Nibb31

Read the CAIB report please or even just wikipedia: https://en.wikipedia.org/wiki/Space_Shuttle_Columbia_disaster

A breach in the reinforced-carbon-carbon panels on the leading edge of the left wing, as I mentioned above with a huge picture. Nothing to do with tiles.

What?

Tile damage didn't bring down Columbia. Seriously, do you really think you're going to come up with something that the folks at NASA haven't thought about already? Have you even read the CAIB report ? Who mentioned the MMU and what orbital module are you talking about ?

What part of "Soyuz has no EVA capability" and "it couldn't reach Columbia's inclination" don't you understand ? Old Soyuz vehicles used to have EVA capability, with an external hatch, handrails, suit checkout, and depress/repress capability. Those capabilities were removed when it was redesigned as a 3-person space-station taxi. So you cannot EVA to or a from a Soyuz TMA. There is no way a Soyuz launched from Baikonur, which is located at a latitude of 45°N can reach a 39° inclination, which is where Columbia was. Please read this thread:

That was what ESA wanted in the final design of the Hermes shuttle. It added so much weight and extra cost that it was the final nail in the project's coffin.

No it couldn't. Soyuz couldn't reach the inclination of Columbia. And Soyuz has no EVA capability. If Challenger had used liquid boosters, it wouldn't have had O-rings so they couldn't have leaked and the accident wouldn't have happened. Also, even if they did have a way to a shut down the SRBs, the damage was done as soon as the burn-through in the ET had happened. Liquid rockets have their own failure modes, they aren't inherently better or safer, they are just different. I think you've been watching too much History Channel.

You're just all mixed up. Buran is not comparable. First of all, the Buran orbiter didn't even have engines and used an entirely different architecture with entirely different requirements. It also only flew a single unmanned test flight, so it's hard to extrapolate on what its actual capabilities would have been. Columbia had two ejection seats for the first test flights, but like Gemini, they wouldn't have been of much help during most of the flight. There was never any provision for ejection of a six or seven person crew (especially as two or three were seated in the lower deck). A Soyuz docking adapter (whatever that is) wouldn't have helped Columbia. Why would the Shuttle carry a female probe-and-drogue system? The other Shuttles had the Russian APAS docking system, inherited from the Shuttle-Mir program, but Soyuz doesn't use APAS. Soyuz was also unable to reach Columbia's inclination and unable to carry everyone back anyway. I suggest you read the thread about the Columbia rescue theories.

Orbital rendezvous and docking was only proven during Gemini VII in december 1965. Apollo was already in full swing by then. NASA wasn't even keen on LOR at first because they didn't know if orbital rendezvous was actually possible.

This is the sort of hole that brought down Columbia: That was produced by an 800 gram chunk of foam that was shot at Mach 0.8 at the wing edge during the CAIB investigation. I doubt a "thin layer" of anything would have protected the Columbia's RCC panels. A protection would either be heavy and protective or thin and useless. You can't have it both ways. If there was an easy fix, don't you think the smart folks at NASA would have implemented it for the RTF ? But again, we've learned our lessons, and nobody is going to be proposing a side-mounted manned vehicle for a long time, so the whole point is moot.

Titanium was considered too expensive. Remember they wanted to build a whole fleet of Shuttles. And aluminium was considered fine as long as the TPS remained intact. Titanium is about 60% heavier than Aluminium, which would have made a huge difference in payload fraction.

There is no reason for Skylon or Dream Chaser to be hit by debris during take off, since they aren't travelling on the side of a huge cryo tank that sheds foam and blocks of ice. It would also introduce a whole lot of failure modes. Does your protective layer burn off like the layer of Kapton on Apollo and then how much does it cost in maintenance? or is it jettisonned, and if so, how? and what happens if the jettison fails?

