This is the first in a series of articles that will explore the ways armed forces could exploit reusable rockets and large satellite constellations, building up a coherent doctrine for their employment. I’ll first focus on how reusable rockets can be used to deliver weapons at intercontinental distances while in the next article I plan to talk about future military satellite constellations and orbital warfare.
To minimize launch costs with the next-generation Starship rocket SpaceX has both reduced manufacturing costs and moved toward full reuse of both the first and the second stage.
The most-important cost savings come from the engines: Raptor 3 produces thrust at a very low price, burning liquid methane and liquid oxygen (so-called “methalox” mixture) very efficiently. (The cost to thrust ratio for Raptor 3 is apparently less than one fifth of other comparable engines)
Lower cost per thrust is very consequential since it fundamentally changes the engineering decisions done during design: it’s much less important to shave off mass from the rocket when you could reach the same performance target more easily by just adding an engine and making the whole rocket bigger.
This helps explain why the fuel tanks of Starship are made of steel with internal reinforcement, a cheaper (but heavier) solution compared to traditional machined aluminium-lithium alloy structures. Many other similar decisions have helped keep the production costs low.
Much of Starship’s design revolves around full reusability, ensuring no new hardware needs to be built for each flight and both the first and second stage can be flown again with as little work as possible. The reuse process starts with recovering both stages: to save weight on landing legs, SpaceX has decided with Starship to add “catching” arms to the launch towers, designed to grab the rocket stage in the final stage of deceleration.
The most important innovation SpaceX has achieved here is designing the first stage, the booster, to be quickly reflown after each launch with no need for refurbishment, a process called “fast reuse”.
I won’t spend much time talking about the reuse of the second stage since it’s still being figured out and I suspect that the refurbishment process is going to take at least a couple of weeks, longer than what I think the decisive stage of a peer war will last.
So I’ll mainly focus here on a semi-reusable architecture that lands and reuses only the booster, built fully exploiting Starship technology. This can be done simply using an expendable version of the Starship second stage but limitations in an architecture designed for civilian use makes the design of a smaller rocket built for military use from Starship tech very attractive (I’ll come back to this later).
This does not mean that fully reusable architectures do not have place in warfare, reusing the second stage could be ideal in the asymmetric conflicts the US has been fighting to help keep costs low. It also would have the added benefits of preserving stockpiles of expendable second stages built up for peer conflicts.
Every space launch vehicle can put payloads on ballistic trajectories, since ballistic trajectories are less energetic than even Low-Earth Orbits. Each kg of space launch capacity can therefore be converted into 1.5 to 2 kg of payload to intercontinental ballistic trajectories, depending on the location of the target and the ballistic arc employed.
Historically this has been very impractical: launch costs were far too high and total launch capacity to orbit was limited and could not be quickly expanded during a war.
However these limitations don’t apply to Starship and other rocket using similar technology, since they have very low launch costs and very high launch cadence: in 2030 SpaceX plans to have 15 Starship launch pads in operation each one capable of launching once per day. Total payload to intercontinental ballistic trajectories using expendable second stages could reach 5000 tons per day at a 100$/kg cost.
The capacity to launch a lot of mass wouldn’t be enough to make Starship a useful military system: it should also have the ability to launch multiple payloads on many different targets, functioning like an ICBM with Multiple Indipendent Reentry Vehicles (MIRV), just on a much larger scale and with the booster going back to the launch pad instead of being expended.
An advantage of using Starship as a large liquid fuel ballistic missile compared to more common solid fuel ICBMs is that the second stage can accurately and quickly change its thrust, enabling the fast deployment of warheads into many different trajectories, even if the targets at hundreds of kilometers from each other. That means that every Starship launch could accurately shower China or Iran with one thousand 300kg warheads travelling at 5-6 km/s. (The US struck about targets during the first day of Epic Fury, 15 starships could have destroyed 10 times the targets)
This high speed (Mach 15-20) is both a problem and an opportunity. The payload needs to be protected by a reentry vehicle (RV) from the heat generated during the reentry process while maintaining some capacity for maneuver, this while not a trivial problem doesn’t require expensive and complex “hypersonic” technology. (In military circles hypersonic refers to technology designed to enable extremely high maneuverability at speeds higher than Mach 5 to complicate intercepts).
