The Quest For Rapid Reusability

[SunlitZelkova]

Background to this discussion:

Spoiler

So over in the Lounge section, I ranted about not wanting to do this project I had about a world where the Soviets landed on the Moon first and the Space Race continued. Something more realistic than For All Mankind, while also trying to see what it would have been like had some of the never built projects I liked as a child come true.

Well, the concept was too interesting, but instead of doing the project over again, I just created this document where I could jot down random ideas and theorize on what such a world would be like, without the rigidity of a format and requirements on what details I come up with.

So what I have been trying to figure out is whether it ever would have been possible to have a rapidly reusable Space Shuttle as the mainstay of the Earth orbital launch fleet. I've done some Googling and these are my findings.

Ideally to fulfill the Integrated Program Plan (the main proposal to succeed Apollo that got watered down into the Space Shuttle) it would need to fly once a week.

One way to help do this would be to have multiple space shuttles, launchpads, and processing facilities, so that multiple shuttles could be prepared for flight at a time. If it takes one month to turn around a Space Shuttle, you just can have four space shuttles and four sets of processing and launch infrastructure, and then a Space Shuttle can launch every week.

Realistically there probably was not enough processing infrastructure to allow such a launch rate, and the maximum turn around time for the Space Shuttle was 54 days- almost two months. So how could this have been improved?

Well, for one thing, SRB recovery and refurbishment took a lot of time. Under this scenario, there is a major movement from one political party to play up the narrative that the Vietnam War is costing the US men and money that would otherwise be used to improve society at home and abroad, combatting Soviet influence. Under this pressure, the President decides to act by ending the Vietnam War instead of escalating it, and use the freed up funding to put more money into the space program. So there is enough $$$ to build a fully reusable Space Shuttle.

So this rules out my personal favorite never built Space Shuttle design, the Lockheed LS-200, and leaves us with either the "Baseline" which as far as I can tell did not have any serious studies, or the North American DC-3. Both had a flyback booster, while the LS-200 and others had some portion of the vehicle expendable. Another option might be Chrysler's SERV/MURP, but it would have been even more technologically risky. But we'll get back to that later.

Now the only issue is getting a good turn around time with the orbiter. From what I've read, here are some of the major issues:

1. SSME inspection involved taking the entire engine apart and putting it back together. This took a lot of time, to say the least.
2. TPS inspection and refurbishment also took a lot of time. Almost every piece of the Space Shuttle TPS was unique, and so it took lots of time to refurbish pieces of it.
3. The Shuttle was originally planned to use "field replaceable units" that were screwed on and would be simple to replace if something broke. Because of how heavy the TPS was, however, these had to be removed to save mass, resulting in numerous components becoming much more labor and time intensive to replace.
4. The use of hypergolics on the OMS/RCS pods required all work on the rest of the orbiter to be stopped due to the toxic nature of the fuels.

How could these issues be alleviated?

The DC-3 and Baseline orbiter-booster configurations were still planned to use a "silica based TPS" which presumably would have just been a variant of the IRL Space Shuttle TPS. It is very hard to solve the issue of hundreds or thousands of unique tiles with a spaceplane shape. Starship doesn't have this issue as much because it is more uniform in shape and is made of steel, which deals with heat better, making it a little safer for the tiles to have gaps in between them for heat expansion. The DC-3 was planned to be made out of aluminum and would not have this luxury: it would require a tight fitting TPS like the Shuttle. On the other hand, the DC-3 was much smaller in size compared to the real life Space Shuttle, and this might decrease the amount of time needed to inspect the TPS. But the booster required TPS inspections too, and it was massive, even larger than the IRL Space Shuttle. This would take an enormous amount of time, but due to the booster having jet engines and being capable of flight at greater distances than the orbiter, perhaps this could be carried out at facilities other than KCS, allowing more boosters to be build and improve turn around times.

The funding issue is eliminated in my scenario, so FRUs should be workable on the Shuttle. This would greatly reduce turn around time to some degree.

Unlike the real life Space Shuttle, the DC-3 was planned to use RL-10s for its orbital maneuvering engines. These used cryogenic fuel and would not require operations to be stopped when something was done with the OMS.

