Nibb31

DC-X was a technological demonstrator for Delta Clipper. It was similar to how X-33 was to be a technological demonstrator for Venture Star. Both DC-X and X-33 were meant to develop the technologies that were required to build a VTVL or VTHL SSTO. However, the main focus wasn't on the SSTO part. It was on reusability and fast-turnaround. In the case of DC-X, the biggest focus was on flight control and powered landing. I think that merging the two programs (using X-33's composite materials and engine technology and DC-X's layout and flight technology) would have been the best of both worlds and would have been likely to make a good reusable first stage. Unfortunately, they were both cancelled for political and technical reasons. DC-X was transferred to NASA after SDIO was cancelled, but NASA was reluctant to spend money on it because it competed with their own X-33 program, so they pretty much let it die.

Why is that? You still need to integrate and fuel the payload, which needs to be done in a clean environment. Being SSTO or multi-stage has no bearing on whether it can sleep outside or has to be kept in a hangar. In fact, if your vehicle is reusable, then it must have a TPS, which you will want to protect as much as possible, so it most likely will need a some sort of VAB or maintenance hangar. And an SSTO must be much larger than a two-stage vehicle with the same payload fraction, you are also going to need a much larger facility than if you had a two stages to cater for.

Again, who cares if they are slow. Mars isn't going anywhere. But they are slow because they are small and light and low-powered. There is no reason why you couldn't build an unmanned rover on the exact same chassis as a manned SEV. You could even build a self-driving dune buggy if it made any sense. It would still be cheaper and lighter than a manned SEV, because it wouldn't have to carry all that life support stuff and it could carry more science equipment instead. On the other hand, going slow has its advantages. It means that you won't miss something important. A human might go faster, but is more likely to miss a tiny rock on the ground. And you could actually afford numerous missions because it would be orders of magnitude cheaper. Yes, but is the lack of latency alone worth spending billions more and risking lives? In the future, latency can also be countered by better AI. We already have automatic drones and self-driving cars. Who knows what technology will be available in 10 or 20 years? You could imagine a robot/drone that could autonomously 3D scan a wide area where you could walk around in HD VR to determine the places that are worthy of a closer look, and then send a sampling robot to get detailed data or samples from those places of interest. That's just an example. Don't get me wrong. I'm not saying we shouldn't send people in the long term. I'm just saying that science as the only justification is not good enough. The only science benefit of sending people to Mars is to learn about sending people to Mars, which is interesting, but circular.

If all the main chutes fail, then you have a fundamental systemic problem that is probably also present in your backup chutes. Redundancy is better served by providing different systems or repurposing existing systems than by duplicating everything. Actually, for the first Commercial Crew missions, it will be landing on parachutes with SDs as a last second braking device (and maybe as a backup if the chutes fail, not sure).

You shouldn't oppose robotic exploration vs manned exploration. In the end, all exploration is driven by humans. We just use the proper tools for the job. Some jobs allow boots on the ground, but human exploration with tools such as telescopes, sensors and robots is just as valid. First, Martian rocks aren't going anywhere, so the latency is no big deal. Actually, since a robot moves rather slowly over the terrain with a whole array of sensors followed by a whole team of geologists, there are actually less chances that it will miss something than if you have a single human geologist with a single set of eyes, who also has to handle the task of navigating, watching his O2 supply, and not falling over. Second, there is no reason that by the time we get the technology required to build an outpost on Mars, we won't also have the technology for better AI and VR to both make the robot autonomous and to provide a shared experience close to actually being there. Surgeons in hospitals already use teleoperation for remote surgical operations. There is a slight latency, but it can be handled by the system and by the surgeon. In the future, a robot could record and extrapolate a 3D map of its environment that an operator could explore in VR and decide what is worth taking a closer look at. We use robots on Earth as tools for exploring extreme environments all the time, because it makes sense to preserve human life rather than to go to the expense of putting it in danger. You can argue that a manned lab would be more versatile, but there is really nothing preventing you from designing a teleoperated lab with the exact same versatility as a manned one. You could have something like a teleoperated Robonaut running the lab and fixing the fleet of rovers and sweeping solar panels, without all the pesky life support and the heavy launcher to bring everything back. On Earth, we use robots as tools to work in extreme environments. I'm aware that it's not as inspiring or romantic, but sending robots to Mars is just using the proper tool for the job. Yes, an outpost and two rovers, like the Ares missions in The Martian. 100 tons on the ground. I get it. It is still limited to a small area and a short period. The rover will always have a limited safety range and the humans will always have a limited supply. If one of your rovers becomes inoperable, that range means walking distance. And you can't grow potatos in Martian regolith. The cost of such an expedition would still be orders of magnitude higher than a fleet of telepresence robots that could cover the entire surface for well over 2 years. There is simply no science that can be done with a human that couldn't also be done by a properly designed teleoperated system.

