When we last left Felinian catronaut Major Thomas Fluffison, he’d just transferred much needed fuel from the Catstrophian rescue ship and moved his ship a safe distance away. Sitting at the controls, he awaited instructions from Ground Control while anxiously eyeing the oxygen gauge. With less than an hour of oxygen remaining, he knew the reentry timing would be tight.

Back in Ground Control, scientists worked feverishly to devise a reentry trajectory that would get Major Tom to the ground in time. There was only one option, Major Tom would have to land in Catstrophian territory. (What, were you expecting a water landing? We’re talking cats here.)

Cats from throughout Catalonia had gathered in stadiums and town squares awaiting word on Major Tom’s fate. Agent Kitten (the spy who’d sabotaged Major Tom’s rocket) wasn’t among them as he’d secured a much better vantage point. Using a multitude of disguises, he’d remained in the launch facility.

After ditching the lab coat, he’d become a janitor, secretary, reporter, and even a security guard. Not a single cat ever questioned his identity. Now back in his lab coat, he sat at an unused terminal in Ground Control looking just like all the other technicians, albeit somewhat smaller. He’d been involved since the beginning and was determined to see it through to the end.

“Ground Control to Major Tom,” crackled the voice over the capsule’s radio. “T minus twenty minutes until reentry burn.”

“Cutting it awfully close,” replied Major Tom, mentally comparing the time required for reentry and his remaining air.

“We know,” came the reply, “but it’s the first opportunity to reach a secluded area suitable for landing.” There was a brief pause. “You’ll be landing in Catstroph.”

Agent Kitten purred to himself. This was even better than he’d hoped.

“Understood,” answered Major Tom realizing survival trumped political considerations. “Preparing for reentry.”

Over the next fifteen minutes, he went over the ship’s systems verifying everything was ready. However, the one system he couldn’t check was the heat shield that would protect the capsule from the intense heat of reentry. He could only hope it hadn’t been damaged on his trip to space.

His final task was to fire the ship’s maneuvering thrusters to rotate his capsule until it was flying backwards. Now the engine firing would reduce his velocity and lower his orbit into the atmosphere. Watching the clock, Major Tom held his paw over the ignition button as he received final instructions on how long to fire the engine.

At the appointed time, he pushed the button and felt himself pushed back into his chair. Watching from the window, he could see the planet below slowly growing larger. After 10 minutes, he shut down the engine, his descent into the atmosphere now assured. All he could now was wait.

After about twenty minutes, the capsule began to shake as it hit the upper atmosphere with a speed of 7.1 kilometers per second (16000 mph). At the same time, Major Tom could see the exterior temperature of the capsule beginning to increase. “Entering atmosphere,” he radioed.

“Trajectory looks good,” came the reply. “Right down the center of the corridor.”

The outside temperature of the capsule continued to increase and Major Tom could now see a dull red glow outside the window. His body was now pushed up against the straps holding him in the chair as the ship slowed. During this time, Major Tom and Ground Control remained in constant contact as he reported ship status and they provided trajectory updates. As he fell deeper into the atmosphere, the capsule’s velocity steadily decreased.

The dull red glow outside had morphed into bright red flames as the capsule plunged deeper into the atmosphere and was now shaking violently. “Altitude seventy-one …” was suddenly replaced with static in the capsule. On the ground, all contact with Major Tom had also been lost.

“Ground Control to Major Tom,” came the urgent call, but there was no reply.

An eerie red glow now filled the capsule as flames engulfed the exterior. Major Tom kept a close eye on the temperature monitor and the exterior temperature soared to over two thousand degrees. Still unable to contact Ground Control, he checked the radio circuits, but could find nothing wrong.

Back on Catalonia, all had grown silent as the minutes slowly passed. After ten minutes, many began to lose hope and sounds of sobbing could be heard across the planet.

Finally, as the exterior temperature of the capsule began to drop, “… Tom. Come in Major Tom,” burst from the radio.

Betraying his usual stoic manner, Major Tom almost yelled in reply. “This is Major Tom! Come in Ground Control.”

Cheers filled Ground Control and even Agent Kitten found himself joining in. Cats across Catalonia shouted with joy and relief as Major Tom’s voice rang out.