There has always been demand for fast transportation. Ever since humanity exists, there has been a need to go from point A to point B because point B was a destination where people needed to meet other people, trade stuff, visit things, etc... Horses, ships, cars, planes were invented to meet a strong demand that already existed. Roads, railroads, shipping lines, and airport infrastructure were built to connect the As and the Bs of the world. Space is not an appealling destination for mass transport. There are no friends or family to visit, there is no business or trade to do, and there isn't even anything much to visit. Space will remain a niche until someone comes up with a strong business model that requires frequent launches to orbit. And that might never happen, just like we have never found a massive interest in building an international airports on the Southern Sandwich Islands or a high speed train bridge to the middle of the Atlantic Ocean. Most people on these forums only look at the technical side of things, but the barriers are rarely technological. When the need for mass transportation arises, the technical solutions will come naturally. The problem is finding the "killer app" for space travel, a compelling reason for people to want to launch stuff into space. Until that happens, reusability and fast turnaround are pointless. Something like Skylon is a bridge to nowhere.

Yes, the USAF is interested in the SABRE engine, but they have no interest in Skylon and have doubts that it's a viable vehicle.

Because an SSTO is always heavier than an MSTO design. A single stage that is going to perform a landing and a launch is always going to be heavier than two stages that do the same job. The engine isn't a huge extra weight, but you still have to carry that whole mostly empty stage back to orbit. The advantage is that you can optimise each engine for the thrust requirement of that part of the mission. Multiple engines also provide the abort capability. Apollo could abort at any time during descent (Apollo 10). The penalty of a single-stage lander makes sense if you are going to leave it at EML1 or 2 to refuel and reuse it in a semi-permanent infrastructure. But in an Apollo/Constellation architecture, it's not worth it. No because the descent engine is larger and more powerful and consumes more propellant than the ascent engine, so you would have to carry more propellant to launch the entire LM than if you just launch the ascent stage. The dV requirements for lunar surface to LLO and from LLO to lunar surface are actually similar ( ~1900m/s), so the amount of propellant you would need to launch the entire LM (ascent stage+descent stage) off the moon is basically the same as the amount carried by the fully fueled LM in the first place. The ascent stage only carried 2300 kg of propellant and a 85 kg engine to produce that dV. The descent stage carried 8200 kg of propellant and a 180 kg engine to produce the same amount of dV. In other words, to launch an entire LM from the surface of the Moon, you would need a fully fueled descent module. In your solution, you would save the 2500 kg of the ascent stage propulsion system, but by the same ratio, you would need something in the order of 30000 kg of propellant to actually land that 8200 kg of descent stage propellant on the lunar surface, which would also require a larger engine, which would also consume more propellant, etc... The rocket equation is a harsh mistress, and that's why we use staging. The Dragon V2 only has a few hundred m/s of dV. You'd need more tanks, then more thrust, then more tanks, etc... You might be able to land a Dragon on the Moon or launch from the Moon to LLO if you filled it with with extra tanks, but you can't do both.

Most of its technologies have never been tested even at a subscale level: the tanks, airframe, the TPS, the engine of course, and probably plenty of other stuff. We have no idea how mature those technologies are for an operational vehicle, how fragile or durable they are, their cost, or their maintenance requirements. That is unproven. There's a huge difference between a paper study and actual engineering. Look at the engineering that goes into producing an airliner or a conventional rocket, which is based on decades of experience, existing facilities, certified suppliers, etc... For Skylon, you need to throw that experience away and reinvent everything, from the supply chain to the manufacturing facility, including tooling, test fixtures, training personnel... You basically need to build a whole industry from scratch. The LH2 is also used for cooling the engine and the ceramic composite skin on reentry. Methane won't work.

That's still LOR because it requires a rendezvous in lunar orbit to refuel your LM/CSM. The difference is that you carry a much heavier LM to the surface and back to orbit, which requires more propellant. It also means that you have no backup plan if something goes wrong with the refueling.

So maybe you should do a search on the forums. Skylon has been discussed over and over for years. There is not enough demand for a quick turn around to be of any use, and there is no indication that it will be cheap. It's the bigger than an A380, and much more complex, it uses multiple unproven technologies and techniques, and there is no demand for building large numbers of it. Why would it be cheaper ? The numbers, when compared to the actual demand for orbital launches, simply don't add up. Reducing costs is a chicken and egg thing. Low cost requires high demand. High demand relies on low cost, but also on an actual business model, that nobody has invented yet. Ultimately, investing billions in a system that only makes sense with launch rates that are 100 times higher than they are today simply doesn't work. And the whole concept revolves around all of those unproven technologies meeting all the planned cost and performance requirements as they do on paper. When was the last time any large engineering project achieved that? The reentry system that vaporizes hydrogen on the leading edges has never been experimented. The fuselage built around the self carrying composite tankage needs a whole need industrial infrastructure, and again, we have no experience with any of those materials on an actual aircraft, let alone in space and reentry conditions. The engines work on paper, but we don't know anything about their maintenance, reliability, or durability. If a single one of those technologies underperforms in any way, then Skylon is not going to orbit and you have wasted billions.

