A Future in Space
In many ways, the idea of deep-space exploration in the 20th century remained the stuff of science fiction rather than the reality of engineering. For this reason, the overall discussion of space developments has deliberately tried to remain pragmatic about what might realistically be achieved in the next 100 years. This said, it is believed that space developments will be the subject of much more attention in the 21st century, although possibly increasingly driven by commercial considerations.
In part, the problems associated with the propulsion systems needed for launch, in-space transportation and landing on distant worlds can still only be solved by 20th century technology, i.e. chemical rockets, albeit improved by 21st century engineering innovations that may dramatically help with cost reduction by making these systems reusable. However, while present-day propulsion systems may not be ideal, they have proved themselves capable of taking the next step towards ever deeper space missions, although subject to one key caveat, i.e. onboard fuel. To-date, the scope of deep-space missions has been limited by the need to carry propellants onboard the spacecraft, although the description of the SpaceX Mars mission might suggest a possible solution by producing the propellent needed for the return journey in-situ on the surface of Mars.
However, over the long-term, research now suggests that the necessary materials may also be collected from other objects in space, i.e. asteroids, which could reduce the mass of the propellant needed to be launched from Earth and carried throughout the mission. If such processes can be developed, then the continued use of chemical rockets may not be a major stumbling block to deeper manned space mission in the near future, although the power requirements to run an increasing number of complex processes, e.g. Advanced Life Support (ALS) systems, might still be questioned.
But surely solar panels can provide the power for further space missions?
The quantity of energy received at some radial distance from the Sun is driven by an inverse square law. In Earth orbit, at 1AU from the Sun, about 1400 watts of power can be received per square metre (W/m2), although the current efficiency (20%) of solar panels might reduce this figure to 250-300W/m2. Of course, deeper space missions to Saturn, which is nearly 10AU from the Sun, would only receive about 14W/m2, which would also be reduced by the 20% efficiency to possibly less than 3W/m2. On the Juno mission, a 45m2 solar array produced 9.6kW or 213W/m2 at 1AU, but only 414watts or 9.2W/m2 at 5.5AU. We might also have to factor in that solar panel efficiency may decrease with time, especially if exposed to strong solar radiations and cosmic rays, plus be subject to a loss of power in the shadow of any celestial body, e.g. planets and moons, such that significant energy storage might be required.
Note: Today, the largest structure in space is the International Space Station (ISS), which can house between 3-6 people and uses about 80kW for normal functions. This power is provided by huge array of solar panels covering some 2400m2, which would have to be extended by the inverse square law, if operated further from the Sun. If we divide 80kW by 6 people, i.e. 13.3kW, it might be seen as comparable to the power usage per capita in the US. Therefore, if some future space-station were positioned at Saturn with a crew of 60, the solar panels would need to be increased by a factor of 1000 to 2,400,000m2. So, while solar panels may provide the power solution for initial exploration, it is unclear that they are necessarily capable of supporting any industrial expansion into space along with an increasing human population.
What other alternatives might be considered?
While energy can be sourced in many forms, we might restrict the alternatives to those that can most readily produce the electrical energy needed to power all the onboard systems. On Earth, electricity is usually produced within centralised power stations by electro-mechanical generators, primarily driven by heat fuelled by fossil combustion or nuclear fission, although other means such hydro-electric and wind turbines are used along with solar photovoltaics and geothermal power – see Energy Developments for further details. However, we might immediately recognise that some of these options are not realistic onboard a spacecraft, where power will be critical to maintain ALS systems and other essential processes. As a generalisation, the power systems onboard present-day spacecraft make-up about 30% of its mass sub-divided into three distinct facets of operation:
- Power generation
- Energy storage
- Power management and distribution
Ideally, these systems will need to have low mass, long life and high energy-density, as well as being extremely reliable. However, in the future, these systems will not only have to provide the energy needs for all onboard systems for the duration of the mission, possibly measured in decades, but become increasingly capable of being deployed to support developing commercial and industrial processes, both in space and ground stations. If we extrapolate this expansion process into the future, we might envisage a space-station or ground station growing in size and housing thousands of people on a permanent basis. By way of an example, if we take the figure of 10kW per capita, then a Mars station with a population of 1000 will a require a 1MW power source, but where the average wattage from the Sun falls from 1362W/m2 to 490W/m2 due to the inverse square law. Based on today’s technology, this would require about 22,000m2 of solar panels, i.e. approaching 40,000 in number, and a considerable energy storage facility for backup.
Note: At this stage, it is unclear that there is an obvious short-term solution to the future power requirements of large space-stations and extended ground-stations encompassing both commercial and industrial operation as well as large human populations. However, it might be speculated that nuclear power plants combined with rechargeable fuel cells may become the most obvious path of development.
Having alluded to some future space developments, while still highlighting the many problems to be overcome, we might now indulge a little more in far-reaching speculation. However, while acknowledging the speculative nature of the following discussion, the following video might be initially referenced as it suggests that some present-day companies are already working on some of these ideas – see Three Companies Developing Game Changing Technologies. However, while accepting the direction of progress, some caution is still required in assessing the timescales between deployable technology and, as yet, unachieved visions of some possible science future.
Note: It will be argued that ground-stations on other worlds may not be the preferred choice for long-term human habitats, but rather space-stations in orbit or simply collocated at some convenient point in space as a way-station to deeper space missions. While it is accepted that ground stations will be developed, it is suggested that these stations might be likened to commercial oil-rigs, where a crew goes to work rather than to live permanently. The main arguments for this prediction is cost-effectiveness and the simulation of gravity necessary for longer-term human well-being.