“Good to hear your voice, Major Tom,” responded a relieved Ground Control. “Altitude thirty-six kilometers and reentry speed is 1.8 kilometers per second (4000 mph).”

All Major Tom could do now was wait. Once his ship had slowed down enough, the parachutes would deploy. After they’d done their work, it would be up to the ship’s retro rockets to get him to the ground. With only fifteen minutes of air left, it’d be close. Nearly half of the remaining air was gone by the time the capsule experienced a sudden jerk, pushing Major Tom down into his chair.

Looking out the capsule’s window, he could see a bleak plain below and in the distance an ocean. Catstroph certainly didn’t look inviting, but at this point he didn’t care where he landed only wanting to feel the ground beneath his paws.

With only three minutes of air left, a loud pop followed by a dull roar could be heard as the parachutes were released and the retro rockets came to life. The capsule slowly descended, the minutes ticking by. As the capsule landed with a soft bump, an alarm sounded; the last of his air was gone. Major Tom tore off his helmet and activated the switch to open the capsule door.

A cold breeze washed over him and he took a long breath. “Come in Ground Control,” he radioed. “Landing complete.”

For a moment there was no reply. Soon, a voice Major Tom didn’t recognize, although based on the accent he was sure it was Catstrophian, answered, “Come in Major Fluffison. We’ve received your message and relayed it to Felinian Ground Control. They send their congratulations. A recovery crew will reach you shortly.”

“Understood,” responded Major Tom.

With some difficulty, he unstrapped himself from the chair. His arms and legs felt heavy after days of weightlessness, but he was able to get outside where the sound of crunching ground was music to his ears. Sitting on the stairs leading from the capsule, he surveyed the area around him. The plain where he’d landed was mostly dirt with a scattering of small bushes. However, to Major Tom it was the most beautiful landscape he’d ever seen.

While waiting for the recovery team, he considered what he’d accomplished. However, he knew it was just the beginning. In the twilight he could see the moon just peeking over the horizon. That would be the next stop: then on to other planets and beyond.

The sound of a helicopter could now be heard. Soon search lights flitted around the capsule and the helicopter landed a short distance away. Several Catstrophian soldiers and a medical team jumped out and hurried over to Major Tom, who wobbly stood up to greet them.

As the group approached, Major Tom noticed one soldier was a major like himself. Stopping in front of the catronaut, he and all the other soldiers gave a crisp salute. “Welcome to Catstroph Major Fluffison, and congratulations.”

Major Tom returned the salute. “Thank you Major, it’s good to be home.”

Then an odd thing happened. The Catstrophian Major pulled a notebook and pen from his pocket. Looking embarrassed, he held out the notebook and pen. “My kittens would never forgive me if I didn’t get your autograph.”

Major Tom smiled, “I’d be most happy to.”

It was as if the flood gates had been opened as all the other soldiers and medical team asked for his autograph as well. Then there were the questions. Everyone wanted to know about his experience in space. It was almost an hour before they finally made their way back to the helicopter. And in all that time, not once did anyone mention cat scratchers.

Now would it be too much to assume that this one instance of cooperation would be enough to end the bitter dispute between Felinia and Catstroph? Hey, we’re talking cats here, so of course it did. Cats across Catalonia had become so invested in Major Tom’s fate that cat scratchers just didn’t seem that important anymore.

Not everyone was happy about this: namely Agent Kitten. After all, without an enemy, Catstroph didn’t need spies and that’s the only job he knew. Plus, as a secret agent, it’s not like he could put it on his resume or use his boss as a reference.

However, if there’s one thing we know about our unemployed spy, it’s that he’s resourceful. It didn’t take him long to find the perfect new career: acting. Normally it takes years and lots of luck to make it as an actor, but Agent Kitten used the skills of his former profession to take what one might politely call a short cut. A kitten does have to eat after all. Within a year, Catalonia had a new number one action star: Agent Kitten.

Getting our catronaut back to the ground safely sure wasn’t easy. And since when have there been corridors in space? Let’s dig into the physics behind Major Tom’s successful return to Catalonia to find out.

