Business, Space, Technology and Society

SpaceX And Orbcomm

34 Comments

This morning’s flight seems to have been a complete mission primary success. No word, though, on recovering the stage. No status updates on relighting engines, entry, etc. Reports of Elon’s and other plane circling the recovery zone. Sea state seems to be good, less than three-foot waves.

[Update a few minutes later]

My response:

34 thoughts on “SpaceX And Orbcomm”

  1. Perhaps the booster was coincidentally hired by the White House upon ocean contact, since that also causes a complete loss of integrity within about a second.

  2. Keep in mind that it is not and never was intended to land in water. They are only doing it to collect data. It must also be tough to land with exactly zero fuel remaining although that’s not really a requirement. A near empty tank is the most explosive I’ve heard.

    Gotta see what badmouthing they will come up with at America Space?

    1. That depends on what occupies the empty space in the tank. About the last thing you want getting into a kerosene tank is air. Use an inert gas to fill the tank and you’re fine.

      1. ” About the last thing you want getting into a kerosene tank is air.”

        I had a 400 gallon kerosene tank in my backyard, it had an air volute in it for most of it’s operating life. I’ve had Kerosene tanks for small heaters in the garage without issue.

        There are reasons to put Helium gas in a rocket fuel tank, but, it’s more for cavitation
        control on the pumps.

        1. I had a 400 gallon kerosene tank in my backyard, it had an air volute in it for most of it’s operating life. I’ve had Kerosene tanks for small heaters in the garage without issue.

          Were you in the habit of dropping it in the ocean with a hot engine next to it?

          Idiot.

          1. “Were you in the habit of dropping it in the ocean with a hot engine next to it?”

            This sounds like thermal stress, independent of the actual fluid inside.

            An engineer would know the difference between thermal stress related failure
            of a tank dome and deflagration/detonation related failure inside of a tank dome.

          2. Some people poke the beehive and run away. Other people smash the beehive on the ground and then roll around in bees.

  3. Cold seawater vs super-heated material with fuel vapor left in the tanks. It does not take a rocket scientist to figure out what happened. Oh, wait…

  4. “(aka kaboom)”

    Maybe too rapid heat transfer into the LOX tank from the water causing rapid vaporization of remaining LOX?

  5. Greg and Andrew both present plausible explanations. The kerosene tank cooling suddenly could go negative pressure, imploding the tank. I’d presume a pressure relief valve on the LOX tank, but too great a heating rate on contact with the ocean could exceed that valve’s capacity. Unless both tanks failed there should be salvageable wreckage this time.

  6. I just have to think that Musk and his design team have _already_ considered all the failure modes of landing a rocket stage in cold seawater with a hot engine and near-empty tanks. So perhaps something else happened?

    However, I agree with Rand that they should start landing on land: there’s plenty of empty area available, heck they could use the Australian outback if needbe. I don’t think the Aussies would mind much, especially if SpaceX hired the locals to retrieve the stage. 😉

    1. The first stage could never make it all the way to Australia. It’d have to moving at nearly orbital velocity to go that far. That might be a possibility when they’re ready to try recovering the upper stage.

  7. Maybe try dropping it on an island in the Bahamas instead?

    Wrong direction, Rand. About the only thing in the general direction of the Orbcomm mission’s terrestrial track big enough to land on is Bermuda and I’m not sure even it was especially close. Bermuda is, in any case, and regrettably for this scenario, fairly heavily populated. The natives wouldn’t be happy about having experimental booster stages dropping in for tea. The significant population of uber-wealthy ex-U.S. and ex-European tax exiles who live there could be counted upon to be even less enthused.

    The lesson of “kaboom” would appear to be that “soft-splash” – having now been tried twice, and having been successful down to sea-contact level both times, but with no more or less intact stage recovery having been possible – has been exhausted as a “learning exercise.” The sea state for this attempt was about as good as it’s ever likely to get. Dunking hot booster stages in cold water just doesn’t look like a useful thing to do again going forward. All the juice has been squeezed out of this particular lime.

