Landing a rocket

Quote: DJTeddyBear

If that would work, why not just use the blimps for the cargo itself, and eliminate the ship?

Probably easier to keep the engine and propeller parts in the water. Possibly more efficient too?

Let's simplify:

You need two things to get into orbit: altitude and speed.

Altitude is to get you out of the atmosphere, which perforce eliminates vehicles like blimps and balloons which can only float in the atmosphere.

Speed is to keep you from falling back to Earth. The minimum orbital speed is around 7.4 kilometers per second, relative to the Earth's surface. If you achieved such speeds inside the atmosphere, then 1) you'll burn due to friction with the air and 2) air resistance and drag will slow you down and make you fall.

Modern launch systems barely reach the required altitude and speed, with little margin available. Manned systems have a bigger margin (and that's why Apollo XIII was able to make the Lunar Orbit Insertion despite loosing an engine on the first stage shortly after launch**)

There have been attempts to launch rockets from high altitude balloons. The problem is the payload a balloon can carry up. For that matter Spaceship One was carried aloft by a mother ship and let loose at altitude. Again the problem is how big a load a plane can carry.

There have been designs using an air-breathing engine, a jet, on the first stage. the problem is the highest performing jets are a pain in the neck to operate at transonic speeds, and don't manage as much thrust as even a solid-fuel rocket.


** Had Apollo XIII not reached its prescribed orbit, the mission would have been aborted. If that had happened, the oxygen tank in the service module wouldn't have blown up. The crew would have to jettison the LM and SM and returned home having failed to reach the Moon. As it was, the extra margin let them go into an even more dangerous situation.

Gemini 11 on 14 September 1966 achieved a record apogee altitude of 1374 km


The Russian satellites have a highly elliptical orbit varying from 500 to 40,000 km altitude. Although this orbit was designed for communications satellite, it would still be a rush to use for tourism. Within 6 hours you would get the Low earth view and the long range view would be from 10% of the distance to the moon.

Quote: Pacomartin

Gemini 11 on 14 September 1966 achieved a record apogee altitude of 1374 km.

Ultimately altitude depends on relative velocity, but I forget what determines the eccentricity of an orbit. A circular orbit and a very eccentric one can have the same mean speed.

Orbital mechanics are a complicated mess. For instance, when chasing the ISS if it's ahead of you, you need to loose speed relative to the Earth. This way you fall into a lower orbit which is faster and will overtake the station. If it's behind you, add speed to move to a higher orbit to slow down (really). It makes flying seem simple in comparison.

When you want to re-enter the planet, you lose enough speed so your orbit will intersect the atmosphere, which will further slow you down and draw you back in. Timing is crucial. A delay of 45 seconds by the Voskhod ][ firing the breaking rockets, had the capsule land over 100 miles off target.

Quote: Nareed

Ultimately altitude depends on relative velocity, but I forget what determines the eccentricity of an orbit. A circular orbit and a very eccentric one can have the same mean speed.

Elliptical orbits have one of their focal points as the center of the earth. Most people assume that the earth is at the center of an ellipse.


In the 17th century, Johannes Kepler discovered that the orbits along which the planets travel around the Sun are ellipses with the Sun (approximately) at one focus, in his first law of planetary motion. Kepler made this difficult observation empirically, but Isaac Newton explained this as a corollary of his law of universal gravitation. As Isaac Newton developed Calculus, it is difficult to explain without a good working knowledge of differential calculus.

Quote: Nareed

Orbital mechanics are a complicated mess. For instance, when chasing the ISS if it's ahead of you, you need to loose speed relative to the Earth. This way you fall into a lower orbit which is faster and will overtake the station. If it's behind you, add speed to move to a higher orbit to slow down (really). It makes flying seem simple in comparison.

The opposite of what you would do if you are moving on the ground.

Quote: Pacomartin

Elliptical orbits have one of their focal points as the center of the earth.

All orbits are elliptical, but some can have such low eccentricities they look circular.

http://www.wsj.com/articles/blue-origin-succeeds-in-vertically-landing-spent-rocket-back-at-texas-launch-site-1448372666

The discussion of orbits has detracted a little bit from the fact that tourists may be going on suborbital tourist flights by 2017 (out of Canaveral),

Quote: Pacomartin

The discussion of orbits has detracted a little bit from the fact that tourists may be going on suborbital tourist flights by 2017 (out of Canaveral),

Ok. Why with so many companies working on suborbital joyrides, has none of them even explored suborbital point-to-point travel?

Granted, it's scary. You'd take off in some form of powered flight (rocket, jet mother ship, etc), reach an absurd height, experience amazing views and some weightlessness then glide to an airport for a regular landing. There's little chance for diversion, and almost zero chance at all for a turn-around.

On the plus side, the Shuttle never had an accident while gliding unpowered home. But then there were only a few shuttle missions overall.

Now, it's not out of the question making a jet aircraft with a rocket engine as well, which would glide unpowered, but also have a reserve of fuel for flight in case it's needed. The problem here lies in managing the compressor blades at supersonic speeds while the engines are off. I imagine a cover or door would be needed.

But you might be able to fly from, say, California to Australia in under 2 hours.

Your luggage would need to shipped separately. I can't imagine a luggage allowance of over 10 kilos in such a flight, likely less.

Quote: Nareed

...On the plus side, the Shuttle never had an accident while gliding unpowered home...

Not exactly. Columbia was lost on descent:

Quote: Space.com article on Columbia Disaster

" On Feb. 1, 2003, the shuttle made its usual landing approach to the Kennedy Space Center. Just before 9 a.m. EST, however, abnormal readings showed up at Mission Control. They lost temperature readings from sensors located on the left wing. Then, tire pressure readings from the left side also vanished.

The Capcom, or spacecraft communicator, called up to Columbia to discuss the tire pressure readings. At 8:59:32 a.m., Husband called back from Columbia: "Roger," followed by a word that was cut off in mid-sentence.

At that point, Columbia was near Dallas, travelling 18 times the speed of sound and still 200,700 feet (61,170 meters) above the ground. Mission Control made several attempts to get in touch with the astronauts, with no success.

It was later found that a hole on the left wing allowed atmospheric gases to bleed into the shuttle as it went through its fiery re-entry, leading to the loss of the sensors and eventually, Columbia itself."

Quote: Ayecarumba

Not exactly. Columbia was lost on descent:

That's actually re-entry. Notice the altitude of over 60 kilometers and the speed above Mach 18.

Besides, the cause was the hole in the leading edge of the wing. The fact that it was an unpowered glider didn't affect the accident at all.