Author Topic: Why Endeavour was built?  (Read 9783 times)

Offline AnlaShok

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Why Endeavour was built?
« on: 03/07/2007 10:44 am »
Why was a fourth Shuttle needed after the Challenger disaster? It was clear then that there would be not so many flights a year (not 60, not even 9), since no commercial satellite launches would be allowed. With five flights a year and an occasional DoD mission, wouldn't three Shuttles have been enough? HL-20 might have been more practical.

Offline Gary

RE: Why Endeavour was built?
« Reply #1 on: 03/07/2007 11:08 am »
HL-20 would have been a new design and so it would have cost more to design, consult, build and test.

Shuttle design was proven to work. Endeavour is basically built out of spare parts. Plus Columbia had a few other issues being heavier than the other Orbiters. This would mean that when the ISS got the go ahead only two shuttles could reach it (or one if either Discovery or Atlantis were down for OMM).

Offline psloss

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RE: Why Endeavour was built?
« Reply #2 on: 03/07/2007 11:17 am »
Quote
AnlaShok - 7/3/2007  6:44 AM

Why was a fourth Shuttle needed after the Challenger disaster? It was clear then that there would be not so many flights a year (not 60, not even 9), since no commercial satellite launches would be allowed. With five flights a year and an occasional DoD mission, wouldn't three Shuttles have been enough?
Maybe, but they flew more frequently than that in the period after Endeavour was delivered: 7 flights per calendar year between '93 and '97, inclusive.  (With the 83/94 reflight in the middle of '97 adding an extra launch/landing.)

After that, the ISS manifest started to dominate and the flight rate fluctuated...

Offline Jim

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Re: Why Endeavour was built?
« Reply #3 on: 03/07/2007 11:27 am »
There was a thread on this already.  

HL-20 more practial for what?  There was no mission for a HL-20.

It was needed because orbiters were periodically taken out of the flight rotation for periods up to a year for inspections and maintanance

Offline AnlaShok

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RE: Why Endeavour was built?
« Reply #4 on: 03/07/2007 05:21 pm »
Quote
Gary - 7/3/2007  2:08 PM

HL-20 would have been a new design and so it would have cost more to design, consult, build and test.

Shuttle design was proven to work. Endeavour is basically built out of spare parts. Plus Columbia had a few other issues being heavier than the other Orbiters. This would mean that when the ISS got the go ahead only two shuttles could reach it (or one if either Discovery or Atlantis were down for OMM).

Quote
psloss - 7/3/2007  2:17 PM

Maybe, but they flew more frequently than that in the period after Endeavour was delivered: 7 flights per calendar year between '93 and '97, inclusive.  (With the 83/94 reflight in the middle of '97 adding an extra launch/landing.)

After that, the ISS manifest started to dominate and the flight rate fluctuated...

Quote
Jim - 7/3/2007  2:27 PM

There was a thread on this already.  

HL-20 more practial for what?  There was no mission for a HL-20.

It was needed because orbiters were periodically taken out of the flight rotation for periods up to a year for inspections and maintanance

Sorry, didn't find that thread, new here…

HL-20 was pretty far in the design process, and Endeavour was anyway 1,7 billion. Considering later estimates for X-38 based CRV, HL-20 would have been like 1-2 billion. As for mission:
- assured manned US access
- safety
- affordable
from http://www.nasa.gov/centers/langley/news/factsheets/HL-20.html

Sadly past decades showed there was the need for a CRV/OSP. Since NASA later planned a X-38 based CRV, HL-20 would have been ready for Freedom/ISS. The same with an OSP. I can understand that X-33s might have been fantasies, but a HL-20 had nothing special new tech or concept.

That time there wasn't yet an ISS, but Freedom on different orbit. So weight problems for Columbia were't yet known. And that time yearly 5 Shuttle flights for Freedom were planned (without HL-20).

Offline Jim

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Re: Why Endeavour was built?
« Reply #5 on: 03/07/2007 06:53 pm »
Columbia always had weight problems.     More than 5 flights per year were planned for Freedom.

The HL-20 was not far along in the design process only mockups were made.   There was no need for a HL-20 until 2000 (ISS) or later.    HL-20 is new tech.  There hasn't been enough lifting body from orbit test results.

Offline Gary

Re: Why Endeavour was built?
« Reply #6 on: 03/07/2007 10:01 pm »
The HL-20 was afforable by who's definition? the shuttle was affordable with missions every two weeks as originally planned. Dont take press blurb for fact, IF the HL-20 had been built only then would true build, design and OPERATIONAL costs have been know. It would not have been a matter or building and launching there would need to be tests, Maintenance, training, etc. This all adds up.

