Ending the space shuttle program

Was any thought given to placing the shuttle on top of boosters so that the tiles would not be subjected to falling debris, or of creating a shroud for the tile?

Are you asking if that was considered during the initial design phase, or if they considered a drastic change to the working shuttle once the problem was discovered?

in the 2nd failure it was not the tiles that were the problem , it was part of the wing that had a hole in it from falling debris from the external tank. so they would have had to put the shuttle above the tank too.

That was actually one of the original plans when the idea was to obtian low launch costs through amortization. Cultural issues and scope creep changed the intended mission through the development process and made that impractical.

In reality it was only due to pride that it flew so long as expendable rockets would have been far less costly.

The problematic debris was foam and/or ice peeling off of the external fuel tank. To counter this, NASA would have needed to place the orbiter above the external fuel tank, regardless of where the boosters would be positioned. The original design facilitated attachment of the orbiter to the tank at three points with a large spread between them. Moving the orbiter upward would have eliminated that stable attachment; it also would have drastically altered the aerodynamics of the whole assembly.

A shroud for the tile (or even just for the RCC wing leading edges) strong enough to provide meaningful protection would have added considerable weight and aerodynamic drag.

My guess is that neither of these options were given much thought beyond what I wrote there - especially since they only flew for about eight more years after the Columbia disaster.

Did they consider redesign after the problem was discovered?

they changed things after both accidents , for example the booster o ring seals were changed after Challenger . Don’t recall what was changed after Columbia.

There isn’t really an option for a simple redesign of locaiton due to the technical challenges they would have had to start over from scratch.

The wings of the space shuttle would have made a rocket unstable if it was on the top, and look at the direction that the main engines on the shuttle are pointing.

A radical redesign of the shuttle wasn’t in the cards for many reasons. It was essentially a failed system near the end of its lifespan. A similar situation happened with the Concorde, one failure and they just pulled it out of service because any significant redesign would never have returned even a fraction of the cost.

There is literally no way to change the architecture of the Space Launch System (SLS) to put the Orbiter Vehicle (OV) ahead of the External Tank (ET) and Solid Rocket Boosters (SRB). The OV contained the three Space Shuttle Main Engines (SSME) that fired from before liftoff to final orbit insertion, and therefore need to be below the tank.

Some consideration was give. To trying to reinforce or protect the reinforced carbon-carbon (RCC) leading edge panels on the wings where the falling icy insulation punctured Columbia but since it is a primary aerosurface it isn’t really possible to enshroud it. Damage and loss of bottom tiles was not a new phenomena, and in fact had been seen since the first test flights but did not represent a catastrophic failure mode unless a large area was left uncovered. The tiles were not exposed to normal airflow as the RCC panels and served to insulate radiation from the airflow moving around the OV outer mold line (OML).

There was an attempt to design a cover over the ramp where the ET mounted where ice would collect after the Columbia failure but it didn’t really prevent ice buildup or protect it from falling toward the wings. After the challenger failure the SRBs were redesigned in a number of ways but the major one was changing the joint design to be similar to that used in the abortive Advanced Fiber-Wound Composite Motor intended for Blue Shuttle launches out of Vandenberg SLC-6, adding a third O-ring that was not in direct flow path with the other two, and heaters to warm the joints, as well as a number of procedural changes and restrictions. A comprehensive explanation of SLS development and the post-Challenger modifications can be found in Dennis R. Jenkins’ Space Shuttle: The History of the National Space Transportation System The First 100 Missions.

The SLS was a far from optimal design in a vast number of ways, but many of the problems it had were not readily foreseeable or were limitations of the technology in the era it was designed. At the time of retirement most of the fleet was nearly thirty years from first flight which is actually a pretty remarkable duration even with the far lower than intended flight rate, and the realized reliability was in line with the technical estimates of a loss of crew and vehicle (LCOV) failure of between 1:50 and 1:100 flights. The primary lesson from the SLS should be that large winged “spaceplane” vehicles are overly complex and untenable, and that heavy lift capability should be separate from crewed launch, at least until launch capability matures. I’m not sure we’ve really learned that lesson, but regardless, modifying the Shuttle to operate with greater safety in line with the o.p. really wasn’t a viable option.

Stranger

A really key point there. The main engines burned a lot “cleaner” than the SRBs (different propellants). So in video you tend to notice the SRBs flame and smoke more than the main engines.

But they are hot, violent and need nothing below them to disturb the flow. The tank wouldn’t last long in that stream. Nevermind the mechanical issues.

I feel like you’re understating things here. The proposal is to put the giant propellant tank directly downstream of the engines fueled by that tank. There are lots of places one can put a propellant tank–above the engine, or off to the side, or in a donut shape around the engine, or buried in a swamp in Florida–but directly downstream of the exhaust is exactly where you would put a tank if you wanted everything to explode as quickly as possible.

All that said, a redesign would have been possible, if not plausible. The main engines would have to be put on the bottom of the External Tank and left off the Orbiter. The STS–using Shuttle-like components–puts the engines there. The orbiter doesn’t need the main engines once the tank has been jettisoned, so there’s no problem there. It has an entirely different set of engines suitable for orbital maneuvering.

It does make the engines expendable, since they would no longer be carried back on the orbiter. This may not have actually raised the price of a launch, though. And of course it would be a very significant redesign, though easier if you didn’t worry too much about loss of payload capacity. Ripping out the engines and plumbing from the orbiters, and designing a kind of mounting system to put it on top, might have been just on the edge of feasible. Of course, it would still cost billions and be worse in every way compared to a modern redesign.

