Catching a Lift

Fundamentally there are three schools of thought for spacecraft that enter and exit planetary atmospheres (spacecraft that stay in space have their own design considerations, and in any case can get much wilder): capsules, spaceplanes, and lifting bodies. Anybody who’s even passingly familiar with spaceflight knows of the Apollo spacecraft, which was a capsule, and the Space Shuttle, which was a true spaceplane. But what of lifting bodies?

They’re interesting, because they have characteristics somewhat in between capsules that just re-enter using their front ends as shields, maximizing the interior volume for a given surface area, and spaceplanes that fly down to earth like airplanes. Lifting bodies, as their name suggests, generate lift using just their bodies. Effectively, it’s a fuselage with no wing, the exact opposite of a flying wing design, which is a wing with no fuselage.

Lifting-Body Spaceplanes: A brief History

Lifting bodies haven’t caught on much, if at all, in aviation proper, but they’ve been of interest to spacecraft designers since the 1930s. Yes, that far back. Eugen Sänger and Irene Bredt were the first to incorporate the lifting-body principle into the design of a spacecraft with their Silbervogel concept. With the advent of World War II the design was pitched for military purposes, specifically a contestant in the “Amerika Bomber” (i.e. a bomber capable of reaching the United States) competition, but Nazi Germany was unable to even begin work on such an advanced craft.

After the war, Walter Dornberger when pitching the same idea to the Americans changed the name from “Amerika Bomber” to “Antipodal Bomber” for obvious reasons, and apparently this enthusiastic group of Germans were successful in stoking American interest in the general idea of a spaceplane.

The original Silbervogel design was even single-stage, albeit to a suborbital rather than orbital trajectory, but payload capacity would have been greatly limited, even more so than thought originally, because it turned out a heavier heat shield than Sänger and Bredt had calculated was necessary. Nevertheless, with the addition of a bigger booster rocket to the concept, the Silbervogel spawned an American descendant by the late 1950s in the form of the lifting-body X-20 Dyna-Soar, which in turn spawned a whole lineage of experimental spacecraft, in fact the direct ancestors of today’s ongoing Dream Chaser project.

NASA rendering of the X-20 Dyna-Soar.

Three experimental lifting-body spaceplanes of the 1960s and 70s.

Spaceplanes’ Achilles Heel

Why are lifting bodies of such great interest? One reason is the key disadvantage of a true spaceplane: the wings are heavy, inhibiting performance, and they’re also very delicate under the stresses of re-entry, making it more likely something will go wrong and the spacecraft will burn up, a fear which was realized for the first time when one of the Space Shuttles, Columbia, disintegrated on re-entry in 2003. The cause? A missing heat-shield tile on one of the wings.

As an aside, the damage to the heat shield on Columbia’s last flight, STS-107, was actually much less severe than the damage suffered by a much earlier flight of the Space Shuttle Atlantis, STS-27, which was launched on December 2, 1988. The damage was severe enough the astronauts could actually see white debris striking the windshield at launch, and while in orbit they used the on-board robotic arm to inspect it. It was impossible to conduct a full assessment, but reportedly they saw enough to convince them they were all going to die on re-entry.

Mission Control refused to believe them, because to them it looked like lights and shadows, the damage no worse than past missions, likely compounded by them being forced to use a lower-resolution encrypted link to Houston due to that Shuttle flight being a classified mission for the Department of Defense. Though it’s worth noting it’s unlikely they could have been rescued, so it probably didn’t matter anyway.

As it happened, they made it back to Earth safe and sound, though the Shuttle had severe heat damage and required a lot more work than usual to get it back into shape. What saved them is that the missing tile happened to be over an antenna, which was a stronger section of the hull. If the tile missing had just been one piece over, the Atlantis would have disintegrated just like the Columbia did 14 years later (though interestingly, all the debris would have fallen over remote parts of the Pacific in this case, not the populous Lower South).

