Odyssey Navigation

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When the Odyssey needs to reverse thrust to try and counter a descent towards the TET, Jack calls for a full OMS (Orbital Maneuvering System) burn. We do not see what information he looks at to determine how fast he is approaching the TET, or how he knows that the OMS system will provide enough thrust.

We do see 4 motor systems on board the Odyssey

  1. The Main Engines (which appear to be Ion Engines)
  2. The OMS system (4 large chemical thrusters up front)
  3. A secondary set of thrusters (similar and larger than the OMS system) on the sleep module
  4. Tiny chemical thrusters like those used to change current spacecraft yaw/pitch/roll (the shuttle’s RCS).

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After Jack calls out for an OMS burn, Vika punches in a series of numbers on her keypad, and jack flips two switches under the keypad. After flipping the switches ‘up’, Jack calls out “Gimbals Set” and Vika says “System Active”.

Finally, Jack pulls back on a silver thrust lever to activate the OMS.

OMS

Why A Reverse Lever?

Typically, throttles are pushed forward to increase thrust. Why is this reversed? On current NASA spacecraft, the flight stick is set up like an airplane’s control, i.e., back pitches up, forward pitches down, left/right rolls the same. Note that the pilot moves the stick in the direction he wants the craft to move. In this case, the OMS control works the same way: Jack wants the ship to thrust backwards, so he moves the control backwards. This is a semi-direct mapping of control to actuator. (It might be improved if it moved not in an arc but in a straight forward-and-backward motion like the THC control, below. But you also want controls to feel different for instant differentiation, so it’s not a clear cut case.)

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Source: NASA

What is interesting is that, in NASA craft, the control that would work the main thrusters forward is the same control used for lateral, longitudinal, and vertical controls:

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Source: NASA

Why are those controls different in the Odyssey? My guess is that, because the OMS thrusters are so much more powerful than the smaller RCS thrusters, the RCS thrusters are on a separate controller much like the Space Shuttle’s (shown above).

And, look! We see evidence of just such a control, here:

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Separating the massive OMS thrusters from the more delicate RCS controls makes sense here because the control would have such different effects—and have different fuel costs—in one direction than in any other. Jack knows that by grabbing the RCS knob he is making small tweaks to the Odyssey’s flight path, while the OMS handle will make large changes in only one direction.

The “Targets” Screen

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When Jack is about to make the final burn to slow the Odyssey down and hold position 50km away from the TET, he briefly looks at this screen and says that the “targets look good”.

It is not immediately obvious what he is looking at here.

Typically, NASA uses oval patterns like this to detail orbits. The top of the pattern would be the closest distance to an object, while the further line would indicate the furthest point. If that still holds true here, we see that Jack is at the closest he is going to get to the TET, and in another orbit he would be on a path to travel away from the TET at an escape velocity.

Alternatively, this plot shows the Odyssey’s entire voyage. In that case, the red dotted line shows the Odyssey’s previous positions. It would have entered range of the TET, made a deceleration burn, then dropped in close.

Either way, this is a far less useful or obvious interface than others we see in the Odyssey.

The bars on the right-hand panel do not change, and might indicate fuel or power reserves for various thruster banks aboard the Odyssey.

Why is Jack the only person operating the ship during the burn?

This is the final burn, and if Jack makes a mistake then the Odyssey won’t be on target and will require much more complicated math and piloting to fix its position relative to the TET. These burns would have been calculated back on Earth, double-checked by supercomputers, and monitored all the way out.

A second observer would be needed to confirm that Jack is following procedure and gets his timing right. NASA missions have one person (typically the co-pilot) reading from the checklist, and the Commander carrying out the procedure. This two-person check confirms that both people are on the same page and following procedure. It isn’t perfect, but it is far more effective than having a single person completing a task from memory.

Likely, this falls under the same situation as the Odyssey’s controls: there is a powerful computer on board checking Jack’s progress and procedure. If so, then only one person would be required on the command deck during the burn, and he or she would merely be making sure that the computer was honest.

This argument is strengthened by the lack of specificity in Jack’s motions. He doesn’t take time to confirm the length of the burn required, or double-check his burn’s start time.

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If the computer was doing all that for him, and he was merely pushing the right button at the indicated time, the system could be very robust.

This also allows Vika to focus on making sure that the rest of the crew is still alive and healthy in suspended animation. It lowers the active flight crew requirement on the Odyssey, and frees up berths and sleep pods for more scientific-minded crew members.

Help your users

Detail-oriented tasks, like a deceleration burn, are important but let’s face it, boring. These kinds of tasks require a lot of memory on the part of users, and pinpoint precision in timing. Neither of those are things humans are good at.

If you can have your software take care of these tasks for your users, you can save on the cost of labor (one user instead of two or three), increase reliability, and decrease mistakes.

Just make sure that your computer works, and that your users have a backup method in case it fails.

6 thoughts on “Odyssey Navigation

  1. I knew I had seen that left “Target” screen before!
    It looks like a direct copy of the one displayed here:

    “RelMo provides a graphic representation of the relative motion between two vehicles, a “chaser” (usually the Shuttle) and the “target” (ISS, HST, or some other free-flying vehicle or payload).
    The origin is target-centered, and the plot of the chaser is projected onto an X-Z (downrange-radial) plot with respect to the target.
    This gives the FDO an at-a-glance view of how the two vehicles will be moving with respect to each other in space.
    This particular example shows a fairly nominal Day-of-Rendezvous scenario with the Orbiter less than one orbit away from the Terminal Initiation (or Ti) burn that will start the direct course for rendezvous operations.”

    As explained here
    http://space.balettie.com/displays_orbit.html

    • I stand corrected. That’s really cool!

      I still have no idea how to read that screen after reading through the documentation (adding “learning how to fly a spacecraft with pure math” to my bucket list), but I get the impression that all the information needed is there.

      edit: just figured out that the dotted line is the target, and the craft is moving right-to-left in time on the graph. Neat little Easter Egg (since it looks like the Odyssey is on a nominal path).

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