Now improving the refurbishment process with those engines is what is really daunting. I want to look at what process SpaceX uses for the Merlin engines on F9, but apparently it is a corporate secret  So I'm not really sure how the refurbishment time might have been decreased. If anyone has any thoughts feel free to share.

According to a r/SpaceXLounge user, a couple of the main bottlenecks in Falcon 9's already impressive flight rate (fastest turn around is something like 21 days I think?) are A) production of second stages and B) the kerolox engines produce soot which needs to be cleaned out.

Starship and the hypothetical Space Shuttle solve the issue of second stage availability. But what about the fuel issue? Starship solves this be using methalox, which burns cleaner. The XLR-129s on the DC-3 would use cryogenic fuel like the RS-25s of the IRL Shuttle, and thus might have a similar refurbishment process.

Another thing that would go a long way in improving Shuttle flight rates would be flying more often and building more vehicles. Part of the reason why Falcon 9 has become so efficient is because of how often it flies. This allows more data to be gathered and iterations to be made.

The DC-3 might not have this luxury, because the necessity of having crew onboard would make each flight a high stakes affair. Inspections times would still be long.

With the TPS being such an issue, it begs the question as to if it would be possible to have an alternative to the silica tile system.

Enter Chrysler's SERV/MURP. It was basically an upsized Apollo CM with aerospike engines. While it also had a modular TPS, it would have had a more uniform shape, perhaps simplifying refurbishment. But the development of an aerospike presents a whole new set of issues.

Therefore, I have come to the conclusion the Space Shuttle was simply never going to have a high flight rate. It just wasn't possible with spaceplanes.

I thus think Big Gemini would have been the most viable option for a big, post-Apollo LEO transport. Big G came in at roughly 18 tons, and the Titan III cost 9.5 million dollars per ton to launch according to an early 90s GAO report: in other words, 171 million dollars per launch in early 1990s dollars, contrasting with a 900,000,000 dollar Space Shuttle launch cost (if the 2010 estimate of 1.5 billion per launch is put into an inflation calculator for 1990). Comparing Titan III to a Saturn IB, the latter costed about 55,000,000 dollars in 1972, while the Big G's booster cost converted to that year is roughly 54,000,000: similar price but far more capability, and Big G was partially reusable, helping to alleviate the cost of the spacecraft itself.

Thus in my world, the American space program will probably become an area of high expenditure with a priority loosely akin to that of the military (although obviously with a far, far lower budget allocation when directly compared) until Elon Musk comes along, wanting to colonize Mars and builds Starship, reviving the long dead idea of a fully reusable spacecraft.

What are your thoughts? Could a fully reusable and economical spacecraft have been built in the 1970s? Or was it never going to happen until the 2020s?

[darthgently]

I remember thinking back in the 80s upon reading about the shuttle tile refurb woes, "if only there were a less expensive spray-on ablative or something".  I think now with robotics removing burnt ablator and evenly spraying new layers could be done in an inexpensive way, but not back then as well as now.  It was just a whistful passing thought with no real knowledge of the implications of the effectiveness of ablators, the mass of requisite ablator materials, or the aerodynamic implications of flying and landing a spaceplace with distorted, uneven, roasted ablator on it (probably shedding loose chunks of it across the Florida peninsula on return).

[kerbiloid]

2 hours ago, SunlitZelkova said:

and then a Space Shuttle can launch every week.

After calculating the cost, the USA declares bankrupcy and joins the USSR. Moon for peace! The Cold War is ended!

2 hours ago, SunlitZelkova said:

Well, for one thing, SRB recovery and refurbishment took a lot of time.

They were assembling SRB out of the heap of details from different SRBs.

2 hours ago, SunlitZelkova said:

Starship doesn't have this issue as much because it

has never been aerobraking at near-orbital speed.

2 hours ago, SunlitZelkova said:

The DC-3 was planned to be made out of aluminum and would not have this luxury: it would require a tight fitting TPS like the Shuttle.

The niobium-shielded DynaSoar looks at them like at plebeians.

2 hours ago, SunlitZelkova said:

Big Gemini

Its killer feature was the foldable Rogallo wing, which was allowing it horizontal landing at the airplane speed after aerobraking with simple heatshield.