It’s far cheaper to use MaRVs (Maneuvering Reentry Vehicles), fairly simple conical reentry vehicles coated with phenolic resins designed to ablate to protect the warhead, with some limited maneuver capabilities to ensure high accuracy. (I’ll talk more about weapon guidance when I describe navigational satellite constellations in the next article)
This approach uses large numbers of cheap warheads (I estimate total cost for each weapon to be about half a milion dollars) to quickly overwhelm enemy air defense systems: here speed the high reentry speed is a huge advantage, compressing the time available for intercepts and making decoys and jamming more effective.
High speed is also incredibly useful to defeat hardened structures: for example the best weapon the US has currently available to destroy deep bunkers is the MOP (Massive Ordnance Penetrator) a 14 ton gravity bomb that requires the use of large bombers, Starship could launch faster and heavier penetrators capable of destroying deeper bunkers built to withstand current US weapons.
The Iran war underlines another advantage of Starship over current US weapons: US armed forces took weeks to move carrier strike groups and other assets to the region, making them vulnerable to Iranian retaliation. Starship could have struck while the protests were still ongoing, catching the Iranians completely unprepared with a salvo of thousands of weapons.
Starship has a huge potential as an offensive system but it’s a glass cannon, incredibly vulnerable to attacks to the fixed infrastructure needed for its operation. Fueling infrastructure is by far the biggest vulnerability, since it’s often shared by multiple launch pads and it’s full of flammable methane that could be ignited even by small drones. The catch arms could be disabled by small but well placed explosions as well.
Finally the large size of Starship makes it especially vulnerable during the initial flight phase, either from orbital interceptors or even a fragmentation warhead launched by an enemy rocket and guided by overflying satellites.
To deal with these issues a military reusable rocket needs to be designed and mass-produced.
To solve problem connected to fixed launch infrastructure this new rocket should use landing legs so it could take off and land from improvised launch pads made up of patches of specialized concrete.
These kind of improvised launch pads have been proven to work during the early stages of starship development, simple concrete only pads only failed under the combined thrust of 33 raptor engines during the first launch of the full starship rocket.
A hypothetical reusable rocket with a scaled down starship first stage using only 7 engines could be capable of launching from hundreds of different pads simultanously, after being refueled by mobile cryogenic tanker trucks.
This would significantly improve the offensive power of the system as well, making surprise attacks even deadlier.
To protect against attacks of similar weapon systems camouflage, decoys and jamming are very important. All fixed infrastructure like fuel depots should be hidden inside deep bunkers with secret locations and layouts, with fake and redundant entrances built.
The kind of massive intercontinental ballistic attacks I described puts ICBMs and long-range bombers under serious threat from conventional attacks: for the first time in history it may possible to disable large part of the enemy nuclear arsenal without using nuclear weapons.
However under the current nuclear doctrine of launch on warning every large scale ballistic strike, nuclear or not, would result in immediate nuclear retaliation while the warheads were still in flight.
I have always thought that launch on warning is the dumbest legacy of the cold war: to protect land based nuclear weapons that are more and more vulnerable to a growing number of weapons millions of people are under constant threat from a hair trigger.
However other nuclear doctrines exist: until not so long ago China’s nuclear doctrine was to retaliate only after nukes were used on its territory. This a far safer option and mutually assured destruction is still ensured by nuclear ballistic missile submarines, by far the most survivable leg of the nuclear triad.
Reusable rockets have the potential to be the most effective way to launch long range strikes, reducing the need for expensive and vulnerable carriers and foreign bases.
The only real issue that their adoption may face (other than corrupt procurement officers) are the consequences on nuclear war. However as I explained at length the moment Starship becomes operational the US armed forces could immediately exploit it to launch strikes, there’s no going back now.
I also think that reusable rockets provide a nice simmetrical response to Chinese investments in ballistic missiles designed to destroy US bases: after all why shouldn’t the US be allowed to strike Chinese bases back with ballistic weapons?