Considering STS-27 was just the second flight after the Challenger disaster (!), a loss of STS-27 would likely have meant the end of the Space Shuttle program, and NASA would have started the 1990s having gone back to the drawing board for human spaceflight. Now, there’s an alternate-history what-if for you!

NASA photo of STS-133 lifting off from Kennedy Space Center.

Sometimes it’s said that if the Shuttle was a capsule such accidents would be much less likely, though simply putting the vehicle on top of the boosters instead of beside them (where foam and debris can easily strike the orbiter…) would have prevented the Columbia disaster.

As early as 1961 the X-20 Dyna-Soar was proposed to fly like this, boosted by a Titan II. A similar configuration was proposed for the Space Shuttle in several concepts. I’m not sure why they went with the “side-mount” as opposed to an “in-line” configuration. If Columbia had launched like this she’d still be with us today.

Spaceplanes’ Advantages

In any case, lifting bodies don’t have wings, and share capsules’ lack of vulnerability to this problem! Additionally, the consensus on this thread at the NASA Spaceflight Forum seems to be that capsules don’t scale up very well beyond maybe a dozen people, which I find quite interesting. Apparently bigger capsules need correspondingly thicker heat shields because they hit the atmosphere harder, so at some point as you scale up it just becomes easier to change the vehicle to generate some lift, i.e. a lifting body.

Spaceplanes have much better cross-range capability, i.e. they have much broader choice of destinations when descending from a given orbit, and have even gentler g-force than lifting bodies, but at the cost of more weight and complexity. My intuition tells me that spaceplanes will only really take off when single-stage-to-orbit becomes viable, and the ability to take off or land from any airstrip will be very useful. Possibly the spaceplane design might be more useful for very large spacecraft, especially if you can use the wings for interior space a la blended-wing bodies or flying wings, but I’m not sure.

NASA rendering of their N-3X concept for a blended-wing-body aircraft. Note this model doesn’t go into space, but a broadly similar-looking vehicle might one day take to the wild black yonder.

Will Dream Chaser fulfill our Dreams of next-generation Spaceplanes?

I wonder, though, if in the future we’ll eventually converge mostly on lifting bodies, at least for your ordinary mid-size spacecraft that can seat, say, a few dozen passengers. What do lifting bodies look like? Well, if you were a space enthusiast in the 1990s or even 2000s you’ve probably seen concepts for them in the form of all those next-generation mini-shuttles we were promised. Yes, lots of them were lifting bodies. The standout champion of the lifting body today is Sierra Nevada Corporation’s Dream Chaser, and it looks adorable, like if the Space Shuttle had a baby:

Behold, the Dream Chaser (photo courtesy of NASA).

The Dream Chaser is designed to fit 3-7 people, and though things don’t look that hot for the poor little thing now, the baby may yet live to grow big and strong and fly all the way to the International Space Station! In 2017 there was a flurry of interest in the idea of sending up Dream Chaser with a crew to service the Hubble Space Telescope, which I personally think was a great idea. How cool would it be to service the Hubble again, upgrade it again for a whole new decade of science and pretty pictures, and with a next-generation space shuttle, no less?

Against all the background noise of the next-generation lifting-body shuttles, perhaps one of the boldest proposals was the Lockheed Martin X-33 from the mid to late 1990s, which was an attempt to develop a single-stage-to-orbit spaceplane.

NASA rendering of the X-33, also known as the VentureStar

Toward exotic Lifting Bodies

You might have noticed that all these concepts look a lot like the Space Shuttle we actually got, or rather much like conventional aircraft. The major reason for this is because most lifting-body designs that have been offered optimize aerodynamics and control in the lower-speed regime and seek to have the vehicle behave like an aircraft, but there’s no particular reason aerodynamics and control couldn’t be optimized for the higher-speed regime instead, and there’s no particular reason a lifting body has to behave much like an aircraft either.

For example, it could land by parachute, it could take off and land vertically, it could land by deploying a flap in front of it and keeping its nose way up at an angle the whole time, even parked on the runway, among myriad other possibilities I’m not even familiar with.

