Remembering SpaceCub

Geoffrey A. Landis

The April 2003 Technology Review had an article about rocketplanes, focussing on the entrepreneurs interested in building small rockets to carry people-- eventually tourists-- to the edge of space, an idea which recently seems to be really taking off (no pun intended).

I found the article particularly interesting and, in some ways even nostalgic. In a small way, I was one of the people who initiated and popularized the concept that a rocket to reach the edge of space without going into orbit would be a worthwhile thing to do, and incited me to write a small commentary on the project.

Almost ten years ago, in 1994, David Burkhead, myself, and a mismatched crew of science-fiction writers, model rocketeers, and techno-junkies started a project to design a home-built suborbital rocket. We called it SpaceCub The idea of SpaceCub was sparked by the (then recent) success of the tail-landing DC-X rocket, and fueled by the thought, wow, wouldn't it be cool to have one of those to fly around in The key insight that gave the project momentum was the realization that, while everybody wants to go to orbit, it would not be nearly as hard to design a vehicle to fly to the edge of space (defined as 50 miles or 100 kilometers, depending on who's doing the definition). That task would be relatively simple, compared to the difficult challenge of getting into orbit-in fact, it might even be in the range of something you could build in your garage.

A backyard rocket? We did a serious design study (well, serious for amateurs), and addressed a load of key questions: winged landing or vertical descent, or maybe a parachute? Do we need dragbrakes, and if so, how do we design them? How much entry heating can we stand? Liquid oxygen or nitrous oxide? As we developed the concept, we publicized it with presentations to various conferences. We got a great reception. Our personal high point was probably December 1994, when the SpaceCub was featured in an article "Slip Gravity's Bounds in Your Homemade Rocket" in Popular Mechanics, along with an artist's conception that for the most part got the details right. According to the writer:

"...Practical? Of course not. Spacecub is designed for 15 minutes of glory. Two minutes after launch, at an altitude of 12 miles, you will break the sound barrier. When your engines shut down, you'll be travelling at Mach 8. Weightless for several minutes, you'll see Earth's curvature and a jet-black sky. On your way down, the engines will reignite to cushion your tail-first landing. Any smooth hard surface will serve as a pad."

artist's conception
Image from the Popular Mechanics article

David Burkhead and I presented SpaceCub for the last time in May of 1995 at the International Space Development Conference. Five hours after we presented the design work on SpaceCub, in his keynote speech Peter Daimandis proposed the X-Prize to the world. His talk echoed precisely our proposed mission: to bring spaceflight within reach of ordinary people with a small re-usable rocket that could reach the edge of space. He added a single criterion: that the X-prize vehicle had to carry a crew of three (SpaceCub had been designed for one).

While a small amount of work on the SpaceCub went on after that, Diamandis' announcement of the X-prize took most of the wind out of the project; our crazy concept had become mainstream, and the bar had been raised from one person to three, just enough to drive unfunded amateurs out of the field. Moving from paper to bending titanium was simply a commitment of too much time, money, and machine-shop time than our amateur (and unfunded) crew had available.

Today, with over two dozen teams working on X-Prize vehicles, the idea of a reusable rocket for ordinary people to fly to the edge of space now looks obvious. Back in early 1994, though, it was (as far as we could tell) quite a new idea, and it took constant patience to keep answering the same question: "so why not go all the way into orbit?" (Because that's tremendously more difficult, that's why!)

We challenged the dominant paradigm of the day-- that a rocket has to go to orbit-- and, with a lot of energy and enthusiasm-- we changed it.

With the design of SpaceCub, we showed that the main challenges people made to the concept were all solvable problems. The work we did on SpaceCub, and the concomitant publicity and just plain proselytizing we did for the concept, was a large part of what changed the mindset toward personal space and set the stage for the X-prize..

Our long-term vision was to move away from the idea of rockets as a high-tech things to be done only by professionals like NASA and billion-dollar aerospace corporations, and to get back to the days of backyard mechanics and barnstormers. To Jeff Greason, John Carmack, Mitch Clapp, and all the many and various people who are, now, working hard to make it happen, I say: right on! I salute you.

spacecub picture
David Burkhead's visualization of Spacecub


Addendum 1:

the origin of SpaceCub

Here is my original post (on the old GEnie computer network), dated March 4, 1994, and the replies to it which defined the main concepts for the SpaceCub:

Geoffrey A. Landis, Mar 04, 1994:

The more I think about it, the more I think that a Cessna-sized "hobby" spaceship might be a real winner. Not Earth to Orbit--that's crazy, for the near term, if you're thinking about something that non-billionaires could afford. But how about something DC-X sized, with a little pilot compartment attached to the side? You could give it a maximum altitude of, say, 150 miles-- low enough that you're not a threat to satellites. This gives it a ballistic range of something like 300 miles; you could do Cleveland- to- Chicago, but not New York to LA. That's okay; this would be basically a fun-flier, not a long- distance ship. You could probably sell one for about $200,000 and get buyers; people pay that much for airplanes. The mass ratio is not all that unreasonable, and best of all, if you live in a reasonably clear spot, you won't need an airport for take-offs. And for speed, of course, it would beat almost anything. Mass ratio is quite reasonable; and since it's not SSTO, you can use gasoline. Here's a question: is it small enough that you could give it a small on-board liquid-oxygen plant? If not, you've got problems. At least until there are enough people with them that you could justify "space" ports to land at around the country with LOX available.

