Tag Archives: space travel

595. Apollo 10

Apollo 10 CSM, viewed from the LEM in lunar orbit.

Apollo 10 is a mission that, from the outside, looks unnecessary. It was anything but that. To appreciate it, you have to project yourself back into the state of ignorance that represented best knowledge in 1969.

I was also guilty of underrating it when I taught middle school science. I called it the most frustrating flight in the history of space flight, which was half true and half exaggeration. I also called the Command Module Pilots NASA’s soccer moms because they got to go to the game, but never got to play.

You have to know your audience, and middle school kids are looking for excitement, not “slow and steady wins the race”. And certainly not “they also serve who only stand and wait.”

In actual fact, without Apollo 10, the would have been no moon landings. There were two basic reasons for this. The LEM had only been tested in low earth orbit, not falling into a gravity well and then clawing its way out again. And we had an entirely inadequate understanding of the conditions on the ground at the proposed landing site. We especially needed to fine tune our understanding of lunar gravity for navigation purposes.

As the NASA history website puts it, “a test of the landing radar, visual observation of lunar lighting, stereoscopic strip photography, and execution of the phasing maneuver using the descent engine” were all performed on Apollo 10’s pass over the proposed landing site. If you want more data, check also here.


On May 18, 1969 Apollo 10 lifted off from Cape Canaveral on its way to the moon. Thomas Stafford was Commander, John Young was Command Module Pilot, and Gene Cernan was LEM Pilot. They entered orbit of the moon three days later. Stafford and Cernan undocked the LEM and began their descent fifty years ago today.

John Young was left alone in the Command Module, the first of seven men who would fly around the moon solo while their companions dropped toward the moon’s surface.

Stafford and Cernan fired the descent stage engine to slow the LEM. There followed a long unpowered descent, a rapid flyby of the proposed landing site, and a rise back up to the level of the CSM.

The reports at the time called it a dress rehearsal for Apollo 11, but it wasn’t that simple.

For comparison let’s look at a mission designed to land. At point A on the figure given here, the descent stage engine would fire briefly, changing from the black orbital path to the green one. At point B, a carefully calculated spot nearly half way around the moon, the descent engine would fire again. The descent from 60 miles to about 8 miles would have been in a flat curve, followed now by a very steep curve. The descent engine would continue to fire until the vehicle landed at point C. This is basically the exact reverse of a launch, as shown Monday.

Later, the ascent stage engine would fire, leaving the descent stage on the moon’s surface, and proceed along the second half of the green curve back up to the 60 mile level.

Apollo 10 (red orbit), on the other hand, passed over the prospective landing site and continued on.

This has always been called a dress rehearsal, so one would assume that the ascent stage would separate somewhere near the surface, fire its engines, and continue back up toward rendezvous separately from the descent stage. That’s what I thought for fifty years.

I was wrong. Imagine that. I probably learn more researching these posts than anyone does who reads them.

In fact, on Apollo 10 the descent stage fired again at point D (the red orbit represents Apollo 10), but it was merely a course correction, and the entire LEM continued up to the 60 mile level.

Apollo 11 would leave from the moon’s surface, starting at zero speed. Apollo 10 at its lowest point was at an altitude of 8 miles and a speed of 3554 miles per hour. Dress rehearsal was a considerable exaggeration. It wasn’t that reports were inaccurate; things were just more complicated than the summaries suggested.

It’s a little like science fiction novels. A two line blurb on the back of a 180 page paperback may not actually lie, but it can certainly give a false impression.

At point A on the trip back up for both missions another burn was necessary to get back onto the black curve. However, the CSM had gone its own way; it wasn’t waiting there for the LEM. The final rendezvous for the LEM and the CSM, which were at different places on roughly the same orbit, would be up to the pilot of the ascent stage, and would take an additional three hours.

At this point on all the moon landing missions, the ascent stage would be by itself. For Apollo 10, the ascent stage still needed to separate from the descent stage before performing the orbital insertion burn using its own engine.

