by Simon Gwozdz
In the past thirty years or so, folks across virtually all affluent nations grew accustomed to a comfort that to our forefathers would appear surreal. The ability to hop into an aluminium tube travelling near the speed of sound and arrive on an entirely different continent a few hours later is one of the greatest achievements of humanity, and the foundations of a modern, globalised civilisation.
In 1968’s 2001: A Space Odyssey, Stanley Kubrick and Arthur C. Clarke painted a vision in which sleek, presumably single-staged spaceships deposit passengers on massive, rotating space stations orbiting Earth for transfers to other destinations across the Earth-Moon system, and likely as far out as Mars.
While Kubrick got glass cockpits and in-flight entertainment screens right (both absent even in the early jet age), reality is disappointingly far behind that lofty vision, where space travel is as routine as air travel is today.
This begs the question: why on Earth, decades after our first cinematic mission to Jupiter, are we still baby crawling around Earth’s orbit, and anything remotely as ambitious as the Apollo programme that happened decades ago appears elusive today?
Not All is Doom and Gloom
In 2020 and 2021 despite the chaos of Covid-19, a few private companies launched both suborbital and orbital space missions with commercial passengers onboard.
Virgin Galactic and Blue Origin took their passengers near, or above, the Karman Line – the universally-accepted boundary of space 100km above us. SpaceX fulfilled its first Commercial Crew Programme contract with NASA to become the third entity (after NASA and Roscosmos) to send humans to the International Space Station, and the first commercial company to do so. As a cherry on top, they threw in a pitch-perfect landing of their reusable booster.
Is human civilisation back on track to our cosmic destiny, or are existing solutions simply not good enough to make a run for the nearest, survivable planet, Mars?
Launch is A Different Ballgame
The analogy between the commercialisation of aviation and access to space is a popular one, although misleading. Commercial planes operate in a much more forgiving environment and are vastly more efficient than rockets because they rely on the ambient air to produce both lift and thrust. Rockets need to carry their own source of oxygen to maintain combustion and to produce thrust because reaching orbital velocities in the excess of seven kilometers per second can only be achieved in vacuum.
As a result, the ratio of propellant to payload in a long-range airliner would typically be 40% and 20% respectively; a rocket would be closer to 90% and 1%. It takes a lot of energy to get into orbit, which reduces the payload (cargo) capacity and therefore increases the cost per kilogram.
Ironically, fuel only accounts for about 2% of the costs – the rest is in the rocket and the launch campaign to put one in space. Even with reusable rockets, the reduced capacity and extra maintenance costs have been producing disproportionately low savings in the cost per kilogram since NASA’s Space Shuttle that was meant to capitalise on reusability in the early 1980s.
Rockets wear out much faster than turbojets because of the vastly faster speeds that heat the rocket’s outer coating as well as the higher expulsion rate of extremely hot, oxygen-rich exhaust gases, creating considerable maintenance issues even if the rocket motor is designed for reusability.
The exact refurbishment costs are not publicly known, but the listed price of a reused SpaceX Falcon 9 is only 20% lower than a brand-new one. So far, the booster rocket with the most logged flights has been launched 10 times, compared to the hundreds of cycles a commercial airliner would complete in that timeframe with minimum downtime in between.
Furthermore, rockets and seawater don’t mix very well when dropped down on a parachute – which is why SpaceX uses a propulsive descent technology to recover their first-stages. By using some of the very scarce propellant for that feat, the payload capacity is instantly reduced by around 30%.
Complicating things further, the upper stage section that delivers the payload into orbit isn’t reusable – the intense reentry heat requires a heavy heat shield that would cannibalise any remaining payload capacity. Thus, it’s always built from scratch and unlikely to ever be recovered.
To bring down the launch costs to where passenger space travel is attainable to the middle class, current rockets must be replaced with simple, cost-effective, even expendable ones. Recent advances in hybrid rocket propulsion, which involves a non-explosive combination of liquid oxidiser and solid fuel with half the complexity of heritage technologies, is extremely promising in achieving just that.
