Space x rocket landing

((Possibly a stupid question))

Why was space x trying so hard to land on a barge? Is it that much more better than landing on land?

Did their rocket split in two - the payload kept going up and the bottom landed?

The US does not have large expanses of uninhabited land, so all rockets launch from the coast and fly over the ocean. And rockets don’t just go straight up - a rocket must reach a horizontal speed of over 7.6 km/s to get into orbit.

So by the time the first stage of the rocket has finished its job, it’s maybe 100 miles off the coast. It takes less fuel to come straight down and land on a barge than to fly back to the launch site.

Conventional space launch rockets are multistage vehicles (typically 2-4 ascent stages plus upper stage propulsion/apogee motors). The reason for this is to reduce the inert (non-propellant) mass that has to be carried along the ascent, and therefore the overall size and thrust of the rocket. In fact, a single state to orbit (SSTO) has been the dream of aerospace engineers and space launch vehicle designers for decades, and while there are systems that are theoretically capable of this performance, none have yet been successfully built and launched, and the amount of payload that an SSTO could carry to orbit in comparison to size is pretty small, although the Chrysler Aerospace SERV proposal for the Space Transportation System offered Shuttle-class payloads in a modular base plug aerospike vehicle with propulsive landing capability. Sadly, nothing ever came out of that proposal as it was too far afield from the winged shuttle that NASA clearly wanted, and we got the Rockwell/Thiokol design instead with its problematic operational history.

SpaceX wants to land the first stage on a barge rather than return to land because they can place the barge on the ground track in mid-ocean and be able to soft land the stage with minimum propellant; done correctly, this requires only 2-3% of the total propellant loadout because the stage is virtually empty and requires very little thrust to land it. Most of the actual slowing of the stage is done by atmospheric drag on the body and deployable gridfins, so the engines are only used to initate a targetted descent and then a single engine to slow for final landing. The second stage continues onto orbit and is later disposed of by sending it back to Earth to burn up during reentry or for higher orbits or Earth escape trajectories like the DSCOVR mission it is sent to a disposal orbit where it will remain for tens of thousands of years.

SpaceX hopes to be able to refurbish and use the first stage in the expectation of reducing launch costs. This is a somewhat dubious prospect in and of itself as much of the cost of a launch isn’t the hardware but all of the integration and test labor that goes into building up a vehicle, and unless they can achieve really high margins against mechanical and thermal stress they’re going to have to do a lot of refurbish and replacing of components on the stage between flights. Given the kinds of conditions a stage and the motors have to endure and the balance between high performance and lightest possible weight, achieving a significant number of reuses of an engine or stage is problematic. (By significant, I mean dozens; a NASA study circa 1970 determined that 50-60 launches a year would be required to justify a reusable system on a cost basis, and Orbital Sciences performed a similar study in the mid-Nineties that came to exactly the same conclusion, which is unsurprising becase we’re essentially using the same materials, propellants, and performance standards as we did four or five decades ago.)

However, achieving success at powered landing is a demonstration of techincal prowess and has other eventual benefits, including feeding into Elon Musk’s eventual goal of human spaceflight to Mars, for which a powered final descent will be mandatory as Mars does not have a thick enough atmosphere to soft-land a crewed vehicle by parachute. There are many other difficulties in sending people to Mars, including enduring spaceflight for longer periods than anyone has presently spent in space, and the difficulties of the overall entry, descent, and landing on Mars which is described by those who have studied the problem (including your humble author) as being the most difficult solid body in the Solar System to land upon.


Nevada could serve fairly well in that role.

But it’s smart to launch orbital missions from low latitudes toward the east, taking advantage of the earth’s rotation. In the US, this suggests that Florida is a good choice for a launch site, with rockets headed out over the Atlantic.

great explanation Stranger, that post ladies and gentlemen is a prime example of why we “dope”

Nevada is sparsely inhabited, but except for parts of the Nevada Test Site/Tonopah Test Range, it is not uninhabited. And you really need a pretty long clear track for safety with very sparsely occupied places along the instantaneous impact point (IIP) in order to meet the maximum range safety expectation of casualty (E[SUB]c[/SUB]) threshold. (FAA wants E[SUB]c[/SUB] < 30 x 10[SUP]-6[/SUP], but the USAF actually demands E[SUB]c[/SUB] < 10[SUP]-5[/SUP] for launches from the Eastern and Western Ranges.)

