Ep 485: Docking, Refueling, and Transferring

This episode was recorded on Wednesday, March 21 at 6:30 pm EDT / 3:3 pm PDT / 22:30 UTC.
It’s one thing to get to space. But once you’ve made it there, what do you want to do? You’ll probably want to dock with another space ship, deliver cargo, refuel. Today we’ll talk about how all that happens.
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Show Notes

Gemini Missions 1962-66
Gemini 4 James McDivitt had first major docking fail
Orbital Mechanics
Basics of Space Flight: Orbital Mechanics
Wally Shirra in 1965 successfully docked Gemini 6A to Gemini 7
‘Dragon by the Tail!’: Video of SpaceX capsule docking with ISS
SpaceX Dragon Docked to Space Station
Salyut 1 and Soyuz 10
Docking spacecraft
Robotic Canadarm 2
Robotic Refueling in Orbit


Podcast Transcription provided by GMR Transcription
Fraser: Astronomy Cast, Episode 485: Docking and Refueling. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, Dr. Pamela Gay, the Director of Technology and Citizen Science at the Astronomical Society of the Pacific and the Director of CosmoQuest. Hey, Pamela, how you doing?
Pamela: I’m doing well. How are you doing, Fraser?
Fraser: Good. And at the time that people are listening to this episode of Astronomy Cast, you may very well be at or near the Astronomical Society of the Pacific, right?
Pamela: Oh, man. So, when’s this one going out? I will be almost to the ASP. I am in the middle, I realized, of eight weeks, eight cities, four continents.
Fraser: I am impressed that you’ve been able to find the time to be anywhere near your house and to be able to record these episodes of Astronomy Cast. And I know the people who join us on the live shows, they don’t know whether they’re coming or going, they don’t know what time it is.
Pamela: I don’t know what time it is. I have no idea.
Fraser: People who never get a chance to see our episodes live are able to watch them. People who normally watch them live can’t watch them. It’s a mixed up, crazy world right now.
Pamela: Well, thank you for playing along with me.
Fraser: No problem.
Pamela: It all ends soon.
Fraser: It all ends, and then you’ll be back home forever.
Pamela: Yes. No.
Fraser: Alright, it’s one thing to get to space, but once you’ve made it there, what do you want to do? You probably wanna dock with another spaceship; deliver cargo, refuel, and today we’re gonna talk about how all that happens. One of the most fascinating times of the history of NASA’s space missions, for me, was the Gemini – or [inaudible] [00:01:57] was called the “Geminee” – but I just call it the Gemini – even though she’s Canadian, too. Anyway, Gemini is the way you say the constellation, right?
Pamela: Yes.
Fraser: Right. My dad’s a Gemini. Anyway, one of the great things about the Gemini Missions was how they did this really incremental approach over the course of the mission’s learning to stay up in space longer and learning to dock spacecraft together, which was the foundation of going on the Apollo program because there was so much docking, and flipping around capsules and stuff, and landing, and getting back to space, and docking again. So, let’s talk about docking. It’s like the second riskiest part of space flight, if getting off the ground, maybe reentering the earth’s atmosphere are the two risky parts. Let’s talk about docking.
Pamela: So, this is my favorite bit of space history because the first poor American schmo who attempted to dock didn’t know orbital mechanics and failed absolutely, totally, and completely in the most spectacular of fails, and it’s because it turns out the way you have to maneuver is as counterintuitive as it can possibly be. You see that thing straight in front of you. Intuitively, pretending you know nothing, what do you think you have to do to catch up with that spacecraft in front of you?
Fraser: You aim towards that thing, and you fire your thrusters, and have it get closer to you.
Pamela: Yeah, and that totally doesn’t work, which is why they failed so delightfully spectacularly. So, back on June 3, 1965, U.S. astronaut Jim McDivitt on Gemini 4 made a go of trying to catch up to his Titan to launch vehicles upper stage. Seemed like not too bad a thing to do, seemed like it should be easy, and the problem is, as we discussed in our last episode. When you fire your thrusters, when you increase your orbital velocity, what actually happens is you go into a higher orbit. You don’t accelerate on the orbit you’re on. You switch to an entirely new orbit.