And, damn it, I bet you could build one for under 200K. If you can buy the engines cheap enough... Now, that's the problem. Wonder if the Russians are selling?


Greg Bennett, Mar 07, 1994:

If you can do a ballistic trajectory up to 150 miles, why is it so crazy to make the tanks bigger and go to LEO? Assume, for the sake of argument, that we can get the mass ratio to a point where SSTO works.

The only difference I can think of is the need for a heat shield to survive reentry.


Geoffrey A. Landis, Mar 07, 1994:

150 miles is easy with single stage. You need about 2.5 km/sec; you can do that with kerosine/oxygen and a mass ratio somewhere around 0.5. Easy!

LEO is hard hard hard with single stage. You have to scratch like mad for every gram of dry mass, and you absolutely can't do it without being very good with advanced materials. You can't let your engine performance drop very much, either/ And you have a whole lot worse problems with reentry. SSTO is not a backyard venture.

Saying, "well, if we can do 150 miles, why not orbit?" is like a home [airplane] builder thinking, "well, if I can build a Veri-EZ, why not build a SR-71?"


David Burkhead, Mar 11, 1994:

As I understand it what Geoffrey wants is for ordinary people like you and me to be able to build that "little private box." Then we could make that 150 mile hop (about 300 miles slant range) ourselves. If you could use avgas as fuel and had an on-board oxygen separator/liquifier you could use the thing as personal transportation.

While it would not be a major contributor to transportation (any more than homebuilt aircraft are likely to put airlines out of business), it would demonstrate conclusively that rockets and space travel do not have to be big government projects.

Two things, I think, are needed for something like that to work: small, cheap, reliable rocket engines and an inexpensive, cheap, and accurate guidance system. A desktop computer can probably be adapted for control, although you'd still need some input either from an inertial platform, GPS or something. As for the rocket, I posed the question earlier about whether liquid fueled rockets might be made as a set of spinnings welded/brazed together. They'd be made in two layers so fuel could be circulated between them for regenerative cooling.


Greg Bennett, Mar 11, 1994:

You've made a good point there. If someone ("they" again) were to build a homebrew rocket that could just do what the DC-X did with a human pilot aboard, the point would be made that rockets don't have to be big government projects.

Already hobbyist rockets are rivaling the V-2 experiments. Last time I saw him, Al Jackson mentioned he had sent his own rocket over 20,000 feet.


Geoffrey A. Landis, Mar 11, 1994:

LOX you can buy from industrial gas suppliers or from hospital supplies. LH2 is a lot harder to come by, and a lot harder to keep. I'd figure LOX and jet fuel.

Hybrids are a bit tougher to refuel.

Rocket engines are expensive, but I'm not sure that if you're not trying to push the utmost efficiency out of them that they have to be expensive. A pressure-fed rocket engine has damn near no moving parts. [If you go pressure-fed, you have to keep the chamber pressure down below about 200 PSI, and lose something like 10% in Isp. I figure it would be worth it].

If somebody had one of these jobs around you could buy for $100,000, I would sell my house and buy one. People buy private airplanes in the $100K range to fly around just for fun, and they aren't nearly as fun.

Of course, I'd really really love the orbital version. But the 300 mile hopper we could build today, with commercial parts.

Many of the details changed slightly, but these initial discussions set the main concept in place. The final SpaceCub mission statement, that the design goal was to reach an altitude of at least 100 km, officially defined as "space," evolved somewhat later in the project. The name SpaceCub was not arrived at until the end of May 94, when I suggested "Rocket-cub," a name shortly modified (I've forgotten by whom) to "SpaceCub".

Addendum 2:

Before SpaceCub, there was in fact one other concept for building a rocket to send a person on a sub-orbital flight into space on a rocket built by private individuals, instead of governments: Robert Truax's "Volksrocket". SpaceCub was different in that we envisioned not a single "stunt" launch, but a reusable vehicle that could be privately owned by dozens or even hundreds of people, but there's no question that Truax's Volksrocket blazed a trail before us.

Addendum 3:

The people involved

In this memoir, I have emphasized my own contributions, at the cost of greatly understating the portion of the work that David Burkhead put in, doing almost all of the main design calculations.

The original SpaceCub cabal (before May 1994) were:

When the project started getting a bit more serious, around June 1994, additional people participating and commenting included:

Page by Geoffrey A. Landis
Copyright 2003