Skip to main content
110 votes

Why is using a space elevator cheaper than rocket power?

With a rocket you have to carry the fuel with you. You are not just propelling the mass of the payload, but also the mass of the fuel. Installing a space elevator is a one-time event that can then be ...
called2voyage's user avatar
  • 23.7k
66 votes

Why is using a space elevator cheaper than rocket power?

In addition to not requiring fuel: A rocket has to accelerate to orbital speed. This takes a lot of energy. A space elevator can climb at a low, constant vertical speed (albeit for a very long climb)...
Hobbes's user avatar
  • 128k
63 votes

Why is using a space elevator cheaper than rocket power?

Here's a simple reason: Most of the rocket's fuel is used just to push the rest of fuel! It sounds strange for those unfamiliar with Rocket equation. The reality is, if we want to accelerate by ...
Heopps's user avatar
  • 9,061
41 votes

Why is using a space elevator cheaper than rocket power?

It boils down to efficiencies of energy conversion and the cost of the technologies doing the conversions. If you have a given mass at Earth's surface that you want in geostationary orbit, you have ...
Tom Spilker's user avatar
  • 18.3k
25 votes

Why is using a space elevator cheaper than rocket power?

Ultimately an elevator is going to be more efficient, because it doesn't have to deal with gravity losses. Let me pose a question to you. What does it take for a rocket to hover in place like Blue ...
Evan Steinbrenner's user avatar
12 votes
Accepted

Would an autogyro be a good solution for a space re-entry vehicle?

Looks like the idea was tested before (https://www.nasa.gov/centers/kennedy/news/rotocapsule.html ):"The design would give a capsule the stability and control of a helicopter, but would not be powered....
akhmeteli's user avatar
  • 294
8 votes
Accepted

Is aerodynamic lift ever useful in rocket flight?

Angling to get lift is going to increase the atmospheric cross-section of the rocket and so increase drag. For any reasonable angle of attack, the drag force is going to be much larger than the lift ...
Russell Borogove's user avatar
8 votes

Why is using a space elevator cheaper than rocket power?

As @Evan Steinbrenner points out in his answer, a stopped space elevator needs use no energy to resist gravity. A hovering rocket must burn an enormous amount of energy just to resist gravity. The ...
SafeFastExpressive'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
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

Is aerodynamic lift ever useful in rocket flight?

As far as I know, no. In order to make a cylindrical rocket as light as possible, they are flown to minimize the side loads to the structure -- as close to a zero angle of attack as possible. If they ...
Mark Adler's user avatar
  • 58.2k
7 votes
Accepted

Inflatable tank/balloon use for recovery

The general ROOST design seems to have assumed an inflatable heat-shield. Note however that 'inflatable' heat-shield is a complex layered structure that still needs to survive hundreds of degrees and ...
GremlinWranger'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
6 votes

Why is using a space elevator cheaper than rocket power?

To add to the answers above, you can also retrieve energy by sending payloads back down the elevator.
DrMcCleod's user avatar
  • 700
6 votes

Why is using a space elevator cheaper than rocket power?

Quite a lot of the answers mention that rockets need to carry the weight of the fuel along with the usual payload, and that requires more energy to lift up. This is correct, but there is also another ...
Pritt Balagopal's user avatar
6 votes

Is aerodynamic lift ever useful in rocket flight?

You said it yourself, Lift is important for guidance and control. As a matter of fact a rocket is designed in such a way, that the center of pressure is aft of the center of gravity. The distance ...
FredCheers's user avatar
6 votes
Accepted

When do aircraft become solarcraft?

I think there are a few misconceptions to clarify here: Rotating bodies can generate lift. This is known as the Magnus effect. Lift is a hydrodynamical phenomenon: Differences in flow velocity above ...
AtmosphericPrisonEscape's user avatar
6 votes
Accepted

What would it take for a balloon to reach an altitude of 65 km (214,000 ft) above the Earth's sea level?

High-altitude ballooning is kind of a gray area as far as space exploration goes, because they can't leave the atmosphere, but they do go high enough to experience space-like conditions (e.g. the ...
Greg's user avatar
  • 4,287
5 votes

Grid Fin lift to drag ratio

For a Grid Fin, what would be the most optimal way of finding the lift to drag ratio? Because Navier-Stokes computations are involved you'll probably want to use a computer with computation fluid ...
Rob's user avatar
  • 3,276
5 votes

Orbital reentry glider with no heat shield

If you want to minimize heating, you need to spend time at high altitudes (>100 km) gradually losing speed. This means you need wings to provide lift. So for now I'm going to ignore the heating issue ...
Hobbes's user avatar
  • 128k
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

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
  • 2,492
4 votes

Why is using a space elevator cheaper than rocket power?

Let's look at the kinetic and gravitational potential energy of a satellite sitting on the launchpad, versus in geostationary orbit. It should be intuitively obvious it has more energy in orbit, so if ...
Phil Frost's user avatar
  • 1,033
4 votes

Why is using a space elevator cheaper than rocket power?

Another factor that's being overlooked: Rockets are extremely high energy machines. Many compromises must be made in order to get the energy density needed to make a rocket reach orbit at all. ...
Loren Pechtel's user avatar
4 votes
Accepted

Challenging the Kármán line from above

For a starting point Falcon 9's Fairing is going 8700 kph (Mach 7.7 sea level) and it has no ablative shell. The returned fairings come back water logged but un-scorched. The interesting point about ...
Elden Crom's user avatar
4 votes
Accepted

Just how much can tall skinny rockets bend? (roughly, safely)

Nothing can be perfectly inflexible without causing undue stress on the hold downs. Similar to using a longer crowbar to gain leverage making any wind load transfer directly to the hold-down clamps, ...
Daryl Morning's user avatar
4 votes
Accepted

Could a rocket launch off water horizontally in stages us using water and air for lift to save fuel?

The biggest problem with this question is the scale of that diagram, to give you an idea: The earth is 63.7x the height of the atmosphere in radius. This means that leaving the earth horizontally ...
Magic Octopus Urn's user avatar
4 votes

When do aircraft become solarcraft?

Some issues with this: Drag is dependent on cross-sectional area, and so is solar radiation pressure. This would mean that different spacecraft would have a different definition of space. We might ...
Michael Stachowsky's user avatar
4 votes

What would it take for a balloon to reach an altitude of 65 km (214,000 ft) above the Earth's sea level?

Your flotation scales with the cubic of radius while surface area and weight scales with the square of radius. In other words, you need a big balloon. Surprisingly, we have become incredibly good at ...
user3528438's user avatar
  • 1,641

Only top scored, non community-wiki answers of a minimum length are eligible