November 2016 - Opening the High Frontier

Mars: how to get there

The first technically feasible idea for going to Mars was proposed by Wernher von Braun over 65 years ago. It consisted of a fleet of 10 chemical rocket powered spaceships that were to be assembled in Earth orbit. Total crew size for the fleet was 70 people.

It was an incredible vision.

Total planned Earth orbit departure mass for the fleet was 37,200 metric tons. That is 90 times the mass of the International Space Station that currently orbits the Earth. It was also a use once fleet.

Obviously, cost was a very significant issue.

So people began looking for ways to reduce the cost to something that was actually affordable.

One of the first follow-on proposals was the solar electric Sun Ship.

This was followed by the nuclear electric Umbrella Ship.

After that came the nuclear electric Mars Ion Rocket.

All of these were significant improvements over von Braun’s original proposal, but they were still too expensive.

There have been many others.

Back in the late 1950’s and early 1960’s, “Project Orion” studied the idea of using nuclear pulse propulsion. This was a concept that used small nuclear bombs and a pusher plate to accelerate a spacecraft. It was a great idea in that it offered both high thrust and high performance. Unfortunately, it also meant mass producing thousands of small easily transported nuclear bombs.

Nuclear thermal powered rockets are another type of spacecraft that have been considered for going to Mars.

Variable thrust ion rockets, otherwise known as VASIMR (Variable Specific Impulse Magnetoplasma Rocket), are another.

They all work. They all have advantages and disadvantages. Unfortunately, none of them are affordable enough to make large scale colonization or trips by private individuals possible.

So what is the answer?

A big part of the problem is that all of these spacecraft have to carry the propellant and supplies for a round trip. Afterall, there are no gas stations and grocery stores in space. This leads us to the ideas of outpost space stations, local sources of propellant, prepositioned supplies, and cycler spacecraft.

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and someday . . . Starships

Look at what has happened to aviation since the Wright brothers made their first powered flight. Look at how it has changed the world.

Imagine what will happen over the next 100 years once spaceflight becomes affordable to everyone. Imagine how that will change the world.

Will we return to the Moon and go to Mars?

Will we mine the asteroids and build space colonies?

Without a doubt.

Will there be starships?

I think so. Unmanned probes on one-way missions at first, and maybe crewed ships sometime after that assuming the EmDrive really does work.

If the EmDrive does work, imagine a space colony equipped with a nuclear electric EmDrive that is capable of accelerating to 20% of light speed. Such a ship could make the trip to Alpha Centauri in 20 to 25 years.

It will be awhile before that happens. First, we will need to build the affordable to everyone combination launch system followed by developing the infrastructure for building space colonies. That will take some time. But once that happens, star travel won’t be far behind.

Between now and then, we will have to make do with watching videos like these. Obviously not the same as the real thing, but it sure is fun to think about what the future might be like as we watch them.

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Outward Bound: Beyond Low Earth Orbit

Once a combination launch system that includes a Skyhook has been built and orbiting hotels and factories are in the process of being built, where do we go next? Low Earth orbit is only two hundred to three hundred miles up, and some astronauts have described low Earth orbit spaceflight as “skimming the cloud tops.” By comparison, the Moon is 240,000 miles away and Mars is measured in many millions of miles. Based on this, low Earth orbit is the equivalent of standing on our doorstep.

So again, where do we go next in our outward bound journey?

Some people want to return to the Moon to mine it for water, oxygen, minerals, helium 3, and as practice before going to Mars.

Some people want to explore the near-Earth asteroids with the idea of either mining them or moving them closer to the Earth where they could be processed.

Others want to build an outpost space station near the Moon that would serve as a jumping off point for trips to the Moon, the near-Earth asteroids, and eventually to Mars.

Some people want to go directly to Mars,

and some want to build space colonies and satellite solar power stations.

The one thing that all of these ideas have in common is the need to go from low Earth orbit velocity to escape velocity. It takes a lot of change in velocity to do that. Change in velocity that requires an upper stage and a lot of propellant. Building an upper stage, filling it with propellant and lifting it into low Earth orbit costs a lot of money even when using a combination launch system. Even if you make the upper stage reusable you would still have to launch another load of propellant to refill it and use it again, and the propellant would still have to be contained in tanks. Bottom line, making the upper stage reusable doesn’t save you very much. So how do we make going from low Earth orbit to escape velocity as affordable as going from the surface of the Earth to orbit on a combination launch system?

