Sunday, August 9, 2015

Fwd: Specific Plans- Jack Knights Information



Sent from my iPad

Begin forwarded message:

From: "Gary Johnson" <gjohnson144@comcast.net>
Date: August 9, 2015 at 10:35:51 AM CDT
To: "'Jack Knight'" <jack77062@sbcglobal.net>
Subject: RE: Specific Plans- Jack Knights Information

Jack thanks I wanted everyone on the original distribution to see your feedback and analysis, hope you don't mind.

Gary

 

From: Jack Knight  
Sent: Saturday, August 08, 2015 8:12 PM
To: Gary Johnson
Subject: Re: Specific Plans

 

Well, let's see.  The LM Ascent stage gross weight  at liftoff was ~10,300 lbs (earth weight) which would have been ~1716 "lbs" on the moon.  The ascent engine thrust was ~3500 lbf.  So the Thrust/Weight ratio was ~2.0. 

 

Comparing that to the SPS engine thrust, which was ~20,000 lbf, suggests that it could lift ~10,000 "lbs" from the moon with the same acceleration, which translates to ~60,000 lbs earth weight.  Not clear, however, how many engines the original concept envisioned because the stack would have been heavier to include the fuel needed slow down to land; but that may have been a separate descent stage.  The total weight of the CSM + LM at TLI ignition was ~100,000 lbs (64,000 lbs CSM and 36,000 lbs LM).  So Wayne's blog is very plausible. 

 

One other benefit, from a trajectory control standpoint, is that when going into and coming out of orbit around the moon, the larger the thrust, the shorter the burn time and the shorter the burn arc, which simplifies guidance. 

Jack K

From: Gary Johnson <gjohnson144@comcast.net>
To: Gary Johnson <gjohnson144@comcast.net>
Sent: Saturday, August 8, 2015 5:25 PM
Subject: FW: Specific Plans

 

Thanks to Wayne's Bog, as I did not know the Apollo SM SPS engine was oversized.

Gary

 

 

 

 

Specific Plans

"A long term strategy and corresponding plans must also be developed . . . a set of notional milestones, launches, and hardware developments that are sufficiently defined so as to allow a cost estimate" – NASA Advisory Council finding April 2015

There is a story, perhaps apocryphal, that in the backseat of the car from NASA Headquarters to the White House to brief President Kennedy on the possibility of a moon landing, the legendary NASA Administrator James Webb decided to double the estimated cost of the program. Whether that part is true or not, the Webb estimate delivered that day in the spring of 1961 was significantly lower than the actual Apollo program.
Norman Augustine's famous book of "Laws" concerning government acquisition states that all program cost estimates are subject to a correction factor of [1+ 0.52/(1+8t3)] where t is the percent of the procurement period completed. Or as he finishes the chapter with Law XXIV: "The most unsuccessful three years in the education of cost estimators appears to be fifth-grade arithmetic."
During the so-called Space Exploration Initiative (SEI) days of the late 1980's, the '90-day-study' came up with a very detailed plan to go to Mars . . . and the cost estimate made that plan dead on arrival at Congress. This lesson has not been lost on the NASA leadership.
A historical example may be in order. Look at the Apollo program hardware, specifically the Service Module and its rocket system the SPS (Service Propulsion System). That rocket engine is tremendously more powerful than the subsequent lunar landing flights needed. Why was such a large rocket engine installed on the Apollo SM? In 1961 when the first real plans for lunar landing were baselined, Direct Lunar Ascent was the designated mode. Some sort of huge lander would drop the entire CM/SM stack onto the lunar surface and the SPS had to be big enough to lift the astronauts, the Command Module, and the Service Module off the lunar surface and put them on a trajectory for the Earth.
To put that big stack – the CM/SM and the Landing Stage on a trajectory to the moon, the puny Saturn V was not big enough. Developing a much larger rocket was required – they called it Nova. Nova would have twice the number of F-1 engines as the Saturn V, tanks twice the diameter, much taller, more stages, etc., etc., etc. Exactly how the Nova rocket would be built was never figured out – it would be too big to fit under the ceiling of the factory at Michoud where the Saturn V first stage was made. The notions of how to transport that rocket to the launch pad were . . . notional.

Then along came some bright boys at Langley headed by John Houbolt who advocated an operationally more complex idea called Lunar Orbit Rendezvous – which only needed the Saturn V already under development.
The Nova rocket, the 100 foot tall Lunar Descent Stage, all went in the dust bin of history were never developed. But the contract for the SPS engine had already been let. Any real need to downsize that engine? No, but much less propellant would be carried in the tanks. If the Apollo CM/SM were somehow magically transported to the surface of the moon, the SPS had enough oomph to lift them off . . . but probably not enough gas onboard to get very far.
LOR was a good idea. Lots of folks are proposing ideas for future space travel. Some of them are actually pretty good. Locking a plan down means new, good ideas can't complete.
History cries out with lessons. Some of them are subtle. Having detailed plans is generally good; believing in them too much is not. In the military they are fond of quoting the maxim: "No battle plan survives its first encounter with the enemy". In space, the enemy is physics and chemistry . . . and finances. It may be that flexibility and leaving options open provides a better path for our long term ambitions in space. Who knows what may be invented in the next five years that could change the entire game plan?
Would we have made it to the moon if we tried to build the Nova rocket to do it? Maybe, maybe not.
The wrong plan can easily come with a forecast cost – a shock to the system – such that the program is never approved. Having a reasonable plan for the next step while keeping the goal in sight might actually be better. Waiting a little while doing some testing and development might be a good idea. Finding creative ways of controlling costs is mandatory.
Meanwhile, anybody seen Zephram Cockrane out there? Or at least the ghost of John Houbolt?

 

 

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