SpaceX Landing Sequence in Detail (Weather at 80%)

Falcon 9 on the pad Monday evening / Image Credit S. Money

Meteorologists with the U.S. Air Force’s 45th Space Wing are estimating an 80% change of good weather for Saturday’s 4:47 AM EST SpaceX launch attempt from Cape Canaveral. Temperature will be in the low 50’s, with the primary concern being thick clouds.

In a wide ranging Reddit AMA (Ask Me Anything) which took place on Monday evening prior to Tuesday’s scrubbed launch, SpaceX founder Elon Musk shed a bit more light on the “autonomous spaceport drone ship” landing effort which will take place some 200 miles out into the Atlantic ocean east of Jacksonville, Fl. Taken with answers provided by SpaceX VP of Mission Assurance Hans Koeingsmann’s responses to questions at a pre-launch press conference held earlier the same day, here is a summary of what will take place.

Following second stage separation and ignition, the Falcon 9’s first stage will fire three of its nine Merlin 1-D engines in the first of three separate burns which will guide it to the 300′ x 150′ self-propelled platform stationed in the Atlantic. Each burn will include a separate ignition event as opposed to a continuous firing of the pivotal center mounted main engine. Including the liftoff itself, as well as the static fire which precedes every SpaceX launch, that brings the total to a remarkable five separate ignition events for each flight which includes a recovery effort.

The first phase, which takes place well above the atmosphere and begins only seconds after stage separation, is the turn around and boost back burn which will redirect the Falcon 9 first stage and bring it back towards the landing zone.

The second burn slows the falling stage to ease its transition into the upper atmosphere. Approximately five minutes into the return flight, with the first stage still outside of the atmosphere, the four “hypersonic grid fins” will deploy. Their job is to control the booster’s pitch in order to more precisely target the landing zone than has been possible in previous efforts while helping to conserve fuel for the final hover and soft landing.

The boost back back sequence and recovery effort is automatic, with no abort modes, and comes with three possible outcomes; a clean miss and water landing with no realistic chance of recovery, a historic first landing, or finally, a hard landing or partial miss, with damage (or destruction) of the booster and possibly some damage to recovery vessel as well.

Keeping outside a 10 mile safety perimeter during the landing phase, a recovery vessel with control capability over the now static booster will approach the ship and command the first stage to safe itself. Remaining LOX will be vented, while RP-1 will stay in the tank, just as it would Koenigmann said “with any airplane.” After 1-2 hours, the recovery crew would then board the vessel and secure the booster.

While the mental picture of a tall, thin rocket stage perched on a four spindly legs aboard a small platform on a pitching ocean might not be one which shouts “stability,” in reality it should not be problem. With 9 engines and whatever fuel remains located at the bottom of the now shortened “stack,” the first stage will in fact be surprisingly stable. Furthermore, equipped with directional thrusters which can counteract most wave action, the platform itself will be quite stable as well.

Steaming Towards Its Hold Position
Image Credit: Elon Musk

In case that isn’t enough however, SpaceX plans to further secure the booster by welding metal plates over the four landing pads.

If all goes well, and that’s one big if, the first stage will be returned to port at Jacksonville, and presumably trucked across I-10 back to McGregor, Tx for analysis and one would think, a history making post-flight full length re-fire as well, although the specifics have not been addressed.

When will we know? And when will we see?

The landing sequence itself is fairly brief, and approximately nine minutes after liftoff, it will all be over one way or another, even as the space bound second stage will still have about a minute of its own burn yet to complete.  That doesn’t mean we will know anything quickly however.

During previous ocean landing efforts, details have been slow in coming out, and video even slower, although in one case it was with good reason. During the April 18th, 2014 landing attempt on the NASA CRS-3 mission, gale force sea conditions kept recovery vessels in port while icing kept a NASA observation plane on the ground. Elon Musk’s aircraft, equipped with a makeshift antenna fashioned in part out of a pizza dish was in the air, but to little avail.

The CRS-4 mission, which lifted off on September 21st did not include landing lags, but did feature a first stage booster flyback towards a pre-determined spot in the ocean, and it is reasonable to assume that SpaceX was sufficiently impressed with the results as to inform its decision to make a full attempt less than four months later.

With conditions more favorable this time, Koenigsmann speculated that it is possible video could be available by the end of the day. Telemetry will be coming in from both the booster itself, as well as from the recovery vessel.  On the other hand, with the landing point over the horizon, data transmission will continue to be a challenge and video upload will take time. Also, with everything taking place well before dawn,  NASA apparently is not going to bother with an aerial based imaging attempt either, meaning the first visual confirmation is likely to come from cameras aboard the platform or the recovery ship. If prior experience is any guide, Saturday might be a very good day to follow Elon Musk on Twitter.

About those odds.

Musk originally cited the chances of success at 50%, but admitted during the AMA that it was “just a guess” and he really had no idea. At the press conference, while struggling mightily (and failing) to say “autonomous spaceport drone ship” multiple times without smirking, Koenigsmann seemed to agree with the general assessment offered by his boss, but at times his demeanor suggested a quiet confidence that the odds could be a bit higher. It is worth contemplating that whereas a year ago SpaceX was expected to have already begun testing an advanced version of the Grasshopper test vehicle at Spaceport America in New Mexico, that has actually yet to take place. Part of the delay is no doubt due to the loss of a  test article in Texas on August 22, but the decision (already made) to go ahead with building the recovery ship and then deploy it so quickly could be taken to mean the New Mexico phase may be curtailed. In other words, SpaceX may be more confident than it is letting on.

And what if it all works out?

Dating back to when SpaceX first began outlining its plans for reusing the Falcon 9, skeptics have repeatedly come back to the proposition that the costs of recovering and prepping the stage for subsequent flights would be problematic.  And, as a recent Space News article points out, arch-rival Arianespace is still telling itself that even as it tinkers with a low level study of possible future reusability options. The scant comfort of denial may have been pierced rather rudely when Elon Musk answered a Reddit question about the Merlin’s 1-D’s 40 cycle design limit thusly:

“There is no meaningful limit. We would have to replace a few parts that experience thermal stress after 40 cycles, but the rest of the engine would be fine.”

Whether you elect to stay up, get up, or just check in later in the weekend, one thing is certain, if the Falcon 9 lights the pre-dawn sky over Cape Canaveral, history may be taking one hell of a ride.

Per Ardua Ad Astra