That was the plan, but things didn’t entirely go well. Just before the separation, the LEM began acting up, corrected itself, then seconds later started a rapid roll. It was later determined that this was due to erroneous computer input. Stafford and Cernan quickly separated and regained control, but it was another of those close calls which could easily have led to a deadly outcome.

The crew rendezvoused and docked with the CSM, then returned to Earth. The ascent stage engine was fired again and went into solar orbit. The necessary data had been obtained for the moon landing in July.


At present, I plan for this to be my last full Apollo mission post. Everybody will cover the anniversary of Apollo 11. Everybody has already watched the movie Apollo 13, and I covered the other landings in 187. The Rest of the Landings. Of course, I reserve the right to change my mind.


594. Into Orbit

Fifty years ago last Saturday, Apollo 10 left for the moon. As you read this, depending when you click in, they are/were part way there. The mission’s big events will have their anniversary Wednesday, and that is when the main post will come.

Meanwhile . . .

From the fifties onward, there were dozens of books by people like Arthur C. Clarke and Wily Ley that explained in great detail how  we would go to space. I read most of them — at least every one I could get my hands on. There were a lot of people like me then. A lot of them spent the last decades working for NASA.

Now our knowledge of the universe is vastly greater, and most kids today know more than the best informed knew then. Still, some basic things get missed, because “everybody already knows them”.

Actually, they don’t. Here is an example, which I need to get out of the way before I talk about Apollo 10 on Wednesday.

Imagine, a rocket leaves Cape Canaveral with rocket engines flaming. The engines only burn for a  fairly short time, for reasons of efficiency; then the rocket coasts upward into orbit.

Right. And wrong. There is one more important thing that happens, but rarely get mentioned any more. A second critical burn has to happen at the high point of the initial orbit (apogee).

A rocket heading for orbit leaves the pad vertically, but it immediately begins to roll over. It needs to gain altitude to get above the atmosphere, but it also needs to gain velocity horizontally, so its upward path is a precisely programmed curve that begins vertically and ends horizontally (i.e. tangent to the surface of the Earth). This tangent is reached long after the rockets have ceased firing, at apogee, roughly half way around the Earth.

Caveat: everything in orbital mechanics is more complicated that the explanation you will get from someone like me. Nevertheless, this should be close enough for our purposes.

Let’s assume that the orbital insertion burn did not happen at apogee. Our craft would have achieved enough speed to reach its orbital altitude, but not enough speed to remain there. It would immediately begin to descend.

Think of a high fly ball to center field — up, then down again. Same Earth, same gravity, same result.

Such a rocket leaving Earth would burn up on reentry. If it were launched from an airless body like the moon, it would end up in an elliptical orbit with its low point very near the surface.

Instead, if all went well and the secondary burn took place when the rocket had reached its orbital altitude, it would change from a sharply elliptical orbit to a more nearly circular one. This is the normal way things get done.

You’ll need to have this in mind when we look at Apollo 10’s “dress rehearsal” on Wednesday.

583. Mutually Assured Destruction

I taught middle school science for twenty-seven years, and every year I taught the manned space program. It was never called for in the required curriculum, but I always managed to shoehorn it in while still teaching everything I was required to. It wasn’t just because I loved the subject, although I did. There were plenty of things in science that I loved but never mentioned.

The plain fact is that seventh graders don’t listen unless you excite them, and the manned space program was exciting.

Here is a schtick I used in my middle-school classroom all through the eighties and nineties. The subject was, “What motivated Americans who didn’t care about space to spend billions to outrun the Russians in the Space Race?”

I would choose two pushy, self-assured young guys and call them to the front of the room. I would put them face to face, about ten feet apart, and say, “Now, imagine each of you has a .45 automatic, and each of you hates the other one. We’ll call one of you America and the other Russia. I don’t want to insult you, so I won’t say which is which.

“Point your guns at each other. (They would gleefully assume the position.) If either one of you fires, the other will have just time enough to pull the trigger, too. You will both go down. If you sneeze, though, you’re a goner. If you blink, you’re a goner. If you look away, same thing.

