Nov 07 2023

The Next Step in Space Travel

The European Space Agency (ESA) has announced they are developing their own commercial space capsule. This will be used initially for cargo, but then eventually for crew as well. They anticipate a maiden voyage in 2028.

I think this is a positive development. It seems we are slowing moving in the direction of increasing collaboration among international government and private space companies. This has existed from the beginning of the space program to some extent, but private companies are taking an increasing role, and more nations are getting involved as well. But what I want to talk about is what this space travel infrastructure will look like, and where that should be heading.

The history of the Apollo mission is a good place to start to frame the challenges of space travel. For Apollos NASA ultimately landed on a complex but workable solution. First you need a really big rocket, one able to life a large payload and give it enough acceleration to get into trans-lunar orbit – to get into orbit around the moon. This required a multi-stage rocket, the Saturn V. On top of that sat the lunar lander then the service module and then the command module (the capsule where the astronauts lived). After acceleration to the Moon was complete, the lunar module would detach and then flip around and dock with the top of the command module, so that astronauts could move between the two vehicles.

Once at the Moon astronauts would enter the lunar descent module and blast down to and land on the lunar surface. When it was time to leave the top of the lunar lander would blast off from the bottom, leaving it behind, and reenter lunar orbit, where it will meet up with the command module and dock again. Once the astronauts were back in the command module, the lunar ascent vehicle was detached (and most were deliberately crashed into the Moon to get seismic readings). The command module and service module would then use some of its remaining fuel to head back to Earth. Once close to Earth and on a reentry trajectory the service module was detached, left to burn up in reentry. The command module then went through its descent process, first breaking with its heat shield and then deploying parachuted for a water landing.

The overall strategy was to leave stuff behind all along the way. Only take with you what you absolutely needed, and when something was no longer needed, get rid of it. This is because fuel in space is precious, and every ounce of mass increases fuel use. This worked for Apollo, but Apollo was designed as a series of one-off missions. Pretty much everything was used up on one mission, including the lunar space suits. This was great for an initial exploratory mission given the technology we had, but once Apollo was done we had nothing to show for it in terms of space travel infrastructure, and this approach is very expensive.

The thinking today is very different – if space travel is going to be anything more than one-off “flags and footprints” missions, we need reusability. The Space Shuttle was supposed to be the first mostly reusable spacecraft, and it was, and it accomplished its goal of reducing the cost of getting stuff into space. But it wasn’t successful enough. We needed more reusability, and a faster turnaround time. NASA, interestingly, went back to its Apollo approach with its post-Shuttle system designs. The Artemis missions are going to be very similar to Apollo. The Space Launch System (SLS) is an expendable rocket system. The Orion capsule that will sit on top of the SLS is considered “partially reusable”.

Meanwhile, SpaceX and other commercial space companies are pushing for full reusability to keep down costs. Hopefully the SLS will be the last gasp of incredibly expensive expendable rockets. The Falcon Heavy and Starship from SpaceX are likely to play a role in the Artemis missions. The Starship is building a version meant to be a reusable lunar lander, and may also have fueling and supply missions. NASA plans on building a Gateway lunar station that will remain in orbit.

This is where I think we need to head. Imagine a system where a rocket, designed specifically an only to get crew and supplies off Earth and into low Earth orbit (LEO). A capsule on this system docks with an LEO space station. The rocket and capsule can then return to the Earth and be fully (or mostly) reusable. From the space station crew and supplies will take a lunar shuttle that has one job – to go from LEO to lunar orbit. It never has to land. It doesn’t need a lot of fuel. It only shuttles between two space stations. Then, lunar landers go from the lunar station down and back up from the lunar surface. Again, that’s its only job, it does it well, and it is fully reusable.

I think we should be working toward this type of platform. From LEO it is also possible to go to Mars. Most of the fuel is used in going to LEO. Crew can then transfer to ships that only go between Earth and Mars, and are optimized for this trip. The LEO platform can also be used to go anywhere in the solar system. Or, a lunar base can be the platform from which we launch to Mars and the rest of the solar system. Once we own the Moon, we own the solar system.

Once we have this kind of infrastructure in place, that will probably be the best type of system for the foreseeable future. Having one ship that will, for example, take off from Earth, travel to its destination, and land, will simply not be practical (as romantic as it may be). It’s a question whether or not if will even be possible. We need chemical rockets to get off Earth, and the rocket equation sets limits on how much fuel you can take with you. For zipping around the solar system we will want big ships with lots of shielding and amenities – ships that you do not want to land and take off from worlds with gravity.

Any space program that is not moving us towards this eventual system is ultimately a dead end. It may provide knowledge and technology that will contribute to such an infrastructure, but will not be part of it.

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