scare.

Let's start with the fantastic stuff first.

If you were anywhere near SpaceX headquarters on April 8th -- or watching the livestream

of their mission control center -- you probably heard a LOT of cheering.

And for good reason: last week, for the first time ever, SpaceX landed the first stage of

their Falcon 9 rocket on a drone ship floating in the ocean.

They’ve landed one of their rockets successfully before, in December 2015. But that time, it

landed on the ground, near the launch pad.

It’s tough to touch down on a ship floating in the ocean, because … well, it’s the

ocean.

The drone ship tends to bob up and down a lot, even with special engines that help keep

it steady.

And you’re trying to gently land a tall, heavy, explosive rocket on that thing, without

it tipping over.

Which … isn’t easy. The other four times they’ve tried it, the Falcon 9 exploded.

But being able to land in the ocean is also a lot more useful than being able to land

on the ground.

Once a Falcon 9 launches, it generally separates from its upper stage and falls back to Earth

hundreds of kilometers away from the launch pad, over the ocean.

By that point, it’s already used a lot of fuel -- and it can’t always carry enough

extra to get to solid ground.

A carefully-placed drone ship means the rocket doesn’t have to fly back -- it can just

land.

So if SpaceX wants to reuse their first-stage rockets and cut down on brand-new rocket manufacturing

costs, they’ll need to master the ocean landing.

And now, they’ve done it once!

After the landing, the ship and rocket were brought back to shore.

The next step is testing this Falcon 9 to make sure it wasn’t too damaged during the

landing. Then, the company hopes to launch it a second time, possibly by early June.

A successful drone ship landing means we’re already a huge step closer to cheaper rocket

launches.

According to SpaceX CEO Elon Musk, they’ll also be trying to land the rockets from the

next two missions -- on April 28th and and May 3rd, which will both be satellite launches.

Those landings will be trickier, because the rockets will need to fly at higher velocities

to get the satellites into orbit, which means they’ll have even less fuel to maneuver

their falls back to Earth.

Hopefully they’ll stick the landings anyway!

Now for the big scare:

On Thursday, April 7th, NASA engineers checked in with the Kepler space telescope and found

out that it had been in Emergency Mode for about a day and a half.

Which -- as you might have guessed from the word “emergency” -- is not good.

By Sunday, Kepler was stable again. But we still don’t know exactly what went wrong.

Ever since it launched in 2009, Kepler has had its fair share of problems:

Like, in 2012 and 2013, two of the four reaction wheels that steer and stabilize the spacecraft,

failed.

This could have ruined Kepler’s entire mission, because its search for exoplanets depends

on its ability to stay precisely pointed at different targets.

But NASA scientists came up with a way to compensate, using the slight push of the Sun’s

radiation as a kind of replacement third reaction wheel.

In May of 2014, Kepler started collecting data again, and it’s been working fine ever

since -- until last week, when it suddenly went into Emergency Mode.

The timing was weird, and unfortunate: the team of NASA engineers found out just 14 hours

before Kepler was set to reorient and prepare for a new phase of its mission.

Before, Kepler was pointed /behind/ itself as it orbited the Sun.

The plan was to turn the telescope so that it pointed /forward/ as it orbited, which

would give it a good view of the center of the galaxy -- where it would continue to search

for exoplanets.

At the same time, telescopes here on Earth would also be observing the center of the

galaxy.

By comparing the ground-based telescope observations with data from Kepler, scientists would be

able to calculate the distances to those exoplanets.

The plans have been put on hold for now, while the Kepler team figures out what made the

spacecraft enter Emergency Mode, and clears it for science operations again.

But on July 1st, Kepler will be at a point in its orbit where it won’t be able to see

the center of the galaxy anymore. So they don’t have very long.

Hang in there, Kepler!

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