A chance discussion on Mastodon results in new changes to Mike.Sierra.Echo – let’s talk the nutty world of Near-Earth Objects (NEOs)! As you’ll recall, I’m writing a novel where humans build a space elevator in the future – over a hundred years from now. The novel is set in the future for a number of reasons, and one of them is because a future space elevator would need a large counterweight and a Mount Everest-sized asteroid would serve that purpose.
So while I write, I’m watching the skies. I found a Mastodon toot about a new asteroid and, well, everything else happened. Here’s how it started:
Michael got back pretty quick: “I regret to report that Hathor is not particularly easy to capture. I can recommend 2008 EV5 as an accessible alternative.” and here’s why he knows: HE LITEREALLY WROTE THE BOOK ON IT. Michael Busch – first a graduate student in planetary science at Caltech – is now a Research Scientist at SETI.
Busch’s background gives him a unique perspective to discuss Mike.Sierra.Echo’s science and he gave out some great advice when I asked: “I looked into 2008 EV5 carefully last night and this morning – I can see why I didn’t pick 2008 EV5 originally. Based on the simulations over at: https://www.spacereference.org/asteroid/341843-2008-ev5 It doesn’t look like 2008 EV5 comes near Earth in 2169. I’d love for Mike.Sierra.Echo to be as accurate as possible – can you please tell me what I’m missing and why I should use 2008 EV5 over 2340 Hathor?”
“For capturing an object into Earth orbit, or for returning a large mass from it to Earth orbit, what matters is the required velocity change,” Busch answers. “Hathor has low MOID (minimum orbit intersection distance), so it can and does pass quite close to Earth, but its orbit is also extremely eccentric (e = 0.45). So the velocity change for rendezvous from Earth and to return to Earth orbit is very high.”
What does that mean for Mike.Sierra.Echo, though? Why would I want to use 2005 EV5 as a space elevator counterweight versus 2340 Hathor? “The biggest factor that makes Hathor less accessible to spacecraft is its eccentricity being so high.”
He’s absolutely right. Orbital Eccentricity is a measure of how circular an orbit is. An eccentricity of 0 means that the orbit a perfect circle. Anything between 0 and 1 is an elliptical orbit. Values greater than 1 is an orbit with the shape of a hyperbola, which is also an escape trajectory. 2340 Hathor’s orbital eccentricity (0.4499) is much higher than 2008 EV5 (0.0835). It’s much easier for a spacecraft to reach asteroids with lower orbital eccentricity, but there’s also another factor: velocity.
When looking at the velocity of both asteroids, 2340 Hathor is moving at 9-18 Km/sec and 2008 EV5 is moving at 4-8 Km/sec. Changing the object of fast-moving objects means considering how much energy it will require to change their speed and direction.
Per Spacereference.org – “2008 EV5 can be reached with a journey of 362 days. This trajectory would require a delta-v of 6.291 km/s. To put this into perspective, the delta-v to launch a rocket to Low-Earth Orbit is 9.7 km/s. There are 320,845 potential trajectories and launch windows to this asteroid.” Here’s the bad news for 2340 Hathor – “This asteroid is not considered a viable target for human exploration by the NHATS study.”
These, and other factors, are what NASA uses to consider Near-Earth Accessible asteroids. 2340 Hathor and 2008 EV5 aren’t on that list, but that’s because NASA is only focused on near-Earth asteroids (NEAs) that may be well-suited to future human space flight round trip rendezvous missions. They aren’t looking for space elevator counterweights … yet. 😉
So … yeah. I’ve got to make some changes to Mike.Sierra.Echo. The time of the rocket launches, the dates when we think 2008 Ev5 will be near Earth mean I need to change some scenes in the book. Better to find out now, than after it hits the bookshelves.
I really appreciate Michael Busch’s feedback and can’t wait to see what he (and other space academics) think about Mike.Sierra.Echo when it comes to life. More information, soon!