Thursday, February 28, 2008

Bait and Switch

Many months ago we pointed out the dangers of specifying a design instead of deriving one from requirements. Many previous entries have expounded on the results. Finally, others closer to the problems are speaking out.

Av Week: "NASA's planned Ares V heavy lift vehicle can't meet its lunar-mission requirements as currently conceived, and will need beefing up...But even with expansion from earlier concepts to a full 10-meter diameter all the way up to the fairing that will cover the Altair lunar lander, allowing the upper stage to carry more propellant, Ares V still falls short, according to Phil Sumrall, advanced planning manager in the Exploration Launch Projects Office at Marshall Space Flight Center. "The payload requirements are very driving and very difficult to get to, and frankly our vehicle today is close but doesn't quite meet those mission requirements," Sumrall told the Third Space Exploration Conference & Exhibit [in Denver] Feb. 26."

Now ARES V might become ARES VI with six engines. The Emperor's common element approach may not employ common elements after all. The SRB casings and fuel could change to get added performance. Time to add back those reduced development and life cycle costs being touted as a benefit of the ARES I/V common concept. It might not fit out the door of the VAB as it grows longer than the Saturn V. Worse still, today's shuttle's launch pad is not wide enough for the ARES VI. One solution offered to that problem involves tipping over the rocket slightly to make it fit. Maybe Steve Cook will just go out and hold it like the leaning Tower of Pisa?

Have to hand it to those ESAS guys. Bragging about how they accomplished in 60 days (ok, it was more like 120) what no one before them could pull off. Now we see the fruit of their efforts.

Haste makes waste.


kT said...

Many other euphemisms are possible.

'The bigger they come, the harder they fall' comes to mind.

RayGun said...

I've really enjoyed reading Rocketsandsuch. Love the writing style.
Sometimes smart people lack common sense.
Common sense has left the Empire.

Dave said...

The "fruit of their efforts" just gets more rotten by the day.

Patchouli said...

You know the payload issue with ares V is because of ares I and them stripping Orion to make it light enough.

Orion can't perform LOI a 900m/sec burn that allows the CSM/LSAM stack to enter lunar orbit.
The LSAM presently has to perform this burn this makes it tanks about 30% larger then they normally would have to be for a given fuel.

This extra tank mass has to be able to be carried by the descent stage all the way to the lunar surface.
The need for total of over 3500M/sec delta V out of the descent stage forces use of a high ISP fuel in this case hydrogen.

"For historical references the Apollo LEM descent stage only needed a delta V of 2450M/sec."

Liquid hydrogen being a very low density and very cold fuel needs very large tanks, plus insulation and a margin of extra fuel to handle boil off for up to 4 weeks parking in LEO plus the 4 day trip out to the moon.