70 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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 ...
jacksonj04's user avatar
55 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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 ...
Hobbes's user avatar
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44 votes
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How were these pictures of spacecraft wind tunnel testing taken?

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 ...
Saiboogu's user avatar
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41 votes
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How was the Skylab Rescue mission supposed to return 5 astronauts?

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 (...
Russell Borogove's user avatar
36 votes
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Does SpaceX use any of Falcon-9's camera data for engineering or status information, or are they "just for PR"?

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 ...
Tristan's user avatar
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33 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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 ...
PearsonArtPhoto's user avatar
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32 votes
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Interstellar Travel Thought Experiment

Does this logic make sense? Has anyone thought of this before? Yes, it's been considered. In the literature it's known as the "incentive trap". There are a couple of academic papers on it, ...
Russell Borogove's user avatar
25 votes

How were these pictures of spacecraft wind tunnel testing taken?

@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 ...
uhoh's user avatar
  • 149k
24 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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 ...
Michael Seifert's user avatar
22 votes

Why did Apollo spacecraft use both AC and DC equipment? Still used in present and future designs?

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. ...
Uwe's user avatar
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21 votes
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What is the advantage of using Helium over Nitrogen when used for pressurising LOx?

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 "...
TooTea's user avatar
  • 1,585
19 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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 ...
Erin Anne's user avatar
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16 votes
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Why aren't linear aerospike engines in common use?

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 ...
SF.'s user avatar
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15 votes
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Why was SpaceWire designed with nine wires?

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 ...
Hobbes's user avatar
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15 votes

Does SpaceX use any of Falcon-9's camera data for engineering or status information, or are they "just for PR"?

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 ...
PearsonArtPhoto's user avatar
  • 121k
15 votes

Why do we not fly to space with helicopters? What are the practical altitude limits?

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*. ...
Erin Anne's user avatar
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15 votes
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Were any other Space Shuttles ever planned?

I think Sagan was being optimistic. The original plan was for a large fleet of shuttles to support a very high mission flight rate, but according to Wikipedia, by 1983, the plan was to hold the fleet ...
Russell Borogove's user avatar
13 votes

How large could launchers become?

SpaceX is proposing launch vehicle, as a first stage, and a second stage that would transit to Mars. Interplanetary Space Transport (ITS). The final size is not really confirmed, and they should ...
geoffc's user avatar
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9 votes

Why aren't linear aerospike engines in common use?

The Everyday Astronaut just released an hour long video investigating this question. Some of the main points are: Aerospikes are especially advantageous to single stage to orbit vehicles, and ...
JanKanis's user avatar
  • 541
9 votes

Closed Loop Space propulsion

That looks like a fairly standard "I don't understand magnets"-engine, with a side order of "I don't understand conservation of momentum". Don't spend too much time thinking about ...
Mark's user avatar
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9 votes
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Composite pressure vessels for manned spaceflight

Question: Why didn't they just make the whole thing out of composite? Answer: to save structural mass. Cored construction (with honeycomb or other materials) can minimize mass, especially compared ...
Woody's user avatar
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8 votes

What are the challenges to landing a spacecraft on Mercury?

The closest we have done thus far is to orbit a spacecraft around Mercury. This was accomplished by a number of flybys first, of Earth, Venus, and Mercury. The mass of Messenger was about 500 kg, ...
PearsonArtPhoto's user avatar
  • 121k
8 votes

Could Space Shuttle's wings be diminished?

Dennis Jenkins' Space Shuttle1 has a good summary of the development history. Original Orbiter designs had a straight, high-aspect ratio wing. But the charts in Jenkins show that after the first ...
Organic Marble's user avatar
8 votes
Accepted

Why were the antennas on the spherical surface of some early satellites spiral-shaped?

Those are spiral antennas. Spiral antennas belong to the class of frequency independent antennas which operate over a wide range of frequencies. Polarization, radiation pattern and impedance of ...
Hobbes's user avatar
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8 votes
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Simulating launch velocity of falcon 9

Source (cropped) Why do plastic rulers make you measure between two lines, instead of starting at the edge? tl;dr: Never use the edge of a ruler or the "zero" of any analog measuring device ...
uhoh's user avatar
  • 149k
7 votes

How did the USA cooperate with western allies during the Apollo program?

The UK did take some advantage of American components, the engine programme for Blue Streak started with licensed American designs that were progressively replaced with indigenous designs. Black Arrow ...
Hobbes's user avatar
  • 128k
7 votes

How large could launchers become?

It's generally thought that the Sea Dragon design was technically feasible; this would be 18000 tons (6 times the mass of Saturn V) at liftoff and deliver 500 tons to LEO, comparable to the SpaceX ITS ...
Russell Borogove's user avatar
7 votes

At which stage of rocket development does systems engineering become critical/useful?

As someone who sometimes works professionally in this very field as a systems engineer, other times in more specific roles, the answer is easy: From the very start.
David Hammen's user avatar
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6 votes

Why was SpaceWire designed with nine wires?

9 is a quite straight forward choice considering the features you need: all signals should be differential you need one data line for each direction you need to transport a clock along with the data ...
asdfex's user avatar
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6 votes
Accepted

Is there anything like a standard for maximum temperature for mission-critical electronics in spacecraft?

The typical temperature range for space-qualified electronics components is -55C to +125C (at the case). The spacecraft is designed to keep the components within their qualified range, usually with a ...
Mark Adler's user avatar
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