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The (relatively) new Kuaizhou family of launch vehicles is described as "quick-reaction", and is based on ASAT and ICBM heritage.

Solid-fueled rockets have been, historically, cheaper to launch on, and can be stored more or less indefinitely, allowing for 'responsive' launch capability.

Once a payload is integrated and the LV has stood up on the pad, is a solid-fueled rocket actually any faster to orbit than a liquid one?

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    $\begingroup$ You ask for the time from lift off to orbit? It does not depend on solid or liquid fuel, it depends on acceleration. $\endgroup$ – Uwe Oct 28 '19 at 21:36
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    $\begingroup$ It all depends on how much acceleration your payload can take. Humans won't take more than a few g, electronics will take far more. $\endgroup$ – hdhondt Oct 28 '19 at 22:25
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    $\begingroup$ I think "quick-reaction" is in reference to preparation time, or time from decision to launch to actual launch. Liquid-fueled rockets might not have propellants loaded until shortly before launch, so loading slows down the "reaction" time (time from decision to launch). Solid-fueled rockets are always "ready to go", just ignite and they are away. So, a solid-fueled rocket might get there faster not because it is actually flying faster, but because it gets off the pad sooner. $\endgroup$ – Anthony X Oct 29 '19 at 3:00
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Once a payload is integrated and the LV has stood up on the pad, is a solid-fueled rocket actually any faster to orbit than a liquid one?

In flight time, no. The time it takes to get from liftoff to orbit depends on your acceleration, which depends on the power-to-weight ratio of the rocket.

A high acceleration is usually avoided for space launch vehicles, because it provides no advantage and costs more. A high acceleration requires a stronger structure for both payload and rocket, and can require a heat shield on the nose of the rocket.

There are examples of military missiles with high acceleration (the Sprint ABM accelerated at 100g). Space launchers are usually in the 1-5G bracket (depending on where in the mission profile you are).

Even a rocket like Vega that is not intended for manned use, and which accelerates quickly right on liftoff limits G-loading to about 5G.

As Antony X said, you do get an advantage in that you don't have to fuel the vehicle on the pad. The associated disadvantage is that you have to handle the solid rocket as live ammunition once it's been fueled, so it can be more cumbersome and expensive to move around.

For ICBMs, not having to fuel them immediately before launch is a big advantage, as it reduces the launch delay from hours to seconds. For space launchers, a launch campaign can take weeks or months, from rocket stages arriving at the launch site to liftoff. Most of this is spent assembling and checking the launcher.

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  • $\begingroup$ Good answer -- I think I asked the wrong question though. As several commenters pointed out, there isn't necessarily anything about solids vs liquids that dictate an 'average' acceleration. New Q coming soon! $\endgroup$ – costrom Oct 29 '19 at 15:36
  • $\begingroup$ Doesn't a higher acceleration save on delta-v? $\endgroup$ – ikrase Oct 31 '19 at 6:06
  • $\begingroup$ @ikrase yes, you can reduce gravity losses by having higher acceleration. In practice, most launchers lift off with a thrust:weight ratio of not much over 1. This may have to do with commonality (most launchers have a 5G limit, so when you design a rocket that will do 10G most payloads cannot be launched by it). $\endgroup$ – Hobbes Oct 31 '19 at 10:50
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When you ignite a solid fuel motor it doesn’t stop and you can’t throttle a sold fuel like a liquid motor. What that idea in mind, liquid motors can take their time getting to orbit because they can follow a more efficient thrust curve for the given altitude. So to answer your question by broadly generalizing, yes they are technically quicker to orbit.

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    $\begingroup$ while - generally - one doesn't throttle a solid motor like a liquid one, the thrust profile can be designed, so they are capable of a similarly efficient thrust curve. $\endgroup$ – JCRM Oct 29 '19 at 11:21
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    $\begingroup$ More surface area = faster burn. Less surface area = longer burn. Example. $\endgroup$ – Magic Octopus Urn Oct 29 '19 at 12:44
  • $\begingroup$ @user33717 Can you give an example of a solid fueled vehicle that is faster to orbit than a liquid fueled one? $\endgroup$ – Organic Marble Oct 31 '19 at 14:44

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