Hey! I resemble that remark!I also suspect that since reusing models used in other timelines is a whole heck of a lot easier than 3D modelling, texturing and rendering brand new ones every time (I see you nixonshead), so the non-Shuttle derived bits of Enterprise look strikingly like those used on ISS IOTL.
Boldly Going: A History of an American Space Station
- Thread starter e of pi
- Start date
I would suggest that the shuttles operate in convoys. This is the first of only two visible alternatives I can see to increasing the number of people and the amount of supplies that can be transported to Mars and the Moon. The second is to increase the carrying capacity on an individual basis per shuttle, and this brings a whole series of problems in its train.
Unfortunately no one will be THAT invested in going to the Moon or Mars. If we're honest (and the need was there) you could probably have a passenger 'pod' the cargo bay of the Shuttle II that could carry up to maybe 100 people but that's FAR more than anyone will need at any plausible pace.
As we're not really touching deeply on the "commercial" side of space flight in TTL it could be that some sort of commercial space travel will "take-off" in the near future but again the incentive isn't as much there with an active and on-going government program and frankly while the Russian's are (IIRC) 'tapping' that market there's not that much they can offer and NASA has zero incentive to 'encourage' it.
Sadly I'm going to guess that while TransHab might go ahead as a NASA project Bigelow won't go anywhere as it's still the same 'chicken/eg' issue as OTL, and as we've noted far less incentive or anyone to offer 'alternative' launch services to support a civilian space flight program.
Now that I've written that out it actually makes me think you MIGHT see someone like Musk proposing to "purchase" a Kepler and a launch for the 'incentive' of stimulation civilian space flight but he'd have to partner with and cooperate with other billionaire's to make it happen. Possible but not so plausible given the lack of a 'destination' to go to on the flight unless "they" can convince the Russian's to open up Mir.
Might be something interesting to explore as a side-track, (dare I say "fan-fic"?
) but not really for the authors.Randy
Yeah I mean the generic idea of power and radiators being on a big ol truss instead of local to each module a la Mir. Although the power tower does have stability issues, nothing insane, it just makes it prone to oscillation. I also get the sense that it's difficult to thrust through the power tower because it really wants to tip over.
LEO is a shit environment for solar power. Really wish we lived in the timeline where NASA developed nuclear power for space stations. I think that could have led to some interesting places.
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It was fun, and had the benefit of being a reasonable European name...but it was mostly to set up if Galileo is or is not an...took me a lot longer than it should have to realize that you guys named Galileo after the vehicle in Star Trek.
It was fun, and had the benefit of being a reasonable European name...but it was mostly to set up if Galileo is or is not an independent space station. (By the way, to address the "three stations Shuttle visits" in the course of the timeline, that's intended to be Enterprise,Mir, and Mir-II. Galileo doesn't count as a seperate station Shuttle visits ITTL in NASA's book. Of course, this means Europe will count Kepler as servicing three space stations: Enterprise,Mir-II, and Galileo. Semantics...it messes with record books.)...took me a lot longer than it should have to realize that you guys named Galileo after the vehicle in Star Trek.
Is it because ISS is the "optimal" design? Or is it a matter of familiarity driving design decision making from the authors?
Or as Polish Eagle points out, does it end up looking this way because NASA's been generally looking at the idea of "tin cans strapped to a long truss with power and heat rejection" since before the Shuttle was first flown?
I also suspect that since reusing models used in other timelines is a whole heck of a lot easier than 3D modelling, texturing and rendering brand new ones every time (I see you nixonshead
Lots of discussion on this which has hit a lot of the high points: NASA IOTL produced the Power Module design as early as the mid-to-late 70s, and basically used that design for every solar array they needed for any station concepts (from Skylab extention to Shuttle extended flights to free-flying power modules to Freedom to ISS) until Ultraflex came onto the scene, in part because of the technical legacy of having actually demonstrated the array deployment mechanism with OAST-1 on STS-41-D in 1984. You could argue once that test was run on the Power Module-heritage array design, any alternative would have to be pretty good to beat out the flight heritage--and the packing for multiple arrays is better than Ultraflex, AIUI. I think that, and maybe weight, is part of why Roll-Out Solar Arrays (ROSA) are beating Ultraflex for the next-generation spacecraft, like Gateway's power module and the ISS solar augmentation/modernization project? Maybe @Radichesonmars knows, and might even be able to say!
The same goes for the ~4.0 to 4.5m diameter space station modules--launch on Shuttle with an OTL-sized bay, and that's the easiest size to build. Of course, there's a lot subtle difference between a Spacelab module, a Spacehab module, an MPLM hull, the Japanese implementation, and others, but many of them are oscure enough I mostly know as slight difference in diameter and surface panel details. Of course, given the quality of ISS models available, riding that horse the direction it's already going and making use of @noxonhead's existing work or licensable models like Chris Kuhn's ISS has a lot of benefit for showing the world to best effect. There's room for innovation in the Shuttle-diameter form factor, as Axiom's module proposals shown (with their tapered ends and built-in thruster units) but we'll what the final flight vehicle looks like if--and hopefully-when we do get to see new commercial space stations designed post-Shuttle in real life. I'm sure we're all looking forward to it.
