Flooding the LOX tanks has a good chance of rendering the tank extremely hard to use again, which means you're closing in on getting just the engines back. Using the LOX tank as an expended pneumatic absorber definitely means you only get the engines back. With the right parachutes and floatation bags, you can get the same impact attenuation and keep the engines out of the water without expending the stage structures, and thus reduce the cost to refly.
Time After Time: Imprints of the Space Transportation System Booster
- Thread starter Rocketdyne_J2
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Why would it render the tank harder to use? They literally found rinsing with clear water worked. And the method of using it to cushion he impact was built in reinforcement for the edges of the LOX tank and ports in the aft end. I didn't ready anywhere where they really thought either was going to be a big problem.
Randy
There's a lot of things in the 60s that they tested pieces of and thought would be easy, but that turned out to be harder in practice if they ever made it out of paper or basic hardware studies. I'd note that by the 80s/90s LRB studies, they favored things like horizontal water landing, floatation bags, and other solutions, not flooding tanks, nor is Rocketlabs flooding tanks on their vehicles today with Electron. You can stabilize effectively without that, so don't borrow the trouble. It's also notable that this isn't a system designed to compare to full expendability of Saturn V parts for Saturn V-class 100-ton-to-LEO payloads, but one that has to compete with 15-20 ton to LEO systems. Cutting the cost of the Saturn V first stage by 50% to launch Saturn V payloads is useful. Cutting the cost of the Saturn V first stage by only 50% to compete with Titan IIID will be woefully inefficient and insufficient.
The actual 'big' consideration wasn't the engines though, it was the fins and having them damaged by impact as the stage fell over, keeping the engines from a dunking was just a bonus. The biggest issue was always how best to get the fins needed to sustain the least damage possible. (Probably should have been more exact about "engines up" rather than "out of the water")
Randy
Sorry that I wasn't able to reply/contribute to the entire page of discussions about the economics of reuse in the 70s-90s, but it really covered all the considerations I will need to be making for that period of history ITL, so I have nothing new to add. The 1980s will indeed see how the decisions made for the ITL Shuttle pan out, as well as be driven heavily by the increased defence spending. The1990s will then be pivotal for this Shuttle's (and its booster's) future, with its influx of commercial payloads and flood of new "schools of thought" about reuse. I really appreciate all of the perspectives that were brought up there.
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This is also the reason that for so long, people were afraid of having designs dunk engines, until RocketLab came along with a relatively simpler engine and as of now uncertain results. The clear water rinse ITL was also just to stall corrosion for the hours it took to get back to shore; much more will need to be done on land to protect the stage from any long-term effects of saltwater, and make it flightworthy again.
Making the changes (e.g. cutting sealable holes at the bottom of the tank for the air to escape) to make it an "airspring" would also make the stage radically different from the S-1C, which means more development cost and technical uncertainty.
I admit that, in real life, whether the tank could survive without shock attentuation is a little more uncertain than this timeline makes it out to be. I based my reasoning on a 1960s paper (will link when I can get it) that did some rough analysis gave a figure (12m/s) for how fast of an impact the S-1C structure as-is could survive, without extra cushioning such as retrorockets or the "airspring" tank. It also arrived at how large (nearly 1 acre of area) a cruciform chute would need to be to achieve this speed with some margin.
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The loss was a parallel to the OTL STS-4 SRBs also being destroyed, although the reasons are different (ITL bad cabling vs. OTL miscalibrated G-switch for the parachute riser cutters).
As eofpi mentioned, this was to make refurbishment easier and more economical by reducing saltwater contact, especially for the engines. Having salt water contamination on the outside and inside of a tank are very different things: outside, you have paint and koropron primer already intended to survive reentry; inside you have bare aluminum that must be kept free of contaminants (or ice will form and the engines are screwed), and survive cryogenic temperatures again. Compared to the LOX tank and engines, the fins are much easier to repair or replace, having been designed to be removed for transportation.
This is also the reason that for so long, people were afraid of having designs dunk engines, until RocketLab came along with a relatively simpler engine and as of now uncertain results. The clear water rinse ITL was also just to stall corrosion for the hours it took to get back to shore; much more will need to be done on land to protect the stage from any long-term effects of saltwater, and make it flightworthy again.
Making the changes (e.g. cutting sealable holes at the bottom of the tank for the air to escape) to make it an "airspring" would also make the stage radically different from the S-1C, which means more development cost and technical uncertainty.
I admit that, in real life, whether the tank could survive without shock attentuation is a little more uncertain than this timeline makes it out to be. I based my reasoning on a 1960s paper (will link when I can get it) that did some rough analysis gave a figure (12m/s) for how fast of an impact the S-1C structure as-is could survive, without extra cushioning such as retrorockets or the "airspring" tank. It also arrived at how large (nearly 1 acre of area) a cruciform chute would need to be to achieve this speed with some margin.
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seawater does ugly things with space Hardware, next to that the holes that flood the Lox tanks must be sealed for launch.