“Now hold that pose for fifty years.”

Clearly, I couldn’t get away with that today, but this was pre-Columbine. My kids were thinking about cops and robbers, not  a terrorist who was out to kill them.

Do I have to point out that the guns represented the American and Soviet nuclear armed arsenal of missiles? It was a demonstration of Mutually Assured Destruction, also known by its entirely appropriate acronym MAD. If either side had attained an overwhelming superiority in number of missiles, the delicate balance would have been disrupted. Witness the Soviet’s parading their missiles in Moscow, and taking them several times around the block to look like they had more than they did.

The balance could be disrupted by having missiles closer to the enemy than the enemy did to us. Witness secret American missile bases in Turkey, on the Soviet border, which led them to put missiles in Cuba. The Cuban Missile Crisis was not an unprovoked Soviet threat.

The balance would have also been disrupted by an effective missile defense system. There is no such thing as defensive in the MAD scenario.

What does this have to do with space travel? Two things, one positive and one negative. The entire business was a race for the nuclear high ground. If either side had managed to put an orbital missile platform into orbit, it would have been bad news for the other side. That was not possible, so each side tried to maximize their capabilities in space while proving to the hundred plus other nations on the Earth that they were the firstest with the mostest.

I would repeat that in Russian if I could write Cyrillic.

All this turned into the Space Race, culminating in a manned lunar landing, It’s nice that something good came out of all that nonsense.

The other side of the coin was a reinforcement of fear of nukes, whether it was bombs, powerplants, or space drives. In the fiction of the sixties, the solar system was filled with nuclear powered spacecraft. In the real world, fear killed the idea.

Should we have nuclear spacecraft? I think so, but it isn’t for me to say. It isn’t for you to say, either. It isn’t even for the people to say.

Why? Because we’ve shifted our focus from the Russians to the Chinese.

If history is a guide, we will have a nuclear spacecraft — a few years after the Chinese launch their first one. We’ll be running behind and playing catch-up as usual.

Remember Sputnik?

582. Newtonian Nukes

Everybody who read the last generation of science fiction juveniles before Apollo knew Newton’s third law:

For every action, there is an equal and opposite reaction.

The demonstrations in popular science books of that same era usually went something like this: imagine a person on a frozen pond wearing ice skates, throwing bricks. Every brick he throws will move him backward. If we could ignore the friction of skates on ice, it would be proportional. That is, if a hundred pound man  . . .

Okay, side issue. Most Americans back then, and even today, don’t think in kilograms or kilometers, nor distinguish mass from weight in everyday thought, so . . .

If a hundred pound man throws a one pound brick at ten miles per hour, it will propel him backward at one tenth of a mile per hour. 1 times 10 = 0.1 times 100. We are ignoring friction from the ice, the atmosphere, and probably a bunch of other things.

So, if you want to go faster, throw more bricks, right? If you throw a thousand bricks, you should be able to go pretty fast, right? Wrong, because the first brick your throw in the new scenario will have to move not only the hundred pound man, but also the other 999 pounds of bricks.

Increasing the amount of fuel carried quickly brings about diminishing returns. More fuel alone is not the answer.

In a Newtonian scenario, the faster the propellant leaves the rocket engine, and the more propellant you use, the faster you can go. LOX and LH are probably near the practical  maximum for propellant speed by chemical reaction. The logical next step would be to use a non-chemical energy source to activate our propellants, such as a nuclear powered rocket. Even that won’t get us to the stars, but it makes sense for travel inside the solar system.

Before Apollo, everyone who read science fiction knew that, which is why the Scorpius and her sisters in the Rip Foster book are nuclear powered. So were the ships in Bullard of the Space Patrol, a marvelous fix-up novel by Malcolm Jameson that no one remembers today. So were the ships in the Dig Allen series (1959 – 1962), six great but forgotten novels, and the ships of the Tom Corbett books, which were not so great and are not completely forgotten.

