Rockets of Today

FALCON — USA, 2010

Finally we get to the good stuff — the brand new wunderkind rocket which is obsoleting all the rusty crap which the space industry has been putting up with for too long. Elon Musk — easily the most important tech visionary of our time, whatever you may think of his behavior — once tried to buy some services from existing rocket companies, and found them so unhelpful and uncompetitive that he decided to take the money he was going to offer them and start a rival company with it instead. In short, he found a market ripe for disruption. He soon found ways to undercut their prices, and in the process, almost by accident, produced some of the most rapid advances in rocketry that had been seen in decades. Many other space startups emerged around the same time, but so far only Space Exploration Technologies Corporation, better known as SpaceX, has made the new venture a sound commercial success on a large scale. They now boast a long track record of successful and profitable launches. SpaceX is far from his only company, of course. In all of his ventures, what separates him from other tech moguls is that he approaches things first as problems of basic physics, then of engineering, and finally of manufacturing processes, rather than in terms of marketing or finance.

Falcon 9 rockets, unlike any from previous eras of spaceflight, are designed to be highly reusable. The first stages soft-land themselves and are ready to go again after some refurbishment. They’ve pretty much perfected the “suicide burn” landing, in which the rocket stops exactly at ground level as smoothly as if you were watching a takeoff in reverse. But the reuse process is still in early stages, with time between landing and takeoff only gradually decreasing from months to weeks, with a turnaround in days still far away. If they succeed in getting a whole fleet of Falcons to do ten launches each, we could see prices falling through the floor, like under one million dollars per ton to orbit... if any competitor ever gives them a reason to lower their profit margin. (We’ve seen Tesla raise prices and then cut them depending on competition, so I would expect SpaceX to do likewise.) In 2020 they reused some boosters over five times, and one of them went up to eleven uses in 2021, and two more did in 2022 (forming a group which Scott Manley called “the Nigel Tufnel club”), but the turnaround time is still weeks rather than days. Four weeks was the record for a while, then three, which by the ambitions the Falcon was designed for is a big success, but it’s still nothing like the quickness that might be possible with methane-burning engines.

booster landing

But even when reuse was still marginal, SpaceX became the number one launch provider in the world, except for the Chinese government at times — twice as busy as any of their commercial competitors. In 2017 they averaged one and a half launches a month, and said they were facing the challenge of speeding up toward a weekly pace, because customers were still backed up in a waiting list. The plan was to do thirty launches in 2018, but this slipped, as things often do with SpaceX due to their “agile” approach to engineering and their “aspirational” scheduling of innovative achievements. For a while, the limiting factor was the rate of manufacturing enough of the latest “Block 5” booster stages. As a result, SpaceX fell behind the pace set by China with the Long March 2, 3, and 4.

But the number of customers has been flattening out. In fact, in 2019 their overall launch rate decreased, and they actually had a three month dry spell with no launches at all. It appears that the queue of customers awaiting the launch of heavy satellites has emptied out. (ULA’s launch cadence has also decreased.) I think they were hoping that lower prices would stimulate demand, but so far, that isn’t happening. Maybe if they were a lot lower. As things are, most launch customers have needs which are fairly inelastic as to price, or they wouldn’t be in the market in the first place. It may be that no amount of price lowering significantly increases the demand for heavy satellite launches, as usually the craft themselves already cost plenty more than the launch does. Perhaps there will eventually be new opportunities for budget-priced large satellites, but if there are, nobody has figured them out yet. It may be years before the demand catches up to the supply.

Well, if no one else has a use for cheap mass-produced launches yet, Musk will have to come up with one himself. And he has: Starlink. It’s a plan to provide fast internet wirelessly using thousands of satellites — tens of thousands, if they grow to the scale they claim they could. At sixty quarter-ton sats per launch, they’ll be doing dozens of flights for this project for the next decade... and once they have the full set aloft they’ll be continuing afterwards with replacement launches, as the early versions of the sat are designed to stay in service for only five years and then ditch into the atmosphere, so that the technology can be continually refreshed. They planned to do about 25 launches a year for this project, starting in 2020. That will bring their cadence numbers up... they did 26 launches in 2020 despite covid, and in 2021 they did 31. By this time they had plenty of boosters available, making five or six new ones per year and only losing one or two. In 2022 they passed the cadence of a launch per week, completing sixty flights, and pushed the number of uses of three of their boosters to fourteen, and one booster to fifteen. With Starlink going full speed, SpaceX was lifting twice as much tonnage to orbit as the rest of the world combined. Even if you don’t count Starlink, 2022 had 27 launches (plus one Falcon Heavy). The Long March 2 is the only other rocket to come close to that, with 24.

