- Hi, it's me Tim Dodd,
the Everyday Astronaut. Have you ever accidentally
used a tablespoon instead of a teaspoon? Or maybe you grabbed a metric wrench when you were trying to
loosen up a 9/16" bolt? Or maybe you've heard someone say that something weighs a ton
and you have to ask them, now is that a imperial
ton or a metric ton? Luckily, when most of us mix up units, it likely just leads to
our food tasting bad, or maybe strips a bolt,
or just simply leads to a really annoying argument between which is the right measurement system. But when NASA and Lockheed Martin mixed up the units for the Mars Climate Orbiter, it led to the loss of a $327
million mission to Mars. Welcome to another episode
of biggest facepalms or spaceflight history,
otherwise known as spacepalms. This is where we're going
to take a look at a mission or an event that almost
certainly lead to everyone in Michigan troll
collectively facepalming. Now this one in particular
is a very well known story. One you may have heard your
physics professor regale you with when talking about
the importance of units. But honestly, I don't
think I've actually heard the correct story all the way through and I definitely didn't
know what truly happened before I made this video. So today, let's take a look
at what was suppose to happen, what wound up happening and why. After all, this is a classic lesson that will be passed down for generations and generations. And it's a fun story to tell. So, let's get started. Three two one (upbeat music) The year 1999, back when
websites look like this. "The Matrix" was released
and the Cher song "Believe" was the number one hit. NASA was hoping to have a big
hit on their hands as well with an exciting new Mars
Orbiter that would study the Martian climate,
known as you guessed it, the Mars Climate Orbiter. NASA set new guidelines for some less expensive and smaller probes for interplanetary missions after a panel on small spacecraft
technology was formed in 1994. These new probes would
be under 1000 kilograms with more focused scientific instruments instead of Swiss Army knife
do it all style spacecraft from years prior. The first mission in this
new program was called the "Mars Global Surveyor"
which launched in 1996, on top of a Delta II from SLC-17A Cape Canaveral
Space Force Station, or Cape Canaveral Air Force Station, as it was known at the time. This first probe would map the surface of Mars with
more detail than ever before, which would help pave the
way for future Mars landers. The Mars Climate Orbiter
was to follow the success of the Mars Global Surveyor and
would be taking with it some of the instruments that
were originally designed for the Mars Global Surveyor. The two would be a mini powerhouse for studying Mars from orbit. The spacecraft found up
being 2.1 meters wide. 1.6 meters tall and two meters deep. It would weigh only 638
kilograms making it capable of being launched on a Delta II with only four solid rocket boosters, but despite its small way, it was still stuffed to the gills with scientific instruments including the Mars Orbiter Camera, the
Mars Orbiter Laser Altimeter, the Thermal Emission
Spectrometer, a Magnetometer and electron reflectometer
the ultra-stable oscillator and a Mars Relay signal receiver. Saying those out loud feels like I was making half of them
up, I probably should have tried to sneak in
the specs on the end line for the rotary girder
to see if any you guys are actually paying attention. The vehicle had eight
monoprop thrusters each with 22 Newtons of thrust
photo trajectory corrections and four smaller 0.9 Newton
thrusters for attitude control. Lastly, it had one larger
main engine a leros 1B that provided 640 Newtons of thrust for the Mars insertion burning. Mars Climate Orbiter had a unique design. It only had a single large
solar panel off to one side, which was capable of 500
watts at Mars, which side no because Mars is 50% further away from the Sun than the Earth is, due to the inverse square
law, a solar panel on Mars is about 45% as powerful
as it is on Earth. On December 11th 1998, at 1845 UTC, the Mars Climate Orbiter took off from Cape Canaveral Air Force
Station SLC-17A beginning its 10 month journey to Mars. One of my favorite things
about this launch is the Star-48B spin stabilized
solid propellant third stage. That's right, its spin stabilize So if there's any minor
offset in the thrust, you can know it out by spinning the stage. Once the burn is complete, there's a YoYo Despin
mechanism that mostly knows how the spin, it stuff like this
that I think is just so cool. So the little probe was on its
way, everything looking good. And like all deep space missions, it's normal to do a few
correction burns along the way to make sure you nail your target. And that's no big deal I mean,
this is done all the time. There were four course
corrections performed on December 21st 1998,
March 4th, July 25th and September 15th 1999. There was another optional
course correction planned just one day prior to
the Mars insertion burn, but it was denied by management because they thought based
on prior trajectories that the probe was on course. Alongside the course corrections, the spacecraft also perform something called angular momentum
desaturations or AMDs. Many spacecraft do this but especially the Mars Climate Orbiter, because it had that
single sided solar panel. It experienced more solar
pressure on one half of the spacecraft than the other. By the way, fun side note, solar
pressure is the momentum of the massless photons exerting
pressure on a spacecraft and it's not solar wind. Solar wind is composed of particles with mass ejected by the sun like nucleons and electrons. Thanks to Scott Manley and
the rest of space Twitter for helping clarify that for me. Okay, so your spacecraft is
