Ep. 479: Rockets pt. 1- What Does "Single Stage To Orbit" Really Mean?

To celebrate the launch of the Falcon Heavy, we figured it was time for an all new series, this time on the rockets that carry us to space. Today we’re going to talk about why single stage to orbit rockets are so difficult to carry out.
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Fraser Cain: Astronomy Cast Episode 479: Single Stage to Orbit.
Welcome to Astronomy Cast, our 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’s it going?
Pamela Gay: It’s going well. By the time folks are listening to this, I will be in Amsterdam where I’m going for the European Testing Conference – which you heard some ads for on previous episodes. Life is good and I’m slightly madly packing still.
Fraser Cain: You’re gonna be testing. You’re gonna be conferencing. You’re gonna have a good time. And I’m back from Iceland having spent the last week with Paul Matt Sutter and 35 of our good friends as we noodled around Iceland and it was an amazing trip. It was absolutely wonderful. I highly recommend going to Iceland. We saw glaciers. We saw waterfalls.
The coolest thing was this amazing bay where glaciers are calving off icebergs into this bay and then these icebergs are sort of flipping over and they’re bright blue when they turn over and then they’re making their way out this bay – because it’s actually a fairly rapid channel – and then they go out into the ocean and then they get thrown back onto this beautiful black sand beach and turned into these crazy ice sculptures all the way up the beach. They call it the Diamond Beach and that was the coolest thing.
Pamela Gay: You saw calving like in process?
Fraser Cain: No, no, no. We didn’t actually see the calving, but we saw the results of it. So, there were tons of these icebergs slowly making their way down. So, I could only assume that it had happened fairly recently. But the craziest part was this enormous storm blew in and we had – it was like once a year – really powerful storm and the winds were – I forget – 45 meters per second. They measure wind speeds in Iceland at meters per second and so you had these gusts of wind. I’ve never experienced wind like this in my lifetime.
It was the craziest thing. But anyway, that had sort of stopped us from being able to do a couple of the events, but Paul and I put on a bunch of shows. We just had a great time. So, if that sounds interesting to you, we’ve got another one coming up, which is gonna be in September. We’re gonna be doing a cruise in the Eastern Caribbean. We’re gonna go to the Kenney Space Center. We’re gonna do live shows on the boat. We’re gonna bring telescopes and binoculars and do observing on the deck, teach you your constellations.
So, check that out. Go to AstroTours.co and then you can find the Sea and the Stars Cruise with Paul. And then, Pamela, you’re gonna be doing an event later on. So, there’s a bunch of stuff. Check out AstroTours.co and you can see the upcoming events. Alright, to celebrate the launch of the Falcon Heavy, we figured it was time for an all-new series – this time on the rockets that carry us to space.
Today, part one, we’re gonna talk about single stage to orbit rockets and why they’re so difficult to make them go. Alright. People are pretty familiar with rockets, but just give that quick explainer on how does a rocket work?
Pamela Gay: The most simple way of looking at it is it’s a highly controlled explosion – where the entire explosion is going out a small shaped exit hole in the opposite direction of the rocket in which you’re hoping to travel. So, with the Saturn V, you want to go up. Therefore, the explosion is pointed downwards. That’s the simple way of looking at it.
The unfortunate reality is your controlled explosion only lasts as long as you have fuel – which means you have to carry a whole lot of fuel with you if you want that explosion to last a long time and it takes a whole lot of stuff to hold in that fuel and control that fuel because – if you stop controlling it – you go kabloom and that isn’t the desire.
Fraser Cain: Right. But I think the thing that’s really interesting about rockets is like, for example, the space launch system with its amazing RS-25 rocket engines, it is throwing out material out the back of the rocket. The explosion is causing the propellant to go out the back of the rocket at like 13 times the speed of sound. And thanks to Newton, if you throw something away from you at 13 times the speed of sound, you get a kick in the opposite direction. For every action, there is an equal and opposite reaction.
Pamela Gay: Conservation of momentum.