But astronomers are not happy about this large increase in the amount of “space junk”, and they’ll be even less happy when competitors start putting up their own satellite swarms. (We ought to build and launch several Hubble-sized telescopes — that might relieve the feelings of the astronomical community significantly.) Several outfits have announced plans for such networks, including Amazon and the Department of Defense. But competing won’t be easy... an outfit called OneWeb just launched about three loads of sats and then went bust. They then got bailed out and resumed launching, though it’s hard to imagine any success coming out of this effort. The Pentagon’s swarm, of course, doesn’t need to compete. The first launches of this swarm will be on Falcons.

With all this makework, the logistics of the Florida space coast may not be up to that pace. Many companies and agencies have to share common infrastructure there, and increasingly often, a delay experienced by anyone affects everyone. SpaceX has been reviewing the sticking points and pushing for changes to support busier schedules.

SpaceX is also now organizing ride-share launches which carry sats from many small customers instead of from a few large ones. If you’re willing to share your orbit, this will underprice being launched on something like an Electron.

The Falcon 9 has nine kerosene-burning “Merlin” engines, all fully gimballed. Its second stage uses a single Merlin, with an oversized bell for efficiency in vacuum — not much smaller than the fuel tanks it’s attached to. That bell is made of exotic niobium alloy, and glows orange in use. They have said that their goal was to put a heat shield onto the second stage and soft-land it too, but they’re backing off from that nowadays. That sounds dubious anyway unless they cut the payload capacity way back, but I can see why they wanted to, as they now say that with reusability of the booster, the loss of the second stage accounts for something like one third of the cost of each flight. They might cost around $20 million or so apiece, by one guess I’ve heard. Musk admitted that this would only be feasible for “some payloads”, but he still wanted to see if they could do it. They also worked on landing and reusing the fairings which cover the payload, bringing them down on parachutes. They tried guiding them to a ship with four arms holding up a big circus-net made of cloth straps, but despite occasional successes, this turned out too unreliable and hazardous, so they settled for letting the fairings splash down. Trying to land them in that net was very difficult, like trying to throw a layup with a potato chip — it’s just too aerodynamically unstable. Though those fairings are very simple things compared to the second stage, they still cost like $5 million, and they have to buy them from a vendor, who apparently has taken advantage of SpaceX’s inability to get them anywhere else to not only keep prices high, but obstruct progress on making a larger size. This may be due to pressure from their other customers who compete with SpaceX.

Anyway, all of these hopes and plans for the Falcon are now fading, as Musk becomes increasingly committed to building an all-new rocket to obsolete it, instead of working on incremental improvements to it. See the Starship article.

They’ve put together a triple booster “Falcon Heavy” version... about five years after they thought they would. With the recent Block 5 upgrades, even the basic Falcon now nearly matches the payload capacity of the Delta IV Heavy, so the Falcon Heavy is a huge leap in lift capacity, and for a few years it was the most powerful rocket in operation. (The Delta looks bigger, but that’s because it’s full of hydrogen. The rocket which supplanted it as most powerful was the SLS.) The Falcon Heavy’s claimed capacity is over sixty tons, without even using a bigger second stage. But that’s if you’re willing to pay them to discard stages instead of recovering them, as the payload limit is quite a bit less if the boosters need to land afterwards. In expendable mode, they can not only burn all the fuel for ascent instead of saving some, they can leave off unnecessary parts such as the landing legs and grid-fins. A regular Falcon can be reused up to about two thirds of its max expendable payload, but the Heavy can only manage about half. But the real point of the Heavy is not to lift giant stuff, but to make it so that they don’t have to expend boosters anymore, or at least only have to expend the center one for the worst cases. By losing the center core they can reach around 90% of the capacity they’d have by expending all three. They occasionally use this kind of launch for heavy geosynchronous payloads — the Pentagon hardly notices the cost of an expended core booster.

Falcon Heavy

The rocket may not actually be able to support a sixty ton payload. (Their standard payload adapter is only designed to support eleven tons — just half of the amount a non-heavied Falcon can supposedly lift to orbit. What the limits of the stack might be with a better adapter, I have no idea. The heaviest loads actually launched are somewhere around twenty tons.) The main benefit of the Heavy is probably for reaching higher orbits. If the destination is geostationary transfer orbit (GTO), for instance, the Heavy would increase the nominal capacity from 8.3 tons to 26.7 tons, without reuse. They claim it could send 16.8 tons to Mars, or 3.5 to Pluto without using a gravitational slingshot. One could do even better by adding a third stage, but they don’t sell one — you’d have to bring your own, and fit it into fairing, which is smaller than that of competing rockets. (A bigger one is on their shopping list.) I will note that these GTO numbers are not that impressive, compared to the huge loads that it can lift to low orbit... the use of kerosene as fuel in the upper stage, instead of hydrogen, reduces its efficiency for reaching distant trajectories. With full booster reuse, the capacity to GTO is actually less than that of the Delta IV Heavy.