Mir-II may also look familiar for anyone who's read @nixonshead's own Snow Flies timeline, though in that case given the Russian reuse of pre-1985-constrcted module hulls we'd argue it's even more excusably convergent than Enterprise's ISS-inspired modules!
Indeed, I think showing off the bay will be a key stop on any video tour of the station astronauts record ITTL, just like the Cupola, the Ops Deck in OV-101, and the crew hab wardroom. Even with doors closed, it's a pretty impressive volume to get a look into--as we may get to.
And the doors opening will indeed be a "classic" shot, I'm sure.As it turns out, no! Confirming this was one of the earliest tasks we asked @nixonshead to check as he started modeling the "new" portions of the station. As it turned out, there were some issues with the station's layout that helped justify turning Node 1 (on the station's nadir side) 45 degrees to eliminate a potential interference between the Japanese lab's external platform and the rotation zone for the port-side truss radiator. As it happens, this conveniently provided a 1991-era excuse for letting us have a clearance for the "bomb-bay" style doors, which in turn means dramatically better access to the bay for various operations (for instance, you can have a module at the end and another near the front, and pull each in and out without having to navigate a Suez-sized alignment challenge. It also has the benefit of not having to work around the aft orbiter attachments or the complexities of the aft dome end and the LH2 sump. It also just looks cool.
This is the fun thing about it: the hangar doors limit access to anything over about 5.5m in diameter, so it's fine for Hubble or anything which uses ISS-heritage (or ITTL Enterprise-heritage) diameter habitat modules or just a little bigger, but for instance you can't quite fit a Conestoga-derived Diana into the bay. You could service it just outside the bay, gaining a lot of the benefits (like the light) but there's still challenges. Technical debt is definitely a theme of this timeline...
The main thing stopping you from bolting together more tanks is the question of what you're doing that needs that many, not to mention providing the power, life support, and all that other good stuff that makes space stations more than just cans in space. An Enterprise space museum is certainly a fun thought--there deserves to be at least one Enterprise finally making it to a museum ship, even ITTL!The second is that right now, NASA is currently sitting on a wealth of knowledge on how to build, fly, outfit and operate External Tank derived stations. NASA is also sitting on Shuttle-C, with its ability to throw a whole metric crapton of stuff into low orbit (way more than Shuttle or even Enterprise ever could) *and* return the expensive bits back to Earth (unlike Enterprise). Even better, while Enterprise could only ever be a one off deal in its lifetime (assuming you don't want to butcher another perfectly functional orbiter), NASA can use Shuttle-C to launch as many External Tank derived successors to Enterprise as funding and time will permit.
So, what's to stop you from strapping two, three, five, or twenty Shuttle-C ETs together and build a giant Earth orbiting station? And if Shuttle-II can continue the trend towards making spaceflight a little closer to dirt cheap, what's to stop NASA from retiring Enterprise after a successor is up and running, keeping the stationkeeping resources topped up, and opening up Enterprise-Hubble-Galileo National Park to tourism? Mir 2 has shown us that space tourism is at least marginally possible. So that perhaps one day, after you've spent some time getting adjusted to space aboard Enterprise II, you could hop aboard a Galileo shuttle over to Enterprise National Park and take a looksee of where we learned how to build things in space. It's like Dry Tortugas, but cooler
Anyway, I'm getting ahead of myself here.
As always excellent work lads and keep em coming!
@Praetor98 , do you mind explaining what you mean to do and what problem you mean it to solve? As @RanulfC says, there's certainly way to cram more people into existing vehicles (shades of the 70-person crew pod Rockwell proposed IOTL for the historical Space Shuttle), but the issue is the need and the price. Shuttle-II ITTL costing a little less per mission than the historical Shuttle as well the dramatically higher flight rate of Shuttle, the Shuttle-C OPAMs, and now Shuttle-II all help reduce the price of an STS flight to something a lot more like their marginal cost than the "program budget of $3 billion divided by two flights per year) logic of some calculations IOTL. That get complicated to discuss quickly, though. Care to elaborate a bit on what your convoys are, and are hoping to solve ? More frequent crew launches, or "batch" launches of smaller vehicles from Earth to orbit, or fleets leaving LEO together?
Ahhh, but ESA does have an incentive to encourage it--they get a share of tourism revenue to Mir-II.
That said, it's still about how large the market is at something close to $30m/seat on Soyuz or Ariane-launched Keplers. Shuttle-II can do better per seat, but that raises the is-NASA-interested problem...it's certainly interesting to think about ITTL.Hehehe. I'm not going to say we haven't had planning meetings for this TL that have sounded like that..."And how do we get into this new platform?"
"Well we had them leave the sump-tube at the end of the External Tank..."
"Ok, that's it.. I quit, you folks are doing this JUST to mess with me. I'm out of here"
Randy
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Nuclear power on stations in interesting, but I think it would come with a number of station design problems including heat rejection, maintenance, and shielding. I know that some of the NASA designs in the 1970s had some very small power plants for which shielding all sides of the nuclear reaction was an acceptable mass costs, but I seem to recall that for other designs this was not done, and that a combination of distance and shielding on one or two sides were seen as acceptable. If the later is the case, then I think that there would only be one acceptable approach vector to the station.
