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This is a purely theoretical question, because I suspect that trying to build a launch system of this sort would pose its own set of very complex problems.

That said, the Wikipedia page for the English Electric Lightning notes that while it was popular at air shows to do the "party trick" of taking off and immediately standing the plane on its tail to show off its ferocious vertical climb ability, while on active duty doing a real intercept, time to altitude could be significantly reduced by taking of, accelerating horizontally to ~430k kts IAS, and only then pulling the nose up to achieve the vertical climb.

Ignoring for a moment how we might actually achieve this goal, but could a similar launch profile help a rocket trying to reach LEO or above? Accelerate horizontally using the rocket for power on some sort of support system (such as wings) which then curves the rocket up to a vertical direction only after a decent speed has been attained.

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  • $\begingroup$ @blobbymcblobby so the one word answer is "Yes". At this point you could turn those links into an answer that I can then accept $\endgroup$
    – dgnuff
    May 27, 2023 at 10:33
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    $\begingroup$ The one word answer is "no". Although getting past Mach 5 is problematic, multiple vehicles have done that. Getting past Mach 10 is highly problematic. Things flying at low altitude (and low means anything below 100 km altitude) melt at such high speeds. The key challenge is that low Earth orbit is Mach 25. One key reason rockets launch vertically is to quickly get out of the Earth's somewhat thick atmosphere. $\endgroup$ May 27, 2023 at 11:00
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    $\begingroup$ The issue with rocket sleds and the like is, it's (relatively) easy to design one where the rocket is smaller, simpler, and cheaper, and you think you've come out ahead. But when you add the rocket + sled together, you find that the system as a whole is larger, more complex, and more expensive than just using a rocket. $\endgroup$
    – Cadence
    May 27, 2023 at 11:55

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No, it wouldn't help.

For an aircraft with wings and an air-breathing engine, accelerating to a certain speed allows the wings to produce a lot of lift, which then shortens the time to climb, which then allows the aircraft to spend more time at the altitudes where the engine operates more efficiently.

An orbital rocket operates for a VERY short period of time. Its initial climb into rarefied atmosphere takes on the order of a minute. It is at its most efficient getting high rapidly to eliminate aerodynamic drag considerations so it can then go sideways/downrange to orbital velocity very very fast. Building up downrange velocity early and low unnecessarily dumps energy into the lower atmosphere and exacerbates gravity loss.

The optimal climb profile for a launch vehicle is determined numerically by programs like SORT, the Simulation to Optimize Rocket Trajectories, for which I contributed some minor changes to what I think was the penultimate version.

On the comments left about rocket sleds: the "win" for the rocket sled is entirely from the energy for the sled not coming from the launch vehicle itself; i.e. the sled is a zeroth-stage before the rocket is released. This is different to your proposal.

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  • $\begingroup$ something that might be a useful appendix to this: there's a term I can't recall for the climb profile typified by fighter/interceptor aircraft. I don't think "zoom climb" is the correct one for regular operations and is instead the profile used for attempting altitude records. If anybody else knows it, I'd appreciate either a comment or just editing it right into that second paragraph. $\endgroup$
    – Erin Anne
    May 27, 2023 at 11:04
  • $\begingroup$ y'know, I think I misread the question because it DOES mention "some sort of support system" and so we're absolutely talking about rocket sleds or an equivalent, which help a little, BUT I still think OP has missed that any halfway decent rocket sled launcher is supposed to go up quite high. Just giving the rocket horizontal velocity down low is still not helpful, so I won't delete this answer unless somebody else tells me that it's quite dumb. $\endgroup$
    – Erin Anne
    May 27, 2023 at 16:10
  • $\begingroup$ Why not? Disregarding other engineering challenges of sled launch, Super Heavy starting horizontally with only 6 engines on a gently curved sled and getting full ignition (all engines) only at a speed around 100 km/h could save 10-20% of fuel. This is what Elon Musk was saying when theorizing about initial acceleration for the rocket before full ignition. $\endgroup$ May 28, 2023 at 2:34
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    $\begingroup$ @TheMatrixEquation-balance And that sounds like a great deal, until you do an all-up assessment of what it'd take to mount a fully-fueled rocket on a sled and accelerate it to 100 km/h on a "gently curved" slope. That's a line of thinking that usually ends up in "or, we could just make the rocket 10% bigger" rather quickly. $\endgroup$
    – Cadence
    May 28, 2023 at 7:25
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    $\begingroup$ Cadence is exactly right--every rocket sled or air launch concept is mired in the old "saving rocket fuel directly translates to thousands of dollars per kilogram saved" way of thinking, but a rocket is actually immensely power-dense and energy-dense and the best way to move it any appreciable distance is with its own rocket engines. The real win is in not throwing it away after every launch, not strapping a metropolitan transit system worth of infrastructure to it to then do ten billion dollars of damage to in a launch accident. $\endgroup$
    – Erin Anne
    May 28, 2023 at 10:10
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Not in theory. Only when practical considerations such as thrust to weight ratio are considered does such a profile yield any savings. It can enable you to get that initial boost needed to climb out of the atmosphere without wasting thrust fighting gravity. But the same thing could be done much more easily with some strapon boosters.

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