Last Thursday I reported on the launch of a new quad of NASA satellites, called the Magnetospheric Multiscale (MMS), which are designed to measure the dynamics of the Earth's magnetic field and a poorly-understood process called magnetic reconnection.
I was able to witness the launch live from a few miles south of the launch pad and today bring you some of the sights, the sounds, and even a little bit of the physics of that experience.
|NASA's MMS spacecraft launches on an Atlas V rocket from Cape Canaveral, Florida on March 12th, 2015 at 10:44 PM EST. Credit: NASA via flickr|
|NASA's Magnetospheric Multiscale (MMS) spacecraft ready for launch from Cape Canaveral's Launch Complex 41, Florida on March 12th, 2015. Credit: NASA via flickr|
Night LaunchFlash forward a few hours to last Thursday night and I was driving around Port Canaveral (where all the big cruise ships launch from Florida), searching for a place to park. The internet suggested that Port Canaveral was the closest and best spot to watch a night launch since the closer beaches and parks close early. Sure enough, even from miles south of the launch pad, the looming Vehicle Assembly Building (526 feet high) was clearly visible across a body of water, as was the spotlighted glow from the launch pad.
This being my first NASA launch, I wasn't sure what size crowd to expect. After all, this was an unmanned satellite launch late at night, at a time when the site sees one to two launches a month. But I was surprised to find hundreds and hundreds of cars and people lining the narrow road towards the port. A single police car was vainly trying to control the traffic and limit where people were parking, but with little effect. A few minutes to 10:44 PM, people scrambled to find a good spot along the road and tuned into the radio countdown.
Even so, the start of the launch caught some off guard, mostly because of the lack of sound. The launch pad brightened in what initially looked like additional lighting in preparation for the launch, and then an incredibly bright spot smoothly and rapidly lifted into the sky. Without the thundering sound that accompanies every televised version of a rocket launch, the sight was surreal and deceptively simple looking.
The rocket lit up then entire sky and waterway as it rose into the air. This was my view, still before any sound was heard. When the sound finally did arrive (more on that below) it was a low rumble that quickly built in intensity, clearly the remnants of a powerful explosion.
|The MMS launch lights up the night sky from miles away. Credit: Tamela Maciel|
|The MMS spacecraft heads east after launch. Credit: Tamela Maciel|
Physics of the Sound DelayThe most surprising thing about the whole launch experience was the amount of time it took the sound to reach us. Of course, I could have worked this out beforehand, knowing how far away I was from the launch pad and the speed of sound in air, but since it took me by surprise, let's do the opposite and work out how far away I was standing from the launch, as the crow flies.
Thanks to a video I filmed of the launch, I can time the number of seconds from when the rocket ignited to when I first heard the low rumble. This was a full 57 seconds, by which point the rocket was already well underway and high up in the sky.
The speed of sound is about 340 meters per second at sea level (plus a little bit for humidity), and is given by the distance sound travels, d, in an interval of time, t:
I know the amount of time the sound took to travel to me as well as the approximate speed of sound, so I can rearrange to find the distance from me to the launch pad.
Plugging in my numbers and converting from meters to miles, I find the distance is about 12 miles.
A rough ruler measurement on a map suggests the actual distance was about 11.8 miles so my estimate was pretty accurate!
The slight difference could be caused by errors in my timing, my ruler measurement on the map, or slightly different air conditions on the night of the launch than the standard speed of sound takes into account.
|Green marker shows the location of the Atlas V launch complex 41 and the red marker shows my viewing location 11.8 miles away. Map created using Google Maps.|
By Tamela Maciel, also known as "pendulum"