Offline simonbp

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Re: Why Endeavour was built?
« Reply #7 on: 03/08/2007 12:47 pm »
The HL-20 couldn't have carried cargo, and it needed a whole launch/landing infrastructure, the spares that Endevour was built from already existed...

But lifting bodies have returned from orbital velocities (see SV-5D/PRIME and BOR-4), and their aerodynamics have been verified ad nauseum in hypersonic wind tunnels. The question is more why you want to use one in the first place...

Simon ;)

Offline Jim

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Re: Why Endeavour was built?
« Reply #8 on: 03/08/2007 02:21 pm »
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simonbp - 8/3/2007  8:47 AM


But lifting bodies have returned from orbital velocities (see SV-5D/PRIME and BOR-4), and their aerodynamics have been verified ad nauseum in hypersonic wind tunnels. The question is more why you want to use one in the first place...


Not true.  those were only a few flights with limited data.  Hypersonic wind tunnels do not operate at reentry velocities.

Offline simonbp

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Re: Why Endeavour was built?
« Reply #9 on: 03/08/2007 10:50 pm »
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Jim - 8/3/2007  9:21 AM

Not true.  those were only a few flights with limited data.  Hypersonic wind tunnels do not operate at reentry velocities.

They don't need to be "reentry velocity", because they have an equivalent Reynolds number (look it up), and thus equivalent aerodynamics. Hypersonics is a 60+ year old science and not at all "unproven". The X-24 and HL-10 designs were tested extensively in exactly the same facilities (and by the same people) as Apollo and Shuttle, both of which seemed to work, and both of which are technically "lifting bodies" because their hypersonic lift/drag is greater than one. Heck, even the MSL entry aeroshell is technically a lifting body, to allow for a guided entry and thus more precise landing ellipse (exactly what lifting bodies were invented for). For more, look at "Wingless Flight" by Dale Reed, the guy basically invented the concept...

Engineering wise, a passenger lifting body would work. Making it work economically and/or politically is the tricky part (and the reason why none have yet flown).

Simon ;)

Offline Jim

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Re: Why Endeavour was built?
« Reply #10 on: 03/09/2007 01:08 am »
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simonbp - 8/3/2007  6:50 PM

Quote
Jim - 8/3/2007  9:21 AM

Not true.  those were only a few flights with limited data.  Hypersonic wind tunnels do not operate at reentry velocities.

They don't need to be "reentry velocity", because they have an equivalent Reynolds number (look it up), and thus equivalent aerodynamics. Hypersonics is a 60+ year old science and not at all "unproven". The X-24 and HL-10 designs were tested extensively in exactly the same facilities (and by the same people) as Apollo and Shuttle, both of which seemed to work, and both of which are technically "lifting bodies" because their hypersonic lift/drag is greater than one. Heck, even the MSL entry aeroshell is technically a lifting body, to allow for a guided entry and thus more precise landing ellipse (exactly what lifting bodies were invented for). For more, look at "Wingless Flight" by Dale Reed, the guy basically invented the concept...

Simon ;)

A little lesson here.  A true "lifting body" is different from a "capsule" with an offset CG that produces lift.

 I guess no test flights are needed since everything is proven.  They must be wasteing money trying, at the moment, to fly subscale CEV models on an ELV.  The first flight fullscale flight of the CEV must be manned, since there is no need for a test entry.  X-38 didn't need any test flights neither because it was "proven"

Equivalent Reynolds number doesn't prove materials.  The shuttle was the first vehicle to flight the whole regime, because they couldn't and still can't duplicate all the conditions and Reynolds number


Offline Gekko0481

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Re: Why Endeavour was built?
« Reply #11 on: 03/11/2007 07:09 pm »
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Gary - 7/3/2007  10:01 PM
the shuttle was affordable with missions every two weeks as originally planned.

Missions every 2 weeks eh? How awesome would that be...stupid budgets...

Offline tgrundke

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Re: Why Endeavour was built?
« Reply #12 on: 03/12/2007 02:37 am »
Well, it isn't so much the budget that got in the way, it was complexity.   The orbiter is one heluva complex and delicate machine - it requires far more TLC than the original planners ever intended.  Long story short, it takes a lot longer to prep the orbiter for flight than originally planned.

That, and NASA really couldn't find enough payloads to justify the original flight rate, anyhow.

Offline ShuttleDiscovery

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Re: Why Endeavour was built?
« Reply #13 on: 03/12/2007 07:10 pm »
I think it is fortunate that Endeavour was built because if fate didn't change, Columbia would've still been lost, leaving only 2 shuttles left. This would have slowed down the ISS assembly rate and as NASA would want to end the program due to Columbia, another shuttle as her replacement would have been impossible.

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