Nibb31

It's not really a good idea to have your first stage thrusting (even on minimal thrust) during separation of the second stage. You really want to cut off your engine before the separation event, clear the first stage and then start your second stage engine when you are at a safe distance from the first stage to not damage it with the plume. If your first stage is on low throttle, you risk recontacting and damaging something, which could be catastrophic. And then, after the RTLS burn, the first stage will be falling down ballistically with the nozzle facing a hypersonic airflow for several minutes before reaching terminal velocity. I'm pretty sure that the plan is to let the atmosphere do its job and to restart the Merlin only at the last minute to save propellant. Restarting a rocket engine in those conditions is pretty much unprecedented and unknown.

There are several steps to reusing a first stage. First you need to demonstrate that you can actually restart the Merlin engine, which isn't exactly trivial, especially when it is facing the airflow. Then, you need to demonstrate that it can actually decelerate and land. Then you want to test the actual launch profile, which is different from an expendable launch. You also need to test navigation systems and avionics. And finally, you want to test the "throwback" manoeuver, which is the extra burn that puts the rocket on a RTLS (Return To Launch Site) trajectory. Before throwing the first stage back to the launch site, you want to make sure that it can actually land safely and not crash into a populated area. After that, you need to do extensive testing to make sure that the first stage wasn't damaged, buckled, or bent, in the process. The whole thing might turn out to be not practical at all. They don't really know. Because rockets are expensive, they will be testing each of these individual steps on actual commercial launches (I assume that customers get a discount for the extra risk or payload loss). The first stages are assumed to be expendable, so after they have done their job, instead of ditching them, they will try out some of their new systems to find out if the RTLS manoeuver is actually practical before actually risking sending one back to the launch pad that might crash into the VAB. Each step actually decreases payload fraction (a reusable F9R will have a payload of approximately 7mt to LEO instead of 11mt for the F9 1.1), so if you are testing on launches that are paid by a customer, it makes sense to minimise payload loss by only testing parts of the RTLS system each time.

You can't just keep outdated space flight hardware "on standby". Maintaining flight readiness means that you maintain 90% of the cost of the program. You need to maintain the outdated infrastructure, tooling, buildings, and ground equipment, keep the personnel trained and busy. Keep procurement lines open for spare parts and consumables or maintain stocks. Keep maintaining and updating procedures, tests, simulations. The actual missions and flight hardware are not the bulk of the cost of manned spaceflight. The most expensive costs are fixed and you have to pay for them whether you fly or not. This is why the STS could actually have been economical if the flight rate was at 50 flights per year as planned. The fixed costs would have been shared over more flights and the cost per flight would have been economical. This is also why the SLS program, with one flight every 1 or 2 years, will be so expensive, and is bound to be cancelled.

For ingress and egress of course. Also for EVA (Orion is designed to be able to act as an airlock when attached to another module) or for contingency situations. Two hatches aire also a safety requirement in case one of them gets jammed for some reason.

In the space industry, a million euro report is the price of some back of the envelope calculations and a very basic feasibility study. This news means that Skylon is on ESA's radar, that's it. Depending on the results of this million euro report, they will decide whether it's worth investing in a 10 million euro paper study. These sort of things take years, so we will not see ESA funding Skylon development in this decade, and then it will take at least 10 years to actually develop and flight test it. So no way is Skylon being considered as a replacement for Ariane 5 instead of Ariane 6.

There is no need for the ISS in your plan. You can do exactly the same thing without the complication of docking the crew and transfer ship to the ISS by directly docking the crew to the transfer ship. Additionally, bringing the Orion along instead of leaving it docked at the ISS adds direct return options if something goes wrong.

What about SLS, Orion, and the CCDEV competition? Have you been living under a rock ?

If WW2 had dragged on a few years longer, Berlin would have been nuked and the war would have ended. There is no way Germany could have developed the technology to reach orbit.

There is no reason for traits like empathy and artistic sensibility to disappear as long as people with those traits reproduce more easily than insensitive sociopaths or psychopaths. As a species we generally choose the individuals with which we want to reproduce among those with genetic traits that we find desirable. A large part of our evolution is induced by that selection of sexual partners.

