4 ms·

Going to space is not entirely about being high. It's about going sideways, fast. And if, at 6,000 feet, air pressure were half that of sea level, nobody would

Going to space is not entirely about being high. It's about going sideways, fast. And if, at 6,000 feet, air pressure were half that of sea level, nobody would live in Denver and most Tibetans would be dead. Half is more like 6,000 meters.

ceejayoz 9y ago
Getting high quickly is important, which is why launch vehicles go up first, then do a gravity turn in thinner air, reducing drag and aerodynamic pressures on the vehicle. It's hard to go horizontally fast when you're fighting thick atmosphere. Air density at the top of Everest is 1/3 of sea level, and because of the Earth's shape, Chimborazo's 20,000 feet (6,000 meters) is actually further from the Earth's center than Everest, so half pressure sounds pretty reasonable: https://www.npr.org/templates/story/story.php?storyId=9428163 https://www.npr.org/templates/story/story.php?storyId=942816...
- 205guy 9y ago
  What you're forgetting is that the same mechanics that make Chimborazo the furthest from the earth's center (the oblate spheroid shape due to spin) also applies to the atmosphere (though probably to a different degree). So over Chimborazo, the atmosphere is also thicker, I'd imagine (could be more, could be less). I haven't looked at the actual measurements, but you might want to before you compare different latitudes. Also, see my other comment for non-engineering difficulties.
  - JoeAltmaier 9y ago
    Ok the troposphere is 4 miles up at the poles, and 12 miles up at the equator. So 6000m (about 3.6 miles) is not even half of 12. Still, its half-pressure. But you have 8 miles to go to get out of it. So maybe somewhere halfway? Seattle? There the troposphere is 6 miles up; Mt Rainier is 2 miles high. Maybe a better deal?
neaanopri 9y ago
Atmospheric density decreases exponentially with height. Total impulse required to blow through drag forces is a nasty nasty power law. It wouldn't be that difficult to make a linear rail launcher in a vacuum, or on the moon. Air resistance really is the whole problem. If you can put the launcher above the atmosphere, it's 100% worth the effort.
- jsmthrowaway 9y ago
  > Atmospheric density decreases exponentially with height. I'm aware. That's the math I did in my comment, solving for 0.5 atm.
  - ceejayoz 9y ago
    The comment you're replying to mixed up meters and feet. The mountain is 6,000 meters, not 6,000 feet.
    - JoeAltmaier 9y ago
      Right; sorry
notahacker 9y ago
Chimborazo is >6000m above sea level tbf and not 6000ft as the OP suggested. It's actually the furthest point from the Earth's centre (the earth's shape gives it a boost over mountains which are higher above sea level but further from the equator) For related reasons, its difficult-to-reach, low oxygen, snow-covered summit is not ideally suited for building and maintaining a space launch site.
- JoeAltmaier 9y ago
  "Not ideal" may overlap with 'tremendously cheap' if the SpinLaunch 10-100x cost factor is true. So a few oxygen masks may be worth the trouble. And a highway goes within a few miles of the peak right now.
  - notahacker 9y ago
    I've been on that highway. Trouble is you're still a few thousand metres of relatively technical climbing or a helicopter ride away from the top. I mean, people can work in some pretty inhospitable conditions if the cost advantages are real, and the payloads you've got to get up there have to be relatively comfortable with being moved to get fired into space anyway, but it's hard to imagine anything on a Cape Carnaveral scale happening there even if Ecuador decides the dollars from supporting space programmes are worth more than the scenery and symbolism
    - wallace_f 9y ago
      I came across the idea of launches from Ecuador while reading about spaeflight. IIRC, I assumed 3,000m launch (assumed a suitable site near Quito exists), and calculated a disappointing, less-than 10% increase in payload, assuming a BFR as the launch vehicle. However, for a kinetic energy launcher, or small rocket like the new record-settinf Japanese SS-520, that improvement would be a lot larger (and more importantly, the logistics a lot easier!). The thing is, with rocket size increasing, payload increases cubically while air resistance is squared. So for the really big rockets, altitude is not as big of a factor as being near the equator. If I am not wrong, propulsive landing on drone ships uses another roughly 10% fuel (depends on launch trajectory, etc). As fossil fuels are non-renewable, and Hydrogen expensive, I am very sure (and even hope to be correct) that in the future we will see launches from high-altitude equatorial regions, using booster-capture technologies and perhaps even terestial-power-assisted launches. Those things may reduce the fuel-cost of escape velocity by 30+%, and when we're sending enough stuff into orbit that this is too advantageous to ignore, we will do it. But for now, the best way to go is to get really good at building bigger rockets.
JoeAltmaier 9y ago
Near the equator you have the earth's rotation going for you. Launch to the east, and start out at 1000mph. A good start indeed!
- dtparr 9y ago
  I mean, sort of. That's less than 6% of the dv you need to get to LEO. If this thing can only add another 3k mph we're still at less than a quarter of the dv needed to get to space today. It might make a reasonable 'first stage' if they can work though the tech needed to get to that 3k without destroying the payload, but it doesn't sounds like it's capable of anything resembling a complete 'launch system' for things wanting to go to space.
  - JoeAltmaier 9y ago
    They give only 'hypersonic speeds' as a metric. That's 4000-8000mph approximately. So not there yet. But don't knock a free 1000mph! Launching to the west means you have to add 1000mph to be standing still, orbit-wise.
    - dtparr 9y ago
      The article specifically says: >All that momentum is then harnessed to catapult a payload into space at speeds one source said could be around 3,000 miles per hour. So that's what I was working off of. Admittedly, it's unclear who that source is. And 8k is still less than half of LEO. And right, I'm familiar with orbital mechanics and would never turn down free dv, but you get ~90% of that even out of somewhere as far off the equator as CCAFS. The bigger benefit would be if you're looking to launch into a low inclination (equatorial) orbit you can avoid the dv required for the plane change, but that would work just as well out of CSG. The altitude itself would be the only advantage I could see over somewhere like CSG.