Fraser Cain: And that is how rockets work and that is why they work in space, in the atmosphere, they work wherever. Throwing things away from you makes you move in the opposite direction, which is everywhere.
Pamela Gay: And rockets are driven by all that basic physics stuff where you are taking liquid gases. So, liquid oxygen is one of the main things that we hear about when we’re listening to prep for launch. And then they kind of expanded into a violently expanding heated gas. That phase shift causes it to go from, “Hey, I’m hanging out. I fit in here nicely” to “I no longer fit. I must explode out the backend of the rocket.”
It’s this explosive change in temperature and volume of space required to hold the stuff and things that drives the material out the backend of your standard rocket. Now, there are other ways to drive stuff out the back end of a rocket. We’ve talked about ion drives before, but that is not going to get you off the surface of the planet.
Fraser Cain: Right, right.
Pamela Gay: To get off the surface of the planet, we’re looking at controlled explosions. And people keep trying to figure out how to do it using jet engines, but we’re not quite there yet.
Fraser Cain: Right. Well, the problem with a jet engine is that it used the atmosphere as its oxidizer. It brings in oxygen, uses compressors to mix it in with the fuel, and that’s what allows a jet to carry less fuel and to be able to fly. With a rocket – because you’re not gonna be able to pull that atmosphere from the air – you need to carry that oxidizer along with you and the oxidizer is heavy. So, that just goes along for the ride.
Alright, and now the traditional, when we think of the rocket we think of the Saturn V rocket. We imagine this gigantic, pointy thing filled with fuel and the key is that it’s gonna have multiple stages. So, why do rockets have these stages?
Pamela Gay: Essentially, it’s so that you don’t have to keep carrying your garbage with you. At a certain point, you have a mostly empty tube because you’ve used up fuel and it is going to save you how much fuel you’re going to use towards the end of your acceleration if you aren’t carrying your garbage with you. So, you use up all of the fuel in the first segment of your rocket and now you have an empty tube filled with hardware.
So, drop it. Now, you’re burning fuel in the second segment of your rocket. You empty all of that out. You drop that. This is part of why rockets launch off the East Coast out over the ocean. It’s because they drop stuff and we don’t want to drop them on people. So, we simply risk anything that happens to be out in the ocean.
Fraser Cain: We’re looking at you, China. Have you seen what they’ve been doing? They’ve been dropping stages of the rockets into suburban areas.
Pamela Gay: Oh, geez. That’s a problem.
Fraser Cain: It’s intended. They don’t have a lot of space. They need to launch their rockets and some people live downrange of the rockets and so stages are coming down in their backyards. You know they’re being kind of careful about it, but still it’s – You should look this up what’s happening with some of these Chinese rocket stages that are happening in China and they’re actually looking to do reusable rockets. But that’s probably a whole other show where we talk about reusable rockets. But let’s get back to single stage.
So, that’s your traditional rocket that you’ve got these multiple stages. Why carry extra engines and just empty tube when you’ve used up all of that fuel? Get rid of it. Move onto the next one. Get rid of it. Move onto the next one. The Saturn V had three stages. A lot of rockets have two stages. When you think about the space shuttle, it had those solid rocket boosters and then that big, main fuel tank.
So, there’s different configurations that go. But the question is obviously this is super wasteful to take beautiful space shuttle main fuel tanks, lovely Saturn V first stages, and just throw them in the ocean. They cost millions of dollars. Why can’t you just launch your rocket to space?
Pamela Gay: Because we’re still working on figuring out how to get the mass to thrust ratios so that you’re in orbit when you’re left with an empty tube. And that’s really kind of the question mark on why hasn’t this happened? Well, it’s because we haven’t figured out how to complete the entire trip to space before our tubes are empty and now what we’re looking at is there’s a number of companies that are like, “Okay. We need to solve this.” And they’re taking a variety of different approaches.
One of my favorite approaches is, “You know we don’t need so much rocket fuel if we’re not trying to launch so much stuff at once.” And this is the approach that’s being used by ARCA. It’s a four-letter acronym that I’ve been unable to figure out what it stands for. On their own website, they just say ARCA everywhere. So, ARCA is a company out in New Mexico that is looking to figure out how to launch just 100 kilograms at a time.
