posted 05-18-2018 11:14 AM               

I seem to remember that five shuttles were to be built plus a sixth non-spaceflight test version (Enterprise). Budget cuts in the 1970s reduced that number to four spaceflight versions (Columbia, Challenger, Atlantis and Discovery). Ultimately, Challenger was destroyed in 1986 and a fifth spaceflight version shuttle was built — Endeavour.

But is it correct that five were to be built from the start?

I also remember that there were plans to convert the Enterprise into a spaceflight version of the shuttle. So I am wondering if that was supposed to be the fifth shuttle or whether that idea of upgrading Enterprise was an idea that came later.

And does anyone also know what the original projections were for the number of shuttle launches? I seem to remember that they imagined something like 100 launches per year and then the number of projected launches got progressively reduced.

posted 05-18-2018 11:58 AM               

Here are some quick answers:

• Orbiters were to fly up to 100 missions.
  
• There was to be a two week turnaround for the orbiters
  
• There was to be a launch every week
  
• A landing test, static test and an orbital vehicle (OV-101, STA-099, OV-102) were part of the development contract, with the intent to upgrade the landing test vehicle to orbital. It was decided later that it would be easier to convert STA-099 into an orbital vehicle than OV-101. OV-103 and OV-104 were added as a follow on production contract. OV-105 was initially just a production spares contract.
  
• Even though the flight rate model was dropping through the years, the goal was to be 24 per year at the time of the Challenger accident.

posted 05-18-2018 12:55 PM               

When the built OV-105, they started constructing spares/parts for a possible OV-106. But nothing substantial had been built by contract termination.

posted 05-18-2018 10:50 PM               

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Originally posted by Jim_Voce:
And even when Columbia was first launched in 1981, there were plans to have a very ambitious number of flights per year. Does anyone remember what the number was?

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The next issue was for an engineering philosophy stating that the way to achieve inexpensive high launch and turnaround rates, was to put enough redundancy in it so that you can launch with systems that aren't working. "So, instead of putting three levels of redundancy, which is normally what had been used, In the shuttle we put in four levels so that while you're counting the thing down if something fails, you just launch anyway because you've got three good systems." (Max Faget, 1997). This turned out to be much more difficult to make work and a lot longer to check out.

The shuttle original proposal was for an orbiter that had a maintenance schedule similar to that of an aircraft, where routine maintenance was performed at scheduled intervals, line items and defects were rectified between flights. A minimum equipment list of allowable faults enabled continued operation between scheduled maintenance. Remembering that the orbiter was one of the first fly-by-wire aircraft, this maintenance philosophy proved to be overwhelming.

The orbiter took much longer to turn around than originally intended, The planned five orbiter fleet was designed for 100 flight/10-year life cycle. If flown as planned, Columbia would have been retired before Endeavour, first flown in 1992, entered service (but if plans worked out, Challenger would never have needed a replacement). What may have replaced the space shuttle and what shape the spaceflight industry would be in may be very different.

Due to the high mission cost, the product development of the shuttle was stifled. Any aircraft design in operation for a similar lifespan would have experienced product improvements over the years. Systems and parts would experience evolution at a higher rate to improve reliability and profitability. The shuttle did not experience such development due partly to the high mission cost, and because it ran under government budgetary constraint (if it ain't broke, don't fix it).

An example is the shuttle general purpose computers (DPS) making up the PASS and BFC. Due to the fail-operational/fail-safe design ran comparatively small software loads (advanced at the time) that required huge amounts of testing before any software change would be permitted (if it ain't broke, don't fix it). I believe that the orbiter computer system hardware and avionics system only received 1 major upgrade during shuttle life.

Many of the items that were originally considered for the shuttle during initial planning, done during the Apollo era, are the same items still being researched and developed today. Fully reusable spacecraft, high dispatch rates, minimum in-service maintenance, and low cost to orbit. Perhaps if an autonomous cargo version of the orbiter had been built, the cost to orbit for freight would have reduced and the shuttle may today be flying next-generation versions called dash 800 or 900 (or Block 5 or 6) at higher flight rates. Perhaps a Falcon Heavy would be lifting a modern, composite construction orbiter, to a commercialised space station in a government/private partnership. Maybe as a staging post to the moon or Mars.

posted 05-19-2018 01:31 AM               

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Originally posted by Hart Sastrowardoyo:
Two of the shuttles would have been a front and a back end (similar to the MPTA, but not using MPTA) later upgraded to flight orbiters after testing.

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posted 05-19-2018 06:42 AM               

The Space Transportation Company (SpaceTran) proposed in 1982 to NASA that they finance an orbiter that they would allow NASA to integrate into their fleet of orbiters. In return, SpaceTran would take over the marketing of the shuttle.

Astrotech also made a proposal to NASA to finance an orbiter in 1984. Astrotech would then lease a portion of the shuttle fleet and do all the marketing.

Obviously neither proposal was accepted. Given that the shuttle was a much more complex operation than expected early in the planning stages, both companies were fortunate that their proposals were rejected.

posted 05-20-2018 09:19 AM               

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Originally posted by oly:
...requiring large payload capabilities suitable for military needs, including the Air Force, who indicated a need for the large payload size and weight. I do not think the Air Force ever utilized the shuttle.

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posted 05-20-2018 09:23 AM               

quote:

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Originally posted by Jim_Voce:
...the original plan to build five shuttles, that two of them would have started out as partially constructed "test articles"

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posted 05-28-2018 09:55 PM               

quote:

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Originally posted by Hart Sastrowardoyo:
One NASA astronaut said it was not both, but either/or, that the shuttles had a lifetime for 10 years OR 100 flights.

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Most aircraft have a fatigue life that is measured by counting flight hours, pressurization cycles, "G" loading and many other variables. For the Orbiter, the original design requirements of 10 years/100 flights would have taken into account a unique set of structural loads that would need to include launch stress and vibration loadings, pressure loadings, temperature changes, etc. Given the rate of assent experienced during launch, the pressure differential rate of change would be a significant factor, as would also the re-entry temp and pressure change.

posted 05-29-2018 02:21 AM               

Aviation was going through leaps and bounds post war, with aircraft like the super constellation first flight in 1951, The 707 first flight in 1957 and the 747 first flight in 1969. each of these aircraft brought new innovation into airliners, and each became outdated relatively quickly. So at the time of design, 10 years was a long time.

posted 05-29-2018 08:28 AM               

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Originally posted by OV-105:
Columbia would have been retired in 1991...

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