The Moon or Mars?

There have been a lot of articles in the news about either returning to the Moon or going to Mars of late.  I think they are great.  Either destination is fine as long as we build the infrastructure that will make spaceflight affordable to everyone in the process.

My reasons for this are simple; whichever program we choose, I don’t want it to be canceled after a handful of missions due to excessive cost like the Apollo program was.  If we make spaceflight really affordable the program will continue and people will find a way to make money in space.  Once that happens we will be on our way towards building a spacefaring civilization and there will be no turning back.

Returning to the Moon or going to Mars without building the infrastructure to make spaceflight affordable will only result in another canceled program and another 40 to 50-year wait before we try again.  The reason for this is simple.  Currently, it costs over $12,000 per pound to go to the International Space Station.  You can check this yourself by going to the SpaceX website and looking up the cost of flying the Falcon 9 launch vehicle.  It is $62 million per flight.  If you look up the amount of useful payload that it can deliver to the International Space Station, the answer is 5,000 pounds.  $62 million divided by 5,000 equals $12,400 per pound.

Another example is the Space Launch System, NASA’s new heavy-lift rocket that is currently in the process of being developed.  The Block 1 version of this rocket is supposed to be able to lift 150,000 pounds into low Earth orbit.  The cost per flight is estimated to be $1.86 billion.  That also comes out to $12,400 per pound.

The Saturn V rocket that was used to go to the Moon in the 1960s would launch 3 astronauts and 140,000 kilograms into low Earth orbit for each Moon mission.  That is a little over 300,000 pounds or 100,000 pounds per astronaut.  100,000 times 12,400 equals $1.24 billion per astronaut in today’s dollars to go to the Moon.  You can be sure that sending an astronaut to Mars will cost more than that.  Even if the reusable first stage rocket technology that is being developed by SpaceX and Blue Origin is able to reduce the cost of getting into Earth orbit by half, the cost per astronaut for going to either the Moon or Mars will still be in excess of $600 million per person.  That is a lot of money.  So much money that no one has been able to come up with a commercial activity in space that can make enough money to justify the expense of manned spaceflight.

As much as I want to see us build a spacefaring civilization, it just isn’t going to happen with launch costs this high.  Anyone who tells you otherwise is either living in a fantasy world or expects to make money on it via government contracts.

So what can we do?

There are 3 things we need to do to make spaceflight affordable if we want to build a spacefaring civilization.

First, build a combination launch system that includes either an air-launched reusable first stage rocket for flying to the lower end of a non-rotating Skyhook or build a 600 MPH ground accelerator for launching a reusable first stage rocket to a non-rotating Skyhook.

Second, build a reusable spacecraft for launching from the upper end of the Skyhook for going either to the Moon or to Mars, as well as single stage reusable lander for the Moon or Mars.

Third, build outpost space stations with local sources of propellant for refueling those spacecraft and landers.

It doesn’t all have to be built at once.  It can be built a piece at a time with jointly funded government/industry programs.  SpaceX and Blue Origin are working on reusable rockets.  Vulcan Inc. is developing the Stratolaunch carrier aircraft for air-launching launch vehicles.  Bigelow Aerospace is developing inflatable space stations.  NASA is building the Orion spacecraft for cis-lunar spaceflight and possibly for going to Mars.  And finally, the US Air Force is developing a Maglev test track that could be used to accelerate a launch vehicle up to 600 MPH.

What else do we need?

Vulcan Inc. needs to develop a horizontal landing reusable first stage launch vehicle for its Stratolaunch carrier aircraft, and either NASA or Bigelow Aerospace needs to add a 200-kilometer long tether to the International Space Station or to a Bigelow space station along the lines of the one shown in this video.

Air-launching and the 200-kilometer long Skyhook will reduce the cost to orbit to 1/3 of what it is today, from $12,000 per pound to $4,000 per pound.  Making the air-launched first stage reusable should reduce the cost to $2,000 per pound.  Increase the length of the Skyhook to 380 kilometers and the cost will drop to $1,500 per pound.  Continue making the Skyhook longer and the price drops even more.  Once the Skyhook is long enough that the upper end is moving at close to escape velocity it becomes possible to place an Orion spacecraft on a free-return orbit to the Moon without the need for an expendable upper stage.  Add a single stage reusable lunar lander and an outpost space station in lunar orbit and now we have an affordable transportation system for going to the Moon.