Star Trek put all these early concepts out of business. Warp speed was a necessity for roaming the galaxy, but it made nuclear rockets look old fashioned. I think that’s too bad. There is still room for them in science fiction, and certainly in real life.

I haven’t mentioned Heinlein yet. The Rolling Stone was nuclear, but he quickly moved on to torch ships, which had the capacity of total annihilation of matter. He never explained how that could be done, but the result would be “propellant” moving at essentially lightspeed. You can’t get faster than that without warp drive. His torch ships roamed the solar system and went on to explore nearby stars.

I stole that schtick for my coreships in Cyan, with a twist. See 23. Star Drives.

In a rational world — which we will probably never inhabit, but we can still write stories about — you would might use chemical rockets to get to LEO (low Earth orbit), nuclear powered rockets to zip around the solar system (fission powered if you were writing in the sixties, fusion powered if you were writing today), and “torch ships” to reach nearby stars. Beyond that, you would need FTL (faster than light) vehicles which, by our present understanding of the universe, are impossible.

Too bad about FTL, but why are we still using chemical propellants in the real world fifty years after Apollo? Fear of nukes, of course. There will be more to say about that on Wednesday.

578. That Odd Spiral

This is the track of Sputnik, the first satellite launched from Baikonur Cosmodrome at latitude 46 degrees north. Launches from Cape Canaveral followed paths that were more flattened out because they were launched from 28 degrees north.

The orbital path shown above was to be found in thousands of publications at the dawn of the space age. Everyone carried the image in their heads, but today I had a hard time finding it on the web. My how times change.

Every space geek in 1960 would have known everything in this post, but then Star Trek came along. Kirk and Spock, and especially Uhura, went at warp speed and walked around on the floor like it was a sound stage in Hollywood. No weightlessness there. Then Star Wars came along and all veracity went out the viewplate.

There were a lot of very basic principles of physics that governed the space program, which Hollywood had to ignore.

Let’s begin on the ground. The Earth rotates eastward at a certain number of miles per hour. (We are channeling 1960 here. None of the published reports on space used the metric system back then.) Any geek with a pencil could figure out rotational speed by dividing equatorial circumference (25,000 miles to any 1960’s space fan, forget the decimals.) by the length of the day. !042 miles per hour eastward at the equator.

A spacecraft in low Earth orbit flies at 17,500 miles per hour. Actually that varies, but that was the figure in all the space enthusiasts books at the time. If you launched a rocket eastward, you started with about 1000 mph of free speed. If you launched westward, it would cost you 2000 mph of extra speed. You wouldn’t gain the natural advantage, and the rocket would be going 1000 mph the wrong way as it sat on the ground.

Everyone launched eastward.

There was actually another reasonable option, launch north or south. We’ll look at that choice at the bottom of the post.

Actually you don’t get all of that speed advantage. The circumference of the Earth is less as you move northward, lowering the eastward speed. If a United World wanted to choose the most advantageous place for a spaceport, it would be at high altitude somewhere on the equator. That happened frequently in science fiction.

Neither America nor Russia had a far southern point suitable for a space port. America’s best choices were Texas and Florida — the same two states Jules Verne pointed out in From the Earth to the Moon. Florida had the added advantage of having the Atlantic ocean to eastward, which provided a place to drop first stages and failed rockets, without landing on anybody’s house.

Russia built in the desert at the same latitude as Portland, Oregon, but they always chose secrecy over other factors.

Launching eastward is an exaggeration, of course. Straight east from either site won’t work; launches had to be aimed south of east to bring the center of the orbit into line with the center of the Earth’s gravity.

You might think that a launch from Canaveral would return to Canaveral after one orbit, but that isn’t true. The Earth is rotating eastward, so a spacecraft launched from Canaveral will pass over a spot about a thousand miles west of Canaveral on its first return. And so forth. Which is why the cosmonauts were a thousand miles off target after one extra orbit in yesterday’s post.

All this gives us that odd spiral at the top of the post.

