- Unfortunately Dr. Spudis closed his discussion board down before I could respond to these replies and comments. So I am going to respond in italics here:
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oldAtlas_Eguy says:
The economics of propellant depots. Depots do not care where the propellant comes from. But even with the cheapest envisioned LV possibly to exist in the next 20 years the BFR/MCT cost of propellant at L2 would be $1,600/kg. BTW the cost of the reusable booster version of the FH for prop delivered to L2 would be greater than $3,200/kg. Now if a Lunar infrastructure for delivery of propellant to L2 to was put in at ~$60-80B development and initial setup with an annual operating cost of $10B that can deliver 17,500mt of prop to L2 a year over the lifetime of all the elements of the system, it can deliver to L2 propellant for $800/kg.
Conclusion is that it will be more than 20 years and probably even a decade after that that a system that can deliver prop to L2 from Earth to do so at the same cost as a Lunar system. But when evaluating LEO that is not the same story. The cost of delivery of prop from Earth by the FHR would be $1,600/kg equal to the same as it would cost to deliver prop from the Moon. The two systems would be direct competitors fro LEO prop sales and it would be available volume that would determine who the front runner supplier would be. BTW the max amount of prop that the before mentioned Lunar system could deliver per year to LEO would be 8,750mt. But that is also equivalent to over 200 FHR flights in one year. A flight rate not likely to be achievable in the next 10 or 15 years but such a delivery amount from Lunar prop could reach such levels in 15 years without much transfer tug hardware.” This kind of confabulation has been used by NewSpace fans for years to fill up the page and is devoid of any real facts.
“We sent animals into orbit, because we were uncertain that humans could live for relatively short periods in orbit.
We currently know that humans can live in orbit for more than a year, but we also know that the human body adapts to micro-gravity and this has various health consequences which begin immediately once in micro-gravity and over months of time, it worsen and have longer effects.
We can assume that in low gravity- the Moon or Mars, the human body will also adapt to this low gravity and have similar
effects as occurs in micro-gravity but we can also assume that differences between micro-gravity and say 1/3 of earth’s gravity are also quite different.
For instance fire is quite different in micro-gravity, whereas fire on Mars would behave fairly similar to how it behaves on Earth.
Or a toilet in micro-gravity has to be different than a toilet in micro-gravity, whereas a toilet on Mars could very similar to a toilet used on Earth. And living areas of enclosed environment like a submarine on Earth are similar to living areas on Mars- this is not the case when in micro-gravity.A reason for exploration is to discover these types of differences, people once thought humans could not go faster than about 20 mph, and now human can travel at hundreds of mph, but there consequence of traveling at over 20 mph- ie, a collision at over 20 mph can be lethal. And we could not possible know about all the consequences of going over 20 mph, without actually going at speeds faster than 20 mph and learn ways of dealing with traveling at these higher speeds.
I would say making a top down type decision of assuming human can only survive in a 1 gee environment, is a policy decision which is criminal or at least, stupid. You would say that but Gerard K. O’Neill said basically the opposite and I will go with him, thanks.
One could decide that you don’t want to go more than 20 mph or that you don’t want to live in environment greater or less than 1 gee, but such personal choices are quite different a public policy type decisions.-particularly when it’s not based upon any information. Oh, but it is based on information- decades of space station debilitation.One aspect is the need to explore Space, another aspect of this, is lower the cost to get into space. No….there is no cheap.
In my opinion NASA needs to explore space in such manner that it’s related to how one can lower the costs to get into space. So in terms of priority of exploration, NASA’s top priority should exploration that could lead to lower the costs of going into space.
If there was commercial lunar water mining this would lower the costs of getting into space. NASA mining lunar water wouldn’t lower the cost of getting into space. So NASA should explore the Moon to determine if and where there could be minable water on the Moon. That NASA has failed to do this over the last 10 years or so, is failure of the agency, whereas not sending crew to Mars, has not been a failure of the agency- rather than desire of doing this first, is the policy failure. That NASA is proposing a useless mission to Mars is the failure.And that it took until 1998 to determine that there could water in the Moon, is another failure of this agency over the many decades, it’s existed. No argument there.
And that NASA do not have system that can refuel rockets in LEO, is another long term failure of the agency and general NASA focus upon having a earth launch owned and operated by the agency as been a failed policy over the decades- it’s the wrong focus of the limited resources NASA is provided to explore Space.” Mars and fuel depots are both completely wrong goals. The need to “refuel rockets in LEO” is a farce invented by the NewSpace mob to justify building hobby rockets.
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Ice on the Moon 
“A reusable Extraterrestrial landing vehicle could operate between the Earth-Moon Lagrange points and LEO and between the Lagrange points and the lunar surface using propellant derived from lunar water. A super heavy lift vehicle is great for deploying heavy cargo within cis-lunar space but its an inefficient crew launch vehicle since it throws away all of its components– every launch. This makes it necessary for the lander to dive 20,000 miles from GEO into LEO to pick up human beings and then boost out of LEO- presumably with propellants taken on at a fuel depot. What a mess. The Super Heavy Lift has to “throw away it’s components” but it can reuse them. And all the humans are on Earth right now so…..
Chemical rockets operating between the Earth-Moon Lagrange points and high Mars orbit would be much more efficient than nuclear rockets operating between LEO and high Mars orbit– because of the substantially lower delta-v requirements when launch vehicles from the Lagrange points. Plus the delta-v requirements to supply water and propellant for interplanetary vehicles launched from the Lagrange points is substantially lower than trying to supply fuel and water from the Earth’s deep gravity well. Nuclear rockets would never be allowed to operate in the magnetosphere, let alone in LEO or GEO.
IVF technology being developed by the ULA will enable us to utilize hydrogen and oxygen very efficiently. That piston engine is no miracle solution and while it might work well maintaining oxygen for an extended mission, hydrogen is a whole different set of problems.
Commercial crew vehicles will been in operation long before the SLS is launching humans into space. Perhaps, but it is meaningless since they are not going anywhere except LEO and that is nowhere.
Marcel