangling your program.

If you have fuel depots, you shoot with all you got, as long as it can get to depot.

If you launch empty EDS, it can also be much bigger without fuel, on the same, probably existing, launcher.

Having a lot of different fuels is not too good for this scheme, that's why it is proposed as a part of the starting strategy to use single fuel/oxidizer line, and i would not go with LOX/LH2 as a first choice, because of the problems with LH2 evaporation (small atom) which negate Isp bonuses from it.

If you ferry fuel with long travelling, high Isp tankers, it makes proportion of mass used for travel much better.
For people, use low Isp, high thrust engines.

50t CBC makes sense, because it is the next size step: 5 - 10 - 20 - 50
100t doesn't yet, from the same reason.

If it's first stage is kerosene fuelled, even better.

 

[DarkenedOne]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel. Worse a wide variety of fuels are in use, and unmanned rendezvous are likely to remain unreliable = possibly destroying both the vehicle and the depot in a collision. Depots in orbit around the Sun are even worse IMHO. Considerable fuel and time is needed to rendezvous in most cases. Storage of hydrogen and oxygen is costly even on Earth. Neil

First of all it really is not just about saving money. The ability to stockpile fuel in space. Thus rather than having to develop a whole new set of expendable spacecraft every time you want to go to a destination outside of LEO, you can simply refuel spacecraft you already have. Since any mission going to the moon or Mars is mostly fuel super heavy rockets are no longer needed.

Secondly it is likely to save money over Constellation like programs because depots eliminate the need for super heavy lift rockets, which as I have said before have proved expensive to develop and maintain. Also it allows you to build reusable spacecraft rather than ones that are discarded after they run out of fuel.

The real reason they have not been considered is like because the technology for autonomous spacecraft docking is very new. However it has been done and it is a worth while technology to mature. When it comes to fuel depots it is clearly a technology that needs to be develop. If you look around fuel depots are a crucial part of every transportation industry. The sooner we move away from building expendable spacecraft and move to reusable ones the better.

 

[DarkenedOne]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel.

Yes, but, my argument against fuel depots is, unless you are using a technology to refill the depot that does not use fuel itself, it defeats the purpose. I can understand a fuel depot on the Moon, or on Phobos or something, anywhere you can locate the depot at the same place where the fuel is being generated. If you put the depot in low earth orbit, the fuel is presumably being sent from Earth, so you probably had to use a rocket to send it there, so, you might as well have sent a earth departure module with sufficient fuel to begin with.

I still haven't heard a good counter-argument to that.

--Brian

Gas trucks use gas to fuel up your local gas station. Oil tanks run on an oil derived fuel. Tanker aircraft use fuel to fly. So what is the problem with using fuel to fill up the depot?

The point is to extend your range without having to develop a whole new rocket. The point is also to allow you to reuse spacecraft like you reuse your car after your done with it.

 

[halman]

Although we may see an Atlas or a Delta capable of putting 100 tons in orbit, it may be that the payload would have to be a fairly small, heavy object. We are already launching payloads which require fairings which are larger than the rocket, but there is a limit to that approach, I believe. Inflatable space stations are a great idea, but you still need to send up the stuff that is going to go inside of them. Research labs need things which are bulky, fragile, or expensive, or all three, and sending up the whole thing in one launch might be more logical than sending up bits and pieces which have to be moved through air locks.

When we get around to returning to the Moon, we are going to want to send up equipment that can be used for excavation, which typically means, heavy, bulky, dense stuff. Launching a nuclear power plant in one piece would be a lot easier than sending up components, I would think. And computers capable of controlling a large number of surface rovers, stationary observatories, and orbital relay satellites, while transferring data back to Earth rapidly, might be hard to assemble in orbit.

If we could create a market for heavy lift, we would develop it. But our spending levels are simply inadequate to establish that kind of market. Committing funding for 10 years at the level Americans spend on cosmetics would be adequate to establish programs which would employ heavy lift, but creating a future we wish to live in is not as important as appearances.

Why isn't kerosene stable in long-term storage? I really believe that hydrogen is not going to be a widely used fuel in the future, because we will be able to accomplish our goals with less esoteric propellants. We could all run our cars on nitromethanol, or whatever it is that they run in top fuel drag racing cars, but we can get by without going to that extreme. Hydrogen has been used because we have sought the absolute ultimate in performance, trying to squeeze as much payload into a rocket as possible. But that kind of philosophy is not conducive to long-term development.

