Posted on January 31, 2021
This is an update of my post published on January 31, 2010:
On this date in 1958, Explorer 1 was launched, becoming the first satellite launched by the United States.
The Soviet Union's successful launch of Sputnik 1 in October of 1957 shocked Americans, and the U.S. was in a hurry to match the feat. The Jupiter C rocket had already been developed, and Pasadena's Jet Propulsion Laboratory was directed to design and build the “payload” (the instruments or equipment) to be carried into Earth orbit by that rocket.
JPL completed the assigned job in less than three months!
The main instrument aboard Explorer 1 was a cosmic ray detector. The experiment on this satellite and another one launched two months later led to the discovery of the belts of charged particles trapped by Earth's magnetic field, called the Van Allen Belts after the experiment's designer.
Explorer 1 made its last transmission back to Earth in May of the year it was launched, but it continued to circle the globe more than 58,000 times before orbital decay caused it to burn up in the atmosphere in 1970.
Orbital Decay (or, should our satellites be brushing longer and flossing more?)
When a satellite is in a low orbit around Earth, it may be slowed by “drag” from the Earth's atmosphere. This sets up a positive feedback loop:
The increased “drag” or friction from the atmosphere causes the satellite to reduce in speed.
Decreased speed causes the satellite to fall to a lower altitude above Earth.
A lower altitude means that the atmosphere the satellite encounters is denser (more molecules of gases per cubic foot).
The denser atmosphere causes even more friction.
Which causes even less speed.
Which causes an even greater fall in altitude.
Which means that the satellite is orbiting in even denser atmosphere.
And so on.
And so forth.
Eventually, the orbit is so low and the atmosphere so thick, the satellite encounters a lot of friction and burns up.
Orbital decay can affect, not only satellites, but also space stations, space shuttles, and even the Hubble telescope. The International Space Station regularly needs orbital boosts to fight against orbital decay.
|International Space Station|
Most satellites orbit our globe high enough that they encounter no atmospheric drag and therefore no orbital decay due to friction.
Instruments on Mars
JPL has had a lot of opportunity to design experiments for a variety of space exploration vehicles. In January 2010 we got some news about one of JPL's programs, the Mars Rover Program.
The bad news was that Spirit, one of the two rovers currently on Mars, had not been able to be UN-stuck from the soft sand that had trapped it since May 1, 2009. The scientists decided to stop attempting to move it but hoped that it would be able to do more science from its "stuck" position. (That didn't really happen, though; Spirit sent its last message to Earth in March, 2010.)
The good news was, Spirit and the Mars Rover Program had already been incredibly successful! As astronomer Phil Plait explained at his excellent blog “Bad Astronomy” (available here on Discover Magazine):
Spirit and Opportunity “had a planned operational lifetime of 90 days. “That was in January 2004. “In other words, Spirit has been on Mars for over 2200 days, and even counting when it first got stuck, it still ran well for more than 20 times its nominal lifespan. Cars these days have a standard warranty for 7 years; how’d you like yours to run for 140 years?
So for me, while this news is not great, it has to be put in context: Spirit is one of the most successful NASA missions of all time. And its sister, Opportunity, is still running like a champ. I hope I’ll be doing as well when I’m 1400 years old.
Opportunity continued to function until mid-2018!!! That was about 55 times longer than its original hoped-for mission!!!
Experiments on Earth