ceejayoz 9y ago

Getting high quickly is important, which is why launch vehicles go up first, then do a gravity turn in thinner air, reducing drag and aerodynamic pressures on the vehicle. It's hard to go horizontally fast when you're fighting thick atmosphere. Air density at the top of Everest is 1/3 of sea level, and because of the Earth's shape, Chimborazo's 20,000 feet (6,000 meters) is actually further from the Earth's center than Everest, so half pressure sounds pretty reasonable: https://www.npr.org/templates/story/story.php?storyId=9428163 https://www.npr.org/templates/story/story.php?storyId=942816...

205guy 9y ago
What you're forgetting is that the same mechanics that make Chimborazo the furthest from the earth's center (the oblate spheroid shape due to spin) also applies to the atmosphere (though probably to a different degree). So over Chimborazo, the atmosphere is also thicker, I'd imagine (could be more, could be less). I haven't looked at the actual measurements, but you might want to before you compare different latitudes. Also, see my other comment for non-engineering difficulties.
- JoeAltmaier 9y ago
  Ok the troposphere is 4 miles up at the poles, and 12 miles up at the equator. So 6000m (about 3.6 miles) is not even half of 12. Still, its half-pressure. But you have 8 miles to go to get out of it. So maybe somewhere halfway? Seattle? There the troposphere is 6 miles up; Mt Rainier is 2 miles high. Maybe a better deal?

neaanopri 9y ago

Atmospheric density decreases exponentially with height. Total impulse required to blow through drag forces is a nasty nasty power law. It wouldn't be that difficult to make a linear rail launcher in a vacuum, or on the moon. Air resistance really is the whole problem. If you can put the launcher above the atmosphere, it's 100% worth the effort.

