Are space elevators realistic?

In 1895, Konstantin Tsiolkovsky, the grandfather of astronautics, proposed for the first time the concept of space elevator. Since that time, there was considerable skepticism towards this concept. However in December 2013, the International Academy of Astronautics “Concludes Space Elevators Seem Feasible” as described in the book “Space Elevators: An Assessment of the Technological Feasibility and the Way Forward”.

Will we ever see an astronaut exploring space launched by a space elevator?

Alternative launching system

A space elevator is a mass transport system to reach space. The concept consists of a very long cable attached near the equator of the planet and extended into space beyond geostationary orbit. Most current concepts are proposed for Earth implementation but it could take place on another planet. This alternative to large rockets would be an asset for space exploration.

In 2003, Dr. Bradley C. Edwards established guidelines for the construction in his book “The Space Elevator: A Revolutionary Earth-to-Space Transportation System”. Most of designs include four basic elements:

  • Anchor station: an anchor that could be on mobile a platform in the ocean or static on the top of a mountain. The location will be preferably near the equator in order to benefit of natural Earth velocity.
  • Ribbon: it has to support a colossal tension which varies with the altitude and a large weight (its own weight and the climber). It is a guide for the climber.
  • Climber: in that case, the cable doesn’t pull the cabin, it must climb by itself. It could carry payloads and crew to space for Earth orbit or for further space destinations. A good velocity is 200 km/h which means a 180 hours (<8 days) trip to geosynchronous orbit (36 000km).
  •  Counterweight: it could be a space rock or a specific station. Earth’s rotation creates upward centrifugal force on the counterweight. Cargo carried from the surface would allowed to be launched into interplanetary space thanks to the considerable velocity gained relatively to the Earth.
Space elevtor mechanics - Credits: unkwon

Space elevtor mechanics – Credits: unknown

Once the expensive job of building the elevator is completed, an indefinite number of loads can be transported into orbit at reduced cost.

This machine could carry payload and human into space, up to geostationary orbit and beyond. The ascension would be less stressful for the human body, safer and cheaper on a routine basis. It is a nice opportunity to make space more accessible to a larger amount of people.

The cost of a space elevator

In his book Leaving Earth (2013), Andrew Rader provides some numbers about big building projects:

“Other notable megaprojects in this price range include (2013 dollars): the Manhattan project ($26 billion), the English Channel tunnel ($17 billion), the Boston “Big Dig” tunnel system ($15 billion), the Arabian canal ($11 billion), the John F. Kennedy airport expansion ($10 billion), the Yucca mountain nuclear waste depository ($9 billion), and the Atlanta-Jackson airport expansion ($9 billion).”

Current estimations start from US$6 to US$20 billion for building one space elevator from Earth’s equator to geostationary orbit. This prices includes: in orbit construction, ribbon, power beaming stations, climbers, anchor station, tracking facilities, insurance, testing and contingency. This budget fits into the range of similar super structures and should provide some revenue.

Currently, the cost for sending a cargo to the geostationary orbit with a thermal rocket is around US$20 000/kg and the cost to send a cargo with a space elevator would be around US$250/kg (Edwards). Most of the price covers the power supply, the maintenance and the operating. It is not crazy to imagine a return on investment within 10 years.

The challenge

Space elevator - Crédits: unkwon

Space elevator – Crédits: unknown

Currently, there are many technologic challenges to build a space elevator. It might be difficult to see such a structure in a near future. Scientists and engineers should fix some remaining problems:

  • The construction of the ribbon: currently, there is not any existing material with a sufficient high tensile strength and with low density capable to comply with the structure requirements yet.
  • Prevent the swing: the ribbon and the climber will undergo some swing generated by the gravitational effect from the Moon and the Sun. It will also suffer from the Coriolis Effect (problem also evocated in the article about artificial gravity).
  • Risk of collision: that will have an impact on the air traffic. Plus, there is a risk of impact with a space object (satellites, debris, meteorites, …)
  • Environmental damage: the system will suffer from corrosion and radiation.

All those problems will jeopardize the total integrity of the space elevator. However, many researches are conducted all around the world about those topics. Astronauts will not escape from the Earth’s gravity via a space elevator tomorrow but we prefer to believe that it’s remain possible.

Next big conference about space elevators takes place in Seattle (USA), August 22-24, 2014 – ISEC Space Elevator Conference

Space elevator and fiction

Space elevators are also very popular in fiction. Sci-Fi novels, fairy tails, anime, manga and comics are fond of crazy technologies and often precursors of innovation: Jules Verne and Hergé went to the Moon a long time before the NASA. Star Trek’s TOS communicator has been inspiration for the first handheld mobile phone. It has also a large place in futuristic games like Syndicate Wars, Civilization IV and, Halo. However, it is underrepresented in TV series and movies: Star Trek and Doctor Who save the situation.

Because we are all Born For Space!

