SpaceX’s manifest still shows its first Falcon Heavy test flight scheduled for 2015, and I’ve not heard of them securing a paying customer for what most would assume to be a risky flight. Also, while SpaceX has described their Dragon capsules as reusable, they currently build and fly a new capsule for every NASA commercial resupply mission, so between the two COTS demo flights and four completed CRS missions, they have six lightly used Dragon capsules just sitting around. Finally, SpaceX has stated that their heat shields are robust enough to survive reentry from the Moon or Mars.

So, if a Falcon 9 can loft a Dragon capsule laden with a couple tons of cargo into LEO, should a Falcon Heavy be able to put a mostly empty Dragon into a free return trajectory around the moon? Now that would be an impressive stunt, showing off the power of the Falcon Heavy, the reusability of the Dragon, and the resilience of their heat shield.

]]>Elon’s way is to spare the whip and instead dangle the carrot in front of the leaders by making it so cheap and enticing that it becomes potentially affordable for rich space enthusiasts that want to travel in space because they can afford it. How simple it can be! These people represent groups of organized people who choose to pool and relinquish their wealth for selfish reasons before their ultimate death. They come to realize they can’t take it with them and they find better ways to utilize their wealth for ultimately selfish reasons even though they promote non-selfish reasons. They are so enthusiastic, they are willing to never return. So, how do you compete with that?

This is essentially an ingenious shell game under the cloak of human pioneering on uninhabited planets. By nurturing rich space enthusiasts to make it as comfortable as possible with no intention of returning it makes it enticing for them to continue along this path.

Each participating player must choose which shell contains the pea after they all get shuffled around a lot. The leaders are likely to buy two choices for every one choice by a rich space enthusiast. Eventually, the leaders will be forced to pay to choose all three shells to eliminate the chance of any rich space enthusiast in participating; much like they have done in the past. This effectively raises the price and demand beyond affordability for a group of rich space enthusiasts that have pooled their wealth.

Why do they do this? Because they fear what the rich space enthusiasts would tell their Twitter and Facebook Followers that may reflect badly on their leadership. By definition, leadership is all about controlling what people think about their leadership by telling their supporters exactly what they want to hear whether it is true or not. So far, no rich space enthusiasts have done such a thing since they know they must adhere to the unwritten rule of compliance with the leaders for the granted privilege of space participation.

Currently, rich space enthusiasts are not allowed to travel to space because the leaders have bought all of the tickets and raised the price/demand of seats on rockets that used to be affordable to rich space enthusiasts. This predictable behavior is easily taken advantage of, making the shell game shufflers rich and powerful beyond their wildest expectations. Their secrets of their successes are not really secret when you zoom out and analyze their strategies from an objective viewpoint instead of a space advocate viewpoint. ]]>

Yes, it is true that von Braun and others had ideas and visions in respect to space travel already in Peenenünde, which guided them over decades and which they would like to achieve over time. However, never was their main work – developing weapons – significantly affected by these dreams. Wernher von Braun was boss of over 10,000 employees, who worked a large variety of weapon programs.

]]>So for a given temperature:

ISP_Disassociated_Hydrogen = sqrt(2) ISP_H2 = 1.41 ISP_H2

ISP_Steam = (1/3) ISP_H2 = 0.33 ISP_H2

ISP_Disassociated_Water = (1/3)sqrt(2) ISP_H2 = 0.74 ISP_H2

I concur with your mass weighted average of the specific impulses, although I agree that there is a danger in just assuming, without proof, that this is the proper way to do it, so let’s derive it from first principles.

Specific impulse (ISP) is defined as the force of thrust (F) divided by rate of consumption of propellant. If we use the mass rate of consumption (m-dot) we get specific impulse in units of velocity, but by using weight instead (m-dot g) we get units of time, which leads to intuitive uses when computing accelerations in units of g. So:

ISP = F / (m-dot g)

If the exhaust consists of a single species of gas, the thrust is equal to the velocity of the exhaust gas (V) times its mass rate of production (m-dot):

F = V m-dot

Substituting this into the first equation, we see that ISP is proportional to the velocity of the exhaust gas:

ISP = V / g

This is the point where we would usually bring up the kinetic theory of gases to point out that the velocity, and thus also the ISP, will be proportional sqrt(T/M) where T is the temperature and M the molecular mass.

But instead, now consider an exhaust consisting of multiple species of gases. Let w_i be the mass fraction of gas “i” and V_i be its velocity, with ISP_i = V_i / g. Sum(w_i) = 1. The rate of production of gas “i” will be m-dot_i = w_i m-dot.

The total thrust, F, will be equal to the sum of the thrust of the individual gases. That is:

F = Sum(F_i)

where

F_i = V_i m-dot_i = V_i w_i m-dot

so

ISP = F / (m-dot g)

= Sum(F_i) / (m-dot g)

= Sum(V_i w_i m-dot) / (m-dot g)

= Sum((V_i / g) w_i)

= Sum(ISP_i w_i)

which is the mass weighted average of the ISP of the individual gas species.

And I agree with your numbers, that if a given temperature will yield an ISP of 1000 sec for molecular H2, it would be 1414 sec for monatomic H, 333 sec for steam and 471 for fully disassociated H2O.

I can’t imagine where they are getting an ISP of 1000 seconds for Project Aquarius.

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