Your standard overweight American couldn’t be launched on one of these rockets. And at 100 kilograms at a time being launched, they only need a single stage and you look at their rockets and you’re like, “Huh, that would fit in my driveway.” They’re cute. They’re tiny and they can launch from New Mexico because they’re a single stage, which means they have no garbage to drop on the rest of the continental United States.
Fraser Cain: Right, but then explain what the process is gonna be for that. So, you’ve got this rocket that is a single stage, but the ARCA rockets aren’t reusable, right?
Pamela Gay: No, no. So, many of the other companies are working on reusable. With ARCA, they have a very different design for their engines than at least I’ve ever seen before. They kind of look like someone took a tube of toothpaste and turned it into a rocket. The butt – instead of having the cone shaped engines that we’re used to – instead has this weird, flat, completely different style engine.
Fraser Cain: It kind of looks like a razor to me.
Pamela Gay: Yeah, I can see that too – an electric razor maybe – and what they’re looking at doing with this electric razor shaped rocket is they believe they can get – first of all – more thrust for their engine and then they’re also confining themselves to trying to launch lower mass payloads.
So, you don’t need to have as much fuel in general to launch that lower mass payload. So, by staying small, by finding a way to – for their limited payload – being able to eke out more thrust per pound of fuel, they’re looking at being able to get up in a single stage and they’re also looking to lower the costs. Here we really have to look at cost per pound versus cost per launch because per pound is really what’s going to matter. If you’re launching a little, tiny rocket, it’s going to have a lot less stuff and things that you have to pay for. Less fuel, less engine bits, all of that brings down the cost.
So, when I say we’re talking about a million dollars a launch it’s like, “Oh, my gosh that’s free compared to 150 million for the Falcon Heavy.” But we’re looking at about $2,000.00 per pound. And so while it is cheaper than the Falcons, it’s not hugely cheaper. It does offer this neat flexibility though of now – instead of having to be able to wait to launch Wallops, having to wait to launch out of Kennedy, any of our East coast launch facilities – they’re now looking at New Mexico. So, Spaceport America has one more purpose for existing.
Fraser Cain: The advantage to this is that you get to put your satellite where you want it to go. You don’t have to tag along with where everyone else is gonna go on some Falcon Heavy. It’s got satellites stacked in it like cordwood. You get to have your satellite follow its own personal trajectory. It’s a custom experience. Okay, so that’s the ARCA. One thing – I don’t know if you knew – some rockets right now I think the Atlas are actually capable of single stage to orbit. They don’t do that and they wouldn’t be able to carry any significant cargo.
Pamela Gay: And they’re not FAA certified to do it
Fraser Cain: No, they’re not certified, but they are – you know like if you run the rocket equation on these rockets and they didn’t really have any kind of payload, the rocket could – with the amount of fuel with it carries, with the amount of thrust that it can put out – it could carry itself entirely to space, but what is the point? I think this is a challenge that people have been struggling with for a long time.
You know originally the space shuttle – with certain levels of its reusability – it was hoped that they could come up with some way to make it a reusable spacecraft – a single stage to orbit. I think the greatest example where NASA took a really big swing at it was the X-33, which was the Venture Star. Do you remember that spacecraft?
Pamela Gay: Right. And the one I always think of is also the DC-X.
Fraser Cain: A very similar configuration.
Pamela Gay: But what’s interesting is these ideas haven’t completely been abandoned. They’re still under development as far as I can tell – the Skylon space plane.
Fraser Cain: We’ll get to Skylon in a second because it’s an interesting take on it. But for those who aren’t aware of what the Venture Star was going to be, it was this collaboration I think with Lockheed Martin. I apologize in advance. But it would take off, fly to space, and then it would have this lifting body design so it would be able to – like the space shuttle – return to land. It would be able to carry some cargo and then it would refuel and then it would be able to launch again – which has a tremendous amount of advantages.
