# Tag Info

71

A 25m diameter rotor has a perimeter of around 78 meters. At that size, at 500rpm, the rotor tips would be going in excess of 1,400mph. At those kind of speeds, even though it doesn't take much power to get a very light rotor going, there is still an awful lot of force involved which has to be handled by the materials to prevent them literally tearing ...

57

At 100 km altitude, you get to the Karman line. This is the altitude where you have to fly at orbital speed to get sufficient lift. This definition is based on the lift equation, which applies to all airfoils including that of a helicopter rotor. So in a helicopter at 100 km altitude, your blades have to travel at orbital speed (27,000 km/h or 17,000 mph) ...

52

There are a number of reasons why spacecraft electronics typically lag what is commercially available by several years. Radiation tolerance Electronics are very susceptible to radiation phenomenon that terrestrial electronics are largely protected from by the Earth's atmosphere and magnetic field. Common radiation-based failure mechanisms are Single-Event ...

44

These appear to be Schlieren photography. Schlieren photography uses a collimated light source to highlight the refractive index changes brought on by density gradients in a fluid - in other words, it can visualize the shockwaves in air that are produced by different shapes. The simplest technique shines collimated light past the object of interest, and ...

41

Seats were installed in the lower equipment bay, instead of some of the usual storage lockers. A Skylab rescue mission would take a few days at most, so the usual luxuries for a 2-week Apollo mission (like being able to go to the lower equipment bay for a little personal-hygiene privacy) could be foregone. The extra seats were mounted in the reverse ...

35

A caveat about this answer: it's not about SpaceX directly, more about the use of self-inspection cameras in general across space and launch vehicles. It is used for engineering and status information. "Selfie" footage has been standard (at least on launch vehicles) since Apollo. Telemetry offers a very limited view of things and is prone to ...

34

Space is really like this (XKCD What if) In theory a plane could reach most of the way to space, but it won't be able to reach orbital speeds. Bottom line, it just isn't practical. Maybe someday a helicopter could lift a rocket up high, which would help a bit, but it really just isn't practical. Also, a balloon might just be better in any case, it can go ...

33

A big part of it is reliability. NASA could probably put in an Intel Xeon chip made in 2012 that has a crazy high amount of processing power. However, the chip that was used, the RAD750, has years of experiments and usage behind it, such as being used in a variety of spacecraft including: Deep Impact comet chasing spacecraft, launched in January 2005 -...

29

One might think that spacecraft would be on the cutting edge of technology. I wouldn't think this would be the case at all. If anything, NASA would want to use hardware (and software) that has been extensively tested throughout years of use, both in NASA and in industry as a whole. The last thing NASA wants is to find a bug in a spacecraft's system at an ...

28

This is an old question, but nobody has properly answered it. The ultimate answer is the Columbia disaster. This disaster demonstrated that the growing expense of, and inherent risks in, the Shuttle program precluded long term use of the Shuttle. From chapter 9, page 210 of the Report of Columbia Accident Investigation Board (emphasis theirs): Even so, ...

28

There are many different constraints that putting a time window around a launch attempt (even a pad abort) can help manage. Orbital constraints, facilities availability and many more. In the case of a Pad Abort, consider the flight path. Ignite the Super Dracos, get high enough for the parachutes to be effective, and land in the ocean just off the coast. ...

25

@Saiboogu's answer is of course correct, this looks to be classic Schlieren photography. It is notable that NASA has also developed two methods to generate faux-Schlieren images or "synthetic Schlieren" images without the need of special optical systems and collimated beams of light inside wind tunnels. These techniques can be applied to real high speed ...

24

The propellor needs to be strong enough not to pull itself apart via centrifugal force. If you go through the math, you find that the maximum stress on the propellor blade will be halfway along its length, and will have the value $$\sigma = \frac{1}{4}\rho L \omega^2,$$ where $\omega$ is the blade's angular velocity (usually measured in radians/second) ...

23

The material used for the seal is silicone rubber. Example materials considered for NDS iLIDS are: Parker S0383-70 (as part of Gask-O-Seal product) Esterline ELA-SA-401 Silicone rubber is the only class of space flight-qualified elastomeric seal material that functions across the expected temperature range. NASA Glenn has tested three silicone ...

22

The cost of running the space shuttle never met the predictions, and was more expensive (Largely due to the standing army of folk it took to prepare and manage it). Then after the Columbia broke up on re-entry the lack of options for aborts, bailouts, etc, and the inherent danger in the foam on the main tank hitting the wings the notion slowly morphed into ...

