Re: Japans Moon Ambitions - They're KIDDING, Right ?

From: Rand Simberg (simberg.interglobal_at_org.trash)
Date: 03/09/05 

Date: Wed, 09 Mar 2005 15:08:21 GMT

On 8 Mar 2005 19:50:15 -0800, in a place far, far away, "Will"
<mclean1382@aol.com> made the phosphor on my monitor glow in such a
way as to indicate that:

>> >> >The last two add failure modes that aren't
>> >> >present with an expendable vehicle.
>> >>
>> >> No, but there are ways to mitigate component failure, by designing
>> >the
>> >> system for regular inspections.
>> >
>> >Yes. But it is an additional failure mode that reusable vehicles
>must
>> >address.
>>
>> Why do you think that they wouldn't?
>>
>
>Do you think that regular inspections will reduce failures from wear
>and fatigue to a negligable level?

It does for aircraft.

>That hasn't worked for manufacturing errors.

That's a different problem. In order to eliminate manufacturing
errors, each unit has to be inspected. For a reusable device, to look
for wear (which is a gradual phenomenon), inspections are only
required once per certain number of flights.

>> >And the last one isn't a different
>> >> category of failure--it's just part of the overall mission profile
>> >> that has to be designed for and tested.
>> >>
>> >
>> >It is a different category in that it is only relevant to reusable
>> >vehicles. It's only part of the mission profile if you recover the
>> >vehicle.
>>
>> I guess I'm failing to see the relevance, if you're saying that this
>> will somehow result in a lower reliability than low-rate expendables,
>> given a sensible flight test program.
>>
>
>What I am is disputing is how much of a reliability improvement you get
>from reusability alone. If you specify that the expendable must fly
>fewer flights, then *that* would effect reliability. But it doesn't
>necessarily follow that the expendable will fly fewer flights, as a
>comparison of STS and Soyuz shows.

You continue to miss the infant mortality issue. *Every* flight of an
expendable is a first flight. Once a reusable has a track record,
chances of it failing to a manufacturing problem is much diminished.
In addition, a reusable can be affordably flight tested before
actually carrying payloads.

>Consider a hypothetical mature expendable with more than 100 flights,
>like Delta II, with a failure rate of ca 2%. Half of that is
>manufacturing error not caught in ground tests. The other half is other
>issues, such as processing errors like ice in the propellant lines,
>tape not removed on stage separation switch, error in loading flight
>software, or wrong commands from ground control.

I would hope that the reusable design would be such as to minimize
such processing errors (e.g., flight software wouldn't require
"loading" for each flight, and "ground control" wouldn't be involved).

>Also design flaws that
>haven't shown up in the first 100 flights, weather, lightning, etc.

In the case of the reusable, a hundred flights would be a reasonable
flight test program. And an affordable one, since the marginal cost
per flight would be much lower...

>> >The optimal solution for the airline industry has limited relevance
>to
>> >reaching space, and even less to reaching orbit.
>>
>> I think that you're deeply mistaken. It has the utmost relevance in
>> doing so affordably and reliably. Sadly, the industry has ignored
>it,
>> because the market hasn't demanded it.
>
>Some of it does, some doesn't. The tricky part is knowing which is
>which. Surely you aren't suggesting that since air-breathing engines
>are optimal for airlines, they are the best way to get to orbit?

No. It's not as tricky as you seem to think.

The things that are similar are:

o Don't throw the vehicle away every flight.
o Build in lots of margin.
o Have an extensive flight test program with gradual envelope
expansion.
o Design for minimum turnaround operations.
o Keep the wheels in the well.

Relevant Pages

  • Re: Spaceship One stepping-stone or dead-end?
    ... > Jeff Findley wrote: ... Then explain to me how the Soyuz launch vehicle was able to put Vostok in ... This is because they throw away the entire vehicle after each flight. ... only serious attempts at reusability were to "copy" the US shuttle ...
    (sci.space.policy)
  • Re: Space Access Update #112 9/19/05
    ... >The key to lowering costs and producing a truly operational system is to fly ... Reusability, or lack of reusability, isn't as important as flight ...
    (sci.space.policy)
  • Re: Total Number Of Launches (Or Attempts) In History?
    ... Reusability is the only way to get reliability up to aircraft levels (even ... rather than just its middle -- and allows repeated testing of each flight ... cheap frequent flight tests are perhaps not impossible ...
    (sci.space.history)
  • Re: Japans Moon Ambitions - Theyre KIDDING, Right ?
    ... >>Do you think that regular inspections will reduce failures from wear ... >>from reusability alone. ... > expendable is a first flight. ... > I would hope that the reusable design would be such as to minimize ...
    (sci.space.policy)
  • Re: Japans Moon Ambitions - Theyre KIDDING, Right ?
    ... >It does for aircraft that don't push performance very hard. ... >> I would hope that the reusable design would be such as to minimize ... >Even commercial aircraft has these error modes: fuel load and flight ... >> o Have an extensive flight test program with gradual envelope ...
    (sci.space.policy)