No, it's already been explained that the first stage only comes down a few hundred kilometers downrange. Boosting it to Florida from a Texas launch would require more delta-V than bringing it back, plus it would add the cost of ferrying out back to the launch site.

Define "best"

They wouldn't invade or share knowledge. If they were hostile, they would just oblitterate us without asking any questions. Have you ever heard of the Dark Forest theory ?

When was the last time humanity has agreed on something? Hell, when was the last time you actually saw a durable consensus in even a single country? I certainly don't think that Humanity "should" do nothing. I simply think that we are not capable of getting everyone to agree on large long term endeavours. I am more on the side of "Humanity should do a lot of stuff, but it won't" because of many reasons. Nothing is ever black or white, and there is no simple solution to every problem. Fixing one problem usually creates other problems. It's the complexity of things that makes life interesting. It's simple common sense that it is in our best interest to stop burning stuff, not only because of emissions, but also because it's going to get harder to find stuff to burn. Yet, we can't get a consensus on that. We also can't agree on using nuclear power instead, because nuclear power has its own (very real) problems. Making decisions is always about choosing the less of two evils. There will always be winners and losers and Humanity is an extremely diverse species, with thousands of religions, cultural backgrounds, economical preoccupations. You will never get every person in every nation to agree on one particular topic.

Each program has its own numbering scheme. Apollo didn't actually skip numbers, it changed its numbering system during the program. Apollo 1 was named retroactively to honor the astronauts killed by the fire. The actual mission would have been AS204, but the accident occured during a ground test among many others. The first actual flights were AS201, AS202, and AS203, which were unmanned tests of the CSM and S-IVB launched with a S-1B. AS stands for Apollo-Saturn, and 2xx means S-1B. The S-V flights were supposed to be numbered AS5xx. They changed the numbering system for AS501 (the first unmanned flight of the Saturn V) to Apollo 4. After that, Apollo 5 to 6 were unmanned tests, Apollo 7 to 10 were the first manned flight tests in LEO and around the Moon, and Apollo 11 to 17 are the well-documented lunar landings. Saturn V is just the name of the rocket chosen by Von Braun. There were lots of iterations in the development of the Saturn family, with S-I, S-IB and S-V being actual rockets, and S-IC and S-II being rocket stages and the S-IVB being the TLI stage... I'm not sure how those numbers came up, but they are probably a mix of design iterations and variants. For the Mercury program, the official names of the missions were Mercury-Redston (MR-x) and Mercury-Atlas (MA-x). The astronauts each named their capsules with callsigns such as Faith-7, Freedom-7 or Sigma-7. The 7 was because there were 7 astronauts in the space program at the time. The tradition of the astronauts naming their spacecraft ended with Gemini, but resumed with Apollo (with names like Spider and Gumdrop, or Snoopy and Charlie Brown, and of course Eagle and Columbia). The Gemini missions were simply numbered from 1 to 12 (officially from I to XII).

I really wouldn't count on that.

We can't even agree on ways to deal with climate change, because there are deniers, most of which are motivated by the fear that reducing CO² emissions will impact their lifestyle and prevent them from driving SUVs. The same would probably be true of any measure to deviate an asteroid. It will cost taxpayer money, and that alone will be enough for people to deny the reality of the threat.

Duplicate thread: http://forum.kerbalspaceprogram.com/showthread.php/41763-UK-s-Manned-Mars-mission-Concept

It works with magic and blue visual effects. What more do you want to know?