Because @e of pi is pestering me to be more candid with my thoughts regarding Enterprise I guess I have two hot takes:
1. The hamster tubes feel very hand wavy. So much basic work still had to be done in the 80s, mostly in the area of material qualification, that it doesn't really feel like the quick and easy solution that the whole Enterprise program is purported to be. I think in reality they would have modified the intertank with a rigid passage.
2. I have the sense that cutting bomb bay doors into the ET would severely compromise its structural integrity, especially against docking and aero loads. I would suspect that they would have needed to install stiffeners around the opening.
I'm generally skeptical of wet workshops, but I think y'all have done a good job of showing that outfitting something like the ET is as involved as building something like ISS. I'm doubly skeptical of lunar habitanks because the work to outfit the tank would probably consume a large chunk of your precious lunar surface stay. I see that JSC study primarily as architectural exploration but I don't think they identified or closed on the major feasibility issues.
~radishes
1. The hamster tubes feel very hand wavy. So much basic work still had to be done in the 80s, mostly in the area of material qualification, that it doesn't really feel like the quick and easy solution that the whole Enterprise program is purported to be. I think in reality they would have modified the intertank with a rigid passage.
2. I have the sense that cutting bomb bay doors into the ET would severely compromise its structural integrity, especially against docking and aero loads. I would suspect that they would have needed to install stiffeners around the opening.
I'm generally skeptical of wet workshops, but I think y'all have done a good job of showing that outfitting something like the ET is as involved as building something like ISS. I'm doubly skeptical of lunar habitanks because the work to outfit the tank would probably consume a large chunk of your precious lunar surface stay. I see that JSC study primarily as architectural exploration but I don't think they identified or closed on the major feasibility issues.
~radishes
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Considering it's a hinging design I think stiffening was implied even in a vacuum the act of opening and closing the doors is going to stress the hinge points significantly.
Reboost, of course--aerodynamic drag is going to pull objects like that down fast, especially since an empty fuel tank tends to have a high area:mass ratio. It would probably start to cut into the Shuttle payload budget too much to lift the things to a longer-term 400+-km orbit, so I don't think it would ever be standard practice to do so--which means that the tanks would be deposited in low orbits whose lifetime is measured in months at most, unless we have a stretch to the Shuttle tank and boosters (which NASA did consider doing for many years--would have doubled the maximum possible upmass on the Orbiter).
I wondered about that. Put that way, it reinforces my very idle suspicion that NASA would either have abandoned the idea, or made the opening much smaller (with stiffeners), perhaps. But it's not something I've spent much time thinking about.
Out of curiosity how often did the Shuttle door hinges need to be replaced?
A solar power unit and electrodynamic tether for propulsion. No reaction mass required.
Pretty sure that only works for equatorial orbits. Be of some use for midlatitude orbits, and useless for polar ones.
Aero loads shouldn't be relevant, though, since it's already in space? I mean, there's some aero drag, but the actual structural loads from that should be practically negligible.
There's also going to be some loading from station reboost burns and tidal loads, but on a tank designed to take launch loads while fully loaded with propellant, I don't think anyone will notice.
Aero torque definitely happens as you try and react the loads on the solar arrays. Here's a nifty animation for the early days of Freedom that gives an exaggerated view of all the different modes that get activated during routine operations:
Part 32: The headaches and hassles of developing the next generation of reusable systems - Diana & Shuttle II
Boldly Going Part 32
NASA’s success in preparing Enterprise to be the home for a new generation of reusable spacecraft came at a critical time for the agency. While the conversion of the station’s LH₂ tank into a spacedock was ongoing, NASA’s budget had been under increasing pressure at home. The agency was transitioning fully to a second generation of space access vehicles, both for surface-to-orbit and for orbit-to-moon. This next generation fleet was planned to combine the capabilities of the Space Shuttle with the increased operability and efficiency of the Shuttle-C propulsion modules for a new generation of spacecraft, as well as the ability to sustain the Minerva lunar outposts without the cost of expending a series of Habitank landers whose pressurized volume was no longer required. Unfortunately for those at NASA hoping for a rapid transition of focus from the moon and station to Mars, the cost of the new Shuttle-II orbiters and the reusable Conestoga’s modifications had blown many optimistic budget predictions out of the water.
NASA had initially hoped the heritage of the 200-Series Shuttle-C OPAMs and the Block II SSME might keep development to under $3 billion before the first test flight, and keep the cost for acquiring the full fleet of five vehicles under $5 billion. By the time the first flight article, OV-301 Independence was delivered for captive-carry testing in 2016, the program budget had already exploded to more than $6 billion for production and testing even with the rest of the fleet still in the early stages of construction. Though free from the operational challenges of hypersonic flight and high-pressure engines, the reusable derivative of the Conestoga lander had to wrestle with a longer logistical tail. Landers might have to return as far as Space Station Enterprise in low Earth orbit for full servicing. To minimize this frequency, primary systems like engines, propellant transfer equipment, and cargo loading gear had to be made robust enough for extended operations in vacuum, not merely for a single flight to the lunar surface. As a result, program costs had grown from the roughly $1.5 billion originally estimated to nearly $3 billion. The new variant’s development approached a quarter of the entire original Conestoga program cost from a clean sheet of paper to Minerva 2’s landing on the moon.