We know that launching rockets is hard and expensive, and therefore the payload has to be as lightweight as possible. But that’s just getting into orbit – to get to Mars we will need something even more efficient, packed into a very limited payload mass.
Colonisation of Mars Won’t Work
Travelling through space is different from travelling from one continent to another – even if you get from point A to point B, space will eventually kill you.
Going to Mars the traditional way would take around seven months of exposure to that harsh environment of outer space. The human body isn’t meant for long-term exposure to solar radiation and microgravity; the health impacts like the loss of muscle/bone mass and damage from solar radiation would be potentially unsurvivable. In comparison, astronauts spent a week on Apollo missions to the Moon, while crews on the International Space Station (ISS) are safely within the confines of the Van Allen Belt and can descend to Earth at any time.
Even rigorous exercise routines meant to alleviate loss of muscle and bone mass merely slow the process down. After a prolonged stint at the ISS, returning crews can barely walk for weeks – so one can’t imagine Mars astronauts donning heavy suits to enjoy the red planet’s grand vistas, let alone to conduct any science on the surface. In order to conquer it, we need propulsion that makes Mars a quicker return journey rather than a lengthy, one-way drama.
Long transfer times also mean that all consumables must be brought along, further increasing the launch mass and cost. While water ice is surprisingly abundant in the solar system, you can’t grow food in space without a well-engineered greenhouse which takes months to yield any crops.
A typical human consumes around a ton of food per year, so three tons for a Mars mission using existing systems is a perfectly reasonable estimate. Of course, it’s possible to send supplies by automated ships in advance – but with the current reliability level of rocket systems (many of which have only around 90% success rate), that only increases the possibility of at least one of these missions failing, bloating the budget even more.
Anti-gravity drives and antimatter sound like attractive options proposed in science fiction, but are unfortunately beyond our current technology. However, the technologies for a drastically better propulsion system already exist.
We’ve already got it
Trying to get to Mars and back with chemical rocket propulsion (which remains the only practical option for launch) is a little like trying to sail across the Atlantic in a canoe. Sure – it’s theoretically possible, but not necessarily wise to attempt. Luckily, we’ve got a great alternative on the horizon.
In the 1960s, NASA tested an engine called NERVA – the Nuclear Energy Rocket Vehicle Application – which used a nuclear reactor to replace the combustion process and superheat hydrogen which is ejected from the rocket, creating a very efficient thrust. This option is at least twice as efficient as chemical rocket propulsion and that means a spacecraft can be sent into a more direct and more energy-consuming trajectory that saves time. The propellant – hydrogen – can also be created from water ice so you won’t need to haul all of it for the return trip.
While the thrust levels produced by a nuclear engine are not high enough for a launch, nuclear propulsion has the improved efficiency to get us to Mars in around three to four months, enabling a possible ‘hit-and-run’ mission with a short surface stay and timely return in the span of less than a year altogether.
Even though NERVA was successful, it’s truly unfortunate that the programme wasn’t continued – the Space Race came to a screeching halt in the wake of America’s successful Apollo missions. Space travel was simply deemed not politically necessary anymore and too pricey in the era of dramatic social upheaval in the 1970s. Science missions shifted their focus to orbiting laboratories which eventually resulted in the construction of the ISS.
When will we do it?
Commercial spaceflight has a pretty good track record doing things on a limited budget, albeit on notoriously unreliable timelines. With SpaceX’s Falcon 9 rockets costing under $30 million per launch and the success of the Inspiration4 flight, the future of commercial space travel seems to be within reach.
With the ongoing work of simplifying launchers and development of next-gen nuclear reactors for space, we also have a very good shot at making Mars missions logistically feasible by 2035 – casual tourists will probably start taking actual trips to the Red Planet and back, much the same way tourists can access Antarctica alongside scientists.
Our generation will become the interplanetary one, much the same way our parents and grandparents witnessed the game-changing impact of commercial aviation. We certainly have a lot to look forward to as far as our vacation options are concerned, a decade or two down the line.