SpaceX Releases Images of Falcon First Stage During Descent

23 Comments
falcon9_relit_stage2

Falcon 9 first stage in a controlled descent toward the Pacific Ocean. At this point, the stage was about 3 meters (9.8 feet) above the water. (Credit: SpaceX)

SpaceX has released two photos showing the first stage of the controlled descent of the Falcon 9 v1.1 launch vehicle’s first stage during a demonstration flight from Vandenberg Air Force Base on Sept. 29.  The images are part of a mission overview on the company’s website that includes the following description:

“Though not a primary mission objective, SpaceX was also able to initiate two engine relights on the first stage. For the first restart burn, we lit three engines to do a supersonic retro propulsion, which we believe may be the first attempt by any rocket stage. The first restart burn was completed well and enabled the stage to survive reentering the atmosphere in a controlled fashion.

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Falcon 9 first stage burns an engine during a controlled descent to the Pacific Ocean. (Credit: SpaceX)

“SpaceX then lit the center engine for a single engine burn. That relight also went well, however we exceeded the roll control authority of the attitude control thrusters. This particular stage was not equipped with landing gear which could have helped stabilize the stage like fins would on an aircraft. The stage ended up spinning to a degree that was greater than we could control with the gas thrusters on board and ultimately we hit the water relatively hard.

“However, SpaceX recovered portions of the stage and now, along with the Grasshopper tests, we believe we have all the pieces to achieve a full recovery of the boost stage.”

  • Robert Gishubl

    The fact the rocket survived re-entry and could re-light the single engine for final landing is impressive and demonstrates this method is achievable. More work still required for spin stabilisation but this si a test program and some problems should be expected. I just would like to see more flights and more tests but I believe there is a limit as to how much SpaceX can spend on development. Next up Pad abort for Dragon.

  • therealdmt

    Just moving mass outwards by deploying the legs may slow down the spin enough. Plus there’s the stabilizer-like fin effect that the legs may give the rocket. Can’t wait until they try it on a Falcon with the new legs, but that looks like it’ll be quite a number of months away (at least 4 flights into the future, iirc).

    That pic just over the water is cool! I didn’t expect to get to see that.

  • Hug Doug

    i’d like to think that the Grasshopper v1.1 will be flying before the next water-landing test occurs.

  • Tonya

    I wouldn’t expect much of an ice skater effect from deploying the legs as their mass compared to the engine block should be tiny.

  • dr

    Why would there be a limit on how much SpaceX can spend in development. I understand that in any given year, they only have so much cash and so many staff, but development should be funded by revenues. So as long as they are a profitable company they can spend and spend and spend.

  • mfck

    The expect stabilizing effect comes from the aerodynamics of the leg fairings, not from the “skater effect”.

  • Michael Vaicaitis

    ISPCS ‏@ISPCS19h
    @SpaceX hopes to have their first flight from @Spaceport_NM in December 2013

    presumably v1.1

  • Tonya

    My comment is in reply to that above “moving mass outwards by deploying legs”. Please take note of context.

  • http://exoscientist.blogspot.com/ Robert Clark

    But the skaters arm mass is also small compared to the mass of the skater. Also the rocket stage will be nearly empty when it is coming in to a landing.

    Bob Clark

  • Hug Doug

    its things like this that make me think i should just get me a twitter account.

  • DBC

    Just for fun, I googled it: “One human arm accounts for approximately 6.5% of your body weight.”

  • Tonya

    And in the same spirit of fun.

    F9.1 first stage dry mass is believed to be around 28t. To compare to a skater, lets use 13% (two arms) to see how much mass the legs would need for as large an effect. 13% of 28t = 3.6t

    As the legs are made of carbon fibre, I suspect they will be much lighter than that. If any engineer wants to trash those numbers, please do, I’d be interested as well.

    Looking at the legs, I do now wonder how they’ll be deployed. Whether they will simply lock in the landing position, or partially deploy whilst descending to provide greater aerodynamic stability. Until the engine fires again in the terminal stage of descent, the weight of the engines would provide stability like a shuttlecock.