I thought the Space Shuttle system was the STS (Space Transportation System), and the Shuttle-derived heavy lift rocket currently in development was the SLS (Space Launch System)?

Even at that it would not be possible to modify the ET and OV; the thrust structure linking the OV and the ET is designed such that the SSMEs are thrusting roughly through the combined center of mass, and would be completely different if the engines were mounted to the aft of the ET (which has no thrust structure). It would require a complete redesign of both structures notwithstanding how it would change the system functionally. However, the configuration you present is essentially exactly how the Soviet Buran system worked, with the orbiter riding on the Energia rocket with four liquid boosters. This was arguably a better configuration for a number of reasons, but while Buran looked superficially like the STS it had significant differences in operation and capability.

Yes, you are correct. I keep getting those muddled because of the similarity in acronym, and because I don’t work on that program (thankfully).

Stranger

Indeed. Don’t forget redesigning the launch tower, too.

The changes made to the orbiter might not be too bad. The engine structure was obviously designed to support a high mostly-axial load–roughly 6x as high as the max liftoff weight of the orbiter+payload. It’s not completely unreasonable that this could have been repurposed for a fixed mount. Though as you say the CoM has moved so there are still some problems.

Th ET would need an SLS-level redesign, though. But that’s happening, so we know it’s possible. Just expensive and silly.

Yeah, the big problem would be that the engines were built into the reusable shuttle. Putting the engines instead underneath the orange main tank, and then changing the shuttle unit to fly home without that weight distribution - it probably would have been cheaper to design a whole new system from scratch. Plus designing the tank to carry the shuttle weight on top. Plus, the tank was throwaway, so then your engines would be throw-away too, adding a huge cost to each flight. IIRC the shuttle was a compromise - a behemoth with 15-foot-diameter payload bay to carry those top secret spy telescopes. Perhaps a simpler craft, man and small payload only would have been a more practical design and save the giant loads for disposable rockets. The smaller craft could have perched on top of a disposable stage. But - how essential was flying home instead of parachuting? Apparently not too urgent.

One item I read said that the space program was very partisan. Kennedy (D) and Johnson pushed for Apollo moon rockets. Nixon ® pushed for the shuttle and cancelled as many Apollos as he could get away with. Carter (D) considered cancelling the Shuttle but too much money had already been spent on it, and then Reagan came along and made it and ISS one of his prestige projects. What comes after has been kicked back and forth with one design and destination after another as we change presidents.

A primary reason for the shuttle payload bay size was constructing a modular zero-gravity space station (later called ISS), even though it was built much later. You can’t build a space station with a little spaceplane the size of Dyna Soar or Dream Chaser.

The original plan was to build the station immediately after the shuttle was operational, but funding delayed that many years.

You could argue that a totally different space architecture would have been better, such as maintaining the Saturn V, launching a totally different space station with three or four 300,000 payloads, and servicing it with a little shuttle. However that is not a different shuttle design, it’s an alternate reality which was never a realistic possibility.

The station’s pervasive impact on the shuttle’s design was discussed during the Columbia Accident Investigation by Bob Thompson, who was the Space Shuttle Program Manager from 1970 to 1981.

Transcript: http://govinfo.library.unt.edu/caib/events/public_hearings/20030423/transcript_am.html

Regarding orbiter placement on the stack, putting it on top and engines on the bottom was evaluated but this had significant drawbacks. The stack would be much taller, making servicing it on the pad more difficult. Before launch and during atmospheric ascent, cross winds on the winged plane’s large surface area would create unpredictable sideways loads on the stack. This in turn would require the entire structure to be beefed up and heavier.

Some various alternative design issues were discussed by Aaron Cohen (who was responsible for the orbiter’s design, development and production) in this video lecture series: https://www.youtube.com/watch?v=xJ2H06sseLM

I recall two or three things that came from analyzing Columbia. The fix they ended up using was to have a camera (on the ISS maybe?) inspect each Shuttle after reaching orbit. If something looked damage, stay in orbit until a rescue flight could come up. They might have also designed a patch for in-orbit repairs to non-leading edge areas, not sure if that got completed or not. For prevention, the main thing they found out was that the glue for big red foam was weak. The original glue was non-enviornmentally friendly (outgassing maybe?), and at some point pre-Columbia NASA switched to a “green” glue. Which they had to keep after C because they couldn’t find a better, still-green alternative. (Which implies the green initiative was a change of law, not a NASA policy)

And no reason to do more than a quick fix when they were in the process of retiring the program and designing a completely new replacement - part of Constellation
Constellation_program

I recall something like a caulk gun that would be used to replace missing tiles.
This describes repairing a thermal blanket on the shuttle.

That isn’t replacing a tile; that is just pulling out the felt gap filler that is put in to space the tiles to allow for thermal expansion during reentry (so they don’t pop one another off). The gap filler was removed because engineers were concerned that if it protruded it might cause localized heating; there is no evidence for this and the analysis was inconclusive, but NASA was seen as needing to do “something” to ameliorate the concerns about Shuttle reliability even if there wasn’t practically anything they could do.

The tiles are of different shapes–nearly every one is unique–so replacing a tile in orbit just isn’t practical even if it were possible to do so, and a single missing tile would not doom the OV to catastrophic failure; shuttles routinely lost a few tiles on reentry on the majority of flights. Repair of the RCC leading edges–which would have been necessary to save Columbia from its fiery doom–is just not practical in space. There was a preliminary plan post-Columbia to fill such gaps with some kind of filler and water ice, but analysis demonstrated that it would not survive for anywhere near long enough to protect the OV during its succession of S-curves during reentry.

Stranger