Perhaps the closest we’ve come to seeing a lifting body of this more exotic type fly is the McDonnell Douglas DC-X from the mid 1990s, which was doing rocket-powered vertical takeoff and landing of spacecraft before Elon Musk made it cool, the objective in this case being a single-stage-to-orbit design no less.

NASA rendering of the McDonnell Douglas DC-XA. Now that looks like a spacecraft from the future. Test flights of this thing actually flew!

In the competition for the X-33, which was NASA putting out trial balloons for a next-generation space shuttle in the 1990s, McDonnell Douglas submitted this beauty of a design, based on their prior work with the DC-X:

NASA rendering of the McDonnell Douglas concept for the X-33.

Is looking Futuristic underrated?

Yes, that’s a lifting body, but it has a shape more like the nose cone of a classic rocket, looking even more streamlined than all the other mini-shuttle concepts that were out there. I find it interesting that it looks so much more futuristic than either the Space Shuttle, the conventional next-generation shuttle concepts, or any of the capsules on offer now (or really anything other than SpaceX Starship). Engineers can make arguments for basic-but-boring designs all they want, but politics is important too, and to the general public something like the McDonnell Douglas X-33 looks more advanced, not to mention cooler.

I would submit this is important. If NASA had embraced a design like this for the successor to the Space Shuttle when the Constellation Program came along in 2004, instead of “Apollo on Steroids” (yes, in 2005 NASA Administrator Mike Griffin actually called it that), I bet it would have generated a lot more public interest and enthusiasm.

Yes, the single-stage-to-orbit design was probably infeasible in the near-term, but a similar shape filled with crew and cargo space instead of fuel tanks should have similar aerodynamic properties and a similar look and cool factor. Launch the thing on top of a big booster rocket, maybe even an off-the-shelf evolved expendable launch vehicle (EELV) like the Atlas V (the same rocket Boeing’s Starliner uses now), and you’d be in business!

Conical high-performance Spaceplanes

Interestingly, these more conical spaceplanes, which are optimized for aerodynamics and control in the higher-speed hypersonic regime, i.e. the earlier part of re-entry as opposed to the later part, are much easier to fit on top of rockets well than the aircraft-like lifting bodies like the Dream Chaser, a compelling property, especially in a world where it looks like vertical launch a la SpaceX with their Dragon and Starship (not to mention flyback reusable boosters) will be the go-to technique for a while to come.

Even more interestingly, these frames can grade even more conical, such as one SRI concept for a “high-performance spaceplane” from the late 1970s; the general idea apparently was studied by DARPA into the 1980s.

Doesn’t look too comfortable for that man, but this was intended for the US Air Force; it would be enough to get the job done. Presumably a civilian spaceliner version of the same frame would be much larger and more spacious.

Artist’s rendering of the same spaceplane in service with the US Air Force.

In the above depiction the craft has a circular cross-section, but studies indicated an elliptical cross-section would be more aerodynamic. They stuck with a circular geometry in their concepts, as that was much better-studied on account of already being in use for “multiple independently targetable reentry vehicle” (MIRV) warheads on intercontinental ballistic missiles (ICBMs).

LGM-118A Peacekeeper MIRV display at the National Museum of the United States Air Force. Photograph courtesy of Wilson44691 of Wikipedia. I’ve been to that museum and seen these very same warheads; they’re a lot smaller than you’d think looking at the pictures, as in they’re easily small enough for one man to carry around.

Sometimes, Science Fiction is harder than you Think…

Back to the spacecraft, what I find really interesting about these high-performance concepts, and the SRI International one in particular, is something RanulfC pointed out at NASA Spaceflight Forum: a scaled-up elliptical version of such a design looks a lot like the Icarus from the original “Planet of the Apes”!

The Icarus from “Planet of the Apes”. Look vaguely familiar? And all this time I thought it was that way just because it looked cool.