The rotation angle isn't very important when docking because the probe-and-drogue docking system rotates the vehicle to the correct angle as soon as it latches.

Back on track, more that its technological shortcomings, the N1 stretched the Soviet logistics and supply chain, with parts built in Moscow and transported by train to Baikonur for final assembly. There were no test facilities at Baikonur, and the program was under constant pressure, so the only actual test of the assembled rocket was the launch. That explains the dismal failure rate. In the end, even if the N1 had been successful, they were still several years behind Apollo. At best, they could have landed on the Moon in the mid-to-late 70s, with much more modest capabilities and much higher risk. The Soviet mission profile was much more dangerous. The LK had limited life support and could only spend an hour or two on the lunar surface. If the cosmonaut had been incapacited in any way, there was no one to help him. Also, the LK couldn't dock with the LOK, it had a sort of hook-and-grid latching system and the cosmonauts transferred by EVA, which was risky. I don't think the UR500 solution, which was Direct Ascent, would have been viable. It would have required a much larger rocket than the N1 or the Saturn V (like the Direct Ascent Apollo would have required Von Braun's Nova rocket), which would have put even more pressure on the program.

That was beautiful !

When you're the biggest producer of large SRMs, you don't really have the choice. Reusability only makes sense with high flight rates, which requires huge demand. Reusability at current flight rates doesn't make much of a saving. However, once you reach high enough flight rates, other economies of scale kick in, which means that cheap disposable boosters make as much sense as expensive reusable boosters.

As you say, the SPS engine was used several times during the flight, so a malfunction would have been detected before separation from the LM. If that happened, the landing would be aborted and they would use the LM engine on a free-return trajectory, like Apollo 13. The chances of the TEI (Trans-Earth Injection) burn failing, after successfully doing the LOI (Lunar Orbit Insertion) and several trajectory corrections were small. Apollo also had an overpowered RCS which carried enough dV to perform a series of TEI burns. If the LM descent stage malfunctioned, they would abort with the ascent stage, like on Apollo 10. The only burn that didn't have any backup at all was the LM ascent. This was identified as one of the most critical items in the mission, so was engineered to be as simple and failure-proof as possible.

The Apollo LM used staging to save weight. A single-stage lander would have to be much larger or would have a much smaller payload fraction. It's the same issue where an SSTO will always have to be bigger and heavier than an equivalent MSTO. The Russian LK was single stage (it had two sets of engines, but those were for redundancy). It used a crasher stage landing technique where the Blok D stage performed most of the descent burn and was dumped just before the final descent. This allowed the LK to land with its tanks nearly full, so it didn't need two stages. On liftoff, it only left a basic frame with the landing legs on the ground. It also had settling rockets to push the legs into the ground after touch down. There is a lot of info out there about the Russian LK and N1 if you look properly. No we wouldn't. The Constellation Altair design was two-staged also. Constellation remains the latest NASA lunar mission reference. That architecture is called Direct Ascent and it requires a much larger lander. This isn't KSP, the dV descent and ascent requirements are actually pretty high. Altair used the descent stage for LOI and descent, the ascent stage for ascent and RV, and the Orion would have done the TEI burn, just like Apollo. That architecture is called LOR (Lunar Orbit Rendezvous) and remains the most efficient architecture in terms of mass, because the laws of physics haven't changed since Apollo. I agree that a reusable single stage lander that would stay at EML-1 would be a good option for a long-term infrastructure.

*yawn* Give anyone taxpayer money, and you will end up with the same amount of bureaucracy that NASA has. Otherwise, it's just confiscation of national property, and you end up in a federal prison for treason or with a revolution on your hands.