Nibb31

I love the idea of an albecurry drive. Sounds spicy. Spelling folks. Learn it.

Not really. It would be "feasible" to build one on the Moon, but to say that we have the technology when the TRL is <2 is pushing it.

It could work for something like building a cubesat and buying a secondary payload launch slot, but for anything bigger, the sums involved are simply beyond the capability of crowdsourcing. 99% of people don't give a damn about space.

Getting the satellite to orbit is what they are contracted to do. If for some reason the payload doesn't reach its proper orbit, it's going to be egg-in-face time for SpaceX after all their spectactular announcements about Mars colonies, reusable spaceships, and DoD lawsuits. This is why they have huge pressure to get it right. Because of their PR, and because they are trying hard to get a piece of the DoD launch business cake, they are under much more scrutiny than another company and they can't afford a failure. SpaceX can only survive if it gets commercial and government customers. Reusablity is secondary.

Just type "Skylon" in the Advanced Search page of the forum.

It's a one-time expense, and a first stage costs several million dollars, so you might make up for it in the long. It's also not much more expensive than building a whole new conventional launch pad, and SpaceX are planning at least 3 of those. You won't need crew quarters at all. Any crew would live on a service ship that would only dock to the rig when necessary. Operations would be much simpler than what Sea Launch does. SpaceX is aiming for pinpoint landing capability. Using a off shore platform wouldn't be much different to landing on a 10x10-meter concrete landing pad. However, it would avoid wasting propellant on the flipback RTLS manoeuver and allow a more optimal trajectory, which would drastically increase payload capacity. I don't think the Gulf of Mexico is that deep, and there are already plenty of oil-rigs out there. It would be ideal to land rockets there from a Texas launch site. I'm not familiar with much of the technicalities of off-shore platforms, but Sea Launch already uses one for launches, and Italy also has a (somewhat smaller) launch platform off the coast of Kenya, so it's not that far fetched.

Never trust 3rd party cloud services. It's better to invest in your own NAS (with mirrored RAID drives) with ownCloud on it. You have your own private cloud service, with no NSA backdoor, no dependency on Microsoft or Google, and only limited by the storage capacity of your own drives.

I don't see what's ridiculous. It's not the first time a rocket has multiple scrubs. It's part of the business. Launch fever has been the cause of many failures, including the loss of Challenger.

Not the launch loop again. It is even less realistic than the space elevator. There are so many technical issues that it isn't even pie in the sky. The biggest issue of the launch loop is that it's impossible to raise it. It would only be stable in a fully powered state with the cable running at 14000km/s inside the sheath. However, it's impossible to go from 0 to 14000km/s instantaneously. The acceleration would have to be progressive and you would have to mechanically raise the 2000km long structure to 80km without the cable ever touching the sheath and without ever compromising the vacuum inside the sheath.

Well, there is no such thing as an SSTO spaceplane, and there won't be before many many years. It is simply not feasible economically. (and don't get me started on Skylon, there are already plenty of Skylon threads in the forum where we've explained why it won't happen. Let's not start another one.)

Pinch rollers still aren't very scaleable or safe, especially as the ribbon surface under the rollers is going to be limited to a very small surface. I can't see a cable car being much heavier than 1 or 2 tons for this application really. It's supposed to be a very thin ribbon, so barely any drag from wind at all. Of course, you need a way to prevent the climber from swaying all over the place in the wind, which would flex the ribbon and fragilise it.

Yes, you get a "first fraction" of dV of less than 1000m/s out of the 9000m/s that you need to reach orbital speed. It's peanuts compared to any conventional rocket first stage that usually provides 3 to 5000 m/s, which means that you still need a full size expendable multi-stage rocket. You might gain 2000 or 3000km/h if you go supersonic, but good luck building an ultra-specialized supersonic carrier that is 4x the size of a 747, as well as finding a place to land the damn thing safely and figuring out the complications of separating a 500 ton rocket in a supersonic airflow. It's a non-starter, economically and technically.

If you step off of a space elevator at 370km, you fall down because you're going much slower than orbital speed. Physics.

As you have noted, air launch already exists. It's nothing more than a reusable first stage that gives you a small boost in dV. You still need a full size expendable rocket to perform the rest of the orbital acceleration. An aircraft costs much more to build, design, and maintain, especially if it's very specialized and can only be used for a couple of launches per month. A dedicated expendable 1st stage will provide a much bigger boost for cheaper. You need to design the rocket to be suspended under the carrier, which means that it has to be strengthened for lateral loads as well as longitudinal loads. This means a heavier structure and a heavier rocket, which means less payload. It's also not very scaleable. Stratolaunch is working on a carrier aircraft that will be the biggest aircraft ever built, yet it will have quite a small payload capacity. To carry something like a fully fueled Falcon 9, you would need a plane so big that there are no runways that could handle it. Basically, you need to build a whole new reinforced airstrip with both aircraft facilities and rocket fueling facilities. And then there's a whole slew of safety problems. If your engine fails to start, you lose the rocket. If you abort the launch, you need to land the carrier with a fully fueled rocket attached underneath. And of course, there's the whole complexity and chain of failure modes related to the separation of a big rocket. Now, as a first stage, yes, it's reusable. However, a plane still sucks as a first stage compared to, for example, an SRB both in terms of performance, cost, and safety. In terms of economy, safety, and performance, air launch is a non starter. The only advantage is flexibility: you can launch at any time to any orbit, which could be of interest for DoD payloads. For commercial payloads, there isn't much point.