I'm pretty sure that docking systems have the same sort of mechanical failsafes to prevent you from undocking with the hatch open.

There won't be two sets of chutes, only one set and Dracos.

There are 4 chutes. You can land safely with 3, and maybe even 2. You don't need 4 more.

There would be a pretty severe diplomatic problem several days before the shenzhou pulled up. Oh, and this is a nice little piece of airlock trivia for you guys. This is a picture of the hatch on the Skylab airlock module. Doesn't it remind you of something ? Yes, that's what you think it is. The Skylab design team had instructions to use as much off-the-shelf hardware as they could, so they ended up being forced to reuse a Gemini gullwing door as a hatch (despite the fact that the window had absolutely no purpose and was blanked out from the inside). This caused some uproar among the engineers, who complained that it was much more expensive to design the rest of the airlock to fit the Gemini hatch than it would have been to use a blank sheet design. But there it is. In the same vein, the Apollo Telescope Mount (the part on top of Skylab) was based on a LM ascent stage, despite the fact that it wasn't even pressurized or accessible by the astronauts.

4 medium-sized parachutes are likely cheaper than 3 large ones. It's likely that these smaller chutes are a more commonly used off-the-shelf design. Higher volume = lower cost.

Yes, Skylab actually decayed faster than planned. Very little was known at the time about the effects of solar activity in the upper atmosphere. There was also a planned reboost mission using an unmanned vehicle, but that was abandoned too, as the US had no use for developing unmanned docking in their plans at the time. Shuttle visiting Skylab would have needed a bit of creative engineering too. Although there were intentions, there was no docking module planned for Shuttle, so it would have needed an Apollo docking module with an airlock because the atmospheres of Apollo and Shuttle were different (Skylab was at 5 psi (0.3 bar), whereas Shuttle ground air pressure). There was also the question of whether Skylab would have been suitable for breathing. It was expected that as everything was powered down, fugus and bacteria would covered everything, making the atmosphere toxic and most of the equipment unusable. In the end, the decay of Skylab was a bit of a relief for NASA, as it helped to justify building Space Station Freedom (even though we all know that it took over a decade to turn into the ISS) instead of being forced to keep on running Apollo-era legacy hardware.

Also cost.

There is a plan. The plan is to launch a Progress and perform a controlled deorbit burn to splash it into the Pacific. http://forum.kerbalspaceprogram.com/index.php?/topic/130021-letting-the-iss-burn-upwhy/#comment-2364491

You do know that KSP is not realistic when it comes to dV, and that ion thrusters are way overpowered in the game, dont you?

None of that requires human presence. Telepresence studies are good enough, are cheaper, and can last for years. That's not what I said. I said that the only reason to send humans is to study how to send humans. All other research can be done orders of magnitude cheaper with robots. There is not a single science experiment (other than human biology study) that can't be done cheaper and easier with an unmanned mission. It will take us at least 20 years to get a boots on Mars mission. Such a mission would only last a couple of months. EVAs will be limited to a couple of hours, and the area of exploration will be limited to a safe radius around the MAV. Humans will have to concentrate primarily spend time on staying alive, not falling over, watching their supply levels, maintaining equipment, eating, sleeping, etc... Science objectives will come second. In that time, we can send multiple robotic expeditions that cover the entire planet for years on stretch, we could send multiple sample return missions all over the planet that would return more science than the samples brought back from a single spot. Robots can keep exploring 24/7 for several years with teams of experts monitoring every sensor for a much more thorough study of the area. And all of that can be done for a fraction of the price of a Mars mission.

