29.08.2018

A major anniversary in space transportation passed almost unnoticed this month.

On August 18, 1993, the DC-X experimental vehicle, built by McDonnell Douglas for the Strategic Defense Initiative Organization, lifted off from White Sands, New Mexico, hovered and translated, and landed vertically under rocket power. It was the beginning of a new era in spaceflight, but one that would unfold quite differently than what many envisioned that day.

In 2008, and again in 2013, the New Mexico Museum of Space History hosted a conference that served as a reunion for those who worked on DC-X, timed to the 15th and 20th anniversaries, respectively. There was no such event—at least publicized like the earlier ones—for the 25th anniversary of the first DC-X flight earlier this month (see “Can lightning strike twice for RLVs?”, The Space Review, August 19, 2013)

That’s too bad, since a lot has happened in the last five years to advance the goals of frequent, low-cost space access that drove the development of the DC-X. Five years ago, SpaceX was still experimenting with a technology demonstrator called Grasshopper, a modified Falcon 9 first stage with bolted-on landing legs that was performing vertical takeoffs and landings much like the DC-X was 20 years earlier. “Just continuing the great work of the DC-X project!” wrote Elon Musk to Bill Gaubatz and Jess Sponable, the former McDonnell Douglas and SDIO program managers, respectively, of DC-X at the 2013 conference.

What a difference five years makes. Since those Grasshopper tests five years ago, SpaceX went on to test landing of first stages of Falcon 9 rockets at sea—sometimes with spectacularly unfortunate results—then started to nail the landings, both on ships and on land. Then came the reuse of the first stages and upgrades to the Falcon 9 that, in its latest Block 5 configuration, enable that first stage to be reflown ten or more times. Today, it’s rare that a launch takes place without attempting a landing, and increasingly common for first stages to be “flight proven”—aka reused. Musk even suggested the company could attempt next year two Falcon 9 launches, using the same first stage, within 24 hours.

SpaceX isn’t alone. Five years ago, people knew Blue Origin was up to something in West Texas, but few knew the details. What emerged in recent years is the company’s New Shepard suborbital vehicle, which has demonstrated vertical landing and reuse and should start carrying people within the next year. That same technology will go into the company’s New Glenn orbital launch vehicle under development, with the first stage making a vertical landing at sea, and Blue Origin has hinted at an even larger rocket, New Armstrong, down the road.

Now, reusability is all the rage. Incumbents in the launch market, like Arianespace and United Launch Alliance, are talking about their own approaches to reusing vehicles, or components of vehicles (like just recovering the first stage engines). Chinese launch vehicle developers are also discussing plans for reusable vehicles, in some cases approaches that look suspiciously like SpaceX’s Falcon 9.

Some purists might dismiss these achievements of the last several years and the overall industry reaction. None of these vehicles are single-stage-to-orbit designs, long the holy grail of spaceflight, albeit an extremely technically challenging goal. In one online forum, a critic called the Falcon 9, even in its latest version, “an expendable vehicle with a bit of reusability kludged in” rather than a vehicle designed from the beginning to be reusable. (There is, of course, SpaceX’s Big Falcon Rocket in development, whose booster and spaceship components are designed for reuse from the beginning; however, not being SSTO may bother the purists.)

But to ignore the progress in recent years because the vehicles flying don’t represent the idealized vision of the DC-X is shortsighted. Moreover, the progress that has been made has largely been the result of private funding, versus government programs. At the 20th anniversary event five years ago, attendees talked about the importance in investing in X-vehicles to develop key technologies. Since then, the most prominent such program involving reusable launch vehicles is DARPA’s Experimental Spaceplane (formerly XS-1), which seeks to develop a reusable first stage capable of making ten flights in ten days. It isn't expected to begin flight tests until 2021.

Advanced technology, though, isn’t necessarily the most important thing when it comes to reusable vehicle development. “When you’re in the commercial sector, it’s not about proving your technological manhood. It’s about making money,” Jeff Greason, then CEO of XCOR Aerospace, said at the 2013 meeting. “Being told that this system is or is not technologically superior isn’t relevant.”

Making money has its perils, too: XCOR Aerospace went bankrupt last year when it failed to raise money and had struggles with its vehicle design. Armadillo Aerospace had gone into “hibernation” just before the 2013 conference and since has faded away, although many of its employees have since gone on to a new venture, Exos Aerospace, making reusable sounding rockets. The company performed the first test of that rocket last Saturday—one week after the 25th anniversary of the first DC-X flight—from Spaceport America in New Mexico.

So, if you cling to the specific vision of 25 years ago, of SSTO reusable launch vehicles such as direct descendants of DC-X flying for little more than the cost of propellant, you’re likely disappointed by the state of things today. But if your interest is on finding ways to reduce the cost, and increase the frequency, of space access in general, the achievements of the last five years in particular—and the velocity of progress seen during that time—should be encouraging.

Quelle: The Space Review

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Quelle: NASA:

During flight 4 on July 31, 1996, landing strut 2 failed to extend, causing the unbalanced vehicle to tip over on its landing pad. The LOX tank exploded and there were indications of secondary explosions in the LH2 tank as well. The ensuing fire damaged large sections of the DC-XA. An investigation board was convened to determine the cause of the accident, which was later determined to be an unconnected helium pressurant line that supplied hydraulic pressure to extend the landing strut.

The conclusion of the program was summed up well by the Reusable Launch Vehicle program director, Gary Payton. He stated, "The way the budget is now, we cannot afford to rebuild the Clipper Graham and will not be able to continue with that takeoff and landing technique, so we will declare victory with the DC-XA."

Like any good experimental vehicle, the DC-XA flew until it was destroyed. We will always be impressed by the lessons this little rocket taught us about the right way to travel to the heavens...

The DC-X Program:

The Delta Clipper Experimental was constructed in 1991-93 at McDonnell Douglas' Huntington Beach facility. It was intended as a one-third scale model of a proposed SDIO single-stage launch vehicle. It first flew in August 1993 and had completed three flights when SDIO terminated the Delta Clipper program. After additional funding was procured, the vehicle flew five more flights before being returned to Huntington Beach for conversion into the DC-XA.

The DC-XA Program:

The Delta Clipper Experimental Advanced was a modified version of the DC-X. It had a lightweight graphite-epoxy liquid hydrogen tank and an advanced graphite/aluminum honeycomb intertank built by McDonnell Douglas; an aluminum-lithium liquid oxygen tank built by Energia; and an improved reaction control system from Aerojet. These improvements reduced dry vehicle mass by 620 kilograms. The DC-XA was operated by NASA and the Department of Defense under the Reusable Launch Vehicle program. The flight vehicle was tested at White Sands during the summer of 1996, and demonstrated a 26-hour turnaround between its second and third flights, a first for any rocket. After the fourth flight, however, the DC-XA suffered severe damage and the program ended due to lack of funding.