In the 60s, NASA had an aversion for using SRBs on manned vehicles for safety reasons. SRBs cannot be shut down, and so they were seen as a hazard. This went out of the window with the Shuttle, because it was either SRBs or no Shuttle. SRBs aren't reusable. The expensive bit of an SRB is molding the solid fuel inside the booster, but that's gone once you've burnt it up. The only thing you get back are the casings, which are basically dumb steel tubes. They reused those casings for political reasons, but there was no cost advantage in doing so. Steel tubes are cheap. There is no Orion rocket. It's called SLS. The difficulty is in recovering liquid engines. If you dunk them in sea water, they are dead. If they land with wings, hydraulics, and landing gear, then they require too much extra weight. If they land with parachutes on the ground, they will dent, ding, flex, break, or whatever. Since launches are always over water, to bring them back to land requires an RTLS manoeuver, which costs extra fuel, and therefore payload penalty. Only until recently has SpaceX been exploring propulsive landing, but that also has a payload penalty. In the end, it's a very difficult engineering problem and the cost of adding reusability simply isn't worth it economically. Reusability only makes sense if there is enough demand to make it worthwhile. Currently, there isn't, so it is more efficient to make rocket engines as cheap as possible so that expending them doesn't carry as much of a penalty.

The big difference is that masses of people wanted and needed to cross the Atlantic. There was huge demand and the crossing time was the price to pay. Therefore, it made sense to build a huge transportation infrastructure. Those ocean liners really stretched the technological and engineering limits of their time. This was only possible because there was already things to do, places to visit, people to meet, friends, family, opportunities, etc... on both sides of the Atlantic. People were lining up to pay the price to start a new life, visit their family, or to meet business partners on the other end. In space, there is no new life, no family, no business trips. You see, building such a huge infrastructure only makes sense in there is massive demand for transportation. Right now, and until there is some hypothetical breakthrough in space business, there simply isn't any demand for mass transportation. And as I have already said, the space elevator is not really a mass transportation system. Its payload capacity is poor, with a very limiting bottleneck. It is certainly not cheap either. If you have an elevator run every two weeks, with a limited payload, a large ground infrastructure and huge upfront construction cost, I fail to see how it is magically cheaper than conventional launchers, which will be using the same advanced materials and power technologies that are required to build an elevator. If there is huge demand, then the 2 week bottleneck will keep it expensive. If there is little demand, then it wont be worth the cost. In the end, individual launch vehicles will always be more flexible, scaleable, and will be required anyway as a backup for when the elevator is down. So why build the elevator in the first place? Getting down from GEO to LEO requires the exact same amount of dV as from going up from LEO to GEO. That is around 4000m/s of dV. Once it reaches GEO, an elevator climber will be carrying the same amount of energy as any other GEO satellite. It will have an orbital velocity of 3km/s and will have had to fight gravity just as much as a rocket to get there. That's pure conjecture. We don't even have any idea of the material cost for building one because the material simply doesn't exist. No do we have a power source for the climbers or any idea of the payload capacity or the speed of the climbers. How can you have any idea "dollar for dollar" of what a space elevator would cost compared to a launch vehicle that would use the same superlight superstrong material or the same magical power source?

By definition, if you want it to stay in orbit attached to a permanent ground station, a space elevator must be linked to a station in geostationary orbit, which for Earth can only be 35,786 km above the equator. Then you need a way to send the power to the climber car. This means either very very long wires (36000km worth of the thinnest copper wire would be heavier than a nuclear reactor) or beamed power (laser or MW...). Now, if you have the technology to beam power over such long distances to a climber vehicle, then that same technology could be used to power a launch vehicle and you wouldn't need to mess with megastructures and nanocarbon tethers in the first place. Most of the serious designs I've seen assume superlong superlight nanocarbon tube ribbons (because it's the only material that has the potential to maybe one day be strong and light enough for the application) and small solar powered roller-propelled climbers. I don't see how a maglev design would help you fight gravity while remaining light and strong.