Such budget overruns on both of NASA’s next-generation vehicles inspired intense Congressional scrutiny. Senior NASA leadership were called to the Hill to justify the overruns in cost and schedule. In the meantime, Congressional focus on preserving the existing lunar program and second-generation reusability project at any cost had led to the ongoing postponement of any of NASA’s plans for Mars. NASA proposals had been floated to terminate the lunar base or even Space Station Enterprise as a way to free the funds...a notion which was dead on arrival in a Congress dominated by those whose constituents were paid for the continuing support of those programs. Even within NASA, the idea of sacrificing continuous station occupation, and once again losing the capability for ongoing lunar access after the hard fight to reacquire it, was deeply unpopular. Thus, only when the new lunar lander was in operation and Shuttle-II entered service for station support could NASA once again hope to turn its eyes towards Mars.
Without such a lofty goal in the near term, NASA’s 2017 operational tempo for Space Station Enterprise and the Minerva Lunar Outpost Armstrong (renamed in 2014 in honor of the late moonwalker) could fade into the background. To support fourteen astronauts on orbit and four on the lunar surface, five Space Shuttle launches and at least two Shuttle-C flights were needed every year. This routine made for a background hum of operations. Still, it was easy for those not paying close attention to lose track of Enterprise Expeditions, Armstrong crews, and the launches to support them. Finding capacity to develop and test Shuttle-II and its ground systems had to compete with a myriad of daily requirements, as operations crews were already stretched to keep up with their other demands. Volunteers willing to put in the additional overtime still stepped forward in large numbers to support the new flagship vehicles, drawn as they were by the lure of the first new large American rocket since Shuttle-C’s introduction in 1998.
The Shuttle-II program found as many complications to its introduction in the late 2010s as its predecessor’s introduction had 35 years earlier. Some issues like the original struggles with the SSME had been solved through extensive experience with Shuttle and with Shuttle-C’s engine pods, as the Block II SSME was now celebrating its second decade of operations. Rocketdyne was still producing or overhauling eight engines a year to support more than one hundred SSME flights, even as they prepared plans for a new Block III SSME which would incorporate a Russian-inspired channel-wall nozzle and main combustion chamber for improved life and reduced manufacturing expense. The program still brought new challenges for the propulsion team, primarily having to do with air-starting the Shuttle-II’s single SSME-69. A series of trials at Stennis during 2012 simulated starting the complex staged-combustion engine using only onboard systems, seeking to optimize startup transients and minimize the risk of a “hard-start”. The process required a complex combination of tank pressurization, pre-starting the lower-complexity RL-10 auxiliary/OMS engines to settle propellant, and closely controlled turbine spin ups to boot strap up to full power. The development program had to compete for test stand time not only against acceptance testing of engines for the operational fleet, but also for test engineer time due to development of the new vacuum-optimized RL-10 intended for the reusable Conestoga. This new engine, though on other test stands, was consumed with near-daily firings to work up to demonstrating the one-hundred-firing life required for orbital reuse without overhaul.
The mix of old and new continued elsewhere in the Shuttle-II vehicle. By using two of the existing liquid rocket boosters bolted together as a side-mounted first stage, Shuttle-II was the beneficiary of one of the best flight records in the history of rocketry. The venerable design had flown two each on more than 120 launches since its introduction on Shuttle-C and STS-116’s application of the liquid booster to conventional Shuttle flights in 1999. Its solid predecessor, though, had defied those who expected it to vanish after Shuttle stopped supporting it. With DoD funding, the solid boosters had made 110 Space Shuttle launches prior to STS-116, and then been used as the base for ATK’s Heimdall launch vehicle. The solid-based launcher was primarily a backup to the LRB-based Atlas III for larger payloads, given Atlas III’s higher performance and slightly lower cost. Still, Heimdall had achieved a respectable flight rate, as its single-stick configuration served as the primary replacement for the Delta II launch vehicle. Between the two National Security Space Launchers, Heimdall had flown first and launched more than seventy national institutional payloads over the previous twenty years [1]. However, winning the majority of the medium and nearly all heavy launches, Atlas III had added almost eighty missions to the LRB’s tally of successes. Thus, the statistical reliability of the LRB was drawn from a background of more than three hundred successful flights. Given that Shuttle-II had only minor modifications to the thrust attachments, NASA was confident in the success of the new vehicle’s first stage.
Novelties in Boeing-Rockwell’s new orbiter design more than made up for the simpler task facing Lockheed Martin’s first stage development team. For the first time, a reusable rocket would have to incorporate significant cryogenic propellant storage into the primary structure. Both Shuttle LRBs and Shuttle-C’s propulsion modules kept their hydrogen and oxygen propellants in tanks which were (with one notable exception aboard STS-37R) disposed of without a thought. The Soviet Buran shuttle’s kerolox orbital maneuvering tanks were both warmer and smaller in mass and volume than the Shuttle-II’s internal second stage hydrogen tanks. For a service life of dozens of missions, Shuttle-II’s composite propellant tanks would have to survive hundreds of cycles being filled and drained of hard cryogens for nominal missions and aborts, then face the heat of entry repeatedly on the other side of the same structures. Even before their integration into a vehicle, the first set of prototype tanks were put through near-daily proof tests throughout 2013 to qualify their ability to survive cryogenic temperatures and pressures without leaks or damage even after dozens or hundreds of cycles.
