Hot answers tagged

68

That is precisely it. Plutonium-238, which is used in the creation of radioisotope thermoelectric generators (RTGs) is very difficult to come by. There are plenty of news articles on this, from Popular Science to Space News. Basically, it comes down to the fact that plutonium-238 is in short supply now, and it is difficult to make more because of nuclear ...


67

Because space isn't about going high; it's about going fast! For example, in a 400 km orbit (like ISS) you need a speed of about 27,500 km/h or 7.66 km per second. So if you would extend a pole, winch or anything else into the lower parts of the atmosphere, it would also move at about 27,500 km/h (if we ignore atmospheric drag and all other ...


58

When the shuttle External Tank stopped being painted white, the weight savings was ~600 lbs (~270 kg). This is not a tremendous amount from a vehicle standpoint, but the tank was carried almost to orbit, so weight shaved off it was a direct addition to payload capability, and that amount could be significant for payloads.


54

There's almost nothing to be gained by a truss. The load being applied is along the axis of the tank. A simple hoop of material is very strong in this orientation. (Try it with a piece of paper, you'll be surprised at how much it can hold--just keep the weight even!) A truss in the tank would only help against loads off axis--and you don't want those in ...


53

The diameter of the stages is the largest size that can be transported by road without extensive "outsize load" issues (permits, having to move traffic lights and signs out of the way etc.). This makes the rocket much cheaper to transport. The fairing size (5.4 m) is dictated by the standard satellite diameter set by the Shuttle and Ariane 5.


43

SpaceX initially was looking to buy an engine but could not find one on the market that would allow them to meet their goals. Once they decided to develop their own, they had to consider their goals: Reliability, and reduced costs. Nine engines means at most any time in the flight profile, you can handle an engine out event. The Saturn V with 5 F-1 ...


41

It's all to do with ullage in the fuel tanks. Newton's laws of motion mean that when a rocket is no longer firing and no force is being applied, the rocket receives no acceleration. It continues at its same velocity (if we assume a perfect model). The fuel in the tanks goes into free-fall, just as the astronauts do when they reach orbit. You've seen those ...


40

The first multistage rocket is much older then one might think. Its from the 14th century CE. Huolongchushui or fire dragon issuing from the water (Chinese: 火龙出水; pinyin: huolóngchushui; literally: 'fire dragon out of water') were the earliest form of multistage rockets and ballistic cruise missiles used in medieval China. The name of the weapon was used ...


39

Look at the STS-122 video. How many astronauts do you see? I see six. Seven astronauts landed with STS-122. The six you see were the crew of STS-122 who spent twelve days in space. They could walk because twelve days in zero g isn't enough time to take a significant toll on musculature, bones, and blood. The seventh returning astronaut, Daniel Tani, who you ...


39

The Falcon 1 was less profitable to maintain, and it didn't have the customer base to support using it. A Falcon 1 launch cost around $10 million, of which about 10% was profit. They also considered a Falcon 1e design, which would carry slightly more to orbit, but only 1100 kg tops. There were a few people who are known to have booked a Falcon 1 launch, ...


38

Putting the rocket nozzles nearer the top wouldn't make the rocket any more stable; this is the well-known pendulum rocket fallacy. In fact, some rockets have used a tractor (engine on top) configuration (Goddard's first liquid-fueled rocket in 1926, for example), but the advantages to the pusher configuration as outlined in the other answers here are ...


37

..what reason is there for having the engine at the bottom, .. For the fundamental logical flaw in the desire to move the engines, please see this answer of Russell Borogove - it comes down to The Pendulum Fallacy (the exact same fallacy I made when considering other reasons for 'engines at bottom of stack'). For more on the The Pendulum Fallacy see links ...


35

Another interesting note is that this mission more than any other mission to the outer solar system can use solar power. Why? Juno is in a polar orbit, and will continually be in the sun. Solar panels are also becoming more powerful than they have previously. Between the two of these, solar was a more attractive option than it has been in the past. If it was ...


34

You bet. Not only gases, but astronaut pee as well! Which could result in spectacular light shows. This happens for several reasons: Spacecraft and the tanks inside them are built to be as light as possible, which means no stronger than necessary. If the pressure inside them gets too high, it must be released to keep the hull from rupturing. The device ...