Fraser: So, by aiming his spaceship at the target and by firing his thrusters, he moved further away from the earth –
Pamela: And slowed down.
Fraser: – and slowed down, which is absolutely – you’re right – is so counterintuitive, right?
Pamela: Yes.
Fraser: You know, you would be rising up higher, you would be seeing that Titan upper stage moving faster than you in orbit, and then you would, of course, now you would aim your spaceship in the direction of where the booster is now, and you would fire your thrusters again –
Pamela: And just make the situation worse.
Fraser: Just make it worse.
Pamela: So, this is one of those things where you really have to drop into a lower orbit, catch up, and then perform a Hohmann transfer orbit to get up into the orbit you meant to be in initially going at the same velocity as the thing you hopefully don’t hit.
Fraser: So, how did they then figure this out later on?
Pamela: They went back to Earth and they learned orbital mechanics. And I wish that it wasn’t as – I mean, I sound totally sarcastic when I say that. I sound like I’m making fun of them, but no, this is what actually happened. They had to come back to Earth having failed to dock Gemini 4, they went to the notebooks, they did the math, they realized Kepler’s laws. That whole equal area and equal time thing totally, totally kicked them. And then ran some paper and pencil simulations because it was the 60s and figured out, “Oh, okay. We need to be in a lower orbit and increase our velocity to bump up, and slow down, and then touch, and yeah, stomach wrong.”
Fraser: It’s funny, right? Because when you just think this through your brain – I mean, I think you really set the stage nicely – when you imagine how you would go about this process, when you think about how, say, when the Dragon launches on a SpaceX, and it’s gonna launch to be able to deliver cargo to the International Space Station, it’s got some sort of window, you kind of imagine this space station flies overhead, and then the falcon takes off, and it’s got the Dragon capsule on the front, and it pushes it into this orbit that’s exactly the same as the International Space Station.
And then the Dragon has some little thrusters that just puff, puff, puffs its way and catches up with – and that’s the way people even describe it – catches up with the Space Station and then docks. But that is not how it works.
Pamela: And what’s really cool is if you ever watch the videos, you get to see the Dragon capsule come from a much lower orbit, rise up in altitude as it catches up with the International Space Station, and then it adjusts its orbit so they’re essentially station-keeping until they grab onto each other.
Fraser: Right. And you used to see that with the space shuttle as well. You would always see these images of the space shuttle rising up below the International Space Station with the earth behind it. So, it’s great. That’s kind of counterintuitive. And so, then, for every maneuver that you’re trying to do, you’ve gotta go through some permutation of this, right?
Pamela: And it becomes really a game of circulization at the right moment in time. This is where the whole idea of station-keeping comes in, and it sounds like something totally out of Star Wars where you have some storm troopers standing next to a desk, but what station-keeping actually means is putting yourself in an orbit so that you are maintaining equal separation with time with the object that you’re interested in. So, later on, like you said, the Gemini missions did things increment by increment by increment, so with the Gemini 6 and 7 missions, they weren’t set up to actually dock and let the astronauts go back and forth between the two spacecraft, but they did want to station-keep.
And Wally Schirra did the piloting – this was back December 15, 1965 – and did that drop into a lower orbit and put yourself into an elliptical orbit such that the point where you catch up with the other spacecraft, you can then fire your engines and not catch up, but you go from that elliptical orbit that’s about to hit them to circularizing your orbit or putting yourself into the exact same elliptical orbit – it depends what orbit you’re catching up to. You match orbits just at the last minute as you’re about to pass each other, so it’s not catching up, it’s crossing orbits and then syncing your orbits.
And he was able to get the Gemini spacecraft so that they were only about 30 centimeters apart, hanging out, orbiting together. And that’s really impressive if you think about it. 30 centimeters is the lower arm of most adult humans, and that’s how close these two spacecraft were orbiting.