The thermal protection system required to keep the heat of entry out of the orbiter’s propellant tanks and major structures also brought new twists on a familiar problem. Thanks to a reduced ballistic coefficient on entry caused by a smaller maximum payload and overall lighter structures, Shuttle-II would encounter a less challenging heat pulse during return to Earth. However, NASA was aiming for reduced hand-labor to turn around their next-generation vehicle, and continued to worry about the risk of tile damage, even thirty years after the loss of Discovery. Thus, NASA had specified that Shuttle-II would use improved ceramic-impregnated thermal blankets to replace the fragile and labor-intensive tiles on even more areas of the vehicle. For the belly and other critical surfaces where the blankets could not be applied, NASA studied new metal-honeycomb sandwich tiles.
With inner and outer refractory skins separated by metal honeycomb voids, the new tiles combined some of the concepts of the “hot-structure” X-15 and X-20 with the piecemeal replaceability and traditional aluminum primary structure of the existing Space Shuttle orbiters. The new metal tiles were more impact and weather-resistant than the fragile ceramic tiles, and the use of mechanical fasteners instead of adhesives made them easier to install and service. Still, it was a radical change and was identified as a key risk. The metal tiles received extensive testing in arcjet wind tunnels even as the first orbiters were beginning to undergo structural assembly in 2013 and 2014. In the meantime, other engineers at NASA prepared contingency plans to cover the new orbiters’ bellies in the same ceramic thermal protection tiles which shielded the original Space Shuttle and the 200-series Shuttle-C OPAMs.
Interfacing with the existing Space Station Enterprise logistics pipeline was critical to the success of the new orbiters. When flying without crew, Shuttle-II would be equipped with a small Docking Module in the forward part of the bay. The small pressurized vestibule would connect to the station with an APAS port and provide a space to connect power, data, and fluids plumbing to Enterprise, Galileo, the reusable Conestoga landers now called the Diana series, and the Mars spacecraft NASA was beginning to study in rough concept. The rest of the bay offered similar payload interfaces to the first-generation Shuttle, enabling the new orbiters to continue to carry existing payloads like MPLMs, Spacelab pressurized and unpressurized pallets, the commercial Spacehab modules, and Canadarm. With the reduced overall length, the pallets used for carrying cryogenic propellants for Galileo and hypergolic propellants for Enterprise’s orbiter-vintage OMS pods would have to be modified, as would procedures for Kepler lifeboat exchange. However, the biggest new challenge was the crown jewel of Shuttle-II’s capabilities: its crew module.
Shuttle-II’s ability to carry crew was distinctly unlike its predecessor. Instead of being integral to the structure, the crew module was a detachable pod, almost a spacecraft unto itself. It would fill the entire flight when used, but could be left home when not needed. By using the entirety of Shuttle-II’s new bay length and 14-ton payload mass for crew support, the Shuttle-II crew pod would actually be more capable than the existing Shuttle. With the lower deck of the MPLM-sized module used for consumables storage and the new Shuttle’s toilet, hygiene facilities, and life support systems, the crew module could carry a total of eight people for a week on independent flights. Trading onboard consumables with additional seating on the upper deck would allow the pod to transfer as many as 14 astronauts to an existing spacecraft or station. This configuration, anticipated as the primary flight mode, would allow rotation of an entire Enterprise expedition on a single flight or a half-expedition with several short-stay “surge” astronauts from international partners. In a “high density” configuration for future stations, NASA and Rockwell even considered replacing all lower-deck facilities other than the toilet with additional seating to boost capability to 22 aboard. This would more than double the record for the existing vehicle, though endurance in such a configuration would be limited and best suited to fast rendezvous or evacuation roles.
Though the orbiter was capable of extensive automatic operations and would normally be expected to land itself without human intervention, the astronaut office was uncomfortable with any vehicle where crew aboard were entirely unable to “put a hand on the stick.” Thus, the crew pod’s commander and pilot sat in a “simulator”-style setup in the front of the compartment, able to see outside through cameras and numerous “glass cockpit” displays. Their only direct view outside the crew module would come through a pair of upward-facing windows for operations using the module’s integrated retractable docking port. There, they would have complete ability to override the computer systems through all phases of flight from launch initiation to wheel-stop on the runway, including over the powerful abort motors mounted fore and aft of the pressure compartment designed to blast the pod and crew safely free of any issues on launch abort or return to Earth.
The biggest loss with the new crew pod was its lack of a dedicated airlock. Though the docking port of the crew module could be used as an improvised airlock, the APAS port’s interior dimensions were difficult to navigate in practice while wearing a suit. This reduced capability reflected the broader limits of the new Shuttle-II: it was a true shuttle to the stations and spacecraft it would serve. Thus, it lacked the “jack of all trades” abilities of its predecessor, and with that came losing capabilities like combining cargo with crew for servicing space probes or other craft as it launched them. However, the plethora of pallets designed for the new orbiter showed this wasn’t a drawback, but a natural result of specialization building on the lessons of the past in pursuit of the optimal next-generation spacecraft.
