Can ten (or more) rockets be used together to launch one massive object?

Question

With computer flight controls where they are today, what would stop us from building a relatively large space station on earth, but then using 10 or 20 or even 100 falcon heavy or Starship or SLS rockets to launch it to orbit?

For an example, let’s say we built a von Braun station with a diameter of 300M that had rockets placed under it evenly every ~47 meters to launch it in one go into orbit? This assumes an extremely strong structure, but in theory, if the launches and flight paths are coordinated well they could avoid any twisting or other non-consistent pressures? Even an empty structure with nothing but the pressure vessel and basic airlock equipment would solve a lot of initial problems. I am assuming lower payload per rocket because the aerodynamics would obviously be affected at lower altitudes.

Is this remotely possible as an alternative to current space construction issues and limited fairing sizes, or are there issues I’m not considering or underestimating?

Answer 1

This is not necessarily as far fetched as you may think, but you seem to focus on lifting a structure and building a rocket system around it.

For instance: in 1968, Boeing studied a post-Saturn vehicle using four Saturn-V cores, with first and second stages in parallel arranged below a massive payload fairing.

Saturn V-4X(U) (Hazegrayart)

This would allow for million pound launches to LEO, and thus is an example of a superheavy vehicle built from multiple other launchers all lifting in parallel.

In terms of your original question, a ring station or similar is extremely unaerodynamic due to the physics of a cylinder being rather disgusting.

It would make more sense to forego the fully constructed station and instead use a couple launches of a more optimised vehicle to lift and construct parts of the station.

Answer 2

It may be possible, but it would be both inefficient and unwise (risky). I agree with many of the comments made below the question. Fundamentally there two competing design criteria: 1) a von Braun Station (vBS) orbiting at 400 km using centripetal force to simulate gravity; and 2) a payload that must withstand one - and only one - launch, and the aerodynamic and thrust forces normal to these centripetal forces.

Sizing the Problem

The 300 m diameter vBS will be too massive to be launched using the 20 Starship/SuperHeavy proposed.

Consider SpaceTech's vBS. It's 190-meter in diameter and composed of 24 cylindrical modules, each 20 meters long 12 meters in diameter. It has a corridor (a torus) and shafts descending between modules. There are 4 main spokes giving access to a central docking point.

We can scale an ISS module to estimate the mass of each vBS module. The Destiny Module is 8.4 m long, 4.2 m in diameter and has a mass of 14,500 kg. The surface area of a cylinder is $2\pi r(r + l)$. Destiny has a surface area of ~138 m^2; the vBS module ~980 m^2, or 7.1 times the area. For a given pressure, pressure vessels normally have wall thicknesses proportional to the radius of the vessel. If we neglect this and assume a linear scaling 7.1x14,500 ~ 103,000 kg.

They assume 40 launches of the SpaceX Starship to "send all the pieces up there". If we assume the additional features - the corridor torus, spokes, and shafts - don't contribute too much more to the mass (unlikely), 24 simultaneous Starship launches could launch this vBS to LEO. (Note the structure will necessarily be much heavier if strengthened to withstand launch as an intact structure.)

Atmospheric Drag

Each Starship has a cross-sectional area of $\pi r^2 = 4.5^2 \pi = 64 m^2 $. I'll assume Starship has similar aerodynamic properties to the Falcon 9, which someone has estimated has a drag coefficient (Cd) of about 0.75. Maximum dynamic pressure ($P_m$) is around 35 kPa for most rockets. The drag force is $D = P_m C_d A = 35*0.75*64 = 1,680 kN$.

The SuperHeavy has a thrust of 74,400 kN. Assuming an all-up weight of 5,000 tonnes, 25,350 kN is used to accelerate the vehicle and the remainder is used to hold the rocket in the air (assuming it is going vertically, which is roughly true at Qmax). Only ~ 6.6 % of the "excess thrust" is used to push through Qmax.