Well it's ONLY "your" thread so it's not like we actually NEED your input or anything for it
Uh, no... This was shown to be "not-a-problem" in the late '50s early '60s well before RocketLab. In fact they admit they got the idea from previous work done. The H1 was extensively and exhaustedly tested by dunking, cleaning, refurbishment and re-firing. The clear water rinse was simply the initial step and it was found that if you ONLY did that and then put the engine in shed for a week before you got back to it the refurbishment was no different than if you got started an hour after dunking. (This included several hours to 24 hours of 'soaking' in salt water mind you) Again no problems encountered. Reuse cost came out to about 5% of the initial engine cost so again it wasn't an issue. The F1 was not so tested but it wasn't seen to be a much 'bigger' issue (again pardon the pun) other than the size factor. The F1A was designed to be even more robust which is why they weren't overly concerned.
Agreed it's not trivial but it's also not that difficult and LOX cleanliness standards and procedures were well understood. Making the S-1C reusable, no matter how it going to make it radically different so I'd say it's a wash (I really need to stop) overall.
Love to see it, though I may have it
Randy
Eh, not as bad as it has been made out to be. If you can avoid it all together that's one thing but if you can't then it's manageable
Randy
So no Challenger? Still, wonderful writing. Can't wait to see how the next few flights go!
Also no Columbia, do propellant tanks are over Wing, away from the heat shield
Would the easiest POD not be USAF simply says they absolutely need the option for it to be used unmanned, so you end up with a Hermes/Dream Chaser style shuttle on top of an expendable mission module on top of an optionally manned two stage boasters whose 1st stage is reusable?
Could you not even make that happen successfully with hardware very similar to OTL Shuttle? Even if kerolox might have been better than hydrogen and solids?
USAF didn't want the ability to use it uncrewed. NRO didn't much care either way, and most of their requirements were being routed through the Big Air Force who still were dreaming of Blue Shuttle, the legacy of Blue Gemini and X-20 and such. NASA actively wanted crew on as many flights as possible, both as a way to fly more astronauts (including non-traditional spaceflight aprticipants) and their own corps. Also, I suspect what you get from a demand like that is less "minishuttle on top of a mission module" and more like Buran--a Shuttle with a mode where it flies with no crew aboard--which doesn't necessarily solve anything if the vehicle configuration is the same (i.e. sidemount).
Yeah if usaf wanted it but required it to be flyable unmanned you eventually get buran style full autonomous flight, which probably Doesn’t get used that much.
An actual USAF shuttle, at least after the 70s, would probably look like the x-37 but with a Horizontal take off and landing first stage capability (either air launched or with a dedicated flyback booster).
STS Dramatis Personae: 1981-1986
OV-102 Enterprise as it appeared on the first ever Shuttle flight, completely clean and with white ETs.
OV-099 Independence on its second flight. This mission was a microcosm of the Shuttle program's differences from previous US space programs: it carried the first US woman into space, deployed two commercial satellites, and featured the first use of the retrievable SPAS free-flyer. Booster 604 would be the last one to have stripes reaching into the thrust structure due to heating and refurbishment issues.
OV-103 Discovery on its fifth flight. Besides launching commercial satellites, 51-G also rendezvoused with and fixed the failed Syncom-IV-3 satellite launched four missions ago. Note the replaced D fin and cable tray on Booster 605.
OV-104 Pathfinder on its third flight. Launching Galileo, this was the second Shuttle-Centaur mission, coming mere days after the last that launched Ulysses. Booster 606's LOX tank had been swapped out after a damaging last landing; this was a routine enough occurrence that Michoud usually had more LOX tanks than complete boosters.
it has not to be risky
One of proposal was that Centaur is empty during launch
After SRB were jettison, the Centaur is filled from ET, before it jettison also.
This version of Shuttle would perfect fit for this system
My impression is that a lot of the risk of the prop in the tank was...overblown by opponents of Lewis in inter-center fighting, especially after vent line changes were implemented from Lewis original version (a version which was possibly viable but JSC wanted to stick an oar in and so demanded changes only once it was late enough to cause problems instead of be incorporated into the initial design). All of that seems to be overshadowed by the performance requirements of the SSME for reaching near the maximum payload of the system at that time to lift Centaur + payload (106% vs 104%), which is much more directly eliminated here.
Adding cross feeds from the External Tanks into the cargo bay does not sound simple or easy while on orbit fueling with hydrogen is a technology that NASA is going to want to develop but also isn't simple or easy. Finally Centaur has a balloon tank meaning the strength comes in part from the pressurisation how it would handle launch while empty with a probe sitting on the top is an unknown question.
I think it's safe to assume that this version of Shuttle-Centaur is closely related to the OTL version, which was a deemed high risk.
I think it's safe to assume that this version of Shuttle-Centaur is closely related to the OTL version, which was a deemed high risk.
I'm not a rocket scientist but a lot of actual ones seemed to think it was dangerous, up to and including the NASA Astronaut Office.