I was watching a special about Apollo 13 on the History Channel and it said that enough energy was produced during it’s return into the atmosphere to light up the city of Los Angeles for a minute and a half.
If every action has an equal and opposite reaction, were they saying that (basically) the rockets used to launch Apollo 13 into space could power LA for 1.5 mins.? Or, did Apollo 13 somehow aquire a butt load of momentum while in space (by slingshotting around the moon or something of that nature) that more energy was created/released upon it’s return into earth’s atmosphere?
Well, it was on TV, so it has to be right somehow…
possible subtle-but-important difference between “lighting up” and “powering”. If they really meant to light the city up so you could see at night, I have no problem with that. You could see the Saturn V’s from the ground when they were miles up, so that’s a heck of a lot of light being given off.
On the other hand, that much energy driving a turbine powerful enough to generate enough electricity to run all the TV’s in Tinseltown? Maybe not.
The Saturn V generated much more energy than was generated by the reentry of the capsule.
Since the moon is not moving relative to the earth, the slingshot effect would be negligible, and all the energy the capsule had was given to it by the Saturn V. Plus, lots of the stuff that the Saturn V had to lift into space was abandoned or burned up in the engines before the capsule reentered, so a whole lot more energy was expended in getting the capsule to the moon and back than was ‘recaptured’ as heat in the atmosphere.
The factoid was about re-entry, or did I misread the OP? So the energy expended by the Saturn V isn’t the juice they’re referring to.
The atmospheric friction against the hull of the re-entering Apollo craft caused a hell of a lot of thermal energy. I suppose it could be used to power LA for 1.5 minutes, if applied to a steam generator. But that factoid smacks of exaggeration.
Assume capsule going at 20km/s and having a mass of 1 tonne (these are from memory but realistic i think).
Assume all energy generated comes from the kinetic energy.
Therefore o.5mv*v=energy
so 0.51000kg20000m/s*20000m/s= 200,000,000,000J
Divide by 50W (J/S for an approx lightbulb) and 90 seconds
= 44444444 bulbs.
Roughly 50million light bulbs and don’t forget this was the sixties so even less electrics than today I think that A) the fact sounds right and B) most of the energy is produced by the Saturn 5.
Finally apologies if I have made a mistake in my calculations or my assumptions are way off.
The energy produced by it re-entering is equivilent to the electrical energy needed for the question. You don’t have to power a generator as its just talking about equivilent amounts of energy.
IANARocketScientist, but you have to keep in mind the “gravity tax”.
A rocket lifting a payload into orbit not only requires the energy to physically lift the payload that high, but in addition for every second it is in flight it has to couteract the 32 ft/sec that Earth’s gravity imposes upon it.
This is not the case when an object is falling down.
In other words, you need to thrust upwards with one gravity of acceleration just to hover in a stationary position. Actually moving upwards requires more thrust on top of that.