In fact, you could launch a spacecraft into orbit from any point on Earth as long as its orbital path circled around the Earth’s center of gravity. Further south is simply more efficient.

You could even launch satellites due north, and we do, from Vandenberg Air Force Base on the west coast of California. Such satellites also spiral around the Earth, but they cover every part of the Earth eventually. Weather and spy satellites use this orbit.

Southeastward launches from Canaveral and Baikonur don’t cross over the far north or the far south.

What about a satellite exactly circling the equator? In low Earth orbit, it would circle the Earth about every 90 minutes. The moon, a quarter of a million miles further out, circles the Earth in 29 1/2 days. Clearly, even for math challenged enthusiasts, the further out the satellite, the slower it travels in orbit. At some distance from the center of the Earth, it would take a satellite one day to circle the Earth. Seen from Earth, it would appear to hang in one spot above the equator.

Everybody should know that, because that is how communication satellites work. The first person to recognize the fact and calculate the distance was Arthur C. Clarke, known even to non-SF readers from 2001, a Space Odyssey. The connection between science and science fiction has always been close.

577. The First Space Walk (2)

The space suit worn by Alexei Leonov on the first human space walk. On display at the Smithsonian National Air and Space Museum. Author: Nijuuf

This is the rest of Tuesday’s post. If you haven’t read it yet, take the time to do so, or this won’t make much sense.

Alexey Leonov had extreme difficulty reentering the airlock. His space suit had over inflated; the boots and gloves had slipped beyond his toes and fingertips, and his suit had increased in girth. He had to vent part of his rapidly depleting oxygen in order to bring his suit down in size, and even then he entered the airlock head first, instead of feet first as planned. Once inside the airlock, he had extreme difficulty contorting his body to close the outer door. All this time, his body was heating up dangerously; surrounded by vacuum, there was nothing to carry away the heat his body was generating.

Once air pressure had been restored in the airlock, Belyayev opened the inner door and Leonov was safe. For the moment. As he said in an article for Smithsonian’s Air and Space magazine in 2005, “the difficulties I experienced reentering the spacecraft were just the start of a series of dire emergencies that almost cost us our lives.”

The mission had achieved it’s goal and it was time to return, but just before the scheduled time for firing retro rockets the cosmonauts discovered that their automatic guidance system was malfunctioning. It took time to prepare for manual entry, so they had to wait one orbit, which would make them miss their return point by a thousand miles. (To find out why it would be a thousand miles, see the post coming on March 25.) Most of that orbit they were out of radio communications. (The Americans had built a string of radio relay stations around the world to maintain constant communication with their astronauts, but the Soviets had not.)

When communications were restored, ground control asked them where they had landed.

Their orbital path was set; the moment of firing their retro rockets would determine where on that orbit they would land. They chose a target just past the Urals. Using the clumsy and difficult manual backup equipment, they achieved the correct attitude and fired the retro rockets in the conical rear portion of the craft called the orbital module. The orbital and landing modules were supposed to separate ten seconds after retrofire. They didn’t.

The two cosmonauts knew immediately that something was terribly wrong. Instead of the steady press of force against their backs as they decelerated, they found themselves whipped about by confused forces that exceeded ten gravities. A communication cable between the two modules had failed to release, and now both modules were whipping about each other, tethered by the cable.

Finally, about 60 miles up, the cable burned through and the cosmonauts were freed. The drogue chute deployed, and then the main. All was peaceful and in order – briefly. Then it became dark as they dropped below cloud cover, the final rocket fired to slow them to landing speed, and they touched down in six feet of snow.

They were 1200 miles beyond their intended landing point.

They blew the explosive bolts to release the hatch. It didn’t open. They had landed in the middle of a forest and the hatch was held shut by a tree. By yanking violently they dislodged it and it fell away, lost in the snow.