The previous video made reference to the plans of the Gateway Foundation to build a space-port, which present-day technology might envisage as being something closer to the science fiction of Kubrick’s film 2001: A Space Odyssey . This rotating spaceport would be 488 metres wide and 86 metres deep and support a crew of 150 and 1250 guests. By way of comparison, the size of the present-day ISS space-station is shown in the inset, where most of this size is taken up by the 45m2 of solar panels. While the details of this space-port design are not the focus of this discussion, we might use it as a yardstick by which to judge how this science future may be realised and why.
Why space-stations and not ground-stations?
It has been suggested that space-stations, rather than ground-stations on the Moon and Mars, might be the preferred option for long-term human habitats. This suggestion is based on two primary considerations, i.e. cost and gravity simulation. While no estimate of the total mass of the gateway space-port (GSP) can be found, we might use the known mass of the ISS at 400,000kg as a comparative guide in the scaled diagram above. If we assume that the GSP spaceport is, at least, 1000 times more massive than the ISS and the biggest launch vehicle, i.e. the BFR, has a lift capacity of 150,000kg, then we might estimate the need for some 3000 launches just to get the materials into space, let alone all the ancillary equipment needed to build it. However, while lifting all this material into space might appear a daunting task, it is technically feasible given enough time and money, but raises the first objection to ground-stations.
Why add to the cost and complexity by moving all the materials onto the surface of the Moon or Mars?
While some ground-stations may be required for commercial and industrial missions, it has been argued that over time most of the operational tasks could be performed by AI-telepresence robotic systems overseen from a geostationary orbiting space-station. If so, the costly ALS systems required for human habitation could be confined to the space-station and avoid the cost of lifting all the materials required down to the surface. In addition, an orbiting space-station could support multiple ground-station operations, while the crew could enjoy much better living facilities, inclusive of Earth-like gravity to mitigate the known health problems of extended time in zero-gravity. At this time, any crew on the ground-stations on the Moon or Mars would have to cope with 11% and 38% Earth gravity respectively, which a rotating space-station could negate. Artificial gravity onboard a rotating space-station might be conceived in terms of an inertial reaction to the centripetal acceleration that acts on a body in circular motion, which can be quantified in terms of four parameters:
- Radius [r] from the centre of rotation
- Angular velocity [ω] or spin rate.
- Tangential velocity [v] or rim speed.
- Centripetal acceleration, where [a=g] is the gravity factor.
We might initially quantify these parameters in terms of Newton’s 2nd law and show the relationship between the tangential velocity [v] and the angular velocity [ω]:
However, our primary interest is the relationship between the angular velocity [ω] and the acceleration [a], which we want to quantify in terms of [g=9.81m/s2], such that we can equate the parameters to Earth’s gravity.
Now there are obviously many solutions to  and  that can produce the required simulation of Earth’s gravity [gE=9.81m/s2], which translate to very different values of angular velocity [ω] that may not meet the overall requirements of an acceptable simulation of gravity that humans can survive long-term. However, the first solution highlighted in the table below corresponds to revolutions per minute falling below a value of 2, which is consider the maximum permissible before the rotation becomes problematic to long-term human habitation.
From  we might see that [g] is directly proportional to the radius [r] and while the table shows a consistent simulation of [1g=9.81m/s2], the corresponding angular velocity [ω] differs by a factor of 30 over the radius range shown. However, experiments suggest that the human physiology is stressed when the revs/min is too high. If so, the table suggests the need for a minimum radius of 250 metres, which would correspond to an angular velocity of [ω=0.198 rad/sec] or 1.892 revolutions/minute. While this dimension is somewhat larger than the envisaged Gateway spaceport, the centrifugal simulation of gravity might still be achieved with a simpler rotating space-station, which only has a limited number of habitat cabins attached to rotating arms. In this design, the rotating arms would be part of a spaceship with a propulsion system that could move between different destination, which might also make it far more cost effective, if the costs could be amortised over multiple missions linked to commercial or industrial enterprises.
So how might such developments come to affect the human ecosystem?
As implied, the future of space developments in the 21st century might become increasingly driven by the commercial or industrial rationale to return a profit rather than the more idealistic notion of ‘boldly going where no one has gone before’ . However, there is possibly a more profound implication that will emerge over a longer period of time, which might be seen as analogous to the initial colonisation of the Americas by early British, French and Spanish expeditions. While these colonies initially started out being tied to the dictates of some far away authority, they ultimately sought to independently govern themselves as autonomous communities. In this context, we might envisage a time when space-stations might grow in scope to resemble an autonomous ‘city-state’ that is no longer dependent on its home planet, i.e. Earth, for resources and may therefore seek to independently determine its own future, irrespective of who originally financed the development. If you follow this line of speculation, it might be realised that space-cities might develop their own form of economic and political governance, such that their social norms may also start to diverge from Earth-bound society. However, there is another factor that might be particularly unique to the development of future space-cities in which people eventually live long-term. While this factor might first be introduced as a form of ‘natural selection’, we might realise that people who choose to live their lives in some future space-city may be selected on the basis of certain abilities and traits, e.g. intelligence and physiology. If so, the gene pool within these future space-cities might be statistically quite different from the outset and may only diverge further from the norms of Earth-bound society, if they accept some of the ideas outlined in terms of Hybrid-AI; the implication of which was outlined in terms of the earlier discussion entitled ‘The Genetic Endgame’ .
Note: In many respect, the future of space exploration and associated developments to facilitate permanent off-world settlements have potential implications that extend far beyond the technology evolutions outlined. Possibly more than any other technology discussed, a potential form of ‘natural selection’ may take place that separates different section of human society in terms of ability, which may become established in a localised gene pool, such as a space-city with a relatively small population. However, it is clear that all the technology developments in this section have the potential to change human society in very profound ways, which will now be taken up in the next discussion entitled ‘