Hadn't become a stable and mature technology.

At the same time, a similar paraglider system was tried for Saturn stages.

So, the foldable paraglider wings were the whole system bottleneck.

15 minutes ago, darthgently said:

I think now with robotics removing burnt ablator and evenly spraying new layers could be done in an inexpensive way, but not back then as well as now

The VA TKS heatshield was just soaked in the ablator, and could be used ten times. Not even a millimeter of its thickness was lost.

Edited December 5, 2023 by kerbiloid

[JoeSchmuckatelli]

Saturation and maturation.

Just an observation, but often times it's not just about effort and will, it's about infrastructure. 

There was a lag between the first Industrial Revolution and the second because it took time for the RR and steam power to permeate the country - which before was a collection of small towns (applies to any country). 

'Modern' example:

... Oh, and that was dial-up

[AckSed]

Here's a site to browse (archive.org because the images would be otherwise broken): Introduction to Future Launch Vehicle Plans

From the archives of sci.space.tech: Fuel Table

A piece of the puzzle of the lack of rapid reuse on the Shuttle was the culture. The example I remember is the stripping down of the RS-25: they could probably have gotten away with less invasive inspections and increased the lifetime and reliability of the engines if it hadn't, but they had already gone to the trouble of installing the process, and no-one would or could argue for less caution on one of the most complex systems ever flown. So they were stripped down and rebuilt after every flight, even if nothing was wrong.

Liquid-fuelled boosters, first flyback then sea-landed, were proposed and would also have assisted in reusability, but the compromises were already settling in even as the 70s dawned. The military's experience with solid rockets was always in the background. They could be stored! They were safe to handle! They gave a kick to all sorts of early rockets at just the right time. Telling Thiokol "no" would have made it a better reusable vehicle but also extended the development. No-one was making the F-1 any more, though the expertise was still around, and there was an improved, simplified F-1A under design when Saturn V production was shut down in 1968. (Yes, it was shut down before Apollo 11.)

Methalox was just not seriously considered for most of the US space program (Ignition! only gives it a passing mention), though propalox is a good might-have-been: oxygen's close boiling point to propane's melting point allowing common bulkheads, propane's self-pressurising nature, and the specific impulse and chilled bulk density being comparable to kerosene were attractive. The issues with clogging/corroding the fuel channels in the rocket nozzle were not. But maybe, with research money flowing in, they find out early that sub-chilling precipitates out the sulphur impurities that caused the damage. Or they literally plate the channels with gold.

Peroxide/kerosene would have made for a good 1st-stage booster that burns very cleanly, but the US has always been twitchy around high-test, 90-98% peroxide or HTP. Ask two different rocket scientists and you'll get three different opinions over how difficult it is to handle. In my humble opinion, it is far safer than the classic UMDH/N2O4.

[kerbiloid]

13 minutes ago, AckSed said:

The example I remember is the stripping down of the RS-25: they could probably have gotten away with less invasive inspections and increased the lifetime and reliability of the engines if it hadn't, but they had already gone to the trouble of installing the process, and no-one would or could argue for less caution on one of the most complex systems ever flown. So they were stripped down and rebuilt after every flight, even if nothing was wrong.

Sometimes the propulsion unit from one shuttle was used on another one, and the actual number of flights per engine was iirc 9.

So, probably their nailing to the ship was not an option.

[tater]

4 hours ago, JoeSchmuckatelli said:

... Oh, and that was dial-up

afwl/philabs is why UNM had decent net access back in the early 80s when I was first online (1983).

[darthgently]

5 hours ago, JoeSchmuckatelli said:

Saturation and maturation.

Just an observation, but often times it's not just about effort and will, it's about infrastructure. 

There was a lag between the first Industrial Revolution and the second because it took time for the RR and steam power to permeate the country - which before was a collection of small towns (applies to any country). 

'Modern' example:

... Oh, and that was dial-up

Remember fidonet?  Still a great fallback protocol when recovering from  Carrington II.  Works fine over packet radio nets

Edited December 5, 2023 by darthgently

[JoeSchmuckatelli]

Too young for Carrier Pigeon

Too old for Zoom 

...but I do remember when email was new and cool.