Fraser: And what’s so amazing, of course, if that he had to do this all by hand. Now, it’s all done mostly by computers, but a lot of the early astronaut pilots, they had to do this all by hand, and they didn’t have the benefit of videogames that would’ve very easily simulated it. If they had been playing Kerbal Space Program, they would have been able to change their brains so that they knew how to make the spaceship go. I mean, man, when you don’t use your telescope, and you’ve got some images in the telescope, and you wanna bring it closer to the middle, because everything is flipped upside down, you have to think in a different way.
In the beginning, you’re always moving the object in the wrong direction, and after a while, you figure it out, and then eventually, you’re able to actually always do it in the right direction. And you can just imagine, for these astronauts, they just didn’t get enough time to really get good at it until they could come up with really good simulations, so that just makes me even more impressed that they couldn’t play all these videogames.
Pamela: Sometimes when I’m prepping for the show, I learn things that I feel like I really should’ve known and totally didn’t know, and one of those things is Buzz Aldrin did a PhD dissertation, and it just completely escaped me that he was actually Dr. Buzz Aldrin because you never hear him called Dr. Aldrin. But yeah, he totally did a PhD, and his doctoral thesis was titled “Line of Sight Guidance Techniques for Manned Orbital Rendezvous”. So, what is now math that we do as part of playing Kerbal Space, what I might assign as a homework assignment in the age of computers was Dr. Buzz Aldrin’s doctoral thesis.
Fraser: Now, let’s talk a bit about some of the other orbital maneuvers that they have to do to do docking. So, I sort of mentioned this briefly early on. Now, you talked about some of the Gemini program, but when they moved into the Apollo missions, they had a lot more of these kinds of docking and rendezvous that they had to do.
Pamela: And this is in part because the configurations they needed their spacecraft in at different points in time varied. How you wanted to launch everything versus how you needed to separate to land on the moon versus how you needed to then remate your spacecraft to get back to Earth, and then jettison a part of your spacecraft to finish getting back to Earth, it was this crazy circus trapeze act with no net, or wires, or swing – just the trapeze artists.
Fraser: And I mean, so they had to do one docking maneuver when they were in Earth orbit, and then they had to do, of course, when they got to the moon, they would go into orbit around the moon, and then they would detach the Lunar Lander. It would go down to the surface of the moon, and then it would come back up, and then it would redock with the command module for them to come back.
Pamela: Yes. And so, you have at one point when it’s taking off, you have your Apollo module is happily downwards with the big command module below. You then flip everything upside down. It was a lot more pieces that got lugged to the moon than what you may think about because when we go to the museum, we see the spidery beetle-looking Lander and then we see the triangular Apollo capsule. But there was a lot more. It was that whole command module that we tend to forget about, and they had to do gymnastics around that, essentially.
Fraser: Now, while the Americans were having their doctoral theses astronauts learning and practicing the ways to do these orbital maneuvers, the Russians didn’t trust their astronauts so much to be able to actually perform these maneuvers, and they turned everything over to computers.
Pamela: Yes. And what’s funny is the way they started their history of doing this. It actually, for them, goes all the way back to 1963 with the early Vostok missions. Now, there is no actual station-keeping involved. It was funny to me, I don’t know if it was funny then – probably not. So, in ’62, they launched Vostok 3 and 4 a couple days apart, then in ’63, they launched Vostok 5 and 6 a couple days apart, stuck them into identical orbits, and they weren’t entirely identical orbits, and the idea was one would catch up to the other. That didn’t actually happen. Instead, they went from about 5 kilometers apart to over time thousands of kilometers apart. And then we have silence on the matter for quite some time.
Fraser: Right, but that idea of the Russians sort of, as I said, not letting their pilots do the docking, they just went to computers.
