The hardest part of getting into space is the first 30 or 40 miles. A fully fueled rocket, at its heaviest, fighting its way through the thickest part of the atmosphere—once you get past this it’s not exactly easy to achieve orbit, but the hardest work has been done. If you have seen videos of a Saturn V launch, it looks as though it will never clear the tower! In fact, it took a solid 12 seconds to do so.
If you follow this video out, you will see an important transition at the 3:07 mark. Staging breaks the rocket into two or more parts and allows us to reach orbit (or deep space) without having to build an absurdly large and powerful single structure.
Sticking with the Saturn V (It’s such an amazing machine!), let’s look at its three stages.
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The first stage, the one that gets the rocket off the ground, has five of the largest rocket engines ever built, and a total thrust (power) of 7.5 million pounds. It is this stage that has to lift the rocket when it is at its heaviest.
But look at the second and third stages. Once the first stage has emptied its fuel tanks, it is dead weight. Get rid of it! The now lighter rocket can continue its upward journey with a much less powerful (1 million pounds of thrust) second stage. And the third stage, the one that gives that final push into orbit? Now down to 200,000 pounds of thrust, with plenty left over to send the Apollo spacecraft toward the moon.
In contrast to the Saturn V, the Space Shuttle fairly leapt off the launch pad.
One of the key differences you note here is that instead of stacking one stage on top of another, there are rockets attached at the side. This is a neat solution that allows staging without having to build a rocket ever taller.
I can’t be sure, but the first rocket I personally remember using this configuration was the venerable Titan III series of rockets, two of which launched the two Voyager space probes to the outer planets.
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Those two side boosters (in eye-rolling NASA fashion, designated Stage 0) are solid rocket boosters. Simple beasts—once you ignite them, they go until they burn out and are then discarded. The Space Shuttle similarly–and disastrously in the case of the Challenger–used the same technology.
The SpaceX Falcon Heavy uses side boosters also, but they employ far more advanced liquid fueled engines, ones that can be shut down, restarted, and throttled up or down. Rather than being dumped in the ocean, they are brought back for reuse, greatly reducing the cost of a launch. In June 2019 I traveled to Florida to witness the night launch of a Falcon Heavy.
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The launch was spectacular, even if it was at 2:30 am and more than seven miles away. What we didn’t expect was that that the two side boosters would return and land less than a mile away from our viewing stand. Here is a daytime video of a similar return of the two boosters. Apologies for the very un-NASA-like excitement and boosterism of the narrators. SpaceX is definitely a commercial enterprise!
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