33

It’s a sense of scale issue. As much as the struts might look like flimsy bits of drainpipe, those rockets are around 15 meters wide, and the struts are more like the heavy steel beams used to hold up entire buildings. So yes, they’re just really strong.


33

Because they don't need to be. Clearly the current design of rockets can be successful. So adding truss structures to the current design would add weight for no reason and take away from the payload capacity.


32

Tracks are heavy, high-friction, and primarily useful in soft/muddy/slippery terrain where the weight distribution is essential to prevent sinking and slipping. They take much more energy to move than wheels, and while on Earth-bound robots that's not so much of a problem, on a lander this is to be or not to be of the mission. They weigh quite a bit. I can'...


32

That's a "bump shield" used for filming the IMAX movie A Beautiful Planet. According to IMAX, their desire to film from aboard the Cupola forced them to design an "exclusive bump shield made of a space-rated clear material" that was "equipped with sliding doors" to allow the cameras to have the clearest possible views. The shields were flown into ...


31

Rockets are cylindrical for the same reason maize silos are cylindrical: A circle has the largest area vs perimeter of any shape and also provides maximum strength from internal pressure. This means you can save on weight for the walls of a rocket when it is cylindrical. A cylinder is not the absolute best aerodynamic shape as the Drag Coefficient section ...


31

The landing legs have a honey-comb filler that can compress to absorb significant energy of a hot landing. (Source: @SpaceX)


30

Can you have a spacecraft based on an Arduino? Sure you can! ArduSat was two kickstarter funded cubesats that were eventually launched from the International Space Station in November 2013. When you think about it, an Arduino easily outperforms for instance the over forty year old Apollo Guidance Computer All of your requirements should be doable, if it is ...


29

SpaceX manufactures their booster in Hawthorne, CA. They then truck it on the highways to McGregor, TX for test firing with all 9 engines. Then it is back on a truck for the drive to Florida to LC-40 at the Air Force station for launch. The diameter of the booster at 12 feet/3.6 meters is the largest they could go and still be road transportable. Delta ...


28

The only satellite I know of that was shaped to have low drag was GOCE, which orbited at 250 km. Since it was vital to ensure that the measurements taken are of true gravity and not influenced by any movement of the satellite, this unique five-metre long arrow-shaped satellite had none of the moving parts often seen in other spacecraft. The satellite, ...


26

In order to use the direct ascent method of landing on the moon, which is where the entire vehicle descends and leaves the moon, you would need a rocket an order of magnitude bigger than the Saturn V, not just a bit bigger. Here's an early comparison NASA made back before they decided to use Lunar Orbit Rendezvous: The C1 became the Saturn I, the C-5 ...


25

For supersonic flow, the Sears-Haack body offers less drag than the shorter teardrop that's optimal in the subsonic regime. Sears-Haack is pretty similar to the German V-2 rocket body. (Note that the proportions of this particular example aren't part the definition of the Sears-Haack shape; for minimal drag you'd have to have an impractical body of infinite ...


24

The specific impulse figure of 40kN•s/kg (i.e. exhaust velocity of 40km/s) and the 31.5km/s of delta-v achieved thereby is not achievable with current propulsion technology -- it’s about 10 times the fuel efficiency of modern chemical rockets. That performance suggests something like a fusion rocket engine.


23

I think you answered your question in the first sentence. I am reminded of this image: Aerodynamics is but one (albeit a large one) of many concerns in the systems engineering of a rocket. Others include manufacturability, propulsion, changing flight regimes, safety, structures, economics, etc... All of these seem to have converged on a simple, more-or-...


22

For Delta IV Heavy, according to Spaceflight101: The CBCs functioning as boosters are attached to the central core using thrust struts that interface with the interstage section of the launcher to transfer loads from the boosters to the rest of the vehicle. Additional attachment points reside in the base of the vehicle right above the engine heat shields. ...


21

A similar question was asked on the Robotics SE. The Wheels provide a lot of flexibility, like with the rocker bogie system. where the rover can climb over obstacles up to twice the diameter of the wheels And Tracks are usually heavier than wheels. Making it more expensive for deployment . It's also easier to maneuver with wheels than rely on the skid ...


21

You can, but it will suffer from a number of problems. These problems can probably be overcome with a short term mission. Problems include: Radiation- Degrading the long term effect of the electronics. Single event upsets- This is probably the biggest danger, a high energy cosmic ray strike could cause a bit flip, potentially changing the code running in a ...


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