Florida is basically the best site in the continental United States for low inclination orbits, but Cape Canaveral AFS is also sitting in the middle of a nature preserve in which no point is more than 30 feet above mean sea level, and many of the launch sites are only a few feet above. NASA is actually very concerned about damage and loss of pads due to rising sea level, subsidence of the underlying land (which is basically a floating sand bar), and an increase in the frequency of hurricanes from global climate change. Wallops Flight Facility (WFF) in Virginia is the other possible East Coast site and is suitable for certain types of missions, but it suffers from a similar problem and is high enough that making the ISS would be problematic even if the ground track could be cleared. Vandenberg is a great site for polar orbit and retrograde launches, but is totally unusable for prograde trajectories. SpaceX is addressing this for their commercial launch capability by intending to launch from Brownsville, TX but that will last only as long as they don’t accidentially send something over the border to Mexico and create an international incident. (I don’t say this in the hypothetical; it’s happened before and the major reason we can only fly very short trajectories out of White Sands and Ft. Wingate in New Mexico.). Ultimately, we may want to build launch vehicles or platforms that can launch from mid-ocean, which is what Bob Truax wanted to do four decades ago.


Would Hawaii be feasible as a launch site? Or too inaccessible relative to assembly locations?

To the OP, perhaps something as simplistic as reduced hazard/liability compared to a terrestrial landing?

Hawaii is in fact a launch site. More specifically, the Pacific Missile Range Facility (aka Barking Sands Missile Range) in Kauai was host to the ORS-4 mission, which attempted to use a small 4-state solid fuelled rocket to put a light payload into orbit. Sadly, the launch failed (and along with it, a cubesat I worked on).

The PMRF is on the west shore of Kauai and thus only suitable for polar orbits. I can’t really see equatorial flights ever happening. No one is going to build a new launch site on the island for environmental reasons, so it would have to be at an existing facility, and there aren’t any suitable ones.

It’s attractive due to its latitude. In particular, Ka Lae (South Point, on the Big Island) is at just 19 degrees north, making it the southernmost land in the 50 states. And to the east there’s nothing but Pacific Ocean for 2000+ miles.

For this reason it has attracted attention as a launch site. But it is indeed remote, and local sentiment has never been in favor of that sort of development (though it is home to a large wind farm).

Another reason is the conflicting requirements of optimum staging velocity vs getting the reusable first stage back.

Lowest total vehicle mass happens with a fairly high staging velocity; for a two-stage vehicle typically around Mach 10-12. When used in expendable mode, Falcon 9 stages at about that velocity. See this graph for a two-stage vehicle: Staging Velocity - joema

In reusable mode Falcon 9’s staging velocity is much lower, around Mach 6. This hurts overall payload performance but decreases the reentry heating and other issues to retrieve and reuse the 1st stage.

For lighter payloads they can kill downrange velocity in the 1st stage and fly it back to land. For higher payloads there is insufficient propellant for this so they must land in on the ocean barge.

It’s a good solution because the 1st stage is about 82% of the total vehicle mass and has nine engines, whereas the expendable 2nd stage only has one engine. They retrieve and re-use the largest, most expensive part.

No, it’s for fuel reasons. They’ve landed one back at KSC and intend to do so on the regular for missions that don’t require as much oomph, but for things going to higher orbits, the first stage needs to keep pushing for longer, which means that it’s too far out to fly back to land.

The ship landing is mainly going to be a thing for the heavy-lifter version (basically three of the current rocket strapped together) – the booster rockets on the sides will be used up early and go back to land in Florida, and the middle one will keep going a bit longer before separating, at which point it’ll be too far out to make it back to terra firma.

Fun fact: there was a study into recovering and reusing Saturn V first stages. It worked basically the same as the film-return capsule on the spy satellites of the time – grab it with a helicopter while it’s swinging under a parachute. Of course, an S-1C would’ve needed a REALLY big helicopter…

Also, there was an abort mode for the Shuttle that involved a similar boostback to land at KSC. NASA was pretty sure it’d work, but wanted to test it on STS-1; mission commander John Young said “Let’s not practice Russian roulette,” and the first shuttle flight just made a normal orbital flight.

Yup. Here’s a pretty good explanation with graphics:

Now will someone go back to 1950 and explain to all the science fiction writers that rockets aren’t going to take off and land in somebody’s back yard? Or even at the handy spaceport that’s where the airport used to be?

Now that rockets can take off and then land wherever they want to (instead of splashing back into the sea), I expect that we’ll have Flying Cars any time now.

