Friday, November 25, 2022

Published in Scientific American!

This morning marks a big moment in my career.  I have long wished to be a popularizer of science, and there are few better venues for this than Scientific American.  I had originally submitted a very technical article about space elevators to them, but they asked for something more 'fun', so I rewrote it.  I am so pleased with the result: Space Elevators are Less Sci-Fi than you Think.  I feel quite elated on this November morning.


Unknown said...

stepehen, i read your article on space elevators in Scientific American. would it be possible or practical to demonstrate the utility of the technology on the moon or Mars with lower gravity issues before attempting it on Earth?

The Engineer said...

Mars has lower required specific strength requirement, but means transporting tonnes of mass there. A lunar design is different. A partial space elevator around Earth may be a good prelim step (two satellites tethered to one another and orbiting together across, say, a 25,000 km span). All lessons learned from tethers in space will be utilized in this project. Thanks for the question.

Unknown said...

As a design student at RISD in the 70's I proposed a space elevator constructed of spent rocket boosters. Delighted that work on this progresses. I would volunteer to be one of the first "climbers" of the elevator, once constructed, but unfortunately, I imagine that I will be either too old or too dead to do this by the time it is complete. I would also be reluctant to climb it if E. Musk had anything to do with its construction - it might be subject to recall.

bjkeefe said...

I would love to read the more technical version, too.

I have a question, prompted by the one that SciAm did publish. I asked it (as Brendan Keefe) in the comments on Facebook, which is where I saw mention of your article.

I'll repeat the question, if you'd rather answer here.

First, some context:

[quote]If you stood on the equator and stared up at a satellite in a geosynchronous orbit (approximately 36,000 kilometers in altitude), it would appear fixed in space, rotating unconnected around the Earth once per day because its speed is just right. Now, that satellite drops a cable to Earth, while simultaneously using fuel to ascend higher. The cable is fastened on the Earth end as the satellite reaches just the right altitude, and the system still rotates along with the Earth.[/quote]

Now, the question:

Why does the anchor satellite have to go to a higher orbit to remain fixed with respect to the Earth's rotation? Or, put another way, why wouldn't the anchor satellite be in the same geosynchronous orbit as the untethered satellites?

Thanks in advance. And thanks for the article, in the first place.

John said...

Congratulations !!!

I found the link : I will read it tonight :)

The Engineer said...

Hey bjkeefe,

Thanks for the question. For a satellite to be in circular orbit around Earth, at any altitude, it requires a specific speed. Highest speed at low-Earth orbit, and less and less as you go up. The particles making up the space elevator cable are moving fastest farther away (the opposite of what would naturally happen). Basically, the GEO point is in a natural orbit, while all other points are in a FORCED circular orbit simply because tension keeps them there.

The higher the far-end (seed spacecraft) attachment ascends, the less mass it would need to be to keep that tension. If it only ascended 1 km higher than GEO, it would need to be the mass of an asteroid. At a total length of 100,000 km, the counterweight mass will be around 1/3 of the cable total mass.

bjkeefe said...

Thanks, Stephen. That makes it clear to me.