Before the Space Shuttle was retired we had the beginnings of a space tourism industry with people like Dennis Tito flying to the International Space Station.  The cost for such a flight was $20 million.  An air-launched reusable first stage launch vehicle flying to the lower end of a 380-kilometer long Skyhook equipped space station would cost 1/8th of that, or approximately $2.5 million.  Obviously, there will be more people wanting to go into space at that price than for what Dennis Tito paid.  Increased demand for flights will justify additional investment in the Skyhook to make it longer as a longer Skyhook will decrease the price even more.  Every time the price goes down the demand for flights will increase.  The increased demand will lead to further increases in the length of the Skyhook.  Eventually, it will reduce the cost of a ride to orbit to $20,000 per person.  That is what I call affordable to everyone spaceflight.

As the number of people in orbit increases, it will eventually become economically worthwhile to develop an off-planet source of consumables such as water and oxygen.  No matter how affordable the combination launch system becomes, it will always be more affordable to get basics such as water, oxygen, and shielding materials from either the Moon or an asteroid due to the lower energy requirements for going to those places.  Once we have access to those materials, building farm modules for growing food in space will also become worthwhile.

Having a NASA program for returning to the Moon or going to Mars will speed up the development of the combination launch system due to the increased demand for flights.  This will speed up the pace of development in commercial manned spaceflight as well as reduce the cost of the NASA program.  It is a win-win combination that will propel us into the solar system and kickstart the building of a spacefaring civilization.

We are that close to making it all happen.

Ad Astra

 

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

Dreams of Space

What are your dreams of space?

People have dreamed about building cities on the Moon and Mars for years.

Some people even dream of making Mars into an earthlike planet – a true second home for mankind.

Others want to go asteroid mining so as to bring home the wealth of the solar system.

There are others who want to build cities in the stars, O’Neill style space colonies scattered throughout the solar system, to develop a truly space based civilization.

They are all worthy and wonderful dreams.  Yet none of them will happen until a way is found to make space travel affordable to everyone.  Affordable to the individual spaceflight is the foundation of all these dreams if any of them are ever to be made real.

Affordable to everyone spaceflight is not just about the big dreams, it is also about the personal dreams of every person who has the courage to dream.  For some, that personal dream might be to spend a week or two in an orbiting hotel watching the Earth pass by underneath.

For others, it might be to get a job in one of the orbiting factories or research stations so as to become part of the new frontier.

Then there are those who dream of starting their own business in space such as a repair and refueling service for satellites that orbit the Earth or to build a farm module where they can make a living growing food for the people who live and work in space.

Other still might dream of getting a job in space so they can use their spare time to build a small spaceship that will allow them to homestead an asteroid.

The possibilities are endless.  The only limitation is your imagination and how hard you are willing to work.

Whatever your dreams of space are, affordable to everyone spaceflight is what will make them possible.  Without it, all these dreams, both large and small, will remain forever unattainable.

Isn’t it time we built a combination launch system that will make all this possible?

 

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

Outpost Space Stations

The idea of using a network of outpost space stations (also known as deep space habitats) scattered around the solar system to assist in making manned spaceflight between the planets affordable has been around for at least 25 years.  Who came up with the idea originally I don’t know, but it is an idea that has its roots in the network of coaling stations that were built all around the world for refueling steamships back in the 1800s.  The steam engines that powered the early steamships were not very efficient and they burned a lot of coal.  So much coal that if a ship had to carry the coal for an entire voyage there wasn’t much room left for cargo to pay for the voyage.  To solve this problem coaling stations were built at strategic locations all around the world so that the steamships would only have to carry enough coal for the journey to the next station.  This reduced the steamship’s propellant fraction and increased its payload fraction, which reduced the cost of shipping people and cargo all around the world to an amount that just about anyone could afford.

This idea also applies to automobiles.  The average automobile only carries enough fuel to give it a range of about 300 miles.  Not a lot of range if you are planning a cross-country trip.  If it was necessary to design a car so that it could go across the country and back on a single tank of fuel, the car would be much larger and much more expensive to build, buy, and operate.  So much more expensive that very few people could afford them.  To solve this problem, a network of gas stations was built around the country.  It is the existence of this network of gas stations that makes automobiles so effective and affordable.  They decrease the car’s propellant fraction and increase its payload fraction.

This is what outpost space stations are about.  They are the refueling stations on the trade routes to the planets and asteroids.  They allow the spaceships traveling between the planets and asteroids around the solar system to only carry the propellant that is needed to travel to the next outpost space station along the route.  This reduces the amount of propellant the spaceship needs to carry and allows it to carry a much larger payload.  This reduces the cost of space travel to an amount that just about anyone can afford.