Exactly. Which not only proves the complexity of such a task, but also how fragile such a closed loop environment would be. It's all so easy to claim that we have it all figured out in theory, but when it comes to engineering the actual systems, there are always things that you forgot to model or that weren't accounted for. Of course, the slightest imbalance can cause your a huge catastrophe, like runaway CO2 levels or losing your crops.

Yes, that's why I said until it runs out of consumables. The time it takes to come down depends on the altitude, but also on solar activity. https://qph.is.quoracdn.net/main-qimg-f40ac09e0a4e9ee309c651b5f9b0b6e1 Based on this chart, it looks like it loses 2 to 4 km every month without a reboost when it's around 400km. But of course, the lower it gets, the more it drops. However, it could probably stay up there several years. Skylab took 5 years to decay from a similar 400 km, but then again, it had less drag than the ISS. However, the ISS typically uses Progress for reboosts, which is unmanned. Unless there is some manual reconfiguration necessary, you could rotate cargo vehicles while the ISS is unmanned, so as long as those systems work, there shouldn't be a problem.

The ISS is controlled from the ground, so it can fly unmanned until something breaks down and needs repairing, or if it runs out of consumables. Ultimately, it would depend on why the ISS was evacuated in the first place.

The case for Mars is not a bible. It has been scrutinized for years and most experts agree that Zubrin's proposals are overly optimistic. a lot of it might look nice in theory, but when you get into the nitty-gritty details of actual engineering, implementation cycles, technology readiness levels, and of course the politics and economics, it is not so simple. Things don't all work as planned. It certainly is possible to harvest chemical elements pretty much anywhere and to synthesize them into pretty much any material you need in a lab, but when it comes to building the actual systems that do that work reliably, automatically, in extreme environments, with minimal maintenance, it's far more complicated than it seems. As I said in my previous post, we haven't even designed a life-supporting closed habitat or a self-sufficient universal factory on Earth. Such systems would already be immensely complex to develop here, so let's get those technologies to a sufficient TRL, and then we can start talking about sending humans who will rely on them to stay alive on another planet. Until then, the Case for Mars is just conjecture. You can't improvise when basic life support is dependent on extremely complex technology. Humans could improvise on Earth, because you can breath pretty much everywhere and you can live and grow stuff anywhere that there is water. Mars is a whole different ball game. You need advanced systems just to keep on breathing, and growing food will depend on complex mining processes, water purification, soil detoxication and imported fertilizers. There is no improvisation there. Yes, I believe that it might make sense to have a scientific outpost on Mars, but colonies and settlements are just science fiction. However, the only science that you'll get from having humans living on Mars is limited to studying how to get humans to live on Mars. It's circular and pointless unless you have another reason to have humans living on Mars, which we don't. Of course it would be spartan. Living there would be somewhere between Scott-Amundsen Station in Antarctica and a submarine. People won't be lining up to move there permanently and raise families. And you have no idea how many orders of magnitude more expensive maintaining an outpost on Mars would be compared to Scott-Amundsen.

Right, I stand corrected. Commercial launch services have existed for decades too. This is not the first time in History. Arianespace, Boeing, LM, Roskosmos have been competing for decades. But you're right, SpaceX has cut launch prices by 50%, which is a great achievement, and they are reaping the benefits at the expense of other providers. However, it's not creating a whole new economy or revolutionizing applications for space technology. I wish it would. The best we can hope for is to see a couple of these constellations getting launched, but that market only represents a boom of 20 to 50 launches, which can be absorbed over a couple of years. After that, things get back to normal. What we really need is a "killer-app" for space, a problem that can only be solved by a huge demand for spaceflight and generates revenue. Once you've got your killer app, all the economies of scale and reusability technologies will start to make sense. I just don't see that happening in the foreseeable future.