  • Michael Vaicaitis

    I have a vague memory of Elon saying that the landing leg system would weigh “about” the same as a Model S, which is 2.1tonnes. Also, that the F9-R is “about” 95.5-96% fuel by mass. Launch mass is given as 505,856kg, so dry mass is “about” 20.2-22.7tonnes. But then there’s also gotta be a fair few tonnes of fuel and that heavy LOX, especially if they’re really hoping for fly-back to launch site. All in all, quite a skinny armed skater.

    “Until the engine fires again in the terminal stage of descent, the weight of the engines would provide stability like a shuttlecock.”

    Nope, not with all that LOX higher up – it’s the gas thrusters that maintain the vertical attitude. Take a look at the recent video at about 2:21-2:27, just after the obsurring vac engine start, you can see a white plume at about 7-8 o’clock on the falling 1st stage. Perhaps it’s just another effect on that video and I’m fooling myself, but it’s a fair bet. Genuine visual evidence or not, either way, without the cold thrusters, the first stage falls straight into a belly flop position.

  • Tonya

    Yep, top heavy with LOX, quite right. If the vanes had significant aerodynamic drag they’d probably help make it unstable, the exact opposite of a shuttlecock.

  • Michael Vaicaitis

    I won’t profess to be an expert on the aerodynamics of a falling cylinder, but I will happily speculate until put in my place.
    The side profile of 55-60m of cylindrical core is surely a more significant aero contributor than the leg profiles. I’d guess that the cylinder is trying to be a (poor) lifting body. The gas thrusters are used to keep the thing upright against the “hardest” air as it falls, thereby reducing that aero contribution, but clearly not enough to completely eliminate an aero induced spin. In the upright cylinder position, the landing legs profile (and the octaweb base) is directly into the airflow, giving them a disproportionate aero contribution.
    Of course, we can’t completely discount the added skinny armed skater effect, but I suspect the aerodynamic effect induced on any “forward” facing surface by a 50tonne rocket falling at hundreds of km/h might be more significant.

  • Michael Vaicaitis

    A quote from a recent Jeff Foust article: “That second relight didn’t work well, though, because the stage was spinning fast enough (due to aerodynamic forces) to push the remaining propellant against the walls of their tanks, shutting off the flow of propellants to the engine.”

  • http://twitter.com/cshotton Chuck Shotton

    Gosh. I’m guessing economics wasn’t your forte in school. If they make $100 in profit, how much can they “spend and spend and spend?” And what if they aren’t profitable yet?

  • Michael Vaicaitis

    “I understand that in any given year, they only have so much cash and so many staff, but development should be funded by revenues.”

    Obviously, the “spend and spend and spend” phrase, relates to the sentence that preceded it – what is your forte?.

    I believe they have been profitable for several years and have several billions worth of business, which is only likely to increase. If they wish they can spend all their profit on development, because they are privately owned, and the owners are not “in it for the money”. Those with some knowledge of SpaceX would know that it is not a typical company. So, in this case, development spend is not mainly constrained by economics per se.

  • spacechampion

    My understanding is that Grasshopper is now officially retired and Falcon 9R will be the next rocket to be testing reentry, flyback and landing.

  • Hug Doug

    yes, the first Grasshopper, the one having flown all the tests done so far, has been retired, according to SpaceX its 8th flight was its final flight. however, they will now be testing a Grasshopper v1.1 at Spaceport America. it will be based on the Falcon 9 1.1 first stage and it will have flight-like legs.

  • Michael Vaicaitis

    Grasshopper v1.1 at both Texas and NM. Texas for low-altitude testing, NM for high. Though seems to me, you have to go through low altitude, to and from high, so we will see.

  • Hug Doug

    You’re right, I should have qualified. low-altitude testing at the McGregor test site (likely only a few brief hops), and high-altitude testing at the Spaceport America test site.

  • Michael Vaicaitis

    “This particular stage was not equipped with landing gear which could have helped stabilize the stage like fins would on an aircraft,” SpaceX officials wrote. “The stage ended up spinning to a degree that was greater than we could control with the gas thrusters on board, and ultimately we hit the water relatively hard.”