The Challenge For The Dragon

Here’s an article describing the pre-rendezvous testing that it will go through. This is misleading, though:

“This is pretty tricky. And also, for the public out there, they may not realize that the space station is zooming around Earth every 90 minutes, and it’s going 17,000 mph,” said SpaceX CEO Elon Musk. “This is something that is going 12 times faster than a bullet from an assault rifle. So it’s hard.”

The velocity relative to earth isn’t really relevant, and doesn’t make it harder. All that matters is the relative velocity between the spacecraft and the ISS. And that, of course, is what they have to demonstrate their ability to control.

[Update a while later]

More thoughts from Tom Jones.

19 thoughts on “The Challenge For The Dragon”

  1. I’m sure he’s getting pretty punchy with all the interviews he’s done lately.

    Both statements are true… they just happen to be unrelated.

  2. It *is* pretty hard to get something substantial going 17000 mph, and harder to make it end up in the same place as something else going 17000 mph, and in the same direction.

    Once you’ve done that though, the actual fly around doesn’t seem that tough.

  3. I guess NASA PAO is writing Musk’s speeches now. It sounds like previous material from them. NASA (now Musk) really needs to quit acting like basic engineering problems are hard. Others do these hard things routinely.

    A marksman trying to hit a target with said rifle bullet has to also deal with wind as well as gravity and sometimes a moving target, and the shooter usually doesn’t have a reaction control system attached to the bullet. Sometimes a sniper will wait days for a few seconds window to dock a bullet into the target. Many pull it off without a press release, because the related equations have been known now for a long time.

    The whole velocity thing isn’t difficult. What’s difficult is a thruster may fail at an inopportune time. Or if you want to talk about going around the Earth, a LOS may happen during the time needed for a crucial firing. Those things can complicate problems. Not necessarily hard things if you have propellant margin, but more complicated.

    1. There likely will be several web feeds. I use Spaceflight Now. That link has status updates and a live video feed. The launch is scheduled for 4:55 a.m. EDT (0855 GMT) tomorrow morning. My alarm clock is set! There’s currently a 30% chance of bad weather tomorrow morning.


      1. Spaceflight now seemed to be the only one without a delay out of NASA, SpaceX, and Spaceflight Now.

  4. I’ve encountered a couple of articles referring to the high speeds of the ISS and Dragon as being a big deal. No mention of the low relative speeds of the docking objects of course. You’d think Dragon was going to approach the ISS at a flat 17,000 mph while the ISS is sitting still from what’s being reported. Science reporting for the win.

    Very excited about the launch–hope it goes well. I even bought a SpaceX shirt (KSC is selling SpaceX/Dragon merchandise now). I’d planned on going to the launch when it was earlier in the month, but the 4:55 a.m. launch time is a bit much to attempt with the kids.

  5. Tom Jones believes NASA could beat SpaceX to crew access with an internally designed/managed booster/capsule system. I’ve posted a comment on his site, asking how NASA would go about it, and am very interested in his answer.

  6. Dragon has not flown as a maneuvering spacecraft…

    Only true regarding the provisions he gives. They did give the dracos a workout on the second F9/first Dragon flight.

    Does anyone know if they’ve developed a flight simulator for the Dragon yet?

  7. One is struck by the hedging, mealy-mouthed passive-aggression and anticipatory crepe-hanging on display in much of the pre-flight “journalism” and commentary, especially that essayed by Astronaut Jones. For someone in an allegedly forward-looking profession, the gloomy Mr. Jones might reasonably consider that ten years hence it is entirely likely that SpaceX will employ more astronauts than NASA – and fly them more often too. Poor-mouthing a potential future employer is something even dim little I know to be counterproductive. If Jones is actually serious in imagining that NASA could somehow pull a usable crew delivery system out of its institutional ass before SpaceX and others are prepared to transport crew – and get a 20% budget increase in the interim to cover the costs – I think the quality of his judgements is obviously deficient.

  8. Can anyone explain this bit from another SpaceX article? ( ) “NASA originally planned for the Dragon to remain docked with the station for about three weeks. But in early June, the angle between the sun and the plane of the station’s orbit will begin resulting in temperatures that will require flight controllers to either bring the capsule home early or keep it at the station for an extended period.”

    I thought Dragon was designed for long duration missions? Is being attached to the station preventing proper temperature control?

    1. This article explains the “solar beta angle cutout”, which I have to admit I didn’t know about.

      If Dragon does not launch on the May 19, the next available launch date would be May 22. Additional launch opportunities are understood to be available through to the end of May, whereupon a solar beta angle cutout period occurs for ten days from June 3 through June 13, during which time ISS spacecraft launches and free-flights are prohibited.

      Solar beta angle cutouts are periods of time where the beta angle of the Sun relative to the ISS (and any free-flying spacecraft in the ISS’ orbit) is high, meaning the Sun effectively shines on the ISS and other vehicles side-on.

      This can cause issues for free-flying ISS Visiting Vehicles (VVs) related to solar array power generation, since, unlike the ISS, the solar arrays on VVs do not have beta rotation capability, meaning they cannot rotate to face the side-on Sun, and thus cannot receive enough sunlight to generate adequate power.

      The free-flying spacecraft cannot orient themselves to face the Sun with their thrusters, since this would preclude them from being in the correct attitude to conduct rendezvous burns with the ISS, and could also cause thermal issues due to permanent shadowing of certain parts of the spacecraft.

      Solar beta angles are not a concern for VVs that are docked or berthed to the ISS, since they can receive adequate power from the ISS via power jumpers connected through the Common Berthing Mechanism (CBM) vestibule or docking mechanism interface.

    1. Sounds like the system worked as intended – it detected an anomaly and aborted. Now, was there a real problem with the engine or just a sensor error? SpaceX has done this before and knows how to handle the problem.

      They test fire all of the engines before each launch, so perhaps it was just a sensor glitch. I wonder if they have more than one sensor on each engine, say 3 sensors with majority voting logic or just one sensor per engine.

    2. Was it #5 that caused the delay the last time? If so, the similarities are striking.

  9. The animation at the top of the page is cool. Have my laptop plugged into my 42″ HDTV with 5.1 surround. The sound FX at lift off had my windows rattling.

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