 

[edkyle99]

... my argument against fuel depots is, unless you are using a technology to refill the depot that does not use fuel itself, it defeats the purpose. I can understand a fuel depot on the Moon, or on Phobos or something, anywhere you can locate the depot at the same place where the fuel is being generated. If you put the depot in low earth orbit, the fuel is presumably being sent from Earth, so you probably had to use a rocket to send it there, so, you might as well have sent a earth departure module with sufficient fuel to begin with.

I still haven't heard a good counter-argument to that.

--Brian

Without a propellant depot, the Earth escape stage has to be launched fully fueled all at once. This requires, for a crewed mission, a Very Big Rocket - Saturn V or bigger. The Constellation cancellation tells us emphatically that NASA is not going to be given enough money to develop such a rocket.

With a depot, big missions can be staged using smaller rockets - rockets that already exist. This method is already proven. ISS weighs 340-ish tonnes right now - nearly three Saturn V mission's worth of mass - and has four spacecraft docked to it. Two of those are or have transferred propellant.

- Ed Kyle

 

[rockett]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel.

Yes, but, my argument against fuel depots is, unless you are using a technology to refill the depot that does not use fuel itself, it defeats the purpose. I can understand a fuel depot on the Moon, or on Phobos or something, anywhere you can locate the depot at the same place where the fuel is being generated. If you put the depot in low earth orbit, the fuel is presumably being sent from Earth, so you probably had to use a rocket to send it there, so, you might as well have sent a earth departure module with sufficient fuel to begin with.

I still haven't heard a good counter-argument to that.

--Brian

Savings comes from reuse of LEO based vehicles. You don't have to RE-launch them fully fueled everytime you want to go somewhere. They stay and are maintained in orbit. You don't buy a new car with a full gas tank everytime you run out do you? (this is a serious question, based on the logic of your statements so far)

 

[pathfinder_01]

Why isn't kerosene stable in long-term storage? I really believe that hydrogen is not going to be a widely used fuel in the future, because we will be able to accomplish our goals with less esoteric propellants. We could all run our cars on nitromethanol, or whatever it is that they run in top fuel drag racing cars, but we can get by without going to that extreme. Hydrogen has been used because we have sought the absolute ultimate in performance, trying to squeeze as much payload into a rocket as possible. But that kind of philosophy is not conducive to long-term development.

The problem with kerosene isn't storage. Kerosene stores well in space. LOX\Kerosene rocket engines generate coke. On earth this isn't a big problem because the engine is only going to be used once (or perhaps serviced then reused in an RLV). They are designed to work with the coking problem. However an engine that cokes itself up might be a poor choice for an in space engine that needs to be used many times without servicing.

Also a Kerosene first stage and hydrogen upper stages have a synergy. The hydrogen upper stage will mass less than a Kerosene one while lox\kerosene is better thrust than lox\loh. You can get better performance than each alone. LOH is expensive, but the cost of propellant is rather a small part of the whole system. A totally Kerosene rocket would have to mass more than a mixed one to do the same work or cut into payload margin.

 

[pathfinder_01]

As far as I know fuel depots for LEO or GEO orbit have not received serious study, because they don't save money until we have thousands of orbiting vehicles that need more fuel.

Yes, but, my argument against fuel depots is, unless you are using a technology to refill the depot that does not use fuel itself, it defeats the purpose. I can understand a fuel depot on the Moon, or on Phobos or something, anywhere you can locate the depot at the same place where the fuel is being generated. If you put the depot in low earth orbit, the fuel is presumably being sent from Earth, so you probably had to use a rocket to send it there, so, you might as well have sent a earth departure module with sufficient fuel to begin with.

I still haven't heard a good counter-argument to that.

--Brian

There are low energy methods to move propellant. You could use electric propulsion to move the propellant from LEO to where it is needed (electric propulsion is way more efficient than chemical). You could use low delta V trajectories with a chemical rocket to move the propellant (they increase the amount of cargo that can be delivered by 1/3 to 1/2 over faster transfers). Once the propellant is located at a strategic point like an L point, it would take very little to go back and forth from moon to lagragine point. A passenger might care about taking a 100 day trip to the moon. Propellant does not.

In addition your craft now only needs to carry enough propellant to reach the next fuel depot instead of for the whole trip. This can simplify construction and likely increase performance since the craft isn’t carrying around so much unused propellant the whole trip.