Saturday, December 1, 2012

Dr. Buzz Aldrin and the Orbital Paradox

"In the hopes that this work may in some way contribute to their exploration of space, this is dedicated to the crew members of this country's present and future manned space programs. If only I could join them in their exciting endeavors!"


--  Edwin "Buzz" Aldrin's  Thesis Dedication, January 1963

Dr. Buzz Aldrin, after his stroll on the moon.
Source: Wikipedia.

Dr. Buzz Aldrin goes down in history as the second man to walk on the moon. He was also the first PhD in space. He submitted his thesis in January of 1963; he was selected as an astronaut in October of that year.* Dr. Aldrin's dramatic and sometimes troubled life story (Dancing with the Stars, three divorces, alcoholism, etc...) sometimes seems to overshadow his scientific accomplishments. But, before walking on the moon, he was the first person on Earth to earn a doctorate in the field of astronautics. MIT actually created its astronautics program specifically for him!

*: Astronaut Jim McDivitt was awarded an honorary doctorate before he flew on Apollo 9, but Aldrin was the first astronaut hired with a ScD (equivalent to a PhD) degree.

The view from Apollo 11, leaving Earth orbit for the moon.
Source: Wikipedia.

Astronautics is the study of space navigation. Dr. Aldrin's research focused on the process of docking two orbiting spacecraft. When Dr. Aldrin was completing his coursework, humans hadn't yet docked two spacecraft in orbit. The first docking occurred on Gemini 8, in 1966. Soon thereafter, Dr. Aldrin flew aboard  Gemini 12 and was able to follow up on his doctoral work with hands-on experience.

Dr. Aldrin in his pre-PhD days.
Source: Time.

Dr. Aldrin's thesis was titled Line-of-Sight Guidance Techniques for Manned Orbital Rendezvous. It's available for download here. His doctoral work was the development a procedure for visually docking (as in, using your eyes to guide the spacecraft). That way, astronauts would be able to supplement computer models, navigational chart data, or radar data with their own visual observations. Being able to rely on a visual docking technique in addition to following computer and instrument guidance means that docking is possible even if those sources of data partially failed.

So, for example, when the rendezvous radar failed during Dr. Aldrin's Gemini 12 mission, he and  Jim Lovell docked their spacecraft to the target vehicle using the onboard computer, navigational charts, and their own observations out the spaceship windows. Such was the success of Dr. Aldrin's visual docking techniques that parts of the dissertation became standard operating procedure for NASA.

The view from the Apollo 11 Command Module: the Lunar Module approaches.
Source: NASA.

Docking spacecraft in orbit poses serious challenges not encountered when docking a boat or connecting two aircraft for a refueling maneuver  Like air travel, space travel works in three dimensions. But unlike air travel, there's the added challenge of working with craft that are in orbit. There's also the confusion created by freefalling around Earth without a feeling of "up" or "down." And, there's what Dr. Aldrin terms an "orbital paradox."

Here's the paradox: If you're trying to pilot your orbiting spaceship to reach a spaceship in a higher orbit, the intuitive course is to (1) aim your spacecraft up, towards the higher orbit, and (2) speed up your spacecraft so it will catch up. Dr. Aldrin describes the surprising result of this maneuver. You'll "end up in an even higher orbit, traveling at a slower speed and watching the second craft fly off into the distance."

Gemini 12 and an Agena Rocket, 15 feet apart.
Source: Wikipedia.

Or, as Neal Stephenson describes it in his novel Anathem: "Things in orbit didn't behave like we were used to. Just to name one example: if I were pursing another object in the same orbit, my natural instinct would be to fire a thruster that would kick me forward. But that would move me into a higher orbit, so the thing I was chasing would soon drop below me. Everything we knew down here was going to be wrong up there."I won't tell you why the main character in Anathem was headed into space, just in case you want to read the book.... it's a great adventure story!

Apollo 9's command and service modules, docked.
Source: NASA.

Aside from PhD dissertations and science fiction, the practical result of the orbital paradox is as follows. When the International Space Station docks with a Soyuz, the Soyuz and the ISS begin their final docking maneuvers at the same altitude and velocity as each other, but with the Soyuz out in front of the ISS. Then the Soyuz will fire its rocket and move towards a slightly higher orbit, because this slows the craft down! Next, the Soyuz will slowly drop back to the lower orbit, moving faster and closer to the ISS the lower it gets. Finally, the spacecraft will back into the ISS, docking with the front of the space station.

Here's a diagram the boyfriend and I drew to explain how the Soyuz moves to that initial, higher orbit:

See how the Soyuz fires its rockets so that, if it wasn't in orbit, it would move directly away from the ISS?
But since both craft are in orbit, the effect of thrust in that direction is to move the Soyuz to a higher, slower orbit.
Then, it can drop back down towards the ISS.

Teaching folks how to achieve orbital docking by sight is not Dr. Aldrin's only academic contribution to space exploration. There's also Dr. Aldrin's novel idea for exploring Mars, called the Mars Cycler. More on that, coming soon!

Sources: Scientific American; buzzaldrin.com; Neal Stephenson's Anathem; Wikipedia.

5 comments:

  1. Who would have ever thought docking was so complex...I enjoyed your synopsis and your drawing!

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    Replies
    1. Thanks for a very clear explanation TB. I've always thought there must be a point in docking at which "point and shove" will work, before Orbital mechanics "bites". I met a few of the FiDos from The Trench at an Astrofest and asked if that was the case an they said Yes from about 100' or so.
      Moving on..do you know what the charts were that Buzz used on Gemini XII? I had read he took them with him to some amusement from other astronauts and got the last laugh when the automatics failed.

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