    The next two SpaceX missions listed on SpaceflightNow’s launch manifest are AsiaSat geosynchronous comsats. Given the circumstances of prior SpaceX missions to GTO, neither of these are probably candidates for another controlled booster stage re-entry test. SpaceX’s next CRS mission is currently shown as scheduled for launch Sept. 12. It would behoove SpaceX to conclude its discussions with KSC and/or Canaveral about just where it can safely recover F9R 1st-stages feet-dry on KSC/Canaveral property and start making plans to do so 60 or so days hence. To achieve three more launches off the pad just used in 60 days is a formidable challenge, but accomplishing that would be a huge feather in SpaceX’s cap, especially if the third of those missions also included the first feet-dry recovery of an F9R 1st stage.

    1. I dunno about that. Have they tried keeping the engine turned on until after the splashdown instead of hovering over the water and falling down? I remember Truax operating engines underwater just fine. I do not know if that would be enough to reduce the temperature gradient from the splashdown or not.

      Perhaps the splashdown can only be done using more robust structures. Still they could at least try to do some more impact tests and try to figure out exactly why the rocket is disintegrating. If they added sensors to measure temperature and hull deformation and stored the results in a recoverable black box it should be good enough to have some idea of why it disintegrates.

      They could also try doing some lower velocity tests with the F9R in a lake once they decide they are not interested in flying it anymore.

    2. If SpaceX had infinite resources and unlimited staff there are probably a lot of questions it could answer. As it has no long-term intention of landing F9R 1st stages in water, no compelling reason to push this particular effort forward seems to exist. They seem to be getting the stages back to accurate bullseyes. That being the case, it’s time to move this show all the way back to the land they always intended to land on.

    3. The Bahamas are, technically, an option for landing F9 1st stages, and I’ll explain why;

      You’re quite right about the azimuths used today and for CRX-3; they are northeast, whereas the Bahamas are located southeast. With those azimuths, you’d need a heck of a lot more delta/v to reach anywhere in the Bahamas than the cape. For example, the CRX-3 splashdown was 271 nautical miles from the pad.

      The thing is, launch azimuths to reach a specific orbit is a trig function of inclination to the equatorial plane (assuming launch latitude is the same or less than orbital inclination) . Inclination is measured from the equator and not from north. So, CRX-3, to reach the 51.5 degree ISS orbit, could (and did) use an azimuth of 45 degrees (roughly north northeast) or, they could have used an azimuth of 135, roughly south southeast. At that azimuth, and at the same downrange distance as on CRX-3, you are on dry land in the Bahamas, and there’s even a paved area for landing on that spot; Parliament Square, surrounded by the Bahamian parliament building, in downtown Nassau. I have no doubt that landing the stage there, especially if unexpected, would generate quite a bit or press interest.

      For the azimuth on today’s launch, and range being less (it was a lofted trajectory) you’d have as possibilities several cays north of Abaco island. However… landing an F9 on the forested centers might not be good, so that leaves the beaches. I wonder of those legs would hold it upright in soft sand? I also wonder how they’d get it out of there.

      Bermuda? Hrmmm. The OG2 satalites went into a high LEO orbit with an inclination of 52 degrees, so the launch azimuth would be darn close to the one used for 51.5 ISS orbit. Less than half a degree difference. A great circle plot of the azimuth shows Bermuda is far to the south of it, plus at 850 nautical miles from the cape, it’s too far. But, your concerns that the inhabitants of the small, densely populated island might object to the F9 dripping in for tea time are quite unwarranted; the launch time used today would place its arrival in that timezone before tea time, so by teatime, it’d all be over except for some lingering smouldering on the part of the local inhabitants.

      In all seriousness, I don’t think it’s possible to land it on dry land with any degree of confidence without rehearsing the full transsonic flight regime (which they can’t do at McGreggor) so it’ll have to wait until the second “grasshopper2” F9R first stage testbed is flying in New Mexico. Without that data and experience, I highly doubt they’d have the accuracy needed to land it precisely enough to attempt a land landing. (also, so far as I know, the top end grid fins that are critical to landing accuracy have only been test flown once, at McGreggor, and in an aerodynamically insignificant regime).

      One complicating detail to bear in mind; the boostback maneuver to land at the Cape is not, precisely, a retroburn; it’s an angled burn relative to the velocity vector, to achieve a reverse of the bearing but also to loft the stage higher; it’s burning to go into a high ballistic arc back. So far as I know they’ve never actually done a true boostback burn, just a retroburn directly into the velocity vector to kill off some velocity.