The transition from the original Space Shuttle fleet to the new Shuttle-II came on the heels of an extended series of ground-side systems testing. Test articles were prepared not only for secondary pallets and the crew pod, but of the airframe itself. The first qualification tanks were assembled with structural test articles for the wings and fuselage to produce OV-300. This vehicle was intended only to fly in atmosphere for captive carry and glide tests to demonstrate basic autonomous and crew-commanded return to a runway, much as OV-101 Enterprise had done for the original Shuttle. Thus, only aerodynamic replicas of the RS-25 main engines and the RL-10 secondary propulsion were fitted. Still, Enterprise herself proved it was possible to underestimate such early production vehicles. Reflecting this, when OV-300 was rolled out of Palmdale in 2016 and ceremonially named Spirit, a plaque was affixed to the forward end of the payload bay marking “spacewalkers: cut here for hydrogen tank access”.
For the moment, OV-300 was atmosphere-bound for testing, like its OV-101 and OV-200 antecedents. Still, with Mars plans becoming more openly discussed as the next logical step, no one was willing to write off any possibilities. The first flight-weight orbiter, OV-301 Independence, began propulsion testing at Stennis in late 2017. Barely a month later, OV-300 completed the first crewed captive carry test on the back of the 747 Shuttle Carrier Aircraft. By the time the series of more than a dozen captive carry and glide flights were completed in 2018, OV-301 was being delivered to Florida for the new system’s maiden launch with the confidence that it would be able to land after its first flight.
Artwork by: @nixonshead (AEB Digtial on Twitter)
[1] Institutional payloads are those launched for US Government agencies such as NASA, NOAA, and others, as well as those launched in support of national security missions.
NASA’s success in preparing Enterprise to be the home for a new generation of reusable spacecraft came at a critical time for the agency. While the conversion of the station’s LH₂ tank into a spacedock was ongoing, NASA’s budget had been under increasing pressure at home. The agency was transitioning fully to a second generation of space access vehicles, both for surface-to-orbit and for orbit-to-moon. This next generation fleet was planned to combine the capabilities of the Space Shuttle with the increased operability and efficiency of the Shuttle-C propulsion modules for a new generation of spacecraft, as well as the ability to sustain the Minerva lunar outposts without the cost of expending a series of Habitank landers whose pressurized volume was no longer required. Unfortunately for those at NASA hoping for a rapid transition of focus from the moon and station to Mars, the cost of the new Shuttle-II orbiters and the reusable Conestoga’s modifications had blown many optimistic budget predictions out of the water.
NASA had initially hoped the heritage of the 200-Series Shuttle-C OPAMs and the Block II SSME might keep development to under $3 billion before the first test flight, and keep the cost for acquiring the full fleet of five vehicles under $5 billion. By the time the first flight article, OV-301 Independence was delivered for captive-carry testing in 2016, the program budget had already exploded to more than $6 billion for production and testing even with the rest of the fleet still in the early stages of construction. Though free from the operational challenges of hypersonic flight and high-pressure engines, the reusable derivative of the Conestoga lander had to wrestle with a longer logistical tail. Landers might have to return as far as Space Station Enterprise in low Earth orbit for full servicing. To minimize this frequency, primary systems like engines, propellant transfer equipment, and cargo loading gear had to be made robust enough for extended operations in vacuum, not merely for a single flight to the lunar surface. As a result, program costs had grown from the roughly $1.5 billion originally estimated to nearly $3 billion. The new variant’s development approached a quarter of the entire original Conestoga program cost from a clean sheet of paper to Minerva 2’s landing on the moon.
Such budget overruns on both of NASA’s next-generation vehicles inspired intense Congressional scrutiny. Senior NASA leadership were called to the Hill to justify the overruns in cost and schedule. In the meantime, Congressional focus on preserving the existing lunar program and second-generation reusability project at any cost had led to the ongoing postponement of any of NASA’s plans for Mars. NASA proposals had been floated to terminate the lunar base or even Space Station Enterprise as a way to free the funds...a notion which was dead on arrival in a Congress dominated by those whose constituents were paid for the continuing support of those programs. Even within NASA, the idea of sacrificing continuous station occupation, and once again losing the capability for ongoing lunar access after the hard fight to reacquire it, was deeply unpopular. Thus, only when the new lunar lander was in operation and Shuttle-II entered service for station support could NASA once again hope to turn its eyes towards Mars.
Without such a lofty goal in the near term, NASA’s 2017 operational tempo for Space Station Enterprise and the Minerva Lunar Outpost Armstrong (renamed in 2014 in honor of the late moonwalker) could fade into the background. To support fourteen astronauts on orbit and four on the lunar surface, five Space Shuttle launches and at least two Shuttle-C flights were needed every year. This routine made for a background hum of operations. Still, it was easy for those not paying close attention to lose track of Enterprise Expeditions, Armstrong crews, and the launches to support them. Finding capacity to develop and test Shuttle-II and its ground systems had to compete with a myriad of daily requirements, as operations crews were already stretched to keep up with their other demands. Volunteers willing to put in the additional overtime still stepped forward in large numbers to support the new flagship vehicles, drawn as they were by the lure of the first new large American rocket since Shuttle-C’s introduction in 1998.