An example of this are the spaceships that were designed by Wernher von Braun for going to Mars in 1948.  These ships were designed for four major propulsive events: first, to accelerate from Earth orbit velocity to Mars transfer orbit velocity; second, to decelerate from Mars transfer orbit velocity to Mars orbit velocity; third, to accelerate from Mars orbit velocity to Earth transfer orbit velocity; and fourth, to decelerate from Earth transfer orbit velocity to Earth orbit velocity.  The total amount of change in velocity required for these four maneuvers is 11.48 kilometers per second.  The amount of propellant required to do this using the low-performance rocket motors of the day required that the spaceships be over 98 percent propellant when departing from Earth orbit.  This meant the empty weight of the spaceship, plus the weight of the crew and all their supplies and equipment, had to be less than 2 percent of the departure mass.  In all of human history, no one has ever come close to building any type of vehicle with a propellant fraction that high and with an empty weight fraction that low.  Even if it were possible to build such a vehicle with existing technology, it would not be affordable on a commercial basis due to the extremely low payload fraction.

Now assume a non-rotating Skyhook in Earth orbit that has an upper endpoint velocity of just short of Earth escape velocity, an outpost space station at the Earth-Moon L2 Lagrange Point with a local source of propellant (either the Moon or a near-Earth asteroid that has been moved to L2), and a non-rotating Skyhook in Mars orbit that has an upper endpoint velocity of just short of Mars escape velocity as well as a local source of propellant (either Mars or one of the Martian moons), and look at what happens to the change in velocity requirement and the propellant fraction of an Earth-Mars spaceship.

Passengers and cargo bound for Mars, fly to the lower end of the Skyhook that is in Earth orbit using the fully reusable combination launch system described in previous posts.  From there they transfer to the upper end of the Skyhook where they transfer to the spaceship that will take them to the outpost space station at the Earth-Moon L2 Lagrange Point where they board the Earth-Mars spaceship.

On the day of departure, the Earth-Mars spaceship leaves the halo orbit at L2 and heads toward Earth where it will perform a gravitational slingshot maneuver as it accelerates to Mars transfer orbit velocity.  The change in velocity for these two maneuvers is approximately 1,500 meters per second.  When the Earth-Mars spaceship gets to Mars it slows down to just under Mars escape velocity and enters a high Mars orbit.  The change in velocity required for this maneuver is approximately 900 meters per second.  The total change in velocity required for this voyage is 2.4 kilometers per second.  That is 1/5th the amount of change in velocity required by the spaceships used in Wernher von Braun’s original Mars fleet.  This difference is due to both the Skyhooks and the outpost space stations with local sources of propellant at both Earth and Mars.

The transfer of passengers and cargo from the Earth-Mars spaceship to Mars will be performed by smaller spacecraft operating from the upper end of the Martian Skyhook using locally supplied propellant.  These spacecraft will also be used to carry locally supplied propellant to the Earth-Mars spaceship for its return trip to Earth.  If it is assumed that the Earth-Mars spaceship uses existing LOX/LH2 chemical rocket motors with oversized expansion nozzles (a specific impulse of 480 seconds), the propellant fraction for the journey to Mars will be 40 percent.  This will leave plenty of room in the mass budget for the Earth-Mars spaceship to make it completely reusable (no drop-off propellant tanks or stages), allow for a spinning section with artificial gravity for the crew and passengers, a hydroponics garden for fresh vegetables, plus plenty of radiation shielding.  If it is assumed that the empty weight fraction for this Earth-Mars spaceship is 40 percent of the departure mass, that will leave 20 percent for the payload.

If a nuclear thermal rocket motor that uses water for reaction mass is used for the propulsion system for the Earth-Mars spaceship, the propellant fraction for the trip to Mars drops to 25 percent and the payload fraction increases to 35 percent.  When used with a combination launch system that includes an escape velocity capable Skyhook, either of these Earth-Mars spaceships would make a trip to Mars mass market affordable on a commercial basis and would operate at a profit for the owners.

Either of these spaceships would also be capable of making trips to the asteroid belt, and to dwarf planets like Ceres, both affordable and possible.  Put an outpost space station in orbit around Ceres with a reusable lander that has the ability to lift water from the surface of Ceres into orbit, and these spaceships would have the ability to take a manned expedition to the moons of Jupiter and to explore the Greek and Trojan asteroids.

As hard as this might be to believe, we really are on the cusp of another Great Age of Exploration.  Only this time, instead of exploring a single planet, we will have people exploring the entire solar system.  All that is required is a combination launch system with a Skyhook and a couple of outpost space stations.  It truly is the beginning of our reaching out to the stars.

 

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