ever so slightly rotating in a direction you don't want. And in order to keep the
reaction wheels inside the spacecraft that helped
maintain orientation from having to work overtime, you can perform an AMD to reset the spacecraft back to
its ideal orientation and keep those reaction wheels
happy and not overworked. Now each and every single
time the spacecraft performs any desaturation maneuver
or any correction burn, or really any maneuver the exact
impulse or the exact amount of time each and every
thruster is fired, is recorded, and then that's sent back down to earth so Mission Control can
calculate exactly how much the spacecraft change its trajectory. Even if it's by the teentiest, tiniest amount during these corrections. But now mind you mission
control can still track the probe and its trajectory in deep space on the way to Mars. But the primary way of doing
so is using Doppler shift and that's not incredibly accurate at some portions of the journey, especially when the changes in velocity are perpendicular to the vantage point. Think of it like this Doppler
can very precisely tell if something is speeding
up or slowing down, moving straight, away or towards you. But it can't really tell if something is speeding up side to side
from Earth's vantage point, which for a good portion
of the journey to Mars, is exactly what's happening. So generally guidance teams
will precisely calculate the vehicle's exact trajectory after the Hohman transfer burn that sends the probe on its way to Mars. And so long as any outside force doesn't act upon the vehicle,
which spoiler it's space. The variables are well
accounted for and well known. The vehicle will end up
exactly where it's calculated to a surprising degree of accuracy. But this also means that
they need to account for each and every thruster fire as even those tiny little impulses change the exact destination of the vehicle. Even if only a tiny amount,
if you do something enough, it ends up adding up over
time to a very drastic change. Now, of course when
you're aiming at a planet that's over 200 million
kilometers away from you, a tiny error could either
mean missing that planet, or perhaps even worse,
smacking right into it. And NASA was aiming to only miss Mars by 200 kilometers or so. So there was very little room for error. And in general, you want to aim and get as close as you can
safely get to the planet that you're trying to be captured by. Now, of course, if you're on a planet that has an atmosphere, you need to take that into consideration and not get too low. But the closer you are, the less energy it takes to get captured into orbit. On September 15th 1999 just one week prior to the Mars encounter
and insertion burn, NASA performed the fourth and final trajectory correction maneuver, which placed its trajectory 226 kilometers above the surface of Mars. Perfect for the Mars orbital insertion. But following that burn, the navigation team
noticed their calculations and their observations didn't match. And in fact, the observed
trajectory kept getting lower and lower to the point where they saw it go all the way
down to just 150 kilometers, but that was still safely above the minimum altitude of 80 kilometers. Now if you go below 80
kilometers Mars's atmosphere will still bite up your
fragile little spacecraft and rip it to shreds. Just imagine that tiny
little fragile solar panel getting knocked about
by the Martian winds. Oh, humanity. Just 24 hours before the
orbital insertion burn as the gravitational effects
of Mars grew stronger the newly observed trajectory was putting the spacecraft at only 100 10 kilometers. But again, that's still above the 80 kilometers that's survivable. So they proceeded despite
some vocal opposition of some of the operators. At 9 o'clock and 46 seconds
UTC on September 23 1999, the insertion burn began. Everything was performing
as planned at first. Miss control expected a loss of signal when the spacecraft went behind Mars, and they had an exact time
they expected that to happen. The first signs of serious
trouble cropped up when the loss of signal
occurred 49 seconds earlier than expected, and it was
even further drilled in by the fact that signal was not
required 21 minutes later as they expected, despite
trying for two full days. - I'm sorry to report that
we have a serious problem with the Mars Climate Orbiter. We may in fact be facing
a loss of mission. - So what actually happened? Was there something wrong
with the insertion burn? Was it that NASA was reading
the oxygen kilometers when the probe was saying miles. Find out after we hear a word from this week's sponsor,
banana for scale. - Are you tired of measuring stuff based on some old guy's feet? (screaming) Are you constantly asking
Siri how many ounces are in a pint, only to
get the wrong answer? - Hey Siri, how many ounces are in a pint? - [Siri] Austin is the
capital of Massachusetts? - Is it just too easy knowing there's a 1000 milliliters in a litre? Or perhaps you're
measuring horses in hands and you just (mumbles) Introducing banana for scale the one true unit of measure. - Okay, so the answer each and every time the spacecraft perform those
desaturation maneuvers, it would report back
what it did to correct for the angular momentum. Now the internal guidance and control was performing perfectly fine. Maintaining control and keeping proper orientation of the
spacecraft no problem. The problem is what the space craft was sending back down to
earth was Newton seconds. And the software in the
ground station was reading those results as pound seconds. And reporting those results to the guidance and navigation teams off by a factor of 4.4 or five times. So in other words, each time the spacecraft did a