The longer the trip, the heavier the vehicle needs to be. Making it a cruise ship with massive shielding simply turns the elevator into a behemoth that is going to need even more power to fight gravity and put even more strain on the tether and is going to require a massive counterweight. Also, because elevators cannot cross each other on the same tether, you can only have one vehicle at a time either going up or down, therefore taking 2 weeks (or a month) for the elevator to do a round trip limits the total payload capacity of the system. I really don't think there is any demand for month-long cruises to GSO and back that would justify the upfront cost of building the thing. The solution to this is multiple tethers, with an even more massive counterweight. However, there are practical limits to all of this... No, the whole idea is highly impractical for manned trips. It could really only be used for cargo, which means that you would still need some high-speed manned GSO shuttle vehicle for it to be of any use. Now, if an infrastructure exists for economical frequent and fast manned launches to GSO, then it makes much more sense to share the cost of that infrastructure with cargo launches rather than to build a separate expensive space elevator system. Besides, you would need to maintain a redundant launch vehicle infrastructure anyway for when the elevator is out of order or for emergencies.

The original plans called for 2kg. That's what you find on Wikipedia and various blogs when you Google "Chang'e 5 sample". Maybe you have better info, but there isn't much to gain in gathering 20 kg rather than 2 kg from such a small area. Science is better served by variety than by quantity, and variety of the samples is limited by the reach radius of the arm. I would guess that 2 kg is more than adequate.

I really doubt it. To reach geostationary altitude in less than a week, your elevator car would need to propell itself vertically at over 200km/h on pinch rollers that would also need to support the weight of the elevator, the payload, the engine, the power source. Even if we could manufacture a 36000km long ribbon with carbon nanotubes, the heat and friction constraints of those rollers on the ribbon material are staggering. If we had the materials to build a space elevator, then we could also build all sorts of reusable vehicles that would be faster and much more flexible. If we had a power source as light, powerful, durable, and compact as what is required to power a space elevator train for a week, then we would have much better propulsion modes than rockets or pinch rollers to reach space.

If that picture is right, then I was wrong. It means that the capsule does not go down to the ground, but that the sample is robotically transferred over in lunar orbit, which adds a lot more complexity and risk of losing stuff. The capsule still looks wildly oversized for a 2kg sample. It's bigger than the entire descent module. I assumed it would be sized more like the Stardust capsule: Or like this early Chang'e 5 concept that used a smaller capsule and direct ascent. This capsule seems awfully wasteful to me, unless the design is to be used for something else... Maybe as a scale model of Shenzhou for validating the heatshield and reentry parameters for a manned lunar mission.

Space elevators, railguns, rotovators, launch loops, and all those other exotic launch methods have also been discussed to death in these forums. http://forum.kerbalspaceprogram.com/threads/58691-Space-Elevator-or-Mass-Driver-Railgun-or-something-else http://forum.kerbalspaceprogram.com/threads/81147-Next-Generation-launch-technologies-achievable-with-CURRENT-technology Insanely expensive, impossible with modern materials, and probably only really useful for hauling cargo, because of the transit time. 36000km is quite a long distance to travel. It will probably never be very practical. Most of these launch methods have in common that they are megastructures that would costs trillions to build. The engineering involved goes way beyond anything we have ever done and there simply isn't enough demand to justify the cost and financial risk.

Adds unnecessary mass. Redundancy isn't just "add three of everything". That is extremely poor engineering practice. It simply multiplies the weight of the vehicle and if there is a flaw in the design, then all three parts will have the same flaw and the same chance to break. Designing a space mission is about designing to requirements. Anything extra increases cost, complexity, weight, and risk. Keep it as simple as possible. Redundancy is usually built into systems by allowing dual use of equipment, for example Apollo could use the LM's descent engine for course corrections if there was a failure with the CSM engine, the EVA suits could be used to transfer the astronauts between the LM and the CSM if the docking mechanism failed, etc... We don't know if artificial gravity is required. Our experience is that people have successfully flown long duration missions on the ISS without it. Most negative effects of microgravity can be countered with medication, diet, and exercice. We also know that centrifuges may have a negative effect on orientation, balance, and maybe also induce side effects on the circulatory system as well as nausea. So right now, there is no reason to include a centrifuge on a Mars mission. It might be required for further destinations, but we really don't know.

That's actually much bigger than I thought it would need to be for a simple sample return capsule. The plans is to return 2Kg of lunar material, but you could nearly fit a person inside that capsule! It's also a whole lot of mass to land on the moon and return... Their plan is to do a LOR so I assume that the mission profile is something like this: - Launch sample capsule (SC), ascent module (AM), descent module with robotic arm (DM), and return module (RM) into lunar orbit. - Detach RM - Land SC+AM+DM. - Pick up samples with DM's arm and load them into SC. - Launch SC+AM - Rendez-vous and dock SC+AM with RM. - Jettison AM and return to Earth At least that's how I'd do it.

It's still a single point of failure with no redundancy. It's also unnecessary.