I mean we’re seeing what’s happening with the SpaceX launches how that level of reusability there’s a certain streamlinedness. It makes it feel like an airplane. You get into the airplane and then you take your cargo and then you land and then other people get into the airplane and then they go again.
Pamela Gay: And the X-33 was a NASA-funded sponsored project that was under development down in Johnson – as well as, of course, with the different companies that were working on it – and it’s one of these things where there’s always the question of, “Will that resurface as something that comes back for continued development or has it simply been covered up and swept in under the military if you believe the most amusing of the conspiracy theories?”
Fraser Cain: I never do.
Pamela Gay: I don’t either, but they amuse me, which is why I do look at them occasionally.
Fraser Cain: But about a decade ago, they abandoned the X-33 project.
Pamela Gay: Yes.
Fraser Cain: They had to build special composite fuel tanks and they couldn’t get them to handle the pressure to be able to hold the fuel and they had to essentially abandon the entire project – although I’m sure there were other difficulties to go along with it.
Pamela Gay: And so while that one has been abandoned, we do see other companies that are working on similar things – McDonnell Douglas with their DC-X Delta Clipper and the one that has a completely different design that so with both the DC-X and the X-33 so McDonnell Douglas versus Lockheed Martin – we were looking at these pretty much triangular spacecraft, fully reusable, launched and took off in a vertical alignment for the DC-X, launched vertical landed on a runway, I believe, for the X-33 or was dropped and took off for the X-33.
It was unclear what they were looking as their final design. With those, it’s all launch and go, launch and go, come back triangle. But I think all of us have ever wanted is that plane, that plane that takes off on a runway – like the 777 I’m getting on tomorrow and then lands safely on the other end having done whatever it needed to do in space – that point-to-point, regular everyday user experience that we were promised in our science fiction.
Fraser Cain: Now we’ll talk about Skylon.
Pamela Gay: So, Skylon takes us back to the idea of the riding a controlled explosion aircraft. It is very reminiscent of the old ‘40s and ‘50s suborbital space jets. It’s being developed by a UK company, Reaction Engines, Ltd, and it’s basically a tube with stubby, tiny wings that have very powerful engines attached to the sides.
Fraser Cain: And the engines are what makes it special.
Pamela Gay: Yeah. We’re starting to look at an interesting hybrid system and this is kind of been every engineer’s dream design where you have something within the atmosphere. It works like a jet engine above the atmosphere, is able to figure out other ways of getting that oxidizer mix into your fuel so you can keep going without having an atmosphere around your spacecraft.
Fraser Cain: I mean man, the Skylon fans are legion and they are excited and they can’t wait for this thing to fly and it is coming out of the UK and the problem right now is that it’s essentially like an engine prototype. There’s not a lot more that’s been built up yet. But if all goes well within the next decade or so, you can imagine this configuration.
This thing sits on the runway, uses its jet engines, goes down the runway, flies up into the air, accelerates using the air as its oxidizer – pulling oxygen out of the atmosphere – gets to a certain speed, gets to a certain altitude, switches to – these engines turn into rockets essentially and it then is able to continue its journey into orbit. And if you can pull that off, it is a very impressive feat.
Pamela Gay: And they’re hoping that they can start testing in the next year with trips to space by ’22. So, we could be within 16 months of seeing test flights. I’m not sure how well I believe that, but I want to believe it and they have fabulous graphics and they say things like they’ll be able to reach speeds of 19,000 miles an hour – which would cut the journey from London to Australia to four hours.
Fraser Cain: I do not want to take that trip, but – That sounds terrifying. But imagine, right? You’ve got this thing. You put in the cargo. It flies to space. It dumps its cargo into space. It then reenters the Earth’s atmosphere, lands on the landing pad, takes another payload. The price is only the price of fuel and you could get the cost of carrying these payloads down to I think it’s about 1,000 pounds – about $2,000.00 per kilogram – to carry this stuff into space, which is good. It’s a very competitive price compared to some of the other options out there.
Pamela Gay: And I think this is one of those times when units were actually friendly. I think it is roughly 1,000 pounds per kilogram or $1,000.00 per pound roughly depending on the day.