jsmthrowaway 9y ago
> Atmospheric density decreases exponentially with height. I'm aware. That's the math I did in my comment, solving for 0.5 atm.
- ceejayoz 9y ago
  The comment you're replying to mixed up meters and feet. The mountain is 6,000 meters, not 6,000 feet.
  - JoeAltmaier 9y ago
    Right; sorry

notahacker 9y ago

Chimborazo is >6000m above sea level tbf and not 6000ft as the OP suggested. It's actually the furthest point from the Earth's centre (the earth's shape gives it a boost over mountains which are higher above sea level but further from the equator) For related reasons, its difficult-to-reach, low oxygen, snow-covered summit is not ideally suited for building and maintaining a space launch site.

JoeAltmaier 9y ago
"Not ideal" may overlap with 'tremendously cheap' if the SpinLaunch 10-100x cost factor is true. So a few oxygen masks may be worth the trouble. And a highway goes within a few miles of the peak right now.
- notahacker 9y ago
  I've been on that highway. Trouble is you're still a few thousand metres of relatively technical climbing or a helicopter ride away from the top. I mean, people can work in some pretty inhospitable conditions if the cost advantages are real, and the payloads you've got to get up there have to be relatively comfortable with being moved to get fired into space anyway, but it's hard to imagine anything on a Cape Carnaveral scale happening there even if Ecuador decides the dollars from supporting space programmes are worth more than the scenery and symbolism
  - wallace_f 9y ago
    I came across the idea of launches from Ecuador while reading about spaeflight. IIRC, I assumed 3,000m launch (assumed a suitable site near Quito exists), and calculated a disappointing, less-than 10% increase in payload, assuming a BFR as the launch vehicle. However, for a kinetic energy launcher, or small rocket like the new record-settinf Japanese SS-520, that improvement would be a lot larger (and more importantly, the logistics a lot easier!). The thing is, with rocket size increasing, payload increases cubically while air resistance is squared. So for the really big rockets, altitude is not as big of a factor as being near the equator. If I am not wrong, propulsive landing on drone ships uses another roughly 10% fuel (depends on launch trajectory, etc). As fossil fuels are non-renewable, and Hydrogen expensive, I am very sure (and even hope to be correct) that in the future we will see launches from high-altitude equatorial regions, using booster-capture technologies and perhaps even terestial-power-assisted launches. Those things may reduce the fuel-cost of escape velocity by 30+%, and when we're sending enough stuff into orbit that this is too advantageous to ignore, we will do it. But for now, the best way to go is to get really good at building bigger rockets.

JoeAltmaier 9y ago

Near the equator you have the earth's rotation going for you. Launch to the east, and start out at 1000mph. A good start indeed!

dtparr 9y ago
I mean, sort of. That's less than 6% of the dv you need to get to LEO. If this thing can only add another 3k mph we're still at less than a quarter of the dv needed to get to space today. It might make a reasonable 'first stage' if they can work though the tech needed to get to that 3k without destroying the payload, but it doesn't sounds like it's capable of anything resembling a complete 'launch system' for things wanting to go to space.
- JoeAltmaier 9y ago
  They give only 'hypersonic speeds' as a metric. That's 4000-8000mph approximately. So not there yet. But don't knock a free 1000mph! Launching to the west means you have to add 1000mph to be standing still, orbit-wise.
  - dtparr 9y ago
    The article specifically says: >All that momentum is then harnessed to catapult a payload into space at speeds one source said could be around 3,000 miles per hour. So that's what I was working off of. Admittedly, it's unclear who that source is. And 8k is still less than half of LEO. And right, I'm familiar with orbital mechanics and would never turn down free dv, but you get ~90% of that even out of somewhere as far off the equator as CCAFS. The bigger benefit would be if you're looking to launch into a low inclination (equatorial) orbit you can avoid the dv required for the plane change, but that would work just as well out of CSG. The altitude itself would be the only advantage I could see over somewhere like CSG.