The Lunar Gateway is a Bad Idea
As exciting as it is for Canada to lend a hand (or rather, robotic arm) to the human space exploration effort, the Lunar Gateway project is another dead end. There is no need for one, and it makes no financial nor scientific sense.
The Lunar Gateway, initially proposed by NASA, is a small space station that would orbit the Moon and support operations in cislunar space. On February 28, Canadian Prime Minister Justin Trudeau announced that Canada would be the first nation to formally commit to the project. However, if the goal is to extend the human reach in space, the resources required would be better invested elsewhere, such as on actually landing on the Moon.
Firstly, there is no special science planned for the Lunar Gateway that cannot instead be conducted in Earth orbit (such as on the International Space Station), on the lunar surface, or with a satellite. It also provides few financial, safety, and engineering advantages over these locations.
On the lunar surface, astronauts have access to water ice in shadowed areas, regolith to shield themselves from radiation and to use as a construction material, and some gravity. None of these are present in orbit.
On the note of radiation, the Lunar Gateway will be situated outside of the Earth’s magnetic field. The magnetic field attenuates and deflects cosmic and solar radiation, reducing the exposure of astronauts and life on Earth. Inhabitants of the Lunar Gateway will be chronically exposed to the full radiation onslaught. An unprotected astronaut on the Moon’s surface would receive a similar dosage, but astronauts could cover their buildings in regolith or simply live underground to avoid this. If any radiation shielding is planned for the Lunar Gateway, it must be transported from Earth.
On the lunar surface, utilization of local resources, the presence of solid ground, and gravity would allow inhabitants to build more extensive surface facilities than would be feasible for in-orbit assembly. A space station will be cramped by necessity, while a surface base could be as large as a geological formation, such as a natural lava tube.
In general, it is far easier to build on a planet or moon than in orbit. While the science of construction on terra firma has been advancing since the first buildings sprang up in Mesopotamia, in-orbit construction is still in its infancy and is highly expensive. The International Space Station’s assembly began in 1998 and is still in progress; so far, it has cost over $150 billion and will continue to rise. Note that it orbits a mere 400 kilometres above the Earth, and that travel to and from it takes only a few hours.
Attempting to assemble a space station around the moon, nearly 400,000 kilometres and three days from Earth, while in-space assembly techniques are still in their infancy, is madness. Transferring the components to lunar orbit from Earth demands substantially more energy, requiring more powerful rockets and higher mission complexity. This dramatically increases the financial expense, risk, and danger; components may fail to be delivered, docking maneuvers may miss, and accidents become drastically more hazardous due to the distance from Earth.
Take for example, the Mir space station fire of 1997, which fortunately, was extinguished successfully. Or to take another example from Mir the same year, when a cargo spacecraft crashed into it, causing a module to depressurize and forcing the astronauts to seal it off. A more recent incident on the International Space Station is the failure of the carbon dioxide removal system in 2010, which could have caused the astronauts to suffocate. Fortunately, no-one was injured or killed in these accidents. But imagine if these incidents had escalated out of control, caused severe injury, or irreparably damaged a critical component, and if safety was half a week away. These risks would be lower on the lunar surface than in orbit, where shielding from radiation and debris is easier, gravity holds objects down and makes fire easier to control, and mineral resources are easy to access.
One cited purpose of the project is to study the effects of cosmic and solar radiation on astronauts outside of the Earth’s protective magnetic field, in preparation for deep-space expeditions to Mars and beyond. There is little benefit to conducting such experiments in lunar orbit. Radiation studies can be conducted on the lunar surface on astronauts in intentionally unshielded habitats (the ethics of which are left as an exercise to the reader), while any zero-gravity experiments can be conducted on the International Space Station. Additionally, astronauts on or near the moon will be at least three days from help in the absence of nuclear propulsion systems. Better that emergencies occur on a well-equipped surface base than a cramped orbital station.
Additionally, any space station or satellite requires occasional maneuvers to prevent its orbit from decay. This is a process known as station-keeping. The International Space Station accomplishes this by spacecraft firing their engines for brief periods of time while docked to it, such as the Russian Soyuz spacecraft. For this purpose, the Lunar Gateway will be equipped with a battery of high-power ion engines, officially known as the Advanced Electric Propulsion System (AEPS). The financial expense includes:
- The engine development cost.
