It’s All About Speed!

When a rocket takes off from the surface of the Earth and flies into orbit it increases its velocity by approximately 9,100 meters per second.  That breaks down to 7,800 meters per second for the speed of orbit and 1,300 meters per second for drag and gravity losses.  That is a lot of speed and it takes a lot of propellant to go that fast.

An example of just how much propellant is required is the Space Shuttle.  Sitting on the launch pad waiting to take-off, the Space Shuttle was 85% propellant, 14% launch vehicle, and 1% payload.  If Earth to orbit spaceflight is ever going to be affordable to everyone, the launch vehicle will need to be both fully reusable, and able to carry a large enough payload that it makes it worth all the trouble.  Up to now, that has not been possible.  To make the Space Shuttle fully reusable it would have been necessary to make it both larger and heavier which would have required a larger propellant fraction and that would have made the payload go to zero.  Obviously, not a very workable solution.

This is where reducing the speed to orbit comes in.

There are a number of ways to do this.  One is to use a ground accelerator that is located on the side of a tall mountain to boost the launch vehicle up to 600 MPH before starting its engines.  This reduces the speed to orbit in two ways, by the speed added to the launch vehicle by the ground accelerator, and by reducing the drag and gravity losses that would have been incurred by the launch vehicle if it had accelerated to this speed and altitude on its own.

Another way to reduce the speed to orbit is to use a Skyhook at the upper end of the flight profile.  Skyhooks can be short or long.  The best way to use a Skyhook is to start small while the flight rate is low and gradually grow it into a longer and stronger version as demand increases.  For this example, a short Skyhook, like the one shown in this video was selected.

The total velocity reduction made possible by the 600 MPH ground accelerator and 200-kilometer long basic Skyhook used in this example is 1,060 meters per second.  This reduction in velocity will triple the amount of useful payload that can be delivered to the Skyhook compared to the same expendable launch vehicle flying to a space station without a ground accelerator or Skyhook.  Increasing the amount of useful payload by a factor of three will reduce the cost to orbit to 1/3 of what it was without the ground accelerator and Skyhook.  If it is assumed that the first stage of this launch vehicle is made reusable like the first stage of the Falcon 9, it then becomes reasonable to assume an additional 50% reduction in launch costs.  This will reduce the cost to orbit to 1/6 of the cost of flying the expendable version of this launch vehicle without the ground accelerator and Skyhook.

And this is only the beginning.  The longer the Skyhook becomes the lower the price becomes.  Once the Skyhook is long enough it then becomes possible to use a fully reusable single stage launch vehicle that will reduce the cost even more.  Best of all, the 600 MPH ground accelerator, the basic Skyhook, the reusable first stage launch vehicle, they can all be affordably built right now with existing materials and technology.

For more information about this and other related cost reducing concepts, read the book “Opening the High Frontier”.

 

Index of Articles

  1. Opening the High Frontier
  2. Skyhook, a Journey to Orbit and Beyond
  3. In the Beginning . . .
  4. Why do Rockets Cost so Much?
  5. Combination Launch Systems
  6. It’s All About Speed!
  7. Visions of the Future
  8. The Call of an Unlimited Future
  9. Combination Launch Systems, part 2
  10. Outward Bound: Beyond Low Earth Orbit
  11. and someday . . . Starships!
  12. Mars: how to get there
  13. Outpost Space Stations
  14. Dreams of Space
  15. The Moon or Mars?
  16. Skyhooks and Space Elevators
  17. Stratolaunch and the X-15
  18. Starship Congress
  19. Making Spaceflight Affordable
  20. How a Combination Launch System Works
  21. Starship Conference 2017
  22. New Worlds Conference 2017
  23. Opening the High Frontier
  24. Building a Spacefaring Civilization
  25. Space Exploration and the Future

Other websites

Videos

Combination Launch Systems

A combination launch system is a launch system that consists of multiple launch technologies that work together to boost a payload into orbit for a small fraction of the cost of current launch vehicles.  It works by reducing the amount of velocity that the rocket-powered components of the launch system need to achieve.  This reduces the propellant fraction and increases the payload fraction of the launch vehicle to such a degree that airliner like operations to orbit and beyond using a fully reusable launch system becomes possible.

There are many different launch concepts that we can build today that can be combined together to do this: subsonic air-launch; supersonic air-launch; ground accelerators; combination air-breathing and rocket motor propulsion systems; reusable launch vehicles; and, Skyhooks.  All of these concepts can be combined together to reduce launch costs.