The Shuttle-II program found as many complications to its introduction in the late 2010s as its predecessor’s introduction had 35 years earlier. Some issues like the original struggles with the SSME had been solved through extensive experience with Shuttle and with Shuttle-C’s engine pods, as the Block II SSME was now celebrating its second decade of operations. Rocketdyne was still producing or overhauling eight engines a year to support more than one hundred SSME flights, even as they prepared plans for a new Block III SSME which would incorporate a Russian-inspired channel-wall nozzle and main combustion chamber for improved life and reduced manufacturing expense. The program still brought new challenges for the propulsion team, primarily having to do with air-starting the Shuttle-II’s single SSME-69. A series of trials at Stennis during 2012 simulated starting the complex staged-combustion engine using only onboard systems, seeking to optimize startup transients and minimize the risk of a “hard-start”. The process required a complex combination of tank pressurization, pre-starting the lower-complexity RL-10 auxiliary/OMS engines to settle propellant, and closely controlled turbine spin ups to boot strap up to full power. The development program had to compete for test stand time not only against acceptance testing of engines for the operational fleet, but also for test engineer time due to development of the new vacuum-optimized RL-10 intended for the reusable Conestoga. This new engine, though on other test stands, was consumed with near-daily firings to work up to demonstrating the one-hundred-firing life required for orbital reuse without overhaul.
The mix of old and new continued elsewhere in the Shuttle-II vehicle. By using two of the existing liquid rocket boosters bolted together as a side-mounted first stage, Shuttle-II was the beneficiary of one of the best flight records in the history of rocketry. The venerable design had flown two each on more than 120 launches since its introduction on Shuttle-C and STS-116’s application of the liquid booster to conventional Shuttle flights in 1999. Its solid predecessor, though, had defied those who expected it to vanish after Shuttle stopped supporting it. With DoD funding, the solid boosters had made 110 Space Shuttle launches prior to STS-116, and then been used as the base for ATK’s Heimdall launch vehicle. The solid-based launcher was primarily a backup to the LRB-based Atlas III for larger payloads, given Atlas III’s higher performance and slightly lower cost. Still, Heimdall had achieved a respectable flight rate, as its single-stick configuration served as the primary replacement for the Delta II launch vehicle. Between the two National Security Space Launchers, Heimdall had flown first and launched more than seventy national institutional payloads over the previous twenty years [1]. However, winning the majority of the medium and nearly all heavy launches, Atlas III had added almost eighty missions to the LRB’s tally of successes. Thus, the statistical reliability of the LRB was drawn from a background of more than three hundred successful flights. Given that Shuttle-II had only minor modifications to the thrust attachments, NASA was confident in the success of the new vehicle’s first stage.
Novelties in Boeing-Rockwell’s new orbiter design more than made up for the simpler task facing Lockheed Martin’s first stage development team. For the first time, a reusable rocket would have to incorporate significant cryogenic propellant storage into the primary structure. Both Shuttle LRBs and Shuttle-C’s propulsion modules kept their hydrogen and oxygen propellants in tanks which were (with one notable exception aboard STS-37R) disposed of without a thought. The Soviet Buran shuttle’s kerolox orbital maneuvering tanks were both warmer and smaller in mass and volume than the Shuttle-II’s internal second stage hydrogen tanks. For a service life of dozens of missions, Shuttle-II’s composite propellant tanks would have to survive hundreds of cycles being filled and drained of hard cryogens for nominal missions and aborts, then face the heat of entry repeatedly on the other side of the same structures. Even before their integration into a vehicle, the first set of prototype tanks were put through near-daily proof tests throughout 2013 to qualify their ability to survive cryogenic temperatures and pressures without leaks or damage even after dozens or hundreds of cycles.
The thermal protection system required to keep the heat of entry out of the orbiter’s propellant tanks and major structures also brought new twists on a familiar problem. Thanks to a reduced ballistic coefficient on entry caused by a smaller maximum payload and overall lighter structures, Shuttle-II would encounter a less challenging heat pulse during return to Earth. However, NASA was aiming for reduced hand-labor to turn around their next-generation vehicle, and continued to worry about the risk of tile damage, even thirty years after the loss of Discovery. Thus, NASA had specified that Shuttle-II would use improved ceramic-impregnated thermal blankets to replace the fragile and labor-intensive tiles on even more areas of the vehicle. For the belly and other critical surfaces where the blankets could not be applied, NASA studied new metal-honeycomb sandwich tiles.
With inner and outer refractory skins separated by metal honeycomb voids, the new tiles combined some of the concepts of the “hot-structure” X-15 and X-20 with the piecemeal replaceability and traditional aluminum primary structure of the existing Space Shuttle orbiters. The new metal tiles were more impact and weather-resistant than the fragile ceramic tiles, and the use of mechanical fasteners instead of adhesives made them easier to install and service. Still, it was a radical change and was identified as a key risk. The metal tiles received extensive testing in arcjet wind tunnels even as the first orbiters were beginning to undergo structural assembly in 2013 and 2014. In the meantime, other engineers at NASA prepared contingency plans to cover the new orbiters’ bellies in the same ceramic thermal protection tiles which shielded the original Space Shuttle and the 200-series Shuttle-C OPAMs.