Pamela: Right, so in’71, we had Soyuz 11, which didn’t survive entirely, by which I mean it didn’t survive, but it did successfully dock with the Salyut 1 so that was a good start to things. Of course, we had the Apollo-Soyuz mission that came later on in the 70s, which actually proved that imperial versus metric isn’t the greatest problem that one could have because the docking technologies developed by the Russians and developed by the Americans were utterly incompatible, so they had to build a docking unit to essentially translate between Russian hull and American hull, so there was that great docking episode.
But since then, docking has really been that thing that means, “Hey, I’m going to a space station,” and this is today’s – and has been in the entirety of both our lifetimes – the primary goal of docking.
Fraser: Is transfer cargo and astronauts to the International Space Station, return cargo back to Earth, and astronauts. That is the vast majority of the orbital maneuvers. I can’t think of any – apart from, say, Deep Impact and LCROSS – I can’t think of any other times – there was of course Rosetta in Filey – but I can’t think of other times that –
Pamela: There was Beagle. But these are all cases of spinning out a spacecraft, not –
Fraser: Yeah, that’s what I’m saying. I’m trying to think of examples where things docked in space, but really, it’s all – the vast majority – is them arriving at the International Space Station.
Pamela: And so, this was with the Soviet Salyuts, this was with the American Skylab, then we had Mir, and the original Soviet idea of doing robotic docking has really been what’s taken over since then where we have Soyuz and Progress spacecraft automatically docked with Mir, the ISS has the Kurs docking system. Europe has the automated transfer vehicle. And so, it’s really robotic after robotic after robotic system. And now, with the International Space Station, we’re continuing this originally Soviet, then Russian, and European tradition of robotic docking. We have NASA’s birthing mechanism rather than a docking port.
But mission after mission after mission nation after nation after nation, this is the direction we’re going. Japan joined in with their transfer vehicle, and all the spacecraft are all setup to essentially robotically go into station-keeping, pull that Gemini maneuver of hovering without touching – I’m not touching you – basically, this is what you want your children in the backseat to do – stay equally distanced and not touch, and then the Canadarm reaches out and grabs the spacecraft.
And so, we’ve gone – and this just makes me giggle to know – and we have gone from robotic docking, meaning a fully automated get together and couple the space craft to an automated hover – not touching – and then an arm reaches out and grabs that spacecraft. It’s lovely.
Fraser: It really is the safest way to go about it. Alright, we’ve been talking about the docking maneuvers. Let’s move on to the refueling side of things. So, where is that happening right now?
Pamela: So, this is where sometimes science fiction makes things seem easier than the paperwork actually allows it to be. We’ve tested the technologies for doing refueling in space, and this is one of those things that’s really on the long-term roadmap as we look ahead to assuming the space launch system moves forward. It’s first several launches are going to go towards getting us a little, tiny space port out in CSA inner space that nominally will be there for construction and refueling.
And as we work on the roadmap to get towards that little space station, NASA has been testing the robotic refueling mission. It hung out on the International Space Station until 2017. Early 2017, it came back to Earth; it was considered a success. It showed that we have the ability to safely have a fuel depot in space, we have the ability to refuel things, we’re just not going to keep doing it for the time being because the space was needed to test other things.
Fraser: I mean, one of the things that’s kind of interesting is when the Soyuz and the Progress vehicles dock to the International Space Station, they don’t transfer the fuel. They don’t transfer their propellant out of those vehicles. They just boost the Space Station by using the thrusters on the vehicle itself. And so, I don’t know if they transfer any propellant at all to the International Space Station, but all of the boosting maneuvers are done by these attached spacecraft, so orbital refueling is not something that’s been done. But then theoretically, it makes a lot of sense, right?
Pamela: With the robotic refueling mission, it wasn’t so much that we were worried about refueling the International Space Station because really you just attach, and you drag in our Soyuz capsule to it. The real question is what do we do with all of the other satellites out there that we’d like to extend their lifetime. We’ve totally upgraded the Hubble Space Telescope, giving it the ability to stay out there a little bit longer. Now, imagine if we had the capacity to go out, grab Kepler, and refuel that little telescope. This would extend the science it would be able to do. It has always been in the roadmap to be able to go out and grab satellites, move them around, pick them up when they’re broken, bring them home.