What makes reentry so difficult is the tremendous amount of energy an object in orbit has. An object in orbit possesses two kinds of energy: kinetic energy (the energy due to an object’s speed) and gravitational potential energy (the energy gained by moving upward in a gravity field). All this energy needs to be dissipated during reentry, but how?

Major Tom did rotate his ship so firing the engine would slow the capsule down, but he only fired the engine for 10 minutes. What good could this possibly do, considering he’s moving at over 17000 mph? Actually, it did everything he needed because it caused his ship to enter that great scrubber of energy, the atmosphere.

That’s right, the atmosphere is what dissipates the capsule’s energy. It does this in two ways: aerodynamic drag and aerodynamic heating. If you’ve ever stuck your hand out of a car while it’s moving, you probably felt the wind trying to push your hand backwards. That’s aerodynamic drag.

Have you ever been riding a bike and tried putting your feet on the ground to brake? They got hot didn’t they? That’s caused by the friction between your feet and the ground. Aerodynamic heating is caused by the friction between air and the fast moving capsule (like 16000 mph fast). This friction converts the energy of the falling capsule into heat.

Now this wouldn’t be Rocket Cat without some equations. To make it easier we’ll give you the aerodynamic drag and heating equations all at once (kind of like yanking off a bandage). Now normally, I'd just include the equations for aerodynamic drag and heating here, but I am trying to curb my overuse of math.

Now if I had had included the equations you'd see that only the air density and capsule velocity are changing during reentry. However, they’re changing in opposite directions: the air density is increasing while the capsule velocity is decreasing. And now for something really special; graphs. The plots below show the typical behavior of capsule velocity, drag, and heating during reentry.

The peak aerodynamic drag load and aerodynamic heating both occur while the capsule in the upper atmosphere where the capsule’s velocity is still very high. Thus, the early part of reentry is the most critical because you have both high drag loads and high heating. It’s in this portion of the atmosphere where most meteorites burn up flashing across the night sky in a final blaze of glory.

We certainly don’t want this happening to the capsule so its entry into the atmosphere must be carefully controlled. So what exactly needs to be controlled? To answer that, consider what happens when you toss rocks into a pond. To skip a rock across the water, you throw it almost parallel to the water. On the other hand, if you loft a rock into the air it will land in the water with a large splash. The difference between these two situations: the angle at which the rock enters the water.

It’s exactly the same for a capsule entering the atmosphere. The angle at which it enters the atmosphere is called its reentry angle. For a too shallow reentry angle, the capsule would bounce off the atmosphere just like our rock skipping across the water. If the reentry angle is too steep, the capsule will “splash” into the atmosphere causing severe drag loads and high temperatures which would destroy the capsule.

A reentry angle between these two extremes defines what’s called the reentry corridor. Yes, there is indeed a corridor in space. If the capsule enters the atmosphere through this corridor, the aerodynamic drag loads and heating will be within the capsule’s design capabilities. Fortunately for Major Tom, he hit the reentry corridor.

Now did reentry have anything to do with Ground Control losing contact with Major Tom or was that merely included for dramatic effect? Of course it was due to reentry. The drama of real science is far superior to the gratuitous stuff.

The event, called Loss of Signal (LOS), is caused by aerodynamic heating making the air around the capsule so hot that it becomes what is known as plasma. In its plasma state, matter is broken down at the atomic level producing charged particles known as ions which prevent radio signals from being transmitted or received by the capsule.

LOS occurs during the period of peak aerodynamic heating and can last up to 15 minutes. Seems the scientists of Felinia didn’t consider this effect causing some anxious minutes during reentry (well maybe that part was for dramatic effect).

Aerodynamic drag and heating on the capsule dissipates most of the capsule’s orbital energy, but not quite all. That’s why the parachutes and retro rockets are needed for the final descent.

And so Major Tom was brought safely back to Catalonia ushering in a new era of cooperation between former enemies Felinia and Catstroph. Certainly not the outcome Agent Kitten had in mind, but in the end, a far better one than he could have ever imagined. After all, it did result in him becoming a worldwide acting sensation. And with that we now take our leave of Catalonia, but certainly plan on returning as events warrant. However, we’ll save those stories for another time.