Sub-orbital spaceflight and further…

I was looking up the Space X booster and what did I notice but this:

In 2017, SpaceX mentioned the theoretical possibility of using Starship to carry passengers on suborbital flights between two points on Earth. Any two points on Earth could be connected in under one hour, providing commercial long‑haul transport competing with long‑range aircraft.^[169][170] SpaceX however announced no concrete plans to pursue the two stage “Earth‑to‑Earth” use case.^{[8][114][171]} 

Over two years later, in May 2019, Musk floated the idea of using single‑stage Starship to travel up to 10,000 km (6,200 mi) on Earth‑to‑Earth flights at speeds approaching Mach 20 (25,000 km/h; 15,000 mph) with an acceptable payload saying it “dramatically improves cost, complexity and ease of operations”.^[172] In June 2020, Musk estimated that Earth‑to‑Earth test flights could begin in “2 or 3 years”, i.e. 2022 or 2023 and that planning was underway for “floating superheavy‑class spaceports for Mars, Moon and hypersonic travel around Earth”.^[173] 

In April 2021, COO Gwynne Shotwell clarified that she believes SpaceX “will be flying large numbers of people on Starship in five years … including point-to-point transportation between two locations on Earth”.^[174] 

Sounds legit. 

Here’s the thing. We don’t really know. 

As the number of launches increases, rocket engine emissions increase in proportion. Rocket engine exhaust contains gases and particles that can affect Earth’s climate and ozone layer. These emissions historically have been assumed to be not much of a threat to the global environment because the space industry was deemed small and unchanging. Whether that assumption holds true for today’s rapidly growing space is an important question that needs scientific attention.

…

The global quantities of these gas emissions from rockets, even at increased launch rates, do not significantly affect the global climate or ozone layer, and they are dwarfed by atmospheric inputs from other sources [Larson et al., 2017].

But… 

particles emitted by rocket engines can affect climate and ozone,

Yet there’s little research on what increased launches will do… Why?

The answer is, in part, related to the history of rocket launches. The annual rate of rocket launches increased rapidly after the start of the space age, peaking at 157 launches in 1967. But then it declined over the next 4 decades, decreasing to only 42 launches in 2005. So for most of the past half century, rocket emissions have been in decline and therefore were not of much interest to researchers working to understand the most significant aspects of climate change and ozone depletion.

But that historic trend reversed in 2005 and, despite the retirement of the Space Shuttle in 2011, launch numbers began rising again. With 114 launches in 2018, the number of launches has been growing at an average rate of about 8% per year for the past decade. Rocket emissions have also been growing, faster than global emissions from other sources with comparable impacts, such as aviation. And this growth is expected to accelerate.

Some people think that by 2030 400 launches a year will be the norm. That’s a mere 9 years away. And what if the Musk plan takes off? That might add multiple other launches into the equation. 

Suddenly we’re seeing a scenario where… 

As the space industry heads toward a future with two or three launches every day, the anticipated surge in emissions directly into the stratosphere (assuming current propellant types) would push the climate impacts of rocket emissions to be comparable in magnitude to other sources of climate change that receive intense study by international groups of scientists, engineers, and scholars.

This would appear to be a problem that should be addressed sooner rather than later. 

Meanwhile, here’s something Musk et al could invest in developing – or better still governments could work together to develop. 

Electrical launch systems include mass drivers, railguns, and coilguns. All of these systems use the concept of a stationary launch track which uses some form of linear electrical motor to accelerate a projectile. 

In essence, a mass driver is a very long and mainly horizontally aligned launch track or tunnel for accelerating payloads to orbital or suborbital velocities. The concept was proposed by Arthur C. Clarke in 1950,^[35] and was developed in more detail by Gerard K. O’Neill, working with the Space Studies Institute, focusing on the use of a mass driver for launching material from the Moon. 

A mass driver uses some sort of repulsion to keep a payload separated from the track or walls. Then it uses a linear motor (an alternating-current motor such as in a coil gun, or a homopolar motor as in a railgun) to accelerate the payload to high speeds. After leaving the launch track, the payload would be at its launch velocity. 

It seems that the environmental impacts of mass drivers would be considerably lower than those of rockets. Of course to minimise environmental impacts further, how about a space elevator? Though so far we’re not quite there with materials strong enough to construct one. Though this might work.