22

There are good reasons why balloons have not been used for launch systems. Fragility of the balloons The highly energetic nature of rocket launches Limited control over balloon trajectory Expense of Helium Flammability of Hydrogen. Balloons are inherently fragile. You have to have very thin, very light materials to make an effective high altitude balloon ...

22

Earth's magnetic field is way too weak to repel against with the force required to launch anything into orbit. Actually, it's really easy to demonstrate that. Take one fridge magnet, place it on the kitchen scale, and write down its weight. Then turn the magnet around and weigh it also with its polarity reversed. You shouldn't see any difference and the ...

21

In space (within the Solar system), you will get mostly two types of "radiation" that have health consequences: Photons of various energy, from long wave radio to gamma rays. High-energy charged particles, mostly electrons and protons ejected from the Sun upper atmosphere (this is known as the solar wind). Main source for these is, of course, the Sun. ...

21

There was no single DC voltage useful for the whole electronic system. A lot of different voltages were needed, for very noise sensitive systems dedicated DC sources were used to avoid interference. Using three phase 400 Hz AC current was a well established method used in aircrafts before. Providing 400 Hz AC enabled the use of aircraft instruments within ...

19

As suggested by OrganicMarble in a comment, nitrogen is miscible with oxygen (you can thus make liquid air). According to NASA Technical Paper 2464, this is a major concern because using "enriched air" instead of pure oxygen as the oxidizer degrades the performance of the engine: The transfer of liquid oxygen (LOX) from a storage vessel to a ...

18

In order to stay within the scope of this question, I will reference one idea that I believe fits the criteria, although that might be disputable. I'll call the idea balloon-tether LAS, and it was published in a journal paper in 2012. The reason this idea is notable is that it started from a study of previously proposed LAS (Launch Assistance Systems), and ...

18

OrganicMarble touched on this in a comment but I think it deserves an answer as well, since the question doesn't stop at the Karman line (approx. 100km if you're really defining it as the height where the velocity required to generate lift exceeds the orbital velocity). In simplest terms: just because there's a few atoms of gas present at some height doesn'...

15

One interesting answer to your question is Copenhagen Suborbitals. They're almost a back-yard project. Our mission is very simple. We are working towards launching a human being into space. This is a non-profit suborbital space endeavour founded and led by Kristian von Bengtson and Peter Madsen, based entirely on sponsors, private donators and ...

15

Money. Most engine designs we're now using are an evolution of the space race era in one form or another, from the times when financing research in rocket engine / nozzle design wasn't such an issue. Linear spike fundamentally changes rocket design, for one engine support structure, and would as such require a revolution in engineering if someone expects it ...

15

There is value added. I was an operator of a satellite that had a video of the satellite being deployed. We were able to see from the video that the deployment was clean. I assume if nothing goes wrong, the only value is PR, but if something does go wrong, video can help considerably. EDIT: This kind of thing is exactly what might be useful from the ZUMA ...

15

Ethernet uses 2 or 4 pairs of wires (2 pairs for lower speeds: 1 pair in each direction; 4 pairs for gigabit Ethernet). SpaceWire uses Data Strobe encoding for higher reliability: instead of sending a single signal per bit, DSE sends 2 signals (Data and Strobe) over 2 wire pairs. These have the property that either Data or Strobe changes its logical ...

15

We don't fly to space with helicopters because we can't. We would if we could, believe me. Aside from all the very valid concerns raised by others, the question doesn't properly account for weight*. Maybe your 32 inch diameter propeller weighs 349 grams, but the 10m one certainly doesn't. Oh no! Now 1kg thrust won't lift it at all! So you need more ...

14

Could you? Well, maybe. Let's take a look at one instance where people were encouraged to do that very feat, for \$10 million. I'm of course talking about the Ansari X-Prize of 10 years ago. This did a few things that were difficult for the time, giving a cash incentive, and helping with some of the permits and other required items to make it happen. Most of ...

14

Aerospikes are notoriously difficult to cool efficiently. With a bell nozzle, you have a minor part of rapidly expanding(+cooling) exhaust touching the broad, actively cooled nozzle - that means little conductive heat transfer, lower temperature gradient, lots of area for coolant plumbing on the outside (or within) the bell, and outer area radiating a lot ...

14

The human body tolerates G-forces best if they're perpendicular to the spine. When you apply a G-force along the spine, the blood will gravitate towards the feet, leaving the head starved of blood, which induces loss of consciousness. Having the head at the lowest position helps to prevent these blackouts. 3G is tolerable even if you're facing down, by the ...

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