Fraser Cain: Right.
Pamela Gay: So, with this particular design space plane, they’re looking at 200 reuses per vehicle, 270 feet long vehicles. So, these are big. We’re looking at roughly the length of a football field and each one will cost just under a billion dollars – depending on unit conversions on the day of the week – and the trick is that 200 different times they can fly. That’s what drives the price down.
Fraser Cain: Yeah, and so you could imagine it could be ready to fly again within a couple of days. It could fly hundreds of times before needing a complete retrofit. So, that is a very exciting technology. But then we really need to just kind of wait to see how this is gonna play out. The challenge is here on Earth and with using chemical rockets – you are never gonna get the rocket equation to work in your favor that a single stage to orbit rocket is ever gonna match the amount of payload that can be carried with a multi-stage rocket.
It’s just you’re having to carry those fancy engines and those really cool wings and all of that tube with you to space to carry the cargo. And so unfortunately, it’s that reusability that gives you the advantage, as opposed to what’s gonna happen with a multi-stage rocket.
Pamela Gay: And as we begin to use lighter weight things, we already have the CanSats, CubeSats, micro CubeSats. We launch tiny stuff on a regular basis. The Bigelow Inflatable Modules don’t weigh that much. One human being who’s not an overweight individual can be launched on some of these things. We’re looking at ways to get that, “I need to get 100 kilograms, 200 kilograms to space and that’s it.” We’re looking at getting the costs for these small things down while also looking for ways to build bigger and bigger rockets.
So, this is a multi-pronged approach. Just like you were saying, “Let’s get that cost of launch vehicle for your one payload of several universities projects that are all CanSats. Okay, fine. Let’s throw all of you into a similar orbit. We’re launching all of you together and it’s cheap. Let’s use Skylon to get these lightweight space station components up and then drop a single human up there. It’s these lighter weight things that we’re opening the door for that will no longer have to ride piggyback waiting for someone with a big, heavyweight cargo to need that lift.
Fraser Cain: Right. Now, we’re gonna – I’m assuming – I don’t know what your plan was for these next few episodes that we’ll be talking about. I’m sure we’re gonna come back around and talk about reusable rockets.
Pamela Gay: Yes.
Fraser Cain: SpaceX with the BFR, with the Big Falcon Rocket, the big, fabulous rocket, I think is kind of planning to be the best of both worlds because you’re gonna have a staged rocket, but both stages are reusable and so it’s going to launch in a stack and then the first stage is gonna return to Earth like we’ve seen happen with the Falcon 9 and then the BFS, the Big Falcon Spaceship, is also gonna be able to return to Earth and land and be reusable and then get stacked back up again and do it all over again.
It feels to me – and as we see this actually play out, that until we get a more exotic kind of fuel – when metallic hydrogen becomes available – that is gonna be I think the lowest cost, the most efficient, most reusable. It’s gonna be that combination approach.
Pamela Gay: It still has that backlog of having to launch out of a very limited geography.
Fraser Cain: Yes.
Pamela Gay: Whereas the single stage to orbit, it’s suddenly allows us to use Mojave, to use all of the West Coast locations, to use Spaceport America in New Mexico, for more than just suborbital to be able to say, “We’re going to launch 100 kilograms to lower Earth orbit in a single stage and hey, we can do all of those launches from this completely new location.” It’s just like opening an extra line at the grocery store. Suddenly, more people can check out faster.
Fraser Cain: Alright. Did you have a plan for how many of these you want to do?
Pamela Gay: I think we keep going until we realize we’ve talked about all of the things that are super cool.
Fraser Cain: Alright. That sounds awesome. Thanks, everyone. We will see you next week, Pamela.
Pamela Gay: See you next week.
Announcer: Thank you for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com, tweet us at Astronomy Cast, like us on Facebook or circle us on Google Plus. We record our show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern, or 2030 GMT. If you miss the live event, you can always catch up over at CosmoQuest.org or on our YouTube page.
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[End of Audio]
Duration: 27 minutes

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