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Reid: With a couple of cargo ships lost in just the last few months, we're often reminded that getting to space can be difficult and dangerous. Over the years, there have been dozens of missions that didn't exactly go as planned, but those failures taught us a lot, like how to better engineer our equipment and to remember to check our math before pressing the launch button.

Take the unmanned Luna 15 Lander, launched by the Soviet Union on July 13th 1969. Which crashed into a mountain. If that date sounds familiar, that's probably because it was just three days before the launch of Apollo 11, which put the first people on the moon. NASA knew about the mission and the soviets agreed to share the lander's location and trajectory so that there were no accidental crashes. The plan was for Luna 15 to land on the moon, collect some surface samples, take some pictures, and come home. And it almost worked.

The blastoff and foreign aid trip to the moon went well, and the probe orbited the moon 50 times. Then on July 21st, as Neil Armstrong and Buzz Aldrin were preparing to return to lunar orbit and head home, Luna 15 started coming in for a landing in the relatively flat area of the moon, known appropriately as the Sea of Crisis, when data started coming in from its altitude sensor. The mission team realized that the terrain was a lot bumpier than they were expecting, but a state commission told them to land anyway. The lander hit a mountain and that was the end of Luna 15.

NASA's also had its share of setbacks, like the loss of the Mars climate orbiter in 1999, which was mainly supposed to do what it sounds like, study the martian atmosphere, but instead it disintegrated because missions scientists didn't convert their measurements to the metric system.

We stick to metric units here on SciShow Space because that's what most of the world, including the scientific world uses. But Americans and many American engineers tend to use systems based on English units, like pounds instead of kilograms. Converting between units isn't particularly hard, but if different groups working on the same project are using different systems, things can get confusing.

So, when they were building the Mars Climate Orbiter, NASA and the engineering firm Lockheed Martin had an agreement: everyone would use SI, the international system of units, also known as metric. But there was a problem with the program that calculated impulse, that's the change in the craft's momentum. The program gave its result in pound-seconds, and sent them off to another NASA programmed piece of software which used the information to figure out where the orbiter was headed. But that program was expecting the results to be in newton-seconds which are about one fifth of a pound second. That's a big difference.

The orbiter reached Mars successfully, and even sent back this one picture, but then the mission team tried to send it to what they thought would be a safe orbit, 226 km above the planet's surface. Because of the glitch, the orbiter ended up 57 km above the Martian surface instead. The mission team lost contact with it, and the 193 billion dollar spacecraft probably broke up in the atmosphere.

Sometimes, though, missions that go wrong can still be salvaged. Take the Akatsuki probe which the Japanese space agency JAXA sent to Venus in 2010. Well, they tried to send it but they missed. However, since the probe is still intact, They're gonna try again this December. Akatsuki was headed to Venus to study both the planet's surface and its atmosphere, looking for things like volcanoes and lightning. JAXA, along with the planetary society, had also run an online campaign where more than 260 thousand people sent their names and other messages to Venus, and the orbiter was carrying 90 aluminum plates with all that information carved into them.

The craft launched just fine, but as it was slowing down so it could be captured by Venus's gravity and start orbiting, its main engine burned out. According to JAXA's later investigation, salt deposits probably clogged up a fuel tank valve and the engine got too hot. So the mission team used Akatsuki's 12 secondary engines to get it into a stable orbit around the sun while they came up with a backup plan.

They realized that if they waited for the probe's orbit around the sun to align with Venus's orbit in just the right way, they could use the secondary engines to get the probe into orbit around Venus, and that alignment is going to happen on December 7th, 2015. Akatsuki's new orbit will be a lot farther out from Venus than was originally planned, but it should still be able to accomplish most of its mission goals, even if the picture is a little fuzzier. If that works, JAXA will have saved a 290 million dollar mission, and after five years orbiting the sun, all those names and messages from Earth will finally reach their destination.

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