I remember I was a nerdy child who went to space camp in the 80s, as one does, and hearing the stories of how they were planning to build these highly maneuverable satellites that would go around, grab satellites that needed to be fixed, pick up space junk – we’re just not there yet. It hasn’t risen to being a high enough priority. But we are on the pathway to test the technology, to show that it’s safe, to do all of the pathfinding that’s needed before we finally have that docking station out in CSA inner space.
Fraser: And you can imagine, some of the more complicated missions that are going to be attempted in the future, especially things like sending humans to Mars, are going to require this refueling. And I think the example that people are pretty familiar with is the idea that’s coming from SpaceX for the BFR. The BFR is going to launch, and they’ve got the regular, the passenger version, and it’s gonna launch atop its first stage booster rocket and get into orbit, and then there’s what they’re calling the tanker, and it’s gonna be filled with methane.
And then the two BFRs are gonna dock end-to-end, and then the tanker is going to dump all its fuel into the spaceship, and now the spaceship is as fueled up as if it was still sitting on the launchpad down on Earth, but it’s in orbit. It’s already gotten out of that accursed gravity well from planet Earth, and now it can perform its maneuver and head off to Mars or other destinations. So, that strategy makes a ton of sense, and you can imagine this future where there are these orbital fuel depots in various orbits. You talked about the Deep Space Gateway, something in low Earth orbit, something in Mars, and if you need to go anywhere, you stop at one of these depots and refuel.
Pamela: And really, I just dream of the day that all these beautiful, completely function spacecraft that we have in fairly low orbit or are doing highly maneuvering things are able to get refueled and our Kepler Spacecraft that is still functioning quite nicely can keep doing its job without fuel being a reason to stop.
Fraser: Well, there’s actually some – I mean, you may not be able to actually refuel them, but there are some spacecraft that are being developed that are kind of like parasites that clamp onto satellites that are out of fuel but are working perfectly well for all other purposes, and they will clamp on, and then they’ll have a thruster and additional solar panels, and they’ll be the ones who keep the spacecraft functioning.
I think the greatest tragedy, the one that people just can’t stop raging about, is the fact that James Webb, there’s no way to refuel it, there’s no way to repair it. It’s gonna be the L2 Legrange point. It’s got 10 years of fuel, and then it’s going to drift out of its position and be useless. It does have a docking ring on it, though, so who knows what’ll happen 10 years from now.
Pamela: Can I just say I’m sad that the telescope won’t live as long as it took to build?
Fraser: Yes, you can say that. But there’s hope. You do have a way for something else to attach to it and boost it. You know, the BFR does only cost $7 million to launch. I wouldn’t be surprised if Elon Musk with some pocket change sends off a reboost spacecraft to keep James Webb going for a few more decades.
Pamela: Yeah, so we’re currently in this metasituation as we record this episode where the U.S. government has nominally completed writing a $1.3 trillion budget that will get us through to September. They’re supposed to vote on it on Friday which is before you hear this episode. We’re currently waiting to see does W first live or die, what is the line item for James Webb Space Telescope? All these things, it’s Schrodinger’s Budget at this moment.
Fraser: Alright, Pamala, thanks. I feel like we have wrapped up our series on getting to space and orbiting.
Pamela: We have, yes.
Fraser: My heart hungers for some cosmology now, so we’ll tack in a completely different direction, but it was a lot of fun. I hope we were able to kind of scratch everybody’s spaceflight itch for a little while, and thanks for tagging along with us.
Pamela: And I think it’s time for an update on particle physics.
Fraser: Whoa, okay, we’re gonna go physics. Fine. No problem. I’m up for that.
Pamela: It’s all part of cosmology.
Fraser: We’ll see you next week.
Pamela: Sounds great. Talk to you later.
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[End of Audio]
Duration: 28 minutes

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