Interplanetary spaceflight

Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.

Space probes have been placed into orbit around all the five planets known to the ancients: The first being Venus (Venera 7, 1970), Mars (Mariner 9, 1971), Jupiter (Galileo, 1995), Saturn (Cassini/Huygens, 2004), and most recently Mercury (MESSENGER, March 2011), and have returned data about these bodies and their natural satellites.

The Japanese ion-drive spacecraft Hayabusa in 2005 also orbited the small near-Earth asteroid 25143 Itokawa, landing on it briefly and returning grains of its surface material to Earth.

Another ion-drive mission, Dawn, has orbited the large asteroid Vesta (July 2011 – September 2012) and later moved on to the dwarf planet Ceres, arriving in March 2015.

The American Vision for Space Exploration, originally introduced by U.S. President George W. Bush and put into practice through the Constellation program, had as a long-term goal to eventually send human astronauts to Mars.

But science fiction writers have a fairly good track record in predicting future technologies—for example geosynchronous communications satellites (Arthur C. Clarke) and many aspects of computer technology (Mack Reynolds).

Many science fiction stories feature detailed descriptions of how people could extract minerals from asteroids and energy from sources including orbital solar panels (unhampered by clouds) and the very strong magnetic field of Jupiter.

Some claim that such techniques may be the only way to provide rising standards of living without being stopped by pollution or by depletion of Earth's resources (for example peak oil).

Although various Spaceguard projects monitor the Solar System for objects that might come dangerously close to Earth, current asteroid deflection strategies are crude and untested.

Simply doing this by brute force – accelerating in the shortest route to the destination and then matching the planet's speed – would require an extremely large amount of fuel.

Recent advances in computing have made it possible to exploit many more features of the gravity fields of astronomical bodies and thus calculate even lower-cost trajectories.

The NASA designs were conceived as replacements for the upper stages of the Saturn V launch vehicle, but the tests revealed reliability problems, mainly caused by the vibration and heating involved in running the engines at such high thrust levels.

Political and environmental considerations make it unlikely such an engine will be used in the foreseeable future, since nuclear thermal rockets would be most useful at or near the Earth's surface and the consequences of a malfunction could be disastrous.

NASA's Deep Space One was a very successful test of a prototype ion drive, which fired for a total of 678 days and enabled the probe to run down Comet Borrelly, a feat which would have been impossible for a chemical rocket.

Dawn, the first NASA operational (i.e., non-technology demonstration) mission to use an ion drive for its primary propulsion, successfully orbited the large main-belt asteroids 1 Ceres and 4 Vesta.

A NASA multi-center Technology Applications Assessment Team led from the Johnson Spaceflight Center, has as of January 2011 described "Nautilus-X", a concept study for a multi-mission space exploration vehicle useful for missions beyond low Earth orbit (LEO), of up to 24 months duration for a crew of up to six.

[19][20] Although Nautilus-X is adaptable to a variety of mission-specific propulsion units of various low-thrust, high specific impulse (Isp) designs, nuclear ion-electric drive is shown for illustrative purposes.

It incorporates a reduced-g centrifuge providing artificial gravity for crew health to ameliorate the effects of long-term 0g exposure, and the capability to mitigate the space radiation environment.

Many ordinary spacecraft and satellites also use solar collectors, temperature-control panels and Sun shades as light sails, to make minor corrections to their attitude and orbit without using fuel.

A cycler could combine several roles: habitat (for example it could spin to produce an "artificial gravity" effect), or a mothership (providing life support for the crews of smaller spacecraft which hitch a ride on it).

[39][40] SpaceX CEO Elon Musk estimates that the reusability capability alone, on both the launch vehicle and the spacecraft associated with the Starship will reduce overall system costs per tonne delivered to Mars by at least two orders of magnitude over what NASA had previously achieved.

under development, a key part of the system SpaceX has designed for Mars in order to radically decrease the cost of spaceflight to interplanetary destinations is the placement and operation of a physical plant on Mars to handle production and storage of the propellant components necessary to launch and fly the Starships back to Earth, or perhaps to increase the mass that can be transported onward to destinations in the outer Solar System.

Non-terrestrial sources of energy and materials are mostly a lot further away, but most would not require lifting out of a strong gravity field and therefore should be much cheaper to use in space in the long term.

And ammonia could be a valuable feedstock for producing fertilizers to be used in the vegetable gardens of orbital and planetary bases, reducing the need to lift food to them from Earth.

A breathable atmosphere of at least 35 kPa (5.1 psi) must be maintained, with adequate amounts of oxygen, nitrogen, and controlled levels of carbon dioxide, trace gases and water vapor.

[49] Scientists of Russian Academy of Sciences are searching for methods of reducing the risk of radiation-induced cancer in preparation for the mission to Mars.

They consider as one of the options a life support system generating drinking water with low content of deuterium (a stable isotope of hydrogen) to be consumed by the crew members.

Hence, deuterium-free drinking water is considered to have the potential of lowering the risk of cancer caused by extreme radiation exposure of the Martian crew.

[50][51] In addition, coronal mass ejections from the Sun are highly dangerous, and are fatal within a very short timescale to humans unless they are protected by massive shielding.

[52][53][54][55][56][57][58] Any major failure to a spacecraft en route is likely to be fatal, and even a minor one could have dangerous results if not repaired quickly, something difficult to accomplish in open space.