a reply to: TrueBrit
Entering the atmosphere with the rocket motor facing the planet would make for a non-optimal profile being acted upon by the friction of
re-entering the atmosphere
The first stage doesn't actually reach orbital velocities, so it won't encounter the stresses of a for example, the former space shuttle when it
reentered the atmosphere. I'm not sure about the exact details but I think the rocket will rotate almost immediately after second stage separation
where the atmosphere is extremely thin, so it's descends tail-first and will then make minor course adjustments to reach the landing site (which will
While writing this post, I ran a search to see how it's supposed to be done, and found that they actually did somewhat of a test of this with the last
Falcon 9 v1.1 launch:
SpaceX achieves controlled landing of Falcon 9 first stage
The first stage was supposed to fire its engines twice after separating from the Falcon 9 rocket's second stage less than 3 minutes after liftoff
Friday. The first burn was expected to slow the rocket's velocity enough to fall into a prescribed landing zone in the Atlantic Ocean a few hundred
miles northeast of Cape Canaveral, and a second firing was to have allowed the rocket to gently settle into the sea.
and begin to focus on the idea of a space plane, capable of lifting off from a runway, exiting the atmosphere, and re-entering it
The problem is a space-plane is extremely difficult to design and build, as it requires extremely efficient engines, that are often required to be
air-breathing, and an extremely high fuel fraction. Given the amount of fuel required, the crew is going to be sitting on a bomb either way. The
overall result is likely going to be a vehicle that is extremely expensive to build and maintain. The Space Shuttle was the closest vehicle to a
space-plane and is a perfect example. It was extremely uneconomical to build and operate, not particularly safe, and never came close to the programs
One space-plane under development is Skylon, but as far as I can tell it hasn't really amounted to anything usable yet and still needs development.
Skylon is a design for a single-stage-to-orbit spaceplane by the British company Reaction Engines Limited (REL). A fleet of such vehicles is
envisaged, using SABRE, a combined-cycle, air-breathing rocket propulsion system, with a designed re-usability up to 200 flights each. In paper
studies, the cost per kilogram of payload carried to low earth orbit in this way is hoped to be reduced from the current £15,000/kg (as of 2011),
including research and development, to around £650/kg, with costs expected to fall much more over time after initial expenditures have amortised.
Aside: It wouldn't surprise me if Skylon was less safe than a conventional rocket, the payload bay is not on top of a giant bomb, rather it is
essentially sandwiched between two giant bombs, somewhat like the Space Shuttle was (which is what caused the loss of the Challenger). A conventional
rocket can on the other hand have an effective escape mechanism
. Skylon is also more complex
and needs an extremely weight efficient design. I suppose since it's partially air-breathing it doesn't need as much oxidizer, so that helps.
SpaceX has already reduced the cost of launching things into space rather significantly through an efficient organisation and simple design - with
further gains to be made by scaling the launch vehicles up and making them partially reusable. So, if we haven't even mastered simple rockets let
alone the organisations that build and operate them - then attempting to go with an extremely complex space-plane that has innate engineering
difficulties, seems like something that while it has merit for the distant future, cannot possibly considered be an alternative to disposable or
partially reusable rockets like Falcon 9 R.
edit on 20/4/14 by C0bzz because: (no reason given)