Nuclear Propulsion for Human Spaceflight

Is nuclear the future? (Source: NASA)

Is nuclear the future? Credit: NASA)

We have sent spacecraft to other planets using traditional chemical rocketry (technique briefly explained in our article here), however this requires an amount of time which is not feasible for human space flight. In order to advance humans to other planets we need to reduce the travel time so that we minimize the exposure to radiation, bone density loss and other adverse effects of space flight. A number of solutions to chemical rocketry have been proposed including solar sails, warp drives, and matter-antimatter engines. Based on current technology it appears that nuclear is the most feasible for reducing spaceflight times within the solar system to allow humans to travel further faster.

Nuclear Thermal Rockets

Nuclear energy is not a new concept to the space industry and has been around longer than you may expect. The Viking missions to Mars in the 1970s used landers which were powered by Radioisotope Thermoelectric Generators (RTGs). Nuclear Thermal Rockets (NTRs) could be a solution to the transport of humans to other celestial bodies in reasonable time frames. Liquid hydrogen is a common type of NTR which has the potential to have two times the specific impulse (efficiency) of chemical rockets.

Schematic of a NTR (Source: Stanford University)

Schematic of a NTR – Credit: Stanford University

In NTRs usually liquid hydrogen is heated through a fission reaction to expand through a nozzle, producing thrust to propel the rocket, and the astronauts on board.  Due to the thrust capability of NTRs they take up less space on the rocket and therefore are capable of carrying a large payload. There are three main types of NTRs; solid core, liquid core, and gas core. The solid core is the simplest of the three and is the only one that has ever been built. Testing of NTRs has only occurred on the ground and no tests in space have been conducted. Since some of the cryogenic hydrogen may not be used for days or weeks in a long mission they are subject to cryogenic boil-off in space which may reduce the restart capability of the rocket. Although a promising technology issues such as cryogenic storage may prevent us from seeing NTRs get off the ground for a couple of years.

Nuclear Fusion Rockets

Perhaps a more distant source of propulsion for spaceflight may be a nuclear fusion rocket. A nuclear fusion rocket would use the energy generated from nuclei of two or more atoms combining to generate thrust and propel the spacecraft. Nuclear fusion is the same thing that powers our sun and other stars. The sun converts the energy generated from fusion to produce light. Although the nuclear fusion rocket technology has not been completely demonstrated on the ground, scientists at the University of Washington (funded by NASA’s Innovative Advanced Concepts Program) have demonstrated fusion using plasma, compression and a magnetic field which seems to be a step in the right direction.

For further information visit:

  • NASA Innovative Advanced Concepts here.
  • University of Washington website.

Theoretically using nuclear fusion rockets you could make it to Saturn in a matter of months in comparison to the almost 7 years it took the Cassini spacecraft to enter Saturn’s orbit. If this technology succeeds the future of human spaceflight would look very different!

Because we are all Born For Space!

Artificial gravity through a rotating system

Will you miss gravity on your way to Mars?

A long mission to Mars currently requires a long journey on-board of a spaceship. Weightlessness imposes some physiological changes on the human body including: bone loss, cardio-vascular perturbations and, muscles deterioration. It also affects the astronaut’s sense of orientation and consequently can generate a lot of stress.

These clinical changes in the human body could affect the astronaut’s health, affect the crew performance and could potentially jeopardize the mission.

How would the centripetal force help humans in space?

Aside of daily exercise for the crew, it may be possible to generate gravity in space with centripetal force, with a rotating system. The Force felt by the astronaut’s body depends on the rotation rate of the system and the distance of the body from the rotation axis. It is possible to generate various gravity levels and therefore the gravity level on different planets or celestial bodies can be simulated. For example, the astronaut could experience the gravity level of the Moon, Mars or Earth.

Centripetal Force - In the scenario , the body feel more gravity on the legs than on the head.

Centripetal Force – In this scenario , the body feels more gravity on legs than on the head.

The artificial gravity generated by rotation has two major disadvantages. Firstly, depending on the configuration of the rotating system, some parts of the astronaut’s body are exposed differently to the gravity. Secondly, the Coriolis Effect disturbs astronaut’s movement by affecting trajectories. For example, similar to being on a carousel, it is very difficult to walk “straight”.

The rotating system design must be the result of trading between physiological needs, rotation rate, radius, and Coriolis Effect. The cost also has a significant impact on the design. Ideally a large rotating system will reduce most disadvantages of the rotation, imagine a giant rotating wheel in space like in a Sci-Fi movie. Unfortunately, the construction of such a spacecraft requires a large amount of money and consequently a large amount of energy.

Giant rotating space wheel - SPL/MIT

Giant rotating space wheel – Crédits SPL/MIT

Otherwise, the crew could be exposed periodically to simulated gravity in a smaller devise. In the movie, 2001: A space Odyssey (1968) by Stanley Kubrick, the crew are placed in a rotating wheel while they are sleeping.

Rotating wheel for astronauts 2001: A space Odyssey (1968) by Stanley Kubrick

Rotating wheel for astronauts
2001: A space Odyssey (1968) by Stanley Kubrick

The human body is perfectly adapted to life on Earth. A long journey in space will transform humans in a new way. Could it be a part of natural evolution?

Because we are all Born For Space!