- The cost of transporting the hardware and propellant (in this case, xenon) to lunar orbit. The required hardware includes the solar arrays required to supply power to the engines and the thermal radiators required to keep them cool.
- Maintenance and propellant replenishment costs.
Any long-term space station must account for these costs or risk drifting out of its planned orbit. The upkeep is further compounded as the station is far from Earth, and the Moon will not have the industrial base required to maintain space stations for the foreseeable future. At present, the benefits of a station in lunar orbit cannot justify the cost.
A space station is also more thermally vulnerable than a surface base. The International Space Station must reject the heat generated by astronauts and equipment into space, or overheat. This is accomplished by an ammonia cooling loop that picks up heat from inside the station, flows through radiator panels, and loses the heat to space via radiation. Radiation is the least effective method of heat rejection compared to convection and conduction, because the latter two use matter as a medium to transport heat. As space is a vacuum, only radiation is a viable thermal management technique, making cooling difficult.
Cooling system malfunctions are extremely dangerous, as demonstrated by close calls on the International Space Station in 2007, 2012, and 2013; the ammonia cooling loop sprang a leak, bleeding coolant into space and endangering the thermal management system. If the system had been allowed to continue losing coolant, the station would have eventually become too hot to be habitable. A surface base can more effectively manage thermal loading, because it can reject heat directly into the ground. This is validated by the research of York et. al. at Harvard University, which indicates that the temperature inside lunar lava tubes is as low as -20 °C.
Humans subjected directly to the vacuum of space are often depicted as freezing instantly in (poor) science-fiction films. In real life, a human is much more likely to stay warm, needing instead to worry about asphyxiation and severe sunburns. To drive this point home, vacuums are widely used to prevent heat loss, such as in Thermos and Dewar flasks, and anything in space is surrounded by a near-perfect one.
One potential advantage of a space station is that its orbit can keep it in continual sunlight and line-of-sight to Earth. Conversely, a lunar surface base may be in darkness for weeks at a time. This can be solved by situating initial bases at the poles. At the poles, there are peaks that are illuminated by the Sun for up to 94% of the year, as discovered by the Lunar Reconnaissance Orbiter. Electrical generation equipment could be situated on peaks such as these, providing near-constant power. An additional advantage is that there are also areas that are in permanent shadow, in which exist deposits of water ice — for humans in space, a substance infinitely more precious than gold.
While there may be some benefit to using the Lunar Gateway as a staging point for lunar landers, it is likely to be insignificant. Cislunar traffic is unlikely to be high for the foreseeable future, especially given the tight-fisted attitude of world governments to allocating funds to space exploration. Mission architectures similar to that of the Apollo program remain the simplest, most feasible, most financially effective means of transporting humans and cargo between the Earth and the Moon. In essence, a lander and an orbiter travel from Earth, the lander travels between the surface and orbit, and the orbiter returns to Earth anything that needs to be returned. An orbital intermediary is simply unnecessary.
Another proposed application of the Lunar Gateway is as a high-speed communications relay. This may have been defensible in the pre-transistor times of von Braun, when a small army of technicians would have been required to maintain the vacuum tubes, necessitating human proximity. However, with the advent of solid-state electronics, a constellation of unmanned communications satellites would achieve the same purpose with far greater effectiveness and lower cost.
Yet another proposed application is using the Lunar Gateway to control robots on the surface and for telepresence. Again, there is no reason this cannot be done from Earth or from a lunar surface base. Due to the limited speed of light, a message sent to the moon will take just over a second to arrive, then the response will take just over a second to return. As a result, robots controlled from Earth will experience a communications lag of about two seconds. However, it is far simpler and cheaper to simply develop protocols to work with or to automate around the time lag than to build a fantastic multi-billion dollar station in Lunar orbit. Two seconds may be too long a lag for an interplanetary game of Fortnite, but it is hardly so long that it impedes effective robot operation for scientific, engineering, and maintenance purposes.
And again, the time-lag would be reduced to negligible levels by operation from a Lunar surface base with the presence of communications satellites.
Finally, exploration of the moon is seen as a useful stepping stone to Mars by reducing the energy required to leave the Earth’s gravity and by acting as a refueling depot. From an astrodynamics perspective, this is senseless.