(On that, my wife and I told the kids recently about *gasp* writing letters to each other when we were long distance dating)

[magnemoe]

2 hours ago, AckSed said:

Here's a site to browse (archive.org because the images would be otherwise broken): Introduction to Future Launch Vehicle Plans

From the archives of sci.space.tech: Fuel Table

A piece of the puzzle of the lack of rapid reuse on the Shuttle was the culture. The example I remember is the stripping down of the RS-25: they could probably have gotten away with less invasive inspections and increased the lifetime and reliability of the engines if it hadn't, but they had already gone to the trouble of installing the process, and no-one would or could argue for less caution on one of the most complex systems ever flown. So they were stripped down and rebuilt after every flight, even if nothing was wrong.

Liquid-fuelled boosters, first flyback then sea-landed, were proposed and would also have assisted in reusability, but the compromises were already settling in even as the 70s dawned. The military's experience with solid rockets was always in the background. They could be stored! They were safe to handle! They gave a kick to all sorts of early rockets at just the right time. Telling Thiokol "no" would have made it a better reusable vehicle but also extended the development. No-one was making the F-1 any more, though the expertise was still around, and there was an improved, simplified F-1A under design when Saturn V production was shut down in 1968. (Yes, it was shut down before Apollo 11.)

Methalox was just not seriously considered for most of the US space program (Ignition! only gives it a passing mention), though propalox is a good might-have-been: oxygen's close boiling point to propane's melting point allowing common bulkheads, propane's self-pressurising nature, and the specific impulse and chilled bulk density being comparable to kerosene were attractive. The issues with clogging/corroding the fuel channels in the rocket nozzle were not. But maybe, with research money flowing in, they find out early that sub-chilling precipitates out the sulphur impurities that caused the damage. Or they literally plate the channels with gold.

Peroxide/kerosene would have made for a good 1st-stage booster that burns very cleanly, but the US has always been twitchy around high-test, 90-98% peroxide or HTP. Ask two different rocket scientists and you'll get three different opinions over how difficult it is to handle. In my humble opinion, it is far safer than the classic UMDH/N2O4.

Think part of the problem with the shuttle is that it was an hyper optimized design, think an formula 1 car not an pickup. This is counter to rapid reuse.
Much the same way advanced fighter jets are very over engineered for counter insurrection fighting, but air-forces hate that sort of subsonic planes, yes you can use F-15 or F-35 at 10 times the mission cost 

[tater]

22 minutes ago, JoeSchmuckatelli said:

...but I do remember when email was new and cool.

My first email addy was in 83. I've had a total of 5 (1 was an ISP that changed its name, so it might just be 4). Every single 1 has been my first name @domain. Just my first name, properly spelled.

My current most used is my apple email for my phone. Only downside s that I get people trying to steal it almost daily. Upside is that people who have a variant version screw up, and I get their emails all the time, which is sometimes amusing—like the guy in London who spends £130 a month on his haircut and hair coloring (odd since his hair is gray/white according to his linkedin), and I get all his receipts. I also have his monthly appt schedule, maybe my wife can stalk him (she's in London for a couple weeks as part of getting another postgrad degree, because she needs all the letters after her name, lol).

[TheSaint]

7 hours ago, tater said:

My first email addy was in 83. I've had a total of 5 (1 was an ISP that changed its name, so it might just be 4). Every single 1 has been my first name @domain. Just my first name, properly spelled.

My current most used is my apple email for my phone. Only downside s that I get people trying to steal it almost daily. Upside is that people who have a variant version screw up, and I get their emails all the time, which is sometimes amusing—like the guy in London who spends £130 a month on his haircut and hair coloring (odd since his hair is gray/white according to his linkedin), and I get all his receipts. I also have his monthly appt schedule, maybe my wife can stalk him (she's in London for a couple weeks as part of getting another postgrad degree, because she needs all the letters after her name, lol).