We have no evidence at all about that. It might be 33%, it might be 10%, it might be 90%. We simply have no idea and not enough data points to extrapolate anything. Not going to happen anytime soon. I think we'll see a Moon base before we see a human-sized centrifuge.

Mars will need to import pretty much everything for many decades. You seem to be seriously underestimating the supply chains that are needed to build pretty much anything our modern society relies on. Something as simple as an electric motor requires several different materials (copper, ferrite, plastic, grease, etc...) which need to be extracted, processed, packaged, cleaned, etc... Something as simple as an air filter is based on fibers, which are extracted from paper, which relies on plants, which relies on agriculture, which relies on fertilizers and machinery, and rubber, which relies on hydrocarbons, which relies also on machinery, and a bio-geological process that never existed on Mars... On Earth we have supply chains for everything that you need to run a factory (power, supplies, parts, tools, cleaning fluids...). Every part of our economy relies on other parts to work. On Earth, you can't build a single self -sufficient factory on Earth that extracts dirt from the ground and turns it into cars (including engines, seats, tires, air-filters...) or mobile phones. Building something like on Mars that is a pipe dream, and an engineering nightmare. And yes, going to Mars will require some sort of business plan, because going there will be expensive. It will have to be paid for by corporations or governments, and you don't get corporations or governments to spend billions of dollars without some sort of return on investment. This is how humans do things: Problem => Solution. Your Pilgrims didn't go to America by accident. They had a Problem: they were persecuted. Their Solution: find a way to escape persecution and create a place where they could live in peace. Then they figured that a good way of doing that was to find a place in this new world that people were talking about. In the case of colonizing Mars, you are trying to find a Problem that suits your Solution. The trouble is, there is no Problem that a Mars colony solves, therefore there is no rational reason for any rational organization to invest billions of dollars in a Mars colony.

You can disagree with reality as much as you want, it's not going to change. Anyone who uses analogies of the colonization of America in the 17th Century as a point of comparison to today's world is completely delusional. People emigrate for only two reasons: safety and comfort, in order to provide a better life for themselves and their family. The Pilgrims were poor and persecuted, therefore they sought a better life that awaited them in America. There is no better life awaiting anybody on Mars. It is not safer or more comfortable, and it's a pretty bad place to want to raise children. You would never be "free" because, even in a self-sufficient colony, you would be dependent on technology, supplies, and energy to keep you breathing and alive, which would all have to be supplied by someone else, either a corporation expecting to make money out of you, or a government for who knows what reason. If you want to settle a new place, you can set up a homestead in the Australian outback, in the middle of the Sahara, or set up shop on an oil-rig in the middle of the ocean, like these guys. Nowadays, the poor and persecuted want to emigrate to the EU or the USA, not Mars. Platinum is used for 2 things: catalytic converters on petrol powered cars and jewellery. As personal transportation is probably going to switch to renewable sources over the next 20 years (we can't keep on burning stuff forever), demand for catalytic converters is going to decrease. The reason platinum is valuable for jewellery is because it's rare. If you increase production by importing it from off-world, you crash the market and it is no longer valuable, and soon it becomes unprofitable. Unless we find some source of free energy in the future, the energy required to extract hundreds of tons of minerals on another planet, to get it out of the gravity well of that planet and to transfer it to Earth will always be immensely expensive. You're better off recycling catalytic converters or even extracting platinum traces from seawater.

Yep, it would also need an aero shroud, which would make it significantly longer. Places that carry dorsal loads can't have a central stabilizer, so they need to be seriously modded to remove the tail fin and use twin stabilizers like the M4 or the SCA.

I've never heard of Farscape, whatever it is, so maybe that's why I didn't get the "joke".