      My personal opinion; if they want to recover a 1st stage without getting it wet, their only viable option at the moment is to try putting it down on a big flat barge. However, a couple of flights at Spaceport America with the second “Grasshopper 2” F9R first stage should tech them what’s needed to try a landing at the Cape. I would not be at all surprised to see a F9 first stage land on land before the end of the year (though I think the first half of next year more likely).

      2. ” if they want to recover a 1st stage without getting it wet, their only viable option at the moment is to try putting it down on a big flat barge. ”

        or an old oil drilling rig.

        Maybe a container ship, go out empty, lay down a decking rig. Land on that.

        I’m sure the SpaceX team has thought of this.

        I imagine the costs are brutal.

      3. I’ve mentioned this before elsewhere, but there are the Florida Cays as well. Many of these are essentially uninhabited sand bars but are still big enough to provide a useable target and along similar trajectories as other islands in the Bahamas. Assuming you are on the 135 degree trajectory. However I agree with ArizonaCJ, testing at White Sands needs to be completed first.

      4. Being neither a ballistician nor an orbital mechanic, I defer to the superior judgement of the gentlemen assembled.

  8. I guess I don’t understand very well the issues involved in trying the splashdown on land. Does the telemetry not at least tell them that the positioning of the landing is exactly where they wanted it, or not? If they have successfully positioned the stage exactly where they want it, why should there be a problem landing it in a deserted area? It doesn’t sound more dangerous than letting a spaceship take off in the first place, assuming the stage is stilll in good enough shape (as evinced by successfully pinpointing where it lands).
    I don’t see any point in continuing to land it in the sea, where they obviously have no real hope of getting it back in good shape (even if it wouldn’t explode) – except if they can’t get permission to land it on land.

    I’ll take that back: I guess it would be nice to develop at least a rudimentary ability to land in the sea in case of emergencies where safe land cannot be reached. You certainly don’t want your rocket going kaboom if you can avoid it. Still, that would be way down the list of priorities; a normal landing on land should be tried as soon as it’s possible. They have already landed a Grasshopper and a Falcon, so there’s no reason to think it wouldn’t work. Unless of course they are already finding out that the first stage is badly battered and isn’t going where they want it to. Which would be a pity.

    1. To the best of my knowledge, SpaceX has had none of the potential problems you list. The stages come back to where they are intended to be and do trouble-free descents – right up until they actually hit water. That being the case, SpaceX should press management at both KSC and Canaveral to let them try a feet-dry landing somewhere on one or the other of these facilities as soon as the next CRS mission. All they really need for a target is some moderate-size concrete-paved area not too close to anything damageable by an explosion of whatever dregs of fuel remain as the stage sets down. Both KSC and Canaveral would appear to be target-rich environments where these few criteria are concerned.

      1. Thanks for the info. Do we actually know that they were able to pinpoint the location of the descent? SpaceX seems to have nice videos and such for the takeoffs, but keep the recovery attempts pretty hidden. Are they releasing the video from this descent?

      2. A recent SpaceX video showed a stage heading toward a notional small pad in a bare area adjacent to the midpoint of the CCAFS runway, just south of the end of Armory Road . Looked plausible.

  9. Even a soft splash turns out to have some unpredictables. Landing in water is for seagulls and other creatures without metallic, mechanically and thermally intricate hardware.

    ‘Targeting practice’ to satisfy government bureaucrats may be the most useful part of the whole water landing exercise.

  10. Is it known how the F9R first stage is going to navigate to the landing pad and land? I suppose most of the way it’s done by GPS, but what about precision positioning above the pad and altitude sensing during touchdown?

    1. If I were directing the design of terminal guidance for return to launch site I might favor a differential GPS beacon near the site, and maybe a final positioning beacon set at the landing pad. Seeing their grasshopper and Falcon 9r test flights, I think they have navigation for touchdown worked out.

      1. I think they have navigation for touchdown worked out.

        Yes, there’s a fair number of possibilities. dGPS or pseudolites are certainly an available one. Optical scene matching is another.

        I’m just wondering what one(s) they are actually using.

  11. The cause of the “Kaboom” Elon Must mentioned as the fate of the 1st stage had been determined; there were parts commonality in certain elements of the flight control system hardware with certain data-storage devices in federal service, so all it took was an old subpoena floating a few miles away… Kaboom.

  12. Elon Musk wrote in a Twitter post. “Detailed review of rocket telemetry needed to tell if [it was] due to initial splashdown or subsequent tip over and body slam.”

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