Approximating the vBS as 24 cylinders, each cylinder has a cross-sectional area of 20*12 = 240 m^2. If we continue the calculation on a per module/rocket basis, Starship would likely be anchored in the middle of the connecting shaft serving two modules & hence not well obscured by the slipstream of the vBS. In addition part of the torus corridor and spokes should be added to the per-booster cross sectional area. A minimum cross sectional area would be 300 m^2 per module, and likely more.

Someone has kindly estimated the Cd for Starship in its belly-flop entry mode, with Cd ~ 2 in this configuration near Mach 1, which is also close to Qmax.

Redoing the calculation (on a per module basis), $D = P_m C_d A = 35*2*300 = 21,000 kN$. This likely underestimates the drag, but it is very similar to the excess thrust of 25,350 kN for each SuperHeavy.

The vast configuration would likely have to delay passage through Qmax until a greater altitude and lower air density. It would also be unlikely to reach it's desired orbital height, if it could reach orbit at all.

In contrast, when launched individually, each module - in an appropriate fairing - would easily be lofted to a 400 km LEO.

Further Considerations

I agree with many of the comments above. In particular I think it highly unlikely that current flight control software could keep 24 SuperHeavy's sufficiently coordinated to prevent breakup of the vBS. In any case, a much heavier support structure would be required to withstand the point loads of the booster and differential loads through the structure due to inevitable minor coordination errors. Vibration of the entire structure would also be an issue - potentially setting up destructive harmonics. Beneath a fairing a single module would be easily dampened against vibration. Finally, the modules and structure would likely need to be strengthened against Qmax.

Launching even a small vBS in this manner would be highly inefficient compared to assembling it in orbit. Such a launch would not be attempted unless there was absolutely no alternative.

p.s. I noticed this lonely question had been sitting by itself for some time, so I thought I'd give it a go. Have pity!

Answer 3

After reading through all of the comments, I'm inclined to agree with you that in principle this may be a feasible idea. The advancements in flight controls have been considerable. We can now reliably land a booster and the possibility of catching a booster or a ship seems like a reasonable next milestone. The possibility of launching multiple rockets in a tight formation seems reasonable, with our present level of technology.

For some launch systems, reliability is high enough to launch humans to space. Because we have good data on the probability of a single rocket launch failing, it is possible to calculate the probability of success for a mission involving multiple rockets that are launching simultaneously.

The question then becomes, is it possible for multiple rockets to launch in a tight formation and share responsibility for lifting a large payload? And, if that is possible, how does the addition of the payload-sharing requirement affect the overall probability of success for the mission?

Let's consider an architecture in which N rockets are placed on N separate launch platforms. The N platforms are pre-arranged in a tight formation in the center of the large ring-shaped space station that we want to launch into orbit. The rockets are all then individually connected to the station with lots of guy wires made out of a strong light-weigh material such as carbon fiber. (See figure below illustrating the concept for just one rocket connected using just a few guy wires).

Theoretically it should be possible to launch all the rockets simultaneously and have them together carry the space space station to orbit.

The space station and numerous guy wires will generate more aerodynamic drag than the individual rockets would normally experience, so the amount of payload each rocket can launch to orbit will be lower than normal, but this is not a showstopper. Only a small fraction of a rocket's delta-v is typically used to overcome aerodynamic drag.

With lots of rockets, the probability of scrubs occurring will be higher than normal too, but again this does not appear to be a showstopper.

It would obviously help if the space station were architected up front to be amenable this style of launch. The plan could involve over pressurizing the habitation modules to give them more structural rigidity to resist the aerodynamic pressure experienced during the launch. Or, inflatable habitat modules could be used to reduce the aerodynamic cross section during launch. We could also give the station some spin on the way up to help it resist hoop stresses and buckling forces as the acceleration increased.

So, "Is this remotely possible as an alternative to current space construction issues and limited fairing sizes..?"

Yes, absolutely. It would also be a spectacular achievement that would no doubt go down in the history books.

The main challenge to moving forward with such an idea is simply that an alternative approach, such as building the station as separate modules, launching them individually, and later assembling them in space, could have certain advantages.