The energy required to make a maneuver in space is measured by a quantity called delta-v; the required change in spacecraft velocity. The greater the delta-v, the more propellant is required for the maneuver. For instance, reaching Earth orbit from the surface requires about 9 km/s of delta-v. The delta-v requirements of a mission determine how much propellant a spacecraft must carry and how well its engines must perform.
An interplanetary mission is typically carried out in three main stages:
- Injection burn: The spacecraft fires its engines to enter a trajectory that will encounter its destination (e.g. Mars).
- Coast: The spacecraft’s engines shut down and it coasts to its destination. Any gravitational slingshots would occur in this stage.
- Insertion burn: The spacecraft fires its engines to slow down, or it may instead decelerate using the destination’s atmosphere (see aerobraking).
A transfer from Earth orbit to Martian orbit requires a minimum delta-v of 3.8 km/s. This assumes that the spacecraft slows down at its destination by flying through the upper layers of the Martian atmosphere; a technique known as aerobraking. Essentially, the spacecraft slows down using air resistance instead of its engines, thereby saving propellant. This method has been used to successfully deliver probes into orbit around planets with atmospheres, such as the Mars Reconnaissance Orbiter in 2006.
If instead the spacecraft starts in lunar orbit, fires its engines to go to Mars, then aerobrakes to Martian orbit, it requires a minimum delta-v of only 2.9 km/s — a savings of 24%. However, this neglects the fact that any payload travelling from the Moon to Mars must first travel from the Earth to the Moon. The Moon has practically no atmosphere with which to aerobrake, so any braking must be accomplished by firing the spacecraft’s engines. Because of this, a transfer from Earth to lunar orbit requires 4.8 km/s of delta-v; a spacecraft needs more fuel to travel to the Moon than it does to reach Mars!
As a result, the total minimum delta-v to send a spacecraft to the Moon, then to Mars, is an absurd 7.7 km/s, which is 102% more energy than is needed to simply send it directly to Mars! In other words, even if there were tanks full of free fuel orbiting the Moon, it would still be less expensive, less complex, and faster to ignore them and go directly to Mars!
The only way to take advantage of the delta-v savings is if part or all of the spacecraft were assembled on the Moon using lunar resources. However, this is likely to be much more expensive and difficult than assembling it on Earth, given the difficulties of operating in a hostile environment without Earth’s industrial base and supply chains. Furthermore, the infrastructure required to mine lunar resources to manufacture propellant and spacecraft must first be sent to the Moon and built before this can happen, increasing the expense yet further. The idea that the Moon is a handy stop-over on the way to Mars and the rest of the Solar System is a complete farce; it makes nothing easier and increases the risk, danger, and cost astronomically.
In summary, the Lunar Gateway project is — as it currently stands — unwise.
The following are projects that will provide far greater scientific and technological return on investment. These will contribute directly to the goal of extending the human reach in space as well as providing potential benefits for life on Earth. These are keystone technologies, for without these, humans will never travel farther from Earth than the Moon.
Firstly, artificial gravity. Zero gravity has been shown through extended stays on Mir and the International Space Station to be highly detrimental to astronaut health, with effects ranging from musculoskeletal degeneration to kidney stones. Astronauts returning from long stays on the International Space Station are often helpless on landing and must be carried out of the landing capsule, because their muscles have wasted away from disuse. This is a luxury that will not be available on Mars. By spinning the spacecraft to generate centrifugal force and simulate gravity, these effects can be mitigated. Although this is not real gravity, it will prevent the detrimental effects associated with zero-gravity. This is similar to the way that one can fill a bucket with water and swing it over one’s head without losing a drop.
This concept can be tested in Earth orbit with an existing spacecraft, such as the SpaceX Dragon or Russian Soyuz capsule. It can be attached with a tether to a dead weight, such as a spent booster rocket. Then, using the maneuvering thrusters, the assembly can be spun and the astronauts inside the capsule will experience pseudo-gravity.
A related, important area of research is the response of the human body to prolonged periods of fractional gravity: The effects of zero and Earth gravity are well known, but nothing is known about what happens in between. The data collected from long-term fractional-gravity experiments is vital for understanding the health effects on explorers and colonists to other worlds. Such experiments could easily be conducted in Earth orbit with the aforementioned artificial-gravity apparatus. Mars has 38% the gravity of Earth, and the Moon 17% — will human bones and muscles still waste away? Will our intrepid Martian colonists be able to visit their family on Earth? We do not know, and we must find out.
