How Hard Can It Be to Land a Rocket on the Moon?

Ever had problems braking from 100 km/h (60 mph) to a full stop when seeing a red light in front of you? Braking is a huge stress factor for your tires, which try to make the most out of friction with the road.

But how would you brake in a rocket to land on the surface of the Moon? Atmospheric friction can no longer be used, since it almost doesn't exist, parachutes are not effective for the same reason, so what is it left?

Engine power, you say? Very well, the Space Shuttle Main Engine (SSMEs) delivers a huge thrust, just over 37 million horsepower. But a space shuttle can't land on the Moon, for various technical reasons, like...lacking a landing strip!

A lunar module's descent engine will have to use throttling for landing and descending from orbit is as delicate as a ballerina performing a pirouette on a string suspended over a lion pit. The string is the really tight trajectory that the module has to respect to avoid destructive deviations and the lion pit is a rocky surface that would smash the module into many useless pieces, astronauts included.

The only real way to land on the Moon is to cut engine power as the lander loses mass through the engine exhaust that slows it, not too much to slam into the ground and not too little to waste all the fuel before the completion of the maneuver.

As NASA plans to send human missions to the Moon during the next decade, they will have to rely on mostly the same technique described here and successfully used by the Apollo Lunar Module (LM) descent engine on six landings in 1969-72.

But if they want to send more mass on the surface, the module won't be enough to handle the performance requirements of future missions. Some prototypes are analyzed and they will have to do something no other engine ever did before: throttle from 100 percent of an approximate 13,000 to 15,000-lb thrust to 10 percent on command for a human-rated spacecraft.

However, most rocket engines are designed for full power, meaning that many things could go wrong if flight characteristics are breached, like the minor detail of liquid hydrogen slowing down and vaporizing in the coolant lines, possibly stalling the engine.

The problem is still being pondered by NASA and contractors, who for now find themselves in the position of being able to build the most powerful engines ever, but unfortunately can't include landing.

As I'm sure not many astronauts would want to go in one-way missions, I am anxiously waiting for an ingenious solution, which must exist, or else we could have never landed on the Moon. We did land on the Moon, right?

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