Re: Ares vs DIRECT

On Dec 5, 12:08 pm, simberg.interglo...@xxxxxxxxx (Rand Simberg)
wrote:
On Wed, 5 Dec 2007 08:30:10 -0800 (PST), in a place far, far away,
behlin...@xxxxxxxxx made the phosphor on my monitor glow in such a way
as to indicate that:



One of the udnerlying ideas behind Ares is to separate the cargo and
crewed vehicles instead of doing it all in one. So having separate
launchers makes sense.

The very idea that separating crew from cargo for ISS missions is silly to
me.

That was one of the dumber (among many dumb ones) "lessons" learned
from the Shuttle.

It wasn't ISS "cargo". It was other payloads unrelated to the crew

Why is that relevant?

Let me expand.

Every time an airliner takes off, it carries cargo not only unrelated
to the crew, but even unrelated to the passengers. It's their own
version of Fedex, using excess cargo capacity to carry cargo in their
excess cargo capacity. It has rarely caused
any problems. This remains a dumb "lesson learned."

Launch vehicles are not airliners, the analogy is not applicable.

Why not? "Because I say so" won't cut it.

If you are going to use the airline analogy, then Valuejet is your
airline.

That's nonsense. Valuejet happened once, out of many thousands of
flights.

Flying unrelated spacecraft with crew does the following:

1. Increases risk to the crew and the amount is not trivial.

How?

More parts means less reliable

What? Why are "more parts" required to carry cargo, and how does
carrying cargo make it less reliable?

2. Increases risks to the companion spacecraft.

How?

Manrating the spacecraft increases weight and complexity.

What does "manrating" mean in this context? Shuttle itself was never
"manrated."

It has cause problems for the companion spacecraft: Syncom-IV-3,
GRO, SPARTAN and some unmentionables are some

How does sharing a ride with a crew "cause problems"?

The shuttle was "manrated" just not completely on all systems.

Spacecraft that flew on the shuttle had extra inhibits and valves and
heavier structure (increased factors of safety). This prevented
Syncom IV and the Spartan from activating. GRO had a latch that hung
up on an antenna when a pyro type device would have been more
reliable. There have been others


Launch vehicles are not airliners because
1. LV are not as reliable
2. LV don't have as many graceful "abort" options. Abort towers are
more like ejection seats
3. airliners don't carry anything as large and hazardous as a fueled
spacecraft.
4. There is nothing "routine" about an LV launch
5. Margins in LV systems are less than airliner
6.

Simple reliability analysis rule of thumb: More parts is less
reliable

More parts exist with the cargo because:
1. the cargo itself is made up of parts and it is not passive
2. The LV must accommodate the cargo in addition to the crew, this
requires more parts

Defintion: Cargo is not just ISS logistics or assembly

Talk to any one who has worked on a spacecraft that flew in the
shuttle. It was a pain in the ass
.

Relevant Pages

  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... >>> it to gain reliability at the expense of performance. ... but your cargo landed up in the Atlantic. ... How about converting the Shuttle to launch and land unmanned and use it ... a stopgap measure to keep U.S. manned spaceflight going without ...
    (sci.space.policy)
  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... >>a lower level of reliability? ... >>"I'm sorry paying customer, but your cargo landed up in the Atlantic. ...
    (sci.space.policy)
  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... >>Greg D. Moore (Strider) wrote: ... >>>a lower level of reliability? ... > more demand for cargo versions, and the cargo doesn't care if it's not ...
    (sci.space.policy)
  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... reliable" model of the 747 just for cargo. ... would only fly over uninhabited areas in its missions, you might well decide to cut back the reliability factor some in favor of lower cost and increased payload if it made mathematical sense in your ...
    (sci.space.policy)
  • Re: Do cargo-hauling astronauts really lift 15 tons?
    ... In the weightless environment of space, ... delivered to the international space station by the shuttle Discovery. ... Does the cargo really weigh that much? ...
    (soc.culture.russian)
Loading