71 votes

Where does space begin on planets without atmospheres?

Yet surely nobody would classify Neil Armstrong's lunar bunny-hops as suborbital spaceflights. Why not? There's no essential difference between a high-eccentricity trajectory with an apolune of 1 ...
Russell Borogove's user avatar
49 votes
Accepted

How did the X-15 control attitude above the Kármán line?

The X-15 had a reaction control system for all three axes using thrusters with hydrogen-peroxide monopropellant. There was an automatic as well as a manual mode. The manual mode used a single three-...
Uwe's user avatar
  • 49k
46 votes

Which object has been to space the most times?

The Space Shuttle Discovery has been to orbit a total number of 39 times, more than any other shuttle vehicle (source: Wikipedia). Contrasting that to other candidate objects: Space Shuttles Atlantis,...
Justin Braun's user avatar
  • 2,275
40 votes

How did the X-15 control attitude above the Kármán line?

The X-15 has a reaction control system. In this image, it's item 2, 13 and 28, labeled 'ballistic control system'. It was operated via a joystick. Detail of two of the thrusters:
Hobbes's user avatar
  • 128k
35 votes

Where does space begin on planets without atmospheres?

Ultimately, "the edge of space" is an agreed upon convention. In other words it is essentially arbitrary, something which only humans even care about (well maybe space aliens too <grin>). Yes, ...
codeslinger's user avatar
13 votes
Accepted

Why is FAI considering lowering the Karman Line to 80km?

tl;dr: The FAI is doing that because they were convinced by Johnathan McDowell's proposal, one that he first forwarded 25 years ago. The FAI's statement must refer to his recent paper on the topic. ✅ ...
uhoh's user avatar
  • 149k
12 votes
Accepted

What is the practical use of the Karman line?

The Karman line is used for two things: to legally separate the airspace above a country (over which the country has jurisdiction) from space (over which the country has no jurisdiction). to ...
Hobbes's user avatar
  • 128k
11 votes
Accepted

Minimum velocity needed to cross Karman line

When you ask about the minimum velocity needed to cross the Karman line there are 2 things you could mean. The first thing is that you could mean the minimum velocity needed on the ground going ...
The Rocket fan's user avatar
10 votes
Accepted

Did the Soviet Union put an unmanned satellite in "very low orbit"above the Kármán line which used aerodynamic attitude control?

I found a few references to the Zenit 4 M/MK/MKM series of reconnaissance satellites, which may have been equipped with stabilizers to help them maintain attitude in tenuous atmosphere, but the ...
Russell Borogove's user avatar
9 votes
Accepted

Is there some fundamental limitation that would prevent steam-powered rockets from reaching space?

There's no fundamental physical limitation, but there's certainly a practical one. The rocket equation is $\Delta V = V_{Exhaust} \ln(M_{Total}/M_{Dry})$. The exhaust velocity of a typical chemical ...
Christopher James Huff's user avatar
9 votes
Accepted

How much delta V did the V2 have?

I am finding significantly different specifications for the V2 from different sources (Astronautix, Wikipedia) -- probably because they weren't all built the same -- but assuming a gross liftoff mass ...
Russell Borogove's user avatar
8 votes

Where does the definition of the Kármán line on Wikipedia come from?

Immediately before the definition section, Wikipedia references Kármán's abstract concept from his autobiography: In the final chapter of his autobiography Kármán addresses the issue of the edge of ...
Russell Borogove's user avatar
8 votes

Where does space begin on planets without atmospheres?

Where does space begin on planets without atmospheres? Where the ratio κ=1 for the ion cyclotron and ion collision frequencies - for Earth that is 118 ± 0.3 km. The lunar surface is surrounded not by ...
Rob's user avatar
  • 3,276
8 votes

What did Karman's original "Karman line" calculations look like?

This is an interesting question and something I had never considered before.. and I think that's kind of the point. The Karman Line has been taken as a fairly universal boundary of space (in the US at ...
phobos's user avatar
  • 471
8 votes

Temperature and Pressure Gradient across Kármán line

Just so you are aware - the Kármán line is not a physical thing. It is an imaginary boundary, that gives a rough, easy to remember height for the border between Earth and space of 100km (although ...
Rory Alsop's user avatar
  • 13.6k
8 votes
Accepted

Why isn't the Kármán line itself considered to be in outer space?