Nice. My oldest email address is from 1995 on Yahoo. I did lose it for a year when Yahoo had their "use it or lose it policy" (I was on the boat in South Africa), but i got it back and have had it ever since. I have emails archived on there from the late 1990s. The address is just first initial and last name, so I get people sending mail to it all the time. I get regular emails from a car dealership in Florida, all sorts of stuff connected to pediatric medicine around New York City, some girl's entire life up in Montreal. (Most of those I corrected.) I had some guy in New Jersey try to set up an eHarmony profile with it. I decided that was a level of drama I didn't need in my life. So I used the lost password function on their site, logged in and deleted his account. I figured he wouldn't try that again. But I still get the occasional marketing email from eHarmony, "It doesn't hurt to look!" (It does when you're already married! )

[tater]

38 minutes ago, TheSaint said:

I had some guy in New Jersey try to set up an eHarmony profile with it. I decided that was a level of drama I didn't need in my life. So I used the lost password function on their site, logged in and deleted his account.

I was getting emails that said stuff like "Fiona liked your profile!" which I first thought was spam. Then I checked and it was some legit UK dating site. Different guy (same first name as the other in London with the haircuts), general contractor... and on the dating site. I did exactly the same thing—though I briefly entertained changing his, um, interests, on the dating site.

One of the 2 guys in the UK also sees a psychiatrist—who emailed me a PDF of his chart. I contacted the office letting them know of their mistake, and that it would be a nasty HIPAA problem over the pond. I get some family pics, I let those people know they are not sending the pics to grandpa, etc. I got time critical email about a house closing in Australia (contacted them as well). I used to get airline reservations for someone running for governor in another state—was waiting for a no-tell motel receipt so I could ask for some political favor, but that never happened, hehe.

[JoeSchmuckatelli]

On 12/5/2023 at 3:05 AM, SunlitZelkova said:

thoughts? Could a fully reusable and economical spacecraft have been built in the 1970s? Or was it never going to happen until the 2020s?

Some verbosity expanding on my infrastructure / maturation and saturation thoughts combined with the Smarter Every Day video posted in another thread. 

The theme is simplicity and redundancy.  Mil-tech is made to be used by basically trained soldiers with only a HS diploma, be reliable and tough.  We really rely on interchangeable parts (even, perhaps especially, where those parts are complex - and it takes a smart tech / highly trained person to fix the thing... Any grunt can swap out the thing).  This takes solid logistics and infrastructure to be feasible. 

... Clearly in the 60s / 70s we had the ability to do great things.  I haven't run a full cost to GDP analysis comparing 1970 and 2020, but the Apollo program cost approx 257 billion in 2020 dollars (while the 2020 GDP was like $20 trillion).  Baseline it looks like a much smaller % of GDP in 2020.  Part of the cost was how cutting edge - even bespoke - everything was. 

But to do what you are suggesting - the industry should look more like SX or the airline industry rather than what I imagine Apollo / SLS looks like. 

Also, a look at material science advances since then - things that are common now were invented then - I don't see that stuff proliferating at the rate necessary for economic saturation absent a hot war. 

https://en.m.wikiversity.org/wiki/Materials_Science_and_Engineering/Timeline_of_Material_Advances

https://www.google.com/amp/s/singularityhub.com/2020/05/21/3-major-materials-science-breakthroughs-and-why-they-matter-for-the-future/%3famp=1

If you look at the ships Columbus used to cross the Atlantic and compare to what purpose built oceanic craft looked like a hundred years later, a lot of 'lessons learned' are baked in. 

Superpower competition, hot and cold wars drove the innovation.  Yes, a more desperate competition (existential) between the US and USSR might have pushed the envelope back in the 70s... But for that to happen the Soviet economy would have had to be much more competitive.  And there would have needed to be a reason to keep it competitive rather than combative.  (Far simpler to just Nuke the ground infrastructure of the enemy than build competing moon bases) 

I kind of think things happen in their own time for a reason. 

E. G. Take one of my story ideas: a 3 ship ARG of sailors and Marines gets transported back to the 1450 Pacific and lands in San Francisco - presuming we can avoid / mitigate the disease process that wiped the continent, could those people have recreated a version of America given our Connecticut Yankee knowledge... And I don't think so. Even if the locals were enthusiastic partners and the Navy was able to acquire horses, cattle and everything else for 'modern' agriculture, trying to shift the local population and economy to even 1800s levels in less than a hundred years seems not feasible