Some customers still fork over willingly for a nonrecoverable overweight launch. They hope the availability of the Heavy will make such launches largely unnecessary. Making the Heavy proved far more difficult than they anticipated, with practically the whole first stage needing a redesign to be able to support the additional thrust and vibration of adding side boosters. This highlights SpaceX’s general philosophy of shaving things as close to the limits as they can reasonably get away with, and leaving only a minimum of safety margin... when they decided to ask more of their booster, the margin they needed wasn’t there. The rebuild job was so challenging, and so hard to test on the ground, that they almost cancelled the project three times, and Musk said that if the rocket just managed to get a safe distance away before it exploded, and not destroy launch pad 39A in the process, he would “consider even that a win, to be honest.” But even the first test flight of the Falcon Heavy put reused boosters on the sides. They used a “silly” payload on the first test — they threw a Tesla roadster into what they hoped would be a Mars transfer orbit, and which ended up going out all the way to the asteroid belt, with the stereo playing David Bowie, and a dummy named Starman in the driver’s seat with its arm on the window sill, wearing one of their new space suits. (In 2010, they tested the first Dragon capsule by launching a wheel of Le Brouère cheese in it, so a degree of silliness is not unprecedented.)

With the Falcon Heavy they considered pulling off a trick known as “asparagus staging”, or as it’s more properly termed, propellant crossfeed. How this works is that with all three boosters burning at full power, the two side ones are also pumping fuel to the middle one’s engines. They run low and drop off in less than two minutes, and hey, the single remaining booster still has nearly full tanks. The traditional approach, as used in the Delta IV Heavy and its ilk, is to just run the center booster at minimum throttle for the later part of the initial burn, until the side ones are gone. But they’re not doing the asparagus trick yet. The reasons for caution are obvious, with all that might go wrong with such a scheme. This idea is dead for now, because it simply isn’t needed — to be honest, more lifting power is the last thing the Falcon Heavy needs. They originally thought the Heavy would be used for about half of their business, but they overestimated the demand for such heavy lift, and every time they improve the regular Falcon 9, it covers more of the weight range which they previously thought would require a Heavy. Nowadays, it looks like this hulking rocket might struggle a bit to find enough work to justify its presence.

Meanwhile, the familiar Falcon version that made it famous, which was apparently known in full as v1.2 “Full Thrust” Block 3, got upgraded to Block 5 (or “Fuller Thrust” as it has sometimes been unofficially termed), increasing its claimed payload capacity by 30% while also meeting NASA’s toughest safety standards for crewed flights. (Block 4, a transitional version with a minor increment to the engine thrust, was used for a few flights in late 2017 and early 2018.) This upgrade includes lots of fixes to the various weak points that have been revealed by inspecting landed boosters, such as replacing the aluminum grid fins with titanium, which is a lot more expensive but should last forever. They hope that the Block 5 will be able to refly up to ten times with no refurbishment at all, just an inspection and cleaning. (But I note that the rocket business in general is prone to the dashing of such hopes.) They pinned all their dreams of rapid and inexpensive reusability onto the Block 5, and started throwing away used Block 3 boosters, rather than saving them — they pretty much considered the successful Block 3 landings to just have been part of the program for learning how to make the Block 5, and didn’t feel like collecting old models that need heavy refurbishment to fly again. After this, they plan to do no further development on the Falcon booster, and eventually replace it with an all-new system. One of NASA’s hurdles was that they should make seven consecutive flights with no changes to the design, so their hope is that this version is truly final. By the end of 2018 they completed ten Block 5 launches with six boosters, one of which was the first to make three flights. But it wasn’t until 2020 that the Dragon 2 crew capsule was ready enough for NASA to put their astronauts into it.

Falcon 9 v1.2 Block 5: mass 564 t, diam 3.7 m, thrust 7600 kN, imp 3.1 km/s, gas generator (kerosene), payload 22.8 t (4.0%) in expendable mode and 15.6 t (2.8%) with reuse, cost $3M/t, record 197/3/3 (8 crewed) as of February 11, 2023.
Falcon Heavy: mass 1420 t, diam 3.7 m (width 12.2), thrust 22800 kN, imp 3.1 km/s, gas generator (kerosene), payload 63 t (3.7%) in expendable mode and 27.5 t (1.9%) with reuse, cost $3M/t, record 4/1/0 through February 2023.
Stage name Block 5
Role (pos) count core (1|S) ×1|3 upper (2)
Diameter (m)   3.70   3.70
Liftoff mass (t) 445    116   
Empty mass (t) ~22.2  ~4.5
Fuel mass (t) ~123     ~32   
Oxidizer mass (t) ~287     ~75   
Fuel type kerosene kerosene
Engine Merlin 1D+ ×9 Merlin 1D Vacuum
Power cycle gas gen gas gen
Chamber pres. (bar) 97   97  
Ox./fuel ratio  ~2.33  ~2.33
Thrust, vac max (kN) 8227     930   
Thrust, SL initial (kN) 7607    
Spec. imp, vac (km/s)   3.10   3.40
Total imp, vac (t·km/s) ~1330      ~371