They made their way out of the spacecraft and waded through snow to a small clearing. Those back at headquarters had not heard their landing signal, but a passing cargo plane had. It circled, and was soon joined by other planes and helicopters, but none of them could land in the rough taiga. Pilots threw a bottle of cognac; it broke. They threw warm clothing which got caught in the trees, but at least two pairs of wolfskin boots made it to the ground.

The light was failing. The cosmonauts returned to their craft for shelter. Leonov was walking in calf deep sweat still trapped in his space suit from his space walk. Both cosmonauts stripped, removed the liners from their space suits and wrung them dry, then put the on again along with the wolf skin boots. They abandoned the useless space suits and crawled into the landing module for the night, well aware that the taiga was filled with bears and wolves, and that this was mating season, when they were most aggressive.

The hatch was out of reach. The lights failed, but the circulation fan ran all night, adding to their misery. The temperature dropped to 22 below zero.

A rescue party arrived on skis the next morning; they chopped trees to build a small log cabin and a big fire. The cosmonauts spent a second night, then skied out to where a second, larger party had chopped down enough trees for a helicopter to land.

I guess they made ‘em tough in those days. I suspect they still do.

576. The First Space Walk (1)

I posted this in 2016, under the title Spacecraft Threatened by Bears. The title was snarky but accurate. Back then I had few followers, so it seems time to post the amazing story again.

My admiration for the people of the early American space program is boundless, but the Russians were no slouches either. They were the first to perform many feats, including the first space walk, during the flight of Voskhod 2 on March 18-19, fifty-four years ago.

I had the great good fortune of living through the early days of manned space flight. I was nine years old when the Russians orbited the first satellite, and the early manned flights came when I was in high school. I watched every American launch with fascination and envy, but the Russian launches were shrouded in secrecy. I knew only the bare minimum that all Americans knew. I’m not sure the president knew much more.

During those early days, nothing was routine. Every mission was dangerous. They still are, of course, but not so much as then. American failures were there for all the world to see, while the Soviets kept their’s secret.

After the breakup of the Soviet Union, information about the early Russian space program became generally available, but by then few people cared. I did, and I sought out the stories.


Oceans are big targets and landing in water cushions the fall. That is why Americans always splashed down. The Soviets were unwilling to land their craft anywhere outside of the USSR for reasons of security. Their hard landings had an effect of the design of their spacecraft.

The first six manned Soviet spaceflights were aboard Vostok craft, which came down on land — hard. Vostok astronauts wore space suits throughout their flights and landed by personal parachute separate from the capsule. Before the second generation Soyuz spacecraft came on line, the Soviets launched two additional manned missions on modified Vostoks called Voskhod.

On Voskhod, an additional rocket was added to the spherical descent module to fire at the last minute. This softened the landing enough so the cosmonauts could remain within the descent module all the way to the ground. Since ejection seats were no longer used, the weight saving allowed Voskhod 1 to carry three astronauts.

Voskhod 1 cosmonauts flew without space suits, as did early Soyuz missions. Voskhod 2 cosmonauts Belyayev and Leonov wore space suits because they were scheduled for the first space walk.

American space walks first took place during the Gemini program (see post 87). That craft had two hatches but no airlock; both astronauts were in vacuum during the entire spacewalk.

To exit his Voskhod in space, Leonov used an inflatable airlock (see drawing above), leaving Belyayev in the craft and unable to aid him. I had known this for several years but just in the last few days found out why. Russian electronics within Vostok and Voskhod were air cooled. American electronics were not. This meant that if a Voskhod were opened to space, the electronics would overheat.

On Voskhod 2, Leonov crawled into the airlock, sealed the inner door and opened the outer one. Belyayev remained in the pressurized descent module.

For ten minutes, Leonov remained within the airlock but exposed to the vacuum of space, then he slipped free and floated on a tether for another ten minutes. He was called back in to terminate his space walk, and his difficulties began.

(Or perhaps they had already begun. Some sources state that he “experienced a disorienting euphoria” during the space walk and other sources state that he suffered bends like symptoms after the space walk was over; I haven’t been able to confirm these statements.)

This post concludes on Thursday.