Not if they can live 2000 years. Interstellar travel for several centuries would be totally feasible if it was only a fraction of their average lifespan. We always assume that ET lives on the same scale as we do. For all we know, they might be microscopic and their interstellar cruisers might be as big as the pin of a needle. They might live for centuries or millenia. They might move or transmit signals so slowly or so fast that we couldn't communicate with them. It could take them 50 years to formulate a message that would be equivalent to a 10 word sentence to us, and all we would see would be a slow variation of background noise. Or they might move around so fast that it would look like teleportation to us. We simply don't know and cannot make any assumptions. There are several key assumptions that we can make: - Assuming that they are technologically advanced enough to have developed interstellar travel implies that they have been around for a long time. - If there are at least two intelligent lifeforms in the uniforms (us and them) then there are probably much more. - The probability that we are not also their first contact is therefore small, so we can assume that they have already encountered many other lifeforms and have developed some sort of protocol for such encounters. Why would they want to make contact with us? What would we possibly have that would be of interest to such an advanced species? - They might want to study us, but then making contact would simply ruin the observation. - They might want to trade something with us, but they might as well take want they want and ignore us. And we don't really have anything unique anyway. - They might want to preemptively wipe us out, which is a good survival tactic, but in that case we wouldn't even notice. We would just be gone in a few hours and we wouldn't understand what hit us. So all in all, IMO, the chances of ET ever making contact with us are small, because it simply doesn't make sense to try to establish a friendly relationship with an inferior species. I'm still a partisan of the Dark Forest theory. You don't survive as a civilization by being friendly. When you don't know the intentions of the other people in the forest, the best way to stay alive is to remain hidden.

The Gemini 11 experiment produced 0.00015g with a 30m tether. It also proved troublesome and showed that whole contraption was pretty risky. Artificial gravity is not required for a 9 month transit. It just makes things complicated and adds a whole lot of very dangerous failure modes: what if the tether breaks? what if a thruster fails and you can't spin down the rotation or you send the counterweight crashing into the hab module? It's a theoretical concept that is unnecessary and totally unproven.

Yes, it's an armchair concept. We come up with similar designs every day in KSP. There is nothing else backing it.

It returns to the launch site. After separation, it performs a "toss back" burn to put itself on a ballistic trajectory that falls back to the launch site. The flight profile of the reusable first stage is more vertical than for an expendable launch in order to minimize the delta-v required for the toss back manoeuver. Of course, this reduces performance. So does the fact that the reusable 1st stage either carries more fuel (and is heavier) or burns for a shorter time (to save some fuel for the fly back manoeuver). So does the fact that the second stage needs to compensate for the shortcomings of the 1st stage. In the end, the reusable F9 has a payload of ~7 tons to LEO instead of ~11 tons for the expendable F9. This makes it a competitor for the Soyuz or Ariane 6 class of launchers rather than for the Atlas V/Delta IV/Ariane 5 class.

You're right about Athena (although it doesn't seem to have been a very successful launcher). Vega uses an liquid upper stage called AVUM, with multiple restart capability, which makes it much more flexible. The reason the Athena IUS upper stage uses solids, is that it was designed for Shuttle payloads, and liquid upper stages were banned from Shuttle flight rules after Challenger. The problem with a 100% solid rocket is that you need to perfectly calculate and custom-build your solid upper-stage for the payload and target orbit. Any variation from the nominal trajectory, and your payload ends up in the wrong place. Although it is technically possible, it isn't very practical for a commercial launcher, where throttling and restartability allows more flexibility.

Yep, but for the price to drop, the market has to grow. It's a chicken and egg thing, and we still don't have a business model to generate demand for access to space.

It seems to me that a lot of peoples' reasoning has been spoilt by the Shuttle and also by Science Fiction. Apart the fact that some of them have had wings, spacecraft have very little in common with airplanes. Airplanes are mass-produced because there is demand for people to go from point A on Earth to point B. Reusable spacecraft can only be mass produced when there is high-enough demand for massive transport to destinations in orbit. There are no destinations in space that are reachable for the masses so there is no demand for a high flight rate. There cannot be high-enough demand unless the cost of getting into space goes down significantly. Reusable spacecraft might, or might not, be the answer to bringing the cost down. We won't know until somebody builds one and develops a viable business model for operating one. Such a business model simply does not exist yet. Until then, the only way to reach production levels that benefit from economies of scale, is through expendable rockets. In effect, the first spaceplane to be built will necessarily be produced in low numbers, and therefore very expensive. A reusable spacecraft will also always be more complex and more expensive than an airplane, because it operates in completely different flight domains with very different requirements and much tighter physical constraints. Spacecraft and airplanes are hardly comparable.