Comment by leoedin | Hacker News Reader

Comment by leoedin | Hacker News Reader

The author has a sever misunderstanding of physics. A weather balloon can get you to the "edge of space", yes, but orbit is an entirely different process. To be in orbit, you need a rotational velocity (travelling around the earth) in the order of 7.8 km/s. A weather balloon can't do that! If you were to simply go to space vertically and turn off the engine, you'd simply fall straight back down again - the only reason you can stay in orbit "indefinitely" is because your rotational velocity is great enough that you're constantly "missing" the earth. (see Newton's canonball - http://en.wikipedia.org/wiki/Newton%27s_cannonball)

The key issue with getting anything to orbit is the fuel cost. It's expensive, and pretty much impossible to avoid. Micro satellites work by weighing very little and fitting in spaces on the rocket that otherwise would be empty. There's still a fuel cost in doing that (Most chemical rockets have a cost to orbit of at least $10,000 / kg). It's unavoidable. The existing micro satellites (ie AmSats) have been launched on the generosity of the launching organisation (unlikely to happen with satellites designed to circumvent governments) and have a very high failure rate.

It's not impossible, but the project would need serious backing. Even more expensive than paying the cost of launching micro satellites would be actually developing their own launch platform (another suggestion in the article).

It's probably another case of a non-specialist reporter oversimplifying the information he was given to the point that the summary is no longer correct.

Hobbyists have sent balloons to "space" at 100,000 feet <http://www.brooklynspaceprogram.org/>; though that obviously isn't going to get you into orbit.

Groups like CU Spaceflight are experimenting with launching rockets from high-altitude balloons. The idea is that the balloon will get you through most of the atmosphere for dirt cheap, hopefully bringing launch costs down within the reach of private citizens.

A project like that could put a satellite in space using a balloon, just not in the way that you're thinking of. :-)

I've read a lot of technical stuff about rockets and space missions lately to the point of hurting my brain. I am not a rocket scientist (yet ;-) but I think what one needs is to launch a single robot in orbit while more components are sent to be assembled up there with balloons e.g. to build a unmanned space station. Could that work?

"... launch a single robot in orbit while more components are sent to be assembled up there with balloons e.g. to build a unmanned space station. Could that work?"

No. What could work, with regard to a space station, is to send up thousands of robotic panels, and insert them into orbit at roughly the same spot. They would communicate with each other to figure out where they are in relation to one another, and then they would, one pair at a time, fire their own thrusters to come together, and permanently join with each other, to form not only the space station itself, but also the station's distributed computing system and sensor network. The robots might even go further, by generating an atmosphere, thus allowing for the station to be occupied by humans. We already have the ability to easily send up such robots, by using Orbital's Pegasus, which is launched by a modified L-1011 from 40,000 feet. All we really need is to design, build and test the robots, such that each is no more than 1,000 pounds, as well as scale up the process of building and launching those rockets, which is covered below, in an article by John Walker, co-author of AutoCAD.

http://www.orbital.com/spacelaunch/pegasus

http://www.fourmilab.ch/documents/rocketaday.html (A Rocket a Day Keeps the High Costs Away)

No. You'd avoid friction. You may be able to accelerate faster, meaning less waste (as you won't be fighting gravity for as long). And you'd gain potential energy by already being up so high. But there's still a minimum amount of energy you need to get to orbital velocity.

If you didn't burn fuel to match speeds, you'd smack into the robot, which will be moving at orbital velocity.

See, the way a satellite stays "up" is by moving really fast in a straight line perpendicular to the earth's surface, like this:

satellite earth

   ^-> falls "down"
   |      /
   |      |
 d-0-b    |
          |
          \

The satellite "falls" towards the Earth, but it's moving so fast that this "falling" just becomes part of a giant circle, around the earth. If it was any faster, it would shoot away (or move to a higher orbit). If it was slower, it would fall down to a lower orbit, and if it was too slow it would hit the atmosphere where it slows down even more (eventually crashing down).

I wonder whether it would be feasible to accelerate a balloon to LEO using an ion engine. It could use the hydrogen or helium in the balloon as reaction mass to go around pressure differential issues and build up horizontal speed as it goes up and loses lift.

Anyone wants to do the math? I'm a bit rusty.

I've had this smae idea many times! I really think its feasible but I can't do the math* either :-(

I've come to think there are many ways to reach orbit with our current levels of technology but it's just too expensive to do the R&D.

* I actually got suck on figuring out the helium required because everytime you add more helium it adds more weight which requires more helium and so on. It must need some kind of complex differential equation.

http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation Delta-V = v_exhaust * ln( mass_initial / mass_final )

It's bit more complicated than that. The balloon lift will decrease with pressure, which will decrease with altitude but so will aerodynamic drag. Ion engines design for satellite operation also prioritize low reaction mass usage and I am not sure the low thrust is a hard limit or a design choice. The device could also use vertical thrust to compensate for the loss of lift and then gradually rotate until it reaches orbital speeds.

It's probably impossible with current propulsion technology, but it would be useful to have a number when it starts to be possible.

If the atmosphere is thick enough to support your balloon, its thick enough that something as low thrust as an ion engine basically won't be able to let you reach a meaningful velocity.

The ion engines used in existing spacecraft produces similar thrust to a piece of printer paper in your hand - the thrusts of the engines are measured in terms of milliNewtons. They are useful in deep space situations, where (due to nuclear reactors or abundant solar cells) you're power rich but propellant poor, and don't have to deal with aerodynamic drag. Over a long period of time, an ion engine can yield big velocities. With drag forces though, they'd simply have no effect on a floating balloon.

A balloon could present a method of getting a lightweight rocket to a very high altitude before engine firing, reducing the drag on the rocket and allowing the rocket engine to be designed just for the very low air pressure environment at those heights (rather than the compromise that modern ground-launched rockets have to make), but the size of the payload would be limited by the balloon size (with approximately 1kg/m^3 of helium, you'd need a lot of helium to lift a rocket of any size).

Sadly, it's not feasible. For a great overview of why, see: http://groups.google.com/group/rec.arts.sf.science/browse_th...

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