The Halo Drive

After 2.5 inches of rain yesterday, another inch and a half today. Exciting. We’ll probably have a desert superbloom as a result. Here’s are a couple of superbloom photos (March 2017), first from the mountainside and the next one in the desert. They’re pretty special.

In Borrego Springs.

So perhaps my rainy, dark two-hour drive to the airport and back today will be worth it.


It’s MLK Day today, and I wish we had more people like him around these days. Our “leaders” today are peformative, not substantive. We’re so busy arguing about culture wars that we forget to do anything real. MLK had a great cause, he spoke truth to power, and he paid the price for that. It’s a good day to remember that.

The rest of the day today will be R&R for me. Rainy day, nothing urgent going on – my favorite kind. I have books to read, camera menus to figure out, and movies to watch. Hell, I might even exercise.


Finally for today, I love the fact that serious universities are spending time researching methods that we might travel among the stars. Here’s a paper from Columbia University that shows how we might travel at a decent percentage of light speed using only solar sails and black holes. It’s called The Halo Drive. In theory it works (they’ve done the math; that’s the point of the publication). Align yourself along the vector a black hole is traveling, positioned ahead of it, shoot a beam of light back toward the black hole at a very specific angle, and voila – the light slingshots around the hole and pushes you ahead with substantial energy gain.

From the paper:

The Halo Drive

An appealing aspect of the halo drive is that no fuel is spent. The spacecraft gradually gains energy during its initial acceleration and then discharges that energy for further acceleration up to terminal velocity – the speed at which the spacecraft returns to its original mass.

The terminal velocity of the spacecraft is 133% the black hole’s speed, to first-order. Critically, this velocity in not sensitive to the mass of the spacecraft, with the only assumption being that said mass is much less than that of the black hole. Accordingly, a major advantage of the halo drive is that Jupiter-mass spacecraft could be accelerated to relativistic speeds.

Beam divergence due to tidal effects on a finite beam width could be mitigated by careful beam shaping. Di- vergence due to diffraction is not expected to lead to noticeable losses for large spacecraft using optical lasers within a hundred Schwarzschild radii. Nevertheless, for this reason, the system is argued to be impractical at distances much greater than this, thereby necessitating relatively expedient acceleration.

An advanced civilization utilizing such a system would first have to have achieved interstellar flight to journey towards the nearest suitable BH. They could then could use BHs in binary systems as way-points throughout the galaxy, of which there are likely O[107] in the Milky Way (Reggiani & Meyer 2013), serving as both accelera- tion and deceleration stations. Alternatively, they could use the larger population of BHs which do not reside in compact binaries (Elbert et al. 2017) via their proper motions, although this would not permit for such high velocities.

All we have to do is reach interstellar space, find black holes, and prepare ourselves for a decades long voyage to the next star system. Simple!