Just any old time…

…waiting, waiting, waiting…

Of course not. They’re gonna land on your boat.

To be fair, nobody in 1950 aside from a handful of (mostly German) engineers had much experience with launching large, much less multi-stage, rockets, and it seemed to be a technology that, like the jet engine, just required some incremental advances in manufacturing and materials science to get to a level of everyday use. Unfortunate, unlike the jet airliner, about which this was true, space launch rocket vehicles and the engines that propel them experience structural, dynamic, and thermal loads and environments that are well beyond any terrestrial experience by an order of magnitude or more. The specific power density output by a rocket engine is well beyond anything that turbojet engine can perform, while the need to carry both fuel and oxidizer while not able to use the ambient atmosphere as a working fluid places some pretty restrictive limits on the performance of a rocket. Even if you could make the structure of a rocket out of superlight ultratechnometal with effectively infinite strength to weight and impervious to heat or impact, the vehicle would still require a massive amount of propellant to ascend to orbit and the same to return without using aerobraking. It was also not clear that rockets would be not terribly reliable and would pose a catastrophic hazard from virtually any kind of wide system failure.

Being able to launch from a spaceport that has about the same level of infrastructure requirements as a modern airport is still the goal of commercial space launch interests, and is the real path to reducing launch cost; going from hundreds of people supporting an individual launch to a crew of about a dozen, and automating the vehicle integration and final checkout testing could drop the amount of labor time those people have to put in down to a cost and launch throughput that could provide a viable several-times-a-week space launch capability. Whether there is actually sufficient demand for that capability remains to be seen; I actually think that this kind of throughput will be most beneficial to smallsat users who want to deploy rapidly developed generations of satellites quickly for commercial/tactical purposes, but getting there will require pushing launch costs to the mid-to-low seven digit territory while assuring good enough reliability that we don’t have shit falling out of the sky on a regular basis posing a hazard to people and shipping.

The challenge is going from “Oooh, ahhh! A launch!” to “Sigh…yet another boring launch,” without becoming complacent and allowing failures to happen or adopting a “good enough is done” philosophy toward efficiency and reliability. It is unclear whether there will be enough really heavy payload launches outside of DoD and space exploration launches to develop and maintain a heavy launch infrastructure. Most heavy payloads to MEO or GEO are constellations of satellites which, once deployed, will operate for decade-long lifespans or more, and there is only so much bandwidth and orbital space to safely occupy. In fact, one of the most important emerging markets in orbital space industries will be salvage, repair/replenish, and retirement of obsolete or inactivated space assets, but this is going to require some revision and development of current space law.


I know this is a legitimate thing, but this phrase still makes me giggle. I await the hordes of Sovereign Citizens to catch hold of this, saying “You have a rocket-shaped truck at the top of your flagpole. That means we are in Space Court, and the judge is acting as Commander under Space Law. You have no jurisdiction under the Kármán line!”

Well, it’s sort of a thing. Unfortunately, there are only a few more-or-less universally adopted conventions about operations in space, and many of them are more guidelines than laws, even in the oft-nebulous world of so-called international law. Along with international finance and commerce, it is an area that really begs for a multinational authority with well-defined if limited powers to oversee operations and commercial use of space and impose legal penalties that will be acknowledged and enforced by individual member states. Lacking this, the problems of pollution of the orbital space environment with debris and abandoned hardware, competitive use of space resulting in conflict, and the potential for rogue actors to disrupt critical space commerce and safety operations will grow as more nations and private agents gain the ability to deploy spacecraft and use bandwidth. Preventing the militarization of space and developing an infrastructure to support egalatarian use of the limited resource that is Earth orbital space is part and parcel with encouraging use commercial and scientific development to a maximum extent, and is something that all nations and commercial space interests should be working toward. Unfortuantely, as with most new developments, everybody is waiting for someone else to take the lead, and the regulations that currently exist often serve only to limit developement and adoption of useful technologies while leaving spacecraft vulnerable to hostile actors and those who see orbital space as the battleground of the future.


Really great analysis, Stranger. This is one part my son (ULA) often brings up. I think he’s used the analogy of a sparkler. OK, after it burn, you’ve got the stick. So how much does that save you on the cost of making another sparkler? I forget what figure he quoted as the percentage of first stage costs attributable to materials, but I thought it might be as low as 10%.

Still, way cool to have so many regular announcements of exciting developments in space travel.

My wife and I are both lawyers, so he regularly sends our way articles on space law. Like you say, they are more what you would call “guidelines.”