Alan

Aug 19, 2019

4 min read

LEO Catchers as a Launch Assist System

I mentioned this topic on this blog a few times:

Looking back at it, I might have neglected to properly link my primary posting I left on the subject, which was

https://forum.nasaspaceflight.com/index.php?topic=35648.20

The topic started re-surfacing due to interest from other people.

The idea has been described in other places.

There are also several academic papers describing multiple variations of the system. You can crawl the links in this post for them, he Stack Exchange question foremost. They are good contributions, almost all of them have have overlap with the versions I have discussed. There are some directions I dislike, such as crashportation. Braking via other fluid mediums is a valid point to raise, but with anything inferior to passive electromagnetic braking (like fluid braking), this concept will never be good enough to matter.

Some Math on the Topic

For the orbital formation of the catcher, I have tried to dig up some equations to do essentially localized stability studies. I asked about it here:

The answer was ultimately the equations in:

Where that gives (x,y,z) second derivative equations, which is what is needed for simulation. This is something I want to return to, because the relative movement of parts in orbit is probably the main issue for structures like this proposed catcher.

Why Should Anyone Care?

In a previous post, I went out of my way to bash most Launch Assist Systems (LAS). Well, things have changed. In spite of growing excitement around New Space, an economically viable LAS looks less likely than ever before.

Reusable first stage boosters is a an astonishing technical achievement that has been fully realized. Most LAS writing unfortunately aim to assist primarily in the first stages of launch. We already have a solution to that problem, and it works fantastically.

Consumption of orbital launch services has yet to catch up to the 4x to possibly 10x marginal price reduction (people are not going to agree on the specific number) from first-stage-reuse. The only thinkable application which could raise to match these newfound capabilities is a handful of competing satellite internet projects. Maybe limited space tourism. If government decided it was a priority again, we could have a thriving manned exploration program again. But don’t hold your breath!

I recently finished reading The Space Barons.

The early history of Blue Origin was a new topic to me, and apparently they went through the dreamy ideas of LAS that the internet bloggers do. They eventually gave up. This does cast somewhat of a new light on the QuickLaunch endeavor, since it came around at a time when there were possibly some free billions in the investment market looking to fund a space gun or something like it… but it was not to be.

The chips are mostly laid out there for this first phase. Many will be targeting cost reductions through larger rocket sizing (which I argue is a fool-hearted idea). Otherwise we should expect to hit a new floor in launch costs. This new reality will be very exciting, but will still remain stuck within a certain cost structure.

If I scroll down a list of proposed LAS, I stop in my tracks and go cross-eyed at the orbital catcher. It has an unassuming academic history, humbly argued in most cases, its flaws (some confused or mistaken), put first. Unlike all space guns, it has no minimum size, allowing for near-term testing if an appetite for it emerged. Its engineering challenges for scaling relate to detailed engineering, not a fundamental conceit baked into its primary parameter selection like all Earth space elevator variations. It’s not demonstrably too costly to ever work like Skylon or a Maglev ???? to accelerate an inferior rocket.

Where my head explodes is the point where the electromagnetic catcher doesn’t just have greater viability, but it would have a combination of throughput and mass-performance which is almost categorically better than any other LAS.

Perhaps there was a time when the need for rockets to lift the initial mass could be seen as a strong negative for the idea. Well, costs of launches are falling, and could fall much more today.

There was also probably a time when people discussing the orbital catcher had to assume that a rocket to launch the payload from the surface would be expendable… or call upon use of a space gun or something equally ridiculous.

Well, 2005 versus 2019 makes a big difference. At this point, a first stage booster used to launch a payload to orbital height (but not velocity) would trivially be a fully reusable part of the system. In papers where people discussed this idea, authors did not have this assumption available. So maybe it’s worth another look?

I want to use an extremely high bar to call an idea “good”. If I could make a short list of the enormously big ideas for space in the next century which are good…

  • First stage propulsive landing and reuse
  • Lunar ISRU of water-ice
  • Low-radiation LEO equatorial orbits for manned stations
  • LEO electromagnetic catcher