The answer to this is the Skyhook that was built for the combination launch system.

In the same way that the lower end of the Skyhook cable is moving at less than orbital velocity for its altitude, the upper end of the Skyhook cable is moving faster than orbital velocity for its altitude. Once the Skyhook is long enough, the upper end of the skyhook cable will be moving at escape velocity. That means that a spacecraft that releases from the upper end of the skyhook cable can be placed on a free return orbit to the Moon, on a path to an outpost space station at L-2, or on an escape trajectory to a near-Earth asteroid without the need to use an upper stage or any of its onboard propellant. In other words, the upper end of the Skyhook will make low Earth orbit to escape velocity spaceflight affordable to everyone.

Once we have this we won’t need to choose between the Moon, Mars, or the asteroids as we will be able to afford all of them all on a commercial basis as profit making ventures.

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Combination Launch Systems, part 2

Component One The first component in a combination launch system is a choice between using an air assisted launch as shown in this video

or a ground assisted launch as shown in this picture.

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As with any competing concepts, there are advantages and disadvantages to both of these systems. Some of the advantages and disadvantages are technical, some are operational, some are financial, some of them vary depending on the other components of the combination launch system, and some are political. There are also a number of design variations to both of these systems, the selection of which is usually determined by the specific needs and goals of the developer. For example, an air launch can be either subsonic or supersonic, and a ground assisted launch can be on rails, with maglev, or trackless. Ground assisted launch can also be enclosed in a tunnel as shown in the picture, out in the open on a mountainside, or on a vertical tower.

Component Two The second key component in a combination launch system is making the launch vehicle reusable. There are a number of ways this can be done with the best choice being determined by the total amount of velocity reduction that is made possible by the air assist/ground assist launch, the non-rotating Skyhook (component three), and the type of propulsion system being used on the launch vehicle (component four). If it is an all-rocket powered launch vehicle with an entry level length Skyhook, the best choice for the initial launch vehicle will be a reusable first stage/expendable upper stage configuration. If air-launched, the launch vehicle will use a winged horizontal landing first stage, if ground accelerator launched on a steep enough slope so that wings are not needed, a vertical landing first stage like the ones being developed by SpaceX and Blue Origin will be best.

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As the length of the Skyhook is increased and the velocity reduction for the launch vehicle increases, it will become possible to combine the expendable upper stage of the launch vehicle with the spacecraft. This will make the launch vehicle into a fully reusable two stage to Skyhook launch system which will further reduce the cost of getting to orbit. As the Skyhook continues to be made longer and the velocity reduction continues to increase, it will eventually become possible to make the launch vehicle into a single stage to Skyhook vehicle. This will reduce the cost of getting into space even more.

Component Three The third key component in a combination launch system is a non-rotating Skyhook (see section 3.2.1 on page 7). A non-rotating Skyhook is a vertically oriented cable that is attached to a space station. Since the speed of orbit goes down with increasing altitude, the lower end of the cable is moving at less than orbital velocity for its altitude, and the upper end of the cable is moving faster than orbital velocity for its altitude. The end result is that a launch vehicle arriving at the lower end of the cable does not have to go as fast as it would need to without the Skyhook. This reduced velocity requirement allows the launch vehicle to carry a larger payload which reduces the cost of getting to orbit.

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A non-rotating Skyhook works on the same principles as an Earth surface to geostationary orbit Space Elevator. The main differences between them are that the Skyhook is much shorter, it does not reach down to the surface of the Earth, and it can be affordably built with currently existing materials and technology.

Component Four The fourth key component in a combination launch system is a combination air-breathing and rocket motor propulsion system. This works by reducing the amount of oxidizer the launch vehicle needs to carry which makes for a smaller and more affordable launch vehicle. The reduced propellant requirement also increases the payload fraction and thereby reduces the cost to orbit.

There are many ways to make a combination air-breathing and rocket motor propulsion system. They can be rocket/ramjet combinations, ducted rocket/ramjet combinations, ducted rocket/ramjet/scramjet combinations, and so on. All of them have different costs, different weights, and different performance advantages. Some of them will require extensive development effort, some will not. The one that reduces the cost to orbit the most will depend on the details of all the other components of the combination launch system, the amount of development work required, and the flight rate.

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