There are also many ways to combine these concepts to make a combination launch system.  They can be as simple as using a vertically oriented ground accelerator to boost an existing expendable launch vehicle up to 600 MPH prior to igniting the rocket motor.  They can be as complex as combining air-launch with a reusable launch vehicle that uses a combination ramjet, scramjet, rocket motor propulsion system, that flies to the lower end of a non-rotating Skyhook.  The hard part is finding the combination that has the lowest user cost to orbit for the lowest possible initial investment, that is sized for the existing launch market and has the potential to grow as the market grows.

Combination launch systems are not new.  The Wright brothers used a catapult to boost their first airplane up to flight speed.  The U. S. NAVY still uses catapults to launch fighter planes from the decks of aircraft carriers.  The world’s first reusable rocket plane, the Bell X-1, was air-launched from a B-29.  Probably the best-known combination lunch system was the X-15 rocket plane that was air-launched from a B-52.  In 1967 they even test flew a mock-up of a scramjet on the X-15.  There were also studies that examined the possibility of supersonic air-launching a rocket-ramjet-scramjet powered delta winged version of the X-15 from the back of the XB-70 at Mach 3 that had a small expendable upper stage rocket for carrying satellites into Earth orbit.

Unfortunately, all of these ideas fell by the wayside in our rush to beat the Russians to the Moon back in the 1960’s.  It wasn’t until SpaceShipOne flew in 2004, the start of Virgin Galactic and Stratolaunch shortly thereafter, as well as SpaceX and Blue Origin developing reusable first stage launch vehicles, that we have seen a serious effort to develop combination launch systems again.  The only negative about this is that none of these new combination lunch systems go far enough.

While all of these concepts, ground accelerators, air-launch, reusable first stage launch vehicles, air-breathing and rocket propulsion systems, and Skyhooks, will reduce the cost of getting to orbit, none of them, by themselves, will make spaceflight affordable to everyone.  To do that we will need a launch system that combines almost all of these concepts together.

Once we have that, the solar system is ours.

 

Index of Articles

  1. Opening the High Frontier
  2. Skyhook, a Journey to Orbit and Beyond
  3. In the Beginning . . .
  4. Why do Rockets Cost so Much?
  5. Combination Launch Systems
  6. It’s All About Speed!
  7. Visions of the Future
  8. The Call of an Unlimited Future
  9. Combination Launch Systems, part 2
  10. Outward Bound: Beyond Low Earth Orbit
  11. and someday . . . Starships!
  12. Mars: how to get there
  13. Outpost Space Stations
  14. Dreams of Space
  15. The Moon or Mars?
  16. Skyhooks and Space Elevators
  17. Stratolaunch and the X-15
  18. Starship Congress
  19. Making Spaceflight Affordable
  20. How a Combination Launch System Works
  21. Starship Conference 2017
  22. New Worlds Conference 2017
  23. Opening the High Frontier
  24. Building a Spacefaring Civilization
  25. Space Exploration and the Future

Other websites

Videos

Why do Rockets Cost so Much?

In the late 1960s and early 1970s, America used the Saturn V rocket to go to the Moon.  The first stage of that rocket had an empty weight of 130,000 kilograms and carried 2,160,000 kilograms of propellant.  It was used only once and then thrown away.

The second stage of the Saturn V had an empty weight of 40,100 kilograms and carried 456,100 kilograms of propellant.  Like the first stage, this stage was used only once and thrown away.

The third stage of the Saturn V had an empty weight of 13,300 kilograms and carried 106,600 kilograms of propellant.  This stage was also used once and thrown away.

The total empty weight of those three stages was 183,400 kilograms.

By comparison, a Boeing 747 has an empty weight of 183,000 kilograms. The 747 can fly 15 hours per day, 11 months per year, and has a useful life of 20 years.  It also carries three hundred plus passengers per flight.

Each Saturn V made only one flight and carried only three passengers.

This is why spaceflight that is based on using expendable rockets costs so much.

This is also why SpaceX and Blue Origin are working so hard to develop reusable rockets.

 

Index of Articles

  1. Opening the High Frontier
  2. Skyhook, a Journey to Orbit and Beyond
  3. In the Beginning . . .
  4. Why do Rockets Cost so Much?
  5. Combination Launch Systems
  6. It’s All About Speed!
  7. Visions of the Future
  8. The Call of an Unlimited Future
  9. Combination Launch Systems, part 2
  10. Outward Bound: Beyond Low Earth Orbit
  11. and someday . . . Starships!
  12. Mars: how to get there
  13. Outpost Space Stations
  14. Dreams of Space
  15. The Moon or Mars?
  16. Skyhooks and Space Elevators
  17. Stratolaunch and the X-15
  18. Starship Congress
  19. Making Spaceflight Affordable
  20. How a Combination Launch System Works
  21. Starship Conference 2017
  22. New Worlds Conference 2017
  23. Opening the High Frontier
  24. Building a Spacefaring Civilization
  25. Space Exploration and the Future

Other websites

Videos