Interfacing with the existing Space Station Enterprise logistics pipeline was critical to the success of the new orbiters. When flying without crew, Shuttle-II would be equipped with a small Docking Module in the forward part of the bay. The small pressurized vestibule would connect to the station with an APAS port and provide a space to connect power, data, and fluids plumbing to Enterprise, Galileo, the reusable Conestoga landers now called the Diana series, and the Mars spacecraft NASA was beginning to study in rough concept. The rest of the bay offered similar payload interfaces to the first-generation Shuttle, enabling the new orbiters to continue to carry existing payloads like MPLMs, Spacelab pressurized and unpressurized pallets, the commercial Spacehab modules, and Canadarm. With the reduced overall length, the pallets used for carrying cryogenic propellants for Galileo and hypergolic propellants for Enterprise’s orbiter-vintage OMS pods would have to be modified, as would procedures for Kepler lifeboat exchange. However, the biggest new challenge was the crown jewel of Shuttle-II’s capabilities: its crew module.
Shuttle-II’s ability to carry crew was distinctly unlike its predecessor. Instead of being integral to the structure, the crew module was a detachable pod, almost a spacecraft unto itself. It would fill the entire flight when used, but could be left home when not needed. By using the entirety of Shuttle-II’s new bay length and 14-ton payload mass for crew support, the Shuttle-II crew pod would actually be more capable than the existing Shuttle. With the lower deck of the MPLM-sized module used for consumables storage and the new Shuttle’s toilet, hygiene facilities, and life support systems, the crew module could carry a total of eight people for a week on independent flights. Trading onboard consumables with additional seating on the upper deck would allow the pod to transfer as many as 14 astronauts to an existing spacecraft or station. This configuration, anticipated as the primary flight mode, would allow rotation of an entire Enterprise expedition on a single flight or a half-expedition with several short-stay “surge” astronauts from international partners. In a “high density” configuration for future stations, NASA and Rockwell even considered replacing all lower-deck facilities other than the toilet with additional seating to boost capability to 22 aboard. This would more than double the record for the existing vehicle, though endurance in such a configuration would be limited and best suited to fast rendezvous or evacuation roles.
Though the orbiter was capable of extensive automatic operations and would normally be expected to land itself without human intervention, the astronaut office was uncomfortable with any vehicle where crew aboard were entirely unable to “put a hand on the stick.” Thus, the crew pod’s commander and pilot sat in a “simulator”-style setup in the front of the compartment, able to see outside through cameras and numerous “glass cockpit” displays. Their only direct view outside the crew module would come through a pair of upward-facing windows for operations using the module’s integrated retractable docking port. There, they would have complete ability to override the computer systems through all phases of flight from launch initiation to wheel-stop on the runway, including over the powerful abort motors mounted fore and aft of the pressure compartment designed to blast the pod and crew safely free of any issues on launch abort or return to Earth.
The biggest loss with the new crew pod was its lack of a dedicated airlock. Though the docking port of the crew module could be used as an improvised airlock, the APAS port’s interior dimensions were difficult to navigate in practice while wearing a suit. This reduced capability reflected the broader limits of the new Shuttle-II: it was a true shuttle to the stations and spacecraft it would serve. Thus, it lacked the “jack of all trades” abilities of its predecessor, and with that came losing capabilities like combining cargo with crew for servicing space probes or other craft as it launched them. However, the plethora of pallets designed for the new orbiter showed this wasn’t a drawback, but a natural result of specialization building on the lessons of the past in pursuit of the optimal next-generation spacecraft.
The transition from the original Space Shuttle fleet to the new Shuttle-II came on the heels of an extended series of ground-side systems testing. Test articles were prepared not only for secondary pallets and the crew pod, but of the airframe itself. The first qualification tanks were assembled with structural test articles for the wings and fuselage to produce OV-300. This vehicle was intended only to fly in atmosphere for captive carry and glide tests to demonstrate basic autonomous and crew-commanded return to a runway, much as OV-101 Enterprise had done for the original Shuttle. Thus, only aerodynamic replicas of the RS-25 main engines and the RL-10 secondary propulsion were fitted. Still, Enterprise herself proved it was possible to underestimate such early production vehicles. Reflecting this, when OV-300 was rolled out of Palmdale in 2016 and ceremonially named Spirit, a plaque was affixed to the forward end of the payload bay marking “spacewalkers: cut here for hydrogen tank access”.
For the moment, OV-300 was atmosphere-bound for testing, like its OV-101 and OV-200 antecedents. Still, with Mars plans becoming more openly discussed as the next logical step, no one was willing to write off any possibilities. The first flight-weight orbiter, OV-301 Independence, began propulsion testing at Stennis in late 2017. Barely a month later, OV-300 completed the first crewed captive carry test on the back of the 747 Shuttle Carrier Aircraft. By the time the series of more than a dozen captive carry and glide flights were completed in 2018, OV-301 was being delivered to Florida for the new system’s maiden launch with the confidence that it would be able to land after its first flight.
Artwork by: @nixonshead (AEB Digtial on Twitter)
[1] Institutional payloads are those launched for US Government agencies such as NASA, NOAA, and others, as well as those launched in support of national security missions.
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Depressingly realistic though clearly in this tl Boeing are less incompetent as that's a much smaller over run than SLS.