desaturation maneuver, it reported back to the
ground what exactly it did. The data with the wrong unit, then was put into the model
for the spacecraft's trajectory by the guidance team. Now since the units were wrong, the calculated trajectory was also wrong. Now the funny thing is because these angular
momentum desaturation burns were so low energy being off by 4.45 times was hardly noticeable. So throughout the journey, every one of those little tiny events was doing a tiny little bit, but the estimated trajectory thought they were doing about
4.45 times more work. This was compounded by
the fact that because the Mars Climate Orbiter had
just a single solar panel, it had to perform over 10
times more desaturation events than its sister spacecraft,
the Mars Global Surveyor, which had two solar panels. So how could this have been prevented? Well, like most things, it'd be easy to put blame
on one person or group but in reality, it's kind of a
whole swath of small problems and putting the blame on anyone doesn't really solve the problem. The first and most obvious
problem and solution is to make sure all units are the same. Lockheed Martin took a lot of flack for delivering units in pounds seconds, as it was intended to be
delivered in Newton's seconds. But oddly, the blame game continues. When it was discovered the
code given to Lockheed Martin was in pound seconds in the first place, and they didn't catch it. Specifically a set of
code called Small forces, which was wrong from day one. Well, and then again, that no one caught the air and quality
control at NASA either. And then you can keep going and saying it was a management problem, considering several things
factors were overlooked starting with the initial
design of the spacecraft. Most notably that no one
from guidance and navigation was on the design team, which
led to a less than desirable and hard to navigate
spacecraft in the first place. But then ignoring the requests of the guidance navigation team to perform the desaturation maneuvers 180
degrees apart from each other would have negated the
problem before it arose. By doing asymmetrical
burns for the desaturation also led to imparting
additional unwanted velocity. And lastly, the teams
were seeing erroneous data that didn't line up with
our calculated trajectories, but it was ignored. This was amplified and
actually quite obvious that something was wrong in
the last week of the mission as the spacecraft got closer to Mars. A few members of the
team spoke up verbally and wanted to do a t-minus
24 hour correction burn to raise the approach. But they were denied because the concerns weren't filed correctly. And due to some mis
organization of authority. Those that spoke up were
seen as out of line. So really like all things, this wasn't a black and white topic. It's fairly nuanced and has
a lot of tiny little things that added up to one big thing. And at the end of the
day, the thing happened and the best thing we
can do is learn from it and prevent it from ever happening again. In fact, the problems discovered with the Mars Climate Orbiter was cross checked with
the Mars Polar Lander, which was also on its way to
Mars at the exact same time. And although it didn't
have the same problem, it ended up not touching down softly for completely different reason. - Volcom Mars op. - CFOM, go ahead. - Yeah, Sam, I'm sorry to
report that all we have is HKTM at this point. It seemed to have been a
nominal no contact MR Pass - Copy that Mark thanks for, thank for hanging in there with us. - But the lesson learned
has been passed down to every new generation of
navigators and engineers. It's a valuable lesson and
hopefully a lesson everyone who designed spacecraft for
the first humans going to Mars has listened to closely. So to summarize, a
spacecraft on its way to Mars needed to fight off the
solar pressure exerted onto the single sided solar panel by doing some angular momentum desaturations with its small attitude thrusters. Each time the vehicle did
a desaturation maneuver, it recorded what it did
and reported it back down to earth where the
recorded thruster firings were misinterpreted by software
as pounds seconds of force instead of Newton seconds,
leading to very tiny deviations in the calculated trajectory. These tiny deviations were so small, they went mostly unnoticed until the spacecraft encountered
Mars at 57 kilometers in altitude, instead of the
calculated 226 kilometers, which likely made the
spacecraft burn up in the Martian atmosphere, leading
to the loss of the mission. So let's not be so hard on ourselves when we make little errors. Or maybe be nicer to each
other understanding each and every single one of
us is capable of mistakes. It's simply part of being human. So what do you think? Did you learn something? Do you think it's just
a simple unit error? Or do you think there's a
lot more to it than that? Let me know your thoughts
and why metric is the better unit of measurement
in the comments below. Now I promise I'll do a few
more of these space POM videos to try and fill the gap between
some of my long form videos. Because trust me, those are getting a bit ridiculous even for me. I owe a huge thank you
to my Patreon supporters for helping make content
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the next time you check back. That's everydayastronaut.com/shop. Thanks everybody. That's gonna do it for me I'm Tim Dodd, the everyday astronaut. Bringing space down to
earth for everyday people. (upbeat music)
Short answer: Units conversion
Medium answer: Measurements reported from the probe were converted due to software that reported in one unit, but actually read back in another.
Long answer: Yeah..... That's what Tim is for; he's like the king of long answers.