I do not think there is a useful distinction to make here. Any border you designate will be somewhat arbitrary. Any time you set one, someone else will argue. And setting the border to be exclusive or ...
Polygnome's user avatar
  • 6,936
7 votes

What would a "Kármán plane" look like, a bird, or a plane?

Based on your initial stipulations, and the wording provided by Wikipedia, the altitude Karman was calculating was the altitude where, at orbital velocity, the lifting effect of aerodynamic forces on ...
Hunting.Targ's user avatar
7 votes
Accepted

At what point does an object lose 50% of escape velocity?

As a spacecraft drifts outwards, slowing down, it stays at escape velocity. The current escape velocity, that is. Escape velocity depends on distance and an object further out needs less velocity to ...
SE - stop firing the good guys's user avatar
6 votes

Is the definition of the Kármán line from Wikipedia right?

Why not? Because the people who started using the Karman line didn't see the need for a more refined definition (e.g. because nobody was going to attempt aerodynamic flight in this region). The ...
Hobbes's user avatar
  • 128k
5 votes
Accepted

what is the relevance of ion cyclotron and ion collision frequency ratio

Answer: Cyclotron and ion collision frequencies define the boundary between the Ionosphere and the Magnetosphere. There is a continuum of decreasing gas density from Earth’s surface to space. So any ...
Woody's user avatar
  • 21.6k
5 votes

Is the equation showed below the right one for an airplane flying at the Kármán line altitude?

I think I solved it... I'm not sure but I think I'm on the right path. You were very close to the right solution, and you were very correct the linked equation is useless in describing actual ...
SF.'s user avatar
  • 55k
5 votes
Accepted

When is/will be the symposium to revisit the Karman line and consider the "McDowell line"?

Symposium will not be held. Source: I asked Jonathan.
Carlos N's user avatar
  • 4,444
5 votes
Accepted

With a 10% increase in Earth's mass, would the Karman line move up or down, and by how much?

It would move Down! By the definition of the Karman line on wikipedia, the lift force and the "centrifugal force" must be equal to the gravitational force and, therefore, each other. This gives the ...
A McKelvy's user avatar
  • 2,482
5 votes

Could you skim along the Karman line using a parafoil?

Using a naive lift calculation at 100km runs into several issues. As you go above about 50km your mean free path for the atoms in the atmosphere is becoming long enough that you no longer have a '...
GremlinWranger's user avatar
4 votes

Karman line analog on other celestial bodies

I will elaborate a bit on Mark's answer starting from the basic formula $R\rho = 2m/(A*Cl)$. Above the troposphere, the density falls exponentially as $rho = rho_0 \exp(-h/H_0)$ where $H_0$ is the ...
Sören Molander's user avatar
4 votes

At what conference did the "von Kármán line" arise, and was discussed for the first time?

It appears this was suggested in 1959 at the First Colloquium on the Law of Outer Space: Jastrow, Robert. "Definition of Air Space." Proceedings of the First Colloquium on the Law of Outer Space,. ...
Diamond's user avatar
  • 484
4 votes
Accepted

Would the >100 km "knee" in Earth's atmosphere still be where MFP exceeded scale height if it were pure Ne or Ar?

There are a lot of phenomena at play here. First of all, you already mentioned there's a factor of changing atmospheric composition. This one is easiest to understand. Consider a very simplistic model ...
Sergei Ozerov's user avatar
4 votes
Accepted

How can I calculate the weight a aero-spacecraft occupant experiences during sub-orbital but non-ballistic trajectories?

My interpretation of your question is this: At 0 horizontal velocity, an aircraft needs to provide 100% of its weight in upward force to maintain its altitude. At orbital velocity, with the surface ...
Russell Borogove's user avatar
3 votes
Accepted

Is a Kármán Rocket Possible?

Why are the rockets not razor sharp Because then the payload fairing would spend a lot of mass for space that wasn't useful to enclose a payload. skinnier The skinnier the rocket, the worse its ...
Russell Borogove's user avatar
3 votes

Why is FAI considering lowering the Karman Line to 80km?

To add to uhoh's excellent answer: first, the original Kármán line was calculated to be at 57 mi (91.5 km) on average (the 100 km value is just to make it "more memorable") (see Kármán line), and 2nd, ...
LoveForChrist's user avatar

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