When life gives scientists lemons, they look at those lemons and say, “how can we use
this to test general relativity?”
Hi everyone, Julian here for DNews. I know we’ve been doing it for a while now, but
launching stuff into space is still pretty tricky. You’ve got to get a giant rocket
on a launchpad without it exploding. You’ve got to start it up without it exploding. You’ve
got to send it into space. Without it exploding.
But assuming the payload still stays intact, sometimes the rocket puts it in the wrong
place. that’s what happened in August of 2014 with a Russian Soyuz-Fregat rocket carrying
two of the European Space Agency’s Galileo satellites. The rocket worked flawlessly most
of the way up there, and then in the last stage it pointed in the wrong direction and
shot them off at an orbit that made them useless for their intended purpose. Ah, so close.
Of course we’re talking close by space standards. Which is just another way of saying the orbits
were really far off. They were supposed to be in circular orbits a constant 23,222 km
(14429 miles) away from the earth. Instead they were set on elliptical orbits, twice
a day they were 2,000 km (1242 miles) too high, and twice a day they were 10,000 km
(6213 miles) too low.
The Galileo program is going to be fine. The plan is to launch 30 satellites to use them
for global positioning, and really 24 of them are needed for the system to be fully operational,
while the remaining 6 are there for backup. So two of them whizzing about in the wrong
place is a minor setback, rather than a dealbreaker.
But, heck, while they’re up there, we may as well do something with them. They’ve
still got fully functioning atomic clocks onboard, so what experiments could you do
with a spacecraft traveling in an elliptical orbit around a massive object while carrying
a super-accurate clock?
If you said test time dilation, you must watch this show a lot. Hi mom!
Yes as you’re probably aware, according to Albert Einstein’s theory of general relativity,
near massive objects, time moves slower. GPS satellites already have to constantly adjust
their atomic clocks back slightly because of their distance from the Earth. And yes,
according to special relativity their speed also means that their clocks should run a
little slower, but the overall effect is the super accurate clocks in space are a little
fast on the order of microseconds.
The wayward Galileo satellites have had some course corrections because they have thrusters
and a bit of hydrazine fuel. Now their orbits change by 8,500 km (5,281 miles) twice a day
instead of 12,000, but that’s still a difference greater than the radius of the Earth (6,371
km) and then some. So what that means is compared to our atomic clocks down here, the misplaced
Galileo clocks with run a little faster, then a lot faster, then a little faster, then a
lot faster as they gets closer and farther away from this massive hunk. I mean the earth,
not me.
Using those differences, we’ll be able to check Einstein’s math. Sure we did it once
before with an atomic clock in 1976 that hitched a ride 10,000 km into space, but that experiment
only lasted a few hours. We can pull data from these satellites for over a year and
be four times more accurate than before. We’ll be able to test the math vs the measurements
to an accuracy of 0.004%. And we’ll be able to do it thanks to a mistake that we turned
into a happy little accident.
And I’ve got more good news, everybody! TestTube now has a newsletter! Get a weekly
round-up of our most popular videos across all our shows at TestTube.com/fwd
So I glossed over how GPS satellites work, and though I’d love to ramble all about
them, Trace’s clock was a little faster than mine and he beat me to it. Check out
the amazing science behind knowing where on Earth you are right here.
Have you
ever turned an almost fail into an epic win? Sure you have, so let us know in the comments,
subscribe for more, and I’ll see you next time on DNews.