Secondly, Mars sample-return missions. A probe is sent to Mars, collects samples, and returns them to Earth. The portion that returns to Earth may manufacture the necessary fuel for the homeward-bound leg using the Martian atmosphere, reducing mission costs. This is a technique called In-Situ Resource Utilization (ISRU).
ISRU research is planned for the Mars 2020 rover, which will carry the MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment) scientific module, which will attempt to produce carbon monoxide and oxygen from the Martian atmosphere. This is a potentially viable fuel combination. Alternatively, the probe may carry an on-board hydrogen supply, which it can combine with the Martian atmosphere to produce methane and oxygen through the Sabatier reaction — another potentially viable fuel combination.
A manned Mars mission would be likely to use a similar mission architecture of carrying humans and supplies to the surface, producing fuel with local resources, then returning humans and samples to Earth. A Mars sample-return mission would allow testing of this architecture in miniature.
Furthermore, probes such as Curiosity, Opportunity, and Viking relied on on-board robotic science packages to analyze samples of Mars. The analytical capacity of these probes is severely limited by the mass budget of the boosters that send them to Mars, limiting scientific return. However, returning the samples to Earth to be subjected to the full fury of terrestrial laboratories and the expert eyes of top human geologists would remove all these limits. We would learn more about how Mars formed, how the Earth formed, how the Solar System formed, how geological processes work both on Earth and on other planets, potentially about abiogenesis, and about what astronauts can expect when they reach Mars.
It is worth noting that a mere three years separated the first landing of a probe on the Moon and the first bootprint, and that there were no successful Lunar sample-return missions before Apollo 11.
Thirdly, closed ecological life-support systems (CELSS). Humans travelling much farther away than the Moon, such as to Mars, the asteroids, or the outer planets, will be months or years away from resupply. Recycling all air, water, and waste is vital, whether on a spacecraft or in a Lunar base. Such systems do not even have to be developed in space — they can be tested in laboratories on Earth, then validated on the International Space Station, reducing resupply costs and improving resilience in the event of malfunctions and emergencies.
Fourthly, space nuclear power. Solar panels will be able to supply power on Mars, but are liable to becoming disabled by dirt, weather, or simply, nightfall. Furthermore, solar panels become useless beyond Jupiter, as the Sun simply becomes too dim. Additionally, bases on the Moon not situated near the poles will need to operate without the Sun for weeks at at time. Nuclear reactors will provide astronauts and their equipment with a powerful, reliable source of energy. NASA has made great strides in the development of lightweight space nuclear reactors, so this technology is well on its way to maturity.
Nuclear-powered rockets would also make travel in space easier by reducing propellant requirements, although this is not vital for the initial expeditions to the Moon or Mars. It is worth noting that the United States has successfully tested nuclear rocket engines through the NERVA (Nuclear Engine for Rocket Vehicle Application) program as early as the 1960s — it is hardly a new technology.
In conclusion, the Lunar Gateway is a pointless flight of fancy that will fail before it begins, because it is not motivated by sound engineering judgement. It is a poor investment of resources and will act only to distract from the ultimate goals of permanent human presence on the Moon, Mars, and beyond.
The space agencies of the United States and Canada should focus on landing boots on the Moon and sending expeditions to Mars; directed, focused efforts such as those will open the door for humankind to expand into the cosmos, not aimless jaywalking in cislunar space. Greater returns — and dare I say, glory — will come from these than from a space station in orbit around it.
The success of the Apollo program shows that the best route is often the simplest, most direct one; it needed no space stations for in-orbit assembly, nor did it require the construction of high-capital space infrastructure. Those will come later, once space travel becomes as routine as air flight.
Roving Mars (Steve Squyres): A spirited, detailed account of the experiences of the Principal Investigator for the Spirit and Opportunity rovers. It delves deeply into both the technical and human demands of such a mission.
The Case for Mars (Robert Zubrin): A proposal for the Mars Direct mission architecture: A cost-effective, minimum-risk, maximum-return human mission to Mars, with a vision for future exploration, permanent presence, colonization, and terraforming. For these reasons, Mars Direct has become NASA’s reference mission architecture for planned Martian expeditions.