20 years ago yesterday the first rocket-propelled, vertical-takeoff, vertical-landing (VTVL) flying machine designed for Earth took off for the first time from the White Sands Missile Range in southeast New Mexico. It was an experimental proof-of-concept craft called the Delta Clipper or DC-X, it was built by McDonnell Douglas (now part of Boeing) for about the price of one single-aisle airliner, and you can read more about it here:
McDonnell Douglas DC-X
VTVL is a launch vehicle configuration that has many fans in the aerospace industry. Some even go so far as to claim that a vertical launch followed by a descent and landing under rocket power is "The way God and Robert Heinlein intended" rockets to work. Hyperbole aside, I'm skeptical that God has any particular opinions when it comes to aerospace vehicle design, and with all due respect to the dean of science fiction, what works matters much more than the preferences of speculative authors. There are appealing attributes to the VTVL concept. The weight and drag penalties of aerodynamic control surfaces are kept to a minimum, compact launch and landing sites are possible, and it's possible that vertical landing results in the lowest recovery weight of any viable reusable launch vehicle technology. The unappealing aspect of VTVL rockets is the obvious insanity of betting the lives of the ship, crew, and passengers on the ability of rocket engines to ignite with rock-solid reliability and guide the vehicle's way to a precision stop with mere seconds of margin. Any more margin than that and the weight advantage over wings disappears.
Landing engine reliability and maneuverability are daunting challenges for VTVL launch vehicles, but the advocates think these dragons can be slain by adequate testing. In the late-1980s this coalition was able to convince the Strategic Defense Initiative Organization (SDIO, better known as Reagan's Star Wars program) that propulsive landing was the easiest way to achieve low-cost reusable launch. SDIO in turn was more than happy to put down $60 million to retire some of the risks that might one day enable a way to launch the dizzying number of spacecraft required to enable the Brilliant Pebbles space-based kinetic kill vehicle concept it was toying with at the time. In the event SDIO was repurposed and disbanded by the time the DC-X flew, and the clipper flew less than a dozen times before it was bought by NASA and almost immediately crashed and burned. In her short life, though, the DC-X demonstrated the principles of reusable, lean operations with a rocket-powered vehicle taking off and landing under its own power.
Though the DC-X died young, a small fleet of similar vehicles now carry the torch of VTVL toward, the faithful hope, one day making space travel as routine as air mail was in Lindbergh's days. John Carmack's Armadillo and Dave Masten's company have matched much of what McDonnell Douglas did in the DC-X days by rapidly iterating the development of small vehicles, though they've both run into serious challenges integrating aerodynamics into their vehicle designs as they've rapidly ascended in altitude and speed. Climbing the scale of financial investment, Blue Origin has flown several rockets closer in size to the DC-X in the last few years. For reasons that are obvious if you've ever seen my resume, I'm fond of Blue, and I helped in a very small way to put together the vehicle shown below (I once spent an afternoon helping to place propellant lines and fasteners around the fuel tank):
Finally, there's the 800-pound gorilla in the room for any discussion of the future of spaceflight, SpaceX. While all the launch vehicles SpaceX has flown so far have been expendable rockets much like those made by their arch-rival from old space, United Launch Alliance, Elon Musk has made it clear that SpaceX intends to transition to fully reusable launchers within the next decade. This makes sense when you consider that propellant cost is insignificant compared to vehicle cost, but seems less economical when you consider how insanely difficult it will be to shoehorn reusability into a throw-away rocket. Still, SpaceX is nothing if not tenacious, and they've already made considerable progress in understanding the flight of rocket-levitated craft at their test site in central Texas:
Personally, the idea of trusting my life to a cluster of braking rocket engines terrifies the nonrational part of my brain and seems nuts to the rational part of my brain. As they say, takeoffs are optional, but landings are mandatory, so the VL part of VTVL carries much more pucker factor for me. Personally, I think air launching and winged recovery are more promising ways to attack the problem of the cost of orbital transport, at least initially, though VTVL vehicles are probably better suited to the transport of oversize payloads like space station and starship components. As my high school theory of knowledge teacher was fond of saying, though, my opinions don't matter. What matters is results, and Carmack, Masten, Bezos, and Musk are all producing impressive results in spades. May the daughters of the Delta Clipper fly on, high, fast, and long into the future:
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