Additionally, I spot a passing resemblance between these high-performance spaceplanes and the Pan-Am Orion III Space Clipper from “2001: A Space Odyssey”:

Yes, this one grades much more toward a Concorde-like design, but you can see the beginnings of a more conical cross-section, especially at the front. A transitional form? Hmm…

Worldbuilding an Alternate History

Eventually, if we converge on lifting-body designs or at least if lifting bodies find a viable niche for spaceflight, will we start out with these low-performance mini-shuttles and progress in the subsequent generation to these more exotic high-performance spaceplanes? That’s an interesting thought, especially to someone like me who’s worldbuilding a whole alternate timeline where spaceflight is much more advanced than in real life.

In my fictional universe the protagonist in “Ten Weeks at Onigaminsing”, set in 1969, takes a ride on a brand-new spacecraft that launches in-line on a rocket booster and is described in-text thus:

[…] the new capsule, a reusable lifting-body spaceplane called the Traumjäger.

Of course “Traumjäger” is just German for “Dream Chaser”, and originally I had in mind something like our very own Dream Chaser, hence the name, but her describing it as both a spaceplane and a capsule is a bit odd. Fortunately, the description is so vague it turns out it describes very well something like the McDonnell Douglas concept for the X-33! Which does indeed look like both a capsule and a spaceplane.

It also lines up rather well with the timeline in general. The first Moon landing is in 1949, and if spaceflight is 20 years ahead the 1950s in this timeline very roughly correspond to the 1970s, which means a conventional lifting-body spaceplane should be viable during that time, giving a decade or two for a second-generation higher-performance lifting-body spaceplane to debut, right in time for the 1969 date given in “Ten Weeks at Onigaminsing”.

This is a somewhat more aggressive timeline than in real life, but keep in mind there’s much more interest and resources as a proportion devoted to spaceflight, and the economy grows so rapidly over the 20th century living standards exceed their present-day level already by 1940, meaning there’s a lot more spare wealth available to sink into such projects. Nuclear pulse propulsion is embraced experimentally starting in the 1950s, with perhaps practical applications taking off in the 1970s, the same decade the first full-fledged space habitat is built in Earth orbit. Moon colonies and Mars colonies already exist in the 1960s. Concorde-style supersonic jetliners debut in 1950. So in a world like that a high-performance spaceplane by 1969 isn’t a stretch at all.

Really high-performance spaceplanes, as in a viable single-stage-to-orbit spaceplane a la the Skylon concept, will have to wait (according to the tentative timeline I’ve penciled in) until around 1990, with higher-performance second-generation nuclear-reactor-powered versions debuting by 2010; by 2020 we know for sure, from “The Hunt for Count Gleichen’s Treasure”, that at least the rich have access to a third-generation version that also has vertical-take-off-and-landing capabilities a la the Harrier jump jet. A fourth-generation version will eschew the jump-jet exhausts in favor of making the whole “wing” into a tiltrotor a la the V-22 Osprey.

Count Gleichen’s spaceplanes will be much like the Skylon, but I expect the more conical hypersonic-optimized cross-sections will continue to enjoy a niche in my universe for a long time to come, perhaps joined by “lenticular re-entry vehicles”, i.e. flying saucers; interestingly, they’re extremely aerodynamic, just hard to control without fly-by-wire systems more sophisticated than what we’ve got now. Even more exotic shapes than these may well proliferate into my world’s 21st century.

NASA rendering from 1962 for lifting-body shapes proposed by Dale Reed. Yes, that’s a flying saucer on the right. NASA higher-ups rejected it as too exotic. Too bad.

Conclusion

Yes, there are many possibilities for lifting-body spacecraft, both as a study of real-life history, the crafting of alternate histories, and hard-science-fictional universes. I’ve been a space enthusiast for pretty much my whole life, and even I learned a lot recently by doing a deep dive down the rabbit hole of lifting-body spaceplanes, especially the more exotic ones; I’m sure even what I’ve outlined here is just the tip of the iceberg of what’s possible, but even that is more than enought to contemplate. The sheer diversity of designs that could and probably will fly someday when we really become a spacefaring civilization is mindboggling